UV-visible Spectroscopic Methods Research Articles

Understanding Nucleophilicity of Pyridine-N-oxides Towards 2,4,6-Trinitrophenylbenzoate Through Simple Absorption Spectroscopic Studies

Aims: Understanding nucleophilicity of poor nucleophiles like pyridine-N-oxides. Background: Nucleophilicity plays a vital role in substitution reactions. It helps to determine the possibility and extent of the substitution reactions. The study of the nucleophilicity of poor nucleophiles is challenging, and it has limited substrate scope. Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative way is important. Objective: Understanding the strength of nucleophilicity of such poor nucleophiles in a quantitative way. Selection of appropriate electrophile for the reactions with the poor nucleophiles-pyridine-N-oxides. Development of suitable methodology for kinetic studies of the reaction. Methods: UV-Vis spectroscopic methods for monitoring the reactions. Results: The kinetic studies revealed that the second-order rate constants of the nucleophilic reactions are 1.67× 102 L mol-1 min-1, 29.8 L mol-1 min-1, 29.51 L mol-1 min-1, where the nucleophiles are p-methylpyridine-N-oxide, pyridine-N-oxide, and p-nitropyridine-N-oxide, respectively. The UV-Vis spectroscopic analysis revealed the nucleophilicity of p-methylpyridine-N-oxide > pyri-dine-N-oxide > p-nitropyridine-N-oxide. Conclusion: This comparative study suggests that the strength of nucleophilicity of the p-methylpyridine-N-oxide is 5.6 times and 66.53 times more than that of pyridine-N-oxide and p-nitropyridine-N-oxide, respectively, whereas the strength of nucleophilicity of the pyridine-N-oxide is 11.87 times more than that of p-nitropyridine-N-oxide.

Indicator-catalyst displacement assay for tandem detection and signal amplification of dimethoate organophosphate pesticide

This paper describes the chemosensing and catalytic amplification properties of [MnIII(TPP)(NCS)]–[PdII(DMSO)Cl2] (1, TPP = 5,10,15,20-tetraphenyl-21H,23H-porphine) for detecting the organophosphate pesticide dimethoate. Complex 1 selectively detects dimethoate, resulting in a visual color change from yellowish-brown to green with a UV–vis spectroscopic method detection limit (MDL) of 22.7 μM. This selectivity is attributed to the formation of a more stable PdII(dimethoate)2Cl2 adduct, resulting in the release of the colored MnIII(TPP)(NCS) unit from complex 1. Interestingly, the free PdII(dimethoate)2Cl2 released acts as a catalyst for the Heck coupling reaction of 5-diethylamino-2-iodo-phenyl ester (2), producing the highly fluorescent 7-diethylaminocoumarin (3). This catalytic process results in significant signal amplification, enhancing the original sensitivity by 25 times, with a spectrofluorimetric MDL of 0.9 μM. The proposed indicator-catalyst displacement assay successfully quantifies dimethoate concentrations in natural water samples, exhibiting good recoveries (92.5–108.1%) and low relative standard deviations (1.2–6.2%).

Ameliorating tannery sludge dewaterability by disintegration of extracellular biopolymers with FeCl3-MnSO4/oxalic acid/sodium percarbonate: Spectroscopic profiling of dissolved organic matter in sludge filtrate

Effectual sludge dewatering techniques are strongly desired by industrial wastewater treatment plants. In this work, we scrutinised the efficacy of various Fenton based complex mediated processes like ferric chloride (FeCl3)/oxalic acid (OA)/sodium percarbonate (SPC) (FOS), FS (without OA), manganese sulphate (MnSO4)/oxalic acid (OA)/sodium percarbonate (SPC) (MOS) and MS (without OA) for which capillary suction time (CST) was attained as follows: MS (204 s) < MOS (180 s) & FS (180 s) < FOS (174 s) at pH 3. This implied the role of chelating agent (OA) in improving sludge dewaterability by disintegrating Extracellular Polymeric Substances (EPS) and releasing converted free water from the sludge flocs. FTIR results of sludge samples revealed the higher release of aromaticity after treatment process. Presence of aromatic carboxylate compounds were confirmed by GC–MS analysis. A detailed inquisition on the dissolved organic matter (DOM) of filtrate samples using 3DEEM fluorescence methods like second derivative Accumulative Fluorescence Emission (AFE), Fluorescence Regional Integration (FRI) and UV–Visible spectroscopic method like multipeak Gaussian fitting were performed that signified Microbial Soluble Products.

