Enhanced phosphate removal by using La-Zr binary metal oxide nanoparticles confined in millimeter-sized anion...

Phosphate removal plays a key role in alleviating the eutrophication of water bodies. Herein, a new bimetallic nanocomposite (La-Zr-D201) was prepared for enhanced phosphate removal by confining binary metal oxide (La-Zr) nanoparticles into the pores of a polymeric anion exchanger (D201). The encapsulated La-Zr oxides retain the specific sorption toward phosphate through ligand exchange. The host D201 provides satisfactory hydraulic properties and mechanical strength, and its macropores covalently bound positively charged ammonium groups could enhance nanoparticles dispersion and phosphate diffusion kinetics. Compared with the monometallic samples (La-D201, Zr-D201) and La-Zr loaded active carbon (La-Zr-AC), La-Zr-D201 possesses a higher adsorption capacity for its special structure and a stronger adsorption affinity toward phosphate. Phosphate removal on La-Zr-D201 was examined as a function of solution pH, reaction time, temperature, and competing anions, and the experiment results showed that the nanocomposite possessed superior phosphate adsorption capacity and selectivity. The underlying mechanism for the specific sorption and the stronger affinity of bimetallic adsorbents toward phosphate than monometallic ones were proved by XPS. Besides, column adsorption demonstrated 1350 BV of synthetic water (2 mg P-PO₄^3-/L) could be treated efficiently by La-Zr-D201, while only 160 BV for the host D201. The binary NaOH-NaCl solution could effectively regenerate the spent adsorbents for repeated use. As a result, La-Zr-D201 possesses great potential in the application of enhanced phosphate removal from wastewater.