Layered Hydroxides Research Articles

Dynamic Morphological Evolution of Co-Based Layered Double Hydroxide Nanosheets Investigated by In Situ Electrochemical-Atomic Force Microscopy

With excellent electrochemical activity, low consumption, and easy synthesis, Co-based layered double hydroxides (LDHs) have been applied to electrochemical energy conversion and storage devices. Understanding the mechanisms of morphological evolution and capacity changes under potential cycles is critical for the design of high-performance materials of Co-based LDHs. Here, we monitored the morphological evolution of two kinds of CoFe-LDH nanosheets and four kinds of CoAl-LDH nanosheets using in situ electrochemical-atomic force microscopy. The CoFe-LDH nanosheets present the growth of granular particles and the deterioration of capacity performances, which might be due to the irreversible conversion of hydroxide into oxyhydroxide under potential cycles. The CoAl-LDH nanosheets maintain more capacity and do not form granular particles under potential cycles, resulting from the electrochemical reaction reversibility of Co2+ and the stability of the host hydroxide layer enhanced by Al3+. The introduction of Al3+ into the Co-based LDH structure is conducive to cyclic stability of capacity compared to that of Fe3+. Additionally, the CoAl-LDH nanosheets with different Co/Al molar ratios present varying degrees of dissolution and variations of capacity under potential cycles. A moderate Co/Al molar ratio of CoAl-LDH nanosheets is beneficial to cyclic stability. These findings would provide a deep insight into the mechanisms of capacity changes based on in situ morphological evolution and support for the optimization of such material performance.

Highly efficient bifunctional layered triple Co, Fe, Ru hydroxides and oxides composite electrocatalysts for Zinc-Air batteries

The preparation of bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great practical significance for the development of zinc-air batteries (ZAB). Layered double hydroxides (LDH) have been widely used in OER due to their low cost and adjustable structure. However, the poor ORR performance of LDH has hindered the development and application of zinc-air battery. In this work, CoFeRu-LDH was synthesized by hydrothermal method and then it was partially oxidized to obtain the oxides/LDH. As a bifunctional catalyst, RuO2, Fe2O3 and LDH have a high activity towards OER, while Co3O4 shows high reactivity towards ORR. Therefore, the catalyst oxides/LDH shows an excellent bifunctional activity with the voltage difference (ΔE) between E10 and E1/2 of 0.734 V. The assembled ZAB with the catalyst as the air electrode has a power density of 163 mW cm−2, a discharge specific capacity of 730 mAh g−1 and cycle stability of up to 210 h, proving its potential practical application in ZABs.

Photocatalytic Activity of the Oxidation Stabilized Ti3 C2 Tx MXene in Decomposing Methylene Blue, Bromocresol Green and Commercial Textile Dye.

Two-dimensional MXenes are excellent photocatalysts. However, their low oxidation stability makes controlling photocatalytic processes challenging. For the first time, this work elucidates the influence of the oxidation stabilization of model 2D Ti3 C2 Tx MXene on its optical and photocatalytic properties. The delaminated MXene is synthesized via two well-established approaches: hydrofluoric acid/tetramethylammonium hydroxide (TMAOH-MXene) and minimum intensive layer delamination with hydrochloric acid/lithium fluoride (MILD-MXene) and then stabilized by L-ascorbic acid. Both MXenes at a minimal concentration of 32mg L-1 show almost 100% effectiveness in the 180-min photocatalytic decomposition of 25mg L-1 model methylene blue and bromocresol green dyes. Industrial viability is achieved by decomposing a commercial textile dye having 100 times higher concentration than that of model dyes. In such conditions, MILD-MXene is the most efficient due to less wide optical band gap than TMAOH-MXene. The MILD-MXene required only few seconds of UV light, simulated white light, or 500nm (cyan) light irradiation to fully decompose the dye. The photocatalytic mechanism of action is associated with the interplay between surface dye adsorption and the reactive oxygen species generated by MXene under light irradiation. Importantly, both MXenes are successfully reused and retained approximately 70% of their activity.

