二氧化钛光催化还原全氟辛酸的基础研究

The PFOA have gained wide attention of the whole world since their widespread usage, persistence, bioaccumulation in the environment and recognized as persistent an organic pollutant.It has been found that wastewaters from paper making and textile manufacturer are the main source of PFOA in the surface and ground water pollution. These micropollution problems could be harmful to people and the environment, especially in the Province of Guangxi, where paper making and textile industries have been developing with great speed in recent years. Therefore, it is desirable to develop an effective treatment against PFOA pollution. Due to the fluorine's electron withdrawing capability,fluorine acts as the reaction center when a nucleophile approaches the perfluorinated carboxylate molecule, reductive remediation of PFOA is feasible. Among various approaches for the reductive decomposition method,the photocatcalytic reduction of PFOA by TiO2 is of particular interest because of its stability, efficiency,and nontoxicity. However,the major challenge in using this method is the low degradation rate due to the fast electron-hole recombination,poor understanding of the simple organic which play more than a hole-scavenger，and the unclear reaction mechanism.In this program， different contents of metal ions doped TiO2 catalysts are prepared using P25 as the carrier by photo reduction method. This study is focused on how the loaded cocatalysts suppress the recombination of the photogenerated electron-hole pairs and hence the photocatalytic activity is improved.The crystal structure,crystal morphology and chemical component are characterized,and the electrochemical properties，such as electrontransfer of metal-TiO2 in the PFOA reduction process are studied by cyclic voltammetry.On the other hand,it was well recorded that a strong reductant,carboxyl anion radical(CO2o?,normal potential E0 (CO2/CO2o?)= ?1.85V)could be formed when oxalic acid or formic acid was employed to scavenge photogenerated holes of excited TiO2,and it had been proposed that photoreduction of PFOA were greatly enhanced by invoking the assistances of CO2o?.Investigation on the simultaneous reduction of PFOA and oxidation processes of some small molecule organics occurring under irradiation on the photocatalyst surface in contact with water not only provides valuable information on the rate of the electron transfer paths at work in the reaction system,but is of great importance in consideration of the fact that the PFOA, which can be photocatalytically reduced, and organic pollutants,which can be removed by photocatalytic oxidation, very often coexist in papermaking or textile waste wastewaters. The results of this work could help for the raise of reaction efficiency of photocatcalytic reduction of PFOA ,a better understanding of the reaction mechanism,and practical application in the future.

我国特别是广西地区造纸与纺织行业的迅猛发展，由此产生的持久性污染物全氟辛酸（PFOA）势必会对当地环境和人体健康造成威胁。结合PFOA的C-F键能高，容易被亲核进攻发生还原反应的特点，开展TiO2光催化还原研究具有比较好的学术价值和实际意义。针对TiO2光催化还原研究存在的关键问题如空穴电子容易复合、空穴俘获剂的结构和性质对还原降解影响不明，本项目提出以金属对TiO2进行改性，解决光生电子累积、空穴和电子容易复合的问题，以期提高还原降解PFOA效率，结合表征手段和电化学分析方法，分析负载金属造成TiO2的晶相、晶格变化对电荷迁移过程造成的影响；并在此基础上系统研究不同有机物作为空穴俘获剂对还原降解PFOA的影响及可行性，分析其结构和性质对TiO2能带、电荷转移过程的影响，深化还原机理研究。该研究对于阐明TiO2光催化还原PFOA机理，提高反应效率，以及为将该技术转入实际应用做出贡献。

持久性污染物全氟辛酸（PFOA）对环境和人体健康造成威胁。结合PFOA的C-F键能高，容易被亲核进攻发生还原反应的特点，开展TiO2和Ga2O3光催化还原研究具有比较好的学术价值和实际意义。针对TiO2和Ga2O3光催化还原研究存在的关键问题如空穴电子容易复合、空穴俘获剂的结构和性质对还原降解影响不明，本项目选择分别选择Ag、Pt、Pd三种金属负载TiO2，制备Ag/AgBr/Ga2O3异质结催化剂，解决光生电子累积、空穴和电子容易复合的问题，并在此基础上系统研究不同有机物作为空穴俘获剂对还原降解PFOA的影响及可行性，分析其结构和性质对光催化剂能带、电荷转移过程的影响，深化还原机理研究。为进一步提高还原降解PFOA效率，研发二种具有磁性的光催化剂Fe3O4@SiO2@BiOBr（FSB）和Fe3O4@rhamnolipid@BiOBr（FRB），通过光催化+介质阻挡放电（DBD）等离子协同降解PFOA，研究结果表明，在DBD体系中加入FSB后，PFOA降解率从73.5%提高至92.9%，脱氟率从21%提高到32.8%；FRB的引入使PFOA的脱氟率从21.0%提高到30.6%，提高了9.6%，该研究为将技术转入实际应用奠定了重要基础。