Intercalation of acrylate anions into the galleries of Zn–Al layered double hydroxide

Acrylate and methacrylate anions containing double bond and carboxylic groups, were intercalated in the interlayer region of a layered double hydroxide of formula: [Zn_0.66Al_0.34(OH)₂](NO₃)_0.34 0.62H₂O. The intercalation compounds obtained have been characterized for their chemical composition and with different instrumental techniques (X-ray powder diffraction, thermal analysis, FT-IR absorption spectroscopy, electron scanning microscopy). Furthermore, they have been used to carry out a preliminary study concerning the in situ polymerization of the intercalated acrylate and methacrylate ions to obtain new interstratified inorgano-organic hybrid materials.     

Synthesis and properties of mecoprop-intercalated layered double hydroxide

This study carried out to elucidate the synthesis of MCPP-LDH hybrid, release pattern of MCPP from MCPP-LDH hybrid and their properties. MCPP-LDH hybrid was synthesized from MCPP and Mg-Al complex. Release pattern of MCPP from MCPP-LDH hybrid was slower in distilled water and soil solution but it was slower in distilled water than soil solution. MCPP-LDH hybrid has shown more stable condition than form of LDH in thermal and acidic condition. Therefore, MCPP-LDH hybrid would lead as functional and benign pesticide to minimize the harmful effects on soil environment by bulk herbicides.     

Peroxydisulfate-assisted sonocatalytic degradation of metribuzin by La-doped ZnFe layered double hydroxide

Metribuzin is an herbicide that easily contaminates ground and surface water. Herein, La-doped ZnFe layered double hydroxide (LDH) was synthesized for the first time and used for the degradation of metribuzin via ultrasonic (US) assisted peroxydisulfate (PDS) activation. The synthesized LDH had a lamellar structure, an average thickness of 26 nm, and showed mesoporous characteristics, including specific surface area 110.93 m² g⁻¹, pore volume 0.27 cm³ g⁻¹, and pore diameter 9.67 nm. The degradation efficiency of the US/La-doped ZnFe LDH/PDS process (79.1 %) was much greater than those of the sole processes, and the synergy factor was calculated as 3.73. The impact of the reactive species on the sonocatalytic process was evaluated using different scavengers. After four consecutive cycles, 10.8 % loss occurred in the sonocatalytic activity of the La-doped LDH. Moreover, the efficiency of the US/La-doped LDH/PDS process was studied with respect to the degradation of metribuzin in a wastewater matrix. According to GC–MS analysis, six by-products were detected during the degradation of metribuzin. Our results indicate that the US/La-doped ZnFe LDH/PDS process has great potential for efficient degradation of metribuzin-contaminated water and wastewater.     

ESR spectra and thermal diffusivity of Zn–Al layered double hydroxide

Zn–Al–NO₃–LDH was synthesized using the co-precipitation method at pH 7±0.1 and ratio Zn/Al=4. The heat treatment of LDH was studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) to investigate the stability of the LDH structure. The in situ electron spin resonance (ESR) spectra of fresh LDH from room temperature up to 190 °C were obtained, which are due to the presence of nitrate radicals in LDH interlayer. ESR spectra of sintered LDH below 200 °C (ex situ ESR spectra) were investigated, which are also due to the nitrate radicals. However, at 200 °C and above, spectra were due to the oxygen vacancies of ZnO, which was formed during the thermal treatment of LDH. Thermal diffusivity of LDH as a function of in situ temperatures results in a nonlinear relation, which is due to the changing water content of LDH when temperature increases. However, thermal diffusivity of LDH as a function of sintered temperatures showed a linear relation and the slope of these data demonstrated the dependency between thermal diffusivity and water content of LDH below 200 °C. For temperature above 180 °C, the thermal diffusivity behavior was mainly due to the ZnO phase in LDH.     

Assessment of thermal and antimicrobial properties of PAN/Zn-Al layered double hydroxide nanocomposites

Polyacrylonitrile-based Zn–Al layered double hydroxide composites (PAN/LDH) have been synthesised with different LDH content by in situ polymerisation technique. The nanocomposites were systematically studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermo gravimetric analysis (TGA), field emission scanning electron microscope (FE SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and antibacterial activity measurement. The successful formation of exfoliated nanocomposite was inferred from the XRD patterns and HRTEM images. The thermal decomposition of PAN was enhanced upon nanocomposite (PAN/LDH) formation. The antimicrobial activity of PAN/LDH nanocomposites is evaluated for antibacterial activity against some clinically important bacterial pathogens and the bacterial growth is monitored at different percentage of LDH. The PAN/LDH composites displayed considerable antibacterial activity, on the contrary the virgin PAN did not possess any antibacterial activity. The likely electrostatic interaction among LDH layers with charged surface of bacterial cell is assumed to be responsible for antimicrobial activity. The prepared nanocomposite has appreciable thermal stability in combination with antibacterial activities by which the material is suitable for packaging and fabrication in textile application.     

