石墨毡负载施氏矿物（GF/Sch）电极净水效果研究

摘  要

电化学水处理技术是一类物理、化学和电场相结合的综合性水处理方法。不同于传统的水处理技术需要外源添加化学物质，电化学水处理过程主要依赖于电子的定向转移以达到污染物降解去除的目的，因而处理效率高、绿色环保。尤其是对于低浓度污染物，电化学水处理技术展示出独特的优势。电极材料是电化学水处理的核心，针对于不同污染物的降解需求，开发高催化性能和传质性能的电极材料，并匹配合适的电化学过程，是实现水质净化的重要研究方向。

施氏矿物（Schwertmannite, Sch）是广泛存在于酸性矿山废水 (Acid mine drainage, AMD)中的铁羟基硫酸盐次生铁矿物，由于其具有大量的硫酸根、铁组分，已被证实是一类优异的异相芬顿催化剂。同时，由于施氏矿物的孔径尺寸和六价铬（Cr(VI)）、砷（As）等含氧阴离子（类）重金属相近，对以Cr(VI)、As为代表的重金属展示出优异的吸附性能。然而，已有的研究中施氏矿物大多以粉末形式参与反应，回收再利用困难，因而在实际工程应用中受到了极大的限制。此外，作为一类重要的铁基材料，电场的引入有望进一步提升施氏矿物对于污染物的吸附及催化性能。然而，目前将施氏矿物作为电极材料的研究尚不多见，如何将施氏矿物固定化以实现电场的引入是亟待解决的科学问题。基于此，本研究以石墨毡为基底，制备出新型的石墨毡负载施氏矿物固定化电极，针对于不同类型污染物的性质，匹配不同的电化学过程实现其高效降解，得到的初步结果如下：

（1）通过涂布的方式，将施氏矿物直接粘黏涂覆在石墨纸导电基底上得到固定化施氏矿物阴极电极材料，搭载浸没式电极反应器，探究了反应体系中的电化学强化Cr(Ⅵ)的去除性能。实验探究了施氏矿物负载量、电压条件等对Cr(Ⅵ)去除效率的影响，优化后确定Sch0.83-C（83%Sch即涂布材料中施氏矿物的质量占比83%）时，施氏矿物能较好的被固定且具有较好的导电性能；施加电压为-2.0 V时，电化学作用去除Cr(Ⅵ)的效率最佳，溶液中Cr(Ⅵ)被去除率接近40%。在该最优实验条件下，固定化的施氏矿物对Cr(Ⅵ)的去除效果是未通电条件下的11倍。

（2）通过化学负载的方法，成功制备了石墨毡作为基底负载施氏矿物的一体化阴极电极材料 GF/Sch，在浸没式反应体系中探究了Cr(Ⅵ)的电还原去除效果。实验分析了电压条件、Cr(Ⅵ)初始浓度、pH以及共存阴阳离子对水中Cr(Ⅵ)去除效率的影响，同时通过SEM、XPS、FTIR表征分析了GF/Sch电极材料反应前后的变化，从而探究电化学还原Cr(Ⅵ)的作用机理。实验确定了反应体系的最优条件，当电压为-2.0 V，pH为3.0时，电化学还原Cr(Ⅵ)的效果最佳，反应速率较快，反应体系中的Cr(Ⅵ)和总Cr的去除率分别达到了96.8%和95.2%。电极材料的循环稳定性测试中，连续运行5次后对电化学还原作用对反应体系中的Cr(Ⅵ)的去除率仍能达到82.0%。且反应体系对于铬的回收率能达到接近90%。

