Search

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. [ABSTRACT FROM AUTHOR]

This paper reports the synthesis of mesoporous polyaniline-titanium dioxide (Pani-TiO2) nanocomposites via a one pot approach in the presence of aniline and titanium iso-propoxide precursor under ice bath conditions. Scanning and transmission electron microscopy showed that the Pani-TiO2 was mesoporous in nature. BET analysis revealed the Pani-TiO2 to have a 2-fold higher surface area than Pani. The shift of the peaks in the FTIR and XRD pattern showed that TiO2 had perfectly intercalated into the Pani matrix, which suggests a strong interaction between Pani and TiO2. The electrochemical properties of Pani and the mesoporous Pani-TiO2 were examined by cyclic voltammetry and charge/discharge studies. The mesoporous Pani-TiO2 electrode exhibited a high specific capacitance of 935 F g-1 at 1 A g-1 current density. The mesoporous Pani-TiO2 displayed excellent cyclic stability up to 2000 cycles and delivered a high energy density of 94.8 Wh kg-1 at a 977 W kg-1 power density. [ABSTRACT FROM AUTHOR]

Two lineages of enterohemorrhagic Escherichia coli O157:H7 (EDL933, Stx1 and Stx2) and 86-24 (Stx2) were investigated to determine the genetic basis of biofilm formation on abiotic surfaces. Strain EDL933 formed a robust biofilm while strain 86-24 formed almost no biofilm on either polystyrene plates or polyethylene tubes. Whole-transcriptome profiles of EDL933 versus 86-24 revealed that in the strong biofilm-forming strain, genes involved in curli biosynthesis and cellulose production were significantly induced, whereas genes involved in indole signaling were most repressed. Additionally, 49 phage genes were highly induced and repressed between the two strains. Curli assays using Congo red plates and scanning electron microscopy corroborated the microarray data as the EDL933 strain produced a large amount of curli, while strain 86-24 formed much less curli. Moreover, EDL933 produced 19-fold more cellulose than 86-24, and indole production in EDL933 was two times lower than that of the strain 86-24. Therefore, it appears E. coli O157:H7 EDL933 produces more biofilm because of its increased curli and cellulose production and reduced indole production. [ABSTRACT FROM AUTHOR]

Background: Bacteria use diverse signaling molecules to ensure the survival of the species in environmental niches. A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole that functions as an intercellular signal controlling diverse aspects of bacterial physiology. Results: In this study, we sought a novel role of indole in a Gram-positive bacteria Paenibacillus alvei that can produce extracellular indole at a concentration of up to 300 μM in the stationary phase in Luria-Bertani medium. Unlike previous studies, our data show that the production of indole in P. alvei is strictly controlled by catabolite repression since the addition of glucose and glycerol completely turns off the indole production. The addition of exogenous indole markedly inhibits the heat resistance of P. alvei without affecting cell growth. Observation of cell morphology with electron microscopy shows that indole inhibits the development of spore coats and cortex in P. alvei. As a result of the immature spore formation of P. alvei, indole also decreases P. alvei survival when exposed to antibiotics, low pH, and ethanol. Additionally, indole derivatives also influence the heat resistance; for example, a plant auxin, 3-indolylacetonitrile dramatically (2900-fold) decreased the heat resistance of P. alvei, while another auxin 3-indoleacetic acid had a less significant influence on the heat resistance of P. alvei. Conclusions: Together, our results demonstrate that indole and plant auxin 3-indolylacetonitrile inhibit spore maturation of P. alvei and that 3-indolylacetonitrile presents an opportunity for the control of heat and antimicrobial resistant spores of Gram-positive bacteria. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are a potential sustainable energy resource by converting organic pollutants in wastewater to clean energy. The performance of MFCs is influenced directly by the electrode material. In this study, a ternary PANI-TiO2-GN nanocomposite was used successfully to improve the performance of both the cathode and anode MFC. The PANI-TiO2-GN catalyst exhibited better oxygen reduction reaction activity in the cathode, particularly as a superior catalyst for improved extracellular electron transfer to the anode. This behavior was attributed to the good electronic conductivity, long-term stability, and durability of the composite. The immobilization of bacteria and catalyst matrix in the anode facilitated more extracellular electron transfer (EET) to the anode, which further improved the performance of the MFCs. The application of PANI-TiO2-GN as a bifunctional catalyst in both the cathode and anode helped decrease the cost of MFCs, making it more practical. [ABSTRACT FROM AUTHOR]

Citrus are the largest fruit crops grown across the globe. It is one of the most profitable crops in terms of economy as well as popular for nutritional benefits. The most interesting aspect about citrus is the availability of several varieties with attractive colours. Approximately 50 % of citrus remains unconsumed after processing as pith residue, peels and seeds. Direct disposal of these wastes cause serious environmental problems in terms of killing natural flora in the soil because of antibacterial properties of limonene oils. Seepage to underground waters or open water bodies affects water quality and aquatic life, respectively. Citrus waste reuse to obtain value added-phytochemicals and pectin is one of the popular topics in industrial research, food and synthetic chemistry. The present article reviews recent advances in exploring the effects of phytochemical compounds obtained from citrus wastes in view of various health aspects. [ABSTRACT FROM AUTHOR]

Ag@CeO2 nanocomposites were synthesized by a biogenic and green approach using electrochemically active biofilms (EABs) as a reducing tool. The as-synthesized Ag@CeO2 nanocomposites were characterized and used in antimicrobial, visible light photocatalytic and photoelectrode studies. The Ag@CeO2 nanocomposites showed effective and efficient bactericidal activities and survival test against Escherichia coli O157:H7, and Pseudomonas aeruginosa. The as-synthesized Ag@CeO2 nanocomposites also exhibited enhanced visible light photocatalytic degradation of 4-nitrophenol and methylene blue than pure CeO2. A photocatalytic investigation showed that the Ag@CeO2 nanocomposites possessed excellent visible light photocatalytic activities compared to pure CeO2. Electrochemical impedance spectroscopy and photocurrent measurements showed that the as-synthesized Ag@CeO2 nanocomposites exhibited excellent and enhanced responses to visible light irradiation. These results suggest that the AgNPs anchored at CeO2 induced visible light photoactivity by decreasing the recombination of photogenerated electrons and holes, and extending the response of pure CeO2 to visible light. Overall, as-synthesized Ag@CeO2 nanocomposites are smart materials that can be used for a range of applications, such as antimicrobial activity, visible light photocatalysis and photoelectrode. [ABSTRACT FROM AUTHOR]