Organic dye doped graphitic carbon nitride with a tailored electronic structure for enhanced photocatalytic hydrogen production

Molecular doping has been considered as an effective approach to realize novel conjugated polymers with tailored morphology, electronic structure and performance. Inspired by these merits, a facile strategy is presented to address the problems of insufficient charge separation and low photocatalytic performance of graphitic carbon nitride (g-C3N4). We designed and synthesized molecularly doped g-C3N4 polymers using basic fuchsin (BF), a common organic dye, as the dopant. BF-g-C3N4 exhibited an enhanced performance for the photocatalytic hydrogen production with a H2 evolution rate of 1619 μmol g−1 h−1, which was ∼4.4 times higher than that of pure g-C3N4 under visible light irradiation. The mechanisms for the enhanced photocatalytic activity were systematically investigated by the techniques of ultraviolet-visible-near infrared diffuse reflectance spectroscopy (UV-vis-NIR DRS), ultraviolet photoelectron spectroscopy (UPS), photoluminescence (PL) spectroscopy, and time-resolved fluorescence decay spectroscopy as well as density functional theory (DFT) calculations. The results suggested that the BF doping can improve the light absorption and change the electronic structure of g-C3N4 polymers. The doped BF molecules can create extended band tails that act as electron trap states, leading to an enhanced efficiency for the separation and transportation of photoinduced electron–hole pairs. This study not only sheds new light on the modification of semiconductor polymers via the cost-effective molecular doping approach, but will also expand the applicability of polymeric photocatalysts.