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Rewiring the microbe-electrode interfaces with biologically reduced graphene oxide for improved bioelectrocatalysis
... The modified electrode has also been used but it possesses toxicity to the microbes which in turn diminishes the performances. Hence, here, the carbon cloth is reported as electrodes because of its low cost than the other electrode materials [6]. Nafion is the mostly used commercial membrane in microbial fuel cell. ...
The present work deals with the effect of phosphotungstic acid (PWA) in the sulfonated poly (ether ether ketone) (SPEEK)/poly amide imide (PAI) polymer matrices. These membranes are prepared using solvent casting method. The complexation and structural analysis are characterized by FTIR and XRD studies respectively. The obtained results of ion exchange capacity, water uptake, and proton conductivity show their physico-chemical properties of the prepared composite membranes significantly enhanced after the incorporation of PWA. At ambient temperature, 5.6 × 10⁻² S/cm is the maximum conductivity achieved for the 20 wt% PWA-doped SPEEK/PAI membrane. The TGA/DTG thermograms show that the membrane retains good thermal stability with 54–57% of char yield which having maximum proton conductivity at different temperatures in the range of about 10⁻² S/cm because of the Keggin unit structure of PWA. The SEM micrograph reveals the dispersion of PWA in the SPEEK/PAI matrices. The insertion of PWA in the SPEEK/PAI matrix exhibiting better properties with Bacillus amyloliquefaciens is used to carry out the performances in the microbial fuel cell for bioelectricity generation. The maximum obtained voltage and power density are 786 mV and 113 mW/m², respectively, with current density of 207 mA/m².
... Conducting or electroactive materials like conducting polymers, metals and metals oxides, nanocarbons, nanohybrids, and transition metal dichalcogenides have long received much attention as conducting platforms due to their excellent compatibility with analytes and/or recognition molecules (Luo et al. 2016;Farka et al. 2017;Rathinam et al. 2018a;Swager 2018;Yang et al. 2018). Additionally, it has been observed that crystal structural quality, chemical composition, surface condition, crystallographic orientation axis, and so on are recognized as critical parameters to achieve excellent signal-tonoise ratios for such materials, especially at nanometric sizes (Rivera-Gill et al. 2013;Matsumoto et al. 2017). ...
Enzyme‐based electrochemical analysis involves electron transfer between enzymes and bioanalytes, whereby redox‐active sites of enzyme catalyze the exchange process during reaction with biomolecules present at the interface of an electrode and a supporting electrolyte. To fulfill this purpose, we incorporated various experimental studies for glucose oxidation in the presence of glucose oxidase enzyme over a conducting materials–electrode interface using an electrochemical technique. It includes conducting polymers, nanometals, transition metal oxides, carbon‐based layered materials, and transition metal oxide dichalcogenides like MoSe2 or its composites modified over Au, Pt, and glassy carbon electrodes. In this chapter, we incorporate the concepts of sensing application mainly using cyclic voltammetry and electrochemical impedance spectroscopic methods. Apart from these, plausible mechanisms of enzymatic reactions over modified electrodes during the oxidation of biomolecules (glucose) are also incorporated. Prior to these essential supporting structures, we also explain the basics of electrochemistry, various factors that affect the electrochemical phenomena, electrode fabrication processes, and issues and future prospects related to enzymatic reactions. This chapter deals with the essential knowledge of charge transfer and electrochemical phenomena at the enzymatic electrode–electrolyte interface.
... Graphene was used by many researchers; it was found to be highly biocompatible and electrically conductive, and to have high specific area (Zhu et al. 2010). Biologically reducible graphene oxide, when used to wire the microorganisms with the electrodes, was seen to be very efficient in reducing the loss of electrons at the electrode-electrolyte interface, hence increasing the electron transfer rate (Krishnaraj et al. 2018a). Biopolymers such as chitosan and alginate have some excellent properties like biocompatibility, nontoxicity, high permeability, and good adhesion and chelating ability. ...
Rapid population growth along with accelerated urbanization and industrialization have increased the rate of generation of wastewater and heightened the need for fresh water. Also, the demand for alternative energy resources is increasing alongside the gradually disappearing fossil fuel resources. Pollutants caused by fossil fuel use are also a growing concern these days. In this context, the development of integrated and sustainable technologies that treat waste and generate renewable energy is gaining a lot of interest. The microbial fuel cell (MFC) is one such technology that is capable of treating wastewater alongside generating electricity. MFCs consist of anode and cathode chambers separated by a cation exchange membrane (CEM), where anaerobic and aerobic conditions, respectively, are maintained. Anode and cathode electrodes in the respective chambers are connected externally through current collectors. An anaerobic condition in the anode chamber induces anaerobic digestion of organic waste, forming electrons and protons; whereas an aerobic condition in the cathode chamber stimulates reduction of protons transferred through CEM, forming water. Electrons produced in the anode chamber flow through the external circuit, generating current. However, like every other technology, MFCs have various limitations like high cost of cell materials, high internal resistance, and low power output. Overcoming these limitations is the main focus of current MFC research. This chapter will give brief information on the various aspects of MFCs, like operating principles, measuring their performance, factors affecting their performance, their various limitations and how to overcome them, and MFC applications.
... Green synthesis of reduced GO (rGO) from GO has been demonstrated using pure cultures of extracellular electrontransfer (EET)-capable bacteria, such as Shewanella oneidensis MR-1, 18,19 Bacillus subtilis 168, 20 Gluconobacter roseus, 21 and Desulfovibrio desulfuricans. 22 EET-capable bacteria have the ability of coupling the oxidation of substrates (electron donor) in their cytoplasm with the reduction of insoluble extracellular electron acceptors for respiration. ...
