SnxTi1−xO2 solid-solution-nanoparticle embedded mesoporous silica (SBA-15) hybrid as an engineered photocatalyst with enhanced activity

Synthesis of hybrids of a porous host-material (with well-dispersed embedded nanoparticles inside the pore), wherein each nanoparticle has precisely controlled properties (size and composition) poses a generic challenge. To this end, a new strategy is proposed to form Sn_xTi_1−xO₂ solid-solution-nanoparticles inside the pores of sphere-like mesoporous silica (SBA-15), with different percentages of Sn in the nanoparticle (varying from 5 to 50 at%), for enhanced photocatalysis. X-ray diffraction confirms the formation of solid-solution nanoparticles in the porous silica hybrid, while the location of nanoparticles and elemental composition are identified using electron microscopy. The hybrid with 5 at% of Sn (Sn_0.05Ti_0.95O₂-sphere-like SBA-15) shows the maximum photocatalytic activity for degradation of rhodamine-B dye (first order rate constant for degradation, k = 1.86 h⁻¹), compared to both pure TiO₂-sphere-like SBA-15 (k = 1.38 h⁻¹) or pure SnO₂-sphere-like SBA-15 (k = 0.14 h⁻¹) or other hybrids in this series. XPS and PL spectra suggest the formation of more oxygen vacancies during the replacement of Ti⁴⁺ with Sn⁴⁺. Electrochemical studies reveal that there is a reduction of charge transfer resistance from 910 kΩ cm⁻² for TiO₂-sphere-like SBA-15, to 332 kΩ cm⁻² for Sn_0.05Ti_0.95O₂-sphere-like SBA-15. These results imply that the enhancement in photocatalytic performance is as a result of delay in recombination of charge carriers. Therefore, the approach followed in the present work to form solid-solution nanoparticles inside a porous host without causing pore blockage, would be a promising route towards increasing reaction rates in catalytic applications of hybrid materials.