Layered Hydroxides Research Articles

Ultrafine Bimetallic Nickel–Cobalt Alloy from a Layered Hydroxide for Oxygen Evolution Reaction and Capacitors

NiCo bimetallic alloys on layer double hydroxide-derived nitrogen-doped carbon support (NiCo@LDH-NC) were derived from bimetallic NiCo-layered double hydroxides (NiCo@LDH). With the structural and compositional advantages, NiCo@LDH-NC exhibits an XRD pattern of NiCo alloy particles supported by X-ray absorption spectroscopy (XAS) analysis, high-resolution transmission electronic microscopy (HR-TEM) imaging, and HR-TEM lattice spacing analysis, which confirms the NiCo alloy particle with coherent substitution of Co strongly aligned with the (111) plane of Ni particles. This resulted in a strained lattice of the NiCo alloy (fcc) with strong interaction between pure Ni and Co metals. The relation of the host Ni (fcc) lattice with dopant Co in NiCo@LDH-NC exhibits a free atom-like electronic structure as compared to host Ni. In the oxygen evolution reaction (OER) of water electrolysis, the monolayer electrode of NiCo@LDH-NC exhibits minimum overpotentials of 330 and 346 mV at 10 and 20 mA cm–2, respectively, with an improved electrokinetics-driven 36.4 mV dec–1 Tafel slope obtained from the Tafel plot. The charge transfer resistance (Rct) value obtained for NiCo@LDH-NC was 2.48 Ω, confirming a faster charge transfer kinetics throughout the electrode-electrolyte interface that influenced the OER activity. This investigation on the NiCo alloy and associated electronics is promising for upgrading the features of the bimetallic alloy nanoarchitecture and their potential for advanced electrochemical processes.

Stable method for electrodepositing network-like magnesium hydroxide layer with superhydrophobicity and enhanced surface performance under structure direction of xanthan gum/glycerol

Investigation of magnesium hydroxide superhydrophobic layer would significantly improve the application of green and low-cost superhydrophobic materials, for the abundant source, low economic cost, nontoxicity and environment friendliness of magnesium hydroxide. In this work, an obviously developed method which is stable and easy for fabricating network-like magnesium hydroxide superhydrophobic layer on iron substrate has been rendered, simply by cathodic electrodeposition with magnesium nitrate aqueous solution under structure direction of glycerin cross-linked xanthan gum, and subsequent surface modification with 1H,1H,2H,2H-perfluorodecyltriethoxysilane. The preparation process could be carried out at tremendously wide range of bath temperature (from 15 °C to 75 °C), xanthan gum/glycerol dissolving temperature (from room temperature to 100 °C), and storage times (from 0 day to 30 days). The superhydrophobic layer obtained at 35 °C bath temperature with addition of xanthan gum/glycerol dissolved at room temperature and stored for 7 days, shows strong water repellency (160.1° water contact angle, 3.2° sliding angle), and excellent self-cleaning performance. The layer also demonstrates good mechanical property according to cross hatch adhesion and tape peeling test, and owns an inhibition current efficiency as high as 99.98%, taking advantage of its extremely high anti-corrosion resistance (Rct = 2.87 × 105 Ω cm−2, Rf = 1.49 × 109 Ω cm−2).

The Structure, Preparation, Characterization, and Intercalation Mechanism of Layered Hydroxides Intercalated with Guest Anions.

Since the intercalation of anions into layered hydroxides (LHs) has a great impact not only on their nucleation and growth but also on their structure, composition, and size, the intercalation chemistry of LHs has aroused the strong interest of researchers. However, the progress in the fundamental understanding of LHs intercalated with guest anions have not been paralleled by a concomitant development of the preparation and performance improvement of such materials. Considering the guidance of a timely in-depth review for scientists in this area, a systematic introduction about the development that is made on the above-mentioned issues is highly needed but yet missing so far. Herein, recent advances in understanding the chemical composition and structure of LHs intercalated with guest anions are systematically summarized. Meanwhile, typical and emerging bottom-up synthesis methods of LHs intercalated with anions are reviewed, and the potential impact of external reaction parameters on the intercalation of anions into LHs are discussed . Besides, different analytical characterization techniques employed in the examination of guest anion-intercalated LHs are deliberated upon. Finally, although progress is slow in exploring the intercalation mechanism, as many examples as possible are included in this review and inferred the possible intercalation mechanism.

