Amorphous manganese dioxide

Table 2. Cycling ability of amorphous manganese dioxide at various sweep scan rates.

Nanomaterials can also be tuned for specific purposes through doping. Specifically, the effect of the presence of manganese oxides on photocatalysis involving primarily titanium dioxide will be considered in this section. Titanium dioxide is a well-known photocatalyst and will be considered separately. K-OMS-2, which has a cryptomelane structure, is illustrated in Figure 8.4. Not all the literature discussed in this section, however, involves OMS tunnel structure materials. For example, amorphous manganese oxide (AMO) is also discussed as a photocatalyst. Manganite (MnOOH) is also included in battery applications. 

Ya.B. considered that the most important adsorbents—porous coal, silica gel, and the powdered manganese dioxide which he had studied experimentally—are amorphous substances, i.e., they do not have clearly articulated crystalline structure. Only thus is it possible to obtain a large developed surface—the most important feature of an adsorbent. In this case, it is natural to consider all the possible values of adsorption activity and a smooth distribution function of surface sectors according to their level of activity. 

An interesting reaction in which emeraldine is formed was observed by Caro [16]. If aqueous solution of free aniline is oxidised with potassium permanganate, and filtered from the separated manganese dioxide, the filtrate is a yellowish liquid, from which ether takes up a yellow amorphous eompound. This latter is converted into a green salt of emeraldine by mere contact with acids. A substance possessing the properties of emeraldine is formed simultaneously with quinone by oxidation of paramido-diphenylamine. A larger yield is obtained if this base is oxidised with an equivalent of aniline, and in this case quinone is not formed [17]. On further oxidation emeraldine yields a darker coloured compound, but it is doubtful if this is aniline black. The formation of emeraldine from paraphenylenediamine and diphenylamine leads to the supposition that it is a phenylated indamiue of the formula ... 

These are the same as for the match compositions. Manganese dioxide, the sulphides of antimony, powdered charcoal, amorphous phosphorus potassium chlorate, glass powder, etc., as frictional materiab chalk, etc., as hlling materials umber and the like as colouring matters glue, gelatin, and dextrin as binding nuterials. 

Rossd used the following composition — Ten parts of gum arable, 300 parts of gum tragacanth, 53-8 parts of potassium chlorate, 6 parts of capHi mortuum, 12 parts of pow dcred glass, parts of potassium dichromate, 3 parts of sulphur, l 2 parts of chalk or colophony, and 6 parts of manganese dioxide. The striking surface for this composition consisted of 5 parts of antimony sulphide, 3 parts of amorphous phosphorus, 1 parts of manganese dioxide, and 4 parts of glue. 

Balistrieri, L.S. and Chao, T.T., Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide, Geochim. Cosmochim. Acta, 54, 739, 1990. 

As would be expected from this affinity sequence, phosphate out-competed Mo for surface sites in multisorbate systems. The work of Balistrieri and Chao (1990) indicated that at pH 7, phosphate has greater affinity for amorphous Fe oxide than does molybdate, whereas the reverse is true for the affinity sequence on manganese dioxide. This difference also was reflected in the abilities of phosphate and molybdate to compete with selenite at pH 7 on the two oxides. 

Crabtree et al. reported the immobilisation of the dimeric mixed-valence species [(tpy)(H20)Mn (0)2Mn (tpy)(H20)] (5) onto titanium dioxide nanoparticles with different degrees of crystallinity. The complex was directly adsorbed onto the titanium dioxide surface for ciystalline titanium dioxide, the manganese(iii)-manganese(iv) dimer transformed to manganese(iv)-manganese(iv) dimer or tetramer-like structure, whereas it remained stable when anchored to titanium-dioxide nanoparticles with low crystallinity. The o>ygen-evolution measurements performed in the presence of CAN showed that the dimeric mixed-valence complex adsorbed on amorphous titanium dioxide support was not catalytically active, whereas the oxidised/dissociated complex formed in the crystalline titanium dioxide nanoparticles showed catalytic activity however, no detailed explanation was provided for the differences in catalytic activity. ... 

Typical particle morphology of amorphous hydrated manganese dioxides, Mn02 H20, prepared by the simple precipitation, and its electrochemical behavior in aqueous electrolyte solution are shown in Fig. 1. 

Fig. 1 (a) SEM image of the amorphous hydrated manganese dioxides, Mn02 H20. Electrochemical behavior of Mn02 H20 electrode in a 1.0 mol dm Na2S04 aqueous solution, (b) cyclic voltammogram at a rate of 1.0 mV s , and (c) rate capability at different rates of 1.0-100 mV s ... 

---