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Paul Heitjans

Publications and source records attributed to Paul Heitjans.

2 recordsLinked to original sources
PubMed2005

Preparation by high-energy milling, characterization, and catalytic properties of nanocrystalline TiO2.

Titanium dioxide (TiO2) is widely used for applications in heterogeneous photocatalysis. We prepared nanocrystalline powders of the anatase as well as the rutile modification by high-energy ball milling of the coarse grained source materials for up to 4 h. The resulting average grain size was about 20 nm. The morphology of the powders was investigated with transmission electron microscopy, X-ray powder diffraction, and BET surface area determination. Measurements of the catalytic activity reveal a maximum as a function of the milling time at about 40 min. This maximum could be explained by a superposition of two counteracting effects. The first one is the increase of the specific surface area resulting in an increase of the catalytic activity, and the second one is a change of the electronic structure at the surface of the TiO2 particles corresponding to a reduction of the surface. The latter one was confirmed by light absorption experiments, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy.

Journal Article↗
PubMed2004

Tracer diffusion measurements in solid lithium: a test case for the comparison between NMR in static and pulsed magnetic field gradients after upgrading a standard solid state NMR spectrometer.

This paper reports on the upgrading of a standard solid state NMR spectrometer, which has been used in combination with a field variable 7 T cryomagnet, to a low-cost combined SFG and PFG NMR spectrometer. Both methods are applied to solid lithium as a simple test case. The results show that under the given conditions SFG NMR and PFG NMR can provide tracer diffusion coefficients for 7 Li diffusion down to about 10(-14) and 10(-13) m2/s, respectively. SFG and PFG NMR are complementary methods. The paper demonstrates advantages and disadvantages of each method with a concrete example and why it is desirable to be able to apply both methods to the same sample.

Diffusion↗