Spontaneous adsorption–oxidation of gaseous elemental mercury via a conjugated unit –NH+˙–Cl*: creation and mechanisms

Abstract

Removing gaseous elemental mercury (Hg⁰) from Hg-containing tail gas is a hot topic and a great challenge. In this study, we developed a novel cost-effective and ultralight material, namely Cl-doped protonated polyaniline-coated multiwall carbon nanotubes (Cl-PANI⁺@MWCNTs), which could remove 98.5% of Hg⁰ at a high space velocity of 200 000 h⁻¹, also possessing excellent reusability, good water resistance, and high thermal stability. Based on characterization analyses combined with density functional theory (DFT) calculations, its creation and mechanisms could be deeply explained, indicating that the low oxidation state of PANI was a prerequisite to achieve excellent Hg⁰ removal owing to its functional unit of –NH–, which promotes the production of –NH⁺˙–Cl* via the protonation and Cl-doping treatments. During the reaction, Hg⁰ is first adsorbed by the –NH⁺˙– antibonding orbital and then bonds with the covalent Cl* on –NH⁺˙– to form HgCl_xPANI. Cost analyses indicated that removing 1 lb of Hg⁰ by using Cl-PANI⁺@MWCNTs was about 63-fold cheaper than the published polypyrrole (PPy) counterpart, moreover the Hg⁰ dynamical adsorption capacity and the breakthrough time were increased by 3.2 times (7.43 mg g⁻¹vs. 1.76 mg g⁻¹, 52.6 h vs. 12.6 h) if taking the removal efficiency of 90% as the breakthrough point. The novel material proposed in this study is of great significance for the development of Hg⁰-removal technology.