Accelerated microwave assisted synthesis of alumino-germanate imogolite nanotubes

Ge-imogolite nanotubes (Al2GeO7H4) can be readily obtained in various lengths, chemical compositions and crystallinities, opening up new perspectives for applications. Their classical synthesis includes the nucleation of roof-tile shaped precursors at room temperature followed by a heat promoted growth (typically 95 degrees C) for at least 4 to 7 days. To circumvent this excessively long synthesis duration, we used microwave assisted heating to accelerate the growth. Micron sized tubes were formed from 1 h at 100 degrees C, and the best results were obtained for 2 hours at 200 degrees C, i.e. approximately 100 fold faster when compared to the conventional heating process. Additionally, tube lengths were shifted towards larger values by one order of magnitude, leading to micron sized Ge-imogolites vs. 100 nm with conventional heating. Specific microwave effects as well as mechanisms leading to these longer tubes are also discussed.