MgAl-layered Double Hydroxide Research Articles

A novel fluorescent DNA sensor system based on polydopamine modified MgAl-layered double hydroxides

In this work, a novel fluorescent DNA sensor system based on polydopamine (PDA) modified layered double hydroxides (Mg/Al-LDH) was designed and PDA-co-LDH composites were examined for DNA sensing owing to their fluorescence quenching capability. We demonstrated that the fluorescence of ssNDA could be effectively quenched after mixing with PDA-co-LDH composites, while the fluorescence could be recovered after the target DNA was added to form dsDNA. Based on the fluorescence changes, the target DNA can be facilely and quantitatively determined by the DNA sensor system. Based on 3σ method, the detection limit is calculated to be as low as 1.0 pM. Moreover, PDA-co-LDH composites have an excellent sensitivity and selectivity that can discriminate the complementary and mismatched target sequences even for the single-base mismatched target sequences. More importantly, this DNA sensor system could be expected for detection of many other molecules through design DNA sequences.

Double doped cerium-based superhydrophobic layered double hydroxide protective films grown on anodic aluminium surface

Cerium doped MgAl-layered double hydroxide (LDHs) were fabricated directly on the anodic aluminium surface and were further modified by PFDTS (1H, 1H, 2H, 2H perfluorododecyl trichlorosilane) through anion exchange reaction to obtain superhydrophobic characteristics for improved corrosion resistance and self-cleaning properties. PFDTS were hydrolyzed in absolute ethanol to obtain CF3(CF2)9CH2CH2Si(O−)3 groups, which were incorporated inside MgAl-LDH and have shown superhydrophobic characteristics by demonstrating the water contact angle of 156.5°. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Contact angle measurements (CA), and self-cleaning properties were analyzed to characterize the LDHs surface. In addition, the capability of the surface against UV radiation exposures (λ = 310 nm) was measured for 30 days of exposure to understand the outdoor applications of superhydrophobic LDHs. The corrosion resistance properties were measured through Electrochemical impedance spectroscopy (EIS) from 1 h to 1200 h to understand the behaviour of coating and its long-term stability. The CeMgAl-LDHs film grown directly on anodized surface results in better barrier properties, while further modification with PFDTS provide a compact system to provide active corrosion resistance, long-term stability, UV radiation protection, and characteristics of self-cleaning against general household items (coffee, tea, cola, basic media, light acidic solution).

Layered double hydroxide nanosheets as efficient photocatalysts for NO removal: Band structure engineering and surface hydroxyl ions activation

We demonstrated the partial Ni2+ substitution for Mg2+ in Mg2Al-layered double hydroxide nanosheet (Ni/LDH) significantly improved its photocatalytic performance in removing the ppb-level NO pollutant from air. With 25 % of Mg2+ substituted, the Ni/LDH delivered the highest NO removal efficiency of 42.10 % (87.2 % of them were mineralized to nitrate) under UV-light irradiation. Such a robust performance with the low energy input (8 W) made Ni/LDH among the top photocatalysts for NO removal. We evidenced the OH− carried by Ni/LDH transformed to ·OH radicals by trapping the photoexcited holes. This unique feature was intriguing as the OH− at layer surfaces of LDH were abundant, fully exposed and dynamically supplemented by atmospheric water, which endowed Ni/LDH with superior ·OH production capability even under low atmospheric moistures. The positive contribution of Ni2+ arose from its function in optimizing band structure and activating the OH− of LDH, leading to enhanced reactive oxidative species production.

Novel fluoride rechargeable dental composites containing MgAl and CaAl layered double hydroxide (LDH)

