SSCC 4493 SURFACE AND COLLOID CHEMISTRYGROUP ASSIGNMENT LECTURER: Dr. Siti Aminah binti Setu
ABSTRACT Based on the study conducted, GMC 8001H shows Type II Isotherm with macroporous type and bottle necked shape. Three straight line graph plotted, BET, Langmuir and Harkins-Jura based on nitrogen adsorption isotherm explained informations on surface area of solids. BET surface area obtained from this study is 1203.6046 m^2 g^(-1) whereas 〖langmuir surface area, S〗_(Langmuir )is 1553.5716 〖 m〗^2 g^(-1). Harkins-jura equation gave out several informations includes Micropore volume, V_( MP ) 0.06627〖cm〗^3, external surface area, S_(ext ) 1078.38 m^2 g^(-1), micropore surface area, S_(MP )125.2246 m^2 g^(-1) and percentage of mesoporosity and microporosity which is 0.1016 %.
INTRODUCTION The BET equation is used for determining the surface area of solids from the nitrogen sorption isotherm at liquid nitrogen temperatures, but the equation has also been used with a wide range of other gases and vapours. Surface area is one of the most important properties for the characterization of microporous materials, such as metal-organic frameworks (MOFs) and zeolites. Most experimental surface areas are reported as either the Langmuir surface area or the BET surface area derived from nitrogen adsorption isotherms at 77 K. The choice between these two surface areas depends on whether the pore sizes support multilayer (BET) or only monolayer (Langmuir) adsorption. However, many MOFs and zeolites have pores that are on the boundary of supporting either monolayer or multilayer adsorption. It is often stated that the BET method should not be applied to microporous materials. Based on previous study, the inherent difficulties in applying the BET method to micropores as follows, the validity of the BET monolayer capacity (nm) is questionable, the monolayer structure is not the same on all surfaces, and the strong adsorption at very low P/P0 may involve localized monolayer coverage and/or primary micropore filling. Despite these reservations, the BET method is still commonly used for the determination of surface area of microporous materials such as MOFs and zeolites because of its convenience, and it is considered a standard procedure for comparing different adsorbents. The BET surface areas calculated from the simulated isotherms agreed very well with the accessible surface areas calculated directly from the crystal structures, as well as experimental surface areas reported in the literature. Based on the adsorption isotherm plot, the type of isotherm is type II, types of pores is microporous while the shape is bottle necked. Meanwhile, for BET surface area plot, the SBET is 1203.6046 m2g-1 and for Langmuir surface area plot, the SLangmuir is 1553.5716 m2g-1. Lastly, for t-plot based on Harkins-Jura Equation, the micropore pore volume is 0.06627 cm3, the external surface area is 1078.38 m2g-1, the micropore surface area is 125.2246 m2g-1, and the percentage of mesoporosity and microporosity is 0.1016%.
INSTRUMENT Specific instrument used for this analysis is 3Flex Physisorption manufactured by Micromeritics (USA). • This type of instrument used to analyse and deliver the accuracy, resolution of experimental data. • In this experiment, we focused on reports of BET surface area. • There are 3 configurable analysis port adapt to the specific needs of our workflow. • This instrument able to analyse with 3 separate absorbent gases simultaneously one at each port in a single analysis. • Isotherm data collection begins in 1-6 torr range (10-9 relative pressure range for N2). • 3Flex Physisorption model contains software advancement. • The interaction with adsorption data is direct. • User-selectable data ranges through the graphic interface allow direct modelling for BET and others (Langmuir, t-plot)
Type of isotherm : Type II Isotherm • Type of pores : Macroporous • Pore shape :
DISCUSSION From the Adsorption Isotherm, it shows that the sample exhibited type II adsorption isotherm, which indicates that the presence of macropores in the sample and represent the multilayer adsorption. The rounded knee area on the graph indicates approximate location of monolayer formation. The Langmuir surface area depends on the adsorption capacity of the adsorbent. The Langmuir constant was calculated first in which the gradient is divided by the intercept. BET on the other hand shows the sample have a very high surface area of 1203.6046 m2/g. From the plot obtained, BET constant C can e calculated and a very high value is obtained, 2419. This indicates the presence of microporosity and high adsorbate interaction energy In adsorption system where Langmuir’s model is followed, the surface area of adsorbent for the formation of monolayer can be calculated. From the graph plotted, surface area of adsorbent for the formation of monolayer 357.1429 m2/g
CONCLUSION In conclusion, this sample is a macroporous sample that exhibit type II isotherm where monolayer are formed. BET shows the sample have a very high surface area of 1203.6046 m2/g Langmuir suraface area plot calculated is 1553.5756 m2/g t-Plot Micropore Volume, VMP: 0.06627 cm3 External surface area, Sext : 1078.38 m2/g Micropore surface area, SMP: 125.2246 m2/g Percentange mesoporosity and microporosity: 0.1016%
POTENTIAL APPLICATION IN INDUSTRY In general, there are a lot of usage of BET in the industry as such: • Activated carbon For example, activated carbon strongly adsorbs many gases and has an adsorption cross section of 0.162 nm2 for nitrogen adsorption at liquid-nitrogen temperature (77 K). BET theory can be applied to estimate the specific surface area of activated carbon from experimental data, demonstrating a large specific surface area, even around 3000 m2/g.However, this surface area is largely overestimated due to enhanced adsorption in microporesand more realistic methods should be used for its estimation, such as the subtracting pore effect (SPE) method 2. Catalysis In the field of solid catalysis, the surface area of catalyst is an important factor in catalytic activity. inorganic materials such as mesoporous silica and layered clay minerals have high surface areas of several hundred m2/g calculated by the BET method, indicating the possibility of application for efficient catalytic materials.
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