The comparative photodegradation activities of pentachlorophenol (PCP) and polychlorinated biphenyls (PCBs) using UV alone and TiO2-derived photocatalysts in methanol soil washing solution

Abstract

Photochemical treatment is increasingly being applied to remedy environmental problems. TiO2-derived catalysts are efficiently and widely used in photodegradation applications. The efficiency of various photochemical treatments, namely, the use of UV irradiation without catalyst or with TiO2/graphene-TiO2 photodegradation methods was determined by comparing the photodegadation of two main types of hydrophobic chlorinated aromatic pollutants, namely, pentachlorophenol (PCP) and polychlorinated biphenyls (PCBs). Results show that photodegradation in methanol solution under pure UV irradiation was more efficient than that with either one of the catalysts tested, contrary to previous results in which photodegradation rates were enhanced using TiO2-derived catalysts. The effects of various factors, such as UV light illumination, addition of methanol to the solution, catalyst dosage, and the pH of the reaction mixture, were examined. The degradation pathway was deduced. The photochemical treatment in methanol soil washing solution did not benefit from the use of the catalysts tested. Pure UV irradiation was sufficient for the dechlorination and degradation of the PCP and PCBs.

Figure 1. Schematic experimental system for photo degradation experiments.

Figure 2. Photocatalytic degradation of PCP with TiO₂, graphene-TiO₂ and without catalyst under 100 W UV light.

The inset represents the logarithmic transform for each curve.

Figure 3. Percentage remained of PCBs after 2 hours photodegradation under UV light with TiO₂, graphene-TiO₂ and without catalyst: (a) congener 8; (b) congener 28; (c) congener 30; (d) congener 31; (e) congener 33; (f) congener 74.

Figure 4. Photocatalytic degradation of PCP with TiO₂, graphene-TiO₂ and without catalyst under: (a) 9 W UV light; (b) 300 W UV light.

Figure 5. Photocatalytic rate constants of PCP degradation with different TiO₂ loading, compared with the one of pure UV irradiation.

Figure 6. Photocatalytic degradation of PCP with TiO₂, graphene-TiO₂ and without catalyst under different pH values: (a) pH = 1; (b) pH = 4; (c) pH = 10; (d) pH = 13.