Surface modification of bio-char by dielectric barrier discharge plasma for Hg0 removal

•Bio-char modified with dielectric discharge plasma achieved better Hg0 removal performance.•Oxygen-containing functional groups were introduced onto carbon surface during discharge process.•Higher Hg0 adsorption capacities were obtained by increasing O2, H2O concentrations and treatment time.

Bio-char (BC) samples were modified by the dielectric barrier discharge (DBD) plasma method to enhance the adsorption capacity for gaseous mercury (Hg0). The discharge gases and treatment time were studied for their influences on surface modification. Surface characteristics of BCs were investigated using nitrogen adsorption method and X-ray photoelectron spectroscopy (XPS) analysis. Hg0 adsorption performance of BCs was tested in a bench-scale fixed bed reactor. The results indicated that surface area and pore volume of samples decreased slightly with the plasma treatment. Oxygen-containing functional groups (OCFGs) especially CO groups increased on carbon surface as a result of the reaction with reactive intermediates. Adsorption data showed that BCs with DBD plasma treatment had higher mercury removal efficiency compared with that of raw BC. Oxygen and water vapor were favorable to surface modification in the process of DBD treatment in this study. Chemisorption was believed to be predominant in Hg0 adsorption process and carbonyl and ester groups might play the key roles. Compared with commercial activated carbons, the modified BC showed an excellent adsorption performance, implying that DBD plasma treatment was a potential surface activation technology to improve Hg0 adsorption capacity on bio-char adsorbents.