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2017
Application of thermoporometry for
characterization of mesoporous silicon:
In search for probe liquid aimed at large pores
Majda, D
Elsevier BV
Tieteelliset aikakauslehtiartikkelit
© Elsevier Inc
CC BY-NC-ND https://creativecommons.org/licenses/by-nc-nd/4.0/
http://dx.doi.org/10.1016/j.micromeso.2017.12.028
https://erepo.uef.fi/handle/123456789/6205
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Accepted Manuscript
Application of thermoporometry for characterization of mesoporous silicon: In search for probe liquid aimed at large pores
D. Majda, T. Ikonen, A. Krupa, V.-P. Lehto, W. Makowski
PII: S1387-1811(17)30811-9
DOI: 10.1016/j.micromeso.2017.12.028 Reference: MICMAT 8717
To appear in: Microporous and Mesoporous Materials Received Date: 11 October 2017
Revised Date: 20 December 2017 Accepted Date: 22 December 2017
Please cite this article as: D. Majda, T. Ikonen, A. Krupa, V.-P. Lehto, W. Makowski, Application of thermoporometry for characterization of mesoporous silicon: In search for probe liquid aimed at large pores, Microporous and Mesoporous Materials (2018), doi: 10.1016/j.micromeso.2017.12.028.
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1
Application of thermoporometry for characterization of mesoporous silicon: In search for probe liquid aimed at large pores
D. Majda
a*, T. Ikonen
b, A. Krupa
c, V-P. Lehto
b, W. Makowski
aa Faculty of Chemistry, Jagiellonian University in Kraków, Gronostajowa 2, 30-387 Kraków, Poland;
b Department of Applied Physics, University of Eastern Finland, Kuopio, Finland;
c Department of Pharmaceutical Technology and Biopharmaceutics, Faculty of Pharmacy, Medical College, Jagiellonian University in Kraków, Medyczna 9, 30-688, Kraków, Poland.
* Corresponding author:
e-mail address: majda@chemia.uj.edu.pl; phone: +48 12 686 23 37 (D. Majda)
Abstract
Characterization of porous samples containing mesopores larger than 10 nm in size is often difficult due to limitations of standard methods. In the present work thermoporometry (TPM) was introduced to address these challenges. Various probe liquids (water, n-heptane, cyclohexane and o-xylene) were previously applied for TPM characterization of mesoporous silicon containing pores of 20-50 nm. The results, obtained with the use of calibration equations, confirmed the necessity of new probe liquid more suitable for characterization of such samples. Octamethylcyclotetrasiloxane was found to be the most appropriate choice.
Mesoporous silicon samples were used as model materials in order to establish an empirical equation between the pore sizes, derived from mercury porometry, and the solid-liquid transition temperature depressions derived from differential scanning calorimetry for the octamethylcyclotetrasiloxane confined inside the pores and in bulk phase. The new calibration equations obtained within this work can be successfully used for characterization of the samples with large mesopores.
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2 Keywords: Porous silicon, Pore size distribution, Thermoporometry, Octamethylcyclotetrasiloxane.
1. Introduction
Mesoporous materials (i.e. solids possessing pores of 2-50 nm in diameter) have nowadays attracted substantial interest due to their increasing use in various fields, such as catalysis [1], adsorption [2], electronics [3], chromatography [4], drug delivery [5, 6] and medical diagnostics [7]. Thorough understanding of mesoporous solids requires specific characterization methods, especially concerning their porosity. Generally, the techniques frequently used for the purpose are based on electron microscopy, X-ray scattering, liquid intrusion or gas sorption. Mercury intrusion porosimetry (MIP) and low temperature sorption of nitrogen are being considered the standard methods, regardless their limitations [8]. MIP is the most popular method for characterization of macropores [9], but in theory, pores from 3.5 nm to 500 µm can be analysed with this technique [10]. However, the high pressure required in measurements may result in crushing of the solid or deformation of the pores. This concern is especially important in assessing accurately the pore sizes of soft materials such as paper or membrane media. Moreover, application of the method is limited to dry samples, because mercury would not displace the liquid water occupying the pores. This could be a disadvantage when characterizing hydrophilic samples.
