Bi2WO6 hollow microspheres with high specific surface area and oxygen vacancies for efficient photocatalysis N2 fixation

In this work, Bi2WO6 hollow microspheres containing oxygen vacancies (OVs-BWO) was synthesized by a solvothermal template-free method. Raman, EPR and XPS spectra provide sufficient evidence for the existence of OVs in the material. Its activity toward photocatalytic nitrogen fixation was evaluated. Experimental results showed that the OVs-BWO with a BET surface area of 80.5 m2·g−1 exhibited the ammonia yield of 106.4 μmol·gcat−1 under simulated sunlight for 2 h, which is ca. 18 times higher than that of equal-area nest-like Bi2WO6 without oxygen vacancies. The enhanced activity is mainly attributed to the metastable electrons within the sub-band (i.e., defect energy level) induced by oxygen vacancies to π anti-bonding orbitals of N2 with a manner of the non-radiative transfer, leading to the activation of nitrogen molecules. The activation and hydrogeneration processes of nitrogen at active site of OVs-BWO were studied by DFT calculation and the possible mechanisms were proposed. The sub-band extends the light absorption region of OVs-BWO to 700 nm. Transient photocurrent response showed that the sub-band electron excitation accelerates the transfer of charges and hinders the electron-hole recombination. It can be perfectly reused five times when air and nitrogen are used as nitrogen sources, thus the OVs-BWO hollow microspheres offer a promising alternative for efficient N2 fixation under ambient conditions.