Hydrotalcite Structure Research Articles

Miniaturization of transition metal hydroxides to hydroxide dots: A direction to realize giant cyclic stability and electrochemical performance

Binary metal hydroxides have tailored to quantum size in situ by manipulating the solvent medium in the co-precipitation process. Bimetallic cobalt-nickel hydroxide dots reveal hydrotalcite structure, and the mean hydrodynamic diameter is restricted to 2.5 nm when Co:Ni molar ratio 1:1. The bandgap values obtain around 2.64 eV using Tauc relation, which is within the quantum confinement region. The fitting results of X-ray photoelectron spectroscopy suggested the presence of redox couple Co2+, Co3+, Ni2+, and Ni3+ in the hydroxides dots, which facilitates more electroactive sites. Again, excellent stability of hydroxide dots in solvent medium obtained by measuring T2 relaxation time. The binary dots electrode exhibits excellent pseudocapacitance performance with specific capacitance of 1926 F g−1 (221 mAh g−1) at 1 A g−1 with outstanding cycling retention of ~96% up to 20 000 cycles. Parallelly, an asymmetric supercapacitor device has been assembled by monitoring different mass loading of active material as +Ve and carbon black as −Ve electrode cells. The ASC device utilizes to brighten a commercial LED to validate the electrode. Also, the specific capacitance of the ASC device has been calculated about 250 F g−1 (353 mAh g−1) with a holding energy density of 85 W h kg−1.

Mg and Ni nano-hydrotalcites modified with gold nanoparticles as platform of enzymatic electrochemical sensors for H2O2 detection

The immobilization of Horseradish Peroxidase enzyme over Magnesium (Mg-nHT) and Nickel (Ni-nHT) nano Hydrotalcite clays were synthesized by the co-precipitation method, and later modified with gold nanoparticles through in-situ synthesis and delamination-restructuration, is reported. The synthesized materials were characterized by Fourier-Transform Infrared Spectroscopy, X-ray diffraction, Scanning Electronic Microscopy, Flame Atomic Absorption Spectroscopy and Cyclic Voltammetry. Results show that the size of the synthetized materials is 26 nm for the gold nanoparticles, and 38.92 nm and 8.44 nm for Mg-AlnHT and Ni-AlnHT, respectively. The clays were used to modify the surface of graphite electrodes (GE); the inclusion of Au nanoparticles in the Hydrotalcites structure improved the enzyme-electrode electric communication. Figures of merit for detection of H2O2 by Differential-Pulse Voltammetry at HRP/Mg-AlnHT/GE, HRP/Ni-AlnHT/GE, HRP-AuNps/Mg-AlnHT/GE and HRP-AuNps/Ni-AlnHT/GE modified electrodes were determined, and respective detection limits of 0.012 μmolL−1, 0.014 μmolL−1, 0.009 μmolL−1, and 0.010 μmolL− 1 were obtained.

The role of rehydration in enhancing the basic properties of Mg–Al hydrotalcites for biodiesel production

An Mg–Al hydrotalcite with a Mg/Al molar ratio of 3 was prepared via co-precipitation. The XRD and FTIR analyses proved the presence of the hydrotalcite structure in the uncalcined solid, its destruction after calcination and its reconstruction after rehydration. TG-DSC analyses revealed a higher thermal stability of the rehydrated solids compared to the uncalcined solid. CO2-TPD analyses showed the presence of stronger and more abundant basic sites for the rehydrated solids. All prepared solids were then tested in the transesterification of sunflower oil [catalyst to oil ratio (CTOR) of 10 wt%, methanol to oil molar ratio (MOMR) of 12:1, temperature of 60 °C and reaction time of 2 h]. The uncalcined and calcined solids all exhibited low activities as evidenced by very low FAME yields (<1.5%). The catalytic activity was significantly improved for most of the rehydrated solids due to their higher basicity. Calcination of the fresh Mg–Al solid at 450 °C followed by subsequent rehydration (Mg6Al2-450RH) allowed the obtainment of a FAME yield of 56%. No biodiesel was formed in the presence of the rehydrated catalysts previously calcined at temperatures greater than 500 °C due to a reduced “memory effect”. The effects of reaction conditions such as the duration of rehydration treatment, reaction temperature, MOMR and CTOR on the activity of Mg6Al2-450RH were also studied. The obtained results in this work demonstrate the potential of rehydrated Mg–Al solids for biodiesel production. They could also be useful for optimizing the preparation conditions of reconstructed hydrotalcites as basic catalysts and contribute to the search for ideal conditions for biodiesel production.

