Kr Adsorption in Porous Carbons: Temperature-Dependent Experimental and Computational Studies†

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Understanding gas adsorption on porous materials is crucial for applications like gas storage and separation.
• The temperature dependence of adsorption energy influences the efficiency and selectivity of these processes.
• Activated carbon is a widely used adsorbent with complex pore structures.

Purpose of the Study:

• To investigate the temperature dependence of krypton adsorption energy on activated carbon.
• To elucidate the role of pore width and thermal effects on adsorption energetics.
• To compare experimental measurements with simulation results.

Main Methods:

• Experimental measurement of adsorption isotherms for krypton on activated carbon from 250 to 330 K.
• Analysis of isotherms using Henry's law to determine adsorption energy.
• Computational modeling of slit pore widths using graphite planes.
• Calculation of adsorbate vibrational dynamics using the stochastic temperature-dependent effective potential (sTDEP) method.
• Density Functional Theory (DFT) with many-body dispersion (MBD) for energetics.

Main Results:

• Adsorption energy weakened by over 10% between 250 and 330 K.
• Thermal displacements of carbon atoms had a negligible impact on adsorption energy.
• Slit pore width significantly affected surface dynamics and adsorbate atom energies.
• A Boltzmann distribution of site occupancies in a pore width distribution led to a large weakening of averaged adsorption energy at higher temperatures.

Conclusions:

• Pore width is a dominant factor influencing the temperature dependence of krypton adsorption on activated carbon.
• Thermal averaging effects, particularly in materials with a distribution of pore widths, significantly reduce adsorption energy at elevated temperatures.
• The findings provide insights into optimizing adsorption processes by controlling pore structure and operating temperature.