Microcystin-LR Adsorption by Activated Carbon.

Area of Science:

• Environmental Chemistry
• Water Treatment Technologies
• Adsorption Science

Background:

• Microcystin-LR (m-LR) is a potent hepatotoxin found in aquatic environments.
• Activated carbons are widely used for water purification, but their efficacy against m-LR varies.
• Understanding adsorption mechanisms is crucial for optimizing toxin removal.

Purpose of the Study:

• To investigate factors controlling microcystin-LR (m-LR) removal by wood-based and coconut-based activated carbons.
• To elucidate the roles of adsorbent surface chemistry and solution chemistry in m-LR adsorption.
• To determine the thermodynamic driving forces for m-LR adsorption.

Main Methods:

• Adsorption experiments using wood-based (microporous and mesoporous) and coconut-based (microporous) activated carbons.
• Modification of adsorbent surface chemistry and solution chemistry parameters.
• Thermodynamic analysis using multiple temperature adsorption chromatography.

Main Results:

• Wood-based carbons showed higher m-LR adsorption than coconut-based carbons.
• Solution chemistry (especially pH) had a greater influence on adsorption than adsorbent surface chemistry.
• Low pH (2.5) significantly increased m-LR affinity for both carbon types, especially coconut carbons (400% increase).
• m-LR adsorption was primarily entropy-driven, except for a hydrophilic, mesoporous carbon where enthalpy also contributed.

Conclusions:

• Adsorbent pore structure (micropore and mesopore volume) is critical for m-LR adsorption due to its molecular dimensions.
• Solution pH plays a significant role, likely through conformational changes of m-LR.
• Adsorption is largely an entropy-driven process, highlighting the importance of pore accessibility and surface interactions.