The development of processes to tune the properties of materials is essential for the progression of nextgeneration technologies for catalysis, optoelectronics and sustainability including energy harvesting and
conversion. Layered carbon nitrides have also been identified as of significant interest within these fields
of application. However, most carbon nitride materials studied to date have poor crystallinity and
therefore their properties cannot be readily controlled or easily related to their molecular level or
nanoscale structures. Here we report a process for forming a range of crystalline layered carbon nitrides
with polytriazine imide (PTI) structures that can be interconverted by simple ion exchange processes,
permitting the tunability of their optoelectronic and chemical properties. Notable outcomes of our work
are (a) the creation of a crystalline, guest-ion-free PTI compound that (b) can be re-intercalated with
ions or molecules using “soft chemistry” approaches. This includes the intercalation of HCl,
demonstrating a new ambient pressure route to the layered PTI$xHCl material that was previously only
available by a high-pressure-high-temperature route (c). Our work also shows (d) that the intercalantfree (IF-) PTI material spontaneously absorbs up to 10 weight% H2O from the ambient atmosphere and
that this process is reversible, leading to potential applications for membranes and water capture in dry
environment
