嚴(yán) 梅,張 青,謝慧芳,孔金明,曲虹霞2

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納米Fe3O4負(fù)載聚苯胺對(duì)染料的協(xié)同催化降解

嚴(yán) 梅1,張 青1,謝慧芳1*,孔金明1,曲虹霞2*

(1.南京理工大學(xué)環(huán)境與生物工程學(xué)院,江蘇省化工污染控制與資源化重點(diǎn)實(shí)驗(yàn)室,江蘇南京210094；2.南京理工大學(xué)化工學(xué)院,江蘇南京210094)

通過(guò)Hemin催化聚合苯胺工藝在納米Fe3O4上負(fù)載導(dǎo)電聚合物聚苯胺(PANI),制備得到了具有高效催化活性的異相類Fenton反應(yīng)用的催化劑PANI@Fe3O4.研究了PANI@Fe3O4/H2O2體系中羅丹明B(RhB)濃度、H2O2濃度、PANI@Fe3O4投加量、pH值以及×OH捕獲劑對(duì)RhB降解的影響.結(jié)果表明,對(duì)于400mg/L的RhB溶液,當(dāng)催化劑投加量為0.5g/L, H2O2濃度為0.04mol/L時(shí),PANI@Fe3O4/H2O2可在pH 3.75~12.0間達(dá)到98%以上的去除率,H2O2的利用率達(dá)到80%.將該體系對(duì)于初始COD為1715mg/L模擬混合染料廢水,可去除70%的COD,PANI@Fe3O4/H2O2體系適用pH值范圍廣,催化活性高,H2O2利用率高且水相中殘留鐵離子少.機(jī)理分析表明,在PANI@Fe3O4中PANI和納米Fe3O4存在明顯的協(xié)同效應(yīng),納米Fe3O4部分溶解釋放出Fe2+,并通過(guò)Fe3+和 Fe2+間的快速電子轉(zhuǎn)移補(bǔ)充催化所需Fe2+.PANI提供反應(yīng)所需H+,并通過(guò)與鐵離子形成配位鍵而減少了鐵離子釋放到水相中.

異相類Fenton反應(yīng)；PANI@Fe3O4；催化劑；協(xié)同效應(yīng)；羅丹明

Fenton技術(shù)由于所需裝置簡(jiǎn)單、原料豐富,從而具有經(jīng)濟(jì)優(yōu)勢(shì),目前在染料廢水、含酚廢水等的處理中得到較多應(yīng)用[1-2].但實(shí)踐和研究也表明,傳統(tǒng)Fenton法存在著一些問(wèn)題,如反應(yīng)活性低、pH值應(yīng)用范圍窄(2~3)、溶液鐵離子含量高(50~80mg/L)以及含鐵污泥處理處置困難等[3-8].在傳統(tǒng)均相Fenton法的改進(jìn)中,除了通過(guò)引進(jìn)電場(chǎng)[9]、磁場(chǎng)、微波[10]、光[11]、其他過(guò)渡金屬等方式催化×OH等活性氧基團(tuán)的生成,提高體系的氧化能力外,異相Fenton工藝也愈發(fā)得到重視[2].異相Fenton法研究方向之一是采用納米零價(jià)鐵[12]、氧化鐵[13-14]或固定化及穩(wěn)定化等方法處理的鐵源[15-16]取代均相溶液中Fe2+/Fe3+,以降低反應(yīng)體系中的鐵含量,防止鐵的積累和沉淀.

納米四氧化三鐵是近年來(lái)受到關(guān)注的一種新興功能材料,具有磁性和導(dǎo)電性,含有Fe2+和Fe3+,而且電子可在鐵的2種氧化態(tài)間迅速發(fā)生轉(zhuǎn)移[17].因此,可用于催化H2O2分解產(chǎn)生×OH等自由基,同時(shí)易于回收和循環(huán)利用[18].但整體而言,Fe3O4/H2O2體系的氧化降解效率較低[18],受pH值影響較大.研究者們?cè)噲D通過(guò)與某些材料的復(fù)合而進(jìn)一步增強(qiáng)四氧化三鐵的催化性能,實(shí)現(xiàn)Fe(II)-HA或Fe(III)-HA間快速的電子傳遞[18].

