The vibrational spectrum of the MnO2− and MnO4− anions in solid argon

Dual-functional effect encompassing adsorption and catalysis by Mn-modified iron-based sorbents for arsenic removal: Experimental and DFT study

Arsenic oxidation plays a crucial role in its removal, which has been identified in numerous studies. However, the mechanisms, especially reaction pathways of arsenic oxidation on sorbent surfaces remain inadequately explored. In this work, the effects of Mn doping on arsenic adsorption and oxidation were first verified by adsorption experiments. Subsequently, DFT calculations were carried out to identify alterations in the adsorption energies, active sites, and oxidation pathways. By integrating the experimental and simulation results, a dual-functional framework encompassing adsorption and catalysis of Mn-modified Fe-based material was distinctly established. For adsorption, the introduction of manganese into iron-based sorbent considerably enhanced As2O3 adsorption owing to the increased active sites available for As2O3 chemisorption and the promotion of surface nucleophilicity. Concerning oxidative catalysis, the incorporation of MnO2 augmented surface catalytic oxidation and provided a substantial amount of active Oload. Consequently, the arsenic oxidation occurring on the Mn-modified sorbent surfaces possessed a lower oxidation RDS energy barrier and a shorter oxidation pathway than those on the bare sorbent surfaces. These experimental and simulation results provide a theoretical basis for the design and application of efficient gaseous arsenic adsorbents.

Study on mutual harmless treatment of electrolytic manganese residue and red mud

Electrolytic manganese residue (EMR) and red mud (RM) are solid waste by-products of the metal manganese and alumina industries, respectively. Under long-term open storage, ammonia nitrogen and soluble manganese ions in EMR and alkaline substances in RM severely pollute and harm the environment. In order to alleviate the pollution problem of EMR and RM. In this study, the alkaline substances in RM were used to treat ammonia nitrogen and soluble manganese ions in EMR. The results confirm the following suitable treatment conditions for the mutual treatment of EMR and RM: EMR-RM mass ratio = 1:1, liquid-solid ratio = 1.4:1, and stirring time = 320 min. Under these conditions, the elimination ratios of ammonia nitrogen (emitted in the form of ammonia gas) and soluble manganese ions (solidified in the form of Mn3.88O7(OH) and KMn8O16) are 85.87 and 86.63%, respectively. Moreover, the alkaline substances in RM are converted into neutral salts (Na2SO4 and Mg3O(CO3)2), achieving de-alkalinisation. The treatment method can also solidify the heavy metal ions-Cr3+, Cu2+, Ni2+, and Zn2+-present in the waste residue with leaching concentrations of 1.45 mg/L, 0.099 mg/L, 0.294 mg/L, and 0.449 mg/L, respectively. This satisfies the requirements of the Chinese standard GB5085.3-2007. In the mutual treatment of EMR and RM, the kinetics of ammonia nitrogen removal and manganese-ion solidification reactions are controlled via a combination of membrane diffusion and chemical reaction mechanisms.

Photoelectron spectra of early 3d-transition metal dioxide molecular anions from GW calculations

Photoelectron spectra of early 3d-transition metal dioxide anions, ScO₂ ^-, TiO₂ ^-, VO₂ ^-, CrO₂ ^-, and MnO₂ ^-, are calculated using semilocal and hybrid density functional theory (DFT) and many-body perturbation theory within the GW approximation using one-shot perturbative and eigenvalue self-consistent formalisms. Different levels of theory are compared with each other and with available photoelectron spectra. We show that one-shot GW with a PBE0 starting point (G₀W₀@PBE0) consistently provides very good agreement for all experimentally measured binding energies (within 0.1 eV-0.2 eV or less). We attribute this to the success of PBE0 in mitigating self-interaction error and providing good quasiparticle wave functions, which renders a first-order perturbative GW correction effective. One-shot GW calculations with a Perdew-Burke-Ernzerhof (PBE) starting point do poorly in predicting electron removal energies by underbinding orbitals with typical errors near 1.5 eV. A higher exact exchange amount of 50% in the DFT starting point of one-shot GW does not provide very good agreement with experiment by overbinding orbitals with typical errors near 0.5 eV. While not as accurate as G₀W₀@PBE0, the G-only eigenvalue self-consistent GW scheme with W fixed to the PBE level provides a reasonably predictive level of theory (typical errors near 0.3 eV) to describe photoelectron spectra of these 3d-transition metal dioxide anions. Adding eigenvalue self-consistency also in W, on the other hand, worsens the agreement with experiment overall. Our findings on the performance of various GW methods are discussed in the context of our previous studies on other transition metal oxide molecular systems.

Identifying MnVII-oxo Species during Electrochemical Water Oxidation by Manganese Oxide

Identifying surface active intermediate species is essential to reveal the catalytic mechanism of water oxidation by metal-oxides-based catalysts and to develop more efficient catalysts for oxygen-oxygen bond formation. Here we report, through electrochemical methods and ex situ infrared spectroscopy, the identification of a Mn^VII = O intermediate during catalytic water oxidation by a c-disordered δ-MnO_x with an onset-potential-dependent reduction peak at 0.93 V and an infrared peak at 912 cm⁻¹. This intermediate is proved to be highly reactive and much more oxidative than permanganate ion. Therefore, we propose a new catalytic mechanism for water oxidation catalyzed by Mn oxides, with involvement of the Mn^VII = O intermediate in a resting state and the Mn^IV−O−Mn^VII = O as a real active species for oxygen-oxygen bond formation.

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A reactive Mn^VII-oxo intermediate was identified during water oxidation by a MnO_x

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The Mn^VII-oxo species was proved to be much more oxidative than permanganate ion

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The Mn^IV−O−Mn^VII = O moiety is a real highly active state for O–O bond formation

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A new mechanism for Mn oxide-catalyzed electrocatalytic water oxidation is proposed

Formation and infrared spectroscopic characterization of three oxygen-rich BiO4 isomers in solid argon

The reactions of bismuth atoms and O2 have been investigated using matrix isolation infrared spectroscopy and density functional theory calculations. The ground state bismuth atoms react with dioxygen to form the BiOO and Bi(O2)2 complexes spontaneously on annealing. The BiOO molecule is characterized to be an end-on bonded superoxide complex, while the Bi(O2)2 molecule is characterized to be a superoxo bismuth peroxide complex, [Bi(3+)(O2(-))(O2(2-))]. Under UV-visible light irradiation, the Bi(O2)2 complex rearranges to the more stable OBiOOO isomer, an end-on bonded bismuth monoxide-ozonide complex. The end-on-bonded OBiOOO complex further rearranges to a more stable side-on bonded OBiO3 isomer upon sample annealing. In addition, the bent bismuth dioxide anion is also formed and assigned.