PTCN/CaO2/vis體系降解海水養(yǎng)殖廢水中CIP:機理與歸趨

曾煜豐,牛夢洋,陳 平,邱燕楠,林弋杰,肖震鈞,方 政,余宗舜,林紫封,羅 錦,呂文英,劉國光

PTCN/CaO2/vis體系降解海水養(yǎng)殖廢水中CIP:機理與歸趨

曾煜豐,牛夢洋,陳 平*,邱燕楠,林弋杰,肖震鈞,方 政,余宗舜,林紫封,羅 錦,呂文英,劉國光**

(廣東工業(yè)大學環(huán)境科學與工程學院,廣東省環(huán)境催化與健康風險控制重點實驗室,粵港澳污染物暴露與健康聯合實驗室,廣東 廣州 510006)

本文擬建立摻磷管狀氮化碳(PTCN)/CaO2/可見光(vis)體系,將其應用于海水養(yǎng)殖廢水中處理目標污染物環(huán)丙沙星(CIP),并探究該體系反應機理及抗生素CIP的環(huán)境歸趨.實驗結果表明,PTCN/CaO2/vis體系具備良好的抗生素降解能力,在實驗條件下CIP的表觀降解速率常數obs為7.15×10-2min-1;單因素實驗表明,在酸性條件下,體系表現出更強的CIP降解效能,水中共存因子對體系降解CIP存在一定的影響;同時,體系降解污染物能力隨CIP濃度降低而逐漸增強;此外,該體系表現出優(yōu)異的可循環(huán)性能,PTCN在5次循環(huán)后,CIP的降解率仍能保持82.5%.體系降解CIP過程中,活性物質O2·-占主導地位,1O2和h+這兩種活性物質也起到一定的貢獻作用;目標污染物CIP在體系中的降解過程包括脫羧反應和哌嗪環(huán)氧化;降解過程中大多數中間產物對水生生物表現出更為友好的特征;最后,通過延長體系降解時間,能有效消除CIP抗菌活性.

環(huán)丙沙星(CIP)；PTCN；CaO2；海水養(yǎng)殖廢水；降解機理

氟喹諾酮類抗生素(FQs)是海水養(yǎng)殖業(yè)中常用的抗生素,據報道,在中國東南主要海水養(yǎng)殖場的淡水、咸水海產品中檢測出約27種FQs[1],其中氧氟沙星(OFX)、諾氟沙星(NOR)、恩諾沙星(ENR)和環(huán)丙沙星(CIP)更是頻繁檢出[2].同時,由于FQs具有較高的穩(wěn)定性[3]和抗生化降解性[4],傳統生物法對FQs去除率很低,排放到水生環(huán)境中能停留較長時間[5],給生態(tài)環(huán)境修復以及各種生物帶來不利影響.在進行抗生素暴露試驗表明,FQs能對生物生育能力[6]和腸道健康[7]等帶來一定的負面影響,其中, CIP更是可通過酶[8]、基因表達[7]和細胞毒性[9–10]等渠道,給環(huán)境帶來過載負荷[11–12].而海水養(yǎng)殖場大多數為沿海建造經營,海水養(yǎng)殖生物長期暴露于含有FQs的水生環(huán)境中[13],經食物鏈富集[14],對海洋生態(tài)穩(wěn)定造成嚴重危害.因此,亟需開發(fā)先進處理技術來去除海水養(yǎng)殖廢水中殘留的FQs.

傳統的廢水處理方法通常對FQs去除率較低,科研人員嘗試開發(fā)其他新技術,如物理吸附、電化學氧化、植物修復、生物降解和光催化等[15–20],這些新技術為FQs的處理提供了豐富的經驗.其中,光催化降解因其高效、環(huán)境友好和低能耗等優(yōu)點,已逐漸成為目前處理FQs的重要手段.隨著光催化技術的發(fā)展,光催化聯合其他氧化劑能更好去除和礦化典型的FQs污染[21].過氧化鈣(CaO2)被稱為固體H2O2[22],能克服消耗過快和利用率低的問題,且具有易儲存和運輸安全的優(yōu)點,在環(huán)境修復中常用來替代H2O2,近年來成為了研究熱點[22–24].此外,CaO2可通過原位產生O2來改善水生環(huán)境缺氧導致的環(huán)境惡化問題[25],因而在環(huán)境有機物污染修復方面,具備一定的前景.此前研究報道過將H2O2聯合光催化劑進行光催化降解有機污染物[26],但目前將CaO2與光催化技術聯合協同修復環(huán)境問題的研究與應用尚為空白.

本文前期研究發(fā)現,磷摻雜石墨狀氮化碳納米片(PCN)光催化劑具有高效的能源生產和環(huán)境修復能力[27],同時,前人的研究也證明摻磷管狀氮化碳(PTCN)的管狀結構能增強光散射及活性位,具有更強的析氫和光催化降解能力[28].基于此,本研究以PTCN為核心光催化劑,擬建立“光催化—氧化”復合體系——PTCN/CaO2/可見光(vis)體系,以海水養(yǎng)殖廢水中的CIP為目標污染物,深入探究該體系的反應降解機制及目標污染物的環(huán)境歸趨.具體研究內容包括:(1)最佳反應條件;(2)共存因子協同和拮抗作用;(3)光催化劑可循環(huán)性;(4)活性物質在體系降解過程中的貢獻;(5)CIP降解中間產物分析及產物毒性預測;(6)抗生素殘留抗菌活性測試.相關研究結果將為海水養(yǎng)殖廢水處理提供一種新思路,對發(fā)展實際水體中的抗生素污染處理技術具有一定的理論意義.

