Novel applications for electrogenic communities: synthesis of graphene electrodes.

FLORENCIA PRETZ; AURELIEN GASNIER; M. LAURA PEDANO; GUSTAVO CURUTCHET; M. BELÉN PRADOS

Simposio; Simposio Ambiente y Bioenergía 2022; 2022

ABIAER

Electrogenicmicroorganisms havethe unique capability of respiring solid extracellular compounds,including electrodes. This aptitude has enabled the development ofenvironmental and industrial processes called BioelectrochemicalSystems (BES). BES can be optimized for the production of energy,bioremediation of diverse compounds and also for the synthesis ofhigher value substances from effluents.However, the development of BES has been hampered by differentfactors, mainly a low rate of charge transfer to the electrodes.Therefore, we are working on the development of novel electrodes. Wehave previously demonstrated that graphene hydrogels (GH), preparedby self-assembly of graphene oxide (GO) through chemical reduction,are suitable to develop dense and conductive biofilms of Geobactersulfurreducens.Therefore, in order to developa sustainable method for the production of GH, we are exploring thepossibility of employing electrogenic communities to catalyze thereduction and self-assembly of graphene hydrogels. These hydrogelscould be employed as process specific electrodes.Inthis work, through a combination of microbiological andelectrochemical techniques, we selected an electrogenic community(M4) from the sediments of a polluted wetland, located in Rio Negro,Argentina. This wetland contains high uranium levels, among others.M4 bacterial cells were inoculated in two different anaerobic culturemedia and incubated at 30ºC. The first was a minimum medium withacetate as electron donor. Different conditions of electron acceptorwere tested: GO 0,14mg/mL and fumarate at 0, 3,5and 35mM. The second one was a rich mediumandGO was added at 0,14mg/mL. Two control experiments were performed: GO in each culturemedia without bacteria and with a sterilized bacterial culture. Wefollowed the reduction process in each vial by visual inspection. Theformed hydrogels were characterized when the structure was stable bySEM, Raman and FTIR. At 48h,signs of GO reduction were observed in every condition tested withviable bacteria. The formation of a hydrogel was evidenced at 7 days,when the consortium was grown in the presence of fumarate 35mMandit got stable 7 days later. In fumarate 3,5mM,the formation of the hydrogel was evidenced after 15 days. In theabsence of fumarate and in the rich medium, a colloidal reduced GOwas observed even after 30 days of culture. The Raman and FTIRspectra of the hydrogels confirmed the reduction of GO by bacteria.The spectra were similar to that obtained with the chemically reducedgraphene oxide. SEM images of the hydrogels showed a 3D-architecturewith interconnected macroporous (similar to the chemically producedGH) and bacteria inside this structure. In conclusion, electrogenicbacterial communities can catalyze the formation of reduced GOhydrogels. We are currently studying the performance of these GH inBES.p { line-height: 115%; text-align: left; orphans: 2; widows: 2; margin-bottom: 0.1in; direction: ltr; background: transparent; text-decoration: none }p.western { font-family: "Liberation Serif", serif; font-size: 12pt; so-language: es-AR }p.cjk { font-family: "Noto Serif CJK SC"; font-size: 12pt; so-language: zh-CN }p.ctl { font-family: "Lohit Devanagari"; font-size: 12pt; so-language: hi-IN }a:link { color: #000080; so-language: und; text-decoration: underline }