Macroporous composite capacitive bioanode applied in microbial fuel cells

Interfacial electron transfer between electroactive biofilm and the electrode was crucial step for microbial fuel cells(MFCs).A three-dimensional multilayer porous sponge coating with nitrogen-doped carbon nanotube/polyaniline/manganese dioxide(S/N-CNT/PANI/MnO2)electrode has been developed for MFC anode.Here,the S/N-CNT/PANI/MnO2 anode can function as a biocapacitor,able to store electrons generated from the degradation of organic substrate under the open circuit state and release the accumulated electrons upon requirement.Thus,the mismatching of the production and demand of the electricity can be overcome.Comparing with the sponge/nitrogen-doped carbon nanotube(S/N-CNT)bioanode,S/N-CNT/PANI/MnO2 capacitive bioanode displays a strong interaction with the microbial biofilm,advancing the electron transfer from exoelectrogens to the bioanode.The maximum power density of MFC with S/N-CNT/PANI/MnO2 capacitive bioanode is 1019.5 mW/m^2,which is 2.2 and5.8 times as much as that of S/N-CNT/MnO2 bioanode and S/N-CNT bioanode(470.7 mW/m^2 and176.6 mW/m^2),respectively.During the chronoamperometric experiment with 60 min of charging and 20 min of discharging,the S/N-CNT/PANI/MnO2 capacitive bioanode was able to store 10743.9 C/m^2,whereas the S/N-CNT anode was only able to store 3323.4 C/m^2.With a capacitive bioanode,it is possible to use the MFC simultaneously for production and storage of electricity.     

Facile fabrication of mesoporous manganese oxides as advanced electrode materials for supercapacitors

Mesoporous manganese oxides (MnO₂) were synthesized via a facile chemical deposition strategy. Three kinds of basic precipitants including sodium carbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃), and sodium hydroxide (NaOH) were employed to adjust the microstructures and surface morphologies of MnO₂ materials. The obtained MnO₂ materials display different microstructures. Great differences are observed in their specific surface area and porosity properties. The microstructures and surface morphologies characteristics of MnO₂ materials largely determine their pseudocapacitive behavior for supercapacitors. The MnO₂ prepared with Na₂CO₃ precipitant exhibits the optimal microstructures and surface morphologies compared with the other two samples, contributing to their best electrochemical performances for supercapacitors when conducted either in the single electrode tests or in the capacitor measurements. The optimal MnO₂ electrode exhibits a high specific capacitance (173 F g^–1 at 0.25 A g^?1), high-rate capability (123 F g^?1 at 4 A g^?1), and excellent cyclic stability (no capacitance loss after 5,000 cycles at 1 A g^?1). The optimal activated carbon//MnO₂ hybrid capacitor exhibits a wide working voltage (1.8 V), high-power and high-energy densities (1,734 W kg^?1 and 20.9 Wh kg^?1), and excellent cycling behavior (93.8 % capacitance retention after 10,000 cycles at 1 A g^?1), indicating the promising applications of the easily fabricated mesoporous MnO₂ for supercapacitors.     

Electrochemically Prepared Manganese Oxide as a Cathode Material for a Microbial Fuel Cell

This work describes the construction of a mediatorless microbial fuel cell (MFC) using the microorganism Acetobacter aceti as the biocatalyst in the anode compartment with glucose as a fuel. The periplasmic membrane bound pyrroloquinoline quinone (PQQ) containing enzymes of these genera provide fast and highly efficient oxidation of a wide variety of substrates and helps in the direct routing of electrons to the anode. We describe our preliminary findings with regard to the use of electrochemically deposited manganese oxide films on carbon substrates as cathode materials in MFCs. Manganese oxide was electrochemically deposited on carbon paper in the presence and in the absence of the surfactant, sodium lauryl sulfate (SLS). Electrochemical characterizations of the electrodeposited films are carried out by cyclic voltammetry and impedance spectroscopy. Structural characterization of the film is carried out by XRD, XPS, and SEM. The XPS studies reveal that the presence of Mn⁴⁺ (as MnO₂) in the absence of SLS and Mn^3+/2+ (as Mn₃O₄or Mn₂O₃ or MnOOH) ion in the presence of SLS. The power output obtained from MnO₂ cathode was 666 ± 9 mW m^?3 and it is the highest value reported for MFCs with cubical configuration with the same cathode.     

