Photocatalytic nanomaterials for cationic dye detoxification from industrial effluents: principles, emerging trends, and engineering strategies

Abstract

Industrial discharge of dye-containing effluents into aquatic environments poses severe ecological and human health risks because of their toxicity, persistence, and potential carcinogenicity. Among different dye classes, cationic dyes are particularly difficult to eliminate due to their high solubility, chemical stability, and strong electrostatic interactions in aqueous media. Photocatalysis has emerged as an efficient and sustainable approach for degrading toxic organic pollutants under light irradiation. This review comprehensively discusses the classification of cationic dyes and recent advances in photocatalytic wastewater treatment technologies. Special emphasis is placed on visible-light-active photocatalysts, including heterojunction nanocomposites, metal and nonmetal doped semiconductors, and bio-inspired materials, which exhibit enhanced light absorption, improved charge separation, and superior photocatalytic stability. The review further highlights the influence of operational parameters and integrated treatment strategies on degradation efficiency. In addition, critical challenges related to catalyst recovery, long-term stability, cost-effectiveness, and practical applicability in real wastewater systems are discussed, together with future research perspectives for sustainable environmental remediation. Mechanistic pathways involving reactive oxygen species generation and electron–hole separation are also summarized to explain enhanced photocatalytic degradation performance under visible light irradiation.