Thiol-rich, porous carbon for the efficient capture of silver: Understanding the relationship between the surface groups and transformation pathways of silver

Abstract The selective capture of silver ions (Ag+) from wastewater is promising for simultaneous water purification and resource recovery but remains challenging. In this work, an adsorbent obtained by grafting sulfhydryl (SH) groups onto activated carbon (AC) from discarded cigarette butts and heated at 80 °C (AC-SH-80) was designed for Ag+ removal and exhibited a high capacity (719.2 mg/g) and remarkable selectivity. For the first time, we report that the adsorption performance of AC-SH is directly related to the structure–activity mode of surface S. Two previously unnoticed Ag+ uptake mechanisms were revealed by a quantitative analysis of the amount of adsorbed and reduced Ag+: (i) the sulfhydryl groups converted the majority of Ag+ to Ag; (ii) a minor amount of Ag+ chelated with C–O and C = O due to electrostatic effects. Benefitting from these Ag+ transformation pathways, AC-SH-80 exhibits remarkable selectivity and can realize the efficient removal of Ag+ from actual wastewater with complex backgrounds. This work uncovers the role of S in the Ag+ capture process to provide a new interpretation of the pathways involved in the adsorption of heavy metal ions to functional group-modified materials.