曾煜丰,牛梦洋,陈 平,邱燕楠,林弋杰,肖震钧,方 政,余宗舜,林紫封,罗 锦,吕文英,刘国光

PTCN/CaO2/vis体系降解海水养殖废水中CIP:机理与归趋

曾煜丰,牛梦洋,陈 平*,邱燕楠,林弋杰,肖震钧,方 政,余宗舜,林紫封,罗 锦,吕文英,刘国光**

(广东工业大学环境科学与工程学院,广东省环境催化与健康风险控制重点实验室,粤港澳污染物暴露与健康联合实验室,广东 广州 510006)

本文拟建立掺磷管状氮化碳(PTCN)/CaO2/可见光(vis)体系,将其应用于海水养殖废水中处理目标污染物环丙沙星(CIP),并探究该体系反应机理及抗生素CIP的环境归趋.实验结果表明,PTCN/CaO2/vis体系具备良好的抗生素降解能力,在实验条件下CIP的表观降解速率常数obs为7.15×10-2min-1;单因素实验表明,在酸性条件下,体系表现出更强的CIP降解效能,水中共存因子对体系降解CIP存在一定的影响;同时,体系降解污染物能力随CIP浓度降低而逐渐增强;此外,该体系表现出优异的可循环性能,PTCN在5次循环后,CIP的降解率仍能保持82.5%.体系降解CIP过程中,活性物质O2·-占主导地位,1O2和h+这两种活性物质也起到一定的贡献作用;目标污染物CIP在体系中的降解过程包括脱羧反应和哌嗪环氧化;降解过程中大多数中间产物对水生生物表现出更为友好的特征;最后,通过延长体系降解时间,能有效消除CIP抗菌活性.

环丙沙星(CIP)；PTCN；CaO2；海水养殖废水；降解机理

氟喹诺酮类抗生素(FQs)是海水养殖业中常用的抗生素,据报道,在中国东南主要海水养殖场的淡水、咸水海产品中检测出约27种FQs[1],其中氧氟沙星(OFX)、诺氟沙星(NOR)、恩诺沙星(ENR)和环丙沙星(CIP)更是频繁检出[2].同时,由于FQs具有较高的稳定性[3]和抗生化降解性[4],传统生物法对FQs去除率很低,排放到水生环境中能停留较长时间[5],给生态环境修复以及各种生物带来不利影响.在进行抗生素暴露试验表明,FQs能对生物生育能力[6]和肠道健康[7]等带来一定的负面影响,其中, CIP更是可通过酶[8]、基因表达[7]和细胞毒性[9–10]等渠道,给环境带来过载负荷[11–12].而海水养殖场大多数为沿海建造经营,海水养殖生物长期暴露于含有FQs的水生环境中[13],经食物链富集[14],对海洋生态稳定造成严重危害.因此,亟需开发先进处理技术来去除海水养殖废水中残留的FQs.

传统的废水处理方法通常对FQs去除率较低,科研人员尝试开发其他新技术,如物理吸附、电化学氧化、植物修复、生物降解和光催化等[15–20],这些新技术为FQs的处理提供了丰富的经验.其中,光催化降解因其高效、环境友好和低能耗等优点,已逐渐成为目前处理FQs的重要手段.随着光催化技术的发展,光催化联合其他氧化剂能更好去除和矿化典型的FQs污染[21].过氧化钙(CaO2)被称为固体H2O2[22],能克服消耗过快和利用率低的问题,且具有易储存和运输安全的优点,在环境修复中常用来替代H2O2,近年来成为了研究热点[22–24].此外,CaO2可通过原位产生O2来改善水生环境缺氧导致的环境恶化问题[25],因而在环境有机物污染修复方面,具备一定的前景.此前研究报道过将H2O2联合光催化剂进行光催化降解有机污染物[26],但目前将CaO2与光催化技术联合协同修复环境问题的研究与应用尚为空白.

