Graphene Zinc Oxide Research Articles

Remarkable performance of GO/ZnO nanocomposites under optimized parameters for remediation of Cd (II) from water

The rapid increase in toxic Cd (II) levels in water demand urgent steps toward its remediation. Here, we synthesized graphene oxide/zinc oxide (GO/ZnO) nanocomposites for Cd(II) ion removal from water, using modified Hummers and chemical precipitation methods to synthesize GO and ZnO nanoparticles, respectively. Nanocomposites were synthesized with 0.1, 0.5, and 1 wt% GO and 2.5 wt% ZnO by solution mixing in ethanol followed by characterization of its morphology, surface chemistry, crystal structure, and specific surface area. Adsorption studies were carried out at room temperature and parameters such as pH, initial metal ion concentration, and contact time were optimized for maximizing Cd(II) removal. Adsorption process followed Langmuir isotherm and pseudo-second-order kinetics. Nanocomposites with GO: ZnO in the weight ratio of 2:98 had the highest adsorption capacity for Cd(II) ions of 4125 ± 796 mg/g. Post-adsorption studies confirmed Cd(II) in the X-ray photoelectron spectra of the composite due to chemisorption of Cd(II) on the GO/ZnO surface. The synergistic effect of enhancement functional groups and the increase in the specific surface area made the GO/ZnO nanocomposite a promising material for effective removal of excess Cd(II) from water and maintaining it within WHO limit.

Hydrothermal synthesis of GO/ZnO composites and their micromorphology and electrochemical performance

In this study, a graphene oxide/zinc oxide (GO/ZnO) composite was synthesized by the one-pot hydrothermal technique using various GO/ZnO ratio compositions. These were characterised by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and Raman spectroscopy. The findings reveal that the GO/ZnO composite has three different micromorphologies: ZnO-nanorods (ZnO-NRs) were embedded and agglomerated over the GO surface; ZnO-microrods (ZnO-uRs) adhered to and separated on the GO surface; and GO was coated by ZnO at 1:1, 1:2 and 1:8 ratios. In addition, the electrochemical performance of the synthesized GO/ZnO composites was investigated using cyclic voltammetry (CV). The results show that the embedded and agglomerate of ZnO-NRs over the GO surface have the best performance, indicated by a larger CV curve area and higher specific capacitance than the GO and other GO/ZnO composites. The results indicate that the incorporation and insertion of GO and ZnO NRs have an effective reversible nature and are promising electrode materials for supercapacitor applications.

The effect of metallic and nonmetallic oxide nanoparticles dispersed Mahua biodiesel on diesel engine performance and emission characteristics

The objective of this study is to evaluate the performance and emission characteristics of a diesel engine using metallic graphene oxide (GO) and nonmetallic zinc oxide (ZnO) nanoparticles in a Mahua biodiesel blend (B20). At a concentration of 75 mg/L, both GO and ZnO nanoparticles were considered and a surfactant (CTAB) and a dispersant (TWEEN 80) were added at a 1:1 ratio for surface modification. The nanofuel samples were analyzed for stability using a spectrophotometer. The nanoparticles mixed with dispersants and surfactants have shown improved stability. In addition, the injection pressure was varied from 200 to 250 bar. Dispersion of GO and ZnO nanoparticles in BD20 improved performance parameters such as BTE and BSFC. In addition, there was a significant decrease in CO, HC, smoke, and NOx emissions. TWEEN 80-added GO and ZnO nanoparticles in B20 achieved the best results, followed by the CTAB-added nanoparticles. In addition, the operating parameters showed a favorable trend toward improvement at higher injection pressures. At 250 bar, BTE was improved by 4.24% and BSFC was reduced by 3.59% compared to diesel. Also, the CO, UHC, NOx, and smoke opacity were reduced by 47.05%, 15.12%, 18.96%, and 37.09% for B20 + ZnO75 mg/L + TWEEN75 mg/L, respectively.