Interlayer Nano-Dots Induced High-Rate Supercapacitors.

The fast OH- transfer between hydroxide layers is the key to enhancing the charge storage efficiency of layered double hydroxides (LDH)-based supercapacitors (SCs). Constructing interlayer reactive sites in LDH is much expected but still a huge challenge. In this work, CdS nano-dots (NDs) are introduced to interlayers of ultra-thin NiFe-LDH (denoted CdSinter. -NiFe-LDH), promoting the interlayer ions flow for higher redox activity. The excellent performance is not only due to the enlarged layer spacing (from 0.70 to 0.81nm) but also stems from anchored interlayer reactive units and the undamaged original layered structure of LDH, which contribute to the improvement of OH- diffusion coefficient (1.6×10-8 cm2 s-1 ) and electrochemical active area (601mFcm-2 ) better than that of CdS NDs on the surface of NiFe-LDH (2.1×10-9 cm2 s-1 and 350mFcm-2 ). The champion CdSinter. -NiFe-LDH electrode displays high capacitance of 3330.0Fg-1 at 1Ag-1 and excellent retention capacitance of 90.9% at 10Ag-1 , which is better than the NiFe-LDH with CdS NDs on the surface (1966.6Fg-1 ). Moreover, the assembled asymmetric SCs (ASC)device demonstrate an outstanding energy density/power density (121.56Whkg-1 /754.5Wkg-1 ).

Effects of Zinc-Layered Hydroxide on Controlled Release of Plant Nutrients and Growth Performance of Kelempayan (Neolamarckia cadamba) Seedlings

The loss of nutrients from conventional fertilisers is often encountered by the agricultural industry. Slow-release fertilisers by nanotechnology application can maintain nutrient availability for effective plantgrowth. Zinc-layered hydroxide nanohybrids have been little explored as controlled release systems offunctional anions, unlike the Layered Double Hydroxides (LDH) that belong to the same family ofanionic clays. The objective of the study was to investigate the effectiveness of zinc-layered hydroxidenanohybrid containing plant nutrient anions as a controlled-release formulation. Two nano-deliverymaterials namely zinc-layered hydroxide nitrate (ZLN) and zinc-layered hydroxide phosphate (ZLP) weresuccessfully synthesised through the co-precipitation and anion exchange methods. The PXRD patterns ofthe resulting nanohybrids, ZLN and ZLP recorded basal spacing of 9.57 and 6.78Å, respectively, at alower 2 angles range of 0-60 o . FTIR analyses confirmed the formation of host-guest nanohybrid whichcomprised the characteristic bands of nitrate and phosphate. Thermogravimetric analyses showed thethermal stability of the nanohybrid obtained where the capability of the host material to function as acontrolled release agent was determined through a controlled release study. Controlled release of plantnutrient sources, nitrate and phosphate from their respective nanohybrids were evaluated using variousrelease medium solutions. The accumulated release of guest anion from interlayer zinc layered hydroxide(ZLH) nanohybrid into pH 4 solution was observed to be faster than pH 6.5. A higher concentration ofsodium carbonate solution showed an increase in the percentage release for both nitrate and phosphateanions into the release medium. A plant growth trial using Kelempayan (Neolamarckia cadamba)seedlings showed that treatment with ZLN and ZLP recorded the highest biomass weight compared toapplication with commercial fertiliser and raw chemicals. The content of N, P and Zn in Kelempayanleaves showed the highest readings for similar treatment. The study found that ZLH has acted as a goodhost for inorganic plant nutrients with slow-release properties and thus has improved the growthperformance of Kelempayan seedlings with better nutrient uptake.

