Special Report: Graphene/nanoparticles composites
Fig. 1 Scheme of hybrid structures, which are the aim of our work. They comprise reduced graphene oxide and covalently attached gold nanoparticles of different sizes and shapes
The work of our group focuses on achieving reduced graphene oxide/nanoparticles (RGO/NP) composites using biological and chemical approaches. The ‘Biosynthesis of graphene modified with nanoparticles’ project, funded by the Foundation for Polish Science within the framework of EU Social Funds, aims at providing a green, synthetic route towards RGO/NPs composites by using bacteria in the key stages of the process. On the other hand, the ‘Synthesis of hybrid nanomaterials of graphene/metal nanoparticles type with controlled structural parameters’ project funded by the National Science Centre Poland is meant to enable a smart-design process of this kind of materials.
In the last few decades, nanotechnology has flourished, providing surprising discoveries. Metamaterials and graphene are two conspicuous examples of breakthroughs that have had a great impact on research conducted all over the world by leading groups. The success of graphene can be ascribed to its unique properties. However, for many budding applications it is necessary to incorporate graphene into functional composite materials such as hybrid structures comprising graphene and metal/semiconductor nanoparticles.1,2 These materials combine the phenomenal features of a 2D carbon lattice with the plasmon/exciton properties of nanoclusters, opening the way to a wealth of sensing, electronics, energy storage and other applications. From a supramolecular point of view they also offer a straightforward route to prepare anisotropic ensembles of nanoparticles with metamaterial properties.
How can we access graphene nanoparticle composites? Since early 2000 chemists have possessed a powerful tool that is a chemical route of graphene synthesis:3 graphite -> graphene oxide (GO)-> reduced to graphene (RGO). Several (successful) attempts at graphene nanoparticle composites synthesis have been reported throughout the last few years which have been predominantly based on using GO. These methods fall into three main categories: (i) post-graphenisation (NPs incorporation before GO reduction), (ii) syn-graphenisation (NPs incorporation simultaneously to GO reduction), and (iii) pre-graphenisation (deposition of NPs on RGO).
Unfortunately, though many synthetic attempts have been undertaken there are several problems that need to be overcome to fully capitalise on the properties of graphene/nanoparticles composites. One issue is the need for green-synthetic methods as harmful chemicals are often used in the synthetic path. To overcome this problem we propose to use bacteria to drive the reduction process of GO and metal salts. Microbial synthetic methods for RGO and nanoparticle-based materials are especially attractive due to the ease of scale-up and robustness. We will primarily focus on using environmental isolates of bacteria that have a well-documented ability to use different species as final electron acceptors.4 We have already confirmed that this is a valid path towards RGO/NPs composites, but work is underway to optimise the process.
Other challenges faced by scientists and engineers interested in graphene/nanoparticles hybrid materials are: achieving nanoparticle uniform distribution over graphene material, nanoparticle size and shape uniformity, as well as control over their spatial distribution. Our approach to tackling these problems is based on covalent grafting of preformed nanoparticles to RGO. This strategy will allow for the synthesis of materials with predefined structure (size, shape and density of packing of nanoparticles) and thus predefined properties. The RGO that we will use will have functional groups installed on its surface as in the method I have co-authored.5 Compatible chemical moieties will be introduced to the nanoparticle organic shell, thus enabling linkage of both materials using standard chemical tools. We are currently developing the strategy using gold nanospheres; however, it will be possible to expand the applicability of this approach to other types of nanocrystals, maximising the applicative potential.
In our work we will also investigate the possibility of metamaterial properties observation in anisotropic assemblies of RGO/NPs hybrids. We aim at achieving an epsilon-near-zero regime for layered materials, which we have recently explored in other systems.6
The projects are held under agreement no. 66/UD/SKILLS/2014 on the use of prize awarded in the SKILLS popularizing contest financed by the Foundation for Polish Science and agreement UMO-2013/09/D/ST5/03875 financed by the National Science Centre Poland.
Bibliography
1. Singh V, Joung D, Zhai L, Das S, Khondaker S I, Seal S (2011): Graphene based materials: Past, present and future. Prog Mater Sci. Elsevier Ltd. 56: 1178-1271. doi:10.1016/j.pmatsci.2011.03.003
2. Bai H, Li C, Shi G (2011): Functional composite materials based on chemically converted graphene. Adv Mater 23: 1089-115. doi:10.1002/adma.201003753
3. Stankovich S, Piner R D, Nguyen S T, Ruoff R S (2006): Synthesis and exfoliation of isocyanate-treated graphene oxide nanoplatelets. Carbon N Y 44: 3342-3347. doi:10.1016/j.carbon.2006.06.004
4. Drewniak L, Maryan N, Lewandowski W, Kaczanowski S, Sklodowska A (2012): The contribution of microbial mats to the arsenic geochemistry of an ancient gold mine. Environ Pollut. Elsevier Ltd. 162: 190-201. doi:10.1016/j.envpol.2011.11.023
5. Collins W R, Lewandowski W, Schmois E, Walish J, Swager T M (2011): Claisen rearrangement of graphite oxide: a route to covalently functionalized graphenes. Angew Chem Int Ed Engl. 50: 8848-52. doi:10.1002/anie.201101371
6. Lewandowski W, Fruhnert M, Mieczkowski J, Rockstuhl C, Górecka E (2015): Dynamically self-assembled silver nanoparticles as a thermally tunable metamaterial. Nat Commun 6: 6590. doi:10.1038/ncomms7590
Dr Wiktor Lewandowski
Faculty of Chemistry
University of Warsaw
tel: +48-22 822 0211 ext. 387
