Synthesis Of Manganese Oxides Micro/Nano-crystals By A Template-assisted Hydrothermal Process And Their Catalytic Properties

Manganese oxides have a wide range of applications in the field of toxic waste treatment,heterogeneous catalysis,adsorbents,battery manufacturing owing to its different types,crystalline phases,and its unique structures.In particular,manganese oxides nanomaterials are attracting the attention of scholars because of its ion exchange,molecular adsorption,electrical and magnetic properties.Among those various manganese oxides production methods people have developed,hydrothermal method occupies an important position.In this thesis,manganese oxide micro/nano materials have been synthesized by a template-assisted hydrothermal method using KMnO₄ as the manganese source and oxidant to investigate the impact of the type and the amount of the reducing agent on the crystalline phases,structures,morphologies of the products.XRD,SEM,TEM,XPS and catalytic performance evaluation methods were characterized to explore the relationship between the microstructure of the product and its catalytic properties.The main research contents and results are listed as follows:1.Hydrothermal synthesis of manganese oxides micro/nano-materials with lignin sulfonate-assisted and its catalytic combustion propertiesManganese oxide micro/nano-materials were prepared by hydrothermal method in the same conditions as Xu:the concentration of KMnO₄ was 0.05g/mL,the reaction temperature was 180?,the reaction time was 24 h,and the influence of the amount of lignin sulfonate?LSN?and pH of the solvent on the structure and properties of the products were mainly investigated.?1?The results showed that with 0.2g LSN or without LSN in 0.1M HNO₃,deionized water or 0.1M KOH medium,flower-like K-?-MnO₂ microscopic structures were obtained.?2?When the amount of LSN was 2g,regular octahedron Mn₃O₄ was obtained both in 0.1M HNO₃ and deionized water solution;in 0.1M KOH solution,Mn₃O₄ octahedron and?-MnOOH microrods was synthesized;increasing the concentration of KOH to 2M,the product was?-MnOOH microrods,or accompanied with a large number of dendritic.?3?Ortho-xylene catalytic combustion experiments was performed to test the products'catalytic properties,and for different K-?-MnO₂,the catalytic activity of the samples using LSN for the decomposition of o-xylene was significantly higher than the activity of samples formed in the absence of LSN case,of which the product prepared in the deionized water represent the best catalytic activity,when the conversion of the o-xylene was 50%and 100%,the decomposition temperatures was 180 and 250?,respectively.The activity of all the products followed the order of K-MnO₂>Mn₃O₄>?-MnOOH.2.Hydrothermal synthesis of manganese oxides micro/nano-materials with alkali lignin-assisted and its Fenton-like catalytic propertiesAlkali lignin was achieved by hydrothermal treatment with natural pine wood in 4M of NaOH solution at 130?for 6h.Manganese oxide micro/nano-materials were prepared by the same method mentioned above using the Alkali or neutral lignin solution with different dilution ratios.?1?When alkaline solution was added and dilution ratio was 1:6,micron rod-shaped?-MnOOH were obtained while Mn₃O₄ octahedral were obtained when increasing the ratio of template solution to 1:3.?2?Adjusting the template solution to neutral,both?-MnOOH microrods and Mn₃O₄ octahedral were synthesized when template solution dilution ratio was 1:6 while MnCO₃ nanoparticles were synthesized when the ratio was 1:3.In this process,the amount and the pH of the template solution play a vital role and increasing the amount of the solution and the acidity of the medium can achive lower valence manganese oxides.?3?The samples'Fenton-like catalytic properties were tested,among these materials,MnOOH possess the best catalytic activity for degradation of methylene blue with H₂O_2,in 60minutes,the degradation rate of the methylene bluereached 89%,while Mn₃O₄ were the worst.3.Hydrothermalsynthesis ofmanganeseoxidesmicro/nano-materialswith toluene-assisted and its Fenton-like catalytic propertiesTo create novel Fenton catalyst,this paper attempts to use toluene-assisted hydrothermal method to modified manganese oxides,and a preliminary study of the performance and the mechanism of its Fenton-like catalytic degradation of methylene blue was conducted.?1?The results showed that flower-like?-MnO₂ microspheres were obtained when the amount of toluene was 0,1,5mL respectively.The degree of crystallization and microscopic particle diameter of the products decreased after adding toluene.?2?The Fenton-like catalytic properties of the materials were also tester by the same method mentioned above,compared to Mn-0,the as-synthesized samples Mn-1 and Mn-5 displayed higher catalytic activity,which may have relationship with the C₆H₅-COO^-adsorbed on the surface of the products.This process begined with the MnO₂ surface adsorption of H₂O₂,and then H₂O₂ was decomposed into HO₂·,at the same time,Mn?IV?is reduced to Mn?II?.Finally,Mn?II?was oxidized by H₂O₂,generating·OH,and the·OH finished the degradation of the methylene blue.