We also examined the thermal stabil

We also examined the thermal stability of the as-synthesized samples in open air at elevated temperature. Samples heated to 200 1C for a duration of 24 h showed no changes in both the X-ray pattern and the color (Fig. 3(b) and (c)). When the samples were heated to 300 1C for a duration of 10 h, the intensity of the XRD peaks was slightly reduced, and the color of the sample changed from white to light yellow (Fig. 3(b) and (c)). If the holding time increased to 24 h, then as can be seen from Fig. 3(b) the intensity of XRD peaks decreased significantly, and the color of the sample changed to dark orange. However, under SEM observation these samples did not show such apparent changes (see Fig. S5(a) in ESIw). Most crystals appeared untouched until the sample was heated to 400 1C for 5 h. After that the crystals broke into smaller particles in ca. 25 nm (see Fig. S5(b) in ESIw). The XRD pattern indicated that the ZIF-8 crystal structure was completely destroyed and ZnO was formed as the final calcination product. The color of the sample turned back to white (Fig. 3(c)). ZIF-8 nanocrystals prepared in methanol can only sustain up to 250 1C.18,22 Thus the ZIF-8 product reported in this work has better thermal stability. The stability in open air was much lower than that in an inert atmosphere or in a vacuum, indicating that the framework structure was quite sensitive either to moisture or oxygen, or both.