Doping/decorating of graphene or reduced graphene oxide (rGO) with heteroatoms provides a promising route for the development of electrocatalysts useful in many technologies, including water splitting. However, current doping approaches are complicated, not eco-friendly and not cost-effective. Herein, we report the synthesis of doped/decorated rGO for oxygen evolution reaction (OER) using a simple approach that is cost-effective, sustainable and easy to scale up. The OER catalyst was derived from the reduction of GO by an exo-electron transferring bacterium, Geobacter sulfurreducens. Various analytical tools indicate that OER active elements such as Fe, Cu, N, P, and S decorate the rGO flakes. The hybrid catalyst (i.e., Geobacter/rGO) produces a geometric current density of 10 mA cm−2 at an overpotential of 270 mV vs. the reversible hydrogen electrode (RHE) with a Tafel slope of 43 mV dec−1, and possesses high durability, evidenced through 10 hours of stability testing. Electrochemical analyses suggest the importance of Fe and its possible role as active site for OER. Overall, this work represents a simple approach towards the development of earth-abundant, eco-friendly and highly active OER electrocatalyst for various applications such as solar fuel production, rechargeable metal-air batteries, and microbial electrosynthesis.
In this study, Pb(II) was used as a target heavy metal pollutant, and the metabolism of Shewanella putrefaciens (S. putrefaciens) was applied to achieve reducing conditions to study the effect of microbial reduction on lead that was preadsorbed on graphene oxide (GO) surfaces. The results showed that GO was transformed to its reduced form (r-GO) by bacteria, and this process induced the release of Pb(II) adsorbed on the GO surfaces. After 72 hr of exposure in an S. putrefaciens system, 5.76% of the total adsorbed Pb(II) was stably dispersed in solution in the form of a Pb(II)-extracellular polymer substance (EPS) complex, while another portion of Pb(II) released from GO-Pb(II) was observed as lead phosphate hydroxide (Pb10(PO4)6(OH)2) precipitates or adsorbed species on the surface of the cell. Additionally, increasing pH induced the stripping of oxidative debris (OD) and elevated the content of dispersible Pb(II) in aqueous solution under the conditions of S. putrefaciens metabolism. These research results provide valuable information regarding the migration of heavy metals adsorbed on GO under reducing conditions due to microbial metabolism.
Improvement of human health and well-being is the final goal of any technological, social and economic development. Conventional technologies only focussed towards the production of economically viable products and hence neglecting the serious threats they posed to the society. Hence, the society requires new technologies, moving towards clean and green technology development. Green nanotechnology is a branch of green technology which considerably contributes to environmental sustainability by producing nano-products and nano-materials without harming human health and the environment and also provide solutions to environmental problems. Green nanotechnology utilizes the prevailing principles of green engineering and green chemistry. Green nanotechnology has following benefits: less waste and greenhouse gas emissions, increase in energy efficiency, and minimized consumption of non-renewable raw materials. This chapter focusses on the recent green technologies like microbial production of nanoparticles and electrosynthesis which utilizes electrochemistry to produce green nanomaterials.
Keywords: Electrosynthesis; Green nanotechnology
Graphene-based materials have attracted great attention in wastewater treatment due to their excellent adsorbability for refractory pollutants. However, the high cost, environmental pollution during preparation and the separation after adsorption are issues that restricted its widespread application. In this study, biologically reduced graphene oxide was prepared via bacterium Shewanella sp. CF8-6 in 12 h, and a 3D poly(vinyl alcohol)/BRGO aerogel (PVA-GA) was further synthesized using PVA as cross-linker. Results showed that BRGO had smooth surface, low ID/IG value (1.26) and smaller layer spacing (0.38 nm), indicating that the reaction process had little damage to GO structure. The prepared PVA-GA had strong mechanical strength and porous network structure, and its BET specific surface area was 59.02 m²/g. Benefit from the excellent structure of PVA-GA, it had good adsorption performance for methylene blue (MB) and Congo red (CR) (with removal rate of 94.62%, 93.97% and adsorption capacity of 135.17 mg/g, 134.24 mg/g at an initial dye concentration of 50 mg/L), and could maintain more than 75% removal rate after 5 cycles. This study developed a relatively mild and green way of graphene-based material synthesis and demonstrated the great potential of PVA-GA as an efficient and safe adsorbent for dye removal from wastewater.
BACKGROUND
The extracellular electron transfer (EET) between microbes and electrode modified by graphene‐based functional material has attracted increasing attention. EET is an important process, through which the anode can act as the acceptor for the electrons produced via the microbial respiration, and it also plays a key role in the organic matter degradation as well as the nutrient cycling in environment.
RESULTS
Our results showed that the interaction between microbes and carbon felt (CF) electrode decorated with bio‐reduced graphene oxide (GO‐br) was significantly enhanced compared with that between the unmodified CF electrode and microbes. The promoted biological current production and cyclic voltammetric (CV) current response indicated the considerable electro‐activity of the GO‐br‐CF electrode. Rdif of the GO‐br‐CF electrode decreased significantly by 97.3% from 2.76×10⁵ ±7644 Ω at the initial incubation stage to 7341±1322 Ω after 58 h incubation time for GO‐br decoration. We also noticed that the GO‐br‐CF electrode intermittently poised at +0.1 V (vs Ag/AgCl/KCl sat.) was favorable for EET. The GO‐br‐CF electrode, which enhanced MFC performance significantly, was further used as the anode in a microbial fuel cell (MFC).
