Nano Layer Assembly Technique To Prepare The Layered Nanocomposite Materials

In recent years, nano-composite materials have been investigated widely by researchers because of their extensive applications in optical, electrical, magnetic, and biological sensors. In compare with the traditional composites, the composition of nano-composite materials is not the simple sum of inorganic phase/inorganic phase and inorganic phase/organic phase, while is the phase combine to form new materials in the range of nanometer to micrometer. The components of nano-composite materials are not only inorganic, organic or both, but also crystalline or amorphous. Thus, nano-composite materials have many advantages in compare with the traditional materials.Inorganic layered materials can be divided into anionic layered compounds, cationic layered compounds and non-ionic layered compounds on the basis of the layer electric charge. Under some conditions, some guest ions with large radius can be intercalated into the interlayer of layered materials, and then the intercalated layered materials can be delaminated into inorganic nanosheets by some treatment. The delaminated nanosheets can be used as the perecursor to to assemble functional materials, and a series of functional materials have been fabricated by nanosheet assembling technology.On the basis of the characteric layered structure of graphite oxide (GO), layered manganese oxide (MnO2) and layered doubled hydroxides (LDHs), we chose these layered inorganic materials with different electric charges as precursor, polydiallyldimethylammonium chloride (PDDA) as a linker, and some nano-composite materials such as graphite oxide/PDDA nanocomposite, manganese oxide/graphite oxide nanocomposite and manganese oxide/LDHs nanocomposite have been fabricated by nanosheet assembling technology. The fabricated nano-composite materials are expected to be used as supercapacitor electrode materials.The main research works are as follows:(1) Research on the fabrication and capacitance of GO/PDDA hybrid nanocomposites. GO is firstly fabricated by Hummer method from natural graphite power. When the obtained GO is soaked in itetramethylammonium hydroxidei solution for 7 days, it is swelled and finially delaminated into GO nanosheets. The assembling behavior between GO nanosheets and PDDA polycations is investigated by both layer-by-layer method and flocculation technology, and the capacitive performance of the assembled hybrid composites is studied. X-ray diffraction (XRD) results show that the multilayer film has a layered structure with a basal spacing of 1.09 nm, and the basal spacing corresponds with the sum of GO nanosheet with one layer and PDDA polycation with one layer. On the other hand, a different assembling process takes place for the flocculated material. The flocculated material also has a layered structure, but its basal spacing changes to 1.49 nm, which corresponds with the sum of GO nanosheet with one layer and PDDA polycation with two layers. UV-visible absorption spectra exhibit that the adsorbed amount of the GO nanosheets is proportion to the adsorption deposition cycles. The obtained nano-materials with different methods show a lamellar characteristic. The flocculated material shows good capacitive behavior and cycling stability, and the specific capacitance value is 176 F/g at a scanning rate of 5 mV/s in 1 mol/L Na2SO4 solution.(2) Research on the fabrication of GO/MnO2 hybrid nanocomposites. (MnO2/PDDA)n and (MnO2/PDDA/GO/PDDA)n multilayer films are obtained by layer-by-layer method. XRD results show that (MnO2/PDDA)n multilayer film has a layered structure with a basal spacing of 0.725 nm, while (MnO2/PDDA/GO/PDDA)n multilayer film can be obtained by using PDDA polycationd as linker, and it has a basal spacing of 0.735 nm. UV-visible absorption spectra exhibit that the adsorbed amount of the GO or MnO2 nanosheets is proportion to the adsorption deposition cycles.(3) Research on the fabrication of MnO2/LDHs hybrid nanocomposites. MnO2 and LDHs nanosheets are chosen as assembling units; the assembling behavior between MnO2 nanosheets and LDHs nanosheets is investigated by both layer-by-layer method and flocculated technology in a nitrogen atmosphere. (MnO2/LDHs)n multilayer film shows a layered structure with a basal spacing of 1.29 nm, which is compatible with the sum of LDHs nanosheet with one layer, MnO2 nanosheet with one layer and one formamide layer. On the other hand, the flocculated material shows a layered structure with a basal spacing of 1.12 nm due to the different existence of formamide molecules in the interlayer.