Development of carbon nanotubes and nanofluids based microbial fuel cell
Introduction
Huge reservoirs of energy locked up as carbohydrates, fatty acids and amino acids are squandered in the form of waste waters and biomass from municipal, industrial and agricultural sources. The non-specificity and poisoning of conventional catalysts make conventional electrochemical cells unsuitable for tapping this energy found in carbohydrates, proteins and other energy rich natural products [1]. But if mediation to microbe reactions is achieved, then microbial fuel cells (MFC) that utilize these fuels to generate electrical power [2], [3], [4] have a promising future. However, as a nascent technology, it has yet to achieve large-scale commercial success. The most common available types of MFC reactor setup either involve biohydrogen production [5], [6], [7] or direct/mediated electron transfer to the electrodes. The performance of high delivering MFC is offset by factors like (i) long lag times before onset of electricity generation, (ii) use of right consortium of bacteria for high power densities, (iii) instability at higher voltages, (iv) selection of appropriate electron mediator and (v) use of expensive electrodes [8], [9], [10], [11]. Hence it is important to choose electrodes and electron mediator to overcome the above-mentioned shortcomings. Since the discovery of multiwalled nanotubes (MWNT) and single walled nanotubes (SWNT), these one-dimensional nanostructured materials have attracted tremendous interest both from fundamental and technological perspectives due to their unique physical and chemical properties. Use of CNTs was an attractive option in an attempt to address the above-mentioned problems, mainly due to their unique morphology and interesting properties such as nanometre size, high accessible surface area, good electronic conductivity and high stability [12]. Qiao et al. also demonstrated the improvement in the MFC performance using CNT-doped polyaniline as anode [13].
Albeit not the most efficient microorganism for the purpose [14], Escherichia coli (DH5α strain) was chosen as the biocatalyst, for its ease in handling and abundant availability, while setting up an anaerobic dual-chambered MFC with each chamber containing the CNT based electrodes and glucose as the substrate. Methylene Blue, Neutral Red and NanoFluids were used in place of electron mediators. The performance of this MFC, using CNT based nanofluids as novel electron mediators and CNT based electrodes, has been discussed and the results have been compared against plain graphite electrode-based MFC.
Section snippets
Microbial preparation and measurements
E. coli (DH5α) was grown in 100 mL of Luria Bertani broth at 37 °C and constant agitation for 12 h. The resting cells were harvested by centrifugation at 3000g at 2 °C for 14 min, were washed twice and resuspended in anodic medium I (100 mM phosphate buffer [pH 7.0], 10 g/L trisodium citrate, 5 g/L peptone, and 5 g/L yeast extract) at an optical density of 0.92 at 660 nm.
Electrode preparations and characterization
MWNTs were synthesized using a single stage furnace thermal CVD facility, by catalytic decomposition of acetylene over Mischmetal (Mm)
Results and discussion
High quality multiwalled nanotubes (MWNTs) were obtained by catalytic chemical vapour deposition (CCVD) technique as described elsewhere [15]. The MWNTs thus obtained, were functionalized, deposited on carbon paper and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and energy dispersive analysis (EDAX) (Fig. 1, Fig. 2). Functionalization of MWNTs with carboxyl groups results in improved chemical reactivity of the surface,
Conclusion
In the present study, the potential of noble metals dispersed on CNTs in generating high energies from even simple bacteria like E. coli has been demonstrated. The idea for the use of novel nanomaterials for electrodes and electron shuttles, capable of boosting the MFC performance has been initiated. Presence of a consortium of bacteria or electrigens like Shewanella putrefaciens, Geobacter sulfurreducens, Rhodoferax ferrireducens, Pseudomonas aeruginosa etc. in place of E. coli may give
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