A novel technique of reducing nanotube clustering for enhanced hydrogen evolution: Two-fold precursor mixing and P-doping synergy of carbon nitride nanotubes

This study proposes a novel two-fold precursor mixing and phosphorus (P) doping synergistical technique of synthesizing g-C₃N₄ nanotubes with enhanced hydrogen evolution via nanotube clustering reduction. The structural, morphological, and photocatalytic properties of nanotubes produced using this technique is investigated. Through a comprehensive analysis of morphology using scanning electron microscope (SEM) and transmission electron microscope (TEM), we demonstrate that the synergistical effect of two-fold precursor mixing and P doping effectively reduces nanotube clustering, resulting in distinct, elongated nanotubes with a homogenous distribution of P (P-C₃N₄-NT). X-ray diffraction (XRD) analyses reveal lattice expansion and shifts in diffraction peaks due to P incorporation. Despite a 26 % reduction in specific surface area (132 m² g⁻¹ for P-C₃N₄-NT vs. 178 m² g⁻¹ for undoped C₃N₄-NT), P-C₃N₄-NT demonstrated superior optical properties with higher absorbance and a narrower band gap (2.88 eV vs. 2.99 eV). A shift in the valence band (0.54 eV) was also observed. P-C₃N₄-NT outperformed C₃N₄-NT with a 67 % increase in H₂ evolution rate (∼1234 µmol h⁻¹ g⁻¹) attributed to improved surface dispersion and reduced clustering. The apparent quantum efficiency (AQE) at 420 nm for P-C₃N₄-NT was ∼1.4 %, which is approximately 2- and 9-fold increase compared to C₃N₄-NT and pristine C₃N₄-P, respectively. X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) analyses confirm the formation of P–N coordination bonds and P–O species, influencing the chemical composition and surface reactivity of the nanotubes. This work underscores the pivotal role of combining two-fold precursor mixing with P doping in boosting the photocatalytic properties of carbon nitride nanotubes via nanotube clustering reduction by modulating surface chemistry, morphology, and electronic structure, leading to significant improvements in hydrogen production efficiency.