One-Step Decoration of Multifunctional Amine and Carboxyl Groups on Microcrystalline Cellulose Surface for Green Synthesis of an Ion Exchanger from Banana Pseudostem toward Water Treatment

Water contamination currently poses an urgent and severe environmental problem at the global level. Although various solutions have been implemented to improve water quality, enhancement still faces numerous challenges. Especially, as pollutants are present in ionic form, their removal becomes difficult due to their solubility, mobility, and persistence in solution. In this study, banana pseudostems were utilized to prepare a multifunctional microcrystalline cellulose material (MCC-A.Am) capable of removing both cations and anions from aqueous solutions. This one-step modification strategy represents a green alternative to conventional multistep synthesis methods that typically require toxic organic solvents. The material underwent comprehensive characterization, including spectroscopic (FTIR, XRD), microscopic (SEM-EDX), thermal (TGA, DSC), and surface chemistry analyses (potentiometric titration, pH_pzc determination, particle size distribution). Adsorption experiments were conducted to evaluate the removal efficiency of Ca²⁺, Cl^-, and NO₃ ^- ions by using MCC-A.Am as the adsorbent. The effect of operational parameters was evaluated, including adsorbent dosage, pH, contact time, and initial ion concentration, while the isotherm curves were best fitted with the Freundlich isotherm model, indicating multilayer accumulation of pollutants on the MCC-A.Am surface. The maximum adsorption capacities for Ca²⁺, Cl^-, and NO₃ ^- increased with the temperature, reaching 112.7, 122.5, and 25.4 mg g^-1, respectively. The thermodynamic data indicate that the adsorption is an exothermic and spontaneous process. Coexisting anions (PO₄ ^3- and SO₄ ^2-) and cations (Na⁺, Mn²⁺, and Mg²⁺) in the solution reduced the adsorption performance of the studied anions and cations, respectively. Comparative experimental results demonstrate that the adsorption capacities of MCC-A.Am for three target ions can reach more than 70% relative to those of commercial mixed bed resin (MB6SR). The results demonstrate that MCC-A.Am possesses a high adsorption capacity for Ca²⁺, Cl^-, and NO₃ ^-, highlighting its potential applicability in practical water treatments.