Iron oxides mesoporous

Brezesinski, T. Groenewolt, M. Antonietti, M. Smarsly, B. 2006. Crystal-to-crystal phase transition in self-assembled mesoporous iron oxide films. Angew. Chem. Int. Ed. 45 781-784. 

A common feature of the dehydroxylation of all iron oxide hydroxides is the initial development of microporosity due to the expulsion of water. This is followed, at higher temperatures, by the coalescence of these micropores to mesopores (see Chap. 5). Pore formation is accompanied by a rise in sample surface area. At temperatures higher than ca. 600 °C, the product sinters and the surface area drops considerably. During dehydroxylation, hydroxo-bonds are replaced by oxo-bonds and face sharing between octahedra (absent in the FeOOH structures see Chap. 2) develops and leads to a denser structure. As only one half of the interstices are filled with cations, some movement of Fe atoms during the transformation is required to achieve the two thirds occupancy found in hematite. 

The pristine MCM-48 silica phase has been synthesized by standard procedures described elsewhere [1]. Wet impregnation technique was used (1.6 molar aqueous solutions of cobalt(II) nitrate (Co(N03)2 6H20) and iron(III) nitrate (Fe(N03)3-9H20) with a ratio of lCo 2Fe) to introduce cobalt iron oxides into the mesoporous MCM-48 molecular sieve. After impregnation the material was calcined at 575° C for 6 hours, followed by a calcination at 600° C for 72 hours (product A) or at 650° C for 72 hours (product B), respectively. 

With the development of nanoscaled catalysts, several recent studies have pointed out the great interest of recording Mossbauer spectra below 4.2 K up to 0.055 K (100,203,204) it allowed the identification at the surface of various support such as mesoporous silica or Zr02, the formation of nanometric iron oxide clusters this identification was not possible in classical low temperature studies conducted above 4.2K, which concluded to the presence of larger particles. The analysis by Mossbauer spectroscopy performed at lower temperature enabled to show that these larger particles were agglomerates of nanometric iron clusters and allowed to reach another level of resolution of ferric particles structures (204). 

Various mesoporous silicas (MCM-48, SBA-15, MCF, MSU) modified with iron oxides introduced by Fe(acac)3 were prepared using the molecular designed dispersion method (Section The mechanism of interaction between the iron acetylace-... 

Iron oxide nanoclusters were synthesized within mesoporous MCM-41 doped with aluminum using evaporation-condensation of volatile Fe(CO)5 [53]. Subsequent calcination in an O2 flow resulted in amorphous y-Fe203 particles with diameters of 2-3 nm evenly distributed through the well-defined hexago-nally packed cyhndrical pores. These results were sohdly confirmed by combination of Mossbauer spectroscopy, XRD, TEM, and STEM (Fig. 4). 

In the chloride and nitrate extractant systems, the iron oxides formed at the initial citrate/Fe(II) MRs of 0,0.001, and 0.01 had similar rate fast Cd desorption reaction rates (Table 3). However, the iron oxide formed at the MR of 0.1 had a significantly slower rate of fast Cd desorption reaction (Table 3), although it had the greatest specific surface area (Table 1). UnUke the iron oxides formed at the initial citrate/Fe(II) MRs of 0,0.001 and 0.01, the surface area of the iron oxide formed at the MR of 0.1 is predominantly composed of micropore surface instead of mesopore surface (Liu and Huang, 1999a). This further confirmed that the fast reaction of Cd desorption could predominantly occur on the mesopore surface of the iron oxides. 

The disadvantage of this approach is that the resulting oxides are not highly crystallised because heat treatment cannot be conducted at a temperature above about 400 °C, where structural collapse occurs. This soft method has not been applied for ordered mesoporous crystalline late transition metal (such as Cu, Co, Ni and Fe) oxides. As a rare case, preparation of mesoporous nickel or iron oxide was reported. However, nickel oxide has an amorphous wall and iron oxide (crystalline y-Fe203) has disordered wormhole mesopores. ... 

Srivastava. D.N. Perkas. N. Gedanken, A. Felner. I. Sonochemical synthesis of mesoporous iron oxide and... 

Lin, Y., X. Y. Wang, G. Qian, and J. J. Watkins. 2014. Additive-driven self-assembly of well-ordered mesoporous carbon/iron oxide nanoparticle composites for supercapacitors. Chemistry of Materials 26 2128-2137. 

Iron-containing mesoporous materials have been widely studied due to the unique catalytic performance of selective reduction, hydrocarbon oxidation, and acylation and alkylation reactions (Vinu et al. 2007). Thus, Tanglumlert et al. (2008) were interested in the room temperature synthesis of Fe-SBA-1 using FeCl3 via the sol-gel process. The results illustrated that up to 6 wt% Fe could be contained in the SBA-1 framework without destroying the mesopore order. Nevertheless, extraframework FeOg clusters were also found, as suggested by electron spin resonance (ESR) spectroscopy. The BET surface area was 1062 m /g, with a pore diameter around 2.1 nm. 

Tian ZR, Tong W, Wang JY, Duan NG, Krishnan W, Suib SL (1997) Manganese oxide mesoporous stmctures Mixed-valent semiconducting catalysts. Science 276 926-930 Tossell JA (1977) SCF-Xa scattered wave MO studies of the electronic stmcture of ferrous iron in octahedral coordination with sulfur. J Chem Phys 66 5712-19 Tossell JA, Vaughan DJ (1987) Electronic stmcture and the chemical reactivity of the surface of galena. Can Min 25 381-392... 

Long JW, I-ogan MS, Rhodes CP, Carpenter EE, Stroud RM, Rolison DR (2004) Nanocrystalline iron oxide aerogels as mesoporous magnetic architectures. J Amer Chem Soc 126 16879 16889. 

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