Zn-Al Layered Double Hydroxides Research Articles

Effect of concentration in the equilibrium and kinetics of adsorption of acetylsalicylic acid on ZnAl layered double hydroxide

• Acetylsalicylic acid adsorption onto ZnAl layered double hydroxide was studied. • The structure of ZnAl was partially reconstructed during kinetics study. • Drug adsorption isotherm was better fitted by Sips model. • Thermodynamic evaluation revealed that the process is exothermic and spontaneous. • The thermal treatment after adsorption allowing reuse for up to 6 cycles. In this work, the adsorption of pharmaceutical acetylsalicylic acid onto calcined ZnAl-layered double hydroxide was studied. The adsorbent solid was synthesized by the continuous coprecipitation method and characterized by the X-ray diffraction (XRD) and FTIR techniques. Adsorption batch experiments were carried out aiming to obtain the best adsorbent solid concentration, to determine the equilibrium time and the best isotherm model. The behavior of the adsorbent after the kinetics tests through XRD and FTIR and the adsorbent regeneration by thermal treatment were evaluated. The results showed that a 90% removal of acetylsalicylic acid was achieved using a solid concentration of 3 g L −1 and 45 min residence time. Adsorption kinetics is driven by two processes: the adsorption on the external surface and by reconstruction phenomenon of LDH structure “memory effect”. XRD patterns and FTIR shows that the ZnAl-C was reconstructed by acetylsalicylic acid after the adsorption. Adsorption equilibrium was studied in different temperatures as 15, 25, and 35 °C, where it revealed that Sips equation was more suitable to describe the isotherms behavior. The thermal regeneration provided the restructuring of the solid from the hydrotalcite phase to the mixed oxide, allowing its reuse up to 6 cycles. The results indicate that the process presents significant potential for the removal of acetylsalicylic acid.

Use of ZnAl-Layered Double Hydroxide (LDH) to Extend the Service Life of Reinforced Concrete.

This work investigated the use of ZnAl-layered double hydroxide (LDH) intercalated with nitrate or nitrite ions for controlling the corrosion of steel in reinforced concrete. The work started by analyzing the stability of the powder in the 1–14 pH range and the capacity for capturing chloride ions in aqueous solutions of different pH. The effect of the ZnAl-LDH on the corrosion of steel was studied in aqueous 0.05 M NaCl solution and in mortars immersed in 3.5% NaCl. It was found that the LDH powders dissolved partially at pH > 12. The LDH was able to capture chloride ions from the external solution, but the process was pH-dependent and stopped at high pH due to the partial dissolution of LDH and the preferential exchange of OH– ions. These results seemed to imply that ZnAl-LDH would not work in the alkaline environment inside the concrete. Nonetheless, preliminary results with mortars containing ZnAl-LDH showed lower penetration of chloride ions and higher corrosion resistance of the steel rebars.

Adsorptive potential of Zn–Al and Mg–Fe layered double hydroxides for the removal of 2–nitrophenol from aqueous solutions

Two layered double hydroxides (LDH) of the type Zn–Al and Mg–Fe were synthesized, characterized and used as adsorbents to uptake 2–nitrophenol (2–NP) from aqueous solutions. XRD, FTIR, SEM, EDS, AFM and N2 adsorption/desorption curves were used to characterize the Zn–Al–LDH and Mg–Fe–LDH. The potential of both layered double hydroxides to adsorb 2–NP was investigated by adsorption kinetics, equilibrium, thermodynamics and consecutive adsorption/desorption cycles. The characterization indicated a high crystallinity degree and a well–organized and lamellar structure, confirming the efficiency of the synthesis. Elovich was the better kinetic model to describe the 2–NP adsorption onto Zn–Al–LDH, while Pseudo–second order was the best for Mg–Fe–LDH. For both LDHs, the adsorption equilibrium followed the Freundlich model. The process was endothermic, being the maximum adsorption capacities of 290 and 165 mg g–1 for Zn–Al–LDH and Mg–Fe–LDH, respectively. LDHs can be applied for five adsorption/desorption cycles with excellent adsorption capacities. It can be concluded that Zn–Al–LDH and Mg–Fe–LDH are promising materials to treat waters and wastewaters containing 2–nitrophenol

