Optoelectronic structure and photocatalytic applications of Na(Bi,La)S2 solid solutions with tunable bandgaps

Amal Ali Abdulallh Baqais, Nina Tymińska, Tangui Le Bahers, Kazuhiro Takanabe

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14 Scopus citations


NaLa1-xBixS2 solid solutions with tunable bandgaps were synthesized, and their optoelectronic structures and photocatalytic performance were investigated via experimental and theoretical approaches. The solid-solution powders with various La/Bi ratios were synthesized with Na2CO3, La2O3 and Bi2O3 as precursors and via sulfurization with flowing CS2 at 800 °C for 2 h. The Vegard’s law behavior of cell parame-ters showed a perfect Bi/La solid solution in the cubic NaLa1-xBixS2 with the associated linear variation of the lattice constants. On the con-trary, the combination of diffuse reflectance UV−Vis spectroscopy with density functional theory (DFT) calculations employing the HSE06 functional reveals a monotonic but non-linear variation of the bandgap of the solid solution. While consistent valence band maxi-mum (VBM) was obtained in NaLa1-xBixS2—consisting mainly of S 3p orbitals—the conduction band minimum (CBM) was contributed by discrete Bi orbitals present at more positive potential than La. As a result, the slight inclusion of Bi caused a drastic shift in the bandgap, and 24% Bi substitution provided an absorption edge closer to that of pure NaBiS2. Systematic DFT calculations on NaLa1-xBixS2 deter-mined the optoelectronic properties for improved photovoltaic and photocatalytic performance with a Bi-rich sample rather than a La-rich counterpart; i.e., there were larger absorption coefficients, smaller effective masses, and larger dielectric constants for Bi-rich samples versus La-rich samples. The NaLa1-xBixS2 particles decorated with Pt nanoparticles show maximum hydrogen evolution performance with x = 0.02-0.06 of Bi samples consistent with the compensating effects between photon absorption capacity and loss of electromotive force with decreasing bandgap.
Original languageEnglish (US)
Pages (from-to)3211-3220
Number of pages10
JournalChemistry of Materials
Issue number9
StatePublished - Apr 3 2019

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Research reported in this work was supported by the King Abdullah University of Science and Technology (KAUST). AB acknowledges Princess Nourah bint Abdulrahman University (PNU) for financial support. NT and TLB acknowledge the PSMN computation center for providing calculation resources.


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