Metal-Free and Heterogeneous Photocatalytic Reduction of 4-Nitroaniline by a Poly(Ethylene Glycol)-Supported Eosin Dye under Visible-Light Exposure

摘要

A new feasible approach for the photoreduction of a chemical pollutant, 4-nitroaniline, to p-phenylenediamine was developed. We highlighted the crucial roles of a polymer backbone and the atmosphere for the efficient heterogeneous reduction of 4-nitroaniline. The novel synthesized poly(ethylene glycol)-derived film containing immobilized eosin dye revealed a high photoreduction rate of 4-nitroaniline. According to laser flash photolysis results the first step of this photoinduced process represents a single electron transfer from eosin radical anion to the 4-nitroaniline to form a nitroaniline radical anion. The in-situ electron paramagnetic resonance spin-trapping experiments evidenced the generation of superoxide radical anion serving as catalyst in the p-phenylenediamine production according to a photoreduction process. The main roles play by poly(ethylene glycol) matrix as efficient reducing agent and hydrogen-donor molecule was also pointed out. A mechanism was proposed to explain the heterogeneous photoreduction of 4-nitroaniline to p-phenylenediamine in the presence of eosin dye-based poly(ethylene glycol) system under air.