Electrochemical Behavior of Morphology-Controlled Copper (II) Hydroxide Nitrate Nanostructures

Nanostructure control is an important issue when using electroactive materials in energy conversion and storage devices. In this study, we report various methods of synthesis of nanostructured copper (II) hydroxide nitrate (Cu2(OH)3NO3) with a layered hydroxide salt (LHS) structure using various synthesis methods and investigate the correlation between nanostructure, morphology, and their pseudocapacitive electrochemical behavior. The variations in nanostructure size and morphology were comprehensively explored by combining X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the electrochemical activity was characterized using cyclic voltammetry. We demonstrate that Cu2(OH)3NO3–LHS nanostructured submicron particles produced by alkaline precipitation with 88% of the copper cations can cycle with a two-electron redox process. Unfortunately, the electroactivity decreases rapidly from the first cycle due to the occurrence of structural transformations and subsequent electrochemical grinding. However, samples obtained by ultrasonication and microwave synthesis, two original synthesis methods for LHS materials, formed of nanosized crystalline domains agglomerated in micron-sized particles, represent a good compromise between capacity and cyclability. Moreover, by using pair distribution function analysis on electrode materials after repeated cycling, we were able to follow the chemical and structural changes occurring in Cu2(OH)3NO3 materials during electrochemical cycling with first a quick transformation to Cu2O and then the appearance of Cu metal and copper acetate Cu(II)2(O2CCH3)4·2H2O.

Engineering a low-cost diatomite with Zn-Mg-Al Layered triple hydroxide (LTH) adsorbents for the effectual removal of Congo red: Studies on batch adsorption, mechanism, high selectivity, and desorption

Engineering a low-cost diatomite with Zn-Mg-Al Layered triple hydroxide (LTH) adsorbents for the effectual removal of Congo red: Studies on batch adsorption, mechanism, high selectivity, and desorption

Corrosion of Synthetic Intermetallic Compounds and AA7075-T6 in Dilute Harrison’s Solution and Inhibition by Cerium(III) Salts

This study addresses the behavior of an aluminum alloy and its components in conditions simulating the presence of atmospheric salts. The corrosion of synthetic intermetallic compounds (IMCs) Al2Cu, Al2CuMg, Al7Cu2Fe, MgZn2, and bulk aluminum alloy 7075-T6 was studied in dilute Harrison’s solution (DHS, 0.35 wt% (NH4)2SO4 + 0.05 wt% NaCl). For IMCs, electrochemical measurements were performed using a microcell, and a standard electrochemical cell was used to study the bulk alloy. Separately measured cathodic and anodic potentiodynamic polarization curves were recorded, and prolonged immersion was characterized using electrochemical impedance spectroscopy. Samples were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Bulk AA7075-T6 was less susceptible to corrosion in DHS than in chloride solution stemming from the beneficial presence of sulfate ions and lower chloride concentration. The susceptibility of IMCs to corrosion in DHS increased in the order Al2Cu < Al7Cu2Fe < Al2CuMg < MgZn2 due to the increased dissolution of Mg in the presence of ammonium ions. The relative nobility of IMCs was determined based on the galvanic current density. Further, the possibility of using cerium chloride, nitrate and acetate salts as corrosion inhibitors in DHS was evaluated. Ce salts acted as inhibitors for the alloy during 14 d testing, forming a Ce hydroxide layer. The degree of protection depended on the type of anion, with acetate Ce salt giving the most efficient protection. For the IMC, however, inhibition by Ce salts did not occur during short measurements in the microcell, indicating the importance of galvanic interaction with the alloy matrix in the inhibition mechanism, which was confirmed by long-term measurements of the alloy.

Layered Copper Hydroxide Salts as Catalyst for the “Click” Reaction and Their Application in Methyl Orange Photocatalytic Discoloration

The 1,2,3-triazoles are an important class of organic compounds that are found in a variety of biologically active compounds. The most usual and efficient methodology to synthetize these compounds is the Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC), preferably by use of click chemistry principles. Therefore, the development of simple, robust, easily accessible and efficient materials as catalysts for this kind of reaction is highly desirable. In this sense, layered hydroxide salts (LHS) emerge as an interesting alternative for the click reaction. Thus, we describe herein the preparation and characterization of copper (II) layered hydroxide salts and their application as catalysts for the CuAAC reaction under solvent-free conditions. This synthetic methodology of CuAAC reaction is attractive as it follows several concepts of green chemistry, such as being easy to perform, allowing purification without chromatographic column, the process forming no sub-products, affording the desired 1,2,3-traizoles in the specific 1,4-disubstituted position in high yield, and having a short reaction time. Moreover, the photocatalysis for the degradation of methyl orange was also highly efficient using the same catalyst.

