The two phases of manganese oxides are prepared by two different mixing modes using the same precipitation method from the solutions of KMnO4 dan maltose, resulting in marked different phase structures and catalytic activities. The oxides synthesized by adding dropwise of the maltose solution into KMnO4 solution (method A) resulted in the formation of layer manganese oxide birnessite, which turns into tunnel structured manganese oxide cryptomelane following the calcination at 600°C for 4 hours. The simultaneous addition of KMnO4 solution and maltose solution (method B) also produced birnessite before calcination, but remain unchanged as birnessite phase after calcination with cryptomelane as minor product. The samples without calcination obtained from method A posseses higher surface area and poor crystallinity compared to that with calcination. The catalytic test using Fenton-like Reaction for methylene blue (MB) degradation indicated the tremendeous difference in their catalytic activities for both samples without and with calcination. The birnessite catalysts (without calcination) prepared using method A show the highest activity and are able to degrade 93% methylene blue within 10 minute, much higher than other samples.
The layer and tunnel manganese oxides are versatile materials and have been proposed for various applications. These materials are prepared by a wide range of methods such as sol-gel, solid-state, precipitation and etc. Here, both manganese oxides of birnessite (layer) and cryptomelane (tunnel) have been successfully synthesized using the precipitation method by the reaction between KMnO4 and glucose with a mole ratio of 3:1. XRD results indicated that the birnessite-type manganese oxide was obtained when the brownish-black precipitate was heated up to 120°C, whereas cryptomelane-type manganese oxide was generated when the as-synthesized sample was further calcined up to 600°C. The birnessite sample displays poor crystalline material with low intensity and broad peak. The heat-treated birnessite up to 600°C leads to the formation much more crystalline tunnel cryptomelane–type mangane oxide. The catalytic activities of the as-synthesized catalysts were tested for the degradation of methylene blue (MB) dye with H2O2 as an oxidant. The birnessite catalyst shows much higher catalytic activity for the degradation of methylene blue compared to the cryptomelane catalyst. The tremendous improved catalytic activity of birnessite catalyst are correlated with its poor crystallinity and higher surface area of as indicated by the BET surface area and the XRD results.
Abstract:Smart devices in an environment can be programmed and coordinated by a workflow in advance to achieve a user's goal. No matter how advanced or smart the devices are, devices can fail during workflow execution. In this paper, we describe an approach to remedy such situations. We apply existing concept of adaptive workflow management to a collection of devices, called a device ecology. Information about the devices are kept in a device hierarchy so that a suitable substitute device that can perform similar task can be retrieved to replace a failed device in order to ensure the workflow can continue execution. A prototype has been implemented as proof of concept.
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