Treatment of paint manufacturing wastewater by electrocoagulation

Treatability of paint manufacturing wastewater (PMW) by electrocoagulation (EC) process was investigated. Effects of operating parameters for the EC process such as electrode type (Al or Fe), initial pH (2–10), current density (5–80 A/m²) and operating time (0–50 min) were evaluated for optimum operating conditions. The highest removal efficiencies for COD and TOC in PMW were obtained with 93% and 88% for Fe and 94% and 89% for Al electrodes at the optimum conditions (35 A/m², 15 min and pH 6.95). Operating costs for removal of PMW at the optimum conditions were calculated for Fe and Al electrodes as 0.187 €/m³ and 0.129 €/m³. Toxicity test was carried out to obtain information about toxic effect of the raw and treated wastewaters at optimum operating conditions. The samples measured by respirometric method contained hardly toxicities. Performance of Al electrode was better than that of Fe electrode in terms of removal efficiency and operating cost.     

Synthesis,characterization and kinetics properties of chromium(III) complex [Cr(3-HNA)(en)2]Cl · H2O · CH3OH

The reaction of chromium(III) chloride, 3-hydroxy-2-naphthoic acid (3-HNA) and ethylenediamine (en) led to the formation of complex [Cr(3-HNA)(en)₂]Cl · H₂O · CH₃OH, Bis(ethylenediamine-κ²N,N′)(3-hydroxy-2-naphthoic acid-κ²O,O′) chromium(III) monochloride monohydrate monomethanol. The kinetics of transfer of Cr(III) from the title compound to the low-molecular-mass chelator EDTA and to the iron-binding protein apoovotransferrin (apoOTf) were carried out by means of UV–Visible (UV–Vis) and fluorescence spectra in 0.01 M Hepes at pH 7.4. The second-order rate constants were calculated, respectively. The results show that Cr(III) can be transferred from the complex to apoovotransferrin.     

3D network-like porous MnCo2O4 by the sucrose-assisted combustion method for high-performance supercapacitors

3D network-like porous MnCo₂O₄ nanostructures have been successfully fabricated through a facile and scalable sucrose-assisted combustion route followed by calcination treatment. Benefiting from its advantages of the unique 3D network-like architectures with large specific surface area (216.15 m² g⁻¹), abundant mesoporosity (2–50 nm) and high electronic conductivity, the as-prepared MnCo₂O₄ electrode displays a high specific capacitance of 647.42 F g⁻¹ at a current density of 1 A g⁻¹, remarkable capacitance retention rate of 70.67% at current density of 10 A g⁻¹ compared with 1 A g⁻¹, and excellent cycle stability (only 6.32% loss after 3000 cycles). The excellent electrochemical performances coupled with facile and cost effective method will render the as-fabricated 3D network-like porous MnCo₂O₄ as a promising electrode material for supercapacitors.     

Modeling and optimizing of electrochemical oxidation of C.I. Reactive Orange 7 on the Ti/Sb–SnO2 as anode via response surface methodology

The decolorization and degradation of an organic dye, Reactive Orange 7 (RO7) in aqueous media by electrochemical oxidation process using Ti/Sb–SnO₂ electrode as anode was modeled and optimized using response surface methodology (RSM) based on central composite design (CCD). The anode electrode was prepared using dip-coating and thermal decomposition method. Accordingly reduced quadratic model was developed to give the substrate color removal efficiency percentage as function of effective parameters such as: initial dye concentration, pH of the solution, electrolyte concentration and current density. The fit of the model is checked by the determination coefficient (R²). In this case, the value of the determination coefficient (R² = 0.9949) is indicated. Maximum color removal efficiency was achieved at the obtained conditions of: pH = 4, concentration of electrolyte = 3.5 g/L and current density = 19 mA/cm². Dye removal rate increased by increasing the concentration of electrolyte, lowering pH and increasing the current density. In optimum conditions, decolorization was obtained completely after 5 min; and the removal of chemical oxygen demand (COD) was reduced to 70.3% after 90 min.     

