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Study of physico-chemical properties of Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite: thermal and acid stability.


Nanocomposite material recently received special attention from scientists. Various research continues to be done, it refers to a very simple idea, which is preparing a new material consisting of blocks of homogeneous particles on the nanometer scale structure and thus have better properties of the original material. Nanocomposite materials consisting of two or more molecules of inorganic/organic. Materials such as carbon nanotube, nanofiber and clay are a widely used material for the preparation of the composite [1].

Clay is a natural mineral of the smectite family of phyllosilicate group shaped crystals with a layered structure. Bentonite is a type of clay with the most attention, due to the ability to swell, has a interlayer space or have larger pores and flexible structure than the natural zeolite pore so it can be engineered to form bentonite pillared with micropore size and/or mesopores which can be used as selective catalysts, separation agents, supporting materials, adsorbents [2]. In addition to the surface layer of bentonite are negatively charged and going on electrostatic forces and van der Waals forces are so weak that cations contained in the interlayers of bentonite easily replaced by other cations [1].

The method is often used in the synthesis of pillared bentonite are intercalation and pilarization method, which is a larger cation insertion as cations alkylammonium, polyhydroxy metal ions, or positively charged colloidal particles into the space between the layers and separate the two layers, the distance of the interlayers will form a greater. Intercalation method will get a pillared bentonite with high specific pillars, acid sites, specific surface area, it has a uniform porosity and high thermal stability which is very useful in catalytic reactions and other physico-chemical processes. Intercalation of the bentonite material can also be done by pillaring agents form metal cations forming metal oxide nanoparticles such as Si[O.sub.2], [Fe.sub.2][O.sub.3], [Al.sub.2][O.sub.3], which acts as a pillar to sustain and stabilize the micropore structure of interlayer clay [3]. Several studies of nanomaterial clay has been done by previous researchers such as nanoclay [4], nanocomposite [5], [6], nanocrystal Ti/clay [7], nanoparticles of Fe/clay [8], [9], nanocomposite polymer/clay [1], nanocatalyst Ru/Al-clay [10]. Silica sol were studied the Silica-Ti sol and Silica-Fe sol. Besides using [Ti.sup.4+] and [Fe.sup.3+] cations, can also be modified silica sol cation using [Al.sup.3+] cation. Negatively charged silica sol will bind to [Al.sup.3+] ions, forming a positively charged colloid surface.

In this research studied the synthesis of pillared bentonite intercalated Silica-Al sol into the interlayer of bentonite to obtain the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite and followed by determined of its physico-chemical properties. The pillaring of silica-Al sol in bentonite was contributed in enhancing and improving the mechanical properties of bentonite. The Silica-Al sol in the form of positively charged colloids will replace cations in the interlayers of bentonite by ion exchange mechanism. Finally, the product was calcined to form the metal oxide serves as a pillar in the interlayer or gallery of bentonite. The pillarization of Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide in the interlayer of bentonite led to an increased distance interlayers of bentonite was called d-spacing or basal spacing d001 and increased the acidity of the surface that plays a role in catalytic activity. The purpose of this study are to synthesizes Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite and determined the physico-chemical properties such as specific surface area, average pore radius, total pore volume, adsorption patterns, surface acidity, thermal and acid stability.


Instruments and Materials

The instruments used in this study are: glassware, sieve with size of 250 mesh, analytical scales, furnace, thermometer, tools muller, pH meter, magnetic stirrer, heating oven, set centrifuges, X-ray Diffractometer (Shimadzu model of X-RD 6000), Infrared Spectroscopy (Shimadzu FTIR 8201 PC), Atomic Absorption Spectrophotometer (AAS) (Perkin Elmer), Transmission Electron Microscopy (TEM) (JEOL Hitachi H-600) and Porosimeter (Quantachrome Instruments NOVA instruments 1994-2007 version 10:01).

The materials used in this study are: Bentonite, tetraethylorthosilane (TEOS), hydrochloric acid (HCl), aluminum nitrate (Al[(N[O.sub.3]).sub.3] x 9[H.sub.2]O), ethanol, sodium hydroxide (NaOH), silver nitrate (AgN[O.sub.3]) and distilled water.

