Highly selective visible-light-triggered CO2 fixation to cyclic carbonates under mild conditions using TiO2/multiwall carbon nanotubes (MWCNT) grafted with Pt or Pd nanoparticles

Irradiation of a series of aromatic epoxides and CO2 in the presence of TiO2, TiO2/MWCNT, Pt//TiO2/MWCNT and Pd/TiO2/MWCNT photocatalysts was investigated with visible light-induced cycloaddition reactions for the production of cyclic carbonates with high activity and selectivity. The catalytic activity order of these catalysts was revealed as follows: Pd/TiO2/MWCNT > Pt//TiO2/MWCNT > TiO2/MWCNT > TiO2. The main features of this protocol are the transformation of CO2 to cyclic carbonates at ambient temperature and under atmospheric pressure. The band gap energies for Pd/TiO2/MWCNT and the Pt/TiO2/MWCNT nanocomposites were estimated from the Kubelka–Munk plots to be ca. ∼2.39 and 2.33 eV, respectively, and they proved to be active catalysts in comparison with bare TiO2 or TiO2/MWCNT, which possess band gap values ca. ∼3.02 and 2.46 eV, respectively. A plausible mechanism explaining the behavior of CO2 with the Pd/TiO2/MWCNT nanocomposite was proposed.