Figure 2.

(a,b) Amounts of fluorescein loaded into MOF NP (obtained from the difference in absorption between the starting fluorescein solution and the supernatant recovered after loading) as a function of external fluorescein concentration fit to Langmuir-type curves. The calculated dissociation constants and maximum payload capacities per mg of NPs are: $K_{\mathrm{D}}^{MIL100}$ = 11 μM, $K_D^{MIL101}$ = 136 μM, $P_{\max }^{MIL100}$ = 649.4 μg, $P_{\max }^{MIL101}$ = 413.5 μg (c,d) Measurements of nitrogen gas absorption by the MOF-NPs. The BET surface area obtained for MIL-100(Fe) NPs is 2004 m²/g and for MIL-101(Cr) is 3205 m²/g. Taking both into account yields a mean area occupied by one fluorescein molecule of 2 nm² for MIL-100(Fe) and 5 nm² for MIL-101(Cr).