Influence of HB2Nb3O10-Based Nanosheet Photocatalysts (B = Ca, Sr) Preparation Method on Hydrogen Production Efficiency

Abstract

Photocatalytic activity of HB2Nb3O10 perovskite nanosheets (B = Ca, Sr) has been systematically investigated in the reactions of hydrogen production, depending on the method of the photocatalyst preparation: using the pristine nanosheets in the parent suspension without reassembly, filtered nanosheets as well as nanosheets restacked by hydrochloric acid. Photocatalytic measurements were organized in such a way as to control a wide range of parameters, including the hydrogen generation rate, quantum efficiency of the reaction, potential dark activity of the sample as well as stability and pH of the reaction suspension. Exfoliation of the niobates into nanosheets allowed obtaining efficient photocatalysts surpassing the initial bulk materials in the activity up to 55 times and providing apparent quantum efficiency up to 20.8% after surface decoration with a Pt cocatalyst. Among the reassembled samples, greater hydrogen evolution activity was exhibited by simply filtered nanosheets that, unlike the HCl-restacked ones, were found to possess much lower specific surface area in a dry state but contain a perceptible amount of tetrabutylammonium cations on the surface. The activity difference, potentially, is associated with the fact that the filtered nanosheets undergo ultrasonic disaggregation before photocatalytic tests much easier than their HCl-restacked counterparts and, thanks to this, have greater active surface in the reaction suspension. In addition, the enhanced activity of the filtered nanosheets may be due to the presence of tetrabutylammonium as an organic modifier on their surface, which is consistent with the high photocatalytic performance of organically modified layered perovskites considered in our previous reports.

Hydrothermally Synthesized ZnCr- and NiCr-Layered Double Hydroxides as Hydrogen Evolution Photocatalysts

“…% aqueous methanol over ZnCr-and NiCr-LDHs are 88 µmol•h −1 •g −1 (φ = 0.013%) and 41 µmol•h −1 •g −1 (φ = 0.0062%), respectively. Undoubtedly, these compounds demonstrate relatively low performance in comparison with the layered oxide photocatalysts tested earlier under the same conditions [98,[102][103][104][105][106][107][108][109]. However, the LDHs under study differ from the aforementioned layered oxides in their intrinsic absorption of visible light, which may make them promising light-sensitive components of composite photocatalysts.…”

“…% aqueous methanol was studied for 5 samples of each LDH with a different crystallite size (Table 2). The experiments were carried out under both ultraviolet irradiation (DRT-125 mercury lamp, 125 W, λ > 220 nm) and purely visible light (LED source, 100 W, λ = 425 nm) in the photocatalytic laboratory setting used in our previous reports [98,[102][103][104][105][106][107][108][109] and described in detail in Information S1. The spectra of the light sources are shown in Figure S4.…”

Highly Efficient Liquid-Phase Exfoliation of Layered Perovskite-like Titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) into Nanosheets

“…Since the UV-vis spectra were recorded without an integrating sphere, the values of optical density observed correspond to the superposition of light scattering and absorption by the dispersed solid phase. Unlike suspensions of bulk non-exfoliated samples [94], those of nanosheets demonstrate practically zero optical density in the visible region (λ > 400 nm), which points to the absence of relatively large particles capable of providing Mie scattering. The ultraviolet range of the spectra used for building calibrations (Figure 2) shows several wide overlapping bands and is individual for n = 1 and n = 3 titanates.…”

“…Physical-chemical exfoliation, combining TBAOH and ultrasonic treatments, has been established to be a powerful technique for producing perovskite nanosheets of the protonated Dion-Jacobson phases. For instance, HB 2 Nb 3 O 10 (B = Ca, Sr) niobates have been used to yield suspensions with nanosheet concentrations 500 and 950 mg/L, respectively, under the exfoliation conditions taken as default in this research [94]. However, this approach proved to be poorly applicable to the protonated Ruddlesden-Popper titanates under consideration, having given relatively low nanosheet yields (c < 5 mg/L, η < 0.5%) (Figure 3b).…”

“…Although there are several reports mentioning the obtainment of their exfoliated forms [83][84][85][86], none of them covers a purposeful preparation of their highly concentrated suspensions, which would be of great interest for catalytic applications. This fact is apparently associated with the relatively lower reactivity of the Ruddlesden-Popper phases towards intercalation reactions, including those with TBAOH, as compared with the Dion-Jacobson ones whose liquid-phase exfoliation has been thoroughly studied [87][88][89][90][91][92][93][94][95][96].…”