**4.4. Application of dye-sensitized photocatalyst for the degradation of phenols**

Dye-sensitized photodegradation of phenol and phenolic compounds showed promising results under visible-light irradiation [7, 11, 26, 69–71]. Vinu et al. [11] reported degradation of phenol, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol using eosin Y and fluorescein-sensitized combustion-synthesized nano TiO2 under visible light. Eosin Ysensitized photocatalyst showed better performance than fluorescein-sensitized photocatalyst. Phenol degradation rate was slowest among the phenolic compounds. Chowdhury et al [7] used eosin Y-sensitized TiO2/Pt for the degradation of phenol under the visible solar light in the presence of triethanolamine as an electron donor. About 93% phenol degradation (initial concentration 40 ppm) was achieved within 90 min using eosin Y-sensitized TiO2/Pt photocatalyst under optimum experimental conditions (pH 7.0, photocatalyst concentration of 0.8 g L−1, triethanolamine concentration of 0.2 M, 0.5% Pt loading on TiO2, visible solar light intensity of 100 mW cm2 ). Mele et al. [26] studied photocatalytic degradation of 4-nitrophenol with polycrystalline TiO2 impregnated with functionalized Cu(II) porphyrin or Cu(II)-phthalocyanine. Cu(II)-based sensitizers provided better results for the degradation of 4-nitrophenol in comparison with metal-free sensitizers. Iliev [69] studied photooxidation of phenol with phthalocyanine-modified TiO2 and Al2O3 under visible light. The degree of photodegradation of phenol in the presence of phthalocyanine-modified TiO2 is much higher than phthalocyanine-modified Al2O3. Superoxide ion was considered as the active species during photodegradation. Grandos et al. [70] used Co(II) and Zn(II) tetracarboxyphthalocyanine (TcPcM)-sensitized TiO2 for the degradation of phenol under visible light. The photodegradation efficiencies were reported to be 4.3 and 3.3% for TcPcCo/TiO2 and TcPcZn/TiO2, respectively. Ghosh et al. [71] demonstrated the photocatalytic degradation of 4-chlorophenol with coumarin-sensitized TiO2 under visible LED light. The degradation rate followed a first-order kinetics and moved toward a limiting value at a photocatalyst concentration of 0.3 g L−1.