本文前期研究发现,磷掺杂石墨状氮化碳纳米片(PCN)光催化剂具有高效的能源生产和环境修复能力[27],同时,前人的研究也证明掺磷管状氮化碳(PTCN)的管状结构能增强光散射及活性位,具有更强的析氢和光催化降解能力[28].基于此,本研究以PTCN为核心光催化剂,拟建立“光催化—氧化”复合体系——PTCN/CaO2/可见光(vis)体系,以海水养殖废水中的CIP为目标污染物,深入探究该体系的反应降解机制及目标污染物的环境归趋.具体研究内容包括:(1)最佳反应条件;(2)共存因子协同和拮抗作用;(3)光催化剂可循环性;(4)活性物质在体系降解过程中的贡献;(5)CIP降解中间产物分析及产物毒性预测;(6)抗生素残留抗菌活性测试.相关研究结果将为海水养殖废水处理提供一种新思路,对发展实际水体中的抗生素污染处理技术具有一定的理论意义.

1 材料与方法

1.1 试剂

CIP,纯度>98%,购自麦克林生化科技有限公司(中国上海).色谱级甲酸、甲醇均购自安培实验技术有限公司(中国上海).常用化学试剂如CaO2、三聚氰胺、亚磷酸(H3PO3)、硫代硫酸钠(Na2S2O3)、异丙醇(IPA)、L-组氨酸(L-Histidine)、2,2,6,6-四甲基哌啶氧化物(TEMPO)、草酸钠(Na2C2O4)、氢氧化钠(NaOH)、硫酸(H2SO4)、硫酸钠(Na2SO4)、碳酸氢钠(NaHCO3)、氯化钠(NaCl)、硝酸钠(NaNO3)和腐殖酸(HA)等购自阿拉丁生化科技有限公司(中国上海),均为分析纯.实验过程所用超纯水(电阻率为18.25mΩ/cm)由尼珂LT-RY10超纯水机(隆暾科技有限公司,中国重庆)制备.

1.2 PTCN制备

PTCN材料的制备通常采用超分子自组装和煅烧的方法合成[28],本研究在前人的基础上进行了适当改进,即将1.0g三聚氰胺溶于100mL超纯水中,搅拌30min后,用亚磷酸将溶液pH值调至1.0,适当搅拌后将混合物转移到带有聚四氟乙烯内衬的高压反应釜中,在180℃下加热10h.冷却至室温后,将混合物离心,用超纯水和乙醇交替洗涤所得针状固体并干燥.最后,在500℃的N2氛围下,以2.5℃/min的加热速率将所得固体煅烧4h,研磨烘干后得到淡黄色的PTCN粉末.同时,合成掺磷片状氮化碳(PCN)及普通氮化碳(CN)用于开展对比实验[27].

1.3 表征方法

利用场发射扫描电镜(SEM, Hitachi SU8220,日本)观察所得PTCN和CaO2材料的形貌和微观结构.利用BrukerAXS和D8Advance衍射仪(XRD, Ultima Ⅲ型,日本)记录Cu Kα辐射下的X射线衍射图谱,用于表征PTCN、PCN和CN材料的晶体结构.在装有Mg Ka X射线源的X射线光电子能谱(XPS)仪(XPS, Thermo Fisher, Escalab 250Xi,美国)上对样品进行XPS分析.所得材料的光响应特征和基团特性在紫外可见近红外分光光度计(UV-vis DRS, Shimadzu, UV-3600Plus,日本)和傅里叶变换红外光谱仪(FT-IR, Thermo Fisher, Nicolet IS50,美国)上进行表征.

1.4 光催化反应实验

本文背景水质为中国广东省汕头市某海水养殖场所排放的海水养殖废水,其相关水质参数如表1所示(若无特殊说明,均为该水基质).

