Abstract
The sol-gel process is a wet-chemical technique (chemical solution deposition), which has been widely used in the fields of materials science, ceramic engineering, and especially in the preparation of photocatalysts. Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the approaches to remove VOCs from indoor air, photocatalytic oxidation (PCO) is regarded as a promising method. This paper is a review of the status of research on the sol-gel method for photocatalyst preparation and for the PCO purification of VOCs. The review and discussion will focus on the preparation and coating of various photocatalysts, operational parameters, and will provide an overview of general PCO models described in the literature.
Highlights
Since the research of photocatalytic water split on TiO2 electrodes was conducted in 1972 [1], the photocatalytic oxidation of aqueous and gaseous contaminants has been extensively studied
The process of photocatalytic oxidation (PCO) has several advantages [15]: (i) it is GRAS (Generally Recognized As Safe): the common photocatalyst is anatase TiO2, an n-type semiconductor oxide which is a component of some toothpastes and pharmaceutical suspensions; (ii) it is a mild oxidant: kinetic studies demonstrate that the ultimate source of oxygen during oxidation is molecular oxygen, a far milder oxidant than hydrogen peroxide or ozone, etc.; (iii) it can be used in ambient temperature: photocatalysis appears to be active at room temperature; (iv) it possesses generality: while several mechanistic pathways for oxidation have been proposed, the dominant view is that the hydroxyl radical is photogenerated on the titania surface
Wang et al [68] reported that TiO2 loading on the surface of YFeO3 can prolong the life of electron-hole pairs and reduce the recombination of them, resulting in the elevation of photocatalytic activity of TiO2/YFeO3 and the narrowing of the band gap energy
Summary
Since the research of photocatalytic water split on TiO2 electrodes was conducted in 1972 [1], the photocatalytic oxidation of aqueous and gaseous contaminants has been extensively studied. The process of PCO has several advantages [15]: (i) it is GRAS (Generally Recognized As Safe): the common photocatalyst is anatase TiO2, an n-type semiconductor oxide which is a component of some toothpastes and pharmaceutical suspensions; (ii) it is a mild oxidant: kinetic studies demonstrate that the ultimate source of oxygen during oxidation is molecular oxygen, a far milder oxidant than hydrogen peroxide or ozone, etc.; (iii) it can be used in ambient temperature: photocatalysis appears to be active at room temperature; (iv) it possesses generality: while several mechanistic pathways for oxidation have been proposed, the dominant view is that the hydroxyl radical (or some other strong oxidant) is photogenerated on the titania surface The potency of this oxidant is responsible for the titania’s broad activity toward various contaminants (such as aromatics, alkanes, olefins, halogenated hydrocarbons, odor compounds, etc.)
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