纳米材料的表征方法

纳米材料的表征及其催化效果评价方式

纳米材料的表征主要目的是确定纳米材料的一些物理化学特性如形貌、尺寸、粒径、等电点、化学组成、晶型结构、禁带宽度和吸光特性等。

纳米材料催化效果评价方式主要是在光照（紫外、可见光、红外光或者太阳光）条件下纳米材料对一些污染物质（甲基橙、罗丹明B、亚甲基蓝和Cr6+等）的降解或者对一些物质的转化（用于选择性的合成过程）。评价指标为污染物质的去除效率、物质的转化效率以及反应的一级动力学常数k的大小。

1 、结构表征

XRD，ED，FT-IR, Raman，DLS

2 、成份分析

AAS，ICP-AES，XPS，EDS

3 、形貌表征

TEM，SEM，AFM

4 、性质表征-光、电、磁、热、力等

UV-Vis，PL，Photocurrent

1. TEM

TEM为透射电子显微镜，分辨率为0.1～0.2nm，放大倍数为几万～百万倍，用于观察超微结构，即小于0.2微米、光学显微镜下无法看清的结构。TEM是一种对纳米材料形貌、粒径和尺寸进行表征的常规仪器，一般纳米材料的文献中都会用到。

The morphologies of the samples were studied by a Shimadzu SSX-550 field-emission scanning electron microscopy (SEM) system, and a JEOL JEM-2010 transmission electron microscopy (TEM)[1]

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一般情况下，TEM还会装配High-Resolution TEM（高分辨率透射电子显微镜）、EDX（能量弥散X射线谱）和SAED（选区电子衍射）。High-Resolution TEM用于观察纳米材料的晶面参数，推断出纳米材料的晶型；EDX一般用于分析样品里面含有的元素，以及元素所占的比率；SAED用于实现晶体样品的形貌特征与晶体学性质的原位分析。

SEM表示扫描电子显微镜，可以获取被测样品本身的各种物理、化学性质的信息，如形貌、组成、晶体结构和电子结构等等。SEM也是一种对纳米材料形貌、粒径和尺寸进行表征的常规仪器，一般纳米材料的文献中都会用到。

The morphologies of the samples were studied by a Shimadzu SSX-550 field-emission scanning electron microscopy (SEM) system, and a JEOL JEM-2010 transmission electron microscopy (TEM)[1].

(a) SEM image of TiO2

nanofibers

SEM一般会装配EDX，用于分析材料的元素成分及所占比率。

AFM是指原子力显微镜，原子力显微镜的优点是在大气条件下，以高倍率观察样品表面，可用于几乎所有样品（对表面光洁度有一定要求），而不需要进行其他制样处理，就可以得到样品表面的三维形貌图象。

The anatase (101) surface and the rutile (001), (100), and (110) surfaces have been characterized by X-ray diffraction (XRD) and by atomic force microscopy (AFM)[2].

4. XRD

XRD是X射线衍射的缩写，通过对材料进行X射线衍射，分析其衍射图谱，获得材料的成分、材料的晶型结构、材料内部原子或分子的结构或形态等信息的研究手段。基本上对于纳米材料的文献都会用到。

The phases of the samples were characterized by X-ray diffraction (XRD), employing a scanning rate of 0.05° per second in a 2θ ranging from 10° to 80°, using a Bruker D8 Advance X-ray diffractometer (Cu Kα radiation, λ = 1.54178 Å)[1]

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5. DRS

DRS是漫反射谱，是通过光在检验物质表面反射测其反射光线的光谱。主要用于测定纳米材料的吸光特性，并据此估算出纳米材料的禁带宽度。可以看出材料在可见光下是否有吸收，一般合成催化材料的文献都会用到该仪器。

The UV−vis DRS was performed at room temperature on VARIAN Cary-5000 from 200 nm to 800 nm, using BaSO4 as the reflectance standard[1]

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图片来自[3]

6. PL

PL是光致发光的缩写，主要可以用来估计纳米材料的电荷分离效率，实验之前要先确定材料的激发波长。一般情况下，弱的荧光强度表示更高的电荷分离效率，所以催化效果也会相应的提高。

The photoluminscence (PL) emission mainly resulted from the recombination of excited electrons and holes, and a lower PL intensity indicated a higher separation efficiency[1].