1 材料與方法

1.1 試劑

CIP,純度>98%,購自麥克林生化科技有限公司(中國上海).色譜級甲酸、甲醇均購自安培實驗技術有限公司(中國上海).常用化學試劑如CaO2、三聚氰胺、亞磷酸(H3PO3)、硫代硫酸鈉(Na2S2O3)、異丙醇(IPA)、L-組氨酸(L-Histidine)、2,2,6,6-四甲基哌啶氧化物(TEMPO)、草酸鈉(Na2C2O4)、氫氧化鈉(NaOH)、硫酸(H2SO4)、硫酸鈉(Na2SO4)、碳酸氫鈉(NaHCO3)、氯化鈉(NaCl)、硝酸鈉(NaNO3)和腐殖酸(HA)等購自阿拉丁生化科技有限公司(中國上海),均為分析純.實驗過程所用超純水(電阻率為18.25mΩ/cm)由尼珂LT-RY10超純水機(隆暾科技有限公司,中國重慶)制備.

1.2 PTCN制備

PTCN材料的制備通常采用超分子自組裝和煅燒的方法合成[28],本研究在前人的基礎上進行了適當改進,即將1.0g三聚氰胺溶于100mL超純水中,攪拌30min后,用亞磷酸將溶液pH值調至1.0,適當攪拌后將混合物轉移到帶有聚四氟乙烯內襯的高壓反應釜中,在180℃下加熱10h.冷卻至室溫后,將混合物離心,用超純水和乙醇交替洗滌所得針狀固體并干燥.最后,在500℃的N2氛圍下,以2.5℃/min的加熱速率將所得固體煅燒4h,研磨烘干后得到淡黃色的PTCN粉末.同時,合成摻磷片狀氮化碳(PCN)及普通氮化碳(CN)用于開展對比實驗[27].

1.3 表征方法

利用場發(fā)射掃描電鏡(SEM, Hitachi SU8220,日本)觀察所得PTCN和CaO2材料的形貌和微觀結構.利用BrukerAXS和D8Advance衍射儀(XRD, Ultima Ⅲ型,日本)記錄Cu Kα輻射下的X射線衍射圖譜,用于表征PTCN、PCN和CN材料的晶體結構.在裝有Mg Ka X射線源的X射線光電子能譜(XPS)儀(XPS, Thermo Fisher, Escalab 250Xi,美國)上對樣品進行XPS分析.所得材料的光響應特征和基團特性在紫外可見近紅外分光光度計(UV-vis DRS, Shimadzu, UV-3600Plus,日本)和傅里葉變換紅外光譜儀(FT-IR, Thermo Fisher, Nicolet IS50,美國)上進行表征.

1.4 光催化反應實驗

本文背景水質為中國廣東省汕頭市某海水養(yǎng)殖場所排放的海水養(yǎng)殖廢水,其相關水質參數如表1所示(若無特殊說明,均為該水基質).

以CIP作為抗生素目標污染物添加到水基質中,配制含10mg/L的CIP海水養(yǎng)殖廢水工作液.室溫條件下,取50mL工作液于100mL燒杯中,加入一定量的催化劑,置于避光環(huán)境中攪拌30min,隨后于藍光(vis,波長范圍為410～530nm, 5.8mW/cm2,由9w藍色LED燈提供)下啟動光催化降解實驗.在既定時間點(0, 5, 10, 15, 20, 25和30min)取定量樣品并加入反應終止劑(Na2S2O3),樣品通過0.45μm的水相濾膜過濾后采用高效液相色譜法(HPLC, SHIMADZU LC16,日本)測定殘留污染物濃度.

表1 海水養(yǎng)殖廢水主要水質參數

為進一步探究目標污染物CIP在海水養(yǎng)殖廢水中的降解動力學,通過擬合偽一級反應動力學模型, 具體見式(1)并計算得出相應的表觀降解速率常數obs.本研究中涉及實驗均嚴格進行3次以上平行實驗,數據最終取平均值分析.

1.5 活性物種探究

通過化學競爭動力學方法對體系進行自由基猝滅實驗,以評估PTCN/CaO2/vis體系下對CIP降解過程中不同自由基的貢獻程度.具體過程為:在1.4節(jié)的基礎上,分別加入異丙醇(IPA, 10mmol/L)用于猝滅羥基自由基(·OH)、L-組氨酸(L-Histidine, 20mmol/L)用于猝滅單線態(tài)氧(1O2)、2,2,6,6-四甲基哌啶氧化物(TEMPO, 1mmol/L)用于猝滅超氧陰離子(O2·-)以及草酸鈉(Na2C2O4, 10mmol/L)用于猝滅空穴(h+).最后,通過自由基貢獻率計算式(2)～(5)評估不同活性物種對降解過程的影響.

式中:為體系中相應自由基(如·OH,1O2, O2·-和h+)對光催化降解目標污染物CIP的貢獻率,%;k為CIP在體系中相應猝滅劑(如IPA, L-Histidine, TEMPO和Na2C2O4)存在下的表觀降解速率常數.

1.6 分析方法

采用 HPLC檢測CIP的降解濃度,其中使用Zorbax Eclipse XDB-C18(4.6mm×250mm, 5μm)色譜柱進行樣品組分分離,柱溫為35℃;流動相分別為甲醇/0.2%甲酸緩沖溶液,體積比為30:70,流速為0.2mL/min;進樣體積為20μL,光電二極管檢測器檢測波長為278nm.

