Prying Apart Ruddlesden−Popper Phases:  Exfoliation into Sheets and Nanotubes for Assembly of Perovskite Thin Films

Protonated Ruddlesden−Popper tantalates and titanotantalates H2An-1BnO3n+1 (A = Na, Ca, Sr, La; B = Ta, Ti) that have acidic interlayer protons were exfoliated using tetra(n-butyl)ammonium hydroxide (TBA+OH-). H2CaNaTa3O10 forms both single sheets and tubular "scrolls" when reacted to make TBAxH2-xCaNaTa3O10 colloids. In contrast, TBAxH2-xA2Ta2TiO10 and TBAxH2-xALaTi2TaO10 (A = Ca, Sr) form sheets exclusively. The n = 2 tantalate TBAxH2-xSrTa2O7 forms high aspect ratio scrolls, as well as smaller amounts of sheets. In contrast to the analogous tantalates, the Ruddlesden−Popper titanates and titanoniobates have weakly acidic interlayer protons and exfoliate only to a limited extent. TBAxH2-xSrNb2O7 forms sheets exclusively, whereas TBAxH2-xCa2Nb2TiO10 forms both sheets and scrolls. The n = 3 titanate H2La2Ti3O10 exfoliates into sheets using n-butylamine, and Na2La2Ti3O10·xH2O forms sheets when exfoliated with TBA+OH-. When reacted with O-(2-aminopropyl)-O'-(2-methoxyethyl) polypropylene glycol 500, H2La2Ti3O10 exfoliates into monodisperse 20 × 100 nm scrolls. The exfoliated tantalates and titanotantalates can be electrostatically adsorbed to a Si/SiO2/PDDA PDDA = poly(diallyldimethylammonium chloride) surface, forming perovskite monolayers. Above pH 9.5, TBAxH2-xSrLaTi2TaO10 sheets tile to densely cover a Si/SiO2 surface derivatized with 4-aminobutyldimethylmethoxysilane (4-ABDMMS) and two bilayers of poly(sodium styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). The exfoliated titanates and titanoniobates generally do not adhere to polycationic surfaces.