Melamine-based metal-organic frameworks for high-performance supercapacitor applications

Melamine-based metal-organic frameworks (MOFs) for high-performance supercapacitor applications are described in this paper. Melamine (Me) is employed as an organic linker, and three metal ions cobalt, nickel, and iron (Co, Ni, Fe) are used ascentral metal ions to manufacture the desired MOF materials (Co-Me, Ni-Me, and Fe-Me). While melamine is an inexpensive organic linker for creating MOF materials, homogenous molecular structures can be difficult to produce. The most effective technique for expanding the molecular structures of MOFs through suitable experimental optimization is used in this work. The MOFs materials are characterized using standard techniques. The kinetics of the materials' reactions are investigated using attenuated total reflectance. X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (P-XRD), Fourier transform infrared (ATR-FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) studies verified the development of the MOFs structure. The surface morphology of the produced materials is investigated using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM). The elements found in MOFs are studied via XPS analysis, energy dispersive X-ray diffraction (EDX), mapping, and mapping. The materials' absorption characteristics were examined by the use of UV-visible absorption spectroscopy. The thermal stability of the materials is examined by thermogravimetric analysis (TGA); these materials are more stable, according to the findings, even at high temperatures. The electrochemical investigation determines the specific capacitance of the materials. The specific capacitance of Co-Me, Ni-Me, and Fe-Me in 3 M KOH electrolyte is 1267.36, 803.22, and 507.59F/g @ 1 A-1, according to the three-electrode arrangement. The two-electrode device maximizes power and energy density by using an asymmetrical supercapacitor in a 3 M KOH electrolyte. The power and energy densities of Co-Me, Ni-Me, and Fe-Me are 3650.63, 2813.21, and 6210.45 W kg-1, and 68.43, 46.32, and 42.2 Wh kg-1, respectively. According to the materials stability test, the MOFs are highly stable after 10,000 cycles. Preliminary results suggest that the materials are suitable for usage in high-end supercapacitor uses.

Utilizing a Fe3O4 Magnetite Nanoparticle for Anode Modification in a Microbial Desalination Cell to Treat Saltwater

The microbial desalination cell (MDC) is a bio-electrochemical system that exhibits the ability to oxidize organic compounds, produce energy, and decrease the saline concentrations within the desalination chamber. The selective removal of ions from the desalination chamber is significantly influenced by the anion and cation exchange membranes. In this study, a three-chamber microbial desalination cell was developed to treat seawater using a synthesize Fe3O4 magnetite nanoparticle (MNP)-modified anode. The impact of different performance parameters, such as temperature, pH, and concentrations of NPs, has been investigated in order to assess the performance of three-chamber MDCs in terms of energy recovery and salt removal. The evaluation criteria of the system included multiple factors such as chemical oxygen demand (COD), Coulombic efficiency (CE), desalination efficiency, as well as system aspects including voltage generation and power density. The highest COD% removal efficiency was 74% at 37 °C, pH = 7, and 30 g/L salt concentration with an optimized NPs concentration of 2.0 mg/cm2 impregnated on anode. The maximum Coulombic efficiency was 10.3% with the maximum power density of 4.3 W/m3. The effect of the nanoparticle concentration impregnated on the anode was clarified by the primary factor of analysis. This research has revealed consistent patterns in the enhancement of voltage generation, COD, and Coulombic efficiencies when incorporating higher concentrations of nanoparticles on the anode at a certain point.

Whole-cell biophotovoltaic systems for renewable energy generation: A systematic analysis of existing knowledge

The development of carbon-neutral fuel sources is an essential step in addressing the global fossil energy crisis. Whole-cell biophotovoltaic systems (BPVs) are a renewable, non-polluting energy-generating device that utilizes oxygenic photosynthetic microbes (OPMs) to split water molecules and generate bioelectricity under the driving of light energy. Since 2006, BPVs have been widely studied, with the order magnitudes of power density increasing from 10-4 mW/m2 to 103 mW/m2. This review examines the extracellular electron transfer (EET) mechanisms and regulation techniques of BPVs from biofilm to external environment. It is found that the EET of OPMs is mainly mediated by membrane proteins, with terminal oxidase limiting the power output. Synechocystis sp. PCC6803 and Chlorella vulgaris are two species that produce high power density in BPVs. The use of metal nanoparticles mixing, 3D pillar array electrodes, microfluidic technology, and transient-state operation models can significantly enhance power density. Challenges and potential research directions are discussed, including a deeper analysis of EET mechanisms and dynamics, the development of modular devices, integration of multiple regulatory components, and the exploration of novel BPV technologies.

In vitro antibiofilm effect of different irradiation doses in infected root canal model

BACKGROUND

Eradication of endodontic biofilms from the infected root canal system is still the main concern in endodontics. In this study, the role of the power density parameter in the efficacy of antimicrobial photodynamic therapy (PDT) with toluidine blue O (TBO) and phycocyanin (PC) activated by a 635 nm diode laser (DL) against Enterococcus faecalis biofilm in the root canal model was investigated.

MATERIALS AND METHODS

The E. faecalis biofilm in the root canal was treated with TBO and PC with different power densities (636, 954, 1273, and 1592 W/cm2). The untreated biofilm represented the control group. After the treatments, the biofilms were analyzed based on the number of colonies per milliliter.

RESULTS

TBO and PC activated with 635 nm DL with a power density of 1592 W/cm2 were more efficient in removing E. faecalis biofilms within the root canals than those with a power density of 636 W/cm2 (p = 0.00).

CONCLUSION

The light power density optimized the bacterial reduction of E. faecalis biofilms in the root canal spaces. These results provide information on the decisive parameters for performing PDT on intracanal biofilms.

Granular activated carbon assisted biocathode for effective electrotrophic denitrification in microbial fuel cells

Granular activated carbon (GAC) has been widely used at the anode of a microbial fuel cell (MFC) to enhance anode performance due to its outstanding capacitance property. To the best of our knowledge, there haven't been any studies on GAC in the cathode for biofilm development and nitrate reduction in MFC. In this study, by adding GAC to biocathode, we investigated the impact of different GAC amounts and stirring speeds on power generation and nitrate reduction rate in MFC. The denitrification rate was found to be nearly two-times higher in MFCs with GAC (0.046 ± 0.0016 kg m-3 d-1) compared to that deprived of GAC (0.024 ± 0.0012 kg m-3 d-1). The electrotrophic denitrification has produced a maximum power density of 37.6 ± 4.8 mW m-2, which was further increased to 79.2 ± 7.4 mW m-2 with the amount of GAC in the biocathode. A comparative study performed with chemical catalyst (Pt carbon with air sparging) cathode and GAC biocathode showed that power densities produced with GAC biocathode were close to that with Pt cathode. Cyclic voltammetry analysis conducted at 10 mV s-1 between -0.9 V and +0.3 V (vs. Ag/AgCl) showed consistent reduction peaks at -0.6V (Ag/AgCl) confirming the reduction reaction in the biocathode. This demonstrates that the GAC biocathode used in this research is effective at producing power density and denitrification in MFC. Our belief that the nitrate reduction was caused by the GAC biocathode in MFC was further strengthened when SEM analysis showing bacterial aggregation and biofilm formation on the surface of GAC. The GAC biocathode system described in this research may be an excellent substitute for MFC's dual functions of current generation and nitrate reduction.

A study on effects of cell phone tower-emitted non-ionizing radiations in an Allium cepa test system

Considering enormous growth in population, technical advancement, and added reliance on electronic devices leading to adverse health effects, in situ simulations were made to evaluate effects of non-ionizing radiations emitted from three cell phone towers (T1, T2, and T3) of frequency bands (800, 1800, 2300 MHz), (900, 1800, 2300 MHz), and (1800 MHz), respectively. Five sites (S1-S5) were selected near cell phone towers exhibiting different power densities. The site with zero power density was considered as control. Effects of radiations were studied on morphology; protein content; antioxidant enzymes like ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione-S-transferase (GST), guaiacol peroxidase (POD), and glutathione reductase (GR); and genotoxicity using Allium cepa. Mean power density (μW/cm2) was recorded as 1.05, 1.18, 1.6, 2.73, and 12.9 for sites 1, 2, 3, 4, and 5, respectively. A significant change in morphology, root length, fresh weight, and dry weight in Allium cepa was observed under the exposure at different sites. Protein content of roots showed significant difference for samples at all sites while bulbs at sites S4 and S5 when compared to control. Antioxidant activity for root in terms of APX, GST, and POD showed significant changes at S4 and S5 and GR at site S5 and SOD at S1, S2, S3, S4, and S5. Similarly, bulbs showed significant changes at sites S4 and S5 for APX while at sites S3, S4, and S5 for POD and S2, S3, S4, and S5 for SOD and S5 for GR and GST. Genotoxicity study has shown induction of abnormalities at different stages of the cell cycle in Allium cepa root tips. The samples under exposure to radiation with maximum power density have shown maximum induction of oxidative stress and genotoxicity.

Sustainable power production from petrochemical industrial effluent using dual chambered microbial fuel cell

Dual chambered microbial fuel cell (DMFC) is an advanced and effective treatment technology in wastewater treatment. The current work has made an effort to treat petrochemical industrial wastewater (PWW) as a DMFC substrate for power generation and organic substance removal. Investigating the impact of organic load (OL) on organic reduction and electricity generation is the main objective of this study. At the OL of 1.5 g COD/L, the highest total chemical oxygen demand (TCOD) removal efficiency of 88%, soluble oxygen demand (SCOD) removal efficiency of 80% and total suspended solids (TSS) removal efficiency of 71% were seen, respectively. In the same optimum condition of 1.5 g COD/L, the highest current and power density of about 270 mW/m2 and 376 mA/m2 were also observed. According to the results of this study, using high-strength organic wastewater in DMFC can assist in addressing the issue of the petrochemical industries and minimize the energy demand.

Bioremediation of hydrocarbon by co-culturing of biosurfactant-producing bacteria in microbial fuel cell with Fe2O3-modified anode

The most common type of environmental contamination is petroleum hydrocarbons. Sustainable and environmentally friendly treatment strategies must be explored in light of the increasing challenges of toxic and critical wastewater contamination. This paper deals with the bacteria-producing biosurfactant and their employment in the bioremediation of hydrocarbon-containing waste through a microbial fuel cell (MFC) with Pseudomonas aeruginosa (exoelectrogen) as co-culture for simultaneous power generation. Staphylococcus aureus is isolated from hydrocarbon-contaminated soil and is effective in hydrocarbon degradation by utilizing hydrocarbon (engine oil) as the only carbon source. The biosurfactant was purified using silica-gel column chromatography and characterised through FTIR and GCMS, which showed its glycolipid nature. The isolated strains are later employed in the MFCs for the degradation of the hydrocarbon and power production simultaneously which has shown a power density of 6.4 W/m3 with a 93% engine oil degradation rate. A biogenic Fe2O3 nanoparticle (NP) was synthesized using Bambusa arundinacea shoot extract for anode modification. It increased the power output by 37% and gave the power density of 10.2 W/m3. Thus, simultaneous hydrocarbon bioremediation from oil-contamination and energy recovery can be achieved effectively in MFC with modified anode.

The influence of different mode of power density during antimicrobial photodynamic therapy for photokilling of Streptococcus mutans

BACKGROUND

The aim of this study was to evaluate the inactivation potency of riboflavin and curcumin plus blue diode laser against Streptococcus mutans with different power densities.

MATERIALS AND METHODS

In this in vitro study, standard-strain S. mutans was exposed to curcumin and riboflavin plus blue diode laser with different power densities (0.4-1.0 W/cm2) as well as chlorhexidine (CHX). The colony forming units (CFUs)/mL was calculated. Data were analyzed by one-way ANOVA.

RESULTS

Antibacterial analysis indicated that the blue diode laser irradiation with curcumin and riboflavin provided a satisfactory reduction of the S. mutans level. In addition, S. mutans was more affected by curcumin + blue diode laser when the power density was set to 1.0 W/cm2 (P < 0.0001). Meanwhile, bacterial suspensions treated with CHX showed maximum colony number reduction, compared with the control (P < 0.0001).

CONCLUSION

This study showed the blue diode laser along with curcumin had strong bactericidal effect on S. mutans, and this effect improved by increasing the power density.

Electrochemical process for petroleum refinery wastewater treatment to produce power and hydrogen using microbial electrolysis cell

This research aims to assess the microbial electrolysis cell (MEC) fed with petroleum refinery wastewater (PRW) to produce power density and bio-electrochemical hydrogen. The MEC produces a maximum bio-electricity of 21.4 mA and a power density of 1200123.90 W/m2 with a loading of chemical oxygen demand (COD) of 17000 mg/L. Due to catalyzed oxidation of complex compounds in PRW with a maintained microbial biofilm growth was observed after 90 d of operation of MEC. Results showed that the oxidation of organic substances in PRW enhanced the size in the growth of microbial film which further increased the generation of electrons leading to current density of 5890 mA/m2. The COD removal efficiency of MEC was found to be 89.9%. The bio-electricity and hydrogen production of the MEC was estimated to be 24.5 mA and 19.2 L respectively when loaded with PRW having a COD of 17500 mg/L after 130 d. Present experiments demonstrate the efficiency of MEC technology efficiency in treating petroleum wastewater with the help of microbial biofilm.

Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235 MJ/Kg, indicating the cell's high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.

Synergistic effect of TiO2 nanostructured cathode in microbial fuel cell for bioelectricity enhancement

Nano-bedecking of electrode with nanoparticles is an effective method to improve power generation of microbial fuel cells (MFCs). In this study, different concentrations (0.25 mg cm^-2, 0.50 mg cm^-2, 0.75 mg cm^-2 and 1.0 mg cm^-2) of TiO₂ nanoparticles of size 10-25 nm were overlaid on the carbon cloth (CC) using spray pyrolysis technique and used as catalytic cathode in a dual-chambered microbial fuel cell treating distillery wastewater. Results evidenced that TiO₂ nanoparticles modified cathode increased the power generation and recorded a highest power and current density of 162.5 ± 2 mW m^-2 and 1.4 ± 0.005 A m^-2, respectively. Carbon cloth coated with 0.50 mg cm^-2 TiO₂ nanoparticles showed 2.8 and 7.3 times higher current and power density as compared to uncoated cathode. MFC operated at a hydraulic retention time (HRT) and organic loading rate (OLR) of 72 h and 59.2 g COD L^-1 d^-1 showed a maximum chemical oxygen demand (COD) removal of 72.3% which was 15.3% higher than the control MFC. Likewise, the coulombic efficiency of control and modified MFC was 33% and 44%, respectively. The maximum NO₃^-- N, NO₂^-- N and NH₄⁺- N removal efficiency of 77.3%, 49.9% and 59.4% were observed for TiO₂ nanoparticles modified electrode which was 19.3%, 11.4% and 10.5% higher than control. TiO₂ modified cathode was effective in enhancing the bioelectricity generation in MFCs.

Synthesis and performance of a cathode catalyst derived from Bauhinia accuminata seed pods in single and stacked microbial fuel cell

The cathode catalyst in microbial fuel cell (MFC) plays a crucial role in scaling up. Activity of biomass-derived activated carbon catalysts with appropriate precursor selection in a natural clay membrane-based MFC of 250 mL was studied. The performance of scaled up MFC of 1.5 L capacity with two different configurations was monitored. Rod-shaped particles with slit-type pores and amorphous graphitic nature with a surface area of 800.37 m²/g was synthesized. The intrinsic doping of heteroatoms N and P in the catalyst was with atomic weight percentages of 4.5 and 3.5, respectively and the deconvolution of N1 spectra confirmed pyridinic N and graphitic N content of 17.3% and 34.1% validating its suitability as a cathode catalyst. Electrochemical characterization of the catalyst coated SS mesh electrode confirmed that a loading of 5 mg/cm² rendered higher catalytic activity compared to bare SS mesh. The maximum power density in catalyst modified cell was 0.91 W/m³ compared to 0.02 W/m³ as obtained in a plain stainless steel electrode cell at a COD removal efficiency of 93.3%. Series, parallel, and parallel-series combinations of 6 cells showed a maximum voltage of 4.15 V when connected in series and a maximum power density of 1.54 W/m³ when connected in parallel. System with multielectrode assembly achieved better power and current density (0.84 W/m³ and 1.97 A/m³) than the mixed parallel series circuitry (0.7 W/m³ and 0.57 A/m³). These performance results confirm that the catalyst is effective in both stacked and hydraulically connected system.

