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 the decoration with a vinyl-terminated silane and subsequently were 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 in an emulsion and mercury cations under dynamic conditions, namely in batch reactor under constant stirring for the oil adsorption and in flow reactor with constant metal concentration for the Hg adsorption. The chemical and structural stability of the COF networks were evaluated via FTIR, EDS, and SEM analysis, respectively. The oil removal study on a 100 ppm solution with a volume of 100 ml was evaluated through UV-Vis measurements and demonstrated a first-order kinetic fitted with 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. Τhe competitiveness of a series of elements against mercury adsorption was examined through dynamic absorption experiments and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). A 96-99 % removal of mercury was observed for 300 minutes of continuous flow of a 10 ppm solution and for a subsequent 90 minutes of bypassing a 100 ppm mercury solution removal percentages of 77-96 % was achieved. 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 for both dissolved oil and mercury removal. The versatility of the functional material allows its dual capacity in heavily polluted aqueous environments.