One-step electrosynthesis of polypyrrole/graphene oxide composites for microbial fuel cell application

Electroactive biofilm communities in microbial fuel cells for the synergistic treatment of wastewater and bioelectricity generation

Increasing industrialization and urbanization have contributed to a significant rise in wastewater discharge and exerted extensive pressure on the existing natural energy resources. Microbial fuel cell (MFC) is a sustainable technology that utilizes wastewater for electricity generation. MFC comprises a bioelectrochemical system employing electroactive biofilms of several aerobic and anaerobic bacteria, such as Geobacter sulfurreducens, Shewanella oneidensis, Pseudomonas aeruginosa, and Ochrobacterum pseudiintermedium. Since the electroactive biofilms constitute a vital part of the MFC, it is crucial to understand the biofilm-mediated pollutant metabolism and electron transfer mechanisms. Engineering electroactive biofilm communities for improved biofilm formation and extracellular polymeric substances (EPS) secretion can positively impact the bioelectrochemical system and improve fuel cell performance. This review article summarizes the role of electroactive bacterial communities in MFC for wastewater treatment and bioelectricity generation. A significant focus has been laid on understanding the composition, structure, and function of electroactive biofilms in MFC. Various electron transport mechanisms, including direct electron transfer (DET), indirect electron transfer (IET), and long-distance electron transfer (LDET), have been discussed. A detailed summary of the optimization of process parameters and genetic engineering strategies for improving the performance of MFC has been provided. Lastly, the applications of MFC for wastewater treatment, bioelectricity generation, and biosensor development have been reviewed.

Preparation of polypyrrole/titanium nitride composite modified biochar and its application research in microbial fuel cells

In this study, the in situ growth method was employed to modify biochar with polypyrrole-titanium (PPy-TiN) nitride composites, aiming to enhance its performance as an anode material in microbial fuel cells (MFCs). A series of characterizations were conducted on the polypyrrole-modified corn straw biochar anode (PPy/CS), titanium nitride-modified corn straw biochar anode (TiN/CS), and polypyrrole/titanium nitride composite-modified biochar anode (PPy-TiN/CS) to evaluate the feasibility of the modification method and identify the optimal modification scheme. Characterization techniques included scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), and Tafel analysis. SEM and FTIR analyses confirmed the successful integration of polypyrrole and titanium nitride with biochar, achieving a minimum solution resistance of 7.80 Ω and charge transfer resistance of 1.79 Ω. Compared to the unmodified electrode, the modified electrodes demonstrated improved performance, highlighting the need for the development of cost-effective, efficient, and durable anode materials.

Recent advances in the role of biocatalyst in biofuel cells and its application: An overview

Biofuel cells have recently gained popularity as a green and renewable energy source. Biofuel cells are unique devices of energy and are capable of converting the stored chemical energy from waste materials such as pollutants, organics and wastewater into reliable, renewable, pollution-free energy sources through the action of biocatalysts such as various microorganisms and enzymes. It is a promising technological device to treat waste to compensate for global warming and the energy crisis through the green energy production process. Due to their unique properties, various potential biocatalysts are attracting researchers to apply them to various microbial biofuel cells for improving electricity and power. Recent research in biofuel cells is focusing on the exploitation of different biocatalysts and how they are enhancing power generation for various applications in the field of environmental technology, and biomedical fields such as implantable devices, testing kits, and biosensors. This review focusing the importance of microbial fuel cells (MFCs) and enzymatic fuel cells (ECFs) and role of different types of biocatalysts and their mechanisms for improving biofuel cell efficiency gathered from recent reports. Finally, its multifaceted applications with special emphasis on environmental technology and biomedical field will be described, along with future perspectives.

Advances in bioelectrochemical systems for bio-products recovery

Bioelectrochemical systems (BES) have emerged as a sustainable and highly promising technology that has garnered significant attention from researchers worldwide. These systems provide an efficient platform for the removal and recovery of valuable products from wastewater, with minimal or no net energy loss. Among the various types of BES, microbial fuel cells (MFCs) are a notable example, utilizing microbial biocatalytic activities to generate electrical energy through the degradation of organic matter. Other BES variants include microbial desalination cells (MDCs), microbial electrolysis cells (MECs), microbial electrosynthesis cells (MXCs), microbial solar cells (MSCs), and more. BESs have demonstrated remarkable potential in the recovery of diverse products such as hydrogen, methane, volatile fatty acids, precious nutrients, and metals. Recent advancements in scaling up BESs have facilitated a more realistic assessment of their net energy recovery and resource yield in real-world applications. This comprehensive review focuses on the practical applications of BESs, from laboratory-scale developments to their potential for industrial commercialization. Specifically, it highlights successful examples of value-added product recovery achieved through various BES configurations. Additionally, this review critically evaluates the limitations of BESs and provides suggestions to enhance their performance at a larger scale, enabling effective implementation in real-world scenarios. By providing a thorough analysis of the current state of BES technology, this review aims to emphasize the tremendous potential of these systems for sustainable wastewater treatment and resource recovery. It underscores the significance of bridging the gap between laboratory-scale achievements and industrial implementation, paving the way for a more sustainable and resource-efficient future.

