THE CATALYTIC ACTIVITY OF METAL AND METAL ALLOY NANOPARTICLES FOR THE REDUCTION OF 4-NITROPHENOL WITH SODIUM BOROHYDRIDE

Nanoparticles (NPs) and in particular metal NPs have attracted many scientists to study their properties in the fields of medicine, optics, electronics, catalysis, etc. Metal NPs are good catalysts as most of their atoms are low-coordinated surface atoms. These atoms are more active than the bulk atoms.

The catalytic reduction of 4-nitrophenol (4-Nip) is one of the most used reactions to test the catalytic activity of metal NPs in aqueous solution. This is because these reactions can be easily monitored by UV-vis spectroscopy. The decrease in the strong absorption of 4-nitrophenolate ions at 400 nm can be readily monitored by UV-vis spectroscopy along with the rise of the 4-phenylamine peak at 300 nm. This reaction is suitable for testing the NPs catalytic activity. Due to its optical properties, the reaction of 4-Nip reduction is used as a prototype for catalysis on many metal NPs.

We are studying the catalytic effect of different metals (Au, Ag and Pt) and metal-alloys NPs on the reduction of 4-Nip by sodium borohydride. In this study we synthesize aqueous metal NPs suspensions by the precursor salts reduction with sodium borohydride. The metal alloys are synthesized similarly using a mixture of salts in the precursor solution.

The reactions are monitored using spectrophotometer following the increase of the 4-Nip signal at 400 nm and the increase of the 4-phenylamine signal at 300 nm.

Primary results indicate that:

1. The order of the metal NPs activity is: Pt
2. The alloys NPs show much better activity than the individual metals towards the reduction of 4-Nip.
3. The best catalyst so far is the Ag-Pt alloy nanoparticle.