Effect Of Redox Mediators Research Articles

Insights into redox mediator supplementation on enhanced volatile fatty acids production from waste activated sludge.

Anaerobic fermentation of waste activated sludge (WAS) for recycling valuable volatile fatty acids (VFAs) is economically valuable. However, the fermentation of protein is the rate-limiting step of VFA production with WAS as a substrate. In this study, the effect of redox mediators (RMs, i.e., riboflavin and lawsone) on the enhanced production of VFAs from WAS was investigated. The results indicate that both RMs can promote protein-dependent fermentation, increasing maximum VFA accumulation by 43.9% and 42.5% respectively. In cultures supplemented with riboflavin and lawsone, VFA production was highly correlated with protease activities, but not with α-glucosidase activities. This implies that RMs affected the redox reaction of amino acids degradation, resulting in an increased release of ammonia. Sequencing results showed that RMs significantly increased the abundance of bacteria related to VFA fermentation and protein/amino acid degradation at the levels of phylum, class, order, family, and even genus.

Effect of redox mediators in pharmaceuticals degradation by laccase: A comparative study

Abstract Bio-catalytic processes have recently attracted attention as an interesting option for the degradation of persistent pollutants as they are capable to catalyze specific reactions at mild conditions and low environmental impact. In this work the potential to transform pharmaceutical micropollutants of a novel laccase from Pycnoporus sanguineus CS43 was compared to the commercial laccases Trametes versicolor and Myceliophtora thermophila. In the absence of redox mediators micropollutants were resistant to degradation, except for the antibiotic amoxicillin that was transformed by all laccases. The influence of natural and synthetic redox mediators (syringaldehyde, p-coumaric acid and ABTS) on the laccase oxidation system was investigated. Results showed the degradation of a complex mixture of pharmaceuticals is both compound and redox mediator dependent. Syringaldehyde resulted as the best redox mediator allowing the highest degradation yields of the antibiotics amoxicillin (80%), sulfamethoxazole (100%) and ciprofloxacin (40%) within 3 h treatment. Overall, commercial laccases showed better catalytic performance in comparison to P. sanguineus CS43 laccase especially in the presence of redox mediators. The successful transformation of pharmaceuticals by the combined action of different laccases and redox mediators demonstrate the potential of these systems for the removal of complex pollutant matrices.

Ordered Mesoporous Titanium Nitride As a Promising Carbon-Free Cathode for Aprotic Li-O2 Batteries

Despite the extraordinary gravimetric energy densities, Li-O2 batteries are still facing a technological challenge;[1] limited round trip efficiency leading to insufficient cycle life. Recently, carbonaceous electrode materials were found to be one of the primary origins of the limited cycle life,[2] as they produce irreversible side products during discharge. A few investigations based on noncarbonaceous materials have demonstrated largely suppressed accumulation of irreversible side products,[3] but such studies have focused mainly on the materials themselves rather than delicate morphology control. As such, here, we report the synthesis of mesoporous titanium nitride (m-TiN) with a 2D hexagonal structure and large pores (>30 nm), which was templated by a block copolymer with tunable chain lengths, and introduce it as a stable air-cathode backbone. Due to the well-aligned pore structure and decent electric conductivity of TiN, the battery reaction was quite reversible, resulting in robust cycling performance for over 100 cycles under a voltage cutoff condition. Furthermore, by protecting the Li metal with a poreless polyurethane separator[4] and engaging a lithium iodide redox mediator[3], the original capacity was retained for 280 cycles under a consistent capacity condition (430 mAh/g). This study reveals that when the appropriate structure and material choice of the air-cathode are coupled with an advanced separator and an effective solution-phase redox mediator, the cycle lives of Li-O2 batteries can be enhanced dramatically. Reference s : [1] J. W. Choi, D. Aurbach, Nat. Rev. Mater. 1 (2016) 16013. [2] M.M. Ottakam Thotiyl, S.A. Freunberger, Z. Peng, P.G. Bruce, J. Am. Chem. Soc.135 (2013) 494−500. [3] N. Feng, P. He, H. Zhou, Adv. Energy Mater. 6 (2016) 1502303. [4] B.G. Kim, J. Kim, J. Min, Y. Lee, J.H. Choi, M.C. Jang, S.A. Freunberger, J.W. Choi, Adv. Funct. Mater. 26 (2016) 1747-1756. Figure 1

