Phenomenological Rule from Correlations of Conduction/Valence Band Energies and Bandgap Energies in Semiconductor Photocatalysts: Calcium Bismuthates versus Strontium Bismuthates

A number of calcium bismuthates were synthesized (25 to 50 mol% in Ca) and characterized by XRD, SEM, EDX, XPS and DRS techniques; the latter provided an estimate of the bandgap energies (Ebg=2.41 to 3.29 eV) via Tauc plots for indirect transitions, whereas XPS established the potentials (vs NHE) of...

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Bibliographic Details
Published in:ChemCatChem 2020-03, Vol.12 (6), p.1551-1555
Main Authors: Shtarev, D. S., Ryabchuk, V. K., Rudakova, A. V., Shtareva, A. V., Molokeev, M. S., Kirichenko, E. A., Serpone, N.
Format: Article
Language:English
Subjects:
Alkaline earth metals
bandgap energies
Calcium
calcium bismuthates
Conduction bands
Correlation
Electronegativity
Energy gap
linear correlation of ECB/EVB with Ebg
semiconductor photocatalysts
strontium bismuthates
Valence band
X ray photoelectron spectroscopy
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Summary:A number of calcium bismuthates were synthesized (25 to 50 mol% in Ca) and characterized by XRD, SEM, EDX, XPS and DRS techniques; the latter provided an estimate of the bandgap energies (Ebg=2.41 to 3.29 eV) via Tauc plots for indirect transitions, whereas XPS established the potentials (vs NHE) of their respective valence bands (and thus the conduction bands). Linear correlations existed between EVB/ECB and Ebg that when compared with those of strontium bismuthates (reported earlier) showed that differences in energies at Ebg=0 eV are related to the difference in the absolute electronegativities of Ca and Sr, from which the following empirical phenomenological rule is postulated: replacing one alkaline earth metal in bismuthates by another causes the points of intersection of the linear correlations ECB(Ebg) and EVB(Ebg) to be displaced by an amount equal to twice the difference in absolute electronegativities of these metals. Semiconductor photocatalysts: Plot of CB energies (ECB) and VB energies (EVB) relative to bandgap energies (Ebg) for bismuthates. Solid lines are the linear correlations ECB(Ebg) and EVB(Ebg) for Ca and Sr bismuthates intersecting at a common point at 0 eV. Vertical lines at 3.3 eV and 1.63 eV denote limits of visible light. Such correlations allowed for postulating a phenomenological rule related to absolute electronegativities of the Ca and Sr metals.
ISSN:1867-3880
1867-3899
DOI:10.1002/cctc.201902236