Iron oxide/hydroxide–nitrogen doped graphene-like visible-light active photocatalytic layers for antibiotics removal from wastewater

Hybrid layers consisting of Fe oxide, Fe hydroxide, and nitrogen doped graphene-like platelets have been synthesized by an eco-friendly laser-based method for photocatalytic applications. The complex composite layers show high photodecomposition efficiency towards degradation of antibiotic molecules under visible light irradiation. The photodecomposition efficiency was investigated as a function of relative concentrations of base materials, Fe oxide nanoparticles and graphene oxide platelets used for the preparation of target dispersions submitted to laser irradiation. Although reference pure Fe oxide/Fe hydroxide layers have high absorption in the visible spectral region, their photodecomposition efficiency is negligible under the same irradiation conditions. The high photocatalytic decomposition efficiency of the nanohybrid layer, up to 80% of the initial antibiotic molecules was assigned to synergistic effects between the constituent materials, efficient separation of the electron–hole pairs generated by visible light irradiation on the surface of Fe oxide and Fe hydroxide nanoparticles, in the presence of conducting graphene-like platelets. Nitrogen doped graphene-like platelets contribute also to the generation of electron–hole pairs under visible light irradiation, as demonstrated by the photocatalytic activity of pure, reference nitrogen doped graphene-like layers. The results also showed that adsorption processes do not contribute significantly to the removal of antibiotic molecules from the test solutions. The decrease of the antibiotic concentration under visible light irradiation was assigned primarily to photocatalytic decomposition mechanisms.

Role of Anions in Stabilizing the [Zn–Al] Layered Double Hydroxides: A Thermodynamic Study

Room-temperature acid solution calorimetry, high-temperature oxide melt solution calorimetry, and low-temperature heat capacity measurements were employed to calculate the thermodynamic stabilities of the [Zn–Al–X] layered double hydroxides (LDH) containing different anions (X = Cl–, CO32–, and SO42–). Cryogenic heat capacity measurements demonstrated a Schottky-type anomaly in the heat capacity of all three LDHs below 11 K. This anomaly is attributed to the tunneling of protons between adjacent oxygen atoms in the LDH interlayer as this creates an energy system similar to a two-level system modeled with a Schottky term. These heat capacity measurements were also used to determine vibrational entropies which, when combined with configurational entropies, provide standard entropies of these LDHs. Enthalpies of formation of LDHs from binary components were determined and combined with the entropies of formation to calculate Gibbs free energies. Based on these values, the order of stability is [Zn–Al–SO4] > [Zn–Al–CO3] > [Zn–Al–Cl]. This trend results from a combination of the interlayer spacing, amount of water in the interlayer, interactions among the interlayer species, and interactions between the metal hydroxide layer and the interlayer.

Corrosion behaviour of additively manufactured 316L and CoCrNi

Alloys such as 316L and the medium‐entropy alloy CoCrNi are known for their excellent strength and corrosion properties. In the present study, bulk samples of 316L and CoCrNi (without and with 0.11 wt.% N) alloys fabricated using powder bed fusion laser beam (PBF‐LB) were tested in the as‐printed state for their corrosion behaviour in 0.5 M H2SO4 without and with added 3 wt.% NaCl. The tests were done using potentiodynamic measurements and the results were compared with those of the conventionally manufactured 316L. By means of angle‐resolved X‐ray photoelectron spectroscopy (ARXPS), the passive film characteristics were studied in terms of composition and film thickness. The 316L fabricated using PBF‐LB showed favourable passivation and corrosion behaviour as compared with its conventionally manufactured counterpart. It was observed that all the alloys fabricated using the PBF‐LB showed similar corrosion behaviour, but with CoCrNi and CoCrNi‐N showing better passivation behaviour than 316L alloys in the presence of NaCl. The ARXPS showed the presence of both hydroxide and oxides in all the alloys, with outer hydroxide layer and inner oxide layer. The ARXPS of both 316L alloys showed the expected presence of Cr–Fe oxide on the surface of as‐passivated samples, whereas the presence of sulphide was also depicted for the conventionally manufactured 316L, supposed to be detrimental to its corrosion behaviour. The CoCrNi‐based alloys showed the presence of only Cr2O3 layer in their passivated state, with Co and Ni acting as noble elements in the formation of the passive film. Upon micro‐alloying with the strong solid solution strengthener N, CoCrNi did not show any negative effect on either the corrosion behaviour or the passivation behaviour of the alloy.