The photoluminescence (PL) spectra were recorded by F-4600 fluorescence spectrophotometer (Hitachi, Japan) under ambient conditions. The excitation wavelength was 315 nm, the scanning speed was 1200 nm/min, and the slot widths of the excitation slit and the emission slit were both 5.0 nm[1]

.

7. XPS

XPS是X射线光电子能谱分析的缩写，XPS可以用来测量：元素的定性分析，可以根据能谱图中出现的特征谱线的位置鉴定除H、He以外的所有元素；元素的定量分析，根据能谱图中光电子谱线强度（光电子峰的面积）反应原子的含量或相对浓度；固体表面分析，包括表面的化学组成或元素组成，原子价态，表面能态分布，测定表面电子的电子云分布和能级结构等；化合物的结构，可以对内层电子结合能的化学位移精确测量，提供化学键和电荷分布方面的信息。 X-ray photoelectron spectroscopy (XPS) measurements were performed on a PHI 5000C ESCA system with Mg KR source operated at 14.0 kVand 25 mA. All the binding energies were referenced to the C1s peak at 284.6 eV from the surface adventitious carbon[4]

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8. Raman

通过对拉曼光谱的分析可以知道物质的振动转动能级情况，从而可以鉴别物质，分析物质的性质。

Raman spectroscopic measurements were performed on a Renishaw inVia Raman System 1000 with a 532 nm Nd:YAG excitation source at room temperature[3].

红外光谱，在有机物分子中，组成化学键或官能团的原子处于不断振动的状态，其振动频率与红外光的振动频率相当。所以，用红外光照射有机物分子时，分子中的化学键或官能团可发生震动吸收，不同的化学键或官能团吸收频率不同，在红外光谱上将处于不同位置，从而可获得分子中含有何种化学键或官能团的信息。一般材料中含有机物的纳米材料会用到FTIR分析（如石墨烯）。

The Fourier transformed infrared spectroscopy (FTIR) was performed on a Nicolet Nexus 670 FTIR spectrophotometer at a resolution of 4 cm-1[3]

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动态光散射，DLS技术测量粒子粒径，具有准确、快速、可重复性好等优点，已经成为纳米科技中比较常规的一种表征方法。随着仪器的更新和数据处理技术的发展，现在的动态光散射仪器不仅具备测量粒径的功能，还具有测量Zeta电位、大分子的分子量等的能力。 Investigate the interaction of EPS with QDs at the two photic conditions (light and dark, described above) by sizing microgels formation measured using dynamic light scattering (DLS; Brookhaven Instruments, Holtsville, NY USA)[5].

11. BET测试法—氮气吸附/解吸分析

BET测试法是BET比表面积测试法的简称，主要可以看出纳米材料的氮气吸附曲线和孔径分布图。

Specific surface areas of the catalysts were measured at 77 K by Brunauer Emmett Teller (BET) nitrogen adsorption desorption (Micromeritics ASAP 2010 Instrument)[6].

