Mesoporous Silica with Different Channel Widths for Cs⁺ Adsorption: A Molecular Dynamics Simulation Study

Area of Science:

• Materials Science
• Nanotechnology
• Environmental Chemistry

Background:

• Mesoporous silica materials offer promising applications for radioactive cesium (Cs+) adsorption and separation.
• Their ordered structures and high surface area are crucial for efficient contaminant removal.
• Understanding Cs+ behavior within these materials is vital for adsorbent design.

Purpose of the Study:

• To investigate the microscopic adsorption and diffusion mechanisms of Cs+ in mesoporous silica channels of varying widths.
• To elucidate the influence of channel size on Cs+ interaction with silica surfaces and co-adsorbed species.
• To provide atomic-level insights for optimizing mesoporous silica-based adsorbents.

Main Methods:

• Molecular dynamics simulations were used to model mesoporous silica with channel widths of 2 nm, 4 nm, and 6 nm.
• Analysis included density distribution, radial distribution function (RDF), hydrogen-bonding networks, and mean square displacement (MSD).
• Investigated the behavior of Cs+, nitrate ions (NO3-), and water (H2O) within the silica channels.

Main Results:

• Cesium ions (Cs+) primarily adsorb near the channel interface, with adsorption weakening as channel width increases.
• Approximately 60% of Cs+ forms inner-sphere complexes with surface -OH groups.
• Nitrate ions (NO3-) exhibit indirect adsorption via electrostatic interactions with Cs+.
• Cesium ion (Cs+) diffusion capacity increases with channel width, while water's hydrogen-bonding network slightly decreases.

Conclusions:

• Channel size significantly regulates Cs+ adsorption and diffusion in mesoporous silica at the atomic level.
• Adsorption capacity is highest in narrower channels (2 nm), where Cs+ is fully captured at the interface.
• Findings offer theoretical guidance for designing efficient mesoporous silica adsorbents through channel engineering.