High Concentration of LiBr in Electrolyte and Graphene-Polydopamine Composite Layer on Li Metal for High Efficient and Long Term Cycling Li-O2 Batteries

For advanced applications such as electric vehicles (EV), Li-O2 batteries are considered as a prospective candidate for next-generation to replace conventional Li-ion batteries. However, the catalytic effect of the redox mediator for oxygen evolution gradually deteriorates during repeated cycling owing to its decomposition at the surfaces of both the oxygen electrode (cathode) and the Li metal electrode (anode).1,2 Here, we designed optimized Li-O2 batteries with a continuously effective redox mediator and a stable protective layer for the Li metal electrode by optimizing the LiBr concentration and introducing a graphene–polydopamine composite layer, respectively.3 These synergistic modifications lead to a reduction of the charge potential to below 3.4 V and significantly improved the stability and cycle life of Li–O2 batteries. Consequently, a high energy efficiency of above 80% was maintained over 150 cycles. Herein, we confirmed that the relationships between all the battery materials should be understood in order to improve the performance of Li-O2 batteries. References W.-J. Kwak, D. Hirshberg, D. Sharon, H.-J. Shin, M. Arfi, J.-B. Park, A. Garsuch, F. F. Chesneau, A. A. Frimer, D. Aurbach, Y.-K. Sun, Mater. Chem. A 2015, 3, 8855. W.-J. Kwak, D. Hirshberg, D. Sharon, M. Arfi, A. A. Frimer, H.-G. Jung, D. Aurbach, Y.-K. Sun, Energy Environ. Sci. 2016, 9, 2334. W.-J. Kwak, S.-J. Park, H.-G. Jung, and Y.-K. Sun, Adv. Energy Mater. 2017, 7, 1702258

Optimized Concentration of Redox Mediator and Surface Protection of Li Metal for Maintenance of High Energy Efficiency in Li–O2 Batteries

AbstractRecently, various approaches for adding redox mediators to electrolytes and introducing protective layers onto Li metal have been suggested to overcome the low energy efficiency and poor cycle life of Li–O2 batteries. However, the catalytic effect of the redox mediator for oxygen evolution gradually deteriorates during repeated cycling owing to its decomposition at the surfaces of both the oxygen electrode (cathode) and the Li metal electrode (anode). Here, optimized Li–O2 batteries are designed with a continuously effective redox mediator and a stable protective layer for the Li metal electrode by optimizing the LiBr concentration and introducing a graphene–polydopamine composite layer, respectively. These synergistic modifications lead to a reduction of the charge potential to below 3.4 V and significantly improve the stability and cycle life of Li–O2 batteries. Consequently, a high energy efficiency of above 80% is maintained over 150 cycles. Herein, it is confirmed that the relationships between all the battery materials should be understood in order to improve the performance of Li–O2 batteries.

The Effects of Redox Mediators and Water Content on Oxygen Evolution for Li-Air Batteries

Chemistries that can demonstrate tolerance to both moisture and atmospheric carbon dioxide have the power to advance the technology readiness level of non-aqueous lithium air batteries. Previously published results have found that lithium iodide as redox mediator in dimethoxyethane solvent containing high water content affords reversible cycling of a lithium oxygen battery via lithium hydroxide[1]. In collaboration with the authors of the previous work, this concept has been extended to explore additional redox mediators and alternative electrolyte mixtures. Quantitative oxygen evolution for the new chemistries was studied using continuous differential electrochemical mass spectroscopy. Oxygen evolution was found for some of the new chemistries employed. Faradaic efficiency for oxygen evolution and Tafel analysis shows complex behaviour. Discharge product analysis shows that some of the new chemistries which afford oxygen evolution also cycle via lithium hydroxide.[1] Liu, et al. Science, 2015, 350, 6260, p530.

Ordered Mesoporous Titanium Nitride as a Promising Carbon-Free Cathode for Aprotic Lithium-Oxygen Batteries.

