The replacing and surpassing of some functions of traditional metal-based photocatalysts by low-cost and high-efficiency non-metal semiconductor materials have become a research hotspot in functional materials. In this paper, the ultra-thin nanoporous g-C.sub.3N.sub.4 nanosheets were successfully embedded with highly dispersed S quantum dots (S QDs) by ultrasonic-assisted in-situ growth method, which originates from the disproportionation reaction of sodium thiosulfate. The formation of the composite was proved by XRD, XPS, AFM, TEM and HRTEM and proved that S QDs with a size of 1-3.5 nm were uniformly embedded in the surface of ultra-thin nanoporous g-C.sub.3N.sub.4, in which a tight and uniform 0D/2D heterojunction structure was designed and built. Meanwhile, the photocatalytic mechanism was investigated. It showed that the tight Z-Scheme heterojunction structure formed between S QDs and g-C.sub.3N.sub.4 improved the redox activity as well as the transfer ability of photogenerated electron holes. The system exhibited excellent photocatalytic efficiency that the complete degradation of RhB was achieved within 90 min under visible-light irradiation and revealed high stability. We believe that this research is important for the development of low-cost and efficient non-metal photocatalysts. Graphical abstract