曾煜豐,牛夢(mèng)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(guó)光

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

曾煜豐,牛夢(mèng)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(guó)光**

(廣東工業(yè)大學(xué)環(huán)境科學(xué)與工程學(xué)院,廣東省環(huán)境催化與健康風(fēng)險(xiǎn)控制重點(diǎn)實(shí)驗(yàn)室,粵港澳污染物暴露與健康聯(lián)合實(shí)驗(yàn)室,廣東 廣州 510006)

本文擬建立摻磷管狀氮化碳(PTCN)/CaO2/可見(jiàn)光(vis)體系,將其應(yīng)用于海水養(yǎng)殖廢水中處理目標(biāo)污染物環(huán)丙沙星(CIP),并探究該體系反應(yīng)機(jī)理及抗生素CIP的環(huán)境歸趨.實(shí)驗(yàn)結(jié)果表明,PTCN/CaO2/vis體系具備良好的抗生素降解能力,在實(shí)驗(yàn)條件下CIP的表觀降解速率常數(shù)obs為7.15×10-2min-1;單因素實(shí)驗(yàn)表明,在酸性條件下,體系表現(xiàn)出更強(qiáng)的CIP降解效能,水中共存因子對(duì)體系降解CIP存在一定的影響;同時(shí),體系降解污染物能力隨CIP濃度降低而逐漸增強(qiáng);此外,該體系表現(xiàn)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(guò)程中,活性物質(zhì)O2·-占主導(dǎo)地位,1O2和h+這兩種活性物質(zhì)也起到一定的貢獻(xiàn)作用;目標(biāo)污染物CIP在體系中的降解過(guò)程包括脫羧反應(yīng)和哌嗪環(huán)氧化;降解過(guò)程中大多數(shù)中間產(chǎn)物對(duì)水生生物表現(xiàn)出更為友好的特征;最后,通過(guò)延長(zhǎng)體系降解時(shí)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(jī)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(jù)報(bào)道,在中國(guó)東南主要海水養(yǎng)殖場(chǎng)的淡水、咸水海產(chǎn)品中檢測(cè)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(shí),由于FQs具有較高的穩(wěn)定性[3]和抗生化降解性[4],傳統(tǒng)生物法對(duì)FQs去除率很低,排放到水生環(huán)境中能停留較長(zhǎng)時(shí)間[5],給生態(tài)環(huán)境修復(fù)以及各種生物帶來(lái)不利影響.在進(jìn)行抗生素暴露試驗(yàn)表明,FQs能對(duì)生物生育能力[6]和腸道健康[7]等帶來(lái)一定的負(fù)面影響,其中, CIP更是可通過(guò)酶[8]、基因表達(dá)[7]和細(xì)胞毒性[9–10]等渠道,給環(huán)境帶來(lái)過(guò)載負(fù)荷[11–12].而海水養(yǎng)殖場(chǎng)大多數(shù)為沿海建造經(jīng)營(yíng),海水養(yǎng)殖生物長(zhǎng)期暴露于含有FQs的水生環(huán)境中[13],經(jīng)食物鏈富集[14],對(duì)海洋生態(tài)穩(wěn)定造成嚴(yán)重危害.因此,亟需開(kāi)發(fā)先進(jìn)處理技術(shù)來(lái)去除海水養(yǎng)殖廢水中殘留的FQs.

傳統(tǒng)的廢水處理方法通常對(duì)FQs去除率較低,科研人員嘗試開(kāi)發(fā)其他新技術(shù),如物理吸附、電化學(xué)氧化、植物修復(fù)、生物降解和光催化等[15–20],這些新技術(shù)為FQs的處理提供了豐富的經(jīng)驗(yàn).其中,光催化降解因其高效、環(huán)境友好和低能耗等優(yōu)點(diǎn),已逐漸成為目前處理FQs的重要手段.隨著光催化技術(shù)的發(fā)展,光催化聯(lián)合其他氧化劑能更好去除和礦化典型的FQs污染[21].過(guò)氧化鈣(CaO2)被稱為固體H2O2[22],能克服消耗過(guò)快和利用率低的問(wèn)題,且具有易儲(chǔ)存和運(yùn)輸安全的優(yōu)點(diǎn),在環(huán)境修復(fù)中常用來(lái)替代H2O2,近年來(lái)成為了研究熱點(diǎn)[22–24].此外,CaO2可通過(guò)原位產(chǎn)生O2來(lái)改善水生環(huán)境缺氧導(dǎo)致的環(huán)境惡化問(wèn)題[25],因而在環(huán)境有機(jī)物污染修復(fù)方面,具備一定的前景.此前研究報(bào)道過(guò)將H2O2聯(lián)合光催化劑進(jìn)行光催化降解有機(jī)污染物[26],但目前將CaO2與光催化技術(shù)聯(lián)合協(xié)同修復(fù)環(huán)境問(wèn)題的研究與應(yīng)用尚為空白.