Formation of mixed-layer sulfide-hydroxide minerals from the Tochilinite-Valleriite group during experimental serpentinization of olivine

Abstract We report the formation of minerals from the tochilinite-valleriite group (TVG) during laboratory serpentinization experiments conducted at 300 and 328 °C. Minerals in the TVG are composed of a mixture of sulfide and hydroxide layers that can contain variable proportions of Fe, Mg, Cu, Ni, and other cations in both layers. Members of this group have been observed as accessory minerals in several serpentinites, and have also been observed in association with serpentine minerals in meteorites. To our knowledge, however, TVG minerals have not previously been identified as reaction products during laboratory simulation of serpentinization. The serpentinization experiments reacted olivine with artificial seawater containing 34S-labeled sulfate, with a small amount of solid FeS also added to the 300 °C experiment. In both experiments, the predominant reaction products were chrysotile serpentine, brucite, and magnetite. At 300 °C, these major products were accompanied by trace amounts of the Ni-bearing TVG member haapalaite, Ni,Fe-sulfide (likely pentlandite), and anhydrite. At 328 °C, valleriite occurs rather than haapalaite and the accompanying Ni,Fe-sulfide is proportionally more enriched in Ni. Reduction of sulfate by H2 produced during serpentinization evidently provided a source of reduced S that contributed to formation of the TVG minerals and Ni,Fe-sulfides. The results provide new constraints on the conditions that allow precipitation of tochilinite-valleriite group minerals in natural serpentinites.

Synchrotron XPS and Electrochemical Study of Aging Effect on Passive Film of Ni Alloys

To investigate aging effect on the passive film of Ni23Cr15Mo and Ni22Cr9Mo3Nb, synchrotron-based X-ray photoelectron spectroscopy (XPS) was used to analyze the structure and composition of the air-formed passive film on the alloys. The corrosion resistance of the two Ni alloys in 1 M NaCl solution was evaluated with electrochemical cyclic polarization measurement. The synchrotron XPS measurement provided detailed information about chemical states of alloying elements in the passive film, showing that the passive film consists of an inner oxide layer and an outer hydroxide layer. The XPS data allowed precise determination of the chemical composition and the thickness of the outer hydroxide layer, the inner oxide layer, and the underlying subsurface alloy layer. The Cr-oxide in the inner layer grows thicker with aging time, leading to Cr-depletion in the subsurface region. Mo and Nb in the alloy form mixed oxides and hydroxides, and aging in air leads to transformation of the lower valence oxides into higher valence oxides. The freshly formed oxide film exhibits similar barrier properties as the aged oxide film. The stability of the passive film formed on Ni22Cr9Mo3Nb seems to be better than that on Ni23Cr15Mo.

Technical basis for extended dry storage of aluminum-clad spent nuclear fuel

This paper presents the technical basis for extended dry storage of aluminum-clad spent nuclear fuel (ASNF). This basis addresses and closes five knowledge gaps defined by the U.S. Department of Energy (DOE) Spent Nuclear Fuel Working Group (SNFWG) in DOE-ID/RPT-1575 “Aluminum-clad Spent Nuclear Fuel: Technical Considerations and Challenges for Extended (>50 Years) Dry Storage.” The SNFWG's primary concern pertaining to dry storage of ASNF is rooted in the presence of (oxy)hydroxide layers adherent to the aluminum cladding of the spent fuel that formed in service, indicating a risk of radiolytic molecular hydrogen (H2) generation in a strong gamma radiation field—a process that can be associated with disintegration of (oxy)hydroxide and the molecular decomposition of chemisorbed and physisorbed water bonded to it. Potential consequences are overpressurization of sealed ASNF dry storage canisters and creation of a flammable atmosphere in sealed and vented canisters. Further, there is the concern that the generation of other chemical species due to chemical reactions, such as nitric acid (HNO3), could lead to canister component corrosion. To address these issues, experimental work was conducted, including investigations of the performance of surrogate aluminum specimens and actual ASNF material featuring adherent (oxy)hydroxide layers during wet or dry storage. Further, a comprehensive characterization of the sample material was completed. Drying experiments were executed, providing better estimations of the amount of residual, chemisorbed, and physisorbed water after ASNF dry storage canister conditioning. These empirical activities allowed for the development of predictive numerical models to simulate the chemical species yield within sealed and vented dry storage canisters for 50 years. The findings of these activities lead to the main conclusion that extending current ASNF dry storage durations by 50 years is both safe and viable.