Study the effect of L-arginine and L-tyrosine on the surface adsorption and micellar properties of long-chain imidazolium-based ionic liquid

The interfacial and bulk properties of the aqueous solutions of the long chain imidazolium-based ionic liquid (IL) viz. 1-decyl-3-methylimidazolium tetrafluoro borate [Dmim][BF4] within L-Arginine and L-Tyrosine have been investigated by surface tension, UV–Visible, fluorescence, viscosity, and FTIR spectroscopy. The surface activity of the [Dmim][BF4]-L-Try was more active on the surface than the [Dmim][BF4]-L-Arg. It's noteworthy to notice that the CMC values of [Dmim][BF4] in water and aqueous amino acids obtained by the UV–Vis spectroscopy method are the same as those determined using the surface tension approach. The additions of AAs function to minimize the CMC values of [Dmim][BF4] as well as the interfacial parameters. An IR probe and the v(C-N) region, which is sensitive to the microenvironment, are used to determine the structure and hydrogen-bonding properties of the IL and two amino acids, specifically the L-Arginine and L-Tyrosine binary systems. The excess IR spectra of the v(C-N) region exhibit positive peaks, which show that the mixing process was insufficient and that complexes with hydrogen bonds had formed in the mixes. The findings could be applied in the pharmaceutical industry to stabilize proteins and prevent protein aggregation.

Phase Transition of Thermally Treated Polyhedral Nano Nickel Oxide with Reduced Band Gap

Nickel oxide (NiO) is a semiconducting material which exhibits a unique electronic structure. Because of its distinctive electronic properties, NiO stands as an intriguing candidate for various applications in optoelectronics, photo catalysis, and energy devices such as solar cells. In the present work efforts have been made to tailor the band gap of NiO. A simple co-precipitation method followed by heat treatment is utilized to synthesize the material. Prior to heat treatment, x-ray diffraction study of the as synthesized material showed the presence of nickel hydroxide [Ni(OH)2]. On calcination for one hour at 1000oC, a single phase NiO wasrevealed. After heat treatment it was noticed that the particle size was found to be increased. The absorption spectra of [Ni(OH)2] and NiO were recorded using UV-Vis spectroscopy method. Using Tauc plot a band gap of 4.2 eV and 1.8 eV for Ni(OH)2 and NiO was observed respectively. It is observed that a significant decrease in band gap of NiO was noticed. Surface morphological study was carried out by using FESEM, which revealed the transformation of sheet like structures of [Ni(OH)2] to polyhedral shaped NiO on calcination. The presence of nickel and oxygen was confirmed by the energy dispersive spectrometry analysis.

A rhodamine-based fluorescent probe bearing 8-hydroxyquinoline group for the highly selective detection of Hg2+ and its practical application in cell imaging.

A highly selective and sensitive fluorescent probe, RHOQ, was designed for the detection of Hg2+ by incorporating an 8-hydroxyquinoline moiety onto a rhodamine molecular platform with a suitable linker. In MeOH-Tris (20 mM, pH = 7.4, 1 : 9, v/v) buffer solution, RHOQ exhibited 550-fold fluorescence enhancement at 594 nm upon addition of Hg2+, with a fast response and a low detection limit (9.67 × 10-8 M). The 1 : 1 binding mode of RHOQ with Hg2+ was established using Job's plot, UV-Vis, and fluorescence spectroscopic titration methods. Furthermore, RHOQ was successfully applied for the detection of Hg2+ in living cells with good membrane permeability.

Transport Mechanism of Paracetamol (Acetaminophen) in Polyurethane Nanocomposite Hydrogel Patches-Cloisite® 30B Influence on the Drug Release and Swelling Processes.

This article describes the swelling and release mechanisms of paracetamol in polyurethane nanocomposite hydrogels containing Cloisite® 30B (organically modified montmorillonite). The transport mechanism, swelling and release processes of the active substance in nanocomposite matrix were studied using gravimetric and UV-Vis spectroscopic methods. Swelling and release processes depend on the amount of clay nanoparticles in these systems and the degree of crosslinking of PU/PEG/Cloisite® 30B hydrogel nanocomposites. The presence of clay causes, on the one hand, a reduction in free volumes in the polymer matrices, making the swelling process less effective; on the other hand, the high swelling and self-aggregation behavior of Cloisite® 30B and the interactions of paracetamol both with it and with the matrix, cause a change in the transport mechanism from anomalous diffusion to Fickian-like diffusion. A more insightful interpretation of the swelling and release profiles of the active substance was proposed, taking into account the "double swelling" process, barrier effect, and aggregation of clay. It was also proven that in the case of modification of polymer matrices with nanoparticles, the appropriate selection of their concentration is crucial, due to the potential possibility of controlling the swelling and release processes in drug delivery patches.