以CIP作为抗生素目标污染物添加到水基质中,配制含10mg/L的CIP海水养殖废水工作液.室温条件下,取50mL工作液于100mL烧杯中,加入一定量的催化剂,置于避光环境中搅拌30min,随后于蓝光(vis,波长范围为410～530nm, 5.8mW/cm2,由9w蓝色LED灯提供)下启动光催化降解实验.在既定时间点(0, 5, 10, 15, 20, 25和30min)取定量样品并加入反应终止剂(Na2S2O3),样品通过0.45μm的水相滤膜过滤后采用高效液相色谱法(HPLC, SHIMADZU LC16,日本)测定残留污染物浓度.

表1 海水养殖废水主要水质参数

为进一步探究目标污染物CIP在海水养殖废水中的降解动力学,通过拟合伪一级反应动力学模型, 具体见式(1)并计算得出相应的表观降解速率常数obs.本研究中涉及实验均严格进行3次以上平行实验,数据最终取平均值分析.

1.5 活性物种探究

通过化学竞争动力学方法对体系进行自由基猝灭实验,以评估PTCN/CaO2/vis体系下对CIP降解过程中不同自由基的贡献程度.具体过程为:在1.4节的基础上,分别加入异丙醇(IPA, 10mmol/L)用于猝灭羟基自由基(·OH)、L-组氨酸(L-Histidine, 20mmol/L)用于猝灭单线态氧(1O2)、2,2,6,6-四甲基哌啶氧化物(TEMPO, 1mmol/L)用于猝灭超氧阴离子(O2·-)以及草酸钠(Na2C2O4, 10mmol/L)用于猝灭空穴(h+).最后,通过自由基贡献率计算式(2)～(5)评估不同活性物种对降解过程的影响.

式中:为体系中相应自由基(如·OH,1O2, O2·-和h+)对光催化降解目标污染物CIP的贡献率,%;k为CIP在体系中相应猝灭剂(如IPA, L-Histidine, TEMPO和Na2C2O4)存在下的表观降解速率常数.

1.6 分析方法

采用 HPLC检测CIP的降解浓度,其中使用Zorbax Eclipse XDB-C18(4.6mm×250mm, 5μm)色谱柱进行样品组分分离,柱温为35℃;流动相分别为甲醇/0.2%甲酸缓冲溶液,体积比为30:70,流速为0.2mL/min;进样体积为20μL,光电二极管检测器检测波长为278nm.

采用超高分辨四极杆组合静电场轨道阱液相色谱—质谱联用仪(Thermo Scientific Ultimate 3000RSLC HPLC系统和Q-ExActive Orbitrap,美国)对CIP的降解中间产物进行检测分析.仪器配备Eclipse Plus C18RRHD (50mm×2.1mm, 1.8μm)及Hypersil GOLD C18 (100mm×2.1mm, 1.9μm)色谱柱进行样品组分分离,柱温为30℃;流动相分别为甲醇和0.1%甲酸缓冲溶液,流速为0.25mL/min;采用正负离子全扫描模式,干燥气为高纯N2.

1.7 毒性预测及抗生素残留抗菌活性测试

通过ecological structure-activity relationship (ECOSAR)软件预测目标污染物CIP以及在降解过程中所产生中间产物的毒性,毒性根据欧盟危险品认证标准(67/548/EEC)和中国新化学物质危害评估导则(HJ/T154-2004)进行评估[29].

在长有大肠杆菌(E.coli)的LB培养基琼脂平板上滴加不同降解时间段(0, 0.5, 1, 2, 4和6h)降解液样品,通过测定抑菌圈大小,即大肠杆菌生长抑制情况来评估抗生素残留的抗菌活性.具体步骤为:将经培养稀释后浓度为1.2´109CFU/mL的大肠杆菌均匀涂布于事先准备好的LB培养基琼脂上,随后滴加10μL降解液样品,于恒温培养箱(37℃)中培养12h后测量琼脂平板上药物敏感区所形成抑菌圈的大小[30].