Synthesis, properties, and application of the new nanocatalyst of double layer hydroxides in the one-pot multicomponent synthesis of 2-amino-3-cyanopyridine derivatives

A new heterogeneous nanocatalyst LDH@3-chloropyltrimethoxysilane@1,3-benzenedisulfonyl amine@Cu (LDH@TRMS@BDSA@Cu) was synthesized and confirmed by analyzes such as Fourier transform infrared spectroscopy, Field Emission Scanning Electron Microscopy, energy scattered X-ray spectroscopy (EDX), elemental mapping, X-ray diffraction analysis, heat gravity/heat derivatization (TGA) and differential scanning calorimetry. The newly synthesized nanocatalyst effectively catalyzed the reaction between different aryl aldehydes, malononitrile, different acetophenones and ammonium acetate in solvent-free conditions and they were converted into 2-amino-3-cyanopyridine derivatives with high efficiency. The reaction showed advantages such as simplicity, high stability, environmental friendliness, excellent efficiency and short time. Also, this catalyst is recyclable and was recycled 4 times without losing significant catalytic power.

Synthesis and Structure Refinement of [Co-Al4-X] LDHs (X = NO3 - and SO4 2-) from Nordstrandite.

[M-Al4-X] LDHs (M = divalent metal and X = anion) are a class of aluminum-rich layered double hydroxides synthesized from both the gibbsite and bayerite polymorphs of Al(OH)3. Henceforth, "g" and "b" are used to indicate gibbsite and bayerite. Despite the differences in the stacking arrangement of the hydroxyl layers in the precursor polymorphs, [M-Al4-X] LDHs whether synthesized from gibbsite or bayerite were seen to be structurally the same. In this work, we report the first ever synthesis of [M-Al4-X] LDHs (M = Zn, Ni, and Co and X = NO3 - and SO4 2-) from nordstrandite, which is yet another polymorph of Al(OH)3. Hereafter, "n" represents the nordstrandite precursor. We report that n-[M-Al4-X] LDHs do not differ structurally from those prepared from gibbsite and bayerite. We also report the structural refinement of n-[Co-Al4-X] LDHs, where X = NO3 - and SO4 2-. This work is also significant as it gives for the very first time the refined structure of a [Co-Al4-NO3] LDH, though there are earlier reports on the synthesis of this LDH from both gibbsite and bayerite. The NO3 - ion in the interlayer makes an angle of ∼48° with the plane of the metal hydroxide layer, and its symmetry reduces from D 3h to C 2v . Similarly, the change in the symmetry of the SO4 2- ion in the interlayer is from T d to C 3v .

Cyclic growth and tillering of layered polycrystalline zinc hydroxide sulfate and the resulting dendritic fractals

Two-dimensional dendritic fractals of layered zinc hydroxide sulfate (LZHS) were allowed to grow on a porous ZnO substrate-coated glass slide in an aqueous ZnSO4 solution through the dissolution-redeposition process. The generated LZHS seeds with polycrystalline structure gradually evolved into two-dimensional dendritic fractals with a diameter of 50∼100 μm through a plant-like growth mode involving tillering and the formation of layered tiller buds at branch ends. Such tiller mechanism is proposed to explain the evolution of LZHS fractals based on results obtained by the scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and energy dispersive X-ray detection. The synthesized polycrystalline LZHS fractals can be topologically converted into hierarchical nanostructured zinc oxide by thermal pyrolysis combined with an alkaline wash process. After the modification by octyltrimethoxysilane, the topological zinc oxide surfaces, corresponding to the immersion time of 2, 4 and 6 h, showed superhydrophobic property with a water contact angle of 153.4°, 157.6°, and 164.7°, respectively. The enhanced hydrophobicity of zinc oxide films compared with the porous ZnO substrate surface is mainly attributed to the topological fractal morphologies and hierarchical nanostructures.

Duplex Coating Combing Vanadate-Intercalated Layered Double Hydroxide and Ce-Doped Sol-Gel Layers on Aluminum Alloy for Active Corrosion Protection.

In this study, a duplex coating system (LDH-V/SG-Ce) of vanadate-intercalated layered double hydroxide (LDH) and Ce-doped sol-gel (SG) layers was developed for the purpose of active corrosion protection of the aluminum alloy AA2024. ZnAl-LDH film was grown in situ on the surface of an aluminum alloy using a hydrothermal method and intercalated with V2O74- anions as corrosion inhibitors, and sealed with a Ce (III)-doped silane coating using a sol-gel technique. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses were used to analyze the microstructure, surface functional groups and structure of the LDH-V/SG-Ce film. The uniform and compact silane layer was covered both in the pores and on top of the LDH film. The results of glow discharge optical emission spectroscopy (GDOES) indicated that V2O74- and Ce (III) ions were loaded in the LDH layer and silane film, respectively. The potentiodynamic polarization results showed that the corrosion current density of the bilayer system in the presence of corrosion inhibitors was reduced to 1.92 × 10-8 A/cm2. Electrochemical impedance spectroscopy (EIS) results showed that the LDH-V/SG-Ce duplex coating could provide effective protection for the aluminum alloy after being exposed to a corrosive solution for 14 days.

