盧 偉,桑穩(wěn)姣*,李 敏,張文斌,賈丹妮,占 誠,賀永健,陳翠珍,向雪蓮

介質(zhì)阻擋放電等離子體老化微塑料及對Zn(II)吸附的影響

盧 偉1,桑穩(wěn)姣1*,李 敏2,張文斌1,賈丹妮1,占 誠1,賀永健1,陳翠珍2,向雪蓮3

(1.武漢理工大學土木工程與建筑學院,湖北 武漢 430070；2.武漢市水務(wù)科學研究院,湖北 武漢 430014；3.宜昌市城市規(guī)劃設(shè)計研究院有限責任公司,湖北 宜昌 443001)

為了在實驗中縮短微塑料的老化時間,更真實地模擬自然老化條件,采用介質(zhì)阻擋放電(DBD)等離子體老化聚乙烯微塑料(PE-MP)和聚丙烯微塑料(PP-MP),同時研究了老化前后PE-MP和PP-MP對Zn(II)的吸附過程和機理.隨著放電時間延長和輸入電壓升高,微塑料表面出現(xiàn)微小裂紋或孔洞,形成含氧官能團.老化后PE-MP和PP-MP對Zn(II)的吸附容量分別提高了22.7%和14.8%.老化前后微塑料對Zn(II)的吸附均符合準二級動力學模型.顆粒內(nèi)擴散模型表明,Zn(II)在微塑料上的吸附過程可分為快速吸附,慢速吸附和吸附平衡3個階段.同時,老化前后微塑料對Zn(II)的吸附均符合Langmuir吸附等溫線模型.熱力學結(jié)果表明,微塑料對Zn(II)的吸附是自發(fā)的吸熱過程. Ca2+、腐殖酸和低pH值不利于微塑料對Zn(II)的吸附.

微塑料；老化；等離子體；吸附；Zn(II)

近年來,尺寸小于5mm的微塑料引起的環(huán)境問題越來越受到人們的關(guān)注[1-3].目前,在海洋[4-5],湖泊[6],河流[7],甚至南極洲[8]和空氣[9]中都發(fā)現(xiàn)了微塑料.微塑料具有較大的比表面積和疏水表面,容易在其表面富集一些有機污染物和重金屬離子,從而導致這些有毒污染物在生物鏈上傳遞[10].另一方面,環(huán)境中的微塑料隨著時間的推移不斷老化[11],這將改變微塑料的表面性質(zhì),促進各種污染物與微塑料之間的相互作用,并進一步增加環(huán)境污染的風險[12]. Liu等[13]發(fā)現(xiàn)與聚乙烯和聚苯乙烯相比,聚丙烯的表面老化性能發(fā)生了較大的變化,表現(xiàn)為快速碎裂和表面氧化.聚乙烯和聚苯乙烯對Co(II)的吸附容量隨老化程度的增加而增加,而不同老化程度的聚丙烯對Co(II)的吸附性能變化不大.Lin等[14]發(fā)現(xiàn)PP-MP在氙燈照射28d老化后,對Pb2+的吸附量是原始的1.7～2.5倍.

在自然條件下,微塑料的老化非常緩慢,極大地限制了對微塑料老化行為的研究.因此,許多研究人員用光輻照,化學氧化,熱處理和γ-射線輻照等技術(shù)代替自然條件來探索微塑料的老化.高級氧化法因其產(chǎn)生的活性物質(zhì)(·OH,H2O2,·SO4-等)能加速微塑料老化而在實驗室研究中應(yīng)用最為廣泛.Fan等[15]研究發(fā)現(xiàn)老化后輪胎磨損顆粒和PE-MP的表面出現(xiàn)了小孔和裂紋,輪胎磨損顆粒和PE-MP的比表面積也有所增加.Lang等[16]用H2O2和Fenton試劑研究了聚苯乙烯(PS)的老化性能,發(fā)現(xiàn)老化不僅增加了PS的比表面積,而且氧化了PS表面的官能團,顯著增加了PS表面的羰基和羧基的含量.然而,這些人工加速老化技術(shù)也存在條件過于單一及無法模擬自然環(huán)境中復雜的老化過程等缺點.DBD等離子體可以產(chǎn)生多種活性物質(zhì)(O3,·OH,H2O2等),以及紫外可見光和局部高溫效應(yīng)[17-18],可以更合理地模擬自然環(huán)境.Galmiz等[19]研究發(fā)現(xiàn),等離子體處理改變了塑料管的表面化學成分和性能.因此,推測DBD等離子體可能是模擬微塑料在自然環(huán)境中老化的潛在技術(shù).

Zn(II)屬于典型的二類重金屬污染物,對水體中的魚類和水生植物有一定的毒害作用,并且能夠在動植物體內(nèi)積累,進而影響生態(tài)系統(tǒng)[20-21].本研究利用DBD等離子體技術(shù)對PE-MP和PP-MP進行老化處理,并對其吸附Zn(Ⅱ)的性能進行研究.以期為探究微塑料的老化和微塑料作為重金屬離子載體給環(huán)境帶來的風險提供參考.