2 结果与讨论

2.1 材料表征

采用超分子自组装和煅烧的方法合成光催化剂PTCN,并通过SEM对PTCN及CaO2的形貌进行了表征,结果如图1(a)～(b)所示.图1(a)显示,制备的PTCN呈类管状形态,与本文前期制备的片状PCN和CN[27,31-32]相比,类管状结构可为光催化过程提供更大的接触面以及更快的电子传导[33],进而提高体系的光催化降解效果.图1(b)显示,实验体系中所用CaO2颗粒呈碎块状,大小较为均匀.同时,采用XRD对合成的PTCN、PCN和CN进行晶体结构分析,如图1(c)所示,CN在13.0 °和27.4 °处表征出2个典型的衍射峰,分别被标记为g-C3N4的(100)和(002)2个平面[27];与CN相比,PTCN显示出相似的特征衍射峰,但PTCN以及PCN在中心位于27.4 °的峰(002)均比CN变得更宽、更弱,散射角更小,两者具有相似的结构[28].

采用XPS分析了合成材料的化学组成和化学状态,结果如图2(a)～(d)所示.在Survey谱图中, PTCN和PCN均可检测到C、N、O和P元素,而CN只能检出C, N和O元素.在C1s谱图中,PTCN、PCN和CN在284.8eV, 286.4eV和288.2eV处均表征出3个主峰,分别代表C—C, C—O, N=C—N[34].在N1s谱图中,3种材料在398.7eV、400.1eV和401.3eV处均表征出3个峰,分别归因为C=N—C, N—C3, NH[35].在P2p谱图中,PTCN和PCN材料在133.4eV处可拟合出特征峰,代表P-N,而CN则在此处没有显示出磷的可检测信号[36].

采用UV-vis DRS分析了样品的光学性质,结果如图3(a)所示,管状结构的形成增强了PTCN在整个波长范围内(200～400nm)的光吸收,这归功于入射光在微纳米结构管内多次反射[36].通过FT-IR进一步揭示了样品的化学结构,结果如图3(b)所示,3种材料均显示出相似的光谱振动,即在802cm-1处尖峰为三嗪单元的典型振动,在1200～1600cm-1处为CN杂环的伸缩振动,表明PTCN保留了和PCN、CN相似的骨架结构,没有引入其他明显的官能团[37].综上表征结果,本实验过程中所使用的光催化剂PTCN成功制备.

图3 PTCN、PCN和CN的紫外—可见光漫反射光谱及傅里叶变换红外光谱

2.2 体系最佳反应条件探究

2.2.1 体系PTCN和CaO2不同比例对CIP降解的影响 在PTCN体系中加入CaO2,期望通过产生更多活性物质来协同增强氧化降解作用.本研究通过设置不同PTCN和CaO2的投加比例,探究其在光催化降解CIP时体系的最佳条件.实验过程中,光催化材料和氧化剂投加比从1:2增加至20:1,并设置2个单独材料作为对照组.结果如图4(a)所示,随着投加比的增加,目标污染物CIP的降解率也呈现相应变化,体系中仅存在CaO2时,目标污染物的降解率几乎为0,CaO2无法在vis激发下降解CIP;当投加比从1:2增加至5:1时,体系降解率相对应增加,从83.1%增加到89.2%;之后当投加比继续增加时,降解率呈减少趋势,到20:1的投加比时,降解率降至74.2%;体系中仅存在PTCN时,虽能降解目标污染物,但在同等光催化反应时间(30min)内,降解能力相较弱于体系中存在CaO2时的情况,仅有57.2%.可见,当体系中存在适量CaO2时,PTCN和CaO2存在协同增强光催化降解现象,能促使体系中产生更多的活性物种,如·OH、O2·-等[38];但当CaO2投加量过多时,目标污染物的降解率反而下降,可能是过多的CaO2占据了PTCN光催化剂表面的活性位点,抑制了其催化活性[39].综上,在PTCN/CaO2/vis体系中,PTCN:CaO2的最佳投加比(质量比)为5:1,即0.02g:0.004g,该投加比对应的CIP降解率是单独PTCN的2.14倍.若无特殊说明,后续实验均按该投加比进行研究.

