Novel Methodology To Aassemble CNTs And Electropolymerize Conducting Polymer At O/W Interface And Their Applications

In face of resource shortages, energy crisis, climate change and many other global issues, human beings hope for the progress of science and technology. New energies, new materials and breakthrough of concepts and technologies are called for. "Liquid-liquid interface" consisting of two immiscible liquids not only exist in plenty of organism and the natural world, many processes such as "phase transfer catalysis", "separation and extraction", "charge transfer" are all related to this as well. Further more, "liquid-liquid interface" could also be applied for the preparation of materials with special structure due to its special physical and chemical properties. During the last twenty to thirty years, with the rise of nano-materials and nano-technology and the development of conducting polymers, "liquid-liquid interface" have demonstrated outstanding advantages in the following two application areas. The first one is the adsorption and assembly of nanoparticles, such as nano-gold and nano-silver, which is based on the fact that the molecules at the liquid-liquid interface are featured with higher self-healing capability and higher activity than those in the bulk liquids. However, as a kind of "one-dimensional" rigid conductive nano-material, the adsorption and assembly of carbon nanotubes at oil-water interface have been scarcely investigated. The second one is the polymerization of conducting polymer, which is based on the different solubility of monomer and electrolyte in the two phases. Currently, most researches are focused on used "liquid-liquid interfacial chemical polymerization" which is also favorable to synthesize rod-like or needle-like conducting polymer. However, the direct electrochemical polymerization at liquid-liquid interface is rarely researched.This thesis focuses on two aspects of the application of liquid-liquid interface:(1) the assembly of carbon nanotubes (CNTs) at liquid-liquid interface from a CNTs suspension, together with the influencing factors and mechanism, was systematically investigated. As an example of application, the novel "CNTs liquid-liquid interface phase transfer method" was applied to adsorb and remove heavy metal ions and CNTs adsorbents from wastewater. (2) For the first time "liquid-liquid electropolymerization method" was prpposed to synthesize conducting polymer PEDOT film. The growth factors, topographic characteristics, and growth mechanism of PEDOT film were also analyzed in detail. Finally, a PEDOT-CNTs composite film was synthesized by the combination method of the above two technologies. The main contents and results were summarized as follows:(1) The process, conditions and mechanism of carbon nanotubes’ transferrence and assembly at liquid-liquid interface were investigated. Mainly two steps were concluded:Firstly, carbon nanotubes were acidic oxidized to disperse in water to form a suspension with colloidal feature. The FT-IR and zeta potential measurement confirmed that carbonyl, hydroxyl and other negative charged groups were generated on the surface of carbon nanotubes during the acidification process. The electrostatic repulsion led AO-MWNTs stably disperse in water. Secondly, by adjusting the pH value or adding appropriate surfactant, AO-MWNTs could transfer and assemble from water to oil-water interface with assistance of a mechanic force. The results showed that when the solution pH was<2 or> 13, or the concentration of cationic surfactant CTAB was in the range of 0.075 mM to 0.440 mM, AO-MWNTs could completely transfer to the interface. And when the CTAB concentration was higher than this range, the phenomenon of "phase inversion" occurred with AO-MWNTs re-distributing to the aqueous phase. While the anionic and nonionic surfactants didn’t have this effect at any concentration. Furthermore, organic solvents also played a role in the transferrence of AO-MWNTs via influencing the o/w interfacial tension. The lower the o/w interfacial tension was, the easier the transferrence of AO-MWNTs was. So from the thermodynamic view, the reduction of the AO-MWNTs surface charge and the decrease of the O/W interfacial tension are the two main factors to complete the transference and the assembly of carbon nanotubes. However, diffferent from other nanoparticles, AO-MWNTs’ transfer form aqueous phase to the oil-water interface needed an external dynamic mechanical force to make and accelerate AO-MWNTs transfer.(2) Ionic liquids, abbreviated as ILs, are a new kind of material composed of organic cations and inorganic anions. And their features and dosage were also found have influence on AO-MWNTs’ transference. The more hydrophobic cation was more favorable for the transferrence of AO-MWNTs. Furthermore, Very stable "Pickering" emulsion stabilized by CNTs/ILs composite was obtained. The emulsion size could be well controlled by AO-MWNTs content, ionic liquid dosage, oil/water volume ratio, with the droplet diameter varying from 3～4 millimeter to tens of micrometers.(3) For the first time, the "carbon nanotube liquid-liquid interface phase transfer method" was applied to adsorb and separate heavy metals from water. Taking Pb2+ as an example, AO-MWNTs suspension was directly used as adsorbent. The adsorption capacity could reach up to 138.29 mg/g at 80 mg L-1. AO-MWNTs and the maximum removal rate was 98.2% when pH value was 10.53. Furthermore, it only took 2-5 minutes to separate Pb2+ burdened AO-MWNTs from wastewater, leaving less than 1 mg/L AO-MWNTs in water. So this method could be considered as an effective and fast way to adsorb and separate heavy metals from water.(4) A novel method named as "liquid-liquid interfacial electropolymerization" was proposed to synthesize conducing polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The core idea of the method was to dissolve supporting electrolyte and monomer in water and oil phase, separately, which could completely resolve the low polymerization efficiency due to the low solubility of monomer in water. Three-electrode electrochemical system was applied with Pt wire as working electrode vertically inserting across the oil-water interface. The polymerization initially occurred at the junction of Pt wire/oil/water and accorded to the "dynamic liquid/solid/liquid three phase interline" growthing modal. Apart from the spreading growth along the oil-water interface, which was contributive to the increase of apparent area of PEDOT film, PEDOT film also had slow growth towards the organic and water phase, which were in favor of the thickening of PEDOT film. EDOT concentration in oil phase influenced its apparent area growth greatly. The growth of PEDOT film towards organic phase was significantly impacted by supporting electrolyte. EDOT distributed concentration in water had influence on the growth towards the water of PEDOT film. Through characterized by SEM and optical photographs, it could be derived that the water-side and oil-side of the PEDOT film showed distinct morphologies. The water-side of the PEDOT film showed a conventional morphology with the Pt wire inserted in water phase, while the oil-side mainly showed porous honeycomb, sometimes nanowire structure. So the liquid-liquid interfacial electrochemical polymerization could also be considered as a template-free methodology to prepare conducting polymer with special microstructure.(5) PEDOT-CNTs composite film was synthesized based on the "carbon nanotubes liquid-liquid interface assembly" and the "liquid-liquid interfacial electropolymerization" technologies. Firstly, a flexible conductive CNTs film formed at flat oil/water interface by using CTAB as inducer and fewer amount of CNTs, and then "liquid-liquid interfacial electropolymerization" was followed. The dispersing states and the concentration of CNTs at oil/water interface had great influence on the apparent area of PEDOT-CNTs film and the polymerization current. With the increase of the concentration of CNTs, the conductivity of the interface would be improved since more CNTs dispersed at oil/water interface, which could speeded the growth of the PEDOT-CNTs film along the interface. However, the thickening of the PEDOT-CNTs film was confined due to the mass transfer hindering by the excessive CNTs at the interface. So the polymerization current firstly increased then decreased with the increasing of CNTs’ concentration. Similarly, the morphology of PEDOT-CNTs film also showed great difference between the water-side and the oil-side. CNTs were found accumulated at the water-side while the oil-side seemed to be similar with the pure PEDOT with micro-nano honeycomb structure. Furthermore, the obtained PEDOT-CNTs film showed high capacitance which might be found application as supercapacitor.