Experimental methods in chemical engineering: Electron paramagnetic resonance spectroscopy‐EPR/ESR

Fast Screening of Coal Fly Ash with Potential for Rare Earth Element Recovery by Electron Paramagnetic Resonance Spectroscopy

Rare earth elements (REYs) are in increasing global demand, but their mining is costly and environmentally destructive. Coal fly ash (CFA) is a promising alternative source of REYs, but it is necessary to identify CFA with sufficiently high REY concentrations. This study proposes the use of electron paramagnetic resonance (EPR) spectroscopy as part of a simple method to identify CFAs with adequate REY concentrations. The EPR spectra of CFA samples taken from 186 Chinese commercial coal-fired power plants were analyzed. The results suggest that CFAs without evident 6-fold resonances are worth recycling (REY concentrations of 416 ± 108 mg/kg), while those with conspicuous 6-fold resonances are not worth recycling (REY concentrations of 55 ± 26 mg/kg). This is probably due to isomorphic substitution of Ca(II) for Mn(II) and REY(III), resulting in low concentrations of Mn(II) and REY(III) in Ca-rich CFAs. This EPR evaluation method does not require specialized sample preparation, professional skills, or secondary data analysis and has potential global significance in the fast screening of CFAs with REY-recycling potential.

On the Origins of Some Spectroscopic Properties of "Purple Iron" (the Tetraoxoferrate(VI) Ion) and Its Pourbaix Safe-Space

In this work, the authors attempt to interpret the visible, infrared and Raman spectra of ferrate(VI) by means of theoretical physical-inorganic chemistry and historical highlights in this field of interest. In addition, the sacrificial decomposition of ferrate(VI) during water treatment will also be discussed together with a brief mention of how Rayleigh scattering caused by the decomposition of Fe^VIO₄²⁻ may render absorbance readings erroneous. This work is not a compendium of all the instrumental methods of analysis which have been deployed to identify ferrate(VI) or to study its plethora of reactions, but mention will be made of the relevant techniques (e.g., Mössbauer Spectroscopy amongst others) which support and advance this overall discourse at appropriate junctures, without undue elaboration on the foundational physics of these techniques.

Oxygen Vacancy Engineering in Titanium Dioxide for Sodium Storage

Titanium dioxide (TiO₂ ) is a promising anode material for sodium-ion batteries (SIBs) due to its low cost, natural abundance, nontoxicity, and excellent electrochemical stability. Oxygen vacancies, the most common point defects in TiO₂ , can dramatically influence the physical and chemical properties of TiO₂ , including band structure, crystal structure and adsorption properties. Recent studies have demonstrated that oxygen-deficient TiO₂ can significantly enhance sodium storage performance. Considering the importance of oxygen vacancies in modifying the properties of TiO₂ , the structural properties, common synthesis strategies, characterization techniques, as well as the contribution of oxygen-deficient TiO₂ on initial Coulombic efficiency, cyclic stability, rate performance for sodium storage are comprehensively described in this review. Finally, some perspectives on the challenge and future opportunities for the development of oxygen-deficient TiO₂ are proposed.