ObjectiveThis study aims to incorporate 2:1 MgAl and 2:1 CaAl layered double hydroxides (LDHs) in experimental dental-composites to render them fluoride rechargeable. The effect of LDH on fluoride absorption and release, and their physico-mechanical properties are investigated. Methods2:1 CaAl and 2:1 MgAl LDH-composite discs prepared with 0, 10 and 30wt% LDH were charged with fluoride (48h) and transferred to deionized water (DW)/artificial saliva (AS). Fluoride release/re-release was measured every 24h (ion-selective electrodes) with DW/AS replaced daily, and samples re-charged (5min) with fluoride every 2 days. Five absorption-release cycles were conducted over 10 days. CaAl and MgAl LDH rod-shaped specimens (dry and hydrated; 0, 10 and 30wt%) were studied for flexural strength and modulus. CaAl and MgAl LDH-composite discs (0, 10, 30 and 45wt% LDH) were prepared to study water uptake (over 7 weeks), water desorption (3 weeks), diffusion coefficients, solubility and cation release (ICP-OES). ResultsCaAl LDH and MgAl LDH-composites significantly increased the amount of fluoride released in both media (P<0.05). In AS, the mean release after every recharge was greater for MgAl LDH-composites compared to CaAl LDH-composites (P<0.05). After every recharge, the fluoride release was greater than the previous release cycle (P<0.05) for all LDH-composites. Physico-mechanical properties of the LDH-composites demonstrated similar values to those reported in literature. The solubility and cation release showed a linear increase with LDH loading. SignificanceLDH-composites repeatedly absorbed/released fluoride and maintained desired physico-mechanical properties. A sustained low-level fluoride release with LDH-composites could lead to a potential breakthrough in preventing early stage carious-lesions.

Porous Layered Double Hydroxide/TiO2 Photocatalysts for the Photocatalytic Degradation of Orange II

Layered Double Hydroxide (LDH)/TiO2 nanocomposites with photocatalytic properties were synthesized by both impregnation and the direct coprecipitation of LDH matrices using a colloidal suspension of TiO2 nanoparticles. While the two methods led to an efficient TiO2 nanoparticle immobilization, the direct coprecipitation allowed us to tune the amount of immobilized TiO2 within the materials. The LDH/TiO2 nanocomposites obtained were deeply characterized by chemical analysis (ICP-AES), Powder X-ray diffraction (XRD), Fourier Transformed Infra-Red (FTIR), Thermogravimetric analysis (TGA), and High-Resolution Transmission Electron Microscopy (HRTEM). Clearly, the immobilization of TiO2 by direct coprecipitation promoted a modification of the textural properties and a net increase in the surface area. The crystallized TiO2 nanoparticles can be distinctly visualized by HRTEM at the surface of the layered material. Several parameters, such as the nature of the chemical composition of LDH (ZnAl and MgAl), the method of immobilization and the amount of TiO2, were shown to play a crucial role in the physicochemical and photocatalytic properties of the nanocomposites. The photocatalytic efficiency of the different LDH/TiO2 nanocomposites was investigated using the photodegradation of a model pollutant, the Orange II (OII), and was compared to a pure TiO2 colloidal solution. The degradation tests revealed that the nanocomposite obtained from MgAl LDH at a low MgAl LDH/TiO2 ratio was the most efficient for the photodegradation of OII leading to complete mineralization in 48 h.

Layered Double Hydroxides for Remediation of Industrial Wastewater from a Galvanic Plant

Owing to their structure, layered double hydroxides (LDHs) are nowadays considered as rising materials in different fields of application. In this work, the results obtained in the usage of two different LDHs to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater are reported. The two compounds MgAl-CO3 and NiAl-NO3 have been prepared through a hydrothermal synthesis process and then characterized by means of PXRD, TGA, FESEM, and FTIR spectroscopy. The available wastewater, supplied by a galvanic treatment company, has been analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES), resulting as being polluted by Fe(III), Cu(II), and Cr(VI). The water treatment with the two LDHs showed that chromate is more efficiently removed by the NiAl LDH through an exchange with the interlayer nitrate. On the contrary, copper and iron cations are removed in higher amounts by the MgAl LDH, probably through a substitution with Mg, even if sorption on the OH− functional groups, surface complexation, and/or precipitation of small amounts of metal hydroxides on the surface of the MgAl LDH could not be completely excluded. Possible applications of the two combined LDHs are also proposed.

Synthesis of Arylsulfonyl Benzenediols by Sandwich Type Polyoxometalate Intercalated MgAl-Layered Double Hydroxides in Water at Room Temperature

This paper reports on the preparation of simple and cost-effective nanocomposite that involved intercalation of sandwich-type polyoxometalate (STPOM) anion [(OCe)3(PW9O34)2]12− into Mg/Al layered double hydroxides (donated as Mg3Al–Ce3W18) using an ion-exchange method. The catalytic performance of nanocomposite catalyst was examined in green synthesis of aryl sulfonyl benzene diols via oxidative coupling between 1,2-benzenediols and sodium benzenesulfinates under mild green condition (; in water at room temperature) with good yields (63–75%). Besides, the nanocomposite catalyst exhibited excellent reusability up to five subsequent runs. SEM, EDX and BET were employed to characterize the as-fabricated nanocomposite.