Preparation of materials

Bentonite sieved using a sieve with size of 250 mesh, washed several times with distilled water then filtered with a vacuum filter and dried at 110[degrees]C. Bentonite dried and sieved using a sieve with size of 250 mesh.

Preparation of pillaring agents

The pillaring agents form silica-[Al.sub.x][(OH).sub.y] sol was prepared by mixed 56 mL of TEOS, 10 mL of HCl 2 M and 12 mL of ethanol and stirred until it forms a sol and then ageing at room temperature for 2 hours. Silica sol was mixed with 100 mL of Al [(N[O.sub.3]).sub.3] x 9[H.sub.2]O 0.75 M (the ratio of Si/Al = 3). Then added with NaOH 0.2 M solution to pH of about 2.7.

Synthesis of Si[O.sub.2] - [Al.sub.2][O.sub.3] / bentonite nanocomposite

The suspension of bentonite was prepared by dispersed of 10 gram bentonite in the destilled water under stirring at room temperature for 24 hours. The pillaring agents was then slowly added to a suspension of bentonite and then the mixed was stirred and heated at 60[degrees]C allowed to react for 3 hours. The results of intercalated was separated by centrifugation and then washed with a mixture of ethanol and water in the ratio 1:1 to free Cl- ions and dried at 110[degrees]C. Once dried crushed into powder and then sieved. Furthermore calcined at 250[degrees]C for 5 hours, in order to obtain the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite composite then characterized by X-ray diffraction method, infrared spectroscopy, TEM, AAS and BET isotherm.


Elemental analysis of Na, Ca, Si and Al in bentonite were analyzed by Atomic Absorbtion Spectrophotometry. The solid were also characterized by x-ray diffraction using a Shimadzu XRD 6000 diffractometer with Cu K[alpha] radiation. Infrared spectroscopy was used to identify the functional groups on the bentonite, TEM image was used to determine morphology of materials, BET NOVA instruments 1994-2007 version 10:01 was used for determining specific surface area and porosity of materials and surface acidity was determined by gravimetric analysis of pyridine adsorb. The test of thermal stability the nanocomposite were calcined at 350[degrees]C, 450[degrees]C and 550[degrees]C for 5 hours. The test of acid stability the nanocomposite were dispersed into solution of hydrochloric acid with various consentration, i.e. 1M, 3M and 5M for 24 hours.


Synthesis of Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite

The Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite material is a derivative of bentonite which the silicate interlayer pillared with Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide in nanometer-sized to form a stable pore structure and high surface area.

Analysis of bentonite

Analysis of bentonite needed to know the content and type of montmorillonite as starting materials to synthesize Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite. Characterization of bentonite by XRD methods, infrared spectroscopy and analysis of atomic absorption spectrophotometry (AAS). The results of cation analysis contained in the bentonite was conducted by AAS as shown in table 1. From the data in table 1 show that the analysis of bentonite is a type of Na-bentonite.

The identification results of bentonite with X-ray diffraction methods can be seen in figure 1. From the diffractogram is seen a broad reflection on the region 20 = 7.47[degrees] and 20.31 [degrees] with a value of d = 1.18 nm and 0.43 nm which is a typical reflection of montmorillonite sample. From these results it can be concluded that the bentonite contains montmorillonite minerals but low intensity. In addition, bentonite is also composed of the mineral feldspar, quartz, sauconite and hectorite.

Infrared spectra data of Na-bentonite samples provide information on the functional groups present in the sample. The results of the infrared spectra of Na-bentonite are presented in fig. 2.

Based on figure 2 can be seen the identification of bentonite which is the absorption peak at wave number 470.63; 794.67; 918.12; 1041.56; 1635.64; 3448.72 and 3626.17 [cm.sup.-1]. The wave number absorption bands at 3626.17 [cm.sup.-1] and 3448.72 [cm.sup.-1] is identified as a -OH band stretching vibrations of octahedral and -OH band stretching vibration of water molecules. This is confirmed by the absorption band at wave number 1635.64 [cm.sup.-1] is a -OH band bending vibration of water molecules. This data is reinforced by Katti [11] which states that the-OH bending vibrations indicated by absorption at 1635 [cm.sup.-1]. Absorption at wave numbers 3448.72 [cm.sup.-1] is the symmetric stretching vibration absorption of hydroxyl groups present on the bentonite either from water molecules, silanol or aluminol. While the absorption at wave numbers around 3626.17 [cm.sup.-1] is -OH band stretching vibration absorption of structural octahedral sheet (Al-OH). This indicates that the sample has absorbed of water.

