Photoionization of N,N,N′N′-tetramethylbenzidine in chromium silicoaluminophosphate microporous materials

Abstract

Silicoaluminophosphate (SAPO) microporous materials with Cr incorporated by ion-exchange and by direct synthesis were impregnated with N,N,N′N′-tetramethylbenzidine (TMB) and photoionized with 300 nm light at room temperature. TMB⁺ cation radicals are produced and characterized by electron paramagnetic resonance and diffuse reflectance spectroscopy. The photoyield is negligible for H-SAPO-n materials indicating that the chromium ion serves as an electron acceptor to enhance the yield of photoproduced TMB⁺ cation radical. The photoyield is dependent on the valence, amount and reduction potential of the metal ion and on the pore size of the SAPO material. Chromium SAPO materials are efficient hosts for the formation and stabilization of TMB⁺ cation radicals.