g-C3N4/(Cu/TiO2) nanocomposite for enhanced photoreduction of CO2 to CH3OH and HCOOH under UV/visible light

Abstract

Cu-modified graphitic carbon nitride (g-C3N4) and titanium dioxide (TiO2) nanocomposites for enhanced photocatalytic CO2 reduction with H2O under UV and visible light irradiations have been investigated. The photocatalysts, prepared by pyrolysis and impregnation were characterized by XRD, FE-SEM, TEM, FT-IR, N-2 adsorption-desorption, XPS, UV-vis DRS and PL spectroscopy. The Cu-metal loaded over TiO2 and g-C3N4 enhanced CO2 reduction efficiency to CH3OH and HCOOH by fostering carrier charge separation. The Cu-metal in the composite as well as the wt.% ratio of g-C3N4 and TiO2 also influenced the photoactivity and products selectivity. The low band gap, electronic structure and visible light absorption capacity of g-C3N4 facilitated the transfer of photo-generated electrons to Cu/TiO2 in the composite. Moreover, the position of the metal in the composite affected the electrons distribution and hence enhanced the photoactivity. The maximum yield of the products detected under visible light were 2574 and 5069 mu mol/g. cat of CH3OH and HCOOH, respectively. The yield of CH3OH under visible light was four fold higher compared to UV-light irradiation. The ratio (30:70) of g-C3N4 and Cu/TiO2 in the composite and the use of visible light improved the efficiency of the photocatalytic system. The stability of the photocatalyst prevailed in continuous CH3OH production under visible light irradiation compared to UVlight in cyclic runs. Possible reaction mechanisms were proposed to understand the movement of electrons and holes and the function of both UV and visible light for CO2 reduction over the g-C3N4/TiO2 (30: 70) photocatalyst.