PW11Fe/CS/CNTs/C復(fù)合膜電極的制備及在H2O2電化學(xué)傳感器中的應(yīng)用

王鑫，章金明，蔣曉薇，韓雷云，王莉莉，黃燕霞，游誠(chéng)航，華英杰，王崇太

(海南師范大學(xué)化學(xué)與化工學(xué)院, 海南 ?？?571158)

PW11Fe/CS/CNTs/C復(fù)合膜電極的制備及在H2O2電化學(xué)傳感器中的應(yīng)用

王鑫，章金明，蔣曉薇，韓雷云，王莉莉，黃燕霞，游誠(chéng)航，華英杰，王崇太

(海南師范大學(xué)化學(xué)與化工學(xué)院, 海南 ?？?571158)

以殼聚糖(CS)為吸附劑和成膜劑，Keggin 型鐵取代雜多陰離子PW11O39Fe(Ⅲ)(H2O)4-(PW11Fe)為電催化劑，碳納米管(CNTs) 為導(dǎo)電助劑，集成吸附法和溶膠-凝膠法將PW11Fe固載在石墨電極表面制備了PW11Fe/CS/CNTs /C復(fù)合膜電極，并用電化學(xué)方法研究了該電極的電化學(xué)行為及其影響因素，同時(shí)研究了電極對(duì)H2O2還原的電催化活性及作為H2O2電化學(xué)傳感器的可能性。實(shí)驗(yàn)結(jié)果表明，PW11Fe/CS/CNTs/C復(fù)合膜電極具有PW11Fe類(lèi)似的電化學(xué)行為及對(duì)H2O2還原的電催化活性，用于H2O2的安培檢測(cè)，電流響應(yīng)靈敏度為0.30 mA·cm-2·(μmol/L)-1，檢出限為7.3 μmol/L (S/N=3)。

Keggin型鐵取代雜多陰離子；循環(huán)伏安；殼聚糖；電催化；碳納米管

將PW11Fe修飾到電極表面的方法已有許多報(bào)道，如電化學(xué)沉積法[7-8]、吸附法[9-10]、電聚合法[6,11]、層-層組裝法[12-13]和溶膠-凝膠法[14-15]等，這些方法根據(jù)研究目的的不同，各有千秋。本文集成吸附法和溶膠-凝膠法，利用殼聚糖(CS)作為吸附劑和成膜劑的特點(diǎn)[16-17]， 通過(guò)CS聚陽(yáng)離子和PW11Fe多陰離子的靜電相互作用，將PW11Fe固定在石墨電極表面。為了提高導(dǎo)電性，在電極制備過(guò)程中加入碳納米管(CNTs)。如此制備的PW11Fe/CS/CNTs/C復(fù)合膜電極，具有制備方法簡(jiǎn)單的優(yōu)點(diǎn)。

1 實(shí)驗(yàn)部分

1.1 試劑和儀器

鎢酸鈉(SCRC國(guó)藥集團(tuán)化學(xué)試劑有限公司), 殼聚糖(上海伯奧生物科技有限公司)，NaOH(天津市河北區(qū)海晶精細(xì)化工廠(chǎng)), 碳納米管 (SWCNTs，-OH型，深圳市納米港有限公司)，丙酮(廣州化學(xué)試劑廠(chǎng)), NaAc (廣州文龍化工有限公司), HAc (天津市福晨化學(xué)試劑廠(chǎng)), HNO3(廣州化學(xué)試劑廠(chǎng)), Na2HPO4(天津市化學(xué)試劑一廠(chǎng)), NaHSO4(廣州化學(xué)試劑廠(chǎng)), Fe(NO3)3(國(guó)藥集團(tuán)化學(xué)試劑有限公司),φ=30% H2O2(西隴化工股份有限公司), 混合磷酸鹽(pH=6.86和4.00,上海雷磁創(chuàng)益儀器儀表有限公司)。上述藥品均為分析純， Keggin型缺位雜多酸鹽Na7PW11O39和鐵取代雜多酸鹽Na4PW11O39Fe(Ⅲ)按參考文獻(xiàn)[18-19]的方法合成。實(shí)驗(yàn)用水為超純水(電導(dǎo)率<5.0 μs·cm-1)。

