Scale-up Preparation Of Nanoparitcles Films At The Liquid/liquid Interface For The Construction Of Electrochemical Sensors

Nano thin-films are the film materials that are constructed with nanoparticles or nanostructures as building units, and have wide applications in the many fields, such as catalysis, sensing, photoelectronics, etc. There are many methods for preparation of nano thin-films, but self-assembly of nanoparticles is closely paid attention by scientific community due to its advantages of simpleness, convenience and no requirement of expensive instruments. Generally, traditional self-assembly is related to hydrophobic nanoparticles with strongly bonded ligands (e.g., alkyl thiol) as stabilizers. Self-assembly of hydrophilic nanoparticles is much difficult. Particularly, those hydrophilic nanoparticles without protection of strongly bonded ligands are apt to aggregate irreversibly in the self-assembling process. But those hydrophilic nanoaprticles is of significance to surface chemistry due to their high surface activity. Thus, it is crucial for nanotechnological study to develop self-assembling methods for hydrophilic nanoparticles and to explore the properties of the assembled nano-films.This study reports a layer-by-layer self-assembly of hydrophilic Au nanoparticles by the ethanol-mediated method and the electrocatalytic properties of the resulting Au nanoparticle film, and develops a controllable self-assembling technique and a rapid self-assembly technique. The main research contents are summarized as follows:(1) Large-area Au nanopaticle monolayer films was prepared with hydrophilic Au nanoparticles at toluene/water interfaces by the ethanol-mediated self-assembling method, and transferred onto the hydrophilic surface of glassy carbon, copper grid, and quartz glass for scanning electron microscopy (SEM) imaging, transmission electron microscopy (TEM) imaging, and UV-vis measurements, respectively. Compared with polycrystalline Au electrodes, both the Au nanoparticle monolayer and bilayer films exhibit satisfied electrocatalytic activity for NO oxidation. Especially on the Au nanoparticle bilayer electrode, the limited detection of NO can reach up to 2.7×10^-8 mol/L, which is not obtained on the reported regular electrodes.(2) In the ethanol-mediated self-assembling method used above, ethanol needs to be added dropwise during the period of nanoparticle assembly, which always makes the self-assembling interface be a disturbed state so that the structure of the resulting nanoparticle films lack reproducibility. Therefore, this study upgraded the above method: the mixture of ethanol and toluene was injected from the bottom of Au nanoparticle solution at a fixed rate, and then ethanol dissolved into toluene can spontaneously diffuse towards water phase, inducing Au nanoparticles to assemble at the toluene/water interface. This modified method not only avoid the disturbance to the assembling interface from adding ethanol, ensuring the structural reproducibility of Au nanoaprticle monolayer, but also control the spacing between nanoparticles by varying the concentration of ethanol in toluene. Additionally, we also studied the influence of ethanol concentration in toluene on the assembly of Au nanoparticles with different sizes.(3) Develop a universal, rapid method for assembly of hydrophilic nanoparticle into large-area monolayer films. Typically, ethanol and toluene were added in turn to a nanoparticle aqueous solution, and subsequently a copious amount of water was pouring into the mixed system. Thus, a large-area nanoparticle monolayer was formed at the toluene/water interface, the assembling process is very rapid, less than 10 s. This"pouring"method can be applied to assemble nanoparticles of different materials with different shapes, such as Au, Ag, SiO₂, Au/Ag alloy, etc, and in principle can prepare nanoparticle monolayer of any size.This study not only discloses the surface activity of Au nanoparticle films, but also develops two assembling techniques for hydrophilic nanoparticles, which is of significance for theoretical and practical investigations of nanomaterials.