Heavy Metal Resistances and Chromium Removal of a Novel Cr(VI)-Reducing Pseudomonad Strain Isolated from Circulating Cooling Water of Iron and Steel Plant

Three bacterial isolates, GT2, GT3, and GT7, were isolated from the sludge and water of a circulating cooling system of iron and steel plant by screening on Cr(VI)-containing plates. Three isolates were characterized as the members of the genus Pseudomonas on the basis of phenotypic characteristics and 16S rRNA sequence analysis. All isolates were capable of resisting multiple antibiotics and heavy metals. GT7 was most resistant to Cr(VI), with a minimum inhibitory concentration (MIC) of 6.5 mmol L^?1. GT7 displayed varied rates of Cr(VI) reduction in M2 broth, which was dependent on pH, initial Cr(VI) concentration, and inoculating dose. Total chromium analysis revealed that GT7 could remove a part of chromium from the media, and the maximum rate of chromium removal was up to 40.8 %. The Cr(VI) reductase activity of GT7 was mainly associated with the soluble fraction of cell-free extracts and reached optimum at pH 6.0～8.0. The reductase activity was apparently enhanced by external electron donors and Cu(II), whereas it was seriously inhibited by Hg(II), Cd(II), and Zn(II). The reductase showed a K _m of 74 μmol L^?1 of Cr(VI) and a V _max of 0.86 μmol of Cr(VI) min^?1 mg^?1 of protein. The results suggested that GT7 could be a promising candidate for in situ bioremediation of Cr(VI).     

Choice of a suitable hetero-aromatic nitrogen base as promoter for chromic acid oxidation of dl-mandelic acid in aqueous media at room temperature

Chromic acid oxidation of dl-mandelic acid in the presence and absence of different promoters has been studied in aqueous media under the kinetic conditions [mandelic acid]_T ? [Cr(VI)]_T and [promoter]_T ? [Cr(VI)]_T at 30 °C. The promoters used in this oxidation reaction, picolinic acid (PA), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), are strong chelating ligands which form complexes with most transition metal ions. The reaction is first-order with regard to [H⁺], [mandelic acid]_T, and [Cr(VI)]_T and also has first-order dependence on [promoter]_T. HCrO₄ ^? was found to be kinetically active in the absence of promoters; in the presence of promoters the Cr(VI)–promoter complexes were believed to be the active oxidants. In this path the Cr(VI)-promoter complex in each case undergoes nucleophilic attack by the mandelic acid to form a ternary complex which subsequently undergoes redox decomposition involving 3e transfer as the rate-determining step. Among the three promoters oxidation is much faster with 1,10-phenanthroline.     

Co-electrodeposition of MnO2/graphene oxide coating on carbon paper from phosphate buffer and the capacitive properties

MnO₂/graphene oxide sheet composite (MnO₂/GOS) has been co-electrodeposited on the thermally treated carbon paper (TTCP) in phosphate buffer solution containing GOS and KMnO₄. The resulted samples have been characterized by scanning and transmission electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron energy spectroscopy. The results show that the synthesized MnO₂ may be δ-MnO₂ and the morphology of MnO₂/GOS is very different from that of MnO₂, indicating that the introduction of GOS in electrolyte can influence the morphology during the deposition. The capacitive properties of the samples are investigated by using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The specific capacitance of MnO₂ for MnO₂/GOS can reach about 829 F g^?1 at discharged current density of 1.0 A g^?1 in 1 M Na₂SO₄ aqueous solution, which is larger than that of MnO₂ deposited on TTCP. The composite of MnO₂/GOS also exhibits excellent cyclic stability with a decrease of 18.5 % specific capacitance after 1,500 cycles.     

