In recent decades, the rising wastewater output from industrial pollution has inflicted severe harm on both surface and groundwater, leading to substantial environmental damage. The elimination of harmful, toxic materials and wastewater remediation are pressing global concerns and pose a formidable challenge for scientists worldwide. Heterogeneous photocatalysis has been recognized as a promising, effective, energy-free, and eco-friendly process capable of completely degrading various organic pollutants. Finding a material that simultaneously satisfies various thermodynamic and kinetic criteria, coupled with good thermal- and photo-stability, is a challenging task necessitating the modification of existing materials or the synthesis of new ones to meet the required standards. This present study comprehensibly elaborates on different approaches to the modification of various photocatalytic systems, both organic and inorganic, in order to obtain more efficient and feasible catalysts for practical applications. In addition, the current status of the application of photocatalysts in dye wastewater treatment is summarized, projecting the future direction for wastewater management by photocatalytic processes.

The presented study was focused on the simple, eco-friendly synthesis of composite hydrogels of crosslinked carboxymethyl cellulose (CMC)/alginate (SA) with encapsulated g-C₃N₄ nanoparticles. The structural, textural, morphological, optical, and mechanical properties were determined using different methods. The encapsulation of g-C₃N₄ into CMC/SA copolymer resulted in the formation of composite hydrogels with a coherent structure, enhanced porosity, excellent photostability, and good adhesion. The ability of composite hydrogels to eliminate structurally different dyes with the same or opposite charge properties (cationic Methylene Blue and anionic Orange G and Remazol Brilliant Blue R) in both single- and binary-dye systems was examined through adsorption and photocatalytic reactions. The interactions between the dyes and g-C₃N₄ and the negatively charged CMC/SA copolymers had a notable influence on both the adsorption capacity and photodegradation efficiency of the prepared composites. Scavenger studies and leaching tests were conducted to gain insights into the primary reactive species and to assess the stability and long-term performance of the g-C₃N₄/CMC/SA beads. The commendable photocatalytic activity and excellent recyclability, coupled with the elimination of costly catalyst separation requirements, render the g-C₃N₄/CMC/SA composite hydrogels cost-effective and environmentally friendly materials, and strongly support their selection for tackling environmental pollution issues.