Metal Hydroxides Research Articles

The Ordering and Arrangement of Intercalated Carboxylate Ions in Anion‐Exchangeable Layered Yttrium Hydroxides

AbstractThe intercalation chemistry is essential in the application of anion‐exchangeable layered metal hydroxides. However, much of the key information regarding intercalated anions, such as the degree of ordering and arrangement is still not clear or missing to date, due to the difficulty in probing the local environment of anions by routine characterization techniques. Herein, we employed solid‐state NMR (ssNMR) spectroscopy to offer valuable complementary insights into the ordering and arrangement of a series of monocarboxylate anions (RCOO−: R=HO, H, CH3, C2H5, and C3H7) within the interlayer space of two layered yttrium hydroxides (LYH‐Cl and LYH‐Br). The results imply that the two smaller carboxylate anions (R=HO and H) are disordered after intercalation, while the larger carboxylate anions (R=CH3, C2H5, and C3H7) are relatively ordered. We further explored if the intercalated anions are parallel arranged as those in sodium salts or antiparallel arranged as those predicted in the majority of previous reports. We uncovered that the intercalated anions are antiparallel arranged based on the formation energy obtained in density functional theory calculations and ssNMR data. Our results therefore contribute to a deeper and comprehensive understanding of the intercalation chemistry of layered rare earth hydroxides.

NiMo/NiFe-LDH heterostructured electrocatalyst for hydrogen production from water electrolysis

Constructing low-cost and efficient catalysts for electrocatalytic water splitting to produce hydrogen is of great significance. In this study, we successfully prepared NiMo/NiFe-LDH electrocatalysts with abundant coupled interfaces using a hydrothermal method and electrodeposition. The synergistic effect between the NiMo alloy and NiFe-LDH nanosheets induces charge redistribution at the interface and accelerates charge transfer, thus improving reaction kinetics and enhancing electrocatalytic performance. Experimental results show that at a current density of 10 mA cm−2, the HER overpotential of NiMo/NiFe-LDH is 35 mV, demonstrating excellent water-splitting performance. This work provides insights into the development of alloy/transition metal hydroxides for efficient water-splitting hydrogen production

Application of dairy wastewater as substrate for bioremediation of coal mine drainage in planted horizontal flow constructed wetland

Coal mine drainage (CMD) is an environmental threat due to its high volume, low pH, presence of toxic metals, and absence of biodegradable organics. The present study aims to treat CMD in a horizontal sub-surface flow constructed wetland (CW) using dairy wastewater as an organic source. CW was planted with Typha angustifolia. Characteristics of synthetic CMD were (except pH, all unit mg/L) pH 1.9; Fe: 100, SO 4 2 − : 1,000, Mn: 6, Zn: 5, Co: 1, Ni: 1, and Cr: 1. CMD was mixed with synthetic dairy wastewater (pH: 5.05, COD: 2,700 mg/L, BOD: 1,600 mg/L) in the ratio of 3:1. Alkalinity of 120–190 mg/L CaCO3 was generated and effluent pH improved from 2.2 to 6.6. Metals precipitated as metal sulfide or hydroxide. Sulfate removal was hindered due to the synergistic toxicity of several metals. Except for Mn, all other effluent parameters were within the discharge limit for disposal in inland surface water.

Stimulated Raman scattering and enhancement mechanisms in alkali metal hydroxide aqueous solutions under laser-induced dynamic pressure

Stimulated Raman scattering (SRS) in lithium hydroxide-water/heavy water (LiOH-H2O/D2O) solutions with varying concentrations was investigated under laser-induced high-pressure conditions using an Nd: YAG laser. The spectra revealed a significant enhancement in SRS signals, characterized by the emergence of low-wavenumber Raman peaks and a shift of the main SRS peak of liquid water to lower frequencies, evolving from a single peak to two or three peaks, which suggested the formation of an ice-like structure. Additionally, the normalized SRS intensity was higher than that of pure water. The enhancement of SRS signals during LiOH dissolution was attributed to the cooperative modulation between hydrogen bonding (HB, O-H:O) by OH- and Coulombic electronic interactions generated by monovalent Li+, which strengthened HB interactions, increased the Raman gain coefficient, and induced structural modifications akin to pressure effects. Besides, the increased density amplified the dynamic high-pressure effects during the laser-induced breakdown (LIB) process, further boosting the SRS signals. This work provides valuable insights into the interaction mechanisms between alkali metal hydroxides and H2O/D2O under laser-induced pressure conditions, offering a comprehensive approach to understanding and enhancing the SRS effect in aqueous solutions.