Insights into properties, synthesis and emerging applications of polypyrrole-based composites, and future prospective: A review

Recent advancements in polymer science and engineering underscore the importance of creating sophisticated soft materials characterized by well-defined structures and adaptable properties to meet the demands of emerging applications. The primary objective of polymeric composite technology is to enhance the functional utility of materials for high-end purposes. Both the inherent qualities of the materials and the intricacies of the synthesis process play pivotal roles in advancing their properties and expanding their potential applications. Polypyrrole (PPy)-based composites, owing to their distinctive properties, hold great appeal for a variety of applications. Despite the limitations of PPy in its pure form, these constraints can be effectively overcome through hybridization with other materials. This comprehensive review thoroughly explores the existing literature on PPy and PPy-based composites, providing in-depth insights into their synthesis, properties, and applications. Special attention is given to the advantages of intrinsically conducting polymers (ICPs) and PPy in comparison to other ICPs. The impact of doping anions, additives, and oxidants on the properties of PPy is also thoroughly examined. By delving into these aspects, this overview aims to inspire researchers to delve into the realm of PPy-based composites, encouraging them to explore new avenues for flexible technology applications.

Graphene Nanocomposites as Innovative Materials for Energy Storage and Conversion-Design and Headways

This review mainly addresses applications of polymer/graphene nanocomposites in certain significant energy storage and conversion devices such as supercapacitors, Li-ion batteries, and fuel cells. Graphene has achieved an indispensable position among carbon nanomaterials owing to its inimitable structure and features. Graphene and its nanocomposites have been recognized for providing a high surface area, electron conductivity, capacitance, energy density, charge-discharge, cyclic stability, power conversion efficiency, and other advanced features in efficient energy devices. Furthermore, graphene-containing nanocomposites have superior microstructure, mechanical robustness, and heat constancy characteristics. Thus, this state-of-the-art article offers comprehensive coverage on designing, processing, and applying graphene-based nanoarchitectures in high-performance energy storage and conversion devices. Despite the essential features of graphene-derived nanocomposites, several challenges need to be overcome to attain advanced device performance.

Putting the electro-bugs to work: A systematic review of 22 years of advances in bio-electrochemical systems and the parameters governing their performance

Wastewater treatment using bioelectrochemical systems (BESs) can be considered as a technology finding application in versatile areas such as for renewable energy production and simultaneous reducing environmental problems, biosensors, and bioelectrosynthesis. This review paper reports and critically discusses the challenges, and advances in bio-electrochemical studies in the 21st century. To sum and critically analyze the strides of the last 20+ years on the topic, this study first provides a comprehensive analysis on the structure, performance, and application of BESs, which include Microbial Fuel Cells (MFCs), Microbial Electrolysis Cells (MECs) and Microbial Desalination Cells (MDCs). We focus on the effect of various parameters, such as electroactive microbial community structure, electrode material, configuration of bioreactors, anode unit volume, membrane type, initial COD, co-substrates and the nature of the input wastewater in treatment process and the amount of energy and fuel production, with the purpose of showcasing the modes of operation as a guide for future studies. The results of this review show that the BES have great potential in reducing environmental pollution, purifying saltwater, and producing energy and fuel. At a larger scale, it aspires to facilitate the path of achieving sustainable development and practical application of BES in real-world scenarios.

A novel and ultrasensitive electrochemical DNA biosensor for pralatrexate detection

An attempt was made to develop a new sensitive biosensor for pralatrexate, as an anticancer drug, based on its interaction with the guanine of fish sperm DNA anchored on a screen-printed electrode (SPE) modified with polypyrrole (PP)/octahedral Pd-doped Co₃O₄ composite (Oh-Pd-doped Co₃O₄ C). Electrochemical techniques like differential pulse voltammetry verified the mechanism of such an interaction on the dsDNA/PP/Oh-Pd-doped Co₃O₄ C/SPE surface. A reduction in the peak current of guanine oxidation elucidated the interaction in acetate buffer with pH = 4.8. The optimization of response was performed for the interaction method according to potential, accumulation time, reproducibility and drug content. The linear dynamic range was estimated at 1.0 nM to 150.0 μM as well as a limit of detection as low as 0.61 nM for the DNA and pralatrexate concentrations. The practical potential of the proposed sensor was verified by determining pralatrexate in its pharmaceutical matrices.