1 材料與方法

1.1 材料

實驗所用試劑: PE-MP,PP-MP,無水乙醇,鹽酸(HCl),氯化鈣(CaCl2),ZnSO4·7H2O (分析純),氫氧化鈉(NaOH)和腐殖酸(HA)購自上海麥克林生化科技有限公司,PE-MP和PP-MP的平均粒徑為150 μm.PE-MP和PP-MP在去離子水和10%鹽酸溶液中浸泡24h,然后用無水乙醇和超純水多次洗滌以去除微塑料表面的有機雜質(zhì)和金屬離子并干燥.

HA儲備液: 稱取1.00g HA,投入到1L的去離子水中,滴加適量的0.1mol/L NaOH使其溶解,用0.45 μm濾膜濾去不溶物.

1.2 實驗裝置

DBD等離子體裝置(南京蘇曼電子有限公司)主要由接觸式調(diào)壓器(TDCG2-1),等離子體發(fā)生電源(CTP-2000K),DBD反應(yīng)器(DBD-50)和數(shù)字示波器組成(DS1102E)[22](圖1).接觸電壓調(diào)壓器采用自耦合電壓調(diào)節(jié);等離子體發(fā)生電源屬于控制電源輸入為AC220V的低溫等離子體實驗電源,其主面板上可顯示輸入電流和電壓;等離子體反應(yīng)器為石英制成的雙層介質(zhì)阻擋反應(yīng)器;數(shù)字示波器可顯示放電過程中的放電電壓和放電頻率等參數(shù).

圖1 實驗裝置示意

1.3 等離子體老化微塑料

將微塑料在DBD等離子體反應(yīng)器中分批老化,每批將3g 微塑料(PE-MP或PP-MP)放入DBD反應(yīng)器中,加入5mL去離子水后,將輸入電壓分別調(diào)整為30,60和90V,輸入電流為0.5A,放電4,8,10和12h后取樣進行清洗和干燥.

1.4 微塑料對Zn(II)的吸附

1.4.1 吸附動力學 分別取0.5g原始或老化微塑料放入錐形瓶中,加入濃度為5mg/L的Zn(II)溶液50mL(pH=6),在25℃,轉(zhuǎn)速為160r/min條件下振蕩48h.分別于0.25,0.5,1.0,2.0,4.0,8.0,12,24,48h取樣,用0.2μm濾膜去除溶液中的微塑性顆粒.取上清液5mL,用原子吸收光譜儀測定Zn(II)含量.每個處理過程設(shè)3組平行,不加PE-MP(或PP-MP)組為對照組.通過測定對照組和處理組的Zn(II)含量差值,計算PE-MP(或PP-MP)對Zn(II)的吸附量.

對所得吸附動力學數(shù)據(jù)用準一級動力學,準二級動力學和顆粒內(nèi)擴散模型擬合.

1.4.2 等溫吸附實驗 用分析純ZnSO4·7H2O配制50mg/L的Zn(II) 儲備液,將Zn(II) 儲備液分別稀釋為0.1,0.2,0.5,1.0,3.0,5.0mg/L.將原始或老化PE- MP(或PP-MP)樣品0.5g放入錐形燒瓶中,加入濃度為0.1～5mg/L的Zn(II)溶液50mL.在25℃,轉(zhuǎn)速為160r/min條件下振蕩48h.后續(xù)實驗步驟與吸附動力學實驗相同.

PE-MP和PP-MP對Zn(II)的吸附等溫線可用Langmuir方程和Freundlich方程描述.

1.4.3 吸附熱力學 采用van't Hoff方程考察熱力學參數(shù),即吉布斯自由能Δ0,焓變Δ0和熵變Δ0的變化,以確定微塑料對Zn(II)吸附過程的熱變性和自發(fā)性,試驗溫度分別為 288,298和 308K.

1.5 分析方法

用掃描電子顯微鏡(SEM,JEM-7500F,日本)觀察老化前后PE-MP和PP-MP的形態(tài)變化.采用傅立葉變換紅外光譜(FTIR,Nexus,美國),X射線光電子能譜儀(XPS,ESCALAB 250Xi,美國)和X射線衍射(XRD,D8Advance,德國)對其表面官能團,表面元素和晶體結(jié)構(gòu)進行分析.用原子吸收光譜儀(CONTRAA-700,德國)測定溶液中的Zn(II)濃度.

