Construction of thiazolo[5,4-d]thiazole based covalent triazine framework/ g-C3N4 heterojunction catalysts for highly efficient photocatalytic H2 evolution

Herein, the covalent triazine framework (CTF) named Tz-TA was synthesized by Schiff base reaction between 4,4 '-(thiazolo[5,4-d]thiazole-2,5-diyl)dibenzaldehyde (TzDA) and terephthalimidamide (TA). The polymer based heterojunctions (PHJs) Tz-TA/g-C3N4-x (x refers to mass percentage of Tz-TA) were constructed by combining gC3N4 and Tz-TA through physical ball milling. Tz-TA/g-C3N4-x catalysts all showed considerably enhanced hydrogen evolution rates (HER) than each of the separate photocatalyst, and among which, Tz-TA/g-C3N4-50 exhibited the highest HER of 5426.28 mu mol g-1h- 1 with a 3 wt% Pt as the co-catalyst under visible light irradiation, which is 4.7 and 2.5 times of g-C3N4 and Tz-TA, respectively. The optoelectronic measurements revealed that the formation of the PHJs enhanced the separation and transport efficiency of photo-generated excitons, and delayed the recombination rates of the electron-hole couples. Coupling with the results from density functional theory (DFT) calculations and free radical analyses, a type II configuration of the PHJs was confirmed, which is accountable for their enhanced photocatalytic hydrogen production (PHP) performance.