Calcined Mg-Al Layered Double Hydroxides Research Articles

Roles of CLDHs and TEA on Portland cement mortar/paste: Strength, hydration and chloride binding

In this study, the synergistic effects of calcined Mg-Al layered double hydroxides (CLDHs) and triethanolamine (TEA) on the hydration properties and chloride binding capacity of cement paste were investigated. The roles of incorporation of CLDHs and TEA in the cement pastes were evaluated by bound chloride rate, physical properties, reaction kinetics and microstructure. Experimental results show that the chloride ions are efficiently trapped by CLDHs at early stage, and the addition of TEA provides further stability. The mechanical strengths are decreased and obtained the low values at the 3 wt% and 6 wt% substitution level of CLDHs, and the negative phenomenon is improved with the incorporation of TEA. From the isothermal calorimetry (ICC), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results, the induction period of C3S process is retarded, but hydration of C3A is accelerated. The enhancement of chloride binding ability is mainly attributed to the recrystallization generation of LDH-Cl and the formation of Friedel’s salt (FS) with the decomposition of calcium hydroxide (CH), which is facilitated by TEA due to the rapid reaction of the aluminum phase. The analyses of scanning electron microscope and energy dispersive spectrometer (SEM-EDS) indicates that the enriched elemental chlorine originated from the immobilization effect of LDHs phase and FS, which is the significant support for the binding properties of chlorides in cementitious materials.

Simultaneous Removal of Phosphate and Nitrate on Calcined Mg-Al Layered Double Hydroxides

Simultaneous Removal of Phosphate and Nitrate on Calcined Mg-Al Layered Double Hydroxides

Uptake of heavy metal ions in layered double hydroxides and applications in cementitious materials: Experimental evidence and first-principle study

The uptake mechanism of heavy metal ions in layered double hydroxides (LDHs) is investigated in this paper via solid-solution exchange experiments and first principle study. The uptake capacities of C-LDHs for heavy metal ions from solutions are experimentally investigated and the structures of LDHs doped with various heavy metal ions are revealed. The doped structures of LDHs are further re-established with first principle calculations. The results show that Cu2+ or Cr3+ ions are immobilized in the form of isomorphic substitution for Mg2+ and Al3+ in the plate of the layered structure, respectively, during reconstruction of calcined LDHs, forming a non-stoichiometric structure. The structure of the Cu2+ doped LDHs is identified as [Mg2+(1−x)(1−z)Cu2+(1−x)zAl3+x(OH)2] An−x/n·yH2O, where z is the molar ratio of Cu2+ to Mg2+. The structure of Cr3+ doped LDHs is identified as [Mg2+1−x Cr3+xzAl3+x(1−z)(OH)2] An−(x+z)/n·yH2O, where z is the molar ratio of Cr3+ to Al3+. The Cu2+ or Cr3+ ions in the hardened cement paste modified with calcined Mg-Al LDHs as immobilizing admixture can be efficiently removed from the pore solution and chemically stabilized in the structure of LDHs.

Use of calcined Mg–Al layered double hydroxides to regulate endocrine disruptor methylparaben in excess as adsorbent and as control releasing agent in normal situations

Calcined Mg–Al layered double hydroxides (CLDH) were studied as potential adsorbents of the methylparaben (MPB), as a function of pH, contact time, temperature, adsorbent dosage and initial concentration, with the objective to reduce the hazardous effects that it can cause to human and its environment. The native layered double hydroxides (LDH) with carbonate as interlayer anion were prepared by a co–precipitation method and calcined at 450 °C for 1 h. The adsorption results showed that the adsorption capacity in removing MPB by CLDH (20.99 mg g−1) was greater than that of the precursor LDH (3.29 mg g−1). As seen from the XRD patterns of CLDH before and after the adsorption, MPB was intercalated into LDH interlayer by reconstruction of the original layered structure through so called “memory effect”. The adsorption isotherm and kinetic studies showed well fitting of experimental data to Langmuir and pseudo–second–order kinetic model, respectively, with a correlation coefficient more than 0.99. In addition, CLDH used as support for MPB displayed its controlled release properties in phosphate buffer solution at pH 7.4. Therefore, we can conclude that the calcined LDH employed in this study can be used not only as adsorbent to remove paraben from aqueous solutions, but also when required as support for the slow release of this endocrine disrupting compound, thus controlling its well and ill effects in different situations.

