Investigation on the electrode process of the Mn(II)/Mn(III) couple in redox flow battery

The Mn(II)/Mn(III) couple has been recognized as a potential anode for redox flow batteries to take the place of the V(IV)/V(V) in all-vanadium redox battery (VRB) and the Br₂/Br⁻ in sodium polysulfide/bromine (PSB) because it has higher standard electrode potential. In this study, the electrochemical behavior of the Mn(II)/Mn(III) couple on carbon felt and spectral pure graphite were investigated by cyclic voltammetry, steady polarization curve, electrochemical impedance spectroscopy, transient potential-step experiment, X-ray diffraction and charge-discharge experiments. Results show that the Mn(III) disproportionation reaction phenomena is obvious on the carbon felt electrode while it is weak on the graphite electrode owing to its fewer active sites. The reaction mechanism on carbon felt was discussed in detail. The reversibility of Mn(II)/Mn(III) is best when the sulfuric acid concentration is 5 M on the graphite electrode. Performance of a RFB employing Mn(II)/Mn(III) couple as anolyte active species and V(III)/V(II) as catholyte ones was evaluated with constant-current charge-discharge tests. The average columbic efficiency is 69.4% and the voltage efficiency is 90.4% at a current density of 20 mA cm⁻². The whole energy efficiency is 62.7% close to that of the all-vanadium battery and the average discharge voltage is about 14% higher than that of an all-vanadium battery. The preliminary exploration shows that the Mn(II)/Mn(III) couple is electrochemically promising for redox flow battery.     

A study of the Ce(III)/Ce(IV) redox couple for redox flow battery application

In this study, the electrochemical behavior of the Ce(III)/Ce(IV) redox couple in sulfuric acid medium with various concentrations and the influence of the operating temperature were investigated. A change of the concentration of sulfuric acid mainly produced the following two results. (1) With an increase of the concentration of sulfuric acid the redox peak currents decreased. (2) The peak potential separation for the redox reactions increased with rising concentration of sulfuric acid from 0.1 to 2 M and then decreased with further increase of the concentration. Elevated temperature was electrochemically favorable for Ce(III)/Ce(IV) couple, which caused an increase of the peak currents for the redox reactions and a decrease of the peak potentials separation. Constant-current electrolysis shows that the current efficiency was 73% for the oxidation process of Ce(III) and 78% for the reduction process at 298 K, and could be improved by elevating the temperature. The open-circuit voltage of the Ce-V cell, after full charging, remained constant at 1.870±0.005 V for more than 48 h, and is about 29% higher than that of the all-vanadium batteries. The coulombic efficiency was approximately 87%, showing that self-discharge of the Ce-V battery was small. The preliminary exploration shows that the Ce(III)/Ce(IV) couple is electrochemically promising for redox flow battery (RFB) application.     

Influence of ionic speciation on electrocatalytic performance of polyaniline coated platinum electrode: Fe(III)/Fe(II) redox reaction

Porous-polyaniline coated Pt electrode (PANI/Pt) was electro-synthesized potentiodynamically in 0.1 M aniline + 0.5 M H₂SO₄ and morphologically characterized by scanning electron microscopy (SEM). Nature of predominant Fe-species in HCl and H₂SO₄ was checked by UV-vis spectrophotometry. Electrocatalysis of Fe(III)/Fe(II) reaction was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for three different solution compositions viz. (i) FeCl₃/FeCl₂ in 1 M HCl, (ii) FeCl₃/FeCl₂ in 0.5 M H₂SO₄ and (iii) Fe₂(SO₄)₃/FeSO₄ in 0.5 M H₂SO₄. For different thicknesses of PANI, the peak current increased irrespective of the nature of the Fe-species, but the polarity of the charge on the Fe-species showed great influence on reversibility of electrocatalysis by PANI/Pt. The Donnan interaction of the polyaniline modified electrode for the three compositions was investigated with respect to [Fe(CN)₆]³⁻/H₂[Fe(CN)₆]²⁻ which are believed to be the predominant species present in K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution in 0.5 M H₂SO₄. The electrocatalytic performance of PANI/Pt for Fe(III)/Fe(II) redox reaction was found superior in HCl compared to that in H₂SO₄.     