本文前期研究發(fā)現(xiàn),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(chǎn)和環(huán)境修復(fù)能力[27],同時(shí),前人的研究也證明摻磷管狀氮化碳(PTCN)的管狀結(jié)構(gòu)能增強(qiáng)光散射及活性位,具有更強(qiáng)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(fù)合體系——PTCN/CaO2/可見(jiàn)光(vis)體系,以海水養(yǎng)殖廢水中的CIP為目標(biāo)污染物,深入探究該體系的反應(yīng)降解機(jī)制及目標(biāo)污染物的環(huán)境歸趨.具體研究?jī)?nèi)容包括:(1)最佳反應(yīng)條件;(2)共存因子協(xié)同和拮抗作用;(3)光催化劑可循環(huán)性;(4)活性物質(zhì)在體系降解過(guò)程中的貢獻(xiàn);(5)CIP降解中間產(chǎn)物分析及產(chǎn)物毒性預(yù)測(cè);(6)抗生素殘留抗菌活性測(cè)試.相關(guān)研究結(jié)果將為海水養(yǎng)殖廢水處理提供一種新思路,對(duì)發(fā)展實(shí)際水體中的抗生素污染處理技術(shù)具有一定的理論意義.

1 材料與方法

1.1 試劑

CIP,純度>98%,購(gòu)自麥克林生化科技有限公司(中國(guó)上海).色譜級(jí)甲酸、甲醇均購(gòu)自安培實(shí)驗(yàn)技術(shù)有限公司(中國(guó)上海).常用化學(xué)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(gòu)自阿拉丁生化科技有限公司(中國(guó)上海),均為分析純.實(shí)驗(yàn)過(guò)程所用超純水(電阻率為18.25mΩ/cm)由尼珂LT-RY10超純水機(jī)(隆暾科技有限公司,中國(guó)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(chǔ)上進(jìn)行了適當(dāng)改進(jìn),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(diào)至1.0,適當(dāng)攪拌后將混合物轉(zhuǎn)移到帶有聚四氟乙烯內(nèi)襯的高壓反應(yīng)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(shí),合成摻磷片狀氮化碳(PCN)及普通氮化碳(CN)用于開(kāi)展對(duì)比實(shí)驗(yàn)[27].

1.3 表征方法

利用場(chǎng)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(jié)構(gòu).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(jié)構(gòu).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(guó))上對(duì)樣品進(jìn)行XPS分析.所得材料的光響應(yīng)特征和基團(tuán)特性在紫外可見(jiàn)近紅外分光光度計(jì)(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(guó))上進(jìn)行表征.

1.4 光催化反應(yīng)實(shí)驗(yàn)

本文背景水質(zhì)為中國(guó)廣東省汕頭市某海水養(yǎng)殖場(chǎng)所排放的海水養(yǎng)殖廢水,其相關(guān)水質(zhì)參數(shù)如表1所示(若無(wú)特殊說(shuō)明,均為該水基質(zhì)).

以CIP作為抗生素目標(biāo)污染物添加到水基質(zhì)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(lán)光(vis,波長(zhǎng)范圍為410～530nm, 5.8mW/cm2,由9w藍(lán)色LED燈提供)下啟動(dòng)光催化降解實(shí)驗(yàn).在既定時(shí)間點(diǎn)(0, 5, 10, 15, 20, 25和30min)取定量樣品并加入反應(yīng)終止劑(Na2S2O3),樣品通過(guò)0.45μm的水相濾膜過(guò)濾后采用高效液相色譜法(HPLC, SHIMADZU LC16,日本)測(cè)定殘留污染物濃度.