A light-enhanced α-FeOOH nanowires/polyaniline anode for improved electricity generation performance in microbial fuel cells

Low power density and poor anode performance seriously limit the potential of practical application of microbial fuel cell (MFC). Utilizing solar energy by developing photoanode is one of the effective pathways to improve the performance of MFC. Here solar energy harvesting was integrated into MFC to achieved the comprehensive utilization of multiple energy sources. A hybrid MFC photoanode (α-FeOOH-NWs/PANI anode) was constructed by loading polyaniline (PANI) and α-FeOOH nanowires (α-FeOOH-NWs) on carbon paper through electro-polymerization synthesis method. Compared with clean carbon paper, nanowires and PANI increased the surface roughness of the electrode, which facilitated the biofilm formation. The electrochemical and photoelectric analysis demonstrated that PANI introduced new electroactive groups and reduced the charge transfer resistance, exhibiting excellent electrochemical and photoelectric activites. The MFC with the α-FeOOH-NWs/PANI photoanode had higher voltage output and power density under light illumination, with the power density of 1.95 W/m² under light, which was 1.4 times higher than that without light. The hybrid α-FeOOH-NWs/PANI photoanode enhanced the separation efficiency of photogenerated electron-hole pairs, thereby improving the photoelectric response capability and generating a high photocurrent. Our research provided a new concept for the combination of solar energy harvesting and MFCs, yielding an overall enhancement of electricity eneration performance in MFC.

A review on graphene / graphene oxide supported electrodes for microbial fuel cell applications: Challenges and prospects

Microbial Fuel Cell (MFC) has gained great interest as an alternative green technology for bioenergy generation along with reduced sludge production, nutrient recovery, removal of COD and color, etc. during wastewater treatment. However, the MFC has several challenges for real-time applications due to less power output and high ohmic resistance and fabrication (electrode and membrane) cost. Several kinds of research have been carried out to increase energy production by reducing various losses associated with electrodes in the MFC. Though, carbonaceous electrodes (carbon and graphite) are the key materials for the anode and cathode side, since these have a higher surface area, good biocompatibility, low cost, and good mechanical strength. Graphene or graphene oxide-based nanocomposite can be an ideal substitute for electrode modifications and an alternative for an expensive anode and cathode catalyst in MFC. Graphene oxide synthesis from waste material such as waste biomass, agricultural, plastic waste, etc. is added advantages of minimizing the cost of the electrodes. But, the synthesis of graphene is quite expensive and has limitations in economic feasibility for bioelectricity production in MFC. Hence, the present review deals with the anode and cathode electrode modification with graphene-based nanocomposites, synthesis of graphene/graphene oxide from various raw materials, and its application in MFC. The current challenges and future outlook on graphene-based composites on MFC performance are also discussed.

Current Progress of Interfacing Organic Semiconducting Materials with Bacteria

Microbial bioelectronics require interfacing microorganisms with electrodes. The resulting abiotic/biotic platforms provide the basis of a range of technologies, including energy conversion and diagnostic assays. Organic semiconductors (OSCs) provide a unique strategy to modulate the interfaces between microbial systems and external electrodes, thereby improving the performance of these incipient technologies. In this review, we explore recent progress in the field on how OSCs, and related materials capable of charge transport, are being used within the context of microbial systems, and more specifically bacteria. We begin by examining the electrochemical communication modes in bacteria and the biological basis for charge transport. Different types of synthetic organic materials that have been designed and synthesized for interfacing and interrogating bacteria are discussed next, followed by the most commonly used characterization techniques for evaluating transport in microbial, synthetic, and hybrid systems. A range of applications is subsequently examined, including biological sensors and energy conversion systems. The review concludes by summarizing what has been accomplished so far and suggests future design approaches for OSC bioelectronics materials and technologies that hybridize characteristic properties of microbial and OSC systems.

A sustainable approach towards utilization of plastic waste for an efficient electrode in microbial fuel cell applications

Microbial fuel cells (MFC) are a novel technique for power generation from wastewater. A number of approaches for the modification of physical as well as chemical properties of the electrodes can be employed to attain the maximum output power density and high power electricity. The use of an active organic linker, extracted from waste residue (plastic), for the synthesis of porous nanostructured materials would be beneficial in the fabrication of electrodes for MFC. Herein, terephthalic acid monomer (t) derived from plastic waste was successfully applied as an electrochemically active linking unit to form an iron-based metal-organic framework (Fe-t-MOF: MIL-53(Fe)). The synthesized Fe-t-MOF was further modified with conducting polymer (polyaniline (PANI)). The produced nanocomposite (Fe-t-MOF/PANI) was coated on stainless steel (SS) disk (as a current collector) for use as an electrode component of the MFC system. The power density, open circuit potential (OCP), and a limiting current density of the MFC are 680 mW/m², 0.67 V, and 3500mA/m², respectively. The technique opted here should help search a novel, efficient, sustainable, and cost-effective route for the modification of the plastic waste into an MFC electrode to achieve bioenergy production through wastewater treatment.