Facile Mechanochemical Synthesis of Compositionally Complex Spinel‐type Oxides, (Co, Fe, Mn)3O4, (Co, Fe, Mn, Ni)3O4, and (Co, Cr, Fe, Mn, Ni)3O4

AbstractIn the current work, a simple mechanochemical route has been employed to preparatively access three spinel‐type compositionally complex ceramics, i. e., (Co, Fe, Mn)3O4, (Co, Fe, Mn, Ni)3O4, and (Co, Cr, Fe, Mn, Ni)3O4. Hydrated nitrate salts of the respective transition metal elements were mechanically ground with ammonium hydrogen carbonate. The resulting paste‐like mixture of metal hydroxides, oxyhydroxides, and carbonates was rinsed with water to remove the byproduct (NH4NO3) and converted into the respective single‐phase spinel‐type oxides via calcination. In situ X‐ray diffraction (XRD) revealed the formation of the spinel‐type structure (Fd m) already at temperatures as low as 150 °C. Typically, the calcination of the precursors at temperatures beyond 500 °C led to the formation of well‐crystallized, single‐phase spinel‐type oxides with nearly equimolar composition and highly homogeneous distribution of the transition metals within the structure. The mechanochemical synthesis route in the present study is considered to be an easy, straightforward, and scalable access to compositionally complex oxides.

An Evaluation of Metal Binding Constants to Cell Surface Receptors in Freshwater Organisms, and Their Application in Biotic Ligand Models to Predict Metal Toxicity

Biotic ligand models (BLMs) predict the toxicity of metals in aquatic environments by accounting for metal interactions with cell surface receptors (biotic ligands) in organisms, including water chemistry (metal speciation) and competing cations. Metal binding constants (log KMBL values), which indicate the affinity of metals for cell surface receptors, are fundamental to BLMs, but have only been reported for a few commonly investigated metals and freshwater species. This review evaluated literature toxicity and uptake data for seven key metals (cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), uranium (U), and zinc (Zn)) and four key competing cations (protons (H), calcium (Ca), magnesium (Mg), and sodium (Na)), to derive average metal binding constants for freshwater organisms/taxa. These constants will improve current BLMs for Cd, Cu, Ni, Pb, and Zn, and aid in developing new BLMs for Co and U. The derived metal binding constants accurately predicted metal toxicity for a wide range of freshwater organisms (75–88% of data were within a factor of two and 88–98% of data were within a factor of three of the ideal 1:1 agreement line), when considering metal speciation, competing cations and the fraction of cell receptors ((fC)M50%) occupied by the metal at the median (50%) effect concentration (EC50). For many organisms, toxicity occurs when 50% of cell surface receptors are occupied by the metal, though this threshold can vary. Some organisms exhibit toxicity with less than 50% receptor occupancy, while others with protective mechanisms show reduced toxicity, even with similar log KMBL values. For Cu, U, and Pb, the toxic effect of the metal hydroxide (as MOH+) must be considered in addition to the free metal ion (M2+), as these metals hydrolyse in circumneutral freshwaters (pH 5.5 to 8.5), contributing to toxicity.