2 結(jié)果與討論

2.1 等離子體老化PE-MP和PP-MP

2.1.1 老化前后PE-MP和PP-MP的形貌特征 如圖2所示,原始PE-MP和PP-MP的表面相對較光滑,隨著放電時間延長和輸入電壓升高,微塑料表面變得越來越粗糙.當電壓和老化時間增加到一定程度時,老化后PE-MP和PP-MP的表面出現(xiàn)細小的裂紋或孔洞.結(jié)果表明,等離子體有效促進了PE-MP和PP-MP的老化,增加了PE-MP和PP-MP的比表面積,這可能會產(chǎn)生更多的吸附位點,有利于污染物的吸附[23].同時,在輸入電壓為 90V,放電時間為10h時,老化效果已經(jīng)很明顯;繼續(xù)延長放電時間,老化效果的提升并不明顯,因此后續(xù)實驗所用的老化微塑料均在此條件下制備.其他類似研究也觀察到了老化微塑料表面的裂縫和孔洞[15,24-25].Ge等[26]發(fā)現(xiàn)等離子體處理不會引起淀粉顆粒完整性的變化,但會導致淀粉顆粒表面的開裂,腐蝕和微沉積.在老化過程中,等離子體產(chǎn)生的活性物質(zhì)和紫外線會導致微塑料分子鏈的斷裂和交聯(lián)反應(yīng),從而破壞微塑料分子中的化學鍵,導致分子鏈斷裂[15].這可能是老化后PE-MP和PP-MP表面形態(tài)發(fā)生變化的原因.

圖2 輸入電壓和放電時間對微塑料表面形貌的影響

′5000

2.1.2 老化前后PE-MP和PP-MP的官能團和表面元素分析 如圖3所示,與原始PE-MP相比,等離子體老化后的PE-MP在3420cm-1處出現(xiàn)一個新峰,代表O-H基團的拉伸振動.此外,在老化PE-MP的1473和2919cm-1處觀察到C-H和C-H2拉伸振動[17].等離子體老化后PP-MP的FTIR譜中沒有觀察到明顯的O-H基拉伸振動,但1377,1473和2918cm-1處的峰比原始PP-MP更尖銳,這可以歸因于C-OH,C-H和C-H2的拉伸振動[27-28].同時,老化PP-MP在1700～1800cm-1處產(chǎn)生了一個代表羰基的新峰.這些現(xiàn)象表明,等離子體可以氧化PE-MP和PP-MP的表面,并引入含氧官能團,這在微塑料的光照或自然老化過程中也會發(fā)生[14,29].PE-MP和PP-MP的表面氧化可能是等離子體產(chǎn)生的自由基和紫外線的共同作用.研究發(fā)現(xiàn),自由基可以攻擊聚苯乙烯等聚合物中的氫原子,破壞C-H鍵.斷裂的C-H很容易與氧氣反應(yīng)形成C-O鍵,然后與空氣中的氫反應(yīng)形成過COOH基團[30-31].含氧官能團的產(chǎn)生將增加PE-MP和PP-MP的親水性,這會增加微塑料與溶液中重金屬接觸的機會[30].

如圖4所示,經(jīng)等離子體老化處理后,C-O鍵增加,而C-C鍵逐漸減少,表明PE-MP和PP-MP已經(jīng)被氧化.原始PE-MP和PP-MP中所含的氧原子可能是由加工過程中加入的添加劑引起的[30,32],老化后氧原子的增加是微塑料被等離子體老化的結(jié)果,這與FTIR的結(jié)果基本一致.

2.1.3 老化前后PE-MP和PP-MP的結(jié)晶度分析 如圖5所示,老化的PE-MP在30°～35°之間出現(xiàn)多個新峰,而老化PP-MP在20°～25°之間的特征峰變得更加尖銳,這表明等離子體老化后PE-MP和PP-MP的結(jié)晶度增加[30,33].結(jié)晶度的提高意味著微塑料更脆,容易產(chǎn)生更小的顆粒,這也是環(huán)境中的塑料更脆弱的原因[34].同時,老化后微塑料的峰與原始微塑料相比沒有明顯的移動,說明PE-MP和PP-MP的尺寸在老化過程中變化不大.

2.1.4 PE-MP和PP-MP的表面能譜分析 如圖6所示,PE-MP和PP-MP的氧含量在等離子體老化后有所增加,表明微塑料的表面在等離子體處理過程中與活性物質(zhì)發(fā)生反應(yīng)產(chǎn)生了含氧官能團.另一方面,吸附Zn(II)后的微塑料EDS結(jié)果顯示老化后微塑料表面Zn(Ⅱ)的占比增大,說明老化在一定程度上促進了微塑料對Zn(Ⅱ)的吸附.這可能是因為含氧官能團的產(chǎn)生提高了微塑料的親水性,增加了微塑料與溶液中Zn(Ⅱ)接觸的機會.

圖5 老化前后微塑料的XRD圖

2.2 吸附動力學

從圖7可知,當達到吸附平衡時,放電等離子體老化后的PE-MP和PP-MP對Zn(II)的吸附量分別比原來的PE-MP和PP-MP提高了22.7%和14.8%.這可歸因于等離子體體系中產(chǎn)生的各種活性物質(zhì)和強紫外線誘導了PE-MP和PP-MP主鏈上C-C和C-H鍵的解離,并產(chǎn)生了含氧官能團,使PE-MP和PP-MP老化后表面變得粗糙,結(jié)晶度增加,表面親水性提高.這些物理化學性質(zhì)的變化顯著促進了老化PE-MP和PP-MP對Zn(II)的吸附[25,35].從表1可知,等離子體老化前后PE-MP和PP-MP對Zn(II)的吸附更符合準二級動力學模型.結(jié)果表明,PE-MP和PP-MP對Zn(II)的吸附是一個復雜的過程,可能包括物理吸附和化學吸附[16].同時,PE-MP和PP-MP對Zn(II)的2值分別從4.735g/(mg×min)降至3.585g/(mg×min)和從3.563g/(mg×min)降至3.131g/ (mg×min),表明老化PE-MP和PP-MP對Zn(II)的吸附速率降低.

