SiO2/TiO2 nanostructured composites with three different ratios of Si:Ti were prepared using the sol-gel method. These materials were characterized using energy dispersive X-ray fluorescence, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, Raman with Fourier transform infrared spectroscopy, and the specific surface area. The band gaps of materials were determined by diffuse reflectance spectra, and the values of 3.20 ± 0.01, 2.92 ± 0.02, and 2.85 ± 0.01 eV were obtained as a result of the proportional increases in the amount of Ti within the composite. The materials exhibit only the anatase (TiO2) crystalline phase and have crystalline domains ranging from 4 to 5 nm. The photodegradation process of methylene blue, royal blue GRL, and golden yellow GL dyes were studied with respect to their contact times, pH variations within the solution, and the variations in the dye concentration of the solution in response to only sunlight. The maximum amount of time for the mineralization of dyes was 90 min. The kinetics of the process follows an apparently first order model, in which the obtained rate constant values were 5.72 × 10-2 min-1 for methylene blue, 6.44 × 10-2min-1 for royal blue GRL, and 1.07 × 10-1min-1 for golden yellow.

No presente estudo, um novo material compósito (SiO2/TiO2/ZnO) foi avaliado para pré-concentração de cobre em amostras de água e alimentos. O sorvente foi caracterizado por microscopia eletrônica de varredura (SEM), infravermelho com transformada de Fourier (FT-IR), análise de dados texturais, fluorescência de raios X por energia dispersiva (EDXRF) e difratometria de raios X (XRD). A pré-concentração em linha e determinação espectrofotométrica na região visível foi baseada na pré-concentração de 20,0 mL de amostra em pH 7,0 através de 50 mg do sorvente, numa vazão de 6,4 mL min-1. Um volume fixo de 0,3 mL de HNO3 0,5 mol L-1 elui os íons cobre que reagem com dietilditiocarbamato (DDTC) 0,3% (m/m) cujo complexo formado (Cu(DDTC)2) é monitorado a 452 nm. A seletividade do sorvente foi examinada avaliando o efeito de íons interferentes. O método proposto forneceu linearidade variando de 20,0 a 230,0 mg L-1 (r = 0,998), fator de pré-concentração de 35,9 e limite de detecção de 5,6 mg L-1. Amostras de água e alimentos foram analisadas com sucesso pelo método proposto e a exatidão foi checada por meio de análises de materiais certificados de referência de proteína e fígado de peixe.

In the present study, a new composite material (SiO2/TiO2/ZnO) for copper preconcentration in water and food samples was evaluated. The sorbent was characterized by scanning electronic microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR), textural data analyses, energy dispersive X-ray fluorescence (EDXRF) and X-ray diffractometry (XRD). The on-line preconcentration and visible spectrophotometric determination was based on loading 20.0 mL of sample at pH 7.0 through 50 mg of sorbent at a flow rate of 6.4 mL min-1. A fixed volume of 0.3 mL of 0.5 mol L-1 HNO3 elutes copper ions, in which react with 0.3% (m/m) diethyldithiocarbamate (DDTC) whose complex formed (Cu(DDTC)2) is monitored at 452 nm. The selectivity of sorbent has been examined by assessing the effect of interfering ions. The proposed method provided linearity ranging from 20.0 to 230.0 mg L-1 (r = 0.998), preconcentration factor of 35.9 and limit of detection of 5.6 mg L-1. Water and food samples were successfully analyzed by proposed method and the accuracy was checked by analysis of certified reference materials of protein and liver of fish.