Mesoporous Hollow Sphere Titanium Dioxide Photocatalysts through Hydrothermal Silica Etching

Robust, monodisperse, mesoporous titanium dioxide (TiO₂) submicrometer hollow spheres were synthesized through a single step hydrothermal silica etching reaction under mild conditions. Efficient silica (SiO₂) removal was achieved without the use of toxic reagents, and a unique controllable silica redeposition mechanism was identified, imparting the hollow spheres with excellent structural integrity. The parameters of the hydrothermal reaction affecting the etching process, including pH, temperature, and silica concentration, were systematically investigated and optimized for the production of silica-templated hollow structures. The resulting processing conditions yielded TiO₂ hollow spheres with a surface area of ∼300 m² g^–1 and anatase phase crystallization, which exhibited high adsorption capacity for methylene blue dye and good photocatalytic activity without requiring high-temperature calcination

Recyclable Graphene Oxide-Supported Titanium Dioxide Photocatalysts with Tunable Properties

A modular synthesis technique was developed for producing graphene-supported titanium dioxide photocatalysts. The modular synthesis allowed for simple tuning of the ratio of particle loading on the graphene oxide (GO) surface as well as good photocatalytic activity of the composite and quick, efficient magnetic separability. GO flakes were used as a support for titanium dioxide nanoparticles and SiO₂ insulated nano-sized magnetite aggregates. Different composition ratios were tested, resulting in a catalyst formulation with photocatalytic activity exceeding that of a commercial photocatalyst by a factor of 1.2 as well as excellent recyclability, with the capability to degrade 3 mg/L methylene blue in aqueous solution over 10 consecutive trials with minimal loss in photocatalytic efficiency. Recovery of the catalyst was achieved by simply exposing the nanocomposite to a magnetic field for ∼1 minute. Furthermore, it was found that the catalyst could be regenerated to its initial efficiency through simple UV treatment to provide additional re-use. To highlight the importance of the nanocomposite to the current water treatment industry, we showed rapid degradation of pharmaceutical compounds caffeine and carbamazepine within 60 min. The nanocomposite shows activity exceeding that of commercial photocatalyst P25 with the added benefit of being fully recoverable, reusable, and easy to produce. Overall, a simple technique for producing and tuning an effective magnetically recyclable nanocomposite was developed which should allow easy scalability and industrial production, a factor critical for the implementation of nano-based water treatment techniques