Preparation And Photocatalytic Properties Of Amorphous Ceria-based Nanomaterials

Ceria?CeO₂?is an important kind of rare earth oxide semiconductors.It has been widely used in the field of photocatalysis due to its Ce⁴⁺/Ce³⁺transformation and high oxygen storage capacity.However,crystalline CeO₂ has low visible light absorption capacity and high carrier recombination rate,which limits the improvement of its photocatalytic efficiency.Compared with the crystalline materials,the structure of amorphous semiconductor is ordered in short range and disorderd in long range.The disordered structure can provide more catalytic activity sites and improve optical properties.The structure modification of CeO₂ is expected to improve its photocatalytic activity.In this paper,three kinds of CeO₂-based nanomaterials with amorphous structure were prepared.The photocatalytic degradation of methylene blue experiments were used to characterize the photocatalytic activity of the materials.The relationship between amorphous structure and material properties was studied.The main contents are as follows:?1?Amorphous CeO₂-SiO₂ materials were prepared using SiO₂ as support.The effects of the preparation methods,Ce/Si molar ratio?rCe:Si?and calcination temperature?T?on the structure and properties were studied.The results showed that the sol-gel method was more conducive to limit crystallization and crystal growth than the direct precipitation method and thermal decomposition method.Amorphous CeO₂was obtained by this method when rCe:Si?0.06 and T?400?.When the Ce/Si molar ratio and calcination temperature were the same,the amorphous CeO₂-SiO₂ had smaller bandgap,larger specific surface area and Ce³⁺proportion than the crystalline sample,but the difference between the carrier separation efficiency is not obvious,and the photocatalytic efficiency has been increased by 6.9%.?2?Three kinds of CeO₂-TiO₂ materials with different crystal structures were prepared using sol-gel method by controlling the Ce/Ti molar ratio.They are crystalline CeO₂@amorphous TiO₂?cC@aT?,amorphous CeO₂@amorphous TiO₂?aC@aT?and crystalline TiO₂@amorphous CeO₂?cT@aC?.The aC@aT sample?rCe:Ti=0.25?has the largest surface area(117 m²·g^-1)and the smallest bandgap?2.35 eV?.However,the photogenerated carrier recombination rate is higer than that of the other two.The aC@cT sample?rCe:Ti=0.05?has the highest carrier-separation efficiency and the highest photocatalytic degradation rate,which is about 5 times that of pure TiO₂.This shows that the crystalline@amorphous core-shell structure is more conducive to carrier separation and photocatalytic activity than the amorphous structure.?3?The crystalline CeO₂@amorphous CeO_2-x core-shell structure materials were prepared by the hydrogen reduction of NaBH₄.Amorphous shell with different contents were obtained by controlling the heating time.The results showed that with the increase of the preservation time,the color of the material gradually becomes darker,the Ce³⁺proportion and the oxygen vacancy concentration gradually increase,the visible and near infrared absorption intensity gradually increased.When the preservation time was60 min,the color of the material was dark brow and had the highest photocatalytic efficiency,which was nearly 40%higher than that of the original crystalline CeO₂sample.When the preservation time exceeds 60 min,the surface defectswere excessive and become the recombination center of the photogenerated electron-hole pair,thus reducing the photocatalytic efficiency.