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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.


Related in: MedlinePlus

a) SERS peak areas for pNTP and product over time, with intermittent illumination; the Raman excitation laser was blocked from the sample between 500 and 1000 s and 1500 and 2000 s. b) The same data as shown in part a but without the dark periods. Spectra were taken with 5 s integration time at 6×103 W cm−2.
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fig3: a) SERS peak areas for pNTP and product over time, with intermittent illumination; the Raman excitation laser was blocked from the sample between 500 and 1000 s and 1500 and 2000 s. b) The same data as shown in part a but without the dark periods. Spectra were taken with 5 s integration time at 6×103 W cm−2.

Mentions: The ratio of product to reactant (Figure 2 c) flattens off at a specific value rather than continuing to infinity. The maximum conversion is dependent on the exact reaction conditions. For example, a much higher conversion is shown in Figure 3. In terms of reaction rate, a factor must be present to set a limit to complete conversion of the full SAM through the forward reaction. Possible contributions are a backward reaction or diffusion processes within the SAM. To test for these contributions to the reaction rate, sample illumination was blocked for significant periods of time. The results of this experiment are shown in Figure 3. It is clear that these dark periods do not have any effect on the peak area of either reactant or product (Figure 3).


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) SERS peak areas for pNTP and product over time, with intermittent illumination; the Raman excitation laser was blocked from the sample between 500 and 1000 s and 1500 and 2000 s. b) The same data as shown in part a but without the dark periods. Spectra were taken with 5 s integration time at 6×103 W cm−2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig3: a) SERS peak areas for pNTP and product over time, with intermittent illumination; the Raman excitation laser was blocked from the sample between 500 and 1000 s and 1500 and 2000 s. b) The same data as shown in part a but without the dark periods. Spectra were taken with 5 s integration time at 6×103 W cm−2.
Mentions: The ratio of product to reactant (Figure 2 c) flattens off at a specific value rather than continuing to infinity. The maximum conversion is dependent on the exact reaction conditions. For example, a much higher conversion is shown in Figure 3. In terms of reaction rate, a factor must be present to set a limit to complete conversion of the full SAM through the forward reaction. Possible contributions are a backward reaction or diffusion processes within the SAM. To test for these contributions to the reaction rate, sample illumination was blocked for significant periods of time. The results of this experiment are shown in Figure 3. It is clear that these dark periods do not have any effect on the peak area of either reactant or product (Figure 3).

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.


Related in: MedlinePlus