Synthesis and Characterization Hierarchical Three-Dimensional TiO 2 Structure via Hydrothermal Method

Transcription

1 IOP Conference Series: Materials Science and Engineering PAPER OPEN ACCESS Synthesis and Characterization Hierarchical Three-Dimensional TiO 2 Structure via Hydrothermal Method To cite this article: N. Syuhada et al 2018 IOP Conf. Ser.: Mater. Sci. Eng View the article online for updates and enhancements. This content was downloaded from IP address on 15/10/2018 at 16:11

2 Synthesis and Characterization Hierarchical Three-Dimensional TiO2 Structure via Hydrothermal Method N. Syuhada 1, B Yuliarto 1, and Nugraha 1,2 1 Advance Functional Materials Laboratory, Department of Engineering Physics, Fakultas Teknologi Industri Institut Teknologi Bandung, 40132, Indonesia 2 Research Center for Nanoscience and Nanotechnology (NRCN), Institut Teknologi Bandung, Fakultas Teknologi Industri, 40132, Indonesia brian@tf.itb.ac.id Abstract. TiO 2 is one of the most potential candidates due to its fascinating properties for multi-discipline fields. One dimensional nanostructure TiO 2 such as nanotube and nanorods has been widely used for many devices technology. Compare with one-dimensional nanostructure TiO 2; the hierarchical TiO2 has not been widely applied. Three dimensional TiO 2 play a promising role for application in many different fields such as photovoltaics, photocatalytic and a gas sensor. Herein, we report that the hierarchically structures TiO 2 have been successfully obtained by the one-pot Hydrothermal process. The growth mechanism of Titania was controlled by Titanium (IV) isopropoxide (TTIP). Ethylene glycol (EG). Hydrochloric acid (HCl). Hexadecyltrimethylammonium bromide (CTAB) molar ratio. TTIP was used as titanium source and CTAB as a soft template. The molar ratio of TTIP. EG. HCl. CTAB was 0.1:0.2:0.4: Those samples were synthesized using the hydrothermal method at 180 o C for 20 h. The purpose of this work was focused on investigating morphology, crystallite size, crystalline phase, and particle size. The properties of these materials were characterized by X- Ray Diffraction, Energy Dispersive Spectroscopy and Scanning Electron Microscope. It was found all particles exhibited unique spherical morphology which arranged by nanorods and good distribution nanoparticle. The Average size of the sphere has range 1 µm to 3 µm with diameter nanorods 60 nm to 100 nm. The TiO 2 spheres were constructed of interconnected nanorods and formed a three dimensional (3D) porous framework. XRD analysis confirmed that sample consisted of pure rutile crystal structure with crystallite size was 50 nm, and EDS revealed an elemental content of Ti % and O %. Keywords. Hierarchical Structure, Three Dimensional TiO 2, Hydrothermal Synthesis. 1. Introduction Nanostructured materials have got great interest as catalysts and other application because of their unique texture and structural characteristics. Much effort has concentrated on the important metal oxide such as TiO 2, SnO 2. VO 2 and ZnO. Titanium dioxide (TiO 2) had been used in fields such as industrial manufacturing, aerospace, ocean exploring, environmental protection, resource development, gas sensing, photocatalysts, photoelectrodes for photo splitting water, ceramic material, cosmetics, medical diagnose, solar cells and even as a food coloring agent and in toothpastes [1]. Titania has been extensively investigated because of the stability of its chemical, physical, optical, and Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

