Building TiO2-doped magnetic biochars from Citrus sinensis peels as low-cost materials for improved dye degradation using a mathematical approach

TiO₂-doped ferromagnetic (TiFeBC) composites were synthesised from lignocellulosic orange peel biochar (BC) material using co-precipitation method. Several characterization techniques (XRD, SEM, EDX, FT-IR, EIS and N₂ adsorption-desorption) were used to confirm the presence of Fe₃O₄ and TiO₂ particles impregnated within the carbonaceous matrix of the biochar. Electrochemical impedance spectroscopy revealed that the sample obtained using 2.5 wt. % of TiO₂ (TiFeBC1) has the lowest charge transfer resistance compared to those of 5 wt.% and 7.5 wt.%. TiFeBC1 was used for the optimization of the degradation of reactive yellow-145 from Cameroon Textile Industry using Fenton process. Optimum operational parameters were found to be: pH of 2.02, initial dye concentration of 75 mg/L, mass of material of 5998 mg/L and a time of 16.01 min. Using the CCD of the Response Surface Methodology, a predicted optimum response of 98.89 % was obtained in agreement with an experimental response of 97.95 % of dye degradation. Analysis of variance presented good correlation between the experimental data and the postulated model (R² = 94.24 % and R²_adjusted = 87.52 %). The degradation reaction was found to obey the first order kinetic rate law (R² = 0.986) with respect to the dye. The study of interfering processes revealed that adsorption and H₂O₂/daylight-assisted degradation are two phenomenon that could possibly contribute to a negligible extent to the elimination of the dye during the Fenton process. The stability and efficiency of TiFeBC1 was evaluated over ten cycles and the material was found to lose approximately 5 % of its efficiency.