An off-on fluorescent probe based on graphene quantum dots intercalated hydrotalcite for determination of ascorbic acid and phytase

A new off-on fluorescent probe was successfully synthesized and used to detect ascorbic acid and phytase. The composite material of hydrotalcite and graphene quantum dots were synthesized through citrate intercalated hydrotalcite using hydrothermal carbonization method. The layered structure of hydrotalcite can prevent the aggregation and promote the uniformity of graphene quantum dots. The off-on fluorescent probe detection mechanism is as follows. Fe3+ ions were firstly added into the solution of the composite material, and the fluorescence was quenched. Then, ascorbic acid was added into the fluorescence probe system, which reduced iron ions and turned on fluorescence to realize the detection of ascorbic acid. In addition, the reaction of phytase and l-ascorbyl-2-phosphate can produce ascorbic acid, further achieving the purpose of phytase detection. The concentration of the analyte and the recovery of the fluorescence intensity show a linear relationship, the linear ranges were 5−300 μmol L−1 and 0.1–4 U mL−1 for ascorbic acid and phytase, respectively. The recoveries of the experiment were 96.3 %–103.1 % and 95.4 %–104.9 %, respectively. The fluorescence method has the advantages of fast, stable, high sensitivity and high selectivity, which has been successfully applied to the determination of ascorbic acid in fruit juice and phytase in feed.

Performance of Cu‐Ce / M‐Al (M = Mg, Ni, Co, Zn) hydrotalcite derived catalysts for hydrogen production from methanol steam reforming

M-Al (M = Mg, Ni, Co, Zn) hydrotalcite was synthesized on the surface of the γ-Al2O3 carrier, and hydrotalcite was calcined to corresponding carrier. Then, A series of Cu-Ce/M-Al catalysts were prepared by the sequential dip method. The catalysts were characterized by the means of XRD, BET, H2-TPR, and XPS, which investigated the effects of different divalent metals M on the structure, properties, and catalytic performance of hydrotalcite derived catalysts for hydrogen production from methanol steam reforming. The main reasons for different effects on the performance of catalysts lie in the difference of the dispersion, reduction temperature, and the content of oxygen vacancies on the surface. Among them, Ce-Cu/Zn-Al catalyst had the best performance. When the reaction temperature was 250°C, the molar ratio of water to methanol was 1.2, and the space velocity of methanol gas was 800 hours−1, the methanol conversion reached 100%, and the H2 production rate was 779.7 STP cm3 kg−1 s−1.

Study on preparation and treatment of phosphorus removal performance with M/Mg/Al (M=Zn/Co/Cu) hydrotalcites

A series of M/Mg/Al (M=Zn/Co/Cu) hydrotalcites were synthesized by co-precipitation method. XRD was used to characterize their structure. The results showed that the prepared hydrotalcites samples have typical hydrotalcite structure with high crystalline. The hydrotalcites samples were used as absorbent in the treatment of phosphorus removal of wastewater. Single factor control variable method was used to study the relationship between the conditions such as the type of metal, synthesis condition, preparation method, calcination time, type of absorbent, and the adsorption ability of phosphorus in wastewater. The results showed that Zn/Mg/Al hydrotalcites have better phosphorus removal ability than the Mg/Al, Co/Mg/Al and Cu/Mg/Al hydrotalcites. Zn/Mg/Al hydrotalcites prepared with the metal ratio of Zn/Mg/A=3:1:1, reaction temperature of 75 °C, pH of 11 has the best phosphorus removal effect. After calcained at 300 °C for 4h, the Zn/Mg/Al hydrotalcites has the best phosphorus removal efficiency of 76.6%. Zn/Mg/Al hydrotalcites have much better phosphorus removal efficiency than active carbon.