Comprehensive study of the formation of stable colloids of Cu[sbnd]Al layered double hydroxide assisted by double hydrophilic block copolymers

The formation of stable aqueous colloidal suspensions of CuAl layered double hydroxide (LDH) assisted by double-hydrophilic block copolymers was investigated. It was of utmost importance since the direct preparation LDH colloids of controlled size is still a major challenge; moreover, regarding the CuAl system, the mechanism of formation of the LDH phase is not well understood yet. CuAl LDH nanoparticles were obtained by complexing Cu2+ and Al3+ cation mixture (Cu2+/Al3+ = 2) with an asymmetric poly(acrylamide)-b-poly(acrylic acid) block copolymer, followed by metal cation hydroxylation. The mechanism of formation of the CuAl LDH was studied and compared to that of MgAl LDH. ICP-MS analysis of the hybrid polyion complex (HPIC) micelles obtained at increasing complexation ratio, i. e. the ratio of the molar concentration of complexing acrylate group of DHBC to M2+ and Al3+ cations (R = AA/(M2+ + Al3+)), showed higher selectivity of DHBC toward Al3+ and, among M2+ cations, for Cu2+ than for Mg2+. Hydroxylation of the HPIC micelles led to macroscopic precipitates at R values below flocculation thresholds, i. e. R1 = 0.43 for DHBC/Cu-Al and 0.13 for DHBC/Mg-Al suspensions, while stable suspensions were formed above R1. The hydrodynamic diameter (Dh) of the colloids determined by DLS decreased from 160 to 50 nm and from 350 to 50 nm in the DHBC/Cu-Al and DHBC/Mg-Al colloids, respectively, when R increased from R1 to 1. XRD and TEM analyses of the dried colloidal suspensions (R > R1) revealed the presence of CuAl LDH and MgAl LDH phases and elemental analyses confirmed that M(II)/Al = 2. Particle sizes were lower in CuAl LDH than in MgAl LDH. Titration curves corresponding to progressive hydroxylation of DHBC/Cu(or Mg)-Al solutions at fixed complexation ratio R allowed establishing that formation of CuAl and MgAl LDH obeyed to a similar sequential mechanism in two steps but involving different aluminum hydroxide precursors according to the different pH values of precipitation. CuAl LDH was obtained by combination of aluminum poly(hydr)oxide species with dissolved copper-based species at pH ~ 5.5, while MgAl LDH resulted from combination of Al(OH)3 and dissolved Mg2+ at pH ~ 8.

A new method for removal of nitrogen in sewage sludge-derived hydrochar with hydrotalcite as the catalyst

The high content of nitrogen in hydrochar produced from hydrothermal carbonization (HTC) of sewage sludge (SS) leads to serious NOx pollution when the hydrochar is used as a solid fuel. Mg-Ga layered double hydroxides (LDHs), Mg-Al LDHs and their calcined samples (layered double oxides, LDO) were prepared. The LDHs and LDO all can notably promote the removal of nitrogen element, in which organic-N was transferred to NH4+-N to cause increasing pH value. Mg-Al LDO showed the highest efficiency for the removal of nitrogen among the catalysts. The thermal decomposition of the N-organic matter with acidic sites in catalyst was the key step to release NH3. The key role of basic sites in Mg-Al LDO was that it can effectively destroy the cell wall and extracellular polymeric substances structure. The lipid-like substance did not participate in the carbonization reaction, but they can be absorbed by the hydrochar. Partial SS floc directly transformed to hydrochar according to “solid-solid” reaction. The reaction pathways of remove nitrogen were proposed.

