We have found that the 3D zeolitic imidazolate framework ZIF-7 exhibits far more complex behavior in response to the adsorption of guest molecules and changes in temperature than previously thought. We believe that this arises from the existence of different polymorphs and different types of adsorption sites. We report that ZIF-7 undergoes a displacive, nondestructive phase change upon heating to above ∼700 °C in vacuum, or to ∼500 °C in CO2 or N2. This is the first example of a temperature-driven phase change in 3D ZIF frameworks. We predicted the occurrence of the high-temperature transition on the basis of thermodynamic arguments and analyses of the solid free-energy differences obtained from CO2 and n-butane adsorption isotherms. In addition, we found that ZIF-7 exhibits complex behavior in response to the adsorption of CO2 manifesting in double transitions on adsorption isotherms and a doubling of the adsorption capacity. We report adsorption microcalorimetry, molecular simulations, and detailed XRD investigations of the changes in the crystal structure of ZIF-7. Our results highlight mechanistic details of the phase transitions in ZIF-7 that are driven by adsorption of guest molecules at low temperature and by entropic effects at high temperature. We derived a phase diagram of CO2 in ZIF-7, which exhibits surprisingly complex re-entrant behavior and agrees with our CO2 adsorption measurements over a wide range of temperatures and pressures. We predicted phase diagrams of CH4, C3H6, and C4H10. Finally, we modeled the temperature-induced transition in ZIF-7 using molecular dynamics simulations in the isobaric-isothermal ensemble, confirming our thermodynamic arguments.

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Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive Cu(2+) detection is very important to prevent over-ingestion, and visual detection using unaugmented vision is preferred for practical applications. In this study, hyperbranched polyethyleneimine-protected silver nanoclusters (hPEI-AgNCs) were successfully synthesized using a facile, one-pot reaction under mild conditions. The hPEI-AgNCs were very stable against extreme pH, ionic strength, temperature, and photoillumination and could act as sensitive and selective Cu(2+) sensing nanoprobes in aqueous solutions with a 10 nM limit of detection. In addition, hPEI-AgNCs-doped agarose hydrogels were developed as an instrument-free and regenerable platform for visual Cu(2+) and water quality monitoring.

Mesoporous Li 3 V 2 (PO 4 ) 3 -carbon (LVP-C) microspheres are synthesized using Baker's yeast cells as both mesoporous structure templates and amorphous carbon sources. We find that the vanadium cations are combined with the negatively charged hydrophilic groups and are self-assembled both on the yeast cell wall surface and inside the cell by electrostatic interaction and metabolism regulation, respectively. The self-assembly leads to the formation of LVP-C microspheres with diameters of 1-8 mm. These microspheres are composed of densely aggregated nanoparticles (20-40 nm) as well as interconnected nanopores (2-15 nm), and hence they are of mesoporous nature. The nanoparticles can be easily brought into contact with electrolyte, and the open mesoporous structure allows lithium ions to easily penetrate into the microspheres. The carbon network (16.4 wt.%) on the surface of the Li 3 V 2 (PO 4 ) 3 nanoparticles facilitates electron diffusion. The mesoporous LVP-C microspheres have a high discharge capacity (about 126.7 mAh g À1 ), only 2% capacity loss of the initial value at the 50th cycle at a current density of 0.2 C, and a high rate capacity of 100.5 mAh g À1 at 5 C in the region of 3.0-4.3 V. The apparent Li + diffusion coefficient is found to be 6.76 Â 10 À10 cm 2 s À1 . The microspheres could be an ideal cathode-active material that fulfills the requirements of rechargeable lithium batteries for high power applications.

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A series of dual-ligand cofunctionalized fluorescent gold nanodots with similar fluorescence and diverse surface properties has been designed and synthesized to build a protein sensing array. Using this "chemical nose/tongue" strategy, fluorescence response patterns can be obtained on the array and identified via linear discriminant analysis (LDA). Eight proteins have been well distinguished at low concentration (A280 = 0.005) based on this sensor array. The practicability of this sensor array was further validated by high accuracy (100%) examination of 48 unknown protein samples.

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