2.2.2 体系初始pH值对CIP降解的影响 pH值是水体中污染物降解的一个关键因素,其影响各种清除剂表面官能团的质子化过程[40].为探究PTCN/CaO2/vis体系的适用pH值范围及最佳pH值,通过使用0.1mol/L的氢氧化钠和0.1mol/L的硫酸调节体系初始pH值,设置不同梯度pH值(pH=3, 5, 7, 9和11,对照组pH值为9.52)来研究目标污染物CIP的降解情况.如图4(b)所示,当pH值从3升高到11时,体系降解速率常数从10.55´10-2min-1下降到6.41´10-2min-1,降解速率常数显著降低了39.2%,说明PTCN/CaO2/vis体系对CIP的降解效率在较高pH值下受到抑制.当体系酸性增强时,CIP的降解率相对应提高,pH值从9下降到3时,降解率相对应从90.6%上升到97.7%;当体系碱性增强时, CIP的降解率反而下降,pH值从9上升到11时,降解率相对应从90.6%下降到81.2%.目标污染物CIP在体系中不同初始pH值下的降解率不同,这是由于CaO2在不同pH值环境下释放的过氧化氢的量不同所致,其释放范围为酸性至弱碱性,即pH=3～8.pH值在此范围内越低,CaO2会释放更多的过氧化氢,而过量的过氧化氢可以清除自由基的氧化[41].这与上一部分所提到的最佳投加比也有一定联系,适量CaO2溶于水中时会生成氢氧化钙以及过氧化氢,有助于体系的光催化降解(式(6));而过量的CaO2溶于水中在生成氢氧化钙的同时也会生成氧气(式(7)),相对应的过氧化氢释放量下降.当pH值上升时,体系中OH-浓度也会相对应增加,过量的OH-与PTCN相互作用形成稳定的带负电化合物,从而导致光催化材料的降解作用被削弱[42];碱性环境也不利于Fenton反应的进行,故在最佳投加比上呈现先增后减的趋势.综上所述,在酸性条件下可以提高过氧化氢的释放速率和利用效率,进而提高光催化降解目标污染物CIP的目的.

图4 PTCN/CaO2/vis体系最佳反应条件探究

2.2.3 体系对不同初始CIP浓度的降解效果 目标污染物CIP不同初始浓度对PTCN/CaO2/vis体系降解效果的影响如图4(c)所示,随着目标污染物CIP的初始浓度增加(从1mg/L到20mg/L),体系降解效果逐渐降低,降解率从100%下降到79.7%,这与体系中单位污染物所对应的活性物质的量有关.当活性物质的量保持不变时,增加污染物浓度会导致相应处理活性物质的量减少,降解速率随之而降低.

2.3 体系共存因子协同拮抗作用探究

在海水养殖废水中,共存物质种类繁多,包括钾、钠、钙等组成的高盐度元素,腐殖酸(HA)等溶解性有机物(DOM),以及富集为营养元素的氮、碳和磷等[43-45].水中的溶解性有机物和无机阴、阳离子对光催化降解反应存在一定影响,如活性物种竞争[46–47]、光屏蔽效应[48]等.基于此,本文进一步研究了海水养殖废水中共存因子的协同拮抗作用.

通过向PTCN/CaO2/vis体系中投加一系列无机阴离子(Cl-, NO3-和HCO3-)、HA和无机阳离子(NH4+, K+, Cu2+和Ca2+),对体系降解目标污染物CIP的影响进行单因素实验(Cu2+的浓度为5mg/L,其他共存因子在反应体系中的浓度为10mg/L).如图5(a)所示,与对照组降解速率常数(obs=7.15´10-2min-1)相比, Cl-, NH4+以及K+对目标污染物CIP的降解起协同作用,速率常数分别提高18.3% (obs=8.46´10-2min-1)、18.2% (obs=8.45´10-2min-1)和17.2% (obs=8.38´10-2min-1);HA, Cu2+, NO3-, HCO3-以及Ca2+对目标污染物CIP的降解起拮抗作用,速率常数的抑制率分别为8.8% (obs=6.52´10-2min-1)、30.3% (obs=4.98´10-2min-1)、31.2% (obs=4.92´10-2min-1)、33.4% (obs=4.76´10-2min-1)和39.6% (obs=4.32´10-2min-1).

