The Preparation Of Pt/La₂Ti₂O₇ Catalysts And Research On The Degradation Efficiency And Mechanism Of Perfluorooctanoic Acid

The globally widespread distribution of perfluoroalkyl substances（PFASs）poses a huge environmental challenge to the biosphere and human.Perfluorooctanoic acid（PFOA）and perfluorooctane sulfonates（PFOS）,represented by PFASs,have been recognized as persistent pollutants with potential carcinogenicity,endocrine disrupting,reproductive and developmental toxicity.Perfluorooctanoic acid(PFOA,C₇F₁₅COOH)is one of the most commonly used PFASs in the environment and has become a global concern due to its widespread presence in water bodies and its ability in bioaccumulation.Therefore,it is very meaningful and necessary to investigate economical and environmentally friendly PFASs treatment technologies.Photocatalytic reduction technology,with its low energy consumption,mild reaction conditions and high efficiency,becomes increasingly important in the application of PFASs degradation.In order to effectively degrade PFOA in water,nanosheet photocatalysts（Pt/La₂Ti₂O₇）were prepared and studied in this thesis,while methanol was used as the electron donor and applied to the photocatalytic reduction technology to achieve the removal of PFOA from water.In this paper,the preparation of the photocatalyst and its characterization,the degradation effect of PFOA and the degradation mechanism of PFOA were studied and evaluated as follows:1.In this paper,lanthanum titanate catalyst was prepared by hydrothermal synthesis method,and Pt nanoparticles were deposited on the surface of La₂Ti₂O₇ by photochemical deposition method to fabricate the novel photocatalyst Pt/La₂Ti₂O₇.Using scanning/projection electron microscope（S/TEM）,dynamic light scattering（DLS）,X-ray diffractometer（XRD）,electrochemical impedance spectroscopy（EIS）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy（Raman）,Fourier transform infrared spectroscopy（FTIR）and ultraviolet-visible-near infrared spectrophotometer（UV-Vis-NIR）and a series of characterization tests to analyze its surface morphology,zeta potential,hydrodynamic diameter,crystallinity,surface Properties such as chemical composition and photoelectric performance proved that platinum（Pt）nanoparticles were successfully deposited on La₂Ti₂O₇.The deposition of Pt changed the energy band structure of the catalyst,which was the main reason for the improvement of the photocatalytic activity of the catalyst.2.Batch degradation experiments of PFOA by photocatalytic reduction were carried out to investigate the effects of photocatalyst and UV presence on the degradation efficacy,and to examine the effects of the presence of different organic electron donors and inorganic salts on the degradation effect of PFOA.The experimental results showed that the combination of photocatalyst and UV₂₅₄constituted a photocatalytic reaction system with a mutually reinforcing effect on the degradation of PFOA.The addition of suitable electron donor can promote the photocatalytic reaction,and the UV/Pt/La₂Ti₂O₇/CH₃OH reaction system had a highest removal performance on the degradation of PFOA.The removal efficiency of PFOA can reach up to 50%under the optimal conditions.The reduction efficiency of this reaction system was improved by 1.67 times compared to that without the addition of electron donor.EDTA,oxalic acid and formic acid were able to inhibit the photocatalytic degradation of PFOA.The presence of NaCl and CaCl₂ inhibited the reductive degradation of PFOA due to the potential photochemical reaction of inorganic salts with UV light.3.The density flooding theory（DFT）calculations were used to analyze the role of Pt as a co-catalyst in the energy band structure,interfacial electron transfer and degradation pathway.The results showed that the Pt/La₂Ti₂O₇ surface has a lower band gap compared to the unfunctionalized pure La₂Ti₂O₇,accompanied by enhanced adsorption energy and increased charge transfer rate promoting further degradation of PFOA.The degradation pathway of PFOA was analyzed by constructing a three-dimensional conformational map,and the results showed that the UV/Pt/La₂Ti₂O₇/CH₃OH photocatalytic system could extract electrons from methanol and convert them into radicals and photogenerated electrons,which resulted in effective reductive degradation of PFOA.