Carbon-Based Composites as Anodes for Microbial Fuel Cells: Recent Advances and Challenges

Owing to the low price, chemical stability and good conductivity, carbon-based materials have been extensively applied as the anode in microbial fuel cells (MFCs). In this review, apart from the charge storage mechanism and anode requirements, the major work focuses on five categories of carbon-based anode materials (traditional carbon, porous carbon, nano-carbon, metal/carbon composite and polymer/carbon composite). The relationship is demonstrated in depth between the physicochemical properties of the anode surface/interface/bulk (porosity, surface area, hydrophilicity, partical size, charge, roughness, etc.) and the bioelectrochemical performances (electron transfer, electrolyte diffusion, capacitance, toxicity, start-up time, current, power density, voltage, etc.). An outlook for future work is also proposed.

Nanocomposite Materials Based on Electrochemically Synthesized Graphene Polymers: Molecular Architecture Strategies for Sensor Applications

The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors.

Graphene family for hydrogen peroxide production in electrochemical system

The development of carbon-based materials to catalyze two-electron (2e^-) pathway of oxygen reduction reaction (ORR) offers great potential for hydrogen peroxide (H₂O₂) production. As a class of novel two-dimensional (2D) carbon materials, graphene and its derivatives have raised increasing attention as excellent noble-metal-free catalysts in 2e ORR due to their unique structure, physical and chemical properties. This review focuses on the synthesis of main graphene family members and graphene based electrodes, as well as their applications for H₂O₂ generation in electrochemical systems. We describe the functions of the graphene family in electrochemical systems, such as accelerating electron transfer and increasing oxygen transfer for cathodes in electrochemical systems, aiming to reveal the enhancement mechanisms of graphene and its derivatives on H₂O₂ production. Furthermore, the challenges and prospects for graphene family used as catalyst for H₂O₂ production in the future are also proposed.

Electrodeposited Hybrid Biocathode-Based CO2 Reduction via Microbial Electro-Catalysis to Biofuels

Microbial electrosynthesis is a new approach to converting C1 carbon (CO₂) to more complex carbon-based products. In the present study, CO₂, a potential greenhouse gas, was used as a sole carbon source and reduced to value-added chemicals (acetate, ethanol) with the help of bioelectrochemical reduction in microbial electrosynthesis systems (MES). The performance of MES was studied with varying electrode materials (carbon felt, stainless steel, and cobalt electrodeposited carbon felt). The MES performance was assessed in terms of acetic acid and ethanol production with the help of gas chromatography (GC). The electrochemical characterization of the system was analyzed with chronoamperometry and cyclic voltammetry. The study revealed that the MES operated with hybrid cobalt electrodeposited carbon felt electrode yielded the highest acetic acid (4.4 g/L) concentration followed by carbon felt/stainless steel (3.7 g/L), plain carbon felt (2.2 g/L), and stainless steel (1.87 g/L). The alcohol concentration was also observed to be highest for the hybrid electrode (carbon felt/stainless steel/cobalt oxide is 0.352 g/L) as compared to the bare electrodes (carbon felt is 0.22 g/L) tested, which was found to be in correspondence with the pH changes in the system. Electrochemical analysis revealed improved electrotrophy in the hybrid electrode, as confirmed by the increased redox current for the hybrid electrode as compared to plain electrodes. Cyclic voltammetry analysis also confirmed the role of the biocatalyst developed on the electrode in CO₂ sequestration.

Customizable design strategies for high-performance bioanodes in bioelectrochemical systems

Bioelectrochemical systems (BESs) can fulfill the demand for renewable energy and wastewater treatment but still face significant challenges to improve their overall performance. Core efforts have been made to enhance the bioelectrode performance, yet, previous approaches are fragmented and have limited applicability, unable to flexibly adjust physicochemical and structural properties of electrodes for specific requirements in various applications. Here, we propose a facile electrode design strategy that integrates three-dimensional printing technology and functionalized modular electrode materials. A customized graphene-based electrode with hierarchical pores and functionalized components (i.e., ferric ions and magnetite nanoparticles) was fabricated. Owing to efficient mass and electron transfer, a high volumetric current density of 10,608 ± 1,036 A/m³ was achieved, the highest volumetric current density with pure Geobacter sulfurreducens to date. This strategy can be readily applied to existing BESs (e.g., microbial fuel cells and microbial electrosynthesis) and provide a feasibility for practical application.