One-pot synthesis of carbon supported calcined-Mg/Al layered double hydroxides for antibiotic removal by slow pyrolysis of biomass waste.

A biochar supported calcined-Mg/Al layered double hydroxides composite (CLDHs/BC) was synthesized by a one-pot slow pyrolysis of LDHs preloaded bagasse biomass. Multiple characterizations of the product illustrated that the calcined-Mg/Al layered double hydroxides (CLDHs) were successfully coated onto the biochar in slow pyrolysis of pre-treated biomass. The as-synthesized CLDHs/BC could efficiently remove antibiotic tetracycline from aqueous solutions. The coating of CLDHs significantly increased the adsorption ability of biochar, and CLDHs/BC exhibited more than 2 times higher adsorption capacity than that of the pristine biochar (BC) in the tested pH range. The maximum adsorption capacity of CLDHs/BC for tetracycline was 1118.12 mg/g at 318 K. The experimental results suggested that the interaction with LDHs on biochar played a dominant role in tetracycline adsorption, accompanied with π–π interaction and hydrogen bond. This study provides a feasible and simple approach for the preparation of high-performance material for antibiotics contaminated wastewater treatment in a cost-effective way.

Perchlorate Uptake from Aqueous Solutions by Calcined Mg-Al Layered Double Hydroxides

The calcined layered double hydroxides (CLDHs) with 3:1 Mg/Al molar ratio were observed to acquire a high removal efficiency of perchlorate. And they were applied into perchlorate adsorption process with the initial 100 mg/L perchlorate solution in order to analyze removal efficiencies of perchlorate on various influential factors. The results represented that 1.5 g/L CLDHs could achieve ideal adsorption efficiencies of perchlorate at the pH range of 7–9 and at the temperature of 25°C. The removal efficiencies of perchlorate increased up to a maximum efficiency with the increasing dose of CLDHs. Acidic or highly alkaline environment adversely affected perchlorate adsorption. The adsorption process was found to be endothermic due to the higher adsorption capacity in CLDHs with the increasing temperature. The removal of perchlorate was best represented by the pseudo second-order kinetics model and Langmuir isotherm model. Co-existing anions tests showed that the anions of higher valence had a more significant effect than the monovalent anions during the adsorption process. Finally, the adsorption process was further validated by the X-ray patterns and Fourier-transform Infrared spectra of CLDHs. Results demonstrated potential utility of CLDHs that could be developed into a viable technology for perchlorate removal from water.

Silylated MgAl LDHs intercalated with MnO2 nanowires: Highly efficient catalysts for the solvent-free aerobic oxidation of ethylbenzene

A novel method for the preparation of silylated MgAl layered double hydroxides (LDHs) intercalated with MnO2 nanowires is presented. The method involves functionalizing the calcined MgAl LDHs (LDOs) with mercaptopropyltrimethoxysilane (MPTS), and then treating the silylated LDOs in the aqueous solution of KMnO4. The results obtained from XRD, FTIR, ICP, XPS and TEM showed that MPTS could be successfully grafted on LDOs via the reaction between –Si(OCH3)3 groups on the silane and the –OH groups on LDOs. LDOs grafted with MPTS could reconstruct their original layered structure by treating them in the aqueous solution of KMnO4, and in the same time, small amount of MnO4− anions were reduced to MnO2 by the grafted –SH groups on MPTS. The formed small amount MnO2 could further catalyze the decomposition of MnO4− in the interlayers of the reconstructed MgAl LDHs to MnO2. The formed MnO2 was finely dispersed on the LDH support in the form of nanowires (about 1.4nm in diameter). The MnO2/MgAl-LDH composites prepared by this method exhibited high catalytic activity, stability and reusability in the solvent-free aerobic oxidation of ethylbenzene.

Solvent-free aerobic oxidation of ethylbenzene over Mn-containing silylated MgAl layered double hydroxides

A novel method for the preparation of Mn-containing silylated layered double hydroxides (LDHs) is presented. The method involves functionalizing the calcined MgAl LDH (LDO) with dimethoxydiphenylsilane (DDS), and then treating it in the aqueous solution of KMnO4 under Ar. The prepared Mn-containing silylated MgAl LDH catalysts have higher Mn amount and more accessible Mn sites than the corresponding Mn-containing MgAl LDH catalysts, and exhibited much higher catalytic activity in the oxidation of ethylbenzene with O2 in the absence of organic solvents than the latter. In addition, the prepared Mn-containing silylated MgAl LDH catalyst was highly stable and reusable.

