100, Nanning , China. Keywords: Nitrogen doping, Rice husk, Pre-support, Titanium dioxide, Complex, Visible-light.

Transcription

1 Materials Science Forum Online: ISSN: , Vol. 814, pp doi: / Trans Tech Publications, Switzerland Visible-light Photocatalytic Performance of N/ Complex Materials Qing G Feng 1, a, Si Y Qin 1, b, Ting Wang 1, c, Xiao F Weng 1, d, Bao L Song 2, e, and Dong B Wang 1, f 1 School of Environment, Guangxi University, East University Road No. 100, Nanning , China 2 School of Chemistry and Chemical Engineering, Guangxi University, East University Road No. 100, Nanning , China a fengqg@gxu.edu.cn, b @qq.com, c @qq.com, d @qq.com, e sblgw@gxu.edu.cn, f w121308@163.com Keywords: Nitrogen doping, Rice husk, Pre-support, Titanium dioxide, Complex, Visible-light. bstract. The TiO 2 complex samples were produced through sol-gel method, using Ti(OC 4 H 9 ) 4, rice husk (RH) and methenamine as the reactants. Some property analyses were conducted, including X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and photocatalytic experiments in the condition of visible-light. The results showed that the size of crystal was limited with the addition of RH in the complex of N/ samples. The particles of TiO 2 were dispersed on the surface of rice husk ash, the skeleton of RH after burning. It can inhibit the phenomenon of agglomerate. The ability of both adsorption and photocatalytie activity of complex samples increased as the surface area increased. Doping N into samples can decrease the forming time, inhibit the transformation of crystal from anatase to rutile to some extent, improve the bond of Ti-O-Si to form and make the absorption spectrum move to the red light part. The complex samples exhibited a certain photocatalytic activity under the visible light region. The reaction rate of visible light photodegradation process arrived min -1, meeting with the first-order reaction kinetics. Introduction Titanium dioxide (TiO 2 ), as a semiconductor photocatalyst, has received widespread concern for its nontoxic, high corrosion-resistant, chemical stability and no second pollution [1-7]. However, it is difficult to separate the photocatalysts from waste water and easy to form agglomerate particles and just adsorb 5% of visible-light. Previous researches find that supporters load and nitrogen doping could solve these problems. Ordinarily, supports are activated carbon [8,9], vycor [10], stainless steel, silica gel [11], zeolite [12], ceramic hollow sphere [13], and so forth. s a kind of agricultural wastes, the rice husk (RH) after burning also owns the properties of large surface area and high adsorption performance which can be easily separated from solution [14]. The high calorific value of RH( kj/mol) [15, 16] can provide an amount of energy internal in the process of calcination. In our work, the new photocatalyst material was prepared through sol-gel method. The structure and performance of N/ complex were discussed, which haven t been reported before. Experimental Preparation of TiO 2 complex. Raw reagents used through the process were analytically pure, and deionized water was made in laboratory. The TiO 2 complex was prepared by sol-gel method [17-19]. The methenamine was added into the ethanol solution with the 10% dosage of total samples. The RH was added into wet gel with the ratio of n(tio 2 ):n(rh)=1:1. fter standing, centrifuging and drying, the xerogel was calcined in muffle furnace at a temperature rise rate of 20 /min in the range of The TiO 2 complex samples were produced after cooling and grinding. Instrument analysis. X-ray diffraction analysis (XRD, Dandong Tongda Instrument Co., LTD), specific surface area analysis (BET, MICROMERITICS, Germin VII), Scanning electron ll rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, US-21/02/16,05:23:51)

2 Size of crystal/nm Materials Science Forum Vol microscopy analysis (SEM, Hitachi.) and Fourier transform infrared spectroscopy analysis (FT-IR, Thermo Nicolet 6700) were used to characterize the property of TiO 2 complex samples. Photocatalytic. The photochemical reactor (Shanghai BILON Instrument Co., LTD, BL-GHX-Ⅴ) was operated throughout dark reaction and photoreaction. Dark reaction begins when TiO 2 complex samples were mixed with methyl orange (MO) solution in the dark. fter stirring for 30 min, turn on the visible-light. The centrifugal separator (Changsha YINGTI Instrument Co., LTD, DD5) and visible spectrophotometer (Shanghai INES Instrument Co., LTD, 722G) were used to separate the supernatant from solution and admeasure the concentration of the supernatant in the maximum absorption wavelength. Results and Discussions XRD diffraction analysis. s is shown in Fig. 1, X-ray diffraction analysis was employed to characterize the phase species and crystal sizes of TiO 2 complex samples ( h). There s only anatase existed in both and N/. t 400,the anatase titanium generates initially. When calcination temperature reaches 600, the diffraction peaks, as 2 θ =25.28 (101), 37.8 (004), (200), (105), (211), can be indexed from the standard diffraction peaks of anatase TiO 2 (JCPDS NO ). The height of main characteristic peak in Fig. 1(b) is obviously higher than that in Fig. 1(a). In Fig. 2, there s characteristic peak of rutile appeared in, but not in N/. These phenomenons indicate that nitrogen doping could promote the formation of crystal and shorten the forming time, as well as inhibit the transformation of crystal from anatase to rutile in some extent. a b Fig. 1 XRD patterns of different samples (a:,b:n/ ) -natase R-Rutile 25 N/TiO 2 N/ 20 N/ R Two Theta/degree 500 o C 6h 600 o C 1h Fig. 2 Compare of XRD patterns between and N/ (500 6h) Fig. 3 Histogram of crystal sizes with three kinds of complex samples D 0.89 /( ) cos (1) M S

