Synthesis And Application Of Nanomaterials In Ionic Liquid Microemulsion

The dispersve and continuous phase of conventional microemulsion can be substituted by ionic liquid (IL) to fabricate IL microemulsion. Thereinto,1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) was used to substitute conventional solvent and form ionic liquid microemulsion (W/IL or IL/W) with water by the aid of non-ionic surfactant TX-100. The as-prepared microemulsion can be considered as a novel and green medium. The IL microemulsion possesses double features of microemulsion and IL, and it can be used as green medium for electro-synthesis, preparation of nanomaterials and organic-synthesis.This dissertation is concentrated on the preparation of a series of nanomaterials by using electrochemical and chemical methods in W/IL microemulsion. The structures, micrographs, properties and applications of the as-prepared nanomaterials have been investigated by X-ray diffraction (XRD), ultraviolet visible absorption spectra (Uv-vis), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectra, cyclic voltammetry (CV) and chronoamperometry. Furthermore, the bimetallic Ag/Au nanoparticles were prepared by underpotential deposition (UPD)-redox replacement technique, and the reduction of benzyl chloride by the as-prepared nanoparticles was also studied. The main points of this dissertation are summarized as follows:(1) The [BMIM]PF6was prepared by two steps method, and the W/IL microemulsion was also prepared according to the phase diagram of TX-100/H2O/[BMIM]PF6ternary system. The electrochemical window of the W/IL microemulsion is2.4V, which confirmed that it can be used as mediu m for electro-synthesis on account of its electrochemical stability. Under the premise of maintaining the stability of the microemulsion structure, the relationships between solubilization of the microemulsion and temperature and CNaCl in water were investigated, which confirmed that it can be also used as medium for chemical reactions.(2) The electrochemical behavior of pyrrole in [BMIM]PF6and W/IL, IL/W, B.C. microemulsions were investigated. The largest current density and the fastest polymerization rate are presented in W/IL microemulsion, which is the most suitable medium for electropolymerization of pyrrole. Then, the PPy films were electrosynthesized potentiostatically in W/IL microemulsion, electrolyte/molecular solvent system (0.25mol L-1[BMIM]PF6/acetonitrile) and [BMIM]PF6. The peak current of the anodic wave of the PPy films grown in W/IL microemulsion (1.2mA) is about three times than that of the films obtained in [BMIM]PF6(0.4mA). Therefore, the W/IL microemulsion as an electrolyte for pyrrole electropolymerization was useful to improve the electrochemical activity. The as-prepared films were characterized by SEM. It is demonstrated that the film grown in W/IL microemulsion is composed of microballs with a mean size of100nm. Because of special conductivity and microstructure of W/IL microemulsion, it can be used as a medium for preparing nanomaterials by electro-synthesis.(3) Pd nanoparticles were prepared by in situ reduction of TX-100in the W/IL microemulsion. It can be seen from UV-vis spectra that the Pd2+was quickly reduced to nano-Pd in two minutes. TEM images show that the average size of the as-prepared Pd nanoparticles is about3nm with a narrow size distribution. In order to investigate the catalytic properties of the Pd nanoparticles dispersed in ionic liquid microemulsion, Heck reaction of the cross-coupling of butyl acrylate with iodobenzene was employed. The effects of reaction time, temperature and base on the Heck reaction are obvious. When the reaction was proceded under100℃, the product yield reached the maximum100%after2h (Et3N was used as base). The yield of the fourth cycle afforded a68%yield in the recycling experiments. In order to extend the application of the system, we also examined other Heck reactions. The product yield of iodobenzene and methyl acrylate, ethyl acrylate and styrene was97%,90%and81%, respectively.(4) Two metal precursors can be dissolved in dispersive and continuous phase of the W/IL microemulsion simultaneously.(NH4)2PdCl6and HAuCl4·4H2O were dissolved in water and [BMIM]PF6phase respectively to prepare bimetallic Pd4Au nanoparticles by in situ reduction and replacement reactions. The Uv-vis spectra and XRD patterns demonstrated that HAuCl4·4H2O is mainly reacted with Pd nanoparticles to form Pd-Au alloy, and the Pd4Au nanoparticles are totally encapsulated by the surrounding Pd atoms. TEM images show that the average size of as-prepared Pd4Au nanoparticles is about4.5nm with a narrow size distribution. The Pd and Pd4Au nanoparticles were supported on carbon tubes (CNTs) for the oxidation of ethanol in alkaline medium. For the same loading mass of metal, the value of forward anodic peak current density (If) on the Pd4Au/CNTs (28.56mA cm-2) is about three times of that on the Pd/CNTs (9.65mA cm-2). The corresponding results of chronoamperometry imply that the Pd4Au/CNTs have better resistance to poisoning and long-term stability for ethanol oxidation.(5) The composite material of Pd nanoparticles and graphene oxide (GO) was prepared by in situ reduction in the W/IL microemulsion. The GO was reduced by hydrazine hydrate to obtain graphene decorated with Pd nanoparticles (Pd/Graphenemic). The as-prepared composite material was used as electrocatalyst for the ethanol electrooxidation under alkaline condition. The SEM and TEM images show that the monodispersed Pd NPs with a mean size of4nm were deposited on the basal planes and the edges of graphene. For comparison, the value of If on the Pd/Graphenemic electrode (45.98mA cm-2) is about1.5times of that on the Pd/Graphenesol electrode prepared in solution (29.82mA cm-2). The corresponding results of chronoamperometry imply that the Pd/Graphenemic has better resistance to poisoning and long-term stability for ethanol oxidation.(6) The bimetallic Ag/Au nanoparticles were prepared by underpotential deposition (UPD)-redox replacement technique on the basis of Au nanoparticles modified glassy carbon (GC) electrode. The as-prepared Ag/Au nanoparticles were characterized by SEM and EDS. The corresponding results imply that the mean size of nanoparticles is about40nm and the surface composition of Ag is about0.03atom%. The as-prepared modified electrodes were used as the working electrodes for the reduction of benzyl chloride. The results of CV demonstrate that the peak potential (-1.62V) on the Ag/Au/GC electrode is more positive than that on the Ag/GC electrode (-1.84V). The Ag/Au/GC electrode has better catalytic activity for benzyl chloride reduction. The chronoamperometry test shows that the Ag/Au/GC electrode possesses good long-term performance in the electrocatalysis.