• • CHT-SH achieved an experimental adsorption capacity of 223.67 mg·g−1 for Pd(II) at pH=2 and room temperature, a 7-fold improvement over pristine chitin (30.6 mg·g−1), enabling efficient recovery from acidic industrial effluents.
• • The adsorption process followed the pseudo-second-order kinetic model and Langmuir isotherm, with a maximum theoretical capacity of 248.89 mg·g−1, confirming monolayer chemisorption and enabling predictable scale-up design.
• • Mechanistic studies (XPS, XRD, DFT) identified synergistic N and S coordination and electrostatic interactions as the primary adsorption pathways, ensuring high selectivity and stability without redox side reactions.
• • CHT-SH retained stable adsorption performance over five consecutive adsorption-desorption cycles, demonstrating operational durability and cost-effectiveness for repeated use in industrial settings.