Polyacrylonitrile-based porous polymer and carbon spheres for adsorption and catalysis
This project describes the preparation of spherical and porous polymer and carbon materials. In terms of nanocomposite materials, nanoparticles of titanium dioxide are embedded in the porous matrix of polymer and carbon spheres. Large polymer spheres and nanocomposites (both in millimeter-size) were prepared via syringe pump by droplet shaping cum phase separation. Polyacrylonitrile (i.e. PAN) was chosen as the shaping polymer. Nanoparticles of titanium dioxide (i.e. P90) were selected as model particles. The shape and inner structure of polymer spheres were investigated from the properties of polymer solution (such as viscosity and surface tension), the falling distance of polymer droplets, gelation rate, and gelation temperature. Hydrogel spheres of micrometer-size were prepared via drop-on-demand (i.e. DOD) ink-jetting shaping cum crosslinking. Sodium alginate (i.e. SA) was chosen as the model polymer for feasibility study. The shape of SA hydrogel microspheres was studied from driving voltage and the properties of SA solution (e.g. viscosity and surface tension). PAN microspheres of micrometer-size were prepared via DOD ink-jetting shaping cum phase separation. The shape of PAN microspheres was studied from shaping parameters (such as driving voltage, shaping frequency, and shaping temperature), the direction and falling distance of microdroplets, gelation rate, and properties of PAN solution (e.g. molecular weight, viscosity, and surface tension). Large polymer spheres and nanocomposites were carbonized to corresponding carbon spheres and nanocomposites. The carbonization process was divided into pre-oxidation and pyrolysis. In pre-oxidation, both oxidation temperature and retention time were studied. The oxidation temperature was influenced by the flow rate of air. In pyrolysis, pyrolysis and activation were done at the same time using carbon dioxide to reopen the surface pores of carbon samples. Important factors are pyrolysis temperature, retention time, and flow rate of atmosphere. Similarly, the pyrolysis temperature was also affected by the flow rate of atmosphere. Large polymer and carbon spheres were applied in adsorption tests. The polymer spheres were used as polar adsorbents while carbon spheres were used as low polar adsorbents. The affinity between solutes (i.e. various phenols and dyes) and adsorbents was investigated by adsorption isotherms. Based on the properties of solutes and adsorbents, several adsorption mechanisms were proposed to explain the interaction between solutes and adsorbents. The adsorption capacity of different adsorbents to selected solutes was also compared in terms of the porous structure of adsorbents. The photocatalytic performance of large polymer and carbon nanocomposites was also examined in terms of the content of nanoparticles. Compared with the photocatalytic rate of P90, both polymer and carbon nanocomposites had lower photocatalytic rates. In carbon nanocomposites, carbon matrix’s absorption to UV light was responsible for the decrease of photocatalytic rates. In addition, the transformation of crystal form of P90 (i.e. anatase phase to rutile phase) was also found after carbonization. XPS results of carbon nanocomposites showed that there were no new bonds forming between nanoparticles and carbon matrix after carbonization. Three carbon materials were inspected for the potential application in oxygen reduction reaction (i.e. ORR). Active species, such as quaternary N (i.e. N-Q) and pyridinic N (i.e. N-6), were found in all three carbon materials. Carbon spheres of “1,000°C, 1 hour” showed the best ORR activity in all three carbon materials. In conclusion, large polymer and carbon spheres were prepared and they showed distinct adsorption performance. Large polymer and carbon nanocomposites were also prepared, which showed quantitative photocatalytic activity towards model organic pollutant. Moreover, some carbon spheres showed promising properties for applications in ORR. Both PAN microspheres and SA hydrogel microspheres were successfully prepared by DOD ink-jetting shaping cum gelation. The preparation of PAN microspheres in this way has not ever been reported in literature.