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1-13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H₂O₂, and electrocatalytically oxidation active for S₂O₄²⁻ through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S₄O₆²⁻, S₂O₄²⁻, and SO₃²⁻, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.     

Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.     

Reductive transformation of 2-nitrophenol by Fe(II) species in γ-aluminum oxide suspension

Fe(II) adsorption onto γ-Al₂O₃ surfaces was studied in view of its high reactivity towards the aqueous reductive transformation of 2-NP. Kinetic measurements demonstrated that rates of 2-NP reduction were highly sensitive to pH, Fe(II) concentration and reaction temperature. An increase in pH, Fe(II) concentration or reaction temperature gave rise to an elevated density of Fe(II) adsorbed to mineral surfaces, which further resulted in an enhanced reaction rate of 2-NP reduction. By using the diffuse double layer (DDL) surface complexation model, the dominant Fe(II) surface complex that was responsible for the high reactivity was predicted to be the strongly bound ≡ SOFe⁺ functional group (represented by ≡ Al_stOFe⁺) onto γ-Al₂O₃ surfaces. In addition, cyclic voltammetry tests showed that the enhanced activity of Fe(II) species was attributed to the negative shift of the redox potential of Fe(III)/Fe(II) couple, resulted from the enhanced concentration of ≡ Al_stOFe⁺ complex.     

Ni(II)-quercetin complex modified multiwall carbon nanotube ionic liquid paste electrode and its electrocatalytic activity toward the oxidation of glucose

A modified electrode Ni(II)-Qu-MWCNT-IL-PE has been fabricated by electrodepositing Ni(II)-quercetin [Ni(II)-Qu] complex on the surface of multi-wall carbon nanotube ionic liquid paste electrode (MWCNT-IL-PE) in alkaline solution. The Ni(II)-Qu-MWCNT-IL-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)-Qu-MWCNT-PE. It also shows good electrocatalytic activity toward the oxidation of glucose. Kinetic parameters such as the electron transfer coefficient α, rate constant k_s of the electrode reaction and the catalytic rate constant k_cat of the catalytic reaction are determined. Moreover, the catalytic current presents linear dependence on the concentration of glucose from 5.0 μM to 2.8 mM, with a detection limit of 1.0 μM by amperometry. The modified electrode for glucose determination is of the property of simple preparation, good stability, fast response and high sensitivity.     

Electrochemical behavior of Fe(II) in acetamide-urea-NaBr-KBr melt and magnetic properties of inductively codeposited Nd-Fe film

The electroreduction of Fe(II) and Nd(III) in MCl_x-acetamide-urea-NaBr-KBr were studied by cyclic voltammetry and chronoamperometry. The reduction of Fe(II) to Fe is an irreversible process, the value of αn_α of the electrode reaction was calculated to be 0.31 and the diffusion coefficient of Fe(II) was calculated to be 9.53 × 10⁻⁷ cm² s⁻¹ at 343 K. Nd(III) cannot be reduced alone in urea melt, but Nd-Fe can be codeposited by induced codeposition. The composition of Nd-Fe film varies with the Nd(III)/Fe(II) molar ratio, at the potential of −1.25 V the maximum content of Nd in Nd-Fe film is 60.4 wt%. The morphology of Nd-Fe film was investigated by SEM and AFM. Nd-Fe film comprises of nanoparticles with the size about 100-200 nm. X-ray diffraction (XRD) shows it is amorphous. After heat-treatment at 1173 K the crystal Nd₂Fe₁₇ phase can be formed. The magnetic properties of the Nd-Fe films were determined using hysteresis loops, at 5 K the coercive field H_c of Nd (62.6 wt%)-Fe amorphous film is 1225 Oe, the remanent magnetization M_R and the saturation magnetization M_S are 5.15 and 15.80 emu g⁻¹, respectively.     