Effect of GO Solution Temperature on the Structural, Optical and Electrical Properties of ZnO Nanostructured for Photoanode Function

The purpose of this study is to determine the effect of different graphene oxide (GO) solution immersion temperature on the structural, morphology, optical, and electrical properties of zinc oxide/graphene oxide (ZnO-GO) nanostructures. The ZnO/GO nanostructures prepared at various GO solution immersion temperature from 75-95℃ using solution immersion method. The structural properties of the samples were investigated using X-ray diffraction (XRD), and the recorded patterns revealed that all the samples had a preferred orientation along the (002) plane. The crystallinity of ZnO/GO nanostructures were enhanced with increasing GO solution immersion temperature. The morphology of ZnO/GO nanostructures was determined using field emission scanning electron microscopy (FESEM). Fourier transformation infrared spectroscopy (FTIR) was used to determine the molecular compounds of ZnO/GO nanostructures. The peak intensity of GO with ZnO nanoparticles is shifted at 744 to 1243 cm-1 when the temperature of GO solutions increases. The UV–visible spectrophotometer was used to examine the optical properties of ZnO/GO nanostructures. It is found that the highest transmittance ZnO/GO nanostructures was obtained at the highest GO solution immersion temperature which is 95℃. Based on the current-voltage(I–V) measurement, the electrical properties of ZnO/GO nanostructures increase when the GO solution immersion temperature increases. Thus, by variation of GO solution immersion temperature the structural, morphology, optical, and electrical behaviour were improved.

Synergistic effect of GO/ZnO loading on the performance of cellulose acetate/chitosan blended reverse osmosis membranes for NOM rejection

Declining freshwater resources along with their pollution are threatening the life existence on earth. To meet the freshwater demand, one of the most appropriate and possible ways which has been adopted all over the world is to reuse wastewater by removing its impurities. Among many water pollutants, natural organic matter (NOM) is found to be responsible as major precursor for the formation of other pollutants. Removal of NOM from wastewater is being done by using membrane filtration systems incorporated with certain nanofillers to increase membranes efficiency and permeability. In this study, novel nanocomposite reverse osmosis (RO) membranes were prepared using cellulose acetate and chitosan in N,N-Dimethyl formamide. Graphene oxide (GO) nanosheets and zinc oxide (ZnO) in different concentration were loaded to modify the membranes for tuning their RO performance. The confirmation of the functional groups is demonstrated by Fourier transform infrared spectroscopy which revealed the specific peaks indicating the formation of the nano-composite membranes. The surface morphology was studied by scanning electronic microscopy which shows a gradual transformation of the membrane surface from voids-free to macro-voids filled surface up to threshold concentration of GO and ZnO. The thermal properties of GO based membranes were analyzed using thermogravimetric analysis and differential scanning calorimetry. The uniform interaction of the GO and ZnO with polymers induced the remarkable thermal properties of the synthesized membranes. Permeate flux and contact angle measurements were considered to estimate their water content (96%) capacity and NOM rejection (96%) using 0.1 ppm humic acid solution. The permeate flux, NOM rejection and the water content changed directly with GO and inversely with ZnO wt% in the membranes up to GO5 (GO:0.14: ZnO:0.03) whereas the contact angle exhibited the inverse relationship with GO and ZnO concentration in casting solution of the synthesized membranes. Hence it can be concluded that prepared RO membranes are suitable for NOM rejection and recommended for water treatment.

Biomass Mediated Synthesis of ZnO and ZnO/GO for the Decolorization of Methylene Blue under Visible Light Source

In this study, zinc oxide (ZnO) as well as ZnO/GO (zinc oxide/graphene oxide) were successfully synthesized. The Carica papaya leaf extract was used to synthesize ZnO and oil palm empty fruit bunch biomass to obtain graphene, which was further used to obtain graphene oxide. The samples were characterized through a variety of analytical methods such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy and UV–Visible spectroscopy in order to understand their morphology, size, structural phase purity, functional groups and optical properties. Various peaks such as O-H, Zn-OH and Zn-O were found in the case of ZnO. Some additional peaks, such as C-C and C=C, were also been detected while analyzing the sample by Fourier-transform infrared spectroscopy. The results of the XRD and SEM studies demonstrated that the synthesized material shows the crystalline nature of the substance in the case of ZnO, and the crystallinity decreases for ZnO/GO. The average crystallite size was found to 80.0 nm for ZnO and 74.0 nm for ZnO/GO. Further, a red shift was shown in the case of ZnO/GO, which was indicated by the UV–Vis absorption spectrum. In the TEM analysis, the particles were shown to be nanosized. For instance, the highest number of particles was found in the range of 100 to 120 nm in the case of ZnO, while 80–100 nm sized particles were found for ZnO/GO. Using synthesized ZnO and ZnO/GO, the decolorization of methylene blue was found to be 64% and 91%, respectively.

Reduced Graphene Oxide-Zinc Sulfide Nanocomposite Decorated with Silver Nanoparticles for Wastewater Treatment by Adsorption, Photocatalysis and Antimicrobial Action.

