Hydrothermal synthesis of TiO2–WO3–bentonite composites: Conventional versus ultrasonic pretreatments and their adsorption of methylene blue

TiO2–WO3–bentonite composites were synthesized via a hydrothermal route with and without an ultrasonic pretreatment, and their effects on the adsorption properties of the methylene blue (MB) dye were explored. The TiO2–WO3–bentonite composites showed a significant increase in specific surface area compared to raw clays. The ultrasonic pretreatment was found to enable a complete exfoliation of Na+-bentonite and lead to a well distribution of TiO2–WO3 nanoparticles in the clay matrix. Spectral changes of MB revealed that the aggregation of dye molecules on the TiO2–WO3–bentonite composite surface depended on both the clay matrix used and the ultrasonic pretreatment. Moreover, the choice of clay and use of ultrasound also influenced the adsorption properties of the composites in terms of rate, efficiency, capacity, and cycling stability. The current synthesis would open a way to fabricate other functionalized clay materials.