  Graphene-based laminates, with ultralong and tortuous nanocapillaries formed
by simply stacking graphene flakes together, have great promises in filtration
and separation. However, the information on liquid water trans-membrane
permeation is lacking, which is the most fundamental problem and of crucial
importance in solution-based mass transport. Here, based on isotope labelling,
we investigate the liquid water transportation through graphene-based
nanocapillaries under no external hydrostatic pressures. Liquid water can
afford an unimpeded permeation through graphene-based nanochannels with a
diffusion coefficient 4~5 orders of magnitude larger than through
sub-micrometer-sized polymeric channels. When dissolving ions in sources, the
diffusion coefficient of ions through graphene channels lies in the same order
of magnitude as water, while the ion diffusion is faster than water, indicating
that the ions are mainly transported by fast water flows and the delicate
interactions between ions and nanocapillary walls also take effect in the
accelerated ion transportation.
