石墨烯-金属卟啉的制备及其催化氧气还原性能的研究

熊乐艳+郑龙珍+邹志君+叶丹+董泽民+亢晓卫+纪忆+黄丹灵

摘要:合成了一系列石墨烯-金属四苯基卟啉(GR-MTPP)的复合材料,并将该复合材料作为电催化剂应用于氧气还原反应中｡通过金属离子与四苯基卟啉发生配位反应得到金属四苯基卟啉(FeTPP､CoTPP､NiTPP､CuTPP､ZnTPP､MnTPP),进一步通过π-π堆积作用合成了一系列新型的石墨烯-金属卟啉复合材料,并将其修饰到玻碳电极上,研究其催化氧气还原的反应｡结果表明,该复合材料在DMF与水的混合溶剂中分散性能良好;石墨烯与金属卟啉的协同作用使其催化氧气还原性能更优;该类复合材料尤其是GR-FeTPP与GR-CoTPP在中性溶液中(pH=7.0)显示出良好的对氧气还原的电催化性能｡GR-FeTPP催化氧气还原的电位在-0.24 V处,响应电流为85 μA;GR-CoTPP催化氧气还原的电位在-0.19 V,响应电流为44 μA｡表明石墨烯-金属卟啉复合材料是氧气传感器良好的电催化剂｡

关键词:石墨烯;金属四苯基卟啉;复合材料;氧气还原反应;电催化剂

中图分类号:TP212.3文献标识码:A文章编号: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

基金项目:国家自然科学基金项目(21163007;21165009);江西省主要学科学术和技术带头人计划项目(20133BCB22007);江西省自然科学基金项目(20132BAB203012)

水中溶解氧的含量对许多化学和生物反应有很大的影响,因此溶解氧生物传感器在环境､医疗､工业､ 环保等方面有着广泛的应用[1,2]｡与传统检测溶解氧的光化学技术(如荧光[3]､化学发光[4])相比,电化学传感的检测方式具有便宜､简易､灵敏度高等优点[5,6]｡

卟啉是一类具有诸多重要酶活性点的仿生性质的大π结构的化合物,可作为一种具有良好电催化性能的的电子媒介体｡卟啉与金属离子螯合形成稳定的金属配位化合物,可以作为氧气还原反应的高效催化剂而被广泛的应用[7]｡然而金属卟啉催化氧气还原反应通常都在酸性溶液中进行,这就限制了其在生物体系中的应用[8]｡石墨烯也是一类二维大π结构的碳纳米材料,具有独特的光学性能､催化性能､电子性能､机械性能以及大比表面积等特点,广泛应用于各个领域[9,10]｡

近年来,卟啉与石墨烯的复合材料被人们广泛关注,二者之间可以通过共价键[11]和非共价键[12]结合起来｡与共价键相比,非共价键(如π-π堆积､静电吸引和氢键等)的结合方式,既能保持卟啉大分子优良的电催化性能,又不会使石墨烯独特的电子特性和结构特征遭到破坏[13]｡

在本研究中,通过π-π堆积作用制备了一系列新型的石墨烯-金属卟啉(GR-MTPP)纳米复合材料｡与金属卟啉相比较,GR-MTPP复合材料催化氧气还原反应的过电位降低,响应电流增加,表明该材料是氧气传感器优良的电催化剂｡

1材料与方法

1.1金属卟啉(MTPP)的制备

将1.5 g四苯基卟啉加入三颈瓶中,加入DMF(N,N-二甲基甲酰胺)至卟啉刚好完全溶解为止｡加热至回流,分别加入1.0 g金属盐(FeCl3､CoCl2､NiCl2､CuCl2､ZnCl2､MnCl2)反应1 h后,加入0.50 g NaCl继续反应,反应时间约为5 h｡减压蒸馏出大部分DMF,冷却,加入大量的冷水使金属卟啉结晶析出,然后加入浓盐酸酸化｡进行抽滤,用去离子水充分洗涤晶体,干燥,用二氯甲烷和无水乙醇的混合溶剂重结晶晶体,得到1.37 g的产品,产率为91.3%｡

1.2石墨烯(GR)的制备

氧化石墨烯(GO)采用石墨粉通过改进的Hummers方法制备｡取50 mL GO(0.25 mg/mL)于圆底烧瓶中,加入14 μL水合肼和150 μL氨水,70 ℃下搅拌12 h,离心､洗涤､干燥,得到石墨烯｡

1.3石墨烯-金属四苯基卟啉复合材料的制备

将GR(0.5 mg/mL)与MTPP(1 mg/mL)按1∶1的体积比分散在混合溶剂(DMF/H2O=4∶1,V∶V)中超声混合10 min,得到GR-MTPP复合材料｡由于GR与MTPP均为具有大π结构的物质,故二者可以通过π-π堆积作用进行结合形成稳定的复合材料,GR与MTPP的结合方式如图1所示｡

1.4修饰电极的制备

电极预处理:玻碳电极分别用0.3 μm和0.05 μm 的Al2O3粉抛光,依次用无水乙醇和去离子水超声洗涤10 min,氮气吹干待用｡分别取5 μL的GR-MTPP､MTPP溶液滴加到电极表面,于4 ℃冰箱中过夜自然干燥,即可得到所需的生物传感器｡