The internal network is shown in bentonite catchment area 400-4000 [cm.sup.-1]. The wave number absorption band at 470.63 [cm.sup.-1] indicates the bending vibration of Si-O-Si. The wave number absorption band at 794.67 [cm.sup.-1] is characteristic of bending vibrations of O-Si-O, whereas the -OH bending vibrations of the Al-Al-OH appears as a weak absorption band at 918.12 [cm.sup.- 1] wave number region [12]. While the absorption band at wave number 1041.56 [cm.sup.-1] indicates the typical absorption Si-O stretching vibrations in the tetrahedral layer. Bentonite characterization results with the infrared spectra indicate the presence of functional groups of the tetrahedral and octahedral sheets which constitute the mineral montmorillonite. Based on the analysis of X-ray diffraction, infrared spectroscopy and AAS results it can be concluded that the bentonite contains montmorillonite type of Na-montmorillonite. In this study, referred to as Na-bentonite.

The intercalation and pillarization of Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide sol particles into bentonite.

Pillarization of bentonite with Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide based on the form of positively charged colloidal particles into the silicate interlayer of bentonite. Creation begins with the produce of Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite. The pillaring agents is a mixture of compounds tetraethylorthosilane (TEOS), ethanol and HCl 2 M. The reaction begins with the hydrolysis of TEOS compound in the presence of acid (HCl) to form silanol groups (Si-OH) where the release of ethanol and formation of silanol groups. Sol was formed and then mixed with a solution of [Al.sup.3+] ions and titrated with NaOH solution in order to form cations Al hydroxide. Reaction formation pillaring agents are as follows:

Si[(OH).sub.4]+[Al.sup.3+]+O[H.sup.-] [right arrow] [[HO-Al-O- Si[(OH).sub.3]].sup.2+]

Pillaring agents

The intercalation into the interlayer of bentonite was done by mixing the sol [[HO-Al-O-Si[(OH).sub.3]].sup.2+] or called silica-Al sol with bentonite dispersed in distilled water. Colloidal particles will replace the intercalated cations in the interlayers of bentonite. The results of intercalated bentonite was washed several times with ethanol: distilled water (1:1) with the goal of eliminating residual [Cl.sup.-] ions. Bentonite must be clean of [Cl.sup.-] ions in order not to disrupt the structure of bentonite when the calcination process. Further calcination formed Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide pillars separating the silicate layer of bentonite.

Characterization of Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite Structural analysis by X-ray diffraction method

The phenomenon of intercalation, pilarization and exfoliation of Si[O.sub.2]- [Al.sub.2][O.sub.3] mixed oxide sol particles into the silicate interlayer of bentonite was analyzed by X-ray diffraction methods were observed with a shift in the peak of the (001) planes. The basal spacing [d.sub.001] has an important role in catalytic processes, ion exchange and intercalation [13]. The Basal spacing determined need to know in order to increase the distance the silicate interlayer of bentonite during pillar formation. If there has been a shift it will show the distance the silicate interlayers of bentonite was characterized by changes in basal spacing. The results of the intercalated bentonite and pillaring of Si[O.sub.2]-[Al.sub.2][O.sub.3] mixed oxide sol particles as shown in figure 3.

