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有机废水具有色度高、毒性强和难处理等特点,可导致严重的环境污染问题[1-4]。在有机废水的处理技术中,高级氧化技术(AOPs)能够产生强氧化性羟基自由基∙OH(E0=2.80 V vs. SHE) [5],可有效降解和矿化各种有机污染物,因而备受青睐[6]。其中,电芬顿技术凭借其环境清洁、避免H2O2药剂投加以及易于实现自动化控制等优点,在AOPs中脱颖而出,被广泛研究[7-8]。
电芬顿过程主要包含2个阶段:H2O2的产生和活化阶段[8]。H2O2的产生主要利用O2的2电子还原反应[9](式(1));而H2O2活化则是依靠Fe2+、Fe2O3等芬顿/类芬顿催化剂,激发生成∙OH [7,10](式(2)~式(3))。在均相芬顿系统中添加适量的Fe2+离子时,由于Fe2+激发H2O2速率远大于H2O2产生速率,使得氧还原反应是电芬顿过程的限速步骤[6]。因此,提高O2的2电子还原产H2O2性能成为电芬顿降解有机污染物的关键。
在电芬顿系统中,产H2O2电极普遍用碳材料制备而成,包括炭黑、活性炭、碳纳米管和石墨烯等,这些碳材料具有成本低、导电性好和催化活性高等优点,被广泛用作氧还原反应中的催化剂[11-12]。在2电子氧还原过程中,阴极氧还原性能受限于常温常压下水中极低的饱和溶解氧(DO)浓度(8.1~8.5 mg·L−1)[13]和缓慢的氧气传质过程(2.70×10−5 m·s−1) [14]。为此,除了常规曝气外,单一浸润性阴极[11,15-16]亦被广泛研究,借助气/液/固三相界面,极大地改善了氧气传质过程,提高了电极产H2O2性能。其中,疏水性阴极普遍由碳材料和粘结剂聚四氟乙烯(PTFE)制得,当粘结剂更换成聚偏氟乙烯(PVDF)和N, N−二甲基乙酰胺(DMA)混合物时可制得亲水性阴极。
以三相界面为基础,本课题组制备了非对称湿润性的半亲半疏阴极[17],有效解决了氧气的传质限制,同时也极大地提高了氧气利用率(37.4%),远高于传统曝气式产H2O2系统(<1%)[11, 18]。而在曝气式电芬顿工艺降解有机污染物过程中,仍然存在着氧气传质限制和低效利用的问题[19],因此,我们尝试将半亲半疏阴极引入电芬顿系统,并探究该系统对有机污染物的去除效果。本研究分别制备了亲水阴极、疏水阴极和半亲半疏阴极,用于均相电芬顿系统中降解有机污染物。首先对3种电极分别进行了结构表征和电化学性能测试,进而探究了阴极浸润性对目标污染物罗丹明B去除效果的影响,并考察了阴极电势和曝气速率对半亲半疏阴极去除罗丹明B性能的影响。
半亲半疏阴极催化电芬顿工艺去除罗丹明B的性能
Performance of electro-Fenton oxidation with the Janus electrode on rhodamine B removal
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摘要: 为解决传统曝气式电芬顿系统中氧气的传质限制和低效利用问题,利用石墨毡疏水化处理与催化剂涂覆的方法制备了一种非对称浸润性的半亲半疏阴极,且对半亲半疏阴极进行了结构表征和电化学性能测试,考察了阴极浸润性、阴极电势和曝气速率对有机污染物去除的影响。结果表明:在−0.4 V (vs. Ag/AgCl)和6 mL·min−1的曝气速率下,半亲半疏阴极在32 min内的罗丹明B去除率高达89.4%,是亲水阴极的8.0倍和疏水阴极的2.2倍,这主要得益于疏水化石墨毡基底的良好O2储存能力以及亲水催化剂层的较大电化学活性面积。Abstract: To address the problems of oxygen mass transfer limitation and low O2-utilization efficiency in conventional aeration-based electro-Fenton (EF) system, the Janus cathode with asymmetric wettability was successfully fabricated by hydrophobic treatment of graphite felt and catalyst coating. Its structure characterization and electrochemical performance test were performed, and the effects of wettability, cathode potential and aeration rate on organic pollutants removal were also investigated. The result showed that at the potential of −0.4 V and the aeration rate of 6 mL·min−1, the removal rate of rhodamine B was 89.4% in the reactor with Janus cathode, which was 8.0 times that with hydrophilic cathode and 2.2 times that with hydrophobic cathode. This good organics removal performance of Janus cathode was attributed to the excellent O2 storage ability in three-dimensional hydrophobic graphite felt substrate and large electrochemical active area in hydrophilic catalyst layer.
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Key words:
- electro-Fenton /
- janus cathode /
- rhodamine B
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表 1 不同浸润性阴极的液体接触角
Table 1. Liquid contact angle of different wettability cathodes
阴极名称 阴极组成 液体接触角/(°) 半亲半疏阴极 疏水气体储存层 116.4 亲水催化剂层 72.7 亲水阴极 原始石墨毡基底 76.3 亲水催化剂层 81.4 疏水阴极 疏水气体储存层 118.2 疏水催化剂层 136.7 -
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