Utilizing non-thermal plasma to introduce chlorine-containing functional groups on multi-walled carbon nanotubes for enhanced elemental mercury removal

Mercury pollution in flue gas is one of the typical atmospheric pollution problems. In this work, multi-walled carbon nanotubes (MWCNTs) were modified by dielectric barrier discharge (DBD) non-thermal plasma (NTP) in an HCl/N2 atmosphere for improving the removal of elemental mercury (Hg0). Optical emission spectroscopy (OES) was performed to detect the reactive species during the discharge. The obtained MWCNTs samples were characterized to investigate the physio-chemical properties changes after NTP modification. The results indicated that the reactive N, ·OH and Cl radicals were generated in plasma and the relative intensities enhance with increase of input voltage. The roughness and defects on the MWCNTs surface were enhanced owing to the plasma etching effect, while the crystal structure maintained intact. Though HCl plasma treatment slightly decreased the BET surface area, it markedly increased the content of C–Cl groups. The plasma-treated MWCNTs exhibited remarkable Hg0 removal performance compared to the pristine MWCNTs which could be ascribed to that the introduced C–Cl groups promoted the oxidative adsorption of Hg0. The effects of the operating parameters on Hg0 removal performance, including the applied voltage, treatment time, and adsorption temperature, were also investigated. The Hg0 adsorption capacities of modified MWCNTs displayed positive correlation between input power and treatment time, depending on the content of C–Cl groups. However, increasing adsorption temperature inhibited Hg0 removal because of the exothermic reaction between the Hg0 and Cl active sites. HgCl2 was the main mercury from in the spent MWCNTs-5-10 and C–Cl groups were believed to function as active sites and convert Hg0 to HgCl2. The mercury leaching rate of the spent MWCNTs-5-10 was 0.0035%, which indicated that the plasma-modified MWCNTs have good environmental leaching stability. [Display omitted] •Multi-walled carbon nanotubes were modified by the combination of non-thermal plasma and chlorination to improve Hg0 removal performance.•Multi-walled carbon nanotubes treated with HCl plasma exhibited better Hg0 removal performance.•The C–Cl groups played dominant roles in Hg0 adsorption, which converted Hg0 to HgCl2.