RESUMO Explorou-se a influência de diferentes precursores carbonosos no desenvolvimento de fotocatalisadores g-C3N4/xerogel de carbono/ZnO. O acoplamento entre o óxido de zinco e o nitreto de carbono grafítico é adequado para impulsionar a degradação de poluentes orgânicos. A função do xerogel de carbono é melhorar a transferência de cargas e aumentar a atividade do catalisador sob radiação solar. Foram usados diferentes taninos comerciais (PHENOTAN AP, AG e BS) para avaliar o efeito do precursor carbonoso nas propriedades do compósito. O óxido de zinco possui estrutura cristalina hexagonal. A espectroscopia de reflectância difusa mostrou que os materiais absorvem radiação na região do espectro visível, sendo o material preparado com PHENOTAN AP o que apresentou maior capacidade de absorção. A análise de microscopia eletrônica de varredura mostrou que os materiais são compostos por aglomerados de partículas que tendem a esfericidade. A análise de espectroscopia de energia dispersiva, feita apenas para o material PHENOTAN AP, mostrou que os elementos que compõe o material estão homogeneamente distribuídos na matriz. Por meio da isoterma de nitrogênio, observou-se que os materiais possuem isoterma do tipo IV-H3, sendo que o material PHENOTAN AP apresentou a maior área superficial. A análise de distribuição de poros mostrou que o diâmetro de maior ocorrência se encontra entre 20 e 40 nm. Por meio da termogravimetria, observou-se o material sintetizado com PHENOTAN AP apresenta maior estabilidade térmica. Foi observado que o precursor utilizado na síntese dos compósitos influencia significativamente a atividade fotocatalítica dos materiais. O compósito que apresentou a maior eficiência na fotodegradação do 4-clorofenol sob radiação solar foi o preparado com PHENOTAN AP devido à sua capacidade de absorção de radiação superior, maior área superficial e maior volume de poros. Não houve adsorção significativa do 4-clorefenol nos materiais produzidos, assim como não foi verificada lixiviação dos fotocatalisadores ternários durante o processo.

ABSTRACT The influence of different carbonaceous precursors on the development of g-C3N4/carbon xerogel/ZnO photocatalysts was explored. The coupling between zinc oxide and graphitic carbon nitride is suitable for boosting the degradation of organic pollutants. The function of carbon xerogel is to improve charge transfer and increase catalyst activity under visible radiation. Different commercial tannins (PHENOTAN AP, AG and BS) were used to evaluate the precursor effect on the composite’s properties. X-ray diffractometry showed that the materials have the hexagonal crystal structure of zinc oxide. Diffuse reflectance spectra obtained exhibited the characteristic behavior of zinc oxide (λ<420nm). Furthermore, the material prepared with PHENOTAN AP had a superior visible light absorption capacity. The scanning electron microscopy analysis showed that the materials are composed of clusters of particles similar to spheres and the materials in particle size. The dispersive energy spectroscopy analysis was performed only for the material prepared with PHENOTAN AP and evidenced that all elements are well distributed in g-C3N4/carbon xerogel/ZnO matrix. The nitrogen adsorption isotherms of the materials showed that the isotherms characteristics (type IV-H3), whereas the material synthesized with PHENOTAN AP has the largest specific surface area. The pore distribution of the materials showed that the materials had most developed porous structure, with pores ranging from 20 nm to 40 nm. Through thermogravimetry analysis it is possible to observe that the PHENOTAN AP has superior thermal stability. It was observed that the precursor used in the synthesis of composites significantly influences the photocatalytic activity of the materials. The composite with the highest photodegradation efficiency of 4-Chlorophenol under solar radiation was prepared with PHENOTAN AP, since it has a superior visible radiation absorption, greater amount of carbon, greater surface area and greater volume of pores. It is also worth noting that there was no significant adsorption of 4-chlorophenol in the materials synthesized, as well as no leaching of the photocatalysts during the process.

Abstract The Zn0.5Cd0.5S/ZnO/carbon xerogel photocatalyst was synthesized through the thermal treatment of ZnO, CdS, and a low-cost carbon xerogel matrix at high temperature (600 ºC). ZnO is one of the most widely used photocatalysts, but it has low visible-light absorption, while Zn0.5Cd0.5S is a visible-light active photocatalyst, which can be used as a co-catalyst to enhance photoactivity under natural radiation and promote charge separation through the creation of Z-scheme heterojunctions. The further addition of the carbon xerogel can be justified by its highly developed porous structure and ability to capture photogenerated electrons, which will also promote charge separation. The creation of the hexagonal Zn0.5Cd0.5S and ZnO phases was confirmed through the X-ray diffractometry technique. The addition of the carbon xerogel led to an increase in the specific surface area of the XC/ZnO (630%) and XC/ZnO-Zn0.5Cd0.5S (320%) and a decrease in particle size when compared to the pure ZnO. Regarding the photocatalytic performance of the materials, the Zn0.5Cd0.5S/ZnO/carbon xerogel displayed an enhanced photocatalytic activity for 4-chlorophenol degradation, with 84% degradation after 300 minutes of artificial solar irradiation. The enhanced photoactivity of the Zn0.5Cd0.5S/ZnO/carbon xerogel composite was further confirmed by chronoamperometry, as the composite presented higher photocurrent generation under light irradiation.

RESUMO O desenvolvimento de novos compósitos oxalato de zinco (ZnC2O4)/xerogel de carbono para aplicações fotocatalíticas foi avaliado. O uso do xerogel de carbono é justificado por sua alta condutividade, que facilita a separação de cargas geradas na estrutura do oxalato de zinco. A eficiência fotocatalítica dos materiais foi avaliada pela decomposição do azul de metileno. Os materiais foram produzidos pela dispersão do oxalato de zinco em gel de carbono, durante sua policondensação em meio ácido. Os difratogramas de raios-X evidenciam a existência da fase ?-ZnC2O4 no compósito desenvolvido. O material apresenta significativa absorção de radiação na faixa de comprimentos de onda visível. O compósito apresentou degradação completa do azul de metileno (10 mg L-1, 0.5 L) no sistema após 3 h sob luz solar simulada, com dosagem de 50 mg L-1 de catalisador, evidenciando o potencial uso desse material em processos de tratamento de efluentes.

ABSTRACT The development of new ZnC2O4/carbon xerogel composites for photocatalytic applications has been evaluated. The use of carbon xerogel is justified by its high conductivity, which facilitates the separation of charges generated in the structure of zinc oxalate. The photocatalytic efficiency of the materials was evaluated by the decomposition of methylene blue. The materials were produced by dispersing zinc oxalate in carbon gel during its polycondensation in acidic medium. X-ray diffractograms show the existence of the ?-ZnC2O4 phase in the developed composite. The material has significant radiation absorption in the visible wavelength range. The composite showed complete degradation of methylene blue (10 mg L-1, 0.5 L) in the system after 3 h under simulated sunlight, with 50 mg L-1 catalyst dosage, showing the potential use of this material in treatment processes. of effluents.

The adsorption kinetics of phosphate on Nb2O5.nH2O was investigated at initial phosphate concentrations 0.25, 0.50 and 1.00 mg.L-1. The kinetic process was described by a pseudo-second-order rate model very well. The adsorption thermodynamics was carried out at 298, 308, 318, 328 and 338 K. The positive values of both ΔH and ΔS suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG values obtained were negative indicating a spontaneous adsorption process. The Langmuir model described the data better than the Freundlich isotherm model. The effective desorption could be achieved using water at pH 12.