Efficiency and mechanism of modified carbon nitride for the co-adsorption of copper and tetracycline from water

Abstract

The escalating contamination of heavy metal ions and antibiotics in the aqueous environment underscores the necessity of developing efficient treatment technologies for their concurrent removal. In this work, a phosphate-modified g-C3N4(PCN) by assembling phytic acid with graphitized carbon nitride was prepared through a hydrothermal reaction. The characterization results reveal that PCN exhibits increased porosity, an enhanced specific surface area, and larger pore volume in comparison to pristine CN. At pH 5.0 and 25 °C, PCN demonstrates remarkable adsorption capacities for Cu (II) (q = 172.3 mg g−1) and tetracycline (TC) (q = 63.1 mg g−1) in a single system, respectively, which correspondingly surpasses those of CN by 7 and 8 times. In systems where Cu (II) and TC coexist, Cu (II) enhances the TC removal rate by acting as a bridge. As Cu(II) concentration increases, TC adsorption efficiency significantly improves. Although common ions in solution influence PCN adsorption, it maintains high efficiency for TC and Cu(II) across various water matrices and in the presence of natural organic matter. Detailed characterization and computational chemical analysis reveal that the enhanced adsorption capacity of PCN is due to increased porosity and the presence of additional functional groups. Surface complexation and adsorption bridging are identified as the key mechanisms for effective Cu(II) and TC adsorption. Additionally, recycling experiments validate its reusability, thereby offering a novel avenue for the removal and recovery of TC and Cu(II) from wastewater.