From the results diffractogram in figure 3 (a) and (b) can be seen the shift of the (001) planes and an increase in the basal spacing [d.sub.001] reflection peak areas at 2[theta] = 7.47[degrees] of Na-bentonite shifted toward 2[theta] = 5.93[degrees] in the bentonite intercalated with basal spacing [d.sub.001] = 1.18 nm or [DELTA][d.sub.001] = (1.18 - 0.96) nm = 0.22 nm to 1.48 nm or [DELTA][d.sub.001] = (1.48 - 0.96) nm = 0.52 nm. This indicates the occurrence of intercalation of silica-Al sol that have larger sizes in the interlayers of bentonite resulted in basal spacing [d.sub.001] on bentonite increases. While the figure 3 (c) is a Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite diffractogram. From the results diffractogram seen the peak in the 2[theta] = 8.9 [degrees] with basal spacing [d.sub.001] = 0.99 nm. Changes in basal spacing showed that the interlayer of bentonite was deformed due to the calcination treatment of shape hydroxide to form oxides or Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide pillars. The material produced in this study called Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite. Pillar formation mechanism can be explained by the following figure 4.

Identification by infrared spectroscopy

Methods of analysis using infrared spektroscopy useful to complement data characteristics of X-ray diffraction. The results of infrared spectra for Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite is shown in figure 5.

From the data that appears on the absorption of infrared spectra above shows that a shift in absorption band of stretching vibrations of Si-O-Si appears on Na-bentonite in the wave number 1041.56 [cm.sup.-1] shifted to 1049.28 [cm.sup.-1] in the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite with a higher intensity and a sharp shift in the direction of wave numbers showed greater interaction between Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide pillars between the silicate interlayer of bentonite.

Analysis of the chemical composition of Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite

Analysis of the chemical composition of the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite was conducted by AAS. The results of the analysis of the composition of Si and Al in the nanocomposite and Nabentonite as shown in table 2.

From the results of measurements of the metal composition Si and Al in table 2 above shows that the number of Si and Al elements on the rise in Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite, indicating that it has been the formation of Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide pillars on bentonite.

Morphological analysis by TEM methods

TEM analysis is used to determine the morphological structure and size of the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite were produced. TEM characterization results are presented in Figure 6. Figure 6 (a) is a TEM micrograph of the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite which delaminated structure. From the pictures it looks a collection of Si[O.sub.2]- [Al.sub.2][O.sub.3] nanoparticles and the composite interlayers are arranged in a disorganized or random which is a delamination structure. The Delamination is a structure that different from general micropore pillared clays. Delamination meso-micropore structure can be formed from intercalation and pilarization to form larger pores. Almost the same results obtained by Yuan et al., [14] in which the synthesis of structural delamination of clay pillared clays showed irregularities due to interlayer delamination meso-micropore structure of the clay. Overlapping the silicate interlayers of bentonite by a aggregate of metal cations on the outer layer of bentonite causes the delamination structures formation of mesopore characterized by widening of basal spacing [d.sub.001]. Figure 6 (b) shows the size of the Si[O.sub.2]-[Al.sub.2][O.sub.3] nanoparticles embedded on the outer layer of bentonite with size about 1-15 nm and an average size of about 6 nm.

The Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite TEM analysis was compared with the Na-bentonite to determine the occurrence of intercalation or delamination on bentonite as shown in Figure 6 (c) and (d). From these results it can be seen the composition and the distance the interlayers of the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite, as shown in Figure 6 (c). The layers are dark and thick in figure 6 (c) is a silicate layer, whereas among the layers visible light which is the distance between the pores or layers of bentonite. From the results obtained by measuring the distance the interlayers of the Si[O.sub.2][Al.sub.2][O.sub.3]/bentonite nanocomposite have varying distances from 2.80 nm to 9.89 nm. This indicates that the distance the interlayers of Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite having micropore size and mostly mesoporous. While a thick layer of silicate in the nanocomposite Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite varies between 6.7 nm to 12 nm. This is probably caused by the deposition of Si[O.sub.2]- [Al.sub.2][O.sub.3] nanoparticles on the silicate layer outside the interlayer of bentonite. When compared with the interlayer of Na-bentonite as shown in figure 6 (d) have the distance between layers is about 1.10 nm to 3.63 nm, mostly micropore structure and a thick layer of silicate about 2 nm. Increasing the distance between the layers caused by the intercalation of the layers of bentonite by pillars Si[O.sub.2]-[Al.sub.2][O.sub.3], as reported [7]-[14].

Analysis of specific surface area and porosity

The results of the analysis of the specific surface area and porosity using a gas sorption analyzer are presented in table 3.

