Pouretedal and Kazemi International Journal of Industrial Chemistry 2012, 3:20 http://www.industchem.com/content/3/1/20 RESEARCH Open Access Characterization of modified silica aerogel us ing sodium silicate precursor and its applicati on as adsorbent of Cu 2+ , Cd 2+ , and Pb 2+ ions HR Pouretedal 1* and M Kazemi 2 Abstract Sodium silicate (Na2O/SiO2 = 1:3.3) as a precursor is used to prepare silica aerogel. The prepared silic a aerogel is modified by mercaptopropyl trimethoxysilane. The modified silica aerogel is characterized using Fourier transform infrared spectroscopy, Brunauer, Emmett, Teller method, and transmission electron microscopy. The adsorp tion and removal of Cu 2+ , Cd 2+ , and Pb 2+ ions from aqueous samples using modified silica aerogel are stu died. The experimental conditions such as pH of samples, initial concentration of cations, contact time, and adsor bent dose are optimized to attain the maximum adsorption capacity. The optimum values are obtained as follow s: contact time = 30 min, adsorbent dose = 0.05 g for Cd 2+ and Pb 2+ ions and 0.1 g for Cu 2+ ions, pH = 6 for C d 2+ and Pb 2+ ions, and pH = 4 for Cu 2+ ions. The equilibrium data are fitted well by the Langmuir and Freund lich isotherm models. The adsorption capacities for Cu 2+ , Cd 2+ , and Pb 2+ ions are found 90.1, 181.8, and 250.0 mg/g, re spectively. Keywords: Silica aerogel, Adsorbent, Sodium silicate, Metal ion, Modification Background Silica aerogels are materials that show unusual properties. The high specific surface area (500 to 1,200 m 2 /g), high porosity (80 to 99.8 %), low density (approximately 0.003 g/ cm 3 ), high thermal insulation value (0.005 W/ mK), ultra low dielectric constant (k = 1.0 to 2.0), and low index of re- fraction (approximately 1.05) are the advantages o f these materials. The nanoporous network of interconnected pr i- mary particles is due to these properties [1]. Because of their unique texture, silica aerogels are promising mate rials as super-thermal insulators, catalytic supports, adsorbents, and host materials for drug delivery systems. The sy nthesis of silica aerogels has received significant attention especially during the last two decades. Some inves tigators have studied the use of different precursors, and many have focused on the modification of synthesis para meters. Re- cently, many research works have been devoted to amb ient pressure drying which makes the production c ommercial and industrial [2-4].
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Pouretedal and Kazemi International Journal of Industrial Chemistry 2012, 3:20
http://www.industchem.com/content/3/1/20
RESEARCH Open Access
Characterization of modified silica aerogel usingsodium silicate precursor and its application asadsorbent of Cu2+, Cd2+, and Pb2+ ionsHR Pouretedal1* and M Kazemi2
Abstract
Sodium silicate (Na2O/SiO2 = 1:3.3) as a precursor is used to prepare silica aerogel. The prepared silica aerogel ismodified by mercaptopropyl trimethoxysilane. The modified silica aerogel is characterized using Fourier transforminfrared spectroscopy, Brunauer, Emmett, Teller method, and transmission electron microscopy. The adsorption andremoval of Cu2+, Cd2+, and Pb2+ ions from aqueous samples using modified silica aerogel are studied. Theexperimental conditions such as pH of samples, initial concentration of cations, contact time, and adsorbent doseare optimized to attain the maximum adsorption capacity. The optimum values are obtained as follows: contacttime = 30 min, adsorbent dose = 0.05 g for Cd2+and Pb2+ ions and 0.1 g for Cu2+ ions, pH = 6 for Cd2+ and Pb2+
ions, and pH = 4 for Cu2+ ions. The equilibrium data are fitted well by the Langmuir and Freundlich isothermmodels. The adsorption capacities for Cu2+, Cd2+, and Pb2+ ions are found 90.1, 181.8, and 250.0 mg/g, respectively.
