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抗生素的大量生产及滥用日益威胁着人类的健康,尤其由细菌耐药性引起的疾病感染,已在地表水、地下水、饮用水等水环境中检出[1]. 电芬顿技术因绿色、高效成为了具有前途和环境友好的抗生素治理技术. 与传统芬顿工艺不同,电芬顿技术不易产生铁泥、即产即用,阴极原位合成的H2O2可消除试剂运输存储风险,其参与芬顿反应产生的羟基自由基(·OH)标准氧化还原电位(E0=2.80 V)次于氟(E0=3.05 V)[2],可去除60%—100%的有机污染物[3]. 气体扩散电极(gas diffusion electrodes, GDEs)能高效累积H2O2的优选阴极,近年来已广泛应用于电芬顿降解水中有机污染物[4-6]. 因此,本综述主要概述了电芬顿基本原理, 并基于气体扩散阴极的改性和反应装置的优化这两个方面阐述如何对电芬顿技术进行改性以提升其对有机污染物的去除效率, 重点论述了基于气体扩散阴极的电芬顿工艺在去除水中抗生素的应用, 并在此基础之上展望了电芬顿发展趋势.
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电芬顿是基于传统芬顿改进而来的一项高级氧化技术,兼具传统芬顿和电化学两种方法的优势,而电芬顿法因能原位合成H2O2,已成为了电芬顿去除水中抗生素的研究热点. 电芬顿2法的基本原理是氧气或溶解氧在阴极表面的反应活性位点处发生两电子氧还原反应(oxygen reduction reaction, ORR)电合成H2O2,并与外加的Fe2+反应生成具有强氧化性的自由基(如∙OH),从而无选择性地去除溶液中的有机污染物,具体的反应方程式见式(1)–(4).
由上述方程式可知,H2O2原位累积量决定了电芬顿法中自由基(如∙OH)的生成总量及速率,继而决定电芬顿对水中有机污染物的去除效率. 因此,阴极上能高效电合成H2O2尤为关键,而对合成H2O2的选择性和氧传质是主要限速步骤,这可通过对气体扩散电极进行改进和优化反应装置来改善.
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在20世纪90年代,Brillas等首次报道了含有炭黑和聚四氟乙烯的GDEs可电生成H2O2,并进一步分解成HO∙和HO2∙氧化4-氯苯胺[7]. 随后,基于GDEs与不同阳极的组合,陆续研究了几种有机污染物的去除,包括苯胺[8]、2,4-二氯苯氧乙酸苯胺[9]等. 传统GDEs是一种薄膜状的多孔电极,由催化层、扩散层和基体组成,呈“三明治”结构[10]. 面向空气的一层为扩散层,其疏水多孔结构可在阻隔液体渗入的同时促使氧气扩散到电极内部的活性位点,而不是先通过溶解在电解质中再到达活性位点. 研究发现,气体扩散层的存在可有效提升H2O2生成速率,在给定电位下,仅依靠空气扩散的 H2O2产率比仅依靠溶解氧的高 0.9—12倍[11]. 面向电解液的一层则为催化层,该层含有丰富的催化活性位点和有利于反应物和产物转移的孔道,电子、氧气和质子在催化层的“气、固、液三相界面”发生ORR生成H2O2. 基体不仅能支撑扩散层和催化层,还能将电子传输到催化层上参与ORR过程,且内部存在有利于氧气到达催化层的孔道. 常用不锈钢网[12]、钛网[13]和镍网[14]等金属网作为基体.
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为进一步提高H2O2产量,研究者采用不同方法修饰传统GDEs,主要为以下三个方面:1)优化电极结构,包括催化层+扩散层+基体、催化层+基体和仅含催化层;2)选择导电性好、对H2O2分解作用小、廉价易得的材料作为基体,比如石墨毡、碳毡、碳布、泡沫镍、碳纤维、碳海绵、碳纸等;3)修饰催化剂,比如引入碳纳米管、乙炔黑、多孔碳等其他碳成分,或者杂原子掺杂修饰及负载金属或金属氧化物等.
