Controversial reports regarding Stöber silica's microporosity and specific surface area remain in the literature despite decades of widespread applications. In this work, Stöber silica samples prepared under controlled reaction time and postsynthesis washing/drying conditions were characterized by nitrogen adsorption at 77 K, transmission electron microscopy, elemental analysis, Fourier transform infrared spectroscopy, thermal analysis, and evolved gas analysis. Our experimental results demonstrated the important but often overlooked effects of reaction time and postsynthesis treatments on Stöber silica's pore characteristics, as evidenced by the strikingly large range of BET specific surface area (11.3-309.7 m(2)/g). A simple micropore filling and blocking mechanism compatible with an existing Stöber silica growth model incorporating both aggregation and monomer addition steps was proposed to explain all our experimental findings. The carbon and nitrogen contents appear to serve well as the indicative link between our experimental variables and the resulting pore blocking by TEOS and its derivatives. A suitable combination of experimental conditions is recommended in order to make microporous Stöber silica samples with large specific surface area, including a short reaction time, water washing, and drying at moderate temperature preferably under vacuum.
The development of a novel nanoarray photoanode with a heterostructure on a transparent conducting oxide substrate provides a promising scheme to fabricate efficient energy conversion devices. Herein, we successfully synthesize the vertically aligned hierarchical TiO2 nanowire/ZnO nanorod or TiO2 nanowire/ZnO nanosheet hybrid arrays, which are proven to be excellent anode candidates for superior light utilization. Consequently, the quantum-dot-sensitized solar cells based on such hybrid arrays exhibit an impressive power conversion efficiency (PCE) under AM 1.5G one sun illumination with improved short-circuit current density (JSC) and fill factor compared to pristine TiO2 nanowire arrays. Combined with the chemical-bath-deposited Cu2S counter electrode, the eventual PCE can be further optimized to as high as 4.57% for CdS/CdSe co-sensitized quantum dot solar cells.
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