磁载导电聚合物/TiO2纳米复合材料可控制备与光催化氧化-吸附协同除砷机理

Nowdays, the removal of trace arsenic compounds in underground by a combined process of photocatalytic oxidation and adsorpion attracts considerable attention in the water pollution control field. However, the photocatalytic mechanism of arsenite on the traditional TiO2-type catalysts is not clear yet, and their low light utilization efficiency, low adsorption capacity and poor separation performance also need to be further improved. To circumvent these above problems, this project aims to develop a novel core-shell magnetic three-component nanocomposite with iron oxides as magnetic core to load well-defined conductive polymer/TiO2 photocatalysts. The photosensitive conductive polymers are expected to narrow the band gap of TiO2 and widen the light absorption spectral range, while magnetic Iron oxide will enhance the ability of arsenic adsorption and magnetic separation. The photocatalytic and adsorption properties of arsenic compounds on the nanocomposites and their interaction mechanisms will be systematically investigated to ascertain the photocatalytic reaction path and mechanisms of arsenite on the composite materials under different illumination conditions, and figure out the effect rule of protonic acid doping and dielectric confinement effect on the photocatalytic activities. The effect of the microstructure, compositions, particle size, types of Iron oxides, pore size distribution and surface properties of the magnetic nanocomposites on the arsenic adsorption property and separation ability will be clarified. Therefore, the synergistic mechanism and structure-function relationship of the arsenic removal by photocatalytical oxidation and adsorption on the magnetic nanocompoistes will be revealed. The effect of co-existed medium such anions and organic matters and the operation conditions on the arsenic adsorption will also be investigated, and a novel magnetically stabilized fluidized bed reactor will be designed to establish the model of mass transfer and reaction of the as-synthesized composite materials. The results of this project will provide a theoretical basis to develop highly-efficient photocatalytical nanosorbents for arsenic removal and their large-scale application in wastewater treatment.

地下水中微量砷光催化氧化-吸附耦合去除是当前水污染控制领域研究热点。本项目针对传统TiO2光催化氧化砷机理不清、光利用率低、吸附能力差和分离困难等问题，拟以铁氧化物为磁核负载导电聚合物/TiO2光催化材料，制备核壳结构磁性三元纳米复合材料，利用导电聚合物实现能带结构窄化和响应光谱拓宽，铁氧化物增强吸附和分离能力。系统考察黑暗和光照条件下砷在复合材料上光催化氧化、吸附性能和作用机制，明确光催化氧化As(III)反应途径和机理，弄清质子酸掺杂和介电限域效应对其光催化活性影响规律，阐明复合材料结构、形貌、组成、负载方式和表面性质对As(V)吸附和磁分离性能的关系；揭示光催化氧化和吸附除砷过程耦合和协同作用机理。考察共存介质和操作条件对砷催化氧化和吸附性能的影响规律，设计新型磁稳定光催化吸附床，建立床层系统下传质、反应和吸附模型。研究成果为新型除砷高效光催化纳米吸附剂的开发和规模应用提供理论基础。

本项目以地下水中微量砷的深度去除为背景，针对目前TiO2材料光催化氧化砷存在的问题，以导电聚合物改性TiO2光催化剂为研究对象，围绕光催化氧化-原位吸附协同除砷工艺和机理开展系统研究。以γ-Fe2O3等铁氧化物为磁核，通过不同导电聚合物如聚苯胺、聚对苯二胺、聚噻吩改性TiO2的负载调控，构建核壳结构磁性异质结纳米复合材料，以拓宽TiO2材料的光谱吸收响应范围和提高光催化氧化As(III)活性。在此基础上，构建磁稳定光催化吸附床反应器，系统研究床内操作条件如流速、磁场强度、光照强度、As(III)初始浓度、磁性光催化剂添加量等强化传质、光催化反应和吸附的规律。研究结果表明，磁载质子酸掺杂聚苯胺对As(V)吸附容量达到37.6 mg/g，比磁性γ-Fe2O3提高5倍以上。核壳结构磁载导电聚合物改性TiO2纳米复合材料的光响应范围普遍拓宽到500nm以上（聚对苯二胺除外），光催化剂禁带宽度减少到2.5 eV以下，在可见光照射下可高效光催化氧化As(III)转变为As(V)，氧化率高达75%~99%之间，光催化氧化As(III)反应符合一级反应动力学，增加光催化剂浓度和降低As(III)初始浓度均可加速反应速率。磁载复合材料对As(III)暗吸附容量低于1.8 mg/g，符合伪二级吸附动力学模型，而在可见光照射下，光催化氧化-吸附协同作用大大提高了砷去除率，砷去除量增加至少2倍以上。自由基捕获实验和ESR结果确认了多种类光生活性物质如羟基自由基、光生空穴和超氧自由基在光催化氧化As(III)反应共同起作用，而超氧自由基作用最大。所设计磁稳定光催化吸附床实验结果表明增加催化剂填充量和光照强度有利于氧化-吸附耦合除砷，而磁场强度和流速存在最佳值分别为100GBs和50 mL/min。项目研究不但增强了对可见光催化氧化As(III)的反应机理和路径的基础认识，加深了对光催化氧化-吸附耦合过程和深度除砷协同过程的认识，而且深入了解磁稳定催化吸附反应床反应器内强化传质对光催化氧化和吸附过程的影响规律，为新型除砷高效光催化纳米吸附剂的开发和规模应用提供理论基础。