3 electronic properties and have an advantage such as biocompatibility, non-toxic, photo corrosion-free, and cost-effective. In those applications, it is a vital factor to control morphology, particle size distribution, phase composition and porosity of TiO 2. TiO 2 exists in three mineral forms: Anatase, Rutile, and Brookite [2]. Anatase type has a tetragonal crystalline structure (dipyramidal habit) and mainly used as a photocatalysts under-irradiation. Rutile type also has a tetragonal crystal structure (prismatic habit) and mainly used as white pigment in paint. Brookite type has an orthorhombic crystalline structure. TiO 2 morphologies have many shapes such as nanotubes, nanowires, nanorods and mesoporous structures [1]. There are numerous methods for synthesis TiO 2 such as chemical precipitation [3] [5], the sol-gel method [5] hydrothermal [6] and solvothermal process [7], Wang et al. [8] reported the synthesis of anatase TiO 2 by sol-gel method using titanium tetra-isopropoxide with ethylene glycol had been obtained the TiO 2 particle with high surface area, well crystallized and small crystallite size. The method of Kim et al.[7] successfully investigated the TiO 2 obtained from Titanium isopropoxide as a precursor in toluene solution with a solvothermal synthesis produced a uniform anatase structure with mid-size particles on the nanoscale level. Among those reports, the sol-gel technique is the most frequently applied, but there are some problems like the precipitates derived from the process are amorphous, and the photocatalytic and photoelectrical conversion efficiency of those TiO 2 are not high enough for the industrial purpose. To improve TiO 2 characteristics, several methods had presented like formed high surface area, improve interfacial charge separation with developing the defect structures and modification the TiO 2 with metal or other semiconductors. Hydrothermal synthesis has become one of the important methods to use in nanomaterial and nanotechnology production. Hydrothermal is the reaction that conducted in steel pressure vessels called autoclaves under controlled temperature or pressure. The temperature can be elevated above the boiling point of water, reaching the pressure of vapor saturation. This method is widely used for the production of small particles in the ceramic industry [1]. Occurring high temperature and pressure condition, the benefit of this method allows to make materials have monodispersed and highly homogeneous nanoparticles. The performance of TiO 2 was influenced by the particle size of the TiO 2 structure. Some authors report that the specifics surface area and surface to volume ratio increase as the size of particle size decrease. The TiO 2 material is expected become an important target in helping solve many serious problems on environmental, pollution and energy crisis based on the use of solar energy on photovoltaic device. In this works, we apply a hydrothermal method to synthesize TiO 2 nanoparticles by using CTAB as a surfactant of the forming agent. Hydrothermal treatment is helpful to crystallize nanoparticle and stabilize the sphere structure. 2. Materials and methods All chemical reagents used in present experiments were obtained from commercial sources and used without purification. The reagent used for the synthesis of titanium dioxide were titanium (IV) isopropoxide (C 12H 28) 4Ti) (Aldrich, 97 % purity), Ethylene Glycol (C 2H 6O 2) (Merck, 99 %), Cetyltrimethylammonium bromide (C 19H 42BrN) (Merck, 97 %), hydrochloric acid (HCl) (Merck 37 %). The molar ratio of TTIP.EG.HCl.CTAB is 0.1:0.2:0.4: Firstly, 3 ml titanium isopropoxide (TTIP) was added into hydrochloric acid (HCl) solution during vigorous stirring (bottle A) at room temperature, then ethylene glycol (EG) were dropped into bottle A under stirring. Secondly, 0.5 g cetyltrimethylammonium bromide was dissolved in 2.5 ml distilled water to form CTAB solution (Bottle B). finally, after stirring for 15 min, bottle B was added into bottle A and stirring for 30 min to form TTIP solution. After stirring the solution was transferred to an autoclave and heated at 180 C for 20 h, after that the autoclave was cooled naturally. The obtained samples were washed with distilled water several times, to collected the resultants and removed the organic solvent is using the centrifuge. Then, dried at 100 C for 3 h and calcination at 550 C for 6 h. The obtained TiO 2 powders were ready for further characterization. 2

4 The phase and crystal structure were studied by X-ray diffraction (XRD) Rigaku with the standard Cu-Kα radiation source, λ = nm) operated at 40 kv and 40 ma at room temperature in the 2Ɵ range from 15 to 65 at a scanning rate of 0.01 s -1. The size and morphology of samples were characterized using scanning electron microscopy (SEM, Hitachi S-4800 microscope) and to analyzed elemental content of samples were using Energy Dispersive Spectroscopy. 3. Results and discussion The one-pot hyhdrothermal method has been used to fabricate the TiO 2 hierarchical microspheres. The key point of this synthesis is to control the hydrolysis rate of the TiO 2 precursor. The addition of EG can retard the hydrolysis rate of precursor during the hydrothermal process and reduce the size of the CTAB surfactant micelles. Then some CTAB miczelles would dissolve into individual molecules and adsorb on the surface the TiO2 crystal nucleus and act as a template to form the structure of TiO 2 hierarchical microsphere. Huang et al. [9] prepared TiO 2 by the sol-gel process at room temperature using tetra-butyl titanate as the precursor without any templates. Antonneli and Ying synthesized TiO 2 by a modified sol-gel method using surfactants as templates. All of them reported the sample was successfully obtained, but samples using surfactant has the smaller particle size, small agglomeration and good uniform of morphology. Figure 1. Diffraction pattern of TiO2 The XRD Pattern of the Titanium dioxide that was synthesized at 180 C and calcined at 550 C for 6 h are shown in Figure 1. X-ray diffraction (XRD) characterization was used to identify the phase and crystal structure of the sample. As shown in Figure 1 the TiO 2 sample has phase crystal of rutile with the tetragonal crystal structure (a = b = nm, c = nm, space group P42/mnm). The diffraction peaks at 27.5, 36.01, 39.26, 41.28, 44.12, 54.4, 56.7, 62.92, and were corresponding to the (110), (101), (200), (111), (210), (211), (220), (301) and (112) planes. The obtained result showed broad rutile peak which is plane 110 has the highest intensity. All diffraction peaks show the complete formation of crystalline rutile phase and were indexed according to the JCPDS card No No peaks related to either the anatase or brookite phases were observed in the XRD pattern. The hydrothermal synthesis route has advantages to obtain phase-pure TiO 2nanoparticles at both lower temperatures and reaction times. From the diffractogram, the widths of the bases of the peaks and its intensity indicate the size of nanocrystals; small crystals could 3

