Integration of surfactant-modified graphene oxide with metal-organic framework-9 for enhancing chromium(VI) adsorption from aqueous media

Background: Chromium(VI) is a highly toxic and carcinogenic contaminant that poses significant threats to human health and environmental safety. Its effective elimination from water requires advanced treatment strategies. Methods: In this study, a novel nanocomposite CTAB@GO@ZIF-9 was synthesized by integrating cetyltrimethylammonium bromide (CTAB), graphene oxide (GO), and zeolitic imidazolate framework-9 (ZIF-9) to enhance Cr(VI) removal from aqueous solutions. Characterization confirmed the successful integration of components, along with improved structural uniformity and material dispersion. Response Surface Methodology (RSM) was employed to optimize the effects of adsorbent mass, initial Cr(VI) concentration, and adsorption temperature. Significant findings: CTAB@GO@ZIF-9 demonstrated superior water stability compared to pristine ZIF-9 due to structural reinforcement by CTAB@GO. RSM optimization revealed that all investigated factors significantly influenced Cr(VI) adsorption capacity. Kinetic results followed the pseudo-second-order model (R² = 0.9643), indicating surface-controlled adsorption via active site interactions. Freundlich isotherm (R² = 0.9861) revealed heterogeneous adsorption, and Langmuir modeling showed a maximum capacity of 518.7 mg/g. Thermodynamic results confirmed a spontaneous and endothermic process. XPS and FTIR analyses indicated dominant nitrogen coordination from ZIF-9 and partial Cr(VI) reduction to Cr(III). Electrostatic attraction from CTAB also aided Cr(VI) uptake. These results validate the efficiency of CTAB@GO@ZIF-9 in Cr(VI) removal.