磺化生物炭活化過硫酸鹽去除水中鹽酸四環(huán)素

董康妮,謝更新*,晏 銘,晏卓逸,熊 鑫

磺化生物炭活化過硫酸鹽去除水中鹽酸四環(huán)素

董康妮1,謝更新1*,晏 銘2,晏卓逸1,熊 鑫1

(1.重慶大學(xué)環(huán)境與生態(tài)學(xué)院,重慶 400044；2.湖南大學(xué)環(huán)境科學(xué)與工程學(xué)院,湖南 長沙 410012)

采用高溫煅燒-磺化法制備磺化改性苧麻生物炭(SBC),并將其作為過硫酸鹽活化劑,實現(xiàn)了對水中鹽酸四環(huán)素(TCH)的高效去除.通過掃描電子顯微鏡(SEM)、比表面積分析儀(BET)、傅里葉變換紅外光譜(FT-IR)對SBC的形貌和結(jié)構(gòu)進行表征,研究了溶液初始pH值、SBC投加量、PS投加量對SBC/PS體系中TCH降解效果的影響,并考察了SBC的重復(fù)利用性能.結(jié)果表明,SBC為片層介孔材料,其表面含有豐富的含氧官能團和黃原酸酯官能團.在初始pH值為3,PS投加量為10mmol/L,SBC投加量為0.5g/L的最優(yōu)條件下,反應(yīng)180min后,SBC/PS體系對TCH的去除率達到89.0%,明顯優(yōu)于SBC、苧麻秸稈原始生物炭(BC)、PS和BC/PS體系.在實驗考察范圍內(nèi),SBC/PS體系對TCH的降解性能隨pH值(pH=3～11)的升高呈先降低后升高再降低的趨勢;隨SBC和PS投加量的升高,TCH的去除率呈先上升后下降的趨勢.自由基淬滅實驗和電子順磁共振(EPR)實驗表明,SBC/PS體系降解TCH的過程中產(chǎn)生了硫酸根自由基(SO4-?)、羥基自由基(?OH)、超氧自由基(O2-?)和單線氧(1O2),1O2起主導(dǎo)作用.循環(huán)利用實驗結(jié)果表明,SBC表現(xiàn)出良好的重復(fù)利用性能.研究認為SBC是一種環(huán)境友好、高效的非金屬碳基過硫酸鹽活化劑,具有良好的應(yīng)用前景.

生物炭；過硫酸鹽活化劑；鹽酸四環(huán)素；磺化改性；催化降解

四環(huán)素類抗生素是一類水溶性較好的廣譜抗生素,被廣泛應(yīng)用于養(yǎng)殖業(yè)和醫(yī)療行業(yè)[1-2].鹽酸四環(huán)素(TCH)是四環(huán)素鹽酸鹽,其更容易被人體和動物吸收,使用更為廣泛[3].但是,四環(huán)素類抗生素不能被動物或人體完全吸收,也難以通過常規(guī)污水處理方法去除[4],這導(dǎo)致四環(huán)素類抗生素極易進入自然水體.目前已在自然水體中廣泛檢測到四環(huán)素類抗生素的存在[5].過量使用四環(huán)素類抗生素會導(dǎo)致其在環(huán)境中的大量累積并產(chǎn)生抗性基因進而威脅到人類和動植物的生存[6-7].

基于過硫酸鹽的高級氧化技術(shù)具有降解四環(huán)素類抗生素的巨大潛能被廣泛應(yīng)用于抗生素等有機污染物的去除[8-9].苧麻秸稈生物炭含有豐富的含氧官能團[10],具有活化過硫酸鹽的潛能[11].但原始生物炭的催化活性有限,相關(guān)研究表明原子摻雜可以增加碳材料表面官能團和表面缺陷,為過硫酸鹽活化提供更多活性位點[13],增強碳材料的活化硫酸鹽的能力.

