Hydroxy Double Salts Research Articles

Fabrication of Mixed-Metal ZIF-7 Membrane by the Self-Conversion of Hydroxy Double Salts for Gas Separation

Fabrication of Mixed-Metal ZIF-7 Membrane by the Self-Conversion of Hydroxy Double Salts for Gas Separation

Adsorption Behavior of Arsenic and Selenium using NiZn Hydroxy Double Salts with Acetate, Chloride, Nitrate and Sulfate Anions

Adsorption Behavior of Arsenic and Selenium using NiZn Hydroxy Double Salts with Acetate, Chloride, Nitrate and Sulfate Anions

Deciphering Metal–Organic Framework Synthesis from Hydroxy Double Salts: In-Situ Insights via Synchrotron X-ray Diffraction and Absorption Spectroscopy

Deciphering Metal–Organic Framework Synthesis from Hydroxy Double Salts: In-Situ Insights via Synchrotron X-ray Diffraction and Absorption Spectroscopy

Double Hydroxyl Salt as Smart Biocompatible pH-Responsive Carrier for 6-Mercaptopurine

Hydroxy double salts are layered materials that are considered to be biocompatible. For this reason, research has been initiated on the possibility of their use in drug delivery. Despite their use for several types of drugs, their potential for controlled release of mercaptopurine (MERC) has not been studied. In this work, the synthesized hydroxy double salt (HDS) material was used as a carrier for this drug for the first time. The effectiveness of HDS synthesis has been proven by such techniques as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Based on the FT-IR and energy-dispersive X-ray spectroscopy (EDS) results, the effectiveness of drug sorption was proven. The exact amount of drug retained was determined by the UV-Vis technique. The obtained results indicate that the drug is evenly distributed on the surface of the carrier, which is important during the controlled delivery of drugs. In the most important stage of the research, the effectiveness of drug release in response to changes in the pH of the environment was proven. The drug is not released into an environment that mimics healthy human tissues. It is released only after contact with the acidic environment that usually surrounds cancer cells. The low cellular toxicity of HDS and significant cytotoxic effect of HDS-MERC were confirmed by in vitro studies on MCF-7 human breast and DU145 prostate cancer cell lines and non-cancerous keratinocytes HaCaT. Interestingly, coupling with the HDS carrier increased the cytotoxic effect of MERC towards DU145 cells. Such an “intelligent” drug carrier for mercaptopurine has not been previously described in the literature. The obtained results indicate its great potential.

Eggshell-Derived Copper Calcium Hydroxy Double Salts and Their Activity for Treatment of Highly Polluted Wastewater.

By using methyl orange (MO) removal as a model reaction, the best temperatures for processing eggshells are 750 °C and above to obtain biobased CaO materials, a raw material for producing CuCa hydroxy double salt (HDS) materials with high efficiency in treatments of highly polluted wastewater (the initial concentration of MO is 500 ppm). Characterization techniques employed in this study include power X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, nitrogen adsorption-desorption analysis, and the colorimetric method, as well as energy-dispersive X-ray, infrared-, and electron spin resonance spectroscopies. Complete MO removal and high chemical oxygen demand (COD) efficiencies (>90%) can be achieved after 3 min treatments of the aqueous MO with the calcined eggshell-derived CuCa HDS materials. The spent, deactivated HDS materials can be regenerated by an acid wash method. The activity of CuCa HDS materials in MO removal is unaffected by eggshell sources, implying that sorting steps may be unnecessary when eggshell food waste (duck, quail, and hen eggshells) is collected to produce biobased CaO. The findings of this study demonstrated that eggshells can be used in place of limestone and could be a more sustainable, renewable, and cost-effective source for material development and other applications.

Adsorption of anionic dye from aqueous environment using surface-engineered Zn/Cu hydroxy double salt-based material: mechanistic, equilibrium and kinetic studies.

Herein, ethylene glycol (EG)-modified Zn/Cu hydroxy double salts (HDS) were synthesized using a facile synthetic approach. The formation of layered structure and presence of EG in the interlayer region were confirmed using PXRD and FTIR techniques. Furthermore, XPS analysis was used to confirm presence of metal ions in synthesized HDS. The surface area and pore size diameter of the HDS was found to be 32.30 m2 g-1 and 2.22 nm, respectively, using BET. The role of HDS was evaluated for its potential application as a sorbent for Congo red (CR) dye uptake. Batch studies were conducted to examine the impact of key variables, i.e., pH, time, adsorbent dosage and dye concentration on adsorption efficiency of HDS. Linear-nonlinear isotherm and kinetic models were employed for detailed analysis of experimental data. Langmuir, Freundlich and Temkin isotherm models were subsequently utilized to fit equilibrium data, among which Langmuir demonstrated to be most accurate. The maximum monolayer adsorption capacity estimated using Langmuir model was computed to be 181.81 mg g-1. The kinetic data follows pseudo-second-order model having good R2 value (0.999). Additionally, thermodynamic study suggested spontaneous and endothermic nature of adsorption process having reusability up to 5 cycles with removal efficiency more than 85%.

