Construction of a magnetic BiOBr-rGO-ZnFe2O4 heterojunction photocatalyst for refinery wastewater treatment under simulated solar light

Abstract

Considering the importance of sunlight as a free, abundant, and sustainable source of energy, in this paper, first, the removal of phenol from model refinery wastewater under simulated solar light was studied. Then magnetic BiOBr-rGO-ZnFe2O4 photocatalyst with different percentages of BiOBr (0, 30, 45, and 55 %) was synthesized and evaluated in degradation of phenol under simulated solar light. The results showed that the sample containing 45 % wt. of BiOBr was the most active and after 3 h, it succeeded in removing 94 % of the phenol from a 20-ppm phenol solution. The characteristics of the synthesized photocatalysts were analyzed by XRD, BET-BJH, UV–Vis DRS, PL, FESEM, TEM, and EDX analyses. The results showed that by increasing the weight percentage of BiOBr from 30 % to 55 %, the crystal size of BiOBr increased from 22 to 29 nm. FESEM analysis showed that with the increasing amount of BiOBr, more lamellar structures were observed in the sample, and in the sample containing 45 % BiOBr, these structures became flower-like. However, with a further increase in the percentage of BiOBr to 55 %, thick and stacked sheet structures were formed, which resulted in the reduction of porosity and surface area according to BET-BJH analysis. According to PL analysis, the addition of BiOBr to rGO-ZnFe2O4 reduced the rate of recombination of charge carriers. However, increasing the weight percentage of BiOBr declined the light absorption and shifted the absorption edge towards the ultraviolet region. The effect of operational parameters such as pH, amount of photocatalyst, initial concentration of phenol, light intensity, and the presence of oxidant as well as the stability of the selected photocatalytic sample was evaluated. Studying the effect of scavengers also showed that the most active species that degrade phenol are the holes formed on the surface of the BiOBr-rGO-ZnFe2O4 photocatalyst.