Z-scheme heterojunction of low conduction band potential MnO2 and biochar-based g-C3N4 for efficient formaldehyde degradation

Abstract

The Z-scheme heterojunction-based photocatalyst often has excellent degradation activity for volatile organic compounds (VOCs). Herein, through unique reduction reaction, we developed a novel MnO2 photocatalyst that has a very low conduction band potential (-1.09 V), compared with those reported MnO2 in the literature. The key experimental evidence was from its XRD results showing much higher content of crystal face (110) in reference to that of standard α-MnO2 (No. 44–0144). Subsequently, a novel biochar/MnO2/g-C3N4 photocatalyst (C/CN/Mnx) was synthesized and displayed that the best formaldehyde degradation (91.78%) is 3.34 times that of g-C3N4 (27.51%) in air containing 0.5 mg L-1 formaldehyde at 3 h. Due to the favorable band potentials, the excited electrons of g-C3N4 combine with the holes of MnO2, thereby retaining low-potential electrons of MnO2, and these electrons from g-C3N4 and MnO2 can be effectively transferred to biochar so that their recombinations are minimized. The introduction of 5 mmol MnO2 can increase the singlet oxygen (1O2) concentration (2.78 × 1011 mm−3) of the photocatalyst by>4 times under visible light irradiation. This MnO2-based Z-scheme photocatalyst provides a platform technology for the photocatalytic degradation of VOCs.