Probability density function curves; 0.5A, 0.25A, 0.5B and 0.25B represent four different membranes, respectively. 

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... 80% of pores have the diameters less than 50 nm. The largest pore size is over 130 nm. Probability density function curves are illustrated on Fig. 6 by using the values of mean pore size and geometrical standard deviation. As shown on Fig. 6, all the membranes have quite similar trends and pore sizes cover a broad range. That is why the separation is quite low even for PEO of molecular weight 400 000 Da. As shown on the SEM images of Fig. 7, the pores of sepiolite membranes are neither spherical nor cylindrical, besides the sepiolite membrane was formed by layers of fibres. This may be the reason for the broad pore size distribution. Pore density and surface porosity were calculated according to the Eqs. (7) and (8). The results are shown in Table 3. The table shows that pore density and surface porosity do not depend very much on the amount of sepiolite used. Instead, they depended highly on the method of clay dispersion. The aggregation of the fibre bundles is prevented by sonifying the clay suspension. As a consequence, the pore density and surface porosity of the membrane increased, resulting in higher flux. This was despite the fact that the membrane thickness increased as a result of sonification. Comparing the thickness of the membrane (43–114 ␮ m) with the diameter of the sepiolite fibre (0.2–0.4 ␮ m), the former is 107.5–570 times as large as the latter. This indicates that the membranes were formed by assembling layers of completely disordered fibres. Therefore, a large portion of the pores formed is dead ended or blocked between layers of fibres. The pore density and surface porosity calcu- lated above are only for the pores which could pass through the entire cross-section of membrane. Fig. 7 shows SEM images of sepiolite membranes. It is very clear that the membrane is constructed by layers of disordered sepiolite. It should be noted that it is easy to prepare pinhole- and crack-free membranes from sepiolite because of its fibrous nature. The SEM image also shows that fibres are better dispersed in the membrane prepared from ultrasonified suspension, unlike the membrane made by applying magnetic stirring, where a network of fibre bundles is observed. 1. Ultrafiltration membranes can be prepared from sepiolite clay material. 2. The method to prepare sepiolite membranes requires only one step (spreading of clay suspension on a smooth surface) before calcination, while the sol–gel method requires three steps (precipitation, peptization and gelling). Thus, the preparation of siepiolite membrane is much simpler. 3. The sepiolite membrane so prepared has a broad pore size distribution due to its multilayer structure of sepiolite fibres. 4. Dispersion of sepiolite fibre is better performed by sonification than by magnetic stirring. The authors wish to thank China Scholarship Coun- cil for the scholarship it provided. The authors also would like to thank NSERC for a Research Grant (CD) and for a postdoctoral ...

Context 2

... 80% of pores have the diameters less than 50 nm. The largest pore size is over 130 nm. Probability density function curves are illustrated on Fig. 6 by using the values of mean pore size and geometrical standard deviation. As shown on Fig. 6, all the membranes have quite similar trends and pore sizes cover a broad range. That is why the separation is quite low even for PEO of molecular weight 400 000 Da. As shown on the SEM images of Fig. 7, the pores of sepiolite membranes are neither spherical nor cylindrical, besides the sepiolite membrane was formed by layers of fibres. This may be the reason for the broad pore size distribution. Pore density and surface porosity were calculated according to the Eqs. (7) and (8). The results are shown in Table 3. The table shows that pore density and surface porosity do not depend very much on the amount of sepiolite used. Instead, they depended highly on the method of clay dispersion. The aggregation of the fibre bundles is prevented by sonifying the clay suspension. As a consequence, the pore density and surface porosity of the membrane increased, resulting in higher flux. This was despite the fact that the membrane thickness increased as a result of sonification. Comparing the thickness of the membrane (43–114 ␮ m) with the diameter of the sepiolite fibre (0.2–0.4 ␮ m), the former is 107.5–570 times as large as the latter. This indicates that the membranes were formed by assembling layers of completely disordered fibres. Therefore, a large portion of the pores formed is dead ended or blocked between layers of fibres. The pore density and surface porosity calcu- lated above are only for the pores which could pass through the entire cross-section of membrane. Fig. 7 shows SEM images of sepiolite membranes. It is very clear that the membrane is constructed by layers of disordered sepiolite. It should be noted that it is easy to prepare pinhole- and crack-free membranes from sepiolite because of its fibrous nature. The SEM image also shows that fibres are better dispersed in the membrane prepared from ultrasonified suspension, unlike the membrane made by applying magnetic stirring, where a network of fibre bundles is observed. 1. Ultrafiltration membranes can be prepared from sepiolite clay material. 2. The method to prepare sepiolite membranes requires only one step (spreading of clay suspension on a smooth surface) before calcination, while the sol–gel method requires three steps (precipitation, peptization and gelling). Thus, the preparation of siepiolite membrane is much simpler. 3. The sepiolite membrane so prepared has a broad pore size distribution due to its multilayer structure of sepiolite fibres. 4. Dispersion of sepiolite fibre is better performed by sonification than by magnetic stirring. The authors wish to thank China Scholarship Coun- cil for the scholarship it provided. The authors also would like to thank NSERC for a Research Grant (CD) and for a postdoctoral ...