Graphene films (GrF) modified with Au nanoparticles are used as an adsorbent for the detection of H2S and SOF2, which are two characteristic products of SF6 decomposed gases. Sensing experiments are conducted at room temperature. Results demonstrate that Au‐modified GrF yields opposite responses to the tested gases and is thus considered a promising material for developing H2S‐ and SOF2‐selective sensors. The first‐principles approach is applied to simulate the interaction between the gases and Au‐modified GrF systems and to interpret experimental data. The observed opposite resistance responses can be attributed to the charge‐transfer differences related to the interfacial interaction between the gases and systems. The density of states and Mulliken population analysis results confirm the apparent charge transfer in Au‐modified GrF chemisorption, whereas the van der Waals effect dominates the pristine graphene adsorption systems. Calculation results can also explicate the significant SOF2 responses on Au‐modified GrF. This work is important in graphene modulation and device design for selective detection.A gas sensor is used to detect SF At the early stages of insulation degradation of electrical equipment, the occurrence of partial discharge (PD) causes the decomposition of SF6 into various products, such as H2S, SO2, SOF2, and SO2F2.6 decomposed gases.Sulfur hexafluoride SF is widel* states around the Dirac point in the Brillouin zone.3,2,2.Graphene is a promising material for various applications, such as energy storage,Graphene sheets are functionalized with metals, chemical treatments, or other modifiers to enhance the chemisorption and selectivity of graphene to target gases.2S and SOF2. Low‐cost and simple LBL deposition was adopted in device fabrication to investigate H2S and SOF2 adsorption responses. Based on first‐principles calculations, we studied the interaction mechanism of the Au‐modified GrF substrate with the gases. To the best of our knowledge, theoretical study combined with experimental data regarding the SOF2 adsorption effect on Au‐modified GrF has not been conducted and a thorough study of H2S adsorption effect is rarely reported.In this study, we used Au‐modified graphene films (Au‐modified GrF) as gas sensors for the detection of H22.1FigureMaterials must be thoroughly analyzed before the investigation of sensing performance. 2 domains in graphene. The Raman spectra of the films show the representative peaks at ≈1356 (D) and ≈1590 cm−1 (G) and the broad bands between 2400 and 3200 cm−1.Raman spectra were determined for structural characterization.Figured111 = 0.235 nm), indicating that AuNPs exist and are highly crystalline. The EDS spectrum further verifies that Au is successfully modified in graphene.Figure7/2 and at 87.94 eV in Au 4f5/2, Au (III) ions at 85.02 eV in Au 4f7/2 and Au (I) ions at 88.37 eV in Au 4f5/2, respectively.7/2. This shift in the bonding energy may be ascribed to the substrate and reduced core‐hole screening in metal particles. Furthermore, a dynamic electron transfer from modified AuNPs to the supported graphene films is confirmed by the existence of positively charged Au (III) and Au (I) ions according to the electrostatic balance principle and theoretical calculation in DFT study. Moreover, according to the N 1s spectra of rGO and Au‐modified sample in Figure XPS spectra are important in valence analysis. 2S and SOF2, were delivered to the graphene‐based sensor device through mass flow‐controlled dilution with clean, pure, and dry helium. FigureRF represents the sensor resistance at the final target gas exposure and RI represents the initial vacuum resistance at the previous rest period. Sensor responseTarget gas molecules, namely, H2S and SOF2. Only the responses associated with these two concentrations were analyzed to investigate the sensing mechanism. For rGO under ambient conditions, 100 and 50 ppm H2S cause 15.78% and 10.53% reduction in resistance, respectively. SOF2 is not sensitive to rGO. Moreover, 100 and 50 ppm SOF2 result in 23.83% and 15.36% reduction in the resistance of Au‐modified GrF, respectively. These findings indicate that Au‐modified GrF exhibits higher sensitivity to SOF2 than rGO. Although Au‐modified GrF is also sensitive to H2S, a positive resistance change was observed. In this system, 100 and 50 ppm H2S increase the resistance by 28.15% and 18.73%, respectively. These sensing performances reveal that the Au‐modified GrF and pure rGO sensors are promising materials for selective detection. Therefore, the sensing behavior was further analyzed.Although humidity and temperature significantly affect the sensor response, specific operating conditions in electrical equipment may reduce this variation. Figure 2S and SOF2 were performed at the same setting. Figure2S and SOF2 flows, respectively, and Figure 2 were flown over the sensor sequentially and recurrently, and the changes in resistance were measured. N2 flow expelled the target gas that had already been existed, for the purpose of exploring its recovery property and preparing the next detection round at the same time. Based on the results in Figure 2S on rGO sensor is much slower compared to the response behavior on Au‐modified GrF. Hence, the response speed of Au‐modified GrF is proved to be better than pure rGO.Further experiments were performed to determine the response properties under repeated gas pulses. For this, a series of sensing experiments involving H2.22.2.1Figure3 configuration and protrude from the graphene plane by 1.87 Å along the Z axis. The bond lengths (2.07 Å) of the three C—Au bonds confirm the partial sp3 configuration of Au atoms. A similar bonding geometry was observed in M‐modified graphene FigureB). According to the partial DOS (PDOS) in Figure A simulation model was constructed for theoretical calculation to investigate the factors affecting sensor performance and the sensing mechanism. We already discussed the nature of the bonding between decorated Au and graphene. The three possible positions2.2.2Figure2S and SOF2 molecules on Au‐modified GrF. TableFigure2S and SOF2 adsorption systems. We focused on the adsorption effects of double molecules on the Au‐modified GrF plane according to previous research, which reported that several molecule adsorption cases were inclined to be unstable at room temperature because of significant decreases in their Ead.Different orientations are required to achieve the most stable adsorption configuration, which exhibits the lowest total energy and highest adsorption energy.2S Adsorption CasesH: In the Au‐modified GrF‐H2S system, H2S is adsorbed parallel to the surface with S atoms closest to Au. The geometric structure of H2S slightly changes as the H—S—H bond angle (91.181°) expands to 91.719° and the H—S bond angle (1.356°) extends to 1.360 and 1.362 Å. H2S molecules also prefer a closer configuration on the Au‐modified GrF plane than that on the pristine graphene, as indicated by the shorter distance between Au‐modified graphene and S (2.401 Å) than that between pristine graphene and H2S (3.108 Å). Hence, H2S molecules are chemisorbed on Au‐modified GrF as evidenced by the high adsorption energy (−0.9 eV) and electron transfer (0.348 e) from H2S molecules to Au‐modified GrF. This electron transfer leads to electron enrichment on the Au‐modified GrF surface. In graphene‐H2S adsorption case, the obtained electron transfer value (0.011 e) indicates the presence of few electron interactions. Nevertheless, the adsorption energy of graphene–H2S (−0.617 eV) presents a relatively strong intermediate between physisorption and chemisorption,2S and pure Au‐modified GrF, we observed an evident difference in DOS near the Fermi level, indicating a decrease in the surrounding DOS. For Au‐modified GrF, the Fermi level shifts upward by 0.043 eV, which is reminiscent of an n‐type effect caused by adsorbed H2S molecules. The magnetic moment further changes to 0.999 μB.2S molecules exhibiting a similar configuration are the stable configuration on Au‐modified GrF; in this configuration, each S atom moves closer to Au. The binding geometry is similar to that of the Au‐modified GrF‐H2S system. The adsorption energy (−1.718 eV) is two times higher than that of Au‐modified GrF‐H2S. Although ≈0.3 electrons per H2S molecule transfer to the Au‐modified GrF complex in the Au‐modified GrF‐2H2S system, the system still exhibits an n‐type sensing nature. The n‐type effect introduced by the two H2S cases could be attributed to the upward shift of the Fermi level by 0.077 eV. This observation is also consistent with the higher adsorption energy of 2H2S on Au‐modified GrF than 1H2S. In fact, our separate PDOS calculation confirms that Au prefers to hybridize S atoms in the H2S valence band, which contributes to the strong interaction between Au and adsorbed H2S. A comparison study using Figure 2S adsorption remains magnetic in the semiconductor system with a magnetic moment of 0.823 μB.We found that the two H2 Adsorption CasesSOF: In the Au‐modified GrF‐SOF2 case, SOF2 prefers the configuration in which SOF2 is located above Au‐modified GrF; in this configuration, S and F atoms bond to Au as indicated by the distance between S and Au (2.508 Å) and F and Au (2.039 Å). The F—S bond extends longer (2.894 Å) than that in the gas phase (1.668 Å) because of the charge transfer, indicating SOF2 rupture. The results of Mulliken population analysis confirm the occurrence of a significant electron transfer (0.624 e) from Au‐modified GrF to SOF2; this phenomenon features a p‐type process with SOF2 as an acceptor. The adsorption energy (−0.961 eV) is similar to that in the Au‐modified GrF‐H2S case. Our DOS calculation results further reveal that the spin‐up and spin‐down channels shift downward by 1.05 eV, indicating the strong p‐type effect of SOF2 adsorption. The adsorbed SOF2 converts the system of Au‐modified GrF from magnetic metal into a nonmagnetic system with magnetic moment quenching. This observation differs from that in the H2S cases, which maintains the magnetic property.2 molecules move closer to Au‐modified GrF, the most stable configuration is where one SOF2 prefers the active state and approaches the Au‐modified GrF plane and the other SOF2 moves away from Au‐modified GrF  because of the inactive SOF2. In the H2S case, this observation differs from that in 2H2S adsorption, in which