Fabrication and study on structure, photocatalysis of TiO2:N Al2O3 material for CO, NO degradation

An Al2O3 overcoated TiO2:N layer was synthesized using the solgel method. XRD, SEM and UV-vis measurements were used to study the structure and optical properties of the material. The XRD results indicated that the TiO2:N layer was identified only as an anatase phase.
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Fabrication and study on structure, photocatalysis of TiO2:N Al2O3 material for CO, NO degradation JOURNAL OF SCIENCE OF HNUE Mathematical and Physical Sci., 2013, Vol. 58, No. 7, pp. 94-99 This paper is available online at http://stdb.hnue.edu.vn FABRICATION AND STUDY ON STRUCTURE, PHOTOCATALYSIS OF TiO2 :N/Al2 O3 MATERIAL FOR CO, NO DEGRADATION Ma Thi Anh Thu1 , Nguyen Manh Nghia2 and Nguyen Thi Hue3 1 Faculty of Natural Sciences, Cao Bang Teacher Training College 2 Faculty of Physics, Hanoi National University of Education 3 Institute of Environmental Technology, Vietnam Academy of Science and Technology Abstract. An Al2 O3 overcoated TiO2 :N layer was synthesized using the solgel method. XRD, SEM and UV-vis measurements were used to study the structure and optical properties of the material. The XRD results indicated that the TiO2 :N layer was identified only as an anatase phase. SEM images showed that the diameter of particles was around 15-30 nm depending on the NH(C2 H4 OH)2 concentration in the sol solution. UV-vis spectrums suggested that a TiO2 :N/Al2 O3 sample can absorb visible light. These results indicate that fabricated material degrades CO, NO better than Degussa P25 commercial TiO2 when exposed to natural light. Keywords: TiO2 , Al2 O3 , photocatalysis.1. Introduction Titanium dioxide is a catalytic material that is used to treat contaminants atroom temperature and normal atmospheric pressure [1, 5-7]. This material is a typicalphotocatalyst which is capable of degrading contaminants with the aid of sunlight orartificial illumination without requiring special conditions such as high temperature orhigh pressure [2, 3]. However, the large bandgap of about 3.2 eV of pure TiO2 in theanatase phase causes the photocatalytic property of TiO2 to be limited in the ultravioletradiation range. This is a major limitation because no more than 5% of solar radiationcan be used to stimulate photocatalysis of TiO2 . Therefore, improving the efficiency ofTiO2 photocatalysis by expanding its absorption region to the visible radiation range haspotential and is therefore attracting the attention of scientists. Recent studies have shownthat TiO2 can absorb visible light by doping metallic elements such as Fe, Co, La, Zr andPt [1, 5, 6], or nonmetal elements such as N, S and C [1, 5, 6]. Among these elements, NReceived September 26, 2013. Accepted October 30, 2013.Contact Nguyen Manh Nghia, e-mail address: nghianm@hnue.edu.vn94 Fabrication and study on structure, photocatalysis of TiO2 : N/Al2 O3 material...seems to be a better choice to dope with TiO2 due to its potential to increase the strengthand uniformity of materials, and to show stronger catalytic properties under natural lightconditions. In this paper we present the synthesis and structural studies, as well as the opticalproperties, of nano TiO2 :N/Al2 O3 materials. The study also focuses on testing thephotochemical catalytic ability of materials to decompose the pollutants CO and NO innatural light conditions.2. Content2.1. Experiment TiO2 was synthesized using a sol-gel process. The sol solution was prepared usinghydrolysis and a condensation Ti(O-iC3 H7 )4 alkoxide. A uniform TiO2 coating layer onthe surface of the χ-Al2 O3 layer was obtained using two different mixtures we call solB1 and sol B2. Sols B1 and B2 consisted of TTIP, DEA and EtOH with a molar ratioof 1:1:34 and 1:2:34, respectively. Titanium tetraisopropoxide (TTIP) and ethyl alcohol(EtOH) with a purity of 99.8% were provided by Wako Pure Chemical Industries Co.,Ltd. Diethylamine (DEA) purchased from the Kishida Chemical Company (Japan) wasused in the preparation of the sol solution. χ-Al2 O3 fibers having a diameter of about 0.1mm and a surface area of 0.015 m2 /g were provided by Alus Co., Ltd. (Japan). Al2 O3fibers were soaked for 60 minutes in the sol solution. The best samples were annealed at470 0 C for 3 hours to obtain crystalline TiO2 in the anatase form [4]. The crystalline structure of the TiO2 layer was determined by X-ray diffraction(XRD, Siemens D5000). Surface morphology and crystal size was measured by scanningusing electron microscopy SEM (Hitachi S-4800). The band gap was calculated fromthe results of absorption spectra measured by a Jasco V670 system. Photocatalyticexperiments were conducted in a 1 m×1 m×1 m sealed test chamber. The light sourceswere 20 W UV lamps with wavelengths of 254 nm, 365 nm and a 10 W visible lightlamp. Photocatalysis materials placed 30cm from the light source were synthesizedTiO2 :N/Al2 O3 , 35 cm×35 cm in size. A pollution gas in the chamber was moved throughthe material several times by convection fan. The concentration of CO and NO weredetermined using a colorimetric method (Shimadzu UV-Vis 2450).2.2. Results and Discussion The XRD patterns of TiO2 /Al2 O3 doped N are illustrated in Figure 1. The spectrumpeaks at 2θ angles 250 , 370 , 480 , 540 and 630 , respectively, correspond to planes ,, , and of the anatase phase. Two diffraction peaks at positions380 and 450 belong to χ-Al2 O3 . This result shows that the sample heated at 470 0 C for 3hours exhibits only an anatase phase and no diffraction peak relating to a rutile or brookitephase was observed. 95 Ma Thi Anh Thu, Nguyen Manh Nghia and Nguyen Thi Hue SEM images of two samples showed that the particle size of B1 and B2 sampleswere 30 nm, and 15 nm, respectively. In both samples, the TiO2 particles were quiteuniform and no cloud phenomenon was seen. The influence of amine concentrationin different samples on particle size was considered. Chemica ...