Keywords: Silica aerogel, Adsorbent, Sodium silicate, Metal ion, Modification
BackgroundSilica aerogels are materials that show unusual properties.The high specific surface area (500 to 1,200 m2/g), highporosity (80 to 99.8 %), low density (approximately 0.003 g/cm3), high thermal insulation value (0.005 W/mK), ultralow dielectric constant (k = 1.0 to 2.0), and low index of re-fraction (approximately 1.05) are the advantages of thesematerials. The nanoporous network of interconnected pri-mary particles is due to these properties [1]. Because oftheir unique texture, silica aerogels are promising materialsas super-thermal insulators, catalytic supports, adsorbents,and host materials for drug delivery systems. The synthesisof silica aerogels has received significant attention especiallyduring the last two decades. Some investigators havestudied the use of different precursors, and many havefocused on the modification of synthesis parameters. Re-cently, many research works have been devoted to ambientpressure drying which makes the production commercialand industrial [2-4].
* Correspondence: [email protected] of Applied Chemistry, Malek-ashtar University of Technology,Shahin-Shahr, 1387763681 IranFull list of author information is available at the end of the article
During this decade, many researchers have attemptedto reduce the cost of aerogel synthesis. In brief, theseattempts took one of two approaches. The first involvedthe use of cheap precursors, and the second is con-cerned with the development of novel drying techniquesthat made it possible to synthesize aerogels at ambientpressure (known as an ambient-drying or evaporativedrying) instead of supercritical drying [5-7]. Most of therecent reports of various forms of silica aerogels such aspowder, granules, films, and bulks utilize at least one ofthe above approaches and sometimes more than oneapproach [8-10].
The applications of the silica aerogel have expanded intomany fields [11,12]. They are used as (1) fillers for paints,varnishes, etc.; (2) thermal and acoustic insulation mate-rials; (3) adsorbents and catalyst supports; and (4) elec-tronic materials such as Cerenkov detectors and sensormaterials.
The existence of heavy metals in wastewaters contri-butes to water toxicity and represents an increasing dan-ger for the environment, human beings, and other livingorganisms. In addition, to rock leaching due to some ex-ternal effects, these effluents discharge from various an-thropogenic sources such as power plants, chemical
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manufacturing, painting, mining, metallurgy, electro-plating, and many other industries [13-15].
In the present study, we report the synthesis of silicaaerogel by using sodium silicate as precursor. The preparedsilica aerogel is modified and applied as adsorbent for theremoval of Cu2+, Cd2+, and Pb2+ ions from aqueous sam-ples. The characterization of prepared silica aerogel is alsoreported in this study.
Results and discussionCharacterization of silica aerogelThe Fourier transform infrared spectroscopy (FT-IR) spec-tra of unmodified and modified silica aerogel are shown inFigure 1. The wide peak with strong intensity was 1,000 to1,100 cm−1, and the weak peak near 800 cm−1 was assignedto the asymmetric and symmetric bending of Si-O-Sibonds, respectively [16-18]. The strong peak near 470 cm−1
is attributable to the bending of the O-Si-O bonds. In thespectra of unmodified aerogel, the wide bond at 3,426 cm−1
and the peaks at 1,640 and 944 cm−1 correspond to the hy-droxyl groups adsorbed on the surface as well as the ben-ding of the H-O-H bonds and the stretching of the Si-OHbonds, respectively. The stretching vibrations of S-H andC-H appeared at 2,564 and 2,932 cm−1, respectively, in thespectra of modified silica aerogel which confirmed themodification of silica aerogel surface with mercaptopropyltrimethoxysilane (MPTMS) [17,18].