In situ electrochemical synthesis of Zn-Al layered double hydroxides for removal of strontium

In situ electrochemical synthesis method of Zn-Al layered double hydroxides (LDHs) was used to treat the simulated strontium containing liquid radioactive waste (LRW) from nuclear power plants. The removal rate of strontium can reach 98.48±0.20 % (the adsorption capacity is 0.45 mg/g) under the optimal experimental conditions of reaction temperature of 60 °C, reaction time of 240 min, Al electrode current density of 45 mA/cm2, Zn/Al current ratio of 3:1 and initial pH of 10. The composite samples were characterized by XRD, FT-IR and SEM. The results of the characterization and the leaching experiments indicated that Zn-Al LDHs was the major phase in the composite samples, and strontium was removed by substituting the zinc in the crystalline lattice of Zn-Al LDHs or by bonding with hydroxyl on the surface or carbonate in the interlayer of Zn-Al LDHs. In situ electrochemical synthesis method of Zn-Al LDHs has been proved feasible for the removal of strontium in LRW.

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.

Ciprofloxacin-intercalated layered double hydroxide-in-hybrid films as composite dressings for controlled antimicrobial topical delivery.

Films based on biopolymers and loaded with antimicrobial agents are convenient pharmaceutical dosage forms for topical application. Inorganic carriers loaded with these agents lead to composite materials, which combined with polymers produce further functionality. Here, hybrid composite films based on layered double hydroxide (LDH) and hyaluronan (HS) as ciprofloxacin (Cip) delivery systems were studied as an alternative for prophylaxis and treatment of opportunistic infections in wounds. Cip-intercalated Zn-Al LDH (LDH-Cip), with high drug loading and crystallinity, were obtained by a precipitation at variable pH method, and then included in a HS dispersion for obtaining the hybrid composite films by solvent casting. Physicochemical characterization of films showed that a composite material where the HS acted as matrix and LDH-Cip aggregates acted as filler were obtained. LDH-Cip were uniformly dispersed along the (LDH-Cip)/HS films, which exhibited roughness in their surface, increasing their swelling capacity in PBS pH=5.8. Controlled releases of Cip toward PBS at pH=5.8 and 7.4 were obtained, and the best fits for the release profiles were found with Higuchi and Korsmeyer-Peppas models, respectively. (LDH-Cip)/HS films exhibited antimicrobial activity against S. aureus. These films would then provide sustained release of Cip after topical administration, maintaining a suitable level of antibacterial activity, combined with the wound healing properties of the HS. The interesting properties shown by the (LDH-Cip)/HS films make them a promising alternative for application in skin wounds.

Designing Dual-Function Nanostructures for Water Purification in Sunlight

The current study aims at combining two building blocks together into well-designed nanostructures to act as dual-function materials; active photocatalysts in sunlight and effective adsorbents for increasing the efficiency of water purification. By these nanostructures, we could avoid the drawbacks of the existing technologies for water purification and remove the industrial pollutants by a dual process; adsorption and photocatalytic degradation. In this trend, Zn-Al layered double hydroxides (LDHs) are combined with graphene oxide to produce a series of nanolayered structures. These nanolayered structures are effective for converting Zn-Al LDHs to be photo-active in sunlight through decreasing its band gap energy from 5.5 eV to 2.5 eV. In addition, these nanolayered structures caused complete decolorization and mineralization of green dyes in sunlight through accelerating the reaction rate of the photocatalytic degradation of dyes seven times higher than that of the pure Zn-Al LDHs. In the same time, they improved the adsorption process of green dyes through creating new micro- and meso-porous structures and high surface area for Zn-Al LDHs. Finally, the well-designed nanostructures between Zn-Al LDHs and graphene oxide led to converting non-photoactive materials to be active in the visible light in addition to a complete and fast removal for organic pollutants.

