The photocatalytic performance of graphene oxide/zinc oxide (GO/ZnO) nanocomposite was investigated for degradation of methylene blue (MB) from wastewater and was compared with that of zinc oxide (ZnO), graphene oxide (GO) and carbon nanotube/zinc oxide (CNT/ZnO). The properties of the GO/ZnO nanocomposite were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM and TEM results revealed the nanostructure of the composite. The photocatalytic process was modeled by response surface methodology (RSM), considering four independent factors. The significance of the model was approved by analysis of variance (ANOVA) (determination coefficient R2 = 0.95, R2adj = 0.91). The optimum conditions of the process were found to be at photocatalyst dosage, initial pH, H2O2 concentration and irradiation time of 2.1 g L-1, 4.5, 3.5 × 10-4 mol L-1 and 140 min, respectively. The removal of MB over GO/ZnO was 99% under the optimum conditions and was superior than that over GO and CNT/ZnO. According to Pareto analysis of the modeling, the irradiation time and photocatalyst dosage were the most effective factors on the decolorization efficiency of methylene blue, respectively.

Graphene oxide (GO) was synthesized from natural graphite using the Hummers method. Graphene oxide/zinc oxide nano composite were synthesized by mixing of GO and ZnO solutions and then freeze drying. The adsorptive performance of the nano composite was investigated in the removal of methylene blue. The statistical study of the adsorption process was carried out by response surface methodology (RSM). Experimental variables such as sample pH, adsorption time, dye concentration and adsorbent dosage were considered for the optimization process. The process was optimized by response surface methodology (RSM) through Box-Benhken method. The optimum conditions, predicted by the RSM were obtained at pH, contact time, initial dye concentration and adsorbent dosage of 6,8.5 min, 5 ppm, 0.02 g, respectively. The removal of methylene blue under optimum conditions was predicted to be 98.17 % and resulted in 97 % in practice. The Pareto analysis suggested that order of relative importance of the factors were as follows: adsorbent dosage > dye concentration > adsorption time > pH. Under optimized conditions, GO/ZnO nano composite showed a higher capacity than GO, carbon nanotube (CNT), ZnO and ZnO/CNT for adsorption of methylene blue. The study revealed that GO/ZnO could be a promising adsorbent for removal of industrial dyes from wastewaters.