CONSLUSION
Overall, the results of this study indicated the decoration of CF electrode with GO‐br could regulate the electrochemical activity of the electrode and the EET process between microbes and electrode. The elevated electrochemical activity and EET were attributed to the rapid decrease in the diffusion resistance (Rdif) of the GO‐br‐CF electrode.
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To explore a green, low-cost, and efficient strategy to synthesis reduced graphene oxide (RGO), the process and mechanism of the graphene oxide (GO) reduction by a model electrochemically active bacteria (EAB), Geobacter sulfurreducens PCA, were studied. In this work, up to 1.0 mg mL⁻¹ of GO was reduced by G. sulfurreducens within 0.5–8 days. ID/IG ratio in reduced product was similar to chemically RGO. After microbial reduction, the peak which corresponded to the reflection of graphene oxide (001) disappeared, while another peak considered as graphite spacing (002) appeared. The peak intensity of typical oxygen function groups, such as carboxyl C–O and >O (epoxide) groups, diminished in bacterially induced RGO comparing to initial GO. Besides, we observed the doping of nitrogen and phosphorus elements in bacterially induced RGO. In a good agreement with that, better electrochemical performance was noticed after GO reduction. As confirmed with differential pulse voltammetry (DPV) and cyclic voltammetry (CV) analysis, the maximum value of peak currents of bacterially induced RGO were significantly higher than those of GO. Our results showed the electron transfer at microbial cell/GO interface promoted the GO reduction, suggesting a broader application of EAB in biological mediated production of RGO.
With graphene oxide (GO), platinum carbon (Pt/C), and reduced graphene oxide (rGO) as cathode catalysts, three types of single-chamber microbial fuel cells (MFCs) were constructed for simultaneous Cu²⁺ removal and electricity production. Results indicated rGO-MFC and Pt/C-MFC had much better Cu²⁺-removing and electricity-generating performance than that of GO-MFC, and rGO-MFC presented preferable electrochemical characteristics compared with Pt/C-MFC. Microbial community analysis indicated Geobacter dominated anodic biofilms and was mainly responsible for organics degradation and electricity generation. The dual bio-selective effects by cathode catalyst and toxic Cu²⁺ resulted in different cathodic microbial communities. At high Cu²⁺ contents, Nitratireductor, Ochrobactrum, and Serratia as efficient Cu²⁺-removing genera played key roles in Pt/C-MFC, and Azoarcus predominant in cathodic biofilms of rGO-MFC might be important contributor for the favorable performance in this case.
Microbial fuel cells (MFCs) are emerging as green, sustainable, and ecofriendly technology for conversion of waste to energy using microorganisms via electrochemical catalytic reactions. Electrode material design plays a crucial role in controlling the output power of MFCs to make this technology viable and cost‐effective. Recently, several efforts have been dedicated toward designing materials for MFCs, mainly featuring two aspects: (i) development of cost‐effective anodes for efficient biofilm formation with high extracellular electron transfer (EET), and (ii) preparation of suitable catalysts with improved oxygen reduction reaction (ORR) at the cathode. Mostly carbon‐based materials are employed as anodes, particularly with different morphologies like paper, fiber, brush, felt, and so on exhibiting distinct surface properties. Carbon materials offer desirable biocompatibility, conductivity, and environment for EET. Metals and metal oxides are studied as non‑carbon‐based anode materials, which provide higher conductivity than carbon‐based materials. Metal oxide nanostructures promote a fast charge transfer process and reduce the internal resistance at the anode. But these electrodes do not offer required compatibility with bacteria and hinder the quality of biofilm. In such scenarios, conducting polymers are examined as efficient anode materials in MFCs. In this chapter, progress in research of various anode and cathode materials is systematically summarized. Their properties, advantages, and shortcomings are discussed, along with a brief outlook on further developmental aspects.
The objective of the present study was to construct a compact retrofit design of Microbial Electrolysis Cell (MEC) within an anaerobic digester. In this design, the cathode chamber is inserted in the anodic chamber for compactness, improved hydrogen production and wastewater treatment efficiency. The performance of the new design is compared with that of a conventional (dual chamber) MEC. A cumulative hydrogen of 40.05 ± 0.5 mL and 30.12 ± 0.5 mL were produced at the current density of 811.7 ± 20 and 908.3 ± 25 mA/m² respectively for conventional and modified MEC system. The cathodic hydrogen recovery (CHR) defined as the recovery of electrons as hydrogen which was observed a maximum of 46.5 ± 0.8 and 38.8 ± 0.5% in conventional and modified MEC. The Coulombic efficiency (CE) defined as the recovery of total electrons in acetate as current was observed as 17.25 ± 0.15 and 16.82 ± 0.1% for conventional and modified MEC. In addition, the wastewater COD removal efficiency was observed to be 77.5 ± 1.0% and 75.6 ± 1.5 in 70 h for conventional and modified MEC designs. As shown in the work below, the modified compact design worked effectively to produce hydrogen under different COD concentrations; anolyte and catholyte concentrations; and applied potentials. Thus the modified compact MEC which is also a retrofit to an existing anaerobic digester can extend the use of anaerobic digesters and improve their economics in waste water treatment.