Structural,thermal and electrical studies of a novel rubidium phosphite tellurate compound

Structural, thermal and electrical properties studies of rubidium phosphite tellurate, RbH(PO₃H)·Te(OH)₆, were performed. An endothermic peak, which reached a completion at about 315 °C accompanied with a weight loss of 4.6 wt.%, was attributed to dehydration. Four types of pellets were produced, namely pellets A, B, C and D. Pellet A was tested with platinum–carbon paper electrode, and pellets B, C and D were tested with gold electrodes. Both pellets A and B were studied from 113 °C to 317 °C for 135 h. Pellet C was first investigated from room temperature to 176 °C for 360 h. After cooling down to room temperature, a second measurement with pellet C was carried out under the same conditions as used for pellets A and B. Pellet D, on the other hand, was heated up to 450 °C, kept at that temperature for 2 h and then cooled down to room temperature prior to the conductivity measurements. It was observed that the conductivities of pellets A and B decreased to values of 5.2 × 10^?8 S cm^?1 and 6.6 × 10^?7 S cm^?1 at 317 °C, respectively, and an unexpected rise in the conductivity (9.89 × 10^?6 S cm^?1 at 317 °C) was seen with pellet C. Dehydration of RbH(PO₃H)·Te(OH)₆ might be responsible for this unexpected rise in the conductivity of pellet C. The monoprotic part RbH(PO₃H) of RbH(PO₃H)·Te(OH)₆ apparently became diprotic (Rb₂H₂P₂O₅) part of Rb₂H₂P₂O₅·[Te(OH)₆]₂ after dehydration. The measured conductivity of pellet D, which was dehydrated prior to the measurement, reached a value of 5.41 × 10^?5 S cm^?1 at 317 °C and showed a good stability over-each-run time and temperatures measurement up to 317 °C. The dehydrated compound, Rb₂H₂P₂O₅·[Te(OH)₆]₂, has also a higher hydrogen density relative to the starting compound, RbH(PO₃H)·Te(OH)₆. It is deduced that completion of the dehydration can be responsible for the unexpected rise in the conductivity of RbH(PO₃H)·Te(OH)₆. This unusual case is important for studies in solid acid proton conductors.     

Electrochemical properties of nanodiamond powder electrodes

Detonation-synthesized nanocrystalline diamond is a novel carbon material. Its increased electrical conductivity, due to the features of giant specific surface area and large numbers of surface defects as well as the cluster structure, makes it possible to be used as an electrode material. Nanodiamond powder electrodes were fabricated and the electrochemistry was investigated by cyclic voltammetry and AC impedance measurement. The results show that nanodiamond powder electrode is electrochemically stable in KCl electrolytes over a wide potential range (− 1.2–2.0 V). The electrode reaction is quasi-reversible in 0.1 M KCl containing the ferricyanide–ferrocyanide redox couple. The electrode reaction rate constant k is estimated to be 2.87 × 10^− 3 cm/s. The peak current increases linearly with the rising of the concentration of [Fe(CN)₆]^3−/4−. The AC impedance spectra have been analyzed and an equivalent circuit proposed.     

A facile method for preparation of iron based catalysts for high temperature water gas shift reaction

Nanocrystalline Fe₃O₄ based catalysts with theoretical particle size of 31–78 nm were synthesized by a facile direct pyrolysis method and employed in high temperature water gas shift reaction. XRD analysis showed that this method led to obtaining the catalysts directly in the active phase with chromium and copper incorporated into magnetite lattice. The results showed that the addition of chromium significantly increases the BET surface area of the pure iron oxide from 14.87 to 35.42 m² g⁻¹. Among the catalysts evaluated, Fe–Cr–Cu catalyst revealed higher activity compared to commercial catalyst and showed high stability during 10 h time on stream.     

The composite material based on Dawson-type polyoxometalate and activated carbon as the supercapacitor electrode

A supercapacitor electrode assembled from activated carbon (AC) and (NH₄)₆[P₂Mo₁₈O₆₂]·14.2H₂O (P₂Mo₁₈) was fabricated for the first time, and showed remarkable electrochemical performance ascribed to the synergy of the double layer capacitance of AC and the pseudocapacitance of P₂Mo₁₈. The investigations indicate that the AC/P₂Mo₁₈ electrode exhibits a specific capacitance of 275 F g^− 1 at a high current density of 6 A g^− 1, which is substantially larger than the 182 F g^− 1 of the AC electrode. In addition, the AC/P₂Mo₁₈ electrode possesses a remarkable rate capability (89%) when the current density is increased from 2 to 6 A g^− 1.     

