Synthesis and Characterization of TiO2@SiO2 and SiO2@TiO2 Core ...

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ScienceDirect Procedia Engineering 170 (2017) 65 – 71

Engineering Physics International Conference, EPIC 2016

Synthesis and Characterization of TiO2@SiO2 and SiO2@TiO2 Core-Shell Structure Using Lapindo Mud Extract via Sol-Gel Method Herny Ariesta Budiartia, Rizky Nanda Puspitasaria , Agus Muhamad Hattaa, Sekartedjoa and Doty Dewi Risantia* a

Department of Engineering Physics, Institut Teknologi Sepuluh Nopember, Surabaya, 60111, Indonesia

Abstract

Core-shell structures were prepared using silica from Lapindo mud extract. The XRD results showed that the extracted silica contains γ-Al2O3 and NaAlSi3O8. Besides, the FT-IR, Raman spectroscopy, and FE-SEM analyses showed that the core particles were not finely covered by the shell. BET measurement indicated that high surface areas are attainable for core-shell structures addition into TiO2 nanoparticles. TiO2/TiO2@SiO2 core-shell structure has 161.100 m2/g and 0.311 cc/g of surface area and pore volume, respectively. Whereas, TiO2/SiO2@TiO2 core-shell structure has surface area of 140.200 m2/g and pore volume of 0.292 cc/g. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). © 2016 The Authors. Published by Elsvier Ltd. Peer-review under responsibility of the organizing committee of the Engineering Physics International Conference 2016 Keywords: core-shell; titania; silica; mud extract; sol-gel

1. Introduction Core-shell structure have played important role in the development of advanced materials science and technology. Plasmonic material have many application in various research field, including energy conversion, optical sensor, catalyst, due to their high photocatalytic activity [1–4]. Core-shell structure is an onion like structure which contains at least two semiconductor materials. It is possible to modified optical properties of the core nanoparticles, for example the shell provides a physical barrier between the core and the surrounding medium [5]. Lapindo mud is placed in Sidoarjo, Indonesia. This mud vulcano is containing 55% of SiO2 [6]. This could be extracted by using co-precipitation method under pH 7 and get high purity that achieve 96,9 wt%. SiO2 nanoparticles is known to applied in many fields technology[7–11]. This work presents a synthesis and characterization of TiO2@SiO2 and SiO2@TiO2 core-shell structure with SiO2 nanoparticle from Lapindo mud extract. 2. Materials and Methods 2.1. Materials Materials used in this research consist of Lapindo mud, Titanium (III) chloride (TiCl3, 15%), ammonium (NH3, 25%), triethylamine and ethanol (absolute EtOH, Merck) were supplied by Merck, titanium tetraisopropoxide (TTIP) and DI-Water were obtained from Sigma-Aldrich, hydrochloric acid (HCl, 37%) and sodium hydroxide (NaOH) were purchased from SAP.

* Corresponding author. Tel.: +62-31-5947188; fax: +62-31-5923626. E-mail address:[email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the Engineering Physics International Conference 2016

doi:10.1016/j.proeng.2017.03.013

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Herny Ariesta Budiarti et al. / Procedia Engineering 170 (2017) 65 – 71