5 promote more intense spreading due to internal reflections that occur in the system. The peaks were rather sharp, which indicated that the samples had relatively high crystallinity. Titanium powder could be controlled by the molar ratio of starting material, washing process and calcinate temperature. Crystalline sized calculated from XRD peaks are listed below in table 1. The average nanocrystal size was determined using the Scherrer equation K D = sin (1) Where D is the average crystallite size, K is the Scherrer constant (0.90), λ is the wavelength of the X- ray radiation ( nm for Cu-Kα), β is the peak position. Table 1. The crystallite size of microsphere TiO 2 Bragg Planes (hkl) Crystallite Size (nm) Average The SEM images showed a spherical hierarchical structure with average uniform size about 1.5 µm (Figure 2). It can be seen that the TiO 2 material is made up of large quantities of microsphere architectures and composed of many nanorods with average diameter distribution in about 62 nm, these nanorods covered the sphere. Those structures indicated that the hierarchical TiO 2 has large specific surface. The literature reported the microsphere TiO 2 showed high specific surface large area leading to high photocatalytic activity due to a large contact area. The result of hierarchical microsphere TiO 2 structure that obtained in this work generally similar with previous studies [10], [11] however, there is probably different result that obtained like particle uniform and difference in particle diameter and surface area. This occurs because of reactant concentration of the solution, acid condition [12], reaction time [12], and hydrothermal temperature [11]. Based on the report the usage of acid can control the hydrolysis reaction of titanium while the reaction time and temperature synthesis give significant influence on crystallite size and surface area [11]. Figure 2. Morphology of Microsphere Hierarchal TiO 2 Energy dispersive X-ray spectrometry (EDX) analysis (Figure 3) of TiO 2nanoparticle showed for Ti element and oxygen. There is no trace of any other impurities that could be seen. However, there is 4

6 2 peak show which is carbon and gold. The Peak of gold could be seen because of the coating material that had been used. Figure 3. Elemental content of hierarchical structure TiO 2 Table 2. Elemental content of sample Element Weight % Atomic % Error % Net Int. K Ratio Z R A F O K Ti K Conclusions A rutile phase Titanium dioxide was synthesized by the hydrothermal route at 180 C for 20 h. SEM images showed the titanium dioxide that was obtained have microsphere hierarchical structured with average uniform size about 1 µm to 3 µm that was arranged by nanorods. The diameter particle of nanorods was 62 nm. A major advantage of this route is the synthesis of titanium dioxide rutile anatase can be performed at moderate temperatures and reaction times. The TiO 2 powder showed good characteristics and good uniform distributed EDS revealed an elemental content of Ti % and O %. This synthesis method provides a simple route to fabricated nanostructured titanium dioxide that can be applied in various fields. Acknowledgments This work was supported by Laboratorium of Advance Functional Material, Department of Engineering Physics Institut Technology Bandung and Indonesia endowment fund for education (LPDP). References [1] M. Malekshahi Byranvand, A. Nemati Kharat, L. Fatholahi, and Z. Malekshahi Beiranvand, A review on synthesis of nano-tio2 via different methods, J. Nanostructures, vol. 3, no. 1, pp. 1 9, [2] G. P. Li, A. Bono, D. Krishnaiah, and J. Collin, Preparation of titanium dioxide photocatalyst loaded onto activated carbon support using chemical vapor deposition: a review paper., J. Hazard. Mater., vol. 157, no. 2 3, pp , [3] F. Pedraza and A. Vazquez, Obtention of TiO2 rutile at room temperature through direct oxidation of TiCl3, J. Phys. Chem. Solids, vol. 60, no. 4, pp , [4] E. Scolan and C. Sanchez, Synthesis and characterization of surface-protected nanocrystalline titania particles, Chem. Mater., vol. 10, no. 10, pp ,

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