Protonation and Photocatalytic Activity of the Rb₂La₂Ti₃O₁₀ Layered Oxide in the Reaction of Hydrogen Production

Abstract

The Rb 2 La 2 Ti 3 O 10 layered oxide was synthesized by the solid-state method. Three phases with different protonation degrees and intercalated water contents were obtained from the initial compound by the treatment with distilled water and hydrochloric acid. The obtained samples were characterized by powder X-ray diffraction, SEM, X-ray microanalysis, BET, DRS, and TG. It was found that the complete ion exchange of Rb + for H + in the layered oxide Rb 2 La 2 Ti 3 O 10 proceeds through the formation of two metastable intermediate phases with average protonation degrees of 0.5 and 0.75, which successively transform from one to another. Each of these phase transformations is accompanied not only by the contraction of the interlayer distance but also by the displacement of adjacent perovskite layers by 1/2 of the cell parameter which results in the change in the space group. The photocatalytic activity of obtained samples decreases with the increase in the protonation degree, which correlates with the decrease in the intercalated water content.

Study of n-alkylamine Intercalated Layered Perovskite-Like Niobates HCa2Nb3O10 as Photocatalysts for Hydrogen Production From an Aqueous Solution of Methanol

“…Table 2 contains optical bandgap energies E g of the samples calculated from their transformed diffuse reflectance spectra (Supporting Information S3) and corresponding maximum wavelengths λ max of absorbed light. According to the presented data, all the samples mainly absorb the radiation of the nearultraviolet region and intercalation of amines slightly increases the E g value because of the interlayer space expansion (Rodionov et al, 2017). Thus, there is no factor of different amounts of available light that could otherwise explain the difference in observed photocatalytic activity of the samples.…”

“…IR spectra (Supporting Information S2) also confirm the formation of the derivatives and point at the presence of water molecules in the interlayer space (1,625 cm −1 ) that is typical of other amine-modified compounds Kurnosenko et al, 2019;Rodionov et al, 2019) due to formation of strong hydrogen bonds. Processing of the TG curve (Rodionov et al, 2017(Rodionov et al, , 2019 corresponding to the initial protonated niobate (Figure 3) confirmed that HCN 3 ·yH 2 O does not contain residual potassium cations from the alkali precursor KCN 3 and exists in the hydrated form HCN 3 ·1.5H 2 O. Thus, its thermal decomposition proceeds in two steps: deintercalation of the interlayer water (30-70 • C) and topochemical condensation of the inorganic matrix (250-350 • C) with the formation of Ca 2 Nb 3 O 9.5 .…”

“…Therefore, the class of layered materials with a perovskite-like structure including Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) phases has been actively studied. Their structure may be presented as an alteration of perovskite blocks and interlayer cations with the general formulae A'[A n−1 B n O 3n+1 ] (for DJ) and A' 2 [A n−1 B n O 3n+1 ] (for RP) (Machida et al, 2005;Compton et al, 2007;Huang et al, 2011;Chen et al, 2012;Rodionov et al, 2012Rodionov et al, , 2017Sabio et al, 2012;Zvereva and Rodionov, 2013). These compounds are amenable to reactions involving their interlayer space, such as intercalation and ion exchange, which provide their unique photocatalytic properties (Zvereva et al, 2011;Silyukov et al, 2015;Rodionov et al, 2018;Shelyapina et al, 2019).…”

Layered Titanate H2Nd2Ti3O10 Intercalated With n-Butylamine: A New Highly Efficient Hybrid Photocatalyst for Hydrogen Production From Aqueous Solutions of Alcohols

“…The bandgap energy of the butylamine-intercalated titanate (3.58 eV) slightly exceeds that of the initial H 2 Nd 2 Ti 3 O 10 (3.46 eV) as can be seen from the Tauc plot of the Kubelka-Munk function (Figure 7). This is quite expected, because the bandgap usually increases with the increase of the interlayer distance in the absence of additional factors (Rodionov et al, 2017d). It is important, that due to the close values of band gap energy, both catalysts absorb the same peaks in the lamp emission spectrum (Figure 2), and thus there is no factor of different amount of available light, which could otherwise contribute to the difference in observed photocatalytic activity.…”

“…A 2 Ln 2 Ti 3 O 10 (A = Li, Na, K, Rb; Ln = La, Nd, Gd, Sm, Dy, Eu) are layered RP perovskite-type compounds with alkali cations in the interlayer space. These compounds are known to exhibit ion exchange and intercalation properties (Gopalakrishnan and Bhat, 1987;Richard et al, 1994;Rodionov et al, 2017d) and are one of the most extensively studied photocatalytic materials (Takata et al, 1997a,b;Rodionov et al, 2012;Kawashima et al, 2017b). Ni-loaded Rb 2 La 2 Ti 3 O 10 was one of the first highly active photocatalysts for water splitting with a quantum efficiency estimated around 5% (Takata et al, 1997a).…”