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A 3D-printed graphene aerogel electrode was proposed for BESs

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The optimized electrode mass transfer resistance was less than 5% of carbon felt

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A high volumetric current density of 10,608 ± 1,036 A/m³ was achieved

Advanced microbial fuel cell for waste water treatment-a review

Petroleum, coal, and natural gas reservoir were depleting continuously due to an increase in industrialization, which enforced study to identify alternative sources. The next option is the renewable resources which are most important for energy purpose coupled with environmental problem reduction. Microbial fuel cells (MFCs) have become a promising approach to generate cleaner and more sustainable electrical energy. The involvement of various disciplines had been contributing to enhancing the performance of the MFCs. This review covers the performance of MFC along with different wastewater as a substrate in terms of treatment efficiencies as well as for energy generation. Apart from this, effect of various parameters and use of different nanomaterials for performance of MFC were also studied. From the current study, it proves that the use of microbial fuel cell along with the use of nanomaterials could be the waste and energy-related problem-solving approach. MFC could be better in performances based on optimized process parameters for handling any wastewater from industrial process.

Recent progress of graphene based nanomaterials in bioelectrochemical systems

The application of graphene (Gr) to microbial fuel cells (MFCs) and microbial electrolysis cell (MECs) is considered a very promising approach in terms of enhancing their performance. The superior Gr properties of high electrical and thermal conductivities, along with: superior specific surface area, high electron mobility, and mechanical strength, are the key features that endorse this. Factors impeding the advancement of a microbial fuel cell into commercialization involve primarily the cost of their components, and their production on a small scale. Gr with such outstanding characteristics can help mitigate these challenges, when used as electrode material. The application of Gr as an anode material improves the efficiency of electron transfer and bacterial attachment. When used as a cathode material, it supports the oxygen reduction reaction. This investigation, presents a thorough analysis of the feasibility of Gr as an electrode material in both MFC and MEC applications - based on experimental results from the investigation. Current technological advancements in the implementation of Gr in MFC and MEC are also highlighted in this review. To summarise, the investigation exposes critical issues impeding the advancement of microbial fuel cells, and proposes possible solutions to mitigate these challenges.

Ice-interface assisted large-scale preparation of polypyrrole/graphene oxide films for all-solid-state supercapacitors

In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. The morphology, chemical structure and electrochemical property were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS), respectively. The lamellar structure of GO and both strong interaction with ice and pyrrole could promote polymerization of pyrrole and improve the compactness of the film. With the aid of GO, the conjugation length of PPy increased, the resistance of the material decreased, and the electrochemical energy storage of the composite film was significantly enhanced. In the case of 2.5 wt% GO, the prepared PPy/GO nanocomposite supercapacitor exhibited a high area specific capacitance of 97.3 mF cm^-2 at 1 mA cm^-2. Furthermore, the PPy/GO film supercapacitor also showed excellent cycling stability and good flexibility.

Improved Simultaneous Decolorization and Power Generation in a Microbial Fuel Cell with the Sponge Anode Modified by Polyaniline and Chitosan

In recent years, microbial fuel cell (MFC) has been regarded as a promising technology for dye wastewater treatment. Compared with traditional anaerobic reactors, MFC has better decolorization effect while producing electricity simultaneously. In this paper, a double-chamber MFC with the sponge anode modified by polyaniline and chitosan-NCNTs was employed for simultaneous azo dye decolorization and bioelectricity generation. The influence of dye concentration, co-substrate concentration, and operating temperature on the performance of MFC with the modified anodes were studied. The results showed that a high decolorization efficiency (98.41%) and maximum power density (2816.67 mW m^-3) of MFC equipped with modified bioanodes were achieved due to the biocompatibility and bioelectrocatalysis of modified material. And the biomass on the modified anode's surface was increased by 1.47 times. Additionally, microbial community analysis revealed that the modification of polyaniline and chitosan-NCNTs improved the selective enrichment of specific communities and the main microorganism was the electroactive and decolorizing bacteria Enterobacter (62.84%). Therefore, the composite anode is capable of fully utilizing the synergistic role of various materials, leading to superior performance of dye decolorization in MFCs. This work provided a strategy for the research on the recovery of biomass energy and decolorization in wastewater treatment. Graphical Abstract.