Biocorrosion resistance and biocompatibility of Mg–Al layered double hydroxide/poly-L-glutamic acid hybrid coating on magnesium alloy AZ31

It is of necessity to seal porous layered double hydroxide (LDH) coating on bioabsorbable magnesium alloys to further enlarge its long-term protection using an organic top layer with good biocompatibility. An Mg-Al LDH coating sealed by poly-l-glutamic acid (PGA) is prepared on the AZ31 magnesium alloy. The LDH coating and PGA coating are synthesized by hydrothermal treatment and vacuum freeze-drying method. The structure and morphology of the coatings are characterized by means of X-ray photoelectron spectrometer (XPS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electronic microscope (FE-SEM) and energy dispersive X-ray spectrometer (EDS). The corrosion protection afforded by the coatings is measured using electrochemical polarization and impedance spectroscopy and hydrogen evolution tests. The results indicate that the appropriate addition of PGA can postpone the time that pH values reach the minimum. The hybrid coatings effectively provide a corrosion protection for the AZ31 alloy. An acceptable cytocompatibility for mouse embryonic fibroblasts (NIH 3T3) of the hybrid coating is shown by methyl thiazolyl tetrazolium (MTT) assay and live/dead staining. Finally, a biodegradation mechanism of the coating is proposed and discussed.

A biocompatible nanoplatform formed by MgAl-layered double hydroxide modified Mn3O4/N-graphene quantum dot conjugated-polyaniline for pH-triggered release of doxorubicin.

In this work, for the first time, a novel pH-sensitive biocompatible multifunctional nanocarrier was fabricated by the combination of MgAl-layered double hydroxide, Mn3O4 nanoparticles, N-graphene quantum dot and polyaniline (PANI/N-GQD/MO/LDH) for doxorubicin (DOX) delivery in breast cancer cells. Electrochemical techniques, including cyclic voltammetry (CV) and differential pulse voltammetry (DPV), were employed for proving the surface modification process. The integration of polyaniline on the surface of the nanocarrier provides ultrahigh DOX encapsulation up to 90% and possesses a slow-release behavior (4% after 72h) under normal physiological conditions. However, releasing ~80% of the drug in a low-pH environment as a model of the extracellular tumor environment happened, presenting a pH-triggered release. The cell viability using MTT assay reveals that the DOX/PANI/N-GQD/MO/LDH had no apparent adverse effect on the viability of human L929 normal cells. Furthermore, a significant inhibition ratio against human breast cancer cell lines (MCF-7) was observed when the cells were treated with the DOX-loaded PANI/N-GQD/MO/LDH nanocarrier, suggesting that this nanocarrier could increase the therapeutic efficacy of DOX. The hemolysis rates (HRs) of human fresh blood, coagulation prothrombin time (PT), activated partial thromboplastin time (APTT), and complement activation (C3 and C4 levels) revealed the excellent blood compatibility of the nanocarrier. Thus, the nano-vehicle designed in this study could be used as a novel multifunctional and synergistic, pH-triggered platform for delivering various anti-cancer drugs and other biomedical applications.

Fabrication of Mg-Al Layered Double Hydroxide Thin Membrane for All-Solid-State Alkaline Fuel Cell Using Glass Paper as a Support

Layered double hydroxides (LDHs) are promising solid electrolytes for all solid-state alkaline fuel cells (AFCs) because of inorganic clay-like materials. However, LDHs were usually obtained as powder, and the formation of thin membranes as a separator of a fuel cell is rather difficult. In this study, a glass paper, non-woven fabric of fine glass fibers with more than 90% porosity, was used as a support for Mg-Al LDH powder, and self-standing, thin membranes for all solid-state AFCs were fabricated. Crystals of Mg-Al LDH were deposited in the inside of the glass paper by repeated immersion in Mg-Al LDH-dispersed solution and drying. Thickness of the obtained Mg-Al LDH thin membrane was about 150 µm, and LDH layer showed c-axis orientation because of the plate-like structure. The H2-O2 fuel cell using the Mg-Al LDH thin membrane as an electrolyte showed open circuit voltage of more than 0.9 V, indicating that the Mg-Al LDH thin membrane is dense and has high gas barrier property. The H2-O2 fuel cell using the Mg-Al LDH thin membrane showed higher power density compared with that using pelletized Mg-Al LDH powder as the electrolyte. The glass paper is proved to be very effective support for making thin Mg-Al LDH electrolyte membrane.

