Synthesis of nano-CeO₂ hollow spheres with high adsorption activity via template-free solvothermal method

Nano-CeO₂ hollow spheres were synthesized via a two-step process. The precursor was synthesized by template-free solvothermal method at 160℃ using ethylene glycol and deionized water as solvent. Then it was calcinated at 500℃ for 1 h in the air to produce nano-CeO₂ hollow spheres. The physical and chemical properties of the precursor and the sample were researched by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The sample after calcination contained the hollow sphere morphology of the precursor. Its diameter was about 300~400 nm, spherical shell thickness was 35 nm approximately and there were worm-like pores on the spherical shell. The possible mechanisms for the formation of precursor in the solvothermal condition, the chemical reactions in the calcination process and the evolution process of the hollow sphere structure were discussed. N₂ adsorption-desorption isotherm of the sample was tested and its specific surface area was 71.984 m²·g^-1 by calculation. It was much higher than the specific surface area of commercial CeO₂ (3.954 m²·g^-1). Also, the adsorption activity of acid orange 7 on the sample was researched. The final adsorption amount of acid orange 7 was 22.8 mg·g^-1 under the experimental conditions. The total removal amount of acid orange 7 was 99.8% and much higher than that of commercial CeO₂ (24.3%). Meanwhile, the process dynamics of the acid orange 7 adsorption on the sample was also studied and it was well in line with the pseudo-second-order process. The linear coefficient R² was 0.99984. The equilibrium adsorption amount of acid orange 7 was 25 mg·g^-1.