Chemical Response of Nanocomposite Membranes of Electroactive Polydiaminonaphthalene Nanoparticles to Heavy Metal Ions

Poly(1,S-diaminonaphthalene) (P1SDAN) is a novel multifunctional but intractable polymer, from which it is difficult to preparing a large uniform membrane directly. A unique electroactive composite membrane was facilely prepared by drop-casting the dispersion of the P1SDAN nanoparticles in 0.1% poly(vinyl alcohol) aqueous solution. The cyclic voltammogram of an electrode modified by the nanocomposite membrane strongly depends on the potential sweeping rate and pH value of the electrolyte solution. The anodic/cathodic peak currents rise linearly with increasing the sweeping rate, but decline with increasing the pH value. The redox and coordination sensitivity of the nanocomposite membrane to heavy metal ions including silver, mercury, and copper ions was explored by open-circuit potential and cyclic voltammetry techniques. The results indicate that the three ions are all spontaneously and non-electrochemically reduced by the P1SDAN and then adsorbed on the membrane surface upon contacting each other, but the reduction extent of silver(I) and mercury(II) ions is much higher than that of copper(II) ion on the basis of the variation of the open-circuit potential. The nanocomposite membrane exhibits stable electroactivity, dense membrane structure, long cyclic lifetime, and strong adhesion onto the electrode, which features are different from those of pure electrosynthesized P15DAN membrane-modified electrode. The cyclic voltammetry of the nanocomposite membrane that was previously soaked in silver and copper ion solutions reveals strong oxidation and weak reduction peaks, while the cyclic voltammogram of the nanocomposite membrane previously soaked in mercury ion solution displays a weak oxidation but no reduction peak. It could be inferred that the silver(0) and copper(I) ions non-electrochemically reduced during soaking stages are more electrochemically oxidized than the reduced mercury(I) which has already been strongly coordinated with P1SDAN. The nanocomposite membrane method proposed in this study enables fabrication of an electrode functionalized by insoluble electroactive nanomaterials which could not be densely and thinly electrodeposited or solution cast.