From the data in table 3 it can be seen that the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite has a specific surface area higher than Na-bentonite. An increase in the specific surface area is due to the increased distance the silicate interlayers resulting from pillar formed Si[O.sub.2]- [Al.sub.2][O.sub.3] oxide on bentonite and formation of delamination structures. The formation of the pillar where the micropore transformed into a new micropore or because of the Si[O.sub.2]- [Al.sub.2][O.sub.3] oxide pillars of mesoporous higher than Na-bentonite, in addition to the structure of the delamination structure led to the formation of mesoporous pores with sizes indicated by the decrease in micropore surface area on bentonite is of 7.74 [m.sup.2]/g to 3.94 [m.sup.2]/g, thus contributing to increasing the specific surface area. However, the increase is minimal, it is caused to an accumulation of Si[O.sub.2]-[Al.sub.2][O.sub.3] nanoparticles on the surface of bentonite resulted in the closing of interlayer or high density pillars lead to the closing some of the pores.

The pillarization also lead to increased porosity in bentonite. Changes in porosity due to the pillarization of Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide into the silicate interlayers of bentonite indicated total pore volume data (table 3). From the data in the table shows that the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite has total pore volume greater than Na-bentonite. Total pore volume is a combination of micropore volume to the volume of mesoporous which shows that the pore size distribution in the form of bentonite micropore and mesopores. This phenomenon were supported by the results of research conducted [14]-[15], which states that the pore size distribution in the pillared clays are of two types namely pore size micropore and mesopores. The micropore pore size due to pillared layers and mesoporous pore size caused by the formation of the delaminated structure on bentonite.

Nitrogen adsorption-desorption isotherm of the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite can be seen in Figure 7. Adsorption isotherm of Na-bentonite and Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite were adsorption isotherm of type II followed by classification BDDT (Brunauer, Deming, Deming and Teller), which indicates that adsorption occurs in solids with pore diameters larger than the diameter of the micropore. This adsorption isotherm according to the BET mechanism that begins with the adsorption of a single layer (monolayer) and then with increasing relative pressure and so formed a second layer evenly until saturation is reached. While the pattern of hysteresis loop of the isotherm is based on IUPAC clacification is a type H3, indicating a cavity shaped pore (slit-shaped) in the layered material. The formation of mesopores in the delaminated bentonite structure produced by the three- dimensional structure of the cations aggregate or Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide nanoparticles. In addition, the intercalation of cations or Si[O.sub.2]- [Al.sub.2][O.sub.3] oxide nanoparticles produced micropore pore size in the interlayers of bentonite.

These results are consistent with those reported [7], [14], which states that the delamination will form a mesoporous structure and shape of the pillars forming micropore structure.

Thermal stability test

Further heating of the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite was done to determine the effect of thermal treatment of the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nancomposite, particularly in the (001) planes. The calcined was carried out for 5 hours at a 350[degrees]C, 450[degrees]C and 550[degrees]C. Then analyzed by X- ray diffraction methods to determine the shift in basal spacing d001 and infrared spectroscopy methods for structural analysis of bentonite stability of functional groups due to thermal treatment.

Structural analysis by X-ray diffraction method

The results of X-ray diffraction analysis of the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite effect of thermal treatment can be seen in figure 8.

The results of XRD patterns of Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite as shown in fig. 8 (left side) the shows a reflections at 2[theta] = 8.9[degrees] which showed that with increasing calcination temperature produces a sharper reflection peaks and no shifting. So we can conclude that the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposites have thermal stability up to 550[degrees]C. As a comparison was prepared the thermal treatment on the Na-bentonite in the same conditions. The results of X-ray diffraction analysis of Na-bentonite as shown in Figure 8 (right side) shows a reflection peak 29 were shifted. This indicates that the Na-bentonite is unstable in the presence of thermal treatment. Besides Nabentonite has a relatively narrow peak reflection, indicating higher crystallinity of Na-bentonite due to the loss of the -OH group from within the framework of the changing structure of bentonite into micropore.

Data stability of basal spacing with thermal treatment both Si[O.sub.2][Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite as shown in figure 9. From fig. 9 shows that bentonite without pilarization relatively less stable against heating.

