In this paper, light-emitting diodes (LEDs), a novel light source, is reported for the photocatalytic degradation of four known pesticides [2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP)] in aqueous solution. 2,4-Dichlorophenoxyacetic acid was further chosen to evaluate the impact of photocatalyst loading and light intensity on the degradation rate. The degradation of 2,4-D under LED irradiation (365 nm) was compared with that using mercury discharge lamp irradiation (350 nm). Irradiation of the different pesticides with a 365-nm LED light source led to their complete mineralization upon prolonged exposure. The degradation rate was slower when mixtures of pesticides were used because of competition between pesticide molecules for adsorption sites, hydroxyl radicals, and holes. A suitable photocatalyst loading was determined to be 2 g/L of TiO2; a linear relationship between the first-order kinetic rate an...

4-chlorophenol (4-CP), a hydroxylated aromatic compound (HAC), is a recalcitrant and toxic organic pollutant found in industrial wastewater and various environmental media. In this paper, visible-light-activated photocatalysis using graphitic carbon nitride (GCN) was used to treat 4-CP in an aqueous media. Graphitic carbon nitride from different precursors (dicyanamide, urea, and melamine), as well as GCN/silver nanocomposites (AgBr, Ag₃PO₄, Ag₂CrO₄, and Ag), were successfully synthesized and characterized by BET, XRD, SEM, EDS, and UV-Vis DRS. The band gaps of the photocatalysts were estimated using the UV-Vis DRS characterization results and Tauc plots. The evaluation of the efficacy of the GCN-based catalysts in degrading 4-CP was conducted with different photoreactors such as a royal blue light-emitting diode (LED), a UV-A LED, LUZCHEM cool white lamps, and a solar simulator. The results showed that GCNs with royal blue LED can effectively degrade 4-CP from aqueous media. Among the different precursors, urea-derived GCN showed the best performance in degrading 4-CP due to its large surface area. GCN/0.3Ag₂CrO₄ nanocomposite showed a synergistic effect for the enhanced photocatalytic degradation of 4-CP. The degradation of 4-CP with a rate constant of 2.64 × 10⁻² min⁻¹ was achieved with a GCN/0.3Ag₂CrO₄ nanocomposite under royal blue LED irradiation.