Density Functional Theory Study On The Mechanism Of Mercury Adsorption By Activated Carbon Fiber

Environment was polluted by emission of harmful trace elements from coal-fired exhaust gas. Therefore, humans paid more attention to emission control than before. Activated carbon fiber(ACF) as an adsorbent had great potential in mercury pollution reduction. However, the mechanism of adsorption was not clearly.Density functional theory B3 LYP of quantum chemistry and lanl2 dz basis set were used in this paper. The basic model for activated carbon fibers surface were developed by four parallel unsaturated carbon ring model or single four carbon ring cluster model. This model was used to investigate the mechanism of adsorption. The main works and achievements in this paper are as follows:Effect of different oxygen-containing functional groups on adsorption capacity of ACF surface was studied. The calculation results show that carbonyl, lactone and semiquinone made mercury adsorption on the ACF surface belongs to chemical mechanism. While carboxyl and phenol functional groups made it belongs to physical mechanism. Moreover, further study on mercury adsorption characteristics of ACF surface with oxygen-containing functional groups on different active sites. It is thought that the influence of oxygen-containing functional groups site on mercury adsorption was not seriously, when the same oxygen-containing functional groups at the adjacent sites on ACF surfaces.Influence of sulphur on ACF surface mercury adsorption characteristics was investigated. Mechanism of ACF surface mercury adsorption was become chemically after contained with sulfur. Effect of SO2, which was from exhaust gas, on ACF surface mercury adsorption characteristics was analyzed. The function of SO2 for ACF surface was not provided a new site, but enhanced adsorption capacity of neighbor sites. In result, the effects of SO2 on ACF surface adsorption were complicated, low concentrations SO2 increased ACF surface adsorption capacity, however, higher concentrations SO2 decreased ACF surface adsorption capacity.Effect of chlorine atom on mercury and its’ ramification adsorption characteristics of ACF surface. Chlorine was bound strongly on the ACF surface according to the relevant bond lengths and reaction path diagram. Both Hg Cl and Hg Cl2 can be adsorbed dissociatively or non-dissociatively. In the case of dissociative adsorption, Hg0 can be desorbed on the surface while Hg Cl remains. The compound, Hg Cl2 was not found to be stable on the surface. Even if it is formed on the surface, it can easily desorb or return to the reactant species. The most probable mercury species on the surface was found to be Hg Cl.Calculation was compatible with the experimental results. The research results show that density functional theory calculation of quantum chemistry was an effective method to study the mechanism of mercury adsorption.