Department of Environment and Energy, Sejong University, Seoul 143-747, South Korea.
Water Res. 2011 Nov 15;45(18):6217-26. doi: 10.1016/j.watres.2011.09.023. Epub 2011 Sep 21.
Changes in the characteristics of a leaf litter-derived humic substance (LLHS) that resulted from its adsorption onto kaolinite or exposure to simulated solar irradiation were tracked using selected spectroscopic descriptors, apparent weight-average molecular weight (MW(w)) and pyrene binding. Heterogeneity within the original bulk LLHS was confirmed by a range of different characteristics obtained from ultrafiltration-based size fractions. In general, trends of some changing LLHS characteristics were similar for the adsorption and irradiation processes when tracked against percent carbon removal. For example, the overall values of specific ultraviolet absorbance (SUVA), MW(w), and humification index (HIX) all decreased with increasing irradiation time and with increasing concentration of mineral adsorbent in the respective experiments, indicating that both processes resulted in less aromatic and smaller-sized LLHS components remaining in solution. In addition, both the adsorption and irradiation experiments resulted in enrichment of the relative distribution of protein-like fluorescence (PLF), implying the PLF-related components had low affinities for phototransformation and mineral surface adsorption. Despite these apparently similar overall trends in LLHS characteristics caused by the adsorption and irradiation processes, closer examination revealed considerable differences in how the two processes altered the original material. Net production of intermediate-sized constituents was observed only with the irradiation experiments. In addition, residual LLHS resulting from the adsorptive fractionation experiments exhibited consistently higher pyrene binding versus the irradiated LLHS despite having comparable MW(w) values. Changes in LLHS characteristics due to adsorption by kaolinite were likely caused by physical mechanisms (primarily hydrophobic interactions between LLHS components and the kaolinite surface) whereas the irradiation-induced changes appear to have been governed by the combined effects of several alteration mechanisms, including the transformation of more condensed aromatic structures to less aromatic constituents, conformational changes resulting from selective photooxidation, and the photochemical disruption of intramolecular charge-transfer interactions.
采用选定的光谱描述符、表观重均分子量 (MW(w)) 和芘结合跟踪了由于在高岭土上吸附或暴露于模拟太阳辐射而导致叶凋落物衍生腐殖质 (LLHS) 特性变化。通过超滤法获得的不同大小的分数，证实了原始大块 LLHS 内的异质性。一般来说，当根据碳去除百分比跟踪吸附和辐照过程时，一些变化的 LLHS 特性的趋势相似。例如，特定紫外吸光度 (SUVA)、MW(w) 和腐殖化指数 (HIX) 的整体值均随着辐照时间的增加和各自实验中矿物吸附剂浓度的增加而降低，这表明这两个过程导致留在溶液中的芳香性和较小尺寸的 LLHS 成分减少。此外，吸附和辐照实验均导致蛋白样荧光 (PLF) 的相对分布富集，这意味着 PLF 相关成分对光转化和矿物表面吸附的亲和力较低。尽管由于吸附和辐照过程，LLHS 特性出现了这些显然相似的总体趋势，但更仔细的检查揭示了这两个过程如何改变原始材料的差异。仅在辐照实验中观察到中间大小成分的净生成。此外，与辐照 LLHS 相比，由于吸附分馏实验产生的残余 LLHS 尽管具有可比的 MW(w) 值，但仍表现出更高的芘结合。由于与高岭土的吸附引起的 LLHS 特性变化可能是由物理机制引起的（主要是 LLHS 成分与高岭土表面之间的疏水力），而辐照诱导的变化似乎是由几种改变机制的综合效应引起的，包括更密集的芳香结构向较少芳香成分的转化、选择性光氧化引起的构象变化，以及分子内电荷转移相互作用的光化学破坏。