(1)优化电极结构
传统GDEs结构主要以基体为支撑中心,两侧分别黏合催化层和扩散层,基于此结构的GDEs在长期使用过程中易发生“水淹”,易使电极催化性能降低[15]. 鉴于此,研究者开发了一种由催化层和基体组成的改进GDEs,其催化层亦可作为气体扩散层,不同制备方法也已被报道,如超声浸渍[16]、轧制[17]、热压制[18]、涂刷[19]和电沉积[20]等. 例如Pan等[20]通过浸渍法将碳纳米管、炭黑和聚四氟乙烯负载到石墨毡的四周及内部,与石墨毡相比,改性石墨毡表现出更高的H2O2生成量. 另外,仅含催化层的一体式GDEs也被报道,不同于传统GDEs,一体式GDEs的催化层兼具催化、扩散及支撑作用. Su等[21]将石墨粉、脱脂棉和PTFE混合压制成矩形片状,在-1.1 V下反应60 min产生567 mg·L−1 H2O2,电流效率为86.7%,热处理炭化脱脂棉可起到造孔作用,削弱氧传质阻力,从而提高H2O2的产率.
(2)选择不同基体
GDEs常见的基体包括不锈钢网、镍网或钛网等金属材质,而一些具有较大的三维活性表面、商业可用性广及易获取的材质,如石墨毡[22]、碳布[23]、泡沫镍[14]、碳海绵[24]、碳纸[25]等经过适当处理后也被用作基体. Yu等[16]采用炭黑(carbon, CB)和聚四氟乙烯(polytetrafluoroethylene,PTFE)对石墨毡进行改性修饰,其H2O2产率是未改性石墨毡的10.7倍,且性能稳定. 已报道的工作中也观察到类似的效果. Pérez等[26]通过气刷法将CB沉积在碳布表面,通过平行板流失电化学装置测试H2O2电合成量,结果表明沉积前后H2O2生成量相差18.5倍,在120 min后改性前的累积浓度约为45 mg·dm−3,而沉积 CB 的碳布累积浓度高达831 mg·dm−3. Guo等[27]通过加热凝固CB-PTFE混合液,最终通过马弗炉固化成圆形块体的集成电极.
(3)修饰催化剂
电芬顿过程中,ORR的弱选择性会使得阴极合成H2O2能力差. 为提高催化效果,不同碳材料已被引入GDEs中催化电合成H2O2. Pan等[28]为了提高石墨毡的电催化氧还原活性,使用炭黑和多壁碳纳米管作为催化剂,共同发挥催化还原作用. 同样,Yu等[29]也发现同时负载碳纳米管和炭黑的石墨毡电催化H2O2的能力提高了20倍左右. 在酸性介质中将O2电还原为H2O2涉及溶解氧在活性位点的吸附和单个吸附的反应中间体*OOH的形成,进而接受质子和电子产生H2O2,而在氧气或 *OOH中保持 O—O 键的倾向决定了 ORR 的选择[30]. 为了提高氧气和OOH中间体的吸附形式和结合能力,杂原子掺杂(如N)是较优选项,因为相比于C原子,N原子的电负性更大. Zhu等[31]将N、S原子引入碳基阴极,氧气通过 N 掺杂调节电子性质来实现吸附,而OOH 结合能力通过 S 掺杂改变自旋密度来调节. 结果表明,经由N、S 共掺杂优化后,H2O2累积量提高了42.47%. 碳材料中的N含量显着影响 ORR 催化活性,诸多研究表明,不同的活性N含量、C官能团含量均对起始电位存在一定影响. 例如石墨N、吡啶N和吡咯N等对H2O2产量存在不同影响. Gao等认为,高含量的石墨N和吡啶N有利于增强ORR活性[32]. 石墨N是2e-途径中产生H2O2的主要活性位点,石墨N含量和H2O2产量存在线性关系,与∙OH浓度之间线性关系较差. 而吡啶N相反,与∙OH浓度之间存在一定的线性关系,与H2O2浓度的线性关系更好. 石墨N主要是通过促进O2在ORR的2e-过程中产生H2O2,吡啶N进一步催化H2O2形成可降解有机物的∙OH,其含量也可提高催化剂的起始电位[33]. 吡咯N则主要影响4e-途径[34-35]. 另外,也有报道称可利用金属纳米结构修饰不同的碳基材料来提高碳的ORR 选择性,包括CoPc [36]、W@Au纳米颗粒[37]和ZrO2纳米颗粒[38]等. 近5年内GDEs产H2O2的研究见表1.
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GDEs是决定H2O2产量的首要因素,因此大部分研究主要围绕阴极性能的优化展开. 相比之下,反应装置的相关研究报告较少,而它对于GDEs发挥产H2O2性能以增强电芬顿技术去除有机污染物的效率至关重要. 因此,总结近年来研究甚广的7种反应装置,其结构示意图如图1所示.
