Urea–nonstoichiometric co-modulated LaMnO3 for ultra-high gaseous Hg0 uptake across a broad temperature range

Abstract

A novel urea–nonstoichiometric co-modulated Mn-perovskite material (2U-La_0.8MnO₃) was developed, exhibiting a remarkable Hg⁰ saturated adsorption capacity of 23.86 mg g⁻¹, surpassing those of all previously reported metal oxides. Furthermore, 2U-La_0.8MnO₃ demonstrated nearly 100% removal of Hg⁰ across a wide temperature range (40–250 °C), along with low apparent activation energy and excellent sulfur resistance. Characterization studies manifested that the introduction of urea and non-stoichiometric co-modulation induced the simultaneous formation of abundant La defects and O vacancies (OVs), boosting the surface reactive oxygen species and Lewis acid sites, decreasing the particle size, and improving the pore structure and surface area. Product analysis revealed that almost all Hg⁰ was oxidized and chemisorbed as HgO, with no Hg²⁺ escaping. Characterization combined with theoretical calculations elucidated that the co-modulation process altered the Hg⁰ removal mechanism from Eley–Rideal to Langmuir–Hinshelwood: OVs dominated the generation of surface adsorbed oxygen (O_ads) via splitting O₂, and Lewis acid was the primary site for Hg⁰ adsorption, followed by the reaction with O_ads to form HgO. Additionally, the co-modulation method significantly enhanced the adsorption capacity of O₂ + Hg⁰ and dramatically reduced the reaction energy barrier. This dual-regulation method provides an innovative strategy for preparing adsorbents with ultra-high Hg⁰ trapping capacity.