表1 海水養(yǎng)殖廢水主要水質(zhì)參數(shù)

為進(jìn)一步探究目標(biāo)污染物CIP在海水養(yǎng)殖廢水中的降解動(dòng)力學(xué),通過(guò)擬合偽一級(jí)反應(yīng)動(dòng)力學(xué)模型, 具體見(jiàn)式(1)并計(jì)算得出相應(yīng)的表觀降解速率常數(shù)obs.本研究中涉及實(shí)驗(yàn)均嚴(yán)格進(jìn)行3次以上平行實(shí)驗(yàn),數(shù)據(jù)最終取平均值分析.

1.5 活性物種探究

通過(guò)化學(xué)競(jìng)爭(zhēng)動(dòng)力學(xué)方法對(duì)體系進(jìn)行自由基猝滅實(shí)驗(yàn),以評(píng)估PTCN/CaO2/vis體系下對(duì)CIP降解過(guò)程中不同自由基的貢獻(xiàn)程度.具體過(guò)程為:在1.4節(jié)的基礎(chǔ)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(guò)自由基貢獻(xiàn)率計(jì)算式(2)～(5)評(píng)估不同活性物種對(duì)降解過(guò)程的影響.

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

1.6 分析方法

采用 HPLC檢測(cè)CIP的降解濃度,其中使用Zorbax Eclipse XDB-C18(4.6mm×250mm, 5μm)色譜柱進(jìn)行樣品組分分離,柱溫為35℃;流動(dòng)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(jìn)樣體積為20μL,光電二極管檢測(cè)器檢測(cè)波長(zhǎng)為278nm.

采用超高分辨四極桿組合靜電場(chǎng)軌道阱液相色譜—質(zhì)譜聯(lián)用儀(Thermo Scientific Ultimate 3000RSLC HPLC系統(tǒng)和Q-ExActive Orbitrap,美國(guó))對(duì)CIP的降解中間產(chǎn)物進(jìn)行檢測(cè)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(jìn)行樣品組分分離,柱溫為30℃;流動(dòng)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(fù)離子全掃描模式,干燥氣為高純N2.

1.7 毒性預(yù)測(cè)及抗生素殘留抗菌活性測(cè)試

通過(guò)ecological structure-activity relationship (ECOSAR)軟件預(yù)測(cè)目標(biāo)污染物CIP以及在降解過(guò)程中所產(chǎn)生中間產(chǎn)物的毒性,毒性根據(jù)歐盟危險(xiǎn)品認(rèn)證標(biāo)準(zhǔn)(67/548/EEC)和中國(guó)新化學(xué)物質(zhì)危害評(píng)估導(dǎo)則(HJ/T154-2004)進(jìn)行評(píng)估[29].

在長(zhǎng)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(shí)間段(0, 0.5, 1, 2, 4和6h)降解液樣品,通過(guò)測(cè)定抑菌圈大小,即大腸桿菌生長(zhǎng)抑制情況來(lái)評(píng)估抗生素殘留的抗菌活性.具體步驟為:將經(jīng)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(zhǔn)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(cè)量瓊脂平板上藥物敏感區(qū)所形成抑菌圈的大小[30].

2 結(jié)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(guò)SEM對(duì)PTCN及CaO2的形貌進(jìn)行了表征,結(jié)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(jié)構(gòu)可為光催化過(guò)程提供更大的接觸面以及更快的電子傳導(dǎo)[33],進(jìn)而提高體系的光催化降解效果.圖1(b)顯示,實(shí)驗(yàn)體系中所用CaO2顆粒呈碎塊狀,大小較為均勻.同時(shí),采用XRD對(duì)合成的PTCN、PCN和CN進(jìn)行晶體結(jié)構(gòu)分析,如圖1(c)所示,CN在13.0 °和27.4 °處表征出2個(gè)典型的衍射峰,分別被標(biāo)記為g-C3N4的(100)和(002)2個(gè)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(jié)構(gòu)[28].

采用XPS分析了合成材料的化學(xué)組成和化學(xué)狀態(tài),結(jié)果如圖2(a)～(d)所示.在Survey譜圖中, PTCN和PCN均可檢測(cè)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(gè)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(gè)峰,分別歸因?yàn)镃=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(méi)有顯示出磷的可檢測(cè)信號(hào)[36].

