Multifunctional Chitosan Tailored γ-Aluminum Oxy-hydroxide Monolith Aerogels for Sustained Environmental Remediation

Abstract

Recently, improving the mechanical properties of monolithic silica and alumina aerogels by incorporating polymers for various applications, particularly for adsorption, has been the focus of research. In this study, we report the modification of the high surface area γ-aluminum oxy-hydroxide (γ-AlOOH) aerogel with biopolymer chitosan having nitrogen functional groups to improve the efficiency of adsorption. The chitosan + γ-AlOOH aerogel were synthesized using the sol-gel method via supercritical drying process. The monolithic chitosan-γ-AlOOH aerogel was optimized at 1% (w/w) chitosan for all aluminum precursors used. The XRD pattern of the synthesized monolithic chitosan-γ-AlOOH aerogel shows amorphous nature, while the FT-IR peaks at 1065 cm-1 and 1387 cm-1 indicated the presence of -OH and -NH= (amide) bonds. TEM images shows nanoneedle shape morphology of chitosan within the γ-AlOOH aerogel with specific surface area of 562.11 m2/g and pore volume of 3.68 cc/g. As synthesized monolithic chitosan-γ-AlOOH aerogel were used for the removal of azo dyes, such as methylene blue (MB) and crystal violet (CV), heavy metal ions [Pb(II), As(III)], and rare earth metals [U(VI)]. The maximum adsorption capacities obtained from the adsorption isotherms are 167 ±3 mg/g for MB, 164 ±2 mg/g for CV, 644 ±5 mg/g for U(VI), and 102 ±2 mg/g for As(III) at pH 7. However, at pH 7 Pb(II) is found to precipitate, therefore, adsorption capacity is carried out at pH 5 with 228 ±1 mg/g. The recyclability of the monolithic chitosan-γ-AlOOH aerogel were 94.55% (MB), 94.48% (CV), 94.65% (Pb(II)), 94.8% (U(VI)), and 95.15% (As(III)). These results highlight the potential of heteroatom-rich biopolymers tailored to alumina aerogels for achieving superior multifunctional adsorption properties.