鑒于此,本研究選擇農(nóng)田廢棄苧麻秸稈制備苧麻秸稈原始生物炭(BC),采用磺化改性摻雜硫原子制備磺化苧麻秸稈生物炭(SBC),并活化過硫酸鹽(PS)降解水中TCH,分析了PS、BC、SBC、BC/PS和SBC/PS體系對水中TCH的去除能力,探究了初始pH值、PS投加量、SBC投加量對SBC/PS體系中TCH降解效果的影響,以及SBC重復(fù)利用性能,通過自由基淬滅實驗和電子順磁共振(EPR)證實了SBC活化PS降解TCH的自由基和1O2途徑.

1 材料與方法

1.1 材料與試劑

苧麻秸稈取自于湖南長沙某地農(nóng)田.

實驗試劑:鹽酸四環(huán)素(C22H24N2O8·HCl)、氫氧化鈉(NaOH)、二硫化碳(CS2)、硝酸(HNO3,質(zhì)量分數(shù):65%～68%)、過硫酸鈉(Na2S2O8)、甲醇(CH4O)、叔丁醇(C4H10O)、糠醇(C4H6O2)、對苯醌(C6H4O2)、高氯酸(HClO4)試劑均購于上海麥克林生化科技有限公司,均為分析純及以上等級.

1.2 實驗儀器

水質(zhì)分析儀(HQ40D,美國哈希),恒溫水浴振蕩器(SHA-B,金壇區(qū)金城海瀾儀器制造廠)、紫外可見光分光光度計(UV-752上海佑科儀器儀表有限公司),管式爐(SGTM-100,洛陽市西格瑪儀器制造有限公司).

1.3 苧麻秸稈原始生物炭(BC)制備

先用超純水清洗干凈,再在電熱鼓風干燥箱內(nèi)80℃烘干至恒重,冷卻至室溫后放入破碎機內(nèi)破碎,過100目篩,密封保存?zhèn)溆?

苧麻秸稈原始生物炭(BC)制備:取適量生物炭原料于坩堝中,將坩堝放置于管式爐的恒溫段,在氮氣氛圍中以10℃/min升至500℃后,保持溫度燒制2h,冷卻至室溫后取出,研磨過100目篩,密封保存?zhèn)溆?將制備的苧麻秸稈生物炭命名為BC.

1.4 磺化改性苧麻秸稈生物炭(SBC)制備

磺化改性參考文獻[13],將0.3g BC分散在100mL 0.1mol/L的NaOH中,加入3mL CS2,在35℃恒溫水浴振蕩器中振蕩24h,過濾分離,并用去離子水清洗生物炭直至中性,在60℃真空干燥箱中干燥12h,冷卻至室溫后取出研磨并過100目篩,用密封袋密封保存?zhèn)溆?

1.5 生物炭材料表征

生物炭的比表面積和孔隙結(jié)構(gòu)采用物理吸附分析儀(美國麥克ASAP 2460)測定,形貌采用超高分辨率場發(fā)射掃描電子顯微鏡(日本日立SU 8020)測定,表面官能團采用傅里葉紅外光譜儀(Nicolet IS10)測定,表面元素采用能譜(日本HORIBA HORIBA EX-350)測定.

1.6 TCH降解實驗

采用自行配置的20mg/L的TCH溶液,取100mL于錐形瓶中,加入0.05g生物炭,先暗吸附1h,然后加入10mmol/L PS 1mL,接觸2h,在預(yù)定時間取2.5mL樣品,加入0.5mL甲醇淬滅反應(yīng),經(jīng)0.22μm濾膜過濾后測定TCH的吸光度并計算其濃度,實驗均在35℃、130r/min的水浴振蕩器中進行,溶液初始pH值采用0.1mol/L的NaOH和HNO3調(diào)節(jié).根據(jù)預(yù)實驗結(jié)果,在pH值為3,PS投加量為10mmol/L,催化劑投加量為0.5g/L的條件下,探究了BC、SBC、BC/PS、SBC/PS和PS體系對水中TCH的降解效果.為了探究不同初始pH值對水體中TCH降解的影響,在PS的投加量為10mmol/L,SBC投加量為0.5g/L的條件下,分別設(shè)置初始pH值為3,5,7,9和11;為了探究不同PS投加量對TCH降解的影響,在pH值為3,SBC投加量為0.5g/L的條件下,分別設(shè)置了PS的投加量為1,5,10,15和20mmol/L;為了探究催化劑的投加量對水體中TCH降解的影響,在pH值為3,PS的投加量為10mmol/L的條件下,分別設(shè)置了SBC的投加量為0.1,0.3,0.5,0.8和1.0g/L;為了鑒定反應(yīng)中產(chǎn)生的活性物種,在pH值為3,PS的投加量為10mmol/L,SBC投加量為0.5g/L的條件下,分別加入0.1mol/L的甲醇(MeOH)、叔丁醇(TBA)、糠醇、對苯醌和高氯酸捕獲活性物種.

