Síntese e caracterização de heteroestrutura NiO/Bi4O5I2-Bi5O7I e estudo da atividade fotocatalítica do corante rodamina B sob irradiação visível

Abstract

The continuous population growth linked to social and economic developments generate, as a consequence, environmental problems that impact human society. Without a doubt, water is the most affected, and its contamination is mainly due to excessive discharges of organic contaminants from the most diverse industrial activities and also have many compounds that are incapable to undergo biodegradation, being inert to conventional water treatments. Heterogeneous photocatalysis (HF), a variant of advanced oxidative processes, has been shown to be an efficient approach in the treatment of waters endowed with recalcitrant organic contaminants, it is based on the generation of free radicals with high oxidizing power, under the action of light. Photocatalysts based on bismuth and other p-block elements show photocatalytic activity under the action of visible light, which makes up about 45% of the solar spectrum. Materials structured in layers, such as bismuth oxyiodide, BiOI and species with high levels of bismuth, Bi4O5I2, Bi5O7I were shown to be efficient in the degradation process of the organic contaminants Rhodamine B. New and unprecedented materials were obtained in this work and prepared via hydrolysis and heat treatment (400°C for 3 hours) starting from simple precursors and heterostructures were prepared with the incorporation of NiO at 1.5 and 3.0% (w/w). The materials showed high purity and good crystallinity, presenting tetragonal, monoclinic and orthorhombic phases for the BiOI, Bi4O5I2 and Bi5O7I samples, respectively. SEM/EDS showed micro-flora morphology hierarchically constructed by stacking nanosheets with thicknesses ranging from 250 – 140 nm. The materials showed excellent absorption in the visible range, with an absorption edge in the range of 650 – 514 nm. The reaction control parameters were 50 mg of photocatalyst, 10 mg.L-1 RhB solution and natural pH of the RhB solution (pH = 4.42). The samples BiOI, Bi4O5I2, 1.5 % NiO/Bi4O5I2-Bi5O7I and 3.0 % NiO/Bi4O5I2-Bi5O7I showed photocatalytic efficiency of 65.14%, 84.12 %, 87.37% and 90.3 % respectively, where it was demonstrated that the applied thermal treatment added to the formation of heterostructures with the incorporation of NiO, better performances were obtained. The values found for the TOC level were 4.15%, revealing a degradation of approximately 96% efficiency in the mineralization of the compounds for the 3.0% NiO/Bi4O5I2-Bi5O7I sample. In order to maximize photocatalytic efficiency, the photoreactor was internally covered with aluminum foil and the material 3.0 % NiO/Bi4O5I2-Bi5O7I showed na efficiency of 99.43 %. The 3.0 % NiO/Bi4O5I2-Bi5O7I material showed stability and high recyclability capacity up to the 5th consecutive cycle, showing good ability and advantage in practical applications. In free radical suppressor tests, the superoxide radical and holes demonstrated dominance in the degradative process. Therefore, this study was able to synthesize, new and unprecedented, in 2 steps, materials with superior photoactive capabilities under the influence of low energy demand sources (LED) and with a high capacity for consecutive reuse, proving to be an environmentally favorable, green, and economically viable approach.