第30卷 第8期 催 化 学 报 2009年8月
V ol. 30 No. 8
Chinese Journal of Catalysi s
August
2009
文章编号: 0253-9837(2009)08-0839-13
综述: 839~851
Received date: 29 April 2009.
*Corresponding author. Tel: +1-510-486-7140; Fax: +1-510-486-7303; E-mail: XChen3@https://www.doczj.com/doc/65425059.html,
English edition available online at ScienceDirect (https://www.doczj.com/doc/65425059.html,/science/journal/18722067).
二氧化钛纳米材料及其能源应用
陈晓波
劳伦斯伯克利国家实验室, 伯克利, 加利福尼亚 94720, 美国
摘要：简要介绍了二氧化钛纳米材料的合成、性质、改性及其在能源方面的应用. 其中合成方法包括溶胶凝胶、水/溶剂热、氧化、沉积和超声/微波助合成法; 性质包括结构和热力学以及电学和光学性质; 改性包括掺杂和敏化; 应用包括光催化、光伏打和光解水.
关键词：二氧化钛; 纳米材料; 掺杂; 敏化; 光催化; 光伏打; 光解水 中图分类号：O643 文献标识码：A
Titanium Dioxide Nanomaterials and Their Energy Applications
CHEN Xiaobo *
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
Abstract: Here we briefly introduce the synthesis, properties, modifications, and energy applications of titanium dioxide nanomaterials. This introduction surveys their synthetic methods (sol/sol-gel, hydro/solvo-thermal, oxidation, deposition, sonochemical, and microwave-assisted approaches), their structural and thermodynamic properties, their modifications (doping and sensitizing), and their applications in photocata-lysis, photovoltaics and solar water splitting.
Key words: titanium dioxide; nanomaterial; doping; sensitizing; photocatalysis; photovoltaics; solar water splitting
Titanium dioxide (TiO 2) is biocompatible and environ-mentally benign and has been widely used as a pigment [1–3]. Manufacture of titanium dioxide pigment is a com-bination of two distinct processes: base pigment particle production and surface treatment, drying and milling. There are two different process routes used to extract and purify TiO 2 from ore to produce core pigment particles: the sulfate process and the chloride process [4].
The sulfate process is the first commercial process for the manufacture of TiO 2. Originally ilmenite is used as a raw material, but beneficiated ores with a much higher TiO 2 assay have been used more recently. The ore is first dried, ground, and classified to ensure efficient sulfation by agita-tion with concentrated sulfuric acid. The resultant metal sulfates are dissolved in water or weak acid, and the solu-tion is treated to ensure that only ferrous-state iron is pre-sent. The solution temperature is reduced to avoid prema-ture hydrolysis and clarified by settling and chemical floc-culation. The clear solution is then further cooled to crystal-lize coarse ferrous sulfate heptahydrate (FeSO 4?7H 2O)
which is separated from the process. The solution is evapo-rated to a precise composition and hydrolyzed to produce a suspension consisting predominantly of clusters of colloidal hydrous titanium oxide. Precipitation is carefully controlled to achieve the necessary particle size, usually employing a seeding or nucleating technique. The suspension is then separated from the mother liquor and extensively washed to remove residual traces of metallic impurities, using chelat-ing agents if necessary. The washed suspension is treated with chemicals which adjust the physical texture and act as catalysts in the calcination step. This process can produce either anatase or rutile crystal forms depending on additives used prior to calcination.
The feedstock for the chloride process is a mineral rutile or synthetic beneficiates containing over 90 percent TiO 2. A suitable ore blend is mixed with a source of carbon and then reacted with chlorine at approximately 900 °C. The reaction yields titanium tetrachloride, TiCl 4, and the chlorides of all the impurities present. The mixed chlorides are cooled and the low-volatile chloride impurities (e.g. iron, manganese,
840 催化学报第30卷
and chromium) are separated by condensation and removed from the gas stream with any unreacted solid starting mate-rials. The TiCl4 vapor is condensed to a liquid, followed by fractional distillation to produce an extremely pure, color-less, mobile liquid TiCl4 intermediate product, freezing at ?24 °C and boiling at 136 °C. The second critical stage in the chloride process is oxidation of the TiCl4 to TiO2 pig-ment particles. Pure titanium tetrachloride is reacted with oxygen in an exothermic reaction to form titanium dioxide and liberate chlorine, which is recycled to the chlorination stage. The high temperature ensures that only the rutile crystal form is produced. After cooling, the gas stream passes through a separator to collect the pigment particles and to remove adsorbed chlorine from the pigment. In both processes, the raw pigment may either be dried, milled, packed, and sold or more likely, especially for rutile pig-ments, surface-treated to produce a range of special prod-ucts for various applications.
