Protonated Forms of Layered Perovskite-Like Titanate NaNdTiO4: Neutron and X-ray Diffraction Structural Analysis

Abstract

Structures of partially and completely protonated Ruddlesden–Popper phases, H0.7Na0.3NdTiO4·0.3H2O and HNdTiO4, have been established by means of neutron and X-ray diffraction analysis and compared among themselves as well as with that of the initial titanate NaNdTiO4. It was shown that while interlayer sodium cations in the partially protonated form are coordinated by nine oxygen atoms, including one related to intercalated water, in the fully protonated compound the ninth oxygen proves to be an axial anion belonging to the opposite slab of titanium-oxygen octahedra. Moreover, the partially protonated titanate was found to significantly differ from the other two in the octahedron distortion pattern. It is characterized by a weakly pronounced elongation of the octahedra towards the Nd-containing interlayer space making Ti4+ cations practically equidistant from both axial oxygen atoms, which is accompanied by a low-frequency shift of the bands relating to the asymmetric stretching mode of axial Ti–O bonds observed in the Raman spectra.

Synthesis and Characterization of Inorganic-Organic Derivatives of Layered Perovskite-like Niobate HSr2Nb3O10 with n-Amines and n-Alcohols

“…Perovskite-like oxides with a layered structure have been intensively studied both experimentally and theoretically due to the unique physicochemical properties exhibited by individual representatives of this class of compounds, such as high catalytic and photocatalytic activity [ 1 ], high-temperature superconductivity [ 2 ], and colossal magnetoresistance [ 3 ]. Most layered perovskite-like oxides capable of ion-exchange reactions [ 4 ] can be transformed into their protonated forms [ 5 , 6 ], which, on the one hand, are proton conductors [ 7 , 8 ] and photocatalysts for water splitting [ 1 , 9 ] and, on the other hand, exhibit the ability to intercalate water [ 10 , 11 ] and other molecules [ 12 , 13 ], give derivatives with grafted organic modifiers [ 14 , 15 , 16 , 17 ], and undergo exfoliation into nanolayers [ 18 , 19 ]. Materials based on layered oxides are promising objects for use as high-temperature ion conductors in fuel cells [ 20 ], catalysts in industrial reactions [ 21 ], as well as in devices for water and air purification [ 22 , 23 ], microelectronics [ 24 ], and photovoltaics [ 25 ].…”

Photocatalytic Hydrogen Production from Aqueous Solutions of Glucose and Xylose over Layered Perovskite-like Oxides HCa2Nb3O10, H2La2Ti3O10 and Their Inorganic-Organic Derivatives

“…[ 30 , 31 , 32 ]. Outstanding photocatalytic properties of these oxides and their protonated forms (A′ = H) appear to be due to the unique structure of the perovskite octahedron BO 6 , providing efficient separation of photogenerated charge carriers, and active involvement of the interlayer space in intercalation and ion exchange reactions [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ], including probable penetration of reactant molecules into this zone during photocatalytic processes [ 43 , 44 ]. The main approaches to the further improvement of layered perovskites’ photocatalytic performance are known to be partial ionic substitution (doping) in the perovskite octahedra [ 45 , 46 , 47 , 48 , 49 ], preparation of composites with solid cocatalysts and photosensitizers [ 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ], creation of Z-schemes [ 58 , 59 , 60 , 61 , 62 ], sensitization with organic dyes [ 63 ], as well as exfoliation into separate nanolayers [ 64 ].…”