Experimental study on phosphorus removal of water by Zn/Mg/Al layered double hydroxide

Zn/Mg/Al layered double hydroxide (Zn/Mg/Al-LDH) was prepared by co-precipitation method. The structure of Zn/Mg/Al-LDH was characterized by XRD. The results show that the samples have typical hydrotalcite structure. They were used as adsorbents to remove phosphorus from wastewater. The effects of pH value, phosphorus concentration, adsorbent dosage, oscillation intensity and reaction time on phosphorus adsorption capacity were investigated by single factor control variable method. The results show that the adsorption equilibrium of Zn/Mg/Al-LDH can be reached after 24 h. The optimal experimental conditions are as follows: stirring rate is 180 R/min, pH value is 6, and reaction temperature is 50 °C. Under above conditions, when the initial phosphorus concentration is 50mg/L, the adsorption capacity of Zn/Mg/Al-LDH for phosphorus is 54.10mg/g when the adsorption equilibrium is reached. When the initial phosphorus concentration is 200mg/L, the adsorption capacity is 69.70mg/g, and the saturated adsorption capacity is 70.37mg/g. In the simulated practical engineering application, when the discharged phosphorus meets the standard, the phosphorus adsorption capacity of Zn/Mg/Al-LDH is 37.09mg/g, and the phosphorus removal rate is as high as 99.76%.

Sequestration and release of nitrite and nitrate in alkali-activated slag: A route toward smart corrosion control

Intercalating the corrosion inhibitive ions in hydrotalcite is a promising approach to improve the long-term efficiency of inhibitors in corrosion protection of steel in reinforced concrete. In this work, the potential of autogenously generating nitrite- and nitrate-intercalated hydrotalcite in alkali-activated slag (AAS) is investigated. The results show that the added nitrite and nitrate ions are preferably uptaken in the interlayer structure of hydrotalcite in AAS, and the sequestered nitrite and nitrate are released upon chloride exposure in seawater and NaCl solution. The incorporation of nitrite and nitrate has little detrimental effects on the chloride binding capacity of AAS but slightly enhances the chloride ingress due to the pore coarsening effect. Similar to ordinary Portland cement (OPC), AAS is more permeable to the chloride in seawater than NaCl solution. However, unlike the release of bound chloride contributed by ettringite formation in seawater-exposed OPC, the enhanced chloride ingress in seawater-exposed AAS is primarily attributed to the aggravated pH reduction at the exposure front due to brucite formation. This study contributes to the design of alkali-activated binders with a smart inhibitor releasing ability for mitigating corrosion of steel in concrete.

Kinetic, isotherm, and mechanism investigations of the removal of nitrate and nitrite from water by the synthesized hydrotalcite Mg–Al

The objective of this work is to test the effectiveness of hydrotalcite as an adsorbent for the retention of nitrate and nitrite ions and to study the influence of various reaction parameters such as pH, adsorbent dose, contact time and initial ion concentration. Hydrotalcites (HTx) of different Mg/Al ratios (x was Mg/Al ratio; 2, 3, 4) were synthesized by the co-precipitation method at constant pH and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR). The results obtained indicate that hydrotalcite (HT3) allows good retention of nitrate and nitrite ions with no pH adjustment. Adsorption increases with decreasing mass of the adsorbent and increases with increasing initial concentration of nitrate and nitrite ions. When the Mg/Al ratio changes from 2 to 4; the electrical charge density between layers weakens; the inter-layer spacing increases and the material shows greater adsorption capacity. The equilibrium isotherm showed that the Langmuir model provided a better fit to the experimental data than the Freundlich model for nitrates and nitrites. The adsorption capacity of HT3 for nitrates and nitrites was found to be 6.92 mg/g and 9.26 mg/g, respectively. The XRD analysis after adsorption showed that materials that had undergone nitrate and nitrite ions adsorption, maintain the hydrotalcite structure.

