【作者】 孙明辉；

【导师】 张延荣；

【作者基本信息】 华中科技大学 ， 环境科学， 2023， 博士

【摘要】 过氧化氢（H₂O₂）作为一种绿色强氧化剂被越来越广泛地应用于化学合成、医药健康、环境治理及燃料电池等领域,但目前工业生产所采用的蒽醌法是一种能源密集型生产方式,步骤繁琐、成本高且会造成严重的环境污染,已经不能满足现代低碳可持续发展需求。而利用可再生太阳能,在催化剂作用下将氧气和水转化为H₂O₂的光催化技术凭借其简便、无污染且安全的特点成为了最具潜力的H₂O₂合成替代技术之一,但目前光催化合成H₂O₂的效率仍然较低不能满足需求。基于此,本论文以光合成H₂O₂中最重要的氧还原过程为研究对象,采用缺陷工程、微纳结构调控、配体修饰等手段增强氧分子在光催化剂表面的吸附、传质及预活化过程;通过构建三相和氟碳/水体系使得催化剂可直接利用高浓度、超快传质的气态氧分子,通过促进氧利用全过程最终实现H₂O₂的高效合成及原位分离,并对反应过程中的载流子动力学及H₂O₂合成机制进行了解析。主要研究内容及结论概括如下:（1）缺陷态BiVO₄制备及其光催化合成H₂O₂研究。采用硼氢化钠与BiVO₄共煅烧制备得到富含氧空位（OVs）缺陷的DBVO光催化剂。OVs作为典型的配位不饱和位点（CUS）能够有效地吸附富集O₂,而有效的化学吸附可以在空间上促进光生电子转移到吸附态氧物种。因此,与BiVO₄相比,DBVO对O₂的吸附容量提升了19倍,达到了4.27 mmol g^-1;光生载流子由捕获位点到活性氧物种的界面转移速率提升了23倍,达到了1.1×10⁷ s^-1;H₂O₂光合成效率提升了32倍,DBVO在可见光照射、无牺牲剂条件下的H₂O₂产率达到了102μmol g^–1 h^–1。（2）缺陷态BiVO₄/WO₃/Ti O₂纳米管制备及其光合成H₂O₂研究。通过电化学手段制备得到缺陷态BiVO₄/WO₃/Ti O₂纳米管复合材料,电化学还原引入的OVs主要集中在BiVO₄上。通过控制还原电位和时间,可以实现OVs类型及浓度的精准调控,极大改善了光电荷利用过程。此外,在纳米限域效应的作用下,水分子在缺陷态BiVO₄/WO₃/Ti O₂纳米管中传质速率是连续流体力学理论预测值的7.6倍以上,具备了部分超流体特性,而且其中溶解氧的扩散流动性也显著增强。在催化剂光电特性和反应物传质行为均得到改善的情况下,复合光催化剂在纯水中实现了252μmol g^-1 h^-1的H₂O₂光合成效率。（3）催化及光电响应双功能Pd-O_x位点于气固液三相界面光合成H₂O₂研究。通过在BiVO₄表面修饰配体再负载Pd纳米颗粒,制备得到Pd/A/BiVO₄光催化剂。在配体和Pd的协同作用下,光催化剂呈现出超疏水/超亲氧的界面特性,在反应过程中处于气液交互界面,可直接利用空气中浓度高、传质快的O₂,而且这种催化剂与产物相对分离的体系降低了H₂O₂被进一步分解的概率,有助于积累得到高浓度H₂O₂溶液。此外,由配体中氨基向Pd的电荷转移实现了催化剂上O₂富集与载流子动力学的改善。因此,相比于两相体系,疏水型Pd/A/BiVO₄在三相体系中的H₂O₂光合成产率提升了13倍,达到了805.9μmol g^-1 h^-1。而且H₂O₂是通过氧还原和水氧化双通道机制合成的,其中一步两电子氧还原反应为主要路径。此外,Pd-O_x不仅是合成H₂O₂的催化活性中心,还具有独特的光电响应特性,是一个双功能活性位点。（4）氟碳/水体系的构建及其光合成H₂O₂研究。通过单体聚合得到了富含三嗪和亚胺结构的疏水型共价有机框架光催化剂TTBA。基于全氟烷烃的超双疏特性,TTBA处于氟碳/水体系中的两相界面处,在无牺牲剂、可见光照射下的H₂O₂光合成效率高达4.9 mmol g^-1 h^-1,这主要是由于在疏水表面间的相互作用下,TTBA和全氟烷烃之间形成了一个超薄致密气层,在纳米限域的气层中反应物氧分子以超流体形式超快传质和供给。而且该体系中生成的H₂O₂可自分离进入水相,从而在合成过程中直接原位获得纯H₂O₂溶液。TTBA上的H₂O₂是经历两步氢原子转移过程生成的,全过程能垒极低,这证实了O₂充足供给对于H₂O₂高效合成的贡献。此外,氟碳/水体系的两相独立分层结构可以实现各种功能化应用,如在水相中加入亚铁离子,构建一个两相原位芬顿体系以实现有机污染物的高效降解。更多还原