Reduced graphene oxide nanosheets decorated with ZnS and ZnS-Ag nanoparticles are successfully prepared via a facile one-step chemical approach consisting of reducing the metal precursors on a rGO surface. Prepared rGO-ZnS nanocomposite is employed as an adsorbent material against two model dyes: malachite green (MG) and ethyl violet (EV). The adsorptive behavior of the nanocomposite was tuned by monitoring some parameters, such as the time of contact between the dye and the adsorbent, and the adsorbent dose. Experimental data were also simulated with kinetic models to evaluate the adsorption behavior, and the results confirmed that the adsorption of both dyes followed a pseudo 2nd order kinetic mode. Moreover, the adsorbent was also regenerated in a suitable media for both dyes (HCl for MG and ethanol for EV), without any significant loss in removal efficiency. Ag doped rGO-ZnS nanocomposite was also utilized as a photocatalyst for the degradation of the selected organic contaminant, resorcinol. The complete degradation of the phenolic compound was achieved after 60 min with 200 mg of rGO-ZnS-Ag nanocomposite under natural sunlight irradiation. The photocatalytic activity was studied considering some parameters, such as the initial phenol concentration, the photocatalyst loading, and the pH of the solution. The degradation kinetics of resorcinol was carefully studied and found to follow a linear Langmuir-Hinshelwood model. An additional advantage of rGO-ZnS and rGO-ZnS-Ag nanocomposites was antibacterial activity against Gram-negative bacterium, E. coli, and the results confirmed the significant performance of the nanocomposites in destroying harmful pathogens.

Optimisation of aqueous phase low density polyethylene degradation by graphene oxide-zinc oxide photocatalysts

Microplastic has become one of the ubiquitous pollutants due to its vast growing number in the environment. This is the first study that utilised Design Expert software to interpret the interaction between pH, temperature and catalyst dosage on the microplastic mass loss. In this study, the applicability of photocatalysis in degrading in low density polyethylene (LDPE) microplastic was investigated by using graphene oxide/zinc oxide (GO-ZnO) photocatalyst under UV light irradiation. The photocatalysts were analysed with a scanning electron microscope with energy dispersive X-ray analysis (SEM-EDX) to identify the surface morphology and particle size. The average crystallite size of ZnO on GO was 16.43 nm. Fourier transform infrared spectroscopy (FTIR) was used to determine the polymer type used as the microplastic model and to confirm the fabrication of GO-ZnO. From the preliminary study, the microplastic mass loss was the highest at 1000 ppm of GO-ZnO dosage. The photodegradation efficiency was found to be the highest at pH 7 solution compared to acidic and alkali condition. In addition, the mass loss of microplastic increased with operating temperature. The reduced quadratic model was developed to predict the microplastic mass loss under the photodegradation of GO-ZnO. The interaction of pH, temperature and catalyst loading was analysed with Box-Behnken Design via Design Expert 12. From the results obtained, the individual impacts of the catalyst dosage as well as the interaction between pH and temperature were significant in affecting the microplastic degradation. The relative importance of the affecting parameters are arranged: photocatalyst dosage> pH and temperature> temperature and photocatalyst dosage> temperature> pH. The optimum condition where the highest microplastic mass loss was reported (microplastic mass loss of 39.47%) were found to be at pH 9.66, 30 ℃, 1500 ppm within 2 h of photodegradation. Furthermore, the reusability of the GO-ZnO was also reported.

A 3D reduced graphene oxide and flower-like ZnO crystal composite for electrochemical detection of reducing small biomolecules

Three-dimensional reduced graphene oxide (3DrGO) and a flower-like zinc oxide (ZnO) crystal were prepared using a hydrothermal method.

Investigation of malachite green removal using graphene oxide-zinc oxide composite from aqueous solution: synthesis, characterization and application

Investigation of malachite green removal using graphene oxide-zinc oxide composite from aqueous solution: synthesis, characterization and application

A "turn-off" photoluminescent sensor for H2O2 detection based on a zinc oxide-graphene quantum dot (ZnO-GQD) nanocomposite and the role of amine in the development of GQD.

