The synthesis and characterization of hydrous cerium oxide nanoparticles loaded on porous silica micro-sphere as novel and efficient adsorbents to remove phosphate radicals from water

Abstract

Abstract Inorganic adsorbents can lower the concentration of phosphate radicals in aqueous solution. However, the traditional adsorbents containing low-valence metal atoms have many defects in the application process, such as low adsorption capacity, easy dissolution in solution, and easy agglomeration of the nano-sized adsorbents and so on. This article presents a novel and effective method to immobilize high-valence Ce element on the porous silica micro-spheres via an impregnation-calcination-activation technique to efficiently remove phosphate radical. The Ce-SiO2 was synthesized via (1) Ce3+ atoms adsorbed on the surface of silica sphere, (2) cerium nitrate hexahydrate transformed into cerium dioxide via thermal decomposition process and (3) anhydrous cerium dioxide transformed into hydrous cerium oxide (HCO) via an acid activation process. The field-emission scanning electron microscope (FESEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results indicate that cerium oxide nanoparticles grow homogeneously on the surface of the silica sphere when the heating rate is 2 °C/min at 90.5 °C and 218.0 °C. The X-ray diffraction instrument (XRD) and X-ray photoelectron spectroscopy XPS results demonstrate that Ce3+ atoms could be oxidized into Ce4+ atoms and produce ample reduced ion-exchange sites. Bath adsorption experiments indicate that 15HCO-SiO2 has excellent properties of removing phosphate ions and the maximum adsorption capacity is 85.5 mg/g. Kinetic and isothermal studies show that the experimental data fit nicely into pseudo-second kinetic and Langmuir models, indicating that the chemical adsorption, as well as the monolayer adsorption, occur simultaneously in the adsorption process. Analysis of the adsorption mechanism analysis suggests that the phosphate ions are sequestered by a reduction and ion-exchange reaction (CeO2 to CePO4).