Reduction Of Azo Dyes Research Articles

Therapeutic Applications of Azo Dye Reduction: Insights From Methyl Orange Degradation for Biomedical Innovations.

This paper emphasizes the possible application of methyl orange reduction as a therapeutic technique, highlighting the potential of azo dye reduction in biomedical fields. The generally used azo dyes are toxic and carcinogenic; hence, they implicitly threaten the environment and health. The degradation of methyl orange, a famous example of azo dyes, is used to describe the degradation process for other azo dyes. This work discusses the ability of different methyl orange degradation methods, focusing on biocatalysts and nanomaterials, among the methods that identified enzymatic degradation with azoreductase enzymes as the method that quickly breaks down azo dyes under mild conditions as the most appropriate method, as well as its specificity as environmentally friendly. Moreover, metal nanoparticles such as silver and gold impellers increase the reducing efficiency because they offer a pivotal surface for the reduction reactions that undergo electron transfer. The complete breakdown of methyl orange is essential in biomedical usage. The strategies for treating azo dye reduction can be extended to next-generation drug delivery systems (DDS), biosensors, and therapeutic agents. Organisms involved in degradation can be functionalized to selectively degrade specific cells or tissues, thus presenting a new targeted therapy. Knowledge of degradation pathways and non-toxic products is essential in creating programs that build better and more efficient therapeutic agents. This work endeavors to illustrate the development of enzymatic and nanomaterials-based approaches to achieve sustainable azo dye decolorisation to open the gateway to developing other biomedical applications that tend to promote environmental and health-friendly solutions.

Cu@Zn@800 bimetallic-based carbon nanomaterials for dark-catalyzed degradation and 4-NP-catalyzed reduction of azo dyes

Metal-organic frameworks (MOFs) were adaptable templates that might be used to create multifunctional materials containing carbon nanostructures. In this work, we had prepared a novel Cu-MOF using fumaric acid (H2FA) and N,N′-bis(pyridin-3-yl)isophthalamide (3-bpia) as the mixed ligands. Then, the Cu-MOF was served as a template to derive bimetallic-based carbon nanomaterials by introducing a second metal through doped ZnO by both re-calcined and directly calcined methods (Cu@Zn@800) and single-metal-based carbon nanomaterials (Cu@800). Cu@Zn@800 was able to catalyze the degradation of azo dyes at a rate higher than 99.40 % because of its capacity to create h+ and ·OH active substances and the uniformity of its metal active sites. Additionally, Cu@Zn@800 might use NaBH4 to decrease 4-NP in 30 s with the rate of decline was over 100 %. Cu@Zn@800 was a special and efficient dual-functional material that might be used in a variety of ways to remove contaminants from water.

The enhancement effect of n-Fe3O4 on methyl orange reduction by nitrogen-fixing bacteria consortium

Although the anaerobic reduction of azo dyes is ecofriendly, high ammonia consumption remains a significant challenge. This work enriched a mixed nitrogen-fixing bacteria consortium (NFBC) using n-Fe3O4 to promote the anaerobic reduction of methyl orange (MO) without exogenous nitrogen. The enriched NFBC was dominated by Klebsiella (80.77 %) and Clostridium (17.16 %), and achieved a 92.7 % reduction of MO with an initial concentration of 25 mg·L−1. Compared with the control, the consortium increased the reduction efficiency of MO, cytochrome c content, and electron transport system (ETS) activity by 11.86 %, 89.86 %, and 58.49 %, respectively. When using 2.5 g·L−1 n-Fe3O4, the extracellular polymeric substances (EPS) of NFBC were present in a concentration of 85.35 mg·g−1. The specific reduction rates of MO by NFBC were 2.26 and 3.30 times faster than those of Fe(II) and Fe(III), respectively, while the enrichment factor of the ribosome pathway in NFBC exceeded 0.75. Transcriptome, carbon consumption, and EPS analyses suggested that n-Fe3O4 stimulated carbon metabolism and secreted protein synthesized by the mixed culture. The latter occurred due to the increased activity of consortium and the content of redox substances. These findings demonstrate that n-Fe3O4 promoted the efficiency of mixed nitrogen-fixing bacteria for removing azo dyes from wastewater. This innovative approach highlights the potential of integrating nanomaterials with biological systems to effectively address complex pollution challenges.