Advanced Interface Engineering of CH3NH3PbI3 Perovskite Solar Cells: The Unique Role of Layered Double Hydroxide Precursor

Top-performing metal halide perovskite solar cells (PSCs) with a solar-to-electric power conversion efficiency (PCE) beyond 22% often are fabricated using sequential deposition method under a controlled atmosphere in a glovebox. Meanwhile, a maximum efficiency of 13.59% was reported for CH3NH3PbI3-based PSC using a vapor-assisted solution processing method (VASP) at fully ambient air condition (in terms of both atmosphere and pressure). Herein, we introduce island-like ZnAl-layered double hydroxide (ZnAl-LDH) precursor as middle layer arrays assembling onto the TiO2 nanoparticles (NPs) of mesoporous TiO2 (mp-TiO2) texture to obtain a surged PCE up to 18.54% with a significant performance improvement of 36.4% for fully ambient VASP processed PSCs. Moreover, this enables us to fabricate hole transporting material-free PSC with a maximum efficiency of 14.45% by using ZnAl-LDH permeated mp-TiO2 as the underneath scaffold. The synergistic effect between ZnO and ZnAl2O4 semiconductors—resulting from LDH calcination—and TiO2 NPs leads to more effective electron extraction, reduces electron back transfer as a recombination barrier, and acts as an interfacial barrier between the UV-photocatalytically active TiO2 NPs and perovskite film as well.

Effects of Cu2+incorporation on ZnAl-layered double hydroxide

The incorporation of copper affects the particle size of LDHs and the coordination number of aluminum.

Room-temperature efficient NO2 gas sensors fabricated by porous 3D flower-like ZnAl-layered double hydroxides

Three-dimensional (3D) flower-like zinc and aluminum-sodium dodecyl sulfate-layered double hydroxides (ZnAl-SDS-LDHs) intercalated by anions were prepared using a simple one-step hydrothermal method.

Stimulation of [formula omitted]transition of g-C3N4 through ZnAl-layered double hydroxide for solar light assisted phenol degradation

The structural framework of graphitic carbon nitride (g-C3N4) was tuned with Zinc Aluminium layer double hydroxide (ZnAl-LDH), and its photocatalytic activity was investigated through solar light assisted phenol degradation of real effluent. The modified g-C3N4 (70%g-C3N4/ZnAl-LDH) possess more efficient inhibition of electron and hole pairs resulting in red shifting of absorption edge which stimulates the n−π∗ electronic transition. Morphological studies confirm that the LDH flocks consistently covered the g-C3N4 sheets affirming a substantial collaboration between two-layered material through electrostatic interlink and charge exchange synergy. Furthermore, 70%g-C3N4/ZnAl-LDH have an increased surface area of 26.292 m2/g and a reduced bandgap energy of 2.55 eV, which results in enhanced photocatalytic activity. The results of experimental study indicate that after 300 min of illumination in slight acidic condition, with 1.5 g/L chemical oxidant dose at 3 L/h reactor flowrate, 70%g-C3N4/ZnAl-LDH exhibits 79.35% degradation of phenol, and under same conditions, g-C3N4 confers 61.25% degradation.

The effect of interlayer spacing on the inhibitor release capability of layered double hydroxide based nanocontainers

