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1.
Cellulose nanocrystal submonolayers by spin coating   总被引:1,自引:0,他引:1  
Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).  相似文献   

2.
高度分散的Pt/TiO2的制备及光催化活性   总被引:1,自引:0,他引:1  
张青红  高濂 《化学学报》2005,63(1):65-70
用柠檬酸作为空穴捕获剂和分散剂, 在温和条件下用光催化还原法将3 nm金属铂沉积在7 nm的锐钛矿相及介孔二氧化钛纳米晶表面. TEM观察显示铂的负载量为w=1.0%时, 多数二氧化钛纳米晶表面沉积了岛状的铂团簇, XPS和电子衍射结果表明铂以游离态存在. 负载w=1.0%~2.0%铂的TiO2在苯酚光氧化反应中活性显著提高. Pt/TiO2在氨气中经550 ℃氮化, 可制得氮掺杂的Pt/TiO2可见光光催化剂, 氮化过程中铂团簇没有烧结和显著长大.  相似文献   

3.
Flat and highly (111) oriented gold and silver films were prepared by physical vapour deposition (PVD) using optimized deposition parameters. On these films, which were characterized with atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), titanium dioxide films were deposited by electron beam evaporation and dip coating. Dip coating from titanium tetraisopropoxide solutions resulted in films with different morphology and coverage depending on the alkoxide concentration (0.009 mol/L – 0.60 mol/L) and the post-treatment. Scanning electron microscopy (SEM) and AFM revealed that the deposited TiO2 consists of amorphous, highly porous islands when the applied alkoxide concentration is high (0.05 mol/L – 0.6 mol/L). At higher temperatures these amorphous TiO2 islands sintered significantly and crystallized to anatase. In contrast, transparent TiO2 films were obtained from low concentrated alkoxide solutions (< 0.01 mol/L) which covered the whole substrate, similar to electron beam evaporated thin films. Sputter profiles with ion scattering spectroscopy (ISS) indicated that the film thickness is in the range of 2 nm when alkoxide solutions with a concentration of 9 mmol/L are used. The deposition of TiO2 by electron beam evaporation normally resulted in significantly reduced TiO2 films, completely oxidized ones were obtained when deposition was performed at elevated oxygen partial pressures (p(O2) > 2 × 10–5 mbar).  相似文献   

4.
Nanocrystals of lead sulfide were grown in TiO2 (titania) thin films prepared by a sol-gel process. The synthetic procedure as well as the structural, optical, and electrical properties of the films are demonstrated. The structures and morphology of PbS nanocrystals were analyzed using HRTEM, SAED, AFM, HRSEM, XRD and EDAX elemental analysis technique. When the concentration of PbS in the titania matrix is 20 mol%, PbS NCs with a diameter of 2.0 nm are created. At a higher PbS concentration (> 40 mole%) in the titania matrix, PbS NCs and PbS clusters are created not only within the TiO2 film but also on the external surface of the TiO2 film. By increasing the PbS concentration up to 50 mol%, PbS nanocrystals of 6–8 nm in diameter are formed within the titania film and PbS clusters with a base size of about 100 nm2 and a height up to about 20 nm were self assembled on the external surface of TiO2 film. Quantum size effect and band gap energies were obtained from shifts of the absorption edge. For electrical measurements, PbS–TiO2 films were deposited on an ITO/glass substrate, and then covered with gold contact. The electrical properties of ITO/PbS NCs–TiO2/Au and ITO/PbS NCs–TiO2/PbS cluster/Au structures were studied. I–V characteristics of the one layer structure are nearly linear and symmetric, while those of the two-layer structure exhibit rectifying behavior.  相似文献   

5.
采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO2和SiO2薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明:3种基底中, 单晶硅基底上TiO2和SiO2薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO2薄膜折射率和透光率差异较大;SiO2薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。  相似文献   

6.
采用溶胶-凝胶法分别在K9玻璃、单晶硅和石英玻璃基底上制备了纳米TiO2和SiO2薄膜。利用SEM、UV-Vis及反射式椭圆偏振光谱仪对薄膜的微观结构及光学特性进行了表征和分析。结果表明:3种基底中, 单晶硅基底上TiO2和SiO2薄膜折射率最大;在非晶态K9玻璃和石英玻璃基底上TiO2薄膜折射率和透光率差异较大;SiO2薄膜在非晶态基底上折射率、透光率相近;3种基底上薄膜的折射率和消光系数都有随波长增大而减小的趋势, 同时Cauchy模型能较好的描述单晶硅基底上两种薄膜在400~800 nm波段的光学性能。  相似文献   

