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1.
本文利用266 nm波长的激光及程序升温脱附的方法研究了甲醇在ZnO(0001)表面的光催化反应. TPD结果显示部分的CH3OH以分子的形式吸附在ZnO(0001)表面,而另外一部分在表面发生了解离. 实验过程中探测到H2,CH3·,H2O,CO,CH2O,CO2和CH3OH这些热反应产物. 紫外激光照射实验结果表明光照可以促进CH3OH/CH3O·解离形成CH2O,在程序升温或光照的过程中它又可以转变为HCOO-. CH2OHZn与OHad反应在Zn位点上形成H2O分子. 升温或光照都能促进CH3O·转变为CH3·. 该研究对CH3OH在ZnO(0001)表面的光催化反应机理提供了一个新的见解.  相似文献   

2.
Sr2CeO4电荷迁移发光的光谱结构规律研究   总被引:1,自引:0,他引:1       下载免费PDF全文
符史流  戴军  丁球科  赵韦人 《物理学报》2005,54(5):2369-2373
利用高温固相反应法分别合成了不同物相形成机理的Sr2CeO4,Sr 2CeO4∶Ca 2+和Sr2CeO4∶Ba2+样品,并对其光谱特性进行 了研究.结果发现,对于由SrO和CeO2直接反应生成的Sr2CeO4(Ⅰ),激发主峰位于256nm 左右;而对于SrCeO3和SrO反应生成的Sr2CeO4(Ⅱ),激发主峰位于279nm左右.在Sr2CeO4(Ⅰ)中掺入Ca2+,其激发光谱随着Ca2+离子浓度的增加逐渐接近于Sr2CeO4(Ⅱ)的激发光谱.激发主峰带应属于CeO6八面体终端Ce4+—O2-键的电荷迁移 带.对于激发光谱中340nm左右的弱激发峰,其峰值波长不受形成机理及Ca2+掺杂的影响,只是其强度 随着 激发主峰的红移而增加,它可能属于CeO6八面体平面上Ce4+—O2-键的电荷 迁移带.形成机理及Ca2+掺杂对发射光谱没有影响.Ca2+在Sr 2CeO 4(Ⅱ)与Ba2+在Sr2CeO4(Ⅰ)和(Ⅱ)中均难 于替代Sr2+的位置.  相似文献   

3.
为了在可见及近红外波段得到具有良好带隙结构的三维光子晶体,利用传输矩阵法分析了MgF2、Ta2O5 以及Ta2O5/MgF2异质结构三维光子晶体的带隙性质.结果表明:Ta2O5/MgF2异质结构三维光子晶体在820~1 020 nm的近红外波段TM模式下具有不受入射光方向影响的全方位光子带隙.该结构有望用于制作近红外光波段的偏振器件.  相似文献   

4.
邻碘甲苯分子光解动力学的飞秒时间分辨质谱研究   总被引:1,自引:0,他引:1  
利用飞秒时间分辨质谱技术研究了邻碘甲苯分子在266 nm激发下的光解动力学. 光解产物碎片通过800 nm强激光场下的多光子电离实现探测. 拟合光解产物C7H7自由基和I原子随泵浦-探测延迟时间变化的信号,得到解离时间为38±50 fs,它反映的是266 nm同时激发nσ*ππ*态后C-I键的平均解离时间. 此外,还利用基态碘原子的共振波长298.23 nm作为探测光,通过共振增强多光子电离方法对解离生成的基态碘原子进行了选择性探测. 拟合I+随泵浦-探测延迟时间变化的信号,得到解离时间为40±50 fs,这与通过800 nm多光子电离得到的解离时间一致,表明解离生成的主要产物是基态碘原子.  相似文献   

5.
研究了气相Ca+-dipropylamine复合物在400~690 nm波长范围内的光解过程。在研究的光谱范围内,蒸发解离得到非反应性产物Ca是最主要的通道。在450~528 nm范围内,反应性产物Ca+-NHC3H7也被探测到。这一反应性通道被认为是Ca+对二丙胺分子中的C-N键的插入活化作用引起的,量化计算与实验现象一致.  相似文献   

6.
通过程序升温脱附谱的方法探究了266 nm激光照射下异丙醇在锐钛矿TiO2(101)表面的光化学,并提出了详细的解离机理.在光照作用下,异丙醇发生分步解离:首先,O-H键断裂生成异丙氧基;然后,仲碳的C-H键在光照的作用下进一步发生解离,从而生成丙酮,两步生成的氢原子均转移到相邻的桥氧上.在升温过程中,这部分氢原子会与分子态的异丙醇发生置换反应,从而以低温水和高温异丙基的形式从表面脱附出来.  相似文献   

