Structural reconstruction of mechanochemically disordered CaFe-layered double hydroxide

Development of Novel Decarboxylation-Urea Method toward Interlayer-Anion-Controlled Layered Double Hydroxides

Layered double hydroxides (LDHs) are representative of a 2D anionic clay. Simple and homogeneous synthesis of interlayer-anion-controlled LDH is essential for studies and industrial production. In this study, we report the one-pot synthesis of an LDH that is selective for interlayer anions, which was labeled as "decarboxylation-urea method". We obtained LDHs intercalated with NO3-, Cl-, and SO42- by removing CO2 in this method. The ionic conductivities of the prepared LDHs were investigated for their applicability to electrolytes, and it was found that Zn-Al LDH intercalated with NO3- showed the highest ionic conductivity (18 mS cm-1). Therefore, the LDH intercalated with NO3- synthesized using the decarboxylation-urea method is promising as an alkaline solid electrolyte.

Surface modification of two-dimensional layered double hydroxide nanoparticles with biopolymers for biomedical applications

Layered double hydroxides (LDHs) are appealing nanomaterials for (bio)medical applications and their potential is threefold. One can gain advantage of the structure of LDH frame (i.e., layered morphology), anion exchanging property towards drugs with acidic character and tendency for facile surface modification with biopolymers. This review focuses on the third aspect, as it is necessary to evaluate the advantages of polymer adsorption on LDH surfaces. Beside the short discussion on fundamental and structural features of LDHs, LDH-biopolymer interactions will be classified in terms of the effect on the colloidal stability of the dispersions. Thereafter, an overview on the biocompatibility and biomedical applications of LDH-biopolymer composite materials will be given. Finally, the advances made in the field will be summarized and future research directions will be suggested.

Synergistic Effect of NiLDH@YZ Hybrid and Mechanochemical Agitation on Glaser Homocoupling Reaction

Herein, we report the synthesis of nickel-layered double hydroxide amalgamated Y-zeolite (NiLDH@YZ) hybrids and the evaluation of the synergistic effect of various NiLDH@YZ catalysts and mechanochemical agitation on Glaser homocoupling reactions. Nitrogen adsorption-desorption experiments were carried out to estimate the surface area and porosity of NiLDH@YZ hybrids. The basicity and acidity of these hybrids were determined by CO₂ -TPD and NH₃ -TPD experiments respectively and this portrayed good acid-base bifunctional feature of the catalysts. The NiLDH@YZ-catalyzed mechanochemical Glaser coupling reaction achieved best yield of 83 % for the 0.5NiLDH@0.5YZ hybrid after 60 min of agitation, which revealed the highest acid-base bifunctional feature compared to all the investigated catalysts. The developed catalyst has proven itself as a robust and effective candidate that can successfully be employed up to four catalytic cycles without significant loss in catalytic activity, under optimized reaction conditions. This work demonstrated a new strategy for C-C bond formation enabled by the synergy between mechanochemistry and heterogeneous catalysis.

Structure-modulated CaFe-LDHs with superior simultaneous removal of deleterious anions and corrosion protection of steel rebar

The three anionic species; chloride (Cl⁻), sulfate (SO₄²⁻), and carbonate (CO₃²⁻), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure. Efficient removal of these deleterious anions at the early stage of penetration is crucial to enhance the lifespan and durability of concrete structures. Here, we synthesize CaFe-layered double hydroxide (CaFe-LDHs) by a simple one-step co-precipitation technique and structural modulation by calcination process. It is applied for the removal of Cl⁻, SO₄²⁻, and CO₃²⁻ anions as well as corrosion inhibition on steel rebar in aqueous solutions. The synthesized CaFe-LDHs with phase transfer show notable improvement of removal capacity (Q_max) toward Cl⁻ and SO₄²⁻ over 3.4 times and over 5.69 times, respectably, then those of previous literatures. Furthermore, the steel rebar exposed to an aqueous solution containing the three anionic sources shows a fast corrosion rate (1876.56 × 10⁻³ mm per year), which can be remarkably inhibited showing 98.83% of corrosion inhibition efficiency when it is surrounded by those CaFe-LDHs. The novel adsorption mechanisms of these CaFe-LDHs-induced crystals and corresponding corrosion protection properties are elucidated drawing on synergy of memory effects and chemical reactions.

The three anionic species; chloride (Cl⁻), sulfate (SO₄²⁻), and carbonate (CO₃²⁻), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure.