聚苯胺(PANI)具有優(yōu)異的導(dǎo)電性能、獨(dú)特的酸摻雜-去摻雜機(jī)理、良好的吸附及催化性能而受到關(guān)注[19-20].Gemeay等[20]研究發(fā)現(xiàn)PANI與b-MnO2的復(fù)合物,可以與H2O2形成催化體系,降解水中活性藍(lán)92(AB-92)、直接紅81(DR-81)和靛藍(lán)胭脂紅(IC)等染料.而PANI與磁性納米Fe3O4復(fù)合,作為催化H2O2生成×OH等自由基并在染料降解方面加以應(yīng)用尚未見文獻(xiàn)報(bào)道.

本課題組前期研究表明以氯化血紅素(Hemin)為催化劑可催化過(guò)氧化氫(H2O2)聚合苯胺單體.因此,本文利用Hemin催化聚合苯胺,在納米Fe3O4上負(fù)載PANI,制備得到PANI@Fe3O4復(fù)合材料,以RhB為有機(jī)染料代表,研究了PANI@Fe3O4在異相Fenton催化降解RhB的應(yīng)用性能及主要影響因素,明確了PANI和納米Fe3O4在構(gòu)建的異相類Fenton體系中的協(xié)同效應(yīng),分析了PANI和納米Fe3O4的作用及降解機(jī)理.

1 材料與方法

1.1 PANI@Fe3O4的制備

在200mL pH=4.00的檸檬酸-檸檬酸鈉緩沖溶液中分別加入0.5g 納米Fe3O4、一定量Hemin溶液及1mL經(jīng)蒸餾純化的苯胺單體.將反應(yīng)體系置于25℃、150r/min水浴恒溫?fù)u床中,每隔15min向反應(yīng)體系中滴加0.2mL 30% H2O2,共添加7次,計(jì)1.5h.滴加完成后,使聚合反應(yīng)繼續(xù)進(jìn)行30min.然后,向反應(yīng)體系中添加15mL 37% HCl,搖床反應(yīng)30min后,靜置16h.

反應(yīng)結(jié)束后,經(jīng)3500r/min離心分離,將所得固體產(chǎn)物PANI@Fe3O4用乙醇和蒸餾水依次洗滌,于60℃烘箱內(nèi)烘干稱重,置于干燥器內(nèi)保存?zhèn)溆?

1.2 RhB降解試驗(yàn)

在100mL設(shè)定濃度和pH 值的RhB溶液中,分別投加催化劑PANI@Fe3O4和氧化劑H2O2,使之在25℃、150r/min的搖床上進(jìn)行反應(yīng),每隔一定時(shí)間取樣,經(jīng)過(guò)0.22mm濾膜過(guò)濾后在紫外-可見分光光度計(jì)(PerkinEImer,Lambda 25)上于552nm處測(cè)定吸光度值,計(jì)算溶液中殘余RhB濃度及其去除率.

試驗(yàn)中,改變RhB起始濃度(100~500mg/L)、H2O2濃度(0~0.12mol/L)、PANI@Fe3O4投加量(0~0.7g/L)、起始pH值(3.75~12.0)等主要影響因素,以確定PANI@Fe3O4/H2O2體系對(duì)RhB降解性能及主要參數(shù).

1.3 混合染料廢水降解試驗(yàn)

將染料甲基橙、甲基藍(lán)、RhB及考馬斯亮蘭各100mg/L配制成模擬混合染料廢水,向其中投加0.5g/LPANI@Fe3O4和0.04mol/L H2O2,在設(shè)定時(shí)間取樣,采用COD消解和測(cè)定儀(HACH, USA)測(cè)定水樣中COD的變化,計(jì)算COD去除率.