1.7 TCH的測定方法

采用紫外可見光分光光度計(UV-752上海佑科儀器儀表有限公司)測定,檢測波長為356nm.

1.8 數(shù)據(jù)處理

根據(jù)TCH的標準曲線計算反應(yīng)過程中不同時刻TCH的濃度,TCH去除率的表達式見式1,暗吸附1h的去除率為吸附去除率,反應(yīng)3h的去除率為總?cè)コ?總?cè)コ逝c吸附去除率的差值即為催化降解率.

式中:表示時刻TCH的去除率,%;0表示TCH初始濃度,mg/L;t表示時刻TCH的濃度,mg/L.

2 結(jié)果與討論

2.1 生物炭材料的表征

2.1.1 BET分析 如圖1a所示,在相對壓力達到0.8～1.0時,BC和SBC的吸附量增長速率顯著增加,具有明顯的H3型滯后回環(huán),屬于典型的Ⅳ型吸附.這表明BC和SBC均是片層材料,都存在介孔.如圖1b所示,在3.8nm處,BC和SBC都有明顯的尖峰,說明BC和SBC孔徑在3.8nm比較多,BC和SBC孔徑分布集中在2～50nm,說明BC和SBC是介孔材料. BC和SBC的比表面積分別為3.003和4.719m2/g,孔體積分別為0.017和0.021m3/g,平均孔徑分別為3.840和3.810nm(表1).

表1 BC和SBC的孔隙參數(shù)

2.1.2 SEM和EDS分析 如圖2所示,BC為表面光滑的片狀結(jié)構(gòu),且表面有許多小孔. SBC表面粗糙,表面有許多半球形突起,表面的小孔被覆蓋.這是由于磺化反應(yīng)在生物炭表面形成黃原酸酯涂層,涂層覆蓋了小孔并形成突起[12-13].由表2可以看出磺化反應(yīng)后,硫元素含量顯著增加,大約是磺化前的10倍,這說明硫原子成功摻雜到生物炭表面.

2.1.3 FT-IR分析 如圖3所示,BC在3442,1624,1439,1078和875cm-1有明顯的特征峰,分別與O-H伸縮振動、C=O、C-OH、-COOH和-OH變形振動有關(guān),這表明BC中含有豐富的含氧官能團. SBC在1626和1439cm-1處的振動是C=S伸縮振動,在1439和1078cm-1的振動分別對應(yīng)C-OH和-COOH的變形振動,在3442和1624cm-1處的振動分別對應(yīng)O-H和C=O的伸縮振動.反應(yīng)后的SBC,在1631cm-1處對應(yīng)的是C=S伸縮振動,在1631cm-1處的特征峰是黃原酸基團的特征峰[14].在1439和1078cm-1處的特征峰強度減弱,這表明含氧官能團和含硫官能團參與了PS的活化.

表2 BC和SBC元素含量分析

注: -為末檢驗.

