Preparation Of Ceria-based Nanomaterials And Their Catalytic Performance For Formaldehyde Oxidation At Room Temperature

Air is a natural resource for human survival.The problem of indoor air pollution,especially formaldehyde pollution,is a serious threat to human life and health.It is urgent to solve the problem of indoor formaldehyde pollution.Cerium dioxide（CeO₂）is widely used in the catalytic field because of its non-toxic,high redox properties and high stability.However,the traditional CeO₂material has problems such as low visible light utilization and high photogenerated electron hole recombination,which limits its application in indoor formaldehyde pollution control.In this paper,CeO₂-based composites that efficiently catalyze the oxidation of formaldehyde under the assistance of room temperature fluorescence have been prepared by improving monomer preparation methods,lanthanum doping,and constructing heterostructures,including water modified monomer CeO₂nanomaterials,lanthanum doped nano CeO₂composites,and nitrogen doped carbon quantum dots（N-CQDs）modified CeO₂composites,The effects of its microstructure,morphology,and photoelectrochemical properties on the catalytic oxidation of formaldehyde under room temperature fluorescence were studied,and the possible mechanism of catalytic oxidation of formaldehyde by CeO₂-based nanomaterials was discussed.Finally,the future prospects of the design of CeO₂based nanomaterials were put forward.The main research contents of this paper are as follows:（1）CeO₂calcined with cerium nitrate and ammonium carbonate as raw materials was modified by water pretreatment to obtain a catalyst for efficient removal of formaldehyde gas at room temperature for the first time.The CeO₂nanomaterial（CeO₂-20-80）obtained from the precursor immersed in 20 m L of deionized water and preheated at 80℃for 120min,and then calcined,has a removal efficiency of 77.3%and a conversion efficiency of44.9%for formaldehyde gas within 180 min,which was much higher than the CeO₂（p-CeO₂）nanocatalyst without water pretreatment（30.0%and 14.0%）.Under indoor fluorescent lamp irradiation,the formaldehyde removal efficiency and conversion efficiency of CeO₂-20-80catalyst reached 80.0%and 67.7%respectively.The formaldehyde conversion of CeO₂-20-80 catalyst was significantly higher than that of the catalyst without light.Through a series of physical representations and density functional calculation,it was found that CeO₂-20-80 catalyst has high specific surface area,rich active oxygen species and high CeO₂（111）crystal surface exposure ratio,which promotes the adsorption and conversion decomposition of formaldehyde molecules.（2）Using cerium nitrate,lanthanum nitrate and ammonium carbonate as raw materials,lanthanum doped CeO₂nanocatalyst for formaldehyde degradation at room temperature was prepared by coprecipitation and calcination.When the amount of lanthanum doped was 1mmol and the amount of ammonium carbonate was 15 mmol,the lanthanum doped CeO₂nanocomposites(La_1.0Ce-AC)prepared performed the best catalytic performance for the oxidation of formaldehyde at room temperature,and the formaldehyde removal efficiency and conversion efficiency were 59.3%and 52.6%respectively in 180 minutes at room temperature,which was stronger than the undoped CeO₂（p-CeO₂）nanomaterial（20.7%and20.9%）.Indoor fluorescence irradiation further increased the formaldehyde conversion rate.The formaldehyde removal efficiency and conversion efficiency of La_1.0Ce-AC catalyst in180 min were 62.7%and 82.0%,respectively,which exceeded that of p-CeO₂nanocatalyst（40.7%and 47.6%）.The formaldehyde conversion efficiency of La_1.0Ce-AC catalyst under fluorescence was significantly improved.The characterization results has explained that the excellent performance of La_1.0Ce-AC catalyst is mainly attributed to the abundant oxygen vacancies,new impurity energy levels and narrow band gaps,high photogenerated carrier separation rate,high conductivity and charge transfer ability of La_1.0Ce-AC catalyst.（3）Nanorod CeO₂was prepared by hydrothermal method,and then N-CQDs/CeO₂nanocomposite material was successfully prepared by using citric acid monohydrate as carbon source and urea as nitrogen source by one-pot hydrothermal method.The catalytic oxidation of gaseous formaldehyde was carried out at room temperature.The experimental results show that N-CQDs/CeO₂has high catalytic oxidation activity for formaldehyde gas at room temperature when the loading amount of N-CQDs is 7%.The removal efficiency and conversion efficiency of formaldehyde after 150 min in dark state are 55.0%and 28.3%,respectively,higher than that of CeO₂（30.0%and 25.0%）.Indoor fluorescent lamp assisted to improve the conversion rate of formaldehyde.The removal efficiency and efficiency rate of formaldehyde were 75.0%and 93.3%after 150 min of fluorescent irradiation,which were higher than that of CeO₂（48.3%and 56.7%）.The improvement of catalytic oxidation performance of formaldehyde at room temperature was attributed to the high specific area and multiple active sites of N-CQDs/CeO₂catalyst;N-CQDs/CeO₂has a stronger response to indoor visible light,which will generate more photogenerated electrons and holes;The introduction of N-CQDs not only improves the conductivity and charge transfer ability of CeO₂,but also forms internal electric field and improves the separation efficiency of photogenerated carriers.