Green and sustainable synthesis of MWCNT@g-C₃N₄@Ag photocatalyst from PET for efficient wastewater treatment

Due to the global water crisis, water reclamation has been at the heart of consideration by the scientific communities in recent years. The main objective of this study was the synthesis of a green and sustainable photocatalyst from waste, specifically polyethylene terephthalate plastic bottles, for the efficient removal of methylene blue (MB). The characterization of the novel MWCNT@g-C₃N₄@Ag photocatalyst was carried out using FESEM, EDS-MAP, Raman, XRD, and DLS analysis. The optimization approach, based on Response Surface Methodology (RSM), demonstrated that the pH and initial concentration were the primary factors in improving MB degradation. Also, increasing the photocatalyst dosage and reaction time were appropriate for MB wastewater treatment. Furthermore, the predicted values showed strong agreement with the experimental results, with R² = 0.95, Adj-R² = 0.93, and a p-value of less than 0.0001. The optimized values were found to be a wastewater concentration of 12.6 mg L^{- 1}, pH of 9, photocatalyst dosage of 0.52 g L^{- 1}, and a reaction time of 231 min, achieving a removal efficiency of 99.89%. MWCNTs@g-C₃N₄@Ag demonstrated superior photocatalytic performance compared to the as-prepared multi-walled carbon nanotubes (MWCNTs). Consequently, MWCNTs@g-C₃N₄@Ag can be recommended as a promising photocatalyst for MB degradation in wastewater due to its environmental friendliness, low-cost precursors, and excellent wastewater purification performance.