Cu-Al Layered Double Hydroxides Research Articles

Synthesis of Cu-Al layered double hydroxides from aluminum saline slags

The use of saline slag, a hazardous waste generated during the recycling of aluminum, as aluminum source for the synthesis CuAl layered double hydroxides (LDH) is for the first time reported in this study. Due to the Jahn-Teller effect, divalent copper–aluminum LDH come usually with impurities and a pure CuAl LDH is not easy to obtain. The effect of synthesis pH has been examined by comparing LDH synthesized at various pH, ranging from 6 to 12 via a co-precipitation method using aluminum obtained from an alkaline extraction of the slag. For comparison purposes, a sample was synthesized at pH = 9 using commercial aluminum Al(NO3)3·9H2O instead of extracted aluminum. The effects of the aging time and calcination temperature are also discussed. The LDH and their calcined metal mixed oxide (layered double oxide, LDO) have been analyzed with several characterization techniques: powder X-ray diffraction (PXRD), N2 adsorption at −196 °C, thermogravimetric analysis (TGA), temperature programmed reduction (TPR), scanning electron microscopy (SEM), transmission electron microscopy and energy-dispersive X-ray spectroscopy (TEM and EDS). Synthesis pH has been proved not only to have a significant effect on the nature of secondary phases but also on the structure and morphology of the samples.

A co-precipitation route for the preparation of eco-friendly Cu-Al-layered double hydroxides with efficient tetracycline degradation.

The construction of novel efficient catalysts for the treatment of organic pollutants in the aqueous environment is essential. The lamellar-like Cu-Al layered double hydroxides (CuAl-LDHs) with various mole ratios were synthesized by a simple route of co-precipitation, and the corresponding degradation characteristic was tested for the removal of tetracycline (TC) using PMS activation. The degradation efficiency of TC over CuAl-LDHs increased up to 93% within 10min for the Cu/Al mole ratio of 3:1 and almost not changed at a higher mole ratio. For further calcining the optimal catalyst at 300 ℃, the degradation efficiency of TC was found to be increased to 96%. Sulfuric radicals and singlet oxygen were analyzed to be the main reason for the change in degradation characteristics, which was proved by radical quenching experiments and electron paramagnetic resonance technique. The parameters including PMS concentration, catalyst dosage, and reaction temperature on the TC degradation as well as the degradation mechanism for PMS activation were elaborated. The best proportion of CuAl-LDHs owned splendid stability and catalytic activity after reusing, which showed enormous potential in practical application.

Synthesis of CuAl-LDHs by Co-Precipitation and Mechanochemical Methods and Selective Hydrogenation Catalysts Based on Them

The paper presents the results of the synthesis and study of CuAl layered double hydroxides (LDHs) as well as their application as catalysts for the selective hydrogenation of crotonaldehyde. Phase-homogeneous LDHs were obtained by co-precipitation and mechanochemical methods, and critical parameters ensuring the formation of the target product were identified. In the case of coprecipitation, the formation of LDH is most affected by the pH of the reaction medium and the CO32−/Al3+ ratio. The optimal CO32−/Al3+ ratio is ca. 0.5–0.8 and pH 9.5–10.0. When mechanochemical synthesis is used, at 500 m·s−2 and 60 min, it is possible to obtain a single-phase CuAl LDH, whereas at higher energies, LDH is destroyed. The mechanochemical method makes it possible not only to reduce the synthesis time and the amount of alkaline wash water but also to obtain more dispersed copper particles with a higher hydrogenating activity. The conversion of 2-butenal (T = 80 °C, P = 0.5 MPa, 180 min, ethanol) for this sample was 99.9%, in contrast to 50.5% for the catalyst obtained by co-precipitation. It is important that, regardless of the conversion, both catalysts showed high selectivity (S = 90–95%) for the double bond hydrogenation.