Tuned CuCr layered double hydroxide/carbon-based nanocomposites inducing sonophotocatalytic degradation of dimethyl phthalate

This study is the first to explore the possibility of utilizing CuCr LDH decorated on reduced graphene oxide (rGO) and graphene oxide (GO) as sonophotocatalysts for the degradation of dimethyl phthalate (DMP). CuCr LDH and its nanocomposites were successfully fabricated and characterized. Scanning electron microscopy (SEM) along with high-resolution transmission electron microscope (HRTEM) both evidenced the formation of randomly oriented nanosheet structures of CuCr LDH coupled with thin and folded sheets of GO and rGO. The impact of diverse processes on the degradation efficiency of DMP in the presence of the so-prepared catalysts was compared. Benefiting from the low bandgap and high specific surface area, the as-obtained CuCr LDH/rGO represented outstanding catalytic activity (100 %) toward 15 mg L⁻¹ of DMP within 30 min when subjected to light and ultrasonic irradiations simultaneously. Radical quenching experiments and visual spectrophotometry using an O-phenylenediamine revealed the crucial role of hydroxyl radicals compared to holes and superoxide radicals. Overall, outcomes disclosed that CuCr LDH/rGO is a stable and proper sonophotocatalyst for environmental remediation.     

Intercalation reaction of layered transition metal disulfides—II: Tetraalkylammonium hydroxide intercalates of 2H-tantalum and 2H-niobium disulfides

The intercalates of 2H-tantalum and 2H-niobium disulfides with tetraalkylammonium hydroxides were prepared in aqueous solutions. All intercalates prepared were hexagonal 2H-polytype, and their a-lattice parameters were similar to those of the original disulfides. The intercalates of both disulfides had similar c-lattice parameters, the values being 23Å in tetramethyl- and tetraethyl ammonium hydroxide intercalates, and 28Å in tetra-n-propyl- and tetra-n-butylammonium hydroxide intercalates, respectively. The increase in the c-lattice parameter was interpreted according to the effective ionic radii of tetraalkylammonium ions in aqueous solutions including alkali metal ions. It was found from this interpretation that the c-lattice parameter of the hydroxide intercalates increased stepwise at regular distances of 5Å corresponding to the increase in the effective ionic radius of the intercalated cations.     

Polyvinyl pyrrolidone-assisted synthesis of flower-like nickel-cobalt layered double hydroxide on Ni foam for high-performance hybrid supercapacitor

Nickel-cobalt layered double hydroxides (NiCo-LDH) were successfully deposited on nickel foam by a facile hydrothermal method using polyvinyl pyrrolidone (PVP) as the structure-directing reagent. The effect of PVP on the morphology and electrochemical performance of binder-free NiCo-LDH electrode for supercapacitor were investigated in detail. The prepared NiCo-LDH presented good dispersivity and appeared different flower-like structure via the addition of PVP. Specially, the NiCo-LDH electrode using 1 g of PVP exhibited a superior performance with a high-specific capacity of 724.9 C g^?1 at a current density of 1 A g^?1 and 577.1 C g^?1 at 10 A g^?1. In addition, a hybrid supercapacitor (HSC) based on the optimized NiCo-LDH as positive electrode and activated carbon as negative electrode was assembled with 6 M KOH as the electrolyte. The HSC device can deliver an energy density of 32.3 Wh kg^?1 at the power density of 387.1 W kg^?1. Moreover, the HSC device exhibited a good cycling stability with a retention rate of 94.0% after 2000-cycle charge-discharge test at 3 A g^?1.     

Application of an ionic liquid-functionalized Mg2Al layered double hydroxide for the electrochemical myoglobin biosensor

In this paper, an ionic liquid 1-carboxyl-methyl-3-methylimidazolium tetrafluoroborate (CMMIMBF₄)-functionalized Mg₂Al layered double hydroxide (LDH) was synthesized and further used for the immobilization of myoglobin (Mb) on the surface of a carbon ionic liquid electrode to get a new electrochemical biosensor. Ultraviolet–visible and Fourier transform–infrared spectroscopies confirmed that Mb in the CMMIMBF₄-LDH remained its native secondary structure, which was attributed to the biocompatibility of the materials used. On the cyclic voltammograms, a pair of well-defined redox peaks appeared, indicating that direct electron transfer of Mb was realized in the modified electrode. The formal peak potential was calculated as ?0.209 V (vs. SCE), which was the typical characteristics of the Mb heme Fe(III)/Fe(II) redox couples. The fabricated Mb sensor exhibited good electrocatalytic activity to the reduction of trichloroacetic acid in the range from 1.0 to 17.0 mmol L^?1 with the detection limit as 0.344 mmol L^?1 (3σ), and the apparent Michaelis–Menten constant was calculated as 13.5 mmol L^?1. Thus, the ionic liquid-functionalized LDH exhibited the potential application in the electrochemical sensor for redox proteins.     

