Simultaneous Nitrite Resourcing and Mercury Ion Removal Using MXene-Anchored Goethite Heterogeneous Fenton Composite.

The integrated system of gas-phase advanced oxidation process combined with sulfite-based wet absorption process is a desirable method for simultaneous removal of SO 2 , NO, and Hg 0 , but due to the enrichment of nitrite and Hg 2+ , resourcing harmless wastewater is still a challenge. To tackle this problem, this study fabricated a bifunctional β-FeOOH@MXene heterogeneous Fenton material, of which the crystalline phase, morphology, structure, and composition were revealed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy, and transmission electron microscopy. It exhibits excellent performance on nitrite oxidation (99.5%) and Hg 2+ removal (99.7%) and can maintain stable outstanding ability after 13 cycles, with superior Hg 2+ adsorption capacity (395 mg/g) and ultralow Fe leaching loss (<0.018 wt %). The synergism between MXene and β-FeOOH appears as follows: (i) MXene, as an inductive agent, directionally converted Fe 2 O 3 into β-FeOOH in the hydrothermal method and greatly reduced its monomer size; (ii) the introduced ≡Ti(III)/≡Ti(II) accelerated the regeneration of ≡Fe(II) via rapid electron transfer, thereby improving the heterogeneous Fenton reaction; and (iii) MXene strongly immobilized β-FeOOH to greatly inhibit Fe-leaching. HO • , • O 2 -- , and 1 O 2 were the main radicals identified by electron spin resonance. Radical quenching tests showed their contributions to NO 2 - oxidation in the descending order HO • > 1 O 2 > • O 2 - . Quantum chemical calculations revealed that • OH-induced oxidation of NO 2 - or HNO 2 was the primary reaction path. Density functional theory calculations combined with X-ray photoelectron spectroscopy and Raman characterizations displayed the Hg 2+ removal mechanism, with Hg 2 Cl 2 , HgCl 2 , and HgO as the main byproducts. This novel material provides a new strategy for resourcing harmless wastewater containing nitrite and Hg 2+ .