Enhanced Removal of Ultratrace Levels of Gold from Wastewater Using Sulfur-Rich Covalent Organic Frameworks

In view of the increasing global demand and consumption
of gold,
there is a growing need and effort to extract gold from alternative
sources besides conventional mining, e.g., from water. This drive
is mainly due to the potential benefits for the economy and the environment
as these sources contain large quantities of the precious metal that
can be utilized. Wastewater is one of these valuable sources in which
the gold concentration can be in the ppb range. However, the effective
selective recovery and recycling of ultratrace amounts of this metal
remain a challenge. In this article, we describe the development of
a covalent imine-based organic framework with pores containing thioanisole
functional groups (TTASDFPs) formed by the condensation of a triazine-based
triamine and an aromatic dialdehyde. The sulfur-functionalized pores
served as effective chelating agents to bind Au3+ ions,
as evidenced by the uptake of more than 99% of the 9 ppm Au3+ solution within 2 min. This is relatively fast kinetics compared
with other adsorbents reported for gold adsorption. TTASDFP also showed
a high removal capacity of 245 mg·g–1 and a
clear selectivity toward gold ions. More importantly, the material
can capture gold at concentrations as low as 1 ppb.