装置1为浸没式,即电极均浸没于溶液中,为了提高阴极表面溶解氧含量,研究者通过空气泵在阴极周边供氧,以提高阴极合成H2O2的能力. 比如,Zhou等[48]通过在GDEs周边曝气增加H2O2产量,从而提高染料去除率. Tian等[49]基于装置1,以罗丹明B为目标污染物,发现以GDEs为阴极的去除率优于非GDEs,可达98%以上;同样,Zhou等[50]也提出类似电芬顿体系可矿化51.4%的对硝基苯酚. 但该装置极大受限于水中溶解氧含量及传质效率的影响,H2O2合成效率低.
装置2—7均为空气扩散式,即电极一侧与液面接触,另一侧与空气接触,氧气通过电极内部进入固-液反应位点,构成水、气、固三相反应界面,从而高效电合成H2O2. 空气扩散式摆脱了水中溶解氧的限制,其H2O2的产量可达浸没式的8倍[51]. Brillas等[7]将GDEs置于聚丙烯空心圆柱形支架底部,然后将其浸入溶液中使电极下表面与液体接触,并将0.06 L·min−1的O2通过空心圆柱流过与空气接触的电极上表面,如装置2所示. 这种装置充分发挥了GDEs产H2O2性能,装置简易,易操作. 已有研究者以该装置为电芬顿阴极,探究∙OH的合成效率[52]和有机污染物的去除性能,如阿替洛尔[53]、甲基橙[54]和酒石黄[55]等. 另有研究者基于装置2设计了一种带有内置空气扩散器的圆柱形的反应装置,在电芬顿体系下运行 180 min 后,可实现矿化80%的电子废水[4]. 除此之外,装置3,即将GDEs壁式固定于气体室一侧的反应装置,也被设计出来以高效产H2O2[56],并进一步用在电芬顿体系中去除苯酚[51]、布洛芬[57]. 不同于装置2垂直放置,装置3采用传统方式平行放置阴极和阳极,传质阻力小,H2O2产率高[55]. 但是,壁式固定的GDEs容易出现不同高度水压差造成的液体渗漏问题,因此在不宜用于过高的容器中. 流通反应装置已被证明可以克服间歇反应装置中传质受限和污染物去除效率低的问题[58],是提高电芬顿对有机污染物去除性能的不错选择. Moreira等[59]设计了一种带有气体室的流通反应器,阴极一侧与气体室连接并通过气泵向室内泵入气体,而另一侧则与电解液接触,如装置4所示. 这种流通式装置可以增强反应物之间的接触面,传质效率高,若选择高∙OH转化率的阴极,其污染物去除性能将优于装置2和装置3,是一种具有开发前景的反应装置. 基于该装置的电芬顿体系中,以金属氧化物为阳极,GDEs为阴极,最佳条件下可在180 min内去除20 mg·L−1的甲氧苄啶. 基于流通反应装置的电芬顿体系也得到广泛研究,包括甲基橙[60]、2,4-二氯苯酚[61]、橙黄II [62]、过氧乙酸[63]、2,4-二氯苯氧乙酸[64]等有机污染物的去除性能研究. 氧气是保证GDEs充分发挥产H2O2性能的基本保障,为了让GDEs在使用过程中有足够的氧来源,往往会在GDEs一侧设置气体室并充入氧气,这样便会增加曝气能耗(约64.1 kWh·kg−1)[22],从而增加运行成本,不利于实际应用. 因此,无需曝气的反应装置便应运而生,如装置5,将GDEs紧贴于反应器一侧,在无需曝气情况下,GDEs利用空气中的氧气高效合成H2O2 [22],并在电芬顿体系下有效降解2,4-二氯苯氧基乙酸 [65]. 同样,将GDEs置于电解液表面,一侧与空气接触,另一侧与液体接触的装置6也能消除曝气成本. 比如将电极固定在液面上方 [27]或者漂浮在电解液[13]均能高效产H2O2并降解有机污染物,如微污染物[66]、苯[67]、磺胺二甲基嘧啶[68]等. 装置5和装置6均采用自然空气代替气泵注入的空气,极大缩减了运行成本,装置简单,与装置3和装置2 相比,更易于规模化. 但是,装置5同装置3一样受水压限制,不适用深度过深的水体,使用时应注意阴极材料承压能力和装置密封性. 装置6采用漂浮式GDEs,无耐压和密封性问题,比装置5更易操作,应用范围较广,但是对阴极具有选择性,一般选用具有浮力的轻质材料或者疏水性的硬质材料. 装置7则是引入文丘里管射流器,当液体流过射流器缩小的过流断面时,流速增大并伴随流体压力降低,因此射流器喉部会产生吸力,将空气引入水流中,且流速增大,使气泡在高剪切速率下破碎成小块,一部分溶解到水中,使氧气达到饱和,其余部分则以气泡的形式存在,这样可使水中溶解氧在短时间内达到过饱和状态,从而保证GDEs有充足的氧气合成H2O2[69-71],该装置在电芬顿中可去除60%—80%的酸品红、罗丹明B、茜素黄R、橙Ⅳ和双氯芬酸[72]. 装置7和装置4均属于流通式反应器,具有较小的传质阻力,但装置7采用了文丘里装置代替曝气设备供氧,运行成本更低,有利于实际应用的开发. 与无需曝气的装置5和装置6相比,装置7结构较为复杂,在规模化生产方面还有待提高.