圖3 BC、SBC、SBC(TCH)的FT-IR圖譜

2.2 不同體系對TCH降解效果比較

如圖4a所示,在反應(yīng)180min后,投加單一PS、BC和SBC的體系中,TCH的去除率分別為29.7%、39.7%和40.1%,BC/PS和SBC/PS體系對TCH的去除率分別為75.5%和89.0%,說明BC/PS和SBC/PS體系通過吸附和催化降解共同作用來實現(xiàn)對TCH的去除,BC/PS體系以吸附作用為主,SBC/PS體系以催化降解作用為主.

僅單獨使用PS時,TCH有部分降解,這可能是在酸性條件下H+可直接活化PS產(chǎn)生SO4-?,促進TCH的降解[15-16].如圖4b所示,單一PS、BC、SBC體系的一級反應(yīng)動力學(xué)常數(shù)分別為0.00321,0.00059和0.00055min-1,BC/PS和SBC/PS體系的一級反應(yīng)動力學(xué)常數(shù)分別為0.00404和0.01120min-1. BC/PS和SBC/PS體系的一級反應(yīng)動力學(xué)常數(shù)均大于單一體系,說明BC、SBC與PS之間存在協(xié)同作用,SBC與PS之間的協(xié)同作用更明顯.

2.3 TCH降解影響因素分析

2.3.1 溶液初始pH值對TCH降解的影響 無論是吸附還是催化反應(yīng)中,溶液的初始pH值都起著重要作用,初始pH值會影響PS和TCH的形態(tài),還會影響自由基的氧化性能[17-18].如圖5a所示,在暗吸附階段,TCH的吸附去除率隨pH值的增大而增大,pH值為11時的吸附去除率約是pH值為3時的2倍,這是因為TCH有3個酸堿中心區(qū),其pa值大小分別為pa1=3.30、pa2=7.44和pa3=9.27[19],TCH等電點位的pH值為5.4,當溶液pH值小于等電點位時,TCH表面帶正電,當溶液pH值大于5.4時,TCH表面帶負電[20],而SBC表面整體帶正電荷,隨著pH值的升高,靜電斥力逐漸減弱,吸附作用逐漸增強,這表明SBC吸附TCH時,靜電作用力扮演重要角色,這與之前研究結(jié)果一致[21].

反應(yīng)180min后,pH值為3的體系TCH的去除率和催化降解率均高于其他體系.在pH值為5時,TCH的去除率最低,這可能是酸性降低,酸活化作用減弱,而酸性降低促進了PS與H2O反應(yīng)生成非自由基離子HSO4-,體系中產(chǎn)生的自由基最少,對TCH的去除率最低[22-23].堿性條件下TCH的去除率大于中性條件,這是因為堿性條件能夠活化PS產(chǎn)生更多自由基[24],但是隨著堿性的增強,TCH的去除率下降,這是因為堿性越強,SO4-?和OH?反應(yīng)生成的?OH越多,而SO4-?是降解TCH的主要自由基[25].

2.3.2 PS投加量對TCH降解的影響 如圖5b所示,反應(yīng)180min后,當PS的投加量從1mmol/L增加到10mmol/L,SBC活化PS產(chǎn)生的SO4-?增加,TCH的去除率也隨之增加.但是當PS的投加量進一步增加,自由基發(fā)生自淬滅[26-27],導(dǎo)致參與TCH降解的SO4-?減少,TCH的去除率降低.

2.3.3 SBC投加量對TCH降解的影響 如圖5c所示,在暗吸附階段,TCH的吸附去除率隨著SBC投加量的增加而增加.反應(yīng)180min后,TCH的去除率呈現(xiàn)先增加后降低的趨勢,這主要是因為SBC投加量從0.1g/L增加到0.5g/L,PS活化的活性位點逐漸增加,產(chǎn)生的自由基也逐漸增加,TCH的去除率逐漸增大[28-29],但是當SBC投加量從0.5g/L增加到1.0g/L,SBC活化產(chǎn)生大量自由基,不能及時與TCH接觸而發(fā)生自淬滅或失活[30],抑制了TCH的降解.

