Chemiluminescence Reactions of a Luminol System Catalyzed by ZnO Nanoparticles

Colloidal ZnO nanoparticles were synthesized by the sol-gel method and were characterized by UV-visible spectroscopy and photoluminescence spectroscopy. The effect of ZnO nanoparticles on the luminol-H2O2 chemiluminescence (CL) system, a popular model CL system, was investigated. It was found that ZnO nanoparticles with a size regime from 6 to 21 nm could enhance the CL of the luminol-H2O2 system, and the strongest CL signal was obtained when the mean diameter of ZnO nanoparticles was 6 rim. To investigate the enhancement mechanism of the CL, we used UV-visible spectroscopy, FT-IR spectroscopy, and CL spectroscopy to study optical properties before and after the CL reaction in the presence/absence of ZnO nanoparticles. The CL enhancement of the luminol-H2O2 system by ZnO nanoparticles should originate from the catalysis of ZnO nanoparticles, which could catalyze the decomposition of H2O2 to produce some reactive intermediates such as hydroxyl radical and superoxide anion. Then, the resulting hydroxyl radical reacted with luminol to form luminol radical, which rapidly reacted with superoxide anion or monodissociated hydrogen peroxide. As a result, the emission was enhanced. Experimental results showed that some organic compounds containing -OH, -NH2, and -SH groups, such as amino acid, ascorbic acid, and dopamine, could inhibit the CL signal of the luminol-H2O2-ZnO system. The above facts indicated that the present system had a wide application for the determination of such compounds.