摘要
以纤维素为原料,利用表面氨化交联聚乙烯亚胺(PEI)制备了一种对阿散酸(p-ASA)具有高效吸附效果的功能化纤维素基气凝胶(Cell@PEI)。结果表明,三维块状的Cell@PEI具有独特的多孔结构、较大的比表面积(241.4
芳香族有机砷化物如对氨基苯胂酸(又名阿散酸,p-ASA)具有治疗球虫肠道寄生虫、提高饲养效率、促进畜禽快速生长和改善肉类色素沉着等作用,已被广泛用作饲料添加
纤维素基气凝胶作为独立于无机气凝胶和有机聚合物气凝胶的第三代气凝胶,具有低成本和优异性能,如密度低、比表面积大(108~1039
本研究在纤维素基气凝胶的基础上,以环氧氯丙烷为交联剂,通过交联反应和冷冻干燥制备聚乙烯亚胺(PEI)功能化纤维素基气凝胶Cell@PEI,对Cell@PEI进行结构表征,同时通过改变pH值、吸附时间和吸附温度等反应条件,考察Cell@PEI对p-ASA的吸附性能及吸附机理。
纤维素粉末(粒径90 μm)、PEI(纯度99%)、环氧氯丙烷(ECH)和p-ASA,均购自上海阿拉丁生物科技股份有限公司;尿素、氢氧化钠(NaOH)、盐酸,均购自国药化学试剂有限公司;以上药品均为分析纯。
紫外可见分光光度计,T6型,北京普析通用仪器有限责任公司;Zeta电位与纳米粒度仪,NanoPlus3型,美国Micromeritics公司;傅里叶变换红外光谱仪(FT-IR),AVAT-AR 360型,美国Nicolet公司;扫描电子显微镜(SEM),Quanta250型,美国FEI公司;比表面积分析仪,ASAP2020型,美国Micromeritics公司;X射线衍射仪(XRD),Miniflex 600型,日本株式会社Rigaku;X射线光电子能谱仪(XPS),ESCALAB 250型,美国ThermoFisher公司;智能恒温培养振荡器,ZWYR-2012C型,上海智城分析仪器制造有限公司;冷冻干燥机,Lab-1A-50型,北京博医康实验仪器有限公司;精密增力电动搅拌器,JJ-1型,金坛市富华仪器有限公司。
将4.0 g纤维素粉末分散在NaOH、尿素和水的混合溶液(质量比7∶12∶81)中。将混合溶液放入25℃的水浴中进行超声处理,得到质量分数为4%的纤维素悬浮液。将悬浮液预冷却至-13.5℃并用电动搅拌器强烈搅拌,得到透明的纤维素溶液。将50.0 g纤维素溶液和4.0 g PEI置于三颈烧瓶中混合,搅拌30 min后加入交联剂ECH(10.0 g),将混合物在70℃条件下反应4 h,形成水凝胶,随后经超纯水置换和循环冷冻干燥(-70℃,12 h),最终制得Cell@PEI,其反应过程如

图1 Cell@PEI的制备反应过程示意图
Fig. 1 Schematic diagram of Cell@PEI preparation reaction process
采用SEM表征样品的表面微观形貌;采用比表面积分析仪的BET模型表征样品的孔径分布和比表面积;采用XRD测定样品晶型结构;采用FT-IR测定样品表面官能团,对600~4000 c
吸附过程在恒温振荡培养箱(温度25℃、转速160 r/min、时间6 h)中进行,用0.1 mol/L NaOH溶液和0.1 mol/L盐酸调节p-ASA溶液的pH值。将一定量Cell@PEI置于50 mL 的p-ASA溶液(50 mg/L)中一定时间,以确保达到吸附平衡。研究吸附剂用量(0.01~0.07 g)、pH值(3~10)、p-ASA的初始浓度和共存离子对吸附参数的影响。反应后,利用紫外-可见分光光度计测定上清液中p-ASA的浓度。随后,分别采用
(1) |
(2) |
式中,C0表示溶液中吸附质的初始浓度,mg/L;Ce表示吸附质剩余浓度,mg/L;m表示吸附剂用量,g;V表示吸附质溶液体积,L。
利用SEM观察纤维素粉末原料和Cell@PEI的表面微观形貌,结果如

