Photocatalytic reduction of carbon dioxide with water vapors over montmorillonite modified TiO2 nanocomposites
Montmorillonite (MMT) modified TiO2 nanocomposites were synthesized by single step sol–gel method. The samples were characterized by XRD, FE-SEM, HR-TEM, FT-IR, N2-adsorption–desorption, UV–vis and photoluminescence (PL) spectroscopy. Modification of TiO2 with MMT controlled the crystal growth and produced anatase phase of delaminated TiO2 pillared montmorillonite. The size of TiO2 nanoparticles reduced from 18.73 to 13.87 nm after adding MMT, while the surface area and pore volume increased. The UV–vis results identified blue shift in TiO2 band gap for the MMT modified samples. In addition, PL spectroscopy revealed significant inhibition in recombination of photogenerated electron–hole pairs. The performance of MMT modified TiO2 samples for reducing CO2 with H2O to hydrocarbon fuels was investigated. The effects of parameters such as MMT loading on TiO2, H2O/CO2 feed ratios, and reaction temperature on TiO2 photocatalytic activity was studied. Loading MMT on TiO2 enhanced the performance of TiO2 and markedly increased CO2 reduction to C1–C3 hydrocarbon fuels. The highest yield rates produced were 441.5 and 103 μmol g cat−1 h−1 for CH4 and CO, respectively under UV light irradiations at 20 wt.% MMT loading, reactor pressure of 0.20 bars and 393 K reaction temperature. These results revealed silicate layers of MMT dispersed in the given TiO2 sol system and vacant d-orbits of the MMT transition metal ions have obvious effect on the photocatalytic activity of TiO2. The possible pathways and reaction mechanisms of CH4 and CO productions were also suggested. Thus, MMT is a potentially attractive material to improve TiO2 as a photocatalyst for application in photocatalytic CO2 reduction.