MgO and Mg(OH)2 thin films prepared by the SILAR method and their CO2 photocatalytic performance

CO 2 photoconversion to solar fuels requires materials with a high affinity to the acidic CO 2 , and MgO and Mg(OH) 2 films represent good candidates due to their basic sites are highly active for CO 2 capture in a wide interval of temperatures. However, the deposition of MgO and Mg(OH) 2 as thin film is difficult to obtain by traditional methods. As an alternative, in this work, the successive ionic layer adsorption and reaction (SILAR) method is proposed to obtain MgO/Mg(OH) 2 mixtures over glass substrates at significantly lower temperatures (200–400 °C). The films were tested as photocatalysts in the CO 2 photoconversion to solar fuels (HCOOH and CH 3 OH) under UV–visible-NIR irradiation. The as-prepared films exhibited the hexagonal structure of the Mg(OH) 2 phase. As the temperature increased, XRD and XPS analysis confirmed the presence of orthorhombic MgO, while the morphology remains with similar grains with an estimated size of 1 µm. The annealing temperatures change the chemical species (Mg–O, Mg–OH, and Mg–CO 3 ) on the films affected their photocatalytic activity. The films exhibited high affinity for CO 2 due to the presence of defects (F and F + centers) in both phases. The photocatalytic behavior was directly related to OH − species present in each sample. According to the results, it seems that fewer hydroxides and defects on the films favored higher efficiencies for the CO 2 photoconversion. In addition, the films were exposed to accelerated weathering tests to evaluate their efficiency for more extended periods. The results indicated that the aged films still have activity for CO 2 photoconversion. Graphical abstract