7.
Cellulose nanocrystals were successfully isolated from cloth hairs using phosphoric acid. The yields, degree of polymerization, morphology, average particle size, crystallinity, chemical structure, and thermal stability of the prepared nanocrystals were investigated. The results demonstrated that yields and degree of polymerization decreased with the increase of concentration of phosphoric acid due to preferential degradation of amorphous cellulose, resulting in high thermal stability and crystallinity. Morphological analysis revealed that hydrolysis was more homogeneous with increasing acid concentration. In comparison with the cellulose nanocrystals prepared with 6.5, 8.0, and 9.5 M H3PO4, those prepared with 11.0 M H3PO4 had the most uniform particle sizes. Moreover, the nanocrystals had important influence on the crystallization of semicrystalline polymer.  相似文献   

8.
采用超声波辐射法制备了具有介孔结构的高浓度氮掺杂TiO2纳米晶(N/TiO2).采用N2物理吸附、X射线粉末衍射、X射线光电子能谱、透射电镜、光致发光谱和紫外-可见漫反射光谱等手段对N/TiO2进行了表征.以波长为400~660nm的可见光为光源,以水体污染物邻苯二甲酸二甲酯为降解对象,考察了不同制备方法对N/TiO2光催化性能的影响.结果表明,超声波辐射使氮掺杂浓度提高了2.2倍,该法制备的N/TiO2同时具有较好的介孔结构,表现了更高的光催化降解邻苯二甲酸二甲酯的活性.其活性提高的主要原因是N/TiO2含有更高浓度的氮和对可见光具有更强的吸收能力.  相似文献   

9.
在钛基体上采用阳极氧化法制备了TiO2纳米管阵列,采用化学浴方法在TiO2纳米管阵列上修饰了Fe2O3纳米颗粒.利用扫描电镜、X射线衍射和紫外可见漫反射光谱等手段对材料进行了表征,同时测试了材料的光电化学性能及其光催化降解亚甲基蓝染料废水的性能.结果表明,Fe2O3纳米颗粒的修饰将TiO2纳米管阵列的光响应拓宽至可见光区域,提高了光电流,Fe2O3/TiO2纳米管阵列的光电流是未修饰的TiO2纳米管阵列的9倍.而在光催化反应中,亚甲基蓝最高降解率可达80%,比未修饰的TiO2纳米管阵列高出30%.  相似文献   

10.
Fe_2O_3/TiO_2纳米管阵列的制备及其光催化性能   总被引:2,自引:0,他引:2  
在钛基体上采用阳极氧化法制备了TiO2纳米管阵列,采用化学浴方法在TiO2纳米管阵列上修饰了Fe2O3纳米颗粒。利用扫描电镜、X射线衍射和紫外可见漫反射光谱等手段对材料进行了表征,同时测试了材料的光电化学性能及其光催化降解亚甲基蓝染料废水的性能。结果表明,Fe2O3纳米颗粒的修饰将TiO2纳米管阵列的光响应拓宽至可见光区域,提高了光电流,Fe2O3/TiO2纳米管阵列的光电流是未修饰的TiO2纳米管阵列的9倍。而在光催化反应中,亚甲基蓝最高降解率可达80%,比未修饰的TiO2纳米管阵列高出30%。  相似文献   

11.
金涛  许頔  刁鹏*  项民 《物理化学学报》2012,28(10):2276-2284
采用溶胶-凝胶法制备了TiO2 纳米晶, 并通过浸渍技术在其表面引入了FeO(OH). 采用紫外-可见(UV-Vis)吸收光谱确定了引入FeO(OH)的最佳Fe3+浓度. 通过电化学法在FeO(OH)-TiO2光阳极上沉积了催化水分解制备氧气的钴基催化剂(CoPi), 得到了FeO(OH)-TiO2/CoPi 复合光阳极. 利用透射电镜(TEM), 高分辨透射电镜(HRTEM), X射线衍射(XRD), 扫描电镜(SEM)对TiO2纳米晶, FeO(OH)-TiO2以及FeO(OH)-TiO2/CoPi复合光阳极进行了表征, 采用电化学和光电化学技术研究了中性条件下FeO(OH)-TiO2/CoPi 复合光阳极的光电催化分解水性能. 结果表明, TiO2纳米晶为梭形的锐钛矿, 其表面修饰的FeO(OH)为针铁矿型, 且当前驱体溶液中Fe3+与TiO2的质量比为0.05%时得到的FeO(OH)-TiO2具有最佳的光吸收效果. 形成FeO(OH)-TiO2/CoPi复合光阳极后, 在光照条件下CoPi 电催化分解水制备氧气的过电位显著降低. TiO2表面FeO(OH)的引入增加了光阳极对可见光的吸收能力, 同时光阳极表面沉积的CoPi有效地利用了FeO(OH)-TiO2产生的光生空穴, 将水氧化形成氧气, 从而在光照条件下显著提高了CoPi催化氧化水的效率.  相似文献   

