Hybrid fabrication and augmented calcination approach for synergistically enhanced surface area and hydrogen storage performance of g-C3N4 nanotubes

The optimal chemical composition for graphitic carbon nitride (g-C 3 N 4 ) nanotubes often requires a higher ratio of cyanuric acid (CA) to melamine (M). This ratio helps in achieving the desired stoichiometry and ensures that the nitrogen content is maximized, which is critical for the electronic and catalytic properties of carbon nitride. This higher ratio of CA could also influence the porosity and surface area of the resulting nanotubes which is important for applications where surface properties are crucial such as catalysis and energy storage. Most often than not, higher surface area nanotubes are mostly achieved using templating techniques which provide a higher degree of control over the shape and size of the nanotubes, allowing for the creation of nanotubes with thin walls and large internal volumes. In this study, we used a combination of a template-free hybrid synthesis technique which involved a two-fold mixing of precursor materials (cyanuric acid and melamine) and a targeted oxidative etching technique involving a two-fold calcination to achieve a high surface area g-C 3 N 4 nanotubes for enhanced hydrogen storage. The validity of this approach was tested on two sets of nanotubes: one with a high molar ratio of M to CA, and the other a high molar ratio of CA to M. Brunauer-Emmett-Teller (BET) analysis revealed g-C 3 N 4 nanotubes with higher mole ratios of CA:M exhibited superior specific surface area, ∼206 m 2 /g and a hydrogen storage capacity of 0.67 wt% under 3.7 MPa of hydrogen charging pressure from pressure composition isotherm (PCI) analysis, in contrast to high molar ratios of M:CA nanotubes with specific surface area and storage capacity of ∼55 m 2 /g and 0.58 wt%, respectively. The addition of targeted oxidative etching involving two-fold calcination to the hybrid synthesis technique resulted in increases in the specific surface area and the hydrogen storage capacities for the two sets of g-C 3 N 4 nanotubes. g-C 3 N 4 nanotubes with a high molar ratio of CA:M recorded a notable specific surface area of 386 m 2 /g and a hydrogen storage capacity of 0.77 wt% which is attributed to increased crystallinity, thinning of nanotube walls and smaller nanotube diameters with the mechanism governed by a combination of oxidative cleavage of C N bonds, recrystallization, and oxidative etching effects. • A novel hybrid synthesis technique was used to fabricate g-C 3 N 4 nanotubes for hydrogen storage. • Higher cyanuric acid to melamine ratio leads to better surface area (206 m 2 /g) and storage capacity (0.67 wt%). • A two-fold calcination improves surface area (386 m 2 /g) and storage capacity (0.77 wt%). • Enhanced surface area and storage capacity linked to smaller nanotube diameters and thinned wall thickness. • Optimized nanotubes show fast kinetics 1.8–2.5 min indicating fast refuelling rates.