The presence of NO9x) gases (NO+NO2) in the atmosphere is a major concern of society because of their associated adverse and harmful effects. In order to remove the NO(x) gases from the air, photocatalysis arises as an innovative and promising technique. Through the use of photochemical oxidation processes the NO and NO2 gases are oxidised to NO3- form and thus removed from the air. In recent years new nanomaterials are being developed by researchers with the aim to enhance their photocatalytic activity to combat the NO(x) pollution. The main focus is devoted to preparing new TiO2 based compounds with the highest specific surface area (SSA), different morphology and chemical modifications. In order to increase the SSA, different substrates were used to disperse the TiO2 nanoparticles: organic and carbon fibres, mesoporous materials, clays composites and nanoporous microparticles. In the other hand, high photocatalytic performances were obtained with nanotubes, self-orderer nano-tubular films and nanoparticles with the lowest size. Conversely, when TiO2 is doped with ions the oxide exhibited a better photocatalytic performance under visible light, which is related to the creation of intermediate energy states between the conduction band and the valence band. Alternatively, visible light photocatalysts different from titanium oxide have been studied, which exhibit a good De-NO(x) efficiency working under λ > 400 nm visible light irradiation.

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A cost-effective and sustainable De-NOx photocatalyst is prepared using zinc acetate and rice husk.ZnO@SiO 2 samples are obtained from the calcination of a homogenised precursor mixture at 600 C.ZnO nanoparticles (70 -180 nm) grow aggregated in spheres and well dispersed (40 -53 m 2 g -1 surface area) covering the silicon skeleton. The corresponding band gap for ZnO@SiO 2 photocatalysts was estimated at 3.1 -3.2 eV. When the samples are irradiated by sunlight in a nitrogen oxide atmosphere the NO  HNO 2  NO 2  NO 3 photochemical oxidation takes place. In comparison to unsupportedZnO and TiO 2 -P25, ZnO@SiO 2 samples exhibit high NO X removal values (70 %) and outstanding selectivity (> 90%), the latter related to the sensitivity of zinc oxide towards NO 2 gas. This new photocatalyst is easily recyclable and reusable.

Calyx-like ZnO nanostructures decorated by WO3 nanoparticles are investigated for NOX degradation and self-cleaning end-uses.

Supported Fe2O3/TiO2 nanocomposites were prepared for the first time by a plasma-assisted route and\ud successfully tested in photocatalytic NOx abatement driven by solar illumination. In particular,\ud a sequential low-temperature (<100 °C) plasma enhanced-chemical vapor deposition (PE-CVD)/radio\ud frequency (RF) sputtering approach was used to fabricate Fe2O3/TiO2 nanocomposites with controlled\ud composition and morphology. The preparation process was accompanied by a thorough multitechnique\ud investigation carried out by complementary techniques, including X-ray photoelectron\ud spectroscopy (XPS), secondary ion mass spectrometry (SIMS), field emission-scanning electron\ud microscopy (FE-SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). The results evidenced\ud the formation of high purity nanocomposites, in which TiO2 content could be tailored by controlled\ud variations of the sole sputtering time, and characterized by an intimate Fe2O3/TiO2 contact, of key\ud importance to exploit the chemical and electronic coupling between the two oxides. The obtained\ud nanomaterials were tested in NO photo-oxidation activated by sunlight, showing a remarkable activity in\ud NOx (NO + NO2) removal and a high selectivity (>60%) in their conversion to nitrate species. Overall, the\ud present performances candidate the present photocatalysts as valuable materials for next-generation\ud technologies aimed at the abatement of harmful gaseous pollutants