Nano-Micrometer-Architectural Acidic Silica Prepared from Iron Oxide of Leptothrix ochracea Origin

作者：Hashimoto Hideki; Itadani Atsushi; Kudoh Takayuki; Fukui Satoshi; Kuroda Yasushige; Seno Masaharu; Kusano Yoshihiro; Ikeda Yasunori; Benino Yasuhiko; Nanba Tokuro; Nakanishi Makoto; Fujii Tatsuo; Takada Jun^*

来源：ACS Applied Materials & Interfaces, 2013, 5(11): 5194-5200.

DOI：10.1021/am401029r

• amorphous silica
• Bronsted acid
• Lewis acid
• acid catalysts
• iron-oxidizing bacteria
• biogenous iron oxides

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 degrees C in a H-2 gas flow leading to segregation of alpha-Fe crystalline particles and then dissolved in 1 M hydrochloric acid to remove the alpha-Fe particles, giving a gray-colored precipitate. It was determined to be amorphous silica containing some amount of iron (Si/Fe = similar to 60). The amorphous silica maintains the nano-microstructure of the starting material-similar to 1-mu m-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 alpha-Fe particles on the micrometer tubule wall. The smallest particle size of the amorphous silica is similar to 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 Bronsted and Lewis acidic centers that do not desorb pyridine, even upon evacuation at 400 degrees 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.

• 出版日期2013-6-12