Adsorption of diclofenac from water solution on layered double hydroxide Mg/Al/CO3 synthesized from sulphate salts and calcined

The diclofenac (DCF) is an emerging pollutant commonly found in aqueous resources. The synthesis of the double layered hydroxide Mg/Al-CO3 (LDH) was carried out by a coprecipitation procedure. The elimination of DCF in water by adsorption onto LDH calcined at 550 °C (LDH550) was studied in this work. The XRD analysis confirmed the presence of the hydrotalcite crystalline species in the LDHs. In the LDH calcination, most of the interlaminar anions were eliminated, and an oxide of Mg/Al was formed. Likewise, the memory effect of LDH550 was verified when rehydrating LDH550 in an aqueous solution. The materials characterization was accomplished by SEM, N2 physisorption, Zeta potential and FT-IR. At 25 °C and pH = 7, the highest adsorption capacity of LDH550 towards DCF was 1517 mg/g, which significantly exceeded the capacities reported for other LDHs and carbon materials. Hence, the LDH calcination largely facilitated the availability and interaction between the anionic sites of the LDH550 sheets and the anionic species DCF−. If the LDH550 was reconstructed and rehydrated (LDH550Reh) before the DCF adsorption, the adsorption capacity of LDH550Reh was very low, confirming that reconstruction restricted the accessibility of DCF to the anionic sites of LDH550Reh. The capacity of LDH550 to adsorb DCF decreased with increasing solution pH and ionic strength, and this tendency was attributed to electrostatic attractions. The adsorption was endothermic because the uptake of DCF adsorbed on LDH550 decreased by reducing temperature. The influence of the operating conditions on the adsorption revealed that the adsorption mechanism of DCF on LDH550 can be mainly electrostatic interactions. A novel approach of this work is that the electrostatic attraction mechanism was further confirmed by zeta potential determination of LDH550 with adsorbed DCF and noticing that the adsorption of the DCF− anions balanced the positively charged sites in LDH550.

A New Method for the Synthesis of Layered Europium Hydroxide Using Propylene Oxide as the Precipitating Agent

A new method for the synthesis of layered europium basic chloride in up to 90% yield was developed. The method is based on hydrolysis of europium chloride in the presence of propylene oxide. The effect of reaction temperature on the yield and composition of the products of europium chloride hydrolysis in the presence of propylene oxide was analyzed. The obtained layered europium basic chloride had pronounced anion exchange properties. The possibility of intercalation of the isonicotinate anion into a layered rare earth hydroxide was demonstrated for the first time. The intercalation of the benzoate or isonicotinate anions into layered europium hydroxide led to luminescence sensitization and decrease in the Eu3+ local symmetry.

Synthesis of ethane-disulfonate pillared layered cobalt hydroxide towards the electrocatalytic oxygen evolution reaction.

We report the synthesis of a hybrid layered cobalt hydroxide sample and its redox behaviors in the electrochemical oxygen evolution reaction (OER). Compound Co7(OH)12(C2H4S2O6)·1.6H2O was synthesized via a homogeneous alkalization reaction using Co(SO3C2H4SO3) and hexamethylenetetramine. This compound comprises cationic host layers of {[Co7(OH)12]2+}∞, which comprise octahedrally (CoOh) and tetrahedrally (CoTd) coordinated Co cations at a CoOh : CoTd ratio of 5 : 2. The ethane-disulfonate ions are combined with the cationic host layers by electrostatic attractions and hydrogen bonding as a hybrid pillared layered framework. This hybrid sample can promote the OER in 1 M KOH with an overpotential as low as ∼410 mV (at a current density of 10 mA cm-2). In situ Raman spectroscopy showed that the sample first evolved into Co(III)-based phases comprising a mixture of layered CoOOH and spinel Co3O4, and the Co(III)-based compounds were converted into Co(IV)-O intermediates containing [CoO6] units at the onsite of the OER. The structural evolution behaviors suggest that the catalyst prefers a topotactic phase transition and the CoOh and CoTd units exhibit different activities in the electrochemical reaction. The electron transfer events involved in the electrochemical reaction were identified by Fourier-transformed alternating current voltammetry.