High-pressure Solvothermal Synthesis Of Boron Nitride And Cerium Oxide Nanomaterials

With the foundation of the high pressure solvent thermal method, we explored the controllable synthesis method of BN and a representative of oxide nanometer material CeO2. We divided high pressure benzene heating method of BN into two parts of low temperature and high temperature. In the low temperature part, we synthesized the BN nano-carpets, and discussed its synthetic conditions, formation mechanism and application value. In high temperature part, we firstly solved the solvent carbonization problem by introducing sulfide additives. Then we prepared hollow-porous BN nanotubes, and discussed the forming mechanism of this unique morphology of BN nanomaterials. Following on these, we successfully synthesized a series of one dimensional BN nanomaterials. Through introducing constant pressure and section pressure into CeO2solvent thermal synthetic reaction, we also prepared porous CeO2nanoball and hollow CeO2nanoball with controllable morphology and good catalytic property. And by these work, we preliminarily understood of the mode of high pressure impressing on solvent thermal synthetic reaction of oxide. After this, we successfully applied high pressure into other oxide system and realized the controllable synthesis. The results are as follows:BN nano-carpets synthesized by high benzene thermal synthesis was composed by BN nanosheets and BN nanorods grew on them. Those BN nano-carpets structures have a larger BET surface area and more structure defects. To improve the reaction temperature on the yield and crystallization quality have a promote role, but too high temperature will lead to solvent carbonization. Improving the pressure in low temperature has an obvious positive effect, but not as in high temperature. Based on careful analysis of reaction coarse products and by-products, we thought NH4N3and NaBF4are important intermediate products. The reaction of NH4N3and NaBF4in different decomposition speed produces BN nanosheets and BN nanorods, respectively. There is a gas-liquid-solid mechanism in the reaction where high pressure and solvent benzene play a key role. The multistage structure of BN nano-carpets can absorb organic aromatic pollutants methylene blue quickly and selectively. The maximum adsorption is272.4mgL-1. In addition, BN nano-carpets adsorbent can be conveniently circularly used by heat treatment.After careful study on raw materials, intermediate products in the reaction system and the relationship of products, we found the problem of Benzene carbonation was caused of excessive amounts of intermediate product NH4N3. Then we successfully solved benzene carbonization in high temperature reaction by introducing thiophene which could promote decomposition of azide and synthesized the hollow-porous BN nanorods which had no individual chip basement in280℃,150MPa. Through the analysis of the different temperature reaction results of using thiophene, we thought the hollow-porous structure was formed because of the effect of high temperature crystallization and nearly supercritical benzene diffusion. In addition, we found that reaction would be accelerated by additive. At the same time, the morphology of samples will continuously change from short rod to linear fibrous. Then by improving the reaction rate through the additional more additives, increasing the amount of raw materials and changing higher efficiency additive, we finally prepared a series of one dimensional BN nanomaterials.Through introducing external constant45MPa pressure in the constant temperature stage, we improved the cerium nitrate-acrylic acid-glycol reaction system and prepared much smaller CeO2porous nanoball than the original. The size of CeO2porous nanoball continuously changes from80nm to45nm in the process of continuously improving pressure to150150MPa. At last, we got a crystal orientation arrangement and similar mesoporous crystal structure. We carefully analyzed the influence of the pressure on each parameter in the process of CeO2homogeneous nucleation. Then we put forward the mechanism of regulating and controlling CeO2nano-aggregation morphology by changing the pressure. Using the catalytic oxidation CO performance as a benchmark, we found that CeO2porous nanoball catalytic performance improved with the decline of particle size (Catalytic performance150MPa>45MPa> no external pressure). The biggest temperature decreasing amplitude was96℃. After that we introduced a pressure differential parameter by changing the constant pressure to sectionalized pressure, we successfully realized the controllable synthesis of CeO2nanoball. We also discussed the mechanism of pressure differential and pointed that the strength brought by diffusion of different solvent determined the size of hollow structure in CeO2nanoball. With the maximum hollow structure size, T90of the fractional pressure sample (45—150MPa) reduces113℃, which is superior to the most known pure CeO2catalyst.