聚多巴胺功能化的四氧化三钴纳米复合材料的制备及电催化性能

王海宁　潘伯广　孙昭　冯涛涛　齐誉洪成林(石河子大学化学化工学院，新疆兵团化工绿色过程重点实验室-省部共建国家重点实验室培育基地，石河子832003)

聚多巴胺功能化的四氧化三钴纳米复合材料的制备及电催化性能

王海宁潘伯广孙昭冯涛涛齐誉＊洪成林＊
(石河子大学化学化工学院，新疆兵团化工绿色过程重点实验室-省部共建国家重点实验室培育基地，石河子832003)

通过简单的自聚合反应在四氧化三钴表面包覆聚多巴胺膜，联合使用纳米铂和辣根过氧化物酶用于电催化还原过氧化氢。结果表明，聚多巴胺的使用增强后续纳米铂的负载量和辣根过氧化物酶的生物活性；四氧化三钴、纳米铂和辣根过氧化物酶的多重信号放大作用，大大增强了该复合材料的催化活性，提高了过氧化氢传感器的灵敏度。优化实验条件下，传感器对过氧化氢的检测范围为0.1～700 μmol·L-1，检测限为0.08 μmol·L-1。

Co3O4；聚多巴胺；多重信号放大；电催化；H2O2

0　Introduction

Hydrogen peroxide(H2O2),as a kind of commonly used oxidizer and reductant,has been widely used in food industry,clinical diagnostics,pharmacy,environmental monitoring,etc[1-3].H2O2plays an important role in the living cells depending on the extent,timing, and location of its production.The disorder of H2O2concentration iscloselyconnectedwithoxidative stress reaction in injury,aging and disease[4].Therefore,accuratelydetectionforH2O2atlowlevel becomesincreasinglyimportant.Electrochemicalsensors are sensitive and efficient since they can analyze biological sample by direct conversion into an electricalsignal[5].Nanomaterials have stimulated intense research over past decades due to their high biocompatibility and large surface area[6-8].

Metal nanoparticles(NPs)and metallic oxides NPs are increasingly applied in the studies of catalysis, semiconductor,energy storage,and semiconductor as a result of their high surface reaction activity and catalytic activity[9-13].As a significant transition metal oxide,Co3O4NPs have been reported and applied incatalysis,electrochemicalsensorsandenergy storage[14-17].Compared with CoO and Co2O3,Co3O4exhibit more broad application prospects in electrochemistry because of its extremely high electrocatalytic activity and theoretical specific capacitance[18-19]. Cheng et al.reported that Co3O4directly grown on Ni foam has superior mass transport property,as well as this strategy is low in cost and facile in preparation[20]. Mu et al.reported that Co3O4NPs exhibited peroxidase -like activity and catalase-like activity[21].However, small molecules like Co3O4nanoparticles usually show poor stability and are easy to aggregate,as a result of the active sites decreased[22-24].

To solve this problem,some research groups wrapped some filming materials around the small molecules,and achieved initial success[24-25].Liu et al. reported porphyrinfunctionalized chain-like Co3O4NPs exhibited higher stability and catalytic activity than those of pure Co3O4NPs[23].Dong et al.reported a novel organic-inorganic hybrid material polypyrrole-Co3O4with good stability was successfully synthesized[26]. Lee et al.reported a very good film-forming biomaterial dopamine[27].Dopamine,as an important catecholamine neurotransmitter with excellent self-polymerizing ability and biocompatibility,has received great attention on filming material in the past few years[28-29]. The stable polydopamine(PDA)film formed by covalentpolymerizationandnon-covalentselfassemblydopamineiseasilylinkedwithmany materials such as metallic nanoparticles and biological molecules through the residual catechol groups on the film surface[30-32].

In this paper,we reported the synthesis of PDA bio-functionalized Co3O4NPs and its application in the electrocatalysis on H2O2.The Co3O4NPs were coveredinPDAfilmbyself-polymerizationof dopamine.With the residual catechol groups on the PDAfilmsurface,uniformlydispersedplatinum nanoparticles(Pt NPs)could be simply and steadily deposited on PDA-Co3O4.Then,the introduction of horseradish peroxidase(HRP)further enhanced the electrocatalytic activity of the nanocomposites.By taking advantages of the excellent biocompatibility, film forming ability of PDA,and high electrocatalytic activity of Co3O4NPs,as well as the combined effect of Co3O4,Pt NPs and HRP,the fabricated Co3O4-PDAPt nanocomposite exhibited excellent electrocatalysis on H2O2.

