Layered Α-zirconium Phosphate Research Articles

Immobilization of Ionic Liquids in Layered Compounds via Mechanochemical Intercalation

A facile mechanochemical intercalation approach was adopted to immobilize 1-butyl-3-methylimidazolium chloride (BMIMCl) in layered α-zirconium phosphate (ZrP). The intercalation compounds with an expanded layer distance were confirmed by X-ray diffraction. Thermogravimetric characterization revealed that a portion of the BMIMCl was intercalated into the ZrP galleries, while a portion was adsorbed on the layer surface. The immobilized BMIMCl was evaluated for catalysis evaluation of the coupling reaction of CO2 and propylene oxide to synthesize propylene carbonate. The immobilized BMIMCl exhibited similar reactivity as free BMIMCl. Overall, the mechanochemical approach proves to be effective in immobilizing ionic liquids in layered compounds and thus may expand the applications of ionic liquids and, meanwhile, improve catalyst separation and recycling.

A novel mediator-free biosensor based on co-intercalation of DNA and hemoglobin in the interlayer galleries of α-zirconium phosphate

A novel mediator-free biosensor was constructed by the co-intercalation of negatively charged DNA and positively charged hemoglobin (Hb) in the interlayer galleries of layered α-zirconium phosphate (α-ZrP) with the delamination-assembly procedure at pH 5.5. X-ray diffraction and field-emission scanning electron microscopy results revealed the featured layered structure for the re-assembled DNA/Hb/α-ZrP composite. Infrared spectroscopy and circular dichroism results confirmed the coexistence of Hb and DNA in the composite and the considerably retained protein conformation of intercalated Hb. The direct electron transfer of Hb was facilitated by the co-intercalation of DNA and Hb. Because of the synergistic effect of α-ZrP host and co-intercalated DNA guest, the DNA/Hb/α-ZrP modified electrode exhibited good electrocatalytic response to H 2O 2 with higher sensitivity of 0.79 A M −1 cm −2 and lower detection of 4.28 × 10 −7 M in the linear range of 7.28 × 10 −7 to 9.71 × 10 −5 M. Furthermore, the electrocatalytic activity of Hb in the DNA/Hb/α-ZrP composite retained at high temperature (85 °C) or in the presence of organic solvent (CH 3CN), which could be the protection of α-ZrP nanosheets.

Direct electrochemistry and electrocatalysis of horseradish peroxidase in α-zirconium phosphate nanosheet film

α-zirconium phosphate nanosheets (ZrPNS) derived via the delamination of layered α-zirconium phosphate (α-ZrP) have been proven to be efficient support matrixes for the immobilization of horseradish peroxidase (HRP). X-ray powder diffraction (XRD) results revealed that ZrPNS in HRP–ZrPNS film remained unorderly structured for the effect of HRP. Fourier transform infrared (FTIR) spectra results revealed that HRP remained the secondary structure in HRP–ZrPNS film. The direct electrochemistry of HRP was realized in HRP–ZrPNS film on a glassy carbon electrode (GCE), showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the HRP heme FeIII/FeII redox couple. The average surface concentration (Γ⁎) of electroactive HRP in HRP–ZrPNS film was estimated to be 1.35×10−10 mol cm−2, which indicated a high loading of enzyme molecules in HRP–ZrPNS film. Based on these, a third generation reagentless biosensor was constructed for the determination of hydrogen peroxide (H2O2). The response time of the biosensor was less than 3 s, and the linear response range of the biosensor for H2O2 was from 1.3×10−6 to 1.6×10−2 M with a correlation coefficient of 0.9997.

