Sonochemical reduction of permanganate to manganese dioxide: The effects of H2O2 formed in the sonolysis of water on the rates of reduction

Abstract

Chemical effects of ultrasound have been actively researched in the field of the synthesis of various metal nanoparticles and nanostructured materials. It is very important to understand the reduction mechanism of metal ions, because the reduction processes can be often applied to the synthesis of various materials. In this study, the sonochemical reduction of MnO4- to MnO2 in water under Ar atmosphere was investigated to discuss the reduction mechanism. It has been reported that H, OH, H2 and H2O2 are formed from the sonolysis of water. To understand the roles of H2O2 on the reduction, the reaction of MnO4- with H2O2 without ultrasonic irradiation was investigated. The obtained results suggested the progress of the following reaction: 2MnO4-+3H2O2-->2MnO2+3O2+2OH-+2H2O. In addition, the rates of the sonochemical reduction of MnO4- were investigated in the presence of 1-propanol, where 1-propanol acted as an OH radical scavenger so that the amounts of the sonochemically formed H2O2 molecules were able to be controlled. The results clearly indicated that the sonochemically formed H2O2 molecules as well as H2 molecules and H atoms play an important role for MnO4- reduction. This mechanism was also supported by the analysis of pH changes during ultrasonic irradiation: the pH value increased as the sonochemical reduction of MnO4- proceeded.

Degradation of congo red induced by air-bubbles in the presence of nanometer TiO2 powders

“…That is, the holes generated on the surface of nanometer rutile TiO 2 particles indirectly degrade the organic pollutants in aqueous solution through Å OH radicals. The generation of Å OH radicals can be proved by the experiment of chemilluminutesescence [26]. In fact, that is the mechanism of photocatalytic degradation.…”

“…At last, it fractures and collapses. Instantly, a great deal of energy in the form of light or heat is released [25,26]. As well known, cavitation is the phenomenon of sequential formation, growth, and collapse of millions of microscopic vapor bubbles (voids) in the liquid.…”

“…Firstly, it has been well known that the cavitation can generally result in the formation of light with a comparatively wide wavelength range. Those lights whose wavelengths are below 375 nm [26], beyond all doubt, can excite the nanometer TiO 2 powders acting as photocatalyst. And then, the photogenerated electron-hole pairs are generated on the surface of nanometer TiO 2 particles.…”

Physicochemical Properties of MnO2Catalyst Prepared via Hydrothermal Process and its Application for CO Oxidation

“…Mn산화물은 pyrolusite (1 X 1), ramsdellite (1 X 2), hollandite (2 X 2), romanechite (2 X 3), todorokite (3 X 3) 등 터널 층상 구조를 가지고 있으며 합성법과 Mn전구체에 따라 다른 구조 를 나타낸다 [21,[23][24][25][26][27]. 가장 일반적인 방법으로 산화-환원 침 전법이 있으며 염기, 약산성 수용액상에서 birnessite, 산성 수 용액상에서 hollandite구조로 제조된다 [21].…”

Physicochemical properties of manganese dioxide synthesized using C2–C5 alcohols as reducing agents and their catalytic activities for CO oxidation

“…The physicochemical properties of MnO 2 can be controlled by using different Mn precursors and synthesis conditions, e.g., sol-gel, gas condensation, microemulsion, solid state, hydrothermal, melting salt reflux, redox precipitation, and sonochemical processes [6,[9][10][11][12][13]. In particular, the crystalline structure of MnO 2 has an effect on its performance as a catalyst for CO oxidation.…”