采用超高分辨四極桿組合靜電場軌道阱液相色譜—質譜聯用儀(Thermo Scientific Ultimate 3000RSLC HPLC系統和Q-ExActive Orbitrap,美國)對CIP的降解中間產物進行檢測分析.儀器配備Eclipse Plus C18RRHD (50mm×2.1mm, 1.8μm)及Hypersil GOLD C18 (100mm×2.1mm, 1.9μm)色譜柱進行樣品組分分離,柱溫為30℃;流動相分別為甲醇和0.1%甲酸緩沖溶液,流速為0.25mL/min;采用正負離子全掃描模式,干燥氣為高純N2.

1.7 毒性預測及抗生素殘留抗菌活性測試

通過ecological structure-activity relationship (ECOSAR)軟件預測目標污染物CIP以及在降解過程中所產生中間產物的毒性,毒性根據歐盟危險品認證標準(67/548/EEC)和中國新化學物質危害評估導則(HJ/T154-2004)進行評估[29].

在長有大腸桿菌(E.coli)的LB培養(yǎng)基瓊脂平板上滴加不同降解時間段(0, 0.5, 1, 2, 4和6h)降解液樣品,通過測定抑菌圈大小,即大腸桿菌生長抑制情況來評估抗生素殘留的抗菌活性.具體步驟為:將經培養(yǎng)稀釋后濃度為1.2′109CFU/mL的大腸桿菌均勻涂布于事先準備好的LB培養(yǎng)基瓊脂上,隨后滴加10μL降解液樣品,于恒溫培養(yǎng)箱(37℃)中培養(yǎng)12h后測量瓊脂平板上藥物敏感區(qū)所形成抑菌圈的大小[30].

2 結果與討論

2.1 材料表征

采用超分子自組裝和煅燒的方法合成光催化劑PTCN,并通過SEM對PTCN及CaO2的形貌進行了表征,結果如圖1(a)～(b)所示.圖1(a)顯示,制備的PTCN呈類管狀形態(tài),與本文前期制備的片狀PCN和CN[27,31-32]相比,類管狀結構可為光催化過程提供更大的接觸面以及更快的電子傳導[33],進而提高體系的光催化降解效果.圖1(b)顯示,實驗體系中所用CaO2顆粒呈碎塊狀,大小較為均勻.同時,采用XRD對合成的PTCN、PCN和CN進行晶體結構分析,如圖1(c)所示,CN在13.0 °和27.4 °處表征出2個典型的衍射峰,分別被標記為g-C3N4的(100)和(002)2個平面[27];與CN相比,PTCN顯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變得更寬、更弱,散射角更小,兩者具有相似的結構[28].

采用XPS分析了合成材料的化學組成和化學狀態(tài),結果如圖2(a)～(d)所示.在Survey譜圖中, PTCN和PCN均可檢測到C、N、O和P元素,而CN只能檢出C, N和O元素.在C1s譜圖中,PTCN、PCN和CN在284.8eV, 286.4eV和288.2eV處均表征出3個主峰,分別代表C—C, C—O, N=C—N[34].在N1s譜圖中,3種材料在398.7eV、400.1eV和401.3eV處均表征出3個峰,分別歸因為C=N—C, N—C3, NH[35].在P2p譜圖中,PTCN和PCN材料在133.4eV處可擬合出特征峰,代表P-N,而CN則在此處沒有顯示出磷的可檢測信號[36].

采用UV-vis DRS分析了樣品的光學性質,結果如圖3(a)所示,管狀結構的形成增強了PTCN在整個波長范圍內(200～400nm)的光吸收,這歸功于入射光在微納米結構管內多次反射[36].通過FT-IR進一步揭示了樣品的化學結構,結果如圖3(b)所示,3種材料均顯示出相似的光譜振動,即在802cm-1處尖峰為三嗪單元的典型振動,在1200～1600cm-1處為CN雜環(huán)的伸縮振動,表明PTCN保留了和PCN、CN相似的骨架結構,沒有引入其他明顯的官能團[37].綜上表征結果,本實驗過程中所使用的光催化劑PTCN成功制備.

圖3 PTCN、PCN和CN的紫外—可見光漫反射光譜及傅里葉變換紅外光譜

2.2 體系最佳反應條件探究

2.2.1 體系PTCN和CaO2不同比例對CIP降解的影響 在PTCN體系中加入CaO2,期望通過產生更多活性物質來協同增強氧化降解作用.本研究通過設置不同PTCN和CaO2的投加比例,探究其在光催化降解CIP時體系的最佳條件.實驗過程中,光催化材料和氧化劑投加比從1:2增加至20:1,并設置2個單獨材料作為對照組.結果如圖4(a)所示,隨著投加比的增加,目標污染物CIP的降解率也呈現相應變化,體系中僅存在CaO2時,目標污染物的降解率幾乎為0,CaO2無法在vis激發(fā)下降解CIP;當投加比從1:2增加至5:1時,體系降解率相對應增加,從83.1%增加到89.2%;之后當投加比繼續(xù)增加時,降解率呈減少趨勢,到20:1的投加比時,降解率降至74.2%;體系中僅存在PTCN時,雖能降解目標污染物,但在同等光催化反應時間(30min)內,降解能力相較弱于體系中存在CaO2時的情況,僅有57.2%.可見,當體系中存在適量CaO2時,PTCN和CaO2存在協同增強光催化降解現象,能促使體系中產生更多的活性物種,如·OH、O2·-等[38];但當CaO2投加量過多時,目標污染物的降解率反而下降,可能是過多的CaO2占據了PTCN光催化劑表面的活性位點,抑制了其催化活性[39].綜上,在PTCN/CaO2/vis體系中,PTCN:CaO2的最佳投加比(質量比)為5:1,即0.02g:0.004g,該投加比對應的CIP降解率是單獨PTCN的2.14倍.若無特殊說明,后續(xù)實驗均按該投加比進行研究.