ChemInform Abstract: Calcined Mg—Al Layered Double Hydroxide as a Heterogeneous Catalyst for the Synthesis of Urea Derivatives from Amines and CO2.

AbstractThe title process gives the ureas in moderate yields and high selectivity (<99%).

Calcined Mg‐Al Layered Double Hydroxide as a Heterogeneous Catalyst for the Synthesis of Urea Derivatives from Amines and CO2

AbstractThe calcined Mg‐Al layered double hydroxides (LDHs) with a Mg/Al molar ratio of 3:1 were synthesized and characterized thoroughly by X‐ray diffraction (XRD), temperature‐programmed desorption (TPD) of CO2, and thermogravimetric analysis (TGA). Thus the calcined Mg‐Al LDHs were used as catalyst for the catalytic synthesis of disubstituted ureas from amines and CO2. The effects of reaction time, reaction temperature, pressure, solvent and calcined temperature on activity have been investigated. The results indicated that aliphatic amines, cyclohexylamine and benzylamine can be converted to the corresponding ureas selectively over the calcined Mg‐Al LDHs catalysts with N‐methyl‐2‐pyrrolidone (NMP) as solvent without using any dehydrating regent. The catalyst can be recycled several times with only slight loss of activity.

Removal of acid orange 10 by calcined Mg/Al layered double hydroxides from water and recovery of the adsorbed dye

This work considers the removal of the acid orange 10 (AO10) water contaminant on different calcined MgAl-layered double hydroxides (MgAl-LDHs). A precursor MgAl-LDH was submitted to hydrothermal treatment and grinding before calcination in order to obtain mixed oxides (MgAl500, MgAlHT500 and MgAlM500 respectively) with different surface characteristics. Adsorption experiments were carried out using different parameters such as pH of the solutions, contact times, temperature and initial dye concentrations to determine optimal adsorption conditions. Adsorbents and adsorption products were characterized by several physicochemical techniques. The kinetic study indicated that the adsorption of AO10 on MgAlHT500 was almost instantaneous and the maximum adsorption was reached in 2h, while it was more gradual for the other two adsorbents. In all cases, the adsorption was higher at a higher temperature (30°C), being more favorable for MgAlHT500: for initial dye concentration of C0=2.2mM, the amounts of AO10 removed from the solution per gram of adsorbent were Cs=1.47mmol/g for MgAlHT500 vs. Cs=0.9mmol/g for MgAlM500 and Cs=0.64mmol/g for MgAl500. The DRX technique analysis suggests the intercalation of AO10 into the LDH due to an increasing in the basal spacing from 7.7Å which corresponds to carbonate containing LDH, to 17.7Å. This could be ascribed to AO10 anions vertically oriented respect to the layers for a high initial dye concentration.

Nitrate adsorption from aqueous solution by MII-Al-CO3 layered double hydroxide

Hydrotalcite compounds were found to have high anion adsorption capacity that enhances their capability to remove anionic contaminants from aqueous systems. In this study, the adsorption of nitrates by various layered double hydroxides (LDHs), such as Mg-Al and Zn-Al, was investigated. The nature and content of divalent cations in LDHs have strong influence on the adsorption process. Calcined Mg-Al LDH with an Mg/Al molar ratio of 3.0 showed higher adsorption capacity compared to other calcined LDHs. The adsorption phenomenon has been well supported by x-ray diffraction and infrared studies.

Adsorption of phosphate by layered double hydroxides in aqueous solutions

Adsorption of phosphate by various calcined layered double hydroxides (LDHs) such as Mg–Al, Zn–Al, Ni–Al, Co–Al, Mg–Fe, Zn–Fe, Ni–Fe and Co–Fe was investigated. LDHs were found to have high anion exchange capacity that enhances their capability to remove anionic contaminants from aqueous system. The nature and content of di- and trivalent cations in LDH have strong influence on the adsorption process. Calcined Mg–Al LDH (CLDH) with Mg–Al molar ratio of 2.0 showed higher adsorption capacity compared to other calcined LDHs as it possessed higher Al3+ content. Results indicate that the adsorption isotherm could be fitted to a linearised form of Langmuir and Freundlich equations. The adsorption phenomenon has been well supported by XRD study. The adsorption process was spontaneous and exothermic in nature and followed first order kinetics. Competitive anions were found to have detrimental effect on the percentage of adsorption.