One pot direct synthesis of mesoporous SnO2/SBA-15 nanocompositeby the hydrothermal method

Vijay K. Tomer a, Ritu Malik b,c, Suman Jangra a, S.P. Nehra b, Surender Duhan a,n

a Nanomaterials Research Laboratory, Department of Materials Science & Nanotechnology, D.C.R. University of Science & Technology,Murthal, Sonepat, Haryana 131039, Indiab Center of Excellence for Energy and Environmental Studies, D.C.R. University of Science & Technology, Murthal, Sonepat, Haryana 131039, Indiac Department of Physics, D.C.R. University of Science & Technology, Murthal, Sonepat, Haryana 131039, India

a r t i c l e i n f o

Article history:Received 13 April 2014Accepted 14 June 2014Available online 21 June 2014

Keywords:SnO2/SBA-15AdhesionDirect loadingMesoporousCeramics

a b s t r a c t

We report a novel one step route for direct loading of SnO2 into the mesoporous framework of SBA-15 bysimultaneous co-condensation of Sn precursor and silica source using the hydrothermal method. HRTEMimages confirm that co-condensation of both Sn and silica species leads to uniform distribution of SnO2

nanoparticles in the framework of SBA-15 whereby retaining the mesoporous characteristics asconfirmed using X-ray diffraction (XRD), N2 adsorption–desorption and energy-dispersive X-ray (EDX)spectroscopy. The mesoporous framework of SBA-15 does not collapse although the efficiency of SnO2

loading decreases with increment of SnO2 content in SBA-15.& 2014 Elsevier B.V. All rights reserved.

1. Introduction

The development of mesoporous materials with high specificsurface area has gained a significant boost with the discovery ofSBA-15 in 1998 [1]. Owing to its tunable pore sizes (3–30 nm) andhigh surface areas [2], SBA-15 has found potential applications inthe area of sensors, catalysis and drug delivery systems [3–5]. SBA-15, functioning as host matrix for metals and metal oxides such asAg, Fe2O3 and TiO2 are more stable in diverse conditions becauseof their well-ordered hexagonal porosities, thermal stability andhigh surface area [3,6,7]. Uniform ordered channels of SBA-15 cancontrol the size of dopant particles and can efficiently preventparticles from agglomeration [3]. SnO2 is an important n-typesemiconductor which possesses unique physicochemical proper-ties for practical use such as photocatalysts, sensors and solar cells[8–10]. Compared with bulk SnO2, mesoporous SnO2 has goodproperties and has outstanding advantages for applications whichdemands for high surface area of material [9].

Recently, composites of SnO2 and SBA-15 were preparedthrough a post-synthesis procedure [4,11]. This post-synthesismethod incorporates SnO2 in the channels of SBA-15 causingpartial or complete blockage of pores which leads to a reductionin the surface area and pore size of SBA-15 [12]. Moreover, thepost-synthesis method causes the agglomeration of tin species onthe surface of SBA-15 leading to a loss in the efficiency of the

obtained nanocomposite [13]. Herein, we present a cost effectiveco-condensation method for direct synthesis of SnO2/SBA-15nanocomposite having high quantum size effect and thermalstability, wherein the SnO2 is introduced in the host matrix duringhydrolysis process. Co-condensation of nanocomposite leads touniform distribution of SnO2 in the SBA-15 matrix wherebyretaining the mesostructure of SBA-15 [7] and could be used infabrication of efficient sensors. In contrast to post-synthesis, thisdirect method of synthesis of SnO2/SBA-15 nanocomposite canavoid the pore blockage and provide well distribution of tinspecies in the framework and surface without significant decreaseof mesopore size. Moreover, direct synthesis method is simpler,economical and energy saving.

2. Experimental

Sample preparation: In a typical procedure, 2 g Triblock copo-lymer (EO20PO70EO20, P123, Sigma Aldrich) was dissolved in 70 mLdistilled water followed by addition of 10 mL HCl (2M). Themixture was stirred at 40 1C until a homogeneous solution wasformed. 4.5 g of TEOS ((C2H5O)4Si, Sigma Aldrich) was then addedto the above solution followed by stirring at 40 1C for 24 h. Themixture was then hydrothermally treated at 100 1C for 24 h. Theproducts were recovered, filtered and dried at 80 1C for 8 h andcalcined at 550 1C for 6 h in air to obtain pure mesoporous SBA-15.