Outstanding Activity and Durability of Supported NiCo2O4 Nanoparticles for Direct Ethanol Fuel Cells

ABSTRACTThe rational design of noble metal‐free electrocatalysts represents one of the basic stones for fuel cell development. With the exploration of eco‐friendly nanomaterials for the investigated alcohol oxidation process, nickel‐based electrodes have been recognized as the most auspicious anodes with promoted activity and stability. In this work, a series of NiCo2O4 nanoparticles were deposited onto graphite sheets (NiCo2O4/T) introducing varied proportions of cobalt oxide species. Co‐precipitation protocol of the respective metallic hydroxides onto the carbonaceous support was followed with consecutive annealing in an air atmosphere at 400°C. The fabricated mixed metallic oxide nanopowder was physically studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X‐ray analysis (EDX), X‐ray photoelectron spectroscopy (XPS), and selected area electron diffraction (SAED). Uniformly arranged nanoparticles were observed on graphite surface as evidenced by SEM and TEM. The cubic lattice structure of formed NiCo2O4 crystals was also confirmed by XRD through the defined peaks of binary metallic oxides clarifying their successful preparation scheme. The electrocatalytic properties of these NiCo2O4/T nanocatalysts were evaluated for oxidizing ethanol molecules in basic solution. Pronounced oxidation current densities were remarkably measured at NiCo2O4/T electrodes in relation to that at NiO/T. Differing the introduced cobalt oxide content into the synthesized nanocatalyst significantly controlled its catalytic performance. NiCo2O4/T‐20 exhibited the highest activity and stability among the prepared nanomaterials. Much decreased charge transfer resistances were also recorded at this electrode demonstrating its promoted electron transfer characteristics. This work could provide a reasonable route for the simple synthesis of comparable transition metallic oxides with promising attitudes for energy generation purposes.

Palygorskite-mediated simultaneous nutrient removal and antibiotic degradation from aquaculture wastewater in lab-scale constructed wetlands

In this study, palygorskite was employed as a substrate in laboratory-scale constructed wetlands (CWs) over a period of 180 days to investigate the removal efficiency of pollutants from mariculture wastewater under high loads of enrofloxacin (ENR) stress. The results indicated that the incorporation of palygorskite into CWs resulted in average effluent concentrations of total phosphorus (TP), total nitrogen (TN), chemical oxygen demand (COD), and ENR reaching 0.07 ± 0.00 mg/L, 1.07 ± 0.06 mg/L, 11.57 ± 1.04 mg/L, and 0.047 ± 0.002 mg/L, respectively. The removal efficiencies reached 96.45 ± 0.04 %, 94.62 ± 0.27 %, 88.61 ± 1.22 %, and 91.14 ± 5.00 % respectively, with phosphorus removal significantly surpassing that reported for similar CWs. This superior performance was mainly attributed to the strong binding mechanisms between phosphorus and the metal oxides and hydroxides leached from the palygorskite. The palygorskite stimulated the secretion of extracellular polymeric substances (EPS), accelerated biofilm establishment, and enhanced the relative abundance of key functional bacteria associated with carbon, nitrogen, and antibiotic removal, thus achieving rapid denitrification and efficient organic matter removal. Monitoring of metals (Ca, Fe, Mn, and Cu) in the CWs effluent suggested that their presence was insufficient to affect cytoplasmic enzyme activity or cause oxidative stress damage to plants. In conclusion, palygorskite serves as an environmentally friendly, high-nutrient removal alternative, apt as a substrate for CWs.

Structural Study on Alkali‐Carboxylate Functionalized Late‐Transition Metal Bis(dithiocarbamate) Complexes

AbstractLithium, sodium, and potassium derivatives of amino‐acid derived bis(dithiocarbamate) complexes of bivalent nickel, palladium, platinum, and copper are readily available by treatment of the carboxylic‐acid functionalized complexes with the respective alkali metal hydroxide. Representative derivatives of the types A4[M(L1)2], A2[M(HL1)2], A[M(HL1)(H2L1)] (N‐dithioato‐iminodiacetate, L1), and A2[M(L2,3)2] (N‐dithioato‐l‐prolinate, L2, and ‐N‐benzylglycinate, L3; A=Li, Na, K; M=Ni, Pd, Pt, Cu) were isolated and characterized by spectroscopic and thermal methods. Six entries were accessible to single‐crystal X‐ray structure determination, revealing the presence of different coordination‐polymeric structures and hydrogen‐bonded assemblies comprising solvent‐separated cations in the solid state. While the transition metal always retains its all‐sulfur coordination with defined geometry, the alkali metals are structurally more flexible. The latter are usually coordinated by carboxylate and water, but additional interactions with sulfur donors are also relevant in some cases.

