Gerd Finger

Optical second harmonic generation (SHG) on p-nitroaniline in large cyrstals of AIPO4-5 and ZSM-5

Abstract Molecular sieves are suitable host matrices to orient molecules of high hyperpolarizability for optical second harmonic generation (SHG). The intensity of the SHG effect of p-nitroaniline (PNA) adsorbed in large AIPO4-5 and ZSM-5 crystals was analyzed as a function of the direction of the plane of polarization of the incident laser light. The SHG effect was found to be strongly direction-dependent. For both AIPO4-5 and ZSM-5, the maximum SHG is obtained if the electric field vector of the incident laser lights oscillations in the direction of the straight channels, thus exciting the pearl-stringlike-incorporated PNA molecules. To have a hihg second harmonic intensity for any technical application requires that a majority of crystals in the sample should be aligned and not used as a disordered powder assemblage. A suitable method to align molecular sieve crystals by means of an electric field is presented.

On synthesis conditions for tailoring AIPO4-5 crystal dimensions

The influence of the gel composition on the dimensions of AIPO 4 -5 crystals formed in the system Al 2 O 3 :P 2 O 5 :(C 2 H 5 ) 3 N:H 2 O:H 2 SO 4 has been studied systematically. A linear correlation between the water content of the reacting gel and both the maximum length and the aspect ratio of the crystals has been found, whereas amine as well as P 2 O 5 contents are controlling the nucleation process. Crystals with sizes ranging from 20 μm to about 750 μm along the hexagonal c -axis can be synthesized with good yields when these correlations are used.

Decomposition of template in SAPO-5 and AlPO4-5 molecular sieves studied by IR and Raman spectroscopy

Abstract The state of the triethylamine (TEA) template in AlPO 4 -5 and SAPO-5 and the characteristics of the framework structure of the molecular sieves were studied by means of IR and Raman spectroscopy. Decomposition of TEA and the formation of OH groups were investigated by DRIFT measurements carried out within the temperature range from 300 to 633 K. It has been found that TEA exists as triethylammonium ions in the as-synthesized samples, and its decomposition occurs via abstraction of ethylene and the stepwise formation of diethyl- and ethylammonium cations. The decomposition mode under a nitrogen atmosphere is different from that under air and requires another temperature. A thermal treatment of both molecular sieves at above 970 K results in a transformation of the structure.

Group behaviour of SAPO-11 molecular sieves containing various metals (Mg, Zn, Mn or Cd, Ni, Cr)

Derivatives of SAPO-11 containing Mg, Zn, Mn, Cd, Ni and Cr as heteroatoms have been synthesized. These additions influence considerably both the properties and the morphology of the crystalline phases synthesized. The products noted as MeAPSO-11 were investigated with light microscopy, scanning electron microscopy (SEM), electron microprobe analysis (EPM), X-ray diffraction (XRD), temperature-programmed XRD, differential thermal analysis (DTA), thermogravimetry (TG), magic-angle spinning nuclear magnetic resonance (MAS NMR) and wet chemical analysis. The materials can be clearly divided into two groups: (1) Mg, Zn or Mn, or (2) Cd, Ni or Cr containing preparations. The results suggest that all metals are incorporated into the framework of SAPO-11 molecular, sieve, though in rather different amounts. The content of heteroatoms decides the properties of the synthesized molecular sieves.

ON THE INNOVATION POTENTIAL OF ALIGNED MOLECULAR SIEVE CRYSTALS

ABSTRACT Our first attempts to align molecular sieve crystals by electric fields are reported. Three promising application fields of aligned molecular sieve crystals are discussed: - materials for frequency doubling (optical second harmonic generation, SHG) - molecular sieve membranes, and - host frameworks to orient guest molecules for spectroscopy.

Faraday communications. A reversible thermal transformation in the molecular sieve AIPO4-5

A reversible thermal transformation occurs at 65 °C in calcined AIPO4-5 as detected by thermogravimetry–differential thermal analysis (TG–DTA), differential scanning calorimetry (DSC) and temperature-programmed X-ray diffraction (TPXRD).