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 SO2, NO, and Hg0, but due to the enrichment of nitrite and Hg2+, resourcing harmless wastewater is still a challenge. To tackle this problem, this study fabricated a bifunctional ß-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 Hg2+ removal (99.7%) and can maintain stable outstanding ability after 13 cycles, with superior Hg2+ adsorption capacity (395 mg/g) and ultralow Fe leaching loss (<0.018 wt %). The synergism between MXene and ß-FeOOH appears as follows: (i) MXene, as an inductive agent, directionally converted Fe2O3 into ß-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 ß-FeOOH to greatly inhibit Fe-leaching. HO•, •O2--, and 1O2 were the main radicals identified by electron spin resonance. Radical quenching tests showed their contributions to NO2- oxidation in the descending order HO• > 1O2 > •O2-. Quantum chemical calculations revealed that •OH-induced oxidation of NO2- or HNO2 was the primary reaction path. Density functional theory calculations combined with X-ray photoelectron spectroscopy and Raman characterizations displayed the Hg2+ removal mechanism, with Hg2Cl2, HgCl2, and HgO as the main byproducts. This novel material provides a new strategy for resourcing harmless wastewater containing nitrite and Hg2+.

A novel Fe-Co double-atom catalyst with high low-temperature activity and strong water-resistant for O3 decomposition: A theoretical exploration.

Developing catalysts with high activity, durability, and water resistance for ozone decomposition is crucial to regulate the pollution of ozone in the troposphere, especially in indoor air. To overcome the shortcomings of metal oxide catalysts with respect to their durability and water resistance, Fe-Co double-atom catalyst (DAC) is proposed as a novel catalyst for ozone decomposition. Here, through a systematic study using density functional theory (DFT) calculations and microkinetic modeling, the adsorption and catalytic decomposition of O3 on Fe-Co DAC have been examined based on adsorption configuration, orbital hybridization, and electron transfer. Based on Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms, the mechanisms of ozone decomposition on Fe-Co DAC were explored by analyzing reaction paths and energy variations. To confirm the water-resistant of Fe-Co DAC, competitive adsorption behavior between O3 and dominant environmental gases was discussed through ab initio molecular dynamic (AIMD) simulation. The dominant reaction mechanism of ozone decomposition is L-H and the rate-determining step is the desorption of the first oxygen molecule from the surface of Fe-Co DAC which has an energy barrier of 0.78 eV. Due to this relatively low energy barrier and high turnover frequency (TOF), the optimal operation window of catalytic O3 decomposition on Fe-Co DAC is <500 K suggesting that catalytic decomposition of O3 on Fe-Co DAC can occur at room temperature. This theoretical study provides new insights for designing novel catalysts for ozone decomposition and fundamental guidance for subsequent experimental research.

Screening the activity of single-atom catalysts for the catalytic oxidation of sulfur dioxide with a kinetic activity model.

An accurate prediction model of catalytic activity is crucial for both structure design and activity regulation of catalysts. Here, a kinetic activity model is developed to study the activity of single-atom catalysts (SACs) in catalytic oxidation of sulfur dioxide. Using the adsorption energy of the oxygen atom as a descriptor, the catalytic activities of 132 SACs were explored. Our results indicate the highest activity when the adsorption energy of oxygen equals -0.83 eV. In detail, single-atom Pd catalyst exhibits the best catalytic activity with an energy barrier of 0.60 eV. Most importantly, this work provides a new insight for developing a highly accurate and robust prediction model for catalytic activity.