Cycloaddition of CO₂to propylene oxide using BiNbO₄/NH₂-MIL-125(Ti) composites as visible-light photocatalysts

A series of BiNbO4/NH2-MIL-125(Ti) hybrid photocatalysts was prepared using different mass ratios of NH2-MIL-125(Ti) to BiNbO4. The crystalline structure of the prepared photocatalysts was analyzed using PXRD. The heterojunction was established as indicated by analyzed peaks correspond to both materials added to the composite, and the intensity in the heterojunction correlates with increasing the amount of BiNbO4 added. Surface area was obtained using N2 adsorption isotherm. The surface area and porosity were increased significantly upon increasing the amount of NH2-MIL-125(Ti) added. Band gap measurements exhibited a red shift towards lower energy values upon increasing the amount of NH2-MIL-125(Ti). Furthermore, the activity of prepared BiNbO4/NH2-MIL-125(Ti) hybrid photocatalysts was examined for the cycloaddition of CO2 to propylene oxide as a photocatalytic model reaction. Interestingly, no polymeric material was observed and selective cyclic propylene carbonate in moderate yield was obtained. Noticeably, the activity of BiNbO4/NH2-MIL-125(Ti) was highest upon the addition of 50 % NH2-MIL-125(Ti) by mass reaching up to 74 % conversion.