Scholarly article on topic 'Enhancement of the Electrocatalytic Properties of Prussian Blue Containing Multilayer Films Formed by Reduced Graphene Oxide'

Enhancement of the Electrocatalytic Properties of Prussian Blue Containing Multilayer Films Formed by Reduced Graphene Oxide Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Anna Pajor-Świerzy, Tomasz Kruk, Piotr Warszyński

Abstract In our work we focused on the electroactive and electrocatalytic properties of multilayer films formed from polyelectrolytes (PE) and Prussian blue nanoparticles (PBn), enhanced by addition of reduced graphene oxide (rGO). Films containing poly(allylamine hydrochloride) (PAH) and PBn were constructed using the layer-by-layer adsorption method. Graphene oxide (GO) was deposited from its aqueous suspension forming additional layers of the film. Then they were exposed to the elevated temperature, 180°C to turn graphene oxide into its reduced form. We demonstrated, by cyclic voltamperometry, that the presence of conductive rGO greatly enhanced the electroactive properties of the PE/PB multilayer films. Simultaneously, they were also up to 40 times more effective for the electrocatalytic redox processes of hydrogen peroxide.

Academic research paper on topic "Enhancement of the Electrocatalytic Properties of Prussian Blue Containing Multilayer Films Formed by Reduced Graphene Oxide"

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Colloids and Interface Science Communications

journal homepage: www.elsevier.com/locate/colcom

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Enhancement of the Electrocatalytic Properties of Prussian Blue Containing Multilayer Films Formed by Reduced Graphene Oxide

Anna Pajor-Swierzy *, Tomasz Kruk, Piotr Warszynski

Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakow, Poland

CrossMark

ARTICLE INFO

Article history:

Received 15 April 2014

Received in revised form 14 May 2014

Accepted 16 May 2014

Available online xxxx

Keywords:

Prussian blue nanoparticles Reduced graphene oxide Multilayer films Electrochemical sensor

ABSTRACT

In our work we focused on the electroactive and electrocatalytic properties of multilayer films formed from poly-electrolytes (PE) and Prussian blue nanoparticles (PBn), enhanced by addition of reduced graphene oxide (rGO). Films containing poly(allylamine hydrochloride) (PAH) and PBn were constructed using the layer-by-layer adsorption method. Graphene oxide (GO) was deposited from its aqueous suspension forming additional layers of the film. Then they were exposed to the elevated temperature, 180 °C to turn graphene oxide into its reduced form. We demonstrated, by cyclic voltamperometry, that the presence of conductive rGO greatly enhanced the electroactive properties of the PE/PB multilayer films. Simultaneously, they were also up to 40 times more effective for the electrocatalytic redox processes of hydrogen peroxide.

© 2014 Elsevier B.V. All rights reserved.

The layer-by-layer (LbL) deposition technique is an efficient method for obtaining functional multilayer films. In the standard LbL process substrates are sequentially dipped in the solutions containing positive or negative polyelectrolytes, which adsorb onto the charged support mainly via electrostatic interactions [1]. The properties of obtained multilayer films largely depend on the type of polyelectrolytes used, number of deposition cycles and conditions of film formation [2]. In addition any charged nano-objects can be incorporated into polyelectro-lyte multilayer structure, including biological molecules (e.g. DNA, proteins, viruses, polypeptides) or inorganic nanoparticles (e.g. silica, clays, gold, magnetite, silver, graphene) [2-5] that allows generation of new functional properties of film covered surfaces.

Prussian blue (PB) as a mixed-valence hexacyanometalate salt is one of the longest known coordination compound. In 1978 Neff reported that PB can be deposited onto electrode surface forming an electroactive layer [6]. Since then the PB films have been extensively studied for the construction of electrochemical sensors and biosensors, in particular for measuring hydrogen peroxide concentration [7]. The control of H2O2 concentration is an important issue in many areas such as environmental protection, medicine or food quality control. Efficient detection of hydrogen peroxide is a key factor for the development of biosensors, as H2O2 is the product of reactions catalyzed by oxidase enzymes [8]. By monitoring the electrochemical response of H2O2, the concentration of the enzymatic substrate can be determined [9].