2 結(jié)果與討論

2.1 不同因素對(duì)RhB降解效果的影響

2.1.1 RhB初始濃度的影響 從圖1可以看出,在較高RhB溶液濃度時(shí),由于PANI@Fe3O4的吸附所起的作用較小,RhB的去除主要由于氧化降解作用.在100~300mg/L范圍內(nèi),30min內(nèi)RhB的去除率隨著起始濃度的升高而有所下降,但當(dāng)時(shí)間延長(zhǎng)到60min,去除率均可達(dá)到99%以上.繼續(xù)增加RhB起始濃度到500mg/L,60min降解率仍保持在93%.可見,PANI@Fe3O4/H2O2體系具有較強(qiáng)氧化能力,可應(yīng)用于高濃度有機(jī)物的氧化降解處理.

2.1.2 H2O2濃度的影響 從圖2可以看出,當(dāng)H2O2濃度從0.002mol/L增加到0.04mol/L時(shí),30min內(nèi)RhB的去除率可由23%增加到83%以上,60min內(nèi)RhB的去除率可由89%增加到97%以上.這是因?yàn)殡S著H2O2濃度的增加,催化產(chǎn)生的×OH自由基也隨之增加.但是繼續(xù)增加H2O2濃度,RhB去除效果增加有限.這可能是因?yàn)檫^(guò)量的H2O2會(huì)由于“捕獲效應(yīng)”而消耗生成的×OH[21]:

H2O2+×OH?×HO2+H2O (1)

根據(jù)RhB與H2O2的反應(yīng)式(2):

C18H31ClN2O3+ 37.5H2O2?

18CO2+36H2O + 2NO3-+ Cl-+ 3H+(2)

[H2O2]/[RhB]的理論摩爾比是37.5,對(duì)于400mg/L的RhB,理論上需要0.032mol/L的H2O2.試驗(yàn)確定的最適0.04mol/L的H2O2用量?jī)H稍高于理論值.

2.1.3 PANI@Fe3O4投加量的影響 從圖3可以看出,復(fù)合材料投加量對(duì)RhB的降解有著顯著影響.當(dāng)投加量在0.5g/L以內(nèi)時(shí),RhB的去除率隨著投加量的增加而明顯增加.繼續(xù)增加用量到0.7g/L時(shí),短時(shí)間RhB的去除率繼續(xù)增加,但時(shí)間延長(zhǎng)到60min后,總?cè)コ逝c0.5g/L用量時(shí)相當(dāng),達(dá)到99%.

2.1.4 初始pH值的影響 Fenton反應(yīng)受pH值影響明顯,傳統(tǒng)Fenton反應(yīng)的適宜pH值約為3.當(dāng)pH值 3時(shí),會(huì)由于鐵離子的水解及聚合物的形成而沉淀,造成×OH自由基形成速度下降,這是Fenton應(yīng)用受限的原因之一.

從圖4可以看出,初始pH值在3.75~12時(shí), RhB的去除率沒(méi)有顯著變化,60min去除率均在98%以上.可見,PANI@Fe3O4具有極寬的pH值適用范圍,從而可更為廣泛地應(yīng)用于染料等高濃度有機(jī)廢水的處理中.

PANI@Fe3O4之所以具有這樣的pH值適應(yīng)性與PANI性質(zhì)有關(guān).作為酸摻雜的PANI,在水中可以釋放出部分H+,使體系pH值下降.測(cè)試結(jié)果表明,投加PANI@Fe3O4后,反應(yīng)體系pH值可維持在3左右,從而很好地滿足了Fenton反應(yīng)所需pH值的要求.

2.2 PANI@Fe3O4/H2O2體系對(duì)于高濃度混合染料廢水的降解

圖5表明,對(duì)于初始濃度為1715mg/L的混合染料模擬廢水,在0.5g/L PANI@Fe3O4用量, 0.04mol/L的H2O2情況下,可在60min去除43.2%的COD,在240min內(nèi)COD去除率達(dá)到70%.結(jié)果表明,PANI@Fe3O4/H2O2體系可以有效降低高濃度染料廢水的COD值.

