Magnetic Chitosan–Halloysite–Biochar Nanocomposite for Efficient Removal of Ni(II) and Cr(VI) from Groundwater

Author

Hazem K.A. Sarhan


Abstract

 The development of efficient, sustainable, and magnetically recoverable adsorbents has attracted considerable attention for the treatment of heavy metal-contaminated groundwater. In the present study, a magnetic chitosan–halloysite–biochar (MCHB) nanocomposite was successfully synthesized and investigated for the simultaneous removal of Ni(II) and Cr(VI) from contaminated groundwater. The composite was prepared through a facile co-precipitation and cross-linking approach and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX), Brunauer–Emmett–Teller (BET) surface area analysis, and vibrating sample magnetometry (VSM). Characterization results confirmed the successful integration of the composite constituents, the presence of abundant surface functional groups, a porous structure, and sufficient magnetic properties for rapid separation after adsorption.

The effects of solution pH, contact time, adsorbent dosage, initial metal concentration, and temperature were systematically evaluated. The optimum operating conditions were achieved at pH 5.0, an adsorbent dosage of 0.50 g L⁻¹, a contact time of 90 min, an initial metal concentration of 50 mg L⁻¹, and a temperature of 25 °C. Under these conditions, the prepared MCHB nanocomposite exhibited high removal efficiencies toward both Ni(II) and Cr(VI).

Adsorption kinetics followed the pseudo-second-order model (R² = 0.998 for Ni(II) and 0.997 for Cr(VI)), while equilibrium data were best described by the Langmuir isotherm model, yielding maximum adsorption capacities of 96.8 mg g⁻¹ for Ni(II) and 90.4 mg g⁻¹ for Cr(VI). Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic, as demonstrated by negative Gibbs free energy (ΔG°) values and positive enthalpy (ΔH°) values. Comparative evaluation with previously reported adsorbents demonstrated that the developed MCHB nanocomposite provides competitive adsorption performance while offering additional advantages, including low-cost raw materials, environmental compatibility, structural stability, and facile magnetic recovery.

Overall, the prepared magnetic chitosan–halloysite–biochar nanocomposite represents a promising and environmentally sustainable adsorbent for the efficient removal of Ni(II) and Cr(VI) from contaminated groundwater, with significant potential for practical water treatment applications.



Keywords

Magnetic nanocomposite; Chitosan; Halloysite nanotubes; Biochar; Ni(II); Cr(VI); Groundwater treatment; Adsorption.



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References


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