采用UV-vis DRS分析了樣品的光學(xué)性質(zhì),結(jié)果如圖3(a)所示,管狀結(jié)構(gòu)的形成增強(qiáng)了PTCN在整個(gè)波長(zhǎng)范圍內(nèi)(200～400nm)的光吸收,這歸功于入射光在微納米結(jié)構(gòu)管內(nèi)多次反射[36].通過(guò)FT-IR進(jìn)一步揭示了樣品的化學(xué)結(jié)構(gòu),結(jié)果如圖3(b)所示,3種材料均顯示出相似的光譜振動(dòng),即在802cm-1處尖峰為三嗪?jiǎn)卧牡湫驼駝?dòng),在1200～1600cm-1處為CN雜環(huán)的伸縮振動(dòng),表明PTCN保留了和PCN、CN相似的骨架結(jié)構(gòu),沒(méi)有引入其他明顯的官能團(tuán)[37].綜上表征結(jié)果,本實(shí)驗(yàn)過(guò)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(jiàn)光漫反射光譜及傅里葉變換紅外光譜

2.2 體系最佳反應(yīng)條件探究

2.2.1 體系PTCN和CaO2不同比例對(duì)CIP降解的影響 在PTCN體系中加入CaO2,期望通過(guò)產(chǎn)生更多活性物質(zhì)來(lái)協(xié)同增強(qiáng)氧化降解作用.本研究通過(guò)設(shè)置不同PTCN和CaO2的投加比例,探究其在光催化降解CIP時(shí)體系的最佳條件.實(shí)驗(yàn)過(guò)程中,光催化材料和氧化劑投加比從1:2增加至20:1,并設(shè)置2個(gè)單獨(dú)材料作為對(duì)照組.結(jié)果如圖4(a)所示,隨著投加比的增加,目標(biāo)污染物CIP的降解率也呈現(xiàn)相應(yīng)變化,體系中僅存在CaO2時(shí),目標(biāo)污染物的降解率幾乎為0,CaO2無(wú)法在vis激發(fā)下降解CIP;當(dāng)投加比從1:2增加至5:1時(shí),體系降解率相對(duì)應(yīng)增加,從83.1%增加到89.2%;之后當(dāng)投加比繼續(xù)增加時(shí),降解率呈減少趨勢(shì),到20:1的投加比時(shí),降解率降至74.2%;體系中僅存在PTCN時(shí),雖能降解目標(biāo)污染物,但在同等光催化反應(yīng)時(shí)間(30min)內(nèi),降解能力相較弱于體系中存在CaO2時(shí)的情況,僅有57.2%.可見(jiàn),當(dāng)體系中存在適量CaO2時(shí),PTCN和CaO2存在協(xié)同增強(qiáng)光催化降解現(xiàn)象,能促使體系中產(chǎn)生更多的活性物種,如·OH、O2·-等[38];但當(dāng)CaO2投加量過(guò)多時(shí),目標(biāo)污染物的降解率反而下降,可能是過(guò)多的CaO2占據(jù)了PTCN光催化劑表面的活性位點(diǎn),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(zhì)量比)為5:1,即0.02g:0.004g,該投加比對(duì)應(yīng)的CIP降解率是單獨(dú)PTCN的2.14倍.若無(wú)特殊說(shuō)明,后續(xù)實(shí)驗(yàn)均按該投加比進(jìn)行研究.

2.2.2 體系初始pH值對(duì)CIP降解的影響 pH值是水體中污染物降解的一個(gè)關(guān)鍵因素,其影響各種清除劑表面官能團(tuán)的質(zhì)子化過(guò)程[40].為探究PTCN/CaO2/vis體系的適用pH值范圍及最佳pH值,通過(guò)使用0.1mol/L的氫氧化鈉和0.1mol/L的硫酸調(diào)節(jié)體系初始pH值,設(shè)置不同梯度pH值(pH=3, 5, 7, 9和11,對(duì)照組pH值為9.52)來(lái)研究目標(biāo)污染物CIP的降解情況.如圖4(b)所示,當(dāng)pH值從3升高到11時(shí),體系降解速率常數(shù)從10.55′10-2min-1下降到6.41′10-2min-1,降解速率常數(shù)顯著降低了39.2%,說(shuō)明PTCN/CaO2/vis體系對(duì)CIP的降解效率在較高pH值下受到抑制.當(dāng)體系酸性增強(qiáng)時(shí),CIP的降解率相對(duì)應(yīng)提高,pH值從9下降到3時(shí),降解率相對(duì)應(yīng)從90.6%上升到97.7%;當(dāng)體系堿性增強(qiáng)時(shí), CIP的降解率反而下降,pH值從9上升到11時(shí),降解率相對(duì)應(yīng)從90.6%下降到81.2%.目標(biāo)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(guò)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(nèi)越低,CaO2會(huì)釋放更多的過(guò)氧化氫,而過(guò)量的過(guò)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(lián)系,適量CaO2溶于水中時(shí)會(huì)生成氫氧化鈣以及過(guò)氧化氫,有助于體系的光催化降解(式(6));而過(guò)量的CaO2溶于水中在生成氫氧化鈣的同時(shí)也會(huì)生成氧氣(式(7)),相對(duì)應(yīng)的過(guò)氧化氫釋放量下降.當(dāng)pH值上升時(shí),體系中OH-濃度也會(huì)相對(duì)應(yīng)增加,過(guò)量的OH-與PTCN相互作用形成穩(wěn)定的帶負(fù)電化合物,從而導(dǎo)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(yīng)的進(jìn)行,故在最佳投加比上呈現(xiàn)先增后減的趨勢(shì).綜上所述,在酸性條件下可以提高過(guò)氧化氫的釋放速率和利用效率,進(jìn)而提高光催化降解目標(biāo)污染物CIP的目的.