New insights into the mechanism of azo dye biodegradation by Lactococcus lactis

Azo dye reduction by syntrophic microbial communities is still unclear, with conflicting observations reported in the literature. In this study, the biodegradation mechanism of a model azo dye by Lactococcus lactis strain LLSP-01 isolated from an acidogenic reactor system was investigated. Proteomics and RT-PCR analysis results showed that LLSP-01 azoreductase (AzoL) was not expressed by the isolate during exposure to Direct Black 22. In contrast, the mechanism appears to involve biosorption by glycoconjugates, particularly exopolysaccharides (EPS) and rhamnolipids, as proteins from the LPS O-antigen metabolism were statistically higher expressed in cells challenged with the target compound. Based on the proteomic observations, it is hypothesized that Direct Black 22 is adsorbed into the biofilm matrix and indirectly reduced by an SDR family oxidoreductase, in a mechanism mediated by riboflavin carriers. Induction of a ring-cleaving dioxygenase in the presence of azo dye indicates further degradation of the resulting aromatic amines. The collected results show that azo dye reduction by L. lactis is mediated by enzymes with broad range specificity, and not the typical azoreductases. This information can assist in the design of new strategies for the bioremediation of textile azo dyes.

Frequency-modulated alternating current-driven bioelectrodes for enhanced mineralization of Alizarin Yellow R

The alternating current (AC)-driven bioelectrochemical process, in-situ coupling cathodic reduction and anodic oxidation in a single electrode, offers a promising way for the mineralization of refractory aromatic pollutants (RAPs). Frequency modulation is vital for aligning reduction and oxidation phases in AC-driven bioelectrodes, potentially enhancing their capability to mineralize RAPs. Herein, a frequency-modulated AC-driven bioelectrode was developed to enhance RAP mineralization, exemplified by the degradation of Alizarin Yellow R (AYR). Optimal performance was achieved at a frequency of 1.67 mHz, resulting in the highest efficiency for AYR decolorization and subsequent mineralization of intermediates. Performance declined at both higher (3.33 and 8.30 mHz) and lower (0.83 mHz) frequencies. The bioelectrode exhibited superior electron utilization, bidirectional electron transfer, and redox bifunctionality, effectively aligning reduction and oxidation processes to enhance AYR mineralization. The 1.67 mHz frequency facilitated the assembly of a collaborative microbiome dedicated to AYR bio-mineralization, characterized by an increased abundance of functional consortia proficient in azo dye reduction (e.g., Stenotrophomonas and Shinella), aromatic intermediates oxidation (e.g., Sphingopyxis and Sphingomonas), and electron transfer (e.g., Geobacter and Pseudomonas). This study reveals the role of frequency modulation in AC-driven bioelectrodes for enhanced RAP mineralization, offering a novel and sustainable approach for treating RAP-bearing wastewater.

Laser-based synthesis of silver nanoparticles embedded in cellulose paper for catalytic reduction of azo dyes and SERS sensing of pesticides

In this study, highly reactive bare silver nanoparticles (Ag NPs) are synthesized using the Pulsed Laser Ablation in Liquid (PLAL) technique. Ag NPs are then coated on the filter paper using the dip coating method. This process converts filter paper into a versatile substrate for catalysis and surface-enhanced Raman Spectroscopy (SERS) based sensing. The successful synthesis of spherical Ag NPs and their effective embedding into the filter paper was confirmed using UV–visible absorption spectroscopy, scanning electron microscopy (SEM), and Energy Dispersive x-ray analysis (EDX). SEM images revealed that the Ag NPs were embedded in the filter paper and attached to the cellulose fibers. The use of Ag NPs embedded filter paper as a catalyst substrate for the reduction of both cationic and anionic dyes demonstrated that higher concentrations of Ag NPs on the filter paper resulted in a faster reduction. In particular, filter paper impregnated with 52 μg of Ag NPs demonstrated a complete reduction of methylene blue and methyl orange in less than a minute and 4 min, respectively. To demonstrate the practical sensing capability of the Ag NPs embedded filter paper, it was utilized as a SERS substrate. This enabled the detection of trace levels of Rhodamine 6G (R6G) and the pesticide molecule chlorpyrifos, demonstrating its potential real-world applications.