2.4 SBC重復(fù)利用性能

如圖5d所示,使用5次后,SBC/PS體系對TCH的去除率從89.0%下降至65.9%.隨著重復(fù)使用次數(shù)增加,吸附位點被占據(jù),吸附去除率不斷降低[31].且第2次使用TCH吸附去除率較第1次下降顯著,這可能是因為吸附過程中,有機小分子堵塞了孔道,導(dǎo)致吸附量下降[18].每次重復(fù)使用,吸附去除率下降的量大于催化降解率下降的量,說明SBC吸附性能下降是SBC/PS體系中TCH去除率下降的主要原因.

2.5 SBC/PS體系去除TCH的機制分析

2.5.1 降解途徑的探討 原子摻雜生物炭活化過硫酸鹽降解污染物的途徑有自由基、非自由基途徑[32].采用MeOH作為SO4-?和?OH的淬滅劑,TBA和對苯醌分別作為?OH和O2-?的淬滅劑來鑒定自由基對TCH降解的貢獻[30].采用糠醇和高氯酸鈉分別鑒定1O2和電子傳遞對TCH降解的貢獻[33-34].如圖6所示,向體系中加入高氯酸鈉,基本沒有抑制TCH的降解,說明電子轉(zhuǎn)移途徑對體系中TCH的降解貢獻很小.加入MeOH、TBA、對苯醌和糠醇均抑制了TCH的降解,其中糠醇的抑制效果最明顯,這表明SBC/PS體系去除TCH過程中產(chǎn)生了SO4-?、?OH、O2-?和1O2,1O2對TCH的降解起主導(dǎo)作用.

圖6 淬滅劑對TCH降解的影響

為了進一步驗證體系中的自由基和非自由基途徑,采用二甲基吡啶氮-氧化物(DMPO)捕獲自由基,采用四甲基哌吡啶酮(TEMPO)捕獲1O2,在降解反應(yīng)進行5min時,通過電子順磁共振儀(EPR)檢測DMPO和TEMP分別與自由基和1O2的加合物.如圖7a所示,1:2:2:1的特征峰是DMPO與?OH結(jié)合形成的,在四重特征峰之間1:1:1:1:1:1的特征峰是DMPO與SO4-?結(jié)合形成的,圖7b中1:1:1:1的特征峰是DMPO與O2-?結(jié)合形成的,圖7c中有明顯的TEMPO-1O2的三重特征峰[35],說明體系中同時存在SO4-?、?OH、O2-?和1O2.綜合淬滅實驗和EPR分析,可以確SO4-?、?OH、O2-?和1O2均是參與TCH降解的活性物種,且1O2是一種對于TCH降解非常有效的活性物種.

2.5.2 SBC/PS體系去除TCH的機制探究 如圖8所示,SBC/PS體系通過吸附和催化降解兩大機制協(xié)同去除TCH.由BET測試可知,經(jīng)過磺化后,苧麻生物炭材料比表面積和孔體積增加,從而促進其通過孔填充效應(yīng)吸附TCH[36].由FT-IR測試可知,SBC材料表面含有豐富的含氧官能團,通過磺化改性后表面增加了含硫官能團,豐富的官能團使得SBC通過π-π作用力、氫鍵作用力、靜電力、Lewis酸堿作用、疏水作用等作用吸附TCH分子[37].

圖 7 SBC/PS體系的EPR圖譜

在催化降解過程中,如式2～4,表面含氧官能團(羥基和羧基)和含硫官能團(黃原酸酯)促進PS結(jié)構(gòu)中O-O鍵斷裂產(chǎn)生SO4-?[19],SO4-?進一步和溶液中的OH-反應(yīng)生成?OH(式5). PS在SBC的催化作用下產(chǎn)生O2-?(式6～7),O2-?通過自由基鏈式反應(yīng)促進SO4-?、?OH和1O2的生成(式8～10)[38].此外,基態(tài)氧分子3O2從SBC上獲得能量被激發(fā)為單線氧1O2(式11),整個體系在SO4-?、?OH、O2-?和1O2的共同作用下促進TCH的降解.