圖4 PTCN/CaO2/vis體系最佳反應(yīng)條件探究

2.2.3 體系對(duì)不同初始CIP濃度的降解效果 目標(biāo)污染物CIP不同初始濃度對(duì)PTCN/CaO2/vis體系降解效果的影響如圖4(c)所示,隨著目標(biāo)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(duì)應(yīng)的活性物質(zhì)的量有關(guān).當(dāng)活性物質(zhì)的量保持不變時(shí),增加污染物濃度會(huì)導(dǎo)致相應(yīng)處理活性物質(zhì)的量減少,降解速率隨之而降低.

2.3 體系共存因子協(xié)同拮抗作用探究

在海水養(yǎng)殖廢水中,共存物質(zhì)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(jī)物(DOM),以及富集為營(yíng)養(yǎng)元素的氮、碳和磷等[43-45].水中的溶解性有機(jī)物和無(wú)機(jī)陰、陽(yáng)離子對(duì)光催化降解反應(yīng)存在一定影響,如活性物種競(jìng)爭(zhēng)[46–47]、光屏蔽效應(yīng)[48]等.基于此,本文進(jìn)一步研究了海水養(yǎng)殖廢水中共存因子的協(xié)同拮抗作用.

通過(guò)向PTCN/CaO2/vis體系中投加一系列無(wú)機(jī)陰離子(Cl-, NO3-和HCO3-)、HA和無(wú)機(jī)陽(yáng)離子(NH4+, K+, Cu2+和Ca2+),對(duì)體系降解目標(biāo)污染物CIP的影響進(jìn)行單因素實(shí)驗(yàn)(Cu2+的濃度為5mg/L,其他共存因子在反應(yīng)體系中的濃度為10mg/L).如圖5(a)所示,與對(duì)照組降解速率常數(shù)(obs=7.15′10-2min-1)相比, Cl-, NH4+以及K+對(duì)目標(biāo)污染物CIP的降解起協(xié)同作用,速率常數(shù)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(duì)目標(biāo)污染物CIP的降解起拮抗作用,速率常數(shù)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(shí)驗(yàn)條件下,K+起到較弱協(xié)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(yīng)競(jìng)爭(zhēng),同時(shí)由于光屏蔽效應(yīng)使得CIP降解速率下降.研究發(fā)現(xiàn),NO3-和HCO3-通常會(huì)與體系中的活性物種反應(yīng)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(jī)物的作用,但其具有選擇性,且氧化能力遠(yuǎn)弱于羥基自由基[50],故對(duì)體系存在一定拮抗作用.

進(jìn)一步,考察了超純水、自來(lái)水、湖水、珠江河水對(duì)PTCN/CaO2/vis體系降解目標(biāo)污染物速率的影響.結(jié)果如圖5(b)所示,PTCN/CaO2/vis體系隨著背景水質(zhì)中雜質(zhì)的不斷減少,降解效率相對(duì)應(yīng)增加,在超純水和自來(lái)水這兩種背景水質(zhì)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(xiàn)削弱趨勢(shì),但體系仍有較好的降解效果,表明PTCN/ CaO2/vis體系可應(yīng)用于多種環(huán)境水以及飲用水中對(duì)CIP進(jìn)行降解處理.