7.
本文系统研究了臭氧修饰对(001)主导晶面锐钛矿型TiO2光催化剂降解甲苯性能的影响. 利用自行搭建的光催化VOCs降解装置对催化剂光降解甲苯的性能进行了测试. 通过多种表征手段,结合原位DRIFTS和DFT计算研究了臭氧表面修饰及甲苯吸附和降解机理. 结果表明,用臭氧进行表面修饰可以显著提高(001)主导晶面TiO2光催化降解甲苯的性能. (001)晶面上丰富的5c-Ti不饱和配位是臭氧分子的吸附位点,其解离后形成的Ti-O键与H2O分子结合,在表面生成大量孤立的Ti5c-OH. Ti5c-OH 是甲苯分子的吸附位,它的形成显著提高了对甲苯分子的吸附能力. 在光照下Ti5c-OH与光生空穴结合能形成·OH自由基. 通过臭氧解离产生的O2也可以与光生电子结合形成超氧自由基. 这些具有强氧化性活性自由基的形成促进了对气相甲苯的光催化降解速率.  相似文献   

8.
在燃烧或大气化学多通道反应中,理解不同产物之间的产品分支比与反应的总速率,对这类基元反应同样重要. 在CCSD(T)/CBS/B3LYP/aug-cc-pVDZ理论水平上,计算所有氘代烷基卤化物CD3CH2F物种的基态势能面. 在CD3CH2F的解离反应中,C-F键解离反应与分子(HF、DF、H2、D2与HD)消除反应存在着争议. 本文使用RRKM方法计算各个步骤的速率常数,并使用稳态方法计算解离产物的相对产物分支比. 在不同的能量下,RRKM方法预测CD3CH2F的1,2-消除DF或HF的主要通道是通过四中心过渡态消除,而1,1-消除D2或H2的主要通道是通过三中心过渡态消除. 在266、248和193 nm光解时,主产物CD2CH2+DF分支比分别为96.57%、91.47%和48.52%;然而,在157 nm光解时,产物分支比计算为16.11%. 基于这些过渡态结构和能量,提出了以下光解离机制:在266、248和193 nm,CD3CH2F→吸收光子→TS5→形成产物→CD2CH2+DF;在157 nm,CD3CH2F→吸收光子→D/F交換的TS1→CDH2CDF→H/F交换的TS2→CHD2CHDF→形成产物CHD2+CHDF.  相似文献   

9.
利用同步辐射真空紫外光电离质谱技术,在不同光子能量下,研究了异补骨脂素(C11H6O3)的低压热解,探测了不同温度下异补骨脂素的热解产物及其与前驱体的比例. 实验结果表明,异补骨脂素的主要热解产物是CO及其依次消去CO的产物(C10H6O2和C9H6O). 利用密度泛函理论计算异补骨脂素的解离途径,并利用过渡态理论计算了竞争通道的反应速率常数. 通过实验和理论的结合,确定了异补骨脂素主要解离路径和相应产物的分子结构.  相似文献   

10.
利用光外差-浓度调制吸收光谱技术测量了b3Πg~a3u+(9,3)带在12065~12445 cm-1的光谱,并研究了He2分子b3Πg(v=9)态与c3g+ 态的预解离相互作用.基于He2分子c3g+ 态的ab initio理论计算势能曲线和b3Πg态的RKR势能曲线,分析了b3Πg(v=9)态的预解离机制,并计算了b3Πg(v=9)态转动能级的预解离线宽,计算结果同实验测量基本一致.  相似文献   

11.
TiN/TiO2 nanoparticle photocatalyst was prepared by ball milling of TiO2 in H2O solution doped with TiN. The photocatalyst was characterized by UV–Vis diffuse reflection spectroscopy, X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Based on the results of the characterization, the mechanism of the increase in photocatalytic activity was investigated. The results show that when the amount of doped TiN is 0.15 wt%, the photocatalytic activity of the TiN/TiO2 is at its peak. Compared with TiO2, the photoabsorption wavelength range of the TiN/TiO2 photocatalyst red-shifts about 30 nm, and the photoabsorption intensity increases as well. The photocatalytic activities of the photocatalyst are higher than that of TiO2 under UV and visible light irradiation. The increase of surface Ti3+ reactive center and the extension of the photoabsorption wavelength are the main factors for the increase in the photocatalytic activity of the TiN/TiO2. Doped TiN neither changes the TiO2 crystal phase nor creates new crystal phase by ball milling.  相似文献   

