Efficient removal of Cr(VI) from wastewater by ZnO-polyacrylic acid/cellulose fiber/polyethylene glycol hydrogel: Synergistic effect of adsorption and photocatalytic reduction

A novel polyacrylic acid/carboxylated nanocellulose fiber/polyethylene glycol hydrogel loaded with nano-ZnO (ZnO-PAA/CNF/PEG: GH-2 (wt(ZnO)% = 12% and wt(PEG)% = 16%)) was synthesized to remove Cr(VI) from wastewater by adsorption synergistic photocatalytic reduction. The effects of ZnO content, PEG content and pH on the removal efficiency of Cr(VI) were investigated. The removal performance and mechanism of Cr(VI) by hydrogels were systematically studied by various techniques. The results showed that when the initial pH = 2, the initial concentration of Cr(VI) = 20 mg/L, the hydrogel dose = 0.5 g/L, and Irradiation power of mercury lamp was 500 W, the removal efficiency of Cr(VI) was 97.22% (dark adsorption for 60 min and photocatalysis for 50 min). The addition of PEG greatly reduced the agglomeration of nano-ZnO in GH-2 and facilitated the separation of photogenerated electron-hole pairs. The adsorption process of Cr(VI) by GH-2 accords with pseudo-second-order kinetics. The photocatalytic process conforms to the pseudo-first-order reaction kinetics. Under the optimal experimental conditions, the removal efficiency of Cr(VI) by GH-2 was still as high as 87.99% after 5 cycles. The removal mechanism of Cr(VI) was mainly through electrostatic attraction, chemical adsorption and photocatalytic reduction. This study provides a feasible method for the synthesis of hydrogel materials with excellent adsorption synergistic photocatalytic performance for the treatment of Cr(VI)-containing wastewater.