Electrochemical decomposition of NO over composite electrodes on YSZ electrolyte

NO decomposition over electrochemical cells that involve a bilayered composite electrode has been investigated. NO was decomposed only after a minimum current density was applied and its conversion increased abruptly with increasing applied current. The compositions of phases and their spatial distribution on the cathode strongly influenced the decomposition activity as a function of the current density since they are directly correlated with the site and number densities of the triple-phase boundary and the electrochemically induced active site, i.e., F-center. The [(La₂Sn₂O₇ + YSZ)/Pt] electrode could convert more than 85% of NO into N₂ at 200 mA/cm² whereas only 27% was decomposed over the platinum electrode although the latter was more electrochemically active at lower current ∼70 mA/cm². The addition of Pt into the [(La₂Sn₂O₇ + YSZ)/Pt] composite electrode not only expands the densities of the tpb and F-centers but also enhances competitive NO adsorption as indirectly confirmed by impedance spectroscopy, both of which promote NO conversion at the lower current density.     

3D NiCo2S4 nanorod arrays as electrode materials for electrochemical energy storage application

It is essential to develop new electrode materials for electrochemical energy storage to meet the increasing energy demands, reduce environmental pollution and develop low-carbon economy. In this work, binder-free NiCo₂S₄ nanorod arrays (NCS NRAs) on nickel foam electrodes are prepared by an easy and low energy-consuming route. The electrodes exhibit superior electrochemical properties both for alkaline and Li-ion batteries. In 3 M KOH electrolyte, the NCS NRAs achieve a specific capacity of 240.5 mA h g⁻¹ at a current density of 0.2 A g⁻¹, and 105.7 mA h g⁻¹ after 1500 cycles at the current density of 5 A g⁻¹ with capacity retention of 87.3%. As the anode for LIBs, it shows a high initial capacity of 1760.7 mA h g⁻¹ at the current density of 100 mA g⁻¹, corresponding coulombic efficiency of 87.6%, and a rate capacity of 945 mA h g⁻¹ when the current density is improved 10 times. Hence, the NiCo₂S₄ nanorod arrays are promised as electrode materials with competitive performance.     

Synthesis of reduced graphene oxide/tungsten trioxide nanocomposite electrode for high electrochemical performance

A facile and well-controllable reduced graphene oxide/tungsten trioxide (rGO/WO₃) nanocomposite electrode was successfully synthesized via an electrostatic assembly route at 350 rpm for 24 h. In this study, hexagonal-phase WO₃ (h-WO₃) nanofiber was well distributed on rGO sheets by applying optimal processing parameters. The as-synthesized rGO/WO₃ nanocomposite electrode was compared with pure h-WO₃ electrode. A maximum specific capacitance of 85.7 F g⁻¹ at a current density of 0.7 A g⁻¹ was obtained for the rGO/WO₃ nanocomposite electrode, which showed better electrochemical performance than the WO₃ electrode. The incorporation of WO₃ into rGO could prevent the restacking of rGO and provide favourable surface adsorption sites for intercalation/de-intercalation reactions. The impedance studies demonstrated that the rGO/WO₃ nanocomposite electrode exhibited lower resistance because of the superior conductivity of rGO that improved ion diffusion into the electrode. To evaluate the contribution of WO₃ to the rGO/WO₃ nanocomposite, the influence of mass loading of WO₃ on the capacitance was investigated.     

Nano-graphite platelet loaded with LiFePO4 nanoparticles used as the cathode in a high performance Li-ion battery

LiFePO₄ nanoparticles were grown on nano-graphite platelet (NGP) using a simple chemical route. The material was used as the cathode in Li-ion rechargeable batteries and exhibited excellent cyclability and rate capability because of the easy electron transport in it. The electrochemical stability of the electrode was improved by the two-dimensional conductive network of the NGP. The resulting electrodes delivered a specific capacity of about 150 mA h g^?1 at a current rate of 135 mA g^?1 (～0.8 C) after 100 cycles with no capacity fade. At elevated current rates, the electrodes exhibited capacities of more than 100 mA h g^?1 at a current density of 2000 mA g^?1 (～12 C) without further incorporation of conductivity agents or coatings.     

Hydrothermal synthesis of Polypyrrole/MoS2 intercalation composites for supercapacitor electrodes

As a pseudocapacitive electrode materials for supercapacitor, Polypyrrole (PPy) exhibit excellent theoretical specific capacitance. However, it suffers from a poor cycling stability due to structural instability during charge-discharge process. In this work, a novel and facile hydrothermal method has been developed for the intercalation composites of PPy/MoS₂ with multilayer three-dimensional structure. The report result shows that the as-prepared electrode possess a outstanding electrochemical properties with significantly specific capacitance of 895.6 F g⁻¹ at current density of 1 A g⁻¹, higher energy density (3.774 Wh kg⁻¹) at power density of 252.8 kW kg⁻¹, furthermore, it also achieve remarkable cycling stability (~98% capacitance retention after 10,000 cycles) which is attributed to the synergistic effect of PPy and MoS₂. This synthetic strategy integrates performance enables the multilayer PPy/MoS₂ composites to be a promising electrode for energy storage applications.     