Electrocatalytic oxidation of methanol on carbon paste electrode modified by nickel ions dispersed into poly (1,5-diaminonaphthalene) film

Poly (1,5-diaminonaphthalene) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 1.0 M nickel chloride solution. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. Also, cyclic voltammetric experiments showed that methanol electrooxidized at the surface of this Ni(II) dispersed polymeric modified carbon paste electrode [Ni/P-1,5-DAN/MCPE]. The mechanism of methanol oxidation changes from diffusion control at low concentration to a catalytic reaction at higher methanol concentration. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed.     

阴丹士林艳绿FFB的间接电化学还原

The indirect electrochemical reduction of Indanthrene Brilliant Green FFB (IBG) was investigated in detail by cyclic voltammetry and electrolytic experiments. Triethanolamine (TEA) was used as ligand to form elec-trochemically active Fe(III)-complexes in alkaline solution. The effects of operating parameters including reaction temperature, current density, concentration of NaOH and Fe(III)-TEA mediator had been studied by orthogonal ex-periments and the mechanism of radicals on electrochemical reduction was discussed. The cyclic voltammetry ex-perimental results show that Fe(III)-TEA complexes are well suited for the indirect electrochemical reduction of IBG. The electrolytic experiments show that high current efficiency (49.9%) can be successfully achieved under op-timized conditions and the current density is found to be the main influence factor.     

Electrochemical synthesis of lepidocrocite thin films on gold substrate—EQCM, IRRAS, SEM and XRD study

Lepidocrocite thin films have been electrochemically synthesised on polycrystalline Au substrates following two ways, direct synthesis and synthesis via green rust (GR). The direct synthesis consists in oxidising Fe(II) species in a 0.4 M NaCl/0.02 M Met-Imidazole/0.01 M FeCl₂ solution at pH 7.5. The synthesis via GR consists in converting a green rust thin film into lepidocrocite thin film by galvanostatic oxidation. The thin films have been characterised by means of electrochemical quartz crystal microbalance, scanning electron microscopy, X-ray diffraction and infrared reflection-absorption spectroscopy.     

The mediation reaction between the external couple Ferri/Ferrocyanide and Os(II) bipyridile poly-vinylpyridile films coated onto glassy carbon electrodes

The oxidation-reduction of the Ferri/Ferrocyanide couple in solution onto modified glassy carbon Rotating Disk Electrodes (RDE) covered by Os(II) bipyridile poly-vinylpyridile (OsBPP) polymer was studied at room temperature. Steady state polarization curves were carried out as a function of the rotation speed, the polymer thickness and the concentration of redox centers within the polymer. This system has the characteristic that the formal redox potentials of both the external redox couple (E⁰′(Fe(CN)₆^3−/4−) = + 0.225 V vs. SCE) and the mediator polymer (E⁰′(OsBPP) = 0.260 V vs. SCE) lie very close. It is demonstrated that diffusion of the Ferri/Ferrocyanide inside the polymer can be ruled out. Since the processes of charge transfer at the metal/polymer and the mediating reaction are fast, the experimental results can be interpreted in terms of a kinetics in which the charge transport in the polymer or the diffusion in the solution may be the rate determining step, according to the experimental conditions. A simple model is considered that allows interpreting the experimental results quantitatively. Application of this model allows the determination of the diffusion coefficient of the electrons within the film, D_e ≈ 10⁻¹⁰ cm² s⁻¹.     

Poly(o-aminophenol) film prepared in the presence of sodium dodecyl sulfate: Application for nickel ion dispersion and the electrocatalytic oxidation of methanol and ethylene glycol

Poly(o-aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode. The electrochemical behavior of the SDS-POAP carbon paste electrode has been investigated by cyclic voltammetry in 0.5 M HClO₄ and 5 mM K₄[Fe(CN)₆]/0.1 M KCl solutions as the supporting electrolyte and model system, respectively. Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode. A good redox behavior of the Ni(III)/Ni(II) couple at the surface of electrode can be observed. The electrocatalytic oxidations of methanol and ethylene glycol (EG) at the surface of the Ni/SDS-POAP electrode were studied in a 0.1 M NaOH solution. Compared to bare carbon paste and POAP-modified carbon paste electrodes, the SDS-POAP electrode significantly enhanced the catalytic efficiency of Ni ions for methanol oxidation. Finally, using a chronoamperometric method, the catalytic rate constants (k) for methanol and ethylene glycol were found to be 2.04 × 10⁵ and 1.05 × 10⁷ cm³ mol⁻¹ s⁻¹, respectively.     

