Novel 3-Hydroxy-2-Naphthoate-Based Task-Specific Ionic Liquids for an Efficient Extraction of Heavy Metals

Area of Science:

• Green Chemistry
• Environmental Science
• Materials Science

Background:

• Ionic liquids (ILs) are promising green alternatives for heavy metal extraction due to favorable properties.
• Leaching of ILs during extraction limits their practical application.
• Novel ILs are synthesized to enhance stability and selectivity for heavy metal ions.

Purpose of the Study:

• Synthesize novel ammonium and phosphonium ionic liquids based on 3-hydroxy-2-naphthoic acid.
• Evaluate their efficacy in extracting seven heavy metals (Ag, Cd, Co, Cu, Mn, Ni, Pb) from aqueous solutions.
• Investigate the impact of alkyl chains and cation type on IL properties, extraction efficiency, and leaching.

Main Methods:

• Synthesized three novel ILs: [P66614][HNA], [P1888][HNA], and [N1888][HNA] via deprotonation-metathesis.
• Tested extraction capabilities in pure water, saline water (30 g L-1 NaCl), and natural water samples with humic acids.
• Analyzed heavy metal extraction percentages and IL leaching after 24 hours.

Main Results:

• All three ILs achieved ≥90% extraction for Cu and Pb in pure water within 24 hours.
• Extraction efficiencies for Ag, Cd, Cu, and Pb were highest in drinking water samples.
• IL [P66614][HNA] showed increased Ag and Cd extraction (up to 41%) in saline samples compared to pure water.
• Leaching was significantly reduced to 0.07% loss, attributed to the hydrophobic 3-hydroxy-2-naphthoate anion.

Conclusions:

• The novel ILs demonstrate high efficiency and selectivity for heavy metal extraction, particularly Cu and Pb.
• The hydrophobic nature of the 3-hydroxy-2-naphthoate anion effectively minimizes IL leaching.
• These findings represent a significant advancement in developing greener and more stable ionic liquids for heavy metal remediation from natural waters.