RESUMO
HYPOTHESIS: Emerging contaminants (ECs) can interact with soft solid/aqueous interfaces of particulate organic matter and microplastics in the aquatic environment but to what extent? It is hypothesized that EC adsorption can be detected using quartz crystal microbalance (QCM), a sensitive gravimetric tool, and their adsorption energetics and uptake capacity can be measured for various substrates of distinct functional group. This in turn reveals the specific vs. nonspecific interactions. EXPERIMENTS: QCM has been used to detect and measure the adsorption of selected pharmaceuticals, amlodipine (AMP) and carbamazepine (CBZ), onto butyl, carboxyl, amine, and phenyl functionalized self-assembled monolayers (SAMs), mapping out the hydrophobic effect, H-bonding capability, and π- interactions. Adsorption free energy (ΔGads) and maximum interfacial concentration (cmax) for these surfaces are compared. Solvatochromic studies to elucidate the likelihood of H-bonding interactions for CBZ and AMP have been conducted using UV-Vis absorption spectroscopy. FINDINGS: Amlodipine and carbamazepine adsorb onto butyl/aqueous interface with respective ΔGads values of -35.8 ± 1.1 and -37.7 ± 0.1 kJ/mol. Nonspecific interaction allows a greater extent of cmax on the hydrophobic/aqueous interface. CBZ does not bind to the phenyl surface. AMP and CBZ exhibit H-bonding and show proclivity for the amine and carboxyl SAMs. Interfacial chemical environment and adsorbate structural properties play a significant role on EC adsorption.