2.2.2 體系初始pH值對CIP降解的影響 pH值是水體中污染物降解的一個關鍵因素,其影響各種清除劑表面官能團的質子化過程[40].為探究PTCN/CaO2/vis體系的適用pH值范圍及最佳pH值,通過使用0.1mol/L的氫氧化鈉和0.1mol/L的硫酸調節(jié)體系初始pH值,設置不同梯度pH值(pH=3, 5, 7, 9和11,對照組pH值為9.52)來研究目標污染物CIP的降解情況.如圖4(b)所示,當pH值從3升高到11時,體系降解速率常數從10.55′10-2min-1下降到6.41′10-2min-1,降解速率常數顯著降低了39.2%,說明PTCN/CaO2/vis體系對CIP的降解效率在較高pH值下受到抑制.當體系酸性增強時,CIP的降解率相對應提高,pH值從9下降到3時,降解率相對應從90.6%上升到97.7%;當體系堿性增強時, CIP的降解率反而下降,pH值從9上升到11時,降解率相對應從90.6%下降到81.2%.目標污染物CIP在體系中不同初始pH值下的降解率不同,這是由于CaO2在不同pH值環(huán)境下釋放的過氧化氫的量不同所致,其釋放范圍為酸性至弱堿性,即pH=3～8.pH值在此范圍內越低,CaO2會釋放更多的過氧化氫,而過量的過氧化氫可以清除自由基的氧化[41].這與上一部分所提到的最佳投加比也有一定聯系,適量CaO2溶于水中時會生成氫氧化鈣以及過氧化氫,有助于體系的光催化降解(式(6));而過量的CaO2溶于水中在生成氫氧化鈣的同時也會生成氧氣(式(7)),相對應的過氧化氫釋放量下降.當pH值上升時,體系中OH-濃度也會相對應增加,過量的OH-與PTCN相互作用形成穩(wěn)定的帶負電化合物,從而導致光催化材料的降解作用被削弱[42];堿性環(huán)境也不利于Fenton反應的進行,故在最佳投加比上呈現先增后減的趨勢.綜上所述,在酸性條件下可以提高過氧化氫的釋放速率和利用效率,進而提高光催化降解目標污染物CIP的目的.

圖4 PTCN/CaO2/vis體系最佳反應條件探究

2.2.3 體系對不同初始CIP濃度的降解效果 目標污染物CIP不同初始濃度對PTCN/CaO2/vis體系降解效果的影響如圖4(c)所示,隨著目標污染物CIP的初始濃度增加(從1mg/L到20mg/L),體系降解效果逐漸降低,降解率從100%下降到79.7%,這與體系中單位污染物所對應的活性物質的量有關.當活性物質的量保持不變時,增加污染物濃度會導致相應處理活性物質的量減少,降解速率隨之而降低.

2.3 體系共存因子協同拮抗作用探究

在海水養(yǎng)殖廢水中,共存物質種類繁多,包括鉀、鈉、鈣等組成的高鹽度元素,腐殖酸(HA)等溶解性有機物(DOM),以及富集為營養(yǎng)元素的氮、碳和磷等[43-45].水中的溶解性有機物和無機陰、陽離子對光催化降解反應存在一定影響,如活性物種競爭[46–47]、光屏蔽效應[48]等.基于此,本文進一步研究了海水養(yǎng)殖廢水中共存因子的協同拮抗作用.

通過向PTCN/CaO2/vis體系中投加一系列無機陰離子(Cl-, NO3-和HCO3-)、HA和無機陽離子(NH4+, K+, Cu2+和Ca2+),對體系降解目標污染物CIP的影響進行單因素實驗(Cu2+的濃度為5mg/L,其他共存因子在反應體系中的濃度為10mg/L).如圖5(a)所示,與對照組降解速率常數(obs=7.15′10-2min-1)相比, Cl-, NH4+以及K+對目標污染物CIP的降解起協同作用,速率常數分別提高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+對目標污染物CIP的降解起拮抗作用,速率常數的抑制率分別為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).

在實驗條件下,K+起到較弱協同作用,Ca2+存在一定的拮抗作用,在水生環(huán)境中,它們都處于穩(wěn)定的氧化狀態(tài),幾乎不捕獲體系中的電子和空穴[49].腐殖酸可與活性物種反應競爭,同時由于光屏蔽效應使得CIP降解速率下降.研究發(fā)現,NO3-和HCO3-通常會與體系中的活性物種反應生成含氮自由基和碳氧自由基[50],即式(8)、(9)所示.盡管這兩種自由基存在氧化有機物的作用,但其具有選擇性,且氧化能力遠弱于羥基自由基[50],故對體系存在一定拮抗作用.

進一步,考察了超純水、自來水、湖水、珠江河水對PTCN/CaO2/vis體系降解目標污染物速率的影響.結果如圖5(b)所示,PTCN/CaO2/vis體系隨著背景水質中雜質的不斷減少,降解效率相對應增加,在超純水和自來水這兩種背景水質下的降解率分別為98.5%和91.8%;而在河水以及湖水中,降解率分別為78.4%和81.3%,雖然降解效率呈現削弱趨勢,但體系仍有較好的降解效果,表明PTCN/ CaO2/vis體系可應用于多種環(huán)境水以及飲用水中對CIP進行降解處理.

