Zeolitic imidazolate framework-8 (ZIF-8) has emerged as a promising adsorbent for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions due to its high surface area, tunable porosity, and excellent chemical stability. This study investigates the feasibility, adsorption capacity, and underlying mechanisms of Cr(VI) removal using ZIF-8 synthesized via an ultrasonic-assisted method. The synthesis involved zinc nitrate hexahydrate, 2-methylimidazole, and ammonium hydroxide, resulting in particles with a distinct rhombic dodecahedral morphology and high crystallinity confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed uniform particle sizes ranging from 1.8 to 2.2 µm, while nitrogen adsorption-desorption analysis indicated a BET surface area of 1373 m²/g and a total pore volume of 0.7 cm³/g, confirming the presence of a microporous structure.
Batch adsorption experiments demonstrated that ZIF-8 exhibited a maximum adsorption capacity (AC) of 30.3 mg Cr(VI)/g under neutral conditions (50 mg/L initial concentration), which increased to 34.3 mg/g at pH 5. However, the AC dropped significantly to below 13.7 mg/g at pH values between 7 and 11, indicating strong pH dependence. This behavior is attributed to competitive adsorption between chromate ions (CrO₄²⁻) and hydroxide ions (OH⁻) for active sites on the ZIF-8 surface. At higher pH, the abundance of OH⁻ ions suppresses Cr(VI) uptake, reducing the effective adsorption capacity. Additionally, X-ray photoelectron spectroscopy (XPS) analysis confirmed that a portion of the adsorbed Cr(VI) was reduced to Cr(III), suggesting that ZIF-8 acts not only as an adsorbent but also as a reducing agent through electron transfer from nitrogen-containing functional groups in the 2-methylimidazole ligands.
Kinetic studies showed that the pseudo-second-order model best fitted the experimental data (R² > 0.94), indicating that chemisorption is the rate-limiting step in the adsorption process. Langmuir isotherm modeling further supported monolayer adsorption onto homogeneous surfaces, with a maximum theoretical capacity of 45.FABP3 Proteinweb 6 mg/g at 100 mg/L initial concentration.C1QA Antibody In stock The Freundlich model also provided a good fit, suggesting some surface heterogeneity.PMID:35216271 Regeneration experiments revealed that NaCl solution (0.1 M) effectively desorbed Cr(VI), achieving a desorption efficiency of 92%, while ethanol regeneration restored 64% of the original adsorption capacity, demonstrating the potential for reuse.
In summary, ZIF-8 proves highly effective in removing Cr(VI) from water through combined adsorption and reduction mechanisms. Its performance is optimal under acidic conditions, and it maintains structural integrity across a broad pH range (5–11). These findings highlight ZIF-8’s potential as a sustainable, multifunctional material for treating Cr(VI)-contaminated wastewater, offering both high removal efficiency and reusability.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