The N2 adsorption-desorption isotherms and pore sizedistribution of unmodified silica aerogel are shown inFigures 2 and 3, and the obtained data are collected inTable 1. The type IV isotherm curves’ well-defined stepclearly indicates that these materials possess mesoporousstructure. The isotherms of nitrogen adsorption exhibitedan abrupt increase at P/P0 is approximately 0.70, which is
Figure 1 FT-IR spectra of unmodified (a) and modified (b) silica
aerogel.
characteristic for capillary condensation within the uni-form mesopores of the materials (Figure 2a). The values ofspecific surface area, pore volume, and pore diameter con-siderably decrease after modification of silica aerogel withMPTMS (Table 1). The average pore diameter of theunmodified and modified silica aerogel is 7.6 and 3.9 nm,respectively. The mean pore diameter of the unmodifiedsilica aerogel is obtained from Brunauer, Emmett, Teller(BET) plot (Figure 2b). The decrease of pore volume hasbeen observed for modified silica aerogel by the filling ofmicropores in the substrate with the modifier [19,20].
Figure 4 shows the TEM images of unmodified andmodified silica aerogel. The synthesized aerogel exhibit aporous network structure which contains 50 to 60 nmspherical solid clusters and pores below 120 nm betweenthem. The particle distribution of aerogels is uniform.Silica aerogels exhibit a porous structure with fine par-ticulate morphology, and the modified aerogel alsoshowed porous structure but with less pores size incomparison with unmodified silica aerogels.
The TGA curve of modified silica aerogel is shown inFigure 5. A little weight loss at temperature 320 °C is seen,and the decomposition of aerogel with weight loss of20.2 % occurred at higher temperature of up to 800 °C. AnXRD pattern (Figure 6) shows an amorphous structure forsynthesized silica aerogel.
Adsorption by modified silica aerogelEffect of pHThe effect of the pH of aqueous samples on the adsorp-tion of Cu2+, Cd2+, and Pb2+ ions by modified silicaaerogel is shown in Figure 7. As seen, the adsorptioncapacity of adsorbent increased with increasing of thesamples’ pH. The characteristic of chelation mechanismand the less insignificant competitive adsorption ofhydrogen ions at higher pH are due to increase of theremoval yield [18-20]. The following reactions may takeplace at the solid-solution interface of modified silicaaerogel with MPTMS at different pHs [21].
SH þ Hþ⇄SHþ2 ð1Þ
SH þ M2þ⇄SHM2þ ð2Þ
SH þ OH−⇄SHOH− ð3Þ
Equation 1 indicates the protonation and deprotonationreactions of the SH groups of MPTMS in silica aerogel.Equation 2 shows the formation of surface complexes ofM2+ ion with the SH groups. The adsorption of OH− ionsfrom the solution through a hydrogen bond on the SHgroups occurred at alkaline pHs (Equation 3). The proto-nation of SH groups (Equation 1) was favored versus the
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Figure 2 Nitrogen adsorption-desorption isotherms (a) and BET plot of unmodified silica aerogel.
complex formation of M2+ (Equation 2) at lower pH. Theavailable sites of adsorbent for complex formation werereduced with protonation of SH groups. On the otherhand, the electrostatic repulsion between the cations andthe surface of modified silica aerogel increased withprotonation of SH groups. Thus, the adsorption of cationsdecreased with decreasing aqueous sample pH. By in-creasing the pH of solutions, the protonation of SHgroups was reduced, and the number of SH sites on thesurface of modified silica aerogel for cations adsorption(Equation 2) increased as well as its adsorption capacity.
However, the adsorption capacity of adsorbents wasreduced at the upper pH of 6 for Cd2+ and Pb2+ and pHof 4 for Cu2+ ion. The increasing adsorption of Cd2+,Pb2+, and Cu2+ with increasing pH shows the ion ex-change mechanism for these ions. A decrease in the re-moval yield at upper optimum pH for each cation is due
to the formation of soluble hydroxy complexes [22]. Thedifference in the adsorption behavior of different heavymetal ions may be because of the difference in their ionexchange capacity on the surface depending on theircharge density, extent of hydrolysis, and solubility ofhydrolyzed metal ions in solution under the present ex-perimental condition [22-24].
Effect of initial concentrationFigure 8 indicates the effect of initial concentration ofcations on the adsorption capacity. The reduction of theremoval yield was observed with the increase of initialconcentration of M2+ ions in range of 50 to 400 mg/L.The sufficient adsorption sites are available for adsorp-tion of cations at a lower initial concentration. Also, thefraction of adsorption for each ion is independent of itsinitial concentration. However, the available sites of
Figure 3 Nitrogen adsorption-desorption isotherms (a) and pore size distribution (b) of modified silica aerogel.
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Table 1 The N2 adsorption–desorption data of
unmodified and modified silica aerogelSilica aerogel BET data
S (m 2/g) P (cm3/g) D (nm)
Unmodified 602.0 1.1455 7.59
modified 387.9 0.4561 3.89
S, Specific surface area; P, pore volume; D, average pore diameter.
adsorbent were reduced at higher concentrations of theadsorbate [21,22].
Effect of contact timeThe influence contact time of adsorbent and adsorbates inthe range of 10 to 60 min is indicated in Figure 9. The con-ditions are optimum pH and 50 mg/L of M2+ ions. The re-moval yield of cations increased with the increasing contacttime until equilibrium is attained at 30 min. Hence, thetime of 30 min is experimentally required to attain equili-brium of the modified silica aerogel with MPTMS.
Effect of adsorbent doseFigure 10 shows the removal yield of cations versus theadsorbent dose in range of 0.01 to 0.12 g. A sharp in-crease in the capacity adsorption was observed for Cd2+
and Pb2+ with the increase of adsorbent dose from 0.01to 0.05 g. Meanwhile, increase in the adsorption is seenup to 0.10 g of adsorbent for Cu2+ ion. Hence, the opti-mal dose is 0.05 g for Cd2+ and Pb2+ and 0.10 g for Cu2+
ion. However, the greater availability of functionalgroups on the surface area with the increase of adsor-bent dose is due to the higher removal percent.
The difference in the removal yield of different cationsat the same conditions such as initial concentration, ad-sorbent dose, and contact time may be attributed to thedifference in their chemical affinity with respect to SHgroups on the surface of the adsorbent [23].
The adsorption of Cu2+, Cd2+, and Pb2+ ions is alsostudied in a sample with initial concentration of 50 mg/L ofeach ion, 0.1 g/L adsorbent, and pH of 5. The removal
Figure 5 Thermogravimetric curve of modified silica aerogel.
efficiencies of 48.2, 60.7, and 76.1 % are obtained for Cu2+,Cd2+, and Pb2+ ions, respectively, at 30 min. However, thedecreasing removal efficiencies of cations are expectedbecause of the limitation of the adsorption capacity of theadsorbent.
Study of adsorption modelThe equilibrium adsorption of Cu2+, Cd2+, and Pb2+ isstudied as a function of initial concentration in the rangeof 50 to 400 mg/L. The Langmuir and Freundlich adsorp-tion isotherms are used to this study. The linear equationsof Langmuir and Freundlich isotherms are represented inEquations 4 and 5, respectively,
Ceq=qeq ¼ l=KLqm þ Ceq=qm ð4Þ
logqeq ¼ logKF þ ðl=nÞ logCeq ð5Þ
Study of adsorption modelwhere qeq (milligram/gram)is the amount of cation adsorbed per unit mass ofadsorbent particles at equilibrium, Ceq (milligram/liter)
Figure 4 TEM images of (a) unmodified and (b) modified silica aerogel.
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1400
1200
1000
800
600
400
200
05 10 20 30 40 50 60 70
Figure 6 XRD pattern of silica aerogel.
is the equilibrium concentration of the cation in the aque-ous phase, KL is the equilibrium constant (liter/milligram)related to the energy of the adsorption and qm is the max-imum adsorption capacity (milligram/gram), KF and n areFreundlich isotherm constants related to the adsorptioncapacity and adsorption intensity, respectively [24,25].