Performance optimization of two-stage constructed wetland-microbial fuel cell system for the treatment of high-concentration wastewater

Constructed wetland-microbial fuel cell (CW-MFC) has attracted much attention because of its dual functions of wastewater treatment and energy recovery. However, its performance in treating high-concentration wastewater is degraded by the decreased dissolved oxygen at the cathode and insufficient electron acceptors. In this study, two CW-MFC systems with cathodic aeration were connected in series to investigate the effects of aeration rate and hydraulic retention time (HRT) on the removal of pollutants and the performance of electricity production in high-concentration wastewater. Results showed that aeration enhanced NH₄⁺-N and TP removal by 45.0-49.8% and 11.5-18.0%, compared with the unaerated condition, respectively. Meanwhile, no significant change regarding COD removal was observed. Aeration enhances the output voltage and power density of the system, especially the first stage CW-MFC, which improved the power production performance by 1 to 2 orders-of-magnitude. Increasing HRT improves the system's pollutant treatment efficiency and power generation performance for high-concentration wastewater. Still, the extension of HRT to 2 days will not contribute much to improving the removal efficiency. Under optimized conditions, the maximum total removal rates of COD, NH₄⁺-N, and TP for the two-stage tandem CW-MFC system were 99.3 ± 0.2%, 92.4 ± 1.6%, and 79.5 ± 3.4%, respectively. Meanwhile, the maximum output voltage and maximum power density of the first-stage CW-MFC were 405 mV and 138.0 mW/m³, respectively. In contrast, the maximum output voltage and maximum power density of the second stage are 105 mV and 14.7 mW/m³, respectively.

Bimetal-organic framework-derived porous CoFe2O4 nanoparticles as biocompatible anode electrocatalysts for improving the power generation of microbial fuel cells

HYPOTHESIS

The relatively lower power density of Microbial fuel cells (MFCs), primarily resulting from weak biofilm habitation and sluggish extracellular electron transfer (EET) at the anode interface, limits their practical implementation on a large scale. To address this challenge, porous CoFe₂O₄ nanoparticles could be used as anode electrocatalysts based on the following considerations: (i) the introduction of CoFe₂O₄ nanoparticles endows the anode with a rough surface that facilitates biofilm formation; (ii) the positively charged Co and Fe ions improve the interfacial affinity of anodes, enabling rapid immobilization and colonization of negatively bacteria; (iii) the multi-valent metal states of Co and Fe can function as electron shuttles, mediating EET process between biofilm and anode.

EXPERIMENTS

CoFe₂O₄ nanoparticles prepared with a bimetal-organic framework (B-MOF) as precursor, were modified to the surface of carbon cloth as the anode of MFCs.

FINDINGS

MFCs equipped with CoFe₂O₄ anode achieved a maximum power density of 1026.68 mW m^-2, which was approximately 3.4 times higher than that of the pristine carbon cloth. Additionally, the biofilm density and viability on the anode were enhanced after CoFe₂O₄ modification. Considering the facile fabrication process and superior electrocatalytic performance, the CoFe₂O₄ nanoparticles are promising electrocatalysts for high performance and cost-effective MFCs.

Synergistic effect of nitrogen and oxygen dopants in 3D hierarchical porous carbon cathodes for ultra-fast zinc ion hybrid supercapacitors

Zinc-ion hybrid supercapacitor is one of the most promising electrochemical energy storage devices for the applications needing both high energy densities and power densities. Nitrogen doping is an effective way to enhance the capacitive performance of porous carbon cathodes in zinc-ion hybrid supercapacitor. However, accurate evidence is yet needed to demonstrate how nitrogen dopants influence the charge storage of Zn²⁺ and H⁺ cations. Herein, we prepared 3D interconnected hierarchical porous carbon nanosheets by a one-step explosion method. The effect of nitrogen dopants on pseudocapacitance was analyzed by the electrochemical behaviors of as-prepared porous carbon samples with similar morphology and pore structure but different nitrogen and oxygen doping levels. Ex-situ XPS and DFT calculation demonstrate that nitrogen dopants promote the pseudocapacitive reactions by lowering the energy barrier for the change of oxidation states of carbonyl moieties. Owing to the improved pseudocapacitance by nitrogen/oxygen dopants and fast diffusion of Zn²⁺ ions in 3D interconnected hierarchical porous carbon matrix, the as-constructed ZIHCs show both high gravimetric capacitance (301 F g^-1 at 0.1 A g^-1) and excellent rate capability (a capacitance retention of 30% at 200 A g^-1).

Rice husk-derived silicon nanostructured anode to enhance power generation in microbial fuel cell treating distillery wastewater

The present study aims to utilize rice husk as a source of silica to prepare rice husk derived silicon nanoparticles (RH-Si) and demonstrate its ability as an anode modifier in a two-chambered H-shaped microbial fuel cell (MFC). The silicon nanoparticles synthesized by magnesiothermal reduction process were spherical in shape and ranged in size from 15 to 60 nm. The anode modified with silicon nanoparticles of 0.50 mg cm^-2 recorded the maximum power and current density of 190.5 mW m^-2 and 1.5 A m^-2 corresponding to 7.6-fold and 3-fold increase as compared to the control . The modified anode also recorded a COD removal and coulombic efficiency of 74% and 49%, respectively in MFC operated with combined distillery and domestic wastewater at a HRT and OLR of 72 h and 59.2 gCOD L^-1 d^-1, respectively. The results evidence that RH derived silicon NPs are good anode modifiers and effective in enhancing bioelectricity generation and COD removal in MFCs.

Carbon nanotubes encapsulating FeS2 micropolyhedrons as an anode electrocatalyst for improving the power generation of microbial fuel cells

The low power density originating from poor electroactive bacteria (EAB) adhesion and sluggish extracellular electron transfer (EET) at the anode interface, is a major impediment preventing the practical implementation of microbial fuel cells (MFCs). Tailoring the surface properties of anodes is an effective and powerful strategy for addressing this issue. In this study, we successfully fabricated an efficient anode electrocatalyst, consisting of carbon nanotubes encapsulating iron disulfide (FeS2@CNT) micropolyhedrons, using simple hydrothermal and freeze-drying methods, which not only strengthened the anode interaction with EAB but also promoted the EET process at the anode interface. As expected, the MFCs with a FeS2@CNT anode yielded an outstanding power density of 1914 mWm-2 at a current density of 4350 mA m-2, which significantly exceeded those of pure CNT (1096.2mW m-2, 2703.3 mA m-2) and carbon cloth (426.8mWm-2, 965.6 mA m-2) anodes. The high-power output can be attributed to the synergistic effect between FeS2 and CNTs, endowing the anode with biocompatibility for biofilm adhesion and colonization, nutrient diffusion, and the presence of abundant Fe and S active sites for EET mediation. Owing to the low cost, facile fabrication process, and excellent electrocatalytic performance toward the redox reactions in biofilms, the synthesized FeS2@CNT electrocatalyst is a promising material for high-performance and cost-effective MFCs with commercial applications.

Impact of reactor configuration on pilot-scale microbial fuel cell performance

Different microbial fuel cell (MFC) configurations have been successfully operated at pilot-scale levels (>100 L) to demonstrate electricity generation while accomplishing domestic or industrial wastewater treatment. Two cathode configurations have been primarily used based on either oxygen transfer by aeration of a liquid catholyte or direct oxygen transfer using air-cathodes. Analysis of several pilot-scale MFCs showed that air-cathode MFCs outperformed liquid catholyte reactors based on power density, producing 233% larger area-normalized power densities and 181% higher volumetric power densities. Reactors with higher electrode packing densities improved performance by enabling larger power production while minimizing the reactor footprint. Despite producing more power than the liquid catholyte MFCs, and reducing energy consumption for catholyte aeration, pilot MFCs based on air-cathode configuration failed to produce effluents with chemical oxygen demand (COD) levels low enough to meet typical threshold for discharge. Therefore, additional treatment would be required to further reduce the organic matter in the effluent to levels suitable for discharge. Scaling up MFCs must incorporate designs that can minimize electrode and solution resistances to maximize power and enable efficient wastewater treatment.

