Fabrication of hollow nanotubes of g-C3N4: Enhanced photocatalytic tetracycline degradation and hydrogen evolution

A porous hollow nanotube-structured graphitic carbon nitride (g-C3N4), designated NCN-1, was synthesized by tuning the melamine/urea precursor ratio and using a combined grinding–calcination strategy. Its photocatalytic performance for tetracycline (TC) degradation and hydrogen evolution under visible light was systematically evaluated. The unique morphology provides a large specific surface area, abundant active sites, and shortened charge migration paths, significantly enhancing charge separation efficiency. NCN-1 achieved 84.2% TC degradation in 70 min, 2.7 and 5.8 times higher than layered (MCN) and bulk g-C3N4 (UCN), respectively. Radical trapping identified •O2⁻ as the primary reactive species, with h⁺ as a secondary contributor. NCN-1 also exhibited exceptional H2 evolution at 2741.50 μmol·g⁻¹ ·h⁻¹ , outperforming MCN and UCN by 11.0- and 31.4-fold. This superior activity stems from three synergistic effects: (i) hierarchical porous nanotube architecture enabling efficient adsorption and mass transport; (ii) enhanced charge separation, confirmed by higher photocurrent and lower charge transfer resistance; and (iii) a slightly widened bandgap with a more negative conduction band, strengthening the reducing power of photogenerated electrons. This work offers valuable insights into rational morphological engineering of high-performance g-C3N4-based photocatalysts.