title: Nano-micrometer-architectural acidic silica prepared from iron oxide of Leptothrix ochracea origin.
abstract: We prepared nano-micrometer-architectural acidic silica from a natural amorphous iron oxide with structural silicon which is a product of the iron-oxidizing bacterium Leptothrix ochracea. The starting material was heat-treated at 500 °C in a H2 gas flow leading to segregation of α-Fe crystalline particles and then dissolved in 1 M hydrochloric acid to remove the α-Fe particles, giving a gray-colored precipitate. It was determined to be amorphous silica containing some amount of iron (Si/Fe = ~60). The amorphous silica maintains the nano-microstructure of the starting material-~1-μm-diameter micrometer-tubules consisting of inner globular and outer fibrillar structures several tens of nanometer in size-and has many large pores which are most probably formed as a result of segregation of the α-Fe particles on the micrometer-tubule wall. The smallest particle size of the amorphous silica is ~10 nm, and it has a large surface area of 550 m(2)/g with micropores (0.7 nm). By using pyridine vapor as a probe molecule to evaluate the active sites in the amorphous silica, we found that it has relatively strong Brønsted and Lewis acidic centers that do not desorb pyridine, even upon evacuation at 400 °C. The acidity of this new silica material was confirmed through representative two catalytic reactions: ring-opening reaction and Friedel-Crafts-type reaction, both of which are known to require acid catalysts.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Itadani
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kudoh
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fukui
authors.forename: Yasushige
authors.initials: Y
authors.lastname: Kuroda
authors.forename: Masaharu
authors.initials: M
authors.lastname: Seno
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kusano
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Benino
authors.forename: Tokuro
authors.initials: T
authors.lastname: Nanba
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakanishi
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Fujii
authors.forename: Jun
authors.initials: J
authors.lastname: Takada
mesh_terms: D000478:Alkylation; D002074:Butanones / Q000737:chemistry; D004852:Epoxy Compounds / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D042743:Leptothrix / Q000737:chemistry* / Q000378:metabolism; D058116:Lewis Acids / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D043942:Nanotubes / Q000737:chemistry*; D010084:Oxidation-Reduction; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D002074:Butanones; D004852:Epoxy Compounds; D005290:Ferric Compounds; D058116:Lewis Acids; C000499:ferric oxide; D012822:Silicon Dioxide; C013690:styrene oxide; C057920:3-buten-2-one