Identification by infrared spectroscopy

The results of infrared spectroscopy to study the effect of thermal treatment on the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite shown in figure 10, shows that by increasing the temperature at 350[degrees]C and 450[degrees]C does not cause damage to the structure of the Si-O-Si, but the intensity of absorption decreased, while heating Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite at 550[degrees]C produces absorption at higher wave numbers is 1056.99 [cm.sup.-1], indicating that with increasing temperature, the interaction between the Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide pillars and the silicate interlayers of bentonite with stronger or more stable. These data reinforce the results of X-ray diffraction analysis that showed that the pillared bentonite Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide particles remained at 550[degrees]C.

While the results of infrared spectroscopy of the Na-bentonite were presented in the figure11. Based on the spectra in figure 11 can be seen that the heating 450[degrees]C causes a shift in vocal vibrations stretching Si-O to a wave number greater shows the growing strength of the interaction of cations [Na.sup.+] with the silicate interlayered of bentonite, in contrast with the heating at 550[degrees]C there is a shift to the wave numbers are smaller indicating the weak interaction between the [Na.sup.+] cations and the silicate interlayers of bentonite. The thermal treatment Na-bentonite at 550[degrees]C, also there was a shift in the wave number 470 [cm.sup.-1] which is the bending vibration of Si-O-Si. This indicated the structural Si-O-Si damage on bentonite.

In addition, there was a shift wave number -OH stretching vibration of 3448.72 [cm.sup.-1] at 350[degrees]C and 3433.29 [cm.sup.-1] to 3417.86 [cm.sup.-1] at 550[degrees]C. Decrease in wave number -OH stretching vibrations in Na-bentonite due to the weakening of the power -OH bond in [Na.sup.+] cation. Decrease in frequency caused by dehydration that affect -OH stretching vibrations, causing a shift toward smaller wave numbers. These data support the results of X-ray diffraction analysis show that Na-bentonite is relatively unstable with warming temperatures above 450[degrees]C.

Effect of acid on the (001) planes

The process of treatment with hydrochloric acid performed to determine the effect of acidic conditions on the stability of the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite and the Na-bentonite structure particular of (001) planes. The Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite respectively included in HCl solution with a concentration of 1M, 3M and 5M for 24 hours. The addition of highly concentrated acid will dissolve inorganic materials and organic materials contained in the nanocomposite and the Na-bentonite. In the provision of highly concentrated acid, bentonite structures can be destroyed which is characterized by the loss of reflection (001) planes [13]. Then analyzed using infrared spectroscopy to determine the presence of major functional groups within the structure of these compounds was identified. To determine whether there is the effect of adding acid to the (001) planes in the silicate interlayers of bentonite, an analysis using X-ray diffraction methods. From the X-ray diffraction data can be known structural damage of bentonite caused by the addition acid at high concentrations is characterized by loss of reflection (001) planes in the area 29 = 5[degrees]-10[degrees].

Analysis of the structure by X-ray diffraction method

The results of structural analysis with X-ray diffraction methods on Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite after the addition of hydrochloric acid at a concentration of 1M, 3M and 5M shown in figure 12, shows that the addition of either hydrochloric acid at a concentration of 1M, 3M and 5M in nanocomposites caused the emergence of a clear of (001) planes, which before the acid treatment, the peak area of (001) planes reflections are not so clear. This is probably due to dissolved organic and inorganic impurities, and the shrinking distance interlayers of bentonite due partly dissolved cluster Si[O.sub.2]-[Al.sub.2][O.sub.3] oxide particles deposited in the interlayers of bentonite. The existence of the particle clusters oxide buildup caused widespread displacement and basal spacing in the nanocomposite. Another possibility is organized repeated delamination structures arranged randomly into a regular pillared structure. From the results of X-ray diffraction can be obtained on the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite basal spacing and the high price of the metal oxide pillars calculated from [[DELTA]d.sub.001] = (d001-0, 96) nm.

