Tuning the Oxygen Release Temperature of Metal Peroxides over a Wide Range by Formation of Solid Solutions

Abstract

Metal peroxides, with a labile peroxy bond, constitute a distinct class of inorganic compounds that can generate singlet oxygen species and works as versatile reagents in many important industrial processes such as in polymer initiation reactions. Even after several decades after their discovery, the number of metal peroxides yet is few and their utility is severely limited by the corresponding decomposition temperatures (T dec ), which cannot be tuned to suit the most desirable condition for a particular reaction. One way of overcoming this would have been to obtain solid solutions of two peroxides with different decomposition temperatures. Surprisingly, in contrast to the vast majority of extended solids such as the oxide, hydroxide, and perovskite families, solid solutions of metal peroxides have remained so far nonexistent. Here, we explore and demonstrate that peroxides of Zn and Mg, ZnO 2 (T dec ∼ 200°C), and MgO 2 (T dec = 300°C) can form solid solutions in the entire solubility range. Importantly, the decomposition temperatures of the solid solutions lie between that for the constituent phases and changes the composition systematically. These findings provide the first genuine chemical system that can potentially be tuned to decompose at different predesigned temperatures to generate reactive oxygen species. ■ INTRODUCTIONMetal peroxides constitute an industrially important family of compounds due to their ability to produce reactive oxygen, 1 their usefulness as polymer initiator, 2−4 their prospect as active energy storage material 5−8 and at the same time, for being relatively safe as compared to organic peroxides. 9−11 To be useful in their applications, the control over the decomposition of the peroxy linkage is of utmost criticality, as this leads to the release of the reactive oxygen species. In their role as radical initiators in various polymer processing, the choice of a metal peroxide is based upon its decomposition temperature (T dec ). This is primarily because the follow-up processes for curing and the degree of polymer cross-linking is dependent upon it. 2−4 These apart, recent discoveries have shown tremendous scope for tuning of T dec of these materials in novel applications. First, for instance, Bruce and co-workers in their pioneering work have demonstrated that regulating the breaking/reforming of a peroxy linkage can radically improve the performance of high energy-density batteries. 7 Second, it has been recently shown that metal peroxide can be utilized as recyclable reagents for C−H activation reactions, which often otherwise require stringent conditions. 12 Therein too, the effectiveness of the process relies on the peroxide T dec . The dependence of their utility upon T dec , which for particular metal peroxides is fixed, 13 has severely limited the operating temperature windows for many industrial processes and the tuning of T dec for metal peroxides has remained an important research challenge for several decades. It may be recalled that borohydrides were another such rare fami...

Formation Mechanism and Excitonic Luminescence of Supercritical-Fluid-Synthesized ZnO Nanoparticles

“…Our hypothesis is that the ZnO phase is obtained via the thermal decomposition of an intermediate ZnO 2 phase, leaving a “ZnO 2 -like” surface able to neutralize the formation of surface defects usually responsible for visible emissions. This theory is supported by previous reports of ZnO 2 formation from ZnO exposition to H 2 O 2 . Here, it is implied that H 2 O 2 allows the formation of ZnO 2 which is quickly thermally converted into ZnO.…”

“…This theory is supported by previous reports of ZnO 2 formation from ZnO exposition to H 2 O 2 . 41 Here, it is implied that H 2 O 2 allows the formation of ZnO 2 which is quickly thermally converted into ZnO. A series of ex situ and in situ characterizations have been performed in order to confirm this mechanism.…”