Sn-BEA zeolite is known to catalyze the aldose-to-ketose isomerization of xylose and glucose; however, the selectivity to pentose and hexose isomers is not stoichiometric, suggesting the formation of other products. In the present study, we have observed near-complete conversion of all pentose and hexose isomers when xylose and glucose were reacted in the presence of Sn-BEA at 140 °C and 200 °C, respectively. The previously unidentified products were identified by nuclear magnetic resonance and mass spectrometry to be hydroxyalkanoic acids and their derivatives. The hydroxyl-rich acids comprise a significant fraction of the converted sugars and are potential monomers for the synthesis of hyper-crosslinked, biodegradable polymers.

Large PbS protruded cubes, edge- A nd corner-truncated cubes and octahedra, and perfect octahedra with sizes over 200 nm have been synthesized in aqueous solution. By using two surface oxide-free tungsten probes to contact a clean particle, these PbS nanocrystals displayed facet-dependent electrical conductivity behaviors. Both {110} and {100} faces are highly conductive at applied voltages beyond 4 V, but the {111} faces can remain nonconductive even at 5 V. An asymmetric I-V curve was recorded when electrical contacts were made simultaneously on the {110} and {111} facets of a truncated cube. A modified band diagram of PbS is constructed to account for the observed facet-dependent effect. Density of states plots for varying numbers of PbS surface planes show larger areas of conduction band electron occupancy for the (110) and (100) planes than that for the (111) planes at a layer thickness of 3.0-3.4 nm. The work represents that, for the first time, the facet-dependent electrical properties of an n-type semiconductor nanocrystal are directly probed. Facet-dependent electrical conductivity should be a general semiconductor property and can be exploited to fabricate single-nanocrystal operating electronic components.