## 1 Introduction  
As is well known, following the pace of world population growth, industry has developed and grown rapidly in recent years. The wastewater generated in these industrial processes may contain hazardous, toxic, and difficult-to-degrade pollutants. This is the case in several industries, such as the textile, paper, food, and hair dye industries, among others, which discharge wastewater containing dyes into bodies of water [1, 2, 3]. If these waters are not adequately treated before discharge, they can reduce oxygen transfer, endanger aquatic life, and alter the chemical composition of the water [1]. In addition, they also present significant risks to human health due to the carcinogenic, mutagenic, and bactericidal properties of certain dyes [2, 4, 5]. Conventional water treatment methods often fail to effectively degrade these persistent pollutants, necessitating the development of more effective, innovative, and environmentally friendly techniques to mitigate the negative impact of these pollutants on the environment [2; 6; 7; 8]  
Advanced oxidation processes (AOPs) have emerged as a fundamental strategy for wastewater treatment and environmental remediation, especially in the case of recalcitrant and difficult-to-degrade pollutants. These processes are characterized by the generation of reactive oxygen species, such as hydroxyl radicals (OH), which can break down complex organic compounds into simpler and less-toxic products [9; 10]. Among the different AOPs, photocatalysis and the electro-Fenton-like process have demonstrated significant potential, each offering unique advantages and limitations concerning efficiency, selectivity, and operating conditions [11]. Photocatalysis harnesses light energy to activate a semiconductor catalyst, generating free radicals that begin the degradation of pollutants. This technique is especially promising for large-scale industrial wastewater treatment because it can operate under relatively mild conditions and use readily available light sources [12]. In contrast, the electro-Fenton-like process, which combines electrochemical methods with the in situ generation of hydrogen peroxide and its decomposition in the presence of a catalyst, stands out for its ability to generate high concentrations of hydroxyl radicals, making it very effective for the oxidation of difficult organic pollutants [13]. In the search for greater process efficiency, catalysts play a fundamental role, since their nature, structure, and activity directly influence the generation of reactive species and pollutant degradation kinetics [14]. Research into advanced catalysts, particularly those based on materials such as carbon nanotubes [15], graphene, and metal oxides [16], has opened new perspectives for optimizing AOPs. Graphitic carbon nitride (g-C\({}_{3}\)N\({}_{4}\)) has recently attracted attention given its non-toxic properties, chemical stability, and efficient visible-light absorption (2.7 eV band gap). However, this material presents several limitations that hinder its photocatalytic activity, such as the fast electron/hole recombination photogenerated, its small specific surface area, and its weak redox capacity [17; 18]. Similarly, zinc oxide (ZnO), a semiconductor with a wide band gap of 3.3 eV, is known for its good stability, non-toxicity, high electron mobility, and strong oxidation potential, but it is restricted to activation under ultraviolet (UV) light [18; 19]. Studies suggest that combining these materials can regulate the band gap structure, modulating the light utilization efficiency and the redox capacity [20; 21; 22]. Consequently, this study explores the combined behavior of g-C\({}_{3}\)N\({}_{4}\) and ZnO as a composite material. Therefore, the development of environmentally friendly, cost-effective, and efficient solid-phase catalysts has become a major issue in the fields of chemistry, engineering, and materials science. Researchers around the world are actively working to develop more environmentally friendly methods for catalyst synthesis.