Constructing crystalline needle-mushroom-like/ amorphous nanosheet carbon nitride homojunction by molten salt method for photocatalytic degradation of tetracycline hydrochloride

Constructing homojunction is one of the effective methods to accelerate electron transport and enhance the photocatalytic performance of semiconductors. Here, we combined two carbon nitride, poly triazine imide (PTI) and graphitic carbon nitride (g-C 3 N 4 ), to form homojunction PTI/g-C 3 N 4 photocatalysts by molten salt method, using guanidine hydrochloride and melamine-cyanuric acid supramolecular self-assembled polymer as precursors, respectively, and LiCl–KCl mixture as reaction medium. The photocatalytic degradation rate of tetracycline hydrochloride (TC-HCl) with the prepared homojunction 2.0MG reached up to 68% and was significantly higher than that of the single component. The photocatalyst maintained outstanding stability after five cycles. The excellent performance was derived from the enhanced light absorption, increased specific surface area, efficient charge separation and stable optical performance of PTI/g-C 3 N 4 homojunction. Moreover, the needle-mushroom-like crystalline PTI were loaded on amorphous g-C 3 N 4 nanosheets or inserted between the nanosheets layers, which inhibited nanosheets stacking and was favorable for carrier transmission. The radicals trapping experiment revealed the dominant role of superoxide radicals for TC-HCl degradation. Finally, the possible photocatalytic mechanism of the PTI/g-C 3 N 4 homojunction was proposed. The transfer of photogenerated electrons and holes followed the "type II heterojunction" path between two carbon nitride components, which effectively accelerated carriers transfer and enhanced photocatalytic performance.