This chapter will introduce the basic concepts of bioelectrocatalysis and the advantages of extremophiles for bioelectrochemical systems. The chapter will discuss electrogenic activity and electron transfer characteristics of extremophiles and their applications in microbial fuel cells, microbial electrolytic cells, microbial desalination cells, and microbial electrosynthesis. The use of extremophilic bioprocesses for production of bioenergy and value-added products from lignocellulosic biomass will also be discussed.
In the recent years, considerable body of research has been carried out in the field of bioelectrochemical systems (BESs) for treatment of wastewater and generation of power. In these systems, different microbes are used for carrying out the transfer of electrons from medium to the anode electrode. The microbes employed are known as electrogens as they have the capacity to transfer electrons. Bacteria such as those belonging to the species such as Geobacter, Betaproteo, Deltaproteo and Desulfurnonas and of genus Shewanella are the commonly explored electrogens in BESs. In the past few years, a renewed interest in microbial fuel cell (MFC) research has developed, yet power generated from these devices has not significantly advanced. The primary reason for this non-advancement is that the research is more focused on improving power generation rather than on elementary understanding of the electron transfer processes. This review focuses on the methods used to study electron transfer processes in biofilms growing on the electrodes and presents several successful applications of MFCs. In this review, we have defined electrochemically active biofilms as biofilms that exchange electrons with conductive surfaces called electrodes.
The present study is focused on enhancing the rheological properties of the electrolyte and eliminating sedimentation of microorganisms/flocs without affecting the electron transfer kinetics for improved bioelectricity generation. Agar derived from polysaccharide agarose (0.05-0.2%, w/v) was chosen as a rheology modifying agent. Electroanalytical investigations showed that electrolytes modified with 0.15% agar display a nine-fold increase in current density (1.2 mA/cm²) by a thermophilic strain (Geobacillus sp. 44C, 60 °C) when compared with the control. Sodium phosphate buffer (0.1 M, pH 7) electrolyte with riboflavin (0.1mM) was used as the control. Electrolytes modified with 0.15% agar significantly improved chemical oxygen demand removal rates. This developed electrolyte will aid in improving bioelectricity generation in Bioelectrochemical Systems (BES). The developed strategy avoids the use of peristaltic pumps and magnetic stirrers, thereby improving the energy efficiency of the process.
While academic-level studies on metabolic engineering of microorganisms for production of chemicals and fuels are ever growing, a significantly lower number of such production processes have reached commercial-scale. In this work, we review the challenges associated with moving from laboratory-scale demonstration of microbial chemical or fuel production to actual commercialization, focusing on key requirements on the production organism that need to be considered during the metabolic engineering process. Metabolic engineering strategies should take into account techno-economic factors such as the choice of feedstock, the product yield, productivity and titre, and the cost effectiveness of midstream and downstream processes. Also, it is important to develop an industrial strain through metabolic engineering for pathway construction and flux optimization together with increasing tolerance to products and inhibitors present in the feedstock, and ensuring genetic stability and strain robustness under actual fermentation conditions.
Nanomaterials based on two-dimensional (2D) atomic crystals are considered to be very promising for various life-science and medical applications, from drug delivery to tissue modification. One of the most suitable materials for these purposes is graphene oxide (GO), thanks to a well-developed methods of production and water solubility. At the same time, its biological effect is still debated. Here we demonstrate that highly purified and thoroughly washed GO neither inhibited nor stimulated the growth of E.coli, ATCC25922; E.coli NCIMB11943 and S.aureus ATCC25923 at concentrations of up to 1 mg ml−1. Moreover, transmission electron microscopy (TEM) of GO exposed bacteria did not reveal any differences between GO exposed and not exposed populations. In contrast, a suspension of insufficiently purified GO behaved as an antibacterial material due to the presence of soluble acidic impurities, that could be removed by extended purification or neutralisation by alkaline substrates. A standardised protocol is proposed for the generation of clean GO, so it becomes suitable for biological experiments. Our findings emphasise the importance of GO purification status when dealing with biological systems as the true effect of material can be masked by the impact of impurities.
Soak liquor is a primary effluent from tannery industry. It poses a threat to the environment and it is necessary
to treat the effluent. The predominant tannery effluent bacteria were isolated, identified and used
for the electricity generation. The present study investigates the use of soak liquor for the first time as a
substrate for electricity generation in Microbial Fuel Cell (MFC). The high salinity and rich organic content
of soak liquor increase the efficiency of MFC. Various electrochemical characterizations such as polarization
curve, cyclic voltammetry, chronoamperometry, electrochemical impedance spectrometry were performed
to analyse the efficacy of the soak liquor. MFC produced a maximum power density (Pmax) of
44.02 mW/m2 with a current density 140.34 mA/m2. The chemical oxygen demand (COD) reduction rate
was found to be 93% ± 4.7% in a cycle period of 168 h. The presence of humic acid was identified in soak
liquor, which might be involved in shuttling of electrons from the microorganisms to the electrode.
Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter showed that both directions for electron transfer would be possible. It was proposed that gram-positive bacteria, in the absence of cytochrome C, would accept electrons using a cascade of membrane-bound complexes such as membrane-bound Fe-S proteins, oxidoreductase, and periplasmic enzymes. Modification of the cathode with the addition of positive charged species such as chitosan or with an increase of the interfacial area using a porous three-dimensional scaffold electrode led to increased current consumption. The extracellular electron transfer from the cathode to the microbe could catalyze various bioelectrochemical reductions. Electrofermentation used electrons from the cathode as reducing power to produce more reduced compounds such as alcohols than acids, shifting the metabolic pathway. Electrofuel could be generated through artificial photosynthesis using electrical energy instead of solar energy in the process of carbon fixation.
