Abstract
The development of processes to tune the properties of materials is essential for the progression of next-generation 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 intercalant-free (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 environments.
Highlights
Intercalation compounds are formed when atomic or molecular guest species are inserted between sheets of a layered host lattice.[1,2,3] The process has widespread importance across elds ranging from battery technology and catalysis to ltration membranes and sequestration of molecular species from the atmosphere.[4,5,6] Perhaps the best known host material is graphite, which can be readily and reversibly intercalated with Li+ ions
We note that the nature and degree of occupancy of the halide ion site has a signi cant effect on the Powder X-ray diffraction (PXRD) patterns of polytriazine imide (PTI) materials, because the high-Z intercalant species (ClÀ and BrÀ) dominate the X-ray scattering intensity over the lighter elements (C, N, H) that determine the layered structures.[19]
We further investigated the procedure by exposing IF-PTI to a LiCl : KCl molten salt mixture, and found that the resulting PXRD pattern corresponded exactly with that of crystalline PTI$LiCl, obtained using molten salt synthesis (Fig. 5b)
Summary
Intercalation compounds are formed when atomic or molecular guest species are inserted between sheets of a layered host lattice.[1,2,3] The process has widespread importance across elds ranging from battery technology and catalysis to ltration membranes and sequestration of molecular species from the atmosphere.[4,5,6] Perhaps the best known host material is graphite, which can be readily and reversibly intercalated with Li+ ions.
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