Preparation Of Carbon Nanotube Composite Hollow Microspheres And Application In Supercapacitors

In recent years, hollow microspheres in the scale range of nanometers to micrometers have attracted continuous interest in the context of chemistry and material science, especially for their potential applications in the fields of catalysis, solar cells, sensors, drug delivery, controlled release, and separation and purification processes. With excellent electrical and mechanical properties of carbon nanotubes (CNTs), CNTs-based composite hollow microspheres, as the unique CNTs-based composite materials, have been focused on and investigated by more and more researchers. Among them, M. A. Correa-Duarte is one of the most excellent scientists, for he and co-workers have used layer-by-layer (LBL) technique via electrostatic interaction to make CNTs adsorbed on the surface of the templates, such as silica, polystyrene, and melamine spherical microspheres. The3-dimensional structure of the hollow cages may possess the unique properties, which are different from other1-dimensional or2-dimensional composite carbon materials and believed to be promising materials for applications in catalyst supports, photovoltaic devices, biosensors, electrochemical capacitors and so on. However, few reports have focused on the application of these unique composite materials up to now.In this paper, an overview of the CNTs-based composite hollow microspheres was given, with many different synthesis methods summarized. Three kinds of hollow microspheres were prepared, with characterization of their morphologies and conductivities. The composite electrodes were also prepared to measure their electrochemical performance. It mainly included several sections as follows.Chitosan (CHI)/carboxyl-functionalized multiwalled carbon nanotube (f-MWNT) hollow microspheres were successfully fabricated via the LBL assembly technique by electrostatic interaction between CHI and f-MWNTs on polystyrene sulfonate (PSS) microsphere templates. It was found that in the assembly process, different pH conditions, such as pH3and pH5, would affect the content of the f-MWNTs and the conductivity of the hollow microspheres. The stepwise growth of CHI/f-MWNT bilayers in different pH media was monitored by zeta potential measurements and scanning electron microscopy (SEM) analysis, with the content of the f-MWNTs compared and the reason analyzed. The morphologies of the hollow microspheres were characterized by transmission electron microscopy (TEM) and SEM. Swelling and collapse of the hollow microspheres occurred during the etching and drying process. Furthermore, thermogravimetric analysis (TGA) was used to compare the difference of the f-MWNT content in different pH media and investigate the influence of the CHI content by different reagents in the etching process, such as DMF and toluene. The conductivities of the final hollow microspheres were measured, resulting in the conclusion that different pH conditions and etching reagents would affect the conductivity of the hollow microspheres.Polyaniline (PANI)/f-MWNT hollow microspheres were prepared via in-situ polymerization of aniline on PSS microsphere templates. The morphologies of the products were characterized by SEM and TEM. Raman spectra were employed to reveal the interactions between PANI and f-MWNTs, and TGA was also used to obtain the contents of PANI and f-MWNTs. The electrochemical performance measurements of the products resulted in the conclusion that the f-MWNTs embedded in the shells accounted for the differences of the electrochemical performance between the pure PANI hollow spheres and the composite hollow spheres.Polyaniline nanofiber (PANInf)/f-MWNT hollow microspheres were prepared via the LBL technique on PSS templates. In order to stabilize the hollow structure, we reported a facile and efficient method to consolidate the composite shells:in-situ polymerization of aniline. The final hollow microspheres had free-standing shells, which were different from the collapsed shells before polymerization and contributed to the maintenance of the spherical hollow structure, confirmed by SEM. The shell thickness and content were obviously changed after polymerization, proved by TEM and TGA. Raman spectra were employed to investigate the interactions between PANInfs and f-MWNTs, in order to find the reason for the stabilization of the final hollow microspheres. The electrochemical performance of the product was measured, indicating that it is a promising electrode material for high performance supercapacitors.