Sepiolite spectra

Figure 6. The XPS spectrum and Ni curve fit for a sample of Spanish sepiolite (loaded with 2%and calcined at 850°C) after reduction at 400°C/lh.

The 29Si CP/MAS-NMR spectrum of untreated sepiolite is presented in Fig. 2a. Three well-resolved resonances of approximately equal intensity occur at -92.7, -94.3 and -98.2 ppm, as well as a significantly less intense resonance (<5%) around -85 ppm, in excellent agreement with previous reports [6,23-24], The resonance at -92.7 ppm is assigned to type 2 (near edge) silicon nuclei, as denoted in Fig. la. Furthermore, the resonances at -94.3 and -98.2 ppm are assigned to type 1 (edge) and type 3 (center) silicon nuclei, respectively [25],... 

Finally, the 29Si CP/MAS-NMR spectrum of a partially dehydrated sepiolite that was subsequently exposed to acetone vapor is presented in Fig. 2c, and is strikingly similar to the spectrum of the original, untreated sepiolite (Fig. 2a). Since zeolitic water molecules are not present in this sample, and in light of the discussion of the partially dehydrated sepiolite sample, it appears that the acetone molecules have penetrated inside the microporous channels and reversed the structural changes that were caused by partial dehydration. Thus Fig. 2c confirms that acetone molecules enter the microporous channels of sepiolite, and are not simply adsorbed on the crystallite exterior surfaces. 

The corresponding H MAS-NMR spectra for the same samples are presented in Fig. 3a, 3b and 3c, respectively. As shown in Fig. 3a, the FI MAS-NMR spectrum of an unheated sepiolite consists of two distinct proton resonances centered near 0 ppm. A sharp resonance at higher field, which gives rise to only a few spinning side bands, is assigned to... 

We observe only the V component of the oxidation products of DMA. We do not observe any changes in the IR spectrum of DMA-treated diatomite after washing the sample with benzene. It is noted that the V and Y components of the oxidation products of DMA are not desorbed during the washing with benzene but the excess DMA and tetramethylbenzidine (TB) are washed out with benzene, IR spectroscopic analysis shows that sepiolite and loughlinite absorb DMA and then react with it more easily than diatomite. The adsorption capacity sequence of DMA for the minerals studied is found to be sepiolite>loughlinite>diatomite. 

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