Macroscopic graphitic carbon nitride monolith for efficient hydrogen production by photocatalytic reforming of glucose under sunlight

Large particulate photocatalysts allow efficient recovery or installation into the substrate, while limiting possible light-catalyst interaction or mass/charge-transfer. In this study, we developed monodisperse organic single-crystal monoliths with controllable dimensions in the range of 10-100 μm. These were prepared on a 10-g scale by a solution-processed molecular cooperative assembly between melamine (M) and trithiocyanuric acid (TCA) and then transformed into the corresponding g-CN (MTCA-CN) by thermal polycondensation. Molecular precursors that are tightly bound in the crystal undergo polycondensation without losing their macroscopic properties depending on the dimensions of MTCA, thereby changing the microstructure, electronic structure, and photocatalytic activity. Such dimensional tunability enables the fulfillment of various catalytic requirements such as particle size, light absorption, charge separation, band edge potential, and mass transfer. As a proof-of-concept, it was shown that MTCA-CN is tailored to have a high rate of evolution of hydrogen (3.19 μmol/h) from glucose via photoreforming under AM1.5G by using MTCA-100 crystals, leading to the formation of g-CN with the more positive highest occupied molecular orbital (HOMO) level. This study highlights the possibility of developing photocatalysts for practical use and obtaining value-added products (VAPs) without losing the photocatalytic activity relevant for wastewater treatment.