Nanoparticle-Catalyzed Clock Reaction

Abstract

Bulk Cu2O or cuprite is the only stable copper(I) compound present in plentiful amount in earth's crust. It is a challenging job to take bulk Cu2O to a nanoregime and to stabilize it in solution. No wonder that Cu2O in its nanoregime would act as a photocatalyst. We report a new synthetic protocol for the first time to obtain monodispersed, stable, exclusively cubic Cu2O nanoparticles in surfactant-free condition and its catalytic action for methylene blue (MB)−hydrazine reaction in aqueous medium. The blue color of the dye, MB, faded away upon the addition of hydrazine, producing colorless leuco methylene blue (LMB) indicating the progress of the redox reaction. The rate of this redox reaction has been found to be enhanced in the presence of the nanocatalyst, Cu2O. The success of the reaction demonstrates a simple ‘clock reaction'. An oscillation between a blue MB color and colorless solution due to formation of LMB is observed on periodic shaking. This oscillation continues for over 15 cycles. Studies on the effect of bulk Cu2O and nanoparticles of CuO and Cu(0) have not been successful for demonstration of the ‘clock reaction'. Thus, the importance of Cu2O nanoparticles in the clock reaction is established beyond doubt. The Cu2O nanoparticles were characterized by different physical methods. TEM studies authenticate the cube shaped monodispersed particles. The electrochemical studies indicate that nano-Cu2O shows a couple of redox peaks which correspond to the redox Cu(II)/Cu(I) system. Kinetic studies authenticate a first-order reaction mechanism. Further, quantum chemical calculations reveal that the nanoparticles reduce the activation energy by ∼17 kcal/mol, thereby making the reaction 2.4 × 107 times faster compared to the gas phase.

Photocatalytic Degradation of Phenol and Phenol Derivatives Using a Nano-TiO2 Catalyst: Integrating Quantitative and Qualitative Factors Using Response Surface Methodology

“…Studies by Pande et al [50] have shown that 15-nm Cu 2 O nanoparticles are able to reduce the activation energy by approximately 71 kJ mol −1 and hence, increase the reaction rate by 2.4 × 10 7 -fold. The reaction rate constant, k app , can be derived from the Arrhenius equation (Equation (7)).…”

Formation mechanism of Cu2O particles using layered CaSi2 as a reduction/oxidation mediator

“…This is because the major oxidation states of Cu are Cu 4 O 3 , Cu 2 O, and CuO, 11 while the Cu 2+ state is considered to be more stable than the Cu + state. 12 The syntheses reported for the production of Cu 2 O are the hydrothermal, 13 polyol, [14][15][16] or glucose-reduction methods, 4 where the oxidation states of Cu are controlled with multiple steps to adjust the pH of the solvent, 16 the amount of reducing agent, 4,17 and the reduction rate. 12 In this report, we focus on layered silicon compounds (CaSi 2 and its derivative layered siloxene).…”

First principles investigation on the stabilization mechanisms of the polar copper terminated Cu2O(111) surface

“…Cu 2 O is also an effective photocatalyst able to decompose water into H 2 and O 2 under visible light [13][14][15][16][17].…”