Graft Polymerization Of Polyacrylonitrile Onto Agricultural Residue Contained Cellulose And Its Adsorption Properties After Modification

With the rapid development of industry and agriculture, the pollution of heavy metal ions inwater has seriously influenced the normal production and human life, and the reutilization ofagricultural residue has also attracted more attention. The effective groups which can chelateheavy metal ions, were introduced onto the surface of agricultural residue through singleelectron transfer-living radical polymerization (SET-LRP) to prepare a kind of high efficientand degradable adsorbent. SET-LRP had displayed its unique advantages of lowpolymerization temperature, ultrafast polymerization rate and simple post-treatment. Modifiedpolyacrylonitrile (PAN) resin has been widely used in wastewater treatment. In this study,peanut shell, wheat straw and corn stalk were used as the substrate, respectively, whichcellulose is increased successively. PAN was grafted onto the surface of peanut shell, wheatstraw and corn stalk, respectively, and then the obtained copolymers were modified. Theadsorption properties of modified copolymers for Hg(II) were studied and compared in detail.Peanut shell-g-PAN was prepared by SET-LRP employing bromine functionalized peanutshell as initiator and Cu(0) powder/N,N,N’,N’-tetramethylethylenediamine (TEMED) ascatalytic system. The cyano groups of peanut shell-g-PAN were converted to amidoximegroups using NH2OH·HCl to prepare adsorbent amidoxime peanut shell-g-PAN (AO peanutshell-g-PAN). Kinetic studies indicated that the polymerization followed first-order kinetics.The adsorption experiments for Hg(II) showed that the optimal pH is6.0, the adsorptionkinetic followed the pseudo-second-order model, the adsorption isotherms of peanutshell-g-PAN for Hg(II) could be explained by the Freundlich isotherm model, and the optimaltemperature was45oC.SET-LRP of acroylonitrile was initiated by the macroinitiator which was prepared by theacylation of hydroxyl with BriB-Br using pretreated wheat straw as substrate. Kinetic plotsmanifested that the polymerization process had the “living” character. AmidoximeWSM-g-PAN (AO WSM-g-PAN) was obtained by modifying WSM-g-PAN withhydroxylamine hydrochloride (NH2OH·HCl) and its adsorption properties to Hg(II) wasstudied in detail. Comparing with WSM, the adsorption capacity of AO WSM-g-PAN forHg(II) increased greatly. Moreover, the maximum adsorption capacity was4.70mmol·g-1atpH=6.0; AO WSM-g-PAN also showed better adsorption selectivity for Hg(II); The adsorption kinetic followed the pseudo-second-order model; The adsorption isothermsprocess of AO WSM-g-PAN for Hg(II) at25oC,35oC,45oC could be described by theFreundlich isotherm model, and the optimal temperature was45oC.Cellulose which was extracted from wasted corn stalk was successfully functionalized byBriB-Br to initiate the polymerization of acrylonitrile(AN), acrylamide(AM) and methylacrylate(MA) through SET-LRP and the copoploymers CS-g-PAN, CS-g-PAM, CS-g-PMAwere obtained. Kinetic studies of AN, AM and MA indicated that the polymerizationprocesses followed first-order kinetics. AO CS-g-PAN and CO CS-g-PMA, which containedamidoxime and carboxyl groups, were obtained by modifying the copolymer CS-g-PAN andCS-g-PMA with NH2OH·HCl and NaOH, respectively. CS-g-PAN, CS-g-PAM, AOCS-g-PAN and CO CS-g-PMA were employed as adsorbents to remove Hg(II), Pb(II), Cd(II)and Cu(II) from aqueous solutions and the results indicated that they showed the maximumadsorption capacity of1.42mmol·g-1,2.26mmol·g-1,8.04mmol·g-1, and3.92mmol·g-1forCd(II), Hg(II), Hg(II) and Hg(II), resectively. The adsorption process of AO CS-g-PAN forHg(II) followed a pseudo-second-order process. The isothermal process of AO CS-g-PAN forHg(II) could be better described by Freundlich isotherm model.