The work presented here comprises three main parts. The first part is a new route to nano-sized γ-MnOOH (manganite). γ-MnOOH has been synthesized via the reduction of KMnO 4 with sucrose and MnSO 4 in acidic medium under refluxing conditions for four and six hours. Characterization of these manganite materials using XRD, FESEM, TEM, TGA and IR were done. The obtained manganite samples using the new route were compared against a conventionally prepared one where synthesis involved the oxidation of MnSO 4 with H 2 O 2 in basic medium. Two new synthetic methods were developed, one involving addition of KMnO 4 into a solution of both sucrose and MnSO 4 while the other involved addition of KMnO 4 solution into sucrose followed by addition of MnSO 4 (s). The latter method yielded smaller particles (up to 30 nm) than the former method (up to 80 nm) and the conventionally prepared manganite (up to 50 nm). The synthesized manganite materials exhibited promising characteristics when tested as electrocatalysts in O 2 reduction. The larger particles gave higher peak currents in CV than smaller particles. When incorporated in Yardney's medium-sized lithium-air battery, the larger (up to 80 nm) particles gave higher specific capacity (up to 2.2 Ah/g), which corresponds to about 38% increase in specific energy of the battery when compared to a battery where no manganite was incorporated.
The second part of the research reported here involves the synthesis of K-OMS-2 and SiO 2 -supported K-OMS-2. K-OMS-2 (or OMS-2 from hereon) was successfully synthesized using a reflux method where, for the first time, oxone or KHSO 5 was used as the oxidant. Nano-sized fibers with widths ranging from 8-40 nm were obtained. We also report for the first time the synthesis and catalytic activity of OMS-2 supported on SiO 2 with surface area ranging from 228 to 513 m 2 /g and weight % OMS-2 ranging from 1.0 to 13.6%. An optimization study on styrene oxidation using OMS-2 and OMS-2/SiO 2 as catalysts was done. Lowering the amount of catalyst and increasing the substrate used in the reaction significantly improved conversion and turnover frequency. Conversions of up to 81% and 19 h -1 TOF were achieved. These were the highest reports of conversion and TOF thus far for styrene oxidation using undoped OMS-2 and 24 hours reaction time. Selectivity towards the more valuable product, styrene oxide, significantly improved when OMS-2 was supported on SiO 2 . The weight % OMS-2 or dispersion of OMS-2 on the SiO 2 support may be a key in optimizing OMS-2/SiO 2 catalysts. The free-radical pathway is indeed involved in the oxidation of styrene and SiO 2 contributes to the generation of epoxide-producing radicals as shown by kinetic and radical trapping experiments. Furthermore, the oxo-metal pathway may favor the production of benzaldehyde.
Finally, a preliminary study on the use of a continuous flow microwave (MW) technique to obtain inorganic nanomaterials is also presented in this thesis. Nanosized [varepsilon]-MnO 2 , OMS-2, CeO 2 , CoOOH, and FeOOH were synthesized using the said microwave technique. Nanoplates and nanofibers of [varepsilon]-MnO 2 were obtained while mainly nanoplates of OMS-2 resulted in the use of the continuous flow MW technique. The obtained OMS-2 product was not pure. This OMS-2 was obtained with some [varepsilon]-MnO 2 . [varepsilon]-MnO 2 cannot be used as a precursor to OMS-2. Microspheres of [varepsilon]-MnO 2 can be obtained by using shorter reactors and more concentrated reactant solutions. Product yields of up to 24% were obtained in using the continuous flow MW reactor, which indicates that there are still some parameters that need to be further optimized to achieve a viable industrial process using the technique reported here. These parameters include reactor geometry, MW power, reactant concentrations, and the use of a carrier gas to alleviate clogging of the reactor. Lower product yields were obtained when the MW oven was replaced with a conventional one.
