title: Colloidal aggregation and structural assembly of aspect ratio variant goethite (α-FeOOH) with nC60fullerene in environmental media.
abstract: Environmental mobility of C60fullerene can be significantly affected in the presence of naturally abundant α-FeOOH. However, α-FeOOH vary significantly in sizes, shapes and associated properties that can greatly influence the fate and transport of C60fullerene in environmental media. Therefore, colloidal hetero-association between well crystallized low aspect (LAsp) α-FeOOH and nC60fullerene may differ substantially to weakly crystallized high-aspect (HAsp) counterpart. In contrast to LAspα-FeOOH, inherent crystal defects and surface charge generation in HAspα-FeOOH facilitated strong Coulombic attraction and aggregation with fullerene in acidic pH. However, LAspα-FeOOH demonstrated subtle entropic depletion mediated interaction with fullerene prevalent in hard rods. Humic acid (HA) encapsulation of HAspα-FeOOH substantially blocked fullerene attachment. Minute enhancement in colloidal stability was detected for HA-coated HAspα-FeOOH and fullerene mixture to HA-coated HAspα-FeOOH alone. To investigate the interfacial assembly of α-FeOOH with fullerene "in situ" differential interference contrast (DIC) microscopic investigations were employed. This study showed significantly different interface behavior of the binary mixtures of fullerene and HAspα-FeOOH NPs, and LAspparticles. On air-water interface, bare HAspα-FeOOH displayed liquid crystalline packing. However, addition of fullerene to HAspα-FeOOH suspension at pH5 produced closed-loop polygonal and circular ring structures. Head-to-tail alignment of magnetic dipoles as well as fullerene hydrophobicity facilitated such assembly formation. "Ex situ" AFM investigation revealed further the presence of magnetically derived ring structure which asserts that the formed "in situ" ensembles were not transient, hence, may abate fullerene transport through environmental interfaces. Barring hydrophobicity assisted attachment of fullerene to LAspα-FeOOHs, the absence of any close-packed structures may unlikely abate fullerene transport as envisaged in case of HAspα-FeOOH. Thus, aspect ratio variation and associated material properties of naturally abundant α-FeOOH may significantly impact fullerene transport through environmental media.
authors.affiliation: Kunming University of Science and Technology, Kunming, 650500, China; Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA, 01003, United States.
authors.forename: Saikat
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, FL, 32310, Unites States.
authors.forename: Nihar R
authors.initials: NR
authors.lastname: Pradhan
authors.affiliation: Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA, 01003, United States.
authors.forename: Hamid
authors.initials: H
authors.lastname: Mashayekhi
authors.affiliation: National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, FL, 32310, Unites States.
authors.forename: Qiu
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Kunming University of Science and Technology, Kunming, 650500, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Pan
authors.affiliation: Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA, 01003, United States. Electronic address: bx@umass.edu.
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D004777:Environment; D037741:Fullerenes / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D057927:Hydrophobic and Hydrophilic Interactions; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D012987:Soil / Q000737:chemistry; D013535:Suspensions; D014867:Water / Q000737:chemistry
chemical_list: D037741:Fullerenes; D006812:Humic Substances; D058085:Iron Compounds; D008903:Minerals; D012987:Soil; D013535:Suspensions; D014867:Water; C094886:goethite; C069837:fullerene C60
keywords: Aggregation; Assembly; Fullerene; Magneto-static; α-FeOOH