A novel study on the adsorption of low concentration Cd(II) and Ni(II) using porous boron nitride: effectiveness, coexisting anion interference, and regeneration

The difficulty of removing low-concentration heavy metals from wastewater and the impact of coexisting anions on adsorption and regeneration performance has been widely recognized. To address this challenge, we synthesized a new adsorbent called porous boron nitride (PBN) and characterized it with X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and nitrogen isothermal adsorption–desorption isotherms. Then, the adsorption kinetics and equilibrium models of PBN for Cd(II) and Ni(II) with a concentration as low as 10 mg/L, along with the impact of anions on adsorption performance and the regeneration of PBN, were investigated. The findings indicated that PBN achieved adsorption equilibrium for Cd(II) and Ni(II) in just 5 min. Furthermore, the adsorption processes fit better with the pseudo-second order kinetic model and the Freundlich isothermal model. Especially, we found that the presence of SO₄²⁻ inhibited the adsorption of Cd(II) and Ni(II), whereas SiO₃²⁻, CO₃²⁻, and PO₄³⁻ promoted adsorption by forming a PBN-anion-metal ternary complex. We determined that the adsorption mechanism involved electrostatic attraction and chemisorption. After regeneration, PBN retained its crystal structure and typical pore distribution, demonstrating excellent adsorption performance for heavy metals.