Studies On The Design, Synthesis And Properties Of Colorimetric Polyacrylonitrile Fibers And Functionalized Polyacrylonitrile Fiber Catalysts

Polyacrylonitrile fiber is widely used in textile and garment area for its uniquestructure and properties. In recent years, the functionalization of polyacrylonitrilefiber has been developed rapidly and become interest of the chemists. Based on thefunctionalization of polyacrylonitrile fiber, this paper provides a colorimetric fiber forheavy metal ions detection and adsorption, a dual colorimetric fiber for acids andbases detection, a tertiary-amine functionalized fiber catalyst, a series of polyaminefunctionalized fiber catalysts, and a proline functionalized fiber catalyst.A4-（2-pyridylazo）-1,3-benzenediol （PAR） functionalized colorimetric fiber forheavy metal ions detection and adsorption has been designed and synthesized. Thisfiber has been fully characterized and PAR has been confirmed to be covalentlygrafted on the fiber by the C–N bond formation. The color change capabilities andmechanism of the fiber have been systemically studied. After adsorbing heavy metalions at pH=6(such as Hg²⁺, Pb²⁺, Cd²⁺, Zn²⁺, Ni²⁺and Cu²⁺), this fiber changed itscolor from red orange to dark-brown. However, no color change was observed forlight metal ions such as Ca²⁺, Mg²⁺and Al³⁺. The selectivity of the fiber increasedwith the pH value decreased. The fiber changed its color only for Hg²⁺and Cu²⁺at pH=3. This fiber also presented a high visual detection limit (1×10^–6mol/L), excellentreusability （>50times） and high photostability （>30days under direct exposure tosunlight with no loss in capability of color change and adsorption for heavy metalions）.A dual colorimetric fiber based on ethyl orange and phenolphthalein for acids andbases has been designed and synthesized. This fiber has been fully characterized.Ethyl orange and phenolphthalein have been confirmed to be covalently grafted on thefiber by the C–N bond formation. The spectroscopic properties, color changecapability and mechanism of the fiber have been systemically studied. This fiberpresented a fresh yellow color in neutral condition, deep pink in acidic condition （pH=0-1） and dark violet in basic condition （pH=13-14）, which was easy to bedistinguished. The color change of the fiber could be induced by many acid or basesolutions such as citric acid, HCl, H2SO4, NaOH, Ca（OH）2and Na3PO4. This fiber also presented excellent reusability （>300times）, good stability in strong acid andbase, and high photostability （>60days under direct exposure to sunlight）.In addition, series of monoamine and polyamine functionalized fiber catalystshave been designed and synthesized. For the monoamine functionalized fiber catalystscontaining primary, secondary and tertiary-amine, the catalytic activities of these fibercatalysts have been evaluated and the tertiary-amine functionalized fiber catalyst withhighest catalytic activity was selected for detail research. The structure and surface ofthe fiber catalyst have been characterized. The Knoevenagel reaction conditions,solvent effect, substrate expansion and reusability have been systemically studied.This fiber catalyst could efficiently catalyze Knoevenagel condensation in variousorganic solvents （yield>90%）. This catalyst was applicable to many substrates andpresented excellent reusability （10times, almost no loss in catalytic activity）.For the polyamine （such as diethylenetriamine and triethylenetetramine）functionalized fiber catalysts, the catalytic activities of these fiber catalysts have beenevaluated and the triethylenetetramine fiber catalyst with the highest catalytic activitywas selected for detail research. The structure and surface of the fiber catalyst havebeen characterized. The reaction conditions, solvent effect, substrate expansion andreusability have been systemically studied. This fiber catalyst could efficientlycatalyze Knoevenagel condensation in water （yield>94%）. Water was used as thesolvent for its green, economic and eco-friendly. This fiber catalyst was applicable tomany substrates and presented excellent reusability （21times, a slightly decrease,after prolonging the reaction time, an almost quantitative yield98%was obatained）.Proline, which is one of the hotspots in the catalytic field, was firstly introducedinto the fiber and a proline functionalized fiber catalysts have been designed andsynthesized. The structure and surface of the fiber catalyst have been characterized.The reaction conditions, solvent effect, substrate expansion and reusability have beensystemically studied. This fiber catalyst could efficiently catalyze Knoevenagelcondensation in acohol （yield>92%）. This catalyst was applicable to many substratesand presented excellent reusability （20times, almost no loss in catalytic activity）.Catalyst loading was only2mol%. Even decreased the catalyst loading to0.5mol%,an almost quantitative yield98%was able to obtain by prolonging the reaction time.