Polyethyleneimine-functionalized graphene and its layer-by-layer assembly with Prussian blue Changsheng Shan a , Lingnan Wang a , Dongxue Han a, ⁎, Fenghua Li a , Qixian Zhang a , Xindong Zhang b , Li Niu a a State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China b State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, PR China abstract article info Article history: Received 28 May 2012 Received in revised form 1 February 2013 Accepted 1 February 2013 Available online 16 February 2013 Keywords: Polyethyleneimine Graphene Prussian blue Layer-by-layer complexation Electrocatalysis The polyethyleneimine (PEI)-functionalized graphene, which showed excellent dispersibility in water, has been simply synthesized in an alkaline solution. The graphene sheets played an important role as connector to assemble the active amino groups in PEI. This composite provided a positive environment for further functionalization. As an example, a [Prussian blue (PB)/PEI–graphene] n multilayer film has been constructed through layer-by-layer complexation method. The resulting [PB/PEI–graphene] n multilayer film demonstrat- ed preferable electrochromic property and excellent electrocatalysis towards H 2 O 2 , which showed promising potential application in electrochemical sensing. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Graphene, a single layer of carbon atoms in a closely packed honey- comb two-dimensional lattice, has attracted a tremendous amount of attention recently [1–4]. Due to its unique electronic, mechanical, and thermal properties [5,6], graphene has been extensively applied in many fields, such as battery [7], field-effect transistors [8], ultrasensitive sensors [9] and electromechanical resonators [10]. However, graphene tends to form irreversible agglomerates through strong π–π stacking and van der Waals interaction. So the prevention of aggregation for graphene sheets is of particular importance because most of the unique properties are only associated with individual sheets [11]. Some methods containing covalent and noncovalent functionalization of graphene have been applied to obtain dispersed graphene in water or organic solvent [12–16]. But synthesis of water-soluble graphene is still a challenge and research hotspot. Polyethyleneimine (PEI, structure shown in Fig. 1) is a water-soluble polymer with amine groups in the molecular backbone, which provides a positive charged structure in the acid solution. Due to its active amine groups, PEI can react with other materials with some certain active groups, such as carboxyl or epoxy groups. These properties of PEI make it an ideal candidate for the modification of graphene and further extend its application. Layer-by-layer (LBL) assembly is concerned as a powerful and versa- tile method for the preparation of functional ultrathin films. In the re- cent decade, the functional film has attracted much attention because of the potential application in separation, sensing, optical and electronic devices, etc. [17–20]. It has been reported that various materials, such as charged polyelectrolyte, nanoparticles, carbon nanotubes, Prussian blue (PB) and polyoxometalate, have been assembled into functional com- posite films [21–24]. It is noticeable that PB is a kind of poly-nuclear and mixed-valent iron cyanide complex which possess repeating unit of Fe(III)[Fe(II)–(CN) 6 ] (FeIIIHCFII) [25,26]. This compound has been employed in electrochromic devices [27,28] and electrochemical bio- sensors [29,30] due to its excellent electrochromic and electrocatalytical properties [31]. Here the PEI was grafted covalently onto graphene sheets via the nucleophilic ring-opening reaction between the amine groups in PEI and epoxy groups of graphene oxide. Since it was positively charged and had an excellent dispersibility in water, the resulting PEI-grafted graphene could assemble with other negatively charged materials by electrostatic interaction to obtain ultrathin composite films with special properties. As an example, a [PB/PEI–graphene] n multilayer film was constructed by layer-by-layer complexation method. Furthermore, this obtained [PB/PEI–graphene] n multilayer film exhibited excellent electrochromic property and preferable electrocatalysis towards H 2 O 2 , which showed a promising prospect for application in electrochemical sensing. 2. Experimental section 2.1. Materials Graphite, hydrazine solution (50 wt.%) and ammonia solution (28 wt.%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Thin Solid Films 534 (2013) 572–576 ⁎ Corresponding author. Tel.: +86 431 85262425; fax: +86 431 8526 2800. E-mail address: dxhan@ciac.jl.cn (D. Han). 0040-6090/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tsf.2013.02.011 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf