聚乙烯亚胺改性纤维素纤维对Cr(Ⅵ)的吸附研究

Polyethyleneimine modified cellulose fiber for Cr(Ⅵ) removal from aqueous solution

采用低浓度H_2O_2氧化纤维素水凝胶纤维,再接枝聚乙烯亚胺(PEI),成功制得PEI改性纤维素纤维(PEI-OCF)吸附剂,并将其用于溶液中Cr(Ⅵ)的去除.同时,利用傅里叶变换衰减全反射红外光谱(ATR-FTIR)和X射线能谱(EDX)分析,确证纤维素上的羟基被H_2O_2氧化成醛基,PEI通过席夫碱反应被接枝到氧化纤维素上.制备优化结果表明,H_2O_2氧化阶段的最佳条件为pH=4.0,H_2O_2质量分数0.2%,氧化时间3.0h,氧化温度85℃;PEI接枝阶段的最佳条件为pH=11.0,PEI质量分数3.0%,接枝时间0.5 h.吸附研究结果显示,Cr(Ⅵ)在PEI-OCF上的吸附具有强烈的pH依赖性,最佳pH值为2.0.在180 min时吸附达到平衡;吸附过程符合准二级动力学模型,且主要由化学吸附控制.与Freundlich模型相比,Langmuir模型能更好地描述吸附过程;当温度为15和25℃时,最大吸附量分别为110.61和119.04 mg·g^(-1).浓度为300和600mg·L^(-1)的共存离子Ca^(2+)、Mg^(2+)和Na^+对PEI-OCF吸附Cr(Ⅵ)的影响较小.上述结果表明,PEI-OCF对Cr(Ⅵ)吸附性能良好,使用中易于分离;且制备过程无需交联剂,使用可降解材料,绿色环保.

Polyethyleneimine modified cellulose fiber（ PEI-OCF） was successfully prepared by grafting polyethylenimine（ PEI） onto oxidized cellulose fiber,which was obtained via hydrogen peroxide（ H2O2） oxidizing cellulose gel. Meanwhile,the removal of Cr（Ⅵ） from aqueous solution by PEI-OCF was carried out. It was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy（ ATRFT-IR） and energy dispersive X-ray spectroscopy（ EDX） that the hydroxyl groups of cellulose were oxidized to aldehyde groups by H2O2,and PEI was introduced onto the oxidized cellulose via Schiff-base reaction. The optimal preparation conditions were investigated in batch mode. Results show that the optimum oxidation conditions were pH of 4.0,0.2% of H2O2 concentration,3.0 h of oxidation time and 85 ℃ of oxidation temperature. At PEI-grafting stage,the optimum conditions were pH11.0,3.0% of PEI concentration,and 0. 5 h of oxidation time at room temperature. Adsorption results show that Cr（Ⅵ） adsorption on PEI-OCF was highly pH-dependent,and the optimum pH was 2.0. The adsorption equilibrium reached at about 180 min. The adsorption system followed pseudo-secondorder kinetic model,and chemisorption was the rate-limiting step. The Langmuir isotherm model gave a better fitting to the equilibrium data than theFreundlich isotherm model. The maximum adsorption capacity was 110.61 and 119.04 mg·g-1 at 15 and 30 ℃,respectively. Coexisting ions under 300 and 600 mg·L-1 of（ Ca2＋,Mg2＋and Na＋） had no significant effect on the adsorption capacity of Cr（Ⅵ）. In conclusion,the prepared PEI-OCF has a good adsorption capacity for Cr（Ⅵ） pollutant and is easily separated from the aqueous solution. Furthermore,the preparation of PEI-OCF is an environmentally friendly process with biodegradable cellulose as raw material and without using any crosslink agents.