Water-soluble carbon nitride as phase-convertible adsorbents for removing heavy metals from water

Current adsorption technologies suffer from inferior interfacial mass transfer and slow reaction rates of heterogeneous adsorbents for water decontamination. By far, it remains challenging to explore a solid material with homogeneous dispersion for reusable applications. Herein, we present a proof-of-concept demonstration of using water-soluble carbon nitride (w-C3N4) as a phase-convertible adsorbent, which will combine the advantages of homogeneous adsorption and heterogeneous separation. The w-C3N4 with various hydrophilic and cyano groups exhibit a high Pb2+ adsorption capacity of 302.3 mg/L, together with fast adsorption kinetics, which is much better than bulk g-C3N4 and activated carbon adsorbents. After the adsorption reaction, the soluble adsorbents can be easily separated from water by increasing the ionic strength of the homogeneous solution, which can be effectively regenerated by diluted acid. The creative integration of homogeneous and heterogeneous processes provides a new avenue for breaking through the limits in host–guest interactions of current adsorption technologies by reversible phase conversion.