CuCr2O4@CaFe-LDO photocatalyst for remarkable removal of COD from high-strength olive mill wastewater

Wastewater from the olive mill constitutes a serious environmental concern, as it is characterized by a high inorganic and organic load. Here, a hybrid photocatalyst based on calcined Ca-Fe-LDH was successfully synthesized for the degradation of phenolic compounds and the removal of chemical oxygen demand (COD) from the high-strength olive mill wastewater (OMW). The catalyst (CuCr₂O₄@CaFe-LDO) displayed a stable ~4.48 µA cm^-2 photocurrent response, a 2.56 eV bandgap and a wide variety of pores with an average size of 12.51 nm. 1.0 g CuCr₂O₄@CaFe-LDO achieved 66% COD removal after 300 mins without an oxidant in the dark, while after 180 mins of reaction, CuCr₂O₄@CaFe-LDO/K₂S₂O₈/sunlight system resulted in ~99% and 98.3% COD and colour removal. Seven phenolic compounds were found in the crude OMW, with hydroxytyrosol (76.84%) and tyrosol (15.14%) being the main ones. The final pH of the sample treated increased from 4.3 to 7.3, which confirmed the degradation of phenolics and fatty acids in the OMW. OH, SO₄^-, h⁺ and O₂^- contributed notably to the degradation of polyphenols and the spent catalyst was easily and rapidly recovered from the bulk solution due to its saturation magnetization of 54.7 emu g^-1.

CuAl LDH/Rice Husk Biochar Composite for Enhanced Adsorptive Removal of Cationic Dye from Aqueous Solution

The preparation of CuAl LDH and biochar (BC) composite derived from rice husk and its application as a low-cost adsorbent for enhanced adsorptive removal of malachite green has been studied. The composite was prepared by a one-step coprecipitation method and characterized by X-ray Diffraction (XRD), Fourier Transform Infra Red (FTIR), Brunauer-Emmett-Teller (BET), and Scanning Electron Microscopy - Energy Dispersive X-ray (SEM−EDX). The result indicated that CuAl LDH was successfully incorporated with the biochar that evidenced by the broadening of XRD peak at 2θ = 24° and the appearance of a new peak at 1095 cm−1 on the FTIR spectra. The BET surface area analysis revealed that CuAl/BC composite exhibited a larger surface area (200.9 m2/g) that the original CuAl LDH (46.2 m2/g). Surface morphological changes also confirmed by SEM image, which showed more aggregated particles. The result of the adsorption study indicated the composite material was efficient in removing malachite green with Langmuir maximum adsorption capacity of CuAl/BC reaching 470.96 mg/g, which is higher than the original CuAl LDH 59.523 mg/g. The thermodynamic analysis suggested that the adsorption of malachite green occurs spontaneously (ΔG < 0 at all tested temperature) and endothermic nature. Moreover, the CuAl/BC composite showed strong potential as a low-cost adsorbent for cationic dye removal since it showed not only a high adsorption capacity but also good reusability. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Mechanochemical synthesis of Fe2O3/Zn-Al layered double hydroxide based on red mud

In this work, using industrial waste red mud (RM) as main starting material, a simple method of mechanochemical synthesis (MCS) was introduced as a green approach to synthesize heterogeneous Fe₂O₃/Zn-Al layered double hydroxide (F/ZA-LDH), which could be used as a new low-cost catalyst for photo-Fenton reaction. The optimum preparation conditions of F/ZA-LDH were as follows: mass ratio of Zn(NO₃)₂·6H₂O to RM (m_Zn:m_RM) 2:1, dry milling time 6 h, H₂O dosage 2 mL, ball-to-powder mass ratio 50:1, and milling speed 250 rpm. The effects of the synthesis conditions on the crystal structure and catalytic activity of F/ZA-LDH were analyzed. The F/ZA-LDH was characterized by XRD, TG, XPS, SEM, (HR)TEM. The characterization results showed the composite had a crystallized hydrotalcite-like structure, and the crystalline phases in the optimum F/ZA-LDH were Fe₂O₃ and Zn-Al LDH. A hetero-interfaces between Fe₂O₃ and Zn-Al LDH existed in the synthesized Fe₂O₃/Zn-Al LDH composite. Furthermore, the possible mechanism for F/ZA-LDH formation in the MCS process was proposed. Overall, our results provide a systematic understanding of the preparation of LDH composite through MCS using RM as main material, and our findings help to develop green technology for reusing RM.