Therefore, in Langmuir isotherm, a plot Ceq/qeq versusCeq should be a straight line with a slope 1/qm and inter-cept as l/KLqm. Also, a plot of log qeq versus log Ceq islinear with the slope 1/n and intercepts log KF accord-ance with Freundlich isotherm. The obtained data from
The data of adsorption isotherms show that the ad-sorptive behavior of cations on modified silica aerogelsatisfies Langmuir and Freundlich assumptions in ac-cordance with the R2 values. As seen, the maximumadsorption capacities for Cu2+, Cd2+, and Pb2+ ionsare found to be 90.1, 181.8, and 250.0 mg/g, respect-ively. The n values are greater than in unity and in-dicate chemisorptions of adsorbates on the adsorbent.Isotherms with n > 1 are classified as L-type iso-therms that show a high affinity between adsorbateand adsorbent [26,27].
linear isotherms are collected in Table 2.
Figure 8 Effect of initial concentration on the removal yield ofFigure 7 Effect of pH on the removal yield of cations; contacttime = 30 min; adsorbent dose = 0.1 g for Cu(II) and 0.05 g forCd(II) and Pb(II); initial concentration = 50 mg/L.
cations; contact time = 30 min; adsorbent dose = 0.1 g for Cu(II)and 0.05 g for Cd(II) and Pb(II); pH = 4 for Cu(II) and 6 for Cd(II)and Pb(II).
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Table 2 Langmuir and Freundlich isotherm constants foradsorption of Cu2+, Cd2+, and Pb2+ ionsAdsorbents Langmuir constants Freundlich constants
qm(mg/g) KL (L/mg) R2 KF n R2
Cu(II) 83.3 0.039 0.971 16.1 3.62 0.897
Cd(II) 200.0 0.052 0.996 25.1 2.62 0.845
Pb(II) 250.0 0.143 0.997 48.3 3.41 0.883
constant of pseudo-first order sorption (L.min-1). The plotof log (qeq − qt) versus t will give a linear relationship fromwhich k1 and qeq can be determined from the slope andintercept in the graph, respectively. The pseudo-first orderequation (Lagergren’s equation) describes adsorption insolid–liquid systems based on the sorption capacity ofsolids [28].
The pseudo-second order chemisorption kinetic equa-
Kinetic rate constants of pseudo-first and pseudo-second order of sorption of Cu , Cd2+ and Pb
Figure 9 Effect of contact time on the removal yield of cations;initial concentration = 50 mg/L; adsorbent dose = 0.1 g for Cu(II)and 0.05 g for Cd(II) and Pb(II); pH = 4 for Cu(II) and 6 for Cd(II)and Pb(II).
Study of kinetic adsorption
The study of adsorption kinetics describes the adsorbateuptake rate and evidently, this rate controls the residencetime of the adsorbate at a solid liquid interface [27-29].The kinetics of the adsorption of Cu2+, Cd2+, and Pb2+ onmodified silica aerogel is studied using pseudo-first orderand pseudo-second order models. The pseudo-first orderequation [27] is generally expressed as follows:
logðqeq−qtÞ ¼ logðqeqÞ−k1t=2:303 ð6Þ
where qeq and qt are the sorption capacities at equilibriumand at time t, respectively (mg.g-1), and k1 is the rate
Figure 10 Effect of adsorbent dose on the removal yield of
cations; initial concentration = 50 mg/L; contact time = 30 min;pH = 4 for Cu(II) and 6 for Cd(II) and Pb(II).
tion [28,29] is expressed as Equation 7,
t=qt ¼ 1=k2qeq2 þ t=qeq ð7Þ
where qeq and qt are the sorption capacity at equilibriumand at time t, (mg.g-1), respectively, and k2 is the rateconstant of the pseudo-second order sorption (g.mg-1.min-1). The pseudo-second-order rate expression hasbeen applied for analyzing chemisorption kinetics fromliquid solutions [29]. If the pseudo-second order kineticsis applicable to the experimental data, the plot of t/qt
versus t should give a linear relationship from which qeq
and k2q2eq can be determined from the slope and inter-cept of the plot, respectively.
