Photochemical degradation of toluene in gas-phase under UV/visible light graphene oxide-TiO2 nanocomposite: influential operating factors, optimization, and modeling

The current study aimed to investigate the removal efficiency of toluene using synthesized titanium dioxide-graphene oxide composites under visible light and UV irradiation. The characterization of synthesized composites was examined by field emission scanning electron microscope equipped with energy dispersive, X-ray diffraction and fourier transforms infrared. In order to find the optimum of the main experimental parameters affecting the removal efficiency of toluene including the length of the reactor, initial concentration, and flow rates, central composite design together with response surface methodology with R software was used. The initial concentration of toluene in the inlet of the reactor as well as its concentration in the outlet was measured using gas chromatography with the flame ionization detector. Analysis of variance results for the quadratic model showed that the highly significant and simple linear regression was established as a predicting model. Multiple and adjusted R-2 were 0.965 and 0.974 for UV irradiation GO-TiO2 model and 0.951 and 0.959 for visible light GO-TiO2 model, respectively. As such, the differences less than 0.2 between multiple and adjusted R-2 in two models indicate that two examined models were fitted well. The highest removal efficiency of toluene using UV irradiation GO-TiO2 and visible light GO-TiO2 was obtained at optimum condition; length of reactor 40 cm, initial concentration of 0.1 ppm, and flow rate equal to 1 l min(-1), with 97.7 and 77.2%, respectively. The results indicated that the removal efficiency of toluene increased considerably with rising the length of the reactor, decreasing flow rates, and initial concentration.