one H2S exhibits equivalent effect to the other H2S. The adsorption energy of the Au‐modified GrF‐2SOF2 system (−1.334 eV) is higher than that in Au‐modified GrF‐SOF2 (0.961 eV). The small amounts of additional energy can be ascribed to the van der Waals interaction, which is supplemented by electrostatic effect caused by chemically inactive SOF2 molecules. The results of DOS analysis further indicate that the Fermi level shifts downward by 0.966 eV compared with that of Au‐modified GrF; this phenomenon demonstrates a p‐type effect. Moreover, Au‐modified GrF‐2SOF2 case maintains its nonmagnetic property similar to the Au‐modified GrF‐SOF2 system.When two SOFF Figure d. The in2.2.32S, which is significantly sensitive to rGO and Au‐modified GrF but exhibits opposite effect compared with each other. As confirmed in our DFT calculations, the pronounced chemisorption effect contributes to the H2S responses on Au‐modified GrF. However, the results also prove that the adsorption interaction with pure graphene is typical physisorption, which contradicts the experimental findings. The factors affecting this discrepancy remain unclear, but we postulate that it could be related to the method used to manufacture pure graphene films. The pure graphene films used in this study were prepared through chemical reduction, which could inevitably harbors heteroatoms, such as N and O. The combined XPS analysis results and Raman spectra reveal the presence of nonoxygenated ring, C—N bonds, hydroxyl C, and carbonyl, which may affect the sensing interaction. This phenomenon must be further investigated through theoretical and experimental studies.Figure 2, sensing experiments were conducted on pure graphene and Au‐modified GrF . This finding could also be attributed to the higher chemical potentials of Au‐modified GrF than the lowest unoccupied molecular orbital of SOF2. Nevertheless, as SOF2 is physisorbed on the pure graphene surface, no charge transfer  is not significant in the graphene‐SOF2 system compared with that in the Au‐modified GrF‐2SOF2 system (−1.334 eV). Therefore, based on our experiment and calculation results, we successfully established an effective approach to manufacture SOF2 sensors.For SOFF Figure b,d to iner Table  could oc2S and the SOF2 sensing results obtained using Au‐modified GrF. Au‐modified graphene exhibits a 28.15% increase in resistance for 100 ppm H2S and 23.83% decrease in resistance after 12 min of exposure to 100 ppm SOF2. The fabricated Au‐modified graphene sensor demonstrates a reverse resistance change because of gas species. The n‐type and p‐type behavior determined through the altered direction of the charge carrier plays a dominant role in the conduction response.2S exhibits an n‐type behavior with electron depletion on itself. An increase in resistance was further observed in the sensing experiment, indicating the n‐type sensing nature of the Au‐modified graphene layer. In DFT calculations, SOF2 presents a p‐type behavior with electron withdrawing capability, in which electrons can be removed from the adsorbent surface. This phenomenon results in decreased resistance, thereby confirming that Au‐modified GrF displays a p‐type sensing behavior. The corresponding correlation between sensing performance and nature of carriers for Au‐modified GrF was obtained under our experiment conditions and illustrated in FigureFigure 32S and SOF2, which are two types of SF6 decomposed gases, has gained importance because they are significantly related to insulation faults in power equipment. As current detection methods suffer from online monitoring shortage, electrochemistry sensors could be a promising technology for online detection.Detection of H2S and SOF2 selective sensors because it yields opposite responses for these gases. The interaction between the Au‐modified GrF surface and these gases was simulated through first‐principles calculations. The results reveal that the opposite responses observed in experiments could be due to the charge‐transfer differences related to the interfacial interaction within gases and Au‐modified GrF systems. Calculation and experimental findings consistently show n‐type H2S functions as an electron donor and p‐type SOF2 as an electron acceptor.Pure graphene films and graphene films incorporated with AuNPs were fabricated as gas sensors through deposition–precipitation method. Sensing experiments conducted at room temperature demonstrated that Au‐modified GrF is a promising material for developing H2. This finding confirms the robustness and the ability to adsorb SOF2 of the sensor compared with the poor performance on pure graphene films. According to the results of DFT calculations, the typical chemisorption effect between decorated Au and SOF2 could be the main reason for this observation and the adsorption of the pristine graphene corresponds to physisorption dominated by van der Waals.The results of sensing experiments further show the strong response of the Au‐modified GrF sensor for SOF2S chemisorption behavior endows Au‐modified GrF with a magnetic system, whereas SOF2 adsorption converts the system into a nonmagnetic one. This result may be utilized in designing novel magnetic sensing or switching devices, but requires further investigation through experimental methods.Our calculation results further show that the H4Experimental Details: Carboxylic functionalized graphene and rGO were purchased from XF NANO, Inc. . Dimethylformamide (DMF), acetone, and absolute ethyl alcohol were purchased from Huihuang Chemical Reagent Co., Ltd . NaBH4 and HAuCl4 were purchased from Aladdin Chemistry Co., Ltd. All chemicals in this work were of analytical grade and used without further purification, and double‐distilled water was used throughout the experiments.4  solution as a precursor under constant sonication for 40 min to reach a stable colloidal state. Briefly, NaBH4  solution was added dropwise to the colloid solution and the solution was vigorously stirred for 30 min. The solution was then subjected to centrifugal separation, and products were collected and washed with distilled water several times. The washed products were dried in a vacuum oven at 60 °C for 12 h to obtain Au‐modified GrF. Au‐modified GrF (5 mg) powder was ultrasonically dispersed in DMF solution (200 mL) for 30 min to achieve good dispersibility.Au‐modified GrF was synthesized through the following chemical reduction procedures.FigureSensors were fabricated using Au‐modified GrF through LBL deposition.λ = 0.15418 nm) at 40 kV and 30 mA. Wide‐angle XRD patterns were collected at a scanning speed of 10° per minute over the 2θ range of 5° to 100°. Raman spectra were determined using a Renishaw inVia Raman microscope configured with a 532 nm wavelength laser and full‐range grating. Scanning electron microscopy (SEM) images were recorded with a Zeiss Auriga Focus Ion Beam/Field‐Emission SEM dual‐cross system operated at 30 kV and 2 nA. The samples were directly exfoliated from the planar sensor. High‐resolution transmission electron microscopy (HRTEM) combined with energy dispersive spectroscopy (EDS) images was recorded with an FEI Tecnai G2 F20 S‐TWIN operated at 200 kV. X‐ray photoelectron spectroscopy (XPS) was performed on a Thermo ESCALAB 250Xi spectrometer with Al Kα (1486.6 eV) radiation. All measurements were conducted under ambient condition.X‐ray diffraction (XRD) patterns were recorded on a Rigaku D/Max‐1200X using Cu Kα radiation  provided by the DMol3 code. The exchange and correlation energies included were identified through a generalized gradient approximation in revised Perdew–Burke–Ernzerhof (PBE) format.k‐point mesh was increased to 6 × 6 × 1 for the Brillouin‐zone integration to obtain accurate results. All calculations were performed in a spin‐unrestricted manner. The convergence tolerance of energy was set at 1.0 × 10−6 Ha in geometry optimization.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


Our calculations suggest that the multilayer dye aggregates at the TiO2 surface can be stabilized by π…π stacking and hydrogen bond interactions. Compared with previous two-dimensional monolayer dye/TiO2 model, the multilayer dye aggregation model proposed in this study constructs a three-dimensional multilayer dye/TiO2 interfacial structure, and provides a better agreement between experimental and computational results in dye coverage and dye adsorption energy. In particular, a dimer forms by π…π stacking interactions between two neighboring azo molecules, while one of them chemisorbs on the TiO2 surface; a trimer may form by introducing one additional azo molecule on the dimer through a hydrogen bond between two carboxylic acid groups. Different forms of multilayer dye aggregates, either stabilized by π…π stacking or hydrogen bond, exhibit varied optical absorption spectra and electronic properties. Such variations could have a critical impact on the performance of dye sensitized solar cells.Multilayer dye aggregation at the dye/TiO However, the existing aggregation models are limited in the lateral direction relative to the TiO2 surface, while dye aggregate structures built outward from the TiO2 surface are neglected. In other words, a monolayer model is assumed. The monolayer model sets an intrinsic limitation on the amount of dye adsorption on TiO2 surface, leadings to theoretical predications that are two orders of magnitude smaller than the experimental results8Substantial first principles calculations have been performed in order to establish an accurate model to describe the nanoscale structures of dye/TiOp-methyl red azo dyes has been evaluated in previous research in the lateral direction relative to the TiO2 surfacep-methyl red azo dyes serves as a good platform to further analyze their intermolecular interactions and thereby construct the multilayer aggregation model.Azo dyes are frequently used in textile and coating industries due to its stability, vivid color, high molar extinction, and low cost252628p-methyl red [4-[2-[4-(dimethylamino)phenyl]diazenyl]-benzoic acid] is used to probe the dye aggregation on TiO2 surface , consistent with previously reported values in the literature1–3. The π…π distance between the two azo molecules are 4.1 Å for both aggregates 2 and 3, while the H…O distance of the hydrogen bond is 1.53 Å for 3. Interestingly, the π…π stacking mode and the hydrogen bond interactions between