Energy absorption and transfer behavior of guest benzoate sensitizers in the interlayer space of Tb3+-doped layered yttrium hydroxide host

Energy absorption and transfer behavior of guest benzoate sensitizers in the interlayer space of Tb3+-doped layered yttrium hydroxide host

Designing effective plating baths for use in the pulse-reverse plating of copper nanocomposite coatings

ABSTRACT The development of the process to produce Metal Matrix Nanocomposite (MMNC) coatings can provide opportunity for the enhancement of mechanical and electrical properties. This research uses speciation-simulating software to screen formulations for producing nanocomposites by pulse-reverse plating (PRP). PRP is used as a controlled delivery mechanism to attract a high concentration of nanoparticles to the coating during the anodic pulse which are subsequently captured in the cathodic pulse. A disadvantage is that the anodic pulse generates passivating hydroxide layers leading to poor adhesion. Speciation plots assess the stabilising effect of chosen complexants (gluconate and glycine) within electrolytes with the aim of diminishing hydroxide formation. To confirm bath formulation effectiveness before nanoparticle incorporation, UV-Vis spectroscopy and electrodeposition were used. Gluconate and glycine both theoretically produce highly stable complexes and also produce uniform copper deposits supporting the stabilisation effect observed in theoretical studies. This work therefore supports the use of these complexants for future stages of this research.

Ni-Co layered double-hydroxide arrays on stainless steel substrate: Interfacial hydroxide layer enhanced electrocatalyst with high stability for oxygen evolution reaction in alkaline media

High-efficiency electrocatalysts for oxygen evolution reaction (OER) are highly desired during large-scale water electrolysis in hydrogen production. In this work, a commercial stainless steel (SS) mesh substrate is activated through an alternate acid etching/alkali-hydrothermal treatment to form an interfacial hydroxide layer. Subsequently, a seamless integrated electrode including Ni-Co layered double hydroxide (NiCo-LDH) nanoarrays and SS substrate is successfully synthesized. The pre-formed interfacial layer guides the growth of NiCo-LDH nanoarrays, and firmly connect NiCo-LDH nanoarray and stainless steel substrate, wherein a durable catalyst with high activity and low resistance nature for OER is constructed. The as-prepared integrated electrode delivers the low OER overpotential of 243 and 292 mV for 10 and 250 mA cm−2 current densities respectively, and excellent long-term durability over 100 h in 1 M KOH solution. Electrocatalysis studies reveal the role of the interfacial hydroxide layer on the growth and catalytic activity of NiCo-LDH nanoarrays, and structural stability in durability test.

EFFECT OF ALKALINE SOLUTION CONCENTRATION ON THE PASSIVATION FILM OF Cu-Ni ALLOY

Passive films formed on a Cu-Ni alloy in various concentrations of alkaline environment were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy and the Mott–Schottky approach. The wide passivation range of the copper-nickel alloy was tested in alkaline solutions of three concentrations. The oxide film on the specimen has a p-type semiconductor property, while the flat band potential (EFB) decreased with increasing solution concentration. The film resistance of the passive films increased with increasing solution concentration. The pAassive films showed a duplex structure, including an inner layer of oxide (Cu2O, NiO) and an outer layer of hydroxide (Cu(OH)2, Ni(OH)2).

Harmonizing nanomaterial exposure methodologies in ecotoxicology: the effects of two innovative nanoclays in the freshwater microalgae Raphidocelis subcapitata

