Controlling Photocatalytic Activity and Size Selectivity of TiO2 Encapsulated in Hollow Silica Spheres by Tuning Silica Shell Structures Using Sacrificial Biomolecules.

Yolk-shell nanostructured photocatalyst which consists of inner core photocatalytic particles and outer silica shell exhibits high photocatalytic efficiency and molecular size selectivity due to the molecular sieving property of the outer shell. Creation of extended porosity in the shell endows it with improved adsorption properties and size selectivity toward targeted reactants. In this study, yolk-shell nanostructured photocatalyst consisting of TiO2 NPs core and porous silica shell with controllable pore size was fabricated through a facile single-step dual-templating approach utilizing oil-in-water (O/W) microemulsions and amphiphilic protein molecules. Addition of optimum amount of protein (ovalbumin) as a sacrificial template together with O/W microemulsion during the synthesis led to the expansion of average pore size from 2.0 to 3.6 nm, while retaining TiO2-encapsulated yolk-shell nanostructures. Photocatalytic degradation tests using gaseous 2-propanol and huge proteins as model substrates clearly revealed that the obtained material (TiO2@HSS_pro) showed superior photocatalytic performances with both improved photocatalytic efficiency and molecular size selectivity due to the increased surface area and expanded pore diameter.

Fabrication of Photocatalytic Paper Using TiO2 Nanoparticles Confined in Hollow Silica Capsules.

TiO2 nanoparticles (NPs) encapsulated in hollow silica spheres (TiO2@HSSs) show a shielding-effect that can insulate photocatalytically active TiO2 NPs from the surrounding environment and thus prohibit the self-degradation of organic support materials under ultraviolet (UV)-light irradiation. In this study, photocatalytically active papers were fabricated by combining TiO2@HSS and cellulose fibers, and their photocatalytic activities and durability under UV-light irradiation were examined. The yolk-shell nanostructured TiO2@HSS, which has an ample void space between inner TiO2 NPs and an outer silica shell, was synthesized using a facile single-step method utilizing an oil-in-water microemulsion as an organic template. The thus-prepared TiO2@HSS particles were deposited onto a cellulose paper either by the chemical adhesion process via ionic bonding or by the physical adhesion process using a dual polymer system. The obtained paper containing TiO2@HSS particles with high air permeability exhibited a higher photocatalytic activity in the photocatalytic decomposition of volatile organic compounds than unsupported powdery TiO2@HSS particles because of the uniform dispersion on the paper with a reticular fiber network. In addition, the paper was hardly damaged under UV-light irradiation, whereas the paper containing naked TiO2 NPs showed a marked deterioration with a considerably decreased strength, owing to the ability of the silica shell to prevent direct contact between TiO2 and organic fibers. This study can offer a promising method to fabricate photocatalytically active papers with a photoresistance property available for real air cleaning.