2.2. Instrumentation Instruments utilized in this research are XRD Philips X’Pert MPD, FT-IR Thermo Nicolet i510, Renishaw inVia Raman Microscope, FE-SEM FEI Quanta 400F and BET analyzer Quantachrome NOVA 1200e 2.3. Synthesis of rutile TiO2 and SiO2 Co-precipitation method was used to prepare rutile TiO2 nanoparticles. 10 ml Titanium trichloride solution (10% TiCl3, Merck) was used after dilution in 20 ml hydrochloric acid solution (37% HCl, SAP). Then, 50 ml ammonium solution (25% NH3, Merck) was added dropwise to titanium trichloride solution, under strong stirring, until a white precipitation is obtained. The resulting suspension was maintained at room temperature overnight, and than filtered and vigorously washed with distilled water to remove the remaining ammonium and chloride ions [12]. The rutile TiO2 nanoparticles were obtained by annealing the precipitate at 1000°C for 7h. Besides, the SiO2 nanoparticles were extracted from Lapindo mud also using co-precipitation method. At first, the Lapindo mud was dried and then grounded with mortar until 250 mesh. After that, the fine Lapindo mud was immersed with HCl [2M] for 24 hours to remove the pollutant, then washed with distilled water, dried, and grounded again to reach 250 mesh. 10 gr prepared Lapindo mud was dissolved in 60 ml NaOH [7M] under stirring for 1 hour at 70°C. Then, 250 ml distilled water was added and filtered with filter paper. The filtered solution was then added with HCl [2M] until pH7 and the white precipitate was obtained. The resulting suspension was maintained at room temperature for 24 hours and subsequently filtered and washed several times with distilled water for remove the acid, alkali, and salt content, then dried for 24 hours at 80°C [6]. 2.4. Synthesis of TiO2@SiO2 and SiO2@TiO2 TiO2@SiO2 nanostructures from mud extract were prepared using sol-gel method. Firstly, Lapindo mud was soaked in HCl, 37% solution for 24 hours and rinsed with aquades for several times, then dried at 80°C for 24 hours. After that, 10 gr prepared Lapindo mud was dissolved in 60 ml NaOH [7M] under stirring for 1 hour at 70°C. Then, 250 ml distilled water was added and filter with filter paper. 150 ml filtered solution and 0.5 gr of rutile TiO2 was then added with HCl [2M] until pH7 and the white precipitate was obtained. The precipitate was filtered and washed several times with distilled water to remove the acid, alkali, and salt content, then dried for 24 hours at 80°C. SiO2@TiO2 core-shell nanoparticles were obtained by using sol-gel reaction [10,11] First, 0.7 ml water, 2 ml ammonia, and 39.5 ml ethanol were mixed with 0.5 gram SiO2 nanoparticles to get the SiO2 solution. 14 ml triethylamine was added to SiO2 solution under stirring at 10oC. The other solution that contains 18 ml ethanol, 6 ml triethylamine, and 0.5 ml TTIP was added by dropwise addition to the SiO2 solution. The mixture solution was vigorously stirred at 10oC for 6 hours. The solution then dried at 100oC before calcination at 600oC for 6 hours. 3. Results and Discussion 3.1. Crystallinity and Interfacial Structure XRD (X-Ray Diffractometers) was used to know the phase, and structure of the nanoparticles. Fig.1 shows the XRD patterns of rutile TiO2, anatase TiO2, SiO2 extracted from mud, TiO2@SiO2 core-shell, and SiO2@TiO2 core-shell nanoparticles. For TiO2@SiO2 nanoparticles (Fig. 1a), the XRD pattern shows that the sample has high crystallinity and all peaks of TiO2 rutile are in good agreement with the JCPDS 00-021-127. The XRD spectra of TiO2@SiO2 from mud extract is decorated by shoulder peak around 2θ = ~24° and the peak intensities are generally weaker than the bare rutile TiO2, which is attributed to the presence of SiO2 in an amorphous state surrounding the rutile [13,14]. Meanwhile in Fig. 1b, it could be seen that SiO2 nanoparticles extracted from Lapindo mud vulcano has peak at 2θ = 24,97o. In addition to that, it was found there is another peak at 2θ = 31.79o and 2θ = 45,56o. The broadened diffraction peak of SiO2 nanoparticles extracted from Lapindo mud volcano indicates an amorphous state of SiO2. From XRD characterization, it is known that SiO2@TiO2 that majority phasae is TiO2 anatase. The main peak of TiO2 anatase is found for SiO2@TiO2 nanoparticles at 2θ = 25,32o. All the peaks of anatase TiO2 are assigned to JCPDS 00-021-1272. Moreover, a weak peak of TiO2 rutile is found at 2θ = 27,36o. However, both core-shell structures from mud extract contains another peak that corresponds to γAl2O3 and NaAlSi3O8 [15].

