Construction of phosphorus-doped carbon nitride/phosphorus and sulfur co-doped carbon nitride isotype heterojunction and their enhanced photoactivity.

Photocatalysis was one of the most promising techniques for environmental remediation. Exploring photocatalysts with high efficiency, low cost and easy preparation was still an ongoing issue. In this work, phosphorus-doped carbon nitride/phosphorus and sulfur co-doped carbon nitride (P-CN/PS-CN) isotype heterojunction was prepared by a two-step calcination method. The composite displayed a sheet-like structure with a surface area of 23 m/g. Compared with pure CN, band gaps of P-CN and PS-CN were only slightly modified during the heteroatom-doping process. Therefore, a well-matched band alignment was constructed, which not only improved the separation efficiency of photogenerated electron-hole pairs, but also well preserved the high oxidizability of holes on valance band and good reducibility of electrons on conduction band. Because of the similarity in physicochemical properties, the interface resistance between P-CN and PS-CN was low, which accelerated the electron transfer and prolonged the lifetime of charge carriers. Although the visible-light utilization was somewhat low in comparison with P-CN and PS-CN, by taking advantage of above merits, P-CN/PS-CN displayed the high photocatalytic activity in rhodamine B degradation, and the reaction rate constant was 0.183 min, about 8.7 and 4.0 times higher than those of P-CN and PS-CN. Besides high catalytic activity, isotype heterojunction displayed good recyclability, since 95.3% of catalytic activity was maintained after the 5 cycle. The method presented here was facile, economic and environmentally benign, thus it was highly attractive for the application in environmental remediation.