The effect of guest molecular architecture and host crystallinity upon the mechanism of the intercalation reaction

Energetics, Interlayer Molecular Structures, and Hydration Mechanisms of Dimethyl Sulfoxide (DMSO)-Kaolinite Nanoclay Guest-Host Interactions

Two-dimensional (2D) kaolinite nanoclay is an important natural mineral with promising application potential, especially tuned with organic intercalates. However, thus far, the organics-kaolinite guest-host interactions, the atomic scale structures of organic intercalates under confinement, and molecular level mechanisms of hydration are rarely systematically explored using both experimental and computational methodologies. We integrated density functional theory with dispersion scheme (DFT-D) with various experimental methods to investigate the intercalation of dimethyl sulfoxide (DMSO) in kaolinite with and without hydration. The kinetic, thermodynamic, and structural impacts of hydration were highlighted. In short, water molecules significantly promote intercalation of DMSO into kaolinite because of favorable intercalation energy, which is enabled by effective hydrogen bonding at the guest species (DMSO and water)-kaolinite interfaces.

Gelation Based on Host-Guest Interactions Induced by Multi-Functionalized Nanosheets

Host–guest interaction, being reversible and stimuli-responsive, is ideal to be applied to the design of hydrogels. We created a gelation system based on the host–guest interactions between the adamantyl groups and β-cyclodextrin (β-CD) polymer. N,N,N-trimethyl-1-adamantylammonium hydroxide (TriMAA) cations were attached to the pre-exfoliated α-zirconium phosphate (α-ZrP) nanosheets by ionic bonding through a displacement reaction with the exfoliating agents. The exfoliated α-ZrP nanosheets with adamantyl groups directly or indirectly attached to the surface act as reversible high-functionality crosslinkers within the β-CD polymer. The gelation occurred at a host-to-guest ratio of 1:10 or 1:5 at room temperature within minutes. The agents used to exfoliate α-ZrP can tailor the surface of the resultant α-ZrP nanosheets and the ionic strength of the system, which directly affects the further gelation results. Plus, the exfoliating agent cations may generate a host-and-guest interaction with the β-CD polymer as well. This gelation process without covalent bonding formation should help fellow researchers to better understand the gelation system and host–guest interactions.

Exfoliation of α-Zirconium Phosphate Using Tetraalkylammonium Hydroxides

α-Zirconium phosphate (α-ZrP), a classical layered compound, has found widespread application. Exfoliation of α-ZrP has been mainly achieved by propylamine (PA) or tetrabutylammonium hydroxide (TBAOH), but the exact mechanism of exfoliation has not been completely elucidated. We examined the feasibility of exfoliation utilizing tetraalkylammonium hydroxide (TXAOH) and investigated the stepwise intercalation/exfoliation mechanism of α-ZrP. All of the TXAOHs examined (carbon number of the branches: 1-4) were able to exfoliate α-ZrP in an aqueous dispersion under ultrasonication. Furthermore, exfoliation of α-ZrP by two different exfoliators (either a mixture of two or sequentially) was also investigated to pinpoint the exfoliation mechanism. Our results indicate that small TXA cations are kinetically preferred to diffuse into the galleries of α-ZrP, while large TXA cations can help open up the galleries and facilitate transport of the already intercalated cations. These findings should help fellow researchers to choose the most suitable exfoliators for their own projects and develop better intercalation/exfoliation systems.

Preparation of Zirconium Phosphate Nanomaterials and Their Applications as Inorganic Supports for the Oxygen Evolution Reaction

Zirconium phosphate (ZrP) nanomaterials have been studied extensively ever since the preparation of the first crystalline form was reported in 1964. ZrP and its derivatives, because of their versatility, have found applications in several fields. Herein, we provide an overview of some advancements made in the preparation of ZrP nanomaterials, including exfoliation and morphology control of the nanoparticles. We also provide an overview of the advancements made with ZrP as an inorganic support for the electrocatalysis of the oxygen evolution reaction (OER). Emphasis is made on how the preparation of the ZrP electrocatalysts affects the activity of the OER.

Combination of intercalation and surface modification in layered zirconium phosphates: investigation of surface stability and reactivity

A two-step intercalation and surface modification procedure was used to synthesize heterofunctional zirconium phosphates (ZrP) with different groups in the interlayer and on the surface. The relationship of the interlayer and surface was then investigated through evaluation of the stability and reactivity of heterofunctional ZrP materials by thermal analysis. Intercalated samples were prepared by the ion-exchange mechanism with variation in the loading, charge, and size of ions. An identical epoxide was used to modify the surface in all investigations. It was found that the two-step procedure could be performed in either order to prepare heterofunctional ZrP materials. In both cases, the contents of the interlayer were found to impact the reactivity of the surface and stability of covalently attached surface groups, with higher interlayer loadings leading to decreased stability and reactivity of surface phosphates.