neighboring carboxylic acid groups have been observed in the crystal structures of azo dyes determined from single crystal X-ray diffraction experiment1 demonstrates more perpendicular adsorption geometry compared with 2 and 3. The angle between its molecule axis and TiO2 surface is 3°–4° larger in 1 than that in 2 and 3. The molecule chemisorbed onto TiO2 surface is more distorted in the case of 2 and 3, due to steric effects introduced by additional azo molecules.In the optimized structure of the azo dye/TiO2 , the mol1 (0.60 eV) >3 (0.56 eV) >2  among 1–3 because it involves three molecules in the unit cell. In contrast, 1 demonstrates the lowest dye coverage (0.14 nmol/cm2). The experimental dye coverage is 147 nmol/cm2 for p-methyl red on TiO2 nanoparticles in a DSSC photoelectrode3 provides adsorption sites for further vertical aggregate expansion , the washing solvent displays vivid color due to dye dissolution; this phenomenon indicates that abundant azo dyes are weakly adsorbed on the TiO2 surface such that they can be easily removed from TiO2 substrate. Previous aggregation models, that involve only stable chemisorption, are not sufficient to explain these experimental observations. In contrast, the multilayer aggregation model which incorporates physisorption (such as π…π interaction and hydrogen bond) provides a plausible explanation to the large amount of weakly adsorbed azo dyes on TiO2 substrates.We also noticed that after rinsing dye/TiO1–3 exhibit two major bands: one in the UV region near 400 nm and the other in the visible region from 500 nm to 900 nm . This peak wavelength is red shifted by 22 nm compared with that of monomer 1, demonstrating that the π…π stacking interaction is effective in tuning optical properties of DSSC (a red shifted UV/vis absorption spectra is desirable for DSSC device performance for a close match with solar spectrum). Trimer 3 stabilized by hydrogen bond between molecules exhibits the most blue-shifted light absorption spectra among 1–3, indicating that hydrogen bond between neighboring carboxylic acid anchoring groups in azo dyes is detrimental for improving the light absorption of a DSSC device. The experimental light absorption spectra of the p-methyl red/TiO2 film exhibit severe H-aggregation and its peak wavelength approaches the UV region at 400 nm3 implies that the aggregate 3 represents a possible interfacial structure. Further aggregation expansion, which is computationally expensive and unreachable at this stage, is expected to further narrow the gap between experimental and theoretical results. Note that the aggregate 3 does not conform to the typical H-aggregate model, which usually exhibit a head-to-head and tail-to-tail conformation. Instead, the direct “face-to-face” interactions via the hydrogen bonds in aggregate 3 essentially lead to partial dipole-dipole cancellation, because both carboxylic acid groups carry partial negative charge as a result of intramolecular charge transfer in azo dyes29303.The calculated UV/vis absorption spectra of o 900 nm . The int1–3 (~600 nm) demonstrate a large red shift against experimental data (~400 nm), which has also been experienced in the simulation based on the monolayer model33341–3 is more reliable and provides a strong support to our multi-layer aggregation model.We also notice that the calculated UV/vis spectra of 1–3 exhibit a series of straight band lines below Fermi level . We also investigated the spectral and electronic properties of the multilayer molecular aggregates as well as their impacts on the DSSC device performance. We show that the π…π stacking induce a red shift, while hydrogen bond leads to a blue shift of the light absorption spectra in the dye/TiO2 system. It is expected that this multilayer model will pave a new way for a deeper understanding of large molecular aggregation systems in DSSC and other relevant applications.In this study, we propose a multilayer dye aggregation model to describe the aggregation phenomena in the dye/TiO2)36 exposing anatase 101 surface is constructed to analyze the multilayer dye aggregation. A very long vacuum layer and c-axis (69.4 Å) of the unit cell is built in order to accommodate the multiple dye molecules in the c-axis extending outward from the TiO2 surface. A bidentate bridging anchoring mode for the carboxylic acid anchoring group on anatase 101, suggested by previous research371–3 are investigated in this study, where 1 represents the monomeric adsorption form; 2 is a dimer joined via π…π stacking effects; 3 is a trimer where a third molecule is placed on top of dimer 2 via hydrogen bond. Upon adsorption, the vacuum layer thickness values are ca. 44 Å for 1, 39 Å for 2, and 23 Å for 3, which are sufficient to minimize interactions between neighbouring layers39404142432. The three interfacial structures 1, 2 and 3 are geometrically optimized in VASP1–3 are calculated via an 8 × 8 × 1 monkhorst-pack grid. The optical absorption spectra are obtained from dielectric constant in Castep2 surface is calculated using:A unit cell of .


The nanocomposite was designed by decorating copper ferrite nanoparticles on graphene oxide (GO) surface via a solution combustion route without the use of template. The as-synthesized GO-CuFe2O4 composite was comprehensively characterized by XRD, FTIR, Raman, SEM, EDX, HRTEM with EDS mapping, XPS, N2 adsorption-desorption and ICP-OES techniques. This nanocomposite was then used in an operationally simple, cost effective, efficient and environmentally benign synthesis of 14H-dibenzo xanthene under solvent free condition. The present approach offers several advantages such as short reaction times, high yields, easy purification, a cleaner reaction, ease of recovery and reusability of the catalyst by a magnetic field. Based upon various controlled reaction results, a possible mechanism for xanthene synthesis over GO-CuFe2O4 catalyst was proposed. The superior catalytic activity of the GO-CuFe2O4 nanocomposite can be attributed to the synergistic interaction between GO and CuFe2O4 nanoparticles, high surface area and presence of small sized CuFe2O4 NPs. This versatile GO-CuFe2O4 nanocomposite synthesized via combustion method holds great promise for applications in wide range of industrially important catalytic reactions.A facile, efficient and environmentally-friendly protocol for the synthesis of xanthenes by graphene oxide based nanocomposite (GO-CuFe Upto now, many investigations have been done on nanocatalysis, but there still remains the challenge of recovery of nanocatalyst from the reaction mixture. For this reason, magnetic nanoparticles have recently emerged as a useful group of nanocatalyst. The separation of magnetic nanoparticles is found to be simple and economical which diminishes the loss of catalyst, resulting in enhanced reusability. In addition, they exhibit high catalytic activity due to their large surface area and have relatively low preparation costs and toxicity. All these properties make them desirable and promising catalysts2122232O4 with a spinel structure, has been widely used in sensors, electronics and catalysis owing to its unique advantages such as environmental compatibility, moisture insensitive, high dispersion, high reactivity, low cost and easy separation by an external magnet. In catalysis, they are found to be a promising material for a variety of catalytic applications. For example, Amini et al. investigated the low temperature CO oxidation over mesoporous CuFe2O4 nanopowders synthesized by a novel sol–gel methodet al. explored the catalytic application of CuFe2O4 nanoparticles for the Friedel–Crafts acylationet al. investigated the catalytic activity of CuFe2O4 nanoparticles for the reduction of 4-nitrophenol to 4-aminophenol with an excess amount of NaBH4Among various magnetic nanoparticles, the copper ferrite, CuFe2 hybridized carbon has received increasing attention as it possesses similar properties to that of graphene. Because of its high surface area, mechanical and electrical properties and thermal stability it has been used as a significant 3O42O42O4222 nanocomposite (GO–SnO2) and used it as an efficient catalyst for the β-enaminones synthesis2O4 nanoparticles and GO, the combination of GO with CuFe2O4 would form a potential catalytic material and more recently, few studies have corroborated this fact272O4) magnetic nanocomposite as a catalyst for biologically important xanthene derivatives syntheses.Graphene oxide, a two-dimensional sheet of sp2244823O451523542O32-SiO2, TiO2-ZrO2, and TiO2-Al2O3 were also prepared by this method2O4 nanocomposite that can enhance the catalytic activity of a reaction by providing more adsorption and reaction sites during the reaction.The methods to synthesize GO-based nanocomposites are diverse, such as hydrothermal2O4 nanocomposite through a solution combustion route and subsequently, for the first time the use of this material as a promising heterogeneous catalyst for xanthenes synthesis have been demonstrated. The xanthenes synthesis was obtained via two-component coupling of aromatic aldehyde and 2-naphthol in the presence of GO-CuFe2O4 nanocatalyst and the same protocol was applied to other xanthene derivatives syntheses. All the reactions proceeded in a shorter period of time compared to traditional catalysts. Moreover, the catalyst can be recycled and reused up to five cycles with minimal loss in activity in a solvent free system. Our methodology may provide insight into the design of nanocatalysts using combustion route for its use in many more industrially important catalytic applications.Herein, we report the successful synthesis of highly porous GO-CuFe3− groups and its lower decomposition temperature and good solubility in water2)2) was used as a common fuel due to its low cost, good availability, high exothermicity, as well as their high coordination ability toward nitrates which help in controlling the size of nanoparticlesCompared to the techniques employed for the preparation of nanocomposites such as solvothermal, hydrothermal and wet impregnation method, SCS is both energy and time efficient. Moreover, it can easily afford porous materials during the combustion process which is advantageous for adsorption of organic reactants on the nanocatalyst2O4 nanoparticles on GO matrix and presence of different functional groups present in the nanocomposite material. 