Layered double hydroxides (LDHs) are innovative nanomaterials (NMs) with a typical nanoclay structure (height <40 nm) consisting of layers of metallic cations and hydroxides stabilized by anions and water molecules. Upon specific triggers, anions can exchange by others in the surrounding environment. Due to this stimuli-responsive behavior, LDHs are used as carriers of active ingredients in the industrial or pharmaceutical sectors. Available technical guidelines to evaluate the ecotoxicity of conventional substances do not account for the specificities of NMs, leading to inaccuracies and uncertainty. The present study aimed to assess two different exposure methodologies (serial dilutions of the stock dispersion vs. direct addition of NM powder to each concentration) on the ecotoxicological profile of different powder grain sizes of Zn–Al LDH-NO3 and Cu–Al LDH-NO3 (bulk, <25, 25–63, 63–125, 125–250, and >250 µm) in the growth of the freshwater microalgae Raphidocelis subcapitata. Results revealed that the serial dilutions methodology was preferable for Zn–Al LDH-NO3, whereas for Cu–Al LDH-NO3 both methodologies were suitable. Thus, the serial dilutions methodology was selected to assess the ecotoxicity of different grain sizes for both LDHs. All Zn–Al LDH-NO3 grain sizes yielded similar toxicity, while Cu–Al LDH-NO3 powders with smaller grain sizes caused a higher effect on microalgae growth; thus, grain size separation might be advantageous for future applications of Cu–Al LDH-NO3s. Considering the differences between exposure methodologies for the Zn–Al LDH-NO3, further research involving other NMs and species must be carried out to achieve harmonization and validation for inter-laboratory comparison.

Inert Mg Incorporation to Break the Activity/Stability Relationship in High-Entropy Layered Hydroxides for the Electrocatalytic Oxygen Evolution Reaction

Ni-based layered double hydroxides (LDHs) have been demonstrated as the most active catalyst for the oxygen evolution reaction in alkaline media but suffer from poor stability. Herein, we report the rational breaking of the activity/stability trade-off by a strategy of inert Mg-involved high-entropy coordination. The as-developed high-entropy FeCoNiMg-LDH nanosheets exhibit not only high catalytic activity (302 mV at 100 mA cm–2) but also an unprecedented stability with almost no performance decline at a large current density of 300 mA cm–2. The combined structural investigations and theoretical calculations reveal that the synergistic electronic coupling provides active Ni in desired electronic states, leading to an optimized adsorption energy of intermediates, while the construction of high configuration entropy as well as the formation of the Mg–O interfacial bond can effectively mitigate phase segregation and transformation and thus improve the stability. The current insights into unveiling the composition–activity–stability of high-entropy coordination may provide valuable guidance for the design of catalysts for various electrochemical reactions.

Constructing Electrocatalysts with Composition Gradient Distribution by Solubility Product Theory: Amorphous/Crystalline CoNiFe‐LDH Hollow Nanocages

AbstractTransition‐metal based layered doubled hydroxides (LDH) as oxygen evolution reaction (OER) catalysts have attracted tremendous research interests. However, it is still a great challenge to strengthen the intrinsic activity of LDH. Herein, hollow CoNiFe‐LDH nanocages with amorphous/crystal phase and element gradient distribution are successfully constructed through the coordinated etching and precipitation process. Utilizing the difference of solubility product constants among transition metal cations to generate the gradient distribution effect in nanocages is proposed for the first time. The distinctive element gradient distribution in hollow CoNiFe‐LDH nanocages results in the composition gradient, which can provide the heterojunctions effect and play an important role in regulating morphology and electronic structure. Density functional theory calculations disclose that the synergistic effect between elements significantly regulates the electron density and enhances the conductivity. When employed as OER electrocatalysts, it exhibits a very competitive overpotential of 257 mV at 10 mA cm−2 combined with a low Tafel slope of 31.4 mV dec−1. This work represents a promising strategy to fabricate highly efficient OER catalysts for electrochemical water splitting and provides new opportunities to understand the promotion mechanism of intrinsic activity.

