Computational study of phosphate adsorption on Mg/Ca modified biochar structure in aqueous solution.

Area of Science:

• Environmental Chemistry
• Materials Science
• Computational Chemistry

Background:

• Phosphate removal from water using biochar is a critical area of environmental research.
• Understanding the molecular mechanisms of phosphate adsorption on biochar is essential for optimizing removal efficiency.

Purpose of the Study:

• To investigate the adsorption of phosphate (H2PO4-) on metal-modified biochar using Density Functional Theory (DFT).
• To compare the adsorption performance of magnesium (Mg) and calcium (Ca) modified biochar.
• To elucidate the mechanisms of phosphate adsorption, differentiating between metal and edge adsorption sites.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model phosphate adsorption.
• Analysis included structural stability, adsorption energy, dipole moment changes, electronic density of states, and Atoms in Molecules (AIM) analysis.
• Two metal modifications (Mg and Ca) were studied on biochar structures.

Main Results:

• Metal-modified biochar exhibited significantly stronger phosphate adsorption than unmodified biochar at the molecular level.
• Calcium-modified biochar demonstrated superior phosphate adsorption compared to magnesium-modified biochar.
• Metal adsorption, primarily driven by electrostatic attraction, was more effective than edge adsorption (covalent bonding), highlighting the role of modified metals.

Conclusions:

• Metal modification, especially with Ca, substantially enhances biochar's capacity for phosphate removal from aqueous solutions.
• The study confirms that the modified metal sites play a dominant role in phosphate adsorption through electrostatic interactions.
• DFT analysis provides crucial insights into the molecular-level mechanisms governing phosphate adsorption on functionalized biochar.