Kinetics and mechanistic modeling of chlorhexidine uptake from aqueous solution using nitrogen-doped achatinidae chitin as adsorbent

Emerging contaminants such as chlorhexidine (CHX), pose significant environmental and health-related challenges because of they have high toxicity index and are persistent in water. This study investigates the adsorptive uptake of CHX from an aqueous medium using nitrogen-doped achatinidae chitin adsorbent (N-ASCA), synthesized from discarded achatinidae shells. The N-ASCA was prepared under a nitrogen atmosphere. N-ASCA surface area increased from 2.85 m²/g to 132.15 m²/g after calcination. The FTIR analysis revealed the presence of functional groups such as hydroxyl, carbonyl, and amide. The XRD revealed a strong crystallinity. The maximum adsorption efficiency of 91 % was obtained at a pH of 8. The adsorption process followed pseudo-second-order kinetics with R 2 value of 0.999. Langmuir model described the isotherm data with precision. The process thermodynamics infer spontaneity with ΔG = -2.79 kJ/mol at 308 K and endothermicity with ΔH = 75.9 kJ/mol. Electrostatic and π-π interactions were found as the mechanistic pathway for chlorohexidine uptake. Post-adsorption XRD analysis revealed new peaks that show successful uptake of chlorhexidine. This was confirmed by the presence of nitrogen and chlorine peaks in the elemental composition of the spent adsorbent obtained via SEM-EDX. Hence, N-ASCA is a sustainable, cost-effective adsorbent for addressing CHX contamination.