Spectroscopic method to estimate 3-Acetyl-11-keto-β-boswellic acid in complex lipid nanocarriers and skin matrices

3-Acetyl-11-keto-β-boswellic acid (AKBA) is a phytoconstituent derived from Boswellia serrata extract. It shows anti-rheumatic activity by selectively and non-competitively inhibiting the 5-Lipoxygenase (5-LOX) enzyme. AKBA is utilized for complex nanocarriers for its effective topical delivery at the arthritic site. There is a demand to develop a rapid, sensitive, and economical UV–Visible spectroscopic method for AKBA, which can be utilized in nanoformulation designing and day-to-day analysis of in vitro and ex vivo samples. In this research work, an analytical method was developed for the estimation of AKBA in two solvent systems, methanol and phosphate buffer saline pH 7.4, using a UV–Visible spectrophotometer. Further, the developed method was validated for linearity, range, limit of detection, limit of quantification, accuracy, precision, solution stability, and specificity as per regulatory guidelines. The method exhibited a linearity range of 10–50 µg/mL in both media with the obtained value of the high correlation coefficient (>0.9995). Interday and intraday precision samples showed less than 2 % relative standard deviation (% RSD) that exhibited the reliability of the developed method. The accuracy study reflected the % recovery between 99 and 101 % in both media. Further, the developed method was explored to quantify AKBA in formulated lipid nanocarriers (LNCs) formulation. The methanol method was effectively used to estimate the entrapment efficiency in LNCs and skin retention of AKBA. For the quantification of AKBA in in vitro release and ex vivo permeation samples, the phosphate buffer saline pH 7.4 method was utilized. Results indicated that the method could quantify the AKBA in the presence of different sample matrices with reproducibility in nature. In conclusion, a sensitive, simple, economical, precise, and accurate UV–Visible spectroscopic method was developed and validated to quantify AKBA.

Strong and selective interactions of palmatine with G-rich sequences in TRF2 promoter; experimental and computational studies

G-rich sequences have the potential to fold into G-quadruplexes (GQs). G-quadruplexes, particularly those positioned in the regulatory regions of proto-oncogenes, have recently garnered attention in anti-cancer drug design. A thermal FRET assay was employed to conduct preliminary screening of various alkaloids, aiming to identify stronger interactions with a specific set of G-rich double-labeled oligonucleotides in both K + and Na + buffers. These oligonucleotides were derived from regions associated with Kit, Myc, Ceb, Bcl2, human telomeres, and potential G-quadruplex forming sequences found in the Nrf2 and Trf2 promoters. Palmatine generally increased the stability of different G-rich sequences into their folded GQ structures, more or less in a concentration dependent manner. The thermal stability and interaction of palmatine was further studied using transition FRET (t-FRET), CD and UV-visible spectroscopy and molecular dynamics simulation methods. Palmatine showed the strongest interaction with T RF2 in both K+ and Na+ buffers even at equimolar concentration ratio. T-FRET studies revealed that palmatine has the potential to disrupt double-strand formation by the T RF2 sequence in the presence of its complementary strand. Palmatine exhibits a stronger interaction with G-rich strand DNA, promoting its folding into G-quadruplex structures. It is noteworthy that palmatine exhibits the strongest interaction with T RF2, which is the shortest sequence among the G-rich oligonucleotides studied, featuring only one nucleotide for two of its loops. Palmatine represents a suitable structure for drug design to develop more specific ligands targeting G-quadruplexes. Whether palmatine can also affect the expression of the T RF2 gene requires further studies. Communicated by Ramaswamy H. Sarma

Investigation of electrochemical, optical, and thermal properties via oligomerization of aminophenol monomer containing halogen and nitro groups using two distinct oxidants