Adsorption of ochratoxin A (OTA) anodic oxidation product on glassy carbon electrodes in highly acidic reaction media: Its thermodynamic and kinetics characterization

We study the thermodynamics and kinetics of the adsorption of a redox couple having quinone nature on glassy carbon electrodes. This couple is produced by the anodic oxidation of mycotoxin ochratoxin A in 10% acetonitrile + 90% 1 M HClO₄ aqueous solution. The quasi-reversible redox couple was studied by both cyclic (CV) and square wave (SWV) voltammetric techniques. The Frumkin adsorption isotherm best described the specific interaction of the redox couple with carbon electrodes. By fitting the experimental data, we obtained values of −28.4 kJ mol⁻¹ and 0.70 ± 0.02 for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the adsorbed redox couple, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.609 ± 0.003 V and 0.45 ± 0.06 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 10.7 s⁻¹ was obtained. SWV was also employed to generate calibration curves. The lowest concentration of mycotoxin was 1.24 × 10⁻⁸ M (5 ppb), measured indirectly with a signal to noise ratio of 3:1.     

Bifunctional redox flow battery-1 V(III)/V(II)-glyoxal(O2) system

Bifunctional redox flow batteries (BRFB) possess functions of both electricity storage and electrochemical preparation, having the potential for increasing the electrical energy utilization. A V(III)/V(II)-glyoxal(O₂) system has been developed. Separators of the BRFB play a key role in BRFB performance. A Nafion solution was sprayed on a gas diffusion layer (GDL) at the Nafion loading of 2 mg cm⁻², and the GDL was then hot-pressed onto a Nafion115 cation exchange membrane, obtaining a modified separator. This separator not only prevents the crossover of vanadium but also has favorable conductivity, obtaining optimal charge and organic electro-synthesis performance of the BRFB. The effects of the concentrations of glyoxal and HCl on the performance of BRFB were also investigated. It is shown that the optimal concentration of glyoxal and HCl should be 1.2 and 3 M, respectively. As a result, the current efficiency of organic electro-synthesis is further increased. An acceptable discharge performance is achieved for a period exceeding 20 h at the current density of 20 mA cm⁻². The average discharge voltage of 0.73 V and the coulombic efficiency of 66% are obtained. It is demonstrated that the principle of the BRFB is feasible. However, further experiments are needed to improve the performance.     

Novel amperometric glucose biosensor based on an ether-linked cobalt(II) phthalocyanine-cobalt(II) tetraphenylporphyrin pentamer as a redox mediator

The development of cobalt(II) phthalocyanine-cobalt(II) tetra(5-phenoxy-10,15,20-triphenylporphyrin), (CoPc-(CoTPP)₄) pentamer as a novel redox mediator for amperometric enzyme electrode sensitive to glucose is described. A glassy carbon electrode (GCE) was first modified with the pentamer, then followed by the immobilization onto the GCE-CoPc-(CoTPP)₄ with glucose oxidase (GOx) through cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) and Nafion^® cation-exchange polymer. The proposed biosensor displayed good amperometric respose charateristics to glucose in pH 7.0 PBS solution; such as low overpotentials (+400 mV versus Ag|AgCl), very fast amperometric response time (∼5 s), linear concentration range extended up to 11 mM, with 10 μM detection limit. The biosensor exhibited electrochemical Michaelis-Menten kinetics and showed an average apparent Michaelis-Menten constant (K^′M) of 14.91 ± 0.46 mM over a storage period of 2 weeks.     

