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Development and Upscaling of SiO2@TiO2 Core-Shell Nanoparticles for Methylene Blue Removal
Summary
Researchers synthesized SiO2-core and TiO2-shell nanoparticles through a reproducible low-cost method and tested their performance for removing methylene blue dye from water through adsorption and UV photodegradation. The core-shell structure exploited the synergy between SiO2 surface area and TiO2 photocatalytic activity to achieve efficient dye removal.
SiO<sub>2</sub>@TiO<sub>2</sub> core-shell nanoparticles were successfully synthesized via a simple, reproducible, and low-cost method and tested for methylene blue adsorption and UV photodegradation, with a view to their application in wastewater treatment. The monodisperse SiO<sub>2</sub> core was obtained by the classical Stöber method and then coated with a thin layer of TiO<sub>2</sub>, followed by calcination or hydrothermal treatments. The properties of SiO<sub>2</sub>@TiO<sub>2</sub> core-shell NPs resulted from the synergy between the photocatalytic properties of TiO<sub>2</sub> and the adsorptive properties of SiO<sub>2</sub>. The synthesized NPs were characterized using FT-IR spectroscopy, HR-TEM, FE-SEM, and EDS. Zeta potential, specific surface area, and porosity were also determined. The results show that the synthesized SiO<sub>2</sub>@TiO<sub>2</sub> NPs that are hydrothermally treated have similar behaviors and properties regardless of the hydrothermal treatment type and synthesis scale and better performance compared to the SiO<sub>2</sub>@TiO<sub>2</sub> calcined and TiO<sub>2</sub> reference samples. The generation of reactive species was determined by EPR, and the photocatalytic activity was evaluated by the methylene blue (MB) removal in aqueous solution under UV light. Hydrothermally treated SiO<sub>2</sub>@TiO<sub>2</sub> showed the highest adsorption capacity and photocatalytic removal of almost 100% of MB after 15 min in UV light, 55 and 89% higher compared to SiO<sub>2</sub> and TiO<sub>2</sub> reference samples, respectively, while the SiO<sub>2</sub>@TiO<sub>2</sub> calcined sample showed 80%. It was also observed that the SiO<sub>2</sub>-containing samples showed a considerable adsorption capacity compared to the TiO<sub>2</sub> reference sample, which improved the MB removal. These results demonstrate the efficient synergy effect between SiO<sub>2</sub> and TiO<sub>2</sub>, which enhances both the adsorption and photocatalytic properties of the nanomaterial. A possible photocatalytic mechanism was also proposed. Also noteworthy is that the performance of the upscaled HT1 sample was similar to one of the lab-scale synthesized samples, demonstrating the potentiality of this synthesis methodology in producing candidate nanomaterials for the removal of contaminants from wastewater.
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