Facile synthesis of hierarchical porous MOFs via competition coordination strategy: A sustainable adsorbent for efficient removal of fluorine-containing drugs

Construction of hierarchically porous structure of metal–organic frameworks (MOFs) can improve the accessibility of active sites and mass transfer rate to improve practical applications effects such as adsorption efficiency. Rapid synthesis of hierarchically porous MOFs (HP-MOFs) at an industrial scale is extremely important from the perspective of sustainable development and economical practicality. Here, we propose a strategy to rapidly synthesize HP-MOFs at room temperature, using hydroxy double salts (HDS) as an intermediate to combine two ligands with different electronegativity to generate competitive coordination during the nucleation stage. Using this method, we can obtain HP-Zn-MOFs within 20 min at room temperature, with larger pores (average pore size > 8 nm) and higher space–time yield (STY > 3000 kg m−3 d−1). All the raw materials are low cost and low toxicity, which is consistent with the concept of green chemistry. More than that, the as-synthesized HP-Zn-MOFs have an excellent adsorption effect in removing fluorine-containing drugs (FCDs) through multiple interactions, showing good reusability, practical application, and good adsorption for other drugs. This work demonstrates the feasibility of the green synthesis of HP-MOFs through competition coordination methods at room temperature, which highlights the potential for the elimination of contaminants.

Facile one-step synthesis of CuZn-HDS/alginate hydrogel beads for highly efficient and selective removal of methyl orange

Hydroxy double salts (HDSs) have shown enormous potential for removing dyes from wastewater. However, the powder form of HDSs limits their potential in commercial applications. Herein, we proposed a facile one-step route to incorporate CuZn-HDS into the copper alginate matrix for methyl orange removal. This strategy could not only shape CuZn-HDS to beads but also significantly enhance the adsorption ability of the matrix. The obtained composite hydrogel beads displayed high water stability and excellent adsorption performance for MO, with more than 98% of MO being removed by CuZn-HDS/Alg-0.5. The maximum adsorption capacity of CuZn-HDS/Alg-0.5 for MO was 763.3 mg·g−1 at 298 K. Besides, the adsorption process matched the pseudo-second-order kinetic model and fitted well with the Freundlich model, suggesting that the adsorption of MO onto CuZn-HDS/Alg-0.5 was a multilayer chemical adsorption process. More importantly, CuZn-HDS/Alg-0.5 could selectively adsorb MO from MO & RhB (Rhodamine B) and MO & MB (Methylene blue) mixed solution. Mechanism studies indicated that the removal of MO was attributed to the electrostatic interaction, complexation interaction and ion exchange interaction between MO and CuZn-HDS/Alg-0.5. This work opens a new route for developing eco-friendly and efficient adsorbents to remove dyes from wastewater.

Effects of acetate and nitrate ions on radical and intercalation reactions initiated by CuZn hydroxy double salts

The role of hydroxy double salts (HDS) in the effective removal of organic contaminants from water is still controversial among researchers. In this work HDS materials, copper-zinc hydroxy acetate (CuZn-HA), and copper-zinc hydroxy nitrate (CuZn-HN) were produced and treated with aqueous methyl orange (MO), acid red 44 (AR44), or congo red (CR) under ambient conditions. Evidence from dye removal testing, materials analyses, and spin trapping measurements suggested possible three removal processes, dye sorption, intercalation reactions, and ·OH radicals assisted oxidation for suitable matching between dye and HDS material. Such three processes are responsible for the complete color (from the aqueous 500 ppm MO and AR44) and TOC removal achieved by using the CuZn-HN. The structural stability of the dye and HDS chemical composition play a key role on the oxidative reactivity and the intercalation ability of the dye in HDS structure.

