Structural Design of Graphitic Carbon-Nitride Photocatalysts for Boosting Hydrogen Production from Water Decomposition

Abstract

Melem-based two-dimensional (2D) conjugated polymer, graphitic carbon nitride (g-C3N4), has been demonstrated to be a promising material for photo-driven water splitting due to its unique electronic band structure and good photochemical stability.1 The search for suitable precursors is an important issue regarding the synthesis of active g-C3N4. Commonly used precursors are nitrogen-rich compounds containing pre-bounded triple or double C-N core structure, such as cyanamide, dicyandiamide, melamine, and urea. 2 g-C3N4 synthesized from urea is active in hydrogen production, which is attributable to the resulting sheet-like structure.3 The 2D carbon nitride polymer offers many technical options to engineer the molecular structure, electronic structure, and texture for promoting the performance of water splitting. Methods that have been applied to modify the carbon-nitride photocatalysts include dye sensitization, copolymerization, hybridization, hard-templating fabrication, loading with cocatalysts (e.g., Pt, RuO2, NiO is effective for hydrogen evolution while PtOx, Co is effective for oxygen evolution), and doping with metal (e.g., Fe, Zn, Cu) or non-metal (e.g., S, B, P, I) atoms.4 The present study develops a novel method to synthesize a melem/g-C3N4 hybrid photocatalyst through temperature-programmed ammonia treatment. This treatment regulates the crystalline phase of g-C3N4 and reproduces melem fragments, which is the building blocks of g-C3N4. The hybridized melem/g-C3N4 structure facilitates separation of photo-generated charges and therefore exhibits excellent performance in hydrogen production from photocatalytic water decomposition. We have evaluated the photocatalytic activities of this melem/g-C3N4 catalyst in an assay of photocatalytic hydrogen evolution from water under visible light irradiation, by using Pt and triethanolamine as the cocatalyst and sacrificial reagent, respectively. The hydrogen evolution quantum yield is unprecedented for photocatalytic reactions using g-C3N4-based catalysts. References X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen, M. Antonietti., Nat. Mater. 8 (2009), 76−82.(a) F. Dong, Y. Sun, L. Wu, M. Fu, Z. Wu., Catal. Sci. Technol. 2 (2012), 1332-1335. (b) J. Liu, T. Zhang, Z. Wang, G. Dawson, W. Chen, J. Master. Chem., 21 (2011), 14398-14401.G. Zhang, Z. A. Lan, L. Lin, S. Lin, X. Wang, Chem. Sci., 10.1039/c5sc04572j .G. Zhang, M. Zhang, X. Ye, X. Qiu, S. Lin, X. Wang, Adv. Mater., 26 (2014), 805-809. Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, 105-3113-E-006-005, and 104-3113-E-006-011-CC2), and by the Ministry of Education, Taiwan, The Aim for the Top University Project to the National Cheng Kung University.