表1 原始和老化PE-MP及PP-MP吸附Zn(II)的動力學參數(shù)

注:e是微塑料在吸附平衡時對Zn(II)的吸附量,mg/g;1是準一級吸附速率常數(shù)h-1;2是準二級吸附速率常數(shù),g/(mg·h),下同.

是吸附時間,h;q是時間時對Zn(II)的吸附容量,mg/g,下同

如圖8和表2所示,原始及老化PE-MP和PP- MP的顆粒內(nèi)擴散模型具有良好的線性關(guān)系.直線未通過原點,表明PE-MP和PP-MP對Zn(II)的吸附速率受粒內(nèi)擴散和外擴散控制,表明對Zn(II)的吸附是一個多階段吸附過程[36-38].吸附過程可分為3個階段:第一階段為快速吸附階段,在吸附物濃度差和靜電引力的作用下,Zn(II)迅速占據(jù)PE-MP和PP-MP表面的吸附位點,吸附1h后,Zn(II)的吸附量達到吸附平衡的50%左右;第二階段為慢吸附階段,Zn(II)與PE-MP和PP-MP的剩余吸附位點緩慢結(jié)合,直至達到第三階段(吸附平衡階段).老化微塑料在達到吸附平衡前的2個階段截距C值大于原始微塑料,這是因為老化后微塑料表面吸附位點的增加增大了Zn(II)在微塑料顆粒內(nèi)部擴散的傳質(zhì)驅(qū)動力.

表2 原始和老化PE-MP和PP-MP吸附Zn(II)的顆粒擴散模型參數(shù)

注:di是顆粒內(nèi)擴散模型的吸附速率常數(shù),g/(mg·h0.5);C為一個與邊界層厚度有關(guān)的常數(shù).

圖8 原始和老化PE-MP和PP-MP的顆粒內(nèi)擴散模型擬合曲線

2.3 吸附等溫線和吸附熱力學

如圖9和表3所示,隨著Zn(II)濃度的增加,原始和老化PE-MP和PP-MP的吸附容量也增加.當不同濃度的Zn(II)溶液達到吸附平衡時,老化的PE-MP和PP-MP的吸附容量高于原始的PE-MP和PP-MP,證實了放電等離子體老化后提高了PE-MP和PP- MP對Zn(II)的吸附容量,這可能是老化處理后微塑料粗糙的顆粒表面產(chǎn)生更大的比表面積和更多的污染物吸附位點[39].

Langmuir(0.9702<2<0.9910)等溫吸附模型比Freundlich(0.9314<2<0.9594)等溫吸附模型具有更高的擬合度.結(jié)果表明,等離子體老化前后PE-MP和PP-MP對Zn(II)的吸附機理均為單層吸附[40].同時,老化后微塑料的2有一定的增加,這表明老化可能會使微塑料表面的吸附位點更加均勻.一些學者研究了Cu2+,Pb2+等金屬在不同類型微塑料上的吸附,也發(fā)現(xiàn)了相似的吸附機理[29,41].與原始PE-MP和PP-MP相比,老化PE-MP和PP-MP的m值分別從0.223和0.275增加到0.274和0.330,這與本研究結(jié)果趨勢相同.可能是由于老化后微塑料表面更加粗糙,增加了Zn(II)的吸附位點,微塑料表面的含氧官能團及結(jié)晶度的提高也可能是影響微塑料對Zn(II)吸附性能的因素.

在Freundlich模型表達式中,1/可以用來描述吸附劑和吸附物之間的結(jié)合能力.當值為1時,吸附為線性等溫線;當1/>1或1/<1時,表明吸附過程分別與化學過程或有利的物理過程有關(guān)[42-44].從表3可以看出,Freundlich模型的參數(shù)1/均小于1,表明吸附是容易發(fā)生的.同時發(fā)現(xiàn),老化后PE-MP和PP-MP的1/值均有所增加,表明老化后PE-MP和PP-MP對Zn(II)的吸附過程也更加復雜.

表3 老化前后PE-MP和PP-MP等溫線模型參數(shù)

注:m為微塑料對Zn(II)的吸附容量,mg/g;L為Langmuir常數(shù),L/mg;F為Freundlich常數(shù),mg1-1/nL1/ng-1;為非均質(zhì)系數(shù),下同.

