The Effect of Surface Area and Crystal Structure on the Catalytic Efficiency of Iron(III) Oxide Nanoparticles in Hydrogen Peroxide Decomposition

Abstract

Iron(II) oxalate dihydrate has been used as a readily decomposable substance for the controlled synthesis of nanosized iron(III) oxides. The polymorphous composition, particle size and surface area of these iron oxide nanoparticles were controlled by varying the reaction temperature between 185 and 500°C. As-prepared samples were characterized by XRD, low-temperature and in-field Mössbauer spectroscopy, BET surface area and the TEM technique. They were also tested as heterogeneous catalysts in hydrogen peroxide decomposition. At the selected temperatures, the formed nanomaterials did not contain any traces of amorphous phase, which is known to considerably reduce the catalytic efficiency of iron(III) oxide catalysts. As the thickness of the sample (≈ 2 mm) was above the critical value, a temporary temperature increase ("exo effect") was observed during all quasiisothermal decompositions studied, irrespective of the reaction temperature. Increasing the reaction temperature resulted in a shift of the exo effect towards shorter times and an increased content of maghemite phase. The maghemite content decreases above 350°C as a result of a thermally in-

Synthesis, Characterization and Applications of Iron Oxide Nanoparticles - a Short Review

“…Indeed, nanomaterials are more effective than conventional catalysts because of two reasons: first, their extremely small particle size (typically 10 -80 nm) provides an excellent surface area-to-volume ratio (Chaturvedi et al 2012). Next, when materials are fabricated on the nanoscale, they show properties not found within their macroscopic counterparts (Chaturvedi et al 2012;Gregor et al 2010). In a study on the catalytic efficiency of iron oxide (α-Fe 2 O 3 ) nanoparticles in hydrogen peroxide decomposition results suggested that, besides the catalytic effect of the high surface area, there is a more complex factor -the surface quality of the catalyst driving their efficiency.…”

“…In addition to the main effect of the sample's crystallinity, other qualitative parameters such as the chemical composition and particle morphology of catalysts are important. As a consequence, iron oxides hematite, magnetite and maghemite are extensively used in the catalysis of a number of reactions such as the synthesis of styrene, photocatalytic production of hydrogen and oxygen, removal of carbon monoxide, catalytic conversion of methane in aromatic compounds, thermal decomposition of ammonium perchlorate as well as in water treatment, catalytic decomposition of hydrogen peroxide, fuel cells and production of biodiesel (Chaturvedi et al 2012;Weddemann et al 2010;Teja and Koh 2009;Gregor et al 2010).…”

“…In recent years, nanoscale transition of metallic oxides, such as iron oxide, including hematite, magnetite, and maghemite, has been attracting growing interest as they exhibit unique electrical, optical and magnetic properties for numerous applications such as production of inorganic pigments, magnetic storage media, development of gas sensors as well as electronic and optical devices, information storage, color imaging, magneto caloric refrigeration, bioprocessing, ferrofluid technology and wastewater treatment adsorbents (Xu et al 2008, Gregor et al 2010Moahapatra and Anand 2010).…”

Photocatalytic Reduction of Aqueous Cr(VI) with CdS under Visible Light Irradiation: Effect of Particle Size

“…The constants (y0 and A) that establish the respective relationship between r0 (mg/L.s), ka (min -1 ), and t1/2 (min) of photoreduction of Cr(VI) and particle diameter of the CdS are obtained by non-linear fit of experimental data to Equation (3). The relationships that favorably approximates the r0, ka, and t1/2 to the photocatalyst particle size are: Figure 7 shows the variations of (a) reaction rate, (r0) with diameter, (b) rate constant, (ka) with diameter, and (c) half-life time t1/2 with diameter, respectively.…”

“…The reductive and oxidative surface reactions involve the transfer (ejection) of electrons or holes to pre-adsorbed reactants. The rates of the surface reactions depend on the efficiency and rate of charge transfer between the photocatalyst and the substrate and on the quantity and quality of the active surface area of the photocatalyst [2,3]. A catalyst with large surface area is usually preferred because it usually provides large area for the adsorption of the solute, more active sites for ejection of charge carrier(s) and for the surface reactions to occur.…”