Efficient behaviour of hematite towards the photocatalytic degradation of NOx gases

Hematite, alpha-Fe2O3, cx has been proven as a new visible photocatalyst towards the decontamination of NOx gases. Three samples were studied: NH (nanometric), RFH-A and RFH-B. The micronic RFH samples were obtained by using resorcinol formaldehyde (RF) as a template. All samples constituted of only the alpha-Fe2O3 iron oxide phase, as revealed by X-ray diffraction, X-ray photoelectron spectroscopy and Raman techniques. The pyrolysis of RF is the reason for the presence of residual carbon in 0.9 and 3.5% of RFH-A and RFH-B samples, respectively. Photochemical oxidation (PCO) is proposed, implying the participation of alpha-Fe2O3. The NO -> NO2 -> NO3 -> PCO process means the oxidation of NO and NO2 toxic gases and their retention as HNO2/NO3-. For the first time, this De-NOx mechanism is validated for hematite, with the adsorbed products (NO3-) identified by infrared spectroscopy. The poor photocatalytic efficiency found with the use of pure hematite, the NH sample, is surpassed through the preparation of C-hematite compounds. Efficient behaviour is observed in this photocatalytic process for the RFH samples, exhibiting total NOx removal efficiency values as high as 17%. (C) 2014 Elsevier B.V. All rights reserved.