因此,在PTCN/CaO2/vis體系最佳實驗條件下,不同共存因子及背景水質對體系降解目標污染物CIP存在較為明顯的協同和拮抗作用;但總體而言,PTCN/CaO2/vis體系在不同實驗條件下仍能擁有較好的污水修復能力,具備良好的潛在應用性.

2.4 光催化劑循環(huán)實驗

為了檢驗PTCN/CaO2/vis體系在海水養(yǎng)殖廢水實際應用中降解目標污染物CIP的可循環(huán)性,進行了光催化劑循環(huán)實驗.從圖5(c)可以看出,在第5次循環(huán)實驗時,PTCN/CaO2/vis體系仍表現出較強的降解能力,表觀降解速率常數obs仍有5.74×10-2min-1,降解率為82.4%,僅下降了6.8%,證明PTCN光催化劑具備良好的可循環(huán)穩(wěn)定性,也進一步證明PTCN/ CaO2/vis體系用于降解海水養(yǎng)殖廢水中目標污染物的可行性.

2.5 活性物質的猝滅

在光催化降解過程中,活性物質往往占據主導貢獻[51].因此,本研究通過采用猝滅劑IPA, L- Histidine, TEMPO和Na2C2O4進行一系列猝滅實驗,分別對應猝滅活性物質·OH,1O2, O2·-以及h+[27,52-53],由式(2)～(5)計算對應活性物質在體系中的降解貢獻率,量化活性物質在PTCN/CaO2/vis體系中降解目標污染物CIP的作用.實驗結果如圖6(a)、(b)所示,當向體系中分別添加4種不同的猝滅劑IPA, L- Histidine, TEMPO和Na2C2O4時,相應的表觀降解速率常數obs分別從7.15′10-2min-1下降為5.64′10-2min-1、2.03′10-2min-1、0.39′10-2min-1和4.64′10-2min-1,通過計算得出·OH,1O2, O2·-和h+的貢獻率分別為21.1%、71.6%、94.5%和35.1%.實驗結果表明,在PTCN/CaO2/vis體系降解目標污染物CIP的過程中,活性物質O2·-占主導地位,1O2和h+這兩種活性物質也起到了一定的貢獻作用,而·OH則貢獻最少.

圖6 PTCN/CaO2/vis體系活性物質的猝滅

2.6 光催化降解過程中CIP降解產物探究及毒性預測

根據以往的報道,目標污染物CIP易受自由基所攻擊的位點包括-F、環(huán)丙基、哌嗪環(huán)和羧基[54].本研究在此理論基礎上,使用超高分辨四極桿組合靜電場軌道阱液相色譜—質譜聯用儀對CIP在PTCN/CaO2/vis體系中的降解產物進行檢測和分析,提出了兩種可能的降解路徑:脫羧反應和哌嗪環(huán)氧化,結果如圖7所示.對于路徑1,CIP (=332)通過脫羧反應生成了TP1 (=288)[55].在路徑2中,CIP (=332)的哌嗪環(huán)因其高電子密度而在體系中首先被攻擊,發(fā)生氧化和裂解生成TP2 (=362).隨后,前后分別失去兩次羰基,形成TP3 (=334)以及TP4 (=306).緊接著,脫去一個氨基以及羰基化反應,生成TP5 (=291).最后,再次失去一個羰基生成TP6 (=263),該路徑與先前的報道基本一致[56].最終,在自由基的氧化還原作用下,這些中間產物可進一步降解,礦化成為CO2, H2O, NH4+, NO3-和F-等無機離子.

圖7 PTCN/CaO2/vis體系下CIP可能的降解路徑

針對目標污染物CIP在降解過程中所產生的中間產物,本研究通過ECOSAR軟件對其進行慢性、急性毒性(LC50和CHV)模擬預測,根據歐盟危險品認證標準(67/548/EEC)和中國新化學物質危害評估導則(HJ/T154-2004),將所得數據進行進一步歸類(如圖8),并闡明相關中間產物的毒性特征.結果表明, 在水生環(huán)境中,母體CIP屬于聯合國毒性預測無害的水平.在PTCN/CaO2/vis體系下,大部分中間產物(TP2-TP5)在魚類、水蚤和綠藻的毒性預測數據中均與母體一致,屬于毒性預測無害的水平,基本表現出對水生生物更友好的特征.然而,值得注意的是,相較于母體CIP而言,TP1和TP6卻表現出更高的毒性,對部分水生生物屬于有毒有害水平.總的來說, PTCN/CaO2/vis體系在降解目標污染物CIP的過程中,大部分中間產物對水生生物表現出更友好特征,但在一定程度上仍存在生態(tài)風險. 在實際處理過程中,可通過延長降解時間來達到深度礦化目的,進一步降低中間產物的毒性.

圖8 CIP和轉化產物的毒理學分析及急性、慢性毒性等級評價

2.7 抗生素殘留抗菌活性測試及體系TOC去除率

在修復CIP污染水體的過程中,通常需要考慮消除其抗生素活性,以避免在生態(tài)環(huán)境中產生抗性基因并減少受污水體的修復難度.為探究PTCN/ CaO2/vis體系降解目標污染物CIP并消除其抗菌活性,以大腸桿菌(E.coli)為指標[57],對體系降解液進行抗生素殘留抗菌活性測試.實驗結果如圖9(a)所示,隨著PTCN/CaO2/vis體系降解時間的推移,降解液所產生的抑菌圈(黑色菱形標記上方)從2.5cm逐漸縮小,在6h降解液測試中抑菌圈完全消失.這說明延長PTCN/CaO2/vis體系反應降解時間至6h時,能將目標污染物CIP的抗生素殘留從海水養(yǎng)殖廢水中完全去除.此外,還研究了PTCN/CaO2/vis體系對目標污染物CIP的礦化效果,結果如圖9(b)所示,可以看出,隨著降解時間的推移,CIP逐漸被礦化,在90min時礦化率已接近50%.表明PTCN/CaO2/vis體系具備消除抗生素活性殘留及有效減輕生態(tài)環(huán)境風險的潛力.