12.
《Composite Interfaces》2013,20(2):195-204
A new layered nanocomposite, HTaWO6/(Pt, TiO2) was synthesized using n-type semi-conductor HTaWO6 as a host material. HTaWO6 and HTaWO6/TiO2were white, while both HTaWO6/Pt and HTaWO6/(Pt, TiO2) were yellow. The yellow color might be attributed to H1-xTaWO6-x/2 formed by the photo-induced phase transformation promoted by Pt. Although HTaWO6/Pt showed absorption in visible light region (λ > 400 nm), the hydrogen evolution activity was negligibly small. On the other hand HTaWO6/(Pt, TiO2) showed excellent photocatalytic activities even under visible light irradiation. The sample containing rutile type titania such as TiO2(P-25) also showed hydrogen evolution activity, but the activity was smaller than that of HTaWO6/(Pt, TiO2). These results suggested that rutile type titania, which can be excited by visible light of wavelength less than 413 nm, played an important role in the visible light-induced photocatalytic activity. The improvement of the hydrogen evolution activity of rutile type titania by intercalating into HTaWO6/Pt may be due to the depression of the recombination of photoinduced electrons and holes by the heterogeneous electron transfer from rutile type TiO2 to HTaWO6/Pt.  相似文献   

13.
刘恩周  樊君  胡晓云  侯文倩  代宏哲 《中国物理 B》2012,21(4):43403-043403
A rare-earth free upconversion luminescent material, 10BaF2:NaF, Na3AIF6, is synthesized by a hydrothermal method. The study of fluorescent spectrum indicates that it can convert visible light (550 nm-610 nm) into ultraviolet light (290 nm 350 nm), and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature. Subsequently, 10BaF2:NaF, Na3AIF6/TiO2 composite photocatalyst is prepared and its catalytic activity is evaluated by the photocatalytic reduction of CO2 under visible light irradiation (λ〉 515 nm). The results show that 10BaF2:NaF, Na3AIF6/TiO2 is a more effective photocatalyst for CO2 reduction than pure TiO2, their corresponding methanol yields are 179 and 0 μmol/g-cat under the same conditions. Additionally, the mechanism of photocatalytic reduction of CO2 on 10BaF2:NaF, Na3AIF6/TiO2 is proposed.  相似文献   

14.
Jin-Ho Yoon  Jung-Sik Kim 《Ionics》2010,16(2):131-135
The present study examined the photocatalytic reaction of titanium dioxide (TiO2)-coated, phosphor composite particles. Nanocrystalline TiO2 layers were directly coated on the alkaline earth aluminate phosphor (CaAl2O4:Eu2+,Nd3+) particles by a sol-gel processing method and their photocatalytic reaction was analyzed according to the degradation of methylene blue aqueous solution under visible light irradiation. Compared with pure TiO2, the TiO2-coated phosphor powders showed a different photocatalytic mechanism and much faster photocatalytic reactivity under visible irradiation than that of pure TiO2, which was almost negligible. The mechanism of the photocatalytic reactivity for the TiO2-phosphor composite was discussed in terms of the energy band structure and phosphorescence. In addition, the TiO2-coated phosphor powders were characterized by X-ray diffraction and transmission electron microscopy.  相似文献   

15.
In order to improve visible light photocatalytic activities of the nanometer TiO2, a novel and efficient Cr,S-codoped TiO2 (Cr-TiO2-S) photocatalyst was prepared by precipitation-doping method. The crystalline structure, morphology, particle size, and chemical structure of Cr-TiO2-S were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) techniques, respectively. Results indicate that the doping of Cr and S, cause absorption edge shifts to the visible light region (λ > 420 nm) compare to the pure TiO2, reduces average size of the TiO2 crystallites, enhances desired lattice distortion of Ti, promotes separation of photo-induced electron and hole pair, and thus improves pollutant decomposition under visible light irradiation. The photocatalytic activities of Cr-TiO2-S nanoparticles were evaluated using the photodegradation of methyl orange (MO) as probe reaction under the irradiation of UV and visible light and it was observed that the Cr-TiO2-S photocatalyst shows higher visible photocatalytic activity than the pure TiO2. The optimal Cr-TiO2-S concentration to obtain the highest photocatalytic activity was 5 mol% for both of Cr and S.  相似文献   

