Investigating the synergetic effect of tungsten oxide doping into the 1,3-dicarbonyl moiety grafted chitosan and phytic acid impregnated sodium alginate for efficient U(VI) adsorption

Abstract

In this work, chemical modification of the chitosan with ethyl acetoacetate was performed through a base-catalyzed reaction in which epichlorohydrin facilitated the insertion as well as nucleophilic substitution reaction to graft the 1,3-dioxo moiety across the linear chains of the base biopolymer to establish specificity and selectivity for U(VI) removal. The modified chitosan (EAA-CS) was intercalated into phosphate rich alginate matrix (PASA). Later on, the WO₃-doped composites with different WO₃ to PASA mass ratio were prepared and characterized using FTIR, XPS, SEM-EDS, XRD, and elemental mapping analysis. WO₃ significantly contributed to chemically stable inorganic-organic composites with improved porous texture. Among the prepared composites, MCPS-3 microspherical beads, having mass ratio of 30.0 % w/w, exhibited excellent sorption capacity for U(VI) at an optimal pH 4.5. The successful U(VI) sorption was validated by the existence of two U4f peaks at 392.25 and 381.36 eV due to U4f_5/2 and U4f_7/2 sub-peaks with an intensity ratio of 3:4, respectively. Batch mode sorption kinetics followed pseudo-second-order rate equation (R² ≈ 0.99, q_e,th ≈ 116.88 mg/g, k₂ = 0.86 × 10^-4 g/mg.min^-1) and equilibrium sorption data aligns with Langmuir (R² = 0.99, q_m = 343.85 mg/g at 310 K and pH = 4.5, K_L = 2.00 × 10^-2 L/mg) and Temkin models (R² ≈ 0.99). Thermodynamic parameters ΔH^o (30.51 kJ/mol), ΔS^o (0.19 kJ/mol.K) and ΔG^o (-25.64, -26.89, and - 27.91 kJ/mol) at 298, 305, and 310 K, respectively, suggested that the uptake process is feasible, endothermic and spontaneous. Based on these findings, it is reasonable to conclude that MCPS-3 could be a better hydrogel-based biomaterial for appreciable uranium recovery.

Keywords: Modified chitosan; Phytic acid; Sodium alginate; Uranium sorption; WO(3) doping.