Enhanced Photoreduction of U(VI) on C3N4 by Cr(VI) and Bisphenol A: ESR, XPS, and EXAFS Investigation

• Published in: Environmental science & technology Vol. 53; no. 11; pp. 6454 - 6461
• Main Authors: Wang, Huihui, Guo, Han, Zhang, Ning, Chen, Zhongshan, Hu, Baowei, Wang, Xiangke
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 04.06.2019
• Subjects: Absorption; Alcohols; Bisphenol A; Carbon nitride; Catalytic activity; Chromium; Conduction; Conduction bands; Electron paramagnetic resonance; electron paramagnetic resonance spectroscopy; Electron spin; Electron spin resonance; Electrons; Environmental cleanup; Fine structure; free radical scavengers; Heavy metals; Hydrogen peroxide; Irradiation; Persistent organic pollutants; Phenols; Photocatalysis; Photocatalysts; Photochemistry; Photoelectron spectroscopy; Photoelectrons; Photoreduction; Pollutants; Radioisotopes; radionuclides; Spin resonance; Ultrastructure; uranium; X ray absorption; X ray photoelectron spectroscopy; X-ray absorption spectroscopy
• DOI: 10.1021/acs.est.8b06913
• ISSN: 0013-936X; 1520-5851

The effect of Cr­(VI) and bisphenol A (BPA) on U­(VI) photoreduction by C3N4 photocatalyst was demonstrated by the batch experiments, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques. The batch experiments manifested that Cr­(VI) and BPA enhanced the photocatalytic activity of C3N4 for U­(VI) photoreduction, whereas U­(VI) photoreduction was significantly diminished with increased pH from 4.0 to 8.0. According to radical scavengers and ESR analysis, U­(VI) was photoreduced to U­(IV) by photogenerated electrons of conduction band edge, whereas Cr­(VI) was reduced to Cr­(III) by H2O2. BPA and its products such as organic acid and alcohols can capture photoinduced holes, which resulted in the enhancement of U­(VI) photoreduction to U­(IV). XPS and XANES analyses demonstrated that U­(VI) was gradually photoreduced to U­(IV) by C3N4 within irradiation 60 min, whereas U­(IV) was reoxidized to U­(VI) with increasing irradiation time. EXAFS analysis determined that the dominant interaction mechanisms of U­(VI) on C3N4 after irradiation for 240 min were reductive precipitation and inner-sphere surface complexation. This work highlights the synergistic removal of radionuclides, heavy metals, and persistent organic pollutants by C3N4, which is crucial for the design and application of a high-performance photocatalyst in actual environmental cleanup.