Adsorptive removal of losartan, bisphenol A, and triclosan in aqueous solutions using a graphene oxide-enhanced MOF-Zn composite

The increasing prevalence of emerging contaminants in aquatic systems represents a critical challenge to ecological and human health. Compounds such as losartan potassium (LO), bisphenol A (BPA), and triclosan (TN) have been identified as priority pollutants due to their environmental persistence, bioaccumulative behavior, and mechanistic involvement in endocrine disruption and the propagation of antimicrobial resistance. This study reports the synthesis of a zinc-based metal-organic framework functionalized with graphene oxide (MOF-Zn@GO) via a reflux method, using 2-aminoterephthalic acid and graphene oxide, designed for the adsorption of LO, BPA, and TN. The MOF-Zn@GO composite was characterized by XRD, FTIR, Raman, XPS, TGA, BET, and zeta potential analysis. XRD patterns, along with TGA results, confirmed that the crystalline structure remained thermally stable after GO incorporation. FTIR and Raman spectra revealed functional groups (-OH, -COOH) and π-conjugated domains from GO. In addition, XPS analysis showed an increase in the signals associated with C-O and C = O bonds, supporting the incorporation of GO into the MOF-Zn structure. The material exhibited a specific surface area of 329.7 m² g⁻¹ and an average pore size of 2.1 nm. The point of zero charge (pHpzc) was determined to be 6.8, indicating favorable surface properties for contaminant adsorption. Adsorption experiments revealed maximum capacities (Qe) of 395 mg g⁻¹ for LO, 275 mg g⁻¹ for BPA, and 300 mg g⁻¹ for TN, attributed to the synergistic effects of hydrogen bonds and π-π interactions provided by graphene oxide. Quantification of pollutant removal was achieved using high-performance liquid chromatography (HPLC) with UV-Vis detection, confirming the high efficiency and analytical precision of the process. Kinetic studies showed that the adsorption process followed pseudo-second-order kinetics and was best described by the Freundlich isotherm model, indicating multilayer adsorption on a heterogeneous surface. Optimal removal was achieved at pH 4.5 for LO and pH 7.5 for BPA and TN, with an adsorbent dosage of 10 mg, the initial pollutant concentration of 15 mg L⁻¹, and an eluent volume of 600 μL. The excellent performance of the adsorbent was demonstrated by the high removal percentages of LO 99.3%, BPA 90.1%, and TN 97.2%. The MOF-Zn@GO composite maintained over 85% of its initial adsorption efficiency after five regeneration cycles, with negligible loss of active sites and excellent structural stability. These findings underscore the material's potential as a robust and reusable adsorbent for the efficient removal of emerging contaminants from aquatic systems, thus contributing to cleaner water management strategies.