In situ coupling of reduction and oxidation processes with alternating current-driven bioelectrodes for efficient mineralization of refractory pollutants

The effective elimination of aromatic compounds from wastewater is imperative for safeguarding the ecological environment. Bioelectrochemical processes that combine cathodic reduction and anodic oxidation represent a promising approach for the biomineralization of aromatic compounds. However, conventional direct current bioelectrochemical methods have intrinsic limitations. In this study, a low-frequency and low-voltage alternating current (LFV-AC)-driven bioelectrode offering periodic in situ coupling of reduction and oxidation processes was developed for the biomineralization of aromatic compounds, as exemplified by the degradation of alizarin yellow R (AYR). LFV-AC stimulated biofilm demonstrated efficient bidirectional electron transfer and oxidation–reduction bifunctionality, considerably boosting AYR reduction (63.07% ± 1.91%) and subsequent mineralization of intermediate products (98.63% ± 0.37%). LFV-AC stimulation facilitated the assembly of a collaborative microbiome dedicated to AYR metabolism, characterized by an increased abundance of functional consortia proficient in azo dye reduction (Stenotrophomonas and Bradyrhizobium), aromatic intermediate oxidation (Sphingopyxis and Sphingomonas), and electron transfer (Geobacter and Pseudomonas). The collaborative microbiome demonstrated a notable enrichment of functional genes encoding azo- and nitro-reductases, catechol oxygenases, and redox mediator proteins. These findings highlight the effectiveness of LFV-AC stimulation in boosting azo dye biomineralization, offering a novel and sustainable approach for the efficient removal of refractory organic pollutants from wastewater.

Treatment of tannery effluent: An effective biological enhancement approach

AbstractThe water pollution due to tannery industries that contaminate river water and other spheres, is a side effect of industry expansion. The research focused on the biological removal of synthetic azo dyes by using biological treatment under aerobic conditions. Through morphological observation, biochemical test, and 16S rRNA sequence analysis the isolated bacteria were determined to be Aeromonas caviae, Enterobacter sichuanensis. Reduction of the organic content present in the tannery effluent and removal of the nutrients that cause pollution or inactivate potential pathogenic microorganisms or parasites. Optimized the azo dye degradation conditions at the temperature of 37°C, at pH 7 in 10% inoculum concentration at the time of 48th hour where novel organism capable of performing effective degradation. The metabolite of an aliquot mixture of the optimized condition was analyzed using Fourier Transform Infrared (FTIR) and the results confirmed the reduction of azo dyes. These results indicate that A. caviae and E. sichuanensis can be utilized as a solution for the remediation of tannery industrial effluent containing azo dyes.

Active metals decorated NiCo2O4 yolk-shell nanospheres as nanoreactors for catalytic reduction of nitroarenes and azo dyes

Transition-metal oxides (TMOs) have received a great deal of research attention and have been widely used in a variety of fields. However, conventional TMOs do not possess high specific surface area, sufficient active site on their surfaces, and limited their applications in catalysis. This study presents a two-step method for synthesizing active metal (M) decorated NiCo2O4 (M/NiCo2O4, M = Pd or Cu) nanospheres with yolk-shell nanostructures. Taking advantage of the unique morphology and the combination of dual active components (i.e., active NiCo2O4 substrate and decorated active metal), the as-prepared M/NiCo2O4 yolk-shell nanospheres can be employed as nanoreactors in the organic reactions. In catalyzing the reduction of a representative nitroarene (i.e., 4-NP) by NaBH4, the Pd/NiCo2O4 nanoreactors exhibit a superior catalytic efficiency to their counterparts (Cu/NiCo2O4 and NiCo2O4). The turnover frequency is much higher than that of various TMOs supported nanocatalysts have been reported over the past five years. Furthermore, the Pd/NiCo2O4 nanoreactors show excellent stability and common applicability of the reduction of various substituted nitrobenzenes and azo dyes. This work provides new rational design concept and preparation strategy for efficient nanoreactors with dual active components and sheds light on the practical application of chemical reactions.

Facile synthesis of C30-AuNPs for the effective catalytic reduction of nitrophenols and azo dyes

A facile and green synthesis approach of C30-AuNPs is developed for the effective catalytic reduction of nitrophenols and azo dyes, and the in-depth mechanism investigation is described by thermodynamic and kinetic analysis.

