PHOTOCATALYTIC ACTIVITY VIA SYNTHESIS OF TiO 2 NANOWIRES CONTROLLED - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS PHOTOCATALYTIC ACTIVITY VIA SYNTHESIS OF TiO 2 NANOWIRES CONTROLLED MICROSTRUCTURE AND SURFACE AREA BY ELECTROSPINNING METHOD. J.S. Lee 1 , Y.I. Lee 2 , D.H. Jang 1 , K.J. Lee 2 , J.G. Park 1 , and Y.H. Choa 1,2* 1 Dept. of Bio-nanoTechnology, Hanyang University, Ansan 426-791, Korea 2 Dept. of Fine Chemical Engineering, Hanyang University, Ansan 426-791, Korea *Corresponding author (choa15@hanyang.ac.kr) Keywords : TiO 2 , Nanowire, Electrospinning, Photocatalytic activity, Photodegradation and porous structure [2]. The crystalline phase is 1 Introduction The volatile organic compounds (VOCs) with water influenced surface area by crystalline size. TiO 2 with and air pollution are widely used in industrial a large surface area and porous structure is expected to prevent the electron – hole recombination and process and domestic activities. The VOCs are known to be toxic and considered to be increase reactant quantity onto the photocatalyst carcinogenics. The most significant problem related surface [3]. As the photocatalytic materials, TiO 2 to the emission of VOCs is generated the potential nano-powders have been widely used in the production of photochemical oxidants such as ozone photocatalytic activity. Various synthesis methods and peroxyacetyl nitrate. The photocatalytic activity such as sol-gel, hydrothermal, and electrochemical of the volatile organic compound is promising for method have been used to fabricate TiO 2 nano- purification of polluted air and water. powders, which were difficult to controlled uniform Since photolysis activity of photochemical water diameter and porous structures. In addition, TiO 2 splitting over TiO 2 photoelectorde was investigated based powders were aggregated easily by physical by Fujishima and Honda in 1972 [1], Many groups properties and reduced surface area by aggregation had been studied environmental remediation of powder [4]. For comparison, One-dimension TiO 2 technologies using photocatalytic activity, which nanowires, though aggregated between grains, were decomposes organic compounds by oxidation of separated wires having sufficiently large surface semiconductor materials with hole (H + ) generated in area, which is expected to high photocatalytic the valence band and with hydroxyl radical (OH - ) efficiency with prevented the electron – hole produced by photocatalytic materials such as TiO 2 , recombination and increased reactant quantity onto SiO 2 , ZnO, CdS. Among them, Titanium dioxide the photocatalyst surface and the production of (TiO 2 ) was generally known to one of the most active oxygen species comparing to powder or bulk materials. popular and promising materials because of its wide The parameters of process such as precursor band-gap, photoactivity, biocompability, chemical concentration, applied voltage, viscosity lead to TiO 2 and thermal stability, and low cost. Especially, TiO 2 nanowires using electrospinning, which have larger has a wide band gap energy (3.2 eV), which is surface area and high porosity compare to powder or performed to high capability of catalytic bulk materials. In addition, electrospinning has decomposition in the reaction of the generated advantages, such as simplicity of process and electron and hole by absorption of photoenergy. In production of continuous nanowires with controlled addition, the TiO 2 in photocatalyst activity has many diameter size from several nanometers to sub advantages such as stable in various solvents under micrometers. The electrospun nanowires can be photoirradiation, available commercially from low obtained calcineded morphology and controlled cost, a simple process, and has strongly ability to crystalline phase by heat treatment. decompose various types of redox reactions. Many groups [5-6] have already prepared that TiO 2 The photocatalytic activity of TiO 2 is largely nanowires were applied to photocatalyst activity. determined by properties such as the dimension, However, most of them have rarely been crystalline phase, morphology, specific surface area,