Graphene is a new material consisting of a single layer of sp2 — bonded carbon atoms. Since its discovery in 2004 [10], graphene has emerged as the "material of the future" due to its unique nanostructure,

* Corresponding author. Tel.: +48 12 63 95 121; fax: +4812 425 19 23. E-mail address: ncpajor@cyf-kr.edu.pl (A. Pajor-Swierzy).

electrical, thermal and mechanical properties [11,12]. It is considered as a promising material for application in various technological fields such as transparent conductive films [13], solar cells [14], electrochemical sensors [15], and for the next generation of electronic devices [16].

Combining the unique properties of graphene with Prussian blue nanoparticles in nanocomposite film may result in the improved sensitivity of electrochemical sensor for hydrogen peroxide, due to the synergistic effect between graphene and PB nanoparticles as it has been already observed [17,18]. In particular, Li et al. deposited PB/graphene nanocomposite film on glassy carbon electrode with an electrochemical deposition method. The PB/graphene/GCE exhibited high electrocatalytic activity for H2O2 detection [17]. Mao et al. used LbL deposition technique to form multilayer films of PB nanoparticles together with cationic polyelectrolyte-functionalized ionic liquid decorated graphene sheets on gold surfaces. They were obtained from GO by reduction with hydrazine. SPR optical signals and electrochemical current responses were monitored upon injecting hydrogen peroxide [18]. In our work we have studied the electroactive properties of the polyelec-trolyte multilayer films formed with PB nanoparticles and thermally reduced graphene oxide using cyclic voltamperometry.

Prussian blue nanoparticles were synthesized by the reaction of FeCl3 and IKi[Fe(CN)6] in the presence of10—2 HCl according to the recipe given in [19]. The size of the Prussian blue nanoparticles was determined by dynamic light scattering (DLS) using the Zetasizer Nano ZS from Malvern Instruments Ltd. The average PB particle size was around 10 nm with the polydispersity index (PDI) less than 0.2. The zeta potential of the Prussian blue nanoparticles was measured by the laser Doppler velocimetry (LDV) technique using Malvern Zetasizer Nano ZS apparatus. The obtained nanoparticles were negatively charged with the average zeta potential around — 50 mV.

http://dx.doi.org/10.1016/j.colcom.2014.05.001 2215-0382/© 2014 Elsevier B.V. All rights reserved.

The multilayer films were formed by the layer-by-layer adsorption method. As first, anchoring layer branched poly(ethyleneimine) (PEI, MW ~ 750 kDa, Sigma-Aldrich) was deposited at the gold surface (electrode or gold plate) from 500 ppm solution at pH = 7. The other polycations used for multilayers construction was PAH (MW ~ 70 kDa, Sigma-Aldrich). The negatively charged Prussian Blue nanoparticles and graphene oxide (Abalonyx AS, Norway), zeta potential — 40 mV, were deposited as anionic layers in the sequence (rGO/PAH/PB/PAH)n. After the formation of multilayer films they were heated in 180 °C by 12 h to obtain reduced form of graphene oxide [20]. The reduction of graphene oxide was confirmed by the change in the FTIR spectra shown in Fig. 1A. The spectrum of graphene oxide (blue line) shows the presence of peaks corresponding to carboxyl (uC=O at 1723 cm-1), hydroxyl (u_OH at 1616 and 1220 cm-1) and epoxy groups (uC_O_C at 1049 cm-1). After the reduction process (red line), the height of all those peaks decreased. The SEM images of the PEl/rGO/PAH/PB/PAH/rGO/PAH/PB multilayer are presented in Fig. 1B. The 10 nm PB nanoparticles can be clearly seen in the graphene sheet background.

The electroactive properties of the nanocomposite multilayer films containing Prussian blue nanoparticles and rGO were analyzed by the cyclic voltamperometry method using Autolab rotating disk electrode and potentiostat/galvanostat (PGSTAT302N) in 0.1 M KCl supporting electrolyte. The details of experimental procedure are given elsewhere [21]. Fig. 2 presents the voltammograms obtained for gold electrode covered with PE/PB multilayer films modified with reduced graphene oxide. They exhibit characteristic peaks, located at around 0.2 V, vs. Ag/AgCl electrode, corresponding to the redox reaction of Prussian Blue in the films, i.e., to the reduction of Prussian Blue (PB) to Prussian White (PW) and to the reverse oxidation process [19,22].

