Robust route to highly porous graphitic carbon nitride microtubes with preferred adsorption ability via rational design of one-dimension supramolecular precursors for efficient photocatalytic CO₂ conversion

The ability to create well-ordered graphitic carbon nitride (g-C₃N₄) assemblies with good surface adsorption for CO₂ represents an important endeavor towards achieving high photocatalytic CO₂ reduction activity that yet remains a significant challenge. Herein, a simple yet robust double-solvent-induced self-assembly strategy is, for the first time, developed to yield supramolecular precursors using a single monomer for crafting one-dimensional (1D), highly porous g-C₃N₄ microtubes that possess remarkable photocatalytic CO₂ conversion performance. Intriguingly, the introduction of water and isopropanol triggers the self-assembly of dicyandiamide under hydrothermal conditions to form a melamine-cyanaurate-like complex (MCC) composed of 1D hexagon-shaped, micron-sized crystals with outstanding thermal stability. Subsequent thermal pyrolysis converts these pillar-like crystals into 1D mesoporous g-C₃N₄ microtubes (denoted MCNM) comprising well-packed nano-leaf-like frameworks (i.e., hierarchical structure). Such unique microtubes are oxygen-doped g-C₃N₄ and mechanically stable, exhibiting improved visible-light harvesting ability, enhanced charge transfer, increased active sites, and preferred adsorption and activation for CO₂, as revealed by a suite of characterization techniques. Consequently, in sharp contrast to bulk g-C₃N₄, the MCNM manifests a markedly improved photocatalytic activity with a CO evolution rate of 45.16 μmolh⁻¹, reflecting an 11.0-fold enhancement and an apparent quantum efficiency of 2.55% at 420 nm. As such, the double-solvent-induced self-assembly may stand out an effective route to organized supramolecular precursors for preparing hierarchically structured g-C₃N₄ for efficient photocatalysis.