在实验条件下,K+起到较弱协同作用,Ca2+存在一定的拮抗作用,在水生环境中,它们都处于稳定的氧化状态,几乎不捕获体系中的电子和空穴[49].腐殖酸可与活性物种反应竞争,同时由于光屏蔽效应使得CIP降解速率下降.研究发现,NO3-和HCO3-通常会与体系中的活性物种反应生成含氮自由基和碳氧自由基[50],即式(8)、(9)所示.尽管这两种自由基存在氧化有机物的作用,但其具有选择性,且氧化能力远弱于羟基自由基[50],故对体系存在一定拮抗作用.

进一步,考察了超纯水、自来水、湖水、珠江河水对PTCN/CaO2/vis体系降解目标污染物速率的影响.结果如图5(b)所示,PTCN/CaO2/vis体系随着背景水质中杂质的不断减少,降解效率相对应增加,在超纯水和自来水这两种背景水质下的降解率分别为98.5%和91.8%;而在河水以及湖水中,降解率分别为78.4%和81.3%,虽然降解效率呈现削弱趋势,但体系仍有较好的降解效果,表明PTCN/ CaO2/vis体系可应用于多种环境水以及饮用水中对CIP进行降解处理.

因此,在PTCN/CaO2/vis体系最佳实验条件下,不同共存因子及背景水质对体系降解目标污染物CIP存在较为明显的协同和拮抗作用;但总体而言,PTCN/CaO2/vis体系在不同实验条件下仍能拥有较好的污水修复能力,具备良好的潜在应用性.

2.4 光催化剂循环实验

为了检验PTCN/CaO2/vis体系在海水养殖废水实际应用中降解目标污染物CIP的可循环性,进行了光催化剂循环实验.从图5(c)可以看出,在第5次循环实验时,PTCN/CaO2/vis体系仍表现出较强的降解能力,表观降解速率常数obs仍有5.74×10-2min-1,降解率为82.4%,仅下降了6.8%,证明PTCN光催化剂具备良好的可循环稳定性,也进一步证明PTCN/ CaO2/vis体系用于降解海水养殖废水中目标污染物的可行性.

2.5 活性物质的猝灭

在光催化降解过程中,活性物质往往占据主导贡献[51].因此,本研究通过采用猝灭剂IPA, L- Histidine, TEMPO和Na2C2O4进行一系列猝灭实验,分别对应猝灭活性物质·OH,1O2, O2·-以及h+[27,52-53],由式(2)～(5)计算对应活性物质在体系中的降解贡献率,量化活性物质在PTCN/CaO2/vis体系中降解目标污染物CIP的作用.实验结果如图6(a)、(b)所示,当向体系中分别添加4种不同的猝灭剂IPA, L- Histidine, TEMPO和Na2C2O4时,相应的表观降解速率常数obs分别从7.15´10-2min-1下降为5.64´10-2min-1、2.03´10-2min-1、0.39´10-2min-1和4.64´10-2min-1,通过计算得出·OH,1O2, O2·-和h+的贡献率分别为21.1%、71.6%、94.5%和35.1%.实验结果表明,在PTCN/CaO2/vis体系降解目标污染物CIP的过程中,活性物质O2·-占主导地位,1O2和h+这两种活性物质也起到了一定的贡献作用,而·OH则贡献最少.