Nanostructured polyaniline-coated anode for improving microbial fuel cell power output

An approach for improving the power generation of a dual-chamber microbial fuel cell by using a nanostructured polyaniline (PANI)-modified glassy carbon anode was investigated. Modification of the glassy carbon anode was achieved by the electrochemical polymerisation of aniline in 1 M H₂SO₄ solution. The MFC reactor showed power densities of 0.082 mW cm^?2 and 0.031 mW cm^?2 for the nano- and microstructured PANI anode, respectively. The results from electron microscopy scanning confirmed formation of the nanostructured PANI film on the anode surface and the results from electrochemical experiments confirmed that the electrochemical activity of the anode was significantly enhanced after modification by nanostructured PANI. Electrochemical impedance spectroscopic results proved that the charge transfer would be facilitated after anode modification with nanostructured PANI.     

Enhanced power production of microbial fuel cells by reducing the oxygen and nitrogen functional groups of carbon cloth anode

The physicochemical properties of anode material are important for the electron transfer of anode bacteria and electricity generation of microbial fuel cells (MFCs). In this work, carbon cloth anode was pretreated with isopropanol, hydrogen peroxide (H₂O₂) and sodium hypochlorite (NaOCl) in order to reduce the anode functional groups. The influence of functional groups on the electrochemical properties of carbon cloth anode and power generation of MFCs was investigated. The anode pretreatments removed the surface sizing layer of carbon cloth and substantially reduced the contents of C‐O and pyridinic/pyrrolic N groups on the anode. Electrochemical impedance spectroscopy and cyclic voltammetry analyses of the biofilm‐matured anodes revealed an enhanced electrochemical electron transfer property because of the anode pretreatments. As compared with the untreated control (612 ± 6 mW m^?2), the maximum power density of an acetate‐fed single‐chamber MFC was increased by 26% (773 ± 5 mW m^?2) with the isopropanol treated anode. Additional treatment with H₂O₂ and NaOCl further increased the maximum power output to 844 ± 5 mW m^?2 and 831 ± 4 mWm^?2. A nearly inverse liner relationship was observed between the contents of C‐O and pyridinic/pyrrolic N groups on anodes and the anodic exchange current density and the power output of MFCs, indicating an adverse effect of these functional groups on the electricity production of anodes. Results from this study will further our understanding on the microbial interaction with carbon‐based electrodes and provide an important guidance for the modification of anode materials for MFCs in future studies. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and characterization of Pd-La(OH)3/C electrocatalyst for direct ethanol fuel cell

The composite nanomaterial of Pd-La(OH)₃/C was successfully synthesized via intermittent microwave heating–glycol reduction method and characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The TEM photograph shows that Pd-La(OH)₃ is well polymerized and dispersed on the carbon support. The performance of the prepared material for ethanol oxidation was evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and chronopotentiometry (CP) measurements in alkaline media. The results reveal that Pd-La(OH)₃/C has significantly higher activity and stability than that of Pd/C with the same Pd loading of 0.1 mg cm^?2. The stable potential reaches to ?0.38 V vs. Hg/HgO at 20 mA cm^?2 on the Pd-La(OH)₃/C electrode in CP curve. Single direct ethanol fuel cell (DEFC) was constructed using Pd-La(OH)₃/C electrode and MnO₂/C electrode as the ethanol anode and air cathode respectively, where the cell voltage can stay at 0.4 V under the current density of 20 mA cm^?2 by discharge test at room temperature.     

