Solvent-Free Synthesis of MnOx-FeOx/Biochar for Hg⁰ and o-Xylene Removal from Flue Gas

Abstract

Volatile organic compounds (VOCs) and Hg adversely affect the health of communities in coal-based economies in countries that depend on coal-fired power plants. In this study, biochar with incorporated Mn–Fe oxide composite was synthesized by co-ball milling of metal ions and biomass, followed by in situ pyrolysis carbonization and oxidation. The scanning electron microscopy (SEM) result shows that the generated metal oxides were incorporated into the biochar matrix rather than being physically deposited. By avoiding wet impregnation in the MnFe loading process, abundant functional groups were preserved on the surface of the materials. MnFe oxide homogeneity and dispersion on biochar were effectively promoted by mechanochemical synthesis for 4 h and showed high Mn and Fe oxidation states and a large amount of Lewis acid of 56.47 mol/g. Effectively promoted by these properties, the Mn–Fe oxides/biochar composite efficiently purified Hg0 and VOC by adsorption and catalytic oxidation from simulated coal-fired flue gas. The mutual inhibitory effect between Hg0 and o-xylene is pounced at high reaction temperatures when catalytic oxidation dominated. The mechanochemical strategy endowed the Mn–Fe oxides/biochar composite with strong magnetic properties, showing a saturation magnetization of 24.33 emu/g, which enabled 100% separation of the material from coal-fired fly ash.

Minireview and Perspective of One-Dimensional Manganese Oxide Nanostructures for the Removal of Air Pollutants

“…73−76 To date, adsorption, solvent absorption, catalytic oxidation, heat treatment, biological absorption, and other methods have been developed to eliminate VOCs. 77,78 Catalytic oxidation is increasingly viewed as the most expected method for treating volatile organic compounds due to its low energy consumption and high efficiency.…”

“…With the vigorous development of industrialization and urbanization in contemporary society, PM2.5 and O 3 have become severe obstacles to human development. The frequency of large-scale simultaneous occurrences of heavy air pollution in each region is increasing, which seriously restricts the sustainable development of the social economy and threatens people’s health. − To date, adsorption, solvent absorption, catalytic oxidation, heat treatment, biological absorption, and other methods have been developed to eliminate VOCs. , Catalytic oxidation is increasingly viewed as the most expected method for treating volatile organic compounds due to its low energy consumption and high efficiency.…”

Perspectives of Engineered Biochar for Environmental Applications: A Review

“…A biochar with a high capacity to adsorb N 2 O (0.057–0.30 mg N 2 O/g char) was obtained by Xiao et al Mercury and its compounds are considered toxic and harmful to humans and animals . Mercury emissions are mainly generated from the tail flue gas of coal-fired power plants. , Biochar loaded with metal oxide composites exhibited high performance for Hg 0 removal. − Qin et al studied the use of iron-based modified biochar for adsorption of Hg 0 , and the reaction path of Hg 0 adsorption on the surface of iron-based modified biochar was assessed. Different adsorption sites were generated during the synthesis of modified biochar, which include iron-based doping sites and oxygen-containing functional group adsorption sites.…”

Synthesis and Adsorbent Performance of Modified Biochar with Ag/MgO Nanocomposites for Heat Storage Application

“…The maximum absorption coefficient was obtained at 121.25 mgg -1 for MgO modified biochar using the impregnation technique investigated by Li et al [7,8]. Rather than standard impregnation, the emerging ball milling approach is a solvent-free modification technique that requires adding oxides to the modified biochar surface [10,11].…”