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(a)

(b)

Fig. 1XRD pattern of core-shell structure (a) TiO2@SiO2 and (b) SiO2@TiO2

Fig. 2 shows FTIR spectra of SiO2 nanoparticles from mud extract, rutile and anatase TiO2 nanoparticles, and core-shell structure of SiO2@TiO2 and TiO2@SiO2 from mud extract. In Fig. 2.a, the band around 1070 cm-1 attributes to the asymmetric stretching vibration of Si – O – Si bond, another band at 3267.29 and 1636.43 cm-1 corresponds to H – O – H stretching (absorbed water) and H – O – H bending water. Besides, the bond at 1015 cm-1 attributes to Si – O stretching, 950 cm-1 corresponds to Si – OH bond, and bond at 1113 cm-1 corresponds to Si – O stretching (longitudinal mode). From the FTIR patterns it is known that core-shell structures also have another peak around 700 cm-1 corresponds to Al – O bond. This FTIR pattern shows that SiO2 nanoparticles denotes the presence of Si – O – Si bond, but the bond of Ti-O-Si which is supposed to be located at 933 cm-1 only sluggishly emerge for SiO2 shell made from mud extract [5–10]. This may suggest that SiO2 mud extract does not fully cover the rutile TiO2 core.

(a)

(b) -1

Fig. 2 FTIR spectra in the range of 500-4000 cm of core-shell structures (a) TiO2@SiO2 and (b) SiO2@TiO2

Fig. 2.b illustrates the FT-IR spectra of core-shell structure SiO2@TiO2. The broad band around 3300 cm-1 is ascribed to HOH vibration because of water absorbance [16]. Si-O-Ti bond for core-shell structure SiO2@TiO2 is seen at 980.56 cm-1. This peak is slightly shifted to the lower wavenumber than the Si-O peak in SiO2 from mud extract at 1003.57 cm-1 (Fig. 2a). The vibration of Si-O-Ti bond could be shifted due to the chemical composition for the powder sample, calibration and resolution of the instrument [19]. The Raman spectra of all nanoparticles and core-shell structures are shown in Fig. 3. Rutile TiO2 have four typical vibrational modes, i.e. B1g (142,948 cm-1), Eg (447,075 cm-1), A1g (610,583 cm-1), and SOE (second-order effect) at 238,706 cm-1. Anatase TiO2 have four sharp Raman bands at Eg (144,183 cm-1) and (639,629 cm-1), B1g (399,382 cm-1), and A1g (520,43 cm-1). The B1g mode is a combination of asymmetric bending of the O – Ti – O bonds in the {001}, {110}, and {-110} planes. The Eg mode is the asymmetric bending of O – Ti – O bond in the {001} plane caused by the opposite moving of the O atom across the O – Ti – O bond. The A1g mode is a symmetric stretching of the O – Ti – O in the {110} plane caused by moving opposite of the O atoms in the adjacent O – Ti – O bonds. Besides, the movements of the atoms of the SOE mode are still elusive [20,21]. Raman

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spectra of core-shell structure of TiO2@SiO2 reveal the same peak as rutile TiO2 spectra, but the intensity of core-shell structures decreases significantly. These results imply that amorphous SiO2 exists surrounding the rutile TiO2. In Fig. 3.b. both Raman spectra of SiO2@TiO2 nanoparticles have Raman peak for TiO2 anatase specifying that in SiO2@TiO2 nanoparticles contain TiO2 anatase as revealed in Fig. 1.

(a)

(b)

Fig. 3 Raman spectra in the range of 100-1000 cm-1 for the nanoparticles and core-shell structures.

