The impact of Eu3+ doping at the Sr2+ and Sn4+ sites in SrSnO3 on its structural and electronic properties was studied and correlated with the photocatalytic efficiency. The compounds were synthesized using a modified Pechini method. Refinement of the synchrotron X-ray diffraction (S-XRD) data showed that the samples had an orthorhombic Pbnm symmetry. The incorporation of Eu into the lattice led to increased short- and long-range disorder, inducing additional distortion in the SnO6. XANES measurements revealed that mixed Eu valences (Eu3+ and Eu2+) were present in Eu-doped samples, and DFT calculations confirmed the presence of these ions at Sr2+/Sr4+ sites in the SrSnO3, resulting in changes in the electronic behavior. The catalytic performance toward Remazol yellow dye photodegradation and the catalysts’ surface properties were also evaluated. The catalytic efficiency followed the order of Sr­(Sn0.99Eu0.01)­SnO3 > (Sr0.99Eu0.01)­SnO3 > SrSnO3. The order was clearly related to selected-site doping that changed the degree of the inter- and intraoctahedral distortion and the introduction of different Eu midgap states, which apparently favor charge separation upon photoexcitation during photocatalysis. The results shown here are of great importance to the functionalization of SrSnO3 and other perovskite materials by lanthanoid ions, especially Eu3+, for effective applications as photocatalysts.

The inadequate discharge of effluents from different sources without prior treatment can impact the characteristics of soil and water, which reflect serious environmental problems. Advanced oxidative processes (AOP) appear as a viable alternative for environmental remediation, including wastewater treatment. Herein, α-MoO3 and α-Fe2O3 semiconductors were synthesized at low temperature by a Pechini-based method and then applied in photocatalysis. The catalytic efficiency was performed under visible light toward the degradation of an organic persistent pollutant (Rhodamine B dye, RhB), commonly present in industries wastewater. The results indicated that the synthesized α-MoO3 or α-Fe2O3 photocatalysts presented a pronounced activity and promoted an efficient RhB degradation after 15 min of reaction. α-MoO3 had a degradation efficiency of 93% and 98%, while α-Fe2O3 showed 67% and 100% RhB degradation without and with the addition of H2O2, respectively. These results suggest that the synthesized oxides have high oxi-reductive capacity, which can be used for a fast and effective photodegradation of RhB and other organic persistent pollutants to minimize environmental impacts.

In the last ten years, stannates with perovskite structure have been tested as photocatalysts. In spite of the ability of perovskite materials to accommodate different cations in its structure, evaluation of doped stannates is not a common task in the photocatalysis area. In this work, Fe 3+ doped BaSnO 3 was synthesized by the modified Pechini method, with calcination between 300 and 800°C/4 h. The powder precursor was characterized by thermogravimetry after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, Raman spectroscopy and UV-visible spectroscopy. Materials were tested in the photocatalytic discoloration of the Remazol Golden Yellow azo dye under UVC irradiation. Higher photocatalytic efficiency was observed under acid media. As no meaningful adsorption was observed at this condition we believe that an indirect mechanism prevails. Fe 3+ doping decreased the band gap and favored the photocatalytic reaction, which may be assigned to the formation of intermediate levels inside the band gap.

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INTRODUÇÃOOs pigmentos cerâmicos, embora tenham sido descobertos há vários anos, continuam sendo pesquisados até hoje em busca de novos tons e cores cada vez mais reprodutíveis e estáveis. Assim, torna-se necessário o desenvolvimento de novos pigmentos e métodos de síntese que superem as desvantagens apresentadas pelo processo industrialmente já consolidado (método convencional -reação no estado sólido) [1]. A palavra pigmento é originária do latim pigmentum, o que denota cor. Na indústria cerâmica os pigmentos podem ser descritos como substâncias inorgânicas constituídos por uma matriz cerâmica de natureza cristalina e um elemento Universidade Federal da Paraíba, João Pessoa, PB, pimentelmp@ufersa.edu.br, daraujomelo@gmail.com, suelymcc@hotmail.com, laischantelle@bol.com.br, mafm.ufrn@gmail.com, rodolfoluiz.engenharia@hotmail.com cromóforo responsável pela coloração, que sejam estáveis termicamente, insolúveis nos vidrados, resistentes a ataques químicos e físicos e que não produzam emissão de gases [2]. Atualmente, muitos setores industriais, como plásticos, cosméticos, vernizes, tinta de impressão para papel e tecido, decoração, materiais de construção, entre outros, utilizam os pigmentos inorgânicos [3, 4]. Particularmente no setor cerâmico estes colorantes são ditos pigmentos cerâmicos e são caracterizados principalmente pela estabilidade térmica elevada [5]. A maior parte dos pigmentos inorgânicos é de substâncias que possuem uma estrutura cristalina determinada. Estruturalmente, um pigmento inorgânico é formado por uma rede hospedeira, na qual se integra o ResumoOs pigmentos inorgânicos são os mais utilizados industrialmente, pois apresentam maior estabilidade química e térmica e podem ser produzidos com um elevado grau de pureza e uniformidade. Essas características levaram ao desenvolvimento de diferentes cores intensas, estáveis e adequadas ao uso como pigmentos. O presente trabalho tem por objetivo sintetizar materiais cerâmicos com estrutura espinélio para uso como pigmento cerâmico e aplicá-los em fritas cerâmicas. O processo de síntese foi realizado pela rota da gelatina e com os pós obtidos foram conduzidos um estudo de evolução de fases cristalinas por meio de difração de raios X, refinamento das estruturas por meio do método Rietveld, espectroscopia na região do infravermelho, microscopia eletrônica de varredura, espectroscopia na região do UV-visível e colorimetria. Foram observadas nos difratogramas reflexões características da estrutura espinélio. O tamanho médio de cristalito e a cristalinidade aumentou com o aumento da temperatura de calcinação. A coloração dos pigmentos variou do azul claro ao violeta azul. Palavras-chave: síntese de espinélio, pigmentos cerâmicos, gelatina. Abstract