N2 Adsorption/Desorption Analysis. The N2 adsorption − desorption isotherms and Barrett−Joyner−Halenda (BJH) pore size distributions of all the samples are shown in Figure 5[7]

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12. 光电流的测定

光生空穴和电子产生之后，空穴被电解液捕获，而电子转移到后接触点，因而产生光电流。因此对光电流的测定可以估计电荷的分离效率以及空穴电子对的复合效率，光电流的增强说明空穴电子对分离效率高并且存在更少的复合。

The photocurrent developed by irradiating the photoanode (TiO2) with either UV or visible light was recorded with an electrochemical workstation (Model CHI660A, CH Instruments Co.). The photoelectrochemical cell was a three-electrode system: a TiO2 film located in the middle of the cell as a working electrode, a saturated calomel electrode as reference, and a platinum wire parallel to the working electrode as a counter electrode. All measurements were conducted at room temperature and ion a N2 atmosphere to obtain highly reproducible data. The electrolyte was 0.5 mol/L Na2SO4 aqueous solution. The working electrode was activated in the electrolyte for 2 h before measurement[1]

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13. ESR

ESR是电子自旋共振的缩写，电子顺磁共振谱仪的主要应用：一是研究矿物中顺磁性杂质离子(浓度低于1%)，如过度元素离子和稀土元素离子的类质同像置换、有序-无序、化学键及晶格参量和局域对称；二是研究于点缺陷有关的电子-空穴中心的类型、浓度、性质等。

The in situ electron paramagnetic resonance (EPR) measurement was performed using an Endor spectrometer (JEOL ES-ED3X) at the liquid nitrogen temperature of 77 K. A microwave with the frequency of 9.42 GHz was used and its power was set at 1 mW[8].

14. ICP-AES or AAS

ICP-AES是指电感耦合等离子体原子发射光谱法，主要用来测定岩石、矿物、金属等样品中数十种元素的含量。AAS是指原子吸收分光光度计，也可以用来测定样品中的元素含量。所以这两个仪器一般用于对于纳米材料的掺杂量的估算。

Elemental analysis for the Ag loading content of in the products were 1.1, 3.2, 5.1, and 8.3%, respectively by ICP-AES were as expected[9].

参考文献

1. Yang, Y. C., Wen, J. W., et al., Polypyrrole-Decorated Ag-TiO2 Nanofibers

Exhibiting Enhanced Photocatalytic Activity under Visible-Light Illumination. ACS Applied Materials & Interfaces, 2013. 5(13): p.6201-6207.

Ahmed, A. Y., Kandiel, T. A., et al., Photocatalytic Activities of Different Well-defined Single Crystal TiO2 Surfaces: Anatase versus Rutile. The Journal of Physical Chemistry Letters, 2011. 2(19): p.2461-2465.

Zhang, Y. H., Zhang, N., et al., Graphene Transforms Wide Band Gap ZnS to a Visible Light Photocatalyst. The New Role of Graphene as a Macromolecular Photosensitizer. ACS nano, 2012. 6(11): p.9777-9789.

Yu, D. H., Yu, X. D., et al., Synthesis of Natural Cellulose-Templated TiO2/Ag Nanosponge Composites and Photocatalytic Properties. ACS Applied Materials & Interfaces, 2012. 4(5): p.2781-2787.

Zhang, S. J., Jiang, Y. L., et al., Aggregation, Dissolution, and Stability of Quantum Dots in Marine Environments: Importance of Extracellular Polymeric Substances. Environmental Science & Technology, 2012. 46(16): p.8764-8772.

Zhang, H., Lv, X. J., et al., P25-Graphene Composite as a High Performance Photocatalyst. ACS nano, 2009. 4(1): p.380-386.

Li, X. C., Zheng, W. J., et al., Morphology Control of TiO2 Nanoparticle in Microemulsion and Its Photocatalytic Property. ACS Sustainable Chemistry & Engineering, 2014. 2(2): p.288-295.

Liu, H., Ma, H. T., et al., The Enhancement of TiO2 Photocatalytic Activity by Hydrogen Thermal Treatment. Chemosphere, 2003. 50(1): p.39-46.

Yu, D. H., Yu, X., et al., Synthesis of Natural Cellulose-Templated TiO2/Ag Nanosponge Composites and Photocatalytic Properties. ACS Applied Materials & Interfaces, 2012. 4(5): p.2781-7. 2. 3. 4. 5. 6. 7. 8. 9.