Metal carbonates: alternative to metal oxides for supercapacitor applications? A case study of MnCO<Subscript>3</Subscript> vs MnO<Subscript>2</Subscript>

We report here the potential competency of MnCO₃ versus MnO₂ for supercapacitor applications. MnCO₃ was synthesized by a hydrothermal method using KMnO₄ as a manganese source and either sugar or pyrrole as carbon source. MnCO₃ synthesized using sugar and pyrrole as carbon source is referred hereafter as MnCO₃(s) and MnCO₃(p), respectively. The synthesized products were characterized by powder X-ray diffraction, scanning electron microscopic and transmission electron microscopic studies. Microscopic studies revealed that MnO₂ possesses micro-flower-like morphology constructed by self-assembled nano-petals. While the morphology of MnCO₃(s) is sub-micron size particles of different shape, the morphology of MnCO₃(p) is crystalline particles of 10–20 nm dia. The capacitive characteristics of MnO₂, MnCO₃(s) and MnCO₃(p) were evaluated in aqueous 0.1 M Mg(ClO₄)₂ electrolyte between 0 and 1 V using cyclic voltammetry and galvanostatic charge/discharge cycling. Specific capacitance (SC) values of 216 and 296 F g^?1 obtained for MnCO₃(s) and MnCO₃(p) are 35 and 85 % higher than SC value of 160 F g^?1 obtained for MnO₂, respectively. Besides better capacitive storage characteristics, MnCO₃(s) and MnCO₃(p) have also exhibited better rate capability and cycle life than MnO₂.     

Hexavalent chromium quantification in solution: Comparing direct UV–visible spectrometry with 1,5-diphenylcarbazide colorimetry

Quantification of Cr(VI) in an aqueous solution is conducted by direct UV–visible spectrophotometry based on the yellow coloring of the chromate ion. Measurements show that absorption follows the Beer–Lambert law over a wide range of concentrations. At pH below the pK_a of 6.4 (HCrO₄^?/CrO₄^?2), the absorption maximum lies at 350 nm wavelength and the linear range spans from 0.5 to 100 mg Cr(VI)/L; above the pK_a (pH 6.4), the absorption maximum is 373 nm and linearity occurs in the range of 0.5–25 mg/L. The wide range of validity of the Beer–Lambert law is advantageous for the measurement of concentrated samples. The standard method of analysis of aqueous Cr(VI) is by colorimetry with the 1,5-diphenylcarbazide (DPC)–Cr(VI) complex. This method, although very sensitive, bears a narrow range of linearity from 0 to 0.8 mg Cr(VI)/L. It is shown that when analyzing Cr(VI) solutions with concentrations in the range of 30–500 mg/L, the DPC method gives inaccurate results and relative standard deviations of 20–50%. This is due to high dilution factors. On the contrary, the direct method performs with high accuracy. Relative standard deviation is only 0.5% at 500 mg Cr(VI)/L. The direct method is fast, reliable, and nondestructive for the sample. The direct method is recommended for the quantification of Cr(VI) at concentrations greater than 1 mg/L.     

Nanoporous gold electrode prepared from gold compact disk as the anode for the microbial fuel cell

The electrodes (anode and cathode) have an important role in the efficiency of a microbial fuel cell (MFC), as they can determine the rate of charge transfer in an electrochemical process. In this study, nanoporous gold electrode, prepared from commercially available gold-made compact disk, is utilized as the anode in a two-chamber MFC. The performance of nanoporous gold electrode in the MFC is compared with that of gold film, carbon felt and acid-heat-treated carbon felt electrodes which are usually employed as the anode in the MFCs. Electrochemical surface area of nanoporous gold electrode exhibits a 7.96-fold increase rather than gold film electrode. Scanning electron microscopy analysis also indicates the homogeneous biofilm is formed on the surface of nanoporous gold electrode, while the biofilm formed at the surface of acid-heat-treated carbon felt electrode shows rough structure. Electrochemical studies show although modifications applied on carbon felt electrodes improve its performance, nanoporous gold electrode, due to its structure and better electrochemical properties, acts more efficiently as the MFC’s anode. The maximum power density produced by nanoporous gold anode is 4.71 mW m^?2 at current density of 16.00 mA m^?2, while this value for acid-heat-treated carbon felt anode is 3.551 mW m^?2 at current density of 9.58 mA m^?2.     