Synthesis and fine spectroscopy tuning of the hyperspectral simulation material based on organic anions intercalated Mg-Al layered double hydroxide

Organic anions have been intercalated into the interlayer of Mg-Al layered double hydroxides (LDHs) via a hydrothermal method to tune the visible and near-infrared reflection spectrum of hybrid pigments based on LDHs. The prepared samples were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric-differential scanning calorimetry, visible and near-infrared spectrophotometry, and CIE 1976 L*a*b* color scales. The effects of the intercalated organic anions on the structure, morphology, color, and spectral characteristics of Mg-Al LDH materials were systematically investigated. The results show that the colored anions of acid green (AG) and acid yellow (AY) have been successfully intercalated into the interlayer space of LDHs through the anion displacement process. The visible light reflection spectrum of LDH matrix can be easily tuned by adjusting the intercalated concentration of anions and the relative ratio of AG and AY, which leads to the color of prepared samples changing from the original white into blue, yellow, green, and dark black. Combined with the color adjusting ability of organic anions and the high hydroxyl property of LDH substrate, the typical visible and near-infrared spectral characteristics of natural green plants can be accurately simulated. The correlation coefficient of spectrum shape between the prepared pigment and green plant in the whole range of 400–2500 nm is as high as 0.94. Moreover, the thermal stability of LDH materials is improved by the intercalated organic anions, whose spectral properties can withstand high temperatures of at least 250 °C. The hybrid materials could be used as a functional pigment to prepare green camouflage coatings, showing their potential application in the field of hyperspectral camouflage.

Ultrahigh flux of graphene oxide membrane modified with orientated growth of MOFs for rejection of dyes and oil-water separation

Metal organic frameworks (MOFs) has broad application prospect in separation, catalysis, and adsorption. By a facile green method, we successfully fabricated prGO@cHKUST-1 composite membrane with the modification of dopamine and orientated growth of MOFs. Mg/Al-layered double hydroxides (Mg/Al-LDHs) was used as a modulator to obtain cubic HKUST-1 (cHKUST-1) with excellent morphology and special properties. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) etc. characterization illustrated successful synthesis of cHKUST-1 and composite membranes. Cubic HKUST-1 can tune the inter-layer spacing of graphene oxide (GO) leading increase in hydrophilicity and flux of the membrane. Meanwhile, the reduction effect of PDA and intercalation effect of MOFs could change the stacked way of GO layers, forming several fuzzy pores and more active sites on membrane surface. The prGO@cHKUST-1 membrane has an excellent rejection for methylene blue (MB) (99.5%) and Congo red (CR) (71.2%). Moreover, the modified membrane exhibited 10 and 5 times higher permeation flux than that of original GO membrane and prGO membrane, respectively. Thus, using orientated growth of MOFs to synthesize GO based composite membrane will provide useful insights in ultrahigh permeation flux membranes of dye and oil-water emulsion separation.

Synthesis of novel core@shell of MgAl layered double hydroxide @ porous magnetic shell (MgAl-LDH@PMN) as carrier for ciprofloxacin drug

MgAl-layered double hydroxide (MgAl-LDH) derived from a metal-organic framework (MOF), was synthesized by hydrothermal method. A biocompatible MgAl-LDH core-porous magnetic nanoparticles (PMN) shell (MgAl-LDH@PMN) was synthesized using solvothermal method and modified with amino groups as a potential pH-controlled drug delivery carrier. MgAl-LDH with a sheet-like morphology was coated with porous Fe3O4 or porous magnetite via the functionalization of (3-aminopropyl) triethoxysilane using a post-synthesis route (MgAl-LDH@PMN-NH2). The core@shell was characterized using a range of techniques such as x-ray diffraction patterns (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic light scattering (DLS) and transmission electron microscopy (TEM). The MgAl-LDH@PMN-NH2 core@shell indicated a spherical morphology and good porosity. Ciprofloxacin (CIPRO) drug was incorporated in the pore channels and surface of the MgAl-LDH@PMN-NH2 and the drug release properties were examined at pH 4.0 and 7.4. The TG results demonstrated that drug loading contents on the modified carrier was 40%. The delayed release property exhibited by MgAl-LDH@PMN-NH2 was attributed to the strong interactions of the drug molecules with the surface amino-functionality and the charged LDH surface. The characterization and drug release was also investigated for the un-modified carrier (MgAl-LDH@PMN) with drug loading 15% under identical conditions. The porosity and functionalization of the PMN shell and the surface charge density of the layered structure of MgAl-LDH are the major reasons for the controlled release of the CIPRO drug. Moreover, the favorable delay in drug release from both core@shells at pH 4 was attributed to the high level of ionization and dissolution. Biocompatibility was evaluated by examination of the cell line MCF-7 response to the un-modified and modified carriers.