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药物生产和消费长期以高于全球人口增长率的速度稳步增长,一般经由未使用的废物、人和动物的排泄物等形式进入周边环境[73]. 药物在环境中的持久性、传播速度和在生物圈中积累的能力各不相同. 然而,它们的高生物活性表明这些药物即使是微量的,也可能导致生物圈发生重大变化[74]. 电芬顿作为研究甚广的高级氧化技术,能产生强氧化性∙OH消除水中有机污染物. 电芬顿对水中抗生素的去除已得到广泛研究,包括磺胺类、喹诺酮类、β-内酰胺类和四环素类等四大类抗生素.
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磺胺类抗生素是最早的抗菌药物,在养殖、医疗、工业等领域已得到广泛应用,它可通过干扰细菌或原生动物的二氢蝶酸合酶和二氢叶酸还原酶,以此达到抗菌效果[75]. 然而,过量使用抗生素会导致其未消纳的部分在水环境中残留,包括养殖废水、沟渠水、湿地水等地表水和地下水[76]. 这些残留的抗生素对各营养级的水生生物造成了不同程度的生态毒性,比如作为初级生产者的藻类比鱼类和甲壳类动物更容易受磺胺类抗生素的影响[77]. 为了从源头上消除抗生素的影响,高效去除有机污染物的电芬顿技术已被作为治理技术用于去除磺胺类抗生素. 表2汇总了近几年基于GDEs的电芬顿体系对磺胺类抗生素的去除效果,主要涉及了甲氧苄啶、磺胺、磺胺甲基嘧啶、磺胺二甲基嘧啶、磺胺甲噁唑、磺胺氯哒嗪、磺胺噻唑和磺胺甲氧嘧啶等8种磺胺类药物. 在不同反应条件和电极组合下,磺胺类抗生素的单位电流去除率为0.3—11.8 mg∙(min∙A-1)−1. 且在同一电芬顿系体下,磺胺类抗生素去除效果存在差异,比如磺胺氯哒嗪>磺胺甲噁唑>磺胺甲基嘧啶>磺胺[27],这与磺胺类抗生素的分子结构有关. 其中,绝对硬度是衡量污染物降解难易的指标之一,绝对硬度越大越难降解,3种磺胺类抗生素绝对硬度大小为磺胺二甲基嘧啶>磺胺噻唑>磺胺嘧啶,实验同步证明磺胺二甲氧嘧啶分子最稳定(0.3 mg∙(min∙A−1)−1),而磺胺嘧啶最容易降解(0.8 mg∙(min∙A−1)−1)[31]. 除此之外,电芬顿体系中pH值、污染物初始浓度、H2O2产量及催化剂量均对磺胺类抗生素的去除性能产生影响,比如由施加电流决定的H2O2产量,施加电流控制阳极和阴极之间的电子转移,并进一步影响H2O2的产生和活化. 磺胺二甲基嘧啶的去除率先随着施加电流的增加而增加,随后趋于平稳,产生这一现象的原因可能是过高的电荷嘧啶和H2O2引起了引发本体溶液中的一些副反应,如阳极析氧、阴极析氢和过量H2O2消除∙OH [68]. 为了更进一步了解磺胺类抗生素的去除机理,Deng等[6]采用LC-MS/MS对磺胺甲基嘧啶的中间产物进行鉴定,推导出3条主要降解路径:1)通过∙OH攻击取代氨基中的氢;2)S—N键通过活性物质氧化裂解; 3)S—C键通过活性物质氧化裂解. 最后,通过上述3种途径形成的副产物进一步的氧化以破坏苯环,直到形成短链酸或CO2、H2O.
