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

Effectiveness of Photocatalytic Filter for Removing Volatile Organic Compounds in the Heating, Ventilation, and Air Conditioning System

“…The value of PF would vary with the VOC concentration if the PCO reaction rate fits the Langmuir-Hinshelwood rate form, which is the most reported rate form for PCO kinetics. [5][6][7]9,24 To simplify this problem, it was assumed that the PCO reaction fits the first-order reaction rate form, 8,25 and this assumption was authenticated in the experiments. Thus, the VOC removal efficiency of the photocatalytic filter ( PF ) could be treated as a constant.…”

“…Degussa P25 TiO 2 powder has a primary particle diameter of 30 nm, a surface area of 50 m 2 /g (Brunauer, Emmett, and Teller [BET]), and a crystal structure of 70% anatase and 30% rutile. 5,6 The TiO 2 coating procedure was described as follows. 8,21,22 First, the TiO 2 powder was suspended in distilled water by the ultrasonic tank (Branson 5200).…”

“…Like water, formaldehyde is supposedly adsorbed on the hydroxyl groups on the surface of the photocatalyst via hydrogen bonding. 6,8 Thus, the competitive interaction between formaldehyde and water is probably stronger than that between toluene and water. The positive effect of RH on the PCO reaction rate by enhancing the formation of hydroxyl radical is partially counteracted by the negative effect of the competitive interaction between water and VOCs.…”

“…Air handling units in typical HVAC systems generally contain: (1) outside air intakes, plenums, ducts, and outdoor air; (2) filters and prefilters; (3) heating and cooling coils; (4) chiller and boiler (to supply hot and chilled water for the coils); (5) cooling towers; (6) humidifier or dehumidifier; (7) supply fans; (8) supply ducts; (9) distribution ducts, boxes, and plenums; (10) damper; (11) return air plenums or ducts; (12) return fan; and (13) exhaust outlets. The primary function of typical HVAC systems is to control the temperature (thermal comfort) and relative humidity (RH) of the supply air.…”

“…This process is effective in controlling a wide variety of VOCs, including alkanes, alkenes, alcohol, aromatics, chlorinated hydrocarbons, aldehydes, and ketones. [5][6][7][8][9] Rather than adsorbing VOCs on sorbent, the photocatalytic filter can oxidize VOCs to carbon dioxide (CO 2 ) and water (H 2 O). Furthermore, many studies showed that the PCO process is able to control the biological contaminations.…”