因此,在PTCN/CaO2/vis體系最佳實(shí)驗(yàn)條件下,不同共存因子及背景水質(zhì)對(duì)體系降解目標(biāo)污染物CIP存在較為明顯的協(xié)同和拮抗作用;但總體而言,PTCN/CaO2/vis體系在不同實(shí)驗(yàn)條件下仍能擁有較好的污水修復(fù)能力,具備良好的潛在應(yīng)用性.

2.4 光催化劑循環(huán)實(shí)驗(yàn)

為了檢驗(yàn)PTCN/CaO2/vis體系在海水養(yǎng)殖廢水實(shí)際應(yīng)用中降解目標(biāo)污染物CIP的可循環(huán)性,進(jìn)行了光催化劑循環(huán)實(shí)驗(yàn).從圖5(c)可以看出,在第5次循環(huán)實(shí)驗(yàn)時(shí),PTCN/CaO2/vis體系仍表現(xiàn)出較強(qiáng)的降解能力,表觀降解速率常數(shù)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(jìn)一步證明PTCN/ CaO2/vis體系用于降解海水養(yǎng)殖廢水中目標(biāo)污染物的可行性.

2.5 活性物質(zhì)的猝滅

在光催化降解過(guò)程中,活性物質(zhì)往往占據(jù)主導(dǎo)貢獻(xiàn)[51].因此,本研究通過(guò)采用猝滅劑IPA, L- Histidine, TEMPO和Na2C2O4進(jìn)行一系列猝滅實(shí)驗(yàn),分別對(duì)應(yīng)猝滅活性物質(zhì)·OH,1O2, O2·-以及h+[27,52-53],由式(2)～(5)計(jì)算對(duì)應(yīng)活性物質(zhì)在體系中的降解貢獻(xiàn)率,量化活性物質(zhì)在PTCN/CaO2/vis體系中降解目標(biāo)污染物CIP的作用.實(shí)驗(yàn)結(jié)果如圖6(a)、(b)所示,當(dāng)向體系中分別添加4種不同的猝滅劑IPA, L- Histidine, TEMPO和Na2C2O4時(shí),相應(yīng)的表觀降解速率常數(shù)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(guò)計(jì)算得出·OH,1O2, O2·-和h+的貢獻(xiàn)率分別為21.1%、71.6%、94.5%和35.1%.實(shí)驗(yàn)結(jié)果表明,在PTCN/CaO2/vis體系降解目標(biāo)污染物CIP的過(guò)程中,活性物質(zhì)O2·-占主導(dǎo)地位,1O2和h+這兩種活性物質(zhì)也起到了一定的貢獻(xiàn)作用,而·OH則貢獻(xiàn)最少.

圖6 PTCN/CaO2/vis體系活性物質(zhì)的猝滅

2.6 光催化降解過(guò)程中CIP降解產(chǎn)物探究及毒性預(yù)測(cè)

根據(jù)以往的報(bào)道,目標(biāo)污染物CIP易受自由基所攻擊的位點(diǎn)包括-F、環(huán)丙基、哌嗪環(huán)和羧基[54].本研究在此理論基礎(chǔ)上,使用超高分辨四極桿組合靜電場(chǎng)軌道阱液相色譜—質(zhì)譜聯(lián)用儀對(duì)CIP在PTCN/CaO2/vis體系中的降解產(chǎn)物進(jìn)行檢測(cè)和分析,提出了兩種可能的降解路徑:脫羧反應(yīng)和哌嗪環(huán)氧化,結(jié)果如圖7所示.對(duì)于路徑1,CIP (=332)通過(guò)脫羧反應(yīng)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(gè)氨基以及羰基化反應(yīng),生成TP5 (=291).最后,再次失去一個(gè)羰基生成TP6 (=263),該路徑與先前的報(bào)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(chǎn)物可進(jìn)一步降解,礦化成為CO2, H2O, NH4+, NO3-和F-等無(wú)機(jī)離子.

