Photocatalytic Metal Oxide-Based Nanocomposites for Environmental Decontamination and Pollution Abatement: A Comprehensive Review

Abstract

The rapid growth of industrialization, urbanization, and agricultural activities has resulted in the large-scale release of hazardous organic and inorganic pollutants into the environment, posing serious risks to ecosystems and human health. Among various advanced treatment technologies, photocatalysis based on metal oxide–derived nanocomposites has emerged as an efficient and environmentally benign strategy for environmental decontamination and pollution abatement. Compared to single-component photocatalysts, metal oxide–based nanocomposites exhibit superior photocatalytic activity due to enhanced charge separation, extended light absorption range, and improved surface redox reactions. This comprehensivereview critically discusses recent advances in the design, synthesis, characterization, and photocatalytic applications of metal oxide–based nanocomposites for the removal of dyes, pharmaceuticals, pesticides, and other emerging contaminants from water and air. The role of heterojunction engineering, defectmodulation, morphology control, and reaction mechanisms is systematically analyzed. Furthermore, current challenges, scalability issues, and future perspectives for practical environmental applications are highlighted. This review aims to provide a consolidated platform for researchers to develop next-generationphotocatalysts for effective pollution control.

Introduction

Environmental pollution from industrial effluents, agricultural runoff, and domestic waste has become a critical global issue, with persistent contaminants like dyes, pharmaceuticals, endocrine disruptors, and VOCs posing health and ecological risks. Conventional treatment methods (adsorption, biological degradation, membrane filtration, coagulation–flocculation) often face limitations such as incomplete removal, sludge generation, and high costs. Advanced oxidation processes (AOPs), particularly semiconductor-based photocatalysis, offer a green, sustainable alternative by using solar energy to generate reactive oxygen species that degrade pollutants into non-toxic products. Metal oxides such as TiO?, ZnO, Fe?O?, MnO?, WO?, and SnO? are widely studied for their stability, low toxicity, and strong oxidizing ability, but single metal oxides are limited by rapid electron–hole recombination and poor visible-light absorption.

Metal oxide nanocomposites overcome these limitations through heterojunction formation between two or more semiconductors, promoting efficient charge separation and enhanced photocatalytic performance. They are classified into:

• Binary systems (e.g., TiO?–ZnO, Fe?O?–TiO?) for simple heterojunctions,

• Ternary systems (e.g., ZnO–TiO?–MnO?) that include metals or carbon-based materials for better light absorption,

• Multicomponent hybrids combining metal oxides with polymers, biochar, or graphene for multifunctionality.

Synthesis methods include chemical routes like co-precipitation and sol–gel, hydrothermal/solvothermal techniques for controlled morphology and crystallinity, and green synthesis using plant extracts or biopolymers. Characterization techniques such as XRD, SEM/TEM, FTIR, Raman, UV–Vis DRS, PL spectroscopy, and BET analysis are employed to determine structural, optical, and surface properties critical for photocatalytic efficiency.

Applications:

• Water treatment: Efficient degradation of organic dyes (methylene blue, rhodamine B) and pharmaceuticals/contaminants.

• Air purification: Removal of VOCs and nitrogen oxides.

• Photocatalytic mechanisms involve light-induced charge separation, electron–hole migration across heterojunctions, and generation of reactive oxygen species (e.g., hydroxyl, superoxide radicals) that degrade pollutants.

Challenges and future perspectives: Large-scale deployment is limited by catalyst stability, recovery, potential ecotoxicity, and reduced efficiency in complex wastewater. Future research should focus on solar-driven systems, environmentally friendly synthesis, immobilized catalysts, and pilot-scale studies to advance practical applications.

In essence, metal oxide–based nanocomposites represent a promising, sustainable approach for environmental remediation, combining enhanced photocatalytic activity with tunable structural and optical properties for water and air decontamination.

References

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Copyright © 2026 Suman Upadhyay, Dr. Leena Rai Kewat, Dr. Rajiv Tiwari. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.