Kinetic studies on the uptake of phenols by linear and cyclic organic sulfonic acid-modified Cu-Al layered double hydroxides

• The adsorption follows a pseudo-second-order kinetic equation. • The Δ G values for adsorption systems ranged from −20 to 0 kJ/mol. • It indicates that adsorption could be classified as physical adsorption. • NP was adsorbed on OS•Cu-Al LDH by hydrophobic interaction. • AP was adsorbed on SCD•Cu-Al LDH by CH/π interactions. Our previous study revealed that Cu-Al layered double hydroxides (LDHs) intercalated with 1-octanesulfonate and sulfonated β-cyclodextrin showed good adsorption selectivity toward m -nitrophenol (NP) and m -aminophenol (AP), respectively. We also found that the adsorption behaviors of these LDHs fit the Freundlich equation. Herein, we performed a kinetic analysis to elucidate the adsorption mechanism of the LDHs for phenols in greater detail. The adsorption results were fitted to a pseudo-first-order kinetic equation, a pseudo-second-order kinetic equation, and an intraparticle diffusion model. The correlation coefficients of the pseudo-second-order kinetic equation for each adsorption process were fairly high, and the measured and calculated equilibrium adsorption amounts were relatively close. Thus, the adsorption of NP and AP by OS•Cu-Al LDH and SCD•Cu-Al LDH, respectively, fits the pseudo-second-order kinetic equation. Because the ΔG values for each system ranged from −20 to 0 kJ/mol, the adsorption processes in these systems may be classified as physical adsorption. Specifically, NP was adsorbed on OS•Cu-Al LDH by hydrophobic interactions, whereas AP was adsorbed on SCD•Cu-Al LDH by CH/π interactions. Our findings provide new insights into the adsorption of phenols onto modified Cu-Al LDHs and could serve as a foundation for future studies on the adsorption properties of LDHs intercalated with anions as guest layers.

Synthesis of linear and cyclic organic sulfonic acid-modified Cu-Al layered double hydroxides and their adsorption properties

Over the past few years, many substances have been investigated for their potential application as adsorbent materials. The combination of a layered double hydroxide (LDH) and CH/π interactions enables selective adsorption through the differences in the electron density of the aromatic ring. Thus, in this study, two organic anions, namely the linear 1-octane sulfonate (OS-) and cyclic sulfonated-β-cyclodextrin (SCD13-), were intercalated into the interlayers of a Cu-Al LDH by coprecipitation (Cu/Al ratio, 3.0; chemical ratio, 2.0). The SCD13- anion was selected because β-cyclodextrin comprises hydrophobic cavities that allow the formation of inclusion compounds. X-ray diffraction (XRD), total organic carbon (TOC) analysis, and inductively coupled plasma-atomic emission spectrometry (ICP-AES) revealed that the as-synthesized OS-Cu-Al LDH and SCD-Cu-Al LDH were both oriented perpendicular to the LDH layer. Subsequent absorption experiments with m-aminophenol (AP) and m-nitrophenol (NP), which have similar structures but different aromatic ring electron densities, confirmed a Freundlich-type adsorption mechanism and revealed that adsorption occurred on a non-uniform surface for both LDHs. The results also revealed excellent NP and AP adsorptions for the linear OS•Cu-Al LDH and cyclic SCD•Cu-Al LDH, respectively. This was attributed to the strong hydrophobic interactions in the former and strong CH/π interactions in the latter. This study shows the potential of using linear and cyclic organic sulfonic acid-modified LDHs for the selective recovery of the desired aromatic organic compounds.

Selective Hydrogenation of 5-Acetoxymethylfurfural over Cu-Based Catalysts in a Flow Reactor: Effect of Cu-Al Layered Double Hydroxides Synthesis Conditions on Catalytic Properties

Cu-containing layered double hydroxides (LDHs) were synthesized by a co-precipitation method at different reaction conditions, such as aging time, pH, precipitation rate and synthesis temperature. The effect of these parameters on the structure and chemical composition of the catalysts were investigated using a set of physical methods, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), H2-TPR and in situ X-ray photoelectron spectroscopy (XPS). It allowed for checking of the reducibility of the samples. 5-Acetoxymethylfurfural was catalytically hydrogenated to 5-(acetoxymethyl)-2-furanmethanol (AMFM) over Cu-containing catalysts synthesized from layered double hydroxides so as to investigate its catalytic properties in flow reaction. It was shown that synthesis pH decreasing from 10 to 8 resulted in rise of AMF conversion that coincided with the higher surface Cu/Al ratio obtained by XPS. Preferable aging time of LDH materials for obtaining the most active catalyst was 2 h, an amount of time that favored the production of the catalyst with high surface Cu/Al ratio up to 0.38. Under optimized reaction conditions, the AMFM yield was 98%. Finally, a synthesis strategy for the preparation of highly efficient Cu-based hydrogenation catalyst with optimized characteristics is suggested.

