Hybridization of [(OH(2))(terpy)Mn(mu-O)(2)Mn(terpy)(OH(2))](3+) (terpy= 2,2':6',2' '-terpyridine) (1) and mica clay yielded catalytic dioxygen (O(2)) evolution from water using a CeIV oxidant. The reaction was characterized by various spectroscopic measurements and a kinetic analysis of O(2) evolution. X-ray diffraction (XRD) data indicates the interlayer separation of mica changes upon intercalation of 1. The UV-vis diffuse reflectance (RD) and Mn K-edge X-ray absorption near-edge structure (XANES) data suggest that the oxidation state of the di-mu-oxo Mn(2) core is Mn(III)-Mn(IV), but it is not intact. In aqueous solution, the reaction of 1 with a large excess Ce(IV) oxidant led to decomposition of 1 to form MnO(4-) ion without O(2) evolution, most possibly by its disproportionation. However, MnO(4-) formation is suppressed by adsorption of 1 on clay. The maximum turnover number for O(2) evolution catalyzed by 1 adsorbed on mica and kaolin was 15 and 17, respectively, under the optimum conditions. The catalysis occurs in the interlayer space of mica or on the surface of kaolin, whereas MnO(4-) formation occurs in the liquid phase, involving local adsorption equilibria of adsorbed 1 at the interface between the clay surface and the liquid phase. The analysis of O(2) evolution activity showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on clay. The second-order rate constant based on the concentration (mol g(-1)) of 1 per unit weight of clay was 2.7 +/- 0.1 mol(-1) s(-1) g for mica, which is appreciably lower than that for kaolin (23.9 +/- 0.4 mol(-1) s(-1) g). This difference can be explained by the localized adsorption of 1 on the surface for kaolin. However, the apparent turnover frequency ((kO(2))app/s(-1)) of 1 on mica was 2.2 times greater than on kaolin when the same fractional loading is compared. The higher cation exchange capacity (CEC) of mica statistically affords a shorter distance between the anionic sites to which 1 is attracted electrostatically, making the cooperative interaction between adsorbed molecules of 1 easier than that on kaolin. The higher CEC is important not only for attaining a higher loading but also for the higher catalytic activity of adsorbed 1.
In this paper, we report the preparation of systematically size and shape controlled LiMnPO 4 nanocrystals under supercritical fluid conditions. The effect of different reaction conditions such as the reaction time, temperature, surfactant and precursor concentration on the size and shape of the LiMnPO 4 nanocrystals was studied in detail. It was noticed that shorter reaction time and lower reaction temperature facilitated the formation of crystalline LiMnPO 4 nanocrystals with size $10 nm. The nanocrystals ranging from 7 to 24 nm were obtained by controlling different reaction conditions. The formation mechanism for the LiMnPO 4 nanocrystals is proposed based on the obtained results. The effect of nanosize on the electrochemical properties of LiMnPO 4 nanocrystals was studied. Improved electrochemical performance was observed for $20 nm sized LiMnPO 4 after conductive carbon coating. This study indicates the importance of LiMnPO 4 nanocrystals below 50 nm size in improving the electrochemical performance of LiMnPO 4 cathodes.
We report a rapid one-pot supercritical fluid approach to prepare the desired size and morphology controlled LiMPO(4) nanocrystals, using oleylamine as both capping and reducing agent.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.