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-C 3 N 4 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-C 3 N 4 -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 m 2 g −1 for P-C 3 N 4 -NT vs. 178 m 2 g −1 for undoped C 3 N 4 -NT), P-C 3 N 4 -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-C 3 N 4 -NT outperformed C 3 N 4 -NT with a 67 % increase in H 2 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-C 3 N 4 -NT was ∼1.4 %, which is approximately 2- and 9-fold increase compared to C 3 N 4 -NT and pristine C 3 N 4 -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.