Conversion mechanism of selenium on activated carbon surface: Experimental and density functional theory study

Abstract

The mechanism of SeO2 capture by activated carbon (AC) was explored via combining experiments with density functional theory (DFT). Adsorption experiments confirmed that after mass loss coefficient correction of AC, the selenium capture capacity of AC reached 7.76 mg/g at 350 °C. AC reached a saturated selenium removal capacity of 9.93 mg/g at 50 min. The weight loss curve recorded the temperature window of selenium desorption on AC surface at about 305 °C. The XPS spectrum revealed that the decomposition and reduction behavior of SeO2 on the AC surface promoted the existence of selenium in the form of Se0. DFT calculations showed that SeO2 was chemically adsorbed on the typical Armchair and Zigzag surfaces of AC, and the adsorption energies of the most stable structures were − 89.77 and − 235.12 kcal/mol, respectively. The effect of temperature on selenium capture via AC was studied by thermodynamic and kinetic analysis. Temperature increase promoted the decomposition and reduction of SeO2 on the AC surface. Kinetic analysis further confirmed that the transformation of Se4+→Se0 was more dominated by decomposition behavior. A part of SeO2 in the gas phase was reduced to Se0 by CO and enriched on AC as elemental selenium.