Constructing broad spectrum response ROQDs/Bi2WO6/CQDs heterojunction nanoplates: Synergetic mechanism of boosting redox abilities for photocatalytic degradation pollutant

Abstract

Rhodium oxide quantum dots (ROQDs) and carbon quantum dots (CQDs) were controllably assembled on [Bi2O2]2+ slices and [WO4]2- slices of thin layered Bi2WO6, respectively, to construct broad spectrum response ROQDs/Bi2WO6/CQDs heterojunctions by a two-step process including photodeposition ROQDs and hydrothermal anchoring CQDs. 0.1%ROQDs/Bi2WO6/4.2%CQDs exhibited optimized photoactivity for 4-chlorophenol (4-CP) degradation (Kapp=2.15×10−2 min−1) under the visible light (420 nm﹤λ﹤800 nm) irradiation, about 9.5 times as that of pristine Bi2WO6 (Kapp=2.26×10−3 min−1). ROQDs-modifying played a crucial role in enhancing photoactivity under the visible light of λ>420 nm, whereas CQDs- modifying played a decisive role under the visible light of λ>550 nm. Built-in electric fields at the ROQDs/Bi2WO6 and CQDs/Bi2WO6 interfaces and the intimate interfaces as charge transfer channels produced significant synergetic effects on promoting charge carrier separation and reducing charge transfer resistance. More importantly, the oxidative power of h+ was enhanced by forming Z-scheme ROQDs/Bi2WO6 heterojunction, thus making more contribution to 4-CP degradation by both h+ and ·OH than ·O2-. In addition, ROQDs and CQDs co-modification further improved light harvesting capacity, enlarged specific surface, pore volume, and average pore diameter, as well as increased surface hydroxyl and absorbed oxygen. Enhanced visible light photoactivity was attributed to the cooperation of all above factors. This work provides a viable avenue to develop efficient double heterojunction photocatalysts for environment purification and solar energy conversion.