Metal oxides and their composites for the remediation of organic pesticides: advanced photocatalytic and adsorptive solutions

Abstract

Metal oxide nanoparticles and their composites have garnered significant attention in water treatment and environmental cleanup due to their unique physicochemical properties. These materials exhibit distinct crystalline structures, tunable morphologies, large surface areas, versatile surface chemistry, and widespread availability. These features make nanostructured metal oxides and their composites highly effective for the selective removal of organic pollutants from the environment, either by adsorption or photodegradation. This article focuses on recent advances, challenges, and opportunities in the use of metal oxides and their composites for the targeted removal of organic contaminants, including insecticides, phenolic compounds, organic dyes, and similar pollutants. The discussion encompasses a broad range of metal oxides and their composites, highlighting their diverse structural, crystallographic, and morphological characteristics that influence their adsorption and photocatalytic performance. Emphasis is placed on the photocatalytic and adsorptive capabilities of these materials, including their photo-stimulation properties and mechanisms. Metal oxides are highlighted as outstanding photocatalysts due to their high photodegradation efficiency, cost-effective synthesis methods, and optimized bandgap engineering. This review serves as a valuable resource for researchers exploring the photocatalytic and adsorptive applications of metal oxide-based materials, particularly in the remediation of hazardous organic pollutants such as pesticides.

Fig. 1. Different stages of pesticide cycle that reach the ground and surface water.

Fig. 2. Chemical, biological, and physical approaches to remove or degrade the organic pollutants in the wastewater.

Fig. 3. Photocatalytic degradation of pesticides using photocatalysts.

Fig. 4. 2,4-Dichlorophenol degradation via photo-reactive TiO₂ nanoparticles, (A) preparation of the photocatalyst; (B) the degredation pathway of 2,4-DCP.

Fig. 5. Preferential removal of pesticides from water by molecular imprinting on TiO₂ photocatalysts.

Fig. 6. Schematic diagram illustrating the plausible photocatalytic mechanism for degradation of Congo red dye using the Pd-doped ZnO photocatalyst. Reprinted with permission from Copyright 2016 Elsevier.

Fig. 7. Photo-degradation pathways for organic pollutants using iron oxide.

Fig. 8. Photocatalytic degradation pathway under the solar light irradiation using the p–n heterojunctions (ZnO–CuO or Fe₃O₄–CuO). Copyright 2016 Elsevier.

Fig. 9. Mechanism pathway of light-induced charge separation in the Fe₂O₃–WO₃ nanocomposite and photo-degradation of Rhodamine B. Copyright 2014 Royal Society of Chemistry.

Fig. 10. The adsorption process in: (A) multiple layers (physisorption); and (B) single (chemisorption).

Ayman H. Kamel