Ultrafast Carrier Dynamics in Exfoliated and Functionalized Calcium Niobate Nanosheets in Water and Methanol

We have characterized the initial charge carrier trapping and recombination processes in suspensions of exfoliated calcium niobate nanosheets derived from the Dion Jacobsen phase KCa 2 Nb 3 O 10 . Niobate nanosheets have previously been found to catalyze hydrogen generation in photochemical water-splitting reactions. Photo-generated charge carriers relaxed with second-order kinetics on a sub-nanosecond time scale that depended on the nanosheet size. Methanol was used as a sacrificial electron donor to separate the electron and hole dynamics, and the photo-oxidation dynamics was found to directly compete with electron−hole recombination. Absorption spectra for trapped carriers were determined and used to separately analyze the trapped electron and hole dynamics in [H 1- x Ca 2 Nb 3 O 10 ] x - ( x = 0.15−0.20) sheets in water. Surface modification by 3-amino-propyl(trimethoxy)silane was found to quench trapped carrier absorptions, resulting in an observed optical gain.