Computational Study of Acidic and Basic Functionalized Crystalline Silica Surfaces as a Model for Biomaterial...

Area of Science:

• Computational Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Plasma methods are used to experimentally functionalize silica surfaces with acidic or basic groups.
• Understanding the stability and properties of these functionalized surfaces is crucial for their application.
• In silico modeling offers a way to investigate surface modifications at the atomic level.

Purpose of the Study:

• To perform in silico modeling of acidic (CH2COOH) and basic (CH2NH2) functionalized silica surfaces.
• To provide insights for characterizing experimentally functionalized silica surfaces.
• To compare the stability and vibrational properties of different functional group loadings.

Main Methods:

• Density functional theory (DFT) calculations were employed to study structures, energetics, and electronic/vibrational properties.
• Classical molecular dynamics (MD) simulations using a Reax-FF reactive force field assessed the mobility of surface chains.
• Simulations were performed on hydroxylated cristobalite surfaces mimicking amorphous silica with varying functional group densities.

Main Results:

• DFT and MD simulations identified moderate basic (CH2NH2) loading (1 group/unit cell) as the most stable functionalization.
• Higher acidic (CH2COOH) loading (2 groups/unit cell) was found to be preferred for acidic functionalization.
• Vibrational frequencies (ν(C═O) and δ(NH2)) were characterized, showing shifts influenced by hydrogen bonding and functional group interactions.

Conclusions:

• The study reveals distinct stability preferences for acidic versus basic functional groups on silica surfaces.
• Computed vibrational fingerprints provide guidance for interpreting experimental spectroscopic data of functionalized silica.
• The findings align with experimental observations, offering deeper insights into surface functionalization mechanisms.