（3）通过化学负载的方法，以石墨毡作为基底负载施氏矿物获得一体化阳极电极材料，装载了浸没式电极反应器，探究了反应体系中电芬顿作用对抗生素的去除效果。实验以环丙沙星（CIP）为目标污染物，探究电压条件、CIP初始浓度、pH、电解质浓度以及常见的水质参数（COD、氨氮、氯离子）对CIP去除效率的影响，同时通过SEM、XPS表征分析了阳极电极材料反应前后的变化，并探究CIP降解的作用机理。实验确定了CIP降解的最优条件，当电压为2.0 V时，CIP的去除率达到了90%以上，TOC降解率达到了60%，电芬顿贡献占90%以上。此外，实验通过EPR测试以及猝灭实验探究明确了羟基自由基（• OH）、硫酸根自由基（SO₄ •-）以及超氧自由基（• O₂-）贡献率分别为56.8%、28.3%、14.9%。实验搭载的GF/Sch电芬顿体系对于四环素类、磺胺类以及基糖苷类抗生素四环素（TC）、磺胺甲噁唑（SMX）、替米考星（TIL）均展示出优异的降解效果（去除率可分别达到87.3%、56.3%、58.7%）。通过液质测试分析推断出电芬顿作用降解CIP主要是通过哌嗪环氧化和裂解、羟基化过程、脱氟、脱氨等途径实现降解。

综上，本研究通过施氏矿物的固定化电极制备和电场的耦合，证实了电场确实可以进一步增强施氏矿物对于水中污染物的去除；进一步制备的石墨毡负载施氏矿物一体化电极材料，在电化学吸附还原重金属和电氧化降解抗生素污染物中均展现出优异的性能，说明其对于不同的电化学净水过程具有较好的应用潜能。本研究通过新型电极材料的开发，以期为羟基硫酸铁矿物的深度应用提供新的方向，并为电化学净水提供新的途径。

关键词：施氏矿物；石墨毡；电化学；重金属；抗生素

WATER PURIFICATION EFFECTIVENESS OF GRAPHITE FELT SUPPORTED (GF/SCH) ELECTRODE 

ABSTRACT

Electrochemical water treatment technology is a comprehensive water treatment method that combines physical, chemical and electric fields. Unlike traditional water treatment technology that requires exogenous addition of chemical substances, the electrochemical water treatment process mainly relies on the direct transfer of electrons to achieve the purpose of pollutant degradation and removal, resulting in high treatment efficiency. Especially for low concentration of pollutants, electrochemical water treatment technology shows unique advantages. Electrode materials are the core of the electrochemical water treatment process. For the degradation of different pollutants, the development of electrode materials with high catalytic and mass transfer properties, and matching the appropriate electrochemical process, is an important research direction to realize water purification.

Schwertmannite (Sch), an iron hydroxysulfate secondary iron mineral widely found in acid mine drainage (AMD), has been shown to be an excellent heterogeneous Fenton catalyst due to its large sulfate and iron fractions. Meanwhile, due to the similarity of the pore size of the Schwertmannite and oxygenated anion (class) heavy metals such as hexavalent chromium (Cr(VI)) and arsenic (As), they exhibit excellent adsorption properties for heavy metals represented by Cr(VI) and As. However, Most of Schwertmannite used in the previous studies were prepared and utilized in the form of powder, which is difficult to recycle and reuse, and thus greatly limited in practical engineering applications. In addition, as an important class of iron-based materials, the introduction of electric field is expected to further enhance the adsorption and catalytic performance of Schwertmannite for pollutants. However, There have been few studies on the use of Schwertmannite as electrode materials, and how to immobilize Schwertmannite to achieve the introduction of electric field is an urgent scientific problem to be solved. In this study, a new type of graphite felt-loaded Schwertmannite-immobilized electrode was prepared using graphite felt as the substrate, and different electrochemical processes were matched to achieve efficient degradation of different types of pollutants, The preliminary results obtained are as follows:

The immobilized Schwertmannite electrode material was obtained by coating Schwertmannite directly onto the Graphite paper conductive substrate, and the electrochemically enhanced Cr(Ⅵ) removal performance in the reaction system was investigated by mounting an immersed electrode reactor. The effects of the loading amount of Schwertmannite and voltage conditions on the removal efficiency of Cr(Ⅵ) were investigated, and it was optimized that Schwertmannite could be better immobilized and had better electrical conductivity when Sch0.83-C(88%Sch 83% by mass of Schwertmannite in the coating material), and The best efficiency of electrochemical removal of Cr(Ⅵ) was achieved at an applied voltage of -2.0 V. The Cr(Ⅵ) was removed from the solution at a rate close to 40%. Under this optimal experimental condition, the removal of Cr(Ⅵ) by immobilized Schwertmannite was 11 times more effective than that under the unenergized condition.

