Development of magnetic La doped Al2O3 core-shell nanoparticle loaded hydrogel for selective recovery of fluoride from aquatic medium

Abstract

The selective removal of pollutants from water bodies is regarded as a conciliation between the rapid expansion of industrial activities and need of clean water for sustainability. Fluoride is one such geogenic pollutant, and various materials have already been reported. Developing an efficient field employable material is however a challenge. Herein, we report the synthesis and competencies of strategically designed magnetic La-doped Al₂O₃ core-shell nanoparticle loaded polymeric nanohybrid as a benchmark fluoride sorbent. A facile synthesis strategy involved fabrication of Fe₃O₄ magnetic core followed by growth of La doped Al₂O₃ shell using sol-gel method. Doping of La₂O₃ into Al₂O₃ structure was optimised (6%), resulting in Fe₃O₄-Al_0.94 La_0.06O_1.5 core-shell particles which provided exceptional fluoride affinity. The obtained magnetic Fe₃O₄-Al_0.94La_0.06O_1.5 core-shell nanoparticles were then loaded (22%) into alginate to form cross-linked hydrogel beads (Fe₃O₄-Al_0.94 La_0.06 O_1.5-Ca-ALG). These prepared hydrogel beads were characterised and utilized for selective recovery of fluoride under different ambient conditions. Driving forces for enhanced fluoride uptake by La doped Al₂O₃ were investigated and explained with the help of both experimental observation and theoretical simulation. Density functional theory calculations indicated significant expansion in the cell volume of Al₂O₃ due to La doping which favoured the fluoride sorption. The calculated defect formation energy for the incorporation of F into Al₂O₃ was found to decrease in the presence of La. XPS analysis suggested direct interaction of fluoride with Al, forming Al-F bond and breaking Al-O bond. Different vital parameters for uptake were optimised. Also, kinetics, isotherm and diffusion models were evaluated. Developed hydrogel beads attained record sorption capacity of 132.3 mgg^-1 for fluoride. Overall, excellent stability, no leaching of constituents, effectiveness for selective fluoride recovery from groundwater, brand it a perfect epitome of sustainable water treatment application.

Keywords: Core-shell; Fluoride; Hydrogel; La doped alumina; Nanohybrid.