Fibrous polyaniline@manganese oxide nanocomposites as supercapacitor electrode materials and cathode catalysts for improved power production in microbial fuel cells.

Fibrous Pani-MnO2 nanocomposite were prepared using a one-step and scalable in situ chemical oxidative polymerization method. The formation, structural and morphological properties were investigated using a range of characterization techniques. The electrochemical capacitive behavior of the fibrous Pani-MnO2 nanocomposite was examined by cyclic voltammetry and galvanostatic charge-discharge measurements using a three-electrode experimental setup in an aqueous electrolyte. The fibrous Pani-MnO2 nanocomposite achieved high capacitance (525 F g(-1) at a current density of 2 A g(-1)) and excellent cycling stability of 76.9% after 1000 cycles at 10 A g(-1). Furthermore, the microbial fuel cell constructed with the fibrous Pani-MnO2 cathode catalyst showed an improved power density of 0.0588 W m(-2), which was higher than that of pure Pani and carbon paper, respectively. The improved electrochemical supercapacitive performance and cathode catalyst performance in microbial fuel cells were attributed mainly to the synergistic effect of Pani and MnO2 in fibrous Pani-MnO2, which provides high surface area for the electrode/electrolyte contact as well as electronic conductive channels and exhibits pseudocapacitance behavior.

Metal-Free Carbon-Based Materials: Promising Electrocatalysts for Oxygen Reduction Reaction in Microbial Fuel Cells.

Microbial fuel cells (MFCs) are a promising green approach for wastewater treatment with the simultaneous advantage of energy production. Among the various limiting factors, the cathodic limitation, with respect to performance and cost, is one of the main obstacles to the practical applications of MFCs. Despite the high performance of platinum and other metal-based cathodes, their practical use is limited by their high cost, low stability, and environmental toxicity. Oxygen is the most favorable electron acceptor in the case of MFCs, which reduces to water through a complicated oxygen reduction reaction (ORR). Carbon-based ORR catalysts possessing high surface area and good electrical conductivity improve the ORR kinetics by lowering the cathodic overpotential. Recently, a range of carbon-based materials have attracted attention for their exceptional ORR catalytic activity and high stability. Doping the carbon texture with a heteroatom improved their ORR activity remarkably through the favorable adsorption of oxygen and weaker molecular bonding. This review provides better insight into ORR catalysis for MFCs and the properties, performance, and applicability of various metal-free carbon-based electrocatalysts in MFCs to find the most appropriate cathodic catalyst for the practical applications. The approaches for improvement, key challenges, and future opportunities in this field are also explored.

Positively charged gold nanoparticles synthesized by electrochemically active biofilm--a biogenic approach.

Positively charged gold nanoparticles [(+) AuNPs] of 5-20 nm were synthesized by using electrochemically active biofilm (EAB) formed on a stainless steel mesh, within 30 minutes, in aqueous solution containing HAuCl4 as a precursor and sodium acetate as an electron donor. Electrochemically active bacteria present on biofilm oxidize the sodium acetate by producing electrons. Simultaneously, stainless steel also provides electrons because of the Cl- ions penetration into the stainless steel. Combined effect of both the EAB and stainless steel mesh enhances the availability of electrons for the reduction of Au3+ in the solution, which makes this synthesis efficient and fast. Therefore, small size, positively charged (+32.72 mV), monodispersed, controlled, easy separation and extracellular synthesis of (+) AuNPs makes this protocol highly significant. As-synthesized AuNPs were characterized by UV-vis, DLS, XRD, TEM, HRTEM, EDX and SAED. (+) AuNPs shows remarkable enhancement in the rate of reduction of methyl orange by NaBH4 because of the electron relay effect.

Synthesis of positively charged gold nanoparticles using a stainless-steel mesh.

A novel, rapid, one-pot, and facile approach was developed to synthesize positively charged gold nanoparticles [(+) AuNPs] by employing an aqueous solution of HAuCl4 x 3H2O as a precursor at 30 degrees C and a stainless-steel mesh as a reducing agent. The penetration of Cl- ions into the stainless-steel surface results in corrosion on the stainless-steel surface and excretion of electrons which are used for reduction of Au3+ --> Au0. As a result, (+) AuNPs 5-20 nm in size, mostly monodispersed, were synthesized within 3 h. The as-synthesized AuNPs were charaterized by UV-vis, DLS, XRD, TEM, HR-TEM, EDX and SAED. The utilization of non-toxic chemicals and easily available materials, and the non-requirement of energy input, make this methodology easy, inexpensive, and efficient. The new findings about the role of the stainless-steel mesh, which provides electrons in the presence of Cl- ions, for the reduction of Au3+ --> Au0, makes it a novel material for (+) AuNPs synthesis.

The removal of 1,4-dioxane from polyester manufacturing process wastewater using an up-flow Biological Aerated Filter (UBAF) packed with tire chips.

1,4-Dioxane is one of the by-products from the polyester manufacturing process, which has been carelessly discharged into water bodies and is a weak human carcinogen. In this study, a laboratory-scale, up-flow biological aerated filter (UBAF), packed with tire chips, was investigated for the treatment of 1,4-dioxane. The UBAF was fed with effluent, containing an average of 31 mg/L of 1,4-dioxane, discharged from an anaerobic treatment unit at H Co. in the Gumi Industrial Complex, South Korea. In the batch, a maximum of 99.5 % 1,4-dioxane was removed from an influent containing 25.6 mg/L. In the continuous mode, the optimal empty bed contact time (EBCT) and air to liquid flow rate (A:L) were 8.5 hours and 30:1, respectively. It was also found that the removal efficiency of 1,4-dioxane increased with increasing loading rate within the range 0.04 to 0.31 kg 1,4-dioxane/m(3)·day. However, as the COD:1,4-dioxane ratio was increased within the range 3 to 46 (mg/L COD)/(mg/L 1,4-dioxane), the removal efficiency unexpectedly decreased.

The Contribution Ratio of Autotrophic and Heterotrophic Metabolism during a Mixotrophic Culture of Chlorella sorokiniana.

The contribution ratio of autotrophic and heterotrophic metabolism in the mixotrophic culture of Chlorella sorokiniana (C. sorokiniana) was investigated. At the early stage of mixotrophic growth (day 0-1), autotrophy contributed over 70% of the total metabolism; however, heterotrophy contributed more than autotrophy after day 1 due to the rapid increase in cell density, which had a shading effect in the photo-bioreactor. Heterotrophy continued to have a higher contribution until the available organic carbon was depleted at which point autotrophy became dominant again. Overall, the increase in algal biomass and light conditions in the photo-bioreactor are important factors in determining the contribution of autotrophy and heterotrophy during a mixotrophic culture.

Environmental factors affecting indole production in Escherichia coli.

A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole as an intercellular signal in microbial communities. Biosynthesis of indole is well-studied, and while carbon sources and amino acids are important environmental cues for indole production in Escherichia coli, other environmental factors affecting indole production for this strain are less clear. This study demonstrates that the environmental cue pH is an important factor for indole production that further controls biofilm formation of E. coli. Moreover, E. coli produced a higher level of extracellular indole in the presence of the antibiotics ampicillin and kanamycin, and the increased indole enhanced cell survival during antibiotic stress. Additionally, we found here that temperature is another important factor for indole production; E. coli produces and accumulates a large amount of indole at 50 °C, even at low cell densities. Overall, our results suggest that indole is a stable biological compound, and E. coli may utilize indole to protect itself against other microorganisms.