12.
A titanium chloromethoxide solution was prepared by reacting TiCl4 with methanol, followed by water addition. The starting solutions were characterized by Fourier Transform Infrared (FTIR) spectroscopy, evidencing that the in situ generated water results in early hydrolysis of the chloroalkoxide. The solution was reacted with molten dodecylamine at room temperature, obtaining a white slurry of amorphous titania nanoparticles. Stable, redispersible TiO2 nanocrystals could be prepared by subsequent solvothermal treatment in oleic acid at 250???C. The use of oleic acid was essential for obtaining crystalline structures, while other surfactants prevented crystallization. The nanocrystals were characterized by X-ray Diffraction and Transmission Electron Microscopy, confirming the formation of anatase TiO2 nanocrystals with a mean size of 3.3?nm. The TiO2 nanocrystals were used for fabricating gas-sensing devices, which were tested towards ethanol vapors. The initial small size of the nanocrystals, and the limited size growth during the high-temperature sensor operation, result in remarkable sensing performances if compared with bulk titania sensors.  相似文献   

13.
Photocatalytic multilayer nanocomposite films composed of anatase TiO2 nanoparticles and lignosulfonates (LS) were fabricated on quartz slides by the layer‐by‐layer (LBL) self‐assembly technique. X‐ray photoelectron spectroscopy (XPS), UV‐vis spectroscopy and atomic force microscopy (AFM) were used to characterize the TiO2/LS multilayer nanocomposite films. Moreover, the photocatalytic properties (decomposition of methyl orange and bacteria) of multilayer nanocomposite films were investigated. XPS results indicated that the intensities of titanium and sulfur peaks increased with the LBL deposition process. A linear increase in absorbance at 280 nm was found by UV‐Vis spectroscopy, suggesting that stepwise multilayer growth occurs on the substrate and this deposition process is highly reproducible. AFM images showed that quartz slide was completely covered by TiO2 nanoparticles when a 10‐bilayer multilayer film was formed. The decomposition efficiency of methyl orange by TiO2/LS multilayer films under the same UV irradiation time increased linearly with the number of TiO2 layers, and the results of decomposition of bacteria under UV irradiation showed that TiO2/LS multilayer nanocomposite films exhibited excellent decomposition activity of bacteria (Escherichia coil).  相似文献   

14.
Titania thin films were synthesized by sol–gel dip-coating method with metallic Ni nanoparticles synthesized separately from an organometallic precursor Ni(COD)2 (COD = cycloocta-1,5-diene) in presence of 1,3-diaminopropane as a stabilizer. Titania was obtained from a titanium isopropoxide precursor solution in presence of acetic acid. A Ni/TiO2 sol system was used to coat glass substrate spheres (6, 4 and 3 mm diameter sizes), and further heat treatment at 400 °C was carried out to promote the crystallization of titania. XRD analysis of the TiO2 films revealed the crystallization of the anatase phase. Transmission Electron Microscopy (TEM) and High Resolution TEM studies of Ni nanoparticles before mixing with the TiO2 solution revealed the formation of Ni nanostructures with an average size of 5–10 nm. High-angle annular dark-field images of the Ni/TiO2 system revealed well-dispersed Ni nanoparticles supported on TiO2 and confirmed by AFM analysis. The photocatalytic activity of the Ni/TiO2 films was evaluated in hydrogen evolution from the decomposition of ethanol using a mercury lamp for UV light irradiation. Titania films in presence of Ni nanoparticles show higher efficiency in their photocatalytic properties in comparison with TiO2.  相似文献   

15.
Ordered mesoporous thin films of composites of rutile TiO2 nanocrystals with amorphous Ta2O5 are fabricated by evaporation‐induced self‐assembly followed by subsequent heat treatment beyond 780 °C. Incorporation of selected amounts of Ta2O5 (20 mol %) in the mesoporous TiO2 film, together with the unique mesoporous structure itself, increased the onset of crystallization temperature which is high enough to ensure the crystallization of amorphous titania to rutile. The ordered mesoporous structure benefits from a block‐copolymer template, which stabilizes the mesostructure of the amorphous mixed oxides before crystallization. The surface and in‐depth composition analysis by X‐ray photoelectron spectroscopy suggests a homogeneous intermixing of the two oxides in the thin film. A detailed X‐ray absorption fine structure measurement on the composite film containing 20 mol % Ta2O5 and heated to 800 °C confirms the amorphous nature of the Ta2O5 phase. Photocatalytic activity evaluation suggests that the rutile nanocrystals in the synthesized ordered mesoporous thin film possess good ability to assist the photodegradation of rhodamine B in water under illumination by UV light.  相似文献   