In this study, two different oligomers of 2-amino-4-chloro-5-nitrophenol (ACNP) with incorporated halogen atom and nitro groups were synthesized by oxidative oligomerization method using two different oxidants, namely H2O2 and ammonium persulfate (APS). Structural characterizations of the obtained products were elucidated by 1H NMR, 13C NMR, FT-IR, UV–Vis spectroscopy methods. The molecular masses of the oligomers were determined through the utilization of Gel Permeation Chromatography (GPC). The analysis revealed that the Mw values of the oligomers synthesized via the oxidative oligomerization method using H2O2 and APS, denoted as OACNP-1 and OACNP-2 were 4150 Da and 2800 Da, respectively. Using the UV–vis spectrophotometer, the optical band gaps were calculated as 2.64 eV, 1.95 eV and 2.14 eV for ACNP, OACNP-1 and OACNP-2, respectively. Thermal properties of the oligomers were investigated using Thermal Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) and Differential Scanning Calorimetry (DSC). The results demonstrated that OACNP-1 exhibited significantly higher thermal stability when compared to both the monomer and OACNP-2. In addition, Fluorescence Spectroscopic analysis of the oligomers revealed that OACNP-1 emitted blue light at 440 nm when excited with light of a wavelength of 370 nm, exhibiting fluorescent characteristics. Furthermore, the surface properties and morphologies of the oligomers were analyzed with the help of Scanning Electron Microscopy (SEM), revealing a flower-like structure for the oxidative oligomerization product, OACNP-1, in the presence of H2O2. In course of a change in the oxidant, the oligomer, OACNP-2, had rough and spongy surface morphology with some pores.

Synthesis and Characterization of Cresol based Benzoxazine–Polyurethane Copolymer for Anti-corrosion Performance of Mild Steel

The cresol based polymeric materials were synthesized by using benzoxazine and polyurethanes as copolymer. Three copolymers were synthesized by varying the quantity of polyurethane content and studied their corrosion inhibition properties. The synthesized monomer, which has cresol as the center core was characterized by the NMR, FT-IR and UV-visible spectroscopic methods. All the obtained benzoxazine polymers were also analyzed by the FT-IR and UV-visible spectroscopy. In relation to corrosion inhibition studies, Tafel and impedance experiments were conducted, revealing that benzoxazine-polymer with a higher polyurethane content has improved anti-corrosive characteristics. Additionally, the physical properties of the materials were also studied such as water absorption and gel content studies. Furthermore, the density functional theory calculation was also carried out for the monomer, which explores the better results that are matched with the other experimental studies.

Physicochemical and antioxidant characterization of commercially available honey sample from Addis Ababa market, Ethiopia

High-quality and genuine honey is crucial to provide consumers with natural honey and prevent any potential health issues. This study aimed to examine the quality of commercial honey available in the Addis Ababa market. A total of 30 honey samples were randomly collected from eight sub-cities of Addis Ababa city. Both High-Performance Liquid Chromatography (HPLC) and UV–Vis spectroscopic methods were used to determine 12 physicochemical and three antioxidant activity parameters in the honey samples according to internationally recognized standards. The findings of this study showed that the hydroxymethylfurfural (HMF), free acidity, and ash content of all commercial honey samples conformed to honey standards. However, except for honey samples collected from processors (19.48 ± 0.4 %) and retail outlets (20.49 ± 0.13 %), all other commercial honey samples failed to meet the moisture content criteria (≤21 %). Proline levels in honey samples taken from the street (67.1 ± 0.52 mg/kg) were also found to be below the required standard. The commercial honey samples contained fructose, glucose, sucrose, and maltose within a range of 33.85 ± 0.65 to 48.61 ± 0.51 %, 33.07 ± 1.58 to 44.3 ± 0.82 %, 0.91 ± 0.05 to 6.23 ± 2.49 %, and 0.51 ± 0.14 to 2.4 ± 0.44 %, respectively. Furthermore, honey samples from market areas showed good Total Phenolic Content (TPC), Total Flavonoid Content (TFC), and antioxidant activity. Overall, the results revealed that all physicochemical parameters, except for proline, moisture, and sucrose content, complied with approved standards (Codex Alimentarius, European Union (EU), and Ethiopia Standard Agency (ESA). Accordingly, it is recommended that stakeholders receive regular training on how to manage honey quality issues and detect adulteration techniques to prevent contaminated honey from reaching the markets.