Comparison of Remazol Brilliant Blue Reactive Adsorption on Pristine and Calcined ZnAl, MgAl, ZnMgAl Layered Double Hydroxides

Layered double hydroxides (LDHs) are promising adsorbents for the removal of various contaminants from water. However, a comprehensive understanding of how ternary LDHs differ from the divalent ones in terms of dye adsorption capacity and the underlying mechanisms still remain unknown. Remazol brilliant blue reactive (RBBR) adsorption on pristine and calcined (C) ZnAl, MgAl, and ZnMgAl LDHs were comprehensively investigated for the first time in this study. The characteristics of the pristine and calcined samples were established with X-ray diffractometer, Fourier transform infrared spectrophotometer, zeta potential analyzer, and Brunauer–Emmett–Teller method. A considerably larger adsorption capacity was obtained with pristine MgAl (220 mg/g) and ZnAl (191 mg/g) compared to that of ZnMgAl (164 mg/g) at all studied initial dye concentrations (10–250 mg/L) and solution pH (3–12). However, when the LDH samples were calcined, the largest RBBR mass adsorbed was achieved with ZnMgAl-C (263 mg/g) followed by MgAl-C (247 mg/g) and ZnAl-C (236 mg/g). In comparison to the pristine samples, the faster adsorption rate and higher adsorption capacity of the calcined samples were attributed to the large specific surface area and enhanced electrostatic interactions due to the higher positive charge obtained after calcination. ZnMgAl-C had the largest surface area and the charge, explaining its superior adsorption capacity over the divalent LDHs. Pseudo-first-order, pseudo-second-order, and Elovich models described the kinetics data well while Freundlich and Redlich–Peterson isotherms suitably fit to the equilibrium data for the pristine and calcined LDHs. Surface adsorption via electrostatic interactions was found to be the effective mechanism for RBBR adsorption on all pristine and calcined LDHs while intercalation was not.

In vitro degradation and cytocompatibility of a low temperature in-situ grown self-healing Mg-Al LDH coating on MAO-coated magnesium alloy AZ31

Basically, Mg–Al layered double hydroxide (LDH) coatings are prepared on the surface of micro-arc oxidation (MAO) coated magnesium (Mg) alloys at a high temperature or a low pH value. This scenario leads to the growth rate of LDH coating inferior to the dissolution rate of the MAO coating. This in turn results in limited corrosion resistance of the composite coating. In this study, a Mg–Al LDH coating on MAO-coated Mg alloy AZ31 is prepared through a water bath with a higher pH (13.76) at a lower temperature (60 °C). FE-SEM, EDS, XRD, XPS, and FT-IR are applied to analyze the surface morphology, chemical compositions, and growth process. Electrochemical polarization, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests are employed to evaluate the corrosion resistance of the samples. The results disclose that the MAO coating is completely covered by the nanosheet-structured LDH coating with a thickness of approximately 3.8 μm. The corrosion current density of the MAO-LDH composite coating is decreased four orders of magnitude in comparison to its substrate; the presence of a wide passivation region in anodic polarization branch demonstrates its strong self-healing ability, indicating the hybrid coating possesses excellent corrosion resistance. The formation mechanism of the LDH coating on the MAO-coated Mg alloy is proposed. Furthermore, the cytocompatibility is assessed via an indirect extraction test for MC3T3-E1 pre-osteoblasts, which indicates an acceptable cytocompatibility of osteoblasts for the composite coating.

Crosslinking acrylamide with EDTA-intercalated layered double hydroxide for enhanced recovery of Cr(VI) and Congo red: Adsorptive and mechanistic study

We prepared ethylenediaminetetraacetic acid (EDTA)-intercalated MgAl-layered double hydroxide (LDH-EDTA), then grafted acrylamide (AM) to the LDH-EDTA by a cross-linking method to yield a LDH-EDTA-AM composite; we then evaluated its adsorptive ability for Congo red (CR) and hexavalent chromium (Cr(VI)) in single and binary adsorption systems. The adsorption process on LDH-EDTA-AM for CR and Cr(VI) achieved equilibrium quickly, and the removal efficiencies were minimally affected by initial pH. The maximum uptake quantities of CR and Cr(VI) on LDH-EDTA-AM were 632.9 and 48.47 mg/g, respectively. In mixed systems, chromate removal was stimulated by the presence of CR, while the adsorption efficiency of CR was almost not influenced by coexisting Cr (VI). The mechanisms involved electrostatic attraction, surface complexation, and anion exchange for the adsorption of both hazardous pollutants. In the Cr(VI) adsorption process, reduction also took place. The removal efficiencies in real contaminated water were all higher than those in the laboratory solutions.