Despite the extraordinary gravimetric energy densities, lithium-oxygen (Li-O2) batteries are still facing a technological challenge; limited round trip efficiency leading to insufficient cycle life. Recently, carbonaceous electrode materials were found to be one of the primary origins of the limited cycle life, as they produce irreversible side products during discharge. A few investigations based on noncarbonaceous materials have demonstrated largely suppressed accumulation of irreversible side products, but such studies have focused mainly on the materials themselves rather than delicate morphology control. As such, here, we report the synthesis of mesoporous titanium nitride (m-TiN) with a 2D hexagonal structure and large pores (>30 nm), which was templated by a block copolymer with tunable chain lengths, and introduce it as a stable air-cathode backbone. Due to the well-aligned pore structure and decent electric conductivity of TiN, the battery reaction was quite reversible, resulting in robust cycling performance for over 100 cycles under a potential cutoff condition. Furthermore, by protecting the Li metal with a poreless polyurethane separator and engaging a lithium iodide redox mediator, the original capacity was retained for 280 cycles under a consistent capacity condition (430 mAh g-1). This study reveals that when the appropriate structure and material choice of the air-cathode are coupled with an advanced separator and an effective solution-phase redox mediator, the cycle lives of Li-O2 batteries can be enhanced dramatically.

APPLICATION OF RESIDUAL YEAST AS A SOURCE OF REDOX MEDIATORS FOR THE ANAEROBIC DECOLORIZATION OF A MODEL AZO DYE

Abstract - This work investigated the anaerobic degradation of the model azo dye Remazol Yellow Gold RNL in batch reactors using discharged residual yeast as the source of redox mediators (RM). Two yeast lysis methods (mechanical lysis and sonication) were tested and optimized to produce a riboflavin-rich yeast lysate. The reactors were operated at 25 o C for 48 hours, evaluating the effect of external carbon source (glucose) and RM (from residual yeast lysate and commercial yeast extract) addition. The results showed that color removal efficiencies for the batch reactors fed with commercial yeast extract reached 90%, whereas those fed with discharged yeast lysate reached 80% (sonication) and 73% (mechanical lysis). These values were statistically higher when compared to reactors operating without RM (48 to 66%), demonstrating that yeast extract enhances azo dye degradation in anaerobic conditions and that the residual yeast is a cheap and alternative source of carbon and of the RM riboflavin.

Effects of redox mediators on α-Fe2O3 exposed by {012} and {104} facets for photocatalytic water oxidation

The mechanism study of redox mediator to transfer the photogenerated electrons is extremely desirable for artificial Z-scheme photocatalytic systems. Here we find that the α-Fe2O3 exposed by {012} and {104} facets can facilitate the reduction of IO3−, which results in increasing the activity of photocatalytic water oxidation significantly. By employing NaIO3 as an electron acceptor, the O2 evolution activity (309.4μmolh−1g−1) of α-Fe2O3 photocatalyst mainly exposed by {012} and {104} facets is 84 times higher than that (3.68μmolh−1g−1) of α-Fe2O3 mostly exposed by {101} and {111} planes. We anticipate that the findings in this work may open the door for further development of enhanced Z-scheme photocatalytic systems.

Investigating the Role of Redox Mediator on the Reaction Stability of Nonaqueous Lithium-Oxygen Batteries

Nonaqueous lithium-oxygen (Li-O2) batteries have attracted intensive research interest owing to their potential to provide gravimetric energy density 3-5 times that of conventional Li-ion batteries.1-2 The practical application of this technology has been hindered by poor cycle life (<100 cycles) and low round-trip efficiency (65-70%). These challenges are related to sluggish reaction kinetics and side reactions at the oxygen electrode.3-4 Applying redox mediator has been demonstrated an effective strategy to improve the reaction kinetics of Li-O2 reactions.5-8 However, limited understanding is available about the effect of redox mediator on the reaction stability of Li-O2 batteries. In this work we will study the effect of redox mediator on the reaction stability of the Li-O2batteries. We first studied the instability in cycling a Li-O2 cell without redox mediator. Applying high-temporal resolution on-line electrochemical mass spectrometry (OEMS), we show that the charging process of the Li-O2 cell consists of several oxygen-evolving stages, followed by CO2 evolution. First, the oxygen gas is evolved at ~2e-/O2 between 3.0 – 3.5 V vs. Li (VLi). As the charge voltage reaches 3.5 VLi, the rate of oxygen evolution starts to decrease accompanied with hydrogen evolution, as shown in Figure 1a. We further characterize the cycled O2-electrode and the electrolyte with 1H NMR. As shown in Figure 1b, the formation of side products including formic acid, acetic acid and acetone is confirmed. It was reported that generation of acetone can be mitigated by cycling with a redox mediator.9 Therefore, it is critical to investigate if and how the redox mediator influence the reaction stability of Li-O2reactions. The effect of redox mediator on charging and cycling instabilities will be discussed. Origin responsible for the instabilities as well as the mitigation mechanism of redox mediator will be discussed. Figure caption: Fig. 1. (a)Voltage and gas evolution profiles during charging of a Li-O2 battery without redox mediator after discharged to 1000 mAh/g. (b) 1H NMR spectrum of the carbon cathode and separator after 5 cycles of galvanostatic discharge and charge without redox mediator. Acknowledgements This work is substantially supported by a grant from the Research Grants Council (RGC) of the Hong Kong Special Administrative Region (HKSAR), China, under Theme-based Research Scheme through Project No. T23-407/13-N, and partially supported by a RGC project No. CUHK24200414.

