Facile fabrication of thiol-modified cellulose sponges for adsorption of Hg2+ from aqueous solutions

Thiol-functionalised cellulose sponges were conveniently synthesised by reacting (2,2,6,6-tetramethylpiperidin-1-yl)oxyl oxidised cellulose nanofibrils (CNF) with (3-mercaptopropyl)-trimethoxysilane (MPTMS) at room temperature. The sponges, whose structures resemble honeycombs, were systematically characterised using Fourier transform infrared spectroscopy, solid-state C-13 nuclear magnetic resonance spectroscopy, elemental analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy and compression tests. It was shown that the sponges could be used to selectively remove Hg2+ from an aqueous solution containing other metal ions and had excellent adsorption capacities of up to 700 mg/g. The sorption isotherm followed the typical Langmuir model and the adsorption kinetics fit a pseudo-second-order model. X-ray photoelectron spectroscopy was applied to confirm that sulfur and oxygen had significant roles in the adsorption of Hg2+. The sponges also showed high reusability after three adsorption-desorption cycles. This paper provides a simple method to prepare highly efficient adsorbents for the adsorption of Hg2+ from aqueous solutions.