Óxido de zircônia com níquel sintetizados por hidrotermal: aplicações fotocatalíticas em corantes e produção de hidrogênio

Abstract

The chemical synthesis of inorganic oxides with applications in the energy sector has been continuously studied, promoting the search for simpler, more environmentally friendly, and economically viable production methods. Zirconia oxide is a semiconductor inorganic compound with a wide range of properties, including catalytic and photocatalytic ones when structurally modified, and is used in the degradation of harmful dyes in wastewater. Ni nanoparticles supported on ZrO2 are also considered promising for the catalytic reforming of methane. In turn, NiO provides active sites that can modify the surface of ZrO2, promoting electrocatalytic properties and stability in alkaline environments. Moreover, when used as a support, it is considered a promising catalyst in CO2 conversion reactions, biomass conversion, biofuel production, methane reforming, and fatty acid deoxygenation. In this study, zirconia and nickel oxides were synthesized through the hydrothermal method with variations in parameters such as temperature, reagents, pH, and synthesis time. In this context, the influence of nickel addition on the structural properties of ZrO2 was evaluated in processes ophotodegradation of organic pollutants and hydrogen production. The monoclinic phase is obtained in pure samples, while the tetragonal phase is obtained concurrently with the insertion of nickel at temperatures above 120ºC. Changing the precursor, increasing the time and temperature favor the formation of the monoclinic phase, as well as nickel hydroxide with a hexagonal structure. Acidic pH was used to favor the reduction of nickel, resulting in the formation of an oxidized phase, NiOOH. Photodegradation tests, conducted under UVC irradiation, of the anionic dye Orange G (OG) and the cationic dye Methylene Blue (MB) showed better results for the pure phase with monoclinic structure, with up to a 93% reduction in the peak corresponding to OG. In all systems, the highest photocatalytic activity occurred using the cationic dye, reaching decolorization percentages of up to 52% after 5 hours of UVC irradiation, with the Ni/ZrO2 sample. Hydrogen production is catalyzed by the presence of Ni/ZrO2 catalysts, which does not occur in pure samples. On the other hand, the presence of the reduced phase NiOOH increases the yield of the hydrogen production reaction through the hydrolysis of sodium borohydride, which may be favored by the intercalation of water molecules in the hydroxide structure.