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β-内酰胺类抗生素一直是最广泛使用的抗菌药物,主要分为青霉素类和头孢类. 阿莫西林是一种α-氨基取代的β-内酰胺类抗生素,属于青霉素类,常用于治疗由革兰氏阴性和革兰氏阳性菌引起的细菌感染[80]. 与其他药物相比,阿莫西林在人体中的新陈代谢率较低,约有80%—90% 被排出体外,常常以未经修饰的形式释放到环境中并被检出[81]. 阿莫西林具有化学稳定性、高毒性和低生物降解性,传统的生物降解技术难以完全分解,因此,迫切需要有效的水处理技术. 已有研究者以阿莫西林为模型污染物,探究电芬顿技术对该抗生素的去除效果,详见表3. 研究者选择了具有强大的两电子氧还原能力和高H2O2产率的GDEs为阴极,探究均相电芬顿体系下阿莫西林的去除效果,其单位电流去除率为2.2—8.2 mg∙(min∙A−1)−1. 从表3可以看出,当反应条件相同时(阿莫西林初始浓度、pH值和Fe2+浓度),不同GDEs电芬顿体系的阿莫西林去除率存在差异. 当H2O2产率约为2.65 mg∙(L∙min−1)−1时,单位电流去除率为4.6 mg∙(min∙A−1)−1 [14],而H2O2产率约为1.53 mg∙(L∙min−1)−1时,单位电流去除率则为2.2 mg∙(min∙A−1)−1 [82]. H2O2产率越高,阿莫西林去除性能越好. 这可能是不同H2O2产率所引起的,因为H2O2 合成速率的提高有助于∙OH的快速生成并缩短阿莫西林的降解时间. 另外,通过使用LC-MS/MS对阿莫西林降解中间产物进行定性分析,可以得知阿莫西林的降解主要是受∙OH的攻击 [14].
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喹诺酮类是第三大抗生素类,占全球市场份额的 17% [83],这类药物已在医院、养殖、制药及城市废水中检出[84]. 喹诺酮类抗生素化学稳定性强且耐高温和水解,同时广泛的抗菌谱可能导致细菌耐药性的增加. 环丙沙星是消耗率高的喹诺酮类抗生素之一,其同样稳定性高且不易生物降解,是污水厂出水检出频率最高的一种抗生素[85],因此常被选作模型污染物以开发有效的治理技术. 目前对环丙沙星的去除包括均相电芬顿技术[86]和非均相电芬顿技术[87],这些技术均在确保H2O2合理充足的条件下展开的,因为过量的H2O2则会引起∙OH消耗反应,使∙OH无法充分参与环丙沙星降解反应,还会浪费不必要的能耗. 其中,非均相电芬顿技术是为了解决均相体系易产生铁泥而开发的,但由于传质效率低等因素限制,非均相体系的去除速率(0.1 mg∙(min∙A−1)−1)仍低于均相体系(0.5 mg∙(min∙A−1)−1),但开发高效的非均相电芬顿技术是往绿色氧化技术发展的不二选择. 另外,了解电芬顿技术的实际可行性有助于该技术的应用. 研究表明,实际水体中的天然有机物和阴离子(HCO3-、Cl-、H2PO4-)可促进环丙沙星降解过程中的抑制反应或替代降解途径,影响着环丙沙星的消除及矿化,尽管如此,GDE非均相电芬顿体系仍能在90 min内完全去除不同水基质中的环丙沙星,具有广阔的应用前景[87]. 除此之外,左氧氟沙星、恩诺沙星、诺氟沙星等其他喹诺酮类抗生素也被选作模型污染物,单位电流去除率为0.4—3.2 mg∙(min∙A−1)−1,详见表4.