如表4所示,在288～308K的條件下,Δ0>0,表明微塑料吸附Zn(II)的過程是吸熱反應(yīng);老化PE-MP的焓變大于原始PE-MP,而老化PP-MP的焓變小于原始PP-MP,這表明老化使Zn(II)與PE-MP表面的相互作用更強,而Zn(II)與PP-MP表面的相互作用減弱[45].Δ0值也>0,表明Zn(II)的自由度和Zn(II)在固液界面的濃度升高.而Δ0<0,表明微塑料吸附Zn(II)是自發(fā)反應(yīng)過程[15],且Δ0的絕對值隨著溫度的升高而增大,表明溫度升高有利于吸附的自發(fā)反應(yīng)程度增強.另一方面,微塑料老化后Δ0的絕對值略有減小,該結(jié)果表明老化會使微塑料吸附Zn(II)的自發(fā)反應(yīng)程度減弱,而老化后微塑料吸附Zn(II)能力增強,這可能是因為老化后微塑料吸附位點增多能夠抵消自發(fā)反應(yīng)程度的減弱.

表4 老化前后PE-MP和PP-MP熱力學參數(shù)

注: Δ0為自由能變化量,J/mol; Δ0和Δ0分別為焓(J/mol)和熵(J/(mol·K),下同.

2.4 環(huán)境因素的影響

如圖10a所示,在pH值3～6范圍內(nèi),微塑料對Zn(II)的吸附能力隨pH值的增加而增加.在較低pH值條件下,H+與Zn(II)競爭吸附位置,導致pH值降低時對Zn(II)的吸附容量降低[38].同時,隨著pH值升高,去質(zhì)子化作用增強及靜電排斥力作用減弱使得微塑料上基團更易與Zn(II)結(jié)合,從而提高其吸附能力.

Ca2+是水體環(huán)境中重要的陽離子,會影響微塑料對Zn(II)的吸附.如圖10b所示,隨Ca2+濃度的增加,老化前后的微塑料對Zn(II)的吸附能力降低.加入8mg/L Ca2+后,原始PE-MP、老化PE-MP、原始PP-MP和老化PP-MP對Zn(II)的吸附容量分別降至0.10,0.13,0.12和0.15mg/g.說明離子強度對微塑料吸附Zn(II)的影響較大.Zn(II)吸附量隨Ca2+濃度而降低,說明Ca2+與Zn(II)發(fā)生了競爭吸附作用,Ca2+搶占了微塑料表面的吸附位點,使微塑料對Zn(II)的吸附容量降低.

如圖10c所示,隨著腐殖酸濃度的增加,老化前后的微塑料對Zn(II)的吸附能力逐漸降低.這可能是因為腐殖酸與Zn(II)的絡(luò)合力大于微塑料對Zn(II)的吸附力,導致Zn(II)會優(yōu)先與腐殖酸絡(luò)合,微塑料的吸附量減少,腐殖酸的存在抑制了微塑料對Zn(II)的吸附[46].另一方面,腐殖酸會占據(jù)微塑料表面的吸附位點,削弱了微塑料對Zn(II)的吸附.

2.5 環(huán)境影響及老化工藝對比

微塑料老化是自然環(huán)境中常見的現(xiàn)象,老化引起的微塑料物理化學性質(zhì)的變化會加速微塑料與環(huán)境中其他污染物的相互作用,對水環(huán)境和生物造成更大的危害.例如,單獨的微塑料或Ag+對大型蚤沒有毒性,而微塑料和Ag+的混合物可能對大型蚤有毒[47].本研究也發(fā)現(xiàn)微塑料的老化會增強對Zn(II)的吸附.微塑料在環(huán)境中的老化一直客觀存在,與自然條件下相比,DBD等離子體能夠顯著縮短微塑料老化時間;同時DBD等離子體系統(tǒng)產(chǎn)生的紫外可見光、活性物質(zhì)以及溫度效應(yīng)等,相比于其他實驗室老化手段能更合理地模擬自然老化環(huán)境.周崇勝等[48]探究自然光老化微塑料的實驗周期長達1年,Mao等[30]探究紫外光老化微塑料的試驗周期也需3個月.而在本研究中,DBD等離子體放電10h左右已有明顯的老化現(xiàn)象出現(xiàn).另一方面,在本研究中,老化后PE-MP和PP-MP對Zn(II)的吸附量分別增加了0.05和0.04mg/g;張瑞昌等[49]研究酸、堿、氧化和高溫-凍融4種老化方式對PE微塑料Zn(II)吸附行為的影響,發(fā)現(xiàn)老化后的PE-MP對Zn(II)的吸附量分別增加了0.023,0.03,0.02和0.015mg/g;王瓊杰等[50]采用紫外光老化600h后,PE-MP和PP-MP對Zn(II)的吸附量分別提高了9.54和40.8 μg/g.這也體現(xiàn)了DBD等離子體老化微塑料對Zn(II)吸附的影響更大.以上結(jié)論表明DBD等離子體有助于在更短時間內(nèi)探究微塑料的老化,也更便于探究老化前后微塑料與重金屬等的相互作用,有助于探索微塑料吸附重金屬對環(huán)境的影響.

3 結(jié)論

3.1 等離子體可明顯縮短PE-MP和PP-MP的老化時間.

3.2 老化后,出現(xiàn)O-H鍵和C-H鍵等的伸縮振動,并在PE-MP表面形成含氧官能團. PE-MP和PP-MP的結(jié)晶度增加,表面起皺,出現(xiàn)裂紋或孔洞.