3 592 Energy and Environmental Materials II (D is the crystal size; λ is the X-ray wavelength; β M is the width of the half diffraction peak; β S is the width of instrument; θ is the diffraction angle) [17] The crystal sizes of anatase were calculated by the Eq. 1. Fig. 3 shows the comparison of crystal sizes among three kinds of complex samples. The crystal sizes of and N/ are smaller than that of N /TiO 2. possible cause is that the addition of RH could limit the size of crystal by the adsorption force of RH. The surface area increases though the crystal size decreases,resulting in better photocatalytic activity. From the analysis of XRD patterns, TiO 2 load on RH could inhibit crystal growing and keep the anatase in a small size range. Nitrogen doping could shorten the forming time and inhibit the transformation from anatase to rutile in some extent. SEM. Fig. 4 (a, b) shows the microtopography of TiO 2 complex samples. In the N/TiO 2 sample, a b Fig. 4 Microtopography of crystal (a:n/tio 2, b:n/ ) There is a block at 5 micrometer size, which doesn t appear in N/ samples. nd on the block, there re plenty of smaller round particles, which can be identified as TiO 2 particles. This phenomenon is called agglomerate caused by sol-gel method. In Fig. 4(b), TiO 2 particles are dispersed on the surface of RH, the skeleton of RH after calcination. The phenomenon of agglomerate can be inhibited under the effect of adsorption force of RH and RH,. It could increase the surface area of samples and promote the photocatalytic activity in theory. BET analysis. Specific surface area analysis was conducted to characterize the adsorptive property of samples, as is shown in Table 1. The BET surface areas of N/ and samples are larger than that of N/TiO 2 samples in the same condition. It implies that load on RH can increase the specific surface area obviously. Combining with the microtopography of complex samples, it may indicate that the support could enhance the reaction rate in photodegradation process. Table 1 Surface area data of various complex samples N/TiO 2 N/ h m 2 g m 2 g m 2 g h m 2 g m 2 g m 2 g FT-IR. Except the analysis of microtopography, the analytic chemical-bond was detected through FT-IR analysis (Fig. 5-8). The peaks at 3390 cm -1 and 1630 cm -1 are separately associated with the contraction of O-H bond in the adsorbed water and the Ti-OH bond on the sample surface. Characteristic peaks in range of 600 cm -1 to 800 cm -1, corresponding to Ti-O bond are observed. There s a small peak at about 920 cm -1 stands for Ti-O-Si bond existed in N/ samples, not in samples. nd the peak at 1060 cm -1 corresponding to Ti-O-N bond hasn t been found in N/TiO 2 samples, neither. This indicates that the siliciumatom has entered into the TiO 2 crystal structure in condition of nitrogen doping. It could be speculated that the Ti-O-N bond had been existed in the sample, but nitrogen was oxidized by air in the cooling stage. When nitrogen got out

4 bs bs Materials Science Forum Vol from samples, the siliciumatom was instead of its position and formed the bond of Ti-O-Si. ccording to previous research, samples being with Ti-O-Si bond have a better performance of photocatalytic activity. Fig. 5 FT-IR spectra of N/TiO 2 and N/ (500 6 h) Fig. 6 FT-IR spectra of N/TiO 2 and N/ (600 1 h) Fig. 7 FT-IR spectra of (6h) Fig. 8 FT-IR spectra of (500 ) N/TiO 2 N/ 8 N/TiO 2 N/ Wavelength/nm Fig. 9 UV-Vis curves of various complex samples (500 6 h) Wavelength/nm Fig. 10 UV-Vis curves of various complex samples (600 1 h) UV-Vis. The UV-Vis analysis was conducted to prove N/ has a better photocatalytic performance. Fig. 9 and Fig. 10 show that the N/ samples have a better absorption specialty above 400nm (visible-light). nd the curves have a tendency of red shift,which indicates that N/ samples have a better photocatalytic performance in visible-light.

