Abstract ZnWO4 crystallizes in a monoclinic wolframite-like structure, which has been studied for applications in heterogeneous photocatalysis for degradation, oxidation, and reduction of various contaminants. This type of tungstate has proved to be an efficient photocatalyst under both ultraviolet and visible light irradiation and, when ZnWO4 forms a heterostructure with other semiconductors or when it is doped with different ions, it has a great efficiency under sunlight irradiation. For instance, the optimization of ZnWO4 efficiency has been attained by its heterojunction with different semiconductors such as ZnO, one of the most used materials for this purpose, but also with other compounds such as BiOBr, FeWO4, TiO2, WO3, Bi2WO6, among others. In addition, doping ZnWO4 with the Ti4+, Bi3+, Ce3+, and Co2+ metal ions or with nonmetals (F- and N3-) can also increase the photocatalytic yield of the material. The photocatalytic properties of ZnWO4-based catalysts have been explored toward inorganic and organic molecules. However, among the variety of target molecules, organic pollutants such as methylene blue, methyl orange, and rhodamine B dyes appear as the most investigated in studies involving photocatalysis in the presence of ZnWO4. In our review, we summarize important literature works, highlighting the advancement in photocatalysis using ZnWO4.

Abstract Titanium dioxide is a widely studied material with well-known applications for anatase and rutile phases. Moreover, brookite, another polymorph, which is more difficult to obtain, has caught scientific community interest, especially for photocatalysis applications. Among many methodologies for TiO2 synthesis, the hydrothermal method stands out, with the possibility of controlling different parameters that lead to a specific phase composition, allowing selective polymorphic obtainment. This method was used to synthesize TiO2 with different anatase/brookite ratios, by the use of different synthesis conditions as pH of the suspension, sodium salt concentration, and temperature, resulting in anatase-brookite photocatalyst with brookite composition ranging from 0 to 35%. The materials were characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, particle size measurement, and scanning electron microscopy. Photocatalysts with the highest brookite amount showed the best photocatalytic results for Remazol golden yellow (RNL) dye decolorization. Moreover, the short-range disorder also played an important role in photocatalytic behavior.

Resumo A classe de óxidos mistos ABO3 conhecida por sua estrutura do tipo perovskita vêm despertando grande interesse científico-tecnológico nas últimas décadas, em função de suas propriedades ópticas, magnéticas e condutoras. Este trabalho teve por objetivo buscar, nos bancos de artigos e de patentes, trabalhos que relacionem a atividade fotocatalítica dos estanatos de metais alcalinos terrosos - BaSnO3, CaSnO3 e SrSnO3 como fotocatalisadores para aplicação ambiental. Os bancos de dados pesquisados foram o Web of Science, Scopus e Scielo para os artigos e USPTO, EPO e INPI para os bancos de patentes. A partir dos critérios de exclusão, 21 artigos de revisão apresentaram parâmetros e condições experimentais distintas. Devido ao excelente desempenho fotocatalítico, os estanatos apresentam-se como candidatos promissores na fotocatálise heterogênea.

Abstract The ABO3 mixed oxide class known for its perovskite-like structure has aroused great scientific and technological interest in recent decades, due to its optical, magnetic and conductive properties. The objective of this work was to search the articles and patent databases for papers that relate the activity of the alkaline earth metal stannates - BaSnO3, CaSnO3 and SrSnO3 as photocatalysts for environmental application. The databases researched were the Web of Science, Scopus and Scielo for articles and USPTO, EPO and INPI for patent banks. From the exclusion criteria, 21 review articles presented different experimental parameters and conditions. Due to the excellent photocatalytic performance, the stannates presented as promising candidates in the heterogeneous photocatalysis. A description of the main papers published in literature is provided for an overview of the literature data about these materials.

Resumo Argilas para o processo de clarificação são largamente utilizadas na indústria de rerrefino de óleos lubrificantes usados, principalmente por sua capacidade adsorvente de reter impurezas. O presente estudo teve objetivo de determinar as condições ótimas do processo de clarificação de lubrificantes usados a partir de argilas naturais e realizar a recuperação de tais argilas. O processo de rerrefino do lubrificante usado foi otimizado a partir de um planejamento experimental. As argilas recuperadas não apresentaram mudanças significativas em suas estruturas originais, de acordo com as técnicas de difração de raios X, espectroscopia no infravermelho e análise termogravimétrica. Os resultados das caracterizações dos lubrificantes atenderam a portaria ANP nº 130, que regulamenta sua comercialização no país. Todos os solventes foram recuperados por destilação a vácuo.