In Situ Generation of Catalytically Active Cu0 Species Derived from Cu-Al Layered Double Hydroxides for Acceptorless Alcohol Dehydrogenation

Abstract A CuO-CuAl2O4 nanocomposite (CuAl NC) synthesized by high temperature calcination of Cu-Al layered double hydroxides (CuAl LDHs) acted as an effective heterogeneous catalyst for acceptorless dehydrogenation of various alcohols. The catalytically active Cu0 species was formed by in situ reduction with alcohol. The catalytic activity strongly depended on the Cu/Al ratio in preparation and calcination temperature. The synthesized catalyst was reusable without loss of its high activity and selectivity.

Enhanced photocatalytic degradation of eco-toxic pharmaceutical waste diclofenac sodium by anion loaded Cu-Al LDH⋅Bi2O3 composites

BackgroundNowadays, the non-steroidal drug diclofenac sodium (DCF) has emerged as hazardous pollutant due to its eco-toxic nature and its efficient elimination from wastewater is emerging as crucial problem. But, low activity, high cost and instability of the conventional photocatalysts restrain their uses. MethodIn this study, different anion impreganted Cu-Al layered double hydroxides (LDH) and Bi2O3 derived heterocomposites have been examined as plausible photocatalysts for degradation of DCF under visible light radiation. These composites have synthesized by simple wet impregnation methods and characterized by several methods such as XRD, HR-TEM, XPS SEM-EDX, XPS, DRS, phototuminescence(PL), BET etc. Significant FindingsThe BET sorption isotherms indicate that the anion loaded composites are having larger specific surface area than the pristine one. Also, upon anion impregnation the zeta potential values shift towards more negative values confirming absorption of anions. They show significantly higher (65% for carbonate and 83% for sulphate) photcatalytic activity compare to the parent hybrid (53%). Here, the anions act as efficient electron scavengers to suppress the electron-hole pair recombination. The individual photocatalytic reactions follow pseudo-first order kinetics. Due to low cost, simpler preparation, enhanced activity and recyclability the anion loaded derivatives can emerge as excellent photocatalyst for eradicating DCF.

Kinetic and equilibrium analyses of lactate adsorption by Cu-Al and Mg-Al layered double hydroxides (Cu-Al LDH and Mg-Al LDH) and Cu-Al and Mg-Al layered double oxides (Cu-Al LDO and Mg-Al LDO)

Lactate is an important metabolite generated during the culture of pluripotent stem cells and is known to inhibit the cell growth. With the increase in the prominence of pluripotent stem cell applications, reliable methods are required to remove metabolites such as lactate for enabling the high-density culture of cells. Herein, we report an investigation of layered double hydroxides (LDHs) and layered double oxides (LDOs) as anion-adsorbents for lactate removal to regenerate the cell culture medium. The lactate absorption ability of Cu-Al and Mg-Al LDH and Cu-Al and Mg-Al LDO adsorbents was evaluated. The influence of various process parameters, including temperature and pH, on the lactate adsorption, were investigated. The kinetics of the adsorption process and equilibrium dynamics were studied, and the maximum adsorption amounts were determined. The Cu-Al LDH, Cu-Al LDO, Mg-Al LDH, and Mg-Al LDO exhibited a lactate adsorption that followed a pseudo-second-order kinetic model, and their apparent activation energies for adsorption were 32.0, 47.4, 95.7, and 61.7 kJ/mol, respectively; these values indicated that chemical adsorption was the underlying mechanism of adsorption. The Langmuir and Freundlich models were analyzed and revealed the nature of the anion-exchange process. This study is expected to promote the high-density culture of cells by ensuring the regeneration of the media by the efficient removal of the undesired lactate.

