Facile synthesis of poly(1,8-diaminonaphthalene) microparticles with a very high silver-ion adsorbability by a chemical oxidative polymerization Original Research Article

Poly(1,8-diaminonaphthalene) (PDAN) was traditionally synthesized by an electrochemical polymerization that has some limitations such as low productivity and single form of a film. Here we report a relatively large mass synthesis of PDAN micrometer particles by a chemical oxidation of 1,8-diaminonaphthalene by (NH4)2S2O8 or FeCl3 with high yield. Elemental analysis, IR, and solid-state high-resolution 13C NMR spectroscopies indicate that the PDAN chain contains imine (single bondNdouble bond; length as m-dashC), amine (single bondNHsingle bondC), and free amine (–NH2) units as linkages between naphthalene rings. A double-stranded ladder or single-stranded structure via the linkages is deduced. The structure and Ag+ absorbability of PDAN particles were characterized by laser particle-size analyzer, wide-angle X-ray diffractometer, IR, and inductively coupled plasma techniques. The Ag+ adsorbability of the particles was examined and optimized systematically by varying the adsorption time, the dose and size of the particles, the temperature, pH, and concentration of Ag+ solution. The fine particles obtained using (NH4)2S2O8 exhibit high adsorbability by complexation between Ag+ and amine/imine groups as well as the redox between Ag+ and free –NH2 group. The Ag+ adsorbance reaches 1.92 g/g (PDAN) with exposure to a solution containing 82 mM Ag+ ion for 24 h at an initial Ag+/PDAN ratio of 103 mmol/g. Total Ag+ adsorbance was 1.92 times the PDAN weight, remarkably surpassing the largest Ag+ adsorbance of 1.36 g/g (the best activated carbon fiber) for 30 days. The PDAN particles could be very useful in collection and removal of heavy metallic ions from water effluents.