圖9 PTCN/CaO2/vis體系抗生素殘留抗菌活性測試及降解CIP的礦化率

3 結論

3.1 本研究通過超分子自組裝和煅燒的方法合成PTCN,成功構建PTCN/CaO2/vis體系降解目標污染物CIP,該體系具備良好的降解活性,在實驗條件下CIP的表觀降解速率常數obs為7.15×10-2min-1.

3.2 單因素實驗結果表明,在酸性條件下,PTCN/ CaO2/vis體系表現出更強的CIP降解效能;在不同共存因子及背景水質下,PTCN/CaO2/vis體系對CIP降解存在不同程度的拮抗和協同作用;體系降解污染物能力隨CIP濃度降低而逐漸增強;光催化劑表現出良好的可循環(huán)性(5次循環(huán)后降解率仍有82.5%).

3.3 PTCN/CaO2/vis體系降解CIP過程中,活性物質O2·-占主導地位(貢獻率為94.5%),1O2和h+這兩種活性物質也起到了一定的貢獻作用.

3.4 目標污染物CIP在PTCN/CaO2/vis體系中的降解過程包括脫羧反應和哌嗪環(huán)氧化;降解過程中的大多數中間產物對水生生物表現出更為友好的特征;延長體系降解時間能有效消除抗菌活性.

[1] Liu X, Steele J C, Meng X Z. Usage, residue, and human health risk of antibiotics in Chinese aquaculture: A review [J]. Environmental Pollution, 2017,223:161–169.

[2] Wang X, Lin Y, Zheng Y, et al. Antibiotics in mariculture systems: A review of occurrence, environmental behavior, and ecological effects [J]. Environmental Pollution, 2022,293:118541.

[3] Mathur P, Sanyal D, Callahan D L, et al. Treatment technologies to mitigate the harmful effects of recalcitrant fluoroquinolone antibiotics on the environment and human health [J]. Environmental Pollution, 2021,291:118233.

[4] Chakraborty J, Nath I, Jabbour C, et al. Novel rapid room temperature synthesis of conjugated microporous polymer for metal-free photocatalytic degradation of fluoroquinolones [J]. Journal of Hazardous Materials, 2020,398:122928.

[5] Janecko N, Pokludova L, Blahova J, et al. Implications of fluoroquinolone contamination for the aquatic environment-A review: Fluoroquinolone in the aquatic ecosystem-A review [J]. Environmental Toxicology and Chemistry, 2016,35(11):2647–2656.

[6] Nguyen T D, Itayama T, Ramaraj R, et al. Chronic ecotoxicology and statistical investigation of ciprofloxacin and ofloxacin to Daphnia magna under extendedly long-term exposure [J]. Environmental Pollution, 2021,291:118095.

[7] Jin M K, Zhang Q, Zhao W L, et al. Fluoroquinolone antibiotics disturb the defense system, gut microbiome, and antibiotic resistance genes of Enchytraeus crypticus [J]. Journal of Hazardous Materials, 2022,424:127509.

[8] Tominaga F K, Boiani N F, Silva T T, et al. Acute and chronic ecotoxicological effects of pharmaceuticals and their mixtures in Daphnia similes [J]. Chemosphere, 2022,309:136671.

[9] Ma J, Chen F, Zhu Y, et al. Joint effects of microplastics and ciprofloxacin on their toxicity and fates in wheat: A hydroponic study [J]. Chemosphere, 2022,303:135023.

[10] Nguyen T D, Itayama T, Ramaraj R, et al. Physiological response of simocephalus vetulus to five antibiotics and their mixture under 48-h acute exposure [J]. Science of The Total Environment, 2022,829: 154585.

[11] Zhao Q, Guo W, Luo H, et al. Deciphering the transfers of antibiotic resistance genes under antibiotic exposure conditions: Driven by functional modules and bacterial community [J]. Water Research, 2021,205:117672.

[12] ?amani? I, Kalini? H, Fredotovi? ?, et al. Bacteria tolerant to colistin in coastal marine environment: Detection, microbiome diversity and antibiotic resistance genes’ repertoire [J]. Chemosphere, 2021,281: 130945.

[13] Zhang X, Zhang J, Han Q, et al. Antibiotics in mariculture organisms of different growth stages: Tissue-specific bioaccumulation and influencing factors [J]. Environmental Pollution, 2021,288:117715.

[14] Han Y, Wang J, Zhao Z, et al. Fishmeal application induces antibiotic resistance gene propagation in mariculture sediment [J]. Environmental Science & Technology, 2017,51(18):10850–10860.

[15] Lima V B, Goulart L A, Rocha R S, et al. Degradation of antibiotic ciprofloxacin by different AOP systems using electrochemically generated hydrogen peroxide [J]. Chemosphere, 2020,247:125807.

[16] Yu R, Wu Z. High adsorption for ofloxacin and reusability by the use of ZIF-8 for wastewater treatment [J]. Microporous and Mesoporous Materials, 2020,308:110494.