2O4 nanocomposite. As shown in −1 in the FT-IR spectra of GO sample is associated with the stretching vibration of the –OH group. The peak at 1728 cm−1 corresponds to the stretching of the –C=O and –COOH groups on GO sheets. The peak at 1616 cm−1 (aromatic C=C) can be ascribed to the skeletal vibrations of un-oxidized graphene domains. The C–O bond is associated with the band at 1047 cm−1. These observations are in good agreement with previous literatures602O4, the presence of two absorption bands at 562 cm−1 and 480 cm−1 can be noticed. The absorption band at around 529 cm−1 belongs to the stretching vibration of Cu2+ in octahedral site and the absorption band at around 436 cm−1 belongs to the stretching vibration of Fe3+ in the tetrahedral site of CuFe2O4 nanoparticles, respectively−1 are still present in the spectrum which suggests the minor reduction of functional groups after the composite synthesis.FTIR spectra were recorded to study the effective incorporation of CuFe2O4 composites, wherein all the peaks can be assigned to cubic CuFe2O4 spinel structure. It is interesting to find that no impurity peaks of copper oxides (Cu2O or CuO) were observed in the spectrum2741632O4, respectively (JCPDS card no: 85-1326). Moreover, no typical diffraction peak of GO (001) or RGO (002) was observed in the XRD spectrum suggesting that the GO in the GO-CuFe2O4 composite was fully exfoliated due to the crystal growth of CuFe2O4 nanoparticles between the interlayer of GO sheets, which results in the low diffraction intensity of GO6566XRD is a powerful technique to analyze the phase purity and crystal structure of the material. 2O4 NPs, Raman measurements were carried out and are shown in 2O4 has two prominent D and G bands at 1354 and 1606 cm−1, respectively. A small shifting of the bands in comparison to that of GO suggest the increase in disorderness on the GO surface. It is well known that the D band arises due to the defects in the graphene sheets whereas the G band arises due to the E2g mode arising due to the sp2 hybridised carbon domainsD/IG = 0.97) of GO-CuFe2O4 was found to be larger than that of GO (ID/IG = 0.86). This suggests the possible electronic interaction between the GO and CuFe2O4 NPs which results in the reestablishment of conjugated graphene oxide network (sp2) after loading of CuFe2O4 nanoparticlesTo further confirm the effective reduction of GO during the composite synthesis and possible electronic interaction between GO and CuFe2O4 and GO-CuFe2O4 nanocomposite, magnetic measurement was carried out by VSM technique at room temperature and the results are shown in 2O4 and GO-CuFe2O4 are an S-like curve that confirms the strong magnetic response to a varying magnetic field. The specific saturation magnetization (Ms) was found to be 13.0 emu/g for CuFe2O4 and 8.1 emu/g for GO–CuFe2O4 composite revealing the superparamagnetic behavior of both the samples. It should be pointed out that the saturation magnetization (Ms) values decreased after the loading of GO. The values of coercivity and remanence are summarized in 2O4 nanocatalyst can be easily separated from the solution phase using an external magnet, which is important in practical applications.In order to check the magnetic properties of the as-obtained pure CuFe−9 mbar. We have investigated the chemical composition and electronic structure of the GO-CuFe2O4 nanocomposite. The presence of the core-level peaks in XPS survey spectra, as shown in 2O4 and GO samples. In 2O4 nanocomposite samples. For GO, the main peak positioned at around 284.5 eV, is assigned to non-oxygenated ring carbon molecules, while alternate peaks at 286.7, 287.8 and 289.1 eV are assigned to the oxygen-containing groups (C–OH), (C=O), and (O=C–OH), respectively  core-level peaks most probably due to FeO. Additionally, the satellite structure between the two peaks at 718 eV was the fingerprint of the electronic structure of Fe3+. 3/2 core level spectrum, which appears at 932.7 eV and is in accordance with Cu2+ states as reported in literatures2O4 particles2O4 nanoparticles (NPs) on graphene oxide sheets.A non-monochromatic Mg Kα (hv = 1253.6 eV) X-ray source and PHOIBOS 150 electron energy analyzer from SPECS GmbH, Germany was used to acquiring X-ray photoelectron spectroscopy (XPS) measurements with the base pressure below 1 × 10ectively . The C 1at of GO . This su2O4 was then ascertained by FESEM which are presented in 2O4 particle to anchor on its surface. Unlike graphene, GO sheets are expected to be “thicker” due to the presence of carbonyl, carboxyl, hydroxyl and epoxy groups above and below the original graphene planes. 2O4 nanocomposite. The crumpled and layered structure of GO can be easily seen in the FESEM images (5b-c). Spherical CuFe2O4 nanoparticles of larger size (~121 ± 2 nm) are found to be homogeneously distributed on the GO surface indicating the agglomeration of synthesized nanoparticles.The structural composition of GO and GO-CuFe2O4. From EDX analysis it was confirmed that SCS could be an excellent and efficient route for the the synthesis of graphene oxide based spinel nanocomposite. The EDX analysis showed that the distribution of the elements in the product was Cu = 14.28%, Fe = 28.95% and O = 56.77%  which sizes are found to be similar (~121 ± 2 nm) nm) to that obtained from FESEM images. The size of the individual CuFe2O4 nanoparticles is of 10 ± 2 nm which can be clearly seen from 2O4 nanoparticles can be attributed to the powerful inherent magnetic interaction of magnetic particlesFurthermore, the energy dispersive X-ray (EDX) analyses were recorded and are shown in the = 56.77% , therebyte. From  TEM imag2O4 NPs can possibly be one factor for the enhanced catalytic activity as described later. The crystalline nature of the composite was further confirmed by SAED analysis which depicts a ring-like structure  than that of CuFe2O4 (22 m2·g−1). The surface area is found to be higher than other reported system synthesized by solvothermal method (35 m2·g−1)2O4 composite were found to be 12 nm , respectively which means 7.43 mg of CuFe2O4 was loaded on graphene oxide sheets (i.e. 25.7% GO content). This 25.7% GO loading was in agreement with the TGA analysis as described above. ICP findings further confirmed that Cu and Fe are present in 1: 2 molar ratios which are consistent with stoichiometry of CuFe2O4 structure.TGA analysis is a useful analytical tool to study thermal stability of materials and to determine the composite composition. Therefore, TGA measurements of GO and GO-CuFe2O4 nanocatalyst. The effects of various reaction parameters on reaction of 2-naphthol with benzaldehyde were also investigated. The products were characterized by FT-IR, 1H-NMR and 13C-NMR spectroscopy.Till now many acid catalyst had been reported and it was found that they are showing an efficient path for synthesis of xanthenes and its derivative. But they suffer a lot of disadvantage notably due to their prolonged reaction time, tedious work condition, use of VOCs and hazardous reaction conditions. To overcome this problem the use of ILs as solvents as well as promoter in the synthesis have been reported, but high cost of imidazole, thiazole and pyridine based IL and use of costly catalyst for the synthesis have been the essential drawbacks. To overcome this drawback use of graphene oxide based nanocomposite can be promising catalytic material. Towards this objective the reaction of 2-naphthol (2 mmol) with benzaldehyde (1 mmol) was chosen as a model reaction at 125 °C under solventless condition to assess the catalytic performance of GO-CuFe2O4 nanoparticles (72% yield)   , entry 42O4 composite can be attributed to the synergistic effect between the CuFe2O4 and the graphene oxide sheets. The presence of GO in the composite could enhance the adsorption of reactant molecules onto the catalytic sites of the GO-CuFe2O4 through π-π stacking and electrostatic interactions, leading to a high conversion rate. Additionally, the introduction of CuFe2O4 NPs into GO matrix results in its uniform dispersion on GO sheets and prevent them from agglomerating, thus increasing the number of active centers on CuFe2O4 nanoparticles. However, with further increase in GO amount beyond 20 wt% led to the lowering of active centres in the composite, which promoted less yield of the desired product. Therefore, 20 wt% was chosen as the required amount to carry out the reaction.This increase in catalytic activity of GO-CuFe2O4 on xanthenes synthesis was examined 2, and Fe(NO3)3 were also compared to GO-CuFe2O4  and it was found that GO-CuFe2O4 is the best catalyst which requires shorter reaction times with higher yield (98%). Furthermore, our catalyst showed higher activity in comparison to other GO-CuFe2O4 system synthesized by other conventional methods like solvothermal and co-precipitation methods  in the presence of GO-CuFe2O and solvent less condition at 125 °C with 20 mg catalyst. The results are summarized in 2O as solvent.After optimizing the reaction conditions, we next investigated the generality of these conditions using 2-naphthol (2 mmol) and several aldehydes (1 mmol) both in HLater on, a wide range of aldehydes containing electron-withdrawing and electron donating groups were investigated. Aldehydes containing electron withdrawing groups such as chloro, bromo, and nitro underwent condensation in short reaction times with excellent isolated yields under both conditions  generated during the synthesis of GO via exhaustive oxidation provide Brönsted acidic sites to GO77782O4 has strong Lewis acid character which originates primarily from the presence of tripositive Fe3+ and dipositive Cu2+ ions. The Lewis acidity of Fe3+ can be attributed due to its higher electronegativity while for Cu2+ this is due to acquirement of a stable and completely filled d-subshell on receiving an electron80812O4 system has two acidic sites (GO as Bronsted site and CuFe2O4 as Lewis acid site) one would expect that Lewis and Brönsted acid site can play a synergistic role in the overall catalytic reaction.The presence of acidic site on catalyst surface plays an important role in the overall catalytic activity of chemical reaction. In general, xanthene syntheses are carried out conventionally with the use of Lewis and Brönsted acid catalysts9102O4, we compared the activity of GO-CuFe2O4 to that of a physical mixture of GO and CuFe2O4. It can be found that the