Gas sorption is another popular technique because it allows assessing a wide range of pore sizes, covering essentially the micro-mesopore range [11]. However, it also has some drawbacks that are often not taken into consideration. For example, at a specific pressure the adsorbate evaporates from large open straight pores, but the pores of the same size that are connected to the surface via narrower channels remain filled (ink bottle effect). Such a
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3 complex mechanism of emptying the pores affects the shape of the desorption isotherm and the resulting pore size distribution [12]. Moreover, for gas sorption techniques, operating on the principle of the micropore filling and the capillary condensation in the mesopores, an understanding of the properties of the liquid phase confined inside the pores (such as density), which may be different from those of the liquid adsorbate under standard conditions, is crucial. Besides, the accuracy and precision of the pore sizes and volumes determined from N2 adsorption isotherms for large mesopores (20-50 nm) is low, as this pore size range corresponds to a very narrow range of relative pressures (ca. 0.90-0.96).
Comparison of the standard methods for porosity characterisation indicates that neither of them is well suited for analysis of large mesopores (20-50 nm). This gap can probably be filled by thermoporometry (TPM), the technique based on the fact that a liquid confined in pores experiences a considerable depression of its liquid to solid transition temperature (∆T).
This is related to the size of the pores according to the Gibbs -Thomson equation [13]. In the standard TPM experiment, the sample is soaked in the liquid medium, whose melting or crystallization profiles are measured with differential scanning calorimetry (DSC). This method is simple, inexpensive and nondestructive. Additionally, it requires only a small amount of sample (ca. 2 mg) and short measurement time (about 30 minutes). Owing to the possibility of using different liquid compounds TPM offers a wide range of potential applications [14]. In the previous papers we compared the use of water and selected n-alkanes in porosity characterization of ordered mesoporous silicas by means of TPM and reported the impact of experimental procedure on the outcomes. Additionally, we provided calibration equations for TPM with various probe liquids and demonstrated the potential of the method for characterization materials whose porosity is difficult to be studied by other techniques [15- 19]. The calibration was performed with the use of several mesoporous silicas SBA-15.
Owing to their ordered pore system, uniform pore size, the ease of tailoring the mesopore
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4 sizes and relatively thick silica walls providing high stability and ensuring long storage time, they were regarded as ideal model mesoporous materials [20]. The aim of the present work is to explore applicability of the previous findings for characterization of porous silicon, differing from SBA-15 silicas in pore sizes and chemical properties of the surface. In addition, since it is difficult to synthesize silicas containing mesopores larger than 20 nm in diameter, porous silicon samples were used as model materials in searching for the liquid that can be employed as a probe in TPM measurements aimed at characterization of large pores (20-50 nm).
2. Experimental
2.1. Materials
Porous silicon (PSi) films were prepared by electrochemical etching of boron-doped silicon wafers with <100> crystal orientation and wafer resistivity of 3 mΩ cm or 20 mΩ cm (Okmetic). The etching was performed by applying a constant current density in an aqueous 38 % hydrofluoric acid (VWR)/ethanol (Altia) electrolyte (3:1 or 1:1, for 3 mΩ cm and 20 mΩ cm wafers, respectively). The porous films were crushed first in a mortar and then milled with a planetary ball mill (Fritsch Pulverisette 7) using zirconia 10 mm milling balls. The particles were sieved through 25/50 µm sieves (Precision Eforming). Sieving was performed both before and after the surface carbonization of the particles to prevent agglomeration. The particles were dipped in hydrofluoric acid (HF) to activate the surface for carbonization at 820 °C under acetylene atmosphere [21]. To obtain larger pores, annealing was made under nitrogen atmosphere before the carbonization. The detailed information of parameters used for the sample preparation were collected in Table 1.
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5 Table 1. Parameters used for PSi sample preparation
2.2. Nitrogen adsorption-desorption isotherms
The adsorption and desorption isotherms of nitrogen at 77 K were obtained using a Micromeritics Tristar II 3020 sorptometer. Prior to the measurement the samples were outgassed for 1h at 65 °C. Specific surface area determination was based on BET formalism.
The mesopore size distributions and average pore size values were calculated from the desorption branch using the classical BJH scheme [22].
2.3. Mercury intrusion porosimetry (MIP)
MIP measurements were carried out using a Quantachrome PoreMaster 60 instrument.
Samples of about 0.13 g were placed in the glass measuring chamber and evacuated to the pressure of 30 mmHg (4 kPa). The values of the parameters used were 0.486 M/m for the surface tension of mercury and 130° for the angle of contact between mercury and pore wall.
