Abstract: A series of modified activated carbons were prepared by modification with nitric acid (HNO3) and magnesium oxide (MgO) to improve their adsorption capacity for SO2, a toxic component in smoke. The modification method included treating the activated carbon in 2 mol/L HNO3 solution at 50 ℃ for 10 h, followed by washing, drying and roasting to introduce oxygen-containing functional groups, such as hydroxyl, carboxyl, and ester groups; subsequently, Mg(NO3)2 was loaded onto the activated carbon and the HNO3-modified activated carbon using an equal-volume impregnation method, followed by drying and roasting again to introduce the alkaline adsorption site, MgO. The adsorption and penetration of modified activated carbon on SO2 (3 000×10-6) were tested at 25~55 ℃. Meanwhile, the adsorption and oxidation properties of modified activated carbon on SO2 were investigated by pore structure analysis, infrared spectral characterization and ion chromatography. The results showed that the dual-modified adsorbents of HNO3 and MgO had the longest SO2 penetration time, which could enhance the SO2 penetration time of activated carbon from 12.9 min to 31.8 min, satisfying the secondary protection time (23 min) against SO2 for non-powered air-purifying gas masks. The hexavalent sulfur and tetravalent sulfur of activated carbon after adsorption of SO2 were tested, and it was found that after the double-modified the ratio of hexavalent sulfur to tetravalent sulfur value increased significantly from 0.62 before modification to 1.26 after modification, indicating that the synergistic modification of MgO and HNO3 can effectively increase the adsorption and oxidation capacity of activated carbon for SO2, and improve the protective performance of the filtering type of gas masks against SO2.

Key words: modified activated carbon, adsorption, oxidation, penetration time, protection efficiency