Bifunctional green nanoferrites as catalysts for simultaneous organic pollutants reduction and hydrogen generation: Upcycling strategy

The upcycling strategy is an approach that includes the conversion of waste into new higher value-added products. This study reports on a new methodology for the environmentally friendly synthesis of MFe2O4 spinel nanoferrites (M = Co, Cu, Fe and Mn) to be used as catalysts applied in the upcycling method. Thus, the reduction of 4-nitrophenol (4-NP), methyl orange, and methyl red to commercially valuable compounds was evaluated, as well as the simultaneous generation of hydrogen in a short time. Therefore, an eco-friendly synthesis was proposed, according to the 12 principles of green chemistry and sustainability. Product were obtained with satisfactory properties in terms of crystallinity, magnetic particle size, and magnetization. The materials exhibited excellent performance in catalytic reduction of 4-NP, whose reduction time decreased in the order MnFe2O4 > Fe3O4 > CoFe2O4 > CuFe2O4. This behavior highlighted the CuFe2O4 nanoferrite, which achieved 4-NP reduction in just 10 s. It proved that it could also be reused for 10 consecutive cycles while maintaining its crystalline structure. The catalyst was also effective in the reduction of azo dyes and subsequent production of substituted aromatic compounds suitable for use in chemical processes. Under the optimized conditions, the green CuFe2O4 catalyst was effective in producing hydrogen by hydrolysis. HGR and activation energy (Ea) values were of the order of 19,600 mL g−1 min−1 and 25.5 kJ mol−1, respectively. The results demonstrated the potential of this simple strategy for the environmental pollutant elimination and power generation.

Enhanced azo dye reduction at semiconductor-microbe interface: The key role of semiconductor band structure

Low-energy environmental remediation could be achieved by biocatalysis with assistance of light-excited semiconductor, in which the energy band structure of semiconductor has a significant influence on the metabolic process and electron transfer of microbes. In this study, direct Z-scheme and type II heterojunction semiconductor with different energy band structure were successfully synthesized for constructing semiconductor-microbe interface with Shewanella oneidensis MR-1 to achieve acid orange7 (AO7) biodegradation. UV–vis diffuse reflection spectroscopy, photoluminescence spectra and photoelectrochemical analysis revealed that the direct Z-scheme heterojunction semiconductor had stronger reduction power and faster separation of photoelectron-hole, which was beneficial for the AO7 biodegradation at semiconductor-microbe interface. Riboflavin was also involved in electron transfer between the semiconductor and microbes during AO7 reduction. Transcriptome results illustrated that functional gene expression of Shewanella oneidensis MR-1 was upregulated significantly with photo-stimulation of direct Z-scheme semiconductor, and Mtr pathway and conductive pili played the important roles in the photoelectron utilization by Shewanella oneidensis MR-1. This work is expected to provide alternative ideas for designing semiconductor-microbial interface with efficient electron transfer and broadening their applications in bioremediation.

Fabrication of core–shell beads, hollow capsules, and AuNP-embedded catalytic beads from an ultrasmall peptide hydrogel

Hydrogel beads have emerged as a new class of soft materials that infuse the noble properties of macro-dimensional hydrogels in tiny, easily operable, and robust droplets. Usually, polymeric hydrogels are used in the production of hydrogel beads due to their high structural rigidity and durability, and low molecular weight hydrogel beads are relatively uncommon. Herein, we employed an ultra-short peptide (Pyrene-Lys-Cys, PyKC) based low molecular weight injectable hydrogel, that remains insoluble in bulk solvents, to create stable hydrogel beads using a simple extrusion technique. To enhance durability and applicability, the beads are coated with a polymeric shell, resulting in a core–shell configuration. The shell of the core–shell beads can be modified through a variety of organic conjugation reactions. Also, the core (hydrogel) can be sacrificed using DMSO, resulting in the formation of hollow organic capsules. Furthermore, the core–shell beads enabled the in-situ synthesis and stabilization of gold nanoparticles on the bead surface. The gold-loaded beads demonstrated remarkable catalytic efficiency in the reduction of p-nitrophenol and hazardous azo dyes. In a nutshell, the extremely modular and customizable nature of the PyKC-based core–shell hydrogel bead may allow it to function as a unified platform for multifaceted applications.

