Abstract This study aimed to describe the preparation of Nb2O5 pellets by uniaxial pressing, to investigate the influence of heat treatment at different temperatures (800, 900, and 1000 °C) on the physical, surface, microstructural, and adsorptive properties of the materials, and to assess their potential as reusable adsorbents for methylene blue removal. Specimens treated at 800 °C contained a mixture of monoclinic and hexagonal phases, with a predominance of monoclinic structures. By contrast, heat treatment at 900 °C and above resulted in complete conversion to the monoclinic phase. The surface of Nb2O5 particles contained basic groups, possibly oxygen ions (O-). Experimental investigations showed that methylene blue adsorption followed second-order kinetics, suggesting chemical diffusion as the dominant process. Maximum adsorption occurred at pH 6.0. Pellets remained intact after the adsorption test. A study was carried out to determine the reusability of pellets over five adsorption cycles in methylene blue solutions at different concentrations. The maximum adsorbed concentration was 10.4 mg.L-1. The adsorption capacity of Nb2O5 specimens gradually decreased from 56% in the first cycle to 25% in the fifth cycle. Despite this reduction in removal efficiency, Nb2O5 pellets showed promise as reusable adsorbents in heterogeneous processes because of their high potential adsorption capacity and easy separation from the reaction medium.

Abstract This paper describes the development of ZnO semiconductors applied as photocatalysts for the degradation of water contaminants, with the shape of ceramic pellets thick enough to maintain their structures, prepared by slip casting and sintering. The samples presented porosities around 40% and densities around 3.4 g/cm3, which represented about 61% of the theoretical density of ZnO. After obtaining the ceramic samples, the degradation of Rhodamine B dye by photocatalysis was evaluated in six cycles of degradation. After the cycles, changes in the surface of the samples were verified, possibly due to leaching during photocatalysis since they presented mean grain sizes of 0.61 μm before and 0.36 μm after the photocatalysis. The ceramic ZnO samples were able to satisfactorily degrade Rhodamine B for several cycles, resulting in successful reuse of photocatalysts and increased facility of removing the photocatalysts from the medium after degradation compared to powders in suspensions.

Resumo A gestão do uso da água no ambiente agrícola é fator decisivo para a construção de métodos produtivos ambientalmente sustentáveis. A fotocatálise é um método promissor para a descontaminação de águas. Este artigo teve como proposta avaliar o potencial fotocatalítico de partículas de ZnO puro e dopado com manganês. Estes materiais foram produzidos pelo método dos precursores poliméricos e caracterizados por difratometria de raios X, adsorção de N2 em baixa temperatura, espectroscopia na região do infravermelho e do ultravioleta e fotoluminescência. Para avaliação da eficiência dos fotocatalisadores obtidos, ensaios de fotodegradação foram realizados utilizando-se o corante azul de metileno sob radiação UVC. As partículas apresentaram-se monofásicas, porém com baixa área superficial específica. A amostra de ZnO com teor de dopagem de 0,25% de Mn apresentou maior eficiência no processo fotocatalítico para a degradação do corante azul de metileno. Esta eficiência foi relacionada com o maior valor de energia de band gap e menor taxa de recombinação eletrônica, o que permite maior formação de radicais de hidroxila, compostos estes responsáveis pela degradação do corante.

Abstract The management of water use in the agricultural environment is a key factor to build new environmentally sustainable productive methods. Photocatalysis is a promising method for water decontamination. This research paper aimed to evaluate the photocatalytic potential of pure and Mn-doped ZnO particles. The materials were obtained by the polymeric precursor method, and characterized by X-ray diffraction, N2 adsorption in low temperature, infrared and ultraviolet spectroscopy, and photoluminescence. In order to evaluate ZnO:Mn particles photoefficiency, experiments were carried out by applying the methylene blue dye solution to photodegradation under UVC exposure. The particles had ZnO single-phase, but low specific surface area. The sample ZnO:0.25% Mn presented higher efficiency in the methylene blue photocatalytic degradation test. This efficiency was related to a higher band gap energy value and a lower rate of electron recombination, which allows greater formation of hydroxyl radicals, which are responsible for dye degradation.