The obtained kinetic rate constants of pseudo-first andpseudo-second order of sorption of Cu2+, Cd2+,and Pb2+
on the modified silica aerogel are collected in Table 3.Fitted equilibrium adsorption capacities derived fromEquation 7 for each cation are similar those observed ex-perimentally. However, correlation coefficients values forthe pseudo-second-order kinetic and pseudo-first ordermodel are close to 1.0. Given the good agreement betweenmodel fit and experimentally observed equilibriumadsorption capacity, in addition to the large correlationcoefficients, this suggests that Cu2+, Cd2+, and Pb2+ ionsadsorption followed pseudo-second order kinetics andwere adsorbed onto modified silica aerogel via chemicalinteraction.
Comparison of adsorption capacity (qm) of Cu, Cdand Pb ions on several adsorbents is given inTable 4.Synthesis of silica aerogelIndustrial grade of sodium silicate (Bahman GostarInvestment Co., Isfahan, Isfahan, Iran) is used as a sourceof cost-effective silica sols. An 83.37 g of sodium silicatewith molar ratio of SiO2:Na2O = 3.3:1 is dissolved in316.62 ml deionized water. The resulting solution is stirred
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Table 3 Kinetic rate constants of pseudo-first and pseudo-second order of sorption of Cu2+, Cd2+ and Pb2+
Adsorbent qexp(mg.g-1) Pseudo-first order Pseudo-second order
2+ 2+ on the modified silica aerogel with initial concentration
in the presence of sulfonated copolymer strong cationicresin as H+-form for 10 min to remove sodium ions. ThepH of silica sol is in the range of 2 to 3 after this ion ex-change, then 1 mol/L NaOH solution is added to the silicasol to raise its pH to the range of 4 to 5 for gelation. Theobtained silica sols are stirred for 2 min and then trans-ferred into a plastic beaker where the sols aged into hydro-gels within about 30 min. Then, the hydrogels areimmersed in deionized water to age them for 24 h at 60 °Cto strengthen the networks of the gels. The obtained gel isalso aged for 48 h in acetone solvent for two times and for72 h in n-hexane solvent at room temperature. Finally, the
aged gels are separated and dried at 50 °C in a saturated at-mosphere of n-hexane. The chemicals n-hexane, acetone,and NaOH (with highest purity) are prepared from petro-chemical company of Iran (Petrochemical Commercial Co.,Tehran, Iran).
Modification of silica aerogelThe surface of synthesized of silica aerogel is modified byMPTMS (purchased from Merck & Co., Inc., WhitehouseStation, NJ, USA). An 11.3 g MPTMS is dissolved in56.85 g n-hexane. The synthesized silica aerogel is added toMPTMS solution and the obtained mixture is stirred for
3 h. Then, the modified silica aerogel is separated andwashed with n-hexane. Finally, the modified silica aerogel isderided in a rich atmosphere of n-hexane for 48 h at roomtemperature and for 5 h at 50 °C.
Methods of characterization
The N2 adsorption-desorption isotherms were measured bythe BET method using nitrogen as an adsorption gas at77 K using Belsorp Mini II instrument (BEL Japan, Inc.,Sumida-ku, Tokyo, Japan). Samples were out gassed at
300 °C for 4 h prior to surface area measurements. The FT-IR spectrum recorded from KBr pellets (99 wt.% of KBr) onNicolet Impact 400D FT-IR spectrophotometer (SpectralabScientific Corporation, Markham, Toronto, Canada). Themorphology of synthesized silica aerogel before and aftersurface modification is studied by Philips CM10 transmis-sion electron microscope (TEM) operating at 120 kV. Thesupporting grids were formvar-covered, carbon-coated, and200-mesh copper grids. A diffractometer Bruker D8 Ad-vance (Bruker Daltonik GmbH, Bremen, Germany) withanode of Cu (λ = 1.5406 Å of Cu Kα) and filter of Ni wasapplied to record the X-ray diffraction (XRD) pattern of sil-ica aerogel. Thermogravimetric analysis (TGA) was carriedout with Shimadzu DT-40 thermal analyzer (Tokyo, Japan).