5 Ct/Co -Ln(Ct/Co) 594 Energy and Environmental Materials II Photocatalytic activity. The photocatalytic activities of TiO 2 complex samples are shown in Fig. 11 and Fig. 12. The concentration of MO reduces along with irradiation time increases. fter 5h, the MO solution could be photodegraded under 70% in degradation ratio. The N/ samples took much less irradiation time (2h) to reach the same ratio. First-order reaction kinetics fitted curves and equations are separately shown in Fig. 12 and Table 2. They indicate that the photodegradation process matches basically with first-order reaction kinetics procedure. dditionally, the constant of reaction rate at 600 1h could reach min -1, which is much larger than others. Two explanations may attribute to the better photocatalytic activity. One is the adsorption of RH and the large surface area of samples; the other is the better photocatalytic activity of visible-light, owing to the Ti-O-Si bond caused by doping nitrogen in samples o C 6h N/TiO o C 6h N/ 600 o C 1h N/TiO o C 1h N/ o C 6h N/TiO o C 6h N/ 600 o C 1h N/TiO o C 1h N/ Irradiation time/min Fig. 11 Photodegradation curves of methyl orange by different complex samples Irradiation time/min Fig. 12 The relationship of Ln(Ct/Co) and irradiation time with various complex samples Calcination temperature/ Table 2 First-order reaction kinetics equations and correlations of different complex samples Keeping time/h Complex Reaction rate constant K/min -1 Correlation r Linear fitting equation N/TiO y = x N/ y = x N/TiO y = x N/ y = x Conclusions The addition of RH in the complex of N/ samples, crystal size could be limited. The particles of TiO 2 could be dispersed, which could inhibit the phenomenon of agglomerate. nd the surface area becomes larger. Doping N into samples can decrease the forming time, and inhibit the transformation from anatase to rutile in some extent. It can promote the bond of Ti-O-Si to form and make the absorption spectrum move to the red light part. The N/ complex samples have a better photocatalytic performance in visible light. The reaction rate arrives min -1, meeting with the first-order reaction kinetics.

6 Materials Science Forum Vol References [1] Ren C J, Li D C, Zhou D L, Liu H, Zhong B H. Sichuan Nonferrous Metals (2004). [2] Pelaez M, Nolan N T, Pillai S C, Seery M K, Falaras P, Kontos G, Dunlop P S, Hamilton J W, Byrne J, O'Shea K. pplcatal B: Environ (2012). [3] Charanpahari, Umare S S, Sasikala R. ppl Surf Sci (2013). [4] Cheng X W, Yu X J, Li B Y, Yan L, Xing Z P, Li J J. Mater Sci and Eng: B (2013). [5] Feng H J, Zhang M H, Yu L E. ppl Catal : Gen (2012). [6] Zhang H R, Tan K Q, Zheng H W, Gu Y Z, Zhang W F. Mater Chem and Phy (2011). [7] Ohno T, kiyoshi M, Umebayashi T, sai K, Mitsui T, Matsumura M. ppl Catal : Gen (2004). [8] Lu C, Yang P, Du Y K, Hua N P, Song H Y. Chinese J Catal (2003). [9] Li Y J, Li X D, Li W J, Yin J, Feng C X. J Inorg Mater (2005). [10] Luo L, Li Z G, Tu F Y, Li Q. Sci & Techn In Chem Ind (2008). [11] Liu Y, Liang P, Li G, Lu H B. cta Chim Sinica (2005). [12] Jiang Y S, Jin W Q, Zhang J, Fang S S. J Inorg Mater (2002). [13] Zhu X F, Yang J K, Xiao B, Wang X P. J Mater Sci & Eng (2004). [14] Feng Q G, Lin Q Y, Gong F Z, Sugita S, Shoya M. J Colloid and Interf Sci (2004). [15] Zhang Y L. Energ Res & Util (1991). [16] Zhang H X. Ji Lin University (2011). [17] Chen Q L, Tang C Q, Xiao X. Mater Sci & Eng (2002). [18] Yu L H, Sun H P. J Dalian Jiaotong Univercity (2010). [19] Zhou B, Bao C L, Feng Z B, Jiang J S, Fang S S. Techn Eq Env Pollut Control (2004).

7 Energy and Environmental Materials II / Visible-Light Photocatalytic Performance of N/ Complex Materials /