Construction of carbon dots modified hollow g-C3N4 spheres via in situ calcination of cyanamide and glucose for highly enhanced visible light photocatalytic hydrogen evolution

In this work, a series of carbon dots (CDs) modified hollow g-C 3 N 4 spheres (HCNS-C x ) were constructed via a double in situ approach using cyanamide and glucose as precursors, respectively. As HCNS-C x was synthesized by one-step in situ thermal polymerization of two precursors, which could make CDs and g-C 3 N 4 keep tight connection and increase the separation of the photogenerated electron-hole pairs. The average diameter and wall thickness of the HCNS-C x are about 355 nm and 55 nm, respectively. Under the visible light irradiation, the H 2 evolution rate (HER) of HCNS-C 1.0 (2322 μmol g −1 h −1 ) was 19 times that of bulk g-C 3 N 4 (122 μmol g −1 h −1 ) and 1.8 times that of HCNS without CDs modification (1289 μmol g −1 h −1 ), respectively. And its apparent quantum efficiency is 17.93% at 420 nm. The specific surface area, light absorption capacity, and charge carrier mobility of HCNS-C x could be dramatically improved due to the introduction of CDs and hollow structures of g-C 3 N 4 spheres, resulting in a significant improvement of photocatalytic activity. • Carbon dots modified hollow g-C 3 N 4 spheres were constructed via an in situ approach. • The hollow sphere structure could increase the specific surface area and light absorption capacity. • CDs could decrease the recombination of electron-hole pairs significantly. • HER of HCNS–C 1.0 is 19 times higher than that of BCN.