VISIBLE-LIGHT-DRIVEN PHOTOCATALYTIC FRAMEWORK FOR ENVIRONMENTAL REMEDIATION USING METAL OXIDE NANOCOMPOSITES, CHARGE SEPARATION ENGINEERING, AND ORGANIC POLLUTANT DEGRADATION FOR SUSTAINABLE WATER PURIFICATION

Abstract

The global water crisis, driven by the escalating discharge of recalcitrant organic pollutants from industrial, agricultural, and pharmaceutical sources into aquatic ecosystems, demands advanced remediation technologies capable of achieving complete mineralization of contaminants under energy-efficient, scalable, and sustainable operating conditions. Visible-light-driven photocatalysis, which harnesses a substantial portion of the solar spectrum through rationally engineered semiconductor nanocomposites, offers an energetically sustainable pathway for organic pollutant degradation, particularly for persistent micropollutants that are difficult to remove using conventional physical and biological treatment processes. This study presents the design, synthesis, and systematic photocatalytic evaluation of a ternary metal oxide nanocomposite system, BiVO₄–ZnO–graphene oxide, engineered through coordinated heterojunction construction, charge-separation optimization, and reactive oxygen species amplification for the visible-light-driven degradation of three representative organic pollutants: methylene blue as a model cationic dye, tetracycline as a pharmaceutical micropollutant, and bisphenol A as an endocrine-disrupting compound.

The optimized ternary nanocomposite achieved methylene blue degradation efficiency of 97.4% within 90 min, tetracycline degradation of 91.8% within 120 min, and bisphenol A degradation of 88.6% within 150 min at an optimum catalyst loading of 1.0 g L⁻¹ and pH 7.0. The apparent rate constant for methylene blue degradation was 3.84 times higher than that of pristine BiVO₄ and 2.16 times higher than that of the binary BiVO₄–ZnO composite, demonstrating the important contribution of graphene oxide as a charge-transfer scaffold. Reactive oxygen species trapping experiments confirmed hydroxyl radicals and superoxide radical anions as the dominant oxidative species, while the Z-scheme charge-transfer mechanism effectively suppressed photogenerated electron–hole recombination. The optimized nanocomposite maintained 92.4% degradation efficiency after five consecutive recycling cycles, demonstrating strong photocatalytic stability and reusability for practical water-treatment applications.