catalytic activity of the reaction system containing physical mixture of GO and CuFe2O4 (74% yield) is similar to those observed for pure CuFe2O4 nanoparticles (72% yield), which is lower than that of GO-CuFe2O4 (98% yield) as shown in 2O4 acidic sites in the xanthene synthesis. Similar synergistic effects in the final catalytic activity were reported in the literatures8384852O4 nanocomposite which was obtained by chemical method, the CuFe2O4 nanoparticles would exhibit strong interactions with graphene oxide sheets, thereby, strongly influencing the catalytic behaviour of the nanocomposite872O4 nanoparticles and graphene oxide sheets. As a result, slower diffusion and decrease of mass transfer of reactant molecules take place which would be the cause for the decrease in yield in case of physically mixed GO and CuFe2O4 NP systemIn order to confirm the importance of synergistic interaction between GO and CuFe2O4 nanoparticles as good catalyst was also demonstrated. As can be seen from 2O4 nanoparticles which provide smaller particle size and higher surface area showed higher activity to that of powder CuFe2O4 samples863O4 samples, pure CuFe2O4 nanoparticles showed higher activity , demonstrating the active role of Cu2+ in the catalytic reaction2786In addition, the crucial role of CuFe2O4 catalyst has been outlined in 204 nanocatalyst initially facilitates the efficient chemical adsorption of reactant molecules and favours the interaction of carbonyl group of aldehyde (IA) to the acidic sites78792+ and Fe3+ of CuFe2O4 nanoparticle that anchored onto the GO surface also co-ordinate with the intermediate by bonding with the –OH group, which further increases its electrophilic nature and helps in the stabilisation of intermediate922O4 NPs with the hydroxyl groups of intermediate help in increasing the electrophilicity of the intermediate and for subsequent nucleophilic attack of the β-naphthol molecule and in the cyclization process. It can be concluded that the Cu2+ and Fe3+ of CuFe2O4 nanoparticle help in activation and stabilization of subsrate molecules during xanthenes synthesis.From all the results discussed above, a plausible mechanism for xanthene synthesis using GO- CuFe2O4 composite are found to be magnetic they can be easily removed from reaction solution with a magnet. Therefore, the catalytic stability of the GO-CuFe2O4 nanocomposite for the reaction of benzaldehyde1 (1 mmol) with naphthol (2 mmol) in the presence of 20 mg of GO-CuFe2O4 nanocomposite as catalyst was studied to give the desired product. After completion of the reaction (monitored by TLC), the catalyst was separated by applying an external magnetic field, washed with deionized water and acetone, and then vacuum dried at 60 °C for 3 h before being used in the subsequent recycling experiment. As shown in 2O4 nanocomposite was still stable even after being recycled five times. The composite showed very high activity (yield 87 and 93%) even after 5th cycle without any accountable loss of activity. The recovered catalyst was characterized by powder XRD which showed similar pattern with fresh sample indicating stability of spinel structure  as compared to original loading 1.96, 3.47 mg of Cu and Fe elements for copper ferrite NPs. This outstanding stability and recyclability of GO-CuFe2O4 nanocomposites can be ascribed to very good interaction between CuFe2O4 NPs and GO sheets which prevents agglomeration of the nanoparticles.Recovery of catalysts is important for the re-usage and application cost of a catalyst. Since GO-CuFeture see . Furtherture see  showed s4)3 3/P2O55CoW12O40.3H2O2O4 catalyst is more effective and less time consuming for synthesis of xanthenes under solventless condition.Later on, to check the efficiency of our catalyst we have compared the activity of our catalyst with other reported catalysts. 3were purchased from Sigma-Aldrich. Cu (NO3)2·3H2O, Fe (NO3)3·9H2O, H2O2 (30%), isopropanol, ethanol, NaNO3, H2SO4 (98%), HCl, KMnO4, urea and silica gel (100–200 mesh) were purchased from Hi-Media. All chemicals were used as received without further purification. 18 Milli-Ω water was used throughout the synthesis.Graphite powder and CDCl2SO4 (98% w/w), followed by stirring at room temperature for 24 h. To the resulting pre-oxidized product, 100 mg of NaNO3 was added to the mixture and stirred for 30 min. Subsequently, the mixture was kept below 5 °C using an ice bath and 3 g of KMnO4 was slowly added to the mixture and the mixture was stirred for 2 h under the ice-water bath. After that about 250 ml distilled water and 20 ml H2O2 (30%) was added to dilute the solution at room temperature. After 10 min, a bright yellow solution was obtained and resulting solution was precipitated for 12 h, and the upper supernatant was collected and centrifuged. Successively, the GO powders were washed with 10% HCl and distilled water three times. The obtained GO was dispersed in distilled water to get a stable brown solution.GO was prepared from natural graphite powder through modified Hummers’ method1001012O4 nanocomposite materials were synthesized by a solution combustion synthesis. Initially solution A was formed by adding 0.242 g (0.001 mol) sample of Cu (NO3)2·3H2O and 0.808 g (0.002 mol) of Fe (NO3)3· 9H2O to 20 mL of water and kept for stirring for 30 min at room temperature to form a homogeneous solution. Later on, solution B was prepared by dispersing 0.150 g of GO in deionized water (1.48 mL) and ethanol (18 mL), followed by 30 min ultrasonic treatment. Then, solution B was added dropwise to solution A under vigorous stirring. After 1 h stirring, urea was added as fuel to prepare the precursor solution. Finally, the precursor solution was heated on a hot plate at 100 °C to remove the solvent until a gel-like precursor was obtained. This precursor was introduced into a preheated muffle furnace at temperature of 400 °C in air and maintained for 10 min, during which combustion reaction took place. A black foam type GO–CuFe2O4 nanocomposite materials was obtained which was characterised by various analytical techniques and used as novel catalyst for xanthene synthesis (The GO–CuFeynthesis .2O4 (10 mg) nanocomposite was stirred at 125 °C for 10–15 min. After the completion of the reaction as monitored by TLC, the reaction mixture was cooled to room temperature and solid obtained was dissolved in EtOAc (20 mL), followed by stirring the mixture for 10 min. Later on, this was filtered to separate the catalyst. The catalyst was washed with ethyl acetate (2 × 10 mL). The combined ethyl acetate extracts were washed with water (2 × 10 mL) and dried over Na2SO4. The crude product thus obtained was washed with hexane and cold ethanol. The purified product was then obtained after column chromatography. All products were characterized by comparison of their physical constants and spectral data with those for authentic samples.A mixture of the aldehyde (1 mmol), β-naphthol (2 mmol), and GO-CuFe2O4 (10 mg) nanocomposite was stirred at 125 °C for 10–20 min in water as solvent. After the completion of the reaction as monitored by TLC, the reaction mixture was cooled to room temperature and solid obtained was dissolved in EtOAc (20 mL), followed by stirring the mixture for 10 min. Later on, this was filtered to separate the catalyst. The catalyst was washed with ethyl acetate (2 × 10 mL). The combined ethyl acetate extracts were washed with water (2 × 10 mL) and dried over Na2SO4. The crude product thus obtained was washed with hexane and cold ethanol. The purified product was then obtained after column chromatography. All products were characterized by comparison of their physical constants and spectral data with those for authentic samples.A mixture of the aldehyde (1 mmol), β-naphthol (2 mmol), and GO-CuFe1H NMR and 13C NMR spectra were recorded on a Bruker spectrometer at 400 MHz using TMS as an internal standard. FTIR spectra of the product were recorded using a Perkin-Elmer FTIR spectrophotometer using NaCl support. Magnetic properties of the sample were measured by vibrating sample magnetometer (Lakeshore VSM) at room temperature. A commercial electron energy analyzer  and a non-monochromatic Mg Kα x-ray source (hv = 1253.6 eV) have been used to perform XPS measurements with the base pressure of <1 × 10−9 mbar. Catalytic reactions were monitored by thin layer chromatography on 0.2 mm silica gel F-254 plates. All the reaction products are known compounds and have been identified by comparing their physical and spectral characteristics with the literature reported values.The catalyst was analysed by X-ray diffraction study using PHILIPS PW 1830 X-ray diffractometer with CuKα source. The compositional information of the products was performed using EDX (JEOL JSM-6480 LV). Raman spectra were recorded using a BRUKER RFS 27 spectrometer with 1064 nm wavelength incident laser light. Field emission scanning electron microscopy (FESEM) of the sample was recorded by Nova Nano SEM/FEI. Transmission electron micrographs (TEM) of the sample were recorded using PHILIPS CM 200 equipment using carbon coated copper grids. The contents of Cu and Fe in the catalyst were analysed using ICP–OES made by Perkin Elmer, USA, ALPHA ATB. Nitrogen adsorption/desorption isotherm was obtained at 77 K on a Quanta chrome Autosorb 3-B apparatus. The specific surface area and pore size distribution were acquired by emulating BET equation and BJH method, respectively. 