Limitation of WO 3 in Zn-Co 3 O 4 Nanopolyhedra by the Pyrolysis of H 3 PW 12 O 40 @BMZIF: Synergistic Effect of Heterostructure and Oxygen Vacancies for Enhanced Nitrogen Fixation.

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 Co 2+ and Zn 2+ encapsulated with H 3 PW 12 O 40 (PW 12 ) as the precursor to synthesize Zn-doped Co 3 O 4 nanopolyhedra loaded with WO 3 nanoparticles. The NH 3 yield of WO 3 /Zn-Co 3 O 4 -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-Co 3 O 4 and WO 3 , respectively. The rhombic dodecahedral geometry of BMZIF is still maintained in the synthesized WO 3 /Zn-Co 3 O 4 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 WO 3 nanoparticles result in abundant oxygen vacancies in WO 3 /Zn-Co 3 O 4 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 WO 3 nanoparticles and p-type Zn-doped Co 3 O 4 nanopolyhedra, and the beneficial combination of POMs and metal-organic framework provides new thinking for the synthesis of efficient nitrogen-fixing photocatalysts.