| Manganese oxides are rich in nature, low cost, environmentally friendly, and havespecial structure, so they have potential applications in many fields, such as super capacitors,batteries, and catalysts. Manganese oxides are versatile in phase, crystalline structure,morphology, and preparation method. So there are many problems that need further researchfor the controllable preparation of manganese oxides. This work focused on the effect ofsolvent and reductant on the products through the oxidation of Mn(OH)2in liquid and thereduction of KMnO4solution respectively. The products were characterized by XRD, SEM,TEM, BET, and CV technologies. The main research contents and results are listed asfollows.1. Manganese oxides were synthesized by an air oxidation method using MnCl2asmanganese source and NaOH as precipitant in water and n-alcohol solvents with differentalkyl chains. The influence of different n-alcohol as solvent on the structure and properties ofthe products was investigated.(1) Experimental results showed that the alcohol solventaffected the phase and crystalline as the growth of Mn3O4was restrained and the growth ofδ-MnO2was promoted with the increase of alkyl chains.(2) The specific capacitance, porevolume, and oxidation state of the product prepared in n-alcohol were higher than of whichprepared in water due to the effect of n-alcohol. And the specific capacitance, pore volume,and oxidation state of the product prepared in n-alcohol increased with the increase of alkylchains.(3) The capacitance of the products prepared in n-alcohol increased monotonicallywith the increase of alkyl chains and was higher than of which prepared in water. Theincrease of specific capacitance, pore volume, and oxidation state was closely relate to thealcohol solvent.2. The influence of different n-alcohol as reductant on the structure and properties of themanganese oxides synthesized by redox reaction method using KMnO4as manganese sourceand oxidant and n-alcohol solvents with different alkyl chains was investigated. Thereduction ability of n-alcohol were investigated by cyclic voltammetry with the modifiedelectrode with the MnO2and Nafion. The results are listed as follow.(1) Experimental results reveal that the products were agglomerated δ-MnO2powders at low temperature and pH=8.0，pH=13.0. With the increase of alkyl chains the size of products increased, interlayer spacingdecreased. The high temperature led to high crystalline.(2) The nitrogenadsorption-desorption isotherm of the samples prepared by alcohol is a type of Ⅳ isothermand hysteresis loop of which is H3type. The specific surface area and pore volume of thesamples prepared by alcohol with the long chin are higher than of which prepared bymethanol at28℃and pH=8.0. The specific surface area and pore volume decreased and theaverage pore diameter increased with the increase of pH. The specific surface area and porevolume increased with the increase of temperature.(3) The oxidation state of productprepared by ethanol is a little higher than of which prepared by other alcohols at28℃andpH=8.0. The oxidation state increased with the increase of pH at the same temperature andwith the increase of temperature at the same pH also.(4) he character of capacitor of theproducts is blend EDLC feature and pseudocapacitor feature. The increase of the temperaturecontribute to the increase of capacitance but the increase of pH is no use. The oxidation stateis the key factor of the capacitance.(5) The curves of the cyclic voltammetry with themodified electrode in different n-alcohol solution were attained. Additionally, preliminaryinterpretation of the effect of small molecular n-alcohol on the product prepared by reducingKMnO4was attained using spike potential and peak current.3. The influence of n-aldehyde as reductant on the product synthesized by reducingKMnO4was investigated. The results are listed as follow.(1) The products prepared byacetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde were agglomerated δ-MnO2powders with lamellar structure.(2) The samples in order of specific surface area, porevolume, and pore diameter: Bed> Ad> Bd> Pd at28℃, pH=8.0.(3) The oxidation state ofproduct synthesized by oxidation of n-aldehyde is higher than by oxidation of n-alcoholapparently at28℃, pH=8.0. The oxidation state of product synthesized from propionaldehyde,butyraldehyde and benzaldehyde agrees with the MnO2theoretical value very well.(4) Thecapacitance of product synthesized by oxidation of n-aldehyde is higher than by oxidation ofn-alcohol apparently at28℃, pH=8.0. There is a positive correlation between capacitance andspecific surface area of products prepared by n-aldehyde. |
PDF Full Text Request