Oxyanion-Binding in a Bioinspired Nanoparticle-Assembled Hybrid Microsphere Structure: Effective Removal of Arsenate/Chromate from Water

We demonstrate a bioinspired assembly wherein the specific interaction of polyamines with multivalent anions allows the assembly of silica nanoparticles to generate hybrid microsphere structures while this very phenomenon further provides ways for the microspheres to adsorb oxyanions like arsenate and chromate. In a typical method based on the biomineralization of diatomaceous biosilica structure, thus produced nanoparticle-assembled microspheres with a porous structure and hybrid functionalities exhibit efficient adsorption and separation of these toxic anions from water. The adsorption follows Freundlich isotherm with an inference for stronger interaction between adsorbate and adsorbent with nonuniform distribution of adsorption affinities. The opportunities to tune the composition with respect to the multivalent anion and their interaction with the polyamine, charge ratio, and so forth, illustrate the design of bioinspired robust structures with efficient oxyanion-binding property and recyclability. The consequence of competing anions shows that the binding selectivity follows the Hofmeister series of counterion interaction. Interestingly, in accordance with a molecular imprinting mechanism, the silica nanoparticle-assembled structure stabilizes and preserves the polyamine-anion nanostructure creating cavities/voids complementary to the adsorbing ions in shape, size, and functional groups. As a result, the polyamine with phosphate as the multivalent anion exhibits efficient binding and removal of these toxic contaminants, which is better than most of the other reported adsorbents.