Engineered biochar with anisotropic layered double hydroxide nanosheets to simultaneously and efficiently capture Pb2+ and CrO42− from electroplating wastewater

Cationic and anionic heavy metal contaminants generally co-exist in practical industrial effluent, and simultaneously removal of these species is a bottleneck for most of the bio-adsorbents because of their contrary charge. In this work, pinewood sawdust derived engineered biochar (BC) was fabricated with MgAl layered double hydroxide (MgAl-LDH) nanosheets, which could efficiently and simultaneously capture heavy metal cations and oxyanions from wastewater. The synergetic effect between loaded MgAl-LDH and BC substantially improves its adsorption performance towards both cationic and anionic contaminants, i.e., Pb2+ and CrO42−. The adsorption capacity of MgAl-LDH/BC for Pb2+ reached 591.2 mg/g, which is 263% higher than that of BC, and in the case of CrO42−, the adsorption capacity is 330.8 mg/g, 416% higher than that of BC. The elimination of Pb2+ was mainly attributed to forming complexations with surface functional groups. While for oxyanions removal, CrO42− can be reduced to Cr3+ by functional groups, and then generated Cr3+ could replace Al3+ via morphic substitution, consequently formed an MgCr-LDH structure. Further, in the continuous fixed-bed column study, 225 bed volume of simulating electroplating wastewater co-existed with Pb2+ and CrO42− can be efficiently treated. Hence, this study sheds light on the engineered biochar design to efficiently and simultaneously capture heavy metal cations and oxyanions and its feasibility on real wastewater purification.

Purification of diazinon pesticide by sequencing batch moving-bed biofilm reactor after ozonation/Mg-Al layered double hydroxides pre-treated effluent

The catalytic ozonation process (COP) using MgAl-layered double hydroxide (MgAl-LDH) nanoparticles was used as a pre-treatment of the sequencing batch moving-bed biofilm reactor (SBMBBR) to degrade diazinon pesticide from aqueous solutions. The structure of the synthesized MgAl-LDH was investigated by X-ray diffraction pattern (XRD), field-emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS) mapping, and Fourier-transform infrared spectra (FTIR). The response surface methodology (RSM) was adopted to optimize the COP variables, including LDH dose (0–1000 mg/L), initial diazinon concentration (50–200 mg/L), initial pH (3–10), and reaction time (10–90 min). Under the optimal conditions, COP effluent was introduced to the SBMBBR for further purification. The dispersive liquid–liquid microextraction (DLLME) method was employed to extract diazinon from aqueous samples. The GC-mass analysis was performed to determine by-products during diazinon degradation reactions. To evaluate system performance, the removal efficiency of chemical oxygen demand (COD), total organic carbon (TOC), and diazinon was compared in processes of aeration, single ozonation process (SOP), COP, SBMBBR, and COP/SBMBBR. The formation of the LDH nanoparticles was confirmed by XRD and EDS mapping analysis. In the COP reactor, under optimal conditions (initial diazinon concentration: 120 mg/L, pH: 8.25, LDH dose: 750 mg/L, and reaction time: 70 min), the removal efficiency of diazinon, COD, and TOC equaled 92, 80, and 74%, respectively. The effluent of COP reactor was treated further in the SBMBBR system with the pH of 6.5–7, hydraulic retention time (HRT) of 24 h, mixed liquor suspended solids attached to bio-carriers (MLSSatt.) of 4500 mg/L, mixed liquor volatile suspended solids attached to bio-carriers (MLVSSatt.) of 3600 mg/L, MLSS of 950 mg/L, and MLVSS of 830 mg/L. The use of COP/SBMBBR resulted in the complete degradation of diazinon pesticide and COD and TOC removal efficiency of 99.37 and 99%, respectively. Therefore, this method can be used for the purification of non-biodegradable industrial wastewater.