Novel ZnO/Ag nanohybrids prepared from Ag+-doped layered zinc hydroxides as highly active photocatalysts for the degradation of dyes and Ciprofloxacin

The design and the synthesis of highly active nanohybrid photocatalysts for environmental remediation is a topical issue in the context of sustainable development. The hybridization of a semiconductor with noble metal nanoparticles (NPs) has been demonstrated to be a versatile strategy to restrict the recombination of photogenerated electron-hole pairs and thus increase the photocatalytic activity. However, the uniform association of nanosized metal particles with ZnO NPs remains a challenge. Herein, a novel synthesis of ZnO NPs hybridized with Ag(0) NPs is presented. Ag+-doped layered zinc hydroxides (LZHs) were prepared in aqueous solution in the presence of triethanolamine and subsequently Ag+ ions were photoreduced into metallic Ag NPs embedded into LZHs. The LZHs not only promote the dispersion of Ag NPs but also limit their growth. The Ag(0)-doped LZHs obtained after hydrothermal treatment was finally transformed into ZnO/Ag nanohybrids by a mild thermal treatment at 300 °C for 5 min, which allows high interface coupling between ZnO and Ag NPs. ZnO associated with 3 mol% Ag exhibits the highest photocatalytic activity for the degradation of dyes (Rhodamine B and Remazol Brillant Blue R) and of the Ciprofloxacin antibiotic. The high photocatalytic performance of the ZnO/Ag(3) nanohybrid originates from the charge transfer in the ZnO/Ag nanohybrid and from the enhanced harvesting of visible light. The ZnO/Ag(3) photocatalyst also exhibits a high practical stability, indicating its great potential for real photocatalytic applications.

Ultrafast Deposition of NiFe Metal-organic Framework Catalysts Boosts BiVO4 Photoanode for Efficient Solar Water Splitting.

The severe photocorrosion of BiVO4 limits its application in solar energy conversion in the long-term photoelectrochemical stability test. Herein, we synthesized a Fe@Ni-MOFs/BiVO4 photoanode by a simple ultrasonic method and ultrafast deposition, which avoids the problems of damaging the surface structure of photoelectrode. The Fe@Ni-MOFs/BiVO4 shows a photocurrent density of 4.89 mA cm-2 at 1.23 VRHE with an onset potential of 0.25 VRHE under one sun illumination. Importantly, a stability over 30 h at 0.7 VRHE can be obtained, which is so far the best stability character for MOFs-based cocatalysts decorated on BiVO4. During operation, Fe@Ni-MOFs transforms into a homogeneous and active hydroxide layer covering the surface, which exposes more active sites for OER reactions. This work demonstrates a simple strategy for MOFs co-catalysts to obtain fast hole transfer capability and reduce carrier recombination, thereby improving PEC performance.

MOF-derived bimetallic coordination polymer@cobalt-aluminum layered double hydroxide for highly selective CO2 adsorption: Experiments, mechanisms

Selective capture of CO2 is one of the most effective strategies for combating the greenhouse effect. In this study, we report the synthesis of a novel adsorbent—an amine-based cobalt-aluminum layered hydroxide with a hafnium/titanium metal coordination polymer (denoted as Co-Al-LDH@Hf/Ti-MCP-AS)—through the derivatization of metal–organic frameworks (MOFs) for selective CO2 adsorption and separation. Co-Al-LDH@Hf/Ti-MCP-AS achieved the maximum CO2 adsorption capacity of 2.57 mmol g−1 at 25 °C and 0.1 MPa. The adsorption behavior followed the pseudo-second-order kinetics and Freundlich isotherm models, indicating that chemisorption occurs on a non-homogeneous surface. Co-Al-LDH@Hf/Ti-MCP-AS also exhibited selective CO2 adsorption in CO2/N2 and excellent stability over six adsorption–desorption cycles. An in-depth analysis of the adsorption mechanism through X-ray photoelectron spectroscopy and density-functional theory and frontier molecular orbital calculations revealed that adsorption occurs through acid–base interactions between amine functional groups and CO2 and that the tertiary amines (N3) have the highest affinity toward CO2. Our study provides a novel strategy for designing high-performance adsorbents for CO2 adsorption and separation.

