Synthesis and characterization of CoAPO-5, a cobalt-containing AlPO4-5

Samples of AlPO₄-5, containing a partial substitution of Co(II) for Al(III), were prepared. The results clearly indicated that, as the level of Co(II) added increased, so did the amount of an impurity phase. At low levels of Co addition, the impurity phase was white and may largely be AlPO₄-5. Above about 14 mole% of cobalt addition, an amorphous cobalt aluminum phosphate impurity phase was formed and increased in content until no crystallization was observed at a 35 mole% Co addition level. Addition of base (NH₄OH, NaOH) resulted in increased impurity levels but promoted single crystal growth. Analytical, X-ray, ion exchange, thermogravimetric, and surface-area measurements indicated that only a portion of the cobalt substituted for aluminum, whereas some was present in the ion-exchange sites. The results further indicate that excess alumina is occluded in the CoAPO-5 channels.     

In situ synthesis of AlPO4-14, CoAPO-44 and ZnAPO-34 films on alumina substrates

The in situ synthesis of AIPO₄-14, CoAPO-44 and ZnAPO-34 films supported on alumina substrates was reported in this paper. Continuous AlPO₄-14, CoAPO-44 and ZnAPO-34 films could be formed on alumina substrates at 170–200°C for 24 h. It was found that after calcination, AIPO₄-14 films peeled off from the alumina supports, while CoAPO-44 films turned to be amorphous. No changes could be observed on ZnAPO-34 films before and after calcination, indicating good thermal stability of ZnAPO-34 films.     

Large AlPO4-5 crystals by microwave heating

Microwave heating is applied to the synthesis of AlPO₄-5. After 60 s of heating, large AlPO₄-5 crystals are obtained. XRD, polarization microscopy, and adsorption measurements prove the regularity of the AFI framework. In an optimized microwave synthesis prismatic AlPO₄-5 crystals up to 130 μm long and 40 μm thick could by synthesized. In a two-step synthesis, however, slightly smaller, but very uniform AlPO₄-5 crystals with a narrow crystal size distribution without any amorphous or crystalline byproducts could be obtained. Several possible mechanisms for the fast crystallization within 60 s by microwave radiation are discussed: an increased dissolution of the gel by lonely water molecules, the almost T-gradient-free and, therefore, convection-free in situ heating, and the existence of organic-inorganic arrays as local microassemblies which could transform directly into the AFI framework.     

Degradation of AlPO4-5 by aqueous salt solutions

Calcined template-free AlPO₄-5 is attacked by liquid water and aqueous salt solutions at 25°C, whereas the “as-made” material is resistant to degradation. The extent to which the framework is attacked increases with the salt concentration and depends on the nature of the anion (OH⁻ > I⁻ > S₂O₃²⁻ > Br⁻ > Cl⁻). Phosphate is released to the solution phase and the pH decreases from ∼ 5.5 to ∼ 3.0. AlPO₄-11 and AlPO₄-25 are also attacked by salt solutions, but the effects are smaller than for AlPO₄-5.     

Water adsorption on AlPO4-11: structural changes

AlPO₄-11 adsorbs water at room temperature, resulting in significant structural changes. These changes have been shown to be readily reversible and have been characterized by X-ray powder diffraction, thermogravimetry, n.m.r., and i.r. spectroscopy. No evidence was found for the presence of chemisorbed water.     

Crystal morphology control of AlPO4-11 molecular sieves by microwave irradiation

AlPO₄-11 molecular sieves with morphologies of aggregated sphere, clump, faggot and rod were successfully synthesized by microwave irradiation using diisopropylamine as template. By adjusting the crystallization time, the morphology of the AlPO₄-11 molecular sieves changed from sphere to clump and then to faggot. With the increasing concentration of HF, the morphology of AlPO₄-11 molecular sieves changed from sphere to rod gradually, which exactly consisted with the variation of the XRD patterns. Slow nucleation rate caused by the chelated function of Al–F may be the main reason to direct the crystal growth on the special direction. Meanwhile, some control experiments including use of HCl and increasing the concentration of water also showed the same preferential growth of the crystals.     

Synthesis of small particle-sized CoAPO-5 and CoAPO-20 by surfactant-assisted method

The small particle-sized molecular sieves CoAPO-5 and CoAPO-20 have been synthesized using surfactant-assisted method hydrothermally. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and ultraviolet visible spectrometer (UV-vis). The results show that the obtained CoAPO-5 and CoAPO-20 have AFI and SOD structure respectively. The CoAPO-5 are bundles of acicular crystal and its sizes vary from 0.1 × 2 μm to 0.1 × 5 μm and the CoAPO-20 show spheric morphology with size distribution about 300-800 nm. It is proved that the surfactant-assisted method is an effective route to synthesize small particle-sized molecular sieves.     