On the addition of HCl 1M seen the peak of the reflection (001) planes in the region 2[theta] = 6.31[degrees] with basal spacing [d.sub.001] = 1.39 nm and pillar height = 0.43 nm, while the addition of HCl 3M causes a shift in the region 2[theta] = 6.71[degrees] with the basal spacing [d.sub.001] = 1.31 nm and pillar height = 0.35 nm, the addition of HCl 5M shift the diffraction angle areas 2[theta] = 6.49[degrees] with basal spacing [d.sub.001] = 1.36 nm and height of the pillar = 0.4 nm. From the calculated basal spacing and height of the pillar oxide produced visible changes in basal spacing and high prices oxide pillars were not significant the silicate interlayers of bentonite after the addition of hydrochloric acid 1M, 3M and 5M. This is due to the density of high pillaring particles resulting rearrangement pillar position. As a result, the distance the interlayers produced insignificant. Another possibility is organized repeated pillar bentonite of the layer structure form delamination (edge to face and edge to edge) to form layered (face to face) so that changes in the distance the interlayers of bentonite. While the results of X-ray diffraction analysis on the effect of adding Na-bentonite acid can be seen in figure 14. From the diffractogram showed that the addition of hydrochloric acid resulted in a shift in the diffraction angle 2[theta] to a smaller area and basal spacing increases. This is because the dissolved organic and inorganic impurities contained in the inter-layer of bentonite, so the distance between the layers of the Na-bentonite greater.

The results of X-ray diffraction to analyze the (001) planes in the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonit nanocomposite and Na-bentonite due to the addition of hydrochloric acid can be seen in figure 13. From these figure show that the 001 planes, both Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite and the Na-bentonite, are relatively resistant to treatment to a concentration of hydrochloric acid 5M.

Identification by infrared spectroscopy

The results of infrared spectroscopy studies of the effects of hydrochloric acid treatment with Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite shown in Figure 14. From these figure showed that the addition of acid does not cause damage to the Si-O bond was characterized by stability stretching vibration absorption band of Si-O-Si at 1049.28 [cm.sup.-1]. But with the addition of hydrochloric acid causes stretching vibration absorption band of Si-O-Si decreased intensity.

The higher the concentration of hydrochloric acid were added, the intensity of absorption in the small area. This is consistent with the reported [13], that the addition of acid will cause a decrease in the intensity of the absorption characteristic stretching vibrations of Si-O-Si. The addition of acid also resulted in a decrease in the intensity of the absorption area of 794.67 [cm.sup.-1] which is the bending vibration absorption of Si-O or Al-O. But with the addition of hydrochloric acid at a concentration of 5M cause the stronger absorption band at 918.12 [cm.sup.-1], where the addition of 1M and 3M acid formed weak absorption band. Absorption band shows Al-OH bending vibrations of the Al-Al-OH where Al is the central octahedral cation. This data is reinforced [12] which states that the bending vibration of Al-OH absorption band appeared weaker in areas wavenumber 918.12 [cm.sup.-1]. This indicates that the nanocomposite structure is not experiencing the damaging effects of acid.

The results of the infrared spectra of Na-bentonite influence of hydrochloric acid as shown in Figure 15. From these images it can be seen that the acid treatment on the Na-bentonite gave rise to two absorption bands in the region of stretching vibrations of Si-O-Si is at 1049, 20 [cm.sup.-1] and 1095.57 [cm.sup.-1]. This indicates that the structural disruption of Si-O-Si in the Na-bentonite, besides that happens dealumination which is characterized by loss of absorption band at wavenumber 918.12 [cm.sup.-1] which is an Al-OH bending vibrations and shifted absorption band at wavenumber 794.67 [cm.sup.-1] to 786.96 [cm.sup.-1] which is the Al-O bending vibrations.

Determination of the surface acidity

Determination of acidity aims to determine the amount of acid sites available on the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite in each sample weight (mmol/g) both Bronsted acid sites and Lewis acid sites without seeing how strong acidic sites. To determine the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonit nanocomposite and Na-bentonite surface acidity on research conducted by the gravimetric method with alkaline pyridine adsorption. Data resulting from the determination of the amount of acid sites on the Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite nanocomposite and Na-bentonite are presented in the figure 16.

