The synergetic role of rice straw in enhancing the process of Cr(VI) photoreduction by oxalic acid.

Based on the goal of green and effective removal of chromium (Cr(VI)) pollution in water and the idea of treating waste with waste, rice straw (RS) was firstly and successfully used in enhancing the photoreduction of highly toxic Cr(VI) to less toxic Cr(III) by oxalic acid (Ox). Batch experiments (the effect of Ox concentration, initial Cr(VI) concentration, RS dosage and coexisting ions) in Ox + RS + UV photoreduction system were designed to investigate the reaction process. Through studying the effect of initial pH in the solution, the change of pH during the photoreduction process and the free radical scavenging test, the Cr(VI) photoreduction mechanism in Ox + RS + UV system was revealed. The role of RS in Ox + RS + UV system was also deduced by the analysis of FT-IR, XRD, Mott-Schottky and the verification test of the role of -OH and SiO on RS. The results showed that RS could significantly synergize Ox to reduce Cr(VI) under UV, 1 mM Cr(VI) in aqueous solution was completely removed in 60 min by Ox + RS + UV system. The Cr(VI) photoreduction mechanism in Ox + RS + UV system consisted of multiple parts: the chemical reduction by Ox(few part), the photoreduction by Ox(some part), and the synergistic photoreduction by RS with Ox(large part). The synergism of RS in Ox + RS + UV system was mainly attributed to its components of SiO and -OH of cellulose.