Sodium nitrate as a methanogenesis suppressor in earthen separator microbial fuel cell treating rice mill wastewater

The microbial fuel cell (MFC) is one of the sustainable technologies, which alongside treating wastewater, can generate electricity. However, its performance is limited by factors like methanogenesis where methanogens compete with the anode respiring bacteria for substrate, reducing the power output. Thus, sodium nitrate, which has been previously reported to target the hydrogenotrophic methanogens, was used as a methanogenic suppressor in this study. The performance of MFC with and without sodium nitrate was studied during the treatment of rice mill wastewater. A significantly higher power density and coulombic efficiency (CE) were noted in the MFC with sodium nitrate (MFC_T) (271.26 mW/m³) as compared to the control MFC (MFC_C) (107.95 mW/m³). Polarization studies showed lower internal resistance for the MFC_T (330 Ω) as compared to MFC_C (390 Ω). Linear sweep voltammetry and cyclic voltammetry indicated a higher electron discharge on the anode surface due to enhancement of electrogenic activity. Considerable reduction (76.8%) in specific methanogenic activity was also observed in anaerobic sewage sludge mixed with sodium nitrate compared to the activity of anaerobic sewage sludge without any treatment. Due to the inhibition of methanogens, a lower chemical oxygen demand (COD) and phenol removal efficiency were observed in MFC_T as compared to MFC_C. The COD balance study showed an increase in substrate conversion to electricity despite the increase in nitrate concentration. Therefore, selective inhibition of methanogenesis had been achieved with the addition of sodium nitrate, thus enhancing the power generation by MFCs.

Meta-analysis of operational performance and response metrics of microbial fuel cells (MFCs) fed with complex food waste

This study reports on a meta-analysis covering the impact of design and operating factors on published MFC performance data to inform MFC research and implementations. Factors of substrate composition, operating phase, electrode material, configuration, and pre-treatments employed were considered. The meta-analysis results indicate that dual-chamber MFCs overall achieve 18% higher COD removal and 73% higher coulombic efficiencies over that of single-chamber MFCs. MFCs using a solid operating phase achieved ˃38% higher coulombic efficiencies than those using a liquid operating phase. Statistical analyses comparing brush vs flat surface anodes revealed that brush anodes can achieve 130% higher power density than flat surface anodes. The use of a platinum catalyst was found to improve power density, as opposed to catalyst-free cathodes. However, coulombic efficiency is less likely to be influenced by the catalyst used and more likely to be dependent on the inclusion of a membrane separator. The meta-analysis results indicate that even in the presence of expensive catalysts like platinum, membrane separators are of prime importance to maintain a stable MFC operation on a long-term basis and achieve high coulombic efficiency in an MFC. Results presented in this paper outline the impact of MFC design choices on performance and can be used to guide future MFC research. These findings can be beneficial for municipalities as it provides a pathway for future MFC design and optimization by analyzing critical associations between MFC response parameters and multiple varying factors.

Electrical generation and methane emission from an anoxic riverine sediment slurry treated by a two-chamber microbial fuel cell

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K₃[Fe(CN)₆]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200 mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8 h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6 h and K₃[Fe(CN)₆] or NaCl concentrations were 200 mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m^-2, respectively. With increasing K₃[Fe(CN)₆] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8 mg/m³·h and 428.0 ± 28.5 → 157.0 ± 35.7 mg/m³·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30 mg/m³·h). Cathode aeration (0 → 8 h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7 mg/m³·h for 6 h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1 mg/m³·h). Our results demonstrate that adding an electron acceptor (K₃[Fe(CN)₆]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

Advancements on sustainable microbial fuel cells and their future prospects: A review

A microbial fuel cell (MFC) is a sustainable device that produces electricity. The main components of MFC are electrodes (anode & cathode) and separators. The MFC's performance is ascertained by measuring its power density. Its components and other parameters, such as cell design and configuration, operation parameters (pH, salinity, and temperature), substrate characteristics, and microbes present in the substrate, all influence its performance. MFC can be scaled up and commercialized using low-cost materials without affecting its performance. Hence the choice of materials plays a significant role. In the past, precious and non-precious metals were mostly used. These were replaced by a variety of low-cost carbonaceous and non-carbonaceous materials. Nano materials, activated compounds, composite materials, have also found their way as components of MFC materials. This review describes the recently reported modified electrodes (anode and cathode), their improvisation, their merits, pollutant removal efficiency, and associated power density.

Evaporation-driven electrokinetic energy conversion: Critical review, parametric analysis and perspectives

Energy harvesting from evaporation has become a "hot" topic in the last couple of years. Researchers have speculated on several possible mechanisms. Electrokinetic energy conversion is the least hypothetical one. The basics of pressure-driven electrokinetic phenomena of streaming current and streaming potential have long been established. The regularities of evaporation from porous media are also well known. However, "coupling" of these two classes of phenomena has not, yet, been seriously explored. In this critical review, we will recapitalize and combine the available knowledge from these two fields to produce a coherent picture of electrokinetic electricity generation during evaporation from (nano)porous materials. For illustration, we will consider several configurations, namely, single nanopores, arrays of nanopores, systems with reduced area of electrokinetic-conversion elements and devices with side evaporation from thin nanoporous films. For the latter (practically the only one studied experimentally), we will formulate a simple model describing correlations of system performance with such principal parameters as the nanoporous-layer length, width and thickness as well as the pore size, pore-surface hydrophilicity, effective zeta-potential and electric conductivity in nanopores. These correlations will be qualitatively compared with experimental data available in the literature. We will see that experimental data not always are in agreement with the model predictions, which may be due to simplifying model assumptions but also because the mechanisms are different from the classical electrokinetic energy conversion. In particular, this concerns the mechanisms of conversion of evaporation-driven ion streaming currents into electron currents in external circuits. We will also formulate directions of future experimental and theoretical studies that could help clarify these issues.

Microbial fuel cells for mineralization and decolorization of azo dyes: Recent advances in design and materials

Microbial fuel cells (MFCs) exhibit tremendous potential in the sustainable management of dye wastewater via degrading azo dyes while generating electricity. The past decade has witnessed advances in MFC configurations and materials; however, comprehensive analyses of design and material and its association with dye degradation and electricity generation are required for their industrial application. MFC models with high efficiency of dye decolorization (96-100%) and a wide variation in power generation (29.4-940 mW/m²) have been reported. However, only 28 out of 104 studies analyzed dye mineralization - a prerequisite to obviate dye toxicity. Consequently, the current review aims to provide an in-depth analysis of MFCs potential in dye degradation and mineralization and evaluates materials and designs as crucial factors. Also, structural and operation parameters critical to large-scale applicability and complete mineralization of azo dye were evaluated. Choice of materials, i.e., bacteria, anode, cathode, cathode catalyst, membrane, and substrate and their effects on power density and dye decolorization efficiency presented in review will help in economic feasibility and MFCs scalability to develop a self-sustainable solution for treating azo dye wastewater.

Cedar Wood-Based Biochar: Properties, Characterization, and Applications as Anodes in Microbial Fuel Cell

In this study, the relationship between pyrolysis temperature of woody biomass and physicochemical properties of derived biochar was investigated for microbial fuel cell (MFC) application. Physical and chemical properties of biochar were characterized for different pyrolysis temperatures. Results showed that biochar obtained at 400 °C was not conductor, while biochars prepared at 600 °C, 700 °C, and 900 °C exhibited decreased electrical resistivity of (7 ± 6) × 10³ Ω.m, (1.8 ± 0.2) Ω.m, and (16 ± 3) × 10^-3 Ω.m, respectively. Rising pyrolysis temperature from 400 to 700 °C exhibited honeycomb-like macroporous structures of biochar with an increase in the specific surface area from 310 to 484 m².g^-1. However, the production of biochar at 900 °C reduced its specific surface area to 136 m².g^-1 and caused the loss of the ordered honeycomb structure. MFCs using anodes based on biochar prepared at 900 °C produced maximum power densities ((9.9 ± 0.6) mW.m^-2) higher than that obtained with biochar pyrolyzed at 700 °C ((5.8 ± 0.1) mW.m^-2) and with conventional carbon felt anodes ((1.9 ± 0.2) mW.m^-2). SEM images of biochar-based anodes indicated the clogging of macropores in honeycomb structure of biochar prepared at 700 °C by growth of electroactive biofilms, which might impede the supply of substrate and the removal of metabolites from the inside of the electrode. These findings highlight that electrical conductivity of biochar is the major parameter for ensuring efficient anodes in microbial fuel cell application. Schematic representation of cedar wood-based biochar and its application as anode 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.

