钯/壳聚糖纳米纤维的微观结构与催化性能关联性研究

Heterogeneous catalyst offers many advantages than homogeneous catalyst including ease of separation, recyclability and reusability, thus the heterogeneous catalyst is currently one of the most active research fields. In the present proposal, we plan to employ the coelectrospinning technique to prepare a series of well-defined palladium/chitosan composite nanofibrous mat. Multiple crosslinking methods and doping of graphene and carbon nanotube will be employed to adjust the microstructure of composite fiber to improve the dispersion and stability of palladium species in the fiber, and circulation of substrates in the fiber. Moreover, the nanofiber structure will not only enhance the catalytic activity of palladium/chitosan fiber, but also facilitate the recovery and recycle of catalyst. The effect of fiber composition and morphology, crosslinking method and nanomaterials doping, palladium immobilization on the microstructure of palladium/chitosan fiber will be carefully analyzed by positron annihilation technique (PAT) and other conventional tools, such as SEM, HR-TEM and XRD. The fiber microstructure of palladium/chitosan fiber will be associated with its catalytic performance and deterioration mechanism in recycle to prepare palladium/chitosan nanofiber catalyst with excellent catalytic activity and stability. This proposal is positive to expand the application of PAT in nanofibrous materials and prepare high active and stable heterogeneous palladium catalyst.

非均相催化剂克服了均相催化剂分离困难、不易回收和难以重复使用等缺点，是催化化学的重要研究方向。本项目拟通过静电共纺制备良好形貌的钯/壳聚糖复合纳米纤维膜，并通过多种交联技术以及碳纳米管和石墨烯掺杂调控纤维的微观物理和化学结构，提高钯催化中心在纤维中的分散性和稳定性，以及反应底物在纤维中的流通性能；同时纳米纤维结构有利于提高催化剂的催化性能，方便催化剂的回收再利用。利用正电子湮没技术（PAT），结合SEM、HR-TEM、XRD等常规表征手段，深入剖析纤维组成和形貌、交联改性、掺杂和钯负载对纤维微观结构的影响规律，并进而与催化剂的催化性能关联起来，从微观角度解析钯/壳聚糖纤维催化性能的影响机理以及在使用过程中的性能劣化内因，最终获得高活性和稳定性的非均相钯催化剂。本项目对于拓展正电子湮没技术在纳米纤维材料分析中的应用以及高活性和稳定性非均相过渡金属催化剂的制备都具有积极的意义。

本项目制备了一系列钯、钴、镍和铁粒子掺杂的交联壳聚糖和聚苯乙烯复合纤维，采用核分析技术正电子湮没寿命谱，结合红外光谱、扫描电镜和透射电镜等分析手段，研究了聚合物组成、交联、制备工艺对纤维微观结构以及内部凝聚态结构的影响规律，进而与纤维的催化性能关联起来。从自由体积的角度分析了掺杂对包埋的金属粒子尺寸和分布、纤维自由体积孔穴尺寸和浓度的影响规律，阐明了过渡金属掺杂复合纤维优良催化活性和稳定性的内在机理，为高活性和稳定性负载型过渡金属催化剂的设计和制备提供了一条行之有效的途径。制备了壳聚糖/聚丙烯酸钠纳米复合纤维，研究纤维的组成、化学结构对Cr2O72-吸附性能的影响规律和吸附机理，从自由体积角度解析了复合纤维优良吸附性能的内在机理。制备了交联壳聚糖/聚氧化乙烯复合纳米纤维，用于载药阿司匹林，体外缓释实验显示药物缓释速率可以通过交联度进行控制，进一步的研究发现交联度的增加不会影响纤维内自由体积孔穴的尺寸，但是会大幅降低其在纤维内的浓度，最终使药物释放速率下降。