2O4 nanocatalyst was synthesized by a simple combustion method. Using this nanocomposite, a facile, efficient and environmentally-friendly protocol for the synthesis of xanthenes was reported. The catalyst was thoroughly characterized by a set of analytical techniques. The formation of spinel nanoparticles was comprehensively demonstrated by EDS mapping and scan techniques. We have for the first time demonstrated the use of GO-CuFe2O4 as highly active and efficient nanocatalyst for the synthesis of xanthene derivatives via one-pot two-component reaction of 2-naphthol with various aryl aldehydes under solventless condition. The results demonstrated that the combination of CuFe2O4 with graphene oxide results in a dramatic enhancement of the catalytic activity of CuFe2O4, which can be attributed to the remarkable synergistic effect between the CuFe2O4 and the graphene oxide sheets. The promising points for the presented methodology are efficiency, generality, high yield, cleaner reaction profile and recyclability which make it a useful and attractive process for the synthesis of xanthenes as biologically interesting compounds.In conclusion, an inexpensive and magnetically recyclable GO-CuFeHow to cite this article: Kumar, A. et al. Greener Route for Synthesis of aryl and alkyl-14H-dibenzo [a.j] xanthenes using Graphene Oxide-Copper Ferrite Nanocomposite as a Recyclable Heterogeneous Catalyst. Sci. Rep.7, 42975; doi: 10.1038/srep42975 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Importantly, the results here confirm that the Ni—Co—S ternary materials behave as an electrode for rechargeable alkaline batteries rather than supercapacitors electrodes in three‐electrode test as commonly described and accepted in the literature. Furthermore, formulas to evaluate the performance of hybrid battery devices are specified.Metal sulfides are commonly used in energy storage and electrocatalysts due to their redox centers and active sites. Most literature reports show that their performance decreases significantly caused by oxidation in alkaline electrolyte during electrochemical testing. Herein, S and N co‐doped graphene‐based nickel cobalt sulfide aerogels are synthesized for use as rechargeable alkaline battery electrodes and oxygen reduction reaction (ORR) catalysts. Notably, this system shows improved cyclability due to the stabilization effect of the S and N co‐doped graphene aerogel (SNGA). This reduces the rate of oxidation and the decay of electronic conductivity of the metal sulfides materials in alkaline electrolyte, i.e., the capacity decrease of CoNi Dai and co‐workers synthesized Co1−xS/reduced graphene oxide hybrid catalysts showing a high oxygen reduction reaction (ORR) current density of 1.1 mA cm−2 at 0.7 V versus RHE with ≈100 μg cm−2 loading density.One effective way to improve the performance of graphene materials, expand and improve their applications is to hybridize them with metal‐based semiconductors to form nanocomposites.On the basis of the above idea, we designed and synthesized N, S co‐doped (S‐rich) graphene‐based nickel cobalt sulfide aerogels (Ni—Co—S/SNGA) with the aim to optimize the performances of metal sulfides, in particlar their cycling performance and illustrate their potential widespread application. The Ni—Co—S/SNGA exhibited improved electrochemical performance as electrodes for rechargeable alkaline batteries and as electrocatalysts for ORR in alkaline electrolyte.2Figure2S4, NiCo2S4, Ni—S, and Co—S) were prepared by one‐step hydrothermal process with different precursor ratios. The materials were freeze‐dried before use. Graphene oxide (GO) was prepared by a modified Hummer's method2‐hybridized carbon frameworks.The main synthetic procedure to prepare Ni—Co—S/SNGA is illustrated by FigureThe morphologies of these materials were investigated by scanning electron microscopy (SEM). From the low‐magnification SEM images , it can be observed that the Ni—Co—S nanoparticles were distributed uniformly on the surface of the porous graphene nanosheets. Porous channels can be observed for all four types of Ni—Co—S/SNGA. From the high‐magnification images Figure2, the Figure2S4/SNGA samples, which correspond to the standard CoNi2S4 Fd‐3m crystal structures (JCPDS No. 24‐0334). XRD patterns of NiCo2S4/SNGA, Ni—S/SNGA, and Co—S/SNGA samples are shown in Figure S2b–d (Supporting Information), the peaks of which can be indexed to the standard diffraction patterns. The weak peaks at ≈24° in 2θ can be assigned as the (002) plane of SNGA. Figure 2S4 nanostructures maintained a uniform urchin‐like morphology with nanorods self‐assembled radially and grown from the center, forming CoNi2S4 nanoclusters and capped by the graphene aerogel (GA), illustrated in Figure 2S4/SNGA in Figure d‐spacing of 0.54 nm which can be indexed to the (111) plane of the Fd‐3m crystal structures of CoNi2S4, in accordance with the XRD results.The crystallographic phases of the four types of Ni—Co—S nanostructures/SNGA were further characterized by powder X‐ray diffraction (XRD). 2S4/GA, CoNi2S4/S, N co‐doped graphene hybrid materials  and CoNi2S4/SNGA samples, respectively. The two sharp peaks at 1353.2 and 1591.3 cm−1 correspond to the D and G peaks of GO and SNGA from the nanocomposites. The I(D)/I(G) value of the GO aerogel varied with the composition of the CoNi2S4 nanostructures and S, N co‐doping indicated that the degree of graphitization decreased with doping although the GO aerogel reduced to graphene.2S4/SNGA possessed the highest I(D)/I(G) value , which proved that this sample has the highest reduction degree of GO which will produce more defects structures among graphene sheets than the other samples.Figure2 C=C graphite bond. The peak at 285.6 eV was attributed to C—S and C=N bonding, indicating S and N co‐doped graphene and consistent with the Fourier transform infrared spectroscopy (FT‐IR) spectrum . The weaker 288.3 eV peak is due to defects and functional groups including C—N, C—O, and O—C—O,Raman spectroscopy was performed to confirm the graphitization and composition of the GO, CoNim KOH as the electrolyte. We investigated the optimized performance of the samples by changing the ratio of nanoparticles to SNGA. From Figure2S4/SNGA, NiCo2S4/SNGA, Ni—S/SNGA, and Co—S/SNGA were 192.1, 190.9, 167.5, and 184.0 mAh g−1, respectively, at a current density of 10 A g−1. The rate capabilities of those samples remained ≈44% of the original values, when the current density was increased by 30 times, as shown in Figure S7c (Supporting Information). The excellent specific capacity values and rate capabilities demonstrated the applicability of this rational design whereby different Ni—Co—S nanoparticles were investigated. The best performing material among the four tested as electrodes is the CoNi2S4/SNGA and the similar value can be seen from NiCo2S4/SNGA. This can be explained as the richer redox centers and the synergistic effect of both nickel and cobalt ions in the sulfides (redox reactions (1)–(3)). Figure 2S4/SNGA electrodes within the voltage range −0.1 to 0.4 V (vs Ag/AgCl) at scan rates ranging from 1 to 50 mV s−1.To explore the electrochemical performance of the as‐synthesized electrodes, we carried out cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements on the as‐synthesized materials by pressing them directly into Ni foams as the working electrode without adding any conductive agents and binders in a three‐electrode test system with 6 I varies as V1/2; for a capacitive process, it varies as V. This relation is expressed as I = baV, with the value of b providing insight regarding the charge storage mechanism. In our system, the pairs of well‐defined redox peaks can be detected in all CV curves. The fitted value of b = 0.65 for the anodic peak current and b = 0.58 for cathodic peak current, the peak current I closely varies as V1/2 (sweep rate) , indicating these redox reactions are semi‐infinite diffusion. From the curves in Figure −1), which can be explained as the polarization of the electrode at a high scan rate. These distinct peaks can be attributed to the reversible Faradaic redox processes of Ni2+/Ni3+ and Co2+/Co3+/Co4+ redox couples based on the following reactions (1–3)As clarified by Dunn and co‐workers,2S4/SNGA samples during different electrochemical steps were carried out. The change in reflections implied the phase changing during this process and confirmed that redox reactions are occurring in bulk, further demonstrating the alkaline battery reactions.Because of these types of reversible redox reactions, we defined these materials in this reaction system for energy conversion and storage as rechargeable alkaline battery electrodes. Ex situ XRD measurements  of CoNi−1). Therefore, the specific capacity values of the materials presented here are slightly lower compared to those recorded at a larger voltage range . When using different CoNi2S4 nanoparticles and SNGA ratios, i.e., 0.14 g of nanoparticles in 70 mg of GO precursors (2:1 CoNi2S4/SNGA), a high specific capacity and rate capacity were achieved compared with other ratios tested. The specific capacity was 318.3, 281.3, 226.5, 192.1, 161.1, and 141.2 mAh g−1 at current densities of 1, 2, 5, 10, 20, and 30 A g−1, respectively. The rate capability was ≈44.3% when the current density was increased 30 times. The best performance of the 2:1 CoNi2S4/SNGA is as the result of an optimum ratio of active materials and porosity. Therefore, all of the other experiments were conducted using this ratio unless stated otherwise. Compared with the CoNi2S4 nanoclusters and the same ratio CoNi2S4/GA, 1:1 and 3:1 CoNi2S4/SNGA samples exhibited higher specific capacity at all current densities.GCD performances for the various synthesized Ni—Co—S/SNGA samples were conducted in the voltage ranges of −0.1 to 0.35 V (vs Ag/AgCl). The intrinsic properties of the CV curves  were employed as depicted in Figure 2S4/SNGA material, the slope was more abrupt indicating that the Warburg resistance  appears not to be the determining factor. This material can therefore store charge more efficiently when used as an electrode.The electronic conductivities of CoNiRs) values, including inherent resistances of the active materials, bulk resistance of electrolyte, and contact resistance of the interface between electrolyte and electrodes. The Rs values were 0.155, 0.192, and 0.185 Ω for CoNi2S4/SNGA, CoNi2S4/GA, and CoNi2S4 nanoclusters, respectively . The relatively low values are similar for all three samples, which suggest the spinel structures of CoNi2S4 nanoparticles could possess metallic electronic conductivity.Rct) values, calculated from the semi‐circle in the high‐frequency region, reflect the diffusion of electrons, and are 0.43, 2.02, and 1.37 Ω for CoNi2S4/SNGA, CoNi2S4/GA, and CoNi2S4 nanoclusters, respectively. The lower capacity value of CoNi2S4 powder samples can be explained by the electrode manufacture procedure (without adding binder), which can lead to leakage and aggregation of the materials that were immersed into the electrolyte especially under the working state. The CoNi2S4/SNGA system possessed the smallest resistance among its other counterparts; its electronic conductivity is the determining factor for the high‐performance rechargeable alkaline battery electrode.Figure S11 (Supporting Information) shows the modified equivalent