Environmental impact of amino acids on the release of selenate immobilized in hydrotalcite: Integrated interpretation of experimental and density-functional theory study

The environmental impact of amino acids on the release of SeO42− immobilized into hydrotalcite (Mg2Al-LDH) which belongs to the layered double hydroxides (LDHs) family was investigated by experimental study and the observed layer structure of hydrotalcite was verified through density-functional theory (DFT) calculations. Glycine, l-cysteine, and l-aspartic acid, which have smaller molecular sizes, can release SeO42− largely due to intercalation, unstabilization of Mg2Al-LDH and simple dissolution, while l-tryptophan and l-phenylalanine caused limited SeO42− release due to their larger sizes and aromaticity. XRD patterns for the solid residues after intercalation of amino acids revealed that the layer distance of Mg2Al-LDH was partially expanded. The main peaks and shoulder features corresponding to d003 diffraction were well explained by DFT simulations using glycine as a model: the layer spacing of the main peak is responsible for the remaining SeO42− and singly stacked glycine molecule and the layer spacing of the shoulder peak was well explained by doubly stacked glycine molecules. Hydrogen bonds between amino acids and hydroxyl ions in the metallic layers of Mg2Al-LDH were responsible for the stable configuration of the intercalated Mg2Al-LDH. This study indicates potential limitations to the stability of low-level radioactive wastes of 79Se in repositories which are affected by smaller molecules of amino acids released through degradation of organic matters in the pedosphere.

Steam reforming of surrogate diesel model over hydrotalcite-derived MO-CaO-Al2O3 (M = Ni & Co) catalysts for SOFC applications

Catalytic steam reforming of diesel fuel has the potential for producing syngas or hydrogen that can be feed to a fuel cell (especially SOFC) for portable power generation. Cost-effective, highly active reforming catalysts with resistance towards carbon formation and sulfur poisoning are critically needed to commercialize such technologies successfully. Thus in the present work, we have explored CaO-Al2O3 based hydrotalcite structure derived catalyst precursors for syngas production via steam reforming of a diesel model compound (n-dodecane). The steam reforming of n-dodecane reactions was also carried out in the presence of 100 ppm of sulfur compounds at a steam-to-carbon ratio of 2. Among all the catalysts tested, the Co-CaO-Al2O3 catalyst gave the best catalytic performance with respect to n-dodecane conversion, stability, and carbon suppression. At 700 °C, the Co-CaO-Al2O3 catalyst possesses > 90% of n-dodecane conversions with a negligible carbon formation (1.04 mg C/g.h) for a period of 24 h. It is also observed that upon deactivation due to sulfur poisoning, the Co-CaO-Al2O3 catalyst can be regenerated by a simple thermal treatment at 750 °C, which is due to the considerably low decomposition temperature behavior of CoSx and CaS species formed for this catalyst. Lower carbon deposition over the Co-CaO-Al2O3 catalyst can be attributed to the better oxygen affinity of Co species and higher normalized basicity than other catalysts.

Highly efficient application of Mg/Al layered double oxides catalysts in the methanolysis of polycarbonate

Polycarbonate (PC) is a very versatile material widely used in industry, agriculture and packaging, etc. The global production of PC generates several million tons of non-biodegradable wastes. In this work, chemical recycling of bisphenol A (BPA) from the PC methanolysis was explored, by using Mg/Al layered double hydroxides (LDHs) and their corresponding layered double oxides (LDOs) as heterogeneous catalysts. Mg/Al-LDHs with different molar ratios were prepared, and their hydrotalcite structures were confirmed by powder X-ray diffraction (XRD). Compared with Mg/Al-LDHs, Mg/Al-LDOs exhibited better catalytic activity for the PC methanolysis. Using Mg3Al-LDO as a catalyst, the PC conversion was 100% and the BPA yield exceeded 98% at 110 °C and 1.0 h. Namely, this method not only significantly reduces the reaction temperature, but also shortens the reaction time, and the solid catalyst Mg3Al-LDO can be easily separated and reused after calcinations again. The effects of experimental parameters on the PC conversion and the BPA yield were investigated. Moreover, the mechanism was described by infrared spectroscopy (IR), gel permeation chromatography (GPC), and scanning electron microscope (SEM). The kinetics of PC methanolysis was also studied, and the results indicated that this process is a pseudo-first-order reaction with an activation energy of 92.41 kJ/mol.

