Designation And Photocatalytic Acetaldehyde Oxidation Performance Of Cerium Oxide Based Composite Photocatalyst

The environmental pollution issue has increasingly attracted global attention,especially indoor toxic organic volatile gases(VOCs),which pose a serious threat to human health.With the continuous improvement of people’s environmental awareness and their own health needs,researchers have proposed many environmental treatment technologies and methods.Among them,photocatalytic technology is widely used because it can convert VOCs into non-toxic and harmless substances(CO2,H2O,etc.)under light conditions.As is well known,the structural characteristics of photocatalysts greatly affect their photocatalytic performance.Previous studies have found that traditional semiconductor photocatalytic materials have defects such as narrow absorption of sunlight in the spectral range and high recombination rate of photo-generated charge carriers.In order to improve photocatalytic efficiency,researchers have proposed various modification strategies for photocatalysts,such as morphology or size regulation,metal(non-metal)doping,noble metal deposition,and heterostructure construction.Among numerous photocatalysts,CeO2,as a new type of rare earth photocatalyst with unique optical properties,has attracted increasing attention from researchers.However,as a semiconductor photocatalytic material,it also faces the application bottleneck problem of traditional materials.In order to improve the visible light response of cerium oxide based photocatalysts and suppress the recombination of charge carrier pairs,this paper further optimized cerium oxide based photocatalysts using modification methods such as morphology regulation and semiconductor recombination,and deeply explored the relationship between crystal surface effect and structure and performance.In the first part,truncated octahedral cerium oxide(CeO2-to)with special morphology was prepared using a one-step solvothermal method using oleic acid and oleylamine as morphology modifiers.Through morphology observation,CeO2-to mainly exposes two crystal planes {100} and {111} simultaneously,while cubic ceria(CeO2-c)and octahedral ceria(CeO2-o)mainly expose single {100} and {111} planes,respectively.The photocatalytic activity test under full spectrum irradiation showed that CeO2-to photocatalytic material significantly enhanced the degradation of gaseous acetaldehyde(CH3CHO),with CO2 generation 1.78 times that of CeO2-c and 7.97 times that of CeO2-o,respectively.In addition,the results of active species capture tests indicate that superoxide radicals(·O2-)and holes(h+)are the main reactive active species in the degradation process of CH3CHO,especially the contribution of ·O2-in the oxidation reaction is the most prominent.Density functional theory(DFT)calculations show that the highly active {100} surface is more conducive to the absorption of acetaldehyde than the {111} surface.It also reveals that the enhancement of photocatalytic activity mainly benefits from the rapid transfer of photogenerated-electrons(e-)driven by the energy difference between {100} and {111} surfaces.Based on all experimental results and DFT theoretical calculations,we also analyzed how the electron transfer mechanism formed by the surface heterojunction of CeO2-to efficiently photocatalytic oxidation of CH3CHO.However,due to the inherent properties of CeO2-to,there are still defects such as high carrier recombination rate and low visible light utilization,which need further improvement.In the second part,a novel n-p heterojunction truncated octahedral cerium oxide/ceriumbased metal organic framework composite photocatalyst(CeO2-to/Ce-MOF)was synthesized by coupling the cerium-based metal organic framework with a flexible template free hydrothermal method based on the CeO2-to nanoparticles.The experimental results show that under visible light irradiation,the CeO2-to/Ce-MOF composite photocatalyst prepared exhibits high photocatalytic activity for the degradation of CH3CHO,with oxidation performance 1.52 times greater than Ce-MOF and 3.04 times greater than CeO2-to,respectively.And the results of active species capture experiments and photoelectric testing indicate that the improvement of photocatalytic performance mainly comes from the inhibitory effect of the internal electric field formed between CeO2-to and Ce-MOF on electron and hole recombination,which improves quantum efficiency and effectively participates in the photocatalytic degradation of CH3CHO reaction under visible light.In the third part,a special n-p heterostructure truncated octahedral ceria/bismuth oxide composite photocatalyst(CeO2-to/Bi2O3)was synthesized by coupling the narrow band gap inorganic semiconductor Bi2O3 with hydrothermal and calcination two-step methods based on the CeO2-to nanoparticles.Under visible light irradiation,the composite photocatalyst CeO2to/Bi2O3 exhibits excellent photocatalytic performance in the degradation of CH3CHO,with CO2 generation 4.33 times greater than Bi2O3 and 4.67 times greater than CeO2-to,respectively.The active species capture experiment and photoelectric testing further explored the catalytic activity mechanism of Bi2O3 combined with CeO2-to.The improvement of its photocatalytic performance may be due to the narrow bandgap of Bi2O3,which can effectively expand the visible light absorption range.Furthermore,the built-in electric field formed by the combination of CeO2-to and Bi2O3 accelerates the transport of photo generated electrons and holes between the CeO2-to and Bi2O3 phases,while also improving the charge separation ability,further enhancing the photocatalytic performance of CeO2-to based photocatalysts.This paper achieved an improvement in the photocatalytic degradation activity of acetaldehyde using CeO2 based composite photocatalyst materials by adopting the above modification schemes.Moreover,by exploring the crystal plane effect of truncated octahedral CeO2 and the influence of truncated octahedrall morphology cerium oxide and other semiconductor heterojunctions on photocatalytic performance,meaningful reference and guidance are provided for the further development of other efficient cerium based photocatalysts.