title: Character of Humic Substances as a Predictor for Goethite Nanoparticle Reactivity and Aggregation.
abstract: Natural organic matter (NOM) is ubiquitous in surface water and groundwater and interacts strongly with mineral surfaces. The details of these interactions, as well as their impacts on mineral surface reactivity, are not well understood. In this work, both the reactivity and aggregation of goethite (α-FeOOH) nanoparticles were quantified in the presence of well-characterized humic substances. Results from monitoring the kinetics of reductive degradation of 4-chloronitrobenzene (4-ClNB) by Fe(II) adsorbed onto the goethite nanoparticles with and without added humic substances demonstrates that, in all cases, humic substances suppressed Fe(II)-goethite reactivity. The ranking of the standards from the least to most inhibitive was Pahokee Peat humic acid, Elliot Soil humic acid, Suwannee River humic acid, Suwannee River NOM, Suwannee River fulvic acid I, Suwannee River fulvic acid II, and Pahokee Peat fulvic acid. Correlations between eight characteristics (molecular weight, carboxyl concentration, and carbon, oxygen, nitrogen, aliphatic, heteroaliphatic, and aromatic content) and 4-ClNB degradation rate constants were observed. Faster kinetic rates of reductive degradation were observed with increased molecular weight and nitrogen, carbon, and aromatic content, and slower rates were observed with increased carboxyl concentration and oxygen, heteroaliphatic, and aliphatic content. With these correlations, improved predictions of the reactivity of Fe(II)-goethite with pollutants based on properties of the humic substances are possible.
authors.affiliation: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States.
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Vindedahl
authors.affiliation: Department of Psychology, University of Minnesota , 75 E River Road, Minneapolis, Minnesota 55455-0366, United States.
authors.forename: Melissa S
authors.initials: MS
authors.lastname: Stemig
authors.affiliation: Department of Civil, Environmental, and Geo- Engineering, University of Minnesota , 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455-0116, United States.
authors.forename: William A
authors.initials: WA
authors.lastname: Arnold
authors.affiliation: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States.
authors.forename: R Lee
authors.initials: RL
authors.lastname: Penn
mesh_terms: D000327:Adsorption; D001578:Benzopyrans / Q000737:chemistry; D001673:Biodegradation, Environmental; D002244:Carbon / Q000032:analysis; D006812:Humic Substances / Q000032:analysis; D007501:Iron / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals / Q000737:chemistry*; D008970:Molecular Weight; D053758:Nanoparticles / Q000737:chemistry*; D009578:Nitrobenzenes / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis; D010100:Oxygen / Q000032:analysis; D025341:Principal Component Analysis; D014867:Water; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; D058085:Iron Compounds; D008903:Minerals; D009578:Nitrobenzenes; D014874:Water Pollutants, Chemical; D014867:Water; C094886:goethite; D002244:Carbon; C010407:4-chloronitrobenzene; D007501:Iron; D009584:Nitrogen; D010100:Oxygen; C005023:fulvic acid