G. Gnana kumar

Recent advances and challenges in the anode architecture and their modifications for the applications of microbial fuel cells.

Microbial fuel cells (MFC), the ergonomic technology connects the liaison of fuel cell architecture and biological resources. Many viable applications like wastewater treatment, biosensors and bioremediation can be made possible with the help of MFCs. This technology is still at its toddler stage and immense works are still in progress to increase the volumetric energy density of MFCs. The overall performance of MFC depends on the cardinal part of the system; anode. A number of anode materials are currently in research to adjudge the better one in terms of the startup time, power output and durability. A wide range of possibilities are now currently available in the fabrication and modification of anode materials to substantially increase the power performances. This review adumbrates the significant requirements of anodes that are essential to be fulfilled, encompasses the aspiring research efforts which have been devoted so far in the anode modification and fabrication strategies to increase the power output, durability and compatibility of the anode interface with the inoculated microorganisms.

Nanotubular MnO2/graphene oxide composites for the application of open air-breathing cathode microbial fuel cells.

Nanotubular shaped α-MnO2/graphene oxide nanocomposites were synthesized via a simple, cost and time efficient hydrothermal method. The growth of hollow structured MnO2 nanotubes preferentially occurred along the [001] direction as evidenced from the morphological and structural characterizations. The tunnels of α-MnO2 nanotubes easily accommodated the molecular oxygen and exhibited excellent catalytic activity towards the oxygen reduction reaction over the rod structure and was further enhanced with the effective carbon support graphene oxide. The MnO2 nanotubes/graphene oxide nanocomposite modified electrode exhibited a maximum power density of 3359 mW m(-2) which is 7.8 fold higher than that of unmodified electrode and comparable with the Pt/C modified electrode. The microbial fuel cell equipped with MnO2 nanotubes/graphene oxide nanocomposite modified cathode exhibited quick start up and excellent durability over the studied electrodes and is attributed to the high surface area and number of active sites. These findings not only provide the fundamental studies on carbon supported low-dimensional transition-metal oxides but also open up the new possibilities of their applications in green energy devices.

One-pot synthesis of magnetite nanorods/graphene composites and its catalytic activity toward electrochemical detection of dopamine

Magnetite (Fe3O4) nanorods anchored over reduced graphene oxide (rGO) were synthesized through a one-pot synthesis method, where the reduction of GO and in-situ generation of Fe3O4 nanorods occurred concurrently. The average head and tail diameter of Fe3O4 nanorods anchored over the rGO matrix are found to be 32 and 11 nm, respectively, and morphology, structure and diameter of bare Fe3O4 nanorods were not altered even after the composite formation with rGO. The increased structural disorders and decrement in the sp(2) domains stimulated the high electrical conductivity and extended catalytic active sites for the prepared rGO/Fe3O4 nanocomposite. The constructed rGO/Fe3O4/GCE sensor exhibited excellent electrocatalytic activity toward the electrooxidation of dopamine (DA) with a quick response time of 6s, a wide linear range between 0.01 and 100.55 µM, high sensitivity of 3.15 µA µM(-1) cm(-2) and a lower detection limit of 7 nM. Furthermore, the fabricated sensor exhibited a practical applicability in the quantification of DA in urine samples with an excellent recovery rate. The excellent electroanalytical performances and straight-forward, surfactant and template free preparation method construct the rGO/Fe3O4 composite as an extremely promising material for the diagnosis of DA related diseases in biomedical applications.

A facile one-pot green synthesis of reduced graphene oxide and its composites for non-enzymatic hydrogen peroxide sensor applications

A simple, environmental benign, time and cost-efficient green approach has been proposed for the reduction of graphene oxide (GO) and the synthesis of reduced GO (rGO)/mono and bimetallic composites using Azadirachta indica extract. The high crystallinity and face-centred-cubic structure of monometallic silver (Ag) and bimetallic silver–gold (Ag–Au) nanoparticles anchored over rGO were determined from the X-ray diffraction patterns. The functional groups involved in the reduction of GO and metallic precursors were identified by the Fourier transform–infrared spectroscopic technique. The obtained morphological images revealed a homogeneous distribution of spherical shaped Ag/Ag–Au nanoparticles with a narrow size distribution anchored over the rGO sheets. The prepared nanostructures exhibited significant electrocatalytic activities towards the reduction of hydrogen peroxide (H2O2), leading to a non-enzymatic electrochemical sensor with a prompt amperometric response. The non-enzymatic sensor responded linearly (R2 = 0.9970) to the concentration of H2O2 over a range of 0.1 to 5 mM with a low level detection limit of 1 μM.

One-pot green synthesis of reduced graphene oxide (RGO)/Fe3O4 nanocomposites and its catalytic activity toward methylene blue dye degradation.

The reduced graphene oxide (RGO)/Fe3O4 nanocomposites were synthesized through a facile one-pot green synthesis by using solanum trilobatum extract as a reducing agent. Spherical shaped Fe3O4 nanoparticles with the diameter of 18 nm were uniformly anchored over the RGO matrix and the existence of fcc structured Fe3O4 nanoparticles over the RGO matrix was ensured from X-ray diffraction patterns. The amide functional groups exist in the solanum trilobatum extract is directly responsible for the reduction of Fe(3+) ions and GO. The thermal stability of GO was increased by the removal of hydrophilic functional groups via solanum trilobatum extract and was further promoted by the ceramic Fe3O4 nanoparticles. The ID/IG ratio of RGO/Fe3O4 was increased over GO, indicating the extended number of structural defects and disorders in the RGO/Fe3O4 composite. The catalytic efficiency of prepared nanostructures toward methylene blue (MB) dye degradation mediated through the electron transfer process of BH4(-) ions was studied in detail. The π-π stacking, hydrogen bonding and electrostatic interaction exerted between the RGO/Fe3O4 composite and methylene blue, increased the adsorption efficiency of dye molecules and the large surface area and extended number of active sites completely degraded the MB dye within 12 min.