電化學(xué)測(cè)量在CHI電化學(xué)工作站(60 D，上海辰華儀器有限公司)上進(jìn)行，使用單室電解池，制備的PW11Fe/CS/CNTs復(fù)合膜電極為工作電極，Pt絲為輔助電極，Ag/AgCl (3 mol/L KCl)為參比電極。每次掃描前，溶液先充N(xiāo)2趕氧10 min。除非指明，實(shí)驗(yàn)溫度為298 K。

1.2 PW11Fe/CS/CNTs/GCE復(fù)合膜電極的制備

室溫下在0.15 mL 0.1 mol/L NaAc-HAc(pH=3.5)的緩沖溶液中加入0.005 g CS 和0.004 g CNTs，超聲5 min，得到CS/CNTs溶膠。然后將CS/CNTs溶膠均勻滴涂到事先用1200#金相砂紙打磨好的石墨電極(Φ=3 mm，S≈0.071 cm2)表面，靜置12 h，這時(shí)電極表面形成一層薄膜，將該電極在0.1 mol/L 的PW11Fe溶液中浸泡12 h后取出自然晾干，便得到PW11Fe/CS/CNTs/C復(fù)合膜電極。

2 結(jié)果與討論

2.1 PW11Fe/CS/CNTS/C復(fù)合膜電極的電化學(xué)行為

圖1(a)是PW11Fe/CS/CNTS/C復(fù)合膜電極在0.1 mol/L NaHSO4-Na2SO4(pH=2.2)溶液中的循環(huán)伏安圖。從圖中可以看到3對(duì)還原氧化波，分別歸屬于Fe(Ⅲ)/Fe(Ⅱ)電對(duì)和2個(gè)W(Ⅵ)/W(Ⅴ)電對(duì)的還原氧化反應(yīng)。第二個(gè)W(Ⅵ)/W(Ⅴ)電對(duì)的還原峰由于和質(zhì)子的競(jìng)爭(zhēng)還原峰重疊而難于區(qū)分，導(dǎo)致峰形有些變形。此外，PW11Fe被CS膜固載在石墨電極表面后，陰極峰電位和陽(yáng)極峰電位之差(ΔEp)與均相溶液相比明顯增大，例如，對(duì)于PW11Fe/CS/CNTS/C復(fù)合膜電極的Fe波，ΔEp=355 mV，而PW11Fe在均相溶液中的ΔEp=(60～90) mV[1-3]，表明固載后電子傳遞的可逆性變差，這是因?yàn)槟さ拇嬖谠黾恿穗娮璧木壒省?/p>

為了考察PW11Fe/CS/CNTs/C復(fù)合膜電極的穩(wěn)定性，將電極置于0.1 mol/L 的NaHSO4-Na2SO4(pH=2.2)溶液中連續(xù)掃描50周，發(fā)現(xiàn)陰極峰電流和陽(yáng)極峰電流的大小以及波形幾乎不變(圖1(b))，表明電極具有較好的穩(wěn)定性。

改變掃描速率，峰電流隨掃描速率的增加而增加。取陰極峰電流和陽(yáng)極峰電流對(duì)掃描速率作圖，得到兩條直線(xiàn)(圖2)，表明電極反應(yīng)受表面過(guò)程控制。

圖1 (a) PW11Fe/CS/CNTs/C復(fù)合膜電極在0.1 mol/L NaHSO4-Na2SO4 (pH=2.2)溶液中的循環(huán)伏安曲線(xiàn)掃描速率：10 mV·s-1，掃描范圍：0.4～-0.85 V(b) 對(duì)Fe中心連續(xù)掃描50圈的循環(huán)伏安曲線(xiàn)Fig.1 (a) Cyclic voltammograms of the PW11Fe/CS/CNTs/C composite film electrode in 0.1 mol/L NaHSO4-Na2SO4 (pH=2.2) solution; scan rate: 10 mV·s-1, scan potential range: 0.4～-0.85 V (b) Cyclic voltammogram of Fe center for continuous scanning 50 cycles

2.2 CNTs劑量對(duì)PW11Fe/CS/CNTS/C循環(huán)伏安行為的影響

在電極的制備過(guò)程中加入CNTs的目的是為了提高膜的導(dǎo)電性。從圖3可以看到，F(xiàn)e(Ⅲ)/Fe(Ⅱ)電對(duì)的峰電流隨著CNTs劑量的增加而增大。但當(dāng)CNTs的劑量超過(guò)0.004 g時(shí)，峰電流反而下降，這是因?yàn)镃NTs達(dá)到一定量時(shí)，在空間上阻止了CS對(duì)PW11Fe的吸附，使膜中電活性成分PW11Fe的含量減少，從而導(dǎo)致響應(yīng)電流減小。因此，在本實(shí)驗(yàn)條件下，CNTs的最佳劑量是0.004 g。

2.3 溶液pH對(duì)PW11Fe/CS/CNTS/C循環(huán)伏安行為的影響

PW11Fe對(duì)質(zhì)子比較敏感，因此合成時(shí)須嚴(yán)格控制反應(yīng)體系的pH值。在均相水溶液中，PW11Fe穩(wěn)定存在的pH值為2.0～8.0[3, 20]。但當(dāng)溶液pH值改變時(shí)，F(xiàn)e(Ⅲ)/Fe(Ⅱ)和W(Ⅵ)/W(Ⅴ)電對(duì)的還原氧化峰電位負(fù)移，且ΔEp增大，電子傳遞的可逆性變差，換言之，高濃度的H+由于與PW11Fe形成“緊密離子對(duì)”，在動(dòng)力學(xué)上有利于促進(jìn)電子的傳遞，提高電極過(guò)程的可逆性[20]。將PW11Fe固載到電極表面后，這種電化學(xué)行為依然可以觀(guān)察到。如圖4所示，當(dāng)溶液的pH從2.2增大到7.0時(shí)，PW11Fe/CS/CNTs/C復(fù)合膜電極的還原氧化峰電位負(fù)移，導(dǎo)致在0.4～-0.8 V的電位范圍內(nèi)，只觀(guān)察到Fe(Ⅲ)/Fe(Ⅱ)電對(duì)的還原氧化峰，且ΔEp明顯增大。

圖2 (a)不同掃描速度下PW11Fe/CS/CNTs/C復(fù)合膜電極在0.1 mol/L NaHSO4-Na2SO4 (pH=2.2)溶液中的循環(huán)伏安曲線(xiàn)；(b)陰極峰電流和陽(yáng)極峰電流與掃描速率的關(guān)系Fig.2 (a) Cyclic voltammograms of the PW11Fe/CS/CNTs/C composite film electrode at different scan rate in 0.1 mol/L NaHSO4-Na2SO4(pH=2.2) solution；(b) Relationship of peak current with scan rate

圖3 不同CNTs劑量下PW11Fe/CS/CNTs/C復(fù)合膜電極在0.1 mol/L NaHSO4-Na2SO4 (pH=2.2)溶液中的循環(huán)伏安曲線(xiàn)Fig.3 Cyclic voltammograms of the PW11Fe/CS/CNTs/C composite film electrode at different dosage of CNTs in 0.1 mol/L NaHSO4-Na2SO4(pH=2.2) solution Scan rate: 10 mV·s-1

圖4 PW11Fe/CS/CNTs/C復(fù)合膜電極在不同pH值的 NaHSO4-Na2SO4溶液中的循環(huán)伏安曲線(xiàn)Fig.4 Cyclic voltammograms of the PW11Fe/CS/CNTs/C composite film electrode in NaHSO4-Na2SO4 solution with different pH； Scan rate: 10 mV·s-1

2.4 PW11Fe/CS/CNTS/C復(fù)合膜電極對(duì)H2O2的電催化性能

PW11Fe/CS/CNTs/C復(fù)合膜電極能否用于檢測(cè)H2O2首先取決于它對(duì)H2O2還原的電催化活性。如圖5(a)所示，在PW11Fe/CS/CNTs/C復(fù)合膜電極體系中加入H2O2，響應(yīng)電流明顯提高，且隨H2O2濃度的增加而增大，表明電極對(duì)H2O2的還原產(chǎn)生了電催化作用，因?yàn)镠2O2在裸碳電極上的還原速率很慢，幾乎觀(guān)察不到H2O2的響應(yīng)電流[3-4]。PW11Fe/CS/CNTs/C電極對(duì)H2O2還原的電催化作用源于其電活性組分PW11Fe中的Fe(Ⅲ)/Fe(Ⅱ)電對(duì)，實(shí)驗(yàn)表明，F(xiàn)e(Ⅲ)很容易從碳電極上獲得電子，并迅速傳遞給H2O2分子使之還原。換句話(huà)說(shuō)，F(xiàn)e(Ⅲ)的存在改變了H2O2分子在碳電極上發(fā)生還原反應(yīng)的途徑，降低了反應(yīng)的活化能，從而導(dǎo)致H2O2還原速率的提高。從另一方面來(lái)看，H2O2分子很容易結(jié)合到PW11Fe/CS/CNTs/C電極的活性位點(diǎn)—Fe中心，并在還原電位下迅速清除來(lái)自電極的電子，產(chǎn)生去極化作用，從而降低了電子傳遞的阻力，使反應(yīng)加速。電化學(xué)阻抗譜證實(shí)了這一點(diǎn)。從圖5(b)中可以看到，在PW11Fe/CS/CNTs/C復(fù)合膜電極體系中加入H2O2，交流阻抗明顯下降，且加入的H2O2越多，交流阻抗的下降越明顯。

圖5 (a)不同濃度H2O2下PW11Fe/CS/CNTs/C復(fù)合膜電極在0.1 mol/L NaHSO4-Na2SO4 (pH=2.2)溶液中的循環(huán)伏安曲線(xiàn)；(b) 不同濃度H2O2下PW11Fe/CS/CNTs/C復(fù)合膜電極的電化學(xué)阻抗譜Fig.5 (a)Cyclic voltammograms of the PW11Fe/CS/CNTs/C composite film electrode at different H2O2 concentration in 0.1 mol/L NaHSO4-Na2SO4 (pH=2.2) solution; Scan rate: 10 mV·s-1 (b) EIS of the PW11Fe/CS/CNTs/C composite film electrode at different H2O2 concentration in 0.1 mol/L NaHSO4-Na2SO4 (pH=2.2) solution; frequency =100 000～0.1 Hz, ΔE=5 mV, E=-0.08 V

鑒于PW11Fe/CS/CNTs/C復(fù)合膜電極對(duì)H2O2還原具有較高的電催化活性，我們用它進(jìn)行了H2O2的安培檢測(cè)實(shí)驗(yàn)，結(jié)果如圖6(a)所示。從圖中可以看到，當(dāng)在插入PW11Fe/CS/CNTs/C復(fù)合膜電極的0.1 mol/L NaHSO4-Na2SO4(pH=2.2) 溶液中連續(xù)滴加5 μmol/L H2O2時(shí)，可以觀(guān)察到迅速且穩(wěn)定的電流響應(yīng)，響應(yīng)電流在5～35 μmol/L的范圍內(nèi)與H2O2濃度成線(xiàn)性關(guān)系(圖6(b))，線(xiàn)性方程為

J(mA/cm2)=1.971 83 +0.304 12[c(μmol/L) ]，

R=0.997 66

從直線(xiàn)的斜率可知，電極對(duì)H2O2響應(yīng)的靈敏度為0.30 mA·cm-2·(μmol/L)-1。根據(jù)方程式(1)[21]估算電極對(duì)H2O2的檢出限為7.3 μmol/L (S/N=3)。

cL=KSb/m

(1)

