Rapid microwave-assisted synthesis of a magnetic biochar@ZIF-67: an efficient nanocomposite-based adsorbent for the dye-contaminated water cleanup

Abstract

In this work, a magnetic waste date seed-derived biochar@zeolitic imidazolate framework-67 (MWDS-B@ZIF-67) was fabricated by the rapid microwave-assisted synthesis method, and used as an efficient nanocomposite-based adsorbent for the adsorptive removal of Tartrazine (TA) and Sunset yellow (SY) dyes from contaminated water. The main feedstock for biochar synthesis was obtained from waste date seeds, which was then decorated with magnetic Fe₃O₄ nanoparticles and ZIF-67 metal–organic frameworks. The as-synthesized adsorbent was fully characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), Brunauer–Emmett–Teller (BET) specific surface area, and Barrett–Joyner–Halenda (BJH) pore size distribution analyses. To investigate and optimize the effects of influential factors like pH (X₁: 2.0–10.0), TA concentration (X₂: 6.0–30.0 mg L⁻¹), SY concentration (X₃: 5.0–25.0 mg L⁻¹), adsorbent mass (X₄: 8.0–40.0 mg), and contact time (X₅: 5.0–25.0 min) on the removal efficiency, the central composite design (CCD)/response surface methodology (RSM)-based analysis of variance (ANOVA) method was applied. The optimum values were achieved as pH 3.0, initial TA and SY dye concentrations of 16 mg L⁻¹ and 12 mg L⁻¹, the adsorbent mass of 20.0 mg, and the contact time of 20.0 min with a removal percentage of 99.06% for TA and 99.54% for SY, respectively. To assess the possible adsorption mechanism of dyes by the adsorbent, different isotherm models were evaluated and the results showed that the adsorption process followed the Langmuir model. According to the Langmuir model, the maximum adsorption capacities of TA and SY were obtained to be 95.91 mg g⁻¹ and 64.87 mg g⁻¹, respectively. Also, the kinetic studies indicated that the adsorption of dyes followed a pseudo-second-order kinetic model. Overall, the results showed that the synthesized adsorbent can be used as a potential candidate for the removal of anionic dye molecules from the contaminated water samples with high efficiency.