Preparation And Characterization Of Meso-/Macroporous Novel Materials Composed By Transition Metal (Mn,Zn Etc.) Oxides

Transition metal oxides with mesoporous or macroporous structure have unique catalytic,optical,electric and magnetic properties due to their characteristic d-orbit electrons and mixed valencies.Such materials have potential applications in areas such as industrial catalysis,energy storage and environment protection.Therefore, they attract considerable attentions both in fundamental research and practical applications since the end of the 20^th century.Although many synthesis methods have been empolyed with porous manganese oxides and ZnO,great challenges still exist in controlling their pore structures.All conditions such as exorbitant activity of the precursor,tendency to form solid phase, and structure collapse during phase transition will cause the destruction of pore structures.In this thesis,a novel two-step method has been employed to synthesis porous manganese oxides and other oxides.Regular shaped precursors were first synthesis by a solution method.Then a following calcination process was carried out to obtain the final porous materials.Regular bar-shaped manganese tartrate was one of the precursors synthesized by a hydrothermal route.Meso-and macroporous Mn₂O₃ with pore size ranging from several to some tens nanometers were then obtained by oxidation of this precursor.Porous ZnO and ferric oxides were also synthesized using the similar route.Spherical and cubic manganese carbonates were other precursors, which were fabricated in H₂O and H₂O-EtOH system respectively.Amorphous mesoporous MnO₂ and macroporous Mn₂O₃ were successfully prepared after annealing of these precursors.XRD,SEM,TG-DTA and N₂ physical adsorption-desorption measurements were applied to characterize the phase,morphology and pore structure of the samples.The results showed that:all mesoporous or macroporous materials retain morphologies of their precursors.The pore characters depend strongly on the annealing temperature and heating rate during the second step.Interestingly,the obtained porous Mn₂O₃ can also act as a precursor. Macroporous MnO₂ knitted by nano-fibres was synthesized by oxidation of this porous Mn₂O₃ under low-temperature hydrothermal reaction.And so did the macroporous Mn₃O₄ aggregated by irregular nanoparticles by reduction.Performance tests were carried out using macroporous manganese oxides(MnO₂, Mn₂O₃ and Mn₃O₄) as the anode active materials in lithium battery.It shows that only macroporous MnO₂ and Mn₃O₄ exhibit charge/discharge performance.They also have high specific capacitance up to 477.7 Ah·g^-1 and 1762 Ah·g^-1 respectively.It indicates that these materials have a high adsorption capacity for Li⁺,which are hopefully to be good electrode materials in supercapacitor.PL measurement was carried out to study the photoluminescence property of macroporous ZnO aggregated by nanoparticles.It proves that ZnO annealed at 800℃shows an extremely strong emission band centered at 500nm excitated at 325nm.The as-synthesized ZnO is likely to be used as a kind of photoluminescence material with shorter wavelength.