Recyclability of Zinc Palmitate-Based Composites in Fatty Acid Methyl Ester Production from Oil Feedstocks at Varied Acidity.

Zinc hydroxide nitrate (Zn5) is one of the layered metal hydroxide materials, which has been extensively reported as an effective bifunctional catalyst for biodiesel production from acidic oils. This report gives a comprehensive summary of the reactivity of Zn5 in the methanolysis of various oil feedstocks, plant oils, free fatty acids, and other acidic oils. Notably, as evidenced by this work, Zn5 is highly effective in converting acidic oils [palmitic acid/palm oil (PO)] to fatty acid methyl ester (FAME or biodiesel) at high yields ranging from 80 to 95%, withstanding acid content up to 10% without soap formation. The high FAME yields result from complex methanolysis and hydrolysis processes, e.g., transesterification of triglycerides in the PO, esterification of palmitic acid, and hydrolysis of the triglycerides. Despite this, Zn5 is nonrecyclable because it is unstable in the reaction media and transforms into zinc hydroxide nitrate/zinc palmitate (Zn5/ZnP) composites. The Zn5/ZnP composites were suitable for use in FAME production from PO at 100 °C for 2 h by using a methanol-to-oil molar ratio of 30:1, yielding high FAME yields of 97 and 70.7% in the first and fourth cycles, respectively. This study added better insight into how to effectively produce FAME from oil feedstocks of varying acidity by using zinc layered hydroxide- or zinc carboxylate-based materials.

Electronic structure engineering of NiFe hydroxide nanosheets via ion doping for efficient OER electrocatalysis

Nickel-iron layered double hydroxides (NiFe-LDH) with tunable catalytic properties have shown promise as an outstanding alternative to ruthenium iridium oxide for the oxygen evolution reaction (OER). However, the intrinsic activity of such electrocatalysts is suboptimal, and a considerable gap remains in understanding the working mechanism. To address this issue, we employ a convenient corrosion method to synthesize Mo-modified nickel–iron hydroxide (Mo-NiFeOxHy) ultrathin nanosheets. Mo-NiFeOxHy demonstrates excellent OER activity, requiring only 216 mV at a current density of 10 mA cm−2, with enhanced stability. Theoretical calculations reveal that the Mo doping induces material distortion, shifting the d-band center closer to the Fermi level, which accelerates the kinetic rate and catalytic activity. In situ Raman experiments show that doping with Mo promotes the rapid formation of high-oxidation-state transition metal hydroxide species, further enhancing the catalytic properties of Mo-NiFeOxHy in OER. This work provides a novel strategy to tailor the structure and composition of NiFe-based electrocatalysts, demonstrating a great potential to break barriers in OER.

Constructing dilute Mg-1.0In binary alloy: A pathway to enhanced anode performance in Mg-air battery

Magnesium anode is a critical material in Mg-air battery; however, the contradiction between mitigating self-corrosion and promoting activation poses a significant obstacle to the rapid advancement of primary magnesium batteries. Herein, this issue is addressed by constructing a dilute Mg-1.0In binary alloy with 1 wt% indium as the anode material. The equiaxed dendrites and moderate indium concentration gradient in the as-cast anode facilitate the formation of a protective surface film, leading to a low corrosion rate of 0.20 mm y−1 and enhancing the stability prior to discharge. Moreover, during the battery discharge process, this unique microstructure enables the redeposition of metallic indium and indium hydroxide, thereby dramatically accelerating the shedding of oxidation products and suppressing side hydrogen evolution reaction. The Mg-1.0In anode in a Mg-air battery delivers a discharge capacity of 1587 mA h g−1 and an average voltage of 1.46 V at 10 mA cm−2, outperforming most of previously reported magnesium anodes and the control samples with various indium contents. This work would inspire the achievement of superior Mg-air battery performance through the use of binary magnesium anode system in as-cast state, as opposed to a more complex and time-consuming multi-component anode design involving heat treatment and plastic deformation.

