L-cysteine-grafted polyacrylonitrile sheets with amphoteric adsorption sites enabling efficient removal of Hg(II) from acidic wastewater.

Conventional adsorbents for Hg(II) are not suitable for acidic environments because they degrade and lose activity. In this study, high-density sulfur and nitrogen-containing porous polyacrylonitrile sheet (HSN-PANS) was developed by grafting l-cysteine. The amphoteric HSN-PANS adsorbent can effectively remove Hg(II) from acidic wastewater, reducing its concentration from 11 mg/L to below the drinking water standard of 1 μg/L at pH 2. It shows high adsorption capacity (764 mg/g), strong anti-interference properties, and excellent selectivity. The adsorption mechanism involves coordination and electrostatic interactions. Thanks to its stable structure and efficient desorption, HSN-PANS demonstrates excellent acid resistance and reusability, retaining 99.9 % adsorption efficiency after 43 cycles. Furthermore, it performs reliably in industrial wastewater treatment. Notably, an HSN-PANS-packed column can treat about 5845 bed volumes (69 L) of Hg(II)-spiked acidic wastewater until reaching a breakthrough point of 1 μg/L, concentrating the adsorbed Hg(II) into 1.8 L of desorbent. This study demonstrates the potential of HSN-PANS as an effective adsorbent for directly and efficiently removing Hg(II) from acidic wastewater, providing a promising solution to reduce Hg(II) emissions in industrial processes.