2.3 降解機(jī)理分析

2.3.1 PANI和Fe3O4的協(xié)同催化作用 據(jù)報(bào)道,聚苯胺(PANI)具有一定的催化性能[22],其與納米Fe3O4結(jié)合,能改善納米Fe3O4的催化性能.為了證實(shí)PANI@Fe3O4中PANI和Fe3O4在H2O2存在條件下的協(xié)同效應(yīng),分別測(cè)定了僅投加H2O2或PANI@Fe3O4;Fe3O4/H2O2及PANI/H2O2體系以及PANI@Fe3O4/H2O2體系作用于400mg/L RhB溶液(此時(shí)溶液初始pH3.75)60min后的RhB的去除率,結(jié)果如圖6所示.

圖6表明,僅H2O2或 PANI@Fe3O4復(fù)合物時(shí),60min后RhB濃度僅下降約7%～8%.其中僅添加PANI@Fe3O4復(fù)合物時(shí)引起溶液中RhB的去除可能主要是因?yàn)椴牧系奈阶饔?在Fe3O4/H2O2和PANI/H2O2體系中,RhB的去除率有所增加,達(dá)到22%和25%.而在PANI@Fe3O4/ H2O2體系中,RhB的去除率得到顯著提高,達(dá)到約99%.由此表明,PANI@Fe3O4中PANI和Fe3O4,存在明顯的協(xié)同效應(yīng),對(duì)于RhB的降解效果得到明顯增強(qiáng).

2.3.2 紫外分析 由圖7可以看到,隨著反應(yīng)的進(jìn)行,RhB在552,510,360,260nm處的4個(gè)特征峰均迅速消失,未檢測(cè)到有新的吸收峰出現(xiàn),其中,552nm處的主要是由于n→π*電子遷移所造成的,而在350nm處峰是由于存在共軛結(jié)構(gòu)引起,如苯環(huán)結(jié)構(gòu)等[23].這說(shuō)明降解過(guò)程中RhB的發(fā)色基團(tuán)和共軛基團(tuán)被迅速破壞了,產(chǎn)生了一些不具發(fā)色或共軛基團(tuán)的中間產(chǎn)物.

2.3.3×OH捕獲劑的影響 叔丁醇是一種羥基自由基捕獲劑[24].由圖8可知,在相同條件下,當(dāng)體系未添加叔丁醇時(shí),PANI@Fe3O4催化H2O2產(chǎn)生大量×OH,快速氧化RhB,60min對(duì)RhB的去除率即可達(dá)99%;而當(dāng)1mol/L叔丁醇的存在對(duì)于RhB的降解存在極明顯的抑制作用,60min后RhB的去除率僅15%左右.這說(shuō)明體系中的×OH對(duì)于RhB的降解起著關(guān)鍵作用.

2.4 PANI@Fe3O4協(xié)同效應(yīng)機(jī)理

試驗(yàn)研究表明,所制備的PANI@Fe3O4復(fù)合材料可以做為H2O2氧化降解RhB等染料的高效催化劑,其中PANI和Fe3O4相互促進(jìn),表現(xiàn)出協(xié)同效應(yīng).

在Fenton反應(yīng)中,反應(yīng)(3)是生成×OH的主要反應(yīng)[2]:

Fe2++H2O2+H+?×OH+Fe3++OH-(3)

而這一反應(yīng)要求pH￡3.催化劑PANI@Fe3O4制備過(guò)程中經(jīng)過(guò)了PANI的質(zhì)子酸摻雜步驟.在此步驟中,質(zhì)子與PANI鏈中的亞胺氮原子成鍵而使其帶正電荷,對(duì)陰離子Cl-擴(kuò)散在PANI鏈外圍[25-26]當(dāng)PANI@Fe3O4被投加到反應(yīng)體系中時(shí),部分H+可被釋放出來(lái)(圖9),而使體系pH下降,從而滿足Fe2+催化H2O2生成×OH的需要.

同時(shí),PANI中氮原子SP3軌道中存在的電子可與從Fe3O4釋放出的帶正電荷的鐵離子形成配位鍵[27-28],從而有效減少游離到溶液中的鐵離子.

測(cè)定結(jié)果表明,反應(yīng)體系中含有的總鐵含量為19.4mg/L、Fe2+為2.8mg/L.

