Dissolved oil and mercury(ii) adsorption under dynamic conditions by thiol-terminated COF-modified sponges

Abstract

In this work, a multi-step approach for the fabrication of a unique sponge-based platform with multiple functionalities and applications in water-remediation technologies under dynamic conditions is presented. Commercial melamine sponges were rendered hydrophobic through decoration with vinyl-terminated silane and subsequently functionalized in situ through a two-step process with a thiol-terminated covalent organic framework (COF). The materials were extensively characterized and applied for the removal of dissolved oil from emulsions and mercury cations under dynamic conditions, namely in a batch reactor under constant stirring for oil adsorption and in a flow reactor with constant metal concentration for Hg adsorption. The chemical and structural stability of the COF networks were evaluated via FTIR, EDS, and SEM analysis, respectively. An oil-removal study was conducted using a 100 ppm solution with a volume of 100 mL, was evaluated through UV-vis measurements and the results demonstrated a first-order kinetics fitted with the Elovich model, which provided the initial rate α = 0.307 mg cm⁻³ min⁻¹ and desorption constant β = 0.323 g cm⁻³ for the active sites of the thiol-terminated sponges. The competitiveness of a series of elements against mercury adsorption was examined through dynamic absorption experiments and inductively coupled plasma optical emission spectrometry (ICP–OES). Mercury removal efficiencies of 96–99% were achieved over 300 minutes of continuous flow of a 10 ppm solution, while 77–96% removal was achieved over a subsequent 90 minutes for a 100 ppm mercury solution. The characterization analysis and the environmental remediation studies between the efficiencies of COF-modified sponges without and with the –SH terminal groups revealed the crucial role of the thiol pendant groups in the removal of both dissolved oil and mercury. The versatility of the functional material enables its dual functionality in heavily polluted aqueous environments.