Job/Unit: I42610 /KAP1 Date: 02-10-14 13:43:18 Pages: 7 FULL PAPER DOI:10.1002/ejic.201402610 Preparation of Alginate/Graphene Oxide Hybrid Films and Their Integration in Triboelectric Generators Luca Valentini,* [a] Nicoletta Rescignano, [b] Debora Puglia, [a] Marta Cardinali, [a] and Josè Kenny [a,b] Keywords: Nanostructures / Organic-inorganic composites / Thin films / Energy conversion / Graphene / Carbohydrates Sodium alginate/graphene oxide (Al/GO) nanocomposite films were prepared by solvent casting. The structure, mor- phology, and electrical properties of Al/GO films were char- acterized by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and thermal analysis. The utilization of such an Al/GO film for a device that uses friction as the charging process to convert mechani- Introduction Alginate (Al) is a water-soluble polysaccharide that is isolated from brown algal species. Alginates are biodegrada- ble, biocompatible, and nontoxic. [1,2] Because of its reversible solubility, alginate can be fabri- cated in various forms, such as films, microspheres, and fi- bers. [3–5] Over the last two decades, alginate fibers have be- come well established in the wound-treatment industry, [6,7] in which their ion-exchange and gel-forming abilities are particularly useful for the treatment of exuding wounds. Despite this, alginates still display some unsatisfactory properties such as low mechanical strength. Modification of alginates with inorganic materials is another way to im- prove alginate properties such as mechanical strength. [8–10] Graphene, a one-atom-thick layer made of sp 2 -hy- bridized carbon atoms obtained for the first time in 2004, [11] can be formally considered the basic building block of all sp 2 -carbon allotropes including carbon nanotubes. Numerous strategies for the preparation of homoge- neously dispersed graphene–polymer composites have al- ready been presented for a variety of advanced polymer ma- trices, [12,13] but there is a general agreement that a lot of research has to be dedicated to the development of easy and cost-effective methodologies towards the large-scale ap- plication of graphene in functional polymer composite ma- terials for technological uses, such as biosensors, energy storage, and electronic devices. [a] Department of Civil and Environmental Engineering, University of Perugia, Strada di Pentima 4, 05100 Terni, Italy E-mail: luca.valentini@unipg.it http://www.unipg.it/materials [b] Institute of Polymer Science and Technology, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain Eur. J. Inorg. Chem. 0000, 0–0 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 cal energy into electric power is reported. The triboelectric generator (TEG) was fabricated by stacking a drop-cast Al/ GO film bewteen indium–tin oxide (ITO)-coated poly(ethyl- ene terephthalate) (PET) and a PET sheet. Furthermore, the utilization of such a TEG as a pressure sensor is also illus- trated. The graphite exfoliation into graphene oxide (GO) sheets, which are easily processable in both aqueous and organic media as single-layer sheets, [14–16] is an alternative route to obtaining larger and soluble graphene quantities. Nanocomposites have been created with GO and water- soluble polysaccharides such as alginates. [17] The presence of hydrophilic organic functional groups facilitates exfoliation and dispersion of GO in aqueous solution, but the material shows insulating properties be- cause of the numerous defects that disrupt the sp 2 structure. Materials that usually are less conductive or insulators when coming into contact with each other and then sepa- rated gives rise to the well-known effect called triboelectric charging. It is worth noting that the insulating property of some polymer nanocomposites allows for a long-time reten- tion of triboelectric charges. [18] The first attempt to create flexible triboelectric genera- tors (TEG) was reported by Wang et al. [19] The same au- thors reported the first self-powered pressure sensors based on TEGs. [20] The general physical process for energy conversion in- volves three steps: charge generation, charge separation, and charge flow. In piezoelectric nanogenerators the piezo- electric potential is created under mechanical strain. Re- cently, flexible triboelectric generators using all-polymer- based materials have been developed. [20,21] They work in different modes: sliding mode and contact mode. For the sliding mode, [20] the potential difference is created by the horizontal in-plane separation of tribo- charged layers, whereas for contact mode, [22] the potential difference (polarization) is induced by the vertical out-of- plane separation of the tribo-charged layers. The chemical groups of GO have been found to improve interfacial interaction between graphene oxide and the al-