Inclusion compounds of a diol host with xylidines: controlled stoichiometries.
The diol host, 1,1'-bis-(4-hydroxyphenyl)cyclohexane (DHPC) and a number of xylidine isomers as guests formed a series of inclusion compounds that gave rise to various host:guest ratios controlled by crystallization temperatures. For the host DHPC with a particular xylidine isomer, the number of guests included generally decreases as the crystallization temperature increases. The crystal structures of these host-guest compounds were elucidated using single-crystal X-ray diffraction. Their thermal stabilities were characterized by TG and DSC analysis. The selectivity of enclathration by the host was measured by carrying out a series of competition experiments. The kinetics of guest decomposition were studied using isothermal and non-isothermal methods and reconciled with the crystal structures.
Removal of organic contaminants from water using nanosponge cyclodextrin
Insoluble nanoporous cyclodextrin (CD) polymers were synthesized using bifunctional isocyanate linkers. The ability of these polymers to remove selected organic pollutants from water at varying concentrations was studied. The investigated pollutants were selected high-priority chlorinated disinfection by-products (DBPs) and a common odour-causing compound in water, 2-methylisoborneol (2-MIB). The unpleasant musty odour imparted by 2-MIB and geosmin in water can be detected by the human nose even at ng L−1 (parts per trillion) levels. Pre-concentration and extraction of water samples containing low levels of pollutants was performed using solid phase extraction (SPE) and subsequently quantified by gas chromatography-mass spectrometry (GC/MS). Here we show that the CD polymers demonstrate excellent absorption efficiency (>99%) with respect to the organic pollutants, considerably better than granular activated carbon (GAC). The recyclability efficiency of these CD polymers is also reported. Copyright © 2007 Society of Chemical Industry
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.