1　Experimental

1.1Chemicals and materials

Cobaltous nitrate(Co(NO3)2·6H2O),polyethylene glycol(PEG),butyl alcohol,chloroplatinic acid(H2PtCl6·6H2O),sodium borohydride(NaBH4),and dopamine were purchased from Alfa Aesar,while horseradish peroxidase(HRP)was from Jianglaibio Co.Ltd. (Shanghai,China).Allotherchemicalswereof analytical grade and used as received without further purification.Phosphatebuffersolution(PBS)of various pH values were prepared by mixing the 0.067 mol·L-1stock solutions of KH2PO4and Na2HPO4at specific ratios.All solutions were established with ultrapure water.

1.2Apparatus

Cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)and I-t curves were performed using a Potentiostat/Galvanostat Model 283 electrochemical workstation(Ametek,USA).The threeelectrode system consisted of a bare or modified gold electrode(GE)which was used as a working electrode, a saturated calomel electrode(SCE)as a reference electrodeandaPtwirecounterelectrode.The transmission electron microscope(TEM)images were obtained with a H600 transmission electron microscope (Hitachi Instruments,Japan).X-ray powder diffraction(XRD)measurements were performed on a Bruker D8 advanced X-ray diffractometer with Cu Kα irradiation (λ=0.154 06 nm)at 40 kV and 40 mA in the scanning 2θ range of 10°and 90°.Fourier-transform infrared(FT-IR)spectroscopic were determined using a Nicolet Avatar 360 FTIR spectrometer.

1.3Synthesis of PDA functionalized Co3O4NPs

Co3O4NPsweresimplysynthesizedby hydrothermal method.In brief,5.0 mL of 1.5 mol·L-1Co(NO3)2solution was added into a sample vial.Then, 7.5 mL of 5%(w/w)PEG and 7.5 mL butyl alcohol were added into the vial with vigorous magnetic stirring.Next,a certain amount of NaOH solution was added into the vial drop by drop and the color of the suspension changed into blue.Then a certain amount of H2O2was dropped slowly and the color further changed into brown-black.The obtained suspension was transferred into a 50 mL Teflon-lined stainless steel autoclave.The autoclave was maintained at 160℃for 10 h after it was tightly sealed.Then,the autoclave was cooled down to room temperature and the black precipitation was washed three times with water and anhydrous ethanol respectively,and then the Co3O4NPs colloid was obtained.The Co3O4NPs colloid was first to be ultrasonically treated for 10 min toensureCo3O4NPsdispersedinthesolution. Subsequently,40 mL pH 7.0 PBS containing 1.5 mg· mL-1fresh dopamine was added.After that,the solution was violently stirred in ice-water bath for 6 h. Finally,the precipitate was washed with water and then the functionalized Co3O4NPs(Co3O4-PDA)were obtained.

The loading of Pt NPs on Co3O4-PDA(Co3O4-PDA-Pt)was synthesized by in situ deposition.Firstly, the obtained Co3O4-PDA solution was dispersed in 4.0 mL of 0.1%(w/w)H2PtCl6with vigorous magnetic stirring and then 0.1 mL of 0.1 mol·L-1fresh NaBH4solution was dripped slowly and vigorous stirred for 0.5 h.After centrifugation,the solution was washed with water and then Co3O4-PDA-Pt nanocomposite was obtained.Forinvestigatingtheelectrocatalytic properties,Co3O4-Pt,PDA-Pt and Co3O4-PDA were also prepared by the same method.

1.4Fabrication of the modified electrodes

10 μL of the Co3O4-PDA-Pt suspension was dipped onto the cleaned bare GE surface to dry at 4℃for 4 h.After the Co3O4-PDA-Pt modified electrode was dried,15 μL of 1 mg·mL-1HRP solution was dipped onto the resulting electrode and then it was maintained upon water for 6 h at 4℃.Finally,the modified electrode was carefully rinsed with water to remove the physically absorbed HRP,then GE/Co3O4-PDA-Pt/HRP was obtained.The schematic representation of the preparation process of GE/Co3O4-PDA-Pt/ HRP modified electrode is shown in Scheme 1.GE/ Co3O4,GE/Co3O4-Pt,GE/Co3O4-PDA/HRP,and GE/ PDA-Pt/HRP were also prepared by the same process.