Recent Advances in Anodes for Microbial Fuel Cells: An Overview

The recycling and treatment of wastewater using microbial fuel cells (MFCs) has been attracting significant attention as a way to control energy crises and water pollution simultaneously. Despite all efforts, MFCs are unable to produce high energy or efficiently treat pollutants due to several issues, one being the anode's material. The anode is one of the most important parts of an MFC. Recently, different types of anode materials have been developed to improve the removal rate of pollutants and the efficiency of energy production. In MFCs, carbon-based materials have been employed as the most commonly preferred anode material. An extensive range of potentials are presently available for use in the fabrication of anode materials and can considerably minimize the current challenges, such as the need for high quality materials and their costs. The fabrication of an anode using biomass waste is an ideal approach to address the present issues and increase the working efficiency of MFCs. Furthermore, the current challenges and future perspectives of anode materials are briefly discussed.

Kinetics and mechanisms of oxytetracycline degradation in an electro-Fenton system with a modified graphite felt cathode

The removal of trace antibiotics from the aquatic environment has received great interest. In this investigation, NaOH activated graphite felt (NaOH-GF) was characterized by multiple-methods, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle, linear sweep voltammetry (LSV) and electron paramagnetic resonance (EPR). The NaOH-GF was then used as the cathode in the electro-Fenton process for oxytetracycline (OTC) degradation, the experiment was carried out in an undivided and light-proof beaker with a Pt anode and a NaOH-GF cathode at pH 3. The results showed that the modification with NaOH enhanced the antibiotics degradation efficiency of graphite felt by increasing the oxygen reduction capacity and hydroxyl radicals yielding rate. Complete OTC removal was achieved at 5.17 mA cm^-2 after 40, 60 and 90 s with initial OTC concentration of 22, 44, and 66 μM, respectively. With an initial OTC concentration of 44 μM, after 30 min the removal rates of chemical oxygen demand (COD) by Raw-GF and NaOH-GF were 59.18% and 83.75%, respectively. The proposed degradation mechanism of OTC was an EF process, which consisted of hydroxylation, secondary alcohol oxidation, demethylation, decarbonylation, dehydration and deamination. This study demonstrates that NaOH activated GF cathode possesses high degradation capacity and good stability. It provides insight into the removal of non-biodegradable antibiotics and may shed light on future to its practical application.

Gold nanoparticle decorated polypyrrole/graphene oxide nanosheets as a modified electrode for simultaneous determination of ascorbic acid, dopamine and uric acid

AuNPs, GO and PPy are combined effectively to form a novel composite showing a huge enhancement in electrochemical performance compared to the single materials.

Simultaneous determination of dihydroxybenzene isomers using a three-dimensional over-oxidized polypyrrole–reduced graphene oxide composite film electrode prepared by an electrochemical method

A 3D-over-oxidized polypyrrole–reduced graphene oxide composite film was prepared by an electrochemical procedure, which showed high electrochemical activity and good selectivity for simultaneous determination of dihydroxybenzene isomers.

A visual approach for analysis and inference of molecular activity spaces

BACKGROUND

Molecular space visualization can help to explore the diversity of large heterogeneous chemical data, which ultimately may increase the understanding of structure-activity relationships (SAR) in drug discovery projects. Visual SAR analysis can therefore be useful for library design, chemical classification for their biological evaluation and virtual screening for the selection of compounds for synthesis or in vitro testing. As such, computational approaches for molecular space visualization have become an important issue in cheminformatics research. The proposed approach uses molecular similarity as the sole input for computing a probabilistic surface of molecular activity (PSMA). This similarity matrix is transformed in 2D using different dimension reduction algorithms (Principal Coordinates Analysis ( PCooA), Kruskal multidimensional scaling, Sammon mapping and t-SNE). From this projection, a kernel density function is applied to compute the probability of activity for each coordinate in the new projected space.

RESULTS

This methodology was tested over four different quantitative structure-activity relationship (QSAR) binary classification data sets and the PSMAs were computed for each. The generated maps showed internal consistency with active molecules grouped together for all data sets and all dimensionality reduction algorithms. To validate the quality of the generated maps, the 2D coordinates of test molecules were computed into the new reference space using a data transformation matrix. In total sixteen PSMAs were built, and their performance was assessed using the Area Under Curve (AUC) and the Matthews Coefficient Correlation (MCC). For the best projections for each data set, AUC testing results ranged from 0.87 to 0.98 and the MCC scores ranged from 0.33 to 0.77, suggesting this methodology can validly capture the complexities of the molecular activity space. All four mapping functions provided generally good results yet the overall performance of PCooA and t-SNE was slightly better than Sammon mapping and Kruskal multidimensional scaling.

CONCLUSIONS

Our result showed that by using an appropriate combination of metric space representation and dimensionality reduction applied over metric spaces it is possible to produce a visual PSMA for which its consistency has been validated by using this map as a classification model. The produced maps can be used as prediction tools as it is simple to project any molecule into this new reference space as long as the similarities to the molecules used to compute the initial similarity matrix can be computed.