Direct electron transfer of hemoglobin in layered α-zirconium phosphate with a high thermal stability

A heme protein hemoglobin (Hb) was reacted with preexfoliated layered α-zirconium phosphate (α-ZrP) platelets. An X-ray diffraction (XRD) pattern of small range showed that the exfoliated α-ZrP platelets reassembled after the addition of Hb molecules, with the protein intercalated between the layers. UV–Vis and Fourier transform infrared (FTIR) spectra analysis displayed that no significant denaturation occurred to the intercalated protein. The bioactivity of Hb was also investigated by testing the electrochemical properties of the Hb/α-ZrP composite. Results showed that the intercalation of Hb into the layered material not only improved the thermal stability of Hb but also enhanced the direct electron transfer ability between protein molecules and electrode. The protein still showed bioactivity after treatment at a temperature as high as 85°C. A pair of well-defined redox peaks at approximately –0.37 and –0.32V was observed on the cyclic voltammograms (CVs) of the Hb/α-ZrP composite modified electrode, and the electrode reactions showed a surface-controlled process with a single proton transfer. The resultant biosensor constructed by the Hb/α-ZrP composite displayed an excellent response to the reduction of hydrogen peroxide (H2O2) with good reproducibility.

Improved quasi-solid dye-sensitized solar cells by composite ionic liquid electrolyte including layered α-zirconium phosphate

The authors reported a composite quasi-solid electrolyte by adding layered α-zirconium phosphate (α-ZrP) to the iodide/tri-iodide ionic liquid, 1-methyl-3-propylimidazolium dihydrophosphate, electrolyte including 4-tert-butylpyridine, which markedly improved photovoltaic properties of quasisolid dye-sensitized solar cells (DSSCs). When adding 6wt% α-ZrP, photoenergy conversion efficiency of the DSSC increases by a factor of more than 2 to 2.61%, compared to a DSSC without α-ZrP. This enhancement is primarily explained by studying dark reaction, diffusion coefficient of tri-iodide ions, exchange current density in the interface of electrolyte/Pt counterelectrode, and lifetime of electrons in mesoscopic TiO2 film.

Enhanced exchange current density and diffusion coefficient of iodide-based liquid electrolyte by layered α-zirconium phosphate

Here, we firstly reported a composite electrolyte prepared by adding α-zirconium phosphate into the iodide/triiodide liquid electrolyte including 4- tert-butylpyridine (TBP). The obtained composite electrolyte exhibited very good electrochemical property. The exchange current density ( I 0) and the diffusion coefficient of triiodide ( D I 3 - ) were both enhanced markedly. It was proved that the intercalation behavior of TBP into layered α-ZrP could be responsible for their enhancement. The mechanism for the enhancement of I 0 and D I 3 - were investigated in detail, supported by X-ray diffraction (XRD) electrochemical impedance spectra (EIS) and limiting current measurements.

Protein/DNA/Inorganic Materials: DNA Binding to Layered α‐Zirconium Phosphate Enhances Bound Protein Structure and Activity

Successful intercalation of calf thymus DNA into the galleries of layered alpha zirconium phosphate (α-Zr(HPO4)2· H2O, α-ZrP) was facilitated by met-hemoglobin (Hb) and tetrabutylammonium (TBA) hydroxide. Intercalation of DNA, in turn, improved the properties of the co-intercalated protein. The protein structure, for example, was improved significantly and activities were enhanced by more than fivefold.

Tuning the Properties of Hb Intercalated in the Galleries of α-ZrP with Ionic Strength: Improved Structure Retention and Enhanced Activity

The influence of ionic strength on the behavior of met-hemoglobin (Hb) bound to layered α-zirconium phosphate (α-ZrP) was investigated. Small increases in the ionic strength (5 mM to 80 mM K2HPO4, pH 7.2) indicated large improvements in the bound protein structure, activity, and stability. The number of ZrP units occupied per bound Hb (stoichiometry) increased from 773 to 2000 units. The Soret absorption band and the corresponding circular dichroism (CD) spectra (Soret) indicated that there are considerable improvements in the protein structure around the heme pocket with increase in ionic strength. Monitoring the UV−CD in the 190−250 nm range indicated only minor changes with ionic strength, and some formation of α-helical coiled coils was indicated. The peroxidase-like activity of the bound Hb increased approximately threefold when the ionic strength was increased from 10 mM to 40 mM K2HPO4 (pH 7.2). Free Hb did not indicate similar improvements in structure or activity. Differential scanning calorimetr...