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四环素作为一种广谱抗生素,也被广泛应用于医药、畜牧、水产等行业. 近年来其在水环境中频繁检出,导致产生对人类健康和生态系统构成严重威胁的抗生素抗性细菌或病原体[91]. 电芬顿技术已被证实是一种最有吸引力的四环素降解技术. Fang等[40]基于多孔碳、CB和PTFE制备了一种新型的GDEs,并自制FeS2,探究在H2O2产量充足条件下(7.27 mg∙(h∙cm−2)−1),非均相电芬顿对四环素的矿化效果. 结果表明,FeS2耦合MoS2和WS2的复合催化剂可100%去除50 mg·L−1的四环素,同时TOC矿化率可达81.3%. 助催化剂MoS2和WS2可加速Fe2+/Fe3+循环,最终增强∙OH自由基,进而提高四环素的降解. 在 MoS2和WS2催化下,H2O2在20 min内可快速分解,几乎达98.10%和96.48%,但单一的FeS2在40 min内仅92.88%的H2O2被分解. 由此可知,助催化剂的使用对高产H2O2的电芬顿体系是一个不错的选择,提高了污染物的去除效率,具有实际可行性. 考虑到非均相铁基催化剂传质慢等问题,有研究者试图将Fe负载到GDEs上,同步实现H2O2合成及∙OH的产生,制备具有多功能特性的阴极材料. Cui等[92]通过一步溶剂热法制备了负载Cu和Fe的高稳定性和高活性双功能集成碳质材料,Cu的引入使得大量电生成的H2O2立即分解为∙OH,使得Cu/Fe-GDE阴极表现出不错的去除性能,5次循环氧化实验中对四环素去除率均达80%. 虽然Cu/Fe-GDE具有促进Fe2+/Fe3+循环和H2O2分解为∙OH的功能,但是过量H2O2也会因副反应的产生降低四环素的去除性能. 由于四环素结构复杂,进一步使用LC-MS/MS鉴定四环素反应中间体,并提出4条潜在的降解途径. 表5汇总了基于GDEs的电芬顿技术对四环素类抗生素的去除情况.
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目前为止,GDEs因自身的独特性质,成为了电芬顿技术中电合成H2O2和降解抗生素的高效阴极. 本文综述了GDEs作为阴极通过两电子氧还原产生H2O2及其去除水中抗生素的应用,包括GDEs的原理、结构及材料改性,并总结了 GDE 产H2O2的相关反应器装置. 对于GDEs 在电芬顿中对水中常见的磺胺类、喹诺酮类、β-内酰胺类及四环素类等检出频率高、检出浓度大、生物效应强等四大类抗生素的降解和矿化也进行了描述和分析. 总体而言,由于GDEs在电合成H2O2和水处理方面具有高的氧气利用率和低能耗优势,因此以 GDEs 作为阴极的电芬顿技术是一种很有前途的水处理方法. 然而,在实际应用中,当其的研究仍然存在一些挑战.
(1)活化H2O2产生活性氧化物是限制基于GDEs的电芬顿技术在实际废水治理中的关键因素. 目前的GDEs大部分侧重于H2O2的合成,缺少H2O2转化为∙OH的研究,这与阴极铁还原性能有关,而GDEs本身铁还原能力较弱,未来需要进一步设计兼具高效合成H2O2和催化H2O2分解成∙OH的多功能阴极,如使用掺杂助催剂Cu的 GDEs 来增强铁还原性能以提高自由基生成率.
(2)侧面放置GDEs、GDEs漂浮于水面和增设文丘里装置是目前直接利用空气中的氧气产生H2O2来最大限度地降低能耗成本的反应器. 然而,为了获得高效稳定的H2O2,可对现有装置进行优化,开发装置简单,操作方便,传质阻力小且易规模化应用的反应器,尤其是能增加反应物接触面的流通式反应器,在一定程度上可提高反应效率. 尤其,对抗生素含量低的实际废水是一个不错的选择.
(3)在实验室研究中,建议根据实际情况进行更多的优化,例如低浓度的电解质(如Na2SO4、NaNO3)和抗生素. 更现实的条件有望为水处理的实际应用提供更直接的指导. 太阳能电芬顿和微生物电芬顿技术可以降低能源消耗和经济成本,因此建议将这些工艺结合到实际的废水处理中,特别是在未来的碳中和社会中.
