N2 adsorption-desorption isotherm

N2 adsorption-desorption isotherms revealed that MCs had hi surface area (>1200 m /g) and large pore volume (>1.0 cm /g). From SAXS patterns of the prepared materials, it was confirmed that pores of SBA-15 and CMK-3 retained highly ordered 2-dimensional hexagonal type arrangement [5], while MCM-48 had 3-dimensional cubic type pore structure. It should be noted that a new scattering peak of (110) appeared in the CMK-1 after the removal of MCM-48 template. Furthermore, the pore size of CMK-1 and the wall thickness of MCM-48 were found to be 2.4 nm and 1.3 nm, respectively. This result demonstrates that a systematic transformation of pore structure occurred during the replication process from MCM-48 to CMK-1 [6]. 

Specific surface area (SSA), total pore volume and average pore diameter were measured by N2 adsorption-desorption isotherms at 77K using Micromeritics ASAP 2020. The pore size was calculated on the adsorption branch of the isotherms using Barrett-Joyner-Helenda (BJH) method and the SSA was calculated using the Brunauer-Emmett-Teller (BET) method. 

Figure 2 shows us the N2 adsorption-desorption isotherm of Beta/montmorillonite composite. At low relative pressure a sharp adsorption of nitrogen indicates the existence of large amount of micropore. The hysteresis shown in figure 2 is ascribed to type H4 which usually can be observed on layered clay and other materials [2], It is obvious that part of the pore structure in montmorillonite is still preserved after calcination under high temperature and the following hydrothermal crystallization. 

Figure 2. N2 adsorption-desorption isotherm of Beta/montmorillonite composite...

N2 adsorption-desorption isotherms show instead occlusion of mesopores between 2 and 9 hours of immersion, possibly due to reaction of silica with SBF. This seems to vanish between 24 and 27 hours, only in the case of ibuprofen-loaded spheres. We suggest that in this latter case the entrapped molecules play a role in the temporary reopening of the pores. 

The N2 adsorption-desorption isotherms of dried chitosan gel and chitosan-zeolite composites are reported in Figure 4 (a). Dried chitosan gels present a surface area lower than 5 m2 g"1 and virtually no porosity, the evaporation of water having brought about the coalescence of the polymer fibrils. The composites with a small amount of zeolites (less than 8 % for the zeolite X composite) present a type 4 isotherm leaning towards... 

The N2 adsorption-desorption isotherms for MSU-Ge-2 show a type-lV adsorption branch associated with a well-defined capillary condensation step at P/Po 0.13, characteristic of uniform mesopores (Fig. 4). The adsorption data indicate a very high Brunauer-Emmett-Teller (BET) surface area of 363 m /g and a pore volume of 0.23 cm /g. Given that the Ge mesostructure is much heavier than the corresponding silica, this surface area is actually equivalent to silica with a surface area of 1,316 m /g. 

Nitrogen physisorption measurements evidence the permanent mesoporosity of the NU-GeSi-A materials (Fig. 11). All the N2 adsorption-desorption isotherms... 

Chemical composition of fresh HTs was determined in a Perkin Elmer Mod. OPTIMA 3200 Dual Vision by inductively coupled plasma atomic emission spectrometry (ICP-AES). The crystalline structure of the solids was studied by X-ray diffraction (XRD) using a Siemens D-500 diffractometer equipped with a CuKa radiation source. The average crystal sizes were calculated from the (003) and (110) reflections employing the Debye-Scherrer equation. Textural properties of calcined HTs (at 500°C/4h) were analyzed by N2 adsorption-desorption isotherms on an AUTOSORB-I, prior to analysis the samples were outgassed in vacuum (10 Torr) at 300°C for 5 h. The specific surface areas were calculated by using the Brunauer-... 

Calculated from the adsorption curve of the N2 adsorption/desorption isotherm. 

Figure 3. (A) XRD patterns and (B) N2 adsorption/desorption isotherms of the calcined mesoporous silica ropes obtained from the C,6TMAB-HNO3-TEOS-(PEO-6000)-H2O system before and after the post-synthesis ammonia treatment at 100 °C and a further hydrothermal stability test in water at 100 °C.

As indicated by XRD patterns, there exist just 2-3 broad peaks in the calcined acid-made materials (Fig. 3A). Moreover, the N2 adsorption/desorption isotherm shown in Fig. 3B, the calcined acid-made mesoporous silica indeed possesses a broad capillary condensation at the partial pressure p/p0 of ca. 0.2-0.4, indicating a broad pore size distribution with a FWHM ca. 1.0 nm calculated from the BJH method. This is attributed to the occurrence of partial collapse of the mesostructure during the high temperature calcination. The hexagonal structure completely collapsed when subjected to further hydrothermal treatment in water at 100 °C for 3 h. Mesoporous silica materials synthesized from the acid route are commonly believed to be less stable than those from the alkaline route [6,7]. 

Figure.2 N2 adsorption /desorption isotherms for the calcined STO-B silica.

The N2 adsorption /desorption isotherms (Figure 2) for calcined STO shows abrupt step at P/Po = 0.1—0.4 and no obvious hysteresis loop at low relative pressure, indicating the pore size of this materials is uniform. The BET specific surface area and BJH pore diameter are 934 m2/g and 4.3nm, respectively. 

Fig.2 N2 adsorption-desorption isotherms of calcined and hydrothermally treated MCM-41 samples, (a) normally synthesized and (b) TPA added (TPA /surfactant = 1 4).