【Abstract】 Hydrogen peroxide（H₂O₂）is increasingly used as a green and strong oxidant in chemical synthesis,medicine and health,environmental treatment and fuel cells,etc.However,the anthraquinone method currently used in industrial production is an energy-intensive production method,with cumbersome steps,high costs and serious environmental pollution,which can no longer meet the needs of modern low-carbon sustainable development.Photocatalysis,which uses renewable solar energy to convert oxygen and water into H₂O₂under the action of photocatalyst,has become one of the most promising alternative technologies for H₂O₂ synthesis due to its simplicity,non-polluting and safety features,but the efficiency of photocatalytic synthesis of H₂O₂is still low to meet the demand.Based on this,this thesis took the most important oxygen reduction process in H₂O₂ photosynthesis as the object of study,and adopted defect engineering,micro-nano structure modulation and ligand modification to enhance the adsorption,mass transfer and pre-activation process of oxygen on the surface of photocatalyst.By constructing a triphase and fluorocarbon/water system,the photocatalyst could directly utilize the high concentration and ultra-fast mass transfer of gaseous oxygen,and finally realized the efficient synthesis and in situ separation of H₂O₂by promoting the whole process of oxygen utilization.The carrier kinetics and the mechanism of H₂O₂ synthesis during the reaction process were also analyzed in depth.The major research contents and conclusions were summarized as follows:（1）Defective BiVO₄ preparation and its H₂O₂photosynthesis.The oxygen vacancies（OVs）-rich defective BiVO₄photocatalysts（DBVO）were prepared by co-calcination of sodium borohydride with BiVO₄.OVs as typical coordination unsaturated sites（CUS）can effectively adsorb and enrich O₂,and the exuberant chemisorption can spatially promote the transfer of photogenerated electrons to the adsorbed oxygen species.Therefore,compared with pristine BiVO₄,the adsorption capacity of DBVO for O₂ was enhanced by 19 times to4.27 mmol g^-1,the interfacial transfer rate of photogenerated carriers from capture sites to active oxygen species was enhanced by 23 times to 1.1×10⁷ s^-1,and the H₂O₂ photosynthesis efficiency was enhanced by 32 times,the H₂O₂yield of DBVO reached 102μmol g^–1 h^–1under visible light irradiation and without any sacrificial agents.（2）Defective BiVO₄/WO₃/Ti O₂ nanotubes preparation and its H₂O₂photosynthesis.Defective BiVO₄/WO₃/Ti O₂ nanotubes composites were prepared by electrochemical methods,and the OVs introduced by electrochemical reduction were mainly concentrated on BiVO₄.By controlling the reduction potential and time,the precise regulation of the type and concentration of OVs could be achieved,which greatly improved the photo-charge utilization process.In addition,under the influence of the nanoconfined effect,the mass transfer rate of water molecules in the defective BiVO₄/WO₃/Ti O₂ nanotubes was more than 7.6 times that predicted value by the continuous hydrodynamic theory,possessing some superfluidic properties,and the diffusive mobility of dissolved oxygen was also significantly enhanced.The composite photocatalyst achieved an H₂O₂ photosynthesis efficiency of 252μmol g^-1 h^-1in pure water with both improved photovoltaic properties of the catalyst and the mass transfer behavior of the reactants.（3）Catalytic and photoelectric corresponding bifunctional Pd-O_x at the gas-solid-liquid triphase interface for H₂O₂ photosynthesis.The Pd/A/BiVO₄photocatalysts were prepared by modifying ligands on the BiVO₄ surface and then loading Pd nanoparticles.Under the synergistic effect of the ligand and Pd,the photocatalyst exhibited superhydrophobic/superhydrophilic interfacial properties,so it was at the gas-liquid interaction interface during the reaction,which could directly utilize the atmospheric O₂ with high concentration and fast mass transfer.Moreover,this relatively separated products and catalysts system reduced the further decomposition probability of the generated H₂O₂,which contributed to accumulate highly concentrated H₂O₂ solutions.In addition,the charge density transfer from the amino group of the ligand to Pd achieved the enrichment of O₂ and the improvement of carrier dynamics on the catalyst surfaces.Thus,the yield of H₂O₂photosynthesis by hydrophobic Pd/A/BiVO₄ in a triphase system was enhanced by a factor of13 to 805.9μmol g^-1 h^-1 compared to a two-phase system.H₂O₂ was synthesized by a two-channel mechanism of oxygen reduction and water oxidation,in which the one-step two-electron oxygen reduction reaction was the the main pathway.Moreover,Pd-Ox was not only a catalytically active center for the synthesis of H₂O₂,but also had a unique photoelectric response property,which was a bifunctional active site.（4）A fluorocarbon/water system construction and its H₂O₂photosynthesis.The hydrophobic covalent organic framework photocatalyst TTBA with triazine and imine structures,was obtained by monomer polymerization.Based on the superamphiphobicity of perfluoroalkanes,TTBA was at the two-phase interface in the fluorocarbon/water system,and the efficiency of H₂O₂ photosynthesis was as high as 4.9 mmol g^-1 h^-1 under visible light irradiation without any sacrificial agents.This was mainly due to the formation of an ultra-thin dense gas layer between TTBA and perfluoroalkanes under the interaction between hydrophobic surfaces,and the ultra-fast mass transfer and supply of reactant oxygen molecules as superfluid was achieved in this nanoconfined gas layer.Moreover,the H₂O₂generated in this system could be self-separated into the aqueous phase,thus obtaining pure H₂O₂ solutions directly during the synthesis process.H₂O₂ on TTBA was generated through a two-step hydrogen atom transfer process with extremely low energy barriers for the whole process,which confirms the contribution of sufficient O₂ supply to the efficient H₂O₂synthesis.In addition,the two-phase independent hierarchical structure of the fluorocarbon/water system could realize various functionalized applications,such as adding ferrous ions to the aqueous phase to construct a two-phase in situ Fenton system for the efficient degradation of organic pollutants.更多还原