Herein, we report a new strategy for the simultaneous degradation of lignocellulosic biomass and bioelectricity generation using a novel three-chamber microbial fuel cell (MFC). Oscillatoria annae, a freshwater cyanobacterium, was used for the hydrolysis of cellulose to glucose. The electrocatalytic activity of the coculture of Acetobacter aceti and Gluconobacter roseus was used to oxidize the glucose for current generation in the MFC. Carbon felt was used as the anode and cathode material. Lignocellulosic materials such as sugarcane bagasse and corn cob were used as substrates. The performances of the MFC with two different substrates were analyzed by polarization studies, coulombic efficiency, percentage of COD removal and internal resistance. The three-chamber MFC produced a maximum power output of 8.78 W/m3 at 20.95 A/m3 and 6.73 W/m3 at 17.28 A/m3 with sugarcane bagasse and corn cob as substrates, respectively.
Graphical Abstract
This work is aimed at finding new strategies for the modification of anode and cathode that can lead to improved performance of microbial fuel cells (MFCs). The electrochemical deposition of chitosan onto carbon felt followed by further modification with alginate led to the formation of a biocompatible platform for the prolific growth of microorganisms on the anode (Chit-Alg(carbon felt anode). The novel modification strategy for the formation of Prussian blue film, on the electrochemically deposited chitosan layer, has helped in circumventing the disadvantages of using ferricyanide in the cathode compartment and also for improving the electron transfer characteristics of the film in phosphate buffer. The anode was tested for its efficacy with four different substrates viz., glucose, ethanol, acetate and grape juice in a two compartment MFC. The synergistic effect of the mixed culture of Acetobacter aceti and Gluconobacter roseus was utilized for current generation. The electrocatalytic activity of the biofilm and its morphology were characterized by cyclic voltammetry and scanning electron microscopy, respectively. The power densities were found to be 1.55 W/m(3), 2.80 W/m(3), 1.73 W/m(3) and 3.87 W/m(3) for glucose, ethanol, acetate and grape juice, respectively. The performance improved by 20.75% when compared to the bare electrode.
For the first time, stable aqueous dispersions of polymer-coated graphitic nanoplatelets can be prepared via an exfoliation/in-situ reduction of graphite oxide in the presence of poly(sodium 4-styrenesulfonate).
Graphene oxide (GO) can be reduced to graphene in a normal aerobic setup under ambient conditions as mediated by microbial
respiration of Shewanella cells. The microbially-reduced graphene (MRG) exhibited excellent electrochemical properties. Extracellular electron transfer
pathways at the cell/GO interface were systematically investigated, suggesting both direct electron transfer and electron
mediators are involved in the GO reduction.
KeywordsElectrogenic bacterial–graphene–green synthesis–extracellular electron transfer
Graphene sheets--one-atom-thick two-dimensional layers of sp2-bonded carbon--are predicted to have a range of unusual properties. Their thermal conductivity and mechanical stiffness may rival the remarkable in-plane values for graphite (approximately 3,000 W m(-1) K(-1) and 1,060 GPa, respectively); their fracture strength should be comparable to that of carbon nanotubes for similar types of defects; and recent studies have shown that individual graphene sheets have extraordinary electronic transport properties. One possible route to harnessing these properties for applications would be to incorporate graphene sheets in a composite material. The manufacturing of such composites requires not only that graphene sheets be produced on a sufficient scale but that they also be incorporated, and homogeneously distributed, into various matrices. Graphite, inexpensive and available in large quantity, unfortunately does not readily exfoliate to yield individual graphene sheets. Here we present a general approach for the preparation of graphene-polymer composites via complete exfoliation of graphite and molecular-level dispersion of individual, chemically modified graphene sheets within polymer hosts. A polystyrene-graphene composite formed by this route exhibits a percolation threshold of approximately 0.1 volume per cent for room-temperature electrical conductivity, the lowest reported value for any carbon-based composite except for those involving carbon nanotubes; at only 1 volume per cent, this composite has a conductivity of approximately 0.1 S m(-1), sufficient for many electrical applications. Our bottom-up chemical approach of tuning the graphene sheet properties provides a path to a broad new class of graphene-based materials and their use in a variety of applications.
The present study evaluates relative functioning of microbial electrochemical systems (MES) for simultaneous wastewater treatment, desalination and resource recovery. Two MES were designed having abiotic cathode (MES-A) and algal biocathode (MES-B) which were investigated with synthetic feed and saline water as proxy of typical real-field wastewater. Comparative anodic and cathodic efficiencies revealed a distinct disparity in both the MES when operated in open circuit (OC) and closed circuit (CC). The maximum open circuit voltage (OCV) read in MES-A and MES-B was about 700 mV and 600 mV, respectively. Salinity and organic carbon removal efficiencies were noticed high during CC operation as 72% and 55% in MES-A and 60% and 63% in MES-B. These discrete observations evidenced ascribe to the influence of microbial electrochemical induced ion-migration over cathodic reduction reactions (CRR).
