Mechanisms on Oxygen Activation for Efficient 2-Chlorophenol Mineralization on CoOx/BiO2–x Nanosheets Under Full-Spectrum Irradiation

Herein, ultrathin CoOx/BiO2–x nanosheets (∼4 nm) have been in situ synthesized by using a microwave-assisted hydrothermal method. The amount-optimized CoOx/BiO2–x nanosheets display 4.7-fold higher photocatalytic activity than classical P25 TiO2 for 2-chlorophenol (2-CP) degradation under full-spectrum irradiation with exceptional mineralization. The high photoactivity is attributed to the excitation-wavelength-dependent O2 activation involved with the mainly produced •O2– via charge separation and 1O2 through energy transfer with ultraviolet–visible (UV–vis, <450 nm) and visible-near-infrared (vis-NIR, >550 nm) light irradiation, respectively. Moreover, the modified CoOx with high dispersion could effectively trap photogenerated holes, thereby promoting charge separation and also facilitating the formation of 1O2 from •O2– by holes. By means of liquid chromatography tandem mass spectra and theoretical simulation, the generated nucleophilic •O2– and electrophilic 1O2 radicals exhibit distinct preferences in attacking different sites of 2-CP, resulting in direct ring-opening processes and ultimately enabling rapid mineralization.