Exploring the Wet Mechanochemical Synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al Layered Double Hydroxides from Oxides, Hydroxides and Basic Carbonates

The synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al layered double hydroxides (LDHs) was investigated with a one-step wet mechanochemical route. The research aims to expand on the mechanochemical synthesis of LDH using a mill designed for wet grinding application. A 10% slurry of solids was added to a Netzsch LME 1 horizontal bead mill and milled for 1 h at 2000 rpm. Milling conditions were selected according to machine limitations and as an initial exploratory starting point. Precursor materials selected consisted of a mixture of oxides, hydroxides and basic carbonates. Samples obtained were divided such that half was filtered and dried at 60 °C for 12 h. The remaining half of the samples were further subjected to ageing at 80 °C for 24 h as a possible second step to the synthesis procedure. Synthesis conditions, such as selected precursor materials and the MII:MIII ratio, were adapted from existing mechanochemical methods. LDH synthesis prior to ageing was successful with precursor materials observably present within each sample. No Cu-Al LDH was clearly identifiable. Ageing of samples resulted in an increase in the conversion of raw materials to LDH product. The research offers a promising ‘green’ method for LDH synthesis without the production of environmentally harmful salt effluent. The synthesis technique warrants further exploration with potential for future commercial up-scaling.

Intercalation of laminar Cu-Al LDHs with molecular TCPP(M) (M = Zn, Co, Ni, and Fe) towards high-performance CO2 hydrogenation catalysts.

A confined space is broadly applied to enhance the dispersion and limit the aggregation of catalytically active sites, especially at high temperatures. In this work, we provided an efficient approach to immobilize transition metal ions (e.g., Zn2+, Co2+, Ni2+, and Fe2+) into the confined space of laminar Cu-Al layered double hydroxides (LDHs) using a range of molecular metalloporphyrins (viz., TCPP(M)) as shuttles. The deprotonated TCPP(M) not only provides nitrogen-based coordination sites to anchor a series of transition metal ions, but also intercalates and diffuses facilely into the interlayer gallery of LDHs by ion exchange. The obtained TCPP(M)@Cu-Al LDHs were then used as solid precursors for the fabrication of a series of heterogeneous catalysts for CO2 hydrogenation via high-temperature calcination. Two restriction forces contributed to the enhanced dispersion of the active species over the catalyst surface structures. Remarkably, the transition metals positioned within the confined space of LDHs significantly affected the catalytic performance of CO2 hydrogenation. Mainly CO, methanol, and methane were found as the C1 products, and their selectivities are highly dependent on the reaction intermediates, as suggested by the in situ DRIFTS study. Moreover, the designed catalysts fabricated via molecular TCPP(M) intercalation exhibited much better performance than the conventional catalysts derived from surface-supported CA-LDHs, due to their better metal dispersion and smaller particle size.

Fabrication of Highly Dispersed Cu-Based Oxides as Desirable NH3-SCR Catalysts via Employing CNTs To Decorate the CuAl-Layered Double Hydroxides.

In this study, three kinds of CuAl-LDO/CNT (LDO, layered double oxide) catalysts were prepared by the assembly of CNTs and CuAl-LDH (LDH, layered double hydroxides) as well as subsequently structural topological transformation. The effects of the assembly method on the surface structure property and the DeNOx performance of the prepared samples were systematically investigated. It was found that three CuAl-LDO/CNT catalysts showed preferable NH3-SCR catalytic performance compared with CuAl-LDO where the catalyst CuAl-LDO/CNTs(I) exhibited optimum NOx conversion (>80%) and N2 selectivity (>90%) within 180-300 °C. Such fine catalytic performance can be attributed to the proper surface acidity and redox ability of the catalyst, which might be correlated with the high dispersion of Cu-based active centers caused by the induced nucleation and effective separation action of LDH by carbon nanotubes. In addition, the outstanding H2O and SO2 resistance of the CuAl-LDO/CNTs(I) catalyst was also obtained because of the synergistic effect between CuAl-LDO and CNTs, which could greatly promote the activation and decomposition of ammonium sulfate at lower temperatures.

