Facile solvothermal assisted g-C3N4 post-grafting with aromatic amine dyes for effective photocatalytic hydrogen evolution

Abstract

A facile solvothermal assisted g-C₃N₄ post-grafting technique with aromatic amine dyes via a Schiff base chemical reaction was successfully developed in this study. Based on this strategy, three D–π–A type aromatic amine organic dyes (TPA-CNCHO, PTZ-CNCHO, and CZ-CNCHO) were covalently grafted onto g-C₃N₄. The resulting composite photocatalyst was characterized using TEM, XPS, FT-IR, UV-Vis DRS, PL, and transient photocurrents, which confirmed the feasibility of the modification strategy. The values for the photocatalytic hydrogen production rates obtained for g-C₃N₄/TPA-CNCHO, g-C₃N₄/PTZ-CNCHO, and g-C₃N₄/CZ-CNCHO were 16232.7, 13266.9, and 11822.8 μmol h⁻¹ g⁻¹ respectively. Each of these values is 40, 33, and 29 times higher than that of pure g-C₃N₄, respectively. Among them, g-C₃N₄/TPA-CNCHO exhibited the highest photocatalytic hydrogen-production activity and the highest recycling usage stability. In addition, a possible mechanism for the separation and transfer of photo-induced carriers was obtained based on DFT calculations and experimental results. This further confirmed that covalently post-grafting g-C₃N₄ with organic aromatic amine dyes through a Schiff base reaction was useful and could effectively enhance the photocatalytic hydrogen evolution reaction. This is a general facile solvothermal method because it can be used for the grafting of other types of functional aromatic organic dyes onto g-C₃N₄.