A novel nuclear spin–lattice relaxation filter for separating the free and absorbed water in a matrix of titanate nanotubes

In complex systems nuclear spin–lattice relaxation (NSLR) often deviates from single-exponential. The existing methods require elaborate analyses to extract the relaxation time (T1). This Letter introduces a novel approach using a standard inversion-recovery pulse segment as a filter for different components and a composite pulse to measure only the decay of the selected component. In a sample of titanate nanotubes embedded in deuterated water, this approach was used to conclusively differentiate between double-exponential and stretched-exponential NSLR. T1 was determined individually for D2O inside nanotubes and outside. It suggested that water fully occupies the inside of nanotubes.