Reactions of Pyrene Excited States with Oxygen on the Surface of Porous Silica Gel and Similar Surfaces

Ruetten, S. A.; Thomas, J. K.

doi:10.1021/jp983313d

Cited by 26 publications

(47 citation statements)

References 21 publications

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“…In previous studies 22- 24 it was clearly shown that O 2 rapidly quenched excited states on several surfaces. The kinetics were shown to be heterogeneous in nature.…”

Section: O 2 Quenchingmentioning

confidence: 88%

“…Arene singlet excited states were shown to quench efficiently, and at room temperature the decay consisted of a mixture of Eley-Rideal, ER, and Langmuir-Hinschelwood, LH, kinetics. 23, 24 The ER mechanism describes quenching by direct collision of O 2 with the excited arene. The LH mechanism describes quenching by O 2 adsorbed on the surface.…”

Section: O 2 Quenchingmentioning

confidence: 99%

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Effect of SiO2 and zeolite surfaces on the excited triplet state of benzophenone, BT; a spectroscopic and kinetic study

Thomas¹

2004

Photochem Photobiol Sci

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Laser flash photolysis has been used to study the triplet excited state of benzophenone B(T), on various surfaces, SiO(2), zeolites NaY, KY, NaX and KX, and in rigid media at room temperature, polyethylene and polymethylmethacrylate. The studies point to similarities of the spectroscopy and kinetics of B(T) in fluid solution, in a solid matrix (polymers) and on a SiO(2) surface. However, stark differences are observed for B(T) in zeolites where the absorption spectrum mimics that of the protonated ketone, and the reactivities of B(T) with C(6)H(12) and CH(3)OH are an order of magnitude smaller than those in liquid C(6)H(12) and CH(3)OH. Inclusion of ammonia, which blocks acidic sites in the zeolite, produces a triplet spectrum which is similar to that in polar solution. The reactivity of the triplet with ammonia in a zeolite is also comparable to that observed for this reaction in polar solution. These data are discussed in terms of the interaction of benzophenone with acidic sites in the zeolites, and to restrictions placed on the reactants in the zeolite cages. The blocking of the zeolite acidic sites by ammonia produces spectral and kinetic data (reactivity with NH(3)) of the triplet that are comparable to those observed in solution. This is one of the few cases where zeolites inhibit rather than promote reactions of a solute adsorbed in them.

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“…In previous studies 22- 24 it was clearly shown that O 2 rapidly quenched excited states on several surfaces. The kinetics were shown to be heterogeneous in nature.…”

Section: O 2 Quenchingmentioning

confidence: 88%

Section: O 2 Quenchingmentioning

confidence: 99%

Effect of SiO2 and zeolite surfaces on the excited triplet state of benzophenone, BT; a spectroscopic and kinetic study

Thomas¹

2004

Photochem Photobiol Sci

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“…Adsorption on high T a silica gel places pyrene in different less favorable locations on the surface, as indicated by the reduced adsorption efficiency and higher oxygen quenching efficiency. 19 On the high T a silica gel, pyrene resides closer to any active sites which can accept electrons after photoirradiation. The closer proximity to the surface active sites results in a faster return of the photoejected electron to the surface-bound cation, decreasing the cation lifetime and increasing the thermoluminescence yields.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, the O 2 quenching rate constant for pyrene on TiO 2 -SiO 2 is 3.5 × 10 6 Torr Ϫ1 s Ϫ1 , and compares well with that measured previously for pyrene on silica alone. 19 The ready access of O 2 to pyrene militates against any shielding effects of TiO 2 .…”

