Synthesis and characterization of graphitic carbon nitride-doped carbon (Cu-Al/Biochar@g-C₃N₄) for quinoline yellow removal by the Fenton process: optimization by the response surface method

This study describes the synthesis and characterization of a biochar doped with graphitic carbon nitride and modified with copper and aluminum (Cu-Al/Biochar@g-C₃N₄). This composite was developed to optimize the removal of quinoline yellow using the Fenton process and the method, employing the response surface methodology. The physicochemical characterizations, notably Fourier-transform infrared spectroscopy (FTIR), highlighted the aluminum-oxygen and copper-oxygen bonds, indicating the successful incorporation of these metals into the biochar matrix. X-ray diffraction (XRD) revealed a crystalline structure with an average grain size of 7.726 nm for the raw biochar and 16.677 nm for Cu-Al/Biochar@g-C₃N₄. The analysis also identified mineral phases such as goethite (FeO(OH)) and calcite (CaCO₃). The results of the BET analysis showed that the raw biochar and the Cu-Al/Biochar@g-C₃N₄ composite exhibit type IV isotherms. The modification of the raw biochar increased the specific surface area of the doped biochar by 10.52 m²/g. Furthermore, EDX analyses confirmed that the raw biochar is typical of pyrolyzed biochar and the efficiency of the impregnation. The influence of the composite mass, pH, and pollutant concentration during the heterogeneous Fenton process allowed us to establish an equilibrium time of 150 min. The optimization of the operational parameters was carried out using a Box-Behnken (BBD) design, varying three parameters: pH (2–6); [E104] (50–100 mg/l) and H₂O₂ (13–65 mM). The results obtained show a degradation percentage of 92.33% under optimal conditions with a high coefficient of determination of R² = 90.56% and R²_adjusted = 82.07%. The recovery and reusability study of the catalyst shows an efficiency after three cycles with a degradation rate of 50.28%. Mathematical modeling-based optimization showed the best conditions at pH 5, a dye concentration of 100 mg/L, a catalyst dosage of 50 mg, and an H₂O₂ concentration of 65 mM, achieving a degradation efficiency of 92.33% in 150 min. These results suggest that Cu-Al/Biochar@g-C₃N₄ is promising for getting rid of quinoline yellow.