In this work, graphene quantum dots (GQD) were prepared through a hydrothermal process. The photoluminescence (PL) emission spectrum for GQD prepared with high NH4OH concentration (sample D1-t) was attained at lower wavelength (406 nm), compared to GQD synthesized with low NH4OH concentration (sample D2-t attained at 418 nm). From these results, a smaller particle size for D1-t was deduced; according to TEM images the GQD particles are around 5 nm. The Raman ID3/IG ratio which is related to C-O groups at the edges of GQD and the full width at half maximum was lower for D1-t than D2-t. This was ascribed to the amine group incorporation at the edges and at the basal planes in D1-t, whilst in D2-t they prefer principally the edges of the GQD structure. The ZnO nanoparticles bonded to GQD (ZnO-GQD, nanocomposites) enhance the PL emission intensity. The H2O2 detection tested by photoluminescence spectroscopy, was found to occur thanks to the ZnO from the nanocomposite and its interaction with H2O2, producing a quenching effect. This quenching was accentuated by the increase of the H2O2 concentration. Such properties suggest the ZnO-GQD nanocomposite as a candidate to be used as a sensor material.

Functionalized graphene oxide-zinc oxide hybrid material and its deployment for adsorptive removal of levofloxacin from aqueous media

This work reports on the synthesis of aspartic acid-functionalized graphene oxide-zinc oxide, as a functional porous material, and its potential to mitigate levofloxacin (LFXN). The adsorbent was characterized by various techniques, including ultraviolet–visible (UV–Vis), Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The average crystallite size of the prepared composite was about 17.30 nm. Batch adsorption studies were carried out to elucidate the adsorption process for LFXN. Different parameters, including contact time, LFXN initial concentration, adsorbent concentration, pH, temperature, and ionic strength were studied. The mechanism and kinetics were studied by fitting the data to Freundlich and Langmuir isotherms, pseudo-first-order and pseudo-second-order kinetic models, respectively. The isotherm data was better fitted to Langmuir isotherm (R2 = 0.999) as compared to the Freundlich model. The maximum adsorption capacity obtained at equilibrium was 73.15 mg/g. For kinetic studies, Pseudo first order was better fitted with R2 = 0.87797, confirming the physisorption process. Thermodynamics parameters revealed that the process was exothermic and spontaneous at low temperatures. The adsorption mechanism was studied and the impregnation of LFXN in the adsorbent was confirmed by FTIR studies. This research proved that the designed GO/Asp-ZnO was a novel and promising adsorbent for the removal of LFXN with an efficiency of 95.12% at 30 mg/L LFXN by 0.6 g/L adsorbent in 24 h at pH = 7 and T = 25 °C.

GO/ZnO nanocomposite - as transducer platform for electrochemical sensing towards environmental applications

Graphene Oxide-Zinc Oxide (GO-ZnO) – a new nanomaterial that has queued the interest of researchers. Their intriguing promising physical and electrochemical features of electrode material have led to its widespread use in electrochemical sensor applications. GO-ZnO based nanomaterial were extensively exploited in the construction of electrochemical sensors due to their adaptability and distinct qualities. On understanding the structural role of these materials, their modification processes are critical for realizing their full potential. The advancement of technology on new concepts and strategies has revolutionized the field of sensor devices with high sensitivities and selectivity. These tools can test a range of contaminants quickly, accurately, and affordably while performing automated chemical analysis in complicated matrices. This paper highlights the electrochemical transducer surface for sensing various analytes and current research activity on GO-ZnO nanocomposite. Additionally, we talked about current developments in GO-ZnO nanostructured composites to identify relevant analytes (i.e., Nitrophenols, Antibiotic Drugs, Biomolecules). While being used in the laboratory, the majority of produced systems have proven to bring about excellent gains. Their monitoring application still has a long way to go before it is fixed due to problems like technological advancements and multifunctional strategies to get around the challenges for improving the sensing systems.

A novel synthesis of graphene oxide-titanium dioxide (GO-TiO2) and graphene oxide-zinc oxide (GO-ZnO) nanocomposites and their application as effective, reusable photocatalysts for degradation of methylene blue (MB) dye

Abstract The current study focuses on graphene oxide (GO) and its composite with zinc oxide and titanium dioxide nanoparticles to develop a simple nano chemistry-based clean and efficient process for the effective degradation of methylene blue (MB) dye. Graphene oxide composite with zinc oxide and titanium dioxide nanoparticles were fabricated via a thermal coupling process that demonstrates exclusive physiochemical properties. A detailed comparison of the structure, morphology, and surface analysis of synthesized GO and nanocomposites, as well as their electrochemical properties, has been accomplished. By using the degradation of methylene blue (MB) dye the photocatalytic function of nanocomposites was studied. Results reveal that the rate constants of GO, GO-TiO2, and GO-ZnO photocatalysts are 1.06 × 10−3 min−1, 2.56 × 10−3 min−1, and 1.63 × 10−3 min−1 respectively which discloses GO-TiO2 nanocomposite shows maximum degradation of MB dye among both catalysts. The reuse of photocatalyst even after five cycles retained the degradation efficiency of 80, 77, and 49% respectively for GO-TiO2, GO-ZnO, and GO when tested against MB. Hence, as a result, it was determined that these photocatalysts are ideal for the remediation of dye-contaminated wastewater.

