Photocatalytic carbon dioxide reduction to methanol catalyzed by ZnO, Pt, Au, and Cu nanoparticles decorated zeolitic imidazolate framework-8

Abstract

Carbon dioxide conversion into valuable industrial products like methanol has gained plenty of attention in recent years. The photocatalytic CO2 reduction is one of the strategies most studied as it is cleaner and has the potential to be more convenient to classical thermochemistry. In this paper, pristine ZIF-8 was decorated with ZnO, Pt, Cu and Au nanoparticles (NPs) to achieve four novel photocatalysts denoted ZnO/ZIF-8, Pt/ZIF-8, Au/ZIF-8, and Cu/ZIF-8 for CO2 reduction to methanol under ultraviolet/visible (UV/Vis) light irradiation at room temperature. All synthesized photocatalysts were fully characterized by XRD, FT-IR, FESEM, TEM, N2 adsorption-desorption, EDS, PL spectroscopy and DRS. DRS revealed successful reduction of the Eg of ZIF-8 up to 71 % after its decoration with NPs. In addition, PL analysis confirmed the efficient hindering of recombination of photoinduced electron-hole pairs in all modified samples. ZnO/ZIF-8 photocatalyst’s features the oxygen vacancies in ZnO NPs, the permanent generation of electron-hole pairs, and an efficient charge-carrier separation due to formation of type II heterojunctions demonstrated higher methanol yield compared to metal NP-impregnated ZIF-8. Interestingly, among metal NPs, Pt/ZIF-8 sample unveiled higher activity toward CO2 photoreduction due to its higher ability to light trapping and higher surface area providing more efficacious interaction of CO2 with the photocatalyst. Moreover, the obtained results demonstrated that methanol production rate over ZnO/ZIF-8 and Pt/ZIF-8 samples can reach 6700 and 5300 μmol.g−1 after 1 h exposure under UV/Vis irradiation, respectively.