TiO2 photocatalysis and related surface phenomena

Photoinduced reactivity of titanium dioxide

A surface science perspective on TiO2 photocatalysis

Formaldehyde (HCHO) is a major indoor pollutant and long-term exposure to HCHO may cause health problems such as nasal tumors and skin irritation. Photocatalytic oxidation is considered as the most promising strategy for the decomposition of HCHO. Herein, for the first time, a direct g-C3N4–TiO2 Z-scheme photocatalyst without an electron mediator was prepared by a facile calcination route utilizing affordable P25 and urea as the feedstocks. Photocatalytic activities of the as-prepared samples were evaluated by the photocatalytic oxidation decomposition of HCHO in air. It was shown that the photocatalytic activity of the prepared Z-scheme photocatalysts was highly dependent on the g-C3N4 content. At the optimal g-C3N4 content (sample U100 in this study), the apparent reaction rate constant was 7.36 × 10−2 min−1 for HCHO decomposition, which exceeded that of pure P25 (3.53 × 10−2 min−1) by a factor of 2.1. The enhanced photocatalytic activity could be ascribed to the formation of a g-C3N4–TiO2 Z-scheme photocatalyst, which results in the efficient space separation of photo-induced charge carriers. Considering the ease of the preparation method, this work will provide new insights into the design of high-performance Z-scheme photocatalysts for indoor air purification.

Enhanced photocatalytic performance of direct Z-scheme g-C3N4–TiO2 photocatalysts for the decomposition of formaldehyde in air

Photocatalytic oxidation for indoor air purification: a literature review

Persistent indoor air contaminants, those originating from emissions by interior furnishings, occupants, and materials of construction, typically exist in concentrations below 100 parts per billion (ppb) on an individual basis. The total of distinct contaminants may number in the hundreds with an equivalent accumulated concentration of one part per million. This study investigated the effects of humidity and trace (sub-ppmv) contaminant levels on the oxidation rates of formaldehyde, toluene, and 1,3-butadiene. The evaluation also included variations in UV intensity and flow residence time. UV intensities from inexpensive mercury fluorescent lamps, those which are expected to be employed in a practical photocatalytic purifier, are in the mW/cm 2 range. For this reason, the study included UV intensities in that range. The reactor element used in the study was a low pressure drop alumina reticulate, wash-coated with Degussa P25 titania. The data indicated that the reaction was first-order for the three reactants at the subppmv level. An important finding was that competitive adsorption between water and trace (sub-ppmv) contaminants has a significant effect on the oxidation rate. The dependencies of humidity and contaminant concentrations on the oxidation rates are explained as being the results of competitive adsorption on available hydroxyl adsorption sites and of changes in hydroxyl radical population levels

TiO2 Photocatalysis for Indoor Air Applications: Effects of Humidity and Trace Contaminant Levels on the Oxidation Rates of Formaldehyde, Toluene, and 1,3-Butadiene

Robert T. Brown

Papers

TiO2 Photocatalysis for Indoor Air Applications: Effects of Humidity and Trace Contaminant Levels on the Oxidation Rates of Formaldehyde, Toluene, and 1,3-Butadiene