Effect of Quinoid Mediators on the Decolorization of Azo Dyes by the Strain CD-2

In the present study, the effects of various quinone compounds on the decolorization rates of azo dyes by the E. coli strain CD-2 were investigated. The results showed that Lawsone was the most effective redox mediator. The optimum concentration for Lawsone is 0.1 mmol/L. The effects of physic-chemical parameters on the Methyl Orange degradation by the strain were determined. The results indicated that, in the quinone mediated decolorization system, strain CD-2 exhibited a good degradation ability in the range of pH from 4 to 9, temperature from 20°C to 50°C and salinity from 1% to 6%. With Lawsone as a redox mediator, a broad spectrum of azo dyes with different structures could be decolorized by the strain. All the results showed that the addition of a redox mediator can be valuable for treating dye-colored wastewaters.

A Prussian blue-carbon paste electrode for selective cathodic amperometric determination of nitrite using a flow-injection analysis system with carrier recycling

A selective, simple, and low cost method for nitrite determination was developed using an FIA system with a Prussian blue-carbon paste electrode (PB-CPE) as an amperometric detector. The electrochemical sensor was prepared by a fast, simple, and inexpensive procedure, and the long-term stability of the electrode was quite satisfactory as the performance was maintained over one year. PB acted as an effective redox mediator for nitrite electroreduction in acidic media, allowing nitrite detection at +0.2V vs. Ag/AgClsat, a potential at which most possible interfering species are not electroactive. Consequently, the proposed method was completely free from interference from nitrate, dissolved oxygen, ascorbic acid, and other species usually present in water and food samples. The electrochemical cell used in the FIA system was similar to a batch injection analysis cell, enabling recirculation of the carrier solution. This is an attractive feature because it allows the use of a high flow rate (6mLmin−1) leading to high sensitivity and analysis speed, while keeping reagent consumption low. Under the optimized conditions, the proposed method had a detection limit of 9μmolL−1 and was successfully employed for nitrite quantification in water and sausage samples. For all analyzed samples, recovery percentages close to 100% were obtained, which is indicative of the accuracy and reliability of the proposed method.

Nickel-phendione complex covalently attached onto carbon nanotube/cross linked glucose dehydrogenase as bioanode for glucose/oxygen compartment-less biofuel cell

Here, [Ni(phendion) (phen)]Cl2 complex, (phendion and phen are 1,10-phenanthroline-5,6-dione and 5-amino-1, 10-phenanthrolin) covalently attached onto carboxyl functionalized multi walls carbon nanotube modified glassy carbon electrode (GCE/MWCNTs-COOH) using solid phase interactions and combinatorial approaches.The attached [Ni(phendion) (phen)]Cl2 complex displays a surface controlled electrode process and it acts as an effective redox mediator for electrocatalytic oxidation of dihydronicotinamide adenine dinucleotide (NADH) at reduced overpotentials. With co-immobilization of glucose dehydrogenase enzyme (GDH) by crosslinking an effective biocatalyst for glucose oxidation designed. The onset potential and current density are −0.1 V versus Ag/AgCl electrode and 0.550 mA cm−2, which indicate the applicability of the proposed system as an efficient bioanode for biofuel cell (BFC) design. A GCE/MWCNTs modified with electrodeposited gold nanoparticles (AuNPs) as a platform for immobilization of bilirubin oxidase (BOD) and the prepared GCE/MWCNTs/AuNPs/BOD biocathode exhibits an onset potential of 0.56 V versus Ag/AgCl. The performance of the fabricated bioanode and biocathode in a membraneless enzyme based glucose/O2 biofuel cell is evaluated. The open circuit voltage of the cell and maximum current density are 520 mV and 0.233 mA cm−2, respectively, while maximum power density of 40 μWcm−2 achieves at voltage of 280 mV with stable output power after 24 h continues operation.