This chapter is a review of the application of Raman spectroscopy in characterizing the properties of graphene, both exfoliated and synthesized, and graphene-based materials such as graphene-oxide. Graphene is a 2-dimensional honeycomb lattice of sp2-bonded carbon atoms and has received enormous interest because of its host of interesting material properties and technological potentials. Raman spectroscopy (and Raman imaging) has become a powerful, noninvasive method to characterize graphene and related materials. A large amount of information such as disorder, edge and grain boundaries, thickness, doping, strain and thermal conductivity of graphene can be learned from the Raman spectrum and its behavior under varying physical conditions. In particular, this chapter will discuss Raman characterization of graphene with artificial disorder generated by irradiations such as electron-beam exposure and oxygen plasma, focusing on the defect-activated Raman D peak.
The preparation of graphitic oxide by methods described in the literature is time consuming and hazardous. A rapid, relatively safe method has been developed for preparing graphitic oxide from graphite in what is essentially an anhydrous mixture of sulfuric acid, sodium nitrate and potassium permanganate.
In this study a simple, fast and effective surface modification method for enhanced biofilm formation, increased electron transfer rate and higher current density generation from microbial fuel cell (MFC) has been demonstrated. This method consists of partial oxidation of carbon felt material by UV/O3 treatment. Results from the electrochemical studies performed suggest that Shewanella oneidensis MR-1 biofilm formation is favored on UV/O3 treated carbon felt electrodes when subjected to an applied potential of-0.3 V vs. Ag/AgCl. Carbon electrodes exposed to 45 min of UV/O3 treatment provided the best electrochemical results and richer bacterial cell attachment. Ozone exposure above 45 min presented decreased MFC performance and current generation. Visual confirmation via SEM images indicated a link between the current generation and the presence of biomass attached to the working electrodes. In addition, we have shown enrichment of the electrode surface with flavin, which correlates with the increased anodic performance.
In this work, the synthesis of silver nanoparticles (AgNPs) from Gluconobacter roseus, their characterization and their antiplatelet activity has been described. Gluconobacter roseus, an electrochemically active bacterium, mediates the synthesis of silver nanoparticles in the solution containing AgNO3 as a precursor and sorbitol as an electron donor. The bacteria act as a whole-cell biocatalyst to oxidise the sorbitol substrate and produce electrons for the reduction of Ag+ ions. The detailed characterization of the purified nanoparticles was carried out using UV-vis spectroscopy, EDAX (Energy dispersive X-ray spectroscopy), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). From the analysis of the UV-vis spectroscopy and EDAX, the formation of AgNPs was confirmed. The average particle size was found out to be 10 nm using TEM. FTIR results indicated the presence of amide groups which might be involved in stabilizing the nanoparticles. After the detailed characterization, the antiplatelet activity of synthesized AgNPs was investigated using aggregation assay and spreading studies. The AgNPs showed dose-dependent antiplatelet activity against ADP-induced activation of the blood platelets. AgNPs significantly decreased the aggregation by up to 87%. Spreading studies were made using Atomic Force Microscopy (AFM). Lactate dehydrogenase (LDH) assay was performed to check the cytotoxicity of the nanoparticles and interestingly the nanoparticles do not confer toxicity to the platelets. AFM is presented as a new method to assess the relative amounts of antiplatelet activity.
The present study evaluates the sequential integration of two advanced biological treatment methods viz., sequencing batch reactor (SBR) and bioelectrochemical treatment systems (BET) for the treatment of real-field petrochemical wastewater (PCW). Initially two SBR reactors were operated in aerobic (SBRAe) and anoxic (SBRAx) microenvironments with an organic loading rate (OLR) of 9.68kg COD/m(3)-day. Relatively, SBRAx showed higher substrate degradation (3.34kg COD/m(3)-day) compared to SBRAe (2.9kg COD/m(3)-day). To further improve treatment efficiency, the effluents from SBR process were fed to BET reactors. BETAx depicted higher SDR (1.92kg COD/m(3)-day) with simultaneous power generation (17.12mW/m(2)) followed by BETAe (1.80kg COD/m(3)-day; 14.25mW/m(2)). Integrating both the processes documented significant improvement in COD removal efficiency due to the flexibility of combining multiple microenvironments sequentially. Results were supported with GC-MS and FTIR, which confirmed the increment in biodegradability of wastewater.
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In this article, we report a three-compartment microbial fuel cell (MFC) system for the simultaneous degradation of cellulose and production of natural pigments such as phycoerythrin and phycocyanin along with bioelectricity generation. Oscillatoria annae, a freshwater cyanobacterium, was used for the conversion of cellulose to reducing sugars, which were fed as a substrate to a coculture of Acetobacter aceti and Gluconobacter roseus for current generation in a three-compartment MFC. Carbon felt modified with a composite film containing chitosan and sodium alginate served as the MFC anode. The cellulose-fed three-compartment MFC produced a maximum power output of 6.62 W m−3 at 17.55 A m−3.
Graphical Abstract
This work couples the catalytic activity of O. annae, a freshwater cyanobacteria, and electrogenic activity of Acetobacter aceti and Gluconobacter roseus for electricity generation and pigment production.
The chemical reduction of graphene oxide is a promising route towards the large scale production of graphene for commercial applications. The current state-of-the-art in graphene oxide reduction, consisting of more than 50 types of reducing agent, will be reviewed from a synthetic chemistry point of view. Emphasis is placed on the techniques, reaction mechanisms and the quality of the produced graphene. The reducing agents are reviewed under two major categories: (i) those which function according to well-supported mechanisms and (ii) those which function according to proposed mechanisms based on knowledge of organic chemistry. This review will serve as a valuable platform to understand the efficiency of these reducing agents for the reduction of graphene oxide.
