Adsorption mechanisms of hydrogen fluoride gas by urea-modified Mg-based adsorbent: The key role of oxygen vacancies

Hydrogen fluoride (HF) gas is a major combustion byproduct in non-ferrous metal smelting, aluminum electrolysis, coal combustion, and waste incineration processes. Due to its high corrosivity and toxicity, which pose a serious threat to human health and environmental ecosystems, it is necessary to strictly control HF emissions from industrial processes or remove it using proper methods. In this study, an oxygen vacancy-containing magnesium-based adsorbent (2NC@Mg(NO₃)₂–500) was successfully synthesized via a one-pot method. This adsorbent demonstrated a maximum HF adsorption capacity of 195.65 mg·g⁻¹ (at 90 % efficiency), significantly exceeding values reported in previous literature. The basic sites of magnesium oxide (MgO) were critical for promoting HF dissociation, while oxygen vacancies facilitated HF adsorption and its conversion to magnesium fluoride (MgF₂). Density functional theory (DFT) calculations further confirmed the experimental findings, demonstrating that oxygen vacancies significantly enhance HF adsorption on MgO by stabilizing fluoride ions (F^-) at the vacancy sites. The subsequent consumption of these vacancies and the conversion of MgO to MgF₂ led to adsorbent deactivation. This study highlights the important role of oxygen vacancies in HF gas adsorption.