Intercalation Mechanism and Interlayer Structure of Hexadecylamines in the Confined Space of Layered α-Zirconium Phosphates

Well-defined hexadecylamine (HDA) intercalated structures, either interdigitated layers, bilayers, or hybrid layers of both, in a confined space of highly functionalized layered alpha-zirconium phosphates (alpha-ZrPs) have been prepared based on the two-step intercalation mechanism and these distinct intercalated structures can serve as a model system to investigate the interactions of two monolayers whose amphiphilic tails are adjacent to each other. At the first intercalation step, the electrostatic interaction between HDAs and alpha-ZrP is dominant and results in an interdigitated layer structure (d(001) = 3.0 nm) and the interdigitated layer is saturated at around phi = 50%, where phi is the weight fraction of intercalated HDAs in the intergallery of alpha-ZrP. For phi higher than 50%, the bilayer structure (d(001) = 4.3 nm) emerges due to further hydrophobic interaction between HDAs initially grafted to alpha-ZrP and unanchored HDAs and the relative fraction of the bilayer structure over the interdigitated layer increases with the increase in the intercalated amount of HDAs. The intriguing morphology of alpha-ZrP tactoids intercalated with HDAs in coexisting bilayers and interdigitated layers is observed by using microtomed TEM and the two-step intercalation has also been verified with TGA and FT-IR. Also, a structural transition from the bilayers to the interdigitated layers is monitored by using in situ synchrotron WAXS showing that the hydrophobically intercalated HDAs are selectively deintercalated at a relatively low decomposition temperature around 220 degrees C.

Humidity effect on electrical properties of layered α-zirconium phosphate

The electrical properties of alkali ions exchanged zirconium hydrogen phosphate Zr(HPO 4) 2·H 2O (α-ZrP) are investigated by impedance spectroscopy technique. Cole–cole plots are used to describe the characteristic changes of electrical properties with relative humidity. The evaluated bulk resistance from the equivalent circuit shows exponential dependence of relative humidity. The surface protons of layered (α-ZrP) contribute to electrical conduction. The largest sensitivity is obtained for K ion exchanged systems.

Preparation and characterisation of histidine– and iron–histidine–α-zirconium phosphate intercalation compounds. Catalytic behaviour of the iron derivatives in oxidation reactions with H2O2

The amino acid histidine (His) easily diffuses into layered α-zirconium phosphate if the layers are first pre-swelled via preparation of a metastable ethanol intercalate α-Zr(HPO4)2·2EtOH. Different materials are obtained by varying the contact time and the His solution concentration. A new compound of composition α-Zr(HPO4)2His1.2·5H2O has been selected for its higher His content and remarkable interlayer spacing of 18.4 A. The FT-IR spectra of this compound show that His interacts with the P–OH groups of the host through the NH2 primary group of the amino acid. Zr(HPO4)2His1.2·5H2O takes up Fe(II) and Fe(III) ions from the respective iron sulfate solutions by ion-exchange. This process, accompanied by a partial release of His to the contact solutions, gives rise to intercalates in which the metal ion∶His molar ratios are close to 1∶1. The reflectance spectra account for the presence, in the interlayer region, of a Fen+∶His = 1∶1 coordinated species. The iron–histidine intercalation compounds have been tested as catalysts in the oxidation of an organic substrate, Indigo Carmine, by H2O2 and the results compared with those obtained with the H2O2 solution alone, with Fenton's and Ruff's reagents (a H2O2 aqueous solution containing respectively iron(II) or iron(III) ions as catalysts) or with H2O2 solutions containing the Fen+–His (1∶1) complex species. The solid catalysts, recovered after reaction, have been re-used for further runs.

