A new photocatalytic reaction process is described that cyano groups (-CN) are successfully grafted on carbon nitride (g-C3N4 materials). The cyano group substitutes the previous surface terminating amino group (-NH2) on g-C3N4 by a radical reaction pathway, modifying the electron structure of the conjugated covalent system and engendering favorable properties for the visible-light driven photocatalysis. Cyanidated g-C3N4 (g-C3N4-xCN) has a narrowed band gap of 2.29 eV, as compared to 2.73 eV for the pristine g-C3N4, showing expanded visible light absorbance to 590 nm. Moreover, the photo-induced charge-carrier separation is improved as well. In consequence, g-C3N4-xCN exhibits significantly enhanced performance in photocatalysis, here exemplifyed with the model coupling reaction towards alkenyl sulfones under green light (520 nm) irradiation. The methodology reported herein reveals the potential of the carbon nitride scaffold to be modified as such and illustrates the possiblities of the as-created novel carbon nitride materials grafted with various functional groups on their surface.