Synergistic non-radiative relaxations and carrier dynamics in black g-C3N4 boost photothermal-assisted photocatalytic hydrogen evolution

Against the backdrop of global efforts to develop sustainable hydrogen fuels, semiconductor-based photocatalytic hydrogen production suffers from insufficient light absorption and inefficient charge separation. Rational structural regulation of photocatalysts is thus required to improve hydrogen evolution performance. Herein, laver-derived biochar was synthesized via calcination and ultrasonic-assisted impurity removal, and then co-calcined with urea through high-temperature polymerization to fabricate carbon-doped black g-C 3 N 4 (BCN) with excellent photothermal performance. Upon 100 s of full-spectrum irradiation from a 300 W xenon lamp, BCN-1.0 achieves a surface temperature of 72.4 °C, much higher than the 48.7 °C of pristine yellow g-C 3 N 4 (YCN). Irradiation endows BCN with improved light-harvesting and heat-release capabilities, which promotes non-radiative relaxation, elevates local surface temperature, and yields a photothermally-assisted hydrogen evolution rate of 9.58 mmol g −1 h −1 , 1.5 times that of YCN (6.39 mmol g −1 h −1 ). The reaction rate hits 15.56 mmol g −1 h −1 when the solution temperature is raised to 45.5 °C. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) characterizations verify that structural modulation of g-C 3 N 4 generates abundant defect sites that serve as non-radiative recombination centers. The energy of trapped charge carriers dissipates through phonon scattering and local lattice vibrations, which suppresses fluorescence emission, enhances intramolecular vibration and non-radiative relaxation, drastically increases local surface temperature, and accelerates hydrogen evolution. This work delivers a pioneering investigation on the application potential of black g-C 3 N 4 for photothermal-assisted photocatalytic hydrogen evolution. Download: Download high-res image (225KB) Download: Download full-size image