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

50 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

Fingerprint

Paraquat
Semiconductor quantum dots
quantum dots
Adsorption
adsorption
Oleic Acid
Quenching
Oleic acid
Ligands
Surface chemistry
oleic acid
dichlorides
quenching
Photoluminescence
Salts
ligands
electron transfer
chemistry
Electrons
salts

Keywords

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

ASJC Scopus subject areas

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

Cite this

Mechanisms for adsorption of methyl viologen on cds quantum dots. / Peterson, Mark D.; Jensen, Stephen C.; Weinberg, David J.; Weiss, Emily A.

In: ACS Nano, Vol. 8, No. 3, 25.03.2014, p. 2826-2837.

Research output: Contribution to journalArticle

Peterson, MD, Jensen, SC, Weinberg, DJ & Weiss, EA 2014, 'Mechanisms for adsorption of methyl viologen on cds quantum dots', ACS Nano, vol. 8, no. 3, pp. 2826-2837. https://doi.org/10.1021/nn406651a
Peterson, Mark D. ; Jensen, Stephen C. ; Weinberg, David J. ; Weiss, Emily A. / Mechanisms for adsorption of methyl viologen on cds quantum dots. In: ACS Nano. 2014 ; Vol. 8, No. 3. pp. 2826-2837.
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AB - 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.

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