Efficient behaviour of hematite towards the photocatalytic degradation of NOx gases

• Hematite, α-Fe2O3, acts as an efficient photocatalyst in De-NOX processes.
• C-hematite compounds can be prepared by using resorcinol—formaldehyde as a template.
• Hematite, under UV–Vis irradiation, promotes the oxidation NO and NO2 toxic gases.
• The NOX gases are retained as nitrate on the surface of hematite particles.
• The presence of carbon greatly increases the efficiency of the PCO process.

Hematite, α-Fe2O3, 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 α-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 α-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%.

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