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

Area of Science:

• Environmental Chemistry
• Materials Science
• Computational Chemistry

Background:

• Selenium dioxide (SeO2) is a toxic environmental pollutant.
• Activated carbon (AC) is a promising adsorbent for pollutant removal.
• Understanding the capture mechanism is crucial for efficient SeO2 remediation.

Purpose of the Study:

• To investigate the mechanism of SeO2 capture by AC.
• To determine the optimal conditions for selenium removal.
• To explore the role of temperature and surface chemistry in the capture process.

Main Methods:

• Experimental adsorption studies at varying temperatures.
• X-ray photoelectron spectroscopy (XPS) for surface analysis.
• Density functional theory (DFT) calculations for adsorption energy and mechanism.
• Thermodynamic and kinetic analysis.

Main Results:

• AC achieved a selenium capture capacity of 7.76 mg/g at 350 °C.
• Saturated selenium removal capacity reached 9.93 mg/g at 50 min.
• SeO2 decomposed and reduced to elemental selenium (Se0) on the AC surface.
• DFT revealed strong chemical adsorption of SeO2 on AC surfaces (-89.77 to -235.12 kcal/mol).
• Elevated temperatures promoted SeO2 decomposition and reduction to Se0.

Conclusions:

• Activated carbon effectively captures and converts SeO2 to elemental selenium.
• Temperature plays a critical role in promoting SeO2 decomposition and reduction.
• The capture process is primarily driven by chemical adsorption and decomposition.
• CO in the gas phase contributes to the reduction of SeO2 to Se0.