In this paper, we report that Staphylococcus aureus isolated from the rumen fluid can display direct electron transfer on carbon felt electrodes and exhibit enhanced microbial electrocatalysis towards the oxidation of complex substrate like cellulose. The phenomena of direct electron transfer and electrocatalysis were investigated in detail by cyclic voltammentry and chronoamperometry. The electron transfer was closer to perfect reversibility with a peak separation value of only 7 mV at a scan rate of 50 mV/s. The enhanced microbial electrocatalysis towards the oxidation of cellulose revealed the potential of the microorganism for application in microbial fuel cells. The pure cultures of S. aureus produced an electrocatalytic current density of 1.4 mA/cm2 as estimated by long-term chronoamperometry for a cellulose concentration of 20 mM. To the best of our knowledge we report for the first time the use of S. aureus for bioelectricity generation with cellulose as a sole source of electron donor.
Interactions of chemically exfoliated graphene oxide (GO) nanosheets and Escherichia coli bacteria living in mixed-acid fermentation with an anaerobic condition were investigated for different exposure times. X-ray photoelectron spectroscopy showed that as the exposure time increased (from 0 to 48 h), the oxygen-containing functional groups of the GO decreased by ∼60%, indicating a relative chemical reduction of the sheets by interaction with the bacteria. Raman spectroscopy and current–voltage measurement confirmed the reduction of the GO exposed to the bacteria. The reduction was believed to be due to the metabolic activity of the surviving bacteria through their glycolysis process. It was found that the GO sheets could act as biocompatible sites for adsorption and proliferation of the bacteria on their surfaces, while the bacterially-reduced GO (BRGO) sheets showed an inhibition for proliferation of the bacteria on their surfaces. It was shown that the slight antibacterial property of the BRGO sheets and the detaching of the already proliferated bacteria from the surface of these sheets contributed to the growth inhibition of the bacteria on the surface of the reduced sheets.
Graphene and graphene related materials are an important area of research in recent years due to their unique properties. The extensive industrial application of graphene and related compounds has led researchers to devise novel and simple methods for the synthesis of high quality graphene. In this paper, we developed an environment friendly, cost effective, simple method and green approaches for the reduction of graphene oxide (GO) using Escherichia coli biomass. In biological method, we can avoid use of toxic and environmentally harmful reducing agents commonly used in the chemical reduction of GO to obtain graphene. The biomass of E. coli reduces exfoliated GO to graphene at 37°C in an aqueous medium. The E. coli reduced graphene oxide (ERGO) was characterized with UV-visible absorption spectroscopy, particle analyzer, high resolution X-ray diffractometer, scanning electron microscopy and Raman spectroscopy. Besides the reduction potential, the biomass could also play an important role as stabilizing agent, in which synthesized graphene exhibited good stability in water. This method can open up the new avenue for preparing graphene in cost effective and large scale production. Our findings suggest that GO can be reduced by simple eco-friendly method by using E. coli biomass to produce water dispersible graphene.
We prepared hydrazine-reduced materials from both graphite oxide (GO) particles, which were not exfoliated, and completely exfoliated individual graphene oxide platelets, and then analyzed their chemical and structural properties by elemental analysis, XPS, TGA, XRD, and SEM. Both reduced materials showed distinctly different chemical and structural properties from one another. While hydrazine reduction of graphene oxide platelets produced agglomerates of exfoliated platelets, the reduction of GO particles produced particles that were not exfoliated. The degree of chemical reduction of reduced GO particles was lower than that of reduced graphene oxide and the BET surface area of reduced GO was much lower than that of reduced graphene oxide.
The discovery of electrotrophs, microorganisms that can directly accept electrons from electrodes for the reduction of terminal electron acceptors, has spurred the investigation of a wide range of potential applications. To date, only a handful of pure cultures have been shown to be capable of electrotrophy, but this process has also been inferred in many studies with undefined consortia. Potential electron acceptors include: carbon dioxide, nitrate, metals, chlorinated compounds, organic acids, protons and oxygen. Direct electron transfer from electrodes to cells has many advantages over indirect electrical stimulation of microbial metabolism via electron shuttles or hydrogen production. Supplying electrons with electrodes for the bioremediation of chlorinated compounds, nitrate or toxic metals may be preferable to adding organic electron donors or hydrogen to the subsurface or bioreactors. The most transformative application of electrotrophy may be microbial electrosynthesis in which carbon dioxide and water are converted to multi-carbon organic compounds that are released extracellularly. Coupling photovoltaic technology with microbial electrosynthesis represents a novel photosynthesis strategy that avoids many of the drawbacks of biomass-based strategies for the production of transportation fuels and other organic chemicals. The mechanisms for direct electron transfer from electrodes to microorganisms warrant further investigation in order to optimize envisioned applications.
Reduction of a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high-surface-area carbon material which consists of thin graphene-based sheets. The reduced material was characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, NMR spectroscopy, Raman spectroscopy, and by electrical conductivity measurements. (c) 2007 Elsevier Ltd. All rights reserved.
Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.
Here we present that graphene oxide (GO) can act as a terminal electron acceptor for heterotrophic, metal-reducing, and environmental bacteria. The conductance and physical characteristics of bacterially converted graphene (BCG) are comparable to other forms of chemically converted graphene (CCG). Electron transfer to GO is mediated by cytochromes MtrA, MtrB, and MtrC/OmcA, while mutants lacking CymA, another cytochrome associated with extracellular electron transfer, retain the ability to reduce GO. Our results demonstrate that biodegradation of GO can occur under ambient conditions and at rapid time scales. The capacity of microbes to degrade GO, restoring it to the naturally occurring ubiquitous graphite mineral form, presents a positive prospect for its bioremediation. This capability also provides an opportunity for further investigation into the application of environmental bacteria in the area of green nanochemistries.
