Effects of the biochar aromaticity and molecular structures of the chlorinated organic compounds on the adsorption characteristics.

Adsorption behaviors of the chlorinated organic compounds (COCs) (i.e., trichloroethylene (TCE), 1,2,4-trichlorobenzene (1,2,4-TCB); 1,2-dichlorobenzene (1,2-DCB); and monochlorobenzene (MCB)) by the commercial rice husk-based biochar (RH500) and the laboratory-prepared biochars from corn stalks under different pyrolytic temperatures (i.e., CS300, CS500, CS700) were examined and interpreted by the pseudo-first-order kinetic model, the double layer model with two energies, and the Freundlich model. It is identified that the first-order adsorption rate constants (k  = 0.06∼0.51 h) were proportional to the high aromaticity and/or low polarity of biochars and the strong hydrophobicity of the COCs. The saturated adsorption capacity for the COCs was followed by the order of RH500 > CS500 > CS700 > CS300. RH500 showed the highest adsorption capacity for the COCs due to its high surface area (SA) and total pore volume (TPV). However, CS500 with low SA and TPV development highlighted the important roles of the aromaticity and/or low polarity on the COCs adsorption. In addition, 1,2,4-TCB showed the highest saturated adsorption capacity on all biochars, followed by TCE, 1,2-DCB, and MCB. The results further revealed the positive effects of the physical properties (α, N , ε , and ε ), the hydrophobicity and electrostatic forces (i.e., π-π interaction and electron donor-acceptor interaction) between the adsorbates and the aromatic moieties of biochar surfaces on the adsorption of COCs.