Depth profiling of soil clay-xanthan complexes using step-scan mid-infrared photoacoustic spectroscopy

摘要

Many soil micro-organisms produce extracellular polysaccharides (EPS); former studies demonstrate that EPS are produced in soil and are closely associated with the surrounding clay particles, and the formed clay-EPS complexes play an important role insoil biogeochemistry. In the present study, experimental clay-xanthan complexes were prepared as models for the soil/biota interface, and the step-scan function of FTIR-PAS technique was initially applied to in situ explore the characteristics of surface layers. The variances of depth profiling spectra of montmorilllonite are higher than that of kaolin, and more xanthan information was observed in the depth profiling spectra of montmorillonite, which was specifically verified by absorption in the region of 600-1200 cm~(-1) .The xanthan structure changed significantly due to the interaction between xanthan functional group and clay surface. The surface of montmorillonite is more hydrophilic than that of kaolin as indicated by absorption at 1640 cm~(-1); montmorillonite seems to interact more easily with hydrophilic xanthan and a much broader surface layer was observed through depth profiling PAS spectra (9.8 mum vs 3.8 mum). The thicker surface layer resulted in stronger water retention capability, and may provide a basis for interpreting the variance of soil quality.