Effect of geometrical configuration of reactor on a ZrP nano-dispersion process using ultrasonic irradiation

This study investigated the position of ultrasonic irradiation source and reactor geometry on fragmentation rate of a layered compound, α-zirconium phosphate (α-ZrP). By numerically solving the acoustic pressure distribution using COMSOL Multiphysics®, it is clarified the mechanism whereby the operating factors influenced the α-ZrP dispersion to make a suggestion of guideline of the process design method. Two vessels made of glass with a flat-bottom and a spherical-bottom, respectively, were used. Although the flat-bottom vessel at lower horn position showed the best performance of fragmentation, the region of high acoustic pressure field in the flat bottom vessel sharply narrowed and the transmittance became prominently low. On the other hand, no significant difference of the transmittance value in the spherical bottom vessel between the cases of low and high horn positions could be observed and the spherical bottom vessel was robust for the horn position. These results suggest that not only the magnitude of acoustic pressure but also the size of high acoustic pressure region is also an important factor and a spherical bottom vessel is one of suitable shape which gives large size of high acoustic pressure region regardless of the horn position.

Preparation of two dimensional layered double hydroxide nanosheets and their applications

Layered double hydroxides (LDHs) with their highly flexible and tunable chemical composition and physical properties have attracted tremendous attention in recent years. LDHs have found widespread application as catalysts, anion exchange materials, fire retardants, and nano-fillers in polymer nanocomposites. The ability to exfoliate LDHs into ultrathin nanosheets enables a range of new opportunities for multifunctional materials. In this review we summarize the current available LDH exfoliation methods. In particular, we highlight recent developments for the direct synthesis of single-layer LDH nanosheets, as well as the emerging applications of LDH nanosheets in catalyzing oxygen evolution reactions and preparing light emitting devices, supercapacitors, and flame retardant nanocomposites.

Transition Metal Titanophosphates with Intercalated Molecular Photoluminescence and Catalytic Properties

In this study, α-TiP layered structure incorporating a heterometal center for organic ligand binding to enhance structural complexity and functionality were prepared. The protons of the α-TiP layer were replaced with zinc ions coordinated by 4-pyridinecarboxylic acid (PCA) and water to form a layer structure, TiZn(PO₄ )₂ (H₂ O)(PCA) (1). The tetrahedral zinc center with coordinated water in 1 is unprecedented in zincophosphate or zinc-MOF systems and is usually only found in metalloenzyme systems. The neutral zincotitanophosphate layers, tightly stacked through hydrogen bonds, showed velcro-like behavior on intercalating 4,4'-trimethylenedipyridine (TMDP) reversibly. It rendered a remarkable luminescence property to 1, emitting blue-to-white light under UV excitation. Surprisingly, the replacement of TMDP for PCA in the hydrothermal synthesis still resulted in 1, plus another structure, Ti₄ Zn₂ (H₂ TPB)(PO₄ )₄ (HPO₄ )₄ (H₂ PO₄ )₂ (2) (TPB=1,2,4,5-tetra(4-pyridyl)benzene). Clearly, in situ C-C cracking and C-C coupling of TMDP simultaneously occurred to generate PCA and TPB and thereafter the oxidant, Zn(NO₃ )₂ , was quantitatively determined to isolate crystal 1 from 2. The structure of 2 also featured α-TiP layers with pedant Zn tetrahedra but formed a three-dimensional neutral framework through TPB. For the first time, α-TiP-derived structures and their properties have been elucidated, which help in understanding intriguing in situ ligand formation and intercalation-induced luminescence, to exploit potential photocatalysis in polymerization.

Covalently immobilized ionic liquids on single layer nanosheets for heterogeneous catalysis applications

Covalently immobilized ionic liquids on sinlge layer α-zirconium phosphate nanosheets can serve as an efficient heterogeneous catalyst for various reactions, such as Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate.

Synergistic flame retardant properties of a layered double hydroxide in combination with zirconium phosphonate in polypropylene

High-performance flame retardant nanocomposites were prepared for polypropylene (PP).

