Polymer-based metal adsorbents via graft copolymerization of polyvinyl alcohol with diaminomaleonitrile: A green chemistry approach

摘要

Synthesis, characterization, and amidoximation of diaminomaleonitrile- functionalized polyvinyl alcohol (PVA) grafts were studied. Ceric ammonium nitrate (CAN) was used as an initiator in an aqueous nitric acid medium under N _2 atmosphere. Optimum conditions for grafting were as follows: monomer concentration [DAMN] = 1.4M, [CAN] = 16 × 10 ~(-2) mol/L, T = 50°C, and t = 2 h. Water uptake of the PVA graft films increased with the increase of grafting yield. The imparted cyano group of the grafted PVA polymer chains (with degree of grafting up to 136%) was converted into amidoxime group by the reaction with hydroxylamine hydrochloride. The grafted polymers were characterized by FTIR spectroscopy, differential scanning calorimetry, and thermal gravimetric analysis. The grafted PVA films are more thermally stable than the ungrafted PVA membrane, because the grafted membrane showed a single degradation pattern despite having two components. A decrease in T _g values is observed as the grafting yield of copolymers increases indicating the incorporation of polydiaminomaleonitrile chains in amorphous copolymers with higher thermal stability. The prepared amidoximated DAMN136-g-PVA was investigated for its properties in removing heavy toxic metals, such as Pb ~(2+), Cd ~(2+), Zn ~(2+), Fe ~(3+), Cu ~(2+), Ni ~(2+), and Co ~(2+) from water. The amidoximated film is characterized by a considerably greater binding ability with respect to heavy metals. The nature of the metal ion also has great importance in the amount binding to the polymeric material. The kinetics of the sorption/desorption process for Co ~(2+), Ni ~(2+), and Zn ~(2+) were investigated.