Glucose precursor carbon-doped TiO2 heterojunctions for enhanced efficiency in photocatalytic reduction of carbon dioxide to methanol

Abstract

An alternative source for carbon-doped TiO2 photocatalysts, synthesized with glucose as precursor, calcined and tested for the reduction of CO2 have been investigated. These samples are characterized using XRD, FTIR, DRUV-Vis, XPS and HR-TEM. Glucose with 6 wt.% loading (6C-TiO2) corresponds to the optimum amount of carbon doped into TiO2 achieving a methanol yield of 19.5 mmol gcat-1 h-1, a more than 2-fold increase from that of bare TiO2 at 9.5 mmol gcat-1 h-1. Moreover, the quantum yield of carbon-doped TiO2 increases by ca. 50% compared to bare TiO2. From XPS results, various surface species with C-OH, C=C and C=O functional groups confer the association of ligand-metal-charge-transfer (LMCT) complex between TiO2 and carbon. The low band gap and UV-vis light absorption capacity of carbon-doped TiO2 facilitates the transfer of photo-generated electrons. 6C-TiO2 demonstrates high photostability with constant yield even after five cycles of testing. The mechanism of the carbon-doped TiO2 in reduction of CO2 to methanol is postulated to be consistent with the LMCT complex phenomena. Therefore, 6C-TiO2 photocatalyst provides heterojunction for localization of electrons, hinders the charge recombination rate and narrows the band gap for enhanced photocatalytic activity under UV-VIS light irradiation.