Limitation of WO3 in Zn-Co3O4 Nanopolyhedra by the Pyrolysis of H3PW12O40@BMZIF: Synergistic Effect of Heterostructure and Oxygen Vacancies for Enhanced Nitrogen Fixation.

Abstract

The photocatalytic nitrogen fixation process is a crucial step toward carbon neutrality and sustainable development. The combination of polyoxometalates and metal-organic frameworks is a viable method to achieve high-efficiency photocatalytic nitrogen fixation. In this work, we employed bimetallic ZIF (BMZIF) composed of Co2+ and Zn2+ encapsulated with H3PW12O40 (PW12) as the precursor to synthesize Zn-doped Co3O4 nanopolyhedra loaded with WO3 nanoparticles. The NH3 yield of WO3/Zn-Co3O4-2 with the best photocatalytic performance can reach 231.9 μmol g-1 h-1 under visible light, about 2.4 and 6.4 times those of pure Zn-Co3O4 and WO3, respectively. The rhombic dodecahedral geometry of BMZIF is still maintained in the synthesized WO3/Zn-Co3O4 nanopolyhedra, with the significant increase in the specific surface area after calcination showing better catalytic performance. At the same time, Zn doping and the formation of WO3 nanoparticles result in abundant oxygen vacancies in WO3/Zn-Co3O4 heterostructures. Oxygen vacancies can supply nitrogen with active sites for adsorption and activation and improve photocarriers' capacity for separation, which can greatly increase the effectiveness of the photocatalytic synthesis of ammonia. This work can easily synthesize the heterostructure based on n-type WO3 nanoparticles and p-type Zn-doped Co3O4 nanopolyhedra, and the beneficial combination of POMs and metal-organic framework provides new thinking for the synthesis of efficient nitrogen-fixing photocatalysts.