Core-shell structural nitrogen-doped carbon foam loaded with nano zero-valent iron for simultaneous remediation of Cd (II) and NAP in water and soil: Kinetics, mechanism, and environmental evaluation

An economical, efficient, and environmentally friendly technology was developed for simultaneous remediation of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in soil and water. In this study, using pinecones powder as the precursor, the core-shell structural nitrogen-doped carbon foam loaded with nano zero-valent iron (nZVI@NCF) was synthesized through Mannich reaction and high-temperature carbon reduction. The nZVI@NCF was applied as the adsorbent and catalyst to simultaneously remediate the composite pollutants of Cd (II) and naphthalene (NAP). Under the optimal conditions, the adsorption capacity of Cd (II) in water and soil were 13.9 mg·g-1 and 1.97 mg·g-1, respectively, and the adsorption process conformed to the pseudo-second-order kinetic model. The degradation rates of NAP in water (10 mg·L-1) reached almost 100% as well as it could reach 59.12% in soil (10 mg·kg-1). In addition, it was proved that the presence of NAP could compete with Cd (II) for the active sites on the surface of the material to inhibit the adsorption of Cd (II), while the co-existence of Cd (II) could improve the degradation of NAP by the nZVI@NCF/PMS system due to the nZVI-Cd bimetallic effect and the pro-oxidant effect of Cd (II) promoting the generation of ROS. The free radical quenching experiment revealed that the generated ·O2- was the main substance that mediated the redox of nZVI/Fe2+/Fe3+ to oxidative NAP during the degradation process. Furthermore, the results of the phytotoxicity test demonstrated that the nZVI@NCF/PMS system could effectively remediate the soil co-contaminated with Cd (II) and NAP as well as improve the soil environment quality. This research will provide new materials and potential technologies for the efficient treatment of the composite pollutants in the environment.