The work analyzes the impact of chitosan and ZnO modification on surface and sorption characteristics of Moringa oleifera biochar. Moreover, statistical analysis was used to validate the experimental data.

What are the main findings?

• Chitosan modification enhanced the surface functional groups of raw M. oleifera biochar.
• The highest and lowest BET surface areas were found for BZ and BC, respectively.
• Chitosan-modified biochar showed a 75% increment in % removal of methylene blue compared to raw biochar.
• ZnO modification decreased the performance of biochar by 16%.
• Kinetics and Isotherm analysis of Chitosan-modified biochar align with statistical analysis.
• The adequate precision ratio was 52.80 and lack of fit p-value was 0.0018.

Industrial effluents contaminated with different types of organic dyes have become a major concern to environmentalists due to the carcinogenic nature of the dyes, which are harmful to human and aquatic life. In recent years, the treatment of contaminated effluents by natural resources has been proposed as the most sustainable solution for this problem. In this work, Moringa oleifera (M. oleifera) seed-derived biochar composites, e.g., Biochar-Chitosan (BC), Biochar-ZnO (BZ), and Chitosan-ZnO (CZ) were produced and characterized. The synthesized materials were then utilized to adsorb a cationic dye, methylene blue. Spectroscopic analysis of the biochar-based composites revealed that the modification of biochar by chitosan and ZnO introduced different functional and active groups in the biochar surface. Pore development in the structure of biochar nanocomposites was visible in surface morphological images. The derived biochar was fully amorphous and increased crystallinity by the ZnO modification. The obtained surface area varied from 0.90 ± 0.00 to 14.48 ± 1.13 m² g⁻¹ for prepared sorbents, where BZ corresponds to the highest and BC corresponds to the lowest surface area, respectively. The basic pH (9) was the most favorable condition for sorption. The sorption reached equilibrium at 90 min. Isotherm revealed the favorability of the Langmuir model over the Freundlich and Temkin models. The highest sorption capacity (~170 mg/g) was found for BC. The BC and BZ showed a 75% increase and 16% decrease in removal due to the chitosan and ZnO modification, respectively. Response surface methodology (RSM) optimization for BC showed similar results to the analytical experiments. The characterization and experimental results prefigure the chemical functionalities as the critical parameter over the surface area for the adsorption process.