Introduction of porous structure via facile carbon-dot modulation: A feasible and promising approach for improving the photocatalytic capability of sulfur doped g-C3N4

•C-dot can serve as pore-forming agent to synthesize porous g-C3N4 without template.•C-dot amount plays a vital role in controlling the properties of the products.•Optimized porous S-C3N4/C-dot composite perform well in antibiotics removal.•Too many or too few C-dot addition would bring in some adverse effects.