From the figure it can be seen that bentonite an increased of acidity from 0.46 mmol/g to 2.01 mmol/g. This is because there is pillars in the Si[O.sub.2]- [Al.sub.2][O.sub.3]/bentonite nanocomposite. Presence of the Si[O.sub.2]-[Al.sub.2][O.sub.3] Lewis acid as well as Br0nsted acid increases the number of sites that has a chance to absorb large amounts of pyridine. The pyridine adsorption results indicate that the formation of Si[O.sub.2]-[Al.sub.2][O.sub.3] pillars in the silicate interlayers of bentonite, increases the acidity of the surface resulting in an increased number of acid sites both Br0nsted acid and Lewis acid.


From research conducted concluded several things, among others:

* Intercalation and pillarization of bentonite with silica-Al sol obtained Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite composite in nanometer-scale pore size varying between 2.8 nm to 9.8 nm.

* The Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonit nanocomposite structure obtained by forming pores resulting from pilarization micropore size and the size of the resulting mesoporous structure formation delamination.

* The Pillarization enhance physico-chemical properties of bentonite such as acidity which increased from 0.46 mmol/g to 2.01 mmol/g, specific surface area increased from 54.93 [m.sup.2]/g to 71.26 [m.sup.2]/g, average pore radius increased from 6.86 nm to 8.02 nm, total pore volume increased from 0.18 mL/g to 0.285 mL/g and thermal stability reaches up to 550[degrees]C and acid treatment on the composite does not cause damage the (001) planes of bentonite.


Thank submitted to Dr. Indriani K, M.Si and Dr. Sutarno, M.Si the criticism and suggestions, to Mr. Didik and Erwin for helping in TEM data measurring as well as to all those who helped me either directly or indirectly so completed the writing of this paper.


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* Ruslan, Karna Wijaya and Triyono

Departement of Chemistry, Faculty of Mathematics and Natural Science, Gadjah

Mada University, Indonesia, 55281

* Corresponding author E-mail:

Table 1 Analysis result of cation in the bentonite

Jenis kation         (%)

[Na.sup.+]           0, 60
[Ca.sup.2+]          0, 04

Table 2. Composition of Si and Al

sample                                             (%)
                                               Si      Al

Na-Bentonite                                 34, 43   7, 74
Si[O.sub.2]-[Al.sub.2][O.sub.3]/bentonite    36, 34   8, 24

Table 3. Result of specific surface area and porosity

Sample                              [S.sub.BET]

Na-Bentonite                          54, 93
Si[O.sub.2]-[Al.sub.2][O.sub.3]/      71, 26
bentonite nanocomposite

Sample                             [S.sub.ext.] ([S.sub.micro])

Na-Bentonite                             47, 19 (7, 74)
Si[O.sub.2]-[Al.sub.2][O.sub.3]/         67, 32 (3, 94)
bentonite nanocomposite

Sample                             [V.sub.p]

Na-Bentonite                         0, 18
Si[O.sub.2]-[Al.sub.2][O.sub.3]/     0, 28
bentonite nanocomposite

Sample                             [V.sub.[micro]p] ([])

Na-Bentonite                              0, 004 (0, 176)
Si[O.sub.2]-[Al.sub.2][O.sub.3]/          0, 002 (0, 278)
bentonite nanocomposite

Sample                             APR

Na-Bentonite                       6, 86
Si[O.sub.2]-[Al.sub.2][O.sub.3]/   8, 02
bentonite nanocomposite


[S.sub.BET] = specific surface area ([m.sup.2]/g)

[S.sub.ext.] = external surface area ([m.sup.2]/g)

[S.sub.micro] = micropore surface area ([m.sup.2]/g)

[V.sub.p] = total pore volume (mL/g)

[V.sub.[micro]p] = micropore volume (mL/g)

[] = mesopore volume (mL/g)

APR = average pore radius (nm)

Fig. 16 Amount of surface acidity

acidity (mmol/g)

Na-Bentonite         0.46
Nanocomposite        2.01

Note: Table made from bar graph.
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Author:Ruslan, Karna Wijaya; Triyono
Publication:International Journal of Applied Chemistry
Article Type:Report
Geographic Code:9INDO
Date:Jan 1, 2013
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