Eutectic molten salt assisted fabrication of microporous biochar for greenhouse gases adsorption

The utilization of eutectic molten salt technology has emerged as a prominent area of investigation aimed at fabricating a novel carbon material sorbent based on biomass wastes. The adsorption mechanism on CO₂ adsorption remains inadequately elucidated as well. Herein, the biochar fabrication process involving eutectic molten salt method at intermediate-low temperature of 550 °C was successfully achieved and investigated in detail. The impacts of molten salt composition, monomer salt's anion and cation, and pyrolysis parameters were firstly studied on the resulting microporous biochar of 1.8 nm pore diameter and 975 m²/g surface area. The optimized conditions are 550 °C, 15 °C min⁻¹ ramp rate, 120 min holding time, Na⁺ cation, NO₃^– anion, and ternary salt KCl/NaNO₃/Na₂SO₄ of 32.5/30.4/37.1. The efficient adsorbent exhibited abundant micropores and a substantial specific surface area, leading to enhanced CO₂ adsorption quantity of 3.75 mmol/g (the calculated capacity is up to 4.54 mmol/g) at pressure state of 1.6 MPa. Investigation into key factors, adsorption kinetics, and adsorption isotherm revealed that CO₂ capture by optimal adsorbent predominantly stemmed from micropore filling, van der Waals forces, hydrogen bonds, and Lewis acid-base interactions. This research contributes novel insights into the utilization of biochar adsorbents for CO₂ capture in the realm of industry.