Lysozyme regulates the extracellular polymer of activated sludge and promotes the formation of electroactive biofilm

The formation of electroactive biofilm from activated sludge on electrode surface is a key step to construct a bio-electrochemical system, yet it is greatly limited by the poor affinity between the bacteria and the electrode interface. Herein, we report a new method to promote the formation of electroactive biofilm by regulating the extracellular polymeric substance (EPS) content in activated sludge with lysozyme. The investigation of the effect of lysozyme treatment on the content of extracellular polymers and the biofilm formation of electroactive bacteria suggests that lysozyme can improve the permeability of the positive bacterial cell membrane and thus increase the EPS content in the activated sludge. The characterizations of electrochemical activity, surface morphology and community structure of the anode biofilm indicate that increasing EPS content promotes the adhesion of the mixed bacteria in the activated sludge on the electrode and results in denser biofilms with better conductivities. The microbial fuel cell (MFC) inoculated with the sludge of high EPS content exhibits the power density up to 2.195 W/m², much higher than that inoculated with the untreated sludge (1.545 W/m²). The strategy of adjusting EPS content in activated sludge with a biological enzyme can effectively enhance the ability of the bacterial community to form biofilms and exhibits great application potentials in the construction of high efficiency bio-electrochemical systems.

Ultralight Iontronic Triboelectric Mechanoreceptor with High Specific Outputs for Epidermal Electronics

The pursuit to mimic skin exteroceptive ability has motivated the endeavors for epidermal artificial mechanoreceptors. Artificial mechanoreceptors are required to be highly sensitive to capture imperceptible skin deformations and preferably to be self-powered, breathable, lightweight and deformable to satisfy the prolonged wearing demands. It is still struggling to achieve these traits in single device, as it remains difficult to minimize device architecture without sacrificing the sensitivity or stability. In this article, we present an all-fiber iontronic triboelectric mechanoreceptor (ITM) to fully tackle these challenges, enabled by the high-output mechano-to-electrical energy conversion. The proposed ITM is ultralight, breathable and stretchable and is quite stable under various mechanical deformations. On the one hand, the ITM can achieve a superior instantaneous power density; on the other hand, the ITM shows excellent sensitivity serving as epidermal sensors. Precise health status monitoring is readily implemented by the ITM calibrating by detecting vital signals and physical activities of human bodies. The ITM can also realize acoustic-to-electrical conversion and distinguish voices from different people, and biometric application as a noise dosimeter is demonstrated. The ITM therefore is believed to open new sights in epidermal electronics and skin prosthesis fields.

Advances in the development of electrode materials for improving the reactor kinetics in microbial fuel cells

Microbial fuel cells (MFCs) are an emerging technology for converting organic waste into electricity, thus providing potential solution to energy crises along with eco-friendly wastewater treatment. The electrode properties and biocatalysts are the major factors affecting electricity production in MFC. The electrons generated during microbial metabolism are captured by the anode and transferred towards the cathode via an external circuit, causing the flow of electricity. This flow of electrons is greatly influenced by the electrode properties and thus, much effort has been made towards electrode modification to improve the MFC performance. Different semiconductors, nanostructured metal oxides and their composite materials have been used to modify the anode as they possess high specific surface area, good biocompatibility, chemical stability and conductive properties. The cathode materials have also been modified using metals like platinum and nano-composites for increasing the redox potential, electrical conductivity and surface area. Therefore, this paper reviews the recent developments in the modification of electrodes towards improving the power generation capacity of MFCs.

Effect of β-cyclodextrin/polydopamine composite modified anode on the performance of microbial fuel cell

The relatively weak microbial adhesion is a bottleneck in improving the power generation performance of microbial fuel cell (MFC). Anode modification is a simple and effective method to solve this problem. A new type of β-cyclodextrin/polydopamine modified carbon felt anode was prepared, and the effects of β-cyclodextrin/polydopamine modified anode on the main performance indexes such as power density and chemical oxygen demand (COD) removal rate of MFC were evaluated. The maximum power density and the output electric energy during the test period of MFC using the modified anode were 102 mW/m² and 84.96 J, which were 364% and 295.3% higher than those of MFC with conventional carbon felt anode, respectively; and the COD removal rate was 124.4% higher than that of MFC with unmodified anode. Modifying the anode with β-cyclodextrin-polyacyclic composite materials is an effective method to improve the overall performance of MFC.

Spatial variability of outdoor exposure to radiofrequency radiation from mobile phone base stations, in Khartoum, Sudan

The wide-spread exposure to constantly evolving wireless technologies believed to pose a serious health threat. Human beings are persistently exposed to RF radiation from mobile phones and their base stations. The current study aimed at classifying and characterizing the exposure to RF radiation from the mobile phone base stations. Spatial distribution measurements were carried out in Khartoum city during two time periods, first in 2012 (pilot survey) and again during Sept. 2019-Jan. 2020, to cover a total of 282 antennas operating with GSM900, GSM1800, and UMTS2100. The tested antennas belong to three mobile communication companies namely Sudani, Zain, and MTN companies, that randomly coded into company A, company B, and company C for security purposes. Measurements were performed using frequency-selective RF analyzer at fixed distances from the antennas/towers. Data were subjected to advanced repeated measures ANOVA, linear discriminant analysis (LDA), and spatial interpolation with ArcGIS. The averages of GSM900, GSM1800, and UMTS measurements were 0.01933 W/m², 0.0067 W/m², and 0.0046 W/m². The high levels of power densities for each single antenna were recorded at 90 m, 110 m, 130 m, and at 150 m distances, for the majority (70%) of the measured antennas and the peak/highest values reported mainly at 110 m distance. Conversely, the discriminant loadings as part of LDA, suggested that, much of variance among measurements is attributed to measurements at 150 m, 170 m, and 190 m distances, while visual illustration of group centroids implied that, the RF signals of the different companies were measured separately which support accuracy of frequency-selective measurements. The LDA has confirmed the ANOVA results that, the overall difference between the three companies was statistically significant for UMTS, and GSM900 measurements but not significant for GSM1800 measurements. Kriging interpolation using ArcGIS provided a strong evidence of great spatial distribution of exposure across the study area, with market places and typical urban residential quarters showing highest levels of RF. Few extreme values exceeding ICNIRP limits are reported but excluded from the calculations because of an issue of normality of data that is considered a prerequisite for parametric data analysis. Existence of extreme levels of RF indicates a need for further investigation and some antennas of Company B are mounted on towers belongs to Company C, implying multi exposure. Unexpected pattern of RF levels continued to increase up to 190 m distance and possibly beyond 190 m is reported for UMTS measurements of Company C.

Impact of light on microalgal photosynthetic microbial fuel cells and removal of pollutants by nanoadsorbent biopolymers: Updates, challenges and innovations

Photosynthetic microbial fuel cells (PMFCs) with microalgae have huge potential for treating wastewater while simultaneously converting light energy into electrical energy. The efficiency of such cells directly depends on algal growth, which depends on light intensity. Higher light intensity results in increased potential as well as enhancement in generation of biomass rich in biopolymers. Such biopolymers are produced either by microbes at anode and algae at cathode or vice versa. The biopolymers recovered from these biological sources can be added in wastewater alone or in combination with nanomaterials to act as nanoadsorbents. These nanoadsorbents further increase the efficiency of PMFC by removing the pollutants like metals and dyes. In this review firstly the effect of different light intensities on the growth of microalgae, importance of diatoms in a PMFC and their impact on PMFCs efficiencies have been narrated. Secondly recovery of biopolymers from different biological sources and their role in removal of metals, dyes along with their impact on circular bioeconomy have been discussed. Thereafter bottlenecks and future perspectives in this field of research have been narrated.