图6 PTCN/CaO2/vis体系活性物质的猝灭

2.6 光催化降解过程中CIP降解产物探究及毒性预测

根据以往的报道,目标污染物CIP易受自由基所攻击的位点包括-F、环丙基、哌嗪环和羧基[54].本研究在此理论基础上,使用超高分辨四极杆组合静电场轨道阱液相色谱—质谱联用仪对CIP在PTCN/CaO2/vis体系中的降解产物进行检测和分析,提出了两种可能的降解路径:脱羧反应和哌嗪环氧化,结果如图7所示.对于路径1,CIP (=332)通过脱羧反应生成了TP1 (=288)[55].在路径2中,CIP (=332)的哌嗪环因其高电子密度而在体系中首先被攻击,发生氧化和裂解生成TP2 (=362).随后,前后分别失去两次羰基,形成TP3 (=334)以及TP4 (=306).紧接着,脱去一个氨基以及羰基化反应,生成TP5 (=291).最后,再次失去一个羰基生成TP6 (=263),该路径与先前的报道基本一致[56].最终,在自由基的氧化还原作用下,这些中间产物可进一步降解,矿化成为CO2, H2O, NH4+, NO3-和F-等无机离子.

图7 PTCN/CaO2/vis体系下CIP可能的降解路径

针对目标污染物CIP在降解过程中所产生的中间产物,本研究通过ECOSAR软件对其进行慢性、急性毒性(LC50和CHV)模拟预测,根据欧盟危险品认证标准(67/548/EEC)和中国新化学物质危害评估导则(HJ/T154-2004),将所得数据进行进一步归类(如图8),并阐明相关中间产物的毒性特征.结果表明, 在水生环境中,母体CIP属于联合国毒性预测无害的水平.在PTCN/CaO2/vis体系下,大部分中间产物(TP2-TP5)在鱼类、水蚤和绿藻的毒性预测数据中均与母体一致,属于毒性预测无害的水平,基本表现出对水生生物更友好的特征.然而,值得注意的是,相较于母体CIP而言,TP1和TP6却表现出更高的毒性,对部分水生生物属于有毒有害水平.总的来说, PTCN/CaO2/vis体系在降解目标污染物CIP的过程中,大部分中间产物对水生生物表现出更友好特征,但在一定程度上仍存在生态风险. 在实际处理过程中,可通过延长降解时间来达到深度矿化目的,进一步降低中间产物的毒性.

图8 CIP和转化产物的毒理学分析及急性、慢性毒性等级评价

2.7 抗生素残留抗菌活性测试及体系TOC去除率

在修复CIP污染水体的过程中,通常需要考虑消除其抗生素活性,以避免在生态环境中产生抗性基因并减少受污水体的修复难度.为探究PTCN/ CaO2/vis体系降解目标污染物CIP并消除其抗菌活性,以大肠杆菌(E.coli)为指标[57],对体系降解液进行抗生素残留抗菌活性测试.实验结果如图9(a)所示,随着PTCN/CaO2/vis体系降解时间的推移,降解液所产生的抑菌圈(黑色菱形标记上方)从2.5cm逐渐缩小,在6h降解液测试中抑菌圈完全消失.这说明延长PTCN/CaO2/vis体系反应降解时间至6h时,能将目标污染物CIP的抗生素残留从海水养殖废水中完全去除.此外,还研究了PTCN/CaO2/vis体系对目标污染物CIP的矿化效果,结果如图9(b)所示,可以看出,随着降解时间的推移,CIP逐渐被矿化,在90min时矿化率已接近50%.表明PTCN/CaO2/vis体系具备消除抗生素活性残留及有效减轻生态环境风险的潜力.

图9 PTCN/CaO2/vis体系抗生素残留抗菌活性测试及降解CIP的矿化率

3 结论

3.1 本研究通过超分子自组装和煅烧的方法合成PTCN,成功构建PTCN/CaO2/vis体系降解目标污染物CIP,该体系具备良好的降解活性,在实验条件下CIP的表观降解速率常数obs为7.15×10-2min-1.

