引用本文:范春莹,谢修鸿,燕爱春,张晋京.土壤胡敏素结构特征及对铜离子的吸附特性[J].土壤学报,2018,55(6):1460-1471.
FAN Chunying,XIE Xiuhong,YAN Aichun,ZHANG Jinjing.Structure and Cu(II) Adsorption of Soil Humin[J].Acta Pedologica Sinica,2018,55(6):1460-1471
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土壤胡敏素结构特征及对铜离子的吸附特性
范春莹,谢修鸿,燕爱春,张晋京
吉林农业大学资源与环境学院,吉林省商品粮基地土壤资源可持续利用重点实验室,长春大学园林学院,吉林农业大学资源与环境学院,吉林省商品粮基地土壤资源可持续利用重点实验室,吉林农业大学资源与环境学院,吉林省商品粮基地土壤资源可持续利用重点实验室
摘要:
以棕壤和赤红壤为供试土壤,在对土壤胡敏素进行结构表征的基础上,采用批量平衡法研究不同反应温度下其对铜离子(Cu2+)的吸附动力学和热力学特征,利用同步辐射X-射线吸收光谱技术探测了Cu2+在胡敏素表面吸附的微观局域结构。结果表明:与胡敏酸相比,胡敏素具有较高的脂族性和极性,但其分子中甲氧基碳、羰基碳、木质素类化合物和酚类化合物的比例较低;随溶液Cu2+浓度、接触时间和反应温度的增加,胡敏素对Cu2+的吸附量也增加;吸附动力学曲线符合假二级动力学方程,吸附过程是需要能量和吸热的缔合反应;吸附等温线符合Freundlich和Langmuir方程,吸附反应是自发、吸热和自由度增加的过程;与胡敏酸类似,胡敏素表面吸附态Cu2+是以扭曲的八面体构型存在,第一配位层(Cu-O)由原子间距为1.91~1.97 Å的4个O原子构成,第二配位层(Cu-C)由原子间距为2.80~2.83 Å的2个C原子组成,证实Cu2+主要以内层复合物形式吸附在胡敏素表面的有机官能团上。上述结果指出,尽管胡敏素的化学组成不同于胡敏酸,但Cu2+在这两种腐殖物质组分表面的局域配位结构相似。
关键词:  胡敏素  铜离子  吸附动力学  吸附热力学  同步辐射X-射线吸收光谱
DOI:10.11766/trxb201802010532
分类号:
基金项目:国家自然科学基金项目(41471196)
Structure and Cu(II) Adsorption of Soil Humin
FAN Chunying,XIE Xiuhong,YAN Aichun and ZHANG Jinjing
Key Laboratory of Soil Resource Sustainable Utilization for Jilin Province Commodity Grain Bases, College of Resource and Environmental Science, Jilin Agricultural University,College of Landscape Architecture, Changchun University,Key Laboratory of Soil Resource Sustainable Utilization for Jilin Province Commodity Grain Bases, College of Resource and Environmental Science, Jilin Agricultural University,Key Laboratory of Soil Resource Sustainable Utilization for Jilin Province Commodity Grain Bases, College of Resource and Environmental Science, Jilin Agricultural University
Abstract:
【Objective】The knowledge about chemical composition and interactions of humic substances with metal ions in the soil is of paramount importance to elucidating behaviors and fates of trace metals in the environments. Adsorption is one of the most important interactions between humic substances and metal ions. Among the three fractions of humic substances, i.e., humic acid, fulvic acid and humin, the last is the least studied because of its hard-to-dissolve nature. So far, it is still unclear how humin adsorbs metal ions and its mechanism. 【Method】In this study, humin was extracted from two zonal soils of East China, i.e., brown soil (Argosol) and lateritic red soil (Ferrosol), with 0.1 mol•L-1 NaOH+0.1 mol•L-1 Na4P2O7 extraction, treated with 10% (v/v) HF-HCl and then prepared into samples for analysis. Structure of the humin was characterized with elemental analysis, solid-state carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) techniques. On such a basis, the batch equilibrium method was used to study adsorption of Cu(II) on humin as a function of exposure duration, adsorbate concentration and reaction temperatures. Local chemical structure of the Cu(II) adsorbed onto the humin was explored with the synchrotron-based X-ray absorption near edge structure (XANES) spectrum and the extended X-ray absorption fine structure (EXAFS) spectrum. Furthermore, comparison was also made between humin and humic acid in chemical compositions and Cu(II) adsorption feature. 【Result】Compared with humic acid, humin is relatively higher in content of C, H, alkyl C, carbohydrate C, di-O-alkyl C, polysaccharides and fatty acids, but lower in content of N, S, O, methoxyl C, aryl C, phenol C, carbonyl C, lignin, phenols and nitrogen-containing compounds. With rising duration of exposure, Cu(II) concentration, and reaction temperature, Cu(II) adsorption on humin increased, too. Kinetics of the adsorption could be best described by pseudo-second order equation with equilibrium achieved in approximately 120 min, and isotherm of the adsorption well fitted the Freundlich and Langmuir equations. The adsorption activation parameters, i.e., activation free energy (ΔG#), activation enthalpy (ΔH#) and activation entropy (ΔS#), indicate that the process of adsorption is an association reaction that requires energy and absorbs heat. Moreover, the low activation energy (Ea) (less than 26 kJ•mol-1) implies that the adsorption reaction is controlled by boundary layer diffusion and Cu(II) was physically adsorbed onto the surface of humin. The adsorption thermodynamic parameters, i.e., standard Gibbs energy (ΔGº), standard enthalpy change (ΔHº) and standard entropy change (ΔSº), indicate that the adsorption reaction is a spontaneous, endothermic process with increasing freedom of motion. Similar to humic acid, humin has Cu(II) adsorbed on the surface in the form of a twisted octahedron, with the first coordination sphere consisting of 4 O atoms 1.91~1.97 Å apart and the second coordination sphere consisting of 2 C atoms 2.80~2.83 Å apart, which demonstrates that Cu(II) is preferentially adsorbed onto the organic functional groups on the surface of humin in the form of inner-sphere compound.【Conclusion】 All the findings demonstrate that humin differs from humic acid in chemical composition. Humin is relatively higher in aliphaticity and polarity. However, the Cu(II)s adsorbed on the surface of the two fractions of humic substances have similar local chemical structure.
Key words:  Humin  Copper ion  Adsorption kinetics  Adsorption thermodynamics  Synchrotron radiation X-ray absorption spectroscopy