Solvent Effects in Ligand Stripping Behavior of Colloidal Nanoparticles

Abstract

Inorganic colloidal nanoparticle (NP) properties can be tuned by stripping stabilizing ligands using a poor solvent. However, the mechanism behind ligand stripping is poorly understood, in part because in situ measurements of ligand stripping are challenging at the nanoscale. Here, we investigate ethanol solvent-mediated oleylamine ligand stripping from magnetite (Fe3O4) NPs in different compositions of ethanol/hexane mixtures using atomistic molecular dynamics (MD) simulations and thermogravimetric analysis (TGA). Our study elucidates a complex interplay of ethanol interactions with system components and indicates the existence of a threshold concentration of ∼34 vol % ethanol, above which ligand stripping saturates. Moreover, hydrogen bonding between ethanol and stripped ligands inhibits subsequent readsorption of the ligands on the NP surface. A proposed modification of the Langmuir isotherm explains the role of the enthalpy of mixing of the ligands and solvents on the ligand stripping mechanism. A good agreement between the MD predictions and TGA measurements of ligand stripping from Fe3O4 NPs validates the simulation observations. Our findings demonstrate that the ligand coverage of NPs can be controlled by using a poor solvent below the threshold concentration and highlight the importance of ligand–solvent interactions that modulate the properties of colloidal NPs. The study also provides an approach for a detailed in silico study of ligand stripping and exchange from colloidal NPs that are crucial for applications of NPs spanning self-assembly, optoelectronics, nanomedicine, and catalysis.

Oriented Linear Self-Assembly of Colloidal Nanocrystals through Regioselective Formation of Hydrogen-Bonded Supramolecular Bridges

“…We suspect that the introduction of PEG into the NC solution induces a dielectric screening effect, which weakens the interaction between OAH ligands and the surface metal atoms of NCs. , This effect can partially strip the OAH ligands from the (100) facets due to their weaker interaction with OAH, whereas the (001) facets remain largely unaffected because of their stronger binding affinity with OAH. Additionally, the desorbed OAH ligands may form hydrogen bonds with PEG, thus hindering their readsorption onto NaYF 4 NCs.…”