Facile preparation of electroactive amorphous α-ZrP/PANI hybrid film for potential-triggered adsorption of Pb(2+) ions

An electroactive hybrid film composed of amorphous α-zirconium phosphate and polyaniline (α-ZrP/PANI) is controllably synthesized on carbon nanotubes (CNTs) modified Au electrodes in aqueous solution by cyclic voltammetry method. Electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM) and X-ray power diffraction (XRD) analysis are applied for the evaluation of the synthesis process. It is found that the exfoliated amorphous α-ZrP nanosheets are well dispersed in PANI and the hydrolysis of α-ZrP is successfully suppressed by controlling the exfoliation temperature and adding appropriate supporting electrolyte. The insertion/release of heavy metals into/from the film is reversibly controlled by a potential-triggered mechanism. Herein, α-ZrP, a weak solid acid, can provide an acidic micro-environment for PANI to promote the electroactivity in neutral aqueous solutions. Especially, the hybrid film shows excellent potential-triggered adsorption of Pb(2+) ion due to the selective complexation of Pb(2+) ion with oxygen derived from P-O-H of α-ZrP. Also, it shows long-term cycle stability and rapid potential-responsive adsorption/desorption rate. This kind of novel hybrid film is expected to be a promising potential-triggered ESIX material for separation and recovery of heavy metal ions from wastewater.

Direct growth of layered intercalation compounds via single step one-pot in situ synthesis

A single step one-pot in situ synthesis method was developed to directly grow layered intercalation compounds. This methodology is expected to be applicable to a wide range of layered materials.

An intelligent displacement pumping film system: a new concept for enhancing heavy metal ion removal efficiency from liquid waste

A concept of electrochemically switched ion exchange (ESIX) hybrid film system with piston-like proton pumping effect for the removal of heavy metal ions was proposed. Based on this concept, a novel ESIX hybrid film composed of layered alpha zirconium phosphate (α-Zr(HPO4)2; α-ZrP) nanosheets intercalated with a potential-responsive conducting polyaniline (PANI) was developed for the removal of Ni(2+) ions from wastewater. It is expected that the space between α-ZrP nanosheets acts as the reservoir for the functional ions while the intercalated PANI works as the potential-sensitive function element for piston-like proton pumping in such ESIX hybrid films. The prepared ESIX hybrid film showed an excellent property of rapid removal of Ni(2+) ions from wastewater with a high selectivity. The used film was simply regenerated by only altering the applied potential. The ion pumping effect for the ESIX of Ni(2+) ions using this kind of film was proved via XPS analysis. The proposed ESIX hybrid film should have high potential for the removal of Ni(2+) ions and/or other heavy metal ions from wastewater in various industrial processes.

Intercalated polyfluorinated Pd complexes in α-zirconium phosphate for Sonogashira and Heck reactions

A direct method was used to effectively intercalate the short fluorous-ponytailed Pd complexes into the ZrP gallery, and the resulting Pd intercalated ZrP could be used as a recoverable catalyst for Sonogashira and Heck reactions.

Electrospun poly(vinyl alcohol)/α-zirconium phosphate nanocomposite fibers

Poly(vinyl alcohol) (PVA)/α-zirconium phosphate (ZrP) polymer nanocomposite (PNC) fibers were successfully prepared by a simple and low-cost electrospinning process. ZrP nanoparticles with two different dimensions, that is, ZrP-500 with a lateral dimension of ∼320 nm and an aspect ratio of ∼500 and ZrP-1500 with a lateral dimension of ∼950 nm and an aspect ratio of ∼1500, were utilized to illustrate the size effect on the electrospun nanofibers. In order to obtain defect-free, uniform PNC fibers, a number of parameters including polymer concentration, feed rate, applied voltage and working distance between the needle tip and the fiber collecting substrate were investigated. Scanning electron microscopic morphological analysis showed smooth and nonwoven electrospun nanofiber mat. Strong intermolecular interactions between the PVA matrix and the included ZrP nanofillers were revealed by the attenuated total reflectance Fourier transform infrared spectroscopy. The incorporation of ZrP nanofillers drastically improved the thermal stability of the PNC fibers. Results of thermogravimetric analysis demonstrated a clear thermal stability dependence on the aspect ratio of the crystalline ZrP nanofillers. The degradation temperature was increased by 90°C for the ZrP-1500 and 60°C for ZrP-500, when the loading level was increased from 1 wt% to 5 wt%. Furthermore, the viscoelastic properties of the PNC solutions were studied by the rheometer. The solutions with higher loading of the nanofiller exhibited higher viscosity and demonstrated different fluid nature when compared with the solutions at lower loading level.