A New Nickel(II) Complex Derived From Bisthiocarbohydrazone: Synthesis, Characterization, Crystal Structure and Antioxidant Activity

A new complex with composition [Ni(L)(PPh3)] (PPh3 = triphenylphosphine) was obtained from the reaction of 1,5-bis(salicylidene)thiocarbohydrazone (L) with an equimolar amount of [NiCl2(PPh3)2]. The complex was identified by FT-IR, 1H NMR and UV-Vis spectroscopic methods and elemental analysis. The solid state structure of [Ni(L)(PPh3)] was established by X-ray diffraction analysis. It was determined that the complex, whose nickel center has a distorted square planar configuration, crystallizes in the monoclinic space group I2/c. Bisthiocarbohydrazone (L) binds to the nickel center through its phenolate O, azomethine N and thioenolate S atoms in a dianionic tridentate mode. The antioxidant capacity of L and Ni(II) complex was examined using the CUPRAC (cupric reducing antioxidant capacity) method. Also, the DPPH (1,1-Diphenyl-2-picrylhydrazyl) method was used to test free radical scavenging activity of the compounds. Antioxidant activity results showed that L exhibited better activity than Ni(II) complex.

The studies on a fluorescent probe of Schiff base modified by 1,2,3-triazole to detecting Al3+ and living cell imaging

A new compound, 5-methyl-2-phenyl-1,2,3-triazole-5-hydrazid (PT) was designed and synthesized based on “click chemistry”. The fluorescence probe 5-methyl-2-phenyl-1,2,3-triazole-5-hydrazid Schiff base (PTSB) was further constructed by a chemical reaction between PT and 4-(diethylamino) salicylaldehyde. PTSB could be used to determine Al3+ in EtOH with high sensitivity and strong anti-interference performance by fluorescence and UV–vis spectroscopic methods. The limit of detection to Al3+ is 5.84 nM and it showed an obvious solvatochromic effect under ultraviolet light. Furthermore, the sensing mechanism of PTSB detecting Al3+ was confirmed in the form of planar structure and 1:1 complexation ratio based on MS, Job's plot, 1H NMR titration, DFT calculation, and the single-crystal structure of PTSB, respectively. PTSB showed less low cytotoxicity to HeLa cells and was successfully used for chromatic bioimaging Al3+ in HeLa cells. It is expected to be developed and utilized as a fluorescence probe for detecting Al3+ in vivo.

Synthesis, Spectral Characterization and Biological Evaluation of Glutaric acid based Macrocyclic Complexes

In the presence of divalent transition metal ions in their chloride forms, glutaric acid and o-phenylenediamine were used to design and synthesize a unique series of macrocyclic complexes. The UV-Visible, IR, ESR, and ESI-MS spectroscopy methods were used to analyze these newly designed complexes. In order to evaluate their thermal behavior, TGA analysis was employed. The intended general formula for the produced complexes was [M(L)X2] (L = ligand, X = Cl- and M = Co2+, Ni2+ and Cu2+). The central metal ions are surrounded by octahedral environment. These macrocyclic complexes were tested for their antimicrobial effectiveness against the selected bacterial strains (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli), as well as fungi strains (Aspergillus niger and Candida albicans) and their efficacy was compared to that of standard drugs Streptomycin and Itraconazole respectively. Moreover, the antioxidant activity of the macrocyclic complexes were also assessed using the DPPH assay.

Surface-Mediated Charge Transfer of Photogenerated Carriers in Diamond.

Solvated electrons are highly reductive chemical species whose chemical properties remain largely unknown. Diamond materials are proposed as a promising emitter of solvated electrons and visible light excitation would enable solar-driven CO2 or N2 reductions reactions in aqueous medium. But sub-bandgap excitation remains challenging. In this work, the role of surface states on diamond materials for charge separation and emission in both gaseous and aqueous environments from deep UV to visible light excitation is elucidated. Four different X-ray and UV-vis spectroscopy methods are applied to diamond materials with different surface termination, doping and crystallinity. Surface states are found to dominate sub-bandgap charge transfer. However, the surface charge separation is drastically reduced for boron-doped diamond due to a very high density of bulk defects. In a gaseous atmosphere, the oxidized diamond surface maintains a negative electron affinity, allowing charge emission, due to remaining hydrogenated and hydroxylated groups. In an aqueous electrolyte, a photocurrent for illumination down to 3.5eV is observed for boron-doped nanostructured diamond, independent of the surface termination. This study opens new perspectives on photo-induced interfacial charge transfer processes from metal-free semiconductors such as diamonds.

