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

CO photoconversion to solar fuels requires materials with a high affinity to the acidic CO, and MgO and Mg(OH) films represent good candidates due to their basic sites are highly active for CO capture in a wide interval of temperatures. However, the deposition of MgO and Mg(OH) 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) mixtures over glass substrates at significantly lower temperatures (200–400 °C). The films were tested as photocatalysts in the CO photoconversion to solar fuels (HCOOH and CHOH) under UV–visible-NIR irradiation. The as-prepared films exhibited the hexagonal structure of the Mg(OH) 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) on the films affected their photocatalytic activity. The films exhibited high affinity for CO 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 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 photoconversion.