Preparation and characterization of polystyrene sulfonic acid-co-maleic acid copolymer modified silica nanoparticles

Two types of silanes, including 3 glycidoxypropyltrimethoxysilane (GPTMS) and 3aminopropyltriethoxysilane (APTES), were grafted onto polystyrene sulfonic acid-co-maleic acid (PSSA_MA) first, followed by the grafting reaction to the silica surface. The modification of PSSA_MA onto silica was confirmed through FTIR (Fourier transform infrared spectrum), NMR (Nuclear magnetic resonance), and TGA (Thermogravimetric analysis). The grafting ratio of PSSA_M A via APTES with 1-ethyl-3-(3dimethylaminopropy1)-carbodiimide (EDC) activation reached 18.0 %. As for GPTMS case, the grafting ratio reached 14.4 %, which was slightly lower than that of APTES case. The grafting mechanisms for both cases were elucidated. The epoxysilane was found to react with maleic acid groups on PSSA_MA only. On the other hand, the atninosilane not only interacted with sulfonic groups but also activated maleic acid groups via EDC. However, without the use of the coupling agent, the grafting degree of PSSA_MA was only 3 %. which signified the essential role of coupling agents in this organically modified silica. The average particle size of silica was around 200 tun with or without organic modification from transmission electron microscopy (TEM) and Zetasizer analysis. The APTES-modified samples showed the highest improvement in the ion adsorption capacity in all investigated cases.