Photocatalytic degradation is one of the environmentally friendly methods used in treating dye wastewater. In this study, a series of MXene/g-C₃N₄ heterostructure photocatalysts with different loading amounts of MXene (1, 4, 8, and 12 wt.%) were successfully synthesized via the wet impregnation method and their photocatalytic activity was evaluated via the degradation of methylene blue under visible-light irradiation. As such, the 1 wt.% MXene/g-C₃N₄ heterostructure photocatalyst achieved a high degradation of methylene blue compared to the pure g-C₃N₄ under visible-light illumination of 180 min. This significant improvement was attributed to the intimate interfacial contact, evidently from the FESEM analysis, which allows the smooth photocharge carriers to transport between g-C₃N₄ and MXene. Additionally, the larger BET surface area demonstrated by the 1 wt.% MXene/g-C₃N₄ heterostructure allowed this sample to have higher adsorption of dye molecules and provided a higher number of reactive sites, which was beneficial for the enhancement of the photocatalytic activity. Nevertheless, it was found that the excessive loading of MXene can substantially impede photocatalytic activity. This was attributed to the decrease in the active sites, as well as the weakened crystallinity of the MXene/g-C₃N₄ heterostructure photocatalyst, evident from the FTIR and XRD analysis. All in all, this study has shown the potential of the MXene/g-C₃N₄ photocatalyst as a promising photocatalyst for highly efficient wastewater treatment applications.

The rapid growth of textile industry has negatively impacted the health and quality of clean water sources, leading to an increase in water pollution disaster. To address these significant water effluent issues, there is a strong need for improved and effective environmental remediation processes to treat effluents containing organic contaminants. The present research explores the photocatalytic and adsorption capabilities of MXene/g-C₃N₄ for the discoloration of methylene blue (MB) by introducing a strong oxidizing agent, such as hydrogen peroxide (H₂O₂). To the best of our knowledge, this study is the first one to demonstrate that the MXene/g-C₃N₄ photocatalyst could efficiently activate H₂O₂, reducing the MB concentration by up to 99.71% and 81.88% in 240 min via photocatalysis and adsorption processes, respectively. The addition of H₂O₂ oxidant in photocatalysis system rapidly reduced the recombination rate of photogenerated electrons-hole pairs by producing powerful hydroxyl and superoxide radicals in the Fenton-like oxidation process. Langmuir–Hinshelwood kinetic modeling excellently described the degradation of MB, showing the highest R² value of up to 0.9896. The thermodynamic parameters, including Gibbs free energy (ΔG° = − 28.203 to − 30.095 kJ/mol), entropy (ΔS° = 94.558 kJ/mol K, enthalpy (ΔH° = 25.255 kJ/mol and activation energy (E_a = 11.066 kJ/mol), confirmed that the system is spontaneous and favorable for MB degradation. The reduction in ΔG° contributed to the expansion of photocatalyst’s pores, while the positive value ΔS° at higher temperatures indicated an increase in the kinetic energy of the degradation system, encouraging a higher rate of diffusion of methylene blue towards MXene/g-C₃N₄. In adsorption modeling, the adsorption of MB followed intraparticle diffusion kinetics and Temkin isotherms, with the highest R² values of 0.9906 & 0.9965, respectively. A series of MXene/g-C₃N₄ heterostructure photocatalysts (1, 4, 8 and 12 wt. %) was synthesized via a wet impregnation method and characterized through TEM and FESEM characterizations. This work provides new insights into the application of MXene/g-C₃N₄ for the improvement of photocatalysis system by introducing a powerful oxidizer.