Superfund Research Program

Photocatalytic Remediation of PCB-contaminated Water and Sediment: Novel Catalysts and Potential Solar Applications

Project Leader: Chia-Swee Hong (Wadsworth Center, New York State Department of Health)
Grant Number: P42ES004913
Funding Period: 1995 - 2000

Project-Specific Links

Final Progress Reports

Year:   1999 

Photocatalytic processes in the presence of titanium dioxide provide an interesting route to destroy hazardous organic contaminants, such as polychlorinated biphenyls. These processes are operational in the UV-A domain with a potential use of solar radiation. 4,4'-dichlorobiphenyl (4,4'-DCB) was tested as a model compound at bench scale. 4,4'-DCB was irradiated in a TiO2 semiconductor aqueous suspension under UV-340. The degradation of 4,4'-DCB followed the Langmuir-Hinshelwood kinetic model at natural pH. The rate constant k was proportional to the concentration of TiO2 up to 5 mg/L. Adsorption equilibrium constant K of 4,4'-DCB was calculated to be 3.59*10⁷ L/mol and was independent of the concentration of TiO2. Pentafluorobenzoyl chloride (PFBC) was used as derivatizing agent for hydroxylated PCBs. The derivatives were identified using capillary gas chromatography-mass spectrometry (GC-MS) and quantified using gas chromatography with electron capture detector (GC-ECD). The primary photoproducts included three hydroxylated PCBs, 4'-chloro-4-biphenyl-ol, 4,4'-dichloro-2-biphenyl-ol, and 4,4'-dichloro-3-biphenyl-ol. Hydroxylation was confirmed to be the major pathway in the photocatalysis. Hydroxylation could occur at all sites despite steric hindrance and/or resonance effects. Other important intermediates were identified as 4-chlorophenyl-ethanone, 4-chlorobenzaldehyde, and 4-chlorophenol. Neither 4-chlorobiphenyl nor biphenyl were detected which indicated that dechlorination was a minor pathway if any.