3.2 单因素实验结果表明,在酸性条件下,PTCN/ CaO2/vis体系表现出更强的CIP降解效能;在不同共存因子及背景水质下,PTCN/CaO2/vis体系对CIP降解存在不同程度的拮抗和协同作用;体系降解污染物能力随CIP浓度降低而逐渐增强;光催化剂表现出良好的可循环性(5次循环后降解率仍有82.5%).

3.3 PTCN/CaO2/vis体系降解CIP过程中,活性物质O2·-占主导地位(贡献率为94.5%),1O2和h+这两种活性物质也起到了一定的贡献作用.

3.4 目标污染物CIP在PTCN/CaO2/vis体系中的降解过程包括脱羧反应和哌嗪环氧化;降解过程中的大多数中间产物对水生生物表现出更为友好的特征;延长体系降解时间能有效消除抗菌活性.

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Degradation of CIP in mariculture wastewater by PTCN/CaO2/vis system: Mechanism and fate.

ZENG Yu-feng, NIU Meng-yang, CHEN Ping*, QIU Yan-nan, LIN Yi-jie, XIAO Zhen-jun, FANG Zheng, YU Zong-shun, LIN Zi-feng, LUO Jin, Lü Wen-ying, LIU Guo-guang*

(Guangdong-Hong Kong-Macao Joint Laboratory for Contaminants Exposure and Health, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, China)., 2023,43(10)：5214～5225

s：Abuse of antibiotics presents a significant threat to both human health and environmental ecology. To combat this issue, a phosphorus-doped tubular carbon nitride (PTCN)/CaO2/visible light(vis) system would be developed and applied to effectively remove the pollutant ciprofloxacin (CIP) from mariculture wastewater. Meanwhile, the reaction mechanism of this system and the environmental fate of the antibiotic CIP would be investigated in this work. Experimental results indicated that the PTCN/CaO2/vis system exhibited excellent potential for degradation of antibiotics. The observed apparent degradation rate constant (obs) of CIP under the experimental conditions was 7.15×10-2min-1. Single-factor experiments had revealed that the system exhibited enhanced CIP degradation efficiency in acidic conditions. However, the presence of co-existing factors in water did influence the system’s ability to degrade CIP. Moreover, as the concentration of CIP increases, the system's capacity to degrade pollutant decreases. Additionally, the system displayed superior recyclability, maintaining a degradation rate of 82.5% after five cycles of PTCN. The process of CIP degradation by the system was primarily dominated by the active ingredient O2·-, while the active substances1O2and h+also contributed to the process. As the target pollutant CIP underwent decarboxylation and piperazine epoxidation, a majority of the intermediate products produced were found to be more environmentally friendly towards aquatic organisms. Finally, by prolonging the system’s degradation time, the antibacterial activity of CIP could be effectively eliminated.

ciprofloxacin (CIP)；phosphorus-doped tubular carbon nitride (PTCN)；CaO2；mariculture wastewater；degradation mechanism

X703.1

A

1000-6923(2023)10-5214-12

2023-03-21

国家自然科学基金资助项目(21906029,22076029,22176042);广州市科技计划项目(202102020774,201903010080)

* 责任作者, 副教授, gdutchp@163.com; ** 教授, liugg615@163.com

曾煜丰(1998-),男,广东揭阳人,广东工业大学环境科学与工程学院硕士研究生,主要从事光催化降解有机新污染物研究.yofone_ 025@foxmail.com.

曾煜丰,牛梦洋,陈 平,等.PTCN/CaO2/vis体系降解海水养殖废水中CIP:机理与归趋 [J]. 中国环境科学, 2023,43(10):5214-5225.

Zeng Y F, Niu M Y, Chen P, et al. Degradation of CIP in mariculture wastewater by PTCN/CaO2/vis system: Mechanism and fate [J]. China Environmental Science, 2023,43(10):5214-5225.