【正文】 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 sam。. 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。). XRD patterns were obtained in the range of 20–70176。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。朱院長是我們恩師，同時也是我們的親人、朋友！ 在此，謹向朱 院長 表示衷心的感謝。 同時在找工作的過程中，我們遇到了很多挫折，朱院長積極對我們進行就業(yè)指導，幫我們選擇優(yōu)秀且合適的企業(yè)，并且聯(lián)系企業(yè)，向優(yōu)秀企業(yè)推薦我們，讓我們順利實現(xiàn)就業(yè)。印象最深刻的一次，是在五 一勞動節(jié)全校教職工都放假期間，我留校做實驗，當時實驗設備出現(xiàn)問題，找朱老師指導，居然發(fā)現(xiàn)朱院長仍在辦公室辦公。 在此首先向朱院長致以深切的感謝及敬意 ! 恩師淵博的學識、嚴謹的治學態(tài)度、孜孜不倦的教誨以及科學的工作方法給了我極大的幫助和影響。因此其催化劑載體、紫外線吸收劑、高效光敏催化劑、防曬 護膚化妝品、塑料薄膜制品、水處理、精細陶瓷、生態(tài)陶瓷及氣敏傳感器元件等領域具有廣泛和潛在的應用前景。 第五章 結論與展望 二氧化鈦的納米材料是一種新型的無機材料，粒徑為 1050nm，相當于普通鈦白粉粒徑的 1/10。 大約在 攝氏度時，衍射峰變得尖銳。從圖 38 可以看出 ,不同 PH 值溶液制備的微粉試樣的衍射峰 2θ 的位置和和數量基本相同。 20 30 40 50 60 70 802 T h e t a ( 176。025507510 012 5Intensity(Counts)[ z hao x unn aT O 4. ra w ] 4 78 6 1 1 5 7 A n a t a s e T i 0 . 7 2 O 2 圖 36 溶液 PH 值為 條件下制備樣品 TO4 的 XRD 衍射圖譜 Anatase(101)Anatase(103) Anatase(004)Anatase(112)Anatase(200)Anatase(105)Anatase(211)Anatase(213)Anatase(204)Anatase(116)Anatase(220)Anatase(107)Anatase(215)Anatase(301)10 20 30 40 50 60 70 802 T h e t a ( 176。 對樣品進行了表征，結果整理如圖 3 37 所示 （樣品 TO5 的圖譜如 32 所示） ，結晶度 衍射峰 2θ的位置 晶粒度（ nm） 半高寬 為 不同 PH 值溶液制備的 納米二氧化鈦 樣品的 XRD 圖 譜 。 步長掃描模式中的 10– 80176。 不同 溶液 PH 值 對