Enhancement of cadmium removal by oxygen-doped carbon nitride with molybdenum and sulphur hybridization.

Graphitic carbon nitride, as a popular material in the field of environmental remediation, still suffers from unsatisfactory performance for heavy metals adsorption owing to lack of specific adsorption sites. In this study, molybdenum (Mo) and sulphur (S) were simultaneously introduced onto the surface of oxygen-doped graphitic carbon nitride (OCN) for the enhancement of Cd2+ adsorption. The synthesized MOS/OCN-1 exhibited substantially increased maximum adsorption capacity of 293.8 mg/g, calculated from Sips isotherm model, which was 8.7 times higher than that for pristine OCN (33.9 mg/g). The adsorption efficiency of MOS/OCN-1 was >94% even under high concentration of coexisting ions (i.e., Ca2+, Mg2+ and Zn2+). MoO3 and MoS2 on the surface of OCN were proven to interact with Cd2+ by forming CdMoO4 and CdS species. OCN provided a stable matrix with a large surface area making more active sites exposed, which greatly facilitated Mo(IV) oxidation and Cd2+ precipitation. Our findings revealed that as well as the well-known Cd-S interaction, Mo atoms in the hybrid composites also played an important role in Cd2+ removal, which opened up the application possibility of OCN with Mo and S hybridization for in-situ Cd2+ remediation.