Nickel-decorated graphite phase carbon nitride photocatalysts coupled with carbazole-based calixarene dyes for high-efficiency visible light-driven hydrogen evolution

The development of artificial devices that mimic the highly efficient and sophisticated photosystems found in nature is a subject worthy of in-depth study. Two calixarene D-pi-A dyes, C4-CZSTP and C4-CZBTP, containing an N-methylcarbazole group as a secondary auxiliary electron donor, are synthesized on the basis of our previously reported calixarene dye C4-BTP. These dyes are then cooperated with Ni-deposited g-C3N4 to prepare ternary photocatalysts, denoted as C4-CZSTP/Ni/g-C3N4, C4-CZBTP/Ni/g-C3N4 and C4-BTP/Ni/g-C3N4, and their photocatalytic performances are evaluated under visible light irradiation. The optimized 4.0 wt% C4-CZSTP/Ni/gC3N4 sample gives a remarkable H2 evolution rate of 5552 mu mol g-1 h-1, representing one of the highest records among the reported analogous systems based on g-C3N4. And after an extended test of 49 h, a total H2 yield of 63.57 mmol g-1 is obtained, corresponding to a turnover number (TON) based on C4-CZSTP moles (TONC4-CZSTP) of 3180. This performance can be attributed to the enhanced light-harvesting and photoelectron conversion of the as-prepared calixarene dyes, the adjusted energy levels and the effective cooperation of the three components. The optimal performance of C4-CZSTP/Ni/g-C3N4 among the three dye-sensitized systems is due to its higher lowest unoccupied molecular orbital (LUMO) value, i.e. stronger electronic driving force from the excited dye to g-C3N4. This study provides an interesting example for the design and preparation of a low-cost, highefficiency and noble metal-free photocatalytic system for solar fuel production.