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

ABSTRACT

In the present work, composites with non-toxic metal oxides, such as TiO₂ and ZnO, and a natural red clay (taua) reach in hematite were used in the photocatalytic degradation of Fenthion. The composite TiO₂/Taua (0.5:1 wt. ratio) and pure TiO₂ 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 TiO₂ and TiO₂/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-Fe₂O₃, E_g = 2.1 eV) in the red clay, reaching 2.1 eV for TiO₂/Taua and 2.0 eV for ZnO/Taua, while the bandgap energies for pure TiO₂ 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 TiO₂/Taua and ZnO/Taua composites were also photocatalytic active to degrade Fenthion (λ > 420 nm), with degradation of 78% (in 180 min) and 85% (in 210 min) respectively. In the optimized conditions (pH 2, 100 mg L⁻¹ of H₂O₂ and 30 mg L⁻¹ 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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Photocatalysis
• pesticide
• Fenthion
• red clay
• sunlight

Acknowledgements

The authors are also thankful to LAMUME – UFBA and LABCAT – UFBA for SEM and EDX analyses.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

Luciana Almeida da Silva

Additional information

Funding

The authors acknowledge the Brazilian research funding agencies Fundação de Amparo a Pesquisa do Estado da Bahia (FAPESB) [grant number APP0050/2016] and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) [grant number Finance Code 001] for financial support.