Adsorption and Kinetics Studies of Cr (VI) by Graphene Oxide and Reduced Graphene Oxide-Zinc Oxide Nanocomposite.

In this work, graphene oxide (GO) and its reduced graphene oxide-zinc oxide nanocomposite (rGO-ZnO) was used for the removal of Cr (VI) from aqueous medium. By employing a variety of characterization techniques, morphological and structural properties of the adsorbents were determined. The adsorption study was done by varying concentration, temperature, pH, time, and amount of adsorbent. The results obtained confirmed that rGO-ZnO is a more economical and promising adsorbent for removing Cr (VI) as compared to GO. Kinetic study was also performed, which suggested that sorption of Cr (VI) follows the pseudo-first-order model. For equilibrium study, non-linear Langmuir was found a better fitted model than its linearized form. The maximum adsorption capacity calculated for GO and rGO-ZnO nanocomposite were 19.49 mg/g and 25.45 mg/g, respectively. Endothermic and spontaneous nature of adsorption was detected with positive values of ΔS (change in entropy), which reflects the structural changes happening at the liquid/solid interface.

Enhanced adsorptional-photocatalytic degradation of chloramphenicol by reduced graphene oxide-zinc oxide nanocomposite

Improper discharge of waste dry cell batteries and untreated antibiotics laden effluents to the environment pose serious threat to the sustenance of the ecosystem. In this study, synthesis of reduced graphene oxide-ZnO (rGO-ZnO) nanocomposite was achieved via a bioreduction process using waste dry cell battery rod as graphene oxide (GO) precursor. The nanocomposite was applied in the ultraviolet photocatalytic degradation of chloramphenicol (CAP) at 290 nm in the presence of hydrogen peroxide. RGO-ZnO nanocomposite was characterized by SEM, TEM, XRD, BET and FTIR. TEM image of the nanocomposite revealed a polydispersed, quasi-spherical zinc oxide on a coarse reduced graphene oxide surface. XRD patterns showed sharp, prominent crystalline wurtzite hexagonal phases of ZnO and rGO. BET surface area of the nanocomposite was 722 m2/g with pore size of 2 nm and pore volume of 0.4 cc/g. % photo-removal efficiency increased with increasing irradiation time but diminished at higher pH, temperature and CAP concentration. Photocatalytic adsorption process fitted more accurately into the Freundlich model (R2 = 0.99) indicating a multilayer adsorption mechanism. 92.74% reduction in chemical oxygen demand (COD) level of veterinary effluent was obtained after treatment with the nanocomposite thus affirming its effectiveness in real waste water samples.

Silica sand-supported nano zinc oxide-graphene oxide composite induced rapid photocatalytic decolorization of azo dyes under sunlight and improved antimicrobial activity.

Here, silica sand-supported heterojunction composite of nano zinc oxide (nZnO) and graphene oxide nanosheet (nZnO-GO@SS) was prepared, and its potential as an efficient photocatalyst for the degradation of methylene blue (MB) and Rhodamine-B (Rh-B) under sunlight was demonstrated. Transmission electron microscopy confirmed the uniform distribution of spherically shaped nZnO of average size of approximately 8 nm over graphene oxide nanosheet (GO) in the composites. Photodegradation yields of 95.3% and 97.5% for 100 ppm of MB and Rh-B dye within 150 and 220 min, respectively, were achieved under sunlight by the prepared nanocatalyst (nZnO-GO), while sand microparticle-supported nanocatalyst (nZnO-GO@SS) demonstrated faster degradation of MB and Rh-B, i.e., within 120 and 160 min, respectively. Furthermore, when the recyclability of the photocatalyst was studied, the nZnO-GO exhibited more than 80% degradation efficiency after five cycles for both the dyes and nZnO-GO@SS demonstrated 10% higher (~90%) removal capability after five cycles of reuse. Furthermore, the antibacterial assay showed complete inactivation of Escherichia coli and Staphylococcus aureus bacterial strain by nZnO-GO@SS. Hence, our proposed strategy for the removal of toxic dyes from the aquatic environment under sunlight proved that sand microparticle-supported nanocatalyst (nZnO-GO@SS) might be a superior, cost-effective, and suitable photocatalytic system for industrial applications toward toxic dye removal and decontamination from industrial wastewater.

