Fabrication of phosphate functionalized chiral nematic mesoporous silica films for the efficient and selective adsorption of lanthanum ions

Excessive consumption and exploitation of rare earth elements (REEs) had led to the serious waste of resources and environmental problems in terms of the abandoned REEs-containing secondary resources, such as optical glasses doped with lanthanum (La). In this article, two types of bio-templated chiral nematic mesoporous silica films (MSFs) were prepared via the direct copolymerization (MSFs-1) and post-grafting (MSFs-2), respectively, for the selective adsorption of La(III). Nanocrystalline celluloses (NCCs) were applied as a structural oriented bio-template and phosphate groups with specific recognition ability for La(III) were modified on the surface of both films. The films retained the well-ordered chiral nematic structure with large surface area and uniform pore size after the removal of NCCs without any disruption of organosilica frameworks. Both MSFs-1 and MSFs-2 showed strong adsorption affinity for La(III) with the maximum adsorption capacity of 77.74 and 69.24 mg g ⁻¹ at pH = 7, respectively. The distribution coefficients for La(III) were 832 mL g ⁻¹ for MSFs-1 and 805 mL g ⁻¹ for MSFs-2, which indicated both films possessed good selectivity for La(III). Owing to this highly ordered chiral nematic mesoporous structure, the adsorption equilibrium could be reached within 3.0 h at 298 K. Furthermore, the MSFs exhibited the excellent regeneration ability, showing potential application possibility for the selective adsorption of La(III).