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

Abstract

A layered perovskite-type oxide intercalated with n-butylamine is reported as an efficient photocatalyst for hydrogen production from aqueous solutions of alcohols for the first time. The hybrid photocatalyst H 2 Nd 2 Ti 3 O 10 ×BuNH 2 was synthesized by solid-state ceramic method followed by protonation, intercalation of methylamine and subsequent substitution by n-butylamine. The product was characterized by powder XRD, TGA, STA-MS, DRS, IR, and Raman spectroscopy, CHN analysis, SEM. Intercalation of n-butylamine caused a dramatic increase in photocatalytic activity of H 2 Nd 2 Ti 3 O 10 in the reaction of hydrogen evolution from aqueous solutions of methanol, ethanol, and n-butanol under UV radiation. While the non-intercalated Pt-loaded H 2 Nd 2 Ti 3 O 10 showed a maximum quantum efficiency of only 2% in the 220-340 nm range, the efficiency for hybrid samples reached 23% under the same conditions and after variation of experimental parameters even 52% efficiency was achieved. This effect may be associated with the significant expansion of the interlayer space, which is considered as a separate reaction zone.

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

“…Reactions of HCN 3 ·yH 2 O with n-alkylamines lead to a series of single-phase amine derivatives with greater c parameters because of intercalation of amines into the interlayer space. In general, the c lattice parameter, which is known to correspond to the interlayer distance of the sample Kurnosenko et al, 2019), was found to be proportional to the length of the n-alkylamine chain that consists with earlier reports Jacobson et al, 1986;Tahara and Sugahara, 2003;Kurnosenko et al, 2019;Rodionov et al, 2019). Since all the samples were successfully indexed in the P4/mmm group without doubling of the c lattice parameter, we suppose that intercalation of amines did not cause a relative shift of adjacent perovskite slabs which is absent in the case of the initial protonated niobate HCN 3 ·yH 2 O.…”

“…At the same time, stretching modes of equatorial (490, 580 cm −1 ) and located in central octahedra (765 cm −1 ) Nb-O fragments are seen not to be influenced by the amines introduction into the inorganic matrix. 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.…”

“…Intercalation of amines also results in the shift of the axial Nb-O stretching mode from 965 to 925 cm −1 . Unlike the Ruddlesden-Popper titanates (Rodionov et al, 2019), this band does not undergo noticeable splitting into two new bands indicating that all niobium-oxygen octahedra adjacent to the interlayer space possess equal axial Nb-O distances, i.e., almost all the interlayer protons of the initial niobate are associated with molecules of amines. At the same time, stretching modes of equatorial (490, 580 cm −1 ) and located in central octahedra (765 cm −1 ) Nb-O fragments are seen not to be influenced by the amines introduction into the inorganic matrix.…”

“…Photocatalytic activity of the samples was measured in the reaction of light-driven hydrogen evolution from an aqueous solution of methanol. The photocatalytic equipment, as well as the experimental conditions, were the same as in our previous work (Rodionov et al, 2019).…”

“…The apparent quantum efficiency of hydrogen generation φ was calculated by the formula φ = ω/ω 0 , where ω is the observed hydrogen evolution rate and ω 0 is the theoretical maximum hydrogen evolution rate if we assume that all incident photons with energy greater than bandgap E g are absorbed with generation of electron-hole pairs, which subsequently lead to hydrogen reduction and alcohol oxidation with a 100% yield without recombination and other side-reactions. For the experimental setup used, ω 0 = 7.5 mmol/h was previously determined via the ferrioxalate actinometry technique (Rodionov et al, 2019).…”