Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts

TLDR

Photodegradation of dyes is a low‑cost, environmentally friendly wastewater treatment that relies on light‑generated charge carriers and radicals to break down dyes into harmless products, with efficiency governed by dye concentration, pH, temperature, light intensity, and photocatalyst charge‑carrier properties. This review aims to discuss the pseudo‑kinetics and mechanisms of photodegradation, clarify key active species and optimal conditions, and provide guidelines for developing efficient photodegradation systems. It examines how operational factors—such as dye type, concentration, pH, temperature, and light intensity—and photocatalyst charge‑carrier properties influence the generation of reactive species and the overall degradation process. The analysis identifies the primary active species and optimal operational conditions, offering actionable guidelines to enhance the efficiency of photodegradation systems.

Abstract

Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems.