石墨烯-金屬卟啉的制備及其催化氧氣還原性能的研究

熊樂(lè)艷+鄭龍珍+鄒志君+葉丹+董澤民+亢曉衛(wèi)+紀(jì)憶+黃丹靈

摘要:合成了一系列石墨烯-金屬四苯基卟啉(GR-MTPP)的復(fù)合材料,并將該復(fù)合材料作為電催化劑應(yīng)用于氧氣還原反應(yīng)中?通過(guò)金屬離子與四苯基卟啉發(fā)生配位反應(yīng)得到金屬四苯基卟啉(FeTPP?CoTPP?NiTPP?CuTPP?ZnTPP?MnTPP),進(jìn)一步通過(guò)π-π堆積作用合成了一系列新型的石墨烯-金屬卟啉復(fù)合材料,并將其修飾到玻碳電極上,研究其催化氧氣還原的反應(yīng)?結(jié)果表明,該復(fù)合材料在DMF與水的混合溶劑中分散性能良好;石墨烯與金屬卟啉的協(xié)同作用使其催化氧氣還原性能更優(yōu);該類復(fù)合材料尤其是GR-FeTPP與GR-CoTPP在中性溶液中(pH=7.0)顯示出良好的對(duì)氧氣還原的電催化性能?GR-FeTPP催化氧氣還原的電位在-0.24 V處,響應(yīng)電流為85 μA;GR-CoTPP催化氧氣還原的電位在-0.19 V,響應(yīng)電流為44 μA?表明石墨烯-金屬卟啉復(fù)合材料是氧氣傳感器良好的電催化劑?

關(guān)鍵詞:石墨烯;金屬四苯基卟啉;復(fù)合材料;氧氣還原反應(yīng);電催化劑

中圖分類號(hào):TP212.3文獻(xiàn)標(biāo)識(shí)碼:A文章編號(hào):0439-8114(2014)11-2611-05

Preparation of Graphene-metalporphyrin Nanocomposite Materials and Its Electrocatalytic Activity for Oxygen Reduction Reaction

XIONG Le-yan,ZHENG Long-zhen,ZOU Zhi-jun,YE Dan,DONG Ze-min,KANG Xiao-wei,JI Yi,HUANG Dan-ling

(Department of Chemistry and Chemical Engineering,East China Jiaotong University,Nanchang 330013,China)

Abstract: A series of graphene-metal-tetraphenylporphyrin(GR-MTPP) nanocomposite materials were prepared and applied in the oxygen reduction reaction as efficient electrocatalysts. MTPPs(FeTPP,CoTPP,NiTPP,CuTPP,ZnTPP and MnTPP) were synthesized via a coordination reaction between metal ions and TPP. Graphene-metal-tetraphenylporphyrin nanocomposition materials were successfully prepared by the π-π stacking interaction and applied in the electrocatalytic oxygen reduction reaction. The results showed that GR-MTPPs exhibited enhanced electrocatalytic activity toward oxygen reduction due to the synergistic effect between the graphene and MTTP. The large electro-active surface area and fast charge transfered of graphene facilitated the electrocatalytic oxygen reduction of MTPP. The GR-FeTPP showed the peak potential at -0.24 V with the current response of 85 μA for the eletrocatalytic reduction of oxygen. The GR-CoTPP showed the peak potential at -0.19 V with the current response of 44 μA for the eletrocatalytic reduction of oxygen. It is indicated that GR-MTPP nanocomposite materials are prominent electrocatalysts for oxygen sensors.

Key words: graphene; metal-tetraphenylporphyrin; nanocomposite material; oxygen reduction reaction; electrocatalyst

基金項(xiàng)目:國(guó)家自然科學(xué)基金項(xiàng)目(21163007;21165009);江西省主要學(xué)科學(xué)術(shù)和技術(shù)帶頭人計(jì)劃項(xiàng)目(20133BCB22007);江西省自然科學(xué)基金項(xiàng)目(20132BAB203012)

水中溶解氧的含量對(duì)許多化學(xué)和生物反應(yīng)有很大的影響,因此溶解氧生物傳感器在環(huán)境?醫(yī)療?工業(yè)? 環(huán)保等方面有著廣泛的應(yīng)用[1,2]?與傳統(tǒng)檢測(cè)溶解氧的光化學(xué)技術(shù)(如熒光[3]?化學(xué)發(fā)光[4])相比,電化學(xué)傳感的檢測(cè)方式具有便宜?簡(jiǎn)易?靈敏度高等優(yōu)點(diǎn)[5,6]?

卟啉是一類具有諸多重要酶活性點(diǎn)的仿生性質(zhì)的大π結(jié)構(gòu)的化合物,可作為一種具有良好電催化性能的的電子媒介體?卟啉與金屬離子螯合形成穩(wěn)定的金屬配位化合物,可以作為氧氣還原反應(yīng)的高效催化劑而被廣泛的應(yīng)用[7]?然而金屬卟啉催化氧氣還原反應(yīng)通常都在酸性溶液中進(jìn)行,這就限制了其在生物體系中的應(yīng)用[8]?石墨烯也是一類二維大π結(jié)構(gòu)的碳納米材料,具有獨(dú)特的光學(xué)性能?催化性能?電子性能?機(jī)械性能以及大比表面積等特點(diǎn),廣泛應(yīng)用于各個(gè)領(lǐng)域[9,10]?

近年來(lái),卟啉與石墨烯的復(fù)合材料被人們廣泛關(guān)注,二者之間可以通過(guò)共價(jià)鍵[11]和非共價(jià)鍵[12]結(jié)合起來(lái)?與共價(jià)鍵相比,非共價(jià)鍵(如π-π堆積?靜電吸引和氫鍵等)的結(jié)合方式,既能保持卟啉大分子優(yōu)良的電催化性能,又不會(huì)使石墨烯獨(dú)特的電子特性和結(jié)構(gòu)特征遭到破壞[13]?

在本研究中,通過(guò)π-π堆積作用制備了一系列新型的石墨烯-金屬卟啉(GR-MTPP)納米復(fù)合材料?與金屬卟啉相比較,GR-MTPP復(fù)合材料催化氧氣還原反應(yīng)的過(guò)電位降低,響應(yīng)電流增加,表明該材料是氧氣傳感器優(yōu)良的電催化劑?

1材料與方法

1.1金屬卟啉(MTPP)的制備

將1.5 g四苯基卟啉加入三頸瓶中,加入DMF(N,N-二甲基甲酰胺)至卟啉剛好完全溶解為止?加熱至回流,分別加入1.0 g金屬鹽(FeCl3?CoCl2?NiCl2?CuCl2?ZnCl2?MnCl2)反應(yīng)1 h后,加入0.50 g NaCl繼續(xù)反應(yīng),反應(yīng)時(shí)間約為5 h?減壓蒸餾出大部分DMF,冷卻,加入大量的冷水使金屬卟啉結(jié)晶析出,然后加入濃鹽酸酸化?進(jìn)行抽濾,用去離子水充分洗滌晶體,干燥,用二氯甲烷和無(wú)水乙醇的混合溶劑重結(jié)晶晶體,得到1.37 g的產(chǎn)品,產(chǎn)率為91.3%?

1.2石墨烯(GR)的制備

氧化石墨烯(GO)采用石墨粉通過(guò)改進(jìn)的Hummers方法制備?取50 mL GO(0.25 mg/mL)于圓底燒瓶中,加入14 μL水合肼和150 μL氨水,70 ℃下攪拌12 h,離心?洗滌?干燥,得到石墨烯?

1.3石墨烯-金屬四苯基卟啉復(fù)合材料的制備

將GR(0.5 mg/mL)與MTPP(1 mg/mL)按1∶1的體積比分散在混合溶劑(DMF/H2O=4∶1,V∶V)中超聲混合10 min,得到GR-MTPP復(fù)合材料?由于GR與MTPP均為具有大π結(jié)構(gòu)的物質(zhì),故二者可以通過(guò)π-π堆積作用進(jìn)行結(jié)合形成穩(wěn)定的復(fù)合材料,GR與MTPP的結(jié)合方式如圖1所示?

1.4修飾電極的制備

電極預(yù)處理:玻碳電極分別用0.3 μm和0.05 μm 的Al2O3粉拋光,依次用無(wú)水乙醇和去離子水超聲洗滌10 min,氮?dú)獯蹈纱?分別取5 μL的GR-MTPP?MTPP溶液滴加到電極表面,于4 ℃冰箱中過(guò)夜自然干燥,即可得到所需的生物傳感器?

1.5試驗(yàn)方法

采用三電極體系,以玻碳電極或修飾電極為工作電極,鉑電極為對(duì)電極,Ag/AgCl(飽和KCl溶液)電極為參比電極,采用循環(huán)伏安(CV)法在0.1 mol/L磷酸緩沖溶液(PBS,pH=7.0)中研究修飾電極的催化氧氣還原性能?

2結(jié)果與分析

2.1紅外光譜表征

在TPP的紅外光譜(圖2)中,波數(shù)3 316 cm-1處為卟啉環(huán)內(nèi)吡咯中的N-H伸縮振動(dòng)特征吸收峰?通過(guò)對(duì)比TPP與各類MTPP的紅外光譜圖可見(jiàn),金屬卟啉的紅外譜圖中N-H的震動(dòng)吸收峰消失,表明金屬離子已取代卟吩環(huán)內(nèi)的吡咯質(zhì)子生成了金屬卟啉?

從GR的紅外光譜(圖3)可知,波數(shù)3 437 cm-1處為羥基峰,2 928~2 974 cm-1處為C-H伸縮振動(dòng)峰,1 620 cm-1處為C=C峰,1 106 cm-1處為C-O-C峰,1 650~1 900 cm-1處未出現(xiàn)C=O峰,說(shuō)明氧化石墨烯還原得比較完全?將GR-MTPP復(fù)合材料的紅外光譜圖與GR及MTPP的紅外光譜圖進(jìn)行比對(duì)可知,各個(gè)GR-MTPP的特征吸收峰與MTPP的相比均發(fā)生偏移(如C-N峰),且這些特征吸收峰的吸收峰值變小;與GR的特征吸收峰相比,吸收峰的峰位置也發(fā)生了偏移且出現(xiàn)了MTPP的特征吸收峰?這些結(jié)果均表明,GR與MTPP之間沒(méi)有產(chǎn)生新的化學(xué)鍵,而是通過(guò)非共價(jià)鍵的方式結(jié)合的?

2.2紫外光譜表征

采用紫外-可見(jiàn)吸收光譜對(duì)GR-MTPP納米復(fù)合材料進(jìn)行了表征?如圖4所示,MTPP在413~426 nm處出現(xiàn)一個(gè)尖的Sort帶吸收峰?在500~620 nm處出現(xiàn)了一些弱的Q帶吸收峰,這些吸收峰為金屬卟啉的特征吸收峰?隨著石墨烯的加入,金屬卟啉的尖峰及Q帶吸收特征峰的位置發(fā)生偏移,峰值增加?這些變化是由于石墨烯與金屬卟啉之間發(fā)生了π-π堆積作用,使得金屬卟啉的大π鍵共軛作用增強(qiáng)所致?其中CoTPP紫外-可見(jiàn)吸收光譜中,隨著石墨烯的加入,CoTPP在414 nm處的特征吸收峰逐漸降低,在432 nm處出現(xiàn)一個(gè)新的吸收峰并逐漸增大,這表明CoTPP通過(guò)很強(qiáng)的π-π相互作用堆疊在石墨烯表面上?

圖5為MTPP及GR-MTPP復(fù)合材料的光學(xué)照片?從圖5可以看出,MTPP及GR-MTPP材料在混合溶劑(DMF/H2O=4∶1)中均有良好的分散性能?將GR-MTPP與MTPP的分散液進(jìn)行比較,加入GR后的復(fù)合材料顏色發(fā)生了變化,且不是單純的顏色變深(如FeTPP由棕黃色變成綠色)?這就表明石墨烯與金屬卟啉之間的相互作用不是簡(jiǎn)單的混合,而是以一種特殊的方式進(jìn)行結(jié)合的?

2.3電催化氧氣還原反應(yīng)

圖6為MTPP和GR-MTPP(在氧氣氣氛和氮?dú)鈿夥障?催化氧氣還原反應(yīng)的循環(huán)伏安?從圖6可知,MTPP和GR-MTPP對(duì)于氧氣還原反應(yīng)均具有良好的催化效果?與MTPP相比,GR-MTPP催化氧氣還原的催化電位均有所正移,電流響應(yīng)也增大很多,表明GR-MTPP復(fù)合材料在催化氧氣還原的過(guò)程中有效地降低了過(guò)電位,其催化活性也得到了很大的提高?GR-MTPP復(fù)合材料催化性能的提高可能是由于MTPP與GR之間的協(xié)同作用產(chǎn)生的?

MTPP和GR-MTPP催化氧氣還原反應(yīng)的催化電位及響應(yīng)電流見(jiàn)表1?由表1可知,MTPP催化氧氣還原的催化電位在-0.61~-0.36 V處,響應(yīng)電流為19~48 μA?而GR-MTPP催化氧氣還原的催化電位正移到-0.49~-0.19 V處,響應(yīng)電流增大到44~85 μA?其中,以GR-FeTPP與GR-CoTPP催化氧氣還原的效果最佳?GR-FeTPP催化氧氣還原的電位為-0.24 V,催化電流增大到85 μA;GR-CoTPP催化氧氣還原的電位降低到-0.19 V,響應(yīng)電流為44 μA?因此,GR-FeTPP與GR-CoTPP是氧氣傳感器良好的電催化劑?

3結(jié)論

本研究利用一種簡(jiǎn)單的方法合成了一系列GR-MTPP納米復(fù)合材料,并采用傅里葉紅外光譜和紫外-可見(jiàn)吸收光譜對(duì)該材料進(jìn)行表征,結(jié)果表明GR與MTPP是通過(guò)強(qiáng)的π-π堆積作用進(jìn)行合成的?將GR-MTPP復(fù)合材料應(yīng)用于催化氧氣還原反應(yīng)的研究,該復(fù)合材料能夠有效地降低氧氣還原反應(yīng)的過(guò)電位,提高了其催化活性?其中,GR-FeTPP催化氧氣還原的催化電位在-0.24 V處,響應(yīng)電流為85 μA;GR-CoTPP催化氧氣還原的催化電位在-0.19 V,響應(yīng)電流為44 μA?GR-FeTPP和GR-CoTPP可以作為氧氣傳感器優(yōu)良的電催化劑,可應(yīng)用于水中溶解氧氣濃度的檢測(cè)?

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[6] WESTBROEK P, TEMMERMAN E. In line measurement of chemical oxygen demand by means of multipulse amperometry at a rotating Pt ring-Pt/PbO2 disc electrode[J].Analytica Chimica Acta,2001,437(1):95-105.

[7] SHI C, ANSON F C. Multiple intramolecular electron transfer in the catalysis of the reduction of dioxygen by cobalt meso-tetrakis(4-pyridyl)porphyrin to which four Ru(NH3)5 groupsare coordinated[J]. Journal of the American Chemical Society, 1991,113(25):9546-9570.

[8] LIU Y, YAN Y L, LEI J P, et al. Functional multiwalled carbon nanotube nanocomposite with iron picket-fence porphyrin and its electrocatalytic behavior[J]. Electrochemistry Communications,2007,9(10):2564-2570.

[9] RATINAC K R, YANG W, RINGER S P, et al. Toward ubiquitous environmental gas sensors-capitalizing on the promise of graphene[J]. Science and Technology,2010,44(4): 1167-1176.

[10] WANG S, GOH B M, MANGA K K, et al. Graphene as atomic template and structural scaffold in the synthesis of graphene organic hybrid wire with photovoltaic properties[J]. ACS Nano,2010,4(10):6180-6186.

[11] XU Y F, LIU Z B, ZHANG X L, et al. A graphene hybrid material covalently functionalized with porphyrin:synthesis and optical limiting property[J]. Advanced Materials,2009,21(12):1275-1279.

[12] ZHANG S, TANG S, LEI J, et al. Functionalization of graphene nanoribbons with porphyrin for electrocatalysis and amperometric biosensing[J]. Journal Electroanalytical Chemistry,2011,656(1-2):285-288.

[13] ZHANG H Q, FENG Y Y, TANG S D, et al. Preparation of a graphene oxide-phthalocyanine hybrid through strong π-π interactions[J].Carbon,2010,48(1):211-216.

[5] JULIANA C D, RITA C S L, FLAVIO S D, et al. A highly sensitive amperometric sensor for oxygen based on iron(II) tetrasulfonated phthalocyanine and iron(III) tetra-(N-methyl-pyridyl)-porphyrin multilayers[J]. Analytica Chimica Acta,2008,612(1):29-36.

[6] WESTBROEK P, TEMMERMAN E. In line measurement of chemical oxygen demand by means of multipulse amperometry at a rotating Pt ring-Pt/PbO2 disc electrode[J].Analytica Chimica Acta,2001,437(1):95-105.

[7] SHI C, ANSON F C. Multiple intramolecular electron transfer in the catalysis of the reduction of dioxygen by cobalt meso-tetrakis(4-pyridyl)porphyrin to which four Ru(NH3)5 groupsare coordinated[J]. Journal of the American Chemical Society, 1991,113(25):9546-9570.

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