Synergistic pre-impregnation and templating strategy for constructing seaweed-based porous biochar with highly efficient Hg2+ adsorption performance

In this study, a high-efficiency seaweed-based porous biochar was synthesized via a combined pre-impregnation and template method for effective removal of Hg 2+ from aqueous solutions. The biochar was fabricated by pyrolyzing hydrochloric acid-impregnated seaweed biomass with ZnCl 2 as a template under nitrogen atmosphere. Key preparation parameters, including pyrolysis temperature (500–800 °C), heating rate (5–20 °C·min –1 ), holding time (60–210 min), and biomass–template mass ratio (0.5:1–5:1), were systematically optimized to enhance adsorption performance of biochar. Under optimal conditions (pyrolysis temperature: 600 °C, heating rate: 10 °C·min –1 , holding time: 150 min, biomass–template mass ratio: 3:1), the prepared biochar exhibited a remarkable adsorption efficiency of 87.12% for 200 mg·L –1 Hg 2+ aqueous solution, with an adsorption capacity of 87.12 mg·g –1 . Cl introduced via pre-impregnation and template method facilitated the formation of stable chloromercury complexes ( e.g ., HgCl 2 ). Oxygen-containing functional groups ( e.g ., –COOH) on the biochar surface promoted Hg 2+ adsorption through coordination bonding and electrostatic interactions. Notably, the ZnCl 2 templating method significantly enhanced the biochar’s specific surface area, creating abundant pore structure for Hg 2+ adsorption. The collaborative pre-impregnation and template strategy significantly simplifies the preparation and modification process of biochar. In addition, it provides a new method for chlorine enrichment and pore structure optimization of biochar, thus achieving breakthroughs in adsorption efficiency, capacity, and process simplification of Hg 2+ removal.