Charge–discharge performance of Cr-substituted V-based hydrogen storage alloy negative electrodes for use in nickel-metal hydride batteries

To improve the charge–discharge cycle durability of a TiV_2.1Ni_0.3 alloy negative electrode with a discharge capacity of ～470 mAh g^?1, the vanadium constituent was partially substituted with chromium. The TiV_2.1?xCr_xNi_0.3 (x = 0.1–0.4) alloys, which were prepared by arc-melting, were composed of two phases, similar to the TiV_2.1Ni_0.3 alloy. Each constituent was distributed in both phases, and the V and Cr content in the primary phase was higher than that in the secondary phase, although the Ti and Ni content was higher in the secondary phase. The maximum discharge capacity for the TiV_2.1?xCr_xNi_0.3 (x = 0.1–0.4) negative electrodes showed a slight decrease as the x value increased, and their cycle durability was significantly improved due to the effective suppression of the dissolution of V. In particular, the loss of discharge capacity per cycle for the TiV_1.7Cr_0.4Ni_0.3 negative electrode was about one-tenth that for the TiV_2.1Ni_0.3 negative electrode. The high-rate dischargeability (HRD) was also greatly improved by increasing the Cr content. At 200 mA g^?1 the variations of the HRD and the charge transfer resistance (R_ct) with the Cr content were similar, while at 400 mA g^?1 the change in the HRD at a lower Cr content was markedly different from the change in R_ct. Moreover, at a lower Cr content the potential at a 50% degree of discharge stagnated at specific discharge currents over 200 mA g^?1. These results strongly suggest that hydrogen diffusion in the primary phase served as the main hydrogen reservoir.     

Removal of Chromium and Organic Pollutants from Industrial Chrome Tanning Effluents by Electrocoagulation

The treatment of industrial chrome tanning effluents by electrocoagulation (EC) in a laboratory‐scale reactor was investigated. Mild‐steel (MS) electrodes have been found to outperform aluminum (Al) electrodes in reducing the Cr(III) concentration to <2 mg L^–1. The conversion of Fe(II) to Fe(III) is slow in the lower pH range (<6), and OH^– ions generated during EC are amply available for Cr(III) removal by precipitation in the case of the MS electrode. Formation of Al(OH)₃(s) in competition with Cr(OH)₃(s) while consuming the OH^– ion is a cause for lower Cr(III) removal with Al. EC with the MS electrode and chemical coagulation (CC) with addition of alkali proved to be equally efficient for removing Cr(III).     

Straightforward synthesis of hierarchical Co3O4@CoWO4/rGO core–shell arrays on Ni as hybrid electrodes for asymmetric supercapacitors

Hierarchical Co₃O₄@CoWO₄/rGO core/shell nanoneedles arrays are successfully grown on 3D nickel foam using a simple, effective method. By virtue of its unique structure, Co₃O₄@CoWO₄/rGO demonstrates an enhanced specific capacitance of 386 F g⁻¹ at 0.5 A g⁻¹ current density. It can be used as an integrated, additive-free electrode for supercapacitors that boasts excellent performance. As illustration, we assemble an asymmetric supercapacitor (ASC) using the as-prepared Co₃O₄@CoWO₄/rGO as the positive electrode and activated carbon as the negative electrode. The optimized ASC displays a maximum energy density of 19.99 Wh kg⁻¹ at a power density of 321 W kg⁻¹. Furthermore, the ASC also presents a remarkably long cycle life along with 88.8% specific capacitance retention after 5000 cycles.     

Electrochemical energy storage performance of heterostructured SnO2@MnO2 nanoflakes

In this work, we report synthesis of SnO₂@MnO₂ nanoflakes grown on nickel foam through a facile two-step hydrothermal route. The as-obtained products are characterized by series of techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-obtained SnO₂@MnO₂ nanoflakes are directly used as supercapacitor electrode materials. The results show that the electrode possesses a high discharge areal capacitance of 1231.6 mF cm⁻² at 1 mA cm⁻² and benign cycling stability with 67.2% of initial areal capacitance retention when the current density is 10 mA cm⁻² after 6000 cycles. Moreover, the heterostructured electrode shows 41.1% retention of the initial capacitance when the current densities change from 1 to 10 mA cm⁻², which reveals good rate capability. SnO₂@MnO₂ nanoflakes products which possess excellent electrochemical properties might be used as potential electrode materials for supercapacitor applications.     

Synthesis and characterization of MnCo2O4 microspheres based air electrode for rechargeable sodium-air batteries

In this work, the nanosized porous MnCo₂O₄ microspheres were synthesized by a hydrothermal method and their electrochemical behaviors were investigated based on a carbon supported composite air electrode for rechargeable sodium-air batteries. Under dry air test condition, the MnCo₂O₄/C air electrode demonstrated a stable working voltage of around 2.1 V vs. Na⁺/Na and a high initial discharge capacity of 7709.4 mA h g⁻¹, based on the active material mass, at a current density of 0.1 mA cm⁻². By a limit on the depth of discharge, the cell exhibited a specific capacity of 1000 mA h g⁻¹ with a high cycling stability up to 130 cycles. The considerable electrocatalytic activity suggests that the as-proposed MnCo₂O₄ is a highly efficient catalyst as air electrode for rechargeable sodium-air batteries.     

Carbon coated porous tin peroxide/carbon composite electrode for lithium-ion batteries with excellent electrochemical properties

A porous tin peroxide/carbon (SnO₂/C) composite electrode coated with an amorphous carbon layer is prepared using a facile method. In this electrode, spherical graphite particles act as supporter of electrode framework, and the interspace among particles is filled with porous amorphous carbon derived from decomposition of polyvinylidene fluoride and polyacrylonitrile. SnO₂ nanoparticles are uniformly embedded in the porous amorphous carbon matrix. The pores in amorphous carbon matrix are able to buffer the huge volume expansion of SnO₂ during charge/discharge cycling, and the carbon framework can prevent the SnO₂ particles from pulverization and re-aggregation. The carbon coating layer on the outermost surface of electrode can further prevent porous SnO₂/C electrode from contacting with electrolyte directly. As a result, the repeated formation of solid electrolyte interface is avoided and the cycling stability of electrode is improved. The obtained SnO₂/C electrode presents an initial coulombic efficiency of 77.3% and a reversible capacity of 742 mA h g⁻¹ after 130 cycles at a current density of 100 mA g⁻¹. Furthermore, a reversible capacity of 679 mA h g⁻¹ is obtained at 1 A g⁻¹.     

Preparation and capacitance performance of nitrided lithium titanate nanoarrays

Nitrided lithium titanate (N-Li₄Ti₅O₁₂) nanoarrays with nanowire and nanotube structures were designed as the electrode materials of lithium-ion supercapacitor for electrochemical energy storage. Two types of TiO₂ nanoarrays were used as the precursor which involved TiO₂ nanowire array prepared by hydrothermal process and TiO₂ nanotube array prepared by anodization process. Li₄Ti₅O₁₂ nanoarrays were formed through hydrothermal reaction or sonochemical reaction of TiO₂ nanoarrays with lithium hydroxide and then calcination treatment process. Finally, N-Li₄Ti₅O₁₂ nanoarrays were formed through nitriding treatment of Li₄Ti₅O₁₂ using ammonia as nitrogen source. The electroactive N-Li₄Ti₅O₁₂ nanowire array and nanotube array exhibited the specific capacitance of 607.2 F g⁻¹ and 814.4 F g⁻¹ at a current density of 1 A g⁻¹, respectively. The corresponding capacitance retention was determined to be 92.1% and 94.2% after 1000 cycles at high current density of 5 A g⁻¹. The corresponding capacitance still kept 182.9 and 352.1 F g⁻¹ at much higher current density of 20 A g⁻¹, presenting reasonable rate capability for N-Li₄Ti₅O₁₂ nanoarrays. The improved capacitance performance of N-Li₄Ti₅O₁₂ nanotube array was ascribed to the more amount of TiN and more accessible nanotube surface area, which contributed to the improved conductivity and fast diffusion of electrolyte ions on the surface of electrode. Both N-Li₄Ti₅O₁₂ nanowire array and nanotube array with well-aligned integrative structure exhibited an excellent cycling stability during continuous charge/discharge process. Well-designed N-Li₄Ti₅O₁₂ nanoarrays with high capacitance, good cycling stability and rate capability presented the promising application as feasible electrode materials of lithium-ion supercapacitors for the energy storage.