不同调节剂制备MOF-Fe的性质及对Se(Ⅳ)的吸附性能
Characteristics and Adsorption Properties of Se(Ⅳ) for MOF-Fe Prepared with Different Conditioning Agents
作者单位E-mail
王锐 湖北民族学院化学与环境工程学院, 恩施 445000  
龚勇 湖北职业技术学院, 武汉 432000  
许海娟 湖北民族学院化学与环境工程学院, 恩施 445000  
魏世勇 湖北民族学院化学与环境工程学院, 恩施 445000
生物资源保护与利用湖北重点实验室, 恩施 445000 
weishiyong2007@126.com 
吴德勇 湖北民族学院化学与环境工程学院, 恩施 445000
生物资源保护与利用湖北重点实验室, 恩施 445000 
 
摘要: 以HF、HCl、H2O和NaAc溶液为调节剂合成了4种MOF-Fe样品,用X射线衍射(XRD)、透射电镜(TEM)、N2等温吸附-脱附、综合热分析(TG/DTG和DTA)和质子电位滴定研究了4种样品的结构与表面性质,以及对亚硒酸根(Se(Ⅳ))等温吸附特性。MOF-Fe(HF)、MOF-Fe(HCl)、MOF-Fe(H2O)和MOF-Fe(NaAc)四种样品均具有八面体MIL-100(Fe)的晶体结构,但它们的结晶度和晶面取向略有差异。4种样品的比表面积分别为1 683、1 517、1 641和1 734 m2·g-1,其总孔体积依次降低,微孔孔径分别为1.27、1.22、1.22和1.17 nm。MOF-Fe(HF)样品的脱羧基失重峰温度最高(415℃),苯环碳化失重峰温度最低(462℃);MOF-Fe(HCl)、MOF-Fe(H2O)和MOF-Fe(NaAc)样品出现了因氧化铁被碳还原所致的失重平台(566~716℃)。样品悬浮液从pH=6.0降到3.0时,消耗H+的量表现为MOF-Fe(H2O) > MOF-Fe(HCl) > MOF-Fe(HF)=MOF-Fe(NaAc),它们的电荷零点(pHZPC)依次为3.1、3.5、3.6和3.5。MOF-Fe(NaAc)、MOF-Fe(HCl)、MOF-Fe(H2O)和MOF-Fe(HF)对Se(Ⅳ)的吸附亲和力依次减小,它们对Se(Ⅳ)的吸附容量(Qm)分别为77.69、107.07、117.40和87.15 mg·g-1。显著性分析显示,MOF-Fe的羟基密度与样品吸附Se(Ⅳ)的Qm显著正相关。研究结果表明,MOF-Fe样品的结构热稳定性和羟基/配位水分子等活性位点密度受合成样品时加入的调节剂影响,用HF作为调节剂合成MOF-Fe样品有利于提高样品中羧基与苯环之间的C-C键合强度和热分解产物的稳定性,降低苯环碳化温度;HCl和H2O作为调节剂有利于提高样品的活性位点密度,可提高MOF-Fe样品对Se(Ⅳ)吸附容量。
关键词: MOF-Fe  调节剂  表面性质  吸附  亚硒酸根
基金项目: 国家自然科学基金(No.41561053,21767009)资助项目。
Abstract: MOF-Fe samples were prepared with HF, HCl, H2O and NaAc as conditioning agents by hydrothermal method. The characteristics of the samples were studied by X-ray diffraction (XRD), Transmission electron microscope (TEM), N2 adsorption/desorption, thermal analysis (TG/DTG and DTA) and proton potentiometric titration. Isothermal adsorption experiments of selenite (Se(Ⅳ)) on the samples were carried out. Crystal structure of all samples are same as MIL-100(Fe), and the morphology are octahedral, while the crystallinities and crystal orientations are different. The BET surface area are 1 683, 1 517, 1 641 and 1 734 m2·g-1, respectively, and total pore volumes of the samples are decreased orderly. The micropore diameter are 1.27, 1.22, 1.22 and 1.17 nm for MOF-Fe(HF), MOF-Fe(HCl), MOF-Fe(H2O) and MOF-Fe(NaAc). The temperature of decarboxylation of MOF-Fe(HF) is highest (415℃), while its carbonization temperature for benzene ring is lowest (462℃) compared with the others. A weight loss caused by redox between iron oxide and carbon appears in MOF-Fe(HCl), MOF-Fe(H2O) and MOF-Fe(NaAc). The sequence of H+ consumed during the process of proton potentiometric titrations for samples is MOF-Fe(H2O) > MOF-Fe(HCl) > MOF-Fe(HF)=MOF-Fe(NaAc), and pH value of zero point charge (pHZPC) are 3.1, 3.5, 3.6 and 3.5 accordingly. The sequence about the affinity of adsorption for Se(Ⅳ) on samples is MOF-Fe(NaAc) > MOF-Fe(HCl) > MOF-Fe(H2O) > MOF-Fe(HF), and the maximum adsorption capacities (Qm) are 77.69, 107.07, 117.40 and 87.15 mg·g-1 correspondingly. The Qm of Se(Ⅳ) on samples have positive correlation with density of hydroxyl for samples observably. This study reveals that the thermostability and density of active site of MOF-Fe are influenced by the conditioning agent when MOF-Fe was prepared. The HF could increase the strength of C-C between carboxyl and benzene ring, decrease carbonization temperature of benzene ring of MOF-Fe, and improve the thermostability of iron oxides after heating. While HCl and H2O could improve the density of active site in samples, then the Qm of Se(Ⅳ) adsorbed on MOF-Fe could be increased.
Keywords: MOF-Fe  conditioning agent  surface properties  adsorption  selenite
投稿时间:2017-12-06 修订日期:2018-01-28
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王锐,龚勇,许海娟,魏世勇,吴德勇.不同调节剂制备MOF-Fe的性质及对Se(Ⅳ)的吸附性能[J].无机化学学报,2018,34(5):906-916.
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