N, S co-doped carbon quantum dots anchoring on copper-vacancy-rich Cu nanowires/Cu foam as the cathode in microbial fuel cells: Role of C-S-Cu active site

Oxygen reduction reaction (ORR) electrocatalysts have been considered as one of the key components in microbial fuel cells (MFCs). Heteroatom-doped carbon quantum dots (CQDs) derived from biomass have attracted wide attention due to their rich functional groups, excellent properties, and environmental friendliness. Herein, orange-peels-derived N, S co-doped carbon quantum dots (N, S-CQDs) are in-situ anchored on copper-vacancy-rich Cu nanowires/Cu foam (V-Cu NWs/CF), obtaining the N, S-CQDs/Cu₂O-Cu NWs, to catalyze ORR in MFCs. The interaction between N, S-CQDs and V-Cu NWs/CF from the N, S-CQDs/Cu₂O-Cu NWs is bridged by the C-S-Cu bond, which is demonstrated to be the active site towards ORR and plays an important role in promoting electron transfer by in-situ Raman and X-ray photoelectron spectroscopy characterizations. In MFCs, the maximum power density (924.5 ± 32.5 mW·m^-2) of N, S-CQDs/Cu₂O-Cu NWs is 1.34 times that of Pt/C (686.5 ± 28.0 mW·m^-2), and its long-term stability also outperforms the Pt/C. This study provides inspiration for synthesis of efficient ORR electrocatalysts with metal-ligand active sites creating by heteroatom-doped CQDs and cationic-metal-vacancy-rich materials.

Microbial fuel cells for bioelectricity production from waste as sustainable prospect of future energy sector

Microbial fuel cell (MFC) is lauded for its potentials to solve both energy crisis and environmental pollution. Technologically, it offers the capability to harness electricity from the chemical energy stored in the organic substrate with no intermediate steps, thereby minimizes the entropic loss due to the inter-conversion of energy. The sciences underneath such MFCs include the electron and proton generation from the metabolic decomposition of the substrate by microbes at the anode, followed by the shuttling of these charges to cathode for electricity generation. While its promising prospects were mutually evinced in the past investigations, the upscaling of MFC in sustaining global energy demands and waste treatments is yet to be put into practice. In this context, the current review summarizes the important knowledge and applications of MFCs, concurrently identifies the technological bottlenecks that restricted its vast implementation. In addition, economic analysis was also performed to provide multiangle perspectives to readers. Succinctly, MFCs are mainly hindered by the slow metabolic kinetics, sluggish transfer of charged particles, and low economic competitiveness when compared to conventional technologies. From these hindering factors, insightful strategies for improved practicality of MFCs were formulated, with potential future research direction being identified too. With proper planning, we are delighted to see the industrialization of MFCs in the near future, which would benefit the entire human race with cleaner energy and the environment.

Fungal-mediated electrochemical system: Prospects, applications and challenges

Microbial fuel cells (MFCs) that generate bioelectricity from biodegradable waste have received considerable attention from biologists. Fungi play a significant role as both anodic and cathodic catalysts in MFCs. Saccharomyces cerevisiae is a fungus with an ability to transfer electrons through mediators such as methylene blue (MB), neutral red (NR) or even without a mediator. This unique role of fungal cells in exocellular electron transfer (EET) and their interactions with electrodes hold a lot of promise in areas such as wastewater treatment where yeast cell-based MFCs can be used. The present article highlights the physico-chemical factors affecting the performance of fungal-mediated MFCs in terms of power output and degradation of organic pollutants, along with the challenges associated with fungal MFCs. In addition, to this comparative assessment of fungal-mediated bio-electrochemical systems, their development, possible applications and potential challenges are also discussed.

Effectiveness of constructed wetland integrated with microbial fuel cell for domestic wastewater treatment and to facilitate power generation

Constructed wetlands (CWs) have gained a lot of attention for wastewater treatment due to robustness and natural pollutant mitigation characteristics. This widely acknowledged technology possesses enough merits to derive direct electricity in collaboration with microbial fuel cell (MFC), thus taking advantage of microbial metabolic activities in the anoxic zone of CWs. In the present study, two identical lab-scale CWs were selected, each having 56 L capacity. One of the CW integrated with MFC (CW-MFC) contains two pairs of electrodes, i.e., carbon felt and graphite plate. The first pair of CW-MFC consists of a carbon felt cathode with a graphite plate anode, and the second pair contains a graphite plate cathode with a carbon felt anode. The other CW was not integrated with MFC and operated as a traditional CW for evaluating the performance. CW-MFC and CW were operated in continuous up-flow mode with a hydraulic retention time of 3 days and at different organic loading rates (OLRs) per unit surface area, such as 1.45 g m^-2 day^-1 (OLR-1), 2.43 g m^-2 day^-1 (OLR-2), and 7.25 g m^-2 day^-1 (OLR-3). The CW-MFC was able to reduce the organic matter, phosphate, and total nitrogen by 92%, 93%, and 70%, respectively, at OLR of 1.45 g m^-2 day^-1, which was found to be higher than that obtained in conventional CW. With increase in electrochemical redox activities, the second pair of electrodes made way for 3 times higher power density of 16.33 mW m^-2 as compared to the first pair of electrodes in CW-MFC (5.35 mW m^-2), asserting carbon felt as a good anode material to be used in CW-MFC. The CW-MFC with carbon felt as an anode material is proposed to improve the electro-kinetic activities for scalable applications to achieve efficient domestic wastewater treatment and electricity production.

Influence of Cr (VI) concentration on Cr (VI) reduction and electricity production in microbial fuel cell

Microbial fuel cell is an efficient technology to reduce pollutants of the heavy metal ions. Herein, a dual-chamber microbial fuel cell (MFC) coupled with abio-cathode and electrochemically active bacteria is fabricated to treat Cr (VI) containing wastewater and harvest bioelectricity simultaneously. To investigate the wide application of MFC for various industries, four different concentrations of Cr (VI) (6 mg/L, 15 mg/L, 40 mg/L, 100 mg/L) are used to explore the removal efficiency of Cr (VI) and the corresponding power performance. We find that the power performance gradually increases with the increment of the initial Cr (VI) concentration. Significantly, a maximum power density of 35.3 mW/m² can be achieved with the initial concentration of 100mg/L Cr (VI), while MFC only generate negligible power density (2.6 mW/m²) without the presence of Cr (VI). Meanwhile, MFC combined with the initial Cr (VI) concentration of 15 mg/L shows the highest Cr (VI) removal of 66.5%. Moreover, partial precipitates are found on the cathode surface and X-ray photoelectron spectroscopy (XPS) analysis has demonstrated that the Cr (VI) is successfully reduced into Cr (III). This study offers an alternative technology to remove Cr (VI) and synchronous electricity generation.

Insight into the effects of dislocations in nanoscale titanium niobium oxide (Ti2Nb14O39) anode for boosting lithium-ion storage

Defect engineering through induction of dislocations is an efficient strategy to design and develop an electrode material with enhanced electrochemical performance in energy storage technology. Yet, synthesis, comprehension, identification, and effect of dislocation in electrode materials for lithium-ion batteries (LIBs) are still elusive. Herein, we propose an ethanol-thermal method mediated with surfactant-template and subsequent annealing under air atmosphere to induce dislocation into titanium niobium oxide (Ti₂Nb₁₄O₃₉), resultant nanoscale-dislocated-Ti₂Nb₁₄O₃₉ (Nano-dl-TNO). High-resolution transmission electron microscope (HRTEM), fast Fourier transform (FFT), and Geometrical phase analysis (GPA) denote that the high dislocation density engraved with stacking faults forms into the Ti₂Nb₁₄O₃₉ lattice. The presence of dislocation could offer an additional active site for lithium-ion storage and tune the electrical and ionic properties of the Ti₂Nb₁₄O₃₉. The resultant Nano-dl-TNO delivers superior rate capability, high specific capacity, better cycling stability, and making Ti₂Nb₁₄O₃₉ a suitable candidate among fast-charging anode materials for lithium-ion batteries. Moreover, In-situ High-resolution transmission electron microscope (HRTEM) and Geometrical phase analysis (GPA) evinces that the removal of the dislocated area in the Nano-dl-TNO leads to the contraction of the lattice, alleviation of the total volume expansion, causing the symmetrization and preserves structural stability. The present findings and designed approach reveal the rose-colored perspective of dislocation engineering into mixed transition metal oxides as next-generation anodes for advanced lithium-ion batteries and all-solid-state lithium-ion batteries.

