Bottom‐Up Strategy to Enhance Long‐Range Order of Poly(Heptazine Imide) Nanorods for Efficient Photocatalytic CO ₂ Methanation

Poly(heptazine imide) (PHI), one of the crystalline or long-range ordered allotropes of polymeric carbon nitride, is a promising polymeric photocatalyst; however, preparation of highly crystalline PHI remains a challenge. Herein, through a bottom-up strategy involving repair of structural defects and increase of specific surface area of melon precursor, we prepared PHI nanorods with dramatically improved long-range order. The resulting PHI exhibited a shift of product selectivity in CO₂ photoreduction from CO to CH₄ with a high methanation activity in contrast to the pristine PHI with relatively low long-range order. The improvement of long-range order for PHI remarkably enhanced the separation efficiency and transfer kinetics of photogenerated charges as well as the adsorption for *CO intermediate. This study revealed the relationship between the precursor structure and PHI crystal growth in ionothermal synthesis, and also showcased the great potential of highly crystalline PHI in artificial photosynthesis.