(Invited, Digital Presentation) Atomic Layer Deposited Templates for Constructing Functional Metal-Organic Framework Thin Films

Metal-organic frameworks (MOFs) are a class of porous crystalline materials featuring high surface area, ordered pore structures and amenability for post-synthetic modification. Integrating MOF thin films with various substrate materials could enable applications in separations, heterogeneous catalysis, chemical sensors and electronic devices. However, it is difficult to find a universal approach to deposit uniform and high-quality MOF coatings on a variety of substrate materials. Previous attempts often require surface modification methods that may not be generally applicable.In this talk, interfacial engineering using atomic layer deposited (ALD) templates will be discussed for forming MOF thin films on various substrates. We found that ALD metal oxides are effective in promoting the heterogeneous nucleation of MOFs and also readily hydrolyzed into hydroxy double salts (HDSs) for rapid transformation to MOFs. With ALD template layers, conformal and functional MOF coatings were integrated on fibers, membranes and laminated structures. Accordingly, we developed a series of MOF-functionalized fibers for adsorption and catalytic degradation of hazardous compounds. Furthermore, we obtained ultra-thin mixed-metal MOF skin layers on porous alumina supports for membrane separation, and achieved large propylene permeance (up to 4.5×10-8 mol·m-2·s-1·Pa-1) and high propylene/propane selectivity over 250. We anticipate that this platform technology will also lead to potential device structures for chemical sensing, energy storage and many other scenarios.

Versatile Layered Hydroxide Precursors for Generic Synthesis of Cu‐Based Materials

The ability to mix multiple elements in a structure is crucial for obtaining Cu‐based nanostructures and microstructures with desirable physicochemical properties. Precursors containing multiple metal cations, such as layered double hydroxides, have been used for the synthesis of multielement materials. However, these precursors experience difficulty containing large cations, which limits the functionalities of the derived materials. Herein, the development of Cu‐based hydroxy double salts (HDSs), versatile precursors that accommodate a broad range of metal cations with homogeneous distributions, is reported. Up to 25 different metal cations are mixed with Cu in an HDS single phase, individually and simultaneously. The HDSs further exhibit useful properties with respect to anion exchange, exfoliation, and phase transformation to metal oxides. During the metal oxide transformation process, the formed crystal structures are mainly dependent on the ionic radius of the secondary metal cations. To prove their utility as precursors, the metal oxides derived from the HDSs are tested and found that they exhibited high catalytic activities for CO oxidation. This study significantly expands the compositional and structural freedom of Cu‐based multi‐elemental materials.

Enhanced photocatalytic reduction of hexavalent chromium ions over Zn-bearing in CuZn hydroxy double salts: Insight into the structural investigation using extended X-ray absorption fine structure

CuZn hydroxy double salts (CuZn-HDS) are often used as adsorbent and Fenton-like catalysts. In this work, we report the photocatalytic activity of CuZn-HDS for Cr(VI) reduction. In detail, CuZn-HDS with different Cu/Zn ratios were prepared as photocatalysts through the metal oxide-assisted hydrothermal method. The CuZn-HDS samples were characterized and applied for photocatalytic reduction of Cr(VI), which is a toxic inorganic pollutant in the wastewater. The CuZn-HDS which has the Cu/Zn ratio of about 4 (CuZn-HDS-4) showed the heist photocatalytic Cr(VI) reduction activity more than other samples, especially for copper hydroxy salts (Cu-HS) which have no Zn in the structure. Thus, the Zn-bearing in CuZn hydroxy double can improve the photocatalytic activity for Cr(VI) reduction compared with Cu-HS. The increase in the Cr(VI) reduction activity of the optimized CuZn-HDS-4 was attributed to the excellent separation and transportation of photogenerated electron-holes pairs, as proven by the photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the atomic structure of the synthesized CuZn-HDS was elucidated by an extended X-ray absorption fine structure technique, which is the first time to report the CuZn-HDS structure. Based on the optical properties, and activity test, a photocatalytic reduction of Cr(VI) over a CuZn-HDS was proposed. Thus, the CuZn-HDS can be employed as a potential photocatalyst for the detoxification of Cr(VI) in wastewater.

