Invited feature article
Supramolecular self-assembly of layer-by-layer graphene film driven by the synergism of π–π and hydrogen bonding interaction

https://doi.org/10.1016/j.jphotochem.2017.09.023Get rights and content

Highlights

  • π–π and hydrogen bonding were employed to drive the self-assembly of graphene film.

  • Different graphene morphology was formed in CHCl3 and DMF.

  • The graphene film exhibited enhanced electrochemical activity toward dopamine.

Abstract

In this paper an organic molecule labeled as UPPY with both π–π interaction unit of pyrene (PY) and hydrogen bonding unit of urediopyrimidinone (UP) was employed as binding module to link the layer-by-layer graphene film. Firstly, UPPY was anchored on the surface of thermal reduced graphene (trGO) with the aids of π–π interactions forming trGO-UPPY. The trGO-UPPY showed different morphology in CHCl3 and N,N-dimethylformamide (DMF) due to the different hydrogen binding mode. Then by the synergism of hydrogen bonding and π–π interactions offered by UPPY, multilayer film of trGO-UPPY was prepared through layer-by-layer technique. The electron-transfer resistance (Ret) of trGO-UPPY/ITO decreased from 53 Ω of bare ITO to 27 Ω. In addition, trGO-UPPY/ITO electrodes exhibited enhanced electrochemical activity toward dopamine (DA). Compared with bare ITO, the oxidation peak current of DA on rGO-UPPY/ITO can be enhanced about 100 times than that of bare ITO.

Introduction

The supramolecular self-assembly afford researchers ideal bottom-up approaches for fabricating novel functional materials and devices with desirable architectures and properties. Design of novel building blocks and assembly strategies is of great importance for materials to self-assembly at nanometer scale. As the zero-dimensional (0D) and one dimensional (1D) functional units, dendrimers [1], [2], nanoparticles [3], [4], fullerenes [5], [6], carbon nanotubes [7], [8] have been widely used as the favorite nanoscale building blocks in the supramolecular chemistry. By means of its single-atom thickness and unprecedentedly large lateral surface, graphene has recently become a novel kind of two-dimensional (2D) building blocks [9], [10]. By using supramolecular self-assembly methods, not only the solubility and conductivity of the graphene have been enhanced, but also complicated graphene based structures such as 2D multilayer film [11], [12], three-dimensional (3D) ball [13], [14] and hydrogels [15], [16] exhibiting novel collective physiochemical properties have also been realized, which significantly expands the practical applications of graphene.

Molecular recognition through noncovalent interactions is the fundamental of supramolecular self-assembly. Because graphene has the large lateral dimension, for the achievement of stable graphene assemblies, those noncovalent interactions with high binding strength are usually needed to overcome the stacking of graphene sheets. Pyrene (PY) derivatives based π–π interactions which have strong affinity with the graphene layer by physical adsorption on the conjugate structure of graphene, would be a potential driving force for graphene assembly [17], [18], [19]. In addition, ureidopyrimidinone (UP) quadruple AADD (A: hydrogen bond acceptor, D: hydrogen bond donor) hydrogen bonding unit possessing very strong binding strength (107 M−1 in CHCl3 or toluene) [20], is also a good candidate in the self-assembly of graphene [21].

Cooperation of noncovalent multi-interactions would be an effective way to fabricate graphene assemblies with desirable architecture and functionality [22], [23], [24]. Through hydrogen bonding and π–π interactions, Cheng et al. prepared graphene oxide (GO) hydrogels and organogels by supramolecular self-assembly from an amphiphilic molecule, which has a polarcarbohydrate head group attached to a pyrene group [25]. In our previous work, by designing and employing a self-assembly precursor of UP terminated pyrene derivatives (labeled as UPPY) (Fig. 1a), a novel hybrid showing graphene-wrapped MWNT morphology with enhanced electrochemical sensitivity was fabricated thanks to the cooperation of the hydrogen bonding and π–π interaction. Benefiting from the quadruple AADD hydrogen bonding arrays of UP, UPPY·UPPY homodimer could be formed (Fig. 1a). Simultaneously, the PY unit could also form strong π–π interaction with nano-carbon material. In this article we want to show that as a binding module, UPPY has universal adaptability to the self-assembly of nano-carbon material due to the contained π–π and hydrogen bonding unit [26].

The Layer-by-Layer (LBL) self-assembly method, initially reported by Decher and Hong is one of the most convenient techniques for fabricating films with finely controlled [27]. LBL films of graphene linked by noncovalent interactions such as electrostatic, hydrogen bonding supplied by the polymer for instance poly (vinyl alcohol), polyacrylic acid and ionic liquid modified on the graphene layer have been prepared [28], [29], [30], [31], [32], [33], [34]. Herein, UPPY unit was further employed to drive the supramolecular self-assembly of graphene film by LBL technique. Firstly, the UPPY was anchored on the surface of thermal reduced graphene (trGO) with the aids of π–π interactions forming trGO-UPPY (Fig. 1b left). Then by the layer-by-layer technique, a 2D graphene multilayer film of trGO-UPPY showing enhanced electrocatalytic properties to the oxidation of dopamine was self-assembled by the synergism of hydrogen bonding and π–π interactions offered by UPPY (Fig. 1b, right).

Section snippets

Regents

Graphene oxide (GO) was prepared from natural graphite by the modified Hummers procedure [35], [36]. Thermal reduced graphene oxide (trGO) was prepared by thermal reduction of GO under the Ar atmosphere at 600 °C for 2 h [37]. UPPY (Fig. 1a) was prepared according to our previous reported methods [26]. Poly(ethyleneimine) (PEI) with the average molecular weight of 50,000 by GPC was purchased from Aldrich. During electrochemical experimental process, Milli-Q water (18 MΩ/cm) was used. N,N

Synthesis and characterization of trGO-UPPY

As depicted in Fig. 1, the engineering design behind the formation of supramolecular film of graphene is the establishment of organic molecule UPPY composed of both a planar conjugated pyrene ring and a ureidopyrimidinon (Fig. 1a). The pyrene group in UPPY can take strong π–π interactions with rGO, thus the UP units were attached to the surface of graphene forming trGO-UPPY (Fig. 1b, left). Driven by the strong AADD hydrogen bonding interactions between the UP units of UPPY, the LBL trGO-UPPY

Conclusion

By using the binding module of UPPY that containing pyrene group and pyrimidinone group simultaneously, the LBL graphene film with high coverage, decreased electron transfer resistant and high electrocatalytic performance toward dopamine could be assembled. This work showed that having two kinds of noncovalent binding unit, UPPY could be a versatile module to drive the supramolecular self-assembly of nano-carbon material.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant No. 21772152); the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry; the Natural Science Foundation of Shaanxi Province (No. 2015JM5224).

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