CO2 adsorption and photocatalytic reduction over Mg(OH)2/CuO/Cu2O under UV-Visible light to solar fuels

Powders of Mg(OH)2, CuO, and Cu2O were effectively coupled by microwave-hydrothermal method, in order to proposed bifunctional materials for both capture and photocatalytic conversion of CO2 under UV-visible light irradiation. This was done to take advantage of the high CO2 adsorption capacity of Mg(OH)2 and the good photocatalytic performance of CuO/Cu2O for CO2 reduction to solar fuels in liquid (CH3OH and HCOH) and gas phase (CH4 and CO). In order to establish correlations between the physical properties and the photocatalytic activity, the composites were characterized by XRD, XPS, UV-Vis DRS, SEM, HRTEM, N2 physisorption and photoelectrochemical techniques. According to the characterization, the synthesis method employed allowed the adequate interaction between Mg(OH)2 with CuO and Cu2O, which not inhibited the ability of Mg(OH)2 for gas adsorption. The best yield to obtain liquid fuels such as CH3OH (6 μmol g−1 h−1) and HCOH (9 μmol g−1 h−1) was obtained using 10% of CuO in the composite. The improved photocatalytic activity in liquid phase was assigned to a high CO2 adsorption and a more negative potential of conduction band. It was found that the presence of Cu2O favored the selectivity towards CH3OH production; as higher Cu+ concentration better selectivity. A reaction mechanism is discussed on the basis of combined CO2 adsorption and photocatalytic activity of the materials involved. Furthermore, it was study the photocatalytic activity in gas phase, and it was determined the presence of CO and CH4 in low concentrations (<0.4 μmol g−1 h−1).