Scheme 1Schematic representation of the preparation of GE/Co3O4-PDA-Pt/HRP

2　Results and discussion

2.1Characterization of Co3O4-PDA-Pt

The morphology and size of Co3O4-PDA-Pt nanocomposites were characterized by TEM.Fig.1(a)gives the image of Co3O4NPs.It can be seen that the diameter of them was about 30 nm.Compared with the Co3O4NPs,the diameter of Co3O4-PDA increased and obvious layer structure can be seen in Fig.1(b). This indicated that the PDA film was successfully coated on the surface ofCo3O4NPs.Withthe abundant amine groups and residual catechol groups of the PDA film,Pt NPs could be linked simply and steadily on the nanocomposite by in situ reduction.As shown in Fig.1(c),a large amount of Pt NPs were uniformly distributed on the Co3O4-PDA surface.

Theas-synthesisednanocompositesarealso determined by XRD and FT-IR.The pattern for the as-prepared Co3O4NPs(Fig.2A(a))exhibited the diffraction peaks at 2θ=19.01°,31.34°,36.91°, 38.73°,44.90°,59.55°,65.36°and 77.22°,which corresponded to(111),(220),(311),(222),(440), (422),(511),(440)and(531)crystal planes and all of which coincided with those for Co3O4cubic(PDF#42-1467,Fig.2A(b)).No impurity peaks were observed, which indicates the high purity of the final products. Fig.2B shows the FT-IR spectra of the as-prepared nanocomposites.As shown in Fig.2B(a),two strong bands at 667 and 565 cm-1appeared,which are assigned to the stretching vibrations of the metaloxygen bond[33].The peak at 667 cm-1is attributed to Co-O vibration in tetrahedral hole in which Co is Co2+, and the another peak at 565 cm-1can be attributed to Co-O vibration in octahedral hole in which Co is Co3+[34-35].This indicated that Co3O4NPs were successfully prepared.Compared with the Co3O4NPs,PDA coated Co3O4NPs showed additional three absorption peaks around 1 296,1 602 and 3 421 cm-1(Fig.2B (b)).The absorption peaks at 1 296 and 1 602 cm-1are attributed to the C-N stretching vibration and phenylicC=C stretching vibrations[36-37].The absorption peaks at 3 421 cm-1is from catechol-OH groups[36].

Fig.1TEM images of Co3O4NPs(a),Co3O4-PDA(b)and Co3O4-PDA-Pt(c)

Fig.2(A)XRD pattern of Co3O4NPs:(a)experimental,(b)PDF#42-1467;(B)FT-IR spectra:(a)Co3O4NPs,(b)Co3O4-PDA

2.2Electrochemical characteristics of different modified electrodes

The electrochemical characteristics of different modifiedelectrodeswereinvestigatedbycyclic voltammetry(CVs)which was carried out at 50 mV· s-1in 0.067 mol·L-1PBS(pH 7.0)containing 0.1 mol· L-1KCl and 5.0 mmol·L-1K3[Fe(CN)6].The CVs of different modified electrodes are shown in Fig.3.As shown in Fig.3a,a pair of well-defined redox peaks corresponding to K3[Fe(CN)6]were observed at the bare GE.After the electrode was modified with the Co3O4-PDAnanocomposite,thepeakscurrent decreased slightly(Fig.3b),which should be caused by the weak conductivity of PDA.After the Co3O4-PDA was loaded with Pt NPs,the Co3O4-PDA-Pt modified electrode exhibited a strongly enhancement to redox peaks current,which was mainly from the large surface area and excellent conductivity of Pt NPs(Fig.3c).ComparedwithFig.3c,afterthe adsorption of HRP,the peaks current decreased obviously(Fig.3d),which was mainly from the weak conductivity of macromolecular zymoprotein.