Effect of high magnetic field annealing on the microstructure and magnetic properties of Co-Fe layered double hydroxide

The effects of high magnetic field (10 T) on the products obtained by calcination of Co-Fe LDH precursors at different temperatures were investigated. The XRD results indicated that Fe^III substituted for Co^III in Co₃O₄ to yield Co^IICo^IIIFe^IIIO₄ under the calcination of Co-Fe LDH precursors at 400 °C. The products obtained by magnetic field annealing at 400 °C had a porous plate-like morphology, whereas the products without magnetic field annealing were composed of nanoparticles. It was seen that CoFe₂O₄ phase could be formed at low temperature (about 500 °C) under the magnetic field annealing. The grain size of products obtained by magnetic field annealing at 800 °C was larger than that of zero magnetic field. It was found that the saturation magnetization was significantly enhanced after magnetic field annealing, especially at lower temperature (≤600 °C). The possible reason for the effects on the microstructure and magnetic properties of products obtained by magnetic field annealing was discussed.     

Tailoring the properties of polyamide thin film membrane with layered double hydroxide nanoclay for enhancement in water separation

This current paper presented a new candidate and potentially to improve the current membrane materials in water filtration process. With that, the primary materials used in this research study is layered double hydroxides (LDH) nanoclay which can be obtained from earth minerals and self-synthesized from inorganic salts were discussed thoroughly to help a better understanding of these materials. However, the current technologies of water separation were still lagging behind and ineffective especially in removal of divalent metal ions and multivalent salts. Infeasibility of reverse osmosis membrane make it not a viable option for divalent salts filtration. With that, nanofiltration (NF) membrane offered as an alternative to substitute available method. In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating layered double hydroxides (LDH) nanoclay. The LDH nanoclay with different loading ratio of 0, 0.05, 0.1, 0.15 and 0.2 were impregnated into polyamide layer on top of polysulfone substrates. The fabricated TFN were characterized in terms of physicochemical properties (SEM and FTIR) and membrane hydrophilicity (contact angle). After the addition of LDH, the morphological structures of TFN membranes were changed and the surface hydrophilicity was enhanced significantly. FESEM images displayed a typical ridge and valley morphology with nodule-like structures. As the LDH loading was increased, the contact angle decreased from 34.56° to 15.76° showing the surface hydrophilicity of membrane is improved. The separation performance of membrane was evaluated in terms of salt rejection ability by cross flow filtration system. The best performance NF membrane was found to be TFN 0.05 with high water flux and MgCl₂ rejection with values of 24.18 L/m².h and 91% respectively. This study has experimentally validated the potential of LDH materials in membrane process for improvement in water separation process.     

Preferential intercalation of isomeric but-2-enedioate anions into the layered double hydroxides

Intercalation of cis-but-2-enedioate anion or trans-but-2-enedioate anion into the layered double hydroxide (LDH), [Mg_0.66Al_0.34(OH)₂]Cl_0.34·0.43H₂O was carried out by the method of ion-exchange procedures. Selective reaction was observed in competitive experiments involving an equal concentration pairs of acids. The trans-but-2-enedioate anion is preferentially intercalated into the Mg-Al-LDH. The obtained intercalation compounds were characterized by X-ray diffraction, infrared and thermogravimetry techniques. The charge density on the oxygens of each of the carboxylate groups for both anions was investigated utilizing ab initio (HF/6-31G) method by G98w. From the X-ray diffraction data, the guest size and the charge density of the oxygen of the guest, the orientation of both anions between the layers was determined and the preferential intercalation mechanism was studied. These results indicate the possibility of a molecular recognition ability of LDHs.     

Intercalation of esters into vanadyl phosphate

Intercalates of vanadyl phosphate with formates and acetates of C₁–C₈ alcohols and dimethylesters of dicarboxylic acids C₂–C₆ were prepared by a displacement reaction of 2-propanol-intercalated VOPO₄. The diffractograms of the intercalates show a series of sharp (0 0 l) reflections, (2 0 0) reflection and in some cases several (h k l) lines with low intensity. The tetragonal lattice parameters of the intercalates were calculated. The intercalates prepared are not stable in air. The C=O stretching vibration in IR spectra of the intercalates prepared was shifted to lower wavenumbers in comparison with the spectra of the pure guests, indicating that all esters are anchored to the host layers by their carbonyl oxygen.     

