Green Photocatalytic Route To Synthesize Cross-Linked Polyacrylamide Flocculant for Flocculation of High Turbid Wastewater

As one of the most important flocculants, polyacrylamide (PAM)-based materials show enhanced capability to purify highly turbid wastewater by prolonging the length of molecular chains and modifying functional groups, which, however, generally involves complex synthetic procedures and expensive functional guests. In this study, exfoliated g-C3N4 colloids (CNCs) were used as sunlight-driven photocatalysts to trigger the radical polymerization of acrylamide (AM) without adding any initiator. More importantly, the CNCs also acted as a cross-linker to prolong the PAM chain, thus promoting the flocculation of turbid water. The CNCs content in the CNCs/PAM hybrid (CNPAM), hybrid dosage, and pH value were optimized. We further studied the effects of stirring speed and time as well as sedimentation time on the flocculation behavior. Under optimal conditions, the CNPAM flocculant could effectively flocculate kaolin suspension with a transmittance of >93%. The fractal dimension analysis indicated floc size increased with the enhancement of the CNC content in the CNPAM flocculant. It was testified that the flocculant had good universality for high turbid water in different concentrations and with the presence of various inorganic salts. This study demonstrates the photocatalysis of CNCs is a green, time-saving, and economical route to prepare crossing-linked CNPAM skeleton and that CNCs are promising efficient flocculants for the purification of high turbid wastewater.