Thiophene-functionalized covalent triazine frameworks for photo-enhanced gold recovery

Abstract

Combining adsorption with photocatalytic reduction may be an ideal emerging strategy for efficient and highly selective gold recovery, but currently reports are rare. In precious metal recovery, cheap and robust covalent triazine frameworks (CTFs) offer industrial feasibility, although having selective binding sites while enhancing semiconductor performance is challenging. In this paper, we report a D-A CTF (named TD-TPTA) with abundant thiophene and triazine functional groups, narrow optical band gap, and excellent photocatalytic activity. Benefiting from the strong interaction between [AuCl4]− (soft acid) and the abundant soft base sites (sulfur atom) on the CTF skeleton, TD-TPTA can achieve highly selective gold capture. Meanwhile, the construction of π-conjugated D-A skeleton significantly improving the photocatalytic activity and achieving efficient photocatalytic reduction of gold. Analysis reveals that through a combination of adsorption and photocatalytic reduction, TD-TPTA has high gold adsorption capacity (1123.8 mg g−1) and fast kinetics even under ultra-low pH conditions (pH = 2). In addition, TD-TPTA can selectively recover 99.45 % of gold from e-waste wastewater. CTF is robust and recyclable, providing significant advantages over currently reported adsorbents.