Estimation of stability constants of Fe(III) with antibiotics and dissolved organic matter using a novel UV–vis spectroscopy method

Determining conditional stability constant (Kcond) is paramount in assessing complex stability, particularly in Fe(III) complexes that are prevalent in actual surface water and wastewater matrices. In this study, existing methods of Kcond determination were evaluated and a novel UV–Vis spectroscopy method was proposed based on the evaluation of these approaches. Model ligands (ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and oxalic acid (OA)), as well as common antibiotics (kanamycin (Kana) and tetracycline (TTC)), were employed to determine the Kcond of the Fe(III)-ligand complexes under neutral conditions (pH 6.5). The obtained fitting results revealed that the logKcond were in the order of Fe(III)-EDTA (7.08) > Fe(III)-NTA (4.67) > Fe(III)-OA (4.32) > Fe(III)-TTC (4.28) > Fe(III)-Kana (3.07). In addition to these single ligands, the methodology was extended to the Fe(III) complexation with humic acid (HA), a complex mixture of organic components, where the fitting result indicated a logKcond of 5.02 M−1. The method's application domain was analyzed by numerical analysis and combined with experimental results. The findings demonstrate that the proposed methodology possesses satisfactory measurement capability for Kcond ranging from 103 to 107 M−1, suggesting its broad applicability to the majority of complexes. This method can provide valuable insights into the impact of Fe(III) complexes within the water matrix.

Laser Synthesis of Cerium-Doped Garnet Nanoparticles.

The application of a pulsed laser ablation technique for the generation of cerium-doped garnet nanoparticles in liquids is investigated. The morphological and optical properties of the obtained nanoparticles are demonstrated. Features introduced by the single crystals of Gd3Al2.4Ga2.6O12:Ce3+, Lu3Al5O12:Ce3+, and Y3Al1.25Ga3.75O12:Ce3+ from which the nanoparticles are generated, as well as the parameters of a liquid media on the garnet nanoparticle generation are experimentally studied using TEM and UV-Vis spectroscopy methods. It is shown how the size, shape, and internal structure of the nanoparticles are related to the external laser ablation conditions, as well as to the laser melting processes of NPs in the colloidal solutions. This work provides important information about the generated nanoparticles, which can be used as building blocks for specially designed structures with predetermined optical properties.

Study of the Influence of the Irradiation Flux Density on the Formation of a Defect Structure in AlN in the Case of the Effect of Overlapping of the Heavy Ion Motion Trajectories in the Near-Surface Layer.

The aim of this paper is to test the previously stated hypothesis and several experimental facts about the effect of the ion flux or ion beam current under irradiation with heavy ions on the radiation damage formation in the ceramic near-surface layer and their concentration. The hypothesis is that, when considering the possibilities of using ion irradiation (usually with heavy ions) for radiation damage simulation at a given depth, comparable to neutron irradiation, it is necessary to consider the rate factor for the set of atomic displacements and their accumulation. Using the methods of X-ray diffraction analysis, Raman and UV-Vis spectroscopy, alongside photoluminescence, the mechanisms of defect formation in the damaged layer were studied by varying the current of the Xe23+ ion beam with an energy of 230 MeV. As a result of the experimental data obtained, it was found that, with the ion beam current elevation upon the irradiation of nitride ceramics (AlN) with heavy Xe23+ ions, structural changes have a pronounced dependence on the damage accumulation rate. At the same time, the variation of the ion beam current affects the main mechanisms of defect formation in the near-surface layer. It has been found that at high values of flux ions, the dominant mechanism in damage to the surface layer is the mechanism of the formation of vacancy defects associated with the replacement of nitrogen atoms by oxygen atoms, as well as the formation of ON-VAl complexes.

Spectroscopic and electrochemical analyses elucidating capacity degradation mechanism of iron-ligand complex and air in all iron aqueous redox flow batteries

Capacity degradation mechanism of all iron aqueous redox flow battery (ARFB) using iron and 2,2-bis(hydroxymethyl)-2,2′,2′'-nitrilotriethanol (Fe(BIS-TRIS)) complex as redox active material for anolyte is analyzed. The capacity degradation occurs by the contact of Fe(BIS-TRIS) and oxygen in air, while this is confirmed by spectroscopic and electrochemical ways including the use of Beer-Lambert’s law. According to the analysis, charging/discharging step of catholyte including Fe(CN)6 does not affect exposure to oxygen, whereas self-discharge occurs at the step of anolyte including Fe(BIS-TRIS) that is exposed to oxygen, promoting its performance decay. This is proved by ARFB single cell tests using the electrolytes. When the electrolytes are open to air, its capacity is considerably degraded within 20 cycles. However, when anolyte is sealed to avoid contact with air, its capacity preserves 96 % of initial value even after 100 cycles. This is because the undesirable self-discharge of Fe(BIS-TRIS) affects the degradation in performance of ARFB single cell. We elucidate effect of oxygen on performance of ARFBs using Fe(BIS-TRIS) with UV–VIS spectroscopic method.