圖10與圖4比較發(fā)現(xiàn),在溶液中存在相同鐵離子濃度的情況下,對(duì)于400mg/L的RhB溶液,傳統(tǒng)均相Fenton可在pH=3.75時(shí)達(dá)到最大去除率(75.6%),并且隨著pH值的升高,去除率明顯下降.

在PANI@Fe3O4催化的異相Fenton反應(yīng)中,H2O2首先與催化劑表面的Fe2+發(fā)生反應(yīng),生成×OH,部分×OH與吸附到催化劑表面的染料反應(yīng),部分×OH游離到溶液中.同時(shí),催化劑中的部分鐵離子(Fe2+或Fe3+)也溶解到溶液中,催化溶液中H2O2分解生成更多游離×OH,進(jìn)攻溶液中的染料分子.

在傳統(tǒng)均相Fenton反應(yīng)中,反應(yīng)(4)是限速步[2]:

Fe3++H2O2+H+?HO2×+Fe2++H+(4)

而在PANI@Fe3O4中,由于電子可在鐵的2種氧化態(tài)間迅速發(fā)生轉(zhuǎn)移[17],從而使得反應(yīng)(3)所需Fe2+不需要完全借助于反應(yīng)(4)就可以完成循環(huán),得到補(bǔ)充.

3 結(jié)論

3.1 PANI@Fe3O4復(fù)合材料是一種適用于異相類Fenton反應(yīng)的高效催化劑,其中PANI和Fe3O4相互促進(jìn),表現(xiàn)出顯著的協(xié)同效應(yīng).

3.2 PANI@Fe3O4/H2O2體系,既可使RhB迅速脫色,又可有效去除體系COD.

3.3 PANI@Fe3O4/H2O2體系具有較強(qiáng)氧化能力和極寬的pH值適用范圍,可應(yīng)用于染料、印染等高濃度有機(jī)廢水的氧化降解處理.

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致謝：感謝南京理工大學(xué)本科生張?chǎng)?徐健康參與了部分測(cè)試工作.

Load of PANI on nano-Fe3O4and synergy catalytic degradation of dyes.

YAN Mei1, ZHANG Qing1, XIE Hui-fang1*, KONG Jin-ming1, QU Hong-xia2*

(1.Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China；2.School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China).

In this study, polyaniline/nano Fe3O4was synthesized via in situ polymerization of aniline in the presence ofnano Fe3O4by Hemincatalysis and was used as an efficient heterogeneous Fenton-like catalyst for dyes degradation. The catalytic activity was evaluated by factors in PANI@Fe3O4/H2O2system, such as initial concentration of dye (Rhodamine B, RhB), concentration of H2O2and pH. For RhB of 400mg/L, more than 98% removal ratios were obtained from pH 3.75 to 12.0 with 0.5g/L PANI@Fe3O4, 0.04mol/L H2O2,and the utilization efficiency of H2O2was as high as 80%. The removal ratio of COD could reached 70% for the mixed dyes wastewater with initial COD 1715mg/L in PANI@Fe3O4/H2O2system. Results showed that PANI@Fe3O4/H2O2system have some advantagessuch as wide pH range, high catalytic activity, high utilization efficiency of H2O2and low iron concentration in water. There was a synergy effect between PANI and nano-Fe3O4in PANI@Fe3O4composite was observed. The dissolution of Fe3O4provide Fe2+and rapid electron transfer from Fe3+to Fe2+, which play the significant role in the formation of×OH. PANI provide H+for the Fenton reaction and prevent leaching of Fe2+/3+by chelating.

heterogeneous fenton reaction；PANI@Fe3O4；catalyst; synergy effect；rhodamine

X703.5

A

1000-6923(2017)04-1394-07

2016-07-02

國(guó)家自然科學(xué)基金資助項(xiàng)目(21575066)

嚴(yán) 梅(1992-),女,安徽來(lái)安人,南京理工大學(xué)碩士研究生,研究方向是水污染控制理論與技術(shù).

* 責(zé)任作者, 曲虹霞, 副教授, qhx@mail.njust.edu.cn; 謝慧芳, 副教授, huifangxie@hotmail.com

, 2017,37(4)：1394~1400