3.3 老化后PE-MP和PP-MP對Zn(II)的吸附能力有提高.微塑料對Zn(II)的吸附反應(yīng)動力學符合準二級動力學模型,老化前后PE-MP和PP-MP對Zn(II)的吸附均以化學吸附為主.

3.4 顆粒內(nèi)擴散模型的擬合具有良好的線性,吸附過程可分為快速吸附,慢速吸附和吸附平衡3個階段.

3.5 吸附平衡數(shù)據(jù)符合Langmuir等溫吸附模型,為單層吸附.熱力學結(jié)果表明,微塑料對Zn(II)的吸附是自發(fā)的吸熱過程,且隨著溫度的升高,吸附的自發(fā)反應(yīng)程度增強.

3.6 pH值、離子強度和腐殖酸對微塑料吸附Zn(II)有明顯的影響.

[1] Zhou X,Hao L,Wang H,et al. Cloud-point extraction combined with thermal degradation for nanoplastic analysis using pyrolysis gas chromatography-mass spectrometry [J]. Analytical Chemistry,2019,91(3):1785-1790.

[2] 孫 璇,俞安琪,王學松,等.富里酸在聚苯乙烯微塑料上的吸附行為[J]. 中國環(huán)境科學,2022,42(1):285-292.

Sun X,Yu A Q,Wang X S,et al. Adsorption behaviors of fulvic acid onto polystyrene microplastics [J]. China Environmental Science,2022,42(1):285-292.

[3] 范秀磊,甘 容,謝 雅,等.老化前后聚乳酸和聚乙烯微塑料對抗生素的吸附解吸行為[J]. 環(huán)境科學研究,2021,34(7):1747-1756.

Fan X L,Gan R,Xie Y,et al. Adsorption and Desorption Behavior of Antibiotics on Polylactic Acid and Polyethylene Microplastics Before and After Aging [J]. Research of Environmental Sciences,2021,34(7):1747-1756.

[4] Anthony L A. Microplastics in the marine environment [J]. Marine Pollution Bulletin,2011,62(8):1596-1605.

[5] Luís G A B,Barbara C G G. Microplastics in the marine environment: Current trends and future perspectives [J]. Marine Pollution Bulletin,2015,97(1/2):5-12.

[6] Wang W,Anne W N,Zhen L,et al. Microplastics pollution in inland freshwaters of China: A case study in urban surface waters of Wuhan,China [J]. Science of the Total Environment,2017,575:1369-1374.

[7] Xiong X,Chenxi W,James J E,et al. Occurrence and fate of microplastic debris in middle and lower reaches of the Yangtze River – From inland to the sea [J]. Science of the Total Environment,2019,659:66-73.

[8] Zhang Y,Gao T,Kang S,et al. Microplastics in glaciers of the Tibetan Plateau: Evidence for the long-range transport of microplastics [J]. Science of the Total Environment,2021,758(prepublish).

[9] Chen G,Feng Q,Wang J. Mini-review of microplastics in the atmosphere and their risks to humans [J]. Science of the Total Environment,2020,703:135504.

[10] Tunali M,Uzoefuna E N,Tunali M M,et al. Effect of microplastics and microplastic-metal combinations on growth and chlorophyll a concentration of Chlorella vulgaris [J]. Science of the Total Environment,2020,743:140479.

[11] Meng J,Xu B,Liu F,et al. Effects of chemical and natural ageing on the release of potentially toxic metal additives in commercial PVC microplastics [J]. Chemosphere,2021,283:131274.

[12] 褚獻獻,鄭 波,何 楠,等.微塑料與污染物相互作用的研究進展[J]. 環(huán)境化學,2021,40(2):427-435.

Chu X X,Zheng B,He N,et al. Progress on the interaction between microplastics and contaminants [J]. Environmental Chemistry,2021,40(2):427-435.

[13] Liu P,Wu X,Huang H,et al. Simulation of natural aging property of microplastics in Yangtze River water samples via a rooftop exposure protocol [J]. Science of the Total Environment,2021,785:147265.

[14] Lin W,Kuo J,Lo S. Effect of light irradiation on heavy metal adsorption onto microplastics [J]. Chemosphere,2021,285:131457.

[15] Fan X,Gan R,Liu J,et al. Adsorption and desorption behaviors of antibiotics by tire wear particles and polyethylene microplastics with or without aging processes [J]. Science of the Total Environment,2021,771:145451.

[16] Lang M,Yu X,Liu J,et al. Fenton aging significantly affects the heavy metal adsorption capacity of polystyrene microplastics [J]. Science of the Total Environment,2020,722:137762.

[17] Xu Z,Xue X,Hu S,et al. Degradation effect and mechanism of gas-liquid phase dielectric barrier discharge on norfloxacin combined with H2O2or Fe2+[J]. Separation and Purification Technology,2020,230:115862.

[18] Huang Q,Fang C. Degradation of 3,3′,4,4′-tetrachlorobiphenyl (PCB77) by dielectric barrier discharge (DBD) non-thermal plasma: Degradation mechanism and toxicity evaluation [J]. Science of the Total Environment,2020,739:139926.