Recent enormous research efforts dedicated to TiO2 ma-terials have been most fascinated with the discovery of the phenomenon of photocatalytic splitting of water on a TiO2 electrode by Fujishima et al. in 1972 [5–7]. An exponential growth of research activities has been seen in nanoscience and nanotechnology in the past decades [8–15]. TiO2 nano-materials, including nanoparticles, nanorods, nanowires, and nanotubes, are widely investigated for various applications in photocatalysis, photovoltaics, batteries, photonic crystals, sensors, ultraviolet blockers, smart surface coatings, pig-ment, and paints [1–24]. Various methods, such as sol-gel, sol, hydrothermal/solvothermal, physical/chemical vapor deposition, electrodeposition, etc., have been successfully used in making TiO2 nanomaterials. In the nanometer scale, new physical and chemical properties emerge and they vary with the sizes and shapes of the nanomaterials. The move-ment of electrons and holes in semiconductor nanomaterials is governed by the well-known quantum confinement, the transport properties related to phonons and photons are largely affected by the size and geometry of the materials, and the specific surface area and surface-to-volume ratio increase dramatically as the size of a material decreases [8– 13]. The high surface area brought about by small particle size is beneficial to most TiO2-based devices, as it facilitates reaction/interaction between the devices and interacting media, which mainly occurs on the surface and depends on the surface area. As the size, shape, and crystal structure of TiO2 nanomaterials change, not only does surface stability vary, but the transitions between different phases of TiO2 under pressure or heat become size dependent as well.
1 Preparation methods
1.1 Sol/sol-gel methods
TiO2 nanomaterials have been synthesized with the sol-gel method, a widely used method in making various ceramic materials. In a typical sol-gel process, the hydroly-sis of a titanium alkoxide or halide precursor and subse-quent condensation finally lead to the formation of TiO2 inorganic framework. This process normally proceeds via an acid-catalyzed hydrolysis step of titanium (IV) alkoxide followed by condensation [25–27]. The development of Ti–O–Ti chains through alcoxolation is favored for low content of water, with low hydrolysis rates and excess tita-nium alkoxide in the reaction mixture. Three-dimensional polymeric skeletons with close packing are resulted from the development of Ti–O–Ti chains, since each Ti is coor-dinated with four O atoms. The formation of Ti(OH)4 is favored with high hydrolysis rates. The presence of a large quantity of Ti–OH and insufficient development of three- dimensional polymeric skeletons lead to loosely packed first-order particles. The formation of Ti(OH)4O+H2 by the coordination of water to Ti(OH)4 is favored in the presence of a large excess of water. Closely packed first-order parti-cles are yielded via a three-dimensionally developed gel skeleton. Ti–O–Ti chains are formed in the reactions of the formed Ti–O+H–H species with other Ti–OH with the pro-duction of water or alcohol. The rate constant for coarsening increased with temperature due to the temperature depend-ence of the viscosity of the solution and the equilibrium solubility of TiO2. Secondary particles were formed by epi-taxial self-assembly of primary particles at longer times and higher temperatures, and the number of primary particles per secondary particle increased with time. The average TiO2 nanoparticle radius increased linearly with time in agreement with the Lifshitz-Slyozov-Wagner model for coarsening [26].