Deciphering the Underlying Mechanism of the Fourth Entity in Medium-Entropy NiCoFeMP toward Boosting Oxygen Evolution Electrocatalysis.

High-/medium-entropy materials have been explored as promising electrocatalysts for water splitting due to their unique physical and chemical properties. Unfortunately, state-of-the-art materials face the dilemma of explaining the enhancement mechanism, which is now limited to theoretical models or an unclear cocktail effect. Herein, a medium-entropy NiCoFeMnP with an advanced hierarchical particle-nanosheet-tumbleweed nanostructure has been synthesized via simple precursor preparation and subsequent phosphorization. Evaluated as the electrocatalyst for oxygen evolution reaction (OER), the medium-entropy NiCoFeMnP displays a lower overpotential of 272 mV at a current density of 10 mA cm-2, and more favorable kinetics than the binary NiFeP, ternary NiCoFeP, quaternary NiCoFeCuP and NiCoFeCrP counterparts, and other reported high-/medium-entropy electrocatalysts. Careful experimental analyses reveal that the incorporation of Mn can significantly regulate the electronic structure of Ni, Co, and Fe sites. More importantly, the Mn introduction and entropy stabilization effect in the reconstructed metal (oxy)hydroxide simultaneously promote the lattice oxygen mechanism, improving the activity. This work sheds new light on the design of high-/medium-entropy materials from an in-depth understanding of the underlying mechanism for improving energy conversion efficiency.

Sulfur-Vacancy Engineering Accelerates Rapid Surface Reconstruction in Ni-Co Bimetal Sulfide Nanosheet for Urea Oxidation Electrocatalysis.

Developing a highly efficient catalyst for electrocatalytic urea oxidation reaction (UOR) is not only beneficial for the degradation of urea pollutants in wastewater but also provides a benign route for hydrogen production. Herein, a sulfur-vacancy (Sv) engineering is proposed to accelerate the formation of metal (oxy)hydroxide on the surface of Ni-Co bimetal sulfide nanosheet arrays on nickel foam (Sv-CoNiS@NF) for boosting the urea oxidation electrocatalysis. As a result, the obtained Sv-CoNiS@NF demonstrates an outstanding electrocatalytic UOR performance, which requires a low potential of only 1.397V versus the reversible hydrogen electrode to achieve the current density of 100mA cm-2. The ex situ Raman spectra and density functional theory calculations reveal the key roles of the Sv site and Co9S8 in promoting the electrocatalytic UOR performance. This work provides a new strategy for accelerating the transformation of electrocatalysts to active metallic (oxy)hydroxide for urea electrolysis via engineering the surface vacancies.

Microwave-assisted hydrothermal synthesis of αβ-Ni(OH)2 nanoflowers on nickel foam for ultra-stable electrodes of supercapacitors

Transition metal hydroxides (TMHs) are considered promising materials for supercapacitors because of their high theoretical capacitance and tunable morphology. Among TMHs, nickel hydroxide stands out for its multiple oxidation states, facilitating charge storage. This paper reports on a novel microwave-assisted hydrothermal technique employed to synthesize mixed-phase nickel hydroxide nanoflowers directly at the surface of nickel foam substrates with improved electrochemical stability compared to pure phases of nickel hydroxide. The analysis of nickel hydroxide in different phases alpha, beta and mixed-phase materials using physiochemical techniques like XRD, SEM, EDX, RAMAN, FT-IR and TGA is explained. The areal capacitance calculated from GCD tests for α-Ni(OH)2, β-Ni(OH)2 and αβ-Ni(OH)2 is estimated 7.35 F/cm2, 2.66 F/cm2 and 5.12 F/cm2 at a current density of 10 mAcm−2. The mass-specific capacitance calculated from GCD tests for α-Ni(OH)2, β-Ni(OH)2 and αβ-Ni(OH)2 is estimated 2311 Fg−1, 688 Fg−1 and 1511 Fg−1 at a current density of 10 mAcm−2. The cyclic stability test revealed the superior cycling performance of nickel hydroxide in mixed-phase as the cathode of an ultralong supercapacitor with nearly 100% capacitance retention after 5000 cycles at 50 mAcm−2. The proposed synthesis technique advances the efficiency and control of nanostructure geometry, providing insights into the design for electrodes of extreme-performance supercapacitors. However, conventional synthesis methods are time-consuming and energy-intensive. These findings underscore the potential of mixed-phase nickel hydroxide as an outstanding electrode material with extended cyclic performance for supercapacitors, contributing to the improvement of energy storage technologies in the renewable energy landscape.