Recent Advances in Stretchable Supercapacitors Enabled by Low-Dimensional Nanomaterials

Supercapacitors (SCs) have shown great potential for mobile energy storage technology owing to their long-term durability, electrochemical stability, structural simplicity, as well as exceptional power density without much compromise in the energy density and cycle life parameters. As a result, stretchable SC devices have been incorporated in a variety of emerging electronics applications ranging from wearable electronic textiles to microrobots to integrated energy systems. In this review, the recent progress and achievements in the field of stretchable SCs enabled by low-dimensional nanomaterials such as polypyrrole, carbon nanotubes, and graphene are presented. First, the three major categories of stretchable supercapacitors are discussed: double-layer supercapacitors, pseudo-supercapacitors, and hybrid supercapacitors. Then, the representative progress in developing stretchable electrodes with low-dimensional (0D, 1D, and 2D) nanomaterials is described. Next, the design strategies enabling the stretchability of the devices, including the wavy-shape design, wire-shape design, textile-shape design, kirigami-shape design, origami-shape design, and serpentine bridge-island design are emphasized, with the aim of improving the electrochemical performance under the complex stretchability conditions that may be encountered in practical applications. Finally, the newest developments, major challenges, and outlook in the field of stretchable SC development and manufacturing are discussed.

One-step electrochemically synthesized graphene oxide coated on polypyrrole nanowires as anode for microbial fuel cell

A novel polypyrrole nanowires coated by graphene oxide (PPy-NWs/GO) has been successfully synthesized by one-step electrochemical method, whose structure was different from previously reported PPy/GO composites. The microbial fuel cell equipped with PPy-NWs/GO as anode was fabricated and compared with PPy-NWs ones. The SEM images show that the synthesized PPy-NWs/GO materials possess more surface areas than PPy-NWs. The electrochemical analysis indicated that PPy-NWs/GO anode had lower charge transfer resistance, which may be attributed to synergistic effect of them. The MFC equipped with PPy-NWs/GO anode have higher circle voltages and the power density is about 22.3 mW/m², which is great higher than that of PPy-NWs about 15.9 mW/m². These improvements of the MFCs may be due to more bacteria on the larger biofilms based on GO nanosheets, indicating that the PPy-NWs/GO is more effective anode for improving electricity generation.

High-performance microbial fuel cell anodes obtained from sewage sludge mixed with fly ash

Microbial fuel cells (MFCs) are promising for converting biomass energy into electricity, and have attracted much research interest. However, few inexpensive high-performance anode materials for MFCs exist. In this study, MFC anodes composed of sewage sludge and different contents of fly ash (0%, 20%, 40%, 60%, and 80%) are fabricated via a one-step carbonization method. The maximum current density of 25.5 A m^-2 is achieved using the electrode with 20% fly ash, which is 37.5% higher than that of the electrode without fly ash. The improved anode performance is attributed to its good hydrophilicity, which is indicated by its water contact angle of less than 60°, facile adsorption of exoelectrogens, low electron transfer resistance, and good biocompatibility. In addition, the mechanical strength of the electrode with 20% fly ash is approximately 18 times that of the electrode without fly ash. This study reveals a promising method to fabricate high-performance MFC anodes and sheds light on the future development of MFCs using abundant municipal solid waste products.

Bacterial Membrane Depolarization-Linked Fuel Cell Potential Burst as Signal for Selective Detection of Alcohol

The biosensing application of microbial fuel cell (MFC) is hampered by its long response time, poor selectivity, and technical difficulty in developing portable devices. Herein, a novel signal form for rapid detection of ethanol was generated in a photosynthetic MFC (PMFC). First, a dual chambered (100 mL each) PMFC was fabricated by using cyanobacteria-based anode and abiotic cathode, and its performance was examined for detection of alcohols. A graphene-based nanobiocomposite matrix was layered over graphite anode to support cyanobacterial biofilm growth and to facilitate electron transfer. Injection of alcohols into the anodic chamber caused a transient potential burst of the PMFC within 60 s (load 1000 Ω), and the magnitude of potential could be correlated to the ethanol concentrations in the range 0.001-20% with a limit of detection (LOD) of 0.13% ( R² = 0.96). The device exhibited higher selectivity toward ethanol than methanol as discerned from the corresponding cell-alcohol interaction constant ( K_i) of 780 and 1250 mM. The concept was then translated to a paper-based PMFC (p-PMFC) (size ∼20 cm²) wherein, the cells were merely immobilized over the anode. The device with a shelf life of ∼3 months detected ethanol within 10 s with a dynamic range of 0.005-10% and LOD of 0.02% ( R² = 0.99). The fast response time was attributed to the higher wettability of ethanol on the immobilized cell surface as validated by the contact angle data. Alcohols degraded the cell membrane on the order of ethanol > methanol, enhanced the redox current of the membrane-bound electron carrier proteins, and pushed the anodic band gap toward more negative value. The consequence was the potential burst, the magnitude of which was correlated to the ethanol concentrations. This novel approach has a great application potential for selective, sensitive, rapid, and portable detection of ethanol.

