Structure-dependent adsorptive or photocatalytic performances of solid and hollow dendritic mesoporous silica & titania nanospheres

Two types of titania-containing dendritic mesoporous silica nanospheres (DMSNs) have been successfully fabricated for organic dyes removal, water splitting, and carbon dioxide reduction by their adsorptive or photocatalytic performances. Hybrid dendritic mesoporous silica&titania nanospheres (DMSTNs) were initially prepared by grafting tetrabutyl orthotitanate (TROT) onto DMSNs. Then, hollow dendritic mesoporous silica&titania nanospheres (HDMSTNs) were realized merely by etching the solid DMSTNs with alkaline solution. The surprising structural evolution from the solid state to the hollow was thoroughly revealed by scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM) for the first time. DMSTNs maintain the dendritic morphology with spherical TiO2 nanoparticles uniformly dispersed. HDMSTNs not only keep the dendritic topology, but also possess the hollow texture with TiO2 nanoparticles unevenly dispersed and aggregated. DMSTNs and HDMSTNs exhibit excellent adsorption capacities for methylene blue, while the latter shows improved adsorption capacity. DMSTNs and HDMSTNs can hardly adsorb methyl orange (MO), nevertheless, the two materials can photodegrade MO with outstanding abilities. Amazingly, the latter exhibits decreased degradation capacity despite of its hollow architecture and higher content of titanium oxide. Furthermore, DMSTNs and HDMSTNs display higher photocatalytic activities over hydrogen generation than that of carbon dioxide reduction under visible light. However, DMSTNs and HDMSTNs show various photocatalytic selectivities and activities for the production of carbon monoxide (CO) and methane (CH4). In short, DMSTNs and HDMSTNs have distinct structural superiorities as adsorbents or photocatalysts for different photocatalytic reactions, respectively.