title: Using chromate to investigate the impact of natural organics on the surface reactivity of nanoparticulate magnetite.
abstract: Chromate was used as a chemical probe to investigate the size-dependent influence of organics on nanoparticle surface reactivity. Magnetite-chromate sorption experiments were conducted with ∼ 90 and ∼ 6 nm magnetite nanoparticles in the presence and absence of fulvic acid (FA), natural organic matter (NOM), and isolated landfill leachate (LL). Results indicated that low concentrations (1 mg/L) of organics had no noticeable impact on chromate sorption, whereas concentrations of 50 mg/L or more resulted in decreased amounts of chromate sorption. The adsorption of organics onto the magnetite surfaces interfered equally with the ability of the 6 and 90 nm particles to sorb chromate from solution, despite the greater surface area of the smaller particles. Results indicate the presence of organics did not impact the redox chemistry of the magnetite-chromate system over the duration of the experiments (8 h), nor did the organics interact with the chromate in solution. Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) results indicate that the organics blocked the surface reactivity by occupying surface sites on the particles. The similarity of results with FA and NOM suggests that coverage of the reactive mineral surface is the main factor behind the inhibition of surface reactivity in the presence of organics.
authors.affiliation: Department of Geology, Wichita State University , 1845 Fairmount Avenue, Wichita, Kansas 67260, United States.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Swindle
authors.forename: Isabelle M
authors.initials: IM
authors.lastname: Cozzarelli
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Elwood Madden
mesh_terms: D000327:Adsorption; D001578:Benzopyrans / Q000737:chemistry; D002840:Chromates / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D013499:Surface Properties; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D001578:Benzopyrans; D002840:Chromates; D006812:Humic Substances; D058185:Magnetite Nanoparticles; D014874:Water Pollutants, Chemical; C005023:fulvic acid