Fe/'[Fe (CN)6j3 + e"

Fe/ Fe''(CN)6

The separation potential of the peaks was around 35 mV, slightly higher than the theoretical value (30 mV) [23], indicating the fast charge transfer between Prussian blue nanoparticles and the electrode surface.

To compare the electroactive properties ofPEl/PB/(PAH/PB)n multilayers with ones for films containing rGO, we determined the current density in the maximum of both reduction and oxidation peaks. The CV measurements were performed for various numbers of PB layers in

800 600 400 200 0 -200 -400 -600 -800

PEI/(rGO/PAH/PB/PAH)4/rGO/PAH/PB

PEI/(rGO/PAH/PB/PAH)3/rGO/PAH/PB

PEI/(rGO/PAH/PB/PAH)2/rGO/PAH/PB

PEI/rGO/PAH/PB/PAH/rGO/PAH/PB

PEI/rGO/PAH/PB

bare electrode

0.2 0.4 0.6

E [V] vs Ag/AgCl

Fig. 2. Voltammetric curves of PE/PB multilayer film modified by rGO with different numbers of layers deposited on gold electrode at a scan rate of 0.1 V/s.

the films. Fig. 3 illustrates the dependence of the current density, JrGO, in the reduction and oxidation peaks for PEl/(rGO/PAH/PB/PAH)n/rGO/ PAH/PB (part A) and of the ratio ofJrGO/J (part B), whereJ is current density of PEl/PB/( PAH/PB) n films, on the number of deposited PB layers. It can be observed that JrGO increases almost linearly with the number PB layers. The ratio of redox current densities, JrGo/J, is practically independent on the number of those layers. It is around 50 for cathodic and 40 for anodic currents respectively. That means that reduced graphene oxide improves the electroactive properties of studied films. This improvement is the result of the synergistic effect between rGO and PB nanoparticles due to the enhancement of electron transfer between surface of PB nanoparticles and gold electrode.

Gold electrodes modified with PE/PB multilayers and the ones containing additionally rGO were used for the evaluation of their electrocat-alytic properties towards redox reaction of hydrogen peroxide. For that purpose we compared the CV curves for PEl/PB/(PAH/PB)4 and PEl/(rGO/PAH/PB/PAH)4/rGO/PAH/PB multilayer films deposited on gold electrode, measured in the mixture of5 mM H2O2 in 0.1 M pH = 7 phosphate buffer solution (PBS, obtained from NaH2PO4 x 2H2O and Na2HPO4 x 12H2O). The voltammograms exhibited characteristic peaks of H2O2 oxidation at the anodic potential of about 1.0 V and reduction at cathodic potential about — 0.9 V, were observed for the PEl/PB/(PAH/PB)4 multilayer films. For the PE/PB films modified by

Fig. 1. (A) FTIR spectra of graphene oxide before (blue line) and after the temperature reduction in 180 °C by 12 h (red line). (B) SEM images of PEl/rGO/PAH/PB/PAH/rGO/PAH/PB films (10 000x magnification). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

number of PB layers

E £ «Î

number of PB layers

Fig. 3. The dependence of redox currents density (JrGO) for the PEI/(rGO/PAH/PB/PAH)n/rGO/PAH/PB film on gold electrode (part A) and the ratio of those current densities to ones obtained for PEI/PB(PAH/PB)n (JrGo/J) (part B) on the number of deposited PB layers (experimental error does not exceed the symbol size).

rGO, the oxidation peak was observed at potential about 0.25 V and the reduction one at — 0.6 V. The overall reaction for the electrocatalytic oxidation and reduction process can be written as [24]:

H2O2^O2 + 2H+ + 2e

"^2OH"

The value of H2O2 redox currents for the PEI/PB/(PAH/PB)4 multilayer films was around 200 |jA and was more than one order of magnitude lower than the respective values for PEI/(rGO/PAH/PB/PAH)4/rGO/PAH/ PB film. Therefore, the presence of reduced graphene oxide in the multilayer structure increases the CV response of the PB covered electrode in the presence of hydrogen peroxide.

