Vanadium-based
materials have been extensively studied as promising
cathode materials for zinc-ion batteries because of their multiple
valences and adjustable ion-diffusion channels. However, the sluggish
kinetics of Zn-ion intercalation and less stable layered structure
remain bottlenecks that limit their further development. The present
work introduces potassium ions to partially substitute ammonium ions
in ammonium vanadate, leading to a subtle shrinkage of lattice distance
and the increased oxygen vacancies. The resulting potassium ammonium
vanadate exhibits a high discharge capacity (464 mAh g–1 at 0.1 A g–1) and excellent cycling stability
(90% retention over 3000 cycles at 5 A g–1). The
excellent electrochemical properties and battery performances are
attributed to the rich oxygen vacancies. The introduction of K+ to partially replace NH4
+ appears to alleviate the irreversible deammoniation
to prevent structural collapse during ion insertion/extraction. Density
functional theory calculations show that potassium ammonium vanadate
has a modulated electron structure and a better zinc-ion diffusion
path with a lower migration barrier.
This paper reports on an approach for separating vanillin and syringaldehyde (VSA) from oxygen delignification spent liquor using non-polar macroporous resin. The effects of temperature and pH on the adsorption isotherms were studied. The adsorption capacity and adsorption equilibrium constant were obtained using the Langmuir adsorption model at pH<4.5, where the ionization of the VSA to ionic forms was negligible. The standard enthalpy change was calculated using the van't Hoff equation and clearly showed that the adsorption is an exothermic process. The effect of pH on the adsorption isotherm is well-described by a modified Langmuir model and shows that the adsorption equilibrium constant decreases significantly with the increasing pH. The VSA adsorbed on macroporous resin was eluted by ethyl ether. The separated VSA contained 37.51% vanillin, 31.88% syringaldehyde. The recoveries of VSA were 96.2 and 94.7%, respectively.
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