Heterogeneous Photocatalysis as an Advanced Oxidation Process for the Abatement of Chlorinated, Monocyclic Aromatic and Sulfurous Volatile Organic Compounds in Air: State of the Art

Abstract

This review focuses on both fundamentals and applicability of heterogeneous photocatalysis as an advanced oxidation technology for degradation of volatile organic compounds (VOC) in air, with peer-reviewed literature data published since 1997 being the backbone of this article. Four key issues are covered. First, the underlying principles of heterogeneous photocatalysis are outlined using the band gap model. Second, a detailed overview is given of chlorinated, monocyclic aromatic and sulfurous VOC recently selected as target compounds in lab-scale photocatalytic degradation experiments. Data on reactor types, photocatalysts, reaction conditions, and reported results are tabulated. The third section deals with reaction products, analytical techniques used for separation and/or identification, proposed reaction pathways, and catalyst deactivation. Finally, effects of process parameters such as gas-phase pollutant and oxygen concentration, relative humidity, temperature, and light intensity on degradation kinetics are reviewed.

KEY WORDS:

• AOP
• photocatalysis
• titanium dioxide air
• volatile organic compounds
• VOC

Notes

¹DCM: dichloromethane; CF: chloroform; TeCM: tetrachloromethane; PtCE: pentachloroethane; VC: vinyl chloride; DCE: 1,2-dichloroethene; TCE: trichloroethene; TeCE: tetrachloroethene; DCB: 1,4-dichlorobut-2-ene/3,4-dichlorobut-1-ene mixture; DCBZ: 1,3-dichlorobenzene.

²CR: continuous reactor; BR: batch reactor; RBR: recirculating batch reactor.

³SG: sol-gel; not sp.: not specified.

⁴[VOC]_gas = VOC gas-phase concentration; [O₂]_gas = oxygen gas-phase concentration; I = light intensity; RH = relative humidity; T = temperature; n.r. : no data reported.

⁵ER: photocatalytic activity is evaluated in terms of (initial) elimination rates (ER) instead of η_removal; n.r.: no data on η_removal and ER are reported.

⁶η_removal in batch reactors (BR) are followed by the corresponding irradiation time (between brackets).

⁷+ : reference contains data on reaction products and/or pathways; n.r.: reference contains no data on reaction products and/or pathways.

⁸+ : catalyst deactivation observed; − : catalyst deactivation not observed; n.r. : no data reported.

¹BZ: benzene; TOL: toluene; Et-BZ: ethylbenzene; XYL: (o-, m-, and p-)xylene.

²AC: activated carbon.

³Data summarized from Ao and Lee (2003), Ao et al. (2003), Ao and Lee (2004), and Ao et al. (2004).