Adsorption and catalytic properties of SiO2/Bi2S3 nanocomposites on the methylene blue photodecolorization process

The decolorization of aqueous solutions methylene blue (C.I. Basic Blue 9), due to the presence of nanocrystalline Bi2S3, supported on SiO2 submicron particles, was investigated here. For this decolorization process, two distinct characteristics, though related, associated to the role of SiO2/Bi2S3 were identified: (i) high methylene blue adsorption capability and (ii) photocatalytic activity to methylene blue photodecolorization. Effects of experimental parameters on the decolorization process, such as methylene blue and nanocomposite concentrations, pH and Bi2S3 particle size were investigated. The maximum adsorption ability of the SiO2/Bi2S3 was approximately 15.6 mg methylene blue per gram. The complete decolorization of a 16 ppm organic dye solution can be achieved, by an adsorption process, in an extremely short time (less than 5 min), using 1.6 g/L of SiO2/Bi2S3 nanocomposite. The study of the decolorization of the dye by an adsorption–photoassisted decolorization process was carried out by irradiation of a suspension prepared with 100 mL of methylene blue solution (8 ppm) and 50 mg of SiO2/Bi2S3. In these conditions the complete decolorization of the dye, adsorbed and in the solution, was achieved in 40 min.