Abstract Layered double hydroxide (LDH) nanoparticles are utilized as nanocontainers for reserving corrosion inhibitors in order to construct a controlled release system with targeted delivery of inhibitive compounds on the corrosion sites of metal. In this way, the NO3− intercalated Zn–Al LDH nanoparticles were synthesized through the co-precipitation route with different interlayer spacing by changing the pH of synthesis. The structure and interlayer spacing were characterized by X-ray diffraction, Fourier transforms infrared spectroscopy, Field emission scanning electron microscopy and high-resolution transmission electron microscopy. The outcomes showed that the greatest interlayer spacing belonged to the LDH particles synthesized at pH = 9.5 ± 0.5. The relation between the interlayer spacing and inhibitor release performance is discussed and conceptualized for the first time in this study. Results revealed that the structure and interlayer spacing strongly depends on the pH of the synthesis process. It was found that the synthesis pH is the most influential parameter affecting the inhibitor release by changing the interlayer spacing and ion charge density. Moreover, the LDH synthesized at pH = 9.5 ± 0.5 with a higher interlayer spacing exhibited the best corrosion inhibition performance. The results from surface characterizations also confirmed the formation of a protective film over the mild steel surface. The obtained material is believed has great potential being an environmentally friendly nanocontainer or nanopigment. It is thus recommended that the obtained material can be utilized to inhibit the metals from corrosion and provide ion-exchange via harsh ions of saline solution at the onset of corrosion.

A novel strategy to construct a visible-light-driven Z-scheme (ZnAl-LDH with active phase/g-C3N4) heterojunction catalyst via polydopamine bridge (a similar "bridge" structure)

A novel strategy to construct a visible-light-driven Z-scheme heterojunction catalyst was employed by crosslinking ZnAl-layered double hydroxide (ZnAl-LDH) nanosheets with the active phase on carbon nitride (g-C3N4) substrates via a polydopamine bridge (a similar "bridge" structure). In this paper, multiple optical and electrochemical detection methods indicated that the 0.5P-LDH_500CN photocatalyst demonstrated excellent visible-light absorption properties, photo-generated electron-hole separation ability and photocatalytic activity for p-nitrophenol under visible-light (> 420 nm), etc. A Z-scheme charge transfer mechanism via PDA bridge was proposed to achieve heterojunction charge separation. This mechanism involved the recombination of photo-induced electrons directly on the ZnAl-LDH_500 valence band through the PDA channel and the holes were captured at the conduction band energy level of the g-C3N4. The detection of active species, including O2-, h+ and OH, further proofed the Z-scheme charge transfer mechanism, which could be speculated that all active species affected the photocatalytic reaction with the order of h+ >OH >O2-. Meanwhile, this work also exposed that the formation of active phase in ZnAl-LDH could synergize with PDA to promote the application of visible-light-active photocatalysts based on g-C3N4 materials in high-efficiency energy.

Preparation of Flower-Like Zn-Al Layered Double Hydroxides as Anode Materials with Improved Electrochemical Performance

In this account, a facile approach for preparation of 3D self-assembled flower-like Zn-Al layered double hydroxides (Zn-Al LDHs) through a one-step hydrothermal method is demonstrated, and the resulting material is successfully utilized as negative electrodes of next-generation Zn secondary batteries. The flower-like Zn-Al LDHs possess larger specific surface area and better ion diffusion channel. Due to the unique flower-like nanostructure, the resulting flower-like Zn-Al LDHs exhibit higher charging efficiency and better cycle performance. This is concluded from the combined data of serial electrochemical tests based on galvanostatic charge-discharge tests and cyclic voltammetry (CV) tests. The galvanostatic charge-discharge tests reveals that flower-like Zn-Al LDHs maintained 95.7% of the initial specific capacity after 600 cycles.

Synthesis and characterization of Zn–Al LDHs/activated carbon composite and its adsorption properties for phosphate and nitrate ions in aqueous medium