16.
The photocatalytic degradation of methylene blue and 4-chlorophenol on nanocrystalline TiO2 (nc-TiO2) under UV irradiation was investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Nanocrystalline TiO2 films were prepared from suspensions containing TiO2-crystallites of different average sizes, the smallest one being 12 nm. The organic substances (either methylene blue or 4-chlorophenol) were applied to these films. The specimens were studied in the pristine state and upon UV exposure. The UV illuminations were carried out both under atmospheric conditions and in situ under ultrahigh vacuum in the ToF-SIMS instrument. Distinct mass signals from the parent molecules and from fragment ions are observed for the as-prepared samples. Upon irradiation with UV light under atmospheric conditions, the surface composition is significantly changed, an observation ascribed to photocatalytic reactions induced by UV photons: the parent molecule signals are strongly diminished whereas fragmentation products are identified to be present at the TiO2 surfaces. UV irradiations carried out under different vacuum conditions in the ToF instrument (ultrahigh vacuum, air or oxygen adsorption) indicate that varying ambient conditions may influence the photocatalytic reaction on the nanocrystalline TiO2 films.  相似文献   

17.
To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Nitrogen and carbon doping TiO2−xyNxCy films were obtained by heating the TiO2 gel in an ionized N2 gas and then were calcined at 500 °C. The TiO2−xyNxCy films have revealed an improvement over the TiO2 films under visible light (wavelength, 500 nm) in optical absorption and photocatalytic activity such as photodegradation of methyl orange. X-ray photoemission spectroscopy, infrared spectrum and UV-visible (UV-vis) spectroscopy were used to find the difference of two kinds of films. Nitrogen and carbon doped into substitutional sites of TiO2 has been proven to be indispensable for band-gap narrowing and photocatalytic activity.  相似文献   

18.
The photodegradation of poly(vinylidene fluoride) (PVDF)/titanium oxide (TiO2) nanofibers under visible light is described, something that has not been previously reported in the literature. Visible light photocatalytic electrospun PVDF/TiO2 nanofiber webs with anatase TiO2 concentration varying from 0% to 20% (0%, 1%, 3%, 5%, 10%, and 20%) are produced, and their ability to degrade a toxic pollutant, Rhodamine B (RhB), is studied. Photodegradation study using UV–vis spectroscopy on PVDF/TiO2 nanofiber webs (with TiO2 concentration of 20%) shows that 80% of RhB is degraded within 6 h at the wavelength of 546 nm, which clearly falls within the visible spectra. The color of RhB solvent catalyzed by PVDF/TiO2 nanofiber webs gradually changes from red to orange, then to yellow, further to light yellow till colorless, which suggests the complete photodegradation of RhB under visible light. To estimate the rate of photodegradation, the reaction constant k is calculated. Based on the k value, PVDF/TiO2 nanofiber webs with 20% TiO2 concentration show the highest degradation rate compared to other PVDF/TiO2 nanofiber webs and pure TiO2 nanoparticles. This study proves the viability of TiO2‐based nanofibers to have catalytic capabilities under low‐energy visible light.  相似文献   

19.
Optical properties and photoluminescence of TiO2 nanowires, synthesized by two-step thermal evaporation process, under different Ar gas flow as carrier have been studied. The gas flow was varied from 50 to 150 sccm in order to find the optimum gas flow to growth TiO2 nanowires. As evidenced by X-ray diffraction patterns, our synthesized nanowires, were found to be crystalline rutile TiO2. Our results indicated a convenient gas flow for controlling diameter size of nanowires was about 100 sccm. In this case, diameters and lengths were, respectively, within the ranges of 40–100 and 400–1800 nm. The experimental data of the reflectance of TiO2 nanowires have been obtained through using spectrometer of wavelength 250–800 nm that has been indicated reflectance decreasing with increasing the gas flow, due to the scattering from the surface of the nanowires and also an increase in voids’ roughness. Under excitation 370 nm, the TiO2 nanowires can emit light peaked at 435 nm. It is believed that peak 435 may be due to free excitons emission.  相似文献   

20.
Carboxylated-azobenzene chromophore modified TiO2 nanowire composites were prepared and characterized. Photocurrent measured with monochromatic incident light irradiation results showed that azobenzene modified TiO2 nanowire electrode had obviously higher photocurrent and broader visible light response covering range of 350-650 nm, and the wavelength position corresponding to the maximum photocurrent was red shift to about 470 nm. After alternate irradiation with UV and visible light, the azobenzene modified TiO2 nanowire electrode exhibited obvious photoelectrochemical switching properties. Furthermore, the photocurrent under visible light irradiation was much higher than that under UV irradiation due to the cis-to-trans isomerization transformation of azobenzene chromophore.  相似文献   

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