Green photocatalytic remediation of Fenthion using composites with natural red clay and non-toxic metal oxides with visible light irradiation.

In the present work, composites with non-toxic metal oxides, such as TiO and ZnO, and a natural red clay () reach in hematite were used in the photocatalytic degradation of Fenthion. The composite TiO/Taua (0.5:1 wt. ratio) and pure TiO were prepared by sol-gel method while ZnO/Taua (0.5:1 wt. ratio) and pure ZnO were prepared by Pechini method. The materials were characterized by XRD, SEM, EDX, and DRS. The anatase phase was formed in both pure TiO and TiO/Taua, while the hexagonal phase was formed in pure ZnO and ZnO/Taua. The bandgap energies for the two composites were narrowed compared to the respective pure oxides as consequence of the hematite (α-FeO,  = 2.1 eV) in the red clay, reaching 2.1 eV for TiO/Taua and 2.0 eV for ZnO/Taua, while the bandgap energies for pure TiO and ZnO were 3.2 and 3.0 eV, respectively. Fenthion was not degraded in the dark, but the concentration droped 20% after 180 min under visible light irradiation without photocatalyst and 60% after 210 min in the presence of the pure red clay. Both TiO/Taua and ZnO/Taua composites were also photocatalytic active to degrade Fenthion ( > 420 nm), with degradation of 78% (in 180 min) and 85% (in 210 min) respectively. In the optimized conditions (pH 2, 100 mg L of HO and 30 mg L of Fenthion), the ZnO/Taua composite was the most efficient, reaching 89% degradation in up to 30 min, with Fenthion sulfoxide as the degradation product.