Mechanistic insights into acid orange 7 azo dye (AO7) reduction using DFT calculations

A major environmental issue is the occurrence of azo-dye chemicals in textile wastewater. Improving the biological process of dye removal requires a good understanding of the degradation reaction mechanism. In this work, we selected the acid orange 7 (AO7) as the azo dye model and the couple redox AQS/AHQS as a redox mediator (RM). The Gibbs free energy and the redox potential of AO7 were predicted through the Density Functional Theory (DFT). The comparison of our results with experimental data shows that the DFT method is very effective in predicting the redox potential of AO7. Then, to propose a new reaction mechanism for the biological degradation of AO7 with the couple AQS/AHQS, the local and global reactivity descriptors were computed with a hybrid PBE0 functional and dnp basis set. The global descriptors showed that AHQS behaves as a nucleophile against AO7 and as an electrophile against AO7 hydrazo-intermediate (AO7-HI). Fukui function analysis shows that the reaction mechanism of AO7 reduction occurs in two steps: a nucleophilic attack leads to the formation of AO7-HI, followed by an electrophilic attack that leads to the formation of aromatic amines. We found that the proposed reaction mechanism obtained by theoreticalcomputation is in good agreement with other mechanisms of azo dyes reduction proposed in the literature.

Synergistic effect of silver NPs immobilized on Fe3O4@L-proline magnetic nanocomposite toward the photocatalytic degradation of Victoria blue and reduction of organic pollutants.

The surface of magnetite (Fe3O4) nanoparticles was subject to modification through the incorporation of L-proline (LP) by simple co-precipitation method in which silver nanoparticles were deposited by in situ method, thereby yielding the Fe3O4@LP-Ag nanocatalyst. The fabricated nanocatalyst was characterized using an array of techniques including Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET), and UV-Vis spectroscopy. The results evince that the immobilization of LP on the Fe3O4 magnetic support facilitated the dispersion and stabilization of Ag NPs. The SPION@LP-Ag nanophotocatalyst exhibited exceptional catalytic efficiency facilitating the reduction of MO, MB, p-NP, p-NA, NB, and CR in the presence of NaBH4. The rate constants obtained from the pseudo-first-order equation were 0.78, 0.41, 0.34, 0.27, 0.45, 0.44, and 0.34 min-1 for CR, p-NP, NB, MB, MO, and p-NA, respectively. Additionally, the Langmuir-Hinshelwood model was deemed the most probable mechanism for catalytic reduction. The novelty of this study lies in the use of L-proline immobilized on Fe3O4 MNPs as a stabilizing agent for the in-situ deposition of silver nanoparticles, resulting in the synthesis of Fe3O4@LP-Ag nanocatalyst. This nanocatalyst exhibits high catalytic efficacy for the reduction of multiple organic pollutants and azo dyes, which can be attributed to the synergistic effects between the magnetic support and the catalytic activity of the silver nanoparticles. The easy recyclability and low cost of the Fe3O4@LP-Ag nanocatalyst further enhance its potential application in environmental remediation.

One pot synthesis of cyclodextrin MOF as a promising heterogeneous catalyst for the reduction of nitroaromatic compounds and azo dyes

One pot synthesis of cyclodextrin MOF as a promising heterogeneous catalyst for the reduction of nitroaromatic compounds and azo dyes

Multi response optimization of waste activated sludge oxidation and azo dye reduction in microbial fuel cell

ABSTRACT Microbial fuel cell technology draws attention with its ability to directly recover electrical energy from various organic materials. In this study, the operating conditions affecting the oxidation–reduction and electricity generation efficiency of MFC were optimized using the Taguchi Experimental Design model. Optimization was carried out for maximum power density, coulombic efficiency, azo dye removal, and COD removal. With the determined optimum conditions (cathode pH of 3.0, cathode oxygen status of anaerobic, anode substrate of pre-treated, external resistance of 100 Ω, cathode electrode type of plain carbon, cathode electrode surface of 22 cm2, cathode conductivity of 20 µs/cm), 177.03 mW/m2 power density, 7.50% coulombic efficiency, 91.26% azo dye removal efficiency and 21.61% COD removal efficiency were obtained. By Pareto analysis, it was determined that the power density, coulombic efficiency and COD removal efficiency were most affected by the substrate type at the anode, and the azo dye removal was most affected by the catholyte pH. The maximum power density and internal resistance of the MFC operated under optimum conditions were determined as 145.11 mW/m2 and 243.30 Ω, respectively by the polarization curve. Cyclic voltammetry was also performed for the electrochemical characterization of MFC operated under optimum conditions. An anodic peak at −183.2 mV and a cathodic peak at −181.2 mV was visible in the CV curve.