Current status, key challenges and its solutions in the design and development of graphene based ORR catalysts for the microbial fuel cell applications.

Microbial fuel cells (MFC) are considered as the futuristic energy device that generates electricity from the catalytic degradation of biodegradable organic wastes using microbes, which exist in waste water. In MFCs, oxygen serves as a cathodic electron acceptor and oxygen reduction kinetics played a significant role in the determination of overall efficiency. A wide range of strategies have been developed for the preparation and substantial modification of oxygen reduction reaction (ORR) catalysts to improve the maximum volumetric power density of MFCs, in which the efforts on graphene based ORR catalysts are highly imperative. Although numerous research endeavors have been achieved in relation with the graphene based ORR catalysts applicable for MFCs, still their collective summary has not been developed, which hinders the acquirement of adequate knowledge on tuning the specific properties of said catalysts. The intension of this review is to outline the significant role of ORR catalysts, factors influencing the ORR activity, strategies behind the modifications of ORR catalysts and update the research efforts devoted on graphene based ORR catalysts. This review can be considered as a pertinent guide to understand the design and developmental strategies of competent graphene based ORR catalysts, which are not only applicable for MFCs but also for number of electrochemical applications.

Ni–Co alloy nanostructures anchored on mesoporous silica nanoparticles for non-enzymatic glucose sensor applications

Uniform sized Ni–Co alloy nanoparticles were effectively confined over the active channels of mesoporous silica nanoparticles (MSN) using a simple chemical reduction method, and the resultant nanostructures exhibited a spherical configuration with a mean diameter of 5 nm. The face-centered cubic (fcc) crystalline structure of Ni and Ni–Co alloy nanoparticles and the amorphous structure of MSN matrix were identified from the diffraction patterns. The MSN supported catalysts were exploited as electrochemical probes for the detection of glucose, and the controlled morphology, smaller particle size, uniform dispersion and active surface of the Ni–Co alloy nanoparticles improved the excellent electrocatalytic activity of MSN/Ni–Co toward the electrooxidation of glucose. The MSN/Ni–Co nanocomposite exhibited good analytical performance for glucose detection, with a linear response ranging from 0.001 to 5.0 mM, a low detection limit of 0.39 μM and a high sensitivity of 536.62 μA mM−1 cm−2. The results of the performed experiments also demonstrated the good reproducibility, long-term stability and high selectivity of the fabricated sensors without the influence of interference from other oxidizable species, which may represent a technically sound and economical new avenue in non-enzymatic glucose sensor applications.

Graphene Oxide/Carbon Nanotube Composite Hydrogels—Versatile Materials for Microbial Fuel Cell Applications

Carbonaceous nanocomposite hydrogels are prepared with an aid of a suspension polymerization method and are used as anodes in microbial fuel cells (MFCs). (Poly N-Isopropylacrylamide) (PNIPAM) hydrogels filled with electrically conductive carbonaceous nanomaterials exhibit significantly higher MFC efficiencies than the unfilled hydrogel. The observed morphological images clearly show the homogeneous dispersion of carbon nanotubes (CNTs) and graphene oxide (GO) in the PNIPAM matrix. The complex formation of CNTs and GO with NIPAM is evidenced from the structural characterizations. The effectual MFC performances are influenced by combining the materials of interest (GO and CNTs) and are attributed to the high surface area, number of active sites, and improved electron-transfer processes. The obtained higher MFC efficiencies associated with an excellent durability of the prepared hydrogels open up new possibilities for MFC anode applications.

Binder free and free-standing electrospun membrane architecture for sensitive and selective non-enzymatic glucose sensors

Novel free standing and binder free non-enzymatic electrochemical sensors were fabricated using in situ grown copper (Cu) nanoparticles on polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) nanofibers. Morphological images showed that Cu nanoparticles were homogeneously anchored over the PVdF-HFP nanofibers and the elemental composition and structure of the prepared composite nanofiber membranes were identified from elemental analysis and diffraction patterns. The fabricated nanofiber membranes were applied in the quantification of glucose and the non-enzymatic electrooxidation of glucose was facilitated at the surface of Cu nanoparticles that were anchored over the PVdF-HFP nanofibers. The fabricated sensor exhibited the linear range covering from 1 μM to 6.055 mM, high sensitivity of 506.62 μA mM−1 cm−2 and low detection limit of 0.011 μM. Importantly, the PVdF-HFP/Cu membrane exhibited favorable reproducibility, long-term stability, and was relatively insensitive to common interfering species in real time applications. The fabricated electrospun PVdF-HFP/Cu nanofiber membrane offers unique advantages, including simple fabrication, good affinity and selectivity to glucose and quick response, which open up new possibilities for exploring the a variety of electrochemical devices with affordable cost and good stability.

The catalytic activity of titania nanostructures in the synthesis of amides under solvent-free conditions

Different shapes and phases of titania nanostructures with the uniform size distribution were synthesized by hydrothermal sol–gel technique. The influence of annealing temperature on the crystalline character, size and phase of the prepared nanomaterials were evidenced from the diffraction analysis. Infrared spectroscopic analysis ensured the structural confirmation of the sulfated titania nanostructures. Catalytic activity of the synthesized nanometric materials in direct amidation of aromatic and aliphatic carboxylic acids with aromatic amines was evaluated. Among the materials studied, sulfated titania nanotubes with the anatase phase exhibited excellent catalytic activity. The employed solvent-free protocol is greener and eradicates the drawbacks associated with the hazardous solvents employed in the prevailing solution phase methodologies.