title: Investigation of adsorptive fractionation of humic acid on graphene oxide using fluorescence EEM-PARAFAC.
abstract: In this study, the adsorptive fractionation of a humic acid (HA, Elliott soil humic acid) on graphene oxide (GO) was examined at pH 4 and 6 using absorption spectroscopy and fluorescence excitation-emission matrix (EEM)-parallel factor analysis (PARAFAC). The extent of the adsorption was greater at pH 4.0 than at pH 6.0. Aromatic molecules within the HA were preferentially adsorbed onto the GO surface, and the preferential adsorption was more pronounced at pH 6, which is above the zero point of charge of GO. A relative ratio of two PARAFAC humic-like components (ex/em maxima at 270/510 nm and at (250, 265)/440 nm) presented an increasing trend with larger sizes of ultrafiltered humic acid fractions, suggesting the potential for using fluorescence EEM-PARAFAC for tracking the changes in molecular sizes of aromatic HA molecules. The individual adsorption behaviors of the two humic-like components revealed that larger sized aromatic components within HA had a higher adsorption affinity and more nonlinear isotherms compared to smaller sized fractions. Our results demonstrated that adsorptive fractionation of HA occurred on the GO surface with respect to their aromaticity and the sizes, but the degree was highly dependent on solution pH as well as the amount of adsorbed HS (or available surface sites). The observed adsorption behaviors were reasonably explained by a combination of different mechanisms previously suggested.
authors: Department of Environment and Energy, Sejong University, Seoul, 143-747, South Korea.
authors: Bo-Mi
authors: BM
authors: Lee
authors: Department of Nano Science & Technology, Sejong University, Seoul, 143-747, South Korea.
authors: Young-Soo
authors: YS
authors: Seo
authors: Department of Environment and Energy, Sejong University, Seoul, 143-747, South Korea. Electronic address: jinhur@sejong.edu.
authors: Jin
authors: J
authors: Hur
mesh_terms: D000327:Adsorption; D005591:Chemical Fractionation; D005163:Factor Analysis, Statistical; D006108:Graphite / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D010087:Oxides / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D006812:Humic Substances; D010087:Oxides; D014874:Water Pollutants, Chemical; D006108:Graphite
keywords: Adsorption; EEM-PARAFAC; Graphene oxide (GO); Humic substances (HS); Size fractionation