綜上,SBC的表面結(jié)構(gòu)有利于其對TCH分子的吸附,表面的羥基、羧基等含氧官能團和黃原酸酯官能團對PS起到活化作用,通過SBC的吸附和催化降解作用,提升了SBC/PS體系對TCH的去除效果.

圖8 SBC/PS體系去除TCH的機制示意

3 結(jié)論

3.1 通過磺化改性成功將硫原子摻雜到生物炭表面,表征結(jié)果表明,磺化改性苧麻生物炭屬于片狀介孔材料,材料表面有黃原酸酯涂層,含有豐富的含氧官能團.

3.2 初始pH值為3,PS投加量為10mmol/L,SBC投加量為0.5g/L,反應(yīng)溫度為35℃時,SBC/PS體系對初始濃度為20mg/L的TCH的去除率達到89.0%,明顯優(yōu)于SBC、BC、PS和BC/PS體系.

3.3 SBC豐富的羥基、羧基等含氧官能團黃原酸酯官能團為PS活化提供了大量活性位點,促進體系中產(chǎn)生SO4-?、?OH、O2-?和1O2,其中1O2是一種對于TCH降解非常有效的活性物種,在TCH的降解中起主導(dǎo)作用.

3.4 SBC/PS體系通過吸附和催化降解兩大機制協(xié)同去除水中TCH,本實驗中,SBC對TCH的吸附去除率最高達到38.4%. SBC表現(xiàn)出良好的重復(fù)使用性能,使用5次后,TCH的降解率仍然可達65%以上. SBC吸附性能下降是SBC/PS中TCH去除率下降的主要原因.

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Removal of tetracycline hydrochloride from aqueous solutions by sulfonated biochar-activated persulfate.

DONG Kang-ni1,XIE Geng-xin1*,YAN Ming2,YAN Zhuo-yi1,XIONG Xin1

(1.College of Environment and Ecology,Chongqing University,Chongqing 400044,China；2.College of Environmental Science & Engineering,Hunan University,Changsha 410012,China).,2022,42(8)：3650～3657

Sulfonated modified ramie biochar (SBC) was prepared by a high temperature calcination-sulfonation method and used as a persulfate activator to effectively remove tetracycline hydrochloride (TCH) from aqueous solutions. The morphology and structure of SBC were characterized by scanning electron microscopy (SEM),specific surface area analyzer (BET) and Fourier transform infrared spectroscopy (FT-IR). Effects of initial pH value and the dosages of SBC and PS on TCH degradation in the SBC/PS system were investigated. Also,reuse properties of synthetic materials were examined. The results showed that SBC were lamellar mesoporous materials with abundant oxygen-containing and xanthate functional groups on their surface. Under the optimal conditions of initial pH value of 3,PS dosage of 10mmol/L and SBC dosage of 0.5g/L,the TCH removal of SBC/PS system reached 89.0% after 180min,which was significantly better than that of SBC,ramie straw original biochar (BC),PS and BC/PS systems. Within the experiment scope of this investigation,the degradation performance of TCH by SBC/PS system exhibited a falling-rising-falling pattern with the increase of pH (pH=3～11). With increasing dosage of PS and SBC,the removal of TCH tended to increase,then drop. Free radical quenching experiments and electron paramagnetic resonance (EPR) experiments showed that the sulfate radical (SO4-?),hydroxyl radical (?OH),superoxide radical (O2-?) and single oxygen (1O2) were produced and1O2played a dominating role in the SBC/PS system during the degradation of TCH.The recycling experiments revealed that SBC had an improved reusability. This study suggested that the SBC was an environmentally friendly and efficient non-metallic carbon-based persulfate activator with a promising prospect of applications.

biochar；persulfate activator；tetracycline hydrochloride；sulfonated modified；catalytic degradation

X703

A

1000-6923(2022)08-3650-08

2022-01-07

裝備預(yù)研教育部聯(lián)合基金項目(6141A020221)

* 責任作者,教授,xiegengxin@vip.sina.com

董康妮(1997-),女,湖北宜昌人,重慶大學(xué)碩士研究生,主要從事水污染治理研究.