The sol method here refers to the non-hydrolytic sol-gel processes and usually involves the reaction of titanium chloride with a variety of different oxygen donor molecules, e.g. a metal alkoxide or an organic ether [28–36]. The con-densation between Ti–Cl and Ti–OR leads to the formation of Ti–O–Ti bridges. The alkoxide groups can be provided by titanium alkoxides or can be formed in situ by reaction of the titanium chloride with alcohols or ethers. For a series of alkyl substituents including methyl, ethyl, isopropyl, and tert-butyl, the reaction rate dramatically increased with greater branching of R, while average particle sizes were relatively unaffected. Variation of R yielded a clear trend in average particle size, but without discernible trend in reac-tion rate. Increasing nucleophilicity (or size) of the halide resulted in smaller anatase crystals. Average sizes ranged from 9.2 nm for TiF4 to 3.8 nm for TiI4. The amount of pas-sivating agent influenced the chemistry [36].
Micelles and inverse micelles are commonly employed to synthesize TiO2 nanoparticles in the sol and sol-gel methods
第8期陈晓波等: 二氧化钛纳米材料及其能源应用 841
[37–42]. In micelles, the hydrophobic hydrocarbon chains of the surfactants are oriented toward the interior of the micelle, and the hydrophilic groups of the surfactants are towards with the surrounding aqueous medium. Reverse micelles are formed in nonaqueous media and the hydro-philic headgroups are directed toward the core of the mi-celles while the hydrophobic groups are directed outward. Micelles are often globular and roughly spherical in shape, but ellipsoids, cylinders, and bilayers are also possible. The shape of a micelle is a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH, and ionic strength. The TiO2 nanoparticles prepared with the above micelle and reverse micelle methods normally have amor-phous structure, and calcination is usually necessary in or-der to induce high crystallinity. However, this process usu-ally leads to the growth and agglomeration of TiO2 nanopar-ticles. The crystallinity of TiO2 nanoparticles initially (syn-thesized by controlled hydrolysis of titanium alkoxide in reverse micelles in a hydrocarbon solvent) could be im-proved by annealing in the presence of the micelles at tem-peratures considerably lower than those required for the traditional calcination treatment in the solid state [40]. This procedure resulted in crystalline TiO2 nanoparticles with unchanged physical dimensions and minimal agglomeration [40].
Surfactants have been widely used in the preparation of variety of nanoparticles with good size distribution and dis-persity [43–50]. Adding different surfactants as capping agents such as acetic acid and acetylacetone into the reac-tion matrix can help synthesize monodispersed TiO2 nanoparticles [43,44]. With the aid of surfactants, different sized and shaped TiO2 nanorods have been synthesized [46,47]. The growth of high aspect ratio anatase TiO2 nano-rods could be achieved by controlled hydrolysis of titanium tetraisopropoxide (TTIP) in oleic acid (OA). A kinetically overdriven growth mechanism led to the growth of TiO2 nanorods instead of nanoparticles [46]. The shape of TiO2 nanocrystals could be modified by changing the surfactant concentration. For example, at low lauric acid concentra-tions, bullet- and diamond-shaped nanocrystals were ob-tained; at higher concentrations, rod-shaped nanocrystals or a mixture of nanorods and branched nanorods were ob-served [49].
Ordered TiO2 nanorods, nanowire, and nanotube arrays TiO2 can be obtained by combining the sol-gel method with an anodic alumina membrane (AAM) template by dipping porous AAMs into boiled TiO2 sol followed by drying and heating processes [51], by sol-gel electrophoretic deposition of TiO2 colloidal suspensions into AAM [52], or using the sol-gel method by templating with AAM[53] and other organic compounds [54]. 1.2 Hydro/solvo-thermal methods
The hydrothermal method has been widely used to pre-pare TiO2 nanomaterials [55–67]. Hydro/solvo-thermal synthesis is normally conducted in steel pressure vessels called autoclaves under controlled temperature and/or pres-sure with the reaction in aqueous/organic solutions. The temperature can be elevated above the boiling point of the water/organics, reaching the pressure of vapor saturation. The temperature and the amount of solution added to the autoclave largely determine the internal pressure produced. The solvothermal method is almost identical to hydrother-mal method except that the solvent used here is non-aqueous. However, the temperature can be elevated much higher than that in hydrothermal method because a variety of organic solvent with high