Ultrasound-assisted synthesis of rose-like carbon nitride nanoflowers: synergistic morphology and electronic modulation for efficient CO2 photoreduction

Abstract

Photocatalytic CO₂ reduction is vital for addressing climate change, yet conventional catalysts like graphitic carbon nitride (GCN) suffer from limited visible-light absorption and inefficient morphology control. This study introduces ultrasound-assisted synthesis to construct sulfur-doped rose-like carbon nitride (RCN), enabling precise morphology control and enhanced S-doping for superior photocatalytic CO₂-to-CO conversion. RCN was synthesized via the solvothermal polymerization of melamine in ethylene glycol with sulfuric acid, followed by ultrasonication to induce cavitation-driven exfoliation and a 3D hierarchical assembly, followed by calcination at 500 °C. SEM revealed RCN's 3D porous rose-like nanoflower architecture (vs. FCN's dense bulk), with a 3.5-fold higher BET surface area (69.2 m² g⁻¹) and improved S-doping (3.8 at% vs. 1.2 at% in FCN). These structural advantages reduced RCN's bandgap (2.74 eV) and suppressed charge recombination, facilitating a CO production rate of 78.2 μmol h⁻¹ g⁻¹, 15× higher than that of pristine GCN. DFT simulations reveal that S-doping-induced lattice distortion and localized charge enrichment lower energy barriers for COOH* intermediate formation. This work reveals the formation of a macromolecular morphology from the deformation of the carbon nitride molecular plane and the mechanism of efficient photocatalytic CO₂ reduction. It offers a green, scalable strategy for designing efficient solar-driven CO₂ reduction catalysts and advances sustainable energy solutions.