Precursor‐Engineering Coupled Microwave Molten‐Salt Strategy Enhances Photocatalytic Hydrogen Evolution Performance of g‐C₃N₄ Nanostructures

Abstract

A precursor‐engineering strategy coupled with a microwave molten‐salt process (PE‐MWMS) is developed to synthesize graphitic carbon nitride (g‐C3N4) with an isotype triazine/heptazine‐based g‐C3N4 heterojunction as a photocatalyst for the hydrogen evolution reaction (HER) under visible light illumination. Four hybrid precursor combinations—thiourea/melamine, thiourea/dicyandiamide, urea/melamine, and urea/dicyandiamide—are used to synthesize g‐C3N4 heterojunctions by the PE‐MWMS process. Control experiments indicate that the precursor components and microwave treatment have a great effect on the HER performance of the g‐C3N4 samples. Samples synthesized with the optimal molar ratios of thiourea/melamine (2:1), thiourea/dicyandiamide (2:1), urea/melamine (3:1), and urea/dicyandiamide (3:1), exhibit the highest HER rates of 3135, 2519, 2844, and 2565 μmol g−1 h−1, respectively. The amounts of heptazine and triazine units in the g‐C3N4 samples can be easily adjusted by changing the ratios of the hybrid precursors and play a decisive role in improving the photocatalytic HER activity. Because of the unique composition and microstructure, the efficient separation of electron–hole pairs, the broadened photo‐absorption edges, and the narrowed band gaps, the as‐obtained triazine/heptazine‐based g‐C3N4 nanostructures exhibit promising activity for HER application.

Activation of Copper Species on Carbon Nitride for Enhanced Activity in the Arylation of Amines

“…Unlike cyanide compounds, dicyandiamide is stable under these conditions and widely used as a precursor for synthesis of carbon nitrides and N-doped carbons. 30,31 The resulting solid was placed in a tubular oven under N2 flow (20 cm 3 min −1 ) and after flushing for 1 h at 373 K the mixture was heated up to 823 K (2.3 K min −1 ramp rate) for 4 h.…”

Construction of a hierarchical ZnIn2S4/C3N4 heterojunction for the enhanced photocatalytic degradation of tetracycline

“…[14][15][16][17][18] Nevertheless, the photocatalytic performance of pristine C 3 N 4 is still unsatisfactory due to its fairly poor active sites, limited utilization of visible light and fast recombination of charge carriers. [19][20][21] Typically, nanostructure engineering and heterojunction design are two effective methods to overcome the above drawbacks currently. Nanostructured photocatalysts can boost photocatalytic efficiency owing to their short diffusion pathways for charge and mass transfer, as well as more exposed active sites.…”

Tremendous boost in the photocatalytic properties of g-C3N4: regulation from polymerization kinetics to crystal structure engineering

“…In addition, microwave treatment can be combined with the molten salt method to prepare g-C 3 N 4 with a uniform DP distribution. Jing et al 56 synthesized a series of triazine/ heptazine-based g-C 3 N 4 heterojunctions by adjusting the proportion of precursors and combining them with the microwave melting salt method, which showed a greatly enhanced photocatalytic H 2 evolution rate under visible light irradiation. The morphology of g-C 3 N 4 was controlled by adjusting the proportion of precursor, and the electron transfer efficiency finally increased.…”