Fig.3CVs of different electrodes at 50 mV·s-1in 0.067 mol·L-1PBS(pH 7.0)containing 0.1 mol·L-1KCl and 5.0 mmol·L-1K3[Fe(CN)6]

Electrochemical impedance spectroscopy(EIS) can also provide useful information on the impedance changes on the electrode surface during the process of electrodes modification.Fig.4 exhibited the impedance of different modified electrodes in 0.1 mol·L-1KCl solution containing 5.0 mmol·L-1K3[Fe(CN)6].As is shown in Fig.4,the Nyquist plot of impedance spectra includes a semicircle portion and a linear portion.The semicircle at high frequency region relates to the electron transfer limited process,and the Warburg linear at low frequencies region relates to the diffusion process[38-39].The semicircle diameter of EIS spectrum equals to the electron-transfer resistance(Ret).It can be seen that the resistance for GE/Co3O4-PDA(Fig.4b) was larger than that at bare GE(Fig.4a),which should also be due to the inhibition effect of PDA biopolymer film for electron transfer.Compared with the Co3O4-PDA modified electrode,the Co3O4-PDA-Pt modified electrode exhibited smaller Ret(Fig.4c).The reason might be the enhancer for electron transfer of Pt NPs. When HRP was immobilized onto the GE/Co3O4-PDAPt surface the resistance of the modified electrode decreased(Fig.4d),which was attributed to the inhibition effect of the enzyme biomacromolecules for electron transfer.The results are also consistent with the previous CVs′(Fig.3).

Fig.4EIS of different modified electrodes in 5.0 mmol· L-1K3[Fe(CN)6]solution

2.3Optimization of working potential

Fig.5Influence of different working potential on current response of GE/Co3O4-PDA-Pt/HRP: (A)current-time curves;(B)corresponding calibration curves

The performance of the electrochemical biosensor usually relates to the working potential.Fig.5 showed the current response to successive addition of 10 μmol· L-1H2O2of GE/Co3O4-PDA-Pt/HRP at the working potential in the range from 0 to-0.40 V.Curves in Fig.5A display typical current-time curves at different working potential for successive addition of 10 μmol· L-1H2O2,and the corresponding calibration curves were shown in Fig.5B.Moreover,in order to compare the influence of working potential more clearly,the slope vs working potential curve was presented in the inset of Fig.5B.It was found that the slope continuouslyincreasedwiththeincreasingofworking potential,and the highest current response appeared at-0.4 V.However,too high working potential results in interference from the matrix species.Therefore, considering the sensitivity of sensor,-0.30 V was chosen for the working potential in the further work.

2.4Electrocatalytic property towards H2O2

To investigate the catalytic activities of different nanocomposites to H2O2,different modified electrodes were tested by CV in 0.1 mol·L-1KCl solution containing 5.0 mmol·L-1K3[Fe(CN)6]and 10 μmol·L-1H2O2at 50 mV·s-1(Fig.6).Compared with Co3O4NPs modified electrode(Fig.6(a)),Co3O4NPs loaded with Pt NPs modified electrode exhibited larger reduction peak current due to the strong catalytic activity of Pt NPs to H2O2(Fig.6(b)).Fig.6(c)shows that GE/Co3O4-PDA-Pt exhibited larger reduction peak current than GE/Co3O4-Pt,which might be because the introduction of PDA enhances the load of Pt NPs.Due to the efficient catalytic performance of bio-enzyme,the reduction peak current was further increased after HRP was immobilized onto the GE/Co3O4-PDA-Pt surface(Fig.6(d)).

Fig.6CVs of different modified electrodes at 50 mV·s-1in 0.067 mol·L-1PBS(pH 7.0)with 10 μmol·L-1H2O2

Comparative experiments were carried out using different modified electrodes by successively adding H2O2to a continuously stirred PBS(pH 7.0)solution at working potential of-0.30 V to further investigate theelectrocatalyticpropertiesofCo3O4-PDA-Pt nanocomposite(Fig.7).As can be seen,GE/Co3O4-PDA-Pt/HRP had the highest current response(Fig.7B (d)).Compared with GE/Co3O4-PDA/HRP(Fig.7B(a)) and GE/PDA-Pt/HRP(Fig.7B(b)),the current response ofGE/Co3O4-PDA-Pt/HRPtoH2O2isgreatly enhanced,which might be ascribed to the excellent conductivity of Pt NPs.Through this conductivity, Co3O4can play its catalytic role better.Due to the efficient catalytic performance of HRP,the currentresponse of GE/Co3O4-PDA-Pt/HRP(Fig.7B(d))was larger than that of GE/Co3O4-PDA-Pt(Fig.7B(c)). Based on these results,we confirmed that the combined effect of Co3O4,Pt and HRP made the nanocomposite exhibit excellent electrocatalytic properties.