1.5试验方法

采用三电极体系,以玻碳电极或修饰电极为工作电极,铂电极为对电极,Ag/AgCl(饱和KCl溶液)电极为参比电极,采用循环伏安(CV)法在0.1 mol/L磷酸缓冲溶液(PBS,pH=7.0)中研究修饰电极的催化氧气还原性能｡

2结果与分析

2.1红外光谱表征

在TPP的红外光谱(图2)中,波数3 316 cm-1处为卟啉环内吡咯中的N-H伸缩振动特征吸收峰｡通过对比TPP与各类MTPP的红外光谱图可见,金属卟啉的红外谱图中N-H的震动吸收峰消失,表明金属离子已取代卟吩环内的吡咯质子生成了金属卟啉｡

从GR的红外光谱(图3)可知,波数3 437 cm-1处为羟基峰,2 928~2 974 cm-1处为C-H伸缩振动峰,1 620 cm-1处为C=C峰,1 106 cm-1处为C-O-C峰,1 650~1 900 cm-1处未出现C=O峰,说明氧化石墨烯还原得比较完全｡将GR-MTPP复合材料的红外光谱图与GR及MTPP的红外光谱图进行比对可知,各个GR-MTPP的特征吸收峰与MTPP的相比均发生偏移(如C-N峰),且这些特征吸收峰的吸收峰值变小;与GR的特征吸收峰相比,吸收峰的峰位置也发生了偏移且出现了MTPP的特征吸收峰｡这些结果均表明,GR与MTPP之间没有产生新的化学键,而是通过非共价键的方式结合的｡

2.2紫外光谱表征

采用紫外-可见吸收光谱对GR-MTPP纳米复合材料进行了表征｡如图4所示,MTPP在413~426 nm处出现一个尖的Sort带吸收峰､在500~620 nm处出现了一些弱的Q带吸收峰,这些吸收峰为金属卟啉的特征吸收峰｡随着石墨烯的加入,金属卟啉的尖峰及Q带吸收特征峰的位置发生偏移,峰值增加｡这些变化是由于石墨烯与金属卟啉之间发生了π-π堆积作用,使得金属卟啉的大π键共轭作用增强所致｡其中CoTPP紫外-可见吸收光谱中,随着石墨烯的加入,CoTPP在414 nm处的特征吸收峰逐渐降低,在432 nm处出现一个新的吸收峰并逐渐增大,这表明CoTPP通过很强的π-π相互作用堆叠在石墨烯表面上｡

图5为MTPP及GR-MTPP复合材料的光学照片｡从图5可以看出,MTPP及GR-MTPP材料在混合溶剂(DMF/H2O=4∶1)中均有良好的分散性能｡将GR-MTPP与MTPP的分散液进行比较,加入GR后的复合材料颜色发生了变化,且不是单纯的颜色变深(如FeTPP由棕黄色变成绿色)｡这就表明石墨烯与金属卟啉之间的相互作用不是简单的混合,而是以一种特殊的方式进行结合的｡

2.3电催化氧气还原反应

图6为MTPP和GR-MTPP(在氧气气氛和氮气气氛下)催化氧气还原反应的循环伏安｡从图6可知,MTPP和GR-MTPP对于氧气还原反应均具有良好的催化效果｡与MTPP相比,GR-MTPP催化氧气还原的催化电位均有所正移,电流响应也增大很多,表明GR-MTPP复合材料在催化氧气还原的过程中有效地降低了过电位,其催化活性也得到了很大的提高｡GR-MTPP复合材料催化性能的提高可能是由于MTPP与GR之间的协同作用产生的｡

MTPP和GR-MTPP催化氧气还原反应的催化电位及响应电流见表1｡由表1可知,MTPP催化氧气还原的催化电位在-0.61~-0.36 V处,响应电流为19~48 μA｡而GR-MTPP催化氧气还原的催化电位正移到-0.49~-0.19 V处,响应电流增大到44~85 μA｡其中,以GR-FeTPP与GR-CoTPP催化氧气还原的效果最佳｡GR-FeTPP催化氧气还原的电位为-0.24 V,催化电流增大到85 μA;GR-CoTPP催化氧气还原的电位降低到-0.19 V,响应电流为44 μA｡因此,GR-FeTPP与GR-CoTPP是氧气传感器良好的电催化剂｡

3结论

本研究利用一种简单的方法合成了一系列GR-MTPP纳米复合材料,并采用傅里叶红外光谱和紫外-可见吸收光谱对该材料进行表征,结果表明GR与MTPP是通过强的π-π堆积作用进行合成的｡将GR-MTPP复合材料应用于催化氧气还原反应的研究,该复合材料能够有效地降低氧气还原反应的过电位,提高了其催化活性｡其中,GR-FeTPP催化氧气还原的催化电位在-0.24 V处,响应电流为85 μA;GR-CoTPP催化氧气还原的催化电位在-0.19 V,响应电流为44 μA｡GR-FeTPP和GR-CoTPP可以作为氧气传感器优良的电催化剂,可应用于水中溶解氧气浓度的检测｡

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[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.

[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.

[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.