Phosphate and nitrate ions are emerging trace pollutants and have been perceived in groundwater, surface water, and water sources. In the present work, a layered double hydroxides (LDHs) of the binary composite Zn–Al LDHs wrapped into activated carbon (Banana bract) (BBAC@Zn–Al LDHs) composite was synthesized via co-precipitation method. The prepared adsorbent was evaluated for the removal performance of phosphate and nitrate ions from aqueous medium. The fabricated composite was examined by SEM, XRD, FTIR, TGA-DSC, EDAX with mapping images and BET techniques. The effects of adsorbent dosage, solution pH, shaking time, temperature and co-ions on phosphate and nitrate adsorption have been investigated. Kinetics of the adsorption process was studied using diffusion and reaction-based kinetic models. The equilibrium isotherm study was performed by Freundlich, Dubinin–Radushkevich and Langmuir isotherm models. BBAC@Zn–Al LDHs composite showed good reusability and stability until the five cycles but remained inactive after the seven cycles. The BBAC@Zn–Al LDHs composite and anions interacted via the following possible mechanisms: electrostatic attraction, surface complexation, and ion exchange. This study paved the new route for designing a novel LDHs wrapped porous carbon adsorbent and exposed that as an efficient and low-cost adsorbent to control the phosphate and nitrate pollution in water.

Development of Highly Ion-Conductive Layered Double Hydroxide As Electrolyte for Solid-State Alkaline Fuel Cells

Layered Double Hydroxides (LDHs) have been studied by many researchers for their interesting properties such as ion exchangers, adsorbents, polymer stabilizer, catalyst, and so on. LDHs are well known as anionic clays include anion species and water molecules in the interlayer which consist of positively charged metal hydroxide layers. It was reported that some types of LDHs prepared by co-precipitated method have high OH- conductivity and high performance as electrolyte for Alkaline Fuel Cells (AFCs)1). On the other hand, it is necessary to develop a newly industrial LDH synthesis method which enables to synthesize the particle and the composition uniformly. Homogeneous precipitation method with Urea is one of the general and promising LDH synthesis method to prepare the uniform LDH, in which pH controlled by hydrolysis of Urea. However only CO3 2- type LDHs are formed by the method. Therefore, we developed the new type synthesis named “decarboxylation method” that enables to synthesize LDH with high crystallinity and selective anion species in inner layer from precursor compounds in one pot. Prepared samples were measured by ICP and XRD to determine the compositions and structures, respectively, and observed by FE-SEM. Several intercalated anion (CO3 2-, SO4 2-, NO3 -, and Cl-) type M(II) (Zn2+, Co2+, and Ni2+)-Al(III)LDHs were successfully prepared by the decarboxylation method with highly crystallinity and uniform particle size distribution. The ionic conductivities on prepared LDHs were measured by the AC impedance method. Each NO3 - type LDH has remarkably higher ionic conductivity than another type LDHs. The NO3 - type Zn-Al LDH has highest conductivity than another cation type LDHs, and its conductivity is via 16 mS/cm at 80 oC under R.H.80%. 1) Y. Furukawa, K. Tadanaga, A. Hayashi, and M. Tatsumisago, Solid State Ionics, 192, 185-187 (2011).

Chloride intercalated Zn-Al layered double hydroxide nanoparticles: novel photoluminescent colloids

The chloride intercalated Zn-Al Layered Double Hydroxides (LDH) synthesized by coprecipitation method followed by hydrothermal route manifest the unexpected photoluminescent properties in their colloids. Constant pH (≈5) and the higher stirring rate were the extraneous factors which affect the LDHs particle size. Optimal Hydrothermal condition was found to be 70° for 7 h. XRD analysis reveals the Rhombohedral phase and TEM reveals average particle size 5–6 nm of Zn-Al LDH. FEG-SEM depicts its hexagonal plate-like structure and EDS focus on the elemental composition of Zn and Al in it. Colloids were synthesized at room temperature by delamination of Zn-Al LDH nanoparticles in formamide. It was observed that Zn-Al LDHs in colloidal form shows photoluminescence because of its high surface area which facilitates molecular interaction with formamide and speeds up the recombination process of excited electron and holes. The study reveals that Photoluminescence of Zn-Al LDHs colloid depends on Zn-Al LDH particle concentration in their colloids.

Flexible Visible-Blind Ultraviolet Photodetectors Based on ZnAl-Layered Double Hydroxide Nanosheet Scroll.

