Effects Of Lanthanum Ions On The Crystal Structure And Photocatalytic Properties Of Cerium Oxide

Cerium oxide?CeO₂?shows a wide application prospect in the catalyst,because of its unique cubic Fluorite Crystal Structure and the change of the valence state of the+3 and+4 of the Ce element.However,as a photocatalyst,it is not enough for the use of visible light because of its large band gap,so different elements were doped to reduce the forbidden band width.In rare earth elements,it's less different between La³⁺and Ce⁴⁺in the ionic radii.Although the valence states of the two are different,they often coexist as solid solutions,such as the coexistence of La³⁺and Ce⁴⁺in fluorocarbon with ion replacement solid solution.Therefore,the study of the influence of La³⁺doping on the crystal structure and photocatalytic performance of cerium oxide?CeO₂?is of theoretical and practical significance.However,there are few studies on lanthanum doped CeO₂ crystals,and few reports have been applied to photocatalytic degradation of organic dyes.Therefore,the synthesis conditions of lanthanum oxide and lanthanum oxide synthesized by hydrothermal method were studied.Different concentrations of lanthanum doped ceria solid solution were synthesized.The different doping amount of lanthanum was used as the main variable,and the 10%La³⁺doped CeO₂ with different morphologies was prepared by the selection of precipitant and surfactant.The crystal structure of doping was detected by XRD,the change of particle size was observed by SEM,and the oxygen vacancy and band gap of CeO₂ after lanthanum doping were also analyzed.The influence of lanthanum ions on the properties of synthetic products is analyzed,and the relationship between the corresponding structures and properties is analyzed.The effects of the doping of lanthanum ions and the particle morphology of the synthesized products on the photocatalytic activity of methylene blue were investigated by using the synthesized samples for the photocatalytic degradation of methylene blue.By studying the crystal structure of the synthesized sample by the doping amount of lanthanum ion,it is found that the XRD spectra of the products obtained in the range of 0%⁸0%La³⁺contents are all clearly with the cubic fluorite type CeO₂ crystal structur.The addition of La³⁺can form La-O chemical bonds in CeO₂ and replace Ce⁴⁺in the form of replacement.Because of the different ionic radius of La³⁺and Ce⁴⁺,the doping of La³⁺makes the diffraction peak shift to different degrees at a low angle,and the width of the half peak is widened.The fitting calculation also confirms that La³⁺will cause the expansion of the lattice of CeO₂,the larger space between the crystal surface and the crystal.Due to the different valence states of La³⁺and Ce⁴⁺,the incorporation of La will affects the lattice oxygen content,the content of adsorbed oxygen and the relative content of Ce³⁺.The morphology of synthesized products can be controlled by adding and adjusting precipitating agents and surface additives.With NaOH as the precipitant without surface additive,the aggregate particles of the synthesized samples at 160?/8h are spherical like nanoparticles,and the particle size decreases with the increase of lanthanum content,and it is difficult to see the single crystal particles;when the hydrothermal reaction increased to the 200?/24 h,10%La³⁺doped CeO₂ with different morphologies can be obtained with different precipitants/surfactants.When NaOH/without surfactants,the surface of the particles is flocculent;when NaOH/CTAB is grown,the crystal particles grow,the CeO₂ cubic grain is visible,the urea/CTAB is spherical,and the urea/PEG is basically flaky.Under the same conditions of hydrothermal synthesis,the synthetic product of lanthanum content(0%⁸0%La³⁺)has no obvious effect on the dark adsorption of methylene blue.The photocatalytic performance of 0%La³⁺,5%La³⁺and 10%La³⁺doped CeO₂ in both ultraviolet and visible light has a certain degree of photocatalytic activity,and the photocatalytic effect is better under the UV light because its energy is higher,10%La³⁺doping shows the best photocatalytic performance,which is consistent with the minimum value of the band gap?2.74 eV?.The band gap is derived from the quantum size effect(the increase in the amount of La³⁺,the increase of the particle size,the increase of the energy gap)and the effect of the impurity energy level(the increase of La³⁺doping amount makes the lattice defects increase and cause the impurity energy."The dark adsorption of methylene blue with 10%La³⁺doped CeO₂with different morphologies decreased in order of spheroidal,flaky,floc and cube order,which is related to the size and specific surface area of the particles.10%La³⁺doped CeO₂ has various catalytic effects both under ultraviolet and visible light sources.The efficiency of UV light is greater than that under visible light,and the photocatalytic degradation efficiency is reduced in order of cube,floc,flake and spherical order,which is consistent with the width of the forbidden band of the corresponding UV visible spectrum from narrow to width.and the photocatalytic degradation efficiency of the samples under visible light is the same.The kinetics of surface methylene blue catalytic degradation follows a pseudo first order expression.