Biocompatible hydroxy double salts as delivery matrices for non-steroidal anti-inflammatory and anti-epileptic drugs

We recently reported the synthesis of two novel biocompatible hydroxy double salts (HDS), [Mg2Zn3(OH)8]Cl2·3.4H2O (MgZn-Cl) and [Fe2.4Zn2.6(OH)8]Cl2·2H2O (FeZn-Cl) (J. Mater. Chem. B 2016, 4, 5789) and showed them to be suitable for the loading and sustained release of naproxen. Here we build on these findings and report the intercalation, storage stability, biocompatibility and drug release properties of MgZn-Cl and FeZn-Cl loaded with diclofenac, ibuprofen, and valproate. All three active pharmaceutical ingredients could be successfully intercalated into both HDS by ion exchange. An increase in interlayer space from ca. 8 Å to 18.5–27 Å was observed after intercalation, consistent with the replacement of the initial chloride ion with the larger drug anions. Confirmation of successful intercalation was provided by IR spectroscopy, elemental microanalysis, and thermogravimetric analysis. 1H NMR revealed that the structural integrity of the drug ions is not affected by intercalation. Drug release studies were performed in conditions representative of the gastrointestinal tract, and showed that the solubility of the drug ions controls the fate of the HDS in an acidic environment. The valproate intercalates dissolved completely within two hours at pH 1.0, whereas the other drug-loaded HDS freed some of their drug payload in the acidic media and the rest at pH 6.8. The HDS are further found to be biocompatible in an in vitro cell viability test, and to remain stable upon storage for 5 years.

Fabrication of 2D bimetallic metal-organic framework ultrathin membranes by vapor phase transformation of hydroxy double salts

At present, the construction of a bimetallic and oriented MOF nanosheet membrane that integrates the advantages of both bimetallic MOF and oriented membranes is highly desirable but also challenging. Herein, we report a vapor phase transformation (VPT) strategy for directly growing a highly oriented bimetallic (Zn/Co) 2 (bIm) 4 (bIm = benzimidazole) nanosheet membrane, based on the conversion of hydroxy double salts (HDS) under bIm ligand vapor treatment. The fabricated strategy includes first the growth of a layer of bimetallic Zn/Co-HDS on a porous tube and then the conversion of the HDS layer into a highly oriented bimetallic nanosheet membrane via the VPT strategy. The formation mechanism of the membrane is discussed. The resulting ultrathin nanosheet membrane with the thickness of about 80 nm exhibits excellent gas separation performance with H 2 permeance of 1.68 × 10 -7 mol m -2 s -1 ·Pa -1 and H 2 /CO 2 ideal separation selectivity of 54.1. This approach shows great potential in large-scale fabrication of nanosheet membranes, especially the bimetallic MOF nanosheet membranes. • A VPT strategy is developed for growing bimetallic MOF nanosheet membrane based on the conversion of HDS. • The achieved bimetallic MOF nanosheet membrane combines the advantages of nanosheets and bimetallic MOFs. • Both HDS layer and VPT strategy cooperatively facilitate the generation of bimetallic MOF nanosheet membrane. • The membrane exhibited excellent molecular sieving performance for H 2 /CO 2 .

Cubic zinc hydroxide nitrate cavity and its lasing action

Layered double hydroxide (LDH) has been promoted and applied as photoluminescent functional materials responding to environmental stimuli in recent years. In this work, a kind of hydroxy double salts, zinc hydroxide nitrate (Zn5(OH)8(NO3)2·2H2O, Zn-HDS) was fabricated from zinc oxide and zinc nitrate solution under ambient conditions. To further obtain the regular morphology of Zn-HDS as cavity, the aforementioned Zn-HDS was dehydrated by aging at 100 °C for 16 h. The effective conversion from amplified spontaneous emissions (ASE) into lasing emissions of a single cubic Zn-HDS cavity was observed with the help of micro-photoluminescence spectra system (μ-PL spectra system) and 325 nm line of a femtosecond pulsed laser as excitation source. The result indicated that the cubic Zn-HDS cavity can be applied as desirable microlaser material for optoelectronic devices.

Bimetallic Zn/Co-ZIF tubular membrane for highly efficient pervaporation separation of Methanol/MTBE mixture

Preparation of defect-free and stable metal-organic framework tubular membrane for liquid separation is still a great challenge. In this work, a high-quality bimetallic Zn/Co-ZIF tubular membrane was fabricated via a novel strategy on a porous ceramic tube for the highly efficient separation of methanol (MeOH)/methyltert-butylether (MTBE) mixture by pervaporation. The strategy includes first the introduction of a thinlayer of Zn/Co hydroxy double salts (HDSs) on the tube surface and then the facile conversion of the HDS layer to a dense and stable bimetallic Zn/Co-ZIF membrane. The achieved membrane can preferentially separate MeOH from the 15 wt% MeOH/MTBE mixture and display an ultrahigh separation performance with flux of 1.96 kg m−2 h−1 and separation factor of 6985. It can also demonstrate an excellent long-term operating stability benefited from the HDS layer acting as an inorganic linker. Therefore, the bimetallic Zn/Co-ZIF membrane has great industrial application potential for the separation of MeOH/MTBE mixture.