Heat transfer from a hot moving steel plate by using Cu-Al layered double hydroxide nanofluid based air atomized spray

The current research is focused on the cooling of a hot moving steel plate by using air atomized spray cooling technique. A new type of coolant, Cu-Al LDH nanofluid, has been prepared and used for heat flux removal. Preparation method of nanofluid and its characteristics has been reported. The cooling effectiveness is reported in terms of cooling rate by varying the concentration of nanofluid in five levels. The results indicate that the cooling rate increases at very low concentration of LDH with respect to base fluid. However, beyond a certain concentration a decreasing trend of cooling rate has been observed.

Abbreviations: CHF: Critical heat flux; HTC: Heat transfer coefficients; LDH:Layered double hydroxide; TEM: Transmission electron microscopy.     

Intercalation of aminonaphthalenes into α-zirconium hydrogenphosphate

Intercalates of 1- and 2-aminonaphthalene (1-AN and 2-AN), 1,5- and 1,8-diaminonaphthalene (1,8-DAN) and 2-aminoanthracene (2-AA) into α-Zr(HPO₄)₂·H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, molecules of aminonaphthalenes are protonated in the interlayer space. 1,5-diaminonaphthalene (1,5-DAN) molecules are arranged in a monomolecular way in the intercalate. The other guest molecules form partially interdigitated bilayers in the interlayer space.     

Study on a new green phosphor Ca12Al14O32Cl2: Tb3+ derived from Tb-doped Ca-Al layered double hydroxide

A new green phosphor Ca₁₂Al₁₄O₃₂Cl₂: Tb³⁺ derived from Tb-doped Ca-Al layered double hydroxide (Tb-doped CaAl-LDH) was prepared through phase transition route. The X-ray diffraction measurement results revealed that the Tb-doped CaAl-LDH transformed into Ca₁₂Al₁₄O₃₂Cl₂:Tb³⁺ phase at 600 °C. With temperature varying from 600, 800–1000 °C, the crystallinity of the Ca₁₂Al₁₄O₃₂Cl₂:Tb³⁺ phase gradually improved. Compositional analyses suggested the chemical formula of the Ca₁₂Al₁₄O₃₂Cl₂:Tb³⁺ phase estimated to be Ca₁₂Al_13.52Tb_0.48O₃₂Cl₂. The Ca₁₂Al_13.52Tb_0.48O₃₂Cl₂ phase can be efficiently excited by near ultraviolet light and show strong green emissions attributed to ⁵D₄→⁷F_J (J = 5, 6) transition of Tb³⁺. The present Ca₁₂Al_13.52Tb_0.48O₃₂Cl₂ may be a promising candidate for green phosphor applied in LED.     

Near-infrared spectroscopy of palladium-containing layered double hydroxides used as catalysts

Three catalysts consisting of layered double hydroxides (LDHs) of magnesium and aluminum, and containing palladium in various forms, were synthesized and subsequently characterized by mid- and near-infrared spectroscopies. The results thus obtained are compared with those for a pure Mg/Al layered double hydroxide. The spectra for the Pd-containing LDHs (particularly the strength of the bands) were found to depend on the particular palladium form present. As a rule, the mid-infrared spectra contained a strong, broad band at 3800-2500 cm⁻¹ due to stretching vibrations of the different types of hydroxyl groups present in the solids and another signal at ca. 1370 cm⁻¹ due to the presence of carbonate ions in the interlayer region. These signals were the strongest in the near-infrared spectra, which were also quite similar, roughly, for all solids.     

Intercalation of sulfonated melamine formaldehyde polycondensates into a hydrocalumite LDH structure

A series of sulfonated melamine formaldehyde (SMF) polycondensates possessing different anionic charge amounts and molecular weights was synthesized and incorporated into a hydrocalumite type layered double hydroxide structure using the rehydration method. For this purpose, tricalcium aluminate was dispersed in water and hydrated in the presence of these polymers. Defined inorganic–organic hybrid materials were obtained as reaction products. All SMF polymers tested intercalated readily into the hydrocalumite structure, independent of their different molecular weights (chain lengths) and anionic charge amounts. X-ray diffraction revealed typical patterns for weakly ordered, highly polymer loaded LDH materials which was confirmed via elemental analysis and thermogravimetry. IR spectroscopy suggests that the SMF polymers are interleaved between the [Ca₂Al(OH)₆]⁺ main sheets via electrostatic interaction, and that no chemical bond between the host matrix and the guest anion is formed. The SMF polymers well ensconced within the LDH structure exhibit significantly slower thermal degradation.