Biological production of graphene hydrogels for electrode applications in bioelectrochemical systems

PRADOS, MARÍA BELÉN; LESCANO, MARIELA; BARCLAY, JEREMÍAS; A. GASNIER; PEDANO, MARÍA L.; SICA, MAURICIO P.; CURUTCHET, G. ; PASQUEVICH, DANIEL

Obregón

Congreso; The Sixth International Symposium on Environmental Biotechnology and Engineering Ciudad Obregón, Sonora, México. November 5th to 9th, 2018 - And ? IV CONGRESO NACIONAL DE TECNOLOGÍAS Y CIENCIAS AMBIENTALES; 2018

Instituto Tecnológico de Sonora, Institute de Recherche pour le developpement

Bioelectrochemical systems (BES) represent a promising technology to turn organic pollutants present in wastewater into a renewable source of energy. These systems are based on electrogenic microorganisms. Currently, the development of this technology requires the optimisation of the electrodes. New materials such as graphene, a single-atom thick 2D carbon nanostructure, are being investigated for BES electrode applications. We have recently demonstrated that graphene hydrogel (GH), prepared by self-assembly of graphene oxide (GO) through chemical reduction, are suitable to develop dense and conductive biofilms of Geobacter sulfurreducens. In addition, we observed that this bacterium was capable of further reducing the graphene. Therefore, with the aim of developing a sustainable method for the production of GH, in this work, we tested the capability of a pure culture of G. sulfurreducens and an electrogenic bacterial consortium to reduce GO, inducing the formation of a hydrogel. The bacterial consortium was previously isolated from the Reconquista river (Buenos Aires, Argentina) sediment.Bacterial cultures were inoculated (10%) in anaerobic culture media (N2:CO2, 80:20) with acetate, as electron donor, and incubated at constant temperature (30º C). Different conditions of electron acceptor were tested: GO 1 mg/ml or GO 1 mg/ml plus fumarate 50 mM. We followed the reduction process by visual inspection, to avoid disruption of the forming hydrogel. After 1 month, the hydrogels were characterized by scanning electron microscopy (SEM), Raman and Fourier Transformed Infrared Spectroscopy (FTIR). At 72 h, the bacterial consortium was reducing GO (the suspension changed it colour from brown to black). The formation of a hydrogel was evidenced at 10 days, when the consortium was grown in the presence of fumarate. In the absence of fumarate, a colloidal reduced GO was observed even after 30 days of culture. G. sulfurredecens was capable of inducing the formation of a hydrogel only after 90 days of culture. SEM images of the GH showed a 3D-architecture with interconnected macroporous, similar to the chemically produced GH. The Raman and FTIR spectrum confirmed the reduction of GO by bacteria.In conclusion, GH production can be effectively achieved with electrogenic bacteria. Importantly, the fastest rate observed is similar to the time required for chemical production of hydrogels. The GH is mechanically stable and easy to handle, an important requisite to consider the material for electrode applications.