Enhancing Oxygen Evolution Reaction Performance with rGO/CoNi-Prussian Blue-Derived Oxyhydroxide Nanocomposite Electrocatalyst: A Strategic Synthetic Approach.

Electrochemical water splitting is a promising approach in the development of renewable energy technologies, providing an alternative to fossil fuels. It has attracted considerable attention in recent years. The benchmark materials used in water splitting are precious metals that are expensive and scarce. Therefore, this work proposes a strategic electrochemical synthesis of a reduced graphene oxide and cobalt-nickel hexacyanoferrate (rGO/CoNiHCF)-derived composite (rGO/CoNiPBd-OOH) to achieve optimized OER performance. The optimum rGO/CoNiHCF was fabricated with the Co:Ni precursors in a 3:1 ratio with a ferricyanide solution of pH = 1.0. Using an alkaline electrochemical treatment, the well-distributed globular particles of CoNiHCF over rGO sheets were converted into layered frameworks of metallic (oxy)hydroxide species, giving the final rGO/CoNiPBd-OOH nanocomposite. This nanocomposite presented favorable kinetic activity resulting in a Tafel slope of 33 mV dec-1, while rGO, CoNiPBd-OOH, and RuO2 exhibited slopes of 80, 47, and 51 mV dec-1, respectively. Although the benchmark RuO2 electrocatalyst showed a lower overpotential (240 mV dec-1) at a current density of 10 mA cm-2, the rGO/CoNiPBd-OOH performed well with an overpotential of 346 mV, combined with superior stability compared to CoNiPBd-OOH and RuO2, maintaining a current density of 10 mA cm-2 for 15 h with an overpotential loss of 6.92%. This work successfully presents an "all-electrochemical" synthesis of a rGO/CoNiHCF-derived material with remarkable electrocatalytic activity for OER assisted by a strategic preparation methodology, which helped to understand the influence of synthetic parameters and choose their conditions to achieve the optimum OER performance.

Construction of a Three-Phase MnS2/Co4S3/Ni3S2 Heterostructure for Boosting Oxygen Evolution.

The rational construction of highly efficient electrocatalysts for the oxygen evolution reaction (OER) plays a critical role in energy conversion systems. Designing heterostructures is a common and effective strategy to improve the performance of electrocatalysts. In this paper, an MnS2/Co4S3/Ni3S2 heterostructure was synthesized on Ni foam using a one-step vulcanization method. It provides a modified electronic structure and plentiful three-phase heterogeneous interfaces that can effectively enrich the active sites and accelerate electron transfer, thereby improving the OER activity. Thanks to the heterostructure, the MnS2/Co4S3/Ni3S2 exhibits a low overpotential of 265 and 304 mV for the OER to reach current densities of 50 and 100 mA/cm2, respectively. Furthermore, the surface reconstruction of MnS2/Co4S3/Ni3S2 has been investigated, which revealed the formation of metal hydr(oxy)oxides evolved during the OER process. This work provides a facile strategy for constructing three-phase heterostructures, shedding light on the development of high-performance, nonprecious metal-based OER electrocatalysts.

