Three kinds of bio-chars derived from various solid wastes, such as municipal solid wastes, agricultural wastes and medicinal residues, were modified by physical and/or chemical modification. The Hg-0 adsorption capacities of the modification bio-chars in flue gas were comparatively studied. Physical modification increased the surface areas of the bio-chars, which was favorable in the physisorption of Hg-0. Chemical modification resulted in the chemisorption of Hg-0. Both physisorption and chemisorptions played a role in Hg-0 capture, whereas chemisorption was more important. The X-ray photoelectron spectroscopy (XPS) analysis results suggested that chemisorption of Hg-0 was due to the C-Cl groups generating on the surfaces of bio-chars during NH4Cl impregnation, which could transform Hg-0 into HgCl2 or other Hg-Cl complexes. The bio-chars modified by combined physical and chemical modification all had an excellent performance for Hg-0 removal, especially for C6WN5 exhibiting higher Hg-0 adsorption than modified activated carbons or modified activated carbon fibers. It indicated that the sequence for Hg-0 removal capacity decreased as: C6WN5 (from agricultural wastes, 11,400 mu g/g) > MW6N5 (from medicinal residues, 840 mu g/g) > W6WN5 (from municipal solid wastes, 160 mu g/g). (C) 2015 Elsevier Ltd. All rights reserved.