[19] Galmiz O,Pavliňák D,Zemánek M,et al. Hydrophilization of outer and inner surfaces of Poly (vinyl chloride) tubes using surface dielectric barrier discharges generated in ambient air plasma [J]. Plasma Processes and Polymers,2017,14(9).

[20] 王忠凱,季軍榮,湯 睿,等.雙有機改性磁性膨潤土對Cu(II)和Zn(II)的吸附研究[J]. 高校化學工程學報,2022,36(2):276-286.

Wang Z K,Ji J R,Tang R,et al. Dually organic modified magnetic bentonite for adsorption of Cu(II) and Zn(II) [J]. Journal of Chemical Engineering of Chinese Universities,2022,36(2):276-286.

[21] Calderon B,Fullana A. Heavy metal release due to aging effect during zero valent iron nanoparticles remediation [J]. Water Research,2015,83:1-9.

[22] Sang W,Lu W,Mei L,et al. Research on different oxidants synergy with dielectric barrier discharge plasma in degradation of Orange G: Efficiency and mechanism [J]. Separation and Purification Technology,2021,277:119473.

[23] Frere L,Paul-Pont I,Moreau J,et al. A semi-automated Raman micro-spectroscopy method for morphological and chemical characterizations of microplastic litter [J]. Marine Pollution Bulletin,2016,113(1/2):461-468.

[24] Liu J,Zhang T,Tian L,et al. Aging significantly affects mobility and contaminant-mobilizing ability of nanoplastics in saturated loamy sand [J]. Environmental Science & Technology,2019,53(10):5805- 5815.

[25] Gao F,Li J,Sun C,et al. Study on the capability and characteristics of heavy metals enriched on microplastics in marine environment [J]. Marine Pollution Bulletin,2019,144:61-67.

[26] Ge X,Shen H,Su C,et al. Pullulanase modification of granular sweet potato starch: Assistant effect of dielectric barrier discharge plasma on multi-scale structure,physicochemical properties [J]. Carbohydrate Polymers,2021,272:118481.

[27] Ding L,Mao R,Ma S,et al. High temperature depended on the ageing mechanism of microplastics under different environmental conditions and its effect on the distribution of organic pollutants [J]. Water Research,2020,174:115634.

[28] Liu P,Shi Y,Wu X,et al. Review of the artificially-accelerated aging technology and ecological risk of microplastics [J]. Science of the Total Environment,2021,768:144969.

[29] Fu Q,Tan X,Ye S,et al. Mechanism analysis of heavy metal lead captured by natural-aged microplastics [J]. Chemosphere,2021,270: 128624.

[30] Mao R,Lang M,Yu X,et al. Aging mechanism of microplastics with UV irradiation and its effects on the adsorption of heavy metals [J]. Journal of Hazardous Materials,2020,393:122515.

[31] Anne A,Stuart B,Katherine D,et al. An overview of degradable and biodegradable polyolefins [J]. Progress in Polymer Science,2010,36(8):1015-1049.

[32] Dong Y,Gao M,Song Z,et al. As(III) adsorption onto different-sized polystyrene microplastic particles and its mechanism [J]. Chemosphere,2020,239:124792.

[33] Yong M,Zhang Y,Sun S,et al. Properties of polyvinyl chloride (PVC) ultrafiltration membrane improved by lignin: Hydrophilicity and antifouling [J]. Journal of Membrane Science,2019,575:50-59.

[34] Liu G,Zhu Z,Yang Y,et al. Sorption behavior and mechanism of hydrophilic organic chemicals to virgin and aged microplastics in freshwater and seawater [J]. Environmental Pollution,2019,246:26- 33.

[35] Wu X,Liu P,Huang H,et al. Adsorption of triclosan onto different aged polypropylene microplastics: Critical effect of cations [J]. Science of the Total Environment,2020,717:137033.

[36] Piperopoulos E,Calabrese L,Mastronardo E,et al. Assessment of sorption kinetics of carbon nanotube‐based composite foams for oil recovery application [J]. Journal of Applied Polymer Science,2019,136(14):47374.

[37] Wang W,Wang J. Comparative evaluation of sorption kinetics and isotherms of pyrene onto microplastics [J]. Chemosphere,2018,193: 567-573.

[38] Dutta D P,Venugopalan R,Chopade S. Manipulating Carbon Nanotubes for Efficient Removal of Both Cationic and Anionic Dyes from Wastewater [J]. Chemistry Select (Weinheim),2017,2(13):3878- 3888.

[39] Zhang H,Wang J,Zhou B,et al. Enhanced adsorption of oxytetracycline to weathered microplastic polystyrene: Kinetics,isotherms and influencing factors [J]. Environmental Pollution,2018,243:1550-1557.

[40] Liu P,Qian L,Wang H,et al. New insights into the aging behavior of microplastics accelerated by advanced oxidation processes [J]. Environmental Science & Technology,2019,53(7):3579-3588.

[41] Yang J,Cang L,Sun Q,et al. Effects of soil environmental factors and UV aging on Cu2+adsorption on microplastics [J]. Environmental Science and Pollution Research,2019,26(22):23027-23036.