Silica-based mixed oxide pillared layered α-zirconium phosphates

Mixed Al–Si, Cr–Si and Fe–Si oxide pillared α-zirconium phosphates have been prepared by intercalation of binary oxide oligomers into colloidal α-zirconium phosphate (ZrP) at reflux temperature. Most of the pillared materials with less than 10 wt.% of trivalent metal oxide are thermally stable on calcination at 773 K and maintain free heights between 1.39 and 1.55 nm. These materials present high BET surface area (152–243 m 2 g −1), large pore volume (0.075–0.115 cm 3 g −1) and high surface acidity (0.79–1.64 mmol g −1). They are more active than pure silica pillared ZrP for acid-catalyzed reactions such as isopropanol dehydration and toluene disproportionation.

Synthesis of resorcinol from meta-phenylenediamine in the presence of zirconium phosphates

Aqueous meta-phenylenediamine was converted to resorcinol and ammonia in the presence of layered α-zirconium phosphates (α-ZrP) and γ-zirconium phosphates (γ-ZrP). The compounds were characterised using TGA–DTA, XRD and adsorption experiments studying the uptake of the relevant organic compounds from aqueous solution. The reactions were carried out in a batch autoclave at 225°C and corresponding autogenous pressure. Leaching of phosphate groups, quantitated by UV–VIS, was noticed for α-ZrP and α-ZrP400 (α-ZrP calcined at 400°C) resulting in a slight drop in the solution pH towards 5.5. XRD powder patterns of α-ZrP taken after reactions showed a slight structural transformation of α-ZrP’s toward (NH 4)Zr 2(PO 4) 3. High resorcinol yields were obtained when using γ-ZrP without any phosphates leaching into solution (pH=8.3). The acid sites on γ-ZrP, however, were poisoned by the product ammonia. Although leaching of phosphates into solution occurred when calcining γ-ZrP at 400°C (pH=2.8), the high yields in resorcinol attained at the end of the second reaction implies that zirconium phosphates can be used as regenerable, heterogeneous reagents.

Proteins Immobilized at the Galleries of Layered α-Zirconium Phosphate: Structure and Activity Studies

Facile immobilization of myoglobin (Mb), lysozyme (Lys), hemoglobin (Hb), chymotrypsin (CT), and glucose oxidase (GO) at the interlayer regions of layered α-zirconium phosphate (α-ZrP) under ambient conditions (pH 7.2, room temperature) is described. The proteins retain their structure and activity after immobilization. The interlayer spacings of α-ZrP (observed in powder XRD experiments) increased from 7.6 Å (for α-ZrP) to 53, 47, 66, 62, and 108 Å when Mb, Lys, Hb, CT, and GO are bound to the matrix, respectively. These XRD data strongly suggest intercalation of the proteins in the galleries. The binding constants of the above proteins with α-ZrP, estimated from the centrifugation method, are in the range of 104−106 M-1. The α, β, and the soret absorption bands of Mb/Hb immobilized on α-ZrP were essentially superimposable with those of the native proteins in solution. The FTIR spectra of the enzyme−α-ZrP composites, measured with an attenuated total reflectance accessory, show that the amide I and amide II bands of the immobilized proteins correlate well with those of the free proteins. The circular dichroism (CD) spectra of immobilized proteins, similarly, are quite similar to those of the corresponding native proteins. These various spectral investigations are consistent with high affinity binding of the proteins to α-ZrP with considerable retention of protein structure. Activities of the immobilized proteins are investigated for comparison with those of the proteins in solution. The hydrolytic activity of immobilized lysozyme is essentially the same as that of the free protein. CT and GO showed small but reproducible increases in their activities upon immobilization. The enzymatic activity parameters, Km and Vmax, observed for the immobilized Mb, lysozyme, and GO are comparable to those of the native proteins. The peroxidase activity of Mb/Hb depended on the substrate structure. Activities are higher for the immobilized Mb when p-methoxyphenol, phenol, and m-aminophenol are used as the substrates. The activities have been lower, on the other hand, when aniline, o-cresol, and o-aminophenol are used as the substrates. In general, the ratio of the specific activities of immobilized Mb to those of free Mb roughly increases with increased substrate oxidation potential. The interlayer spacings observed for the protein−α-ZrP composites show a strong correlation with the average size of the protein, and this method may be useful for the determination of protein size. The binding affinities of the proteins correlate with their respective pI values, with the exception of Hb, suggesting the role of electrostatic interactions in the binding process. The average area occupied per protein molecule is larger than the average area of cross section of the proteins, and the area occupied correlates with the reciprocal of the corresponding binding constants. These studies indicate that the hydrophilic character of the matrix and its surface charge are important attributes that influence the bound protein behavior. Enhanced activity of Mb with specific substrates and improved activities of CT and GO are additional advantages of immobilization. Control over the immobilized protein properties is important for their application in biosensors and biocatalysis.