Fig.7Current response to successive addition of 10 μmol·L-1H2O2of different modified electrodes: (A)current-time curves;(B)corresponding calibration curves

Fig.8Current response to H2O2additions on GE/Co3O4-PDA-Pt/HRP

Fig.8 showed the typical current-time curves at GE/Co3O4-PDA-Pt/HRP with successive additions of H2O2at-0.30 V.A linear detection range from 0.1 to 700 μmol·L-1with a detection limit(LOD)of 0.08 μmol·L-1was observed.The regression equation is I/ μA=2.867×105cH2O2/(mol·L-1)+19.47(R2=0.998 2).The GE/Co3O4-PDA-Pt/HRPbiosensorexhibitedhigher sensitivity of 1 014.6 μA·L·mmol-1·cm-2than those of polyaniline-graphene composited thin film electrode (325.4 μA·L·mmol-1·cm-2)[40],hierarchical porous Co3O4electrode(389.7 μA·L·mmol-1·cm-2)[15]and Pd-TiO2electrode(554 μA·L·mmol-1·cm-2)[41],and nanoporous Ag@BSA/Au electrode(101.3 μA·L·mmol-1· cm-2)[42].Theresults indicatedthatthe fabricated Co3O4-PDA-Pt nanocomposite modified electrode H2O2sensor exhibited high sensitivity and wide dynamic measurement range,which mainly due to the high electrocatalyticactivityofCo3O4NPs,excellent biocompatibility,film forming ability of PDA and the synergies in Co3O4,Pt NPs and HRP.

3　Conclusions

This work reported that PDA bio-functionalized Co3O4NPs were successfully synthesized through a simple and cost-effective strategy and first applied to the research of electrocatalysis on H2O2.Co3O4NPs,as a new peroxidase-like,were wrapped with PDA by a simple self-polymerization in mild basic solution.It was found that the introduction of PDA film enhanced the stabilities of Co3O4NPs and Pt NPs and the combined effect of Co3O4and Pt NPs greatly improved the electrocatalytic properties of Co3O4-PDA-Pt nanocomposite.Thehighelectrocatalyticactivityand stabilityoftheproposednanocompositeprovide potentialapplicationsforelectrochemicalsensors, catalysis,and fuel cells.

Acknowledgements:ThisworkwassupportedbyScientific Research Foundation for Changjiang Scholars of Shihezi University,the National Natural Science Foundation of China(Grant No.21065009),Bingtuan Innovation Team in Key Areas(Grant No.2015BD003),and the Key Project of Chinese Ministry of Education(Grant No.210251).

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Preparation and Electrocatalytic Properties of Polydopamine Functionalized Co3O4Nanocomposite

WANG Hai-NingPAN Bo-GuangSUN ZhaoFENG Tao-TaoQI Yu＊HONG Cheng-Lin＊
(School of Chemistry and Chemical Engineering,Key Laboratory of Materials-Oriented Chemical Engineering of Xinjiang Uygur Autonomous Region,Engineering Research Center of Materials-Oriented Chemical Engineering of Xinjiang Bingtuan,Shihezi University,Shihezi,Xinjiang 832003,China)

Polydopamine(PDA)bio-functionalized Co3O4nanoparticles(NPs)were successfully synthesised and first applied to the research of electrocatalysis on H2O2.Co3O4NPs,as a peroxidase-like,were wrapped with PDA by a simple self-polymerization in mild basic solution.Then,uniformly dispersed platinum nanoparticles(Pt NPs) were deposited on PDA-Co3O4.It is found that the introduction of PDA film enhanced the load of Pt NPs,and the combined effect of Co3O4,Pt NPs and horseradish peroxidase(HRP)amplified the electrical signal of H2O2sensor. Under optimal conditions,a wide linear detection range from 0.1 to 700 μmol·L-1with a detection limit of 0.08 μmol·L-1was observed.

Co3O4;polydopamine;multiple signal amplification;electrocatalysis;H2O2

TB333

A

1001-4861(2016)08-1441-08

10.11862/CJIC.2016.190

2016-03-26。收修改稿日期：2016-06-24。

国家自然科学基金(No.21065009)、教育部重点资助项目(No.210251)和兵团重点领域创新团队计划(No.2015BD003)资助。

＊通信联系人。E-mail：hcl_tea@shzu.edu.cn，qy01_tea@shzu.edu.cn