Metal chalcogenide nanoparticle gel networks: their formation mechanism and application for novel material generation and heavy metal remediation via cation exchange reactions

METAL CHALCOGENIDE NANOPARTICLE GEL NETWORKS: THEIRFROMATION MECHANISM AND APPLICATION FOR NOVEL MATERIALGENERATION AND HEAVY METAL REMEDIATION VIA CATIONEXCHANGE REACTIONSby IRINA R. PALAMay 2012Advisor: Dr. Stephanie L. BrockMajor: ChemistryDegree: Doctor of PhilosophyThe dissertation research is focused on (1) uncovering the mechanism of metalchalcogenide nanoparticle (NP) gel formation; (2) extending the cation exchange reactionprotocol to zinc sulfide gel networks, with the goal of accessing new aerogel chemistriesand understanding the factors that drive the process; and (3) conducting a quantitativeanalysis of the ability of ZnS aerogels to remove heavy metal ions from aqueoussolutions.The mechanism of metal chalcogenide NP gel formation was investigated usingRaman spectroscopy and X-ray Photoelectron Spectroscopy to probe the chemicalchanges that occur during the gelation process. These techniques suggest that the bondingbetween the particles in the CdSe NP gels is due to the oxidation of surface selenidespecies, forming covalent Se–Se bonds. Treating the gel networks with a suitablereducing agent, such as a thiol, breaks the covalent bond and disperses the gel network.The addition of sodium borohydride, a “pure” reducing agent, also breaks down the gelnetwork, strengthening the hypothesis that the reducing character of the thiols, not their