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Functional Engineering of Perovskite Nanosheets: Impact of Lead Substitution on Exfoliation in the Solid Solution RbCa2-xPbxNb3O10

Tuning the chemical composition and structure for targeted functionality in two-dimensional (2D) nanosheets has become a major objective in the rapidly growing area of 2D materials. In the context of photocatalysis, both miniaturization and extending the light absorption of UV active photocatalysts are major assets. Here, we investigate the solid solution between two photocatalytic systems known from literature to evolve H-2 from water/methanol under UV-RbCa2Nb3O10 (E-g = 3.7 eV) -and visible light irradiation - RbPb2Nb3O10 (E-g = 3.0 eV) - by synthesizing hypothetical RbCa2-xPbxNb3O10. While the calcium niobate can easily be exfoliated into individual nanosheets via cation-proton exchange and subsequent treatment with tetra-n-butyl-ammonium hydroxide (TBAOH), the lead niobate barely yields nano-sheets. Spectroscopic and microscopic analysis suggest that this is caused by volatilization of Pb during synthesis, leading to a local 3D linkage of RbPb2Nb3O10 perovskite units with Pb deficient units. On the one hand, this linkage progressively prevents exfoliation along with an increasing Pb content. On the other hand, introducing Pb into the perovskite blocks successively leads to bandgap narrowing, thus gradually enhancing the light harvesting capability of the solid solution. Finding a compromise between this narrowing of the bandgap and the possibility of exfoliation, visible light sensitized nanosheets can be engineered in good yield for an initial molar ratio of Ca:Pb >= 1:1.

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