All measurements were performed both in the low pressure range (1 - 50 kPa), and in the high pressure range (50 kPa - 400 MPa), allowing analysis of the pore size distributions from 10 to 250 µm, and from 3 nm to 10 µm, respectively.
2.4. Thermoporometry (TPM)
Thermoporometry experiments were performed using a Mettler Toledo apparatus DSC 822e, with the sensitivity of 4.10−6 W, equipped with a liquid nitrogen cooling system (Criofab).
The calibrations of heat flux and temperature were done according to the manufacturer user guide using the n-octane, indium and zinc standards. The tolerance in the temperature calibration was 0.2°C. The melting point depression was determined relative to that of the excess phase, hence each experiment was internally calibrated for the temperature [14].
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6 Before the actual measurement, the sample was placed in an aluminium pan, heated to 400 °C and kept at this temperature for 30 minutes in order to remove water from the pores. After cooling down to room temperature, the appropriate probe liquid was added and the pan was hermetically sealed with an aluminium lid. In studies where water was used as the probe liquid the pre-treatment was skipped. To avoid any super-cooling effect, the samples were quenched far below the equilibrium freezing temperature at a cooling rate β = 10 K/min and then heated with β = 2 K/min. The cooling and heating rates were chosen according to previous experiments described in detail elsewhere [16, 19]. After the TPM experiment a small hole was made in the crucible’s lid and the sample was heated up to 200 °C in order to evaporate the liquid component and determine its mass. The measurements were repeated a few times to confirm their reproducibility. Pore size distribution was determined from the solid to liquid DSC profiles.
3. Results and discussion
The N2 adsorption and desorption isotherms (Fig. 1SI in supporting materials), attributed to type IV with H1-type hysteresis, confirmed mesoporosity of the studied materials and differences in pore sizes [11]. This conclusion is corroborated by the pore size distributions (PSD, Fig. 1a) as well as the values of porous parameters obtained from analysis of N2 adsorption/desorption isotherms (Table 2). The results are in agreement with MIP outcomes (Fig. 1b). The main differences in the pore size given by N2 and MIP are observed for the samples with the smaller and the larger pores. Probably the differences origin from the limitation of both methods: large pore size cannot be precisely investigated by nitrogen isotherms while small pores are difficult to be studied by MIP. Moreover, for the samples T5 and T6 the PSD profile is wide, thus the value of the pore diameter (the maximum of the peak) is not strictly defined. Differences in pore volume for T6 seem to have the same reason.
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7 However, the most visible dissimilarity are observed for T3. This sample was prepared from wafer of the smallest resistivity and etching current density. Such conditions led to the material with relatively small specific surface area that seems to play an important role in intrusion process.
Fig. 1. a) Pore size distribution (PSD) profiles derived from low temperature N2 desorption isotherms based on BJH model and (b) from mercury intrusion porosimetry (MIP).
Table 2. Textural parameters of the porous silicon samples obtained from N2 desorption isotherm and mercury porosimetry. SSABET refers to specific surface area, D to pore width (diameter) and V to total pore volume.
DSC profiles of solid to liquid phase transition of liquid confined in porous material usually exhibit two separated peaks. The first endothermic peaks correspond to the melting of the probe confined in the pores while the second ones result from the melting of the probe outside the pores (bulk phase) [11]. Part of DSC profiles illustrating phase transition of water, n- heptane, cyclohexane, orto-xylene and octamethylcyclotetrasiloxane (OMSTS) confined in pores of the samples with the smallest (T1) and with the widest pores (T5 and T6) are shown in Fig. 2. Unabridged profiles for all studied materials are provided in supplementary materials (Fig. 2SI and 3SI).
In the TPM measurements water was employed as a first-choice probe liquid. Water’s heat of fusion, ∆Hm = 334 J/g, is large thus enhances the sensitivity of the DSC technique and allows measurements with higher precision [11]. On the other hand, n-alkanes with non-polar molecules exhibiting weaker surface-fluid interactions, can be used for investigation porosity of hydrophobic materials. Among them n-heptane was found to be the most appropriate for TPM [17]. In our previous investigations we found out that water and n-heptane used as a probe liquid in TPM provide reliable results only for pores up to 10 nm in size [18, 19]. For
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8 larger pores the ∆T becomes smaller. Thus, for large pores the differences in melting temperature in pores and in bulk phase can be so small that the melting peaks overlap. Indeed, in DSC profiles obtained with water and n-heptane for T5 and T6 (Fig. 2a and 2b, respectively) the peaks corresponding to the pores are not well separated from those originating from the bulk phase. This seriously hinders data interpretation. The problem can be solved by decreasing heating rate that would give better peak separation but simultaneously it would decrease measurements accuracy and drastically increase experimental time and costs [23].