圖7 PTCN/CaO2/vis體系下CIP可能的降解路徑

針對(duì)目標(biāo)污染物CIP在降解過(guò)程中所產(chǎn)生的中間產(chǎn)物,本研究通過(guò)ECOSAR軟件對(duì)其進(jìn)行慢性、急性毒性(LC50和CHV)模擬預(yù)測(cè),根據(jù)歐盟危險(xiǎn)品認(rèn)證標(biāo)準(zhǔn)(67/548/EEC)和中國(guó)新化學(xué)物質(zhì)危害評(píng)估導(dǎo)則(HJ/T154-2004),將所得數(shù)據(jù)進(jìn)行進(jìn)一步歸類(如圖8),并闡明相關(guān)中間產(chǎn)物的毒性特征.結(jié)果表明, 在水生環(huán)境中,母體CIP屬于聯(lián)合國(guó)毒性預(yù)測(cè)無(wú)害的水平.在PTCN/CaO2/vis體系下,大部分中間產(chǎn)物(TP2-TP5)在魚(yú)類、水蚤和綠藻的毒性預(yù)測(cè)數(shù)據(jù)中均與母體一致,屬于毒性預(yù)測(cè)無(wú)害的水平,基本表現(xiàn)出對(duì)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(xiàn)出更高的毒性,對(duì)部分水生生物屬于有毒有害水平.總的來(lái)說(shuō), PTCN/CaO2/vis體系在降解目標(biāo)污染物CIP的過(guò)程中,大部分中間產(chǎn)物對(duì)水生生物表現(xiàn)出更友好特征,但在一定程度上仍存在生態(tài)風(fēng)險(xiǎn). 在實(shí)際處理過(guò)程中,可通過(guò)延長(zhǎng)降解時(shí)間來(lái)達(dá)到深度礦化目的,進(jìn)一步降低中間產(chǎn)物的毒性.

圖8 CIP和轉(zhuǎn)化產(chǎn)物的毒理學(xué)分析及急性、慢性毒性等級(jí)評(píng)價(jià)

2.7 抗生素殘留抗菌活性測(cè)試及體系TOC去除率

在修復(fù)CIP污染水體的過(guò)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(chǎn)生抗性基因并減少受污水體的修復(fù)難度.為探究PTCN/ CaO2/vis體系降解目標(biāo)污染物CIP并消除其抗菌活性,以大腸桿菌(E.coli)為指標(biāo)[57],對(duì)體系降解液進(jìn)行抗生素殘留抗菌活性測(cè)試.實(shí)驗(yàn)結(jié)果如圖9(a)所示,隨著PTCN/CaO2/vis體系降解時(shí)間的推移,降解液所產(chǎn)生的抑菌圈(黑色菱形標(biāo)記上方)從2.5cm逐漸縮小,在6h降解液測(cè)試中抑菌圈完全消失.這說(shuō)明延長(zhǎng)PTCN/CaO2/vis體系反應(yīng)降解時(shí)間至6h時(shí),能將目標(biāo)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(duì)目標(biāo)污染物CIP的礦化效果,結(jié)果如圖9(b)所示,可以看出,隨著降解時(shí)間的推移,CIP逐漸被礦化,在90min時(shí)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(fēng)險(xiǎn)的潛力.

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

3 結(jié)論

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

3.2 單因素實(shí)驗(yàn)結(jié)果表明,在酸性條件下,PTCN/ CaO2/vis體系表現(xiàn)出更強(qiáng)的CIP降解效能;在不同共存因子及背景水質(zhì)下,PTCN/CaO2/vis體系對(duì)CIP降解存在不同程度的拮抗和協(xié)同作用;體系降解污染物能力隨CIP濃度降低而逐漸增強(qiáng);光催化劑表現(xiàn)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(guò)程中,活性物質(zhì)O2·-占主導(dǎo)地位(貢獻(xiàn)率為94.5%),1O2和h+這兩種活性物質(zhì)也起到了一定的貢獻(xiàn)作用.

3.4 目標(biāo)污染物CIP在PTCN/CaO2/vis體系中的降解過(guò)程包括脫羧反應(yīng)和哌嗪環(huán)氧化;降解過(guò)程中的大多數(shù)中間產(chǎn)物對(duì)水生生物表現(xiàn)出更為友好的特征;延長(zhǎng)體系降解時(shí)間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

國(guó)家自然科學(xué)基金資助項(xiàng)目(21906029,22076029,22176042);廣州市科技計(jì)劃項(xiàng)目(202102020774,201903010080)

* 責(zé)任作者, 副教授, gdutchp@163.com; ** 教授, liugg615@163.com

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

曾煜豐,牛夢(mèng)洋,陳 平,等.PTCN/CaO2/vis體系降解海水養(yǎng)殖廢水中CIP:機(jī)理與歸趨 [J]. 中國(guó)環(huán)境科學(xué), 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.