Novel thiol-functionalized covalent organic framework as adsorbent for simultaneous removal of BTEX and mercury (II) from water

A novel thiol-functionalized covalent organic framework (COF-S-SH) was prepared as an adsorbent for the simultaneous removal of BTEX (benzene, toluene, ethyl benzene and xylenes) and Hg(II) ion from water. The COF-S-SH was obtained via a Schiff-base reaction between a new triamino-monomer (TABPB) and 2,5-divinylterephthalaldehyde, followed by the thiol-ene “click” reaction between 1,2-ethanedithiol and the vinyl groups. The COF-S-SH was characterized by FT-IR spectrum, energy-dispersive X-ray spectrum, 13C MAS NMR spectrum, nitrogen adsorption–desorption isotherms, thermo-gravimetric analysis, scanning electron microscope, X-ray diffraction, and zeta potential. The new adsorbent showed high binding ability with the maximum adsorption capacities (Qmax) of 150.2–255.8 mg/g for BTEX and 588.2 mg/g for Hg(II). The adsorbent also presented fast adsorption kinetics with rate constants of 0.01043–0.05002 g/mg/min for BTEX and 7.254 × 10−4 g/mg/min for Hg(II). Moreover, the adsorbent had good binding selectivity for Hg(II) against common metal ions in water. The adsorbent also showed good simultaneous uptake ability and good reusability for BTEX and Hg(II), and it has been applied to simultaneously removing BTEX and Hg(II) in the simulated sewage with the removal efficiencies of 63.6, 82.1, 94.6, 95.3 and 94.1% for benzene, toluene, ethyl benzene, m-xylene and Hg(II), respectively. Especially, it can reduce the low-concentration Hg(II) in the simulated sewage to a level lower than the drinking water limit. Therefore, COF-S-SH can be used as an excellent adsorbent material for simultaneously removing BTEX and Hg(II) in from the produced water and wastewater in petroleum chemistry industries.