【作者】 赖泽锋；

【导师】 王琪珑； 崔得良；

【作者基本信息】 山东大学 ， 无机化学， 2008， 博士

【摘要】 在本文中,我们借鉴水热合成立方氮化硼过程中积累的经验,并结合溶剂热反应过程的具体特点,首次将选相原位合成方法用于控制溶剂热合成氮化硼的反应过程,并初步探讨了其中的关键影响因素以及晶体生长过程控制方法。在优化的实验条件下,我们利用该方法成功制备了立方氮化硼纳米晶,并发现了氮化硼晶体生长的基本规律。另外,我们还首次提出了一种新的水热恒压合成方法,并将它应用于可控制备氮化碳材料的探索中。具体内容如下:为了增强溶剂热合成氮化硼反应过程的可控性,提高反应原料的利用率和样品的产率,我们用三卤化硼与有机碱的配合物取代三卤化硼作为反应原料制备氮化硼。在综合考虑配合物的化学稳定性、热稳定性以及在溶剂中的溶解度等因素后,确定吡啶（C₅H₅N）与三溴化硼（BBr₃）的配合物C₅H₅N·BBr₃作为硼源。利用红外光谱、拉曼光谱、核磁共振以及热分析对该配合物的性质进行了系统的分析,在此基础上确定了主要的实验参数;进一步地,以氮化锂（Li₃N）作为氮源,在吡啶中与C₅H₅N·BBr₃反应制备了氮化硼纳米晶,并对反应过程的关键因素进行了系统研究。结果表明,反应温度、反应原料摩尔配比和反应体系的压力等对产物的物相和结晶质量具有重要影响。利用C₅H₅N·BBr₃为原料合成氮化硼时,虽然在一定程度上提高了原料的利用率和氮化硼的产率,但是由于受到实验方法自身的限制,还无法真正实现氮化硼的可控制备。为了加强对反应过程的控制,我们进一步将选相原位合成方法应用于溶剂热合成氮化硼的探索中。在实验过程中我们发现:低的反应温度有利于六方氮化硼（hBN）生成,而升高反应温度则利于提高立方氮化硼（cBN）的含量。在保持其他条件不变的情况下,将反应温度提高到320℃可以得到结晶质量较好且粒度较大的cBN晶粒;如果L₃N相对过量,那么hBN将被抑制,样品的主要物相变成了cBN和正交氮化硼（eBN）。当配合物C₅H₅N·BBr₃与Li₃N的摩尔比为1:5时,利用选相原位合成方法在250℃可以制备粒径接近单分散的氮化硼纳米晶。另外,预先向反应釜充入高纯氮气,使反应过程一开始就在较高的压力下进行,制备的氮化硼样品结晶质量较差。利用苯和吡啶的混合溶剂合成氮化硼时,尽管制备的样品整体结晶质量不高,但是有利于对晶体生长过程的调控,能够得到粒度较大的hBN微晶。与立方氮化硼类似,beta相氮化碳（β-C₃N₄）具有一系列优异的性能和重要的应用价值,因此有关它的可控制备方法的探索具有重要的意义。为了实现β-C₃N₄的可控制备,我们提出了一种新的水热恒压合成方法,利用这种方法,通过相对独立地调变水热反应体系的温度和压力,初步尝试了用水热恒压合成方法制备氮化碳,并对反应过程的关键影响因素进行了系统研究。结果表明,提高反应温度（高于NaN₃的分解温度）不仅有利于氮化碳的生成和稳定,而且有利于减少甚至避免氧化铁杂质的产生;提高反应体系的压力能够抑制氮原子结合成氮分子的过程,减少氮源的损失和促进氮化碳形成;经过初步优化实验条件后,在300℃和160 MPa可以制备具有较高β-C₃N₄含量的氮化碳样品。对于氮化硼和氮化碳材料,它们的物相结构、结晶质量和粒度直接决定了它们的应用范围和价值。为了克服已有方法的缺陷,实现氮化硼和氮化碳材料在物相、结晶质量以及粒度方面的可控制备,我们提出了选相原位合成和水热恒压合成方法,并利用它们开展了初步的研究探索。尽管这些方法还远未达到完善的程度,但是它们为氮化硼和氮化碳等材料的制备和体块晶体的生长提供了一种温和的、更为可控的途径。更多还原

