Activated carbons modified with sewage sludge derived phase and their application in the process of NO2 removal

Highly porous wood-based activated carbon was treated with species extracted from the surface of pyrolyzed sewage sludge. Their deposition on the external surface was visible by a change of the color of the carbon and on internal surfaces, by a decrease in porosity. The as-received carbon and its impregnated counterpart were heat treated at 950 °C at an inert atmosphere. Data for the adsorption on NO2 was carried out from dry and moist (70% humidity) air. The results indicated that for all materials a significant amount of NO2 was reduced to NO and released from the system. Heat treatment increases the capacity possibly as a result of an increase in basicity. The addition of the inorganic phase has a positive effect only when adsorption is run in moist conditions and inorganic nitrates and nitrites were formed. Otherwise, the NO2 adsorbed and nitric and nitrous acids formed on the surface significantly increase the acidity of the carbons by the formation of oxygen-containing groups and organic nitrates.