Mechanisms for adsorption of methyl viologen on cds quantum dots

Mark D. Peterson, Stephen C. Jensen, David J. Weinberg, Emily A. Weiss

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

This paper describes the surface composition-dependent binding of the dichloride salt of methyl viologen (MV2+) to CdS quantum dots (QDs) enriched, to various degrees, with either Cd or S at the surface. The degree of enrichment is controlled synthetically and by postsynthetic dilution of the QDs in their solvent, THF. NMR shows the Cd-enriched QDs to contain a relatively dense (2.8 ligands/nm2) surface layer of oleic acid, in the form of Cd-oleate, and S-enriched QDs to contain relatively sparse (1.0 ligands/nm 2) surface density of native ligands containing both oleic acid and octadecene. Electron transfer-mediated photoluminescence quenching of the QDs by MV2+ serves as a probe for the binding affinity of MV2+ for the surfaces of the QDs. Diluting Cd-enriched QDs removes Cd-oleate from the surface, exposing the stoichiometric CdS surface beneath and increasing the quenching efficiency of MV2+, whereas diluting S-enriched QD does not change their surface chemistry or the efficiency with which they are quenched by MV2+. The photoluminescence quenching data for all of the surface chemistries we studied fit well to a Langmuir model that accounts for binding of MV2+ through two reaction mechanisms: (i) direct adsorption of MV2+ to exposed stoichiometric CdS surfaces (with an equilibrium adsorption constant of 1.5 × 105 M-1), and (ii) adsorption of MV2+ to stoichiometric CdS surfaces upon displacement of weakly bound Cd-oleate complexes (with an equilibrium displacement constant of 3.5 × 103 M-1). Ab initio calculations of the binding energy for adsorption of the dichloride salt of MV2+ on Cd- and S-terminated surfaces reveal a substantial preference of MV2+ for S-terminated lattices due to alignment of the positively charged nitrogens on MV2+ with the negatively charged sulfur. These findings suggest a strategy to maximize the adsorption of redox-active molecules in electron transfer-active geometries through synthetic and postsynthetic manipulation of the inorganic surface.

Original languageEnglish
Pages (from-to)2826-2837
Number of pages12
JournalACS nano
Volume8
Issue number3
DOIs
Publication statusPublished - Mar 25 2014

Keywords

  • Langmuir isotherm
  • cadmium oleate complex
  • cadmium sulfide nanocrystal
  • electron transfer
  • enrichment
  • photoluminescence quenching

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

Fingerprint Dive into the research topics of 'Mechanisms for adsorption of methyl viologen on cds quantum dots'. Together they form a unique fingerprint.

  • Cite this