Photoinduced electron transfer from N, N, N′, N′-tetramethylbenzidine incorporated into layered zirconium phosphate studied by ESR and diffuse reflectance spectroscopies

N, N, N′, N′-Tetramethylbenzidine was introduced into layered α-zirconium phosphate (α-ZrP) during synthesis of α-ZrP and by impregnation. N, N, N′, N′-Tetramethylbenzidine (TMB) was photoionized at room temperature by 370 nm visible light irradiation by a monophotonic process to form stable TMB + radical cations which were detected by electron spin resonance and diffuse reflectance spectroscopies. TMB is incorporated into α-ZrP only on the external surface both during synthesis of α-ZrP and by impregnation. No net photoyield difference is seen between these two incorporation methods. The half-life of photoinduced TMB + ion in α-ZrP is about 10 h at room temperature which is an order of magnitude higher than in micelles or amorphous silica gel.

Photoinduced charge separation of phenothiazine derivatives in layered zirconium phosphate at room temperature

The photoionization of alkylphenothiazines in layered α-zirconium phosphate (α-ZrP or ZrP) has been studied by electron spin resonance (ESR) and diffuse reflectance spectroscopies. Alkylphenothiazines (PCn where n=1, 2, 3, 4, 6, 8, 10, 16) were synthesized and used to study the effects of the alkyl chain length. Phenothiazine and N-alkylphenothiazines were incorporated into ZrP by impregnation and ion-exchange methods. By both methods N-alkylphenothiazines are only incorporated onto the external surface of zirconium phosphate rather than into the interlayer space. The alkylphenothiazines photooxidize at room temperature to form stable alkylphenothiazine cation radicals (PCn+) which are measured by ESR and diffuse reflectance. The framework of ZrP is suggested to be the electron acceptor. Both the photoyield and the decay rate of the alkylphenothiazine cation radical depend on the alkyl chain length. As the alkyl chain length of the PCn+ cation radical increases from methyl to hexyl, the photooxidation yield increases; and as the alkyl chain length increases further from hexyl to hexadecyl, the photooxidation yield decreases. However, the decay rate of the PCn+ cation radical gradually increases from methyl to hexadecyl which is explained in terms of a greater inductive effect for longer alkyl chains on the PCn+ cation radicals. Also, the resolution of the ESR spectrum decreases with increasing alkyl chain length which is interpreted as being due to decreasing mobility of the radical which should also decrease the decay rate. Both impregnation and ion-exchange methods are reasonably effective for incorporating alkylphenothiazine molecules into ZrP for efficient photooxidation. The photoyields of N-alkylphenothiazines in ZrP are larger than in silica gel which suggests that ZrP assemblies can be utilized for solar energy conversion and storage.

