Study On Preparation And Photocatalytic Oleic Acid Esterification Of BiOBr/CeO₂@ACSs Composite

Solar photocatalytic oxidation technology is not only one of the effective methods that researchers have been advocating to control persistent organic pollutants in the environment,but also widely used in energy fields such as photocatalytic hydrogen production,CO₂ reduction,and nitrogen fixation.Therefore,we combine the clean solar photocatalysis technology with the green treatment and reuse of oil and fats to solve the problem of oil resource utilization and develop new application fields of solar photocatalysis technology.As an important component of oil and fats,fatty acids are of great significance for the development and utilization of oils and fats.To this end,we choose oleic acid as the research object,carry out basic physicochemical properties research,and provide theoretical basis for the comprehensive utilization of oil resources.In this thesis,BiOBr was used as a photocatalyst to explore its application in photocatalytic oleic acid isomerization and esterification.Based on the difficulty in recovering powder photocatalyst and the fact that reaction efficiency can be improved by increasing the adsorption of oleic acid,activated carbon spheres are introduced into the photocatalytic oleic acid esterification.The main research contents and results are as follows:?1?This work reported a systematic investigation on BiOBr photocatalyzed oleic acid isomerization process in different?air,N₂ and O₂?atmospheres and proposed the cis-trans isomerization mechanism.The crystal structures,optical properties,microscopic morphologies of as-prepared BiOBr were characterized by XRD,UV-vis DRS,SEM and TEM.The photocatalyzed oleic acid isomerization products over BiOBr in different atmospheres were analyzed with FT-IR and ¹H NMR for comparisons.The results demonstrate that there are significant differences for the photocatalytic oleic acid isomerization process in different atmospheres,and N₂ atmosphere is the most favorable atmosphere,while the presence of O₂ will inhibit the formation of elaidic acid.Moreover,density functional theory?DFT?was employed to calculate the charge density and energy difference of ground states between cis-and trans-isomers of oleic acid.Combined with theoretical and experimental findings,the radical cation transition states and photocatalytic isomerization mechanism were discussed and proposed.Our findings should provide new insights and basic data for understanding the photocatalytic isomerization of unsaturated fatty acids.?2?BiOBr/CeO₂@ACSs composite photocatalysts were synthesized by suspension polymerization-impregnation method.Firstly,XRD and EDS confirmed that the composite photocatalytic system was constructed successfully.SEM found that BiOBr/CeO₂@ACSs photocatalyst not only has the well-developed pore structure,but also has no obvious change in the morphology of the impregnated BiOBr,which are still nanosheets with closely varying shapes and sizes.The DRS results demonstrate that the introduction of CeO₂@ACSs increases the BiOBr absorption capacity in the visible region.Secondly,when the ratio of methanol/oil is 16/1,reaction time and temperature is 12 h and 80�C,respectively,the photocatalytic oleic acid esterification performance of BiOBr/CeO₂@ACSs was evaluated.It was found that the conversion of oleic acid to methyl oleate was as high as 96%.Simultaneously,the photo-esterification and the photocatalytic esterification process of BiOBr and CeO₂@ACSs were compared under the same conditions.The results showed that the conversion rates of oleic acid were 16.7%,44%and 32%,respectively,illustrating that the photocatalytic esterification of oleic acid is the interaction of light and catalyst.Finally,combining the well-developed pore structure and the excellent conductivity of CeO₂@ACSs with the fact that Ce⁴⁺as a Lewis acid site could adsorb reactant oleic acid,we proposed the catalytic mechanism that photogenerated e^-activated oleic acid and h⁺oxidized methanol.