【導(dǎo)讀】光電池、抗菌等領(lǐng)域，帶來巨大的環(huán)境、社會、經(jīng)濟效益。銳鈦礦型二氧化鈦具有良好。二氧化鈦的合成已經(jīng)建立了許多方法，比如溶膠―凝膠技術(shù)、水熱合成法、化學(xué)氣相沉積法、直接氧化法等等。其中，溶膠―凝膠法是最常用的方法，是因。并結(jié)合納米二氧化鈦樣品X射線衍射和掃描電鏡表征的結(jié)果,找出制備二氧?；伒淖顑?yōu)配比和最佳條件。陶瓷原料、催化劑、傳感器等，需求量不大，沒有形成大的生產(chǎn)規(guī)模。需求大大增加，成為鈦白工業(yè)和涂料工業(yè)的一個新的增長點。納米二氧化鈦的生產(chǎn)企業(yè)或公司近十幾家。目前全世界超細TiO2的生產(chǎn)能力估。水中的有機物，在環(huán)保等領(lǐng)域中具有極廣闊的應(yīng)用前景。表的光催化材料已經(jīng)得到了廣泛的關(guān)注和研究。在眾多的光催化材料中納米級。成為研究最多，應(yīng)用廣泛的半導(dǎo)體材料。自1939年Geffcken和Berger的報道問世以來，這種方。其制作簡單、操作方便、條件易控、產(chǎn)品均一性良好、純度高等優(yōu)點成為目前納米TiO2的常用的制備方法之一。

　　

【正文】 (3) the overall reaction is M(OR)n+H2O→MO n/2+nROH (4) where M= Si, Ti, Zr, etc and R = alkyl group. The relative rates of hydrolysis and polycondensation strongly affected the structure and properties of metal oxides. Factors that crucial in the formation of metal oxides includes reactivity of metal alkoxides, water to alkoxides ratio, pH of reaction medium, nature of solvent and additives and reaction temperature. By varying these process parameters, materials with different surface chemistry and microstructure can be obtained. Typically, in sol gel method, the solgel derived precipitates are amorphous in nature. Therefore, it is require for further heat treatment to induce crystallization. To induce transition from amorphous to anatase phase, generally an annealing temperature higher than 300 176。C is required, and this will result in the dramatic growth of the particle sizes. However, titania for photocatalytic activity is dependent on both particle size and degree of crystallinity . In this work, nanocrystalline anatase and rutile TiO2 particles with crystallite size ranging from 7 to 14 nm have been derived via sol gel precipitation of alkoxides followed by calcination. The effect of pH towards the development of titania nanocrystal structure and their performance as photocatalyst is investigated. II EXPERIMENTAL SECTION Synthesis. TiO2 nanocrystal were prepared by sol gel hydrolysis precipitation of titanium (IV) isopropoxide (Ti(OC3H7)4) (Sigma Aldrich, 97%), followed by calcination treatment. A specific amount of titanium isopropoxide was dissolved in isopropyl alcohol ( Merck, 95%) solution and the solution was dropped slowly into distilled water, pH was adjusted by HNO3 for acidic condition and NaOH for basic condition. Molar ratio of water to alkoxide was 110. Upon dropping, white precipitates of hydrous oxide were produced instantly, and the mixture was stirred vigorously for 4 hours at room temperature. The precipitates were centrifuged and were redispersed in ethanol to minimize agglomeration. This process was repeated five times. The resulting materials were then dried and annealed at 400176。C. Characterization. The titania samples were characterized by powder Xray diffraction (XRD) with Bruker D8 powder diffractometer (40 kV, 30mA) using CuKα radiation (λ= 197。). XRD patterns were obtained in the range of 20–70176。 by step scanning mode with the step size of 176。. The crystallite size and peak broadening was determined based on anatase (101) and rutile (110) diffraction using Scherrers equation. Specific surface area of the samples was calculated using formula as : S=6103/ρL (5) Where, S is the specific surface area (m2g1), L is the average crystallite size, and ρ is the density of titania ( gcm3) .The morphologies and particle size of titania particles were examined using a field emission scanning electron microscope (FESEM SUPRA 35VP ZEISS). Photocatalytic degradation studies were performed by mixing g TiO2 powder into 30 ppm methyl orange (MO) in quartz tube and sealed with stopper. The quartz tubes were then irradiated by UV light (Germicidal 36 watt) for 5 hours and samples were collected for every 1 hour. The concentration of the degradated methyl orange was determined using UVVis spectrometer (PerkinElmer Lambda 35). III RESULTS AND DISCUSSION Figure 1 shows the Xray diffraction (XRD) patterns of the powder samples prepared in initial solution with different pH. As seen in figure 1, distinct peaks were noted in the XRD patterns at 176。. It is also noticed that pH affects particles size and degree of crystallinity. A trace of rutile was found in sample prepared at pH 1 at 176。 corresponding to anatase phase (110). In this case, it is found that high acidity in medium solution will favor the formation of rutile phase while lower acidity will favor anatase formation [11, 12]. The results show high acidity favor formation of rutile. This mechanism may be explained using the concept of partial charge model [13]. According to this model, hydrolysis of titanium cation is occurred at strong acidity condition. In this condition, a stable species of [Ti(OH)(OH2)5]3+ will form, but due to the positive charge of hydroxo group , these species are not able to condense. When acidity is not sufficiently low to stabilize these precursor, deprotonation will takes place forming new species of [Ti(OH)2(OH2)5]2+. However, these species also do not condense probably because of spontaneous intramolecular oxolation to [TiO(OH2)5]2+ [14]. Condensation to both anatase and rutile starts when the solution activity is sufficient enough to allow further deprotonation to [TiO(OH)(OH2)4]+, which can undergo intramolecular of deoxolation [TiO(OH)3(OH2)3]+ depending in exact pH. In lower pH region, deoxolation does not happen and oxolation leads to linear growth along the equatorial plane of cations. This reaction leads to rutile formation due to oxolation between resulting linear chains. Meanwhile, in higher pH values, when deoxolation occurs, condensation can proceed along apical direction and leads to the skewed chain of anatase structure. Therefore, based on this study, it is believe that the determination of resulting crystal structure is affected by pH values [13,15]. The higher acidity promotes rutile formation and lower acidity will lead to anatase formation. Figure 1. XRD patterns of nanocrystalline titania samples prepared by sol gel method with various pH condition as (a) pH 9, (b) pH 7, (c) pH 5, (d) pH 3 and (e) pH 1. The crystallite size was determined by Scherrer equation and summarized in Table 1. It was found the crystallite size vary from 7 to 14 nm and specific surface area ca. ranging from 112 to 194 m2g1Table 1. Crystallite size and specific surface area of s