(2) The integrated cathode electrode material GF/Sch with graphite felt as substrate loaded with Schwertmannite was successfully prepared by chemical loading method, and the removal effect of Cr(Ⅵ) by electroreduction was investigated in the submerged reaction system. The effects of voltage conditions, initial Cr(Ⅵ) concentration, pH, and coexisting anions and cations on the removal efficiency of Cr(Ⅵ) in water were analyzed, and the changes of GF/Sch electrode materials before and after the reaction were analyzed by SEM, XPS, and FTIR characterization, so as to investigate the mechanism of electrochemical reduction of Cr(Ⅵ). The optimum conditions of the reaction system were determined, and the best effect of electrochemical reduction of Cr(Ⅵ) was achieved when the voltage was -2.0 V and the pH was 3.0. The reaction rate was faster, and the removal rates of Cr(Ⅵ) and total Cr in the reaction system reached 96.8% and 95.2%, respectively. In the cyclic stability test of the electrode material, the removal rate of Cr(Ⅵ) in the reaction system by electrochemical reduction could still reach 82.0% after 5 times of continuous operation. The recovery rate of Cr(VI) in the reaction system was approaching 90%.

(3) The integrated anode electrode material GF/Sch with graphite felt as substrate loaded with Schwertmannite was successfully prepared by chemical loading method, and a submerged electrode reactor was loaded to investigate the removal of antibiotics by electro-Fenton action in the reaction system. The experiments used ciprofloxacin (CIP) as the target pollutant to investigate the effects of voltage conditions, initial concentration of CIP, pH, electrolyte concentration, and common water quality parameters (COD, ammonia nitrogen, and chloride ions) on the removal efficiency of CIP, and meanwhile, the changes of the anode electrode material before and after the reaction were analyzed by SEM and XPS characterization, as well as the mechanism of the action of the degradation of CIP was explored. The optimal conditions for CIP degradation were determined experimentally, and the removal rate of CIP reached more than 90%, TOC degradation rate of 60% has been achieved when the voltage was 2.0 V, with the electro-Fenton contribution accounting for more than 90%. In addition, the contributions of hydroxyl radicals (• OH), sulfate radicals (SO₄ •-), and superoxide radicals (•O₂-) were 56.8%, 28.3%, and 14.9%, respectively, as determined by the EPR test and bursting experiment. The GF/Sch electrofenton system demonstrated excellent degradation of tetracycline, sulfonamide, and basiglycoside antibiotics tetracycline (TC), sulfamethoxazole (SMX), and tilmicosin (TIL) (87.3%, 56.3%, and 58.7% removal, respectively). It was deduced from the liquid-quality test analysis that the degradation of CIP by electro-Fenton action was mainly achieved through piperazine epoxidation and cleavage, hydroxylation process, defluorination and deamination.

In summary, this study confirmed that the electric field could further enhance the removal of pollutants in water through the immobilized electrode preparation and coupling of Schwertmannite with the electric field; the graphite felt-loaded Schwertmannite integrated electrode materials further prepared showed excellent performance in electrochemical adsorption and reduction of heavy metals as well as in electro-oxidative degradation of antibiotic pollutants, which demonstrated that they have a good potential to be applied in different electrochemical water purification processes. It shows that it has good potential for different electrochemical water purification processes. In this study, through the development of new electrode materials, we aim to provide a new direction for the in-depth application of ferric hydroxysulfate minerals and a new way for electrochemical water purification.

key words: Schwertmannite;Graphite felt; Electrosorption; Heavy metal; Antibiotic

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