SnO2/SBA-15 nanocomposite was synthesized as follows:required amount of SnCl2 �2H2O (Merck) was dissolved in 10 mLdistilled water to form a homogeneous solution. This aqueous salt

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Materials Letters

http://dx.doi.org/10.1016/j.matlet.2014.06.0880167-577X/& 2014 Elsevier B.V. All rights reserved.

n Corresponding author. Tel.: þ91 9813170944.E-mail address: surender6561@yahoo.co.in (S. Duhan).

Materials Letters 132 (2014) 228–230

solution of SnO2 was added to the P123þH2OþHCl solutionbefore the addition of TEOS and further following the same routeas for pure SBA-15. The influence of SnO2 loading for determining

framework shrinkage was investigated by varying the wt% of SnO2

in SBA-15. The products were designated as SnO2/SBA-15(X),where X was the content of SnO2 in wt%. The values of X in ourexperiment were 1, 5, 10, 15 and 20 for five different SnO2/SBA-15samples.

Characterization: Low angle and Wide angle X-ray data wereacquired on a Bruker D8 advance diffractometer using CuKαmonochromatic radiation (λ¼1.5418 Å) at 40 kV and 40 mA. BETmeasurements were conducted by N2 physiosorption (Microme-trices Tristar 3000) at 77 K. HRTEM experiments were obtained onTECNAI G20, operating at 200 kV equipped with energy-dispersiveX-Ray spectroscopy.

3. Results and discussion

Fig. 1 shows the wide angle XRD pattern (2θ¼151�801) of SBA-15 and SnO2/SBA-15(X) nanocomposites. As could be seen, in thelower concentrations (X¼1 and 5 wt%) of SnO2, the characteristicspeaks of SnO2 are almost invisible. This shows the amorphousnature of SBA-15 at low loading of SnO2. As the concentration ofSnO2 increases (X¼10 wt%), small diffraction peaks at 2θ¼26.91,34.21, 38.21, 52.31, 54.91, 57.81, 64.61, 66.21 and 78.31 correspond-ing to (110), (101), (200), (211), (220), (002), (112), (301) and (321)planes of SnO2 (JCPDS no. 03-1116) respectively are observed. Asthe wt% of SnO2 increases further (15 and 20 wt%), well resolvedcharacteristics peaks of SnO2 are observed. This gradual strength-ening of diffraction peaks of SnO2 results from the increment inloading of SnO2 concentration in SBA-15 framework. The inset inFig. 1 gives low angle XRD patterns in the (0.5–3.01) 2θ-range forSBA-15 and SnO2/SBA-15(X) nanocomposites. Three well resolvedpeaks were obtained for all the samples which demonstrate thatthe prepared samples are of highly ordered hexagonal mesoporousstructure. For pure mesoporous SBA-15, these peaks are indexed tothe (100), (110) and (200) reflections of the hexagonal space groupp6mm similar to as described by Zhao et al. [1]. It is observed thatthe peak intensities of SnO2/SBA-15(X) decrease and get shiftedtoward higher angles with increasing the wt% of SnO2 nanoparti-cles. This may be due to decrease in d-spacing caused bysubsequent loading of SnO2 in the mesoporous channels of SBA-15. These results clearly shows that the structural ordering isreduced continuously [3].

The BET curves of SBA-15 and SnO2/SBA-15(X) are shown inFig. 2. All the samples exhibit type IV characteristics curveaccording to the IUPAC classification and exhibit a H1 type broadhysteresis loop which is generally exhibited by mesoporous solids[1]. The shape of type IV curves is also well maintained afterloading of SnO2 nanoparticles inside SBA-15 showing that themesoporous structure is well preserved. This was consistent withthe result of low-angle XRD. The results listed in Table 1 showsthat there is a decrease in the surface area and pore size of thesamples with the increase in SnO2 concentration. This is becauseof the continuous blockage of channels of SBA-15 due to the

Fig. 1. Wide angle XRD patterns and LAXRD (inset) of SnO2/SBA-15(X) nano-composites.

