Photocatalytic reduction of Cr(VI) by char/TiO2 composite photocatalyst: optimization and modeling using the response surface methodology (RSM)

Abstract

The photocatalytic reduction of Cr(VI) using pyrolytic char/TiO (PC/TiO) composite catalyst under simulated solar irradiation was studied. Response surface methodology (RSM) and experimental design were used for modeling the removal kinetics and for the optimization of operational parameters. RSM was developed by considering a central composite design with four input variable, i.e. catalyst concentration, initial concentration of Cr(VI), pH, and % (v/v) methanol concentration for assessing individual and interactive effects. A quadratic model was established as a functional relationship between four independent variables and the removal efficiency of Cr(VI). It was found that all selected variables have significant effect on Cr(VI) removal efficiency; however, the pH, the % concentration of methanol, and their interaction exhibited the major effects. Within the studied experimental ranges, the optimum conditions for maximum Cr(VI) removal efficiency (72.1 %) after 60 min of photocatalytic treatment were: catalyst concentration 55 mg L, Cr(VI) concentration 20 mg L, pH 4, and 5 % (v/v) methanol concentration. Under optimum conditions, Cr(VI) reductive removal followed pseudo-first-order kinetics, and nearly complete removal took place within 90 min. The results revealed the feasibility and the effectiveness of PC/TiO as photocatalyst in reduction reactions due to their ability of e-h pair separation increasing the transfer of the photogenerated e to the catalyst's surface and thus the reduction of Cr(VI).

Fabrication of Hydrotalcite-like Copper Hydroxyl Salts as a Photocatalyst and Adsorbent for Hexavalent Chromium Removal

“…Moreover, the lower Eg enhances the light absorption of this material, resulting in more production of electrons for the Cr(VI) reduction. To compare with the other, Cu-HyS-urea exhibited excellent Cr(VI) reduction and was comparable with the other composite materials such as Fe3O4-ZnAl-layered double hydroxide/TiO2 composites [44], acid modified g-C3N4 [45], MWCNTs-Fe3O4@PES nanofibers [46], and char/TiO2 composite photocatalyst [47], which are difficult to synthesize. Thus, Cu-HyS-urea can be an alternative photocatalyst for practical wastewater management with easy preparation and high Cr(VI) removal efficiency.…”

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