We determined the hydrogen peroxide redox current density using the value of current in the reduction and oxidation peaks in the second CV cycle. Fig. 4 presents the dependence of that current densities for gold electrode modified with PEI/( rGO/PAH/PB/PAH)nrGO/PAH/PB (part A) and of the ratio of JrGO/J (part B) on the number of deposited PB layers. Here J denotes the respective current densities measured for the films with the same number of PB layers but without rGO. It can be noticed that JrGO for oxidation and reduction of hydrogen peroxide increases almost linearly with the number of deposited PB layers. It

means that the sensitivity of this kind of electrocatalytic sensors can be controlled by the number of adsorbed Prussian blue layers. The values of H2O2 cathodic current density for the PE/PB multilayer films modified with reduced graphene oxide were around thirty times (fifteen times for anodic) higher than the ones for films without it. The ratio JrGO/J seems to slightly increase with the number of layers that indicates that thicker films are more effective as hydrogen peroxide sensor layers.

Fig. 5 presents the results of cyclic voltamperometry measurements obtained for multilayer films containing four layers of PB nanoparticles deposited on gold electrode, in various concentrations of hydrogen peroxide in phosphate buffer solution. The measurements were performed for concentration of H2O2 ranging from 0.2 to 10 mM for PE1/PB/(PAH/PB)3 films and from 0.01 to 10 mM for the ones modified with rGO. For the concentrations below 0.2 mM the current densities for films without rGO were below the detection limit.

The current densities for oxidation and reduction of hydrogen peroxide increase with growing concentration of hydrogen peroxide. The nonlinear increase can be the result of the consumption of hydrogen peroxide in the redox reactions, which cannot be compensated by its transport from the bulk. Some kinetic limitations can be the alternative reason of the nonlinear behavior. When the redox reaction of peroxide with PB is relatively slow, it could limit a rate of electrocatalytic process and thus, nonlinear dependence of the reduction and oxidation current on the concentration of H2O2 should be observed [25].

1200 1000 800 600

• anodic current density

• cathodic current density

-à" 400

number of PB layers

number of PB layers

Fig. 4. The comparison of the hydrogen peroxide oxidation (black circle) and reduction (red circle) current density of PEI/(rGO/PAH/PB/PAH)nrGO/PAH/PB (partA) andJrGO/J (partB) on the number of deposited PB layers. The results were obtained in pH = 7 phosphate buffer solution in the presence of 5 mM H2O2, (experimental error does not exceed the symbol size). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

H2O2 + 2e

2 1200

£ «Î 1000

• anodic current

• cathodic current

0 2 4 6 8 10

concentration of H2O2 [mM]

ïb 20 о

2 4 6 8 10

concentration of H2O2 [mM]

Fig. 5. The dependence of the current density for PEl/(rGO/PAH/PB/PAH)3rGO/PAH/PB film modified gold electrode (part A) andJrGO/J (partB) for the oxidation (black circle) and reduction (red circle) of hydrogen peroxide on the concentration of H2O2, obtained in pH = 7 buffer solution (experimental error does not exceed the symbol size). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The values of current densities obtained for films with rGO are much higher (around 20-40 times, cf. Fig. 5B) than the ones received for multilayers without this compound. Moreover, for the H2O2 concentration below 0.5 mM the redox currents could still be measured over the background level down to practically 5 цМ. Reduced graphene oxide is by itself electrocatalytically active towards hydrogen peroxide but the redox currents for the films PAH/rGO were at least four times lower (data not shown). Thus, the multilayers containing both Prussian blue nanoparticles and reduced graphene oxide are more electrocatalytically active towards H2O2, which indicates the possibility of the application of those hybrid PE/PB/rGO multilayers as the effective sensor layers for the electrochemical detection of hydrogen peroxide.

Acknowledgments

The work was supported by the Polish National Science Center, grant nos. 2012/07/N/ST4/00350 - PRELUDIUM ST4,2012/07/N/ST5/00173 -PRELUDIUM ST5 and COST Action CM1101. The authors wish to thank PhD Joanna Krysciak-Czerwenka for the FTIR spectrum measurements.

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