Evaluating high temperature photoelectrocatalysis of TiO2 model photoanode

Sunlight concentration has been demonstrated as one promising strategy for practically photoelectrochemical (PEC) water splitting with exceeding 10% solar-to-hydrogen efficiency. However, the operating temperature of PEC devices, including the electrolyte and photoelectrodes, can be elevated to 65 ℃ naturally due to the concentrated sunlight and the thermal effect of near-infrared light. In this work, high temperature photoelectrocatalysis is evaluated using titanium dioxide (TiO2) photoanode as a model system, which is believed to be one of the most stable semiconductors. During the studied temperature range of 25–65 ℃, a linear increment of photocurrent density with a positive coefficient of 5.02 μA cm−2 K−1 can be observed. The onset potential for water electrolysis shows a significant negative shift by 200 mV. An amorphous titanium hydroxide layer and a number of oxygen vacancies generate on the surface of TiO2 nanorods, promoting the water oxidation kinetics. During long-term stability testing, the NaOH electrolyte degradation and TiO2 photocorrosion at high temperatures could cause the decaying photocurrent. This work evaluates the high temperature photoelectrocatalysis of TiO2 photoanode and reveals the mechanism of temperature effects on TiO2 model photoanode.

Synthesis of Zinc Layered Hydroxide with 2-Napthoxyacetic Acid (BNOA) with Chloride as Counter Ions via Ion Exchange Method

Synthesis of Zinc Layered Hydroxide with 2-Napthoxyacetic Acid (BNOA) with Chloride as Counter Ions via Ion Exchange Method

Al-Fe LAYERED HYDROXIDE WITH BENTONITE CLAY AND APPLICATION FOR THE REMOVAL OF DYE FROM AQUEOUS SOLUTIONS

The research was aimed to investigate the effect of decolourisation of Alizarin yellow dye from aqueous solutions using Al-Fe layered Hydroxide clay.Batch adsorption technique was employed to determine the optimum values of some parameters i.e initial dye concentration (10 – 50 mg/l), contact time (10 – 50 minutes) and adsorbent dose (0.1 – 0.5 g). The results obtained indicate that the dye concentration decreases with increase in contact time and adsorbent dosage.The Adsorption isotherms observed showed that the Langmuir adsorption Isotherm was best fitted having the maximum decolourisation of 76.89 mg/g and R2 value of 0.986. The Al-Fe layered Hydroxide prepared was characterized by SEM, FT-IR and XRD before and after the adsorption process. The SEM results showed the porosity was roughly filled after the adsorption. The FT_IR spectra showed the presence of OH, C=O and N-CH at 3625 cm-1, 1633 cm-1 and 2806 cm-1. The XRD results indicate that the crystalline structure was not altered after the adsorption process. In this research, a low cost and effective adsorbent was used for the removal of Alizarin Yellow dye in an aqueous solution.

Synthesis, Characterization and Phytotoxicity Assessment of Intercalated Insect Pheromone, Lignoceric Acid-Zinc Layered Hydroxide Nanohybrid

Synthesis, Characterization and Phytotoxicity Assessment of Intercalated Insect Pheromone, Lignoceric Acid-Zinc Layered Hydroxide Nanohybrid

Thermal Decomposition of H2S at Low Temperature on Mo-Containing Catalysts Derived from MAlO (M = Mg, Co, and Ni) Layered Double Hydroxides

It is increasingly attractive to simultaneously recover the resources of hydrogen and sulfur by catalytic decomposition of hydrogen sulfide (H2S). Restricted by the low yield and high reaction temperature, searching for materials with excellent catalytic activity and stability on thermal decomposition of H2S is significant. A high dispersion and sulfidation degree of MoS2 phases with a promoter (Co or Ni) were prepared with the help of interaction between the layers of hydroxides (CoAl or NiAl) and Mo anions. The NiAlMo-s catalysts exhibited outstanding catalytic activity at 500 °C with H2 yield reaching 49.6%. Several characterizations verified that the excellent performance resulted from the Lewis acid on the surface. Accumulation of sulfides reduced stability, while generation of NiMoS contributed to good stability. Generally, these results will be beneficial to enrich the theory of designing H2S decomposition catalysts. Also, these findings will offer potential application of the resource recovery technology on H2S decomposition.