circuit model of our system, the equivalent series resistance . For comparison, the specific capacity value of the 3000th cycle of CoNi2S4/GA, CoNi2S4/NGA, and CoNi2S4/SGA was ≈85.1%, 77%, and 93% of its initial value under the same test conditions; moreover, the S element signal in XPS for CoNi2S4/GA and CoNi2S4/NGA could hardly be detected . The specific capacity value of the 3000th cycle for CoNi2S4 powdery sample was ≈76.5% of its initial values after cycling. The TEM mapping images  and XPS data  after cycling confirmed the composition and structure stability of the CoNi2S4/SNGA samples. Sulfur and nitrogen can also be detected from the elemental mapping images from the TEM and metal–sulfide binding can be inferred from the XPS data, which indicates that the CoNi2S4/SNGA structure is very stable and can slow down the electrochemical transformation of the metal sulfides to metal hydroxides. The morphology of CoNi2S4 nanorods became rough  after the cycling showed the Rs and Rct are 0.294 and 1.85 Ω, respectively, which increased fractionally compared with their initial values, and have comparable or slightly smaller values compared with the reported similar binder‐free metal sulfide materials before cycling.2S4/SNGA, Ni—S/SNGA, and Co—S/SNGA samples. The 3000th cycles of all these four samples possessed capacity retention higher than ≈89% . Moreover, the specific capability and low resistance  indicate these Ni—Co—S/SNGA possess high performance. By comparing the electrochemical performances of these samples, the functions of S and N doping can be clarified. Nitrogen doping could be used to improve the electron conductivity and ion electroactivity of the graphene aerogel and sulfur doping can help stabilize the metal sulfides. These evidences proved the general usability of this structure to improve the performances of the Ni—Co—S materials used for rechargeable alkaline batteries electrodes, especially the cycling performances.Lou and co‐workers reported that the surface of metal sulfides can be electrochemically transformed to metal hydroxides upon repeated cycling processes.2S4/SNGA electrode for practical applications, a solid‐state hybrid battery was fabricated by using the CoNi2S4/SNGA pressed into nickel foam as the positive electrode, the SNGA pressed into nickel foam as the negative electrode, 2 m KOH‐PVA solution as the gel electrolyte, and commercial glassy fiber paper as the separator. Solid‐state hybrid battery has similar structures as reported previously to so‐called asymmetric supercapacitors. The electrochemical reactions at the anode were as stated by reactions (2)–(4). The negative electrode is a graphene aerogel based electrical double layer capacitor (EDLC); it has the mechanism of electrostatic adsorption for energy storage at the interface of the electrodes. The device is based on the electrodes of rechargeable alkaline battery and EDLC; we defined it as a hybrid battery, as they possess obvious redox peaks with semi‐infinite diffusion reactions. Figure2S4/SNGA) at various scan rates (10–200 mV s−1) in the voltage range of 0–1.6 V. Clearly, the CV curves showed hybrid capacity of both an electric double‐layer capacitor and a redox reaction of a battery. The volumetric specific capacity of the devices was calculated from the GCD curves 2‐SDs,2@C‐SDs,3−x/MoO3−x//PANI/carbon fabric‐Ads,2@MnO2//H‐TiO2@C‐ADs,2//Fe2O3 ADs,9S8//Co3O4@RuO2‐ADs,2//RGO‐ADs.−1 within 8000 cycles. The Coulumbic efficiency of the hybrid battery stayed at ≈100%. The cycling performances are better than or comparable to the similar PVA gel electrolyte based solid‐state devices . Moreover, with the new gel electrolyte dropping on the solid‐state hybrid battery, the capacity increased dramatically with several hundreds of cycles increasing together with the internal resistance change , indicating the main reason for the decline in performance is further water evaporation in the gel electrolyte thus causing the internal resistor to increase and limiting the contacting reaction sites with the active materials.In order to evaluate the CoNi2 saturated KOH. Thus, we have also explored the use of Ni—Co—S/SNGA materials as ORR catalysts. Figure2‐saturated 0.1 m KOH at room temperature. The peak potential of Co—S/SNGA nanostructures (0.75 V vs RHE) is more positive than other Ni—Co—S/SNGA nanostructures, with similar values of NiCo2S4/SNGA (0.746 V vs RHE). The ORR performances of the four materials evaluated based on Ni—Co—S/SNGA nanostructures were further compared by rotating‐disk electrode (RDE) measurement in O2‐saturated 0.1 m KOH at 1600 rpm with a sweep rate of 10 mV s−1, as shown in Figure −2. As reported, with the increase of Ni3+ parts in Ni—Co—S, the ORR catalysts show poorer performance.2S4/SNGA from Figure S21b (Supporting Information), while the electron transfer number remained stable at 3.8–3.95, indicating a four‐electron pathway of this sample. The CoNi2S4/SNGA material also showed a four‐electron type reaction while the Ni—S/SNGA showed a mixed two‐ and four‐electron hybrid pathway. With an increase of Ni ion in the hybrid structures, the ORR performance decreased. Moreover, from the comparison experiments , the ORR performances of NiCo2S4/SNrGO are similar to that of NiCo2S4/SNGA, which indicates that the aerogel structures have almost no influence on the interaction of each component.Ni—Co—S ternary systems can also be used as electrocatalyts as they have noble‐metal‐like catalytic properties, while their stability should be influenced when used in an alkaline electrolyte especially in O2‐saturated 0.1 m KOH, higher than Co—S nanoparticles and Co—S/GA. The usability of these structures can also be evidenced by NiCo2S4/SNGA, with the ≈91.5% retention  after 12 000 s in the current–time chronoamperometric responses.Stability is another important index to evaluate the performance of ORR catalysts. As expected, the SNGA wrapped Co—S nanostructures showed better performance, and maintained ≈88.6% of the initial value after 12 000 s of current–time chronoamperometric responses at a rotation rate of 1600 rpm in O32S4/SNGA samples showed the best performance, which delivered a high specific discharge capacity of 318.3 mAh g−1 at 1 A g−1. The capacity can retain 44.3% of the initial value when the current density increased 30 times. The capacity retention of ≈95.8% of the initial specific capacity after a long GCD cycle of 10 000. The high‐rate hybrid battery based on CoNi2S4/SNGA as the positive electrode and SNGA as the negative electrode delivered a high volumetric power density of 17.5 W cm−3 while it retained its high volumetric enegy density of 1.95 mWh cm−3 at the current of 1 mA. The hybrid battery showed an excellent cycling performance and the capacity decrease was only ≈0.002% cycle−1 within 8000 cycles. When used as electrocatalysts in ORR, it was observed that an increase of Ni ion in the hybrid structures decreased the performance. Remarkably, SNGA structures capped with metal sulfide represent enhanced stability for ORR. Moreover, we confirmed the commonly regarded supercapacitor electrodes based on Ni—Co—S ternary materials as electrode in rechargeable alkaline batteries from a kinetic view. We have also proposed accurate caculation formulas to evaluate the performance of the hybrid battery devices, which could serve as a standardization for performance comparisons in future work for hybrid batteries.In summary, we have developed Ni—Co—S/SNGA materials as a viable alternative to the existing materials to improve the electrochemical performances especially the cycling performances of Ni—Co—S ternary metal sulfide materials for both rechargeable alkaline battery electrodes and ORR catalysts. The CoNiThe excellent performance of our materials is due to an increased stability and resistance against oxidation rendering them potential candidates for other applications such as metal‐ion and Li—S batteries and other electrocatalysis like oxygen evolution reaction catalysis.1.The synthesis of four kinds of nickel cobalt sulfide nanostructures; graphene oxide; nickel cobalt sulfide/S, N co‐doped reduced graphene oxide hybrid materials; S, N doped graphene‐based nickel cobalt sulfide aerogel; and S, N co‐doped graphene aerogel;2.Materials characterization;3.Electrochemical properties testing and devices fabrication.Detailed experimental sections can be found in the Supporting Information.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


Phosphorylation of histone H2AX on serine 139 (γH2AX) is an early step in cellular response to a DNA double-strand break (DSB). γH2AX foci are generally regarded as markers of DSBs. A growing body of evidence demonstrates, however, that while induction of DSBs always brings about phosphorylation of histone H2AX, the reverse is not true - the presence of γH2AX foci should not be considered an unequivocal marker of DNA double-strand breaks. We studied DNA damage induced in A549 human lung adenocarcinoma cells by topoisomerase type I and II inhibitors , and using 3D high resolution quantitative confocal microscopy, assessed the number, size and the integrated intensity of immunofluorescence signals of individual γH2AX foci induced by these drugs. Also, investigated was spatial association between γH2AX foci and foci of 53BP1, the protein involved in DSB repair, both in relation to DNA replication sites (factories) as revealed by labeling nascent DNA with EdU. Extensive 3D and correlation data analysis demonstrated that γH2AX foci exhibit a wide range of sizes and levels of H2AX phosphorylation, and correlate differently with 53BP1 and DNA replication. This is the first report showing lack of a link between low level phosphorylation γH2AX sites and double-strand DNA breaks in cells exposed to topoisomerase I or II inhibitors. The data are discussed in terms of mechanisms that may be involved in formation of γH2AX sites of different sizes and intensities. Phosphorylation of histone H2AX on serine 139 (γH2AX) is an early step in cellular response to DNA damage, when the damage results in formation of a double-strand break (DSB). Regions rich in γH2AX can extend over a stretch as long as 0.5 to 2 Mb, can be asymmetric in relation to a DSB, but do not cover the regions of active transcription –11. γH2AHere, we studied DNA damage and γH2AX foci induced by DNA topoisomerase inhibitors. It has been shown previously