Synthesis Of Sulfonated Poly(Aryl Ether Nitrile)s And Adsorption Properties Of Their Nanofiber Membranes

In recent years,heavy industry has made continuous development and progress.Behind the progress,the ecological environment has been continuously destroyed.A large number of heavy metal ions contained in industrial wastewater accumulate continuously through the food chain,slowly encroachment on human health,and the treatment of heavy metal polluted water resources has become an important part of ecological environment protection.In this paper,a series of sulfonated Poly(aryl ether nitrile)s(SPEN)with different degrees of sulfonation were synthesized,and then SPEN series nanofiber membranes were prepared by electrostatic spinning technology and their adsorption properties were tested.Finally,nano TiO₂ was introduced to prepare SPEN/TiO₂ composite fiber membrane and further study on the adsorption properties of composite nanofiber membrane.Firstly,sulfonated polyarylene ether nitrile(SPEN-50,SPEN-60 and SPEN-70)with sulfonated degree of 50%,60%and 70%were synthesized by nucleophilic aromatic substitution polymerization with 2,5-dihydroxy benzenesulfonic acid potassium salt,bisphenol A and 2,6-difluorophenonitrile as raw materials according to different material ratios.The structure and molecular design of SPEN series polymers were confirmed by IR and ¹H NMR spectra,and they all had high molecular weight(Mw>150 kg/mol).The results of solubility study show that SPEN series polymers have good solubility in polar solvents at room temperature.In addition,SPEN series polymers also have high glass transition temperature(205-220?),thermal decomposition temperature(405-422?)and tensile strength(64-78 MPa).Then a series of nanofiber membranes were prepared by electrostatic spinning technique based on SPEN.SEM results showed that the nanofiber membranes had good morphology and the average fiber diameter decreased with the increase of SPEN sulfonation.The adsorption performance of this series of fiber membranes was tested using Cu²⁺solution as the contaminant source.The adsorption performance of SPEN polymer films and nanofiber membranes on Cu²⁺was studied comparatively.The results showed that the adsorption capacity of the nanofiber membranes for Cu²⁺was increased by more than 40%compared with the conventional films,and in addition,the adsorption capacity of the nanofiber membranes gradually increased with the increase of sulfonation?The adsorption performance of this series of nanofiber membranes was enhanced with the increase of pH and temperature,the adsorption capacity of this series of nanofiber membranes could still maintain more than 80%of the initial adsorption capacity after 8 adsorption and desorption cycles.The SPEN-70 nanofiber membrane was used for the adsorption of other metal ions,and it was found that SPEN-70 has the adsorption capacity for Pb²⁺,Fe³⁺,Ag⁺,Cr⁶⁺,Mn²⁺,Co²⁺,Ni²⁺and Zn²⁺.The adsorption kinetics study showed that the adsorption rate of this series of nanofiber membranes was controlled by chemisorption,the adsorption isotherm study calculated the theoretical maximum adsorption capacity of 61.27 mg/g for Cu²⁺by this series of nanofiber membranes.Finally,based on SPEN-70 polymer,a series of SPEN-70/TiO₂ composite fiber membranes with nano-TiO₂ content ranging from 1 to 6 wt%were prepared by ultrasonic dispersion technology.Infrared spectroscopy and X-ray diffraction proved that nano-TiO₂containing a large number of hydroxyl groups on the surface was successfully introduced into the composite nanofiber membrane.The microscopic morphology observation results showed that concave microspheres appeared in the composite fiber membrane after the introduction of nano TiO₂,and the diameter of microspheres increased with the increase of nano TiO₂ content.It was found that 1-3 wt.%nano-TiO₂ addition could improve the adsorption performance of the composite nanofiber membrane while maintaining the structural stability.So the subsequent study focused on the adsorption performance of the composite nanofiber membrane with 1-3 wt.%nano-TiO₂ content.The adsorption performance of composite nanofiber membranes with 1-3 wt.%nano-TiO₂ content was enhanced with the increase of pH and temperature;the adsorption capacity of more than 68%of the initial adsorption capacity was maintained after 8 adsorption and desorption cycles.The adsorption kinetics of Cu²⁺adsorption by composite nanofiber membranes with 1-3 wt.%nano-TiO₂ content showed that the adsorption rate of composite nanofiber membranes was greatly increased after the addition of small amount of nano-TiO₂,and the adsorption capacity was increased by 69%,82%and 88%in 30 min compared with that before the addition of nano-TiO₂,respectively.The adsorption isotherm study showed that the theoretical maximum adsorption capacity of the composite nanofiber membrane for Cu²⁺was increased to 71.89,74.68 and 76.04 mg/g.