Catalytic Reduction of Congo Red to Low-Toxicity Forms Using a Low-Cost Catalyst Based on Modified Bentonite Material

AbstractThe reduction of azo dyes to less toxic and more easily biodegradable amine derivatives is an effective strategy for the treatment of industrial wastewater. The present work aimed to study the reduction reaction of azo dye Congo red (CR) catalyzed by nanoparticles (NPs) of chromium oxides (Cr2O3NPs) immobilized on bentonite in the presence of NaBH4. Cr(III) ions were intercalated using ion exchange reactions to obtain Cr-bentonite, and then the immobilized chromium cations were treated using NaBH4 leading to the formation of Cr2O3NPs-bentonite. The physicochemical properties of the samples were investigated using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS), atomic absorption spectrometry (AAS), UV–Visible diffuse reflectance (UV–Vis DR), and Fourier-transform infrared (FTIR) spectroscopy techniques. The results showed the formation of various chromium species, in which the most dominant were chromium oxide nanoparticles, on the bentonite surface with an average particle size between 20 and 35 nm. Line-scan analysis showed a reactive catalytic surface due to the excellent distribution of Cr on the bentonite surfaces. The best-performing catalyst, Cr2O3NPs-bentonite, displayed significant catalytic activity compared to the bentonite and Cr-bentonite materials, with a full reduction time of 630 s and a rate constant, kapp, equal to 0.034 s–1. The resulting products (benzidine and sodium 3, 4-diaminonaphthalene-1-sulfonate) from the catalytic reduction exhibited low toxicity compared to the CR dye; these products are easy to use in chemical synthesis. All results collected from this work indicated that this low-cost catalyst can be exploited to eliminate other dyes from the environment.

Magnetic Fe3O4@MIL-100(Fe) core-shells decorated with gold nanoparticles for enhanced catalytic reduction of 4-nitrophenol and degradation of azo dye

In this contribution, the metal-organic framework Fe3O4@MIL-100(Fe) have been successfully synthesized via in situ single-step hydrothermal route, where Fe3O4 not only acts as a core but also provide Fe(III) for uniform growth of MIL-100(Fe) shell around Fe3O4 microspheres. Compared with Fe3O4, both surface area and pore volume of Fe3O4@MIL-100(Fe) is significantly enhanced while the magnetism is slightly affected. The synthesis procedure is facile since it eliminates the need of the functionalization of Fe3O4 core with mercaptoacetic acid (MAA), addition of external iron source and repeated cycles of growth and washing. The as-prepared MIL-100(Fe) were decorated with gold nanoparticles (Au NPs) by deposition-reduction method for the first time and applied for fast detection and reduction of 4-Nitrophenol (4-NP) and azo dye to reduce their environmental and health issues. With N2 physisorption, XRD, TEM, SEM, VSM and FT-IR characterization, the metallic Au NPs were identified to be highly dispersed in the Fe3O4@MIL-100(Fe) cages without affecting the magnetism. For Au/Fe3O4@MIL-100(Fe), complete reduction of 4-NP and azo dye occurred within 16 min with reaction rate constant (k) of 0.25 and 0.2 min−1, respectively superior to Fe3O4 core and Fe3O4@MIL-100(Fe), which is attributed to well dispersive Au NPs, texture, and core shell surface of Fe3O4@MIL-100(Fe). Furthermore, the excellent reusability of Au/Fe3O4@MIL-100(Fe) makes it attractive to be used for multiples cycles in catalysis.

Energy production from mucilage biomass and reduction of azo dye in microbial fuel cells

Energy production from mucilage biomass and reduction of azo dye in microbial fuel cells