Study On Ion Exchange And Halochromic Fiber Based On Polyacrylonitrile

Three kinds of functional fibers based on commercially available polyacrylonitrile fiber were synthesized and characterized.A reusable ion exchange fiber containing polyamino-polycarboxylic acid ligands was prepared via the stepwise modification of polyacrylonitrile fiber with diethylenetriamine and chloroacetic acid. The amination and carboxylmethylation conditions were optimized, and the modified fiber was characterized by elemental analysis, XRD, SEM and FTIR. For Cd2+ in water, this chelating fiber has prominent adsorption abilities such as low adsorption limitation (0.001 mg/L), high adsorption capacity (1.34 mmol/g) and fast response speed (half saturation adsorption time less than 0.5 minute based on 1 mg/mL Cd2+). The effectiveness of this chelating fiber has been proved by using it to treat actual sewage water, where the concentration of Cd2+ was reduced from 0.540 mg/L to below 0.001 mg/L. Moreover, this chelating fiber is also very effective for treating other metal ions such as Cu2+, Ca2+, Zn2+, Mg2+, Pb2+, Ni2+, Ag+ and Hg2+.A novel halochromic fiber was synthesized by first aminating commercially available polyacrylonitrile fiber with ethylenediamine and then immobilizing phenolphthalein covalently through a Mannich reaction. The fiber was characterized by XRD, SEM, FTIR and UV-vis spectroscopy. The halochromic properties, response speed and durability of this functional fiber have been investigated. This halochromic fiber exhibited remarkable color change from pale yellow to violet in a wide range of alkaline solutions (pH>10.1) with short response time (<1 s for 20 wt-% NaOH) and strong recycle stability (>300 times).A novel naked-eye colorimetric fiber for heavy metal ions was synthesized by aminating the commercially available polyacrylonitrile fiber with ethylenediamine and then immobilizing the 4-(2-pyridylazo)-resorcinol (PAR) covalently through Mannich reaction. The fiber was characterized by XRD, SEM and FTIR. The colorimetric property, response speed and selectivity of this functional fiber have been investigated. This fiber can selectively respond to heavy metal ions, such as Hg2+, Pb2+, Cd2+, Zn2+, Ni2+, Cu2+ in near neutral solutions and change color from red-orange to dark brown, but light metal ions, such as Ca2+, Mg2+, Al3+ can't induce the color change. Moreover, the fiber can selectively respond to Hg2+ and Cu2+ at pH 3 but doesn't respond to other heavy metals under the same conditions. The naked-eye colorimetric detection limit of this fiber for heavy metal ions can reach 10-6 mol/L.