图2 纤维素粉末及Cell@PEI的SEM图和改性及吸附前后Cell@PEI的EDS图
Fig. 2 SEM images of cellulose powder and Cell@PEI; EDS images of Cell@PEI before and after modification
由吸附前后Cell@PEI的EDS图(见
采用比表面积分析仪,根据BET模型和N2吸附-脱附方法测定Cell@PEI和纤维素粉末的孔径分布和比表面积,结果如

图3 纤维素粉末和Cell@PEI的N2吸附-脱附等温线
Fig. 3 N2 adsorption-desorption isotherm curves of cellulose powder and Cell@PEI

图4 纤维素粉末和Cell@PEI的XRD谱图
Fig. 4 XRD patterns of cellulose powder and Cell@PEI

图5 改性及吸附前后纤维素材料的FT-IR谱图
Fig. 5 FT-IR spectra of cellulose materials before and after modification and adsorption

图6 不同吸附条件对Cell@PEI吸附性能的影响
Fig. 6 Effects of different adsorption conditions on the adsorption perfomance of Cell@PEI
当溶液pH值为4.0,p-ASA初始浓度为60 mg/L,吸附时间为250 min时,改变吸附剂用量,得到不同吸附量和去除率。
当吸附剂用量为0.02 g,吸附时间为250 min时,Cell@PEI对pH值为4.0的不同初始浓度下p-ASA的吸附性能如
共存离子可与p-ASA竞争吸附剂上的吸附位点,本研究探究了3种常见的共存阴离子对Cell@PEI吸附p-ASA的影响,添加0.02 g Cell@PEI,控制p-ASA溶液pH值为4.0,初始浓度为60 mg/L,吸附时间为250 min,改变共存阴离子种类和浓度,进行吸附实验,结果如
当吸附剂用量为0.02 g,对pH值为4.0、初始浓度为60 mg/L的p-ASA进行吸附实验,探究吸附时间对Cell@PEI吸附p-ASA的影响,结果如

图7 吸附动力学分析
Fig. 7 Adsorption kinetics analysis
将Cell@PEI对p-ASA的吸附量随时间变化的数据用准一级动力学模型和准二级动力学模型进行拟合,结果如
为进一步研究Cell@PEI与p-ASA的相互作用机制,利用Langmuir和Freundlich模型分析其吸附过程,对不同温度下的等温吸附数据进行拟合,拟合结果如

图8 吸附等温线分析
Fig. 8 Adsorption isotherm analysis
注 Qm为最大吸附量,mg/g。
为了阐明p-ASA与Cell@PEI的分子间相互作用,本研究通过吸附前后Cell@PEI的XPS谱图探究了p-ASA的吸附机理,结果如

图9 Cell@PEI吸附机理研究
Fig. 9 Adsorption mechanism analysis of Cell@PEI
分析FT-IR谱图(见
Cell@PEI对p-ASA的吸附是气凝胶界面上发生的静电相互作用的化学吸附过程。在吸附过程中p-ASA上具有较强还原活性的极性氨基,其偶极矩是由极性氨基的表面电荷分布不均匀所致。
本研究分别选用0.2 mol/L和0.5 mol/L的NaOH溶液为解吸剂,对吸附p-ASA后的Cell@PEI进行解吸再生研究。

图10 Cell@PEI解吸再生分析
Fig. 10 Analysis of desorption and regeneration of Cell@PEI
本研究以纤维素为原料,利用聚乙烯亚胺(PEI)进行氨基改性,合成具有阿散酸(p-ASA)吸附功能的新型三维块状氨化纤维素气凝胶(Cell@PEI),对Cell@PEI进行了理化性能分析及吸附机理探索。
3.1 在Cell@PEI对p-ASA的最佳吸附条件(p-ASA溶液pH值4.0,初始浓度为60 mg/L,吸附时间6 h,吸附温度25℃,Cell@PEI添加量0.02 g)下,最大吸附量为205.6 mg/g。
3.2 Cell@PEI对p-ASA的吸附过程是化学吸附过程,符合准二级动力学方程;同时符合Freundlich等温吸附方程,属于非均匀、多分子层吸附,且吸附更易在低温下进行。
3.3 吸附再生实验结果表明,用2种不同浓度NaOH溶液循环再生5次后,Cell@PEI的平衡吸附量分别为110.9 mg/g和105.4 mg/g,去除率分别达77.2%和73.4%,表明Cell@PEI再生5次后仍可对水体中大部分p-ASA进行吸附,具有良好的再生使用效果。
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