Controllable Synthesis And Property Of Manganese Oxide And Nanocomposite

Manganese oxide materials with different crystalline structures and morphologies have been synthesized by a hydrothermal method.Due to the intercalated and exfoliated characteristic of layered manganese oxides, polymer with manganese oxide nanocomposites have been prepared by using long alkylammonium intercalation manganese dioxide as precursors, and their electrochemical or optical properties were studied.MnO2 nanosheets obtained by delaminating the layered manganese oxide can be used as the building blocks to fabricate inorganic or organic -inorganic nanocomposite films through the electrostatic layer-by-layer adsorption technique or electrophoretic deposition.Reaction conditions,mechanisms, the relationships among structure,composition and electrochemical or optical properties of materials were characterized by means of XRD, ICP-AES,UV-vis,FT-IR,XPS,TG-MS,TEM,HRTEM,FESEM,AFM and electrochemical test.A series of different crystallines of manganese oxide nanomaterials, includingα-,β- and Na[2×4]type one-dimensional tunnel manganese oxides,δ-type layered manganese oxide,and amorphous manganese oxide, were prepared by a hydrothermal method.For KMnO₄-MnSO₄ reaction system,the products with different crystalline structures and morphologies can be selectively formed by varying the hydrothermal reaction time and the initial reactant concentration.After hydrothermal treatment for 8 h at 160℃,α-MnO₂ nanowires can be obtained;Elongating hydrothermal time to 72 h,β-MnO₂ microcrystals with a prismatic morphology were obtained. Under the process of hydrothermal reaction,α-MnO₂ nanowires became self-assembled into bundles and subsequently underwent a phase transformation toβ-MnO₂ microcrystals.When hydrothermal treated for 30 min,amorphous mesoporous manganese oxide nanomaterials can be obtained.The products showed a BET surface area of 196 m²Â·g^-1and a narrow pore size distribution of 3.7 nm.A specific capacitance value of 323 F·g^-1was obtained in 1 mol·L^-1Na₂SO₄ solution.After 3000 cycles of operation,the capacitance retention was 96%of initial value.For H₂O₂-Mn(NO₃)₂-NaOH reaction system,the hydrothermal temperature is critical to the crystalline structure of final products.The product of Na-birnessite was obtained at 120℃,and Na[2×4]one-dimensional tunnel manganese oxides nanobelts was obtained at 200℃.Increase hydrothermal temperature was conducive to formation of tunnel-type manganese oxides.Conducting polymer-intercalated layered manganese oxide nanocomposites were synthesized via exchange reaction of conducting polymers(polyaniline and polypyrrole)with n-octadecyltrimethylammonium-intercalated manganese oxide in N-methyl-2-pyrrolidone solvent by a delamination/reassembling process,and their electrochemical properties as electrode materials for supercapacitors were studied.The resulting nanocomposites possessed superior electrochemical performance than each pristine component,which was due to intercalation of conducting polymers into manganese oxide can improve the electrical conductivity and bidimensionality.Polyaniline-intercalated manganese oxide nanocomposites showed a specific capacitance of 330 F·g^-1,which was much larger than the values of layered manganese oxide(208 F·g^-1)and polyaniline(187 F·g^-1).In addition,the electrochemical cycle performance of the nanocomposites significantly improved than the single component.Linear low-density polyethylene(LLDPE)/layered manganese oxide nanocomposites(LLDPE/MnO₂)were synthesized by direct melt compounding of LLDPE in the organic modified layered manganese oxides with dioctadecyldimethylammonium cations.When the melt compounding time was 10 min,the LLDPE intercalated layered manganese oxides nanocomposites were obtained.Elongating the melt compounding time to 30 min,the completely exfoliated LLDPE/MnO₂ nanocomposites could be obtained.The LLDPE/MnO₂ exfoliation nanocomposites showed high UV-shielding efficiency and enhanced thermal stability,which can be attributed to the molecular dispersion of MnO₂ nanolayers in the LLDPE matrix.Inorganic multilayer thin films comprising MnO₂ nansheets and LDHs nanosheets,and organic-inorganic multilayer thin films(PEI/MnO₂)_n comprising polyethylenimine(PEI)and MnO₂ nanosheets,were prepared by the electrostatic layer-by-layer adsorption technique.UV-vis spectra showed the multilayer films increased uniformly.The electrochemical properties of(PEI/MnO₂)_n multilayer films were studied.The area specific capacitance values of(PEI/MnO₂)_n films enhanced almost linearly with increasing in the number of bilayers.A specific capacitance value of 288 F.g^-1was obtained for(PEI/MnO₂)₁₀film,and the capacitance decreased 10 %of initial value over 1000 cycles.Delamination of layered manganese oxide into colloidal nanosheets occurred when manganese oxide intercalated with tetramethylammonium ions was ultrasonically dispersed in acetonitrile organic solution.An oriented layered manganese oxide thick film with(00l)plane parallel to the substrate was obtained by electrophoretic deposition of negatively charged manganese oxide nanosheets on ITO-coated glass substrate.