Facile synthesis of bimetallic MOF crystals with controllable morphology and topology by the self-converted strategy of hydroxy double salts (HDSs)

Controllable synthesis of metal organic frameworks (MOFs) crystals with definite morphology and topology plays an important role in determining the property and application of MOFs materials, especially bimetallic MOFs which have exhibited an improved performance in many fields due to the incorporation of the second metal ion. Herein, we for the first time report a simple and convenient method of the self-conversion of hydroxy double salts (HDSs) for synthesizing bimetallic MOFs with controllable morphology and topology by merely adjusting the synthesis conditions. As the sample, we employed Zn/Co-HDS as metal source and 2-methylimidazole (HMeIm) and 2-ethylimidazole (HEtIm) as organic ligands, respectively, to investigate the effects of the synthesis conditions on the morphology and topology of Zn/Co bimetallic MOF. The arbitrary transformation with two topologies (SOD and dia) and four morphologies (2D nanosheets, rhombic dodecahedron, truncated rhombic dodecahedron and truncated cubes) of the bimetallic Zn/Co(MeIm)2 was achieved by adjusting synthesis solvent, reaction time and ligand concentration. Analogously, three other topologies (ANA, RHO and QTZ) were also discovered in the bimetallic Zn/Co(EtIm)2 by simply adjusting the synthesis conditions. It is thought that the different synthesis conditions in the preparation of bimetallic MOFs are closely related to the supersaturation of crystal growth unit, thus affecting the morphology and topology of the products. Therefore, this novel synthesis strategy is highly efficient for preparing bimetallic MOFs with controllable morphology and topology.

Pre-programed hydroxy double salt templates for room-temperature controlled synthesis of mixed-metal zeolitic imidazolate frameworks

Bimetallic hydroxy double salts pre-programed through co-precipitation were found as excellent templates for mixed-metal MOFs.

Anion-exchangeable modulated fluorescence strategy for sensitive ascorbic acid detection with luminescent Eu hydroxy double salts nanosunflowers derived from MOFs

To improve the sensitivity and avoid the interference of other substances to the detection of ascorbic acid (AA), luminescent Eu hydroxy double salts (Eu HDSs) sunflowers were developed for fluorescence turn-off detection of AA based on anion-exchangeable strategy. Such Eu HDSs nanoprobe was synthesized by using a leaf-like metal–organic-framework-5 (MOF-5-L) as both precursor and template and europium (III) trifluoroacetate trihydrateas a second precursor. The mechanism of the luminescence inhibition of the Eu HDSs nanosunflowers was studied, and the intercalation of anionic AA− species into an interlayer of Eu HDSs helped to enhance luminescence inhibition, which was quite different from the reported redox-based fluorescent sensing system. Because of the existence of space effect and hydrogen bond between the AA and the OH group on the Eu HDSs surface, such nanoprobe showed excellent sensitivity and selectivity for AA detection, with the detection limit of 1.46 nM. Moreover, the nanoprobe was successfully used for sensitive and selective AA assays in human body fluids, proving that the proposed sensing platform has great potential in the clinical diagnosis and drug screening.

Formation of copper hydroxy double salts derived from metal oxides and their catalytic activity in degradation of methyl orange

This work reports the preparation and application of copper hydroxy double salts (Cu-M HDS) as catalysts for degradation of a model wastewater dye pollutant, methyl orange (MO), under ambient conditions. The Cu-M HDS (M = Ca, Zn, La and Pb) were derived in 30 min from hydrothermal treatment of aqueous copper (II) nitrate and the corresponding metal oxide. All Cu-M HDS systems were highly active for catalytic wet oxidation (CWO) of MO, with complete oxidation of 500 ppm MO possible in less than 10 min under ambient (pH 7.0, 30 °C) conditions, with no requirement for additional oxidants. Dissolved oxygen is crucial for activity, as indicated by poor conversions under anaerobic conditions. Decolorization follows first-order kinetics, with catalyst systems having high surface area and Cu content (Cu-Ca HDS, Cu-La HDS) being most rapid. These features, coupled with favorable reusability profiles and ease of fabrication and use, highlight the potential of Cu-M HDS systems in water remediation strategies.