Fig. 2. Part of DSC profiles illustrating phase transition of water (a), n-heptane (b), cyclohexane (c, d), orto-xylene (e) and octamethylcyclotetrasiloxane (f) confined in pores of the samples with the smallest (T1) and with the wider pores (T5 and T6).
Another liquid employed for porosity characterization was cyclohexane. It is quite commonly used for TPM because it is nonpolar and has well-defined solid liquid and solid-solid phase transitions [24]. In this work we used not only the liquid to solid but also more energetic solid to solid phase transition (Fig. 2c, d). The later is the evolution from a rigid crystal state (ordered, monoclinic) to a plastic crystal phase (disordered) [25]. Unfortunately, the temperature depression observed for samples with large pores is too small for the effortless data interpretation (Fig. 2c).
o-Xylene has been proposed by Dessources et al. as a probe solvent for characterization of materials exhibiting meso- and macropores [26]. However, as it can be seen in Fig. 2e, the overlapping of the melting peaks in pore and in bulk phase does not allow simple interpretation.
Octamethylcyclotetrasiloxane (OMCTS) was presented and investigated as probe liquid for NMR crioporometry by Vargas-Florencia et al. but it has never been applied for TPM [27].
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9 OMCTS is chemically inert, non-volatile, non-toxic and has a bulk melting point near 20 °C.
Furthermore, it also wets both hydrophilic and hydrophobic surfaces [27]. DSC profiles of melting OMCTS contained inside the porous silicon samples exhibit well separated peaks regardless the pore size [Fig. 2f and Fig. 3SIef]. This confirms potential of OMCTS as the probe liquid in TPM.
In order to transform the DSC profiles into the pore size distribution (PSD) the temperature axis must be converted into a pore size scale and the heat flow output into the differential pore volume. The basis for relating temperature to pore diameter is through the Gibbs–Thompson equation (1):
dV K dA dV
dA H T T
T
T ls =−
− ∆
=
−
=
∆ ρ
γ 0
0 (1)
where ∆T is the melting point depression, T0 is the bulk melting temperature, γls is the surface tension of liquid–solid interface, ρ is the density, ∆H is the specific enthalpy of melting, and dA/dV is the curvature of the solid–liquid interface which is 1/r for cylinders and 2/r for spheres, where r is the radius of the curvature [13].
The detailed procedure of such conversion was described earlier [11, 15]. Generally, the heat flow curve, dQ/dt, is converted to dVp/dRp according to the equation:
ρ
f p
p p
H m dR
T d T d
dt dt dQ dR
dV
∆
∆
= ∆ ( ) 1
)
( (2)
where d(∆T)/dt is the scanning rate of the DSC experiment, m the mass of dry porous material, and ∆Hf and ρ the heat of fusion and density for the probe fluid, respectively. The relation d(∆T)/dRp may be based on the Gibbs-Thomson equation but because of unavoidable disregard of the temperature dependence of the parameters used therein it may introduce systematic deviations in the calculated PSD and lead to erroneous results. In order to avoid this problem a calibration procedure, based on the reference materials with known pore sizes is recommended. Detailed calibration procedure was described elsewhere [16, 19].
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10 Pore size distributions of all porous silicon samples can be found in supporting materials (Fig.
4SI). The water- and heptane-based PSDs were calculated with the use of empirical equations established for a series of mesoporous SBA-15 silicas, reported in our previous papers [15- 19]. Additionally, the similar calibration curves were obtained for cyclohexane and o-xylene (Fig. 5SI). The pore sizes derived as maxima of PSDs follow the same trend as the corresponding ones obtained from MIP. However, as it can be seen in Fig. 3, the numerical values are close only for the narrow-pore samples. For the pores larger than 20 nm the pore size is underestimated. Water is the only probe liquid that provide similar values of pore size but the intensity of PSD peaks (and thus the values of pore volume) are generally lower. This leads to the conclusion that the previously established empirical equations are suitable for characterization of silicon containing narrow pores but cannot be successfully used for the samples with larger mesopores, therefore further investigations are needed.