【Abstract】 Based on the knowledge obtained from prepaing boron nitride by hydrothermal synthesis,together with the consideration of the characteristics of solvothermal process,a novel in-situ phase-selective synthesis route has been successfully introduced to the preparation of BN for the first time.Both the key factors affecting the preparation and the growth mechanism of BN crystals were preliminarily explored and discussed.Following these strategies,BN nanocrystals have been obtained under optimized conditions.And now we are able to control the growth process of BN to some extent.Furthermore,another new constant-pressure hydrothermal synthesis method has also been developed and used to synthesize carbon nitride.And products containing graphitic（g-）and beta（β-）carbon nitride have been attained.The detailed results are presented as follow:To control the solvothermal reaction process effectively,and to improve the yield of BN samples,the boron tribromide was replaced by the complex resulting from the reactions between boron tribromide and pyridine（C₅H₅N·BBr₃）.On the basis of comprehensive characterization of this complex by FTIR,Raman,NMR and TG-DTA, the key experimental parameters were determined.Furthermore,BN nanocrystals were prepared by reacting lithium nitride（Li₃N）with the above complex in dry and oxygen-free pyridine under solvothermal conditions.The results indicate that the temperature,molar ratio of the reactants and pressure play important role in determining the phases and crystalline quality of BN products.Although the yield of BN samples have been obviously improved by using the complex C₅H₅N·BBr₃ as the boron source,it is still quite difficult to prepare BN nanocrystals in controllable way due to the intrinsic disadvantages of solvothermal synthesis method.In order to overcome this problem,the in-situ phase-selective solvothermal route is thus developed and employed.And the experimental results indicate that,the formation of hexagonal boron nitride（hBN）is favoured at comparatively low temperature,while the content of cubic boron nitride（cBN） increases with increasing temperature.And quite large cBN micro-crystals can be prepared when the temperature increased to 320℃.Hexagonal BN can be suppressed by adding excessive Li₃N into the reaction solution,at the same time,the formation of cBN and orthorhombic boron nitride（eBN）is promoted.The pressure also affects the phase and crystalline perfection of BN samples.If high purity nitrogen is impelled into the autoclave beforehand to make the reaction start with higher pressure,the crystalline quality of the obtained BN samples will become rather poor.Besides,the mixture of benzene and pyridine has also been used as the solvent during the in-situ phase-selective solvothermal syntheis of BN.Though reducing the crystalline quality of the samples,the mixture solvent favours the bulk crystal growth of BN;and large hBN micro-crystals have been obtained.Beta carbon nitride（β-C₃N₄）has a set of extreme properties similar to or even superior to cBN.In this study,another new constant-pressure hydrothermal synthesis route has been developed and used to explore the controlled synthesis of carbon nitride.As this method is employed,carbon nitride can be synthesized by adjusting the temperature and pressure independently.And the key factors influencing the phases and cyrstalline perfection of carbon nitride have been investigated.The results reveal that,the formation and stabilization of carbon nitride are facilitated at higher temperature（i.e.,above the decomposition temperature of NaN₃）,and the impurities containing iron oxide are reduced,or even eliminated.Increasing the reaction pressure will inhibit the forming of nitrogen molecules to reduce the loss of nitrogen source, and promote the production of carbon nitride.By optimizing the preparation parameters,a sample with quite highβ-C₃N₄ content has been prepared at 300℃and 160 MPa.Generally,the potential application and practical value of both BN and C₃N₄ are determined by their phase structure,crystalline perfection and the particle size.To synthesize cBN andβ-C₃N₄ with specific crystalline perfection and particle size under moderate conditions,we have developed several new methods,e.g.in-situ phase -selective synthesis method,and constant-pressure hydrothermal synthesis method. And a series of experimental investigations have been carried out.Although these methods are still far from being perfect,they at least prove the possibilities of synthesizing cBN andβ-C₃N₄ in a moderate and controllable way.更多还原