XRD patterns were obtained with a Rigaku D/MAX-IIA diffractometer system equipped with Ni-filtered Cu-Ka radiation. N2 adsorption/desorption isotherms were measured with a Micromeritics ASAP 2010 system. NH3-TPD was conducted under He flow of 30 ml/min and a heating rate of 20 °C/min. 

Figure 2. N2-adsorption-desorption isotherms (left) and X-ray diffraction patterns in the low angle region, important for mesoporous structures (right) for samples A-C, calcined at 550°C and steamed at 650 and 815°C, respectively, c, calcined s, steamed.

N2 adsorption-desorption isotherms and pore size distribution of sample II-IV are shown in Fig. 4. Its isotherm in Fig. 4a corresponds to a reversible type IV isotherm which is typical for mesoporous solids. Two definite steps occur at p/po = 0.18, and 0.3, which indicates the filling of the bimodal mesopores. Using the BJH procedure with the desorption isotherm, the pore diameter in Fig. 4a is approximately 1.74, and 2.5 nm. Furthermore, with the increasing of synthesis time, the isotherm in Fig. 4c presents the silicalite-1 material related to a reversible type I isotherm and mesoporous solids related to type IV isotherm, simultaneously. These isotherms reveals the gradual transition from type IV to type I. In addition, with the increase of microwave irradiation time, Fig. 4c shows a hysteresis loop indicating a partial disintegration of the mesopore structure. These results seem to show a gradual transformation... 

Fig. 4. N2 adsorption-desorption isotherms of (a) sample 11, (b) sample III, and (c) sample IV, and pore size distribution of (a ) sample II, (b1) sample III, and (c ) sample IV of micro-mesoporous composite materials.

Figure 4. N2 adsorption-desorption isotherms and pore size distribution curves of SBA after different treatments (al.bl) pH=2 (a2,b2) pH=7 (a3,b3) pH=l 1 (cl.dl) parent (c2,d2) vapor at 723K and (c3,d3) calcination at 1073K...

Although the surface area, pore diameter and total volume of AMM samples decreased (as a result of post-synthesis alumination), their pore size distributions are still very narrow. For example, Figure 2 shows that, even having an AI2O3 loading of 10 wt.%, AMM-10 has N2 adsorption-desorption isotherms similar to that of PSM material. The capillary condensation for mesopores is in a very narrow range of P/Po = 0.2-0.35. A sharp pore size distribution peak (25-30 A) is obtained from the isotherm. The results indicate that the uniform mesoporous structure of MCM-41 is still well maintained after post-synthesis alumination. 

The nitrogen adsorption-desorption isotherms were obtained at 77K by AutoSorb-1-C (Quantachrome). Prior to measurement, the PSM and AMM samples were outgassed at 300°C for 3 h. The specific surface areas of the samples were determined from the linear portion of the BET plots. The pore size distribution was calculated from the desorption branch of N2 adsorption-desorption isotherm using the conventional Barrett-Joyner-Halenda (BJH) method. 

Figures 1(a) and 1(b) show the N2 adsorption-desorption isotherms of PSM and AMM samples after treatment in boiling water for 1 day and 10 days, respectively. After 1 day in boiling water, the two AMM samples (i.e. AMM-1 and AMM-5) show slightly higher N2 adsorption than that of PSM. Due to the addition of Na+, Br or Cl" in the synthetic gel mixture, the synthesis of PSM was under the presence of those...

Figure 1. N2 adsorption-desorption isotherms of PSM and AMM samples before any treatment (solid mark) and after treatment in boiling water for (a) 1 day and (b) 10 days...

The X-ray diffraction (XRD) patterns of the sample were measured using Rigaku D-Max. II VC X-ray diffractometer using nickel filtered Cu Ka (X= 1.5406 A) radiation. The specific BET surface area and average pore sizes were determined by N2 adsorption-desorption isotherms at 77 K using an Omnisorp-lOO. Diffuse reflectance UV-spectra were obtained using Perkin Elmer Lambda 5 spectrophotometer using mesoporous silica MCM-41 or MCM-48 as a standard. The details are already reported earlier [27]. 

The N2 adsorption-desorption isotherm at -196°C and the micro- and mesopore size distributions are presented in figure 2. In the partial pressure range -0.02-0.3 the upward deviation indicates the presence of supermicropores (15-20A) or small mesopores (20-25A). From the De Boer t-plot the presence of an important microporosity can be deduced, so a unique combined micro- and mesoporosity is present for this type of material. Indeed, this combined pore system is confirmed when considering the micropore (Horvath-Kawazoe) and mesopore (Barrett-Joyner-Halenda) size distributions with maxima at respectively 6A and 17.5 A pore diameter (figure 5). An overview of the surface area, micro- and mesoporosity data of the unmodified PCH can be found in table 1. 

Powdered, particulate MCM-41 molecular sieves (Si/Al = 37) with varied pore diameters (1.80, 2.18, 2.54 and 3.04 nm) were synthesized following the conventional procedure using sodium silicate, sodium aluminate and C TMAB (n = 12, 14, 16 and 18) as the source materials for Si, A1 and quaternary ammonium surfactants, respectively [13]. Each sample was subjected to calcination in air at 560 °C for 6 h to remove the organic templates. The structure of the synthesized material was confirmed by powder X-ray diffraction (XRD) and by scanning/transmission electron microscopy. Their average pore sizes were deduced from the adsorption curve of the N2 adsorption-desorption isotherm obtained at 77 K by means of the BJH method (Table 1). 

Figure 1. N2 adsorption/desorption isotherms and pore size distribution of MCM-41 containing various T-atoms.

---