Synthesis Of Nanomaterials Via Liquid-Liquid Interface Modulated By Ionic Liquids

As greener solvents, ionic liquids (ILs) possess lots of special features compared to the traditional volatile organic solvents:(1) wide liquidus temperature range (-96～400℃) and high thermal stability;(2) negligible vapor pressure and non-flammability;(3) high ionic conductivity, large electrochemical window and high electrochemical stability;(4) excellent solvents for a wide range of inorganic and organic materials;(5) low interface tensions and high nucleation rates;(5) designability of structures and properties. These features make ILs attractive for extractions, separations, organic synthesis and electrochemistry. In contrast to their successful applications in these areas, the use of ILs in inorganic synthesis is still in its infancy and needs to be fully exploited. Therefore, it is interesting but challenging to utilize ILs for the preparation of inorganic nanomaterials with novel morphology and improved properties.In this thesis, the immiscible ILs-H2O interface and the oil-H2O interface modulated by ILs have been utilized for the synthesis of inorganic nanomaterials. In these methods, the precursor is dissolved in one phase and the reducing agent or sulfide in the other phase, and the reaction occurs at the liquid-liquid interface. Designability of ILs has been utilized to tailor physico-chemical properties of the liquid-liquid interface by changing anionic nature and/or alkyl chain length of imidazolium cations of the ILs, and then to tune the structure and morphology of nanomaterials produced at the interface. In addition, an IL-assisted method for the preparation of inorganic nanocrystals via the thermolysis of a single molecular precursor was also systematically studied. The main contents are as follows.Chapter1. Inorganic nanomaterials synthesis assisted by ILs, developed in the recent years, is reviewed in detail. The use of ILs in the preparation of nano-metals,-oxides,-metal chalcogenides and-metal salts is highlighted, in which ILs play important roles as template, capping agent, structure directing agent, reaction agent or solvents. The role of ILs in inorganic nanomaterials synthesis gradually transforms from solvent and template to all-in-one agent. At the same time, some limitations in the applications of ILs in the preparation of inorganic nanomaterials are also discussed, and the prospect for the future development in this field is presented.Chapter2. The immiscible ILs-H2O interface is utilized for the preparation of Ag films assembled by differently shaped Ag nanoparticles. For this purpose, the precursor of AgNO3and reducing agent of o-ethoxyaniline (OEA)were dissolved in water and IL, respectively. They meet at the interface to generate Ag nanoparticles and then assemble into films. The Ag films, including large nanoplates, nanobelts and quasi-cubes, can be easily obtained at [C10mim][PF6]-,[C]omim][Tf2N]-, and [C10mim][BF4]-H2O interface, respectively. Meanwhile, the change of alkyl chain length of ILs can be used to tailor morphology and structure of the nanoparticles and their assembled films, and uniformity of the samples was enhanced with increasing alkyl chain length. However, compared with the variation of anions, the change of alkyl chain length of the ILs shows a weaker effect on the morphology and structure of the products. The structures and morphologies of as-prepared samples are characterized by SEM、TEM、HRTEM、SAED and XRD, and the possible growth mechanism is proposed. The SERS sensitivity of the as-synthesized films were examined using P-Aminothiophenol (PATP) as a probe molecule, in which the large nanoplate and long nanobelt Ag films exhibited highly enhanced SERS responses.Chapter3. We further demonstrate the facile strategy for the tunable synthesis of ZnS NPs and their self-assembly films at the interface of ILs-H2O.The precursors of zinc diethyldithiocarbamate and the sulfiding agent (Na2S) were dissolved in the ILs and water, respectively, and they meet at the interface to generate ZnS NPs and then assemble into films. The films can be further transferred to arbitrary substrates. The ZnS films, deposited at [C8mim][PF6]-、[C8mim][Tf2N]-and [C8mim][BF4]-H2O interface, are assembled by wormlike, dragonlike along with flowerlike and spherical particles, respectively. The as-prepared films become more and more structured with the increase of alkyl chain lengths from C2,to C12for [Cnmim][Tf2N] ILs. The ZnS films are characterized by SEM、EDXS、TRTEM、SAED、XRD and FTIR, and the results indicate that the films prepared from the [C8mim][PFf6]-H2O interface can be indexed to hexagonal wurtzite ZnS, while those from C8mimTf2N-and C8mimBF4-H2O interfaces are cubic ones. ZnS films could be also deposited at the interface of toluene-and1,2-dichloroethane-H2O interfaces, but they are irregular, shapeless and fragile compared with those obtained from ILs-H2O interface. This implied that ILs played crucial roles in determininig the morphology and structures of ZnS films. The continuous nonpolar domains are restricted in a continuous polar network including small water clusters and take shape as a typical wormlike micelle which directed the formation of typical wormlike ZnS particles. Furthermore, various ZnS films exhibit tunable wettability from superhydrophobicity to hydrophilicity.Chapter4. A novel method was developed for successful fabrication of CuS nanostructures with various morphologies. In this method, the precursor of copper cupferronate [Cu(cup)2] in CHCl3reacted with thiourea in water at the ionic liquids (ILs)-modulated CHCl3-H2O interface to generate various CuS nanostructures by using a solvothermal reaction process. The structures of the products and their morphologies of flowers, nanoparticles, urchins and large nanodisks were examined by XRD, SEM, TEM, HRTEM and UV-vis. Influence of the factors, such as the alkyl chain length of imidazolium cations and the anionic nature of the ILs, the molar ratio of Cu(cup)2to thiourea, the volume ratio of IL to organic solvent, the reaction temperature and the reaction time, on the morphology of the products were studied systematically. The results show that ILs play an important template role in directing the formation of CuS nanostructures and the possible growth mechanism for the formation of CuS nanostructures was suggested. Furthermore, the as-prepared CuS samples exhibited high catalytic activity for photodegradation of methyl orange and thermal decomposition of ammonium perchlorate.Chapter5. With the assistance of the ionic liquid of trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethyl pentylphosphinate), we have successfully synthesized short nanorods, quasi-nanospheres and faceted CdS nanoparticles via thermal decomposition of cadmium diethyldithiocarbamate complexes. It was shown that the shape, size and crystallinity of the products could be controlled through delicate regulation of the reaction temperature, monomer concentration, reaction time, and ionic liquid ratio. We found that higher temperature was beneficial to the good crystallinity, while the lower temperature and higher monomer concentration were in favor of anisotropic structures. The used ionic liquid contributed to the formation of hexagonal phase CdS nanocrystals, and its ratio played an important role in determining the ultimate morphology of products. The possible mechanism for the formation of CdS nanocrystals was proposed. Furthermore, the as-prepared CdS samples demonstrated a highly photocatalytic activity for the degradation of methyl orange under UV irradiation.Chapter6. The main contributions of the current research are summarized and the works that need be done in the future are proposed.