Effective in-situ reduction of Cr(Ⅵ) from leather wastewater by advanced reduction process based on CO_2~(·-) with visible-light photocatalyst

摘要

Advanced reduction process (ARP) has drawn an increasing interest as a new manner for removing oxidative pollutants in water. In this paper, we demonstrate the possibility of in-situ reduction of Cr(VI) by CO2 center dot- produced from formate originally existing in leather wastewater by visible-light-driven ARP containing black TiO2 photocatalyst. The prepared black TiO2 with nanotube structure achieves remarkable enhanced the reduction rate of Cr(VI) as high as 96.2% (k = 0.0114 min(-1)) in the presence of formate, which is approximately 4.75 times than that of 56.3% (k = 0.0024 min(-1)) in the absence under 120 min visible-light irradiate at unadjusted pH. The results exhibit a distinct contrast with commercial TiO2 (P25). A series of control experiments are also performed, indicating that formate is able to convert the oxidative environment into a highly reductive one, and the formate concentration, black TiO2 dosage and pH may greatly impact on the Cr(VI) reduction rate. According to the electron spin resonance (ESR) measurement, CO2 center dot- radicals can be directly verified as dominate radical in this system. Moreover, this system appears to be attractive for creating photochemical systems where in-situ production of CO2 center dot- radicals may be realized by using formate. Then this in-situ ARP system will provide a new perspective for the Cr(VI) removing, which makes leather wastewater treatment much easier and more sustainable in the future. (C) 2020 Elsevier Ltd. All rights reserved.