[17] Zhang Q, Tong Y, Wang Z, et al. Improved alkaline water electrolysis system for green energy: Sulfonamide antibiotic-assisted anodic oxidation integrated with hydrogen generation [J]. Journal of Materials Chemistry A, 2023,11,10.1039.

[18] McCorquodale-Bauer K, Grosshans R, Zvomuya F, et al. Critical review of phytoremediation for the removal of antibiotics and antibiotic resistance genes in wastewater [J]. Science of The Total Environment, 2023,870:161876.

[19] Han Y, Yang L, Chen X, et al. Removal of veterinary antibiotics from swine wastewater using anaerobic and aerobic biodegradation [J]. Science of The Total Environment, 2020,709:136094.

[20] Wang C, Yu R. Highly efficient visible light photocatalysis of tablet- like carbon-doped TiO2photocatalysts via pyrolysis of cellulose/ MIL-125(Ti) at low temperature [J]. Journal of Solid State Chemistry, 2022,309:122992.

[21] Antoniou M G, Boraei I, Solakidou M, et al. Enhancing photocatalytic degradation of the cyanotoxin microcystin-LR with the addition of sulfate-radical generating oxidants [J]. Journal of Hazardous Materials, 2018,360:461–470.

[22] Chen M, Chen Z, Wu P, et al. Simultaneous oxidation and removal of arsenite by Fe(iii)/CaO2Fenton-like technology [J]. Water Research, 2021,201:117312.

[23] Ali M, Tariq M, Sun Y, et al. Unveiling the catalytic ability of carbonaceous materials in Fenton-like reaction by controlled-release CaO2nanoparticles for trichloroethylene degradation [J]. Journal of Hazardous Materials, 2021,416:125935.

[24] Hou C, Zhao J, Zhang Y, et al. Enhanced simultaneous removal of cadmium, lead, and acetochlor in hyporheic zones with calcium peroxide coupled with zero-valent iron: Mechanisms and application [J]. Chemical Engineering Journal, 2022,427:130900.

[25] Cai T, Zheng W, Chang Q, et al. Carbon dot-boosted catalytic activity of CaO2by tuning visible light conversion [J]. Journal of Materials Chemistry A, 2022,10(14):7792–7799.

[26] Wang T, Zhao C, Meng L, et al. Fe?O?P bond in MIL-88A(Fe)/BOHP heterojunctions as a highway for rapid electron transfer to enhance photo-Fenton abatement of enrofloxacin [J]. Applied Catalysis B: Environmental, 2023,334:122832.

[27] Li D, Wen C, Huang J, et al. High-efficiency ultrathin porous phosphorus-doped graphitic carbon nitride nanosheet photocatalyst for energy production and environmental remediation [J]. Applied Catalysis B: Environmental, 2022,307:121099.

[28] Guo S, Deng Z, Li M, et al. Phosphorus-doped carbon nitride tubes with a layered micro-nanostructure for enhanced visible-light photocatalytic hydrogen evolution [J]. Angewandte Chemie International Edition, 2016,55(5):1830–1834.

[29] Lv Y, Liu H, Jin D, et al. Effective degradation of norfloxacin on Ag3PO4/CNTs photoanode: Z-scheme mechanism, reaction pathway, and toxicity assessment [J]. Chemical Engineering Journal, 2022,429: 132092.

[30] Xiao Z, Zheng Y, Chen P, et al. Photocatalytic degradation of ciprofloxacin in freshwater aquaculture wastewater by a CNBN membrane: mechanism, antibacterial activity, and cyclability [J]. Environmental Science: Nano, 2022,9(8):3110–3125.

[31] Li D, Liu Y, Wen C, et al. Construction of dual transfer channels in graphitic carbon nitride photocatalyst for high-efficiency environmental pollution remediation: Enhanced exciton dissociation and carrier migration [J]. Journal of Hazardous Materials, 2022,436: 129171.

[32] Wu Y, Jin X, Liu H, et al. Synergistic effects of boron nitride quantum dots and reduced ultrathin g-C3N4: Dual-channel carrier transfer and band structure regulation boost the photodegradation of fluoroquinolone [J]. Separation and Purification Technology, 2022, 303:122185.

[33] Ma H, Liu X, Liu N, et al. Defect-rich porous tubular graphitic carbon nitride with strong adsorption towards lithium polysulfides for high- performance lithium-sulfur batteries [J]. Journal of Materials Science & Technology, 2022,115:140–147.

[34] Weng Z, Lin Y, Han B, et al. Donor-acceptor engineered g-C3N4enabling peroxymonosulfate photocatalytic conversion to1O2with nearly 100% selectivity [J]. Journal of Hazardous Materials, 2023,448: 130869.

[35] Gou N, Yang W, Gao S, et al. Incorporation of ultrathin porous metal-free graphite carbon nitride nanosheets in polyvinyl chloride for efficient photodegradation [J]. Journal of Hazardous Materials, 2023, 447:130795.

[36] Liang Q, Zhang C, Xu S, et al. In situ growth of Cds quantum dots on phosphorus-doped carbon nitride hollow tubes as active 0D/1D heterostructures for photocatalytic hydrogen evolution [J]. Journal of Colloid and Interface Science, 2020,577:1–11.

[37] Guo S, Tang Y, Xie Y, et al. P-doped tubular g-C3N4with surface carbon defects: Universal synthesis and enhanced visible-light photocatalytic hydrogen production [J]. Applied Catalysis B: Environmental, 2017,218:664–671.

