Exploration of the synergistic regulatory mechanism of hydroxide and fluoride modification on the photocatalytic activity of 2D g-C3N4†

Exfoliation and hetero-element doping are common procedures for band gap engineering and enhancing the photocatalytic properties of g-C₃N₄. A novel and facile strategy for simultaneous exfoliation and hetero-element doping is still in high demand. Herein, we prepared hydroxide and fluoride doped ultrathin g-C₃N₄ nanosheets through the single-step solvothermal exfoliation of bulk g-C₃N₄ (BCN) using varying concentrations of ethanol and hydrofluoric acid (HF). The microscopic and spectroscopic analysis confirmed the doping of hydroxide groups and fluoride groups (HO⁻/F⁻ groups) into g-C₃N₄ nanosheets (HF-CNS). The HO⁻ groups are primarily located at the terminal amino groups of the heptazine rings in HF-CNS, while the F⁻ groups are likely incorporated into the g-C₃N₄ lattice by forming C–F bonds. The UV-vis absorption spectra and DFT calculations showed that the electronic band structure, and hence charge carrier recombination, can be tuned by varying the HF amount during the exfoliation process. BET-specific surface area was increased from 18.65 m² g⁻¹ for BCN to 159.87 m² g⁻¹ for HF-CNS. The transient photocurrent increased from 5 μA to 20 μA. HF-CNS significantly improved the photocatalytic degradation of tetracycline, achieving 99% removal in 50 minutes, compared to 20% for BCN. Tetracycline degradation followed pseudo-first-order kinetics, with apparent rate constants (K) increasing from 0.0028 min⁻¹ for BCN to 0.0793 min⁻¹ for HF-CNS, a 30-fold enhancement. The photocatalytic hydrogen evolution for HF-CNS was 11 times higher than that of BCN. The HF-CNS exhibited remarkable stability and reusability, indicating its potential as a promising photocatalyst for green hydrogen production and degradation of organic pollutants.