Physicochemical investigation of the enhanced removal of methylene blue from aqueous solution using polydopamine/silver nanoparticles

Abstract

Polydopamine/Ag (PDA/Ag) nanoparticles were synthesized for methylene blue (MB) removal from aqueous solution as a model dye. These particles were prepared in a modified literature procedure in which polydopamine (PDA) nanoparticles were first prepared via the oxidative polymerization of dopamine (DA) under alkaline conditions in the presence of oxygen. Subsequently, nanoparticulate PDA/Ag was accessed from direct reduction of silver precursor [Ag(NH3)2]+ ions by catechol amino groups in the PDA structure to form Ag nanoparticles (AgNPs) fixed on the PDA surface. Confirmation of the formation of the PDA and PDA/Ag nanoparticles, plus characterization of their surface morphologies was achieved. In the MB adsorption studies, the various factors affecting the dye adsorption and thermodynamic parameters were investigated in detail. This adsorption process can be described well by the Langmuir model. In order to gain a deeper molecular insight into this process, we investigated some possible local model structures of PDA/Ag nanoparticles and MB interaction with these structures using density functional theory (DFT) calculations. The results indicated that the adsorption energies (E ads) of MB on the PDA/Ag nanoparticles were higher than the E ads of MB on PDA nanoparticles, which was consistent with the experimental results. Our results provide a significant new finding for the role of Ag nanoparticles in the MB adsorption process on PDA/Ag nanoparticles. Readily accessible nanoparticulate PDA/Ag was shown to be a highly effective adsorbent for MB from aqueous solution and thus has significant potential for applications in wastewater dye removal.