Zinc Oxide–Graphene Nanocomposite-Based Sensor for the Electrochemical Determination of Cetirizine

A nanocomposite electrode of graphene (Gr) and zinc oxide (ZnO) nanoparticles was fabricated to study the electrochemical oxidation behavior of an anti-inflammatory drug, i.e., cetirizine (CET). The voltametric response of CET for bare CPE, Gr/CPE, ZnO/CPE, and the ZnO-Gr nanocomposite electrode was studied. The modifier materials were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) to comprehend the surface morphology of the utilized modifiers. The influence of pH, scan rate, and accumulation time on the electrooxidation of CET was examined. It was found that the electrochemical oxidation of CET was diffusion-controlled, in which two protons and two electrons participated. The detection limit was found to be 2.8 × 10−8 M in a linearity range of 0.05–4.0 µM. Study of excipients was also performed, and it was found that they had negligible interference with the peak potential of CET. The validation and utility of the fabricated nanocomposite sensor material were examined by analyzing clinical and biological samples. Stability testing of the nanocomposite electrode was conducted to assess the reproducibility, determining that the developed biosensor has good stability and high efficiency in producing reproducible results.

Effect of CuO/rGO and ZnO/rGO Hybrid Additional Layers on Supercapacitor Performance

Increasing the specific electrical capacitance of supercapacitors has been received great attention from both researchers and industry. Herein, how to achieve this by coating the surface of reduced graphene oxide (rGO) with copper(II) oxide (CuO) and zinc oxide (ZnO) is reported. The CuO/rGO and ZnO/rGO hybrid layers were prepared via chemical reactions between graphene oxide (GO) and salts of copper and zinc, respectively. The crystallographic structures and surface morphologies of composite materials were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Cyclic voltammetry (CV) and electrical capacitance measurements were used to analyze the electrochemical properties of the composites. The results show that CuO and ZnO increased the specific electrical capacitance of rGO, while the composite CuO/rGO and ZnO/rGO materials have good chemical stability with a higher specific electrical capacity (465.73 F×g−1) than CuO/rGO (167.52 F×g−1), ZnO/rGO (185.48 F×g−1), rGO (113.50 F×g−1), and annealed graphite (53.12 F×g−1). The mechanism of increasing the specific capacitance depending on whether the composite CuO/rGO and ZnO/rGO materials act as a pseudocapacitor and/or an electrical double-layer capacitor is elucidated.
 HIGHLIGHTS
 
 One challenging problem for supercapacitor improvement is increasing its specific electrical capacitance
 CuO/rGO and ZnO/rGO hybrid layers were prepared using graphene oxide and copper and zinc salts
 The composite CuO/rGO and ZnO/rGO materials have better chemical stability with a higher specific electrical capacity than CuO/rGO, ZnO/rGO, rGO, and annealed graphite
 
 GRAPHICAL ABSTRACT

Preparation of rGO/ZnO photoanodes and their DSSCs performance

Abstract In this study, we report a mild and controllable preparation method for graphene oxide (GO) and ZnO ultrafine powder, respectively. On this basis, reduced graphene oxide (rGO)/ZnO composite powder for the photoanodes of dye-sensitized solar cells (DSSCs) was synthesized by chemical reduction method. Phase composition, microstructure, chemical structure, conductivity, and specific surface area were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Raman, and Brunauer-Emmett-Teller (BET) method, respectively. Photoelectric performance of DSSCs was studied by the current density-voltage (J-V), electrochemical impedance spectra (EIS) photoelectric test system. As rGO possesses higher adsorption capacity and excellent conductivity, hence it may effectively promote separation of electrons and holes, transmission ability of electrons and holes, and utilization of the light. By contrast, the as-synthesized zinc oxide (ZnO) may increase adsorption capacity of dye molecules, so photoelectric conversion efficiency (PCE) of the solar cells is increased by means of synergistic effects. When adding rGO in the rGO/ZnO composite powder at 1.25 wt%, PCE reaches to 6.27%, an increase of 20.6% more than that of pure ZnO as the photoanode.