Kinetics of reduction of Se (IV) by vitamin C with green synthesis of cluster-grapes nanoparticles: A Mechanistic approach on electron-transfer of nanoparticle growth rates

Abstract

• Kinetics and mechanistic study of reduction of Se(IV) by vitamin C in acidic solutions. • Green synthesis of selenium nanoparticles of cluster-grapes nature for the first time by using Vitamin C. • Characteristics of synthesized of the synthesized cluster-grapes nanoparticles. • Prospective mechanistic for the nanoparticles growth pathway. • Information on the electron-transfer pathway in the rate-determining step In a series of spectrophotometric investigation studies on some redox reactions involving vitamin C (ascorbic acid) as a reducing agent for reduction of metal ion oxidants in aqueous acidic solutions. It was surprising when the naked eye observations noticed the rabidly turning of selenium dioxide Se(IV) solution from colorless into deeply bright crimson color of colloidal aggregate sol when just mixed with solution of excess vitamin C in either neutral or acidic media. Then, the formed crimson color was gradually turned into crystals of dark purple color on keeping it aside for a long time or on drying in either sunlight or into an electric oven. This result suggests the occurrence of phase-transition with formation of selenium nanoparticles. The formed selenium nanoparticles were characterized by FTIR, XRD as well as the SEM and TEM microscopic morphology. It has been found the formation of such selenium nanoparticles of cluster-grapes nature for the first time. This phenomenon and the great importance of such nanoparticles in biotechnology applications encouraged us to follow the rate of nanoparticles growth through the reduction of selenium dioxide by vitamin C on using a conventional spectrophotometer. A first-order dependences in both selenium (IV) and vitamin C concentrations; second-order overall kinetics have been revealed. Free-radical intervention was detected during the oxidation progression. The influence of [H + ] on the rate constants showed that the oxidation was of acid-inhibition nature. In view of the evaluated kinetic parameters, a plausible reaction mechanism of two-electron transfer pathway of inner-sphere nature was suggested and discussed.