Knowledge Management System Of Institute of process engineering,CAS
六方氮化硼（h-BN）具有优异的化学稳定性、耐热耐腐蚀性以及良好的绝缘性和润滑性，在绝缘体、陶瓷及复合材料增强剂和高温固体润滑剂等领域具有广泛应用。其中，多孔h-BN因具有较高的比表面积、特殊的孔结构，在储氢、催化、吸附分离等领域应用前景广阔。目前，多孔h-BN的制备方法主要有自组装法、高温分解法、模板法、化学反应法，存在原料毒性较高、反应温度较高、模板难以去除、制备方法复杂等问题，亟待开发清洁、节能的高效制备方法。本论文以硼酸、三聚氰胺为原料，在相对较低的温度下通过两段焙烧法制备多孔h-BN材料。首先，通过实验研究确定了合成多孔h-BN的较优工艺条件，制备得到了具有高比表面积的多孔h-BN纳米片；然后，系统研究了多孔h-BN纳米片对金属离子的吸附性能，确定了吸附过程的主要影响因素；最后，探索研究了多孔h-BN纳米片对Cu2+的吸附过程机理，并通过实验数据计算确定了吸附模型。本论文在以下几方面取得了创新结果：（1）研究了高比表面积多孔h-BN的较优工艺条件。明确了前驱体的物相、组成和制备方法，系统考察了反应物配比及焙烧制度（温度、气氛、时间）对多孔h-BN结构和形貌的影响，确定了较优的工艺条件：采用冷却结晶的方式制备前驱体，三聚氰胺/硼酸摩尔比为1:2，于NH3气氛下，先在600℃下焙烧2 h，再在700℃下焙烧3 h，在此条件下，制备得到了弱结晶的多孔h-BN纳米片，比表面积可达321 m2/g。（2）确定了多孔h-BN纳米片对金属离子吸附过程的主要影响因素。吸附过程受溶液的pH、初始浓度、接触时间等影响。以Cu2+为例，当pH在2-5时，其对Cu2+的吸附量随着pH值的增加而显著增加；在pH为5、初始浓度＞3000 ppm、吸附时间达到120 min后达到吸附平衡，最大吸附量达819 mg/g。在含有Cu2+、Fe3+、Cr3+、Ni2+的混合金属溶液中，其对各金属离子均具有较好的吸附效果。（3）提出了多孔h-BN纳米片对金属离子的吸附过程机理。通过对比多孔h-BN吸附前后的FTIR、SEM和XRD图，推测多孔h-BN纳米片较高的吸附容量与其表面连接的-NH2有关；Zeta电位测试表明，在pH＞3时，多孔h-BN纳米片表面带负电荷，从而可能促进对正价金属离子的吸附；多孔h-BN纳米片对Cu2+的静态实验数据符合Langmuir等温吸附模型，动力吸附过程符合拟二级动力模型，被吸附的Cu2+以Cu2Cl(OH)3的形式存在。;Porous hexagonal boron nitride (h-BN) has excellent chemical stability, heat and corrosion resistance as well as good insulation and lubricity. It has a good application prospect in insulators, ceramics, composite reinforcements and high temperature solid lubricants, etc. Among them, porous h-BN has great superiority in the fields of hydrogen storage, catalysis, and adsorption separation due to its high specific surface area and special pore structure. At present, the preparation methods of porous h-BN mainly include self-assembly method, pyrolysis method, template method and chemical reaction method. But there are some problems such as high toxicity of raw materials, high reaction temperature, difficulty in template removal, and complex preparation methods. It is urgent to develop efficient, cleaning and energy saving preparation methods. In this paper, porous hexagonal boron nitride materials were synthesized through a facile two-step roasting process by using boric acid and melamine as raw materials. Firstly, the optimum process conditions for the synthesis of porous hexagonal boron nitride were determined through exploration experiments and porous h-BN nanosheets with high specific surface area were prepared; Secondly, the adsorption performance of porous h-BN nanoplates on metal ions was systematically studied and the main influencing factors of the adsorption process were determined. Finally, the adsorption mechanism of porous h-BN nanoplates for Cu2+ was explored and the adsorption model was calculated and analyzed by experimental data.The main innovative results of this paper can be summarized as follows:(1) The optimal preparation process of porous hexagonal boron nitride with high specific surface area was investigated. The phase, composition and preparation method of the precursor were clarified. The effects of reactant ratio and calcination system (temperature, atmosphere and time) on the structure and morphology of the porous h-BN were systematically investigated and the optimum process conditions were determined: A precursor was prepared by cooling crystallization; the molar ratio of melamine/boric acid was 1:2.Then it was first calcined at 600° C for 2 h, and calcined at 700° C for 3 h in NH3 atmosphere. Under these conditions, the weakly crystalline porous h-BN nanosheets with a specific surface area of 321 m2/g were obtained.(2) The main influencing factors of metal ions on porous h-BN nanosheets were determined. The adsorption process is affected by pH, initial concentration, contact time, etc. Taking Cu2+ as an example, when the pH was between 2-5, the amount of adsorbed Cu2+increased with the increase of pH, and the adsorption equilibrium was reached at a pH of 4.5, initial concentration>3000 ppm, and adsorption time reaching 120 min. The maximum adsorption capacity for Cu2+ was 819 mg/g. And in a mixed metal solution containing Cu2+, Fe3+, Cr3+, and Ni2+, it had a good adsorption effect on each metal ion. (3) The adsorption mechanism of porous h-BN nanosheets on metal ions was proposed. By comparing the FTIR, SEM and XRD patterns before and after the adsorption of porous h-BN nanosheets, it was inferred that the higher adsorption capacity of porous h-BN nanosheets was related to the surface-linked -NH2. Zeta potential measurements showed that at pH>3, the surface of porous h-BN nanosheets is negatively charged, which may promote the adsorption of positive valence metal ions; the experimental data of porous h-BN nanosheets for Cu2+ accorded with the Langmuir isotherm adsorption model. And the kinetic adsorption process accorded with the pseudo second-order kinetic model; the adsorbed Cu2+ by the porous h-BN nanosheets was in the form of Cu2Cl(OH)3.
|张晶. 多孔六方氮化硼的调控制备与金属离子的吸附性能研究[D]. 中国科学院研究生院,2018.|
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