3.2. Morphology

Fig. 4 FE-SEM images of (a) rutile TiO2 nanoparticles, (b) TiO2@SiO2 nanoparticles, (c) SiO2 nanoparticles, (d) SiO2@TiO2 and EDX of core-shell structures

Fig. 4 illustrates the secondary electron images of the core nanoparticles and core-shell structure nanoparticles. As shown in Fig 4a and b, rutile TiO2 with diameter about 400 nm and 800 nm has been coated with SiO2 nanoparticles from mud extract. However, the SiO2 nanoparticles do not fully cover the rutile TiO2 core. The extracted SiO2 nanoparticles, shown in Fig. 4c. are small spherical-sized of ~50 nm and appear to be quite smooth on the surface. While for SiO2@TiO2 nanoparticles (Fig. 4d), it could be seen that SiO2 nanoparticles are covered by anatase TiO2 and giving an overall cloudy appearance. The EDX spectra (Fig. 4) confirms the presence of SiO2 as well as the existence of NaAlSi3O8, as correspond to peak around 2θ = 31° in XRD result.

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3.3. Surface area and pore size distribution The nitrogen adsorption/desorption isotherms and BJH pore size distribution of TiO2, TiO2/TiO2@SiO2 and TiO2/SiO2@TiO2 are shown in Fig. 5. Some characteristics of the samples, such as BET surface area, micropore area, average pore diameter, micropore volume, mesopore volume and total pore volume are listed in Table 1. According to IUPAC nomenclature, the absorbent pores are classified into three groups: micropore (diameter 50 nm) [22]. The BET measurements confirmed the absence of micropores in all nanoparticles. The pore diameter for TiO2, TiO2 containing TiO2@SiO2 core-shell and SiO2@TiO2 core-shell is found to be 7.679, 7.73 and 7.632 nm, respectively, indicating that there is no significant change in pore diameter. The mesopore volume was obtained by subtracting mesopore volume from the corresponding total volume [23]. The mesoporosities (percentage of mesopore to total pore volume Vmes/Vtot) were calculated and found to be 53, 71 and 61% for TiO2, TiO2 containing TiO2@SiO2 core-shell and SiO2@TiO2 core-shell, respectively. For samples with TiO2@SiO2 and SiO2@TiO2 core-shell addition, the macroporosity slighly increased along with mesoporosity when compared to TiO2 nanoparticles. Further study is needed to investigate the pore size evolution by addition of core-shell nanoparticles. The BET surface area was found to be 116 to 161 m2/g in the case of TiO2 nanoparticles and TiO2/TiO2@SiO2 nanocomposite, respectively. This sizeable increase in surface area by addition of TiO2@SiO2 core-shell may be due to the SiO2 limiting the agglomeration of TiO2 particles [24,25]. Table 1. The physical properties of the as-synthesized samples

Macropore

Pore Volume Total

Surface Area (m2/g)

Pore Diameter

Mesopore Volume

(nm)

(cc/g)

TiO2(A:R)

116.137

7.679

0.084

0.0005

0.157

TiO2(A:R)/ TiO2(R)@SiO2

161.100

7.730

0.222

0.0009

0.311

TiO2(A:R)/ SiO2@TiO2(A)

140.200

7.632

0.204

0.0011

0.335

Photoanode types

(a)

Volume (cc/g)

(cc/g)

(b)

Fig. 5 (a) Nitrogen adsorption/desorption isotherm, (b) BJH pore size distribution of TiO2, TiO2/TiO2@SiO2 and TiO2/SiO2@TiO2

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4. Conclusion SiO2 nanoparticles from mud extract contains another peak that corresponds to γ-Al2O3 and NaAlSi3O8. Core-shell structures have been synthesized but the present result indicates that particularly for TiO2@SiO2 the core was not fully covered by the shell. The pore size distribution shows that the as-synthesized nanocomposite containing core-shell structure is mesoporous. The material with large surface area and mesoporous nature would increase the adsorption of dye on it, which in turn will improve photosensitivity to solar radiation. Acknowledgements The authors would like to thank to Directorate General of Higher Education Ministry of Research Technology and Higher Education Republic of Indonesia for funding this research scheme Penelitian Unggulan Perguruan Tinggi 2015-2016. The author (HAB) would also like to thank to Indonesia Endowment for Education for supporting her thesis research. 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