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Investigation of the Kinetics of a Surface Photocatalytic Reaction in Two Dimensions with Surface-enhanced Raman Scattering.

van Schrojenstein Lantman EM, Gijzeman OL, Mank AJ, Weckhuysen BM - ChemCatChem (2014)

Bottom Line: Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface.As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol.A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

View Article: PubMed Central - PubMed

Affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands).

ABSTRACT

Heterogeneous catalysis is a surface phenomenon. Yet, though the catalysis itself takes place on surfaces, the reactants and products rapidly take the form of another physical state, as either a liquid or a gas. Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface. Surface-enhanced Raman spectroscopy is an ideal technique to probe these self-assembled monolayers as it gives molecular information in a measured volume limited to the surface. We show how surface-enhanced Raman spectroscopy can be used to determine the reaction kinetics of a two-dimensional reaction. As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol. A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

No MeSH data available.


a) Time‐dependent SERS measurements (blue–red: low–high signal intensity) of the reaction over time on a sample with a 1 % surface coverage of pNTP. b) The first (top) and last (bottom) spectrum of the time series shown in part a. Spectra were taken at 50 s integration time.
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fig4: a) Time‐dependent SERS measurements (blue–red: low–high signal intensity) of the reaction over time on a sample with a 1 % surface coverage of pNTP. b) The first (top) and last (bottom) spectrum of the time series shown in part a. Spectra were taken at 50 s integration time.

Mentions: Besides describing reactions quantitatively, reaction kinetics in combination with SERS can also be employed to examine other relations. In the case of discrimination between first and second‐order reactions, it is insightful to examine the reaction rate of diluted SAMs. In this particular reaction, we have studied a mixed SAM under exactly the same reaction conditions as those described in Figure 2. The vast difference is in the consistency of the SAM: roughly 1 % of the SAM consists of pNTP, the rest is thiophenol, which acts as a 2 D “solvent”. The reaction rate of a pure first‐order reaction would be independent of the initial reactant concentration [Eq. (1)], whereas a hundredfold dilution is expected to result in a similar decrease in reaction rate [Eq. (3)]. This is exactly the case, as shown in Figure 4. The small quantity of pNTP in the SAM still reveals the SERS signal. The reduced intensity of the reactant peak is likely to owe to some degree of degradation or reorganization of the SERS substrate. This can negatively influence the reaction rate if it is of second (or higher) order, resulting in a lower measured reaction rate. In the case of first‐order reaction kinetics, bleaching will not affect the reaction rate.


Investigation of the Kinetics of a Surface Photocatalytic Reaction in Two Dimensions with Surface-enhanced Raman Scattering.

van Schrojenstein Lantman EM, Gijzeman OL, Mank AJ, Weckhuysen BM - ChemCatChem (2014)

a) Time‐dependent SERS measurements (blue–red: low–high signal intensity) of the reaction over time on a sample with a 1 % surface coverage of pNTP. b) The first (top) and last (bottom) spectrum of the time series shown in part a. Spectra were taken at 50 s integration time.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4834625&req=5

fig4: a) Time‐dependent SERS measurements (blue–red: low–high signal intensity) of the reaction over time on a sample with a 1 % surface coverage of pNTP. b) The first (top) and last (bottom) spectrum of the time series shown in part a. Spectra were taken at 50 s integration time.
Mentions: Besides describing reactions quantitatively, reaction kinetics in combination with SERS can also be employed to examine other relations. In the case of discrimination between first and second‐order reactions, it is insightful to examine the reaction rate of diluted SAMs. In this particular reaction, we have studied a mixed SAM under exactly the same reaction conditions as those described in Figure 2. The vast difference is in the consistency of the SAM: roughly 1 % of the SAM consists of pNTP, the rest is thiophenol, which acts as a 2 D “solvent”. The reaction rate of a pure first‐order reaction would be independent of the initial reactant concentration [Eq. (1)], whereas a hundredfold dilution is expected to result in a similar decrease in reaction rate [Eq. (3)]. This is exactly the case, as shown in Figure 4. The small quantity of pNTP in the SAM still reveals the SERS signal. The reduced intensity of the reactant peak is likely to owe to some degree of degradation or reorganization of the SERS substrate. This can negatively influence the reaction rate if it is of second (or higher) order, resulting in a lower measured reaction rate. In the case of first‐order reaction kinetics, bleaching will not affect the reaction rate.

Bottom Line: Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface.As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol.A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

View Article: PubMed Central - PubMed

Affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands).

ABSTRACT

Heterogeneous catalysis is a surface phenomenon. Yet, though the catalysis itself takes place on surfaces, the reactants and products rapidly take the form of another physical state, as either a liquid or a gas. Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface. Surface-enhanced Raman spectroscopy is an ideal technique to probe these self-assembled monolayers as it gives molecular information in a measured volume limited to the surface. We show how surface-enhanced Raman spectroscopy can be used to determine the reaction kinetics of a two-dimensional reaction. As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol. A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

No MeSH data available.