RESUMO
Crystal-to-glass transformation is a powerful approach to modulating the chemical and physical properties of crystals. Here we demonstrate that the glass transformation of cobalt hexacyanoferrate crystals, one of the Prussian blue analogues, increased the concentration of open metal sites and altered the electronic state while maintaining coordination geometries and short-range ordering in the structure. The compositional and structural changes were characterized by X-ray absorption fine structure, energy dispersive X-ray spectroscopy, and X-ray total scattering. The changes contribute to the flat band potential of the glass becoming closer to the redox potential of CO2 reduction. The valence band energy of the glass also shifts, resulting in lower band gap energy. Both the increased open metal sites and the optimal electronic structure upon vitrification enhance photocatalytic activity toward CO2-to-CO conversions (9.9 µmol h-1 CO production) and selectivity (72.4%) in comparison with the crystalline counterpart (3.9 µmol h-1 and 42.8%).
RESUMO
NiFe layered double hydroxides (LDHs) intercalated with dioctyl sulfosuccinate with varied Fe3+/(Ni2+ + Fe3+) ratios (0.04-0.25) were prepared by constant-pH co-precipitation from an aqueous solution of Ni and Fe perchlorates at room temperature. The interlayer dioctyl sulfosuccinate was exchanged with carbonate by the reaction of the product with an aqueous solution of sodium carbonate. The basal spacing of the NiFe-LDHs containing carbonate varied (0.80-0.90 nm) depending on the Fe3+/(Ni2+ + Fe3+) ratio; larger basal spacing was attained from the LDH with smaller Fe3+/(Ni2+ + Fe3+) due to the weaker attractive force between the LDH layer and the interlayer anion, proving that the Fe3+/(Ni2+ + Fe3+) ratios were associated with the layer charge density of NiFe-LDHs.
RESUMO
Bismuth oxyhalides and layered alkali titanates are promising components to design high-performance hybrid photocatalysts. In this work, a hybrid photocatalyst composed of lepidocrocite-type layered cesium titanate (Cs0.7Ti1.77Li0.23O4, CsTLO) and bismuth oxyiodide (BiOI) was designed rationally based on lattice matching. BiOI formed on the layered titanate by ion exchange of CsTLO with Bi cations and subsequent growth of BiOI nanodisks (6 nm in the thickness and 125 nm in the lateral size) in an aqueous solution of cesium iodide, resulting in the hybrid where BiOI nanodisks were lying flat on the layered titanate and exposed the (001) facet predominantly. The present hybrid exhibited efficient photodegradation of methylene blue (4, 10, and 14 times higher than that of CsTLO, Bi-TLO, and BiOI, respectively), which was ascribed to the efficient charge transfer in the bulk and at the interface assisted by the built-in internal electric fields and the high activity of (001) BiOI for direct oxidation of the pollutant.
RESUMO
All-inorganic iodide perovskites were prepared by a mechanochemical reaction between a layered cesium titanate and bismuth (or antimony) triiodide under ambient conditions. The layered cesium titanate was a sacrificial template and also acted as a milling media for the formation of the perovskite nanoparticles with the size of a few nanometres.
RESUMO
Ion exchange of layered alkali titanates (Na2Ti3O7, K2Ti4O9, and Cs2Ti5O11) with several alkali metal halides surprisingly proceeded in the solid-state at room temperature. The reaction was governed by thermodynamic parameters and was completed within a shorter time when the titanates with a smaller particle size were employed. On the other hand, the required time for the ion exchange was shorter in the cases of Cs2Ti5O11 than those of K2Ti4O9 irrespective of the particle size of the titanates, suggesting faster diffusion of the interlayer cation in the titanate with lower layer charge density.
