PMC:5551755 / 13656-16949
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{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/5551755","sourcedb":"PMC","sourceid":"5551755","source_url":"https://www.ncbi.nlm.nih.gov/pmc/5551755","text":"3.1. Series 1: Effect of Water\nFigure 1 shows the X-ray diffraction patterns of the natural clay, the pillared clay using the traditional method and the samples of series 1 (1 to 5). Regarding to the natural clay, the material composition is based mostly on montmorillonite (2θ = 5.8°; 17.7°; 19.8° and 35.1°) and quartz (2θ = 26.6°) [34].\nThe shift of the first reflection, which was due to the (001) plane, to smaller angles (2 theta axis) shows that the basal spacing increased (Table 4), indicating that the clay cations were exchanged for the prepared polyhydroxy cations.\nThe pillared clays using the traditional methods (2 and 3) presented more intense (001) reflections compared to samples 1, 4, and 5; indicating a more organized structure of the lamellae. This more organized structure is reflected in the values of the basal spacing and the surface areas obtained (Table 4). Sample 1 presented the lowest values of surface area (142 m2/g) and basal spacing (16.8 Å) due to the amount of water used to expand the clay (100 mL). In methods 4 and 5, 500 and 900 mL of water, respectively, were removed before the stage of pillarization. As a consequence of this removal of water, these samples presented lower surface areas (149 m2/g) in comparison with PILCs obtained by methods 1, 3 and traditional (higher than 200 m2/g). Therefore, the amount of water used to expand the lamellae also exerts a great influence in the cationic exchange of natural clay cations by the prepared oligomers, translating into a decrease in surface area when fewer amounts of water (methods 4 and 5) are used. Similar results were obtained with samples 2 and 3, indicating that the minimum relation of clay/water to obtain materials with elevated basal space and surface area (above 200 m2/g) is 1/50.\nFigure 2 presents a comparison between the basal spacing, the concentration of the clay suspension and the surface area BET of this series of samples. The best results were obtained through method 3, where elevated amount of water in the clay suspension was used (1/100) and was maintained until the end of the process. For samples 4 and 5, a drastic reduction of surface area occurred due to the removal of water from the clay suspension before the stage of pillaring, which proves that the high quantity of water (diluted suspensions) generates materials with elevated basal spacing and surface areas.\nTable 5 presents the textural parameters (BET surface area, micropore area, external area, total pore volume and micropore volume) of series 1 materials.\nWhen the pillared clay prepared by the traditional method is compared with natural clay, the external area values, which include the external surface plus the meso and macropore area, did not vary. The micropore volume is approximately 10 times larger in the pillared clay due to the increase in basal space. Because of this increase in the micropore volume, the micropore area is approximately 10 times larger. This area is responsible for the increase in total area (BET) in the pillared material. Methods 4 and 5 presented the closest results to those when using the traditional method, with surface areas above 200 m2/g, a micropore area of 180 m2/g and a pore volume (total and micro) similar to the related values in the literature [2,35].","divisions":[{"label":"title","span":{"begin":0,"end":30}},{"label":"p","span":{"begin":31,"end":339}},{"label":"p","span":{"begin":340,"end":577}},{"label":"p","span":{"begin":578,"end":1789}},{"label":"p","span":{"begin":1790,"end":2393}},{"label":"p","span":{"begin":2394,"end":2547}}],"tracks":[]}