基于气体扩散电极的电芬顿技术去除水中抗生素的研究进展
Research progress on antibiotics removal in wastewater by electro-Fenton based on gas diffusion electrodes
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摘要: 最大限度地减少抗生素对环境的负面影响是一项巨大的挑战,而高效产H2O2的气体扩散电极(gas diffusion electrodes,GDEs)在电芬顿技术去除水中抗生素中具有很大的需求. GDEs作为电芬顿阴极对H2O2的电合成有更高的氧利用率、低能耗和高成本效益,已在抗生素废水处理的关键基础研究中得到了很好的发展. 在本文中,介绍了电芬顿-H2O2法的基本原理,重点关注了GDEs作为电芬顿阴极的研究现状,并着重分析改性方式. 同时,对GDEs与反应器装置组合的H2O2合成效率进行总结. 此外,研究了通过GDEs高效合成H2O2的电芬顿体系对水中磺胺类、喹诺酮类、β-内酰胺类和四环素类等四大类抗生素的去除效果和降解机制,为GDEs应用于电芬顿体系的深入研究提供参考. 最后,分析和展望了GDEs在H2O2生产和水处理的应用前景.Abstract: Minimize the negative impact of antibiotics to the environment is a huge challenge, high efficiency H2O2 production of gas diffusion electrode (GDEs) is in great demand for the removal of antibiotics from water by electro-Fenton technology. As an electro-Fenton cathode, GDEs has a higher oxygen utilization rate, low energy consumption and low costfor the electrosynthesis of H2O2. Ithas been well developed in the key basic research of antibiotic wastewatertreatment. In this review, we introduce the basic principle of electro-Fenton-H2O2 method, focus on the research status of GDEs as electro-Fenton cathode, and analysis the modification methods of cathode. At the same time, the H2O2 synthesis efficiency of GDEs combined with reactor unit was summarized. In addition, we studied the removal effect and degradation mechanism of sulfonamides, quinolones, β-lacamides and tetracyclines in water by electro-Fenton system with high efficiency synthesis H2O2 by GDEs, so as to provide a reference for further study of the application of GDEs in electro-Fenton system. Finally, the application of GDEs in H2O2 production and water treatment is analyzed and prospected.
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Key words:
- electro-Fenton /
- air diffusion cathode /
- hydrogen peroxide /
- antibiotics
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表 1 近5年内GDEs产H2O2的研究
Table 1. Studies on H2O2 production by GDEs in recent five years
电极类型
Electrode运行参数
Operating parameterH2O2产量(时间)
H2O2 yield (time)参考文献
References硝酸修饰CB-PTFE-不锈钢网 3 mA·cm−2,O2=2 L·min−1 104 mg·L−1 (120 min) [39] N/S修饰CB-PTFE-不锈钢网 25 mA·cm−2,O2=0.4 L·min−1 7.95 mg·(h∙cm−2)−1(150 min) [31] N修饰PC/CB-PTFE-不锈钢网 20 mA·cm−2,O2=0.6 L·min−1 546.82 mg·(h∙cm−2) −1(120 min) [40] CNT-PTFE-不锈钢网 7 mA·cm−2,O2=0.4 L·min−1 118.2 mg·L−1 (90 min) [41] 叔丁基蒽醌-CNT-PTFE-不锈钢网 7 mA·cm−2,O2=0.4 L·min−1 150.6 mg·L−1 (90 min) [41] AC-PTFE-不锈钢网 −0.8 V vs Ag·AgCl,O2=0.07 L·min−1 70 mg·L−1 (120 min) [41] CB-PTFE-镍网 7.2 mA·cm−2 3.17 mg·(h∙cm−2)−1 (150 min) [14] CoS2/MWCNT-GDE 100 mA·cm−2,O2=0.5 L·min−1 56.9 mmol·L−1 (180 min) [42] Gr/CNT-海绵 -1.3 V vs SCE,O2=2.5 L·min−1 376 mg·L−1 (60 min) [43] CB-PTFE-海绵 -2 V vs Ag/AgCl 177.9 mg·L−1 (90 min) [13] NCB/CNT-PTFE-活性碳布 57 mA·cm−2,O2=1.5 L·min−1 42.15 mg·(h∙cm−2)−1 (120 min) [23] PC-全氟化树脂-活性碳毡 20 mA·cm−2 8.5 mg·(h∙cm−2)−1 (120 min) [44] Gr-全氟化树脂-碳布 1.25 mA·cm−2,O2=0.2 L·min−1 2.81 mg·(h∙cm−2)−1 (120 min) [45] MWCNTs/CB-PTFE-石墨毡 12 mA·cm−2,O2=0.6 L·min−1 309 mg·L−1 (120 min) [28] CB-PTFE-石墨毡 240 mA·cm−2 101.67 mg·(h∙cm−2)−1 (120 min) [22] N-Gr/CB-PTFE-石墨毡 7 mA·cm−2,O2=0.3 L·min−1 301.252 mg·L−1 (120 min) [46] 2%二甲基硅油/CB-PTFE-石墨毡 110 mA·cm−2,O2=0.1 L·min−1 131.3 mg·L−1 (120 min) [47] Gr-PTFE-脱脂棉 -1.1 V vs SCE,O2=2 L·min−1 567 mg·L−1 (60 min) [21] CB-PTFE 4 mA·cm−2 345 mg·L−1 (60 min) [27] 表 2 磺胺类抗生素的去除
Table 2. Removal of sulfonamide antibiotics
目标污染物
Targeted contaminants
运行参数
Operating parameters
去除性能/(mg∙(min∙A−1)−1)
Removal property
参考文献
References
甲氧苄啶
20 mg∙L−1阳极:BDD,阴极:GDE,
Fe2+=20 mg∙L−1,pH=32.7 [59] 磺胺
239 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.5 mmol∙L−1,pH=38.0 [78] 磺胺嘧啶
10 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.2 mmol∙L−1,pH=30.8 [31] 磺胺噻唑
10 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.2 mmol∙L−1,pH=30.5 [31] 磺胺二甲氧嘧啶
10 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.2 mmol∙L−1,pH=30.3 [31] 磺胺二甲基嘧啶
193 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.5 mmol∙L−1,pH=31.2 [79] 磺胺二甲基嘧啶
14 mg∙L−1阳极:DSA/RuO2–IrO2,阴极:GDE
Fe2+=0.3 mmol∙L−1,pH=38.0 [68] 磺胺二甲基嘧啶
84 mg∙L−1阳极:DSA/RuO2–IrO2,阴极:GDE
Fe2+=0.3 mmol∙L−1,pH=33.5 [68] 表 3 β-内酰胺类抗生素的去除
Table 3. Removal of β-lactam antibiotics
目标污染物
Targeted contaminants
运行参数
Operating parameters
去除性能/(mg∙(min∙A−1)−1)
Removal property
参考文献
References
阿莫西林
50 mg∙L−1阳极:MMO,阴极:GDE
Fe2+=0.3 mmol·L−1, pH=34.6 [14] 阿莫西林
50 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.3 mmol·L−1,pH=32.2 [82] 阿莫西林
100 mg∙L−1阳极:Ti/SnO2-Sb,阴极:GDE
Fe2+=0.5 mmol·L−1,pH=38.2 [28] 表 4 喹诺酮类抗生素的去除
Table 4. Removal of quinolone antibiotics
目标污染物
Targeted contaminants
运行参数
Operating parameters
去除性能/(mg∙(min∙A−1)−1)
Removal property
参考文献
References左氧氟沙星
68.3 mg∙L−1阳极:Ti/RuO2–IrO2,阴极:GDE
Fe2+=0.2 mmol·L−1,pH=30.4 [86] 环丙沙星
30 mg∙L−1阳极:镀铂钛板,阴极:GDE
Fe2+=0.1 mmol·L−1,pH=2.50.5 [88] 恩诺沙星
158 mg∙L−1阳极:BDD,阴极:GDE
Fe2+=0.5 mmol·L−1,pH=33.9 [89] 环丙沙星
10 mg∙L−1阳极:DSA,阴极:OCNTs/FeOCl@NGDE,
pH=30.1 [87] 诺氟沙星
31.9 mg∙L−1阳极:BDD,阴极:CoFe-LDH@GDE,
pH=33.2 [90] 表 5 四环素类抗生素的去除
Table 5. Removal of terracycline antibiotics
目标污染物
Targeted contaminants
运行参数
Operating parameters
去除性能/(mg∙(min∙A)−1)
Removal property
参考文献
References
四环素
50 mg∙L−1阳极:Pt,阴极:GDE
FeS2=0.75 g,pH= 77.4 [40] 四环素
50 mg∙L−1阳极:Ti/RuO2–IrO2,阴极:Cu/Fe-GDE,
pH= 31.3 [92] 四环素
20 mg∙L−1阳极:Pt,阴极:CuFeO2-NO/PBC-GDE,
pH= 50.07 [93] 四环素
20 mg∙L−1阳极:DSA,阴极:GDE
Fe2+=0.3 mmol·L−1,pH= 32.1 [72] -
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