Application of TiO 2 Supported on Nickel Foam for Limitation of NO x in the Air via Photocatalytic Processes.

TiO 2 was loaded on the porous nickel foam from the suspended ethanol solution and used for the photocatalytic removal of NO x . Such prepared material was heat-treated at various temperatures (400-600 °C) to increase the adhesion of TiO 2 with the support. Obtained TiO 2 /nickel foam samples were characterized by XRD, UV-Vis/DR, FTIR, XPS, AFM, SEM, and nitrogen adsorption at 77 K. Photocatalytic tests of NO abatement were performed in the rectangular shape quartz reactor, irradiated from the top by UV LED light with an intensity of 10 W/m 2 . For these studies, a laminar flow of NO in the air (1 ppm) was applied under a relative humidity of 50% and a temperature of 28 °C. Concentrations of both NO and NO 2 were monitored by a chemiluminescence NO analyzer. The adsorption of nitrogen species on the TiO 2 surface was determined by FTIR spectroscopy. Performed studies revealed that increased temperature of heat treatment improves adhesion of TiO 2 to the nickel foam substrate, decreases surface porosity, and causes removal of hydroxyl and alcohol groups from the titania surface. The less hydroxylated surface of TiO 2 is more vulnerable to the adsorption of NO 2 species, whereas the presence of OH groups on TiO 2 enhances the adsorption of nitrate ions. Adsorbed nitrate species upon UV irradiation and moisture undergo photolysis to NO 2 . As a consequence, NO 2 is released into the atmosphere, and the efficiency of NO x removal is decreasing. Photocatalytic conversion of NO to NO 2 was higher for the sample heated at 400 °C than for that at 600 °C, although coverage of nickel foam by TiO 2 was lower for the former one. It is stated that the presence of titania defects (Ti 3+ ) at low temperatures of its heating enhances the adsorption of hydroxyl groups and the formation of hydroxyl radicals, which take part in NO oxidation. Contrary to that, the presence of titania defects in TiO 2 through the formation of ilmenite structure (NiTiO 3 ) in TiO 2 /nickel foam heated at 600 °C inhibits its photocatalytic activity. No less, the sample obtained at 600 °C indicated the highest abatement of NO x due to the high and stable adsorption of NO 2 species on its surface.