Dual 2-dimensional CuSe/g-C3N4 nano-heterostructure for boosting immobilization of elemental mercury in flue gas

Abstract

With the rapid development of Hg0 treatment methods in flue gas, the key challenge at the current stage is the trade-off between adsorbent performance, treatment cost and environmental friendliness. A series of dual 2-dimensional CuSe/g-C3N4 nano-heterostructures (CSCN) were successfully synthesized through an incipient wetness impregnation method followed by in-situ selenization, and further used for gaseous elemental mercury immobilization. The results had shown that the as-synthesized CSCN with CuSe loading ratio of 20% (20CSCN) achieved the maximum mercury removal performance. Up to 95.09% of Hg0 removal efficiency was achieved by 20CSCN under rigorous experimental conditions with the gas hourly space velocity and initial Hg0 concentration of 240000 h−1 and 180 ug/m3, respectively. After a 10 h adsorption test, the equilibrium adsorption capacity of 20CSCN reached 9.113 mg/g. Owing to the generation of dual 2-dimensional heterojunctions, the mercury removal performance of 20CSCN was superior to the contrast 20CSCN(mix) prepared by simply mechanically mixing. Besides, the acidic gases (NO and SO2) in the flue gas will adversely affect the Hg0 capture performance of CSCN, while O2 and CO2 exhibited a neutral effect on the Hg0 capture. Based on the analysis of XPS and TPD results, the chemical reaction rate was the main rate-controlling step and the chemisorption dominated the conversion of Hg0 on heterojunctions, which was in accordance with the Mars-Maessen mechanism. The active Se ligands on the surface of the heterojunction, as the main activity center of chemical reaction, could rapidly capture Hg0 in the flue gas to form stable HgSe. This can effectively avoid the secondary pollution caused by the re-release of Hg0 from Hg-containing waste exposed to the environment, because of its low Hg-leaching characteristic.