Fig. 3. Pore diameter obtained from N2-BJH and TPM measurements versus pore diameter derived from MIP experiments
Since it is difficult to synthesize model silicas containing mesopores larger than 20 nm in diameter, porous silicon samples were used as model materials in search for a liquid that can be employed as a probe in TPM measurements aimed at characterization of large mesopores.
To establish the calibration relationships the pore sizes previously determined from the MIP were plotted versus the inverse of the melting point depression and fitted with linear functions (Fig. 4). It stays in agreement with the literature reports that usually consider the relationship between D and 1/∆T to be linear [11]. In such case, the slope of the fitted line represents the parameter of the Gibbs-Thompson equation (eq. 1) while the intercept reflects the thickness of the non-freezing layer. Although it is also known that the thickness of the non-freezing layer depends on temperature (which introduces subtle non-linearity into the correlation between D
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11 and 1/∆T) the analysis of the experimental data showed that the relations D (1/∆T) observed for all the studied systems were linear [28].
Fig. 4. Fitting relations between the pore diameters (D) obtained from MIP measurements and the inverse of melting point depression of water (a), n-heptane (b), cyclohexane (c, d), o-
xylene (e) and OMCTA (f) with linear functions.
Empirical equations obtained for water and n-heptane indicate presence of surprisingly thick non-freezing liquid layer. In our previous works we observed that for larger pores the thickness of non-freezing water or n-heptane was the biggest, however, the values of 10 or 7 nm seem to be inflated [16, 19]. In the case of o-xylene the obtained equation is physically incorrect due to a negative value of the intercept. The most reliable are equations obtained for cyclohexane (solid-liquid) and OMCTS. The thickness of non-freezing liquid is 1.3 nm in both cases and R2 coefficient is high (for OMCTS it is the highest).
PSDs for silicon samples obtained with the use of the new calibration equations were presented in Fig. 6SI. They follow the trends observed previously. Only water-TPM allows to obtain high intensity of the PSD peak for sample with the smallest pores (T1). Three liquids:
water, n-heptane and OMCTS used as a probe in TPM can reflect complex character of PSD profiles observed for T5. However, the values of the pore size derived as the maxima of PSD peaks show that water and n-heptane cannot give reliable results for the wide-pore samples (Fig. 5). Thus, OMCTS seems to be the best recommendation for characterization of such materials by means of TPM.
Fig. 5. Pore diameter obtained from N2-BJH and TPM measurements with use of new established calibration equations versus pore diameter derived from MIP experiments
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12 Comparison of pore volume obtained from TPM as PSD peaks area with corresponding data derived from MIP is presented in Fig. 6a.
Fig. 6. The values of pore volume obtained from TPM as PSD peaks area versus corresponding data derived from MIP (a) and BJH (b).
The PSD plots based on TPM experiments have for most cases almost the same tendency as BJH results, suggesting that nitrogen sorption better reflects the pore volume than MIP. The results provided in Fig. 6b confirm this observation. Thus, in order to find the calibration equation for pore volume the relation between the volumes derived from BJH and the corresponding ones obtained from OMCTS-TPM were plotted (Fig. 7).
Fig. 7. Fitting relations between the pore volume (V) obtained from N2-BJH measurements and the corresponding data derived from OMCTS-TPM experiments with linear functions.
Since the intensity of PSD profile for T1 is really small, indicating that large OMCTS molecules (molecular size 1.1 nm) are not able to penetrate the whole volume of small pores, the result for T1 was excluded from the calibration [29]. Linear fitting provided the equation that was applied for further characterization of studied materials. Based on it the PSDs were plotted and presented in Fig. 8 while the values of pore diameter and pore volume were collected in Table. 3. The results of OMCTS-TPM stays in agreement with data obtained using the other methods. This observation confirms that the OMCTS can be successfully used as a probe liquid in TPM and the empirical equations provided in this work can be applied for characterization of the materials containing large mesopores.
Fig. 8. Pore size distribution profiles derived from TPM with use of OMCTS as a probe liquid
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13 Table 3. Pore diameter (D) and pore volume (V) obtained from N2-BJH, MIP and OMCTS- TPM
4.