Fig. 2. (a) N2 adsorption–desorption isotherms of SBA-15 and SnO2/SBA-15(X) nanocomposites.

Table 1Physicochemical properties of SBA-15 and SnO2/SBA-15(X) nanocomposites.

Sample d-Spacingd100 (nm)

Unit cell parameter,ao (nm) (ao¼2�d100/√3)

Totalsurfacearea

Pore size dP(nm)

Pore volume(cm3/g)

Pore wallthickness dW (nm)(dW¼ao�dP)

Effective SnO2

wt%TheoreticalSnO2 loading(wt%)

SBA 10.95 12.644 793.76 8.64 1.18 4.004 – –

X¼1 10.54 12.170 721.28 7.99 1.07 4.18 0.74 (74%) 1X¼5 10.08 11.639 678.17 7.17 0.99 4.469 3.51 (70%) 5X¼10 9.79 11.304 609.46 6.35 0.91 4.954 6.47 (64%) 10X¼15 9.43 10.899 556.87 5.58 0.82 5.319 8.85 (59%) 15X¼20 9.03 10.426 497.38 4.76 0.75 5.666 10.68 (53%) 20

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incorporated SnO2 nanoparticles. This causes a pore filling effectwhere the diameter of empty pore channel decreases leading to anincrease in pore wall thickness [3,11]. At the initial lower concen-tration of SnO2 in SBA-15 (1 wt%), the SnO2 nanoparticles hasmaximum tendency to locate themselves inside the empty poresof SBA-15. Hence a drastic change was observed in the totalsurface area with an increase in SnO2 concentration from 0 to1 wt%. However, as the concentration of SnO2 increases further,this tendency decreases because of chocking of pore walls due toalready occupied adsorption sites by SnO2 nanoparticles. Thiscauses the comparatively less depreciation in total surface areafrom 1 to 5 wt% SnO2. The decrease in loading efficiency of SnO2

nanoparticles is justified with the EDX analysis in Table 1.The HRTEM image of SBA-15 and EDX spectra (inset) of SnO2/

SBA-15(20) nanocomposite are shown in Fig. 3. The inset imageconfirm the 2D p6mm regular hexagonal mesostructure of nano-composites [1]. Long range pore order of uniform channels withevenly dispersed SnO2 nanoparticles were observed in the hex-agonal channels of SBA-15. The distance between two consecutivecenters of hexagonal pores, average wall thickness and the porediameter for pure SBA-15 as estimated from HRTEM image is12.7 nm, 4.1 nm and 8.5 nm, respectively, which is quite consistentwith the results obtained from BET analysis. In the EDX spectra, noother element was detected apart from Si, O and Sn whichconfirms the purity of nanocomposite. The EDX results in Table 1depicts that the efficiency of SnO2 loading in SBA-15 decreasescontinuously on account of higher loading of SnO2 in the SBA-15.The possible reason for this inversely proportional behaviorof experimental wt% SnO2 loading to that of theoretical wt%SnO2 loading in SBA-15 might be due to the continuous blockageof pores with successive incorporation of SnO2 which leads tothe depreciation of effective Si–OH bonding sites for SnO2

nanoparticles.

4. Conclusion

In the present work, the mesoporous SnO2/SBA-15 nanocom-posite was synthesized by direct loading of Sn precursor during

the synthesis of SBA-15. The simultaneous co-condensation of tinspecies with silica source leads to homogeneous distribution ofSnO2 nanoparticles in the SBA-15 mesoporous framework and thehexagonal mesostructure was well preserved during the directloading procedures. The decrease in the specific surface area andpore size of the nanocomposite shows that the small pores weregradually filled and blocked by SnO2. The volumes and surfaceareas of blocked and filled pores were deducted from the totalsurface and volume of host SBA-15, but the structural order ofSBA-15 has not been changed. Thus, the direct loading of SnO2 intoSBA-15 host is a facile method without much decrease in thesurface area of the nanocomposite.

Acknowledgments

Surender Duhan is grateful to UGC, New Delhi (Grant No. F. No.41-997/2012(SR)) for providing Major Research Grant.

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Fig. 3. HRTEM image showing long range channels and hexagonal pores (inset) of SBA-15 and EDX spectra of SnO2/SBA-15 (20) (inset).

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