Non-enzymatic glucose sensor with high sensitivity based on Cu-Al layered double hydroxides

The Cu-Al layered double hydroxides (CuAl-LDHs) composites were prepared via one-step co-precipitation method and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Glucose could be oxidized electrocatalytically on the CuAl-LDHs composites modified glassy carbon electrode(CuAl-LDHs/GCE) in alkaline solutions as an enzyme-free sensor with high sensitivity (detection limit of 0.02 μmol L−1), fast response (less than 5 s) and wide linear range (0.1–240 μmol L−1). Furthermore, the proposed sensor showed strong anti-interference ability in the presence of dopamine, ascorbic acid, uric acid, acetaminophen and other carbohydrate compounds. The CuAl-LDHs/GCE was used successfully for the determination of glucose in human blood samples.

Mechanochemical synthesis of dodecyl sulfate anion (DS−) intercalated Cu-Al layered double hydroxide

Dodecyl sulfate anion (DS−) was successfully intercalated into the gallery space of Cu-Al layered double hydroxides (LDH) by a non-heating mechanochemical route, in which basic cupric carbonate (Cu2(OH)2CO3) and aluminum hydroxide (Al(OH)3) were first dry ground and then agitated in SDS solution under ambient environment. The organics modified Cu-Al LDH showed good adsorption ability toward 2,4-dichlorophenoxyacetic acid (2, 4-D). The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), CHS elemental analysis and Scanning electron microscopy (SEM). The LDH precursor prepared by ball-milling could directly react with SDS molecules forming a pure phase of DS− pillared Cu-Al LDH, which was not observed with the LDH product through the ion-exchange of DS− at room temperature. The process introduced here may be applied to manufacture other types of organic modified composites for pollutants removal and other applications.

Mechanochemical synthesis of Cu-Al and methyl orange intercalated Cu-Al layered double hydroxides

In this study, a mechanochemical route to synthesize a Cu-Al layered double hydroxide (LDH) and a methyl orange (MO) intercalated one (MO-LDH) was introduced, in which basic cupric carbonate (Cu2(OH)2CO3) and aluminum hydroxide (Al(OH)3) with Cu/Al molar ratio at 2/1 was first dry ground for 2 h and then agitated in water or methyl orange solution for another 4 h to obtain the LDH and MO-LDH products without any heating operation. The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Thermogravimetry (TG), Differential scanning calorimetry (DSC) and Scanning electron microscopy (SEM). The products showed high crystallinity phase of Cu-Al and MO intercalated Cu-Al LDH with no evident impurities, proving that the craft introduced here was facile and effective. The new idea can be applied in other fields to produce organic-inorganic composites.

Sorption of cesium, strontium, and yttrium radionuclides from the aqueous phase on layered double hydroxides

Sorption of 137Cs, 85,90Sr, and 90Y from aqueous solutions on the solid phase of layered double hydroxides (LDHs) and layered double oxides (LDOs) of various compositions was studied. On the solid phase of Mg-Al and Cu-Al LDHs and Mg-Al LDO, the Sr and Cs radionuclides are very weakly sorbed from aqueous solutions containing 10−5 M of the corresponding element (Cs+ or Sr2+). Introduction of EDTA ions into Mg-Al LDH increases the distribution coefficients K d of Sr by a factor of more than 40. After 96-h contact of the solid and liquid phases, K d of radioactive Sr in sorption from aqueous solution on Mg-Al LDH and Mg-Al LDH-EDTA is 2.4 and 100 ml g−1, respectively. The Sr and Y radionuclides are efficiently sorbed from aqueous solutions containing 10−5 M Sr2+ and Y3+ on the Mg-Nd LDH solid phase. After 5-min contact of the solid and liquid phases, K d of Sr exceeds 105 ml g−1. For Y, the distribution coefficients equal to 700–800 ml g−1 are attained after 30-min contact of the solid and liquid phases. Aging of the Mg-Nd LDH precipitate does not affect its sorption properties toward Sr and Y radionuclides. With an increase in the Sr(NO3)2 concentration in the solution from 10−5 to 10−1 M, the distribution coefficients K dz of Sr drastically decrease (virtually to zero) and those of Y change insignificantly.