式中，K為信噪比，Sb為空白的標(biāo)準(zhǔn)偏差，m為直線(xiàn)的斜率。

圖6 (a) 在PW11Fe/CS/CNTs/C復(fù)合膜電極體系中連續(xù)滴加5 μmol/L H2O2時(shí)的計(jì)時(shí)電流響應(yīng)曲線(xiàn)(b)響應(yīng)電流與H2O2濃度的關(guān)系支持電解質(zhì)：0.1 mol/L NaHSO4-Na2SO4 (pH 2.2) 溶液Fig.6 (a) Chronoamperometric response of the PW11Fe/CS/CNTs/C composite film electrode towards H2O2 on successive addition of 5 μmol/L H2O2 Supporting electrolyte: 0.1 mol/L NaHSO4-Na2SO4 (pH=2.2) solution, Applied potential: -0.084 V (b) The relationship of response current with H2O2 concentration

3 結(jié) 論

以CS為吸附劑和成膜劑，CNTs為導(dǎo)電助劑，將PW11Fe固載到石墨電極表面制備的PW11Fe/CS/CNTs/C復(fù)合膜電極，對(duì)H2O2的還原具有明顯的電催化活性，應(yīng)用于H2O2的安培檢測(cè)，電流響應(yīng)靈敏，檢出限低，因此有可能在H2O2電化學(xué)傳感器方面獲得應(yīng)用。

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PreparationofPW11Fe/CS/CNTs/CcompositefilmelectrodeandapplicationinH2O2electrochemicalsensor

WANGXin,ZHANGJinming,JIANGXiaowei,HANLeiyun,WANGLili,HUANGYanxia,YOUChenghang,HUAYingjie,WANGChongtai

(School of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158, China)

A composite film electrode PW11Fe/CS/CNTs/C was prepared by the integration of adsorption method and sol-gel method using chitosan as both an adsorbent and film-forming agent, Keggin type Fe(Ⅲ)-substituted heteropolyanion PW11O39Fe(Ⅲ)(H2O)4-(PW11Fe) as an electrocatalyst, carbon nano tubes (CNTs) as a conductivity improver in this paper. The electrochemical behavior and its influence factors of the as-prepared electrode were investigated by using the electrochemical method. The electrocatalytic activity towards H2O2reduction and the possibility also used to be an electrochemical sensor detecting H2O2were evaluated. The results showed that the PW11Fe/CS/CNTs/C composite film electrode possessed a similar electrochemical behavior with PW11Fe and a high electrocatalytic activity towards H2O2reduction. For detecting H2O2reduction. Applied to detect H2O2, the electrode exhibits a high sensitivity of 0.30 mA·cm-2·(μmol/L)-1and a detection limit of 7.3 μmol/L (S/N=3).

Keggin-type iron substituted heteropolytungstate; cycle voltammetry； chitosan；electrocatalysis；carbon nano tubes

O646

A

0529-6579(2017)05-0079-06

10.13471/j.cnki.acta.snus.2017.05.011

2017-04-05

國(guó)家自然科學(xué)基金( 21606061)；海南省國(guó)際科技合作項(xiàng)目(KJHZ2014-08)；海南省自然科學(xué)基金項(xiàng)目(20162022)；海口市重點(diǎn)科技項(xiàng)目(2016-032)；海南省科協(xié)青年科技英才創(chuàng)新計(jì)劃項(xiàng)目(201502)；全國(guó)大學(xué)生創(chuàng)新創(chuàng)業(yè)訓(xùn)練項(xiàng)目(201511658004)

王鑫 (1991年生), 男；研究方向電化學(xué)儲(chǔ)能與光能轉(zhuǎn)換材料；E-mail : 544317402@qq.com

華英杰(1966年生)，女；研究方向：電化學(xué)儲(chǔ)能與光能轉(zhuǎn)換材料；E-mail:521000hua282@sina.com；王崇太(1962年生)，男；研究方向：電化學(xué)儲(chǔ)能與光能轉(zhuǎn)換材料；E-mail: oehy2014@163.com