Preparation Of Functional Oxide Nanomaterials By Molten Salts Method

This paper is focused on the controlled synthesis of inorganic functional nanomaterials by molten salts method,including controlled synthesis of 1D oxides nanomaterials,and the study on their properties.The contents are related to how to select molten salt to prepare different oxides,the formation mechanism of 1D oxide and the properties of some prepared oxide and so on.The results may be helpful to the preparation of nanomaterials by molten salt method.1.Large-scale preparation and catalytic properties of one-dimensionalα/β-MnO₂ nanostructuresOne-dimensionalα- andβ-MnO₂ single crystalline nanostructures were prepared by the molten salt route.The products were characterized by XRD,SEM,FT-IR, nitrogen adsorption-desorption techniques.Bothα- andβ-MnO₂ nanostructures exhibited large aspect ratio with diameter of tens of nanometers and length as long as several micrometers.The formation mechanism ofα/β-MnO₂ nanostructures were proposed based on the time-dependent experiments.The formation of theα-MnO₂ nanowires was based on the curling of the nanosheets,while the formation of theβ-MnO₂ nanorods went through a heterogeneous nucleation and dissolutionrecrystallization process.The as-preparedα- andβ-MnO₂ nanostructures showed excellent catalytic performance in the fenton-like reaction.Here,we selected Rhodamine B(RB),Congo red(CR) or Ethylene blue(EB) as organic pollutants to decompose.The order of the catalytic activities isα-MnO₂＞β-MnO₂＞commercial MnO₂.The BET surface areas ofα-MnO₂,β-MnO₂ and commercial MnO₂ were respectively 89.3,41.1 and 7.6 m²/g,which is consistent with the catalytic activities. When we selected theβ-MnO₂ and commercial MnO₂ with the same surface,we found that the catalytic activity ofβ-MnO₂ was higher than that of commercial MnO₂,so the catalytic activity was also affected by the surface state of the catalyst because the reacting agent was absorbed on the catalyst's surface before the catalytic reaction.Different morphologies of the crystals resulted in different exposed crystallographic facets that showed different adsorption ability to the reacting agent and then different catalytic activity.In addition,we also study the stability of catalyst,after duplicating the Fenton-like reaction 10 times with the preparedα-MnO₂,β-MnO₂ as the catalyst,the result showed they have good stability.2.Molten salt synthesis of one-dimensional Mn₂O₃ nanofibersThis experiment mainly focuses on the conditions for molten salt synthesis of Mn₂O₃ nanostructures.The products were characterized by XRD,TEM,SEM and FT-IR techniques.Here,we selected NaNO₃ and NaCl as molten salts and the reaction temperature of 420℃,TEM image shows all the products are uniform nanowires with the diameter of around 30 nm and the length of several micrometers. The formation mechanism of the product was investigated as the curling of the nanosheets without phase transformation.The experimental results indicated that chloride ion plays an important role in the formation of Mn₂O₃ nanowires.The product was mixture of nanoparticles and nanowires when there was no chloride ion, and the product was uniform 1-D nanostructures in presence of chloride ion.The investigation of the catalytic decomposition of methylene blue solution in the presence of H₂O₂ showed that the catalytic activity of prepared Mn₂O₃ is higher than the Mn₂O₃ calcined from MnO₂.In addition,the influence of H₂O₂ content was also studied.3.Molten salt synthesis of one-dimensional CaIn₂O₄ nanorodsIn this experiment,we select chloride as molten salt to synthesize CaIn₂O₄.The products were characterized by XRD,SEM,TEM techniques.TEM shows they are uniform rods with diameter of ca.200 nm and the length of several micrometers.In this experiment,we selected the coprecipitation as the precursor,which decreased the reaction temperature significantly.