ZnO with engineered surface defects as a competent photocatalyst for CO2 photoreduction into valuable fuels under simulated solar light irradiation

Photocatalysis is one of the eco-friendly methods in greenhouse gases abatement by utilizing renewable resources such as sunlight. This study examined defective ZnO nanoparticles that serve as carbon dioxide (CO2) adsorption and activation sites in photocatalytic reactions. The defective ZnO nanoparticles were synthesized via a facile precipitation-hydrothermal method by only controlling the concentration of NaOH as the precipitating agent. The rough surface of ZnO were formed due to the heating treatment, where it conveniently removed the attached inorganic molecules on ZnO surfaces. The roughness surface of ZnO was observed by using Transmission Electron Microscopy (TEM) analysis, in which the pores with bright spot can be observed. Additionally, the defects originating from oxygen vacancies (VO), zinc interstitials (Zni) and carbonates groups (CO32−) was successfully optimized over variation of NaOH concentrations proven by Photoluminescence (PL) and X-Ray Photoelectron Spectroscopy (XPS) analysis. Here, 1 : 4 ZnO exhibited the highest CH4 yield (1.3 ×10-1 µmol) and 3-fold production than commercial ZnO (4.8 × 10-2 µmol). The reusability of 1 : 4 ZnO was demonstrated by conducting 4 cycles of stability test, which revealed a robust photocatalyst of 7.7% performance reduction after 4th cycle. A schematic mechanism pertaining to the novel defective ZnO nanoparticles in CO2 photoreduction to valuable fuels was proposed in this study, which undoubtedly will contribute a positive effect to industry’s long-term sustainability.