Mixed alumina chromia pillared layered α-zirconium phosphate materials: acidity and catalytic behaviour for isopropyl alcohol decomposition

The surface acidity and the catalytic behaviour of a series of mixed alumina chromia pillared α-zirconium phosphates have been studied. The acid properties of these catalysts have been evaluated by measurements of the NH 3 thermal programmed desorption, pyridine adsorption and dehydration of isopropyl alcohol at 220°C. Both surface acidity and catalytic activity show a marked dependence on the Al Cr ratio, but they are not a monotonic function of the catalyst composition. The most acid materials were those with Al Cr ratios between 20 80 and 40 60 . From this ratio, the acidity is gradually reduced with increasing Al concentration. The activity of the mixed alumina chromia pillared materials for isopropyl alcohol decomposition is considerably enhanced with respect to the analogous chromia pillared compounds of the order of 20 times for maximum activity. The most active materials were those with the highest micropore volumes. All catalysts show selectivities higher than 99% for the dehydration of isopropyl alcohol.

NMR investigation on molecular mobility of pyrazole and pyridazineintercalated in layered α-zirconium phosphate

Intercalation compounds of α-zirconium phosphate with pyrazole and pyridazine have been investigated by solid state NMR measurements, in order to have information about the proton conduction mechanism. 13C chemical shifts, obtained under CP MAS conditions, show that both heterocycle guest molecules are in the protonated state, at least partially. Proton spin-spin relaxation experiments have been carried out in the temperature range 200–400 K. At 273 K no molecular motions occur in either sample on the measurement time scale. With increasing temperature, a narrow component appears in the free induction decay of the pyrazole intercalate, which can be assigned to proton containing fragments involved in translational diffusion. This component is absent when all the mobile acidic protons are substituted by deuterons; this excludes translational mobility of the guest molecules and supports the Grotthus type mechanism previously proposed. No significant changes are observed in the free induction decay of the pyridazine intercalate with increasing temperature, thus indicating hindered rotation up to 350 K. These interpretations agree with the results obtained for both intercalation compounds from spin-lattice relaxation experiments in the temperature range 150–350 K.

Mixed alumina–chromia pillared layered α-zirconium phosphate

Mixed aluminium(III)–chromium(III) oligomers have been intercalated into colloidal α-zirconium phosphate by in situ, polymerisation from buffered mixed Al–Cr solutions at the reflux temperature. Single mixed species are formed in a wide range of added Al : Cr ratios, between 10 : 90 and 70 : 30. All materials have high basal spacings between 25.7 and 42.1 A at room temperature. 27Al MAS NMR studies suggest that the mixed Al–Cr oligomeric species intercalated at high Al : Cr ratios are higher polymers than the tridecamer [AlO4Al12(OH)24(H2O)12]7+. On calcination at 400 °C most intercalation compounds maintained free heights between 13.5 and 24.8 A, suggesting that true pillared materials are formed that are thermally stable up to 700–800 °C, after which they began to decompose into Cr2O3 and collapsed structures of aluminium zirconium phosphate. The surface of zirconium phosphate shows strong affinity for aluminium at high Al : Cr ratios as indicated by XPS analysis. The mixed alumina–chromia pillared α-zirconium phosphate materials presented high BET surface areas (158–634 m2 g–1) and high micropore volumes (0.072–0.322 cm–3 g–1) up to an Al : Cr ratio of 70 : 30. Above this ratio, the materials are barely porous with low surface areas.

Preparation of Layered α-Zirconium Phosphate with a Controlled Degree of Hydrolysis via Delamination Procedure

The hydrolysis of α-Zr(HPO4)2 · H2O has an appreciable influence on its ion exchange, intercalation, proton conductivity, and catalytic properties; it is furthermore of importance for the preparation of pillared porous materials. Direct hydrolytic attack in alkaline media can be carried out only for the surface phosphate groups of the layered crystals. To overcome this difficulty the crystals were first delaminated by an intercalation of methylamine; the colloidal dispersion was left 24 h to hydrolyze at fixed pH value (in the range 9-12) and finally, after regeneration in H form by acidification, the hydrolyzed Zr(HPO4)2-x-(OH)2x · n H2O materials were separated from the solution. The hydrolytic cycle can be repeated several times if high degrees of hydrolysis are desired; however, the stability of the α layer was found to be seriously compromised for high degrees of hydrolysis, and amorphous products were generally obtained for x values higher than 0.8-0.9.