Abstract
Herein, we present a novel bottom-up preparation route for heptazine-based polymers (melon), also known as graphitic carbon nitride. The growth characteristics of isolated 1D melon strings in microporous templates are presented and studied in detail. Removal of the microporous silicate template via etching is accompanied by the self-assembly of a 1D melon to stacked 3D structures. The advantages and limitations of the bottom-up approach are shown by using microporous templates with different pore sizes (ETS-10, ZSM-5, and zeolite Y). In accordance with the molecular size of the heptazine units (0.67 nm), a 1D melon can be deposited in ETS-10 with a pore width of about 0.78 nm, whereas its formation in the smaller 0.47 nm pores of ZSM-5 is sterically impeded. The self-assembly of isolated 1D melon to stacked 3D structures offers a novel experimental perspective to the controversial debate on the polymerization degree in 2D sheets of graphitic carbon nitride as micropore sizes below 1 nm confine the condensation degree of heptazine to isolated 1D strands at a molecular level. The growth characteristics and structural features were investigated by X-ray diffraction, N2 physisorption, scanning transmission electron microscopy/energy-dispersive X-ray analysis, 13C CP-NMR spectroscopy, and attenuated total reflection–infrared spectroscopy.
Highlights
Heptazine-based allotropes of carbon nitride have emerged as a prominent class of materials known as graphitic carbon nitride (g-CN)
We show that the formation of heptazine units in pores smaller than the sizes of the heptazine units, as for example found in ZSM-5 (0.47 nm), is unfeasible for steric reasons and marks the molecular limit for templating g-CNs
The growth characteristics of carbon nitride polymers in microporous templates were investigated for CN/template composites with increasing M/T ratios as described in the Experimental Section
Summary
Heptazine-based allotropes of carbon nitride have emerged as a prominent class of materials known as graphitic carbon nitride (g-CN). The formation of bulk g-CN on the external surface of the ETS-10 crystals is clearly visible by a characteristic yellow coloration of the composites prepared with M/T ratios above 0.6 (Figure S6).
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