Exploiting nickel-organic-frameworks in the temperature-controlled synthesis of carbonized nickel nanoparticles for magnetic purification of acidic water

Abstract

This work explores the effect of carbonization temperature (600 °C vs. 1000 °C) on the microstructure, magnetic properties, and adsorption performance of nickel organic framework (NiOF)-derived nanoparticles (NPs) for the remediation of acidic water using Cr(VI) and methylene blue (MB) as typical heavy metal and organic dye,respectively. Carbonizing NiOF at 600 °C resulted in the formation of Ni NPs with both face-centered cubic (FCC) and hexagonal-close-packed (HCP) crystal structures, that were further encapsulated in multilayered graphitic carbon, preventing the oxidation of the Ni NPs. However, carbonizing NiOF at 1000 °C, resulted only in the formation of FCC Ni NPs. After ethanol purification, these NPs showed their ferromagnetic character that allows for a rapid and efficient magnetic recovery. Further purification through double water washing markedly improves adsorption kinetics, achieving equilibrium for Cr(VI) and methylene blue within 5–12 minutes. This enhancement is attributed to greater accessibility of active sites and increased surface functional group density. Adsorption analyses confirm pseudo-first-order kinetics, consistent with a predominantly physical adsorption mechanism, while equilibrium data fit well to Langmuir, Freundlich, and Sips isotherm models. These findings underscore the carbonization temperature as a critical parameter for tailoring the structural, magnetic, and adsorption properties of NiOF-derived NPs, enabling the design of high-performance, magnetically recoverable adsorbents for water purification.