Speciation analysis of chromium in water samples using nanometer zirconium dioxide and direct ultrasonic slurry sampling with electrothermal atomic absorption spectrometry

A new analytical procedure for the determination of chromium Cr(III) and Cr(VI) species in different water samples was developed. The method involves solid-phase extraction (SPE), direct ultrasonic slurry sampling (DUSSS), and subsequent electrothermal atomic absorption spectrometry (ETAAS). The nanometer-sized zirconium dioxide (ZrO₂) was used as the sorbent material. The optimal conditions for the proposed solid phase extraction were: 50 mg ZrO₂, 20 min extraction time, pH 2.5 for Cr(VI) and pH 8.0 for Cr(III) and for the ETAAS measurement: 1500°C pyrolysis and 2300°C atomisation temperatures, 1.5 g L^?1 Mg(NO₃)₂ as matrix modifier. The samples were sonicated directly in the autosampler cup, using an ultrasonic probe at 20% power setting for 10 seconds prior to injection into the graphite tube with ?vov platform. In this way, all drawbacks due to the elution procedure were eliminated. The limit of detection and limit of quantification for Cr(III) obtained under optimised conditions were 0.48 μg L^?1, and 1.61 μg L^?1, respectively, and for Cr(VI) 0.27 μg L^?1 and 0.90 μg L^?1. The pre-concentration factors attained for both the species were 25. The effects of alkaline, alkaline earth and some metal ions and some anions were also examined. The relative standard deviation estimated from six replicate measurements at a concentration of 0.4 μg L^?1 for both Cr(III) and Cr(VI) with a pre-concentration factor of 25 was 2.96% and 4.06%, respectively. The accuracy of the method was confirmed by analysis of the standard reference material SRM 1643e “Trace Elements in Water?. The proposed technique is simple, sensitive, environmentally friendly, and the risk of contamination is low. Hence, it was successfully applied to spiked synthetic and real water samples with recoveries ranging from 91.3% to 109.2%     

Reed straw derived active carbon/graphene hybrids as sustainable high-performance electrodes for advanced supercapacitors

Reed straw-derived active carbon@graphene (AC@GR) hybrids were prepared by one-step carbonization/activation process using a mixture of reed straw and graphene oxide (GO) as raw materials and ZnCl₂ as activation agent. The as-prepared hybrids exhibit high specific surface area in a range of 1971–2497 m² g^?1, abundant porosity, as well as excellent energy storage capability. The symmetric C//C supercapacitor using the hybrid obtained at 700 °C as electrodes demonstrates superior cycling durability, ca. 90 % retention after 6000 cycles at 2 A g^?1, and a high energy density of 6.12 Wh kg^?1 at a power density of up to 4660 W kg^?1 in 6 M KOH aqueous electrolyte. The excellent capacitive performance is attributed to the synergistic effect of AC and GR.     

Comparative Study of Chromium Biosorption by Mesorhizobium amorphae Strain CCNWGS0123 in Single and Binary Mixtures