investigated that the properties of crystalline phase 2.2 Characterization and crystalline size with controlled calcination The morphology of the electrospun PVP/TiO 2 temperature and specific surface area of synthesized composite nanowires and the calcined TiO 2 TiO 2 nanowires using electrospinng were evaluated nanowires was characterized by FE-SEM (Hitachi S- by the photocatalyst activity of gaseous. 4800). A measurement of 200 random wires taken In this paper, TiO 2 nanowires with large surface from SEM image was determined average diameter area and different crystalline phase were fabricated and diameter distribution. The crystalline phase by using electrospinning process, and photocatalyst transformation and crystallite size of the TiO 2 activities were studied by measuring the degradation nanowires were characterized by a XRD patterns of quantifying VOCs gas such as gaseous using Cu K α radiation (Rigaku, D/MAX-2500/PC). acetaldehyde and amoonia. In the electrospinning The surface area and porosity of TiO 2 nanowires process, it can be easily obtained to nanowires with were measured by Brunauer-Emmett-Teller (BET, controlling surface area and microstructure by Quantachrome Autosorb-1) and calculated by changing the condition such as contents of TiO 2 Barrett-Joyner-Halenda (BJH) method from precursor and calcination temperature. The isotherm data. crystalline phase of the synthesized nanowires was controlled by heat treatment. TiO 2 nanowires were 2.3 Measurement of photocatalytic activity characterized by X-Ray Diffraction (XRD) for The reactor for the decomposition of gas was used to confirming the crystalline phase. The morphology of TiO 2 photodegradation as shown in Fig. 1. The TiO 2 nanowires were observed by the FE-SEM. The photocatalytic activities of the TiO 2 nanowires were surface area, porosity, and pore size distribution of evaluated by decompositions monitoring of TiO 2 nanowires were characterized as Brunauer- acetaldehyde gas and ammonia gas. The reaction Emmett-Teller (BET). container (Tedlar Bag) contained TiO 2 nanowires and 3dm 3 of gaseous were positioned under the UV light, which was irradiated using 20W Blacklight 2 Experimental UV lamp (Sankyo, F20T10BLB, Wavelength : 2.1 Preparation of TiO 2 nanowires 365nm) with 1mW/Cm 2 of irradiation intensity. The concentration of decomposition of acetaldehyde gas The synthesis method of TiO 2 nanowires was and ammonia gas was measured by using Gastec basically introduced as in previous work [7]. The Standard Detecting Tubes System (Gastec, Gas TiO 2 sol was prepared by titanium (IV) isopropoxide Sampling Pump : GV-100S, Acetaldehyde and (TTIP; 97%, Sigma-Aldrich) with a mixture of Ammonia Detecting Tube Number : No. 92M and anhydrous ethanol (99.5+%, Sigma-Aldrich) and No. 3La) acetic acid (100%, Dae Jung). Next, Poly (vinylpyrrolidone) (PVP; M w 1 300 000, Sigma- Aldrich) was dissolved in anhydrous ethanol 3 Result and discussion (99.5+%, Sigma-Aldrich) and added to the TiO 2 sol solution. The precursor mixture was stirred for 10 3.1 Morphology of TiO 2 nanowires min at room temperature and loaded into a syringe The PVP/TiO 2 composite nanowires were connected to a needle of 30 gauge inner diameter. A synthesized by electrospinning as shown in the Fig. direct-current electric field was applied between the 2 (A). In the previous work, we performed needle and collector using a high voltage. The experiment to controlling PVP concentration and mixture solution was fed at a rate of 0.3 ml/hr using applied voltage [7]. In the electrospinning process, it a syringe pump. Samples were collected on is important to formation of uniform, smooth and aluminum foil of a drum collector. The distance non-bead wires. The solution viscosity and applied between the needle tip and collector (TCD) was voltage in the electrospinning conditions had fixed at 10 cm. The electrospun PVP/TiO 2 composite important parts in the formation of TiO 2 smooth nanowires were dried at 60 °C for 12 h. The wires. The lower and higher solution viscosity was PVP/TiO 2 nanowires were calcined in the range of confirmed formation of beads and increased average 500 °C to 800 °C for 3 hr.