Polyacrylonitrile-based nanoparticle-doped porous microspheres: Intermediates for functional carbon-based nanocomposites
Recently, nanocomposites are becoming attractive and popular in the field of material science. Among them, nanoparticle-polymer composites, have already found a wide range of applications, such as catalysis and adsorption, depending on their composition, size and porous structures. Porous nanocomposites could be used in the form of monoliths , membranes  and microspheres . Among them, porous microspheres have received particular attention as catalyst support in chemical reactors because they can allow faster mass transfer compared to monoliths. Furthermore, porous microspheres can be easily recycled when adding certain magnetic materials. Traditionally, polymer microspheres can be obtained by two methods: i) heterogeneous polymerization (emulsion , suspension, dispersion and precipitation), and ii) shaping polymers in solution (solvent evaporation, spray-dry, spray, dispersion and ink-jet printing cum phase separation). However, heterogeneous polymerization suffers from the disadvantages of many components and parameters during the preparation process and traditional shaping methods (spray and dispersion) are already very well established. Ink-jet printing cum phase separation, as a new and not yet well established method, can allow preparation of microspheres of smaller size (down to 10 µm) and with rather narrow size distribution. Based on the firm and comprehensive experiences on NIPS (non-solvent induced phase separation) in our group , the pore structures of final microspheres can be finely adjusted. After pyrolysis, polymer spheres will convert into carbon spheres which have high surface area and higher thermal stability, which are necessary properties for catalysis or adsorption. Polyacrylonitrile (PAN) is chosen as the candidate polymer because carbon yield after pyrolysis is high and the nitrogen content in the carbon material can have additional advantages.
Using PAN as the matrix polymer, by ink-jet printing method for droplet shaping and non-solvent induced phase separation (NIPS) for modulating pore structures, we would like to prepare porous polymer microspheres with sizes in the range of 10-100 μm with suitable pore structures (high pore volumes and high surface areas, > 200 m2). After pyrolysis, the polymer spheres would shrink and their pore structures would further develop. To control the distribution of functional nanoparticles (catalytic, magnetic) in the polymer matrix and thus in carbon matrix after pyrolysis is also an interesting objective.
- O. Mechling, Poröse Polymer- und Kohlenstoff-basierte TiO2 Nanokomposite, Dissertation, Universität Duisburg-Essen, 2015
- A. Wittmar, M. Ulbricht, Ind. Eng. Chem. Res. 2017, 56, 2967
- M. Ulbricht, Polymer 2006, 47, 2217
The financial support from Chinese Scholarship Council (CSC) is kindly acknowledged.