There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
Acetobacter aceti and Gluconobacter roseus, which are known to be responsible for the spoilage of wine, are used for current generation in batch-type microbial biofuel cells and it has been shown for the first time that these two microorganisms do not require mediators for the transfer of electrons to the anode. Three biofuel cells were constructed with two cells containing the pure cultures of each of the microorganisms as the biocatalyst (A-MFC, G-MFC) and the third cell was constructed with the mixed culture of these two microorganisms as the biocatalyst (AG-MFC). The performance of the biofuel cells was evaluated in terms of open circuit voltage (OCV), fuel consumption rate, internal resistance, power output, and coulombic efficiency. The mixed culture cell (AG-MFC) exhibits a better overall performance compared to the other cells.
A novel concept for a biofuel cell is presented. Enzyme based fuel cells suffer from enzyme instability when a long time of operation is required. Hence, a system that will continuously produce the biocatalyst needed for the system is necessary. A hybrid of an enzyme-based microbial fuel cell was developed. The redox enzyme glucose oxidase from Aspergillus niger was displayed on the surface of Saccharomyces cerevisiae using the Yeast Surface Display System in a high copy number and as an active enzyme. We have demonstrated its activity both biochemically and electrochemically and observed much higher activity over yeast cells not displaying glucose oxidase as well as over purified glucose oxidase from Aspergillus niger. Further, we were able to construct a biofuel cell, where the anode was comprised of the yeast cells displaying glucose oxidase in the presence of a mediator (methylene blue) and the cathode compartment was comprised of the oxygen reducing enzyme laccase from Trametes versicolor and a redox mediator. Our constructed biofuel cell displayed higher power outputs and current densities than those observed for unmodified yeast and a much longer time of operation in comparison with a similar cell where the anode is comprised of purified glucose oxidase.
Electricity production from acetate, glucose and xylose with humic acid as mediator was investigated in two chambers microbial fuel cells (MFCs). Acetate produced the highest voltage (570 mV with 1000 Omega) and maximum power density (P(maxd)=123 mW/m(2)) due to a simpler metabolism than with glucose and xylose. Glucose and xylose resulted in P(maxd) of 28 mW/m(2) and 32 mW/m(2) at lower voltage of 380 mV and 414 mV, respectively. P(maxd) increased by 84% and 30%, for glucose and xylose respectively, when humic acid (2g/l) was present in the medium. No significant effect was found with acetate since the internal resistance possessed a limiting effect. The increase of P(maxd) due to humic acid presence was attributed to its ability to act as mediator. Even though pH decreased to 5 with glucose and xylose, due to production of acetate and propionate, the voltage remained on the same level of 250-350 mV.
Electrochemical impedance spectroscopy (EIS) has been used to determine several electrochemical properties of the anode and cathode of a mediator-less microbial fuel cell (MFC) under different operational conditions. These operational conditions included a system with and without the bacterial catalyst and EIS measurements at the open-circuit potential of the anode and the cathode or at an applied cell voltage. In all cases the impedance spectra followed a simple one-time-constant model (OTCM) in which the solution resistance is in series with a parallel combination of the polarization resistance and the electrode capacitance. Analysis of the impedance spectra showed that addition of Shewanella oneidensis MR-1 to a solution of buffer and lactate greatly increased the rate of the lactate oxidation at the anode under open-circuit conditions. The large decrease of open-circuit potential of the anode increased the cell voltage of the MFC and its power output. Measurements of impedance spectra for the MFC at different cell voltages resulted in determining the internal resistance (R(int)) of the MFC and it was found that R(int) is a function of cell voltage. Additionally, R(int) was equal to R(ext) at the cell voltage corresponding to maximum power, where R(ext) is the external resistance that must be applied across the circuit to obtain the maximum power output.
We provide the first evidence that the size (diameter) of carbon nanotubes (CNTs) is a key factor governing their antibacterial effects and that the likely main CNT-cytotoxicity mechanism is cell membrane damage by direct contact with CNTs. Experiments with well-characterized single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) demonstrate that SWNTs are much more toxic to bacteria than MWNTs. Gene expression data show that in the presence of both MWNTs and SWNTs, Escherichia coli expresses high levels of stress-related gene products, with the quantity and magnitude of expression being much higher in the presence of SWNTs.
Prospects of microbial cell factories developed through Fig. 3. Nyquist plot of the biofilm formed on the (a) bare carbon felt electrode and (b) RGO modified carbon felt electrode
- M Gustavsson
- S Y Lee
Gustavsson, M., Lee, S.Y., 2016. Prospects of microbial cell factories developed through
Fig. 3. Nyquist plot of the biofilm formed on the (a) bare carbon felt electrode and (b) RGO modified carbon felt electrode.
- N K Rathinam
N.K. Rathinam et al.
Bioresource Technology 256 (2018) 195-200
Recent progress in electrodes for microbial fuel cells
- J Wei
- P Liang
- X Huang
Wei, J., Liang, P., Huang, X., 2011. Recent progress in electrodes for microbial fuel cells.
Bioresour. Technol. 102 (20), 9335-9344.
Recent progress in electrodes for microbial fuel cells
- Wei