Section: Co-adsorption Of Pyrenementioning

confidence: 99%

Photoinduced electron transfer at solid surfaces: the TiO2–SiO2 system

Ruetten

Thomas

2003

Photochem Photobiol Sci

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Small particles of TiO2 have been synthesized on porous silica. XRD and spectral measurements place the sizes of the particles at about 50 A. With these small particles the band gap of the semiconductor material is markedly blue shifted with respect to bulk TiO2. This enables the direct excitation of co-adsorbed arenes on the TiO2-SiO2 material. Direct excitation of TiO2 leads to Ti3+, by photoinduced extraction from the SiO2. Direct excitation of pyrene on the material leads to a shortened fluorescence lifetime and lower quantum yield. Meanwhile, the yield of pyrene cation radical increases compared to that on pure SiO2. The production of Ti3+ on the pyrene samples, by direct excitation of the TiO2, leads to a shortened pyrene fluorescence lifetime and decreased quantum yield, the quantum yield decreasing to zero at high enough Ti3+. Removal of Ti3+ by O2 causes the original properties of the pyrene fluorescence to return.

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“…This is a Langmuir-Hinshelwood (LH, ref 17) mechanism, which is observed at room temperature with coadsorbed N,N′-dimethylanaline (DMA) 18 and at sample temperatures below 260 K with added oxygen. 14 The adsorption of pyrene on silica gel is relatively strong, and movement on the surface within the time of photoinduced reactions is limited. 13 For example, it has been shown previously 10c that the movement of coadsorbed ferrocene is responsible for the quenching of the pyrene triplet, indicating that pyrene moves slowly on the SiO 2 surface.…”

Section: Introductionmentioning

confidence: 99%

Photoinduced Reactions of Pyrene with Carbon Tetrachloride on Porous Silica Gel

Ruetten¹

1999

J. Phys. Chem. B

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Polyaromatic compounds such as pyrene are adsorbed to the porous silica gel surfaces, and the photoinduced reactions of these species on these surfaces are studied. The pyrene singlet excited state and triplet state are quenched on the surface with coadsorbed carbon tetrachloride (CCl4). Temperature studies with evacuated samples indicate that quenching occurs by CCl4 adsorbed on the surface and not by bombardment from the gas phase. The dynamic quenching rate constant of the pyrene singlet excited state increases after high-temperature pretreatment of the silica. It is suggested that this results from an increase in the rate of diffusion of carbon tetrachloride on the surface after the high-temperature removal of surface silanol groups. The dynamic quenching rate constant of the singlet excited state increases with the silica gel pore size, and the highest rate constant is observed on the 150 Å silica surface, which has been pretreated at 600 °C. A large pore size (smaller surface area) and a dehydroxylated surface both contribute to the increased dynamic rate constant, which results from increased movement of carbon tetrachloride over the surface. Carbon tetrachloride does not adsorb strongly on the porous silica gel surface, and evacuation of the CCl4−SiO2 sample removes CCl4 from the surface. Desorption occurs only after several minutes of evacuation and is monitored by the pyrene singlet excited state lifetime. The desorption time depends on the pore size and surface silanol group concentration. Photoinduced products are generated on the silica surface after extended UV irradiation of the sample. Product composition is dependent on the reaction conditions, but typically chloropyrene, dichloropyrene, and polychlorinated species are among the products. The overall picture is that for reactions of polyaromatics such as pyrene on SiO2, coadsorbed CCl4 only quenches the pyrene fluorescence via surface diffusion of CCl4. Surface diffusion can be increased by decreasing the surface silanol group concentration from preheating the silica at high temperatures. The photoinduced reaction is electron transfer to give the pyrene cation and electron attachment to CCl4. Subsequent reaction gives rise to chlorinated products of pyrene.

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Reactions of Pyrene Excited States with Oxygen on the Surface of Porous Silica Gel and Similar Surfaces

Cited by 26 publications

References 21 publications

Effect of SiO2 and zeolite surfaces on the excited triplet state of benzophenone, BT; a spectroscopic and kinetic study

Effect of SiO2 and zeolite surfaces on the excited triplet state of benzophenone, BT; a spectroscopic and kinetic study

Photoinduced electron transfer at solid surfaces: the TiO2–SiO2 system

Photoinduced Reactions of Pyrene with Carbon Tetrachloride on Porous Silica Gel

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