[42] Akram M,Xu X,Gao B,et al. Adsorptive removal of phosphate by the bimetallic hydroxide nanocomposites embedded in pomegranate peel [J]. Journal of Environmental Sciences,2020,91:189-198.

[43] Sahoo S,Uma,Banerjee S,et al. Application of natural clay as a potential adsorbent for the removal of a toxic dye from aqueous solutions [J]. Desalination and Water Treatment,2014,52(34-36): 6703-6711.

[44] Yang Z,Zhu T,Xiong M,et al. Tuning adsorption capacity of metal–organic frameworks with Al3+for phosphorus removal: Kinetics,isotherm and regeneration [J]. Inorganic Chemistry Communications,2021,132:108804.

[45] Wang F,Pan Y,Cai P,et al. Single and binary adsorption of heavy metal ions from aqueous solutions using sugarcane cellulose-based adsorbent [J]. Bioresource Technology,2017,241:482-490.

[46] 杜曉麗,尹子杰,陳夢瑤,等.徑流溶解性有機物對生物滯留介質(zhì)去除Cu2+和Pb2+的影響[J]. 中國環(huán)境科學,2021,41(9):4142-4148.

Du X L,Yin Z J,Chen M Y,et al. Effect of dissolved organic matter in runoff on the removal of Cu2+and Pb2+by bioretention medium [J]. China Environmental Science,2021,41(9):4142-4148.

[47] Abdolahpur Monikh F,Vijver M G,Guo Z,et al. Metal sorption onto nanoscale plastic debris and trojan horse effects in Daphnia magna: Role of dissolved organic matter [J]. Water Research,2020,186: 116410.

[48] 周崇勝,范銘煜,丁云浩,等.常見微塑料的自然光解老化 [J]. 環(huán)境化學,2021,40(6):1741-1748.

Zhou C S,Fan M Y,Ding Y H,et al. Insights into natural photo-aging of common-used microplastics [J]. Environmental Chemistry,2021,40 (6):1741-1748.

[49] 張瑞昌,李澤林,魏學鋒,等.模擬環(huán)境老化對PE微塑料吸附Zn(II)的影響[J]. 中國環(huán)境科學,2020,40(7):3135-3142.

Zhang R C,Li Z L,Wei X F,et al. Effects of simulated environmental aging on the adsorption of Zn(II) onto PE microplastics [J]. China Environmental Science,2020,40(7):3135-3142.

[50] 王瓊杰,張 勇,張陽陽,等.老化微塑料對水體中重金屬銅和鋅的吸附行為研究[J]. 環(huán)境科學學報,2021,41(7):2712-2726.

Wang Q J,Zhang Y,Zhang Y Y,et al. Adsorption of heavy metal ions Cu2+and Zn2+onto UV-aged microplastics in aquatic system [J]. Acta Scientiae Circumstantiae,2021,41(7):2712-2726.

Dielectric barrier discharge plasma aging of microplastics and its effect on Zn(II) adsorption.

LU Wei1,SANG Wen-jiao1*,LI Min2,ZHANG Wen-bin1,JIA Dan-ni1,ZHAN Cheng1,HE Yong-jian1,CHEN Cui-zhen2,XIANG Xue-lian3

(1.School of Civil Engineering and Architecture,Wuhan University of Technology,Wuhan 430070,China；2.Wuhan Water Science Research Institute,Wuhan 430014,China；3.Yichang Institute of Urban Planning & Design Co.,Ltd,Yichang 443001,China).,2022,42(8)：3744～3754

In order to shorten the aging time of microplastics and mimic the natural aging conditions in the experiment,dielectric barrier discharge (DBD) plasma was used in the aging experiments of polyethylene microplastics (PE-MP) and polypropylene microplastics (PP-MP). And the adsorption process and mechanism of Zn(II) on PE-MP and PP-MP before and after aging was investigated. With the extension of discharge time and the elevation of input voltage,tiny cracks or holes appeared on the surface of microplastics and oxygen-containing functional groups were formed. The Zn(II) adsorption capacity of aged PE-MP and PP-MP was increased by 22.7% and 14.8%,respectively. The adsorption of Zn(II) on microplastics before and after aging conformed to the pseudo-second-order kinetic model. The intra-particle diffusion model showed that the adsorption process of Zn(II) on microplastics could be involved three processes: rapid adsorption,slow adsorption and adsorption equilibrium. In addition,the adsorption of Zn(II) on microplastics before and after aging conformed by Langmuir model. The thermodynamic results indicated that the adsorption of Zn(II) on microplastics was a spontaneous endothermic process. Ca2+,humic acid and low pH were not conducive to the adsorption of Zn(II) by microplastics.

microplastics；aging；plasma；adsorption；Zn(II)

X52

A

1000-6923(2022)08-3744-11

2022-01-10

國家自然科學基金資助項目(51108360,51208397)

* 責任作者,副教授,whlgdxswj@126.com

盧 偉(1996-),男,江西宜春人,武漢理工大學碩士研究生,主要從事高級氧化方面研究.發(fā)表論文2篇.