The synergistic effect of phosphomolybdic acid on rhodium-based metal–organic frameworks for the efficient selective photocatalytic reduction of CO2 to CO

Abstract

In this work, PMA@NH₂-MIL-68(Rh) with a mangosteen spherical structure was successfully synthesized by a hydrothermal method for the photocatalytic reduction of carbon dioxide. The electronic structure and morphology of PMA@NH₂-MIL-68(Rh) composites were characterized using Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). Results showed that the 0.63% PMA@NH₂-MIL-68(Rh) composite achieved the optimal catalytic performance, yielding 387.28 μmol·g⁻¹ CO and 11.75 μmol·g⁻¹ CH₄. The production of CO by 0.63% PMA@NH₂-MIL-68(Rh) was nearly fifteen times more than that by NH₂-MIL-68(Rh). This prominent photocatalytic activity was caused by four active species, including photoelectrons (e⁻), photo-holes (h⁻), Mo⁵⁺ and superoxide free radicals (˙O²⁻). The cycling and stability results showed that PMA@NH₂-MIL-68(Rh) had no significant change in the photocatalytic degradation effect of CO₂ after five-time repeated, indicating that PMA@NH₂-MIL-68(Rh) composites have acceptable stability.