Facile synthesis of Zn-Mn bimetallic MOF for adsorptive removal of methyl paraben from aqueous solution

Abstract A zinc-manganese bimetallic metal-organic framework (Zn-Mn MOF) was synthesised using room temperature, and its adsorption performance was evaluated against methyl paraben (MePr), an emerging endocrine-disrupting compound. The adsorbent exhibited high removal efficiencies for MePr, corresponding to the synergistic effect of Zn and Mn, and its high specific surface area (SSA) of 1657.2 m 2 /g. The synthesised MOF was characterised using FTIR, Raman spectroscopy, XRD, FE-SEM, and BET analyses, which revealed the development of a microporous framework with a hexagonal morphology and high SSA. FTIR verified incorporation of the 2-methylimidazole linker, while XRD showed sharp ZIF-8-type reflections with slight shifts attributable to Mn incorporation; XPS further confirmed the chemical states of the metal centres within the framework. To conduct adsorption batch studies, pH, adsorbent dosage, concentration, contact time, and temperature were chosen as variables. The kinetic analysis estimated that the adsorption followed pseudo-second order kinetics with R 2 > 0.99. The adsorption isotherm studies were defined by the Langmuir model, achieving a maximum adsorption capacity of 52.38 mg/g. The adsorption thermodynamics confirmed that the process is spontaneous and exothermic. Key mechanisms include hydrogen bonding with N/O sites, π-π stacking through imidazole linkers, and electrostatic interactions from Zn-Mn centres. The removal performance of methyl paraben was evaluated by spiking it into various real-world water matrices under diverse water quality conditions. Reusability studies further confirmed the effective performance of the prepared adsorbent in multiple cycles of operation. The results established that Zn-Mn MOF can be an efficient adsorbent for emerging organic contaminants.