Abstract

Hexagonal boron nitride (hBN)-magnetite (Fe3O4) nanocomposites (hBN-Fe3O4 NCs) were prepared through in situ coprecipitation via the green route usingCallistemon citrinus(CC) and used as adsorbents for the removal of Cr(VI) ions from aqueous solution. The synthesized hBN-Fe3O4 NC was characterized by X-ray diffraction, energy-dispersive X-ray (EDX) spectroscopy and field emission scanning electron microscopy (FE-SEM). The specific surface area was measured using the Brunauer–Emmett–Teller (BET) technique, and magnetic measurements were conducted with a vibrating sample magnetometer (VSM). The functional groups on the surface of hBN-Fe3O4 NC were examined using FTIR spectroscopy. When hBN-Fe3O4 NC was used as an adsorbent for removing Cr(VI) ions from K2Cr2O7 solution, the results showed a very high removal efficiency, almost 100% at low pH. The results showed that removal efficiency decreased with an increase in the pH of the solution. The pseudo-second-order kinetic and Freundlich adsorption isotherm models best fit the data for the adsorption of Cr(VI) on the surface of hBN-Fe3O4 NC. The maximum adsorption capacity was estimated as 208.6 mg/g at 50 °C. Thermodynamic studies showed that the adsorption process was endothermic and spontaneous. Cr(VI) ions adsorbed on the surface of hBN-Fe3O4 NC could be reused at least eight times for adsorptive removal of Cr(VI) with good efficiency. The adsorption mechanism was explored, which indicates that physical adsorption dominates the sorption process, while some contributions from the chemisorption process are also present. A life cycle analysis of the NC production process was also conducted.

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