The effects of different activating agents on the physical and electrochemical properties of activated carbon electrodes fabricated from wood-dust of Shorea robusta

This study focuses on the effects of activating agents on the physical and electrochemical properties of activated carbon (AC) electrodes, fabricated from wood dust of Shorea robusta. Three different activating agents namely H₃PO_4, KOH and Na₂CO₃ have been used to prepare ACs, which were named as: Sr–H₃PO₄, Sr–KOH and Sr–Na₂CO₃. The ACs were characterized by TGA/DSC, XRD, Raman, SEM, FTIR and BET. All the as prepared ACs were found to be amorphous in nature. The oxygen surface functionality was developed at the surface. The surface area of Sr–H₃PO₄, Sr–KOH and Sr–Na₂CO₃ were found to be 1269.5 m²/g, 280.6 m²/g and 58.9 m²/g respectively. The activated carbon-electrodes were then fabricated and supercapacitive performances were evaluated by “three electrode system” in aqueous 6M KOH using cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS).The GCD performed at 1A/g revealed the specific capacitance values were 136.3 F/g, 42.2 F/g and 59.1 F/g for Sr–H₃PO₄, Sr–KOH and Sr–Na₂CO₃-electrodes, respectively. Energy density for Sr–H₃PO₄ electrode was found to be 3.0 Wh/kg at 99.6 W/kg power densities. Moreover, it also displayed imposing cyclic stability of about 96.9 %, 89.5 % and 78.5 % after 1000 cycles of charge/discharge respectively. The overall electrochemical performance of Sr–H₃PO₄ showed outstanding supercapacitive performances demonstrating the high possibility of this material to be used for the EDLC application in supercapacitive energy storage. The Nyquist plot also showed the lowest internal resistance of about 0.4 Ω for Sr–H₃PO₄ electrode.

Anodic and cathodic biofilms coupled with electricity generation in single-chamber microbial fuel cell using activated sludge

Microbial fuel cell (MFC) is used to remove organic pollutants while generating electricity. Biocathode plays as an efficient electrocatalyst for accelerating the Oxidation Reduction Reaction (ORR) of oxygen in MFC. This study integrated biocathode into a single-chamber microbial fuel cell (BSCMFC) to produce electricity from an organic substrate using aerobic activated sludge to gain more insights into anodic and cathodic biofilms. The maximum power density, current density, chemical oxygen demand (COD) removal, and coulombic efficiency were 0.593 W m^-3, 2.6 A m^-3, 83 ± 8.4%, and 22 ± 2.5%, respectively. Extracellular polymeric substances (EPS) produced by biofilm from the biocathode were higher than the bioanode. Infrared spectroscopy and Scanning Electron Microscope (SEM) examined confirmed the presence of biofilm by the adhesion on electrodes. The dominant phyla in bioanode were Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria, while the dominant phylum in the biocathode was Proteobacteria. Therefore, this study demonstrates the applicable use of BSCMFC for bioelectricity generation and pollution control.

Improvement of capacitive performance of polyaniline based hybrid supercapacitor

This study focuses on synthesis of polyaniline composites and application as electrode material in the fabrication of hybrid supercapacitors. Hybrid supercapacitors were fabricated using aluminum foil as current collector, and conductive Polyaniline (PANI) composites as electrode materials. Cobalt oxide (Co2O3), ammonium peroxydisulfate (APS) were used along with PANI in the preparation of electrodes of the supercapacitor. Polyaniline and its various composites were used in the cathode and activated carbon in the anode (positive electrodes) of the asymmetric hybrid supercapacitor. Electrochemical performance of the supercapacitors has been evaluated on the basis of capacitive properties (i.e. capacitance, energy density and power density). Area of the supercapacitor, applied voltage for charging and composition of cathode materials have been optimized in this study. The optimum area of the supercapacitor was found 30 cm2 at optimum voltage 5 V. The result showed that supercapacitor fabricated using polyaniline (PANI) as cathode material with Al foil as current collector provided highest capacitance of 249 F/g, Energy density of 31 Wh/kg and Power density of 18 W/kg. Among various PANI composites (Ni-PANI, Cu-PANI, CNF-PANI) synthesized in this study, Ni-PANI composite showed highest capacitance of 336 F/g, energy density of 42 Wh/kg, and power density of 31 W/kg. The result indicates that Ni-PANI composite has high potential as cathode materials for the hybrid supercapacitor.

Three-dimensional flower-like nickel doped cobalt phosphate hydrate microarchitectures for asymmetric supercapacitors

Development of asymmetric supercapacitors (ASCs) using hierarchical three-dimensional (3D) morphologies is becoming crucial in energy storage applications due to the greater power density rather than batteries. Herein, 3D flower-like Co₃(PO₄)₂·8H₂O (CPH) and nickel doped CPH (Ni-CPH) microarchitectures were synthesized by a silicone oil bath method at low temperatures without calcination. The synthesized microarchitectures-based electrodes (bare CPH and Ni-CPH) revealed battery-like properties during the electrochemical study. Importantly, the Ni-CPH electrode showed improved electrochemical performance compared to the bare CPH electrode material. The specific capacity values of the CPH and Ni-CPH electrode materials were calculated to be 74 and 108 mAh g^-1 at 0.5 A g^-1, respectively. Furthermore, for the Ni-CPH electrode, 78% of capacity retention was obtained after 9000 cycles at 5 A g^-1. Additionally, an ASC was developed while employing the optimized Ni-CPH electrode (positive-type) and activated carbon (negative-type) and it showed superior electrochemical results. The ASC device exhibited excellent capacity retention (94%) after 9000 cycles at 2 A g^-1. Also, this device delivered a high energy density of 23.4 Wh kg^-1 and a power density of 2103 W kg^-1. Finally, several portable electronic devices were successfully tested using the obtained good energy and power density results from the ASC device for energy storage applications.

Engineering triangular bimetallic metal-organic-frameworks derived hierarchical zinc-nickel-cobalt oxide nanosheet arrays@reduced graphene oxide-Ni foam as a binder-free electrode for ultra-high rate performance supercapacitors and methanol electro-oxidation

The rigorous fabrication of electrode materials using upper-ranked porous precursor especially metal organic frameworks (MOFs) are challenging but appealing task to procure electrochemical energy storage and conversion system with altitudinous performance. Herein, we replenish the rational construction of atypical electrode of hollow Zn-Ni-Co-oxide (ZNCO) nanosheet arrays onto rGO garnished Ni foam (rGO/NF) via two step solution based method. Firstly, 2D Zn-Co-MOFs derived nanoleave arrays are prepared by co-precipitation method. Next, hollow and porous ZNCO nanostructure from 2D solid nanoleave arrays are achieved by ion-exchange and etching process conjoined with post annealing treatment. The as-fabricated hierarchical ZNCO nanosheet arrays offer large numbers of electroactive sites with short ion-diffusion pathways, reflecting the outstanding electrochemical performance in-terms of excellent specific capacity (267 mAh g^-1) ultra-high rate capability (83.82% at 50 A/g) and long-term cycling life (~90.16%) in three electrode configuration for supercapacitor (SCs). Moreover, the hollow and porous ZNCO nanostructure responds as immensely active and substantial electrocatalyst for methanol oxidation with lowest onset potential of 0.27 V. To demonstrate the practicability, hybrid supercapacitor (HSC) device is constructed using ZNCO@rGO-NF nanostructure as positive and rGO decorated MOF derived porous carbon (rGO-MDPC) as negative electrode. The as-assembled ZNCO//rGO-MDPC ASC device delivers higher energy density of 61.25 Wh kg^-1 at the power density of 750 W kg^-1 with long-term cyclic stability (<6% to its initial specific capacity value) after 6000 cycles.

