Constructing bio-templated 3D porous microtubular C-doped g-C₃N₄ with tunable band structure and enhanced charge carrier separation

For the first time, the bio-templated porous microtubular C-doped (BTPMC) g-C₃N₄ with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio-templates and in-situ carbon dopant. Prior to the thermal condensation process, the impregnation strategies (i.e. direct wet and hydrothermal impregnation) of urea on the treated kapok fibre (t-KF) were compared to obtained well-constructed bio-templated porous microtubular C-doped g-C₃N₄. The details on a physicochemical characteristic of the fabricated samples were comprehensively analyze using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), N₂ adsorption-desorption, Thermogravimetric (TGA), and UV-vis spectroscopy. Our finding indicated that the hydrothermal impregnation strategy resulted in well-constructed microtubular structure and more carbon substitution in sp²-hybridized nitrogen atoms of g-C₃N₄ as compared to the direct wet impregnation. Also, compared to pure g-C₃N₄, the fabricated BTPMC g-C₃N₄ exhibited extended photoresponse from the ultraviolet (UV) to visible and near-infrared regions and narrower bandgap. The bandgap easily tuned with the increased t-KF loading in urea precursor which responsible for in-situ carbon doping. Moreover, as compared to pristine g-C₃N₄ dramatic suppression of charge recombination of the BTPMC g-C₃N₄ was confirmed through photoluminescence, photocurrent response, and electrochemical impedance spectroscopy. The resultants BTPMC g-C₃N₄ possesses more stable structure, promoted charge separation, and suitable energy levels of conduction and valence bands for photocatalysis application.