Mesoporous chitosan derivatives for effective uranyl sorption: Synthesis, characterization, and mechanism-application...

Two sorbents were developed from chitosan aminophosphonation: via one-pot process to produce aminophosphonated derivative (r-AP), followed by further pyrolysis to produce mesoporous improved biochar (IBC). Sorbents structures were elucidated using CHNP/O, XRD, BET, XPS, DLS, FTIR, and pH_ZPC-titration. The IBC exhibits an improved specific surface (262.12 m²/g) and mesopore size (8.34 nm) compared to its organic precursor (r-AP), 52.53 m²/g and 3.39 nm. IBC surface is also enriched with high electron density heteroatoms (P/O/N). These unique merits of porosity and surface-active-sites improved sorption efficiency. Sorption characteristics were determined for uranyl recovery, and binding mechanisms were elucidated using FTIR and XPS. The maximum sorption capacity increased from 0.571 to 1.974 mmol/g for r-AP and IBC, respectively, roughly correlated with the active-sites density per mass. Equilibrium occurred within 60/120 min, and the half-sorption-time (t_HST) was decreased from 10.73 for r-AP to 5.48 min for IBC. Langmuir and pseudo-second-order equation fits experimental data well. Sorption is endothermic for IBC (whereas exothermic with r-AP), spontaneous, and governed by entropy change. Both sorbents show high durability over multiple-cycles with desorption efficiency >94 % over seven cycles using NaHCO₃ (0.25 M). The sorbents efficiently tested for U(VI) recovery from acidic ore leachate with outstanding selectivity coefficients.