16.
Summary: Cellulose nanocrystals (CNC) were extracted from Kraft pulp of Eucalyptus urograndis. The CNC were isolated by acid hydrolysis with H2SO4 64% (w/w) solution, for 20 minutes at 45 °C. The morphology and crystallinity of the CNC were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The AFM image supports the evidence for the development of crystals of cellulose in nanometric scale. These nanoparticles were used as reinforcement material in carboxymethyl cellulose (CMC) matrix. Nanocomposites films were prepared by casting. The nanocomposites were characterized by thermal (TGA) and mechanical (DMA) analyses. A large reinforcing effect of the filler was observed. The tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and the thermal resistance increased slightly. The improvements in thermo-mechanical properties suggest a close association between filler and matrix.  相似文献   

17.
Chiral carbonaceous nanotubes (CNT) were successfully used in plasmon‐free surface‐enhanced Raman scattering (SERS) for the first time. Further modification of TiO2 nanocrystals on the chiral CNTs successfully realized the recycling of SERS substrate as chiral CNT/TiO2 hybrids. The high SERS sensitivity of methylene blue (MB) over the chiral CNT/TiO2 hybrids is ascribed to the laser‐driven birefringence induced by the helical structure, which provides much more opportunities for the occurrence of Raman scattering. The TiO2 nanocrystals highly dispersed on the surface and inside the hollow cavity of chiral CNTs can completely degrade the MB under the solar light irradiation, leading to the self‐cleaning of SERS substrate. The present research opens a new way for the application of chiral inorganic materials in plasmon‐free SERS detection.  相似文献   

18.
Adhesion force is one of the most important factors in microelectromechanical systems (MEMS), especially for microassembly. It depends on operating conditions and is affected by the contact area. In this study, the adhesion force between MEMS materials and AFM tips was analysed using AFM's point-mode spectroscopy. The aim was to study the effectiveness of various coatings in MEMS adhesion surfaces. For this purpose, five silicon surfaces were used, four of which were coated, and one was noncoated. Two of them were deposited by single-layer coating (Au and Ag). The other two were deposited by double-layer coating (TiO2/Au, TiO2/Ag) on a Si (1 0 0) substrate. The depositing was accomplished by the thermal evaporation method. Composite materials and analysis were reviewed by observing the SEM image. The experimental results showed that the method of deposition helped to decrease the adhesion force between the probe tip and the surface of the specimens, and double-layer coating had stronger effect on decreasing the adhesion force than the single-layer coating.  相似文献   

19.
将电沉积法和化学浴沉积法结合,分别将CdTe和CdS量子点纳米晶材料引入到TiO2纳米管阵列上制备CdTe/CdS量子点共敏化TiO2光电极。利用扫描电镜、X射线衍射和X射线能量色散光谱等测试手段对所得样品的形貌、晶型和组分进行表征。在模拟太阳光照射条件下,通过电化学工作站测试其光电化学性能。研究结果表明,相对于单一量子点敏化CdS/TiO2和CdTe/TiO2光电极而言,共敏化CdTe/CdS/TiO2光电极表现出更好的光电转化性能,短路电流密度和光电转换效率分别可以达到3.1 mA·cm-2和1.85%。此外,采用电化学阻抗测试技术对材料性能提升的原因进行深入的探究。  相似文献   

20.
将电沉积法和化学浴沉积法结合,分别将CdTe和CdS量子点纳米晶材料引入到TiO_2纳米管阵列上制备CdTe/CdS量子点共敏化TiO_2光电极。利用扫描电镜、X射线衍射和X射线能量色散光谱等测试手段对所得样品的形貌、晶型和组分进行表征。在模拟太阳光照射条件下,通过电化学工作站测试其光电化学性能。研究结果表明,相对于单一量子点敏化CdS/TiO_2和CdTe/TiO_2光电极而言,共敏化CdTe/CdS/TiO_2光电极表现出更好的光电转化性能,短路电流密度和光电转换效率分别可以达到3.1 m A·cm~(-2)和1.85%。此外,采用电化学阻抗测试技术对材料性能提升的原因进行深入的探究。  相似文献   

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