The appearance of chromium in the aqueous effluent is a major concern for the modern industry. In this work, Mesorhizobium amorphae strain CCNWGS0123 was investigated as a biosorbent to remove chromium from aqueous solutions. The optimum pH for Cr(III) and Cr(VI) biosorption were 4 and 2, respectively. This isolate showed an experimental maximum Cr(III) adsorption capacity of 53.52 mg?L^?1, while the result was 47.67 mg?L^?1 for Cr(VI), with an initial 100 mg?L^?1 Cr ions and 1.0 g?L^?1 biomass. In terms of time equilibrium, Cr(III) ion was more readily adsorbed than Cr(VI) by this isolate. The biosorption data of both ions fit the Langmuir isotherm better than that of Freundlich model. Meanwhile, this organism exhibited a good capability to release Cr ions, with desorption efficiency of 70 % for Cr(III) and 76 % for Cr(VI). Fourier transform infrared spectroscopy analysis showed that –OH, –COO, –NH, amide I, and C=O were involved in Cr(III) and Cr(VI) binding. The biosorbent was further characterized by scanning electron microscopy and energy-dispersive X-ray spectrometry, which indicated an accumulation of chromium on the cellular level. In the binary mixtures, the removal ratio of total Cr and Cr(III) increased from pH?2 to 4. The highest removal ratio of the total Cr was observed in the 25/25 mg?L^?1 mixture at pH?4. In addition, the removal efficiency of Cr(VI) was closely influenced by Cr(III) in the mixture, decreasing to 23.57 mg?g^?1 in the 100/100 mg?L^?1 mixture system, due to the competition of Cr(III). The potential usage of the chromium-resistant rhizobium for the remediation of chromium-contaminated effluents has been demonstrated based on the above results.     

Speciation and determination of chromium ions by dispersive micro solid phase extraction using magnetic graphene oxide followed by flame atomic absorption spectrometry

A selective, simple and fast dispersive micro solid phase extraction method using magnetic graphene oxide (GO) as an efficient sorbent has been developed for the extraction, separation and speciation analysis of chromium ions. The method is based on different adsorption behaviour of Cr(VI) and Cr(III) species onto magnetic GO in aqueous solutions which allowed the selective separation and extraction of Cr(VI) in the pH range of 2.0–3.0. The retained Cr(VI) ions by the sorbent were eluted using 0.5 mL of 0.5 mol L^?1 nitric acid solution in methanol and determined by ?ame atomic absorption spectrometry. Total chromium content was determined after the oxidation of Cr(III) to Cr(VI) by potassium permanganate. All effective parameters on the performance of the extraction process were thoroughly investigated and optimised. Under the optimised conditions, the method exhibited a linear dynamic range of 0.5–50.0 µg L^?1 with a detection limit of 0.1 µg L^?1 and pre-concentration factor of 200. The relative standard deviations of 3.8% and 4.6% (n = 8) were obtained at 25.0 µg L^?1 level of Cr(VI) for intra- and inter-day analysis, respectively. The method was successfully applied to the speciation and determination of Cr(VI) and Cr(III) in environmental water samples.     

Performance studies of electrolyte-supported solid oxide fuel cell with Ni–YSZ and Ni–TiO2–YSZ as anodes

Redox cycling of Ni-based anode induces cell degradation which limits the cell's lifetime during solid oxide fuel cell operation. In the present study, the redox testing of electrolyte-supported cells has been investigated with TiO₂-added NiO–YSZ anode matrix. Button cells were fabricated by die-pressing YSZ powder as electrolyte, and onto which NiO–YSZ or NiO–TiO₂–YSZ anode and LSM–YSZ composite cathode were painted. The electrochemical performance and stability have been evaluated by measuring current–voltage characteristics followed by impedance spectroscopy after each redox cycling. Anode matrices before and after cell operation have been characterized by X-ray diffraction (XRD), elemental dispersive X-ray (EDX), and scanning electron microscopy (SEM). During cell operation the peak power density decreases from 111 mW cm^?2 (239 mA cm^?2) to 84 mW cm^?2 (188 mA cm^?2) between 23 and 128 h with five redox cycles for cell having NiO–YSZ (40:60) anode. But for cell with NiO–TiO₂–YSZ (30:10:60), the anode peak power density was constant and stable around 85 mW cm^?2 (194 mA cm^?2) throughout the cell run of 130 h and five redox cycles. No loss in the open circuit voltage was observed. SEM and XRD studies of NiO–TiO₂–YSZ (30:10:60) anodes revealed formation of ZrTiO₄, which may be responsible for inhibition of Ni coarsening leading to stable cell performance.     

