ZIF-8 as an adsorbent for the removal of Allura Red from aqueous solutions before determination by UV-vis spectrophotometry

Zeolitic imidazolate framework-8 (ZIF-8) is a highly effective metal-organic framework (MOF) that was synthesized and characterized to examine its exceptional adsorption of Allura Red (AR) using UV-Vis spectrophotometry at a wavelength of 504 nm. The highest extraction efficiency (95%) at pH 6, with an equilibrium time of 30 min, using 8 mg of adsorbent for 10 ml of solution containing 2 mg L−1 of Allura Red, was obtained without the addition of salt, with an adsorption capacity of 36.49 mg g−1. A desorption study was performed in the presence of 0.5 mol L−1 ammonia solution for Allura Red. The synthesized ZIF-8 was characterized using several techniques, including X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, Field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) surface area analysis. Significantly, the point of zero charge (pH PZC) for ZIF-8 was found to be 8, emphasizing its efficiency. A variety of isotherm models were employed to evaluate adsorption performance, including the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin models. The equilibrium data indicated that the Langmuir model best described the adsorption process of (AR). For the adsorption kinetics, the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were tested. The results clearly showed that the adsorption followed the pseudo-second-order and intraparticle diffusion models. Additionally, thermodynamic parameters, including Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH), were assessed. The results clearly showed that the adsorption process was both exothermic and spontaneous, further supporting the effectiveness of ZIF-8 in removing pollutants.