Visible-blind ultraviolet (UV) photodetectors have received a great deal of attention for realizing Internet of Things technologies as well as for monitoring the level of UV exposure to humans. Realizing next-generation flexible and visible-blind UV photodetectors requires development of new functional material systems with easy fabrication, selectively strong UV light absorption, environmental friendliness, and high stability regardless of ambient conditions. Herein, flexible visible-blind UV photodetectors are successfully fabricated on the basis of two-dimensional ZnAl-layered double hydroxide (LDH) nanosheets with scroll structures grown on flexible substrates. The ZnAl-LDH nanosheet scrolls exhibit highly resistive semiconducting properties with a band gap of 3.2 eV and work function of 3.64 eV. The photodetector based on the ZnAl-LDH shows photoresponse in the UV spectral range below 420 nm, indicating visible-blind spectral response. In addition, the UV photodetector shows a maximum responsivity of 17 mA/W under illumination with 365 nm light. Moreover, the flexible photodetector shows reproducible photoresponse even after 1000 bending cycles, which indicates the acceptable stability of the ZnAl-LDH nanosheet scrolls.

One pot synthesis of ZnO-CuO nanocomposites for catalytic peroxidase like activity and dye degradation

In this study, we report a low temperature chemical decomposition method for the synthesis of ZnO-CuO nanocomposites from ZnAl-layered double hydroxides (ZnAl-LDHs) supported copper terephthalate based metal organic frameworks [Cu-(BDC) MOFs]. The Cu-(BDC) MOFs arrays on the surface of ZnAl-LDHs nanosheets are obtained via in situ nucleation and directed growth from the terephthalate (BDC) anion intercalated ZnAl-LDHs. Cu(II) ion coordinates with BDC ligand in a bidentate bridging fashion to form Cu-(BDC) MOFs. The as prepared Cu-(BDC) MOFs are strongly and uniformly anchored onto the surfaces of ZnAl-LDHs. Decomposition of the resultant ZnAl-LDH supported Cu-(BDC) MOF precursor in alkaline solution for 24 h leads to the formation of ZnO-CuO nanocomposites. The structures and morphology of the nanocomposites are discussed with the results of scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) images, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The resulting ZnO-CuO nanocomposites show peroxidase like catalytic activity towards orthophenylene diamine oxidation (OPDox) and rhodamine 6 G (R6 G) dye degradation.

Phosphorus recycling from urine using layered double hydroxides: A kinetic study

Layered double hydroxides (LDH) are anionic clay minerals that have the potential to recycle phosphate (P) from urine and may yield efficient P fertilisers. The efficient P recovery requires P uptake to be relatively fast, ensuring small adsorption columns to reduce process costs. This study assesses the kinetics of P adsorption and desorption of three phase-pure MgAl LDH with varying Al content and a phase-pure ZnAl LDH, all prepared by coprecipitation. The adsorption kinetics (0–24 h) in agitated suspension showed that 90% of the capacity is reached within 5 h, with similar rate constants for model solution as for synthetic urine. The LDH with low Al content maintain structural properties during adsorption, while crystallinity reduces for LDH with high Al content. The combination of XRD analysis, speciation modelling and kinetic information suggest that P uptake by LDH includes a fast step of ligand exchange, followed by slower step of anion exchange in the interlayer. The latter process dominates in LDH with high Al content whereas the former dominates the LDH with low Al content. The XRD analysis and speciation modelling furthermore suggests precipitation as an additional P removal mechanism. The P desorption (0–2 weeks) showed that >95% of P could be desorbed from MgAl-LDH whereas only 51% of adsorbed P is desorbed from the ZnAl LDH. Continuous flow pilot-scale adsorption columns with pelletized MgAl LDH granules (1 mm diameter) recovered >70% of urine-P at residence times of only 1 min, up to point of 70% of exchange capacity beyond which the recovery decreased. These results show that the LDH technology for P recovery is efficient to recycle P into high potential fertilisers.