Molecular-level green chemistry based design of a custom binding site for targeted Cu (II) ion removal in bio-retention system.

Bioretention systems are increasingly prioritized for urban stormwater management due to their small physical footprint and robust pollution-sequestration capabilities. This study explores how to best remove dissolved copper (Cu(II)) from urban storm water by introducing custom based tunable organoclay modified with quaternary ammonium salts (QASs). The study finds a strong correlation between surface chemistry and heavy metal remediation by altering the clay media's hydrophilic and hydrophobic characteristics. Cu(II) removal from a hydrophilic organoclay modified with a linear-chain QAS was 93%, which is a significant improvement over conventional systems. Additionally, this modified layer improved the bioretention system's chlorophyll-b content, plant growth, and Cu(II) uptake. Furthermore, adsorption analysis, fitting the Langmuir isotherm, revealed that functionalization creates three distinct adsorption sites (surface, interlayer, and modifier), surpassing the capacity of unmodified clay. In addition to three binding sites, additional binding sites were identified as Cu(II) leaching observed due to the dry cycle of the bioretention system. This study implies that the clay layer with hydrophilic organoclay in the bioretention system could provide good binding sites for the efficient removal of Cu(II) in urban storm water.