Carbon materials derived from waste tires as high-performance anodes in microbial fuel cells

In this study, carbonized waste tires were directly used as a high-performance anode material in microbial fuel cells (MFCs). The effect of the pyrolysis temperature used for waste tire carbonization on the current output performance was investigated to determine the optimal pyrolysis temperature. Thermal gravimetric analysis/differential scanning calorimetry showed that tire carbonization started at 200°C and ended at about 500°C; the weight loss was about 64%. When used in an MFC, the electrode obtained from waste tires carbonized at 800°C gave a current density of 23.1±1.4Am^-2, which is much higher than that achieved with traditional graphite felt anodes (5.5±0.1Am^-2). The results of this study will be useful in optimizing the design of carbonized waste tire anodes for enhancing MFC performances and will alleviate the environmental problems caused by waste tires.

Pseudocapacitive-dye-molecule-based high-performance flexible supercapacitors

Currently, the development of novel, cheap and high-performance electrode materials for flexible energy-storage devices is being intensively pursued. Organic dyes are regarded as one of the most common water pollution sources, and their discharge not only damages the ecological balance but also wastes a lot of valuable chemical raw materials. With intrinsic redox functional groups, two types of widely used dyes including anthraquinone derivatives and phenothiazine dyes can be effectively removed from their effluent by a facile galvanostatic polymerization method, and resource utilized as electrochemical energy-storage materials. Based on this, a new kind of flexible supercapacitor based on dye molecules has been successfully fabricated, and exhibits excellent electrochemical performance, demonstrating a wise strategy for simultaneous wastewater treatment and preparation of functional devices.

Electrochemical Polymerization of Hydroquinone on Graphite Felt as a Pseudocapacitive Material for Application in a Microbial Fuel Cell

Here we reported the use of electropolymerization to achieve the transformation of aqueous hydroquinone to solid-phase polyhydroquinone (PHQ) with pseudocapacitive characteristics, and the application of this redox-active product to shuttle electron transfer in the anode system of a microbial fuel cell (MFC). The microscopic and spectroscopic results showed that the treatment of the graphite felt (GF) substrate with acids was effective in improving the amounts of surface-bound oxygen-containing groups, enabling better adhesion of PHQ onto the GF surfaces. The electrochemical measurements indicated that the resulting PHQ–AGF (acid treated GF) possessed high pseudocapacitance due to the fast and reversible redox cycling between hydroquinone and benzoquinone. The MFC equipped with the PHQ–AGF anode achieved a maximum power density of 633.6 mW m⁻², which was much higher than 368.2, 228.8, and 119.7 mW m⁻² corresponding to the MFC with the reference PHQ–GF, AGF, and GF anodes, respectively. The increase in the power performance was attributed to the incorporation of the redox-active PHQ abundant in C–OH and C=O groups that were beneficial to the increased extracellular electron transfer and enhanced bacterial adhesion on the anode.

Carbon-Based Microbial-Fuel-Cell Electrodes: From Conductive Supports to Active Catalysts

Microbial fuel cells (MFCs) have attracted considerable interest due to their potential in renewable electrical power generation using the broad diversity of biomass and organic substrates. However, the difficulties in achieving high power densities and commercially affordable electrode materials have limited their industrial applications to date. Carbon materials, which can exhibit a wide range of different morphologies and structures, usually possess physiological activity to interact with microorganisms and are therefore fast-emerging electrode materials. As the anode, carbon materials can significantly promote interfacial microbial colonization and accelerate the formation of extracellular biofilms, which eventually promotes the electrical power density by providing a conductive microenvironment for extracellular electron transfer. As the cathode, carbon-based materials can function as catalysts for the oxygen-reduction reaction, showing satisfying activities and efficiencies nowadays even reaching the performance of Pt catalysts. Here, first, recent advancements on the design of carbon materials for anodes in MFCs are summarized, and the influence of structure and surface functionalization of different types of carbon materials on microorganism immobilization and electrochemical performance is elucidated. Then, synthetic strategies and structures of typical carbon-based cathodes in MFCs are briefly presented. Furthermore, future applications of carbon-electrode-based MFC devices in the energy, environmental, and biological fields are discussed, and the emerging challenges in transferring them from laboratory to industrial scale are described.