Fast hydrothermal and microwave synthesis of high purity methylated imogolite nanotubes

To take advantage of the many potential applications of hybrid imogolites, a one-pot reproducible and fast synthesis route is desirable. However, the current protocols are time consuming, necessitating heating for several days to temperatures of around 90 °C, and often lead to turbid solutions. Here, a new synthesis is developed at higher temperature that produces a purer nanotube dispersion within a few hours. In this work, we increased the reaction temperature from 90 °C to 150 °C and even 200 °C, using either a conventional resistive oven or a microwave. Characterization of the suspensions obtained after different thermal treatment durations using several characterization techniques, including FTIR spectroscopy, SAXS, XRD, UV–visible spectroscopy and TEM microscopy, we show that high purity limpid methyl-imogolite suspensions can be obtained within 3 h at 150 °C and 1 h at 200 °C. We also evidence that nanotubes are intermediate species that are obtained in a limited time window that varies with temperature and heating mode. At low heating duration, their precursor, metastable proto-imogolite, is predominant while at high heating duration, imogolite decomposes to form aluminum hydroxides. Increasing the temperature within the corresponding time window results in an increase of the nanotube length.