Fig. 3(a) shows the thermal gravime

Fig. 3(a) shows the thermal gravimetric analysis (TGA) of the as-synthesized samples performed under helium flow. The TGA curve is similar to that reported for micrometre sizedZIF-8 crystals conducted in nitrogen.4 It exhibited a gradual weight-loss step of 11.8% up to ca. 200 1C, corresponding to the removal of guest molecules (these should mainly be H2O) from the cavities or unreacted species (e.g. 2-methylimidazole) from the surface of the nanocrystals. A long plateau was shown in the temperature range of 200–500 1C, indicating high thermal stability of the sample. In situ non-ambient XRD measurements were conducted in vacuum to further illustrate the thermal stability of the product. The sample was heated stepwise from 30 to 450 1C under vacuum, and XRD patterns were measured at different temperatures in between. The results (see Fig. S4 in ESIw) showed that the sample couldmaintain the ZIF-8 framework structure even after 5 h of heating at 450 1C. It is worthy of note that during these measurements significant amounts of guest molecules (again these should mainly be water) were released from the samples, but the release of the guest molecules did not damage the framework structure, as evidenced from the unchanged XRD patterns.