Leipeng Ji,Zhisong Liu,Zihao Li,Wenjun Huang,Haomiao Xu,Zan Qu,Naiqiang Yan
The gypsum from flue gas desulfurization or the neutralization (D/N gypsum) process of acid wastewater, is an industrial by-product in nonferrous metal smelters. The S and Ca sources of D/N gypsum have significant application prospects. However, the S(IV) reduction is difficult due to the electronic inactivity of CaSO 4 and the stability of the S-O band. Our experimental results indicated that the start-up temperature of CaSO 4 reduced by CH 4 is 900 ℃. However, adding H 2 S gas with a H 2 S/CaSO 4 (S/Ca) ratio of 0.2, the start-up temperature of CaSO 4 reacted with CH 4 decreases to 650 ℃. With the increase of the S/Ca ratio from 0.04 to 0.2, the yield of CaS increased to 94.97%, and the selectivity toward CO 2 formation increases to 71.67%. In-situ diffuse reflectance Fourier transformations spectroscopy (in-situ DRIFTs) results indicate that adding H 2 S generates the new sulfide groups on the surface of CaSO 4 , resulted from the S(-II) in H 2 S changing the distribution of valence electrons of O and activating O. Moreover, the density functional theory (DFT) calculation results exhibit that the activation energy for the first O dissociation decreases to 2.89 eV in the presence of H 2 S. Furthermore, H 2 S optimized the reaction path of CH 4 and improved the selectivity toward CO 2 formation. Comparing to 1000 ℃ without H 2 S, under 800 ℃ with H 2 S, the consumption of CH 4 reduces to 45%, and the CO 2 selectivity increases to 71.67%. Thus, we have developed a method of CaSO 4 low-temperature reduction and provide a theoretical basis for its application in engineering.
Rechargeable magnesium batteries are a potential selection for large-scale energy storage technologies, but development of cathode materials is the major difficulty at present. Organic polyimides are promising magnesium battery cathodes with the open and amorphous frameworks as well as enhanced charge delocalization. However, only two carbonyls are redox-active out of four for each imide unit, which largely limits the capacity. Herein, a new polyimide containing disulfide bond is fabricated and studied as cathode for rechargeable magnesium batteries. This polyimide shows a high capacity beyond the traditional two-electron principle. A mechanism study demonstrates that carbonyl enolization and disulfide bond break/formation occur in the redox process, leading to formation/break of sulfur-oxygen bond. This sulfur-oxygen bond enhances enolization and electron delocalization, resulting in an improved capacity. Further theoretical computation indicates a charge transfer within this sulfur-oxygen bond. The two-electron reduction state exhibits quite low HOMO and LUMO energy levels, which makes the disulfide bonded polyimide have a higher tendency to accept more electrons and a higher oxidation stability after reduction.
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