Nitrogen adsorption measurements

MCM-41 samples have been characterized by means of powder X-ray diffraction (X Pert Philips, CuKa radiation), nitrogen adsorption measurements at 77 K (Quantachrome Autosorbl) and Field Emission Scanning Electron Microscopy (Assing FESEM Supra 25) before soaking in SBF and after different immersion times. 

Nienow (1983a) observed a delay in the start of particle growth when binder was added to a bed of porous particles and stable fluidization under conditions which produced quenching with non-porous particles. Nitrogen adsorption measurements showed that the pore surface area of alumina decreased as spraying proceeded, indicafing that an effective reduction in pore volume was taking place. 

Nitrogen adsorption measurements were done using a Micromeritics model ASAP 2010 adsorption analyzer (Norcross, GA). Adsorption isotherms were measured at -196°C over the interval of relative pressures from 10 6 to 0.995 using nitrogen of 99.998% purity. Before each analysis the sample was degassed for 2 hours at 150°C under vacuum of about 10 Torr in the degas port of the adsorption apparatus. 

Figure 3. Nitrogen adsorption measurement a) calcined MCM-41, b) outer surface silylated, c) APTES-functionalized material and d) grafted rhodamine dye.

The volumetric method is mainly used for the purpose of determining specific surface areas of solids from gas (particularly nitrogen) adsorption measurements (see page 134). The gas is contained in a gas burette, and its pressure is measured with a manometer (see Figure 5.4). All of the volumes in the apparatus are calibrated so that when the gas is admitted to the adsorbent sample the amount adsorbed can be calculated from the equilibrium pressure reading. The adsorption isotherm is obtained from a series of measurements at different pressures. 

The following data refer to the adsorption of /t-butane at 273 K by a sample of tungsten powder which has a specific surface area (as determined from nitrogen adsorption measurements at 77 K) of 6.5... 

Seaton NA, Walton JPRB, and Quirke N. A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. Carbon, 1989 27(6) 853-861. 

M. Kruk, M. Jaroniec, and A. Sayari, Application of large pore MCM-41 molecular sieves to improve pore size analysis using nitrogen adsorption measurements, Langmuir 13, 6267-6273 (1997). 

It is essential to take into account a number of potential sources of experimental error in the determination of an adsorption isotherm. In the application of a volumetric technique involving a dosing procedure it must be kept in mind that any errors in the measured doses of gas are cumulative and that the amount remaining unadsorbed in the dead space becomes increasingly important as the pressure increases. In particular, the accuracy of nitrogen adsorption measurements at temperatures of about 77 K will depend on the control of the following factors ... 

This encouraging preliminary synthetic work needs to be followed by a detailed structural analysis of the Pc network materials. In particular, the potential nanoporosity of the 3-D system is to be explored using nitrogen adsorption measurements. Should a high surface area be obtained, these materials would offer an interesting alternative to zeolite encapsulated Pcs for efficient heterogeneous catalysis. 

The porous nature of the Qo crystals has now been examined in more detail by Kaneko and his co-workers (Setoyama et al., 1996 Thess et al., 1996). The Cw powder was recrystallized from carbon disulfide and then studied before and after annealing by heat treatment The nitrogen adsorption measurements revealed that the recrystallized material was both microporous and mesoporous the mesoporosity was completely removed by heat treatment, but the sample remained microporous. Since the micropores and the molecules appeared to be of similar size, it was concluded that the micropores were largely in the form of molecular defects and lattice vacancies. 

Characterization Powder X-ray diffraction patterns (XRD) were recorded with a Rigaku D/Max-llA diffractometer with Cu Ka radiation. TEM images were taken on a JEM-2010 microscope (JEOL), operated at 200 kV. Scanning electron microscopy (SEM) was obtained with a Philip XL30. Nitrogen adsorption measurements were performed at 77 K using a Micromeritics Tristar 3000 analyzer. The samples were pretreated at 473 K under the blow of the N2 for at least 3 h. 

The specific pore volume can be determined from nitrogen adsorption measurements if the adsorbent is meso- or microporous. For macroporous adsorbents with pore diameters above 1000 A, the pore volume can be determined by mercury penetration measurements by integrating the pressure volume curve. The total pore volume of meso- and microporous adsorbents can be calculated by assuming that, in the range 0.95 < pjpo < 1, all pores in the adsorbent are filled with condensed gas. The total pore volume is then simply calculated as ... 

More recentfy Mohlin and Gray (9J) determined adsorption isotherms on cellulose fibers for a variety of adsorbates (solutes). From the experimental type II isotherms specific surface areas of the fibers were computed, for eadi solute, with the results en in Table 11. The agreement observed between the different solutes is quite remarkable considering that the area of the solute molecule on the potymer surface must be known or estimated. Hie sirface area determined by nitrogen adsorption measurements at —196° was included for the purpose of comparison. The sli t di arity could possibly indicate that the area available to the smaller nitrogen molecule may be somewhat larger (1.9 compared to 1.6 m g" ). 

The other interesting observation concerns the surface area determined using the H2O monolayer capacity. We notice that the surface area values are far away from the surface area values determined from the nitrogen adsorption measurements. 

Most of the surface area values determined with water correspond to 30 - 40% of the surface area values calculated from the nitrogen adsorption measurements. Furthermore, the evolution of this ratio seems to be related to the nitrogen 5 bet value of silica. Indeed for the samples having 5bet(N2) values equal or higher than 200 m /g, the water measured surface area corresponds to 40 - 50% of the latter. 

After the TPR experiment, the samples exhibit a gray-red color, which is typical for copper metal clusters. The existence of large metal clusters after severe reduction was detected by XRD, which shows two reflections at 20 = 44.0 ° and 59.5 ° typical for copper metal The structural integrity of the samples after TPR has been confirmed by XRD and nitrogen adsorption measurements. Nevertheless, the location of the CuO clusters and the copper metal clusters after reduction still remain uncertain. It has been shown previously that the channel diameter influences the cluster size at least in the first redox cycle [4]. Clusters initially located in the channels will, however, migrate to the outer surface after several redox cycles accompanied by agglomeration [13],... 

Metallic nanopartides were deposited on ceramic and polymeric partides using ultrasound radiation. A few papers report also on the deposition of nanomaterials produced sonochemically on flat surfaces. Our attention will be devoted to spheres. In a typical reaction, commerdally available spheres of ceramic materials or polymers were introduced into a sonication bath and sonicated with the precursor of the metallic nanopartides. In the first report Ramesh et al. [43] employed the Sto-ber method [44] for the preparation of 250 nm silica spheres. These spheres were introduced into a sonication bath containing a decalin solution of Ni(CO)4. The as-deposited amorphous clusters transform to polyciystalline, nanophasic, fee nickel on heating in an inert atmosphere of argon at a temperature of 400 °C. Nitrogen adsorption measurements showed that the amorphous nickel with a high surface area undergoes a loss in surface area on crystallization. 

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