Fully Condensed Poly (Triazine Imide) Crystals: Extended π-Conjugation and Structural Defects for Overall Water Splitting.

Conventional polymerization for the synthesis of carbon nitride usually generates amorphous heptazine-based melon with an abundance of undesired structural defects, which function as charge carrier recombination centers to decrease the photocatalytic efficiency. Herein, a fully condensed poly (triazine imide) crystal with extended π-conjugation and deficient structure defects was obtained by conducting the polycondensation in a mild molten salt of LiCl/NaCl. The melting point of the binary LiCl/NaCl system is around 550 °C, which substantially restrain the depolymerization of triazine units and extend the π-conjugation. The optimized polymeric carbon nitride crystal exhibits a high apparent quantum efficiency of 12 % (λ=365 nm) for hydrogen production by one-step excitation overall water splitting, owing to the efficient exciton dissociation and the subsequent fast transfer of charge carriers.

Carbon Vacancies in a Melon Polymeric Matrix Promote Photocatalytic Carbon Dioxide Conversion.

Photosynthetic conversion of CO2 into fuel and chemicals is a promising but challenging technology. The bottleneck of this reaction lies in the activation of CO2 , owing to the chemical inertness of linear CO2 . Herein, we present a defect-engineering methodology to construct CO2 activation sites by implanting carbon vacancies (CVs) in the melon polymer (MP) matrix. Positron annihilation spectroscopy confirmed the location and density of the CVs in the MP skeleton. In situ diffuse reflectance infrared Fourier transform spectroscopy and a DFT study revealed that the CVs can function as active sites for CO2 activation while stabilizing COOH* intermediates, thereby boosting the reaction kinetics. As a result, the modified MP-TAP-CVs displayed a 45-fold improvement in CO2 -to-CO activity over the pristine MP. The apparent quantum efficiency of the MP-TAP-CVs was 4.8 % at 420 nm. This study sheds new light on the design of high-efficiency polymer semiconductors for CO2 conversion.