Adsorption of metal ions
The adsorption of Cu2+, Cd2+, and Pb2+ ions by modifiedsilica aerogel as an adsorbent is studied in a batch proced-ure. The synthetic stock solutions of metals ions are pre-pared by dissolving required quantity of analytical grade ofnitrate salts of Cu2+, Cd2+, and Pb2+ ions in deionizedwater. The stock solutions were further diluted with deio-nized water to the desired concentration for obtaining thetest solutions. All chemical nitrate salts and nitric acid areused from Merck (Merck & Co., Inc., Whitehouse Station,NJ, USA).
A known weight of adsorbent (e.g., 0.01 to 0.12 g) wasequilibrated with 50 mL of the cation solution of knownconcentration (e.g., 50 to 400 mg/L) in a polyethylene vesselat room temperature in a thermostatic mechanical shakerfor a known period (10 to 60 min) of time. Mechanicalshaker is used for all the adsorption experiments for agita-ting the sample for a desired contact time. The pH of sam-ples is controlled in the range 2 to 7 with addition of
Table 4 Comparison of adsorption capacity (qm) of Cu, Cd and Pb ions on several adsorbents
Adsorbent Ions qm (mg/g) References
Synthesized silica aerogel from tetramethoxysilane modified with mercapto Cu 51.0 [24]
Chitosan crosslinked with both epichlorohydrin and triphosphate, Cu, Cd, Pb 130.7, 83.7, 199.9 [32]
In this work Cu, Cd, Pb 83.3, 200.0, 250.0
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1.0 mol/L of HNO3 and NaOH solutions by pH-analyzer ofMetroholm 661 (Metroholm Company, Ionenstrasse,Herisau, Switzerland). After equilibration the suspensionwas centrifuged for 15 min at 7,000 rpm, and the samplesolution then was analyzed using Atomic AdsorptionSpectrometer (AAS, Perkin Elmer 300, PerkinElmer Inc.,Waltham, MA, USA) operating with an air acetylene flame.The effect of several parameters, such as pH, adsorbateconcentrations, contact time, and adsorbent dose isoptimized.
The percent of removal is calculated using Equation 8,
%Removal ¼ ½ðC0−CeqÞ=C0 �  100 ð8Þ
where C0 and Ceq are the initial and equilibrium concen-tration of metal ions of sample solution (mg/L).
ConclusionsSodium silicate as a safe and inexpensive precursor can beused to prepare silica aerogel with a high surface of600 m2/g. The modification of prepared silica aerogel isdue to the application of it as a suitable adsorbent to re-move some heavy metals such as Cu(II), Cd(II) and Pb(II)ions from aqueous samples in the range of 50 to 400 mg/L.The high removal yields (76 % to 99 %) in short contacttime of 30 min at the presence of low dose of adsorbent(0.05 to 0.1 g) are the precious advantages of modified silicaaerogel.
Competing interests
The authors declare that they have no competing interests.
Author details1Faculty of Applied Chemistry, Malek-ashtar University of Technology,Shahin-Shahr, 1387763681 Iran. 2Department of Chemistry, Islamic AzadUniversity, Shahreza Branch, Shahreza and Fadak Group, Isfahan37541-13115, Iran.
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doi:10.1186/2228-5547-3-20
Cite this article as: Pouretedal and Kazemi: Characterization of modifiedsilica aerogel using sodium silicate precursor and its application asadsorbent of Cu2+, Cd2+, and Pb2+ ions. International Journal of IndustrialChemistry 2012 3:20.