Effect of substitution position of carbazole based conjugated polymers on the photocatalytic hydrogen evolution activities of conjugated polymer/g-C3N4 heterojunction catalysts

Abstract

Conjugated polymers/Graphitic carbon nitride (g-C3N4) based heterojunctions have been widely investigated in photocatalytic hydrogen Production (PHP). How to design high-performance conjugated polymers matched with g-C3N4 is the critical issue. Here, two linear D-A type conjugated polymers (BSO-S27 and BSO-S36) were synthesized by Suzuki coupling reaction between dibenzothiophene-5,5-dioxide and N-methylcarbazole units. The substitution sites of N-methylcarbazole are 2,7- positions for BSO-S27 and 3,6- positions for BSO-S36, respectively. The different substitution position leads to that BSO-S27 and BSO-S36 exhibit different optical absorption, energy level, and charge transport ability. Through the composition with g-C3N4 nanosheets (CN), BSO-S27/CN and BSO-S36/CN heterojunctions were formed. PHP results demonstrate that both BSO-S27 and BSO-S27/CN exhibit higher hydrogen evolution rate (HER) than BSO-S36 and BSO-S36/CN photocatalysts (BSO-S27: 1783.5 μmol g−1 h−1; BSO-S36: 1112.5 μmol g−1 h−1; BSO-S27/CN: 23078.2 μmol g−1 h−1; BSO-S36/CN: 15732.6 μmol g−1 h−1). And the hydrogen evolution mechanism of BSO-S27/CN and BSO-S36/CN are discussed deeply. These results demonstrate that regulating substitution position is a feasible method to design high-performance conjugated polymers or polymer heterojunctions as photocatalysts.