Depth profiling of clay–xanthan complexes using step-scan mid-infrared photoacoustic spectroscopy
Depth profiling of clay–xanthan complexes using step-scan mid-infrared photoacoustic spectroscopy
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DOI：
10.1007/s11368-010-0225-3
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发表时间：
2010-04
影响因子：
3.6
通讯作者：
C. Du;Guiqin Zhou;Huoyan Wang;Xiaoqin Chen;Jian-min Zhou
中科院分区：
文献类型：
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作者：
C. Du;Guiqin Zhou;Huoyan Wang;Xiaoqin Chen;Jian-min Zhou
目的许多土壤微生物产生胞外多糖，黄原胶是由细菌产生的一种高相对分子质量的天然多糖；以往的研究表明，胞外多糖是在土壤中产生的，并与周围的粘土颗粒密切相关。形成的粘土-EPS复合体在土壤生物地球化学中起着重要的作用。材料与方法应用傅里叶变换红外光声光谱(FTIR-PAS)技术对土壤粘土矿物(高岭土和蒙脱石)与黄原胶的界面层进行了研究，并首次将FTIR-PAS技术的阶跃扫描功能应用于原位探索表层特征。结果与讨论FTIR-PAS光谱对土壤粘土矿物和黄原胶的表征具有良好的性能；蒙脱石的深度剖面谱比高岭土的深度剖面谱变化大，在蒙脱石的深度剖面谱中观察到更多的黄原胶信息，特别是在600~1,200 cm−1处的吸收证实了这一点。黄原胶更多地吸附在蒙脱石表面，导致更厚的表面层；粘土-黄原胶复合体(吸附在蒙脱石表面和与黄原胶结合)的含水率增加。黄原胶对粘土-黄原胶复合体的保水能力有较大的贡献，但高岭土-黄原胶复合体的贡献小于蒙脱石-黄原胶复合体。结论蒙脱土表面亲水性强于高岭土，吸附在1,640 cm−1处，因此蒙脱石更容易与亲水性黄原胶相互作用，吸附黄原胶的量大于吸附黄原胶的量，深度剖面PAS谱显示蒙脱石的表面层比高岭土更宽(9.8μm vs.3.8μm)。蒙脱石的表面层越厚，保水能力越强，有利于形成更复杂的有机矿物复合体。
PurposeMany soil micro-organisms produce extracellular polysaccharides (EPS), and xanthan is a high-molecular-weight natural EPS produced by the bacterium; former studies demonstrate that EPS are produced in soil and are closely associated with the surrounding clay particles. The formed clay–EPS complexes play an important role in soil biogeochemistry. In the present study, experimental clay–xanthan complexes were prepared as models for the soil/biota interface, and the interface layers were investigated using spectroscopic method.Material and methodsFourier transform infrared photoacoustic spectroscopy (FTIR-PAS) was applied to examine interface layer of soil clay minerals (kaolin and montmorillonite) and xanthan; specifically, the step-scan function of FTIR-PAS technique was initially applied to in situ explore the characteristics of surface layers.Results and discussionSoil clay minerals and xanthan were characterized using FTIR-PAS spectra with excellent performance; the variances of depth profiling spectra of montmorillonite were higher than that of kaolin, and more xanthan information was observed in the depth profiling spectra of montmorillonite, which was specifically verified by the absorptions in the region of 600 to 1,200 cm−1. More xanthan was adsorbed in the montmorillonite surface, which resulted in a thicker surface layer; moisture content clay–xanthan complexes (both absorbed in montmorillonite surface and combined with xanthan) increased. Xanthan was likely to significantly contribute to the water retention capability of clay–xanthan complex, but the contribution of kaolin–xanthan complex was less than that of montmorillonite–xanthan complex.ConclusionsThe surface of montmorillonite was more hydrophilic than that of kaolin due to the absorption in 1,640 cm−1; thus, montmorillonite was easier to interact with hydrophilic xanthan, more xanthan was adsorbed, and a much broader surface layer was observed through depth profiling PAS spectra (9.8 μm vs. 3.8 μm). Thicker surface layer in montmorillonite resulted in a stronger water retention capability and will promote the formation of much more complicated organomineral complexes.