用恒电流法研究Fe（Ⅲ）EDTA对银的氧化过程

本文采用银旋转圆盘电极,在氟离子、溴离子、碘离子以及其他照相辅加剂存在下对Fe(Ⅲ)EDTA氧化金属银的过程进行了研究,以恒电流法做为检测手段,初步探讨了Fe(Ⅲ)EDTA络合物对金属银漂白过程机理。实验揭示了各种卤离子在Fe(Ⅲ)EDTA对银的氧化过程中的行为。pH和Fe(Ⅲ)EDTA浓度对该氧化还原反应的影响,以及某些含有巯基的化合物对Fe(Ⅲ)EDTA氧化反应的加速作用机理。     

Electrochemical and spectroscopic characterization of poly(1,8-diaminocarbazole): Part II. Electrochemical, in situ vis/NIR and Raman studies of redox reaction of PDACz in protic and aprotic media

Electrochemical redox reactions of poly(1,8-diaminocarbazole) (PDACz) films in aqueous (0.1 M HClO₄) and nonaqueous (0.1 M LiClO₄ in acetonitrile) solutions were studied by cyclic voltammetry, in situ vis/NIR and Raman spectroscopy. It has been demonstrated that spectroelectrochemical behavior of the polymer is strongly dependent on the nature of the solution used for doping-undoping but not on the medium used for electropolymerization. A redox couples Fe²⁺/Fe³⁺, Fe(CN)₆^4−/3− and tertrathiafulvalene were used as the probes for the studies of electroactivity of the oxidized polymer films. The results were discussed in terms of different mechanism of deprotonation process of the polymer in aqueous solution of 0.1 M HClO₄ and in 0.1 M LiClO₄ solution in aprotic acetonitrile and the reaction schemes in the two media are proposed.     

Ammonium phosphate slurry rheology and particle properties—The influence of Fe(III) and Al(III) impurities, solid concentration and degree of neutralization

Ammonium phosphate slurries are produced from impure phosphoric acid that contains Fe(III), Al(III) and Mg(II) ions. The insolubility of these metal ions and the onset of solid formation determined as a function of pH or mole ratio (MR) of ammonia to phosphoric acid were consistent with the trend for the pH of formation of the first hydrolysis product that decreases in the following order: Fe(III)<Al(III)<Mg(II). The hydrolysis products of Fe(III) formed at pH>2.0 or MR>0.5 initiate ammonium phosphate crystallization, reduce the size of particles formed and generate attractive interparticle forces. Similarly, the Al(III) hydrolysis products formed later at pH>2.6 MR>0.7), will also initiate further crystallization, adsorb on particles and produce attractive forces. The attractive forces and the high number concentration of particle—particle interactions are responsible for the increased viscosity and non-Newtonian flow behavior displayed at increasing Fe(III) and Al(III) concentration. Mg(II) ions are not hydrolyzed at MR<1.0 so its effect on rheology is negligible and its effect at MR<1.0 is also small as its concentration is much smaller than that of Fe(III) and Al(III) ions. The change in slurry viscosity with the degree of neutralization is also explained in terms of particle size distribution, solubility and solids concentration variations.     

Removal of Cr(VI) from water using Fe(II)-modified natural zeolite

In this study, natural zeolite aggregates with the particle size of 1.4–2.4 mm were modified by Fe(II). The unmodified zeolite and Fe(II)-modified zeolite (Fe-eZ) were subjected to batch and column tests to study the Cr(VI) sorption, transport, and retardation. Modification of the natural zeolite with Fe(II) resulted in an increase in Cr(VI) sorption to 6 mmol/kg. The Cr(VI) sorption followed a pseudo-second-order kinetics with a rate of 17 mmol/g h and a rate constant of 0.7 g/mmol h. Cr(VI) removal from solution increased with an increase in ionic strength, but decreased as the solution pH increased. At a Cr(VI) input concentration of 100 mg/L, unmodified zeolite did not show any Cr(VI) retardation at all. In contrast, the observed retardation factor of Fe-eZ for Cr(VI) increased by a factor of 6. The hydraulic conductivity of the zeolite showed little change before and after Fe(II) modification and before and after Cr(VI) sorption, suggesting its good mechanical stability to be used as packing materials for permeable reactive barriers in groundwater remediation.