Phosphorylation Triggered Growth of Metal Phosphate on Halloysite and Sepiolite Nanoparticles: Preparation, Entrapment in Chitosan Hydrogels and Application as Recyclable Scavengers

We herein explored a straightforward transformation of abundant clay and polysaccharides into highly-reactive water-cleaning adsorbents. A trivial surface-functionalization of sepiolite and halloysite by phosphoryl chloride allowed for grafting phosphates on the surface of the clay layers (inside of the lumen for halloysite or in the external surface for sepiolite). Gelation of the electrolytic solution of phosphorylated clay-chitosan afforded self-standing beads where inorganic nanoparticles were embedded inside of the entangled porous polysaccharide network. The resulting hydrogels exhibited excellent adsorption for anionic Congo red, cationic Malachite green and neutral salicylic acid. Interestingly, they displayed enhanced capacity compared to their shrinking nanocomposite xerogel and powder analogues, thereby highlighting the importance of their shaping as self-standing microspheres. The beads can be easily recovered from water medium and reused several times. This strategy seems attractive to scavenge persistent chemicals and may replace the solvent and time-consuming chromatography columns.