Confined synthesis of g-C3N4 modified porous carbons for efficient removal of Cd ions

Carbon nitride (C3N4) nanosheets have excellent adsorption capacity, environmental friendliness, and high stability for heavy metal removal. However, its application in Cd-polluted soil is difficult as aggregation induces the specific surface area to substantially decrease. In this study, a series of C3N4 nanosheet-modified porous carbons (C3N4/PC-X) were pre -pared by a simple one-step calcination of mixed aerogels with different mass ratios (X) of carboxymethyl cellulose (CMC) and melamine. These were based on the confined effect of the CMC aerogel, whose 3D confined region controls the C3N4 morphology and prevents the aggregation of nanosheets. The resulting C3N4/PC-4 exhibited a porous structure with interpenetrating C3N4 nanosheets and carbon rods. C3N4/PC-4 was characterized by SEM, elemental analysis, XRD, FTIR and XPS, and the existence of C3N4 nanosheets was confirmed. Compared with that of unmodified porous carbons, the adsorption capacity of C3N4/PC-4 for Cd ions increased 3.97 times, up to 273.1 mg/g. The adsorption kinetics and ad-sorption isotherm analyses showed that the adsorption properties were in agreement with the quasi-second-order and Freundlich adsorption models. Moreover, the material had a good passivation effect on the Cd ions in the soil. The confined synthesis of aerogels could be extended to the preparation of other nanostructures.