Single layer graphene as an electrochemical platform.

Over the past decade, there has been a great deal of interest in graphene with regards to its electrochemical behavior. Previous studies have focused on understanding fundamental processes such as charge transfer and molecular transport at the graphene-electrolyte interface as well as on applications of graphene in electronic, optical, and mechanical systems. We present illustrative examples of large area, single layer graphene platforms for applications such as optical and sensing devices as well as microfluidic systems. Three examples of graphene modified with thin polymer films are discussed. We have explored the use of graphene as an electrochemical platform for surface-generated electrogenerated chemiluminescence (ECL) using poly-[Ru(v-bpy)3](2+), where v-bpy is 4-vinyl, 4'-methyl 2,2'-bipyridine, as a model system. We found that while graphene can sustain ECL conditions, there was film degradation during ECL, as demonstrated by a decrease in ECL intensity upon potential cycling even in the presence of a graphene coating ("graphene blanket"). Using poly 3,4-ethylenedioxythiophene (EDOT), we demonstrate a facile method of fabricating electrochromic electrodes from large area graphene. The oxidation of NADH at graphene was catalyzed using an electrodeposited layer of 3,4-dihydroxybenzaldehyde as an effective redox mediator. In addition, we describe the fabrication and characterization of a microfluidic device based on a solution-gated field effect transistor which was able to detect changes of 60 mV per pH unit change in an inverted cell design. On the other hand, a 29 mV shift in the Dirac point per unit pH change was measured with our microfluidic devices, and a ca. 10% FET conductance change was measured when we continuously changed the pH in solution from 6.91 to 7.64 in the microfluidic channel, demonstrating local microfluidic pH sensing (albeit non-Nerstian) in real time.

Anchorage of anthraquinone molecules onto activated carbon fibers to enhance the reduction of 4-nitrophenol

BACKGROUND The development of carbon materials with redox functional groups on their surface is an attractive alternative for faster treatment of contaminants with electron withdrawing groups like 4-nitrophenol (4NP). In the search for better catalytic materials, this paper reports the anchorage of two anthraquinones on the surface of polyacrilonitrile activated carbon fibers (ACFs). RESULTS 2-aminoanthraquinone (AAQ) and anthraquinone-2,6-disulfonate (AQDS) were anchored on SOCl2 treated carbon materials. The results show that fixation of AAQ and AQDS on ACFs caused changes in the surface area and the pore size distribution of ACFs, but only AQDS materials (8.3% in weight) showed an improvement in the catalytic properties of the material (49%) towards the reduction of 4NP to 4-aminophenol, providing sodium sulfide as the electron donor. HPLC and spectrometric scans at the end of the reduction experiments showed that AQDS remained anchored on ACFs. CONCLUSIONS Immobilized AQDS on ACFs was shown to be an effective solid-phase redox mediator improving the reductive transformation of 4NP. Other applications for the method of immobilization of redox mediators on the surface of ACFs were reported in other fields of study such as energy storage and microbial fuel cells. © 2014 Society of Chemical Industry

Effects of redox mediators on nitrogen removal performance by denitrifying biomass and the activity of Nar and Nir

Abstract In this study, effects of four kinds of redox mediators on denitrification performance, nitrate and nitrite reductase activities were investigated, including anthraquinone (AQ), 2-methyl-1,4-naphthoquinone (ME), lawsone (LAW) and anthraquinone-2,6-disulphonate (AQDS). Experimental results demonstrated that the optimum dosing concentrations of AQ, ME and LAW were 75, 25 and 75 μM. The maximum total nitrogen removal rates increased to 26.02, 20.16 and 33.50 mg-N/g-VSS/h at each optimum dosing concentration, which were approximately 1.60, 1.25 and 2.08 times higher compared to that without redox mediator addition. Unlike AQ and ME, addition of LAW appeared to have suppressed the accumulation of nitrite with peak vales about 21.60 mg/L compared to that of 121.9 mg/L with AQ and 180 mg/L with ME addition. Among four kinds of redox mediators, ME increased the nitrate reductase activity about 1.97 folds, and AQDS enhanced the nitrite reductase activity about 2.08 folds compared to the controls. The unbalance of affected nitrate reductase and nitrite reductase activities by redox mediator was considered as the main reason for nitrite accumulation in this study.

