Department of Environment and Energy, Sejong University , Seoul, 143-747, South Korea.
Environ Sci Technol. 2016 Jul 19;50(14):7364-72. doi: 10.1021/acs.est.6b01286. Epub 2016 Jul 11.
Adsorption isotherms of extracellular polymeric substances (EPS) on graphene oxide (GO) and reduced GO (rGO) were studied using fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) combined with Fourier transform infrared spectroscopy (FTIR). Chemical reduction of GO resulted in a greater extent of carbon adsorption with a higher degree of isotherm nonlinearity, suggesting that heterogeneous adsorption sites were additionally created by GO reduction. Two protein-like and two humic-like components were identified from EPS by EEM-PARAFAC. Adsorption of protein-like components was greater than that of humic-like components, and the preferential adsorption was more pronounced for GO versus rGO. Adsorption of protein-like components was more governed by site-limiting mechanisms than humic-like components as shown by the higher isotherm nonlinearity. 2D-COS provided further information on the adsorption of secondary protein structures. Adsorption of the EPS structures related to amide I and aromatic C-C bands was greater for rGO versus GO. Protein structures of EPS were more favorable for adsorption in the order of α-helix → amide II → β-sheet structures with increasing site limitation. Our results revealed successful applicability of EEM-PARAFAC and 2D-COS in examining the adsorption behavior of heterogeneous biological materials on graphene materials.
采用荧光激发-发射矩阵平行因子分析（EEM-PARAFAC）和二维相关光谱（2D-COS）结合傅里叶变换红外光谱（FTIR）研究了细胞外聚合物（EPS）在氧化石墨烯（GO）和还原氧化石墨烯（rGO）上的吸附等温线。GO 的化学还原导致碳吸附程度更大，吸附等温线非线性程度更高，表明 GO 的还原额外产生了不均匀的吸附位。通过 EEM-PARAFAC 从 EPS 中鉴定出两种类蛋白和两种类腐殖质成分。类蛋白成分的吸附量大于类腐殖质成分，GO 对 rGO 的优先吸附更为明显。类蛋白成分的吸附更受限于位阻机制，而非类腐殖质成分，这表现为吸附等温线的非线性更高。2D-COS 进一步提供了有关次级蛋白质结构吸附的信息。与酰胺 I 和芳族 C-C 带相关的 EPS 结构的吸附量在 rGO 上大于在 GO 上。随着位阻的增加，EPS 结构中的蛋白质结构更有利于吸附，顺序为α-螺旋→酰胺 II→β-折叠结构。我们的结果表明，EEM-PARAFAC 和 2D-COS 成功适用于研究异质生物材料在石墨烯材料上的吸附行为。