Enhanced energy storage performance and theoretical studies of 3D cuboidal manganese diselenides embedded with multiwalled carbon nanotubes

The burst of energy produced from the sustainable energy sources need to be harnessed by energy storage systems. Development of novel and advanced energy storage devices such as supercapacitors discover an enormous future ahead. Recently, hybrid supercapacitors (electric double layer capacitor (EDLC) and pseudocapacitors) trend to be used as energy storage interfaces for their improved efficacy in energy density without altering the power density. In the ongoing workplan, transition metal selenides MnSe₂ and its hybrid with multiwalled carbon nanotubes (MWCNTs) are synthesized by a simplistic hydrothermal protocol. Certainly, cubic phases of MnSe₂-MWCNT(MS/CNT) manifested superior electrochemical performance in both symmetric and asymmetric full cell configurations in contrast to prestine MnSe₂(MS). The asymmetric MS/CNT cell achieved an excellent charge storage capability with an high energy density of 39.45 Wh kg^-1 at a power density of 2.25 kW kg^-1 maintaining an energy density of 14.5 Wh kg^-1 at a high power density of 4.5 kWh kg^-1 and also revealed long term stability over 5000 consecutive charge/discharge cycles (capacitance retention of 95.2%). Furthermore, the preferable growth along (200) direction in the presence of MWCNTs favoured in enriching the supercapacitive property of MS. The quantum capacitance of MnSe₂surfaces and MS/CNT heterostructure has been estimated using density functional theory simulation to confirm the experimental outcomes. Theoretical investigation simultaneously exposed the contribution of (200) plane of MnSe₂ and MWCNTs cultured in enhanced DOS (density of states) near the Fermi level that remarkably promoted the energy storage efficiency of MS/CNT.

Nickel ferrite/MXene-coated carbon felt anodes for enhanced microbial fuel cell performance

In recent years, the modification of electrode materials for enhancing the power generation of microbial fuel cells (MFCs) has attracted considerable attention. In this study, a conventional carbon felt (CF) electrode was modified by NiFe₂O₄ (NiFe₂O₄@CF), MXene (MXene@CF), and NiFe₂O₄-MXene (NiFe₂O₄-MXene@CF) using facile dip-and-dry and hydrothermal methods. In these modified CF electrodes, the electrochemical performance considerably improved, while the highest power density (1385 mW/m²), which was 5.6, 2.8, and 1.4 times higher than those of CF, NiFe₂O₄@CF, and MXene@CF anodes, respectively, was achieved using NiFe₂O₄-MXene@CF. Furthermore, electrochemical impedance spectroscopy and cyclic voltammetry results confirmed the superior bioelectrochemical activity of a NiFe₂O₄-MXene@CF anode in a MFC. The improved performance could be attributed to the low charge transfer resistance, high conductivity and number of catalytically active sites of the NiFe₂O₄-MXene@CF anode. Microbial community analysis demonstrated the relative abundance of electroactive bacteria on a NiFe₂O₄-MXene@CF anodic biofilm rather than CF, MXene@CF, and NiFe₂O₄@CF anodes. Therefore, these results suggest that combining the favorable properties of composite materials such as NiFe₂O₄-MXene@CF anodes can open up new directions for fabricating novel electrodes for renewable energy-related applications.

Effects of ultrasonication on the properties of maize starch/stearic acid/ sodium carboxymethyl cellulose composite film

Ultrasonic treatment can improve the compatibility between a hydrophobic material and a hydrophilic polymer. The light transmittance, crystalline structure, microstructure, surface morphology, moisture barrier, and mechanical properties of a composite film with or without ultrasonication were investigated. Ultrasound increases the film's light transmittance, resulting in a film that has good transparency. Ultrasonication did not change the crystalline structure of the polymer film, but promoted V-type complex formation. The surface of the film became smooth and homogeneous after the film-form suspension underwent ultrasonic treatment. Compared to the control film, after ultrasonication at 70% amplitude with a duration of 30 min, the average roughness and maximum roughness declined from 212 nm to 17.6 nm and from 768.7 nm to 86.5 nm, respectively. The composite film with ultrasonication exhibited better tensile and moisture barrier properties than the nonsonicated film. However, long-term and strong ultrasonication will destroy the polymer structure to some extent.

Simultaneous Investigation of Three Effective Parameters of Substrate, Microorganism Type and Reactor Design on Power Generation in a Dual-Chamber Microbial Fuel Cells

Background:

Endophytic bacteria reside inside healthy plant tissues and provide several benefits to their host, and help them to tolerate various stresses. Aminocyclopropane-1-carboxylate deaminase (ACCD) production is one of the mechanisms by which these bacteria help the plant to survive under ethylene stress

Objectives:

The main focus of this study was to isolate endophytic bacteria and effectively screen them for ACCD production. The selected isolate was identified and assessed for plant growth-promoting potential under pot conditions.

Materials and Methods:

Endophytic bacteria were isolated from root nodules of Pisum sativum plants, grown in northern India (Haryana state). ACCD activity was initially screened on DF minimal salt medium with ACC as a sole nitrogen source. To narrow down the number of the isolates, another screening method was adopted using a modified medium containing indicator dyes along with ACC. The strain producing ACCD as well as a significant amount of Indole 3 acetic acid (IAA) was identified using 16S rDNA gene sequencing and amplification of acdS gene. Its ability to promote plant growth was evaluated under pot culture conditions.

Results:

Twenty-six endophytic bacteria were isolated from nodules of P. sativum plants. Sixteen isolates showed growth on DF minimal salts medium supplemented with ACC along with negative control. On the modified medium containing indicator dyes, two isolates, PJN13 and PJN17, showed zones of the color gradient. The ACC deaminase activity was further confirmed by enzymatic assay. The strains PJN13 and PJN17 produced 160 and 130 µM of α-ketobutyrate m.g^-1 protein h^-1, respectively. The IAA production in the strain PJN13 (79.04 ± 0.78 µg.mL ^-1) was significantly more than that in the strain PJN17 (38.36 ± 1.89 µg.mL^-1). It could enhance pea plant growth parameters, including root and shoot length and fresh and dry weight from 1 to 4 times compare to the control (untreated pea plants) under pot conditions. The results of 16S rDNA amplification and sequencing showed that PJN13 has maximum similarity to Bacillus mojavensis, and the sequence submitted to GenBank under accession number MH298523. Also, a band about 800 bp was amplified for the acdS gene.

Conclusions:

Though Bacillus is known as a predominant non-rhizobial endophytic genus, however in the present study, a B. mojavensisBacillus mojavensis PRN2 (MH298523) was reported for the first time as an endophyte from the nodules of pea plants. The isolated strain possesses ACC deaminase activity along with IAA production capability, and high potentials as PGPE (Plant growth-promoting endophyte) for plant growth, so it has potential to be used as biofertilizers in pea fields.

MnCo2O4 coated carbon felt anode for enhanced microbial fuel cell performance

A highly efficient anode is very crucial for an improved microbial fuel cell (MFC) performance. In this study, a binder-free manganese cobalt oxide (MnCo₂O₄@CF) anode was synthesized using a conventional carbon felt (CF) by a facile hydrothermal method. A large electrochemically active and rough electrode surface area of MnCo₂O₄@CF anode improved the substrate fluxes and microbial adhesion/growth. Furthermore, the electrochemical tests on the synthesized anode confirmed the superior bioelectrochemical activity, reduced ion transfer resistance, and excellent capacitance. This resulted in an improved power density (945 mW/m²), which was 3.8 times higher than that of CF anode. The variable valence state, high stability and biocompatibility of MnCo₂O₄@CF resulted in continuous current density performance for five MFC cycles. High-throughput biofilm analysis revealed the enrichment of electricity producing phylum of Proteobacteria and Bacteroidetes (∼90.0%), which signified that the modified MnCo₂O₄ anode accelerated the enrichment of electro-active microbes.

Power density of microbial electrochemical system responds to mass transfer characters of non-ion-selective microbial separator

The microbial separator (MS) was promising alternative of ion exchange membrane for biocathode microbial electrochemical system (MES). Four microbial separators developed from porous matrixes were equipped in biocathode MESs. The power generation of MESs responded to cross-separator transfer characters of ions, dissolved oxygen (DO) and chemical oxygen demand (COD). The MES with carbon felt (CF) obtained 31% higher maximum power density at 70 ± 3 mW m^-2 and 51% higher current density at 271 ± 21 mA m^-2 than those of cation exchange membrane (CEM) separator. All MSs showed higher ionic conductivity than CEM. However, the power variation was mainly due to cathodic equilibrium potential changes rather than internal resistance. The power density demonstrated negative correlation with mass transfer coefficients of DO and COD. The cross-separator transfer of COD caused cathode variation and was identified as the primary parameter for further optimization of MES with microbial separators.