Facile synthesis and characterization of poly(levodopa)-modified silica nanocomposites via self-polymerization of levodopa and their adsorption behavior toward Cu2+

In this study, a facile surface functionalization method was applied to synthesize poly-levodopa (PDOPA)-modified silica nanocomposites (denoted as SiO2-PDOPA). The adsorption capacity of SiO2-PDOPA was found to be higher than that of unmodified SiO2 NPs. The successful preparation of SiO2-PDOPA was confirmed by Fourier transform infrared spectroscopy, transmission electron microscopy, and thermo gravimetric analysis. The adsorption behavior was investigated using SiO2-PDOPA as adsorbents and Cu2+ as a model heavy metal pollutant. Various adsorption parameters, including contact time, solution pH, temperature, and initial Cu2+ concentrations were studied. The results showed that pH could markedly affect the adsorption process of SiO2-PDOPA to Cu2+. The optimum pH for Cu2+ adsorption was found to be 7.0. The adsorption kinetic data were analyzed using pseudofirst-order, pseudosecond-order, and intraparticle diffusion models. The adsorption isotherms could be described by Langmuir and Freundlich isotherm models. The fitting results showed that the adsorption kinetics and isotherms were better described by the pseudosecond-order and Langmuir model, respectively. The values of thermodynamics constants, including entropy change (ΔS 0 ), enthalpy change (ΔH 0 ), and Gibbs free energy (ΔG 0 ) were determined at different temperatures. Results suggested that the adsorption process of SiO2-PDOPA to Cu2+ is a feasible, endothermic, and spontaneous process.