The influence of Cd-impure gyrolite on the hydration of composite binder material based on α-C2S hydrate

In this study, we determined the parameters of a composite binder material (CBM) synthesis on α-C₂S hydrate basis as well as analyzed and explained the early stages of its hydration process. In addition, the utilization possibility of gyrolite impured with Cd²⁺ ions in the binder composite material was presented. The results have shown that α-C₂S hydrate was the dominant product of the hydrothermal synthesis at 175 °C after 16 h. The CBM was prepared by mixing synthetic α-C₂S hydrate with quartz sand and milling the mixture in a vibrating cup mill. The hydration study on both pure CBM and CBM with gyrolite (2.5, 5 or 7.5 % by mass) impured with Cd²⁺ ions (~97 mg Cd²⁺ g^?1) was conducted. The results showed that the additive of gyrolite impured with Cd²⁺ ions accelerates the initial hydration reaction (maximum heat flow of this stage increases from 0.006 W g^?1 for pure binder to 0.009 W g^?1 for the samples with 7.5 % gyrolite) while decreases both the rate of the main reaction (maximum heat flow of the pure binder estimated to be 0.0016 W g^?1, whereas it is 0.0009 W g^?1 in case of 7.5 % gyrolite additive) and total heat after 5 h of the hydration (approximately by 10 J g^?1).     

Application of polyaniline/bacterial extracellular polysaccharide nanocomposite for removal and detoxification of Cr(VI)

Polyaniline/bacterial extracellular polysaccharide (Pn/EPS) nanocomposite was prepared by in situ polymerization of aniline using ammonium peroxydisulfate as oxidant. Transmission electron micrograph showed that the surface of the nanocomposite was rough, providing good possibility for adsorption of Cr(VI). Under optimized conditions, the nanocomposite removed 97.3 % (25 mg L^?1) of Cr(VI) from aqueous solution. The Freundlich isotherm model and pseudo-first order rate expression better described the adsorption equilibrium of Pn/EPS nanocomposite. X-ray diffractogram peak for Cr₂O₃ (2θ = 24.5) in the nanocomposite confirmed the reduction of Cr(VI). Fourier transform infrared spectroscopy pattern of the nanocomposite confirmed the ionic interaction between Cr species and surface functional groups. The results of the study indicate that Pn/EPS nanocomposite could be used for the removal and detoxification of Cr(VI) from aqueous solution.     

Thin film nonstoichiometric chromium oxide-based cathode material for rechargeable and primary lithium batteries

The application of nonstoichiometric chromium oxide-based thin film cathodes in lithium rechargeable and primary batteries operating at high rates has been demonstrated. Films of varying composition have been obtained by anionic Cr (VI) species electrodeposition on a 1X18N10Т grade stainless steel cathode from fluoride-containing electrolytes. The effect of film doping by Li⁺ ions during its electrosynthesis has been сonsidered. As-prepared films were studied by scanning and transmission electron microscopies, 3D optical profiler, thermogravimetric analysis, chemical analysis, and X-ray diffraction (XRD). The main phase components of the electrodeposited films regardless of Li⁺ in an electrolyte are Cr₂O₃, α-CrOOH, β-CrOOH, and metallic chromium as shown by XRD pattern refinement. The electrochemical reduction rate in a non-aqueous electrolyte (1 M LiClO₄ in PC/DME) correlates with the chromium oxide-hydroxide component content of film. Primary CrO _x -Li CR2325 mock-up cathode coating can be discharged in a pulsed mode at 10 Ω external resistance with 80–84 mA cm^?2 current densities for 10–100 ms. Thin film cathodes electrodeposited in the presence of lithium ions become rechargeable when the lithium content of the film reaches 0.02 wt.%. Mock-ups of CR2325 coin battery with a thin film cathode doped with lithium ions can be discharged more than 40 times with 136 mAh g^?1 specific capacity, 461 Wh kg^?1 specific energy and 154 W kg^?1 power density at 30 kΩ external resistance. The simplicity of thin film preparation makes this technology promising for thin film lithium batteries.