The critical role of surface area optimization in carbon quantum dots modified g-C3N4 for photocatalytic enhancement

•The layer distance of g-C3N4 has been opened via carbon quantum dot modification.•Its surface area was enlarged by 3.56 times, enhanced the photocatalytic activity.•A simple and fast hydrothermal process has been proposed and optimized. G-C3N4 has shown great potential in photocatalytic degradation. However, the layered structure of g-C3N4 may prevent the contaminant adhesion in the interlayers, which greatly limited its active surface area for photocatalysis. Herein, a simple and fast hydrothermal process was optimized: with appropriate synthesis temperature, carbon dots dispersed into the interlayer of g-C3N4 without destroying the frame structure, opened the layer distance of g-C3N4, enlarged its surface area by 3.56 times, and enhanced its photoresponse and photoredox capacity significantly. Excellent photocatalytic activities were observed towards organic dyes Rhodamine B (RhB). This work provides a new approach to optimize the layered g-C3N4 via surface area modification, which enhanced the design and fabrication of a g-C3N4-based photocatalyst.