Abstract Clarification process using clays is widely used in the used lubricating oils re-refining industry, mainly because of its adsorbent capacity to retain impurities. This study aimed to the determination of optimal conditions for used lubricating oil clarification process, using natural clays as well as its recovery to be re-used to the process. The re-refining process of used lubricating oil was optimized from experimental design. Recovered clays showed no significant changes in their original structures, according to the X-ray diffraction, infrared spectroscopy, and thermogravimetric analyzes. The results of used lubricating oil characterizations were in accordance to the ANP resolution no 130, which regulates its commercialization in the country. All solvents were recovered by vacuum distillation.

Resumo Estanatos de metais alcalinos terrosos na forma pura com estrutura perovskita (MSnO3, M= Ca2+, Sr2+, Ba2+) têm sido utilizados como fotocalisadores. Neste trabalho, perovskita de CaSnO3 foi sintetizada pelo método Pechini modificado, em 800 ºC, e caracterizada por difração de raios X, espectroscopia de UV-vis, espectroscopia de infravermelho e espectroscopia Raman. Avaliou-se a degradação fotocatalítica do corante remazol amarelo ouro (RNL) sob luz ultravioleta. O difratograma de raios X mostrou que o método de síntese utilizado favoreceu a formação do CaSnO3 ortorrômbico. O espectro Raman indicou que um material com elevada ordem a curto alcance foi obtido apesar da temperatura de síntese relativamente baixa, em comparação ao método do estado sólido. A maior atividade fotocatalítica foi alcançada em pH 3, que apresentou descoloração de 51% e aumento de atividade de 35% em relação à adsorção (ausência de radiação). O ponto de carga zero (PZC) e os resultados fotocatalíticos indicaram que em pH 3 existiu uma predominância de um mecanismo direto, enquanto em pH 6 prevaleceu o mecanismo indireto.

Abstract Pure forms of alkaline-earth stannates with perovskite structure (ASnO3, A= Ca2+, Sr2+, Ba2+) have been used as photocatalysts. In this work, CaSnO3 perovskite sample was synthesized by a modified Pechini method at 800 ºC and characterized by X-ray diffraction (XRD), UV-visible spectroscopy, infrared spectroscopy and Raman spectroscopy. The photocatalytic degradation of remazol golden yellow (RNL) dye under UV radiation was evaluated. The XRD pattern showed that the synthesis method favored the orthorhombic CaSnO3 crystallization. According to the Raman spectrum, a material with high short-range order was obtained despite of the relatively low synthesis temperature, compared to the solid-state reaction one. The highest photocatalytic activity was attained at pH 3, which presented 51% discoloration and improved activity of 35% compared to discoloration solely due to adsorption (absence of radiation). The point of zero charge (PZC) and the photocatalytic results indicated that a direct mechanism prevailed at pH 3, whereas an indirect mechanism prevailed at pH 6.

A grande maioria dos estudos fotoluminescentes foram realizados com materiais cristalinos, cuja emissão ocorre em temperaturas criogênicas, limitando a aplicação destes materiais. Por sua vez, determinados sólidos com alta densidade de defeitos (amorfos), como titanatos, tungstatos, zirconatos, entre outros, apresentam fotoluminescência à temperatura ambiente, semelhante à do silício amorfo. Essa descoberta levou à necessidade de se desenvolver novos modelos para explicar o comportamento desses materiais, mais adequados ao estudo desses materiais. Esta revisão tem como objetivo explicar os resultados de fotoluminescência, utilizando uma abordagem teórico-experimental, com base nas recentes pesquisas desta propriedade em óxidos amorfos.

The majority of the studies about photoluminescence had been carried out with crystalline materials, whose emission occurs at cryogenic temperatures, limiting the application of these materials. In turn, some amorphous solids, as titanates, tungstates, zirconates, among others, present photoluminescence at room temperature, seemed with silicon. This discovery led to the necessity of developing new models to explain the behavior of these materials. This revision intends to elucidate the results on photoluminescence, using a theoretical-experimental treatment, on the basis of the recent researches of this property in amorphous oxides.