Fabrication of glass immobilized amorphous organotitanium polymer for enhancing catalytic turnover frequency and stabilities in photocatalytic reduction of CO2

Abstract

Visible light-driven reduction of CO2 to methanol is an important issue. Previously, semiconductor based photocatalysts have been widely researched. In recent years, metal-organic frameworks (MOFs) also attracted much attention of researchers on photocatalysis. However, charge mobility on the MOFs is inefficient, which results in easy recombination of the excited electrons. Therefore, the turnover frequency (TOF) over the MOFs is extremely low in the photoreduction of CO2. Enhancing adsorption of visible light and the carrier separation would be effective ways to promote the catalytic performance. Herein, we report a glass immobilized amorphous organotitanium polymer. The band gap for ligand-to-metal charge transfer was 2.21 eV. Moreover, the polymer may contain a continuous Ti-O-Ti-O chain, which facilitates charge migration and prolongs the lifetime of the excited electrons. Photoreduction of CO2 was carried out in 0.2 M ethylenediamine (EDA) aqueous solution. The TOF was enhanced by over 500 times as compared to that over the NH2-MIL-125(Ti) powder. In addition, the immobilized polymer exhibited better solvent stability and thermal stability than the NH2-MIL-125(Ti). Annealing at 300 ℃ for 15 min under N2 atmosphere, the band gap of the immobilized polymer basically remained changed, but the MOF powder failed.