Photoinduced Charge Separation of N,N,N‘N‘-Tetramethylbenzidine in Chromium Ion-Exchanged Zeolite X at Room Temperature

Abstract

Chromium ion-exchanged zeolite X microporous materials were examined for the photoionization of N,N,N‘N‘-tetramethylbenzidine (TMB) with 320-nm irradiation at room temperature. Photoionization of chromium-containing zeolite X results in the formation of N,N,N‘N‘-tetramethylbenzidine radical cations (TMB+ •), which are characterized by electron spin resonance (ESR) and diffuse reflectance spectroscopy (DRS). ESR studies indicate that Cr(V) acts as an electron acceptor. The photoyield and stability of the photoproduced TMB+ • cation radicals is higher in Cr(V)−X zeolite than in other hosts such as silica gels, zirconium phosphate, mordenite, and silicoaluminophosphates. The study delineates the importance of the size/shape features of the host system on the stability of the photoproduced TMB+ • cation radicals.

Photoinduced Charge Separation of Pyrene in Chromium Containing Silicoaluminophosphate (SAPO-5) Microporous Materials at Room Temperature

“…The bands observed in the UV region in Cr(V) doped Ca 2 PO 4 Cl, vanadates, and phosphates have been assigned to O → Cr 5+ charge transfer bands. − The ESR studies described later also suggest that Cr(V) is present in the calcined samples. Thus, we assign the two optical bands in the UV region to Cr(V) formed by oxidation of Cr(III) during calcination consistent with previous reports from our laboratory. ,, The two bands in the visible region observed near 450 and 620 nm for CrAPSO-5 are typically assigned to d−d transitions of Cr(III) either in an octahedral or in a distorted octahedral environment. These are assigned to 4 A 2g → 4 T 1g and 4 A 2g → 4 T 2g transitions.…”

“…We have earlier observed that Cr containing SAPO-5 and zeolite X show higher yields of methylphenothiazine and N , N , N ‘, N ‘-tetramethylbenzidine cation radical as compared to other transition metal ion containing microporous materials. ,, Thus, it is of interest to study the photoionization of pyrene in Cr containing SAPO-5 materials. The ESR spectra of pyrene-impregnated Cr(III) liquid state ion-exchanged SAPO-5 show a signal at g = 2.003 due to Py +• assigned to pyrene cation radical prior to irradiation.…”

“…have been reported to provide appropriate spatial organization of both donor and acceptor molecules to retard BET reaction. − By incorporating built-in donor/acceptor components, the electronic properties of the host system can be further tuned and BET can be further minimized. Thus, heterogeneous systems such as zeolites and microporous silicoaluminophosphates (SAPO) and mesoporous MCM-41 materials have been found to be promising hosts as compared to homogeneous systems. − …”

Two-step synthesis of agglomeration-free peroxidase-like Co3O4 nanoparticles–carbon nitride nanotube hybrids enabling a high redox activity

“…Our nding is consistent with the previous study on TMB cation-free radicals. 28 These results imply that a Co 3 O 4 NPs-CNNT hybrid in the presence of TMB and H 2 O 2 should show the superior peroxidase-like redox activity because the charge-transfer of TMB cation-free-radicals 29 and the Fenton-based reaction 30…”

Kinetics of oxidation of an organic amine with a Cr(V) salen complex in homogeneous aqueous solution and on the surface of mesoporous silica

“…[16][17][18][19][20] TMB is also an efficient photosensitizer for reductions of various substrates in both solution and micelles. [21][22][23][24] The spectral and electrochemical features of TMB seem well suited to address some of the key factors responsible for the kinetic and mechanistic differences, as well as similarities between homogeneous and heterogeneous electron transfer that we wish to discuss in this work.…”