Solvent Etching Process for Graphitic Carbon Nitride Photocatalysts Containing Platinum Cocatalyst: Effects of Water Hydrolysis on Photocatalytic Properties and Hydrogen Evolution Behaviors

Effect of Morphological Modification over g-C3N4 on Photocatalytic Hydrogen Evolution Performance of g-C3N4-Pt Photocatalysts

In this study, the morphological properties of g-C3N4 in g-C3N4-Pt photocatalysts were modified by a simple hydrothermal treatment for photocatalytic hydrogen evolution. In addition, the morphological modification effect of g-C3N4 on the hydrogen evolution performance was investigated. The long-time hydrothermal treatment clearly changed the morphology of g-C3N4 by building extended melem units with more oxygen functional groups at the defect edges of the extended melem units, which was evidenced by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) measurements. The different morphological features of g-C3N4 resulted in lower photoluminescence (PL) emission intensity in PL spectra and a smaller semicircle radius in electrochemical impedance spectroscopy (EIS) data. This indicates the more efficient charge separation of the g-C3N4-Pt photocatalyst with a modified morphology. Consequently, morphologically modified g-C3N4-Pt showed a higher photocatalytic hydrogen evolution rate due to the better charge separation efficiency.

The Growth of Extended Melem Units on g-C3N4 by Hydrothermal Treatment and Its Effect on Photocatalytic Activity of g-C3N4 for Photodegradation of Tetracycline Hydrochloride under Visible Light Irradiation

In this work, the growth of extended tri-s-triazine units (melem units) on g-C₃N₄ (CN) by hydrothermal treatment and its effect on the photodegradation efficiency of tetracycline hydrochloride (TC) is investigated. The CN-180-x and CN-200-6 samples were prepared using different hydrolysis times and temperatures, and they were characterized by multiple physicochemical techniques. In addition, their photodegradation performance was evaluated under visible light irradiation. Compared to the CN, CN-180-6 possesses remarkable photocatalytic degradation efficiency at 97.17% towards TC removal in an aqueous solution. The high visible-light-induced photo-reactivity of CN-180-6 directly correlates to charge transfer efficiency, numerous structural defects with a high specific surface area (75.0 m² g^-1), and sufficient O-functional groups over g-C₃N₄. However, hydrothermal treatment at a higher temperature or during a longer time additionally induces the growth of extended melem units on the surface of g-C₃N₄, resulting in the inhibition of the charge transfer. In addition, the superoxide radical is proven to be generated from photoexcited reaction and plays a key role in the TC degradation.

Anion-Cation Co-Doped g-C3N4 Porous Nanotubes with Efficient Photocatalytic H2 Evolution Performance

Graphitic C₃N₄-based materials are promising for photocatalytic H₂ evolution applications, but they still suffer from low photocatalytic activity due to the insufficient light absorption, unfavorable structure and fast recombination of photogenerated charge. Herein, a novel anion-cation co-doped g-C₃N₄ porous nanotube is successfully synthesized using a self-assembly impregnation-assisted polymerization method. Ni ions on the surface of the self-assembly nanorod precursor can not only cooperate with H₃P gas from the thermal cracking of NaH₂PO₂ as an anion-cation co-doping source, but, more importantly, suppress the shape-collapsing effect of the etching of H₃P gas due to the strong coordinate bonding of Ni-P, which leads to a Ni and P co-doped g-C₃N₄ porous nanotube (PNCNT). Ni and P co-doping can build a new intermediate state near the conduction band in the bandgap of the PNCNT, and the porous nanotube structure gives it a higher BET surface area and light reflection path, showing a synergistic ability to broaden the visible-light absorption, facilitate photogenerated charge separation and the light-electron excitation rate of g-C₃N₄ and provide more reaction sites for photocatalytic H₂ evolution reaction. Therefore, as expected, the PNCNT exhibits an excellent photocatalytic H₂ evolution rate of 240.91 μmol·g^-1·h^-1, which is 30.5, 3.8 and 27.8 times as that of the pure g-C₃N₄ nanotube (CNT), single Ni-doped g-C₃N₄ nanotube (NCNT) and single P-doped g-C₃N₄ nanotube (PCNT), respectively. Moreover, the PNCNT shows good stability and long-term photocatalytic H₂ production activity, which makes it a promising candidate for practical applications.