Kinetic Analysis of Catalytic Reduction of 4-Nitrophenol by Metallic Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes

Abstract

We present a study on the catalytic reduction of 4-nitrophenol by sodium borohydride in the presence of metal nanoparticles. The nanoparticles are embedded in spherical polyelectrolyte brushes, which consist of a polystyrene core onto which a dense layer of cationic polyelectrolyte brushes are grafted. The average size of the nanoparticles is approximately 2 nm. The kinetic data obtained by monitoring the reduction of 4-nitrophenol by UV/vis-spectroscopy could be explained in terms of the Langmuir−Hinshelwood model: The borohydride ions transfer a surface-hydrogen species in a reversible manner to the surface. Concomitantly 4-nitrophenol is adsorbed and the rate-determining step consists of the reduction of nitrophenol by the surface-hydrogen species. The apparent reaction rate can therefore be related to the total surface S of the nanoparticles, to the kinetic constant k related to the rate-determining step, and to the adsorption constants K Nip and K BH4 of nitrophenol and of borohydride, respectively. In all cases, an induction time t 0 was observed of the order of minutes. The reciprocal induction time can be treated as a reaction rate that is directly related to the kinetics of the surface reaction because there is a linear relation between 1/(kt 0) and the concentration of nitrophenol in the solution. All data obtained for t 0 so far and a comparison with data from literature indicate that the induction time is related to a slow surface reconstruction of the nanoparticles, the rate of which is directly related to the surface reaction.

Improving gold catalysis of nitroarene reduction with surface Pd

“…These initial reactant concentrations were within range of other published studies. [11,12,14,15] All reactions were monitored for total t = 26.5 min using a Shimadzu 2450 UV-Vis spectrophotometer. Reaction spectra were acquired every 2 min.…”

Natural reducing agents for electroless nanoparticle deposition: Mild synthesis of metal/carbon nanostructured microspheres

“…If NaBH 4 is in excess with respect to 4-nitrophenol then its concentration can be assumed constant and the reaction rate becomes pseudo-first-order in the concentration of 4-nitrophenol [22,23,54,[57][58][59]. Fig.…”

“…An apparent rate coefficient k app was calculated near time zero from linear fits of curves such as the one in Fig. 5b [54,[57][58][59], yielding k app = 0.0015  0.0002 s -1 .…”

Catalytic Activity of BiVO4-graphene Nanocomposites for the Reduction of Nitrophenols and the Photocatalytic Degradation of Organic Dyes

“…Reduction reactions of other nitrophenols by NaBH 4 were also studied on BiVO 4 -graphene nanocomposites. 38 As shown in Figure 3(b), the absorbance spectrum of 3-nitrophenolate ions showed a peak at 390 nm. When the yellow color was discharged, the peak at 390 nm also decreased.…”