Henkel‐like Decarboxylation Produces Mononuclear Arylalkalis, [4‐(CH3)3N(C6H4)M]+ which Hydrolyse and Undergo Surprising SN2 Reactions Between Alkali Hydroxides and (CH3)3NC6H5+

AbstractBenzoate substituted with a cationic quaternary ammonium group at the para‐position, [4‐(CH3)3N(C6H4)CO2], forms mononuclear alkali metal ion complexes, [4‐(CH3)3N(C6H4)CO2M]+ (M=Li, Na, K, Rb and Cs), which are observed by electrospray‐ionisation mass spectrometry. When mass selected and subjected to collision‐induced dissociation each of these complexes undergoes decarboxylation to produce the mononuclear arylalkali complex cations, [4‐(CH3)3N(C6H4)M]+, which subsequently react with water via hydrolysis to yield the quaternary ammonium cation, (CH3)3NC6H5+. The unexpected product ions, [M((CH3)2NC6H5)]+, [M(CH3OH)]+, and M+, which are associated with the hydrolysis pathway, suggest an unusual reaction occurring within the exit channel ion‐molecule complex, [(CH3)3NC6H5+MOH]+. DFT calculations were used to examine the: decarboxylation reaction of [4‐(CH3)3N(C6H4)CO2M]+, which readily proceeds via a four‐centred transition state; the hydrolysis and SN2 reactions accounting for formation of products in the exit channel, which are connected via a roaming mechanism in which the metal hydroxide moiety migrates from the para‐hydrogen of (CH3)3NC6H5+ to one of the methyl groups.

Ultrasound-assisted synthesis of Co(OH)2 nanoflowers and nanosheets as battery-type cathode for high-performance supercapacitors

The depletion of traditional energy resources and the escalating environmental concerns have compelled researchers to pursue green energies, among which the supercapacitors possess a crucial function in electrochemical energy storage systems. In this study, the Co(OH)2 nanoflowers and Co(OH)2 nanosheets have been respectively synthesized utilizing a safe and facile ultrasound-assisted method in the solvent with different pH values, and the product is denoted as Co(OH)2-7.5 and Co(OH)2-9.5, accordingly. The Co(OH)2-7.5 exhibited a specific surface area of 188.3 m2 g, significantly greater than that of Co(OH)2-9.5. Additionally, these Co(OH)2 electrode materials showed battery-type electrochemical response, and the Co(OH)2-7.5 presented an impressive specific capacity of 371.6 C g−1. When integrated into a hybrid supercapacitor (HSC) device with activated carbon (AC) as anode, the device exhibited an exceptional cycling stability after 10000 cycles at 10 A g−1. Furthermore, the Co(OH)2-7.5//AC HSC delivered an impressive energy density (De) of 30.2 W h kg−1 at the power density (Dp) of 888.6 W kg−1, and this De surpassed the 26.4 W h kg−1 of Co(OH)2-9.5//AC HSC. The Co(OH)2 in this work shows good application potential in the field of supercapacitors. The straightforward and efficient synthesis technique can be further applied to the synthesis of many other transition metal hydroxides with remarkable electrochemical properties.

A novel sequential extraction method for the measurement of Cr(VI) and Cr(III) species distribution in soil: New insights into the chromium speciation

The distribution characteristics of Cr(VI) species in contaminated soil is crucial for soil remediation; however, there is currently a lack of methods for analysing anionic Cr(VI) species in soil. This study has developed a novel sequential extraction method for speciation of Cr(VI) and Cr(III). Besides extraction experiments, simulated chromium species were prepared to verify the presence of proposed chromium species. The results show that Cr(VI) species in soil can be categorized into water-soluble Cr(VI), electrostatically adsorbed Cr(VI), Cr(VI) specifically adsorbed by minerals containing exchangeable Ca2+, Cr(VI) specifically adsorbed by hydrous metal oxides, calcium chromate Cr(VI) and stable complexed adsorption Cr(VI). These Cr(VI) species can be selectively extracted by specific solutions through ion exchange or weak acid dissolution. The most stable Cr(VI) species is Cr(VI) complexed by hydrous iron oxides through bidentate ligand binding; only by dissolution of hydrous iron oxides can this Cr(VI) species be leached. The distribution of Cr(VI) species is closely linked to particular soil compositions including exchangeable Ca2+ and hydrous iron oxides which determinate the Cr(VI) adsorption in soil. Cr(III) species comprise Fe-Cr coprecipitate hydroxides Cr(III), Fe-Mn oxide-bound Cr(III), organic matter-bound Cr(III) and residual Cr(III). Their distribution depends on the types of reductants present in the soil.