Efficient removal of phosphate by a millimeter-sized nanocomposite of titanium oxides encapsulated in positively charged polymer

Removal of phosphate from industrial is important to prevent the occurrence of eutrophication and adsorption may serve as a powerful supplement to chemical or biological phosphate sequestration. Here, a novel nanocomposite material Ti-NS is proposed to enhance phosphate removal from aqueous system by impregnating titanium oxides inside a millimeter-sized polymer (NS). The resulting Ti-NS possesses two distinct sites for phosphate removal, the ammonium groups bound to the NS matrix and the loaded titanium oxide nanoparticles. The maximum adsorption capacity of Ti-NS occurs at near-neutral pH, and exhibited fast kinetic behavior for phosphate uptake which could be well described by the pseudo-first-order model and intraparticle diffusion model. Compared with NS host, Ti-NS exhibits much higher capacity and preference toward phosphate removal in the presence of competing anions at greater levels. SEM-EDS and XPS study confirmed that phosphate uptake by Ti-NS was involved in two distinct adsorption interactions, i.e. ion exchange to the quaternary ammonium groups of host and ligand exchange reactions to the hydroxyl groups of titanium oxides. Cyclic adsorption and regeneration runs in fixed-bed indicated that Ti-NS is of great potential for phosphate removal from the water containing competitive anions at higher levels. Moreover, the exhausted nanocomposite can be effectively regenerated by NaOH-NaCl solution for recycle use with negligible capacity loss. All the results demonstrated that prepared Ti-NS was a promising alternative adsorbent for efficient phosphate removal from contaminated water.