Work

Transforming contaminant ligands at water–solid interfaces via trivalent metal coordination

Year: 2024

Type: article

Abstract: • HA contributed a limited TC binding through intermolecular weak interactions. • Unique fluorescence induced by Al 3+ –TC coordination tracked TC migration. • Coordination with Al 3+ /Fe 3+ immobilized over 90 % TC on HA flocs. • High binding energy from coordination drove superior interfacial binding. In environmental matrices, the migration and distribution of contaminants at water–solid interfaces play a crucial role in their capture or dissemination. Scientists working in environmental remediation and wastewater treatment are increasingly aware of metal–contaminant coordination; however, interfacial behaviors remain underexplored. Here, we show that trivalent metal ions (e.g. Al 3+ and Fe 3+ ) mediate the migration of pollutant ligands (e.g. tetracycline (TC) and ofloxacin) to the organic solid interface. In the absence of Al 3+ , humic acid (HA) colloids (50 mg/L) capture 26.1 % of the TC in water (initial concentration: 10 mg/L) via weak intermolecular interactions (binding energy: −5.71 kcal/mol). Adding Al 3+ (2.5 mg/L) significantly enhances the binding of TC to an impressive 94.2 % via Al 3+ mediated coordination (binding energy: −84.89 kcal/mol). The significant increase in binding energy results in superior interfacial immobilization. However, excess free Al 3+ competes for TC binding via direct binary coordination, as confirmed based on the unique fluorescence of Al 3+ –TC complexes. Density functional theory calculations reveal the intricate process of HA–Al 3+ binding via carboxyl and phenolic hydroxyl sites. The HA–Al 3+ flocs then leverage the remaining coordination capacity of Al 3+ to chelate with TC. As well as providing insights into the pivotal role of metal ion on the self-purification of natural water bodies, our findings on the interfacial behavior of metal–contaminant coordination will propel coagulation technology to the capture of microscale pollutants.

Source: Environment International

DOI: 10.1016/j.envint.2024.109008

Authors: Qiandi Wang, Qiongying Xu, Wenzong Liu, Meng Jiao, Zhuqi Chen, Aijie Wang