VPI-5, AlPO4-8, and MCM-9: similarities and differences

Comparison of X-ray powder diffraction data from AlPO₄-8, MCM-9, and VPI-5 show similarities suggesting that AlPO₄-8 and MCM-9 may be mixtures of phases, one of which is VPI-5. Argon adsorption isotherms imply that MCM-9 does contain Si-VPI-5, whereas AlPO₄-8 does not contain VPI-5.     

Preparation and photostability of porphyrins incorporated into AlPO4-5 molecular sieves by crystallization inclusion

Cationic porphyrins such as tetrakis(N-alkylpyridyl)porphyrins2,3, tetrakis(N-methylpyridyloxy)-phthalocyanines5 or tetrakis(N-alkylpyrido)tetraazaporphyrin6,7 in either metal-free or zinc-containing forms are incorporated readily into AlPO₄-5 molecular sieves by crystallization inclusion. The dye molecules, which are much larger than the channel diameter of the molecular sieve, are encapsulated in mesopores as revealed from adsorption isotherms. The chromophores are predominantly present as monomers as gleaned from u.v./vis spectra. The surprisingly strongly enhanced photostability, in comparison to the photostability in solution, is a direct proof for the encaged state of the porphyrins and a fundamental prerequisite for any potential application under visible light conditions.     

AlPO4 solid solutions containing Ca and Zn phosphates

Portions of an Al₂O₃·3H₂OH₃PO₄CaO compositional triangle were examined at 300°C for a solid solution of Ca (presumably in the form of Ca(H₂PO₄)₂) in the Cristobalite AlPO₄ crystal structure. X-ray diffraction patterns of the various compositions showed the existence of such a solid solution including a lattice parameter change. The limit of the solid solution was approximated at composition 2CaO, Al₂O₃·3H₂O, 6H₃PO₄. This solid solution, however, proved to be unstable at 800°C, but was stabilized by the addition of $\text{1}\text{4}$ mole ZnO at the limit composition.Three points in an Al₂O₃·3H₂OH₃PO₄ZnO compositional triangle were also examined and evidence of solid solution found including a lattice parameter change.     

Influence of admixtures on the crystallization and morphology of AlPO4 crystals

The influence of various uni-, bi-, tri- and tetravalent admixtures on the crystallization and morphology of AlPO₄ has been studied in detail. AlPO₄ crystals were synthesized under hydrothermal conditions. It was found that the phase formation and morphology vary with the type of admixture and its concentration. The crystals were hexagonal, rhombohedral, rounded, irregular, rod shaped and massive in habit. With an increase in the concentration of admixtures, two phases (berlinite and metaphosphates) of the respective admixtures crystallize simultaneously.     

Formation mechanism of nanocrystalline ceria in aqueous solutions of cerium(III) nitrate and hexamethylenetetramine

The formation mechanism of ceria nanoparticles in solutions of cerium(III) nitrate and hexamethylenetetramine has been studied for the first time, using UV/visible spectroscopy and x-ray diffraction. The process has been shown to involve, as an intermediate step, the formation of cerium(III) hydroxycarbonate. The effects of synthesis temperature and solution composition on the micromorphology of the powders have been investigated.     

Concentration-dependent luminescent behaviour of Rhodamine 6G in AlPO4 xerogel monoliths

Homogeneous monolith of AlPO₄ gel doped with Rhodamine 6G (Rh6G) in different dye concentration is prepared by one step process with sol–gel method using the precursors Al(lact)₃ and H₃PO₄. The optical properties of AlPO₄ gel doped with Rh6G have been characterized by UV–vis absorption spectra and fluorescence spectra. Rh6G molecular J-dimers and H-dimers even multimers are analyzed by excitation spectra based on Exciton theory. The structure of AlPO₄ gel doped with Rh6G is investigated by ²⁷Al and ³¹P Magic Angle Solid Nuclear Magnetic Resonance (MAS NMR), ²⁷Al {³¹P} Rotational Echo Double Resonance (REDOR) NMR and ²⁷Al Triple Quantum Magic Angle Spinning (TQ-MAS) NMR. Based on the results of optical spectra and the structural analysis by NMR techniques, The AlPO₄ gel doped with Rh6G dye with molar ratio of Rh6G/Al(lact)₃ of 1 × 10^?4 displays excellent optical properties.