Kinetics of Photo-Induced Reduction of m-Nitroacetophenone with TiO₂ Powder

Abstract

The photo-induced reduction rate of m-nitroacetophenone (NAP) in the presence of TiO₂ powder (anatase and rutile forms) is obtained by measuring the time-courses of the concentration of a product, m-aminoacetophenone (AAP). This photo-induced overall reaction in the ethanol is expressed as

NO₂C₆H₄COCH₃ + 3C₂H₅OH → NH₂C₆H₄COCH₃ + 3CH₃CHO + 2H₂O

The photo-induced reduction rate of NAP is dependent on the TiO₂ and initial NAP concentrations. The time courses of the AAP concentration normalized by the initial NAP concentration decrease with increasing initial NAP concentration. These characteristics can be interpreted by the non-linear differential equation as follows,

d[AAP]/dt = k([NAP]₀ − [AAP])(2k₀t − 6[AAP])

where [NAP]₀ is the initial NAP concentration. The rate constants, k₀ and k, express the oxidation rate of ethanol and the reduction rate of NAP, respectively. The value of k₀ is dependent on the initial NAP and TiO₂ concentrations. It takes a maximum value of 4.0 g/dm³ for anatase and 1.0 g/dm³ for rutile when the initial NAP concentration is about 1.0 mmol/dm³. Then, the maximum value for anatase is 11.1 times that of rutile. The value of k₀ decreases with increasing initial NAP concentration. The k value is independent of the TiO₂ and initial NAP concentrations, and the same value for both anatase and rutile forms is obtained.