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TiO2 nanotube semiconductors contain free spaces in their interior that can be filled with active materials such as chemical compounds, enzymes, and noble metals, giving them a fundamental advantage over colloids. Although the unique shape of semiconductor nanotubes makes them promising for a range of potential applications, significant developmental research is required. In this research, a novel TiO2 nanotube photocatalyst was prepared that has a p-n junction. The photocatalyst particle surface is physically divided into reduction and oxidation surfaces, which poses a potential driving force for the transport of photogenerated charge carriers. The structure of this nanotube catalyst was characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The catalyst activity was evaluated by coating the catalyst on HEPA filters and determining the destruction rate of toluene in air. The p-n junction nanotube catalyst was shown to have a much higher photocatalytic destruction rate than that of commercially available, nonnanotube structured material, and a higher destruction rate for nanotube catalysts that did not contain a p-n junction.

The rapid small‐scale column test (RSSCT) is a scaled‐down version of a pilot‐ or full‐scale granular activated carbon (GAC) column. Simple equations for selecting the design and operating parameters of RSSCTs from the full‐scale process design variables are presented, and their limitations are discussed. Carbon usage rates and breakthrough profiles for RSSCTs are compared with pilot‐column results. Case studies representing high and low levels of synthetic organic chemicals, in the presence and absence of background dissolved organic carbon (DOC), and weakly and strongly adsorbing organics are reviewed. For DOC removal, RSSCT and pilot performances were compared for five surface waters and one groundwater.