The solvothermal synthesis of Co NPs with PTC as a growth agent was repeated using Co16–calixarene 1 as an independent nucleation agent. Initial studies included oleic acid as a co-surfactant, based on our previous studies and the reaction conditions above. However, the mean particle sizes were too small and the polydispersities were too large to meet our criteria for seeded growth with stoichiometric control. We attribute this to the effects of oleic acid on Co NP growth, including surface passivation, suppression of decarbonylation, and digestive ripening, any of which can perturb NP nucleation and growth under thermal conditions.
Earlier studies have established that multivalent calixarenes can provide a useful platform for controlling nucleation events during NP synthesis.,,, We have also obtained evidence that prenuclear “capped cluster” intermediates are generated by the thermolysis of octakis-[propargyl–Co2(CO)6]tetra-C-methyl resorcinarene (Co16-C1R), a truncated version of 1. Briefly, heating Co16-C1R in refluxing ODCB and in the presence of oleic acid produced Co NPs below 4 nm, presumably via coalescence of capped-cluster intermediates. The calixarene-stabilized Co NPs were resistant to digestive ripening or aggregative growth after prolonged heating; in contrast, Co nanoclusters coated with monovalent alkynes increased in mean size and polydispersity when kept under similar conditions.
4. Design of New Materials for Environmental Protection and Extraction Purposes
Based on fundamental thermodynamics, chelating ligands are selected for their incorporation into polymeric frameworks to give new materials (recyclable) for environmental protection. Within this context, new calixarene derivatives and non-macrocyclic (EDTA derivatives) containing materials are synthesised, characterised and their extraction properties toward pollutant ions are investigated. Extensive research is being carried out on the interaction of new calixarene derivatives and toxic metal cations such as mercury(II), cadmium(II), lead(II), copper(II), as well as calixpyrrole derivatives and their interaction with polluting anions.
3.2. Calixarene and Resorcarene derivatives - Cation Interactions
Calixarene derivatives form an important class of macrocyclic ligands and a new methodology for the synthesis of these compounds has been recently developed at Surrey. They are unusual in that they contain both hydrophobic and hydrophilic regions. The reaction medium plays an important role in complexation processes involving calix(4)arene derivatives to the extent that the selective binding of the hydrophilic cavity for a cation can be altered as a result of conformational changes taking place between the solvent and the ligand. This important observation makes it possible to consider the solvent effect on the complexing abilities of calixarene derivatives toward metal cations in 'allosteric' media and the implications of these findings in solvent extraction technology. Extensive research is undergoing on resorcarene-cation interactions.
In addition to the work on calixarene-complexed rare earth ions, we have also initiated an investigation of the synthesis and incorporation of porphyrin- and crown ether-complexed rare earth ions into silica sol gels. Just started this summer, in the first months of this work we have focused on the synthesis and characterization of some complexes published in the literature and examining their solubilities in the TEOS sol-gel precursor. These ligands may prove interesting in that, because of their planar structure, they do not completely surround the rare earth ion, but leave open coordination sites that might show intermediate levels of fluorescence in the gels compared to either uncomplexed rare earth ions (which show no florescence until the gel has been annealed to glass at 800 ˚C) of from complexes containing the thenoyltrifluoroacetonate (tta) with phenanthroline ligands (which show fluorescence in gels dried only at 90 ˚C). This project has, to date, included the work of six undergraduate students over three summers and one senior project student. Both students working on the project this past summer are senior chemistry majors who are continuing their work now during their year-long senior project. This grant has allowed me to continue to pursue a new direction in my research program that parallels my continuing collaborative work with my physics colleague on the spectroscopy of uncomplexed rare earth ions in sol-gel matrices.