α-Fe2O3/SiO2 composites for the enhanced photocatalytic NO oxidation

alpha-Fe2O3 catalyst supported on rice husk ash (RHA) with enhanced photochemical NO oxidation is reported. The Fe2O3/SiO2 composites are prepared through the calcination of RH and FeCl3 at temperatures of 600 and 900 degrees C, during 1 and 4 h. Fe2O3 crystalizes covering the cob-shaped silica skeleton. The thermal procedure determines the mineralogical composition, crystalline growth and surface area of samples. Samples obtained at 600 degrees C are alpha-Fe2O3 (hematite) with low levels of Fe2SiO4 and exhibit a microstructure constituted of meso/macropores, with surface area values of 19.6 and 16.1 m(2) g(-1). At 900 degrees C only pure hematite is obtained but the microstructure is denser with very small surface area. Increasing the time of calcination to 4 h, hexagonal plates and truncated pseudocubes large crystals are obtained. All the samples exhibit light absorption in the 300 to 900 nm UV-vis range. The photocatalytic oxidation of NO molecules is related to the surface area of the samples. In the best case an NO conversion value of 24% is found, the highest reported for hematite photocatalysts. Moreover, the selectivity of NO -> NO2 -> NO3- oxidation process reaches values as high as 72% with the presence of large hexagonal plate hematite crystals. The existence of particles, which exhibit {001} facets, favors the adsorption of NO2 molecules and, therefore, the achievement of the photochemical oxidation process. (C) 2017 Elsevier B.V. All rights reserved.