Generally, graphitic carbon nitride (g-C₃N₄) has three-dimensional (3D) bulk form and small specific surface area with limited photocatalytic efficiency. We designed one-dimensional (1D) carbon nitride tubes via supramolecular self-assembly using melamine-cyanuric acid complex and ionic liquid. PMCA showed highly enhanced visible-light- active photocatalytic performance for HER. Morphology transformation from 3D to 1D occurred and phosphorous was doped on C₃N₄ network. These factors induced changes in chemical structures, surface areas, band energies and PL lifetimes which significantly affect HER activity. The morphology change appeared without damaging the basic repeating units, whereas surface area and porosity was advanced relative to bulk material. The up-shifted CB potential of PMCA caused enhancement in hydrogen reduction ability because of P-doping effect. Furthermore, PMCA exhibited 5.5 times improved HER photocatalytic performance and stable during 5 h reaction.