Conclusions
In the present work the weakness of standard techniques for characterization of mesoporous materials with pores larger than 10 nm in size was pointed out and thermoporometry was proposed as an alternative method. Based on a series of well characterized mesoporous silicon samples the TPM calibration equations were found for the liquids most often reported in the literature (water, n-heptane, cyclohexane and o-xylene). In summary, the following conclusions could be derived: a) regardless of the liquid used as the TPM probe, the previously established empirical equations are suitable for characterization of the narrow- mesopore silicon samples but cannot be successfully used for the ones containing larger mesopores; b) a series of silicon samples with large mesopores can be employed as model materials in order to establish calibration equations for TPM; c) only octamethylcyclotetrasiloxane (OMCTS) turned out to be the appropriate liquid for porosity characterization of wide pore silicon with use of TPM; d) the empirical equations for pore diameter and pore volume studied by OMCTS-TPM were established; e) the new-found calibration equations can be successfully applied for samples containing large mesopores that makes OMCTS-TPM, which is really fast, highly reproducible and does not require special equipment, very attractive for such investigations.
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Table 1. Parameters used for PSi sample preparation
T1 T2 T3 T4 T5 T6
Wafer resistivity [mΩ cm] 20 20 3 20 20 20
Etching current density [mA/cm2] 20 40 10 40 40 20
Annealing (temperature [°C]; time [min]) no no 700; 45 600; 45 700; 45 700; 45
Table 2. Textural parameters of the porous silicon samples obtained from N2 desorption isotherm and mercury porosimetry. SSABET refers to specific surface area, D to pore width (diameter) and V to total pore volume.
Sample N2 liq.(BJH) MIP
SSA BET [m2/g]
D [nm]
V [cm3/g]
D [nm]
V [cm3/g]
T1 131 12.7 0.60 14.6 0.63
T2 161 16.8 1.08 16.9 0.97
T3 47 19.7 0.38 20.7 0.17
T4 118 19.8 0.99 19.5 0.91
T5 80 37.1 1.06 38.0 0.87
T6 39 37.2 0.74 41.1 0.53
Table 3. Pore diameter (D) and pore volume (V) obtained from N2-BJH, MIP and OMCTS-TPM
BJH MIP OMCTS-TPM
Próbka D [nm]
V [cm3/g]
D [nm]
V [cm3/g]
D [nm]
V [cm3/g]
T1 12.7 0.60 14.6 0.63 12.9 0.19
T2 16.8 1.08 16.9 0.97 16.4 0.98
T3 19.7 0.38 20.7 0.17 18.9 0.30
T4 19.8 0.99 19.5 0.91 18.8 0.94
T5 37.1 1.06 38.0 0.87 35.1 1
T6 37.2 0.74 41.1 0.53 34.1 0.72
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Fig. 1. a) Pore size distribution (PSD) profiles derived from low temperature N2 desorption isotherms based on BJH model and (b) from mercury intrusion porosimetry (MIP).
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Fig. 2. Part of DSC profiles illustrating phase transition of water (a), n-heptane (b), cyclohexane (c, d), orto-xylene (e) and octamethylcyclotetrasiloxane (f) confined in pores of the samples with the smallest (T1) and with the wider pores (T5 and T6).
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Fig. 3. Pore diameter obtained from N2-BJH and TPM measurements versus pore diameter derived from MIP experiments
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Fig. 4. Fitting relations between the pore diameters (D) obtained from MIP measurements and the inverse of melting point depression of water (a), n-heptane (b), cyclohexane (c, d), o-xylene (e) and
OMCTA (f) with linear functions.
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Fig. 5. Pore diameter obtained from N2-BJH and TPM measurements with use of new established calibration equations versus pore diameter derived from MIP experiments
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Fig. 6. The values of pore volume obtained from TPM as PSD peaks area versus corresponding data derived from MIP (a) and BJH (b).
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Fig. 7. Fitting relations between the pore volume (V) obtained from N2-BJH measurements and the corresponding data derived from OMCTS-TPM experiments with linear functions.
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Fig. 8. Pore size distribution (PSD) profiles derived from TPM with use of OMCTS as a probe liquid
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Dorota Majda Kraków 30.11.2017
Jagiellonian University in Krakow Faculty of Chemistry
30-387 Kraków, Gronostajowa 2 +48 12 686 23 37
Poland
Highlights:
Octamethylcyclotetrasiloxan was used for the first time as the probe liquid in thermoporometry;
Empirical equation between pore size of mesoporous silicon and solid-liquid transition of octamethylcyclotetrasiloxane in the pores was determined for the first time.
The new calibration equation was recommended for characterization of the samples with mesopores of 20-50 nm in diameter.