that camptothecin (CPT), a topoisomerase I (topo1) inhibitor, as well as mitoxantrone (MTX) and etoposide (ETP), topoisomerase II (topo2) inhibitors, induce DNA Damage Response (DDR) in a cell cycle-dependent manner. CPT induces DNA double-strand breaks (DSBs) and γH2AX exclusively in S-phase, at the sites of DNA replication –16. IndeIn this study we have turned our attention to three previous observations: (i) γH2AX foci induced by topo1 and topo2 inhibitors in S-phase do not necessarily coincide with sites of DNA replication , 20; , while the second (“dim” foci) included small size and low brightness foci (less than 0.25 μm3 volume and less than 35 gray levels). Figure In order to study γH2AX foci of various size and brightness we exposed A549 cells to CPT, MTX or ETP according to a protocol described in Figure We first analyzed ‘bright’ γH2AX foci in untreated cells, thought to report predominantly DNA damage induced by endogenous oxidants . In untrThe number of “dim” γH2AX foci in untreated cells was far greater than the “bright” ones Figure . In the Phosphorylation of H2AX foci induced by the three topoisomerase inhibitors varied in size and brightness . The “brThe numbers of “bright” γH2AX foci induced by CPT correlated with the numbers of DNA replication foci Figure  and wereMTX also induced “bright” γH2AX foci . HoweverThe number of “bright” γH2AX foci in the cells treated with ETP was relatively low  in cells treated with CPT and ETP, at distances shorter than 1 μm . In untrAnalysis of normalized cross-correlation (L) function revealed that, in cells treated with CPT, replication and “bright” γH2AX foci coincided at distances shorter than 0.5 μm . This efNo significant correlation between replication regions and “dim” γH2AX foci was observed in cells treated with topoisomerase II inhibitors (ETP and MTX) and in control –7G. On tThe number of “dim” γH2AX foci in MTX treated cells correlated with the number of replication foci and was similar (in early S) or lower (in mid and late S) than the number of “bright” foci Figure . The samIn the case of ETP the number of “dim” γH2AX foci was much greater than of “bright” foci Figure  and the It is now generally accepted that mammalian cells respond to induction of DSBs by phosphorylation of histone H2AX in nucleosomes located over long stretches of DNA on both flanks of the break –3. It apThe fact that γH2AX foci detected by immunofluorescence come in a variety of sizes and intensities was often explained as due to kinetics of their regression as a function of time following their induction by the DSB. Here we present quantitative analysis of sizes of these foci, the levels of phosphorylation, position relative to foci containing 53BP1 , and DNA replication sites to substantiate our assertion that γH2AX foci that are small in size and contain low levels of the phosphorylated histone H2AX are formed in response to DNA damage or stress but not the presence of DSBs.As this notion contradicts the generally established  opinLow intensity γH2AX immunofluorescence may adopt a form of a relatively uniform level of evenly distributed staining or small foci characterized by fluorescence levels only slightly exceeding the noise level. Their appearance is dependent on the quality of immunofluorescence staining, the type of the objective lens used, and the image processing techniques leading to a final image. We note the fact that several nuclear proteins we studied look as uniformly distributed in a live cell image of an FP-tagged fusion protein, but appear as grainy or dotty after fixation and immunofluorescence detection of the endogenous or the fusion protein. Even if the subnuclear distribution of γH2AX (more uniform or more foci-like) is contested, this does not alter the final conclusion of the reasoning presented here. Whether the low level phosphorylation is induced in a form of small foci or of somewhat larger sites, in both cases we do not observe any association with 53BP1 or DNA replication factories. If γH2AX were associated with DSBs only, such an association should be present, and it should be close to a 1-to-1 relationship. A high correlation between γH2AX and 53BP1 is found only in the case of “bright”, but not the “dim” foci γH2AX foci in CPT-treated cells in S-phase.1 into S-phase in control, untreated cells. The signal representing nonspecific binding of the secondary antibody, which is used to detect γH2AX, is not expected to depend on the level of replication,The number of “dim” γH2AX foci increases as cells move from GThere is a statistically significant higher number of “dim” γH2AX foci in CPT-treated cells that do not replicate DNA, than in untreated ones. CPT is not expected to induce DSB in cells not replicating DNA, thus the “dim” γH2AX foci in such cells can reasonably be interpreted as a chromatin modification unrelated to DSBs, yet still associated with a CPT insult,The majority of “dim” γH2AX foci are not located close to 53BP1 or DNA replication sites, while the “bright” γH2AX foci are mostly associated with DNA replication (in CPT or MTX treated cells). If “dim” γH2AX were just representing an early stage of phosphorylation at DSB sites, 53BP1 would be expected to be present in (at least) some of these sites as well. No such correlation was seen,If the ‘dim” γH2AX foci were marking DSBs induced at the sites of DNA replication in a very early stage of S-phase, incorporation of some EdU would be detected at these sites. We, as well as others, have shown that EdU is a sensitive marker of replication, with no detectable nonspecific staining or background . Our micFurther arguments in favor of the notion that the minor phosphorylation sites do not constitute a nonspecific background, a technical artifact, or a phenomenon related to DSBs, are based on the following observations:The arguments presented above essentially exclude the possibility that the “dim” foci are the markers of DSBs. The question may be asked therefore what kind of DNA or chromatin lesions may generate them. The following events may be accountable for it:1 cells. γH2AX immunofluorescence of these cells was decreased by over 50% by the short (1 h) cells exposure to the classical ROS scavenger N-acetyl-L-cysteine [It is likely that in the case of the untreated, control cells the reactive oxygen species (ROS) generated during oxidative phosphorylation are responsible for the “constitutive H2AX phosphorylation” as described by us before . Consistcysteine .CPT binds to both topo1 and DNA with hydrogen bonds stabilizing, the otherwise transient, covalent topo1-DNA complex , 35. ThiThe anthracycline antibiotic MTX, binds to DNA by intercalation elongating the ds DNA helical structure , 37. FurETP inhibits the re-ligation reaction of topo2 after it nicks the two strands of DNA, trapping it in a cleavable complex consisting of two topo2 subunits covalently linked to the 5′ ends of DNA. Because the two subunits interact strongly with each other to hold the two ends of DNA together this structure is not directly recognized as a true DSB by cells –42. FurtNeedless to say, the constitutive phosphorylation of H2AX as reported in the case of untreated, control cells and related to the production of oxidative species by mitochondria  and presIt should be noted that in addition to the effect of topoisomerase inhibitors on DNA replication, as discussed above, also their impact on transcription may play a role in inducing H2AX phosphorylation that can lead to the “dim” foci. It was shown that DNA breaks resulting from collision of elongating RNA polymerase with the inhibitor-DNA binding sites take place only on a single (template) DNA strand whereas the non-template strand within the transcription bubble remains intact , 44. It A549 human lung adenocarcinoma cells were obtained from ATCC and maintained as described previously . Exposur2+ and Mg2+ for at least 1 h with 7 or more replacements of the washing solution. Care was taken not to allow the sample to dry.Before immuno-labeling, cells were permeabilized with 0.5% Triton-X 100 and blocked overnight with BSA  in moist chamber in 4°C. DNA damage response and repair of double strand breaks (DSB) were detected by fluorescence immunostaining of γH2AX [® EdU AlexaFluor647N Imaging Kit; Molecular Probes/ Thermo Fisher Scientific). The labeling procedure was carried out according to the manufacturer instructions. After labeling, samples were mounted on glass slides using ProLong Gold Antifade Mountant (Molecular Probes/Thermo Fisher Scientific).In order to label newly replicated chromatin, incorporation of EdU, followed by ‘click’ reaction with a fluorescent label was performed  was used to image fixed cells. The following instrumental parameters were used: 63× HCX PL APO CS NA 1.4 oil immersion lens, confocal iris set at 1 Airy disc, excitation 488 nm (Ar laser), 561 nm (DPSS laser) and 633 nm (HeNe laser), emission detection bands 500–550 nm for AlexaFluor488 (immunofluorescence of 53BP1), 570–620 nm for AlexaFluor555 (immunofluorescence of γH2AX) and 660–720 nm for AlexaFluor647N (EdU Click-iT detection). Registration was performed in sequential mode, with a scanning rate of 8000 Hz (resonant scanner), 8 bit dynamic range, with 16 averaged frames for one confocal plane. One 3D stack consisted of at least 80 confocal slices, confocal planes  were separated by 130 nm along z axis.3D images were deconvolved using Huygens Deconvolution & Analysis Software . Quantitative analysis of the deconvolved images representing replication factories or γH2AX or 53BP1 foci was used to determine their position, number and volume. Raw images were used to estimate mean fluorescence intensity of individual γH2AX foci.3 or a mean intensity over 35 a.u. were classified as “bright” foci. The foci characterized by a lower volume and fluorescence intensity were classified as ‘dim’  of positions of γH2AX foci and replication or 53BP1 foci was characterized over a range of distances using normalized Ripley's K functions (L-functions). The functions were calculated for each nucleus. Detailed description of the algorithm was given in our previous paper , 20. Brit-test was used in statistical analysis, using a value of t < 0.05 as a measure of significance. The number of nuclei analyzed for each drug treatment in each sub-stage of S phase was at least 18 (the exact numbers are provided in An independent student's