Comparative study of moxifloxacin removal using Ulva, layered double hydroxide, and their green hybrid nanocomposite supported by DFT mechanistic analysis

The removal of pharmaceutical contaminants from water bodies has been a matter of concern in environmental studies. This comparative study investigated the adsorption of Moxifloxacin hydrochloride (MOX) on Magnesium-Zinc (-iron) layered double hydroxide (MZF/LDH) @ Ulva nanocomposites, MZF/LDH, and Ulva spp. macroalgae from water under various conditions, including different contact times, pH values, adsorbent dosages, MOX concentrations, and temperatures. The physicochemical parameters of the statistical monolayer model were used to understand the functional groups of MOX, the active site density of MZF/LDH@ Ulva , and the sorption capacity at saturation. The MZF/LDH@ Ulva nanocomposite, which is a promising covering material with a high maximum monolayer adsorption capacity (Q sat = 215.6 mg/g at 328 K), showed a spontaneous and endothermic process of adsorption during the removal of MOX molecules. The adsorbents were comprehensively characterized using spectroscopic, microscopic, crystallographic, thermal, elemental, and surface area analyses. The maximum adsorption occurred within 60 min at a pH of 9 with an adsorbent dosage of 9 mg/20 mL of moxifloxacin solution. The equilibrium adsorption isotherms were described by the Langmuir isotherm model, with a maximum adsorption capacity of 463.96 mg/g at 25 °C for the nanocomposite. MZF/LDH@ Ulva exhibited effective antibacterial and antifungal activity against Staphylococcus aureus and Candida albicans , respectively, as demonstrated by minimum inhibitory concentrations (1.56 mg/mL and 6.26 mg/mL, respectively), accompanied by a reduction in optical density (OD 600 ), showing measurable inhibition of the growth of microbes at low concentrations. A quantum chemical method combining the PBE0 hybrid functional (Density Functional Theory) with the Conductor-like Polarizable Continuum Model (CPCM) to model solvent effects, complementary DFT/PBE0/CPCM (water) calculations provided molecular-level insights into the adsorption mechanism. Energy decomposition analysis revealed that electrostatic interactions dominate (46-% of total attraction), with measurable dispersion contributions (25–30%), suggesting the physisorption mechanism. The novelty of this work is based on the use of the MZF/LDH@ Ulva green macroalgae green method for pharmaceutical pollutants, which exhibit favorable adsorption kinetics and antimicrobial activity against bacterial and fungal pathogens, suggesting potential applicability in water treatment.