液相脉冲放电合成Ni-P合金纳米粉机理的原位XAFS/SAXS研究

Recently enacted regulations limiting the emission of pollutants and the continuing decline in the quality of petroleum feedstocks have made sulfur and nitrogen removal one of the paramount problems in the refining industry. It has been recognized that current hydrotreating catalysts are not adequate to meet the regulated levels, and this has given rise to widespread research efforts to develop a new generation of catalysis materials. Our team has prepared this new Ni-P alloy nanoparticles catalysis with a novel, low-cost, facile and effective method called pulse discharge in liquid. In order to better develop this active catalysis, the synthesis mechanism that is the reduction-nucleation and growth of this nanoparticles has to be thoroughly studied. However, the traditional experiment methods are not able to insight into the atomic or molecular levels limited by the time- and space-resolution. Herein, we introduced the in situ synchrotron facilities and in situ spectrum like atom emmission spectrum and fluoresecne spectrum to investigate the reduction-nucleation and growth reactions in real time, real environments and real materials. The in situ X-ray Absorption Fine Structure (XAFS) will be employed to capture the chemical valence and the coordination number change of Ni2+ during the reduction process; the small angle x-ray scattering(SAXS) will be used to monitor the nuclei coalesce and nanoparticle growth during the growth process; and finally, the in situ spectrum like atom emmission spectrum and fluoresence will be introduced to monitor the active particles during the discharge process. Finally, the outside reaction conditons will be regulated to intervene the synthesis process on purpuse. Consequently, the entire synthesis process of Ni-P alloy nanoparticles will be thoroughly studied, and its reduction-nucleation-growth mechanism will be completely interpreted. Based on the above all research, the size, structure and morphology controlled synthesis of Ni-P nanoparticles is expected to be achieved.

Ni-P合金纳米粉表面活性高、比面积大，具有良好的导电导热性和抗氧化能力，在化工、机械、航天等领域有广阔的应用前景。本课题组采用快捷、环保、低成本的液相脉冲放电法，制备出不同形貌和结构的Ni-P合金纳米粉。因对Ni-合金纳米粉的合成机理即还原-形核-生长机理并不清楚，不易控制Ni-P合金纳米粉的形貌和结构。但纳米粉的性能很大程度上取决于其尺寸、形貌和结构。而传统非原位实验方法受限于低时空分辨率，是对动态合成过程的静态反映，缺乏对中间过程的实验数据支撑。因此，本项目将采用高时空分辨率的原位同步辐射XAFS和SAXS技术和原位光谱监测技术，辅以传统非原位实验手段，研究脉冲放电过程中高能活性粒子对反应的激发作用，监测合成过程中离子化合价和配位环境变化、Ni-P核的偶联和集聚长大过程，构建Ni-P合金纳米粉的还原-形核-生长机理模型，通过外场条件有目的地调控，初步实现Ni-P合金纳米粉的可控制备。

非晶Ni-P纳米粉体具有独特的物理化学性质，作为催化剂、电池电极材料、涂层材料具有广阔的工业应用前景。然而，人们对非晶Ni-P纳米粉体的结构描述与形成机制还知之甚少。而纳米粉的性能很大程度上取决于其尺寸、形貌和结构。本课题采用液相脉冲方法制备非晶Ni-P纳米粉体。采用先进的同步辐射实验技术，结合常规结构表征手段，研究了放电脉冲产生的高能活性粒子对化学反应的激发机制；非晶Ni-P纳米颗粒的局域结构、形成机制；不同外场条件对Ni-P纳米颗粒形貌、尺寸和结构的影响。 .首先，利用自行搭建的发射光谱实验装置分析了脉冲放电过程中产生的活性粒子。发现非晶Ni-P纳米颗粒的形成过程由脉冲放电产生的活性粒子•H、P+、O触发，Ni原子由Ni2+直接被•H和eaq-还原形成，P原子由H2PO2-经歧化反应间接形成，P原子的形成晚于Ni原子。给出了Ni-P纳米颗粒形成的总化学反应方程式。.其次，采用XAFS技术分析了非晶Ni-P纳米颗粒中Ni原子的近邻结构和P原子的近邻结构，发现Ni的近邻结构类似于晶体Ni中的情形，而P的近邻结构类似于晶体Ni3P中的情形。因此根据这一结构特征，构建了一种含有23个Ni原子和3个P原子的局域结构模型，来描述Ni-P纳米颗粒的非晶结构。.随后，采用HRTEM观测了所形成粒子的形貌特征，用XAFS和原位QXAFS技术研究了非晶Ni-P纳米颗粒形成过程中原子近邻结构的变化，用原位SAXS技术研究了非晶Ni-P纳米颗粒粒径的变化。综合以上实验结果提出了非晶Ni-P纳米颗粒形成过程的四阶段模型，即：Ni晶核的形成、Ni-P纳米颗粒的形成、Ni-P纳米颗粒的非晶化和非晶Ni-P 纳米颗粒的自催化生长。.最后，研究了温度、反应物浓度、反应物浓度比、放电脉冲、放电电压对非晶Ni-P纳米颗粒形貌、尺寸的影响。Ni-P纳米粉体最佳制备条件为：温度75℃、反应物中NiSO4的浓度为0.3M、反应物浓度比（NiSO4/NaH2PO2）为1:3、放电脉冲数n为60、放电电压U为1000V。 .本课题研究获得的成果对非晶Ni-P纳米粉体的可控制备提供了实验依据和理论指导，有利于拓展非晶Ni-P纳米粉体材料的实际应用领域。