Abstract
We have successfully prepared mesoporous TiO2 photocatalysts with highly thermal stability and tunable pore sizes through an ionic-liquid templated sol-gel method. The mesoporous structure was directed by self assembly of a hydrophilic ionic liquid, butbleyl-3-methylimidazolium chloride (BMIMCl), in a benzyl alcohol (log Kow= 1.2) oil phase. Phosphate ions were incorporated into the TiO2 framework to stabilize the pore structure against thermal induced collapse. Four salts, including NH4NO3, NH4Cl, CaCl2 and NaCl, were used as auxiliary reagents to expand pore sizes of the porous TiO2 samples. After removal of BMIMCl at 550 °C, the porous TiO2 samples exhibited a large specific surface area of 164 m2/g and an arrearage pore size of 4.2 nm. Addition of the salts effectively expand the pore size in the order of NH4NO3 (16.8 nm) > NH4Cl (13.7 nm) > CaCl2 (12.4 nm) > NaCl (8.7 nm), while the surface areas were maintained in the range of 154-199 m2/g. The ionic radii and valence states of the cations/anions (Na+: 116 pm, Ca2+: 114 pm, NH4+: 140 pm, NO3-: 189 pm, Cl-: 181 pm) determined the pore sizes. Expanded pores assist the adsorption of bisphenol A into the pore channels of the porous TiO2 samples because of capillary condensation. Improved adsorption capability promotes photocatalytic performance. Compared to the porous sample having the pore size of 4.2 nm, the samples having the pore size of 13.7-16.8 nm enhanced the photocatalytic activity by 6.7-9.3 times although they have similar surface areas.
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