Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia StrategyP-32

Study Of In-situ And Ex-situ Porosity Of Mesoporous Silica Gel
M L Palash1,2, Sourav Mitra3, Kyaw Thu1,2, Bidyut Baran Saha1,3
1Green Asia Education Center, Kyushu University, Japan
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Japan
3
International Institute for Carbon-Neutral Energy Research, Kyushu University, Japan
2Abstract
This study adopts a direct experimental approach for determining ex-situ irregular shaped pore
distribution analysis of adsorbent material using Atomic Force Microscopy (AFM) operated in Phase
mode. In-situ Porosity is estimated from N2 adsorption/desorption isotherm data using Non Local Density
Function Theory (NLDFT). AFM is used to obtain the surface topographic information of RD and B typesilica gel which are then undergone by image processing to acquire information related to the pore size
and its distribution. A comparative study then performed to cognize the trend of in-situ and ex-situ
porosity.
detection based only height images.
Estimation of the surface energies wasbeyond the scope of this experiment.
Operating frequency of the cantilever (NCHR,Nanoworld) was set to a slight lower than it’sresonant frequency where the gradient of thewaveform of frequency vs amplitude graph isthe steepest. The operating point wasoptimized after taking several images. Ascanning area was set to 5 μm × 5 μm with
512×512 resolution and 1 Hz scanningfrequency.

1. Introduction
This adsorption-desorption is a surface
based phenomenon and it is considered thatthe monolayer and multilayer adsorption ofgas molecules take place on the surface of thematerial. One of the surface characteristic isporosity which have significant influence inadsorption-desorption[1] . For determining theporosity and the surface area there are
multifarious methods are available, among
them imaging techniques are more straightforward and allows direct visualization of thesurface and even inside of the material[2].
Atomic Force Microscopy is a probe based
microscopy technique that can be used tovisualize the surface in Nano-scale and it canbe operated in ambient condition. In this work,
we have introduced a novel technique fortaking surface images of spherical silica gel.
which were visualized and analyzed withdifferent tips and modes to find the optimized
mode for imaging. Additionally, we havedeveloped a method for quantitative analysis
of surface porosity based on depth based poredetection technique.

Figure. 1. 3D topographic image of RD typesilica gel taken by AFM

3. Result and Discussion
3.1 Qualitative study
This imaging part focused on taking the3D images of the surface of silica gel tounderstand the surface morphology visually.
Figure 1 shows the 3D image of the surface ofthe silica gel of 25µm2 scan area. Before

2. Experimental
AFM (SMP-9700, Shimadzu Corp.) wasoperated in phase mode which outputs heightimages along with phase change related
information. In this experiment, only theheight image was considered. The reason
behind avoiding phase data was to focus the89

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-32
taking the images sample was treated by astandard procedure to elude the vapor andcontamination. For example, silica gel wasdegassed at 85℃ for 2 hours and preserved ina sealed container and during the scan thehumidity of the chamber was reduced tominimum. Later the surface was scanned withthree different tips setting the Operating point
to 0.4 V (Figure 1 (b)) to confirm thereproducibility. Image flattening, filtering,
drift correction was performed to get clear
visualization.

3.2.3 In-situ Pore Size Distribution
The 3Flex™ Surface Characterization
Analyzer has been used to investigate the N2
adsorption/desorption isotherms. The surface
area of each composite adsorbent has been
investigated using Brunaure-Emmett-Teller(BET) method whilst the Non-Local Density
Functional Theory (NLDFT) has been used toestimate the In-situ pore volume. Cumulative
representation of the NLDFT pore size
distribution shows that for both the silica gel
sample follows the similar trend (Figure 3).
However, the rise of the curve for RD typesilica gel has begun early indicating it consistof comparatively small pores of similar width.
On the other hand, cumulative count of
surface porosity by AFM shows differenttrend. Lower slope of the curve indicates thepore width of larger range of dimensions.
However, both of the silica gels show similar
trend in surface porosity.

3.2 Quantitative Analysis
3.2.1 Image filtering:
The scanned image having height
information was post-processed to eliminate
the tilt and drift problem. To eliminate theseunwanted topographic disorders 2D-FFT wasused.
3.2.2 Ex-situ pore detection:
Ex-situ irregular shaped pores weredetected using watershed method, where firstgrain location was identified then location
was confirmed with segmentation method[3].
The identification of grain location isdifferent than conventional methods. At firstthe local minima of the pores are identified.
Then the repetitive steps took place tocompare with the other local minima in close
contact. Then the pore boundaries are marked
by identifying the overlapping points. The
image was cropped to 600 nm×600 nm for
identifying the pores conveniently. The
identified pores are counted using inverse
grain detection method. The pore countinformation is shown in Figure 2, where porecount of two different silica gel are presented.

100%

Cumilative count80%0%0Pore countB-type2010304050
Mean pore radius [nm]607030
Pore width [nm]405060

Reference020204. Conclusions:
AFM images were used to determine thepore distribution using depth based analysis.
Surface textures which do not constitute thepores were removed by 2D-FFT filtration
before pore detection and counting. Direct
identification of ex-situ pores by AFM
indicates the different trend of pore
distribution compare to indirect estimation ofin-situ pores.

RD-type

1010Figure 3. Comparative representation of in-situ
and ex-situ pore size distribution

400RD typeB type
NLDFT RD type
NLDFT B type

40%20%

50

3060%80[1]Figure 2. Pore counting by direct visualization

90K. Thu, A. Chakraborty, B. B. Saha, K. C.
Ng, Appl. Therm. Eng. 2013, 50, 1596–1602.

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-32
[2]
[3]

S. Yao, K. Jiao, K. Zhang, W. Hu, H. Ding,
M. Li, W. Pei, Chinese Sci. Bull. 2011, 56,2706–2712.
P. Klapetek, Quantitative Data Processingin Scanning Probe Microscopy: SPM
Applications for Nanometrology, 2012.

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