(668b) A Tale of Two Cities - TiO2 Impregnated Mesoporous Silica Nanoparticles and TiO2 Coated Thin Films As Photocatalysts in Wastewater Treatment

Nanosized semiconductor photocatalysts (like TiO₂) can be employed for removal of organic pollutants in water, by their advanced oxidation. The present work employs TiO₂ in two forms for evaluation.

The first form is by depositing TiO₂ nanoparticles inside the pores of radial pore nano-spherical silica (RPNS, a new form of radially arranged pores in mesoporous silica, see figure), used in a slurry batch reactor, enabling us to recover and reuse the catalyst multiple times, without aggregation. For the second system, we used TiO₂ coated thin films in a batch reactor, without the need of catalyst recovery, due to its direct deposition on the substrate itself. RPNS was made by the emulsion method and TiO₂ coating on quartz tube was by dip-coating.

The specific surface area and mean pore diameter of RPNS are 668 m²/g and 5.7 nm, respectively. Furthermore, the optimized catalyst (36.7 wt.% TiO₂ containing RPNS), for photodegradation of the rhodamine B (RhB) dye-pollutant, shows the highest photocatalytic activity (first order reaction rate constant of 2.41 h^-1 , see figure) within different types of mesopores. This is a unique design of radial pore-alignment and reactivity in mesoporous systems achieved by us (through relative rates of pore diffusion, adsorption and reaction), to obtain one of the best overall degradation rates.

In contrast, the TiO₂ coated films show different turnover frequency, due to the resultant varied film thickness and different activation level of catalysts. The best performance is a turnover value of 0.342 mol/mol h^-1. This has the dual advantage of a high turnover frequency and also continuous dye degradation-operation in wastewater treatment, without catalyst loss. It was optimized by us via an experimentally validated mathematical model developed and solved to this end.

Thus, together, these two configurations show contrasting design of known TiO₂ catalyst for appropriate field deployment choice.