Effects of Redox Mediators on the Catalytic Activity of Iron Porphyrins towards Oxygen Reduction in Acidic Media

AbstractThe effects of different redox mediators on the oxygen reduction reaction (ORR) catalyzed by an iron porphyrin complex, iron(III) meso‐tetra(N‐methyl‐4‐pyridyl)porphine chloride [FeIIITMPyP], in 0.1 M triflic acid were investigated by cyclic voltammetry (CV) and spectroelectrochemistry in conjunction with density functional theory (DFT) calculations. The formal potentials of the FeIIITMPyP catalyst and the redox mediators, as well as the half‐wave potentials for the ORR, were determined by CV in the absence and presence of oxygen in acidic solutions. UV/Vis spectroscopic and spectroelectrochemical studies confirmed that only the 2,2′‐azino‐bis(3‐ethylbenzothiazioline‐6‐sulfonic acid)diammonium salt (C18H24N6O6S4) showed effective interactions with FeIIITMPyP during the ORR. DFT calculations suggested strong interaction between FeIIITMPyP and the C18H24N6O6S4 redox mediator. The redox mediator caused lengthening of the dioxygen iron bond, which thus suggested easier dioxygen reduction. Consistent results were observed in electrochemical impedance spectroscopic measurements for which the electron‐transfer kinetics were also evaluated.

A novel modification of poly(ethylene terephthalate) fiber using anthraquinone-2-sulfonate for accelerating azo dyes and nitroaromatics removal

Polymer fibers have been used as biofilm carriers and membrane materials for wastewater treatment. However, little information was available about its chemical modification using quinone compounds for accelerating biotransformation of refractory pollutants. Present studies show that poly(ethyleneterephthalate) fiber cloth (PETFC) could be modified by anthraquinone-2-sulfonate (AQS), an effective redox mediator, using a chemical method under mild conditions. AQS-modified PETFC (AQS-PETFC) exhibits better hydrophilicity and biocompatibility than unmodified PETFC. Further experiments show that the addition of AQS-PETFC resulted in the increased anaerobic biotransformation rates of various azo dyes and nitroaromatics. Their removal rates were about 1.6–3.7-fold higher than those in the absence of AQS-PETFC. Moreover, the decolorization efficiencies of azo dyes could remain over 93.7% of their original value during 5 runs. Therefore, AQS-PETFC as a novel functional material has potential applications for wastewater treatment.

Bioelectrocatalytic Oxygen Reduction Reaction by Bilirubin Oxidase Adsorbed on Glassy Carbon and Edge-Plane Pyrolytic Graphite Electrodes: Effect of Redox Mediators

Bioelectrocatalytic Oxygen Reduction Reaction by Bilirubin Oxidase Adsorbed on Glassy Carbon and Edge-Plane Pyrolytic Graphite Electrodes: Effect of Redox Mediators

Ionic Liquid of a Gold Nanocluster: A Versatile Matrix for Electrochemical Biosensors

Ionic liquids are room-temperature molten salts that are increasingly used in electrochemical devices, such as batteries, fuel cells, and sensors, where their intrinsic ionic conductivity is exploited. Here we demonstrate that combining anionic, redox-active Au25 clusters with imidazolium cations leads to a stable ionic liquid possessing both ionic and electronic conductivity. The Au25 ionic liquid was found to act as a versatile matrix for amperometric enzyme biosensors toward the detection of glucose. Enzyme electrodes prepared by incorporating glucose oxidase in the Au25 ionic liquid show high electrocatalytic activity and substrate affinity. Au25 clusters in the electrode were found to act as effective redox mediators as well as electronic conductors determining the detection sensitivity. With the unique electrochemical properties and almost unlimited structural tunability, the ionic liquids of quantum-sized gold clusters may serve as versatile matrices for a variety of electrochemical biosensors.