[38] Wang Z, Zhang Y, Tan Z, et al. A wet process for oxidation-absorption of nitric oxide by persulfate/calcium peroxide [J]. Chemical Engineering Journal, 2018,350:767–775.

[39] Fang Z, Liu Y, Chen P, et al. Insights into CQDs-doped perylene diimide photocatalysts for the degradation of naproxen [J]. Chemical Engineering Journal, 2023,451:138571.

[40] Song W, Wang X, Wang Q, et al. Plasma-induced grafting of polyacrylamide on graphene oxide nanosheets for simultaneous removal of radionuclides [J]. Physical Chemistry Chemical Physics, 2015,17(1):398–406.

[41] Xue G, Zheng M, Qian Y, et al. Comparison of aniline removal by UV/CaO2and UV/H2O2: Degradation kinetics and mechanism [J]. Chemosphere, 2020,255:126983.

[42] Zhao Y, Li J, Zhang S, et al. Efficient enrichment of uranium(VI) on amidoximated magnetite/graphene oxide composites [J]. RSC Advances, 2013,3(41):18952.

[43] Peng Y Y, Gao F, Yang H L, et al. Simultaneous removal of nutrient and sulfonamides from marine aquaculture wastewater by concentrated and attached cultivation of Chlorella vulgaris in an algal biofilm membrane photobioreactor (BF-MPBR) [J]. Science of The Total Environment, 2020,725:138524.

[44] Wang D, Song C, Zhang B, et al. Deciphering dissolved organic matter from freshwater aquaculture ponds in Eastern China based on optical and molecular signatures [J]. Process Safety and Environmental Protection, 2021,155:122–130.

[45] You X, Zhang Z, Guo L, et al. Integrating acidogenic fermentation and microalgae cultivation of bacterial-algal coupling system for mariculture wastewater treatment [J]. Bioresource Technology, 2021, 320:124335.

[46] Antonopoulou M, Papadopoulos V, Konstantinou I. Photocatalytic oxidation of treated municipal wastewaters for the removal of phenolic compounds: optimization and modeling using response surface methodology (RSM) and artificial neural networks (ANNs) [J]. Journal of Chemical Technology & Biotechnology, 2012,87(10): 1385–1395.

[47] Wu Y, Wang F, Jin X, et al. Highly active metal-free carbon dots/g-C3N4hollow porous nanospheres for solar-light-driven PPCPs remediation: Mechanism insights, kinetics and effects of natural water matrices [J]. Water Research, 2020,172:115492.

[48] Passananti M, Temussi F, Iesce M R, et al. The impact of the hydroxyl radical photochemical sources on the rivastigmine drug transformation in mimic and natural waters [J]. Water Research, 2013,47(14):5422– 5430.

[49] Wang C, Zhu L, Wei M, et al. Photolytic reaction mechanism and impacts of coexisting substances on photodegradation of bisphenol a by Bi2WO6in water [J]. Water Research, 2012,46(3):845–853.

[50] Cao Z, Yu X, Zheng Y, et al. Micropollutant abatement by the UV/chloramine process in potable water reuse: A review [J]. Journal of Hazardous Materials, 2022,424:127341.

[51] Chen M, Guo C, Hou S, et al. In-situ fabrication of Ag/P-g-C3N4composites with enhanced photocatalytic activity for sulfamethoxazole degradation [J]. Journal of Hazardous Materials, 2019,366:219–228.

[52] Chen P, Blaney L, Cagnetta G, et al. Degradation of ofloxacin by perylene diimide supramolecular nanofiber sunlight-driven photocatalysis [J]. Environmental Science & Technology, 2019,53(3): 1564–1575.

[53] Liu X, Han M, Liu Y, et al. Profiles and potential mobility of antibiotic resistance genes in different bioelectrochemistry-enhanced constructed wetlands [J]. Chemical Engineering Journal, 2022,450: 138005.

[54] Cao Y, Yuan X, Chen H, et al. Rapid concurrent photocatalysis- persulfate activation for ciprofloxacin degradation by Bi2S3quantum dots-decorated MIL-53(Fe) composites [J]. Chemical Engineering Journal, 2023,456:140971.

[55] Yu X, Zhang J, Zhang J, et al. Photocatalytic degradation of ciprofloxacin using Zn-doped Cu2O particles: Analysis of degradation pathways and intermediates [J]. Chemical Engineering Journal, 2019, 374:316–327.

[56] Li X, Qiu Y, Zhu Z, et al. Construction of magnetically separable dual Z-scheme g-C3N4/α-Fe2O3/Bi3TaO7photocatalyst for effective degradation of ciprofloxacin under visible light [J]. Chemical Engineering Journal, 2022,440:135840.

[57] Ou H, Ye J, Ma S, et al. Degradation of ciprofloxacin by UV and UV/H2O2via multiple-wavelength ultraviolet light-emitting diodes: Effectiveness, intermediates and antibacterial activity [J]. Chemical Engineering Journal, 2016,289:391–401.

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

國家自然科學基金資助項目(21906029,22076029,22176042);廣州市科技計劃項目(202102020774,201903010080)

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

曾煜豐(1998-),男,廣東揭陽人,廣東工業(yè)大學環(huán)境科學與工程學院碩士研究生,主要從事光催化降解有機新污染物研究.yofone_ 025@foxmail.com.

曾煜豐,牛夢洋,陳 平,等.PTCN/CaO2/vis體系降解海水養(yǎng)殖廢水中CIP:機理與歸趨 [J]. 中國環(huán)境科學, 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.