MnAl-Layered Double Hydroxide Nanosheets Infused with Fluorouracil for Cancer Diagnosis and Therapy

Nanotheranostic materials with a layered double hydrotalcite (LDH) structure, containing manganese as a contrast agent for MRI and fluorouracil (FU) as a model anticancer drug, were prepared. The manganese was rationally included in the two-dimensional (2D) LDH construction by co-precipitation (CP) at low suprasaturation at a theoretic Mn/Al ratio of 2. The anticancer drug was strategically introduced in the layered solid by two synthetic approaches, that is, CP at low suprasaturation and CP coupled with ion exchange (IE). The materials were extensively characterized for their composition, structure, texture, morphology, and oxidation state by AAS, XRD, N2 physisorption, FT-IR, SEM, TEM, TGA, DR UV−vis, and XPS. The results of physicochemical characterization revealed high-quality 2D materials in which manganese mainly exists as Mn2+ and Mn3+ while the mass loading of FU was 6.96 and 5.28% for the samples prepared by CP and CP coupled with IE, respectively. The nanomaterials exhibited high r1 and r2 relaxivities, particularly at pH = 7.4. The mathematical models used to fit the experimental data revealed a quasi-Fickian diffusion of the FU release from MnAl-LDH.

Examination of the Deactivation Cycle of NiAl- and NiMgAl-Hydrotalcite Derived Catalysts in the Dry Reforming of Methane

The importance of the dry reforming of methane (DRM) lies in its capability to upgrade two greenhouse gases (CH4 and CO2) into synthesis gas (CO and H2), which is one of the main building block for synthesizing hydrocarbons. However, the Ni-based catalysts for DRM reaction usually have a major catalytic stability drawback. This works aims to assess the catalytic activity and stability of two Ni-based catalysts obtained from hydrotalcite (HT) precursors (i.e., NiAl-HT and NiMgAl-HT). The precursors, calcined (-c), reduced (-R) and spent samples were characterized by a series of techniques to gain insight into the influence of MgO over Ni-based catalyst in the drying reforming of methane. An in-situ ageing cycle process to speed up the deactivation of hydrotalcite-derived catalysts showed that the NiMgAl-HTc-R catalyst displayed a higher activity and resistance to coke formation (stability) than NiAl-HTc-R because of the introduction of Mg into hydrotalcite structure in the catalyst precursor. The presence of this element enhances several factors involved in the stability of Ni-based catalysts for the DRM process such as the reducibility and textural features of the catalysts, size and dispersion of Ni0 nanoparticles and also maintains a good compromise between the acid and base properties of the solid catalysts.

Preparation and performance study of hydrotalcites /PLA composites

3D printing technology is known as the core technology of “the third industrial revolution”. Poly (lactic acid) (PLA) is a new type of biodegradable thermoplastic resin, which is renewable. It has a wide range of raw materials. It also has the properties of high strength, good biocompatibility, excellent mechanical properties, thermoplastic and transparency. Hydrotalcite (HT) was synthesized by coprecipitation method and modified to prepare the HT/PLA composites. The results show that the structure of HT is good. After KH550 surface modification, a large number of OH and Si-O groups are introduced into PLA surface. TG results show that the HT sample has good thermal stability. Compared with pure PLA, the glass transition temperature and crystallization temperature of HT / PLA composites decreases, while the melting temperature increases.

Oxygen-vacancy-rich cobalt–aluminium hydrotalcite structures served as high-performance supercapacitor cathode

Appropriate oxygen vacancy was introduced into CoAl LDHs by reduction treatment, which improved the supercapacitor performance of its.

A novel Mg-Sn-Zn-Al-Mn magnesium alloy with superior corrosion properties

The corrosion behaviors of the hot-pressed Mg-Sn-Zn-Al-Mn magnesium alloys with the addition of Al in different proportions have been investigated. Paraffin coating technique was applied to Mg powders before production. After debinding at 300 °C, the sintering process was applied at 610 °C under 50 MPa pressure for 70 min. All of the alloys were immersed in Hank’s solution for 10-days. The results indicated that the corrosion properties of the alloys were affected by the production method (hot pressing) and alloying element addition. After immersion, magnesium hydroxide (Mg(OH)2), hydroxyapatite (HA), and Mg-Al hydrotalcite structures were determined by the X-ray diffraction (XRD) analysis on the surfaces of Mg-Sn-Zn-Al-Mn alloys. The Mg-Al hydrotalcite protective layer was effective in preventing corrosion. Superior corrosion properties (weight loss: 1.2%, total volume of evolved H2 gas: 4 ml/cm2, corrosion rate: 0.39 mm/year) were obtained from TZAM5420 alloy (5 wt.%Sn, 4 wt.%Zn, 2 wt.%Al, 0.2 wt.%Mn).

Influences of Magnesium Content in Rehydrated Mixed Oxides on Furfural Conversion

In this study, Mg-Fe catalysts with various molar ratio (Mg/Fe 1:1-10:1), prepared by calcination and subsequent rehydration of hydrotalcite structures, were characterized, tested and evaluated as suitable catalysts for the aldol condensation of furfural with acetone. XRD analyses confirmed that the layered structure was completely restored by rehydration in the catalysts with Mg:Fe molar ratio 3:1 and 4:1. TPD-CO2 showed that the catalysts of this molar ratio had the highest basicity. Rehydrated Mg-Fe catalysts were tested in aldol condensation carried out in a glass batch reactor at 60 °C, atmospheric pressure, 2 wt% of catalyst and acetone/furfural molar ratio 10:1. The catalysts with Mg/Fe molar ratio of 3:1 and 4:1 showed total furfural conversion. As high basicity causes a high activity of the catalyst, our results suggest that the rehydrated mixed oxides with molar ratio 3 to 4:1 were promising new catalysts for the aldol condensation of furfural with acetone.

Thermal stability changing caused by chromium (iii) in the carbonated magnesium-aluminum hydrotalcite

There are several purposes for investigating hydrotalcite clays and one of them is due to its importance as an anionic adsorbent and ion exchanger, which make them capable of removing various pollutants from water. The most common hydrotalcite structure is based on double lamellar hydroxide of magnesium and aluminum, containing carbonate anions in the interlayer space. However, it is common to investigate the co-substitution of aluminum with other trivalent cations, especially transition metal cations, due to their binding properties. In this work, it was investigate the co-substitution of chromium (III) and aluminum in a sample of magnesium-aluminum carbonated hydrotalcite, comparing it with the same composition without this co-substitution. Thermal stability, crystallinity and morphology were investigated, showing that chromium contributes to the adsorptive capacity at low temperature.

Mn(III) active site in hydrotalcite efficiently catalyzes the oxidation of alkylarenes with molecular oxygen

Developing efficient heterogeneous catalytic systems based on easily available materials and molecular oxygen for the selective oxidation of alkylarenes is highly desirable. In the present research, NiMn hydrotalcite (Ni2Mn-LDH) has been found as an efficient catalyst in the oxidation of alkylarenes using molecular oxygen as the sole oxidant without any additive. Impressive catalytic performance, excellent stability and recyclability, broad applicable scope and practical potential for the catalytic system have been observed. Mn3+ species was proposed to be the efficient active site, and Ni2+ played an important role in stabilizing the Mn3+ species in the hydrotalcite structure. The kinetic study showed that the aerobic oxidation of diphenylmethane is a first-order reaction over Ni2Mn-LDH with the activation energy (Ea) and pre-exponential factor (A0) being 85.7 kJ mol−1 and 1.8 × 109 min−1, respectively. The Gibbs free energy (ΔG≠) was determined to be -10.4 kJ mol-1 K-1 for the oxidation based on Eyring-Polanyi equation, indicating the reaction is exergonic. The mechanism study indicated that the reaction proceeded through both radical and carbocation intermediates. The two species were then trapped by molecular oxygen and H2O or hydroxyl species, respectively, to yield the corresponding products. The present research might provide information for constructing highly efficient and stable active site for the catalytic aerobic oxidation based on available and economic material.