“…Furthermore, by introducing a ZIF-67-derived Co 3 O 4 @C metal-free co-catalyst onto TiO 2, the same group achieved the significantly enhancement of H 2 evolution rates via photocatalytic water splitting [7]. Another successful approach to TiO 2 modification in order to overcome these limitations was the fabrication of composite heterostructures with carbonbased nanomaterials such as carbon nanotubes (CNTs) [5,8,9], graphene oxide (GO) [10,11], reduced graphene oxide (r-GO) [12][13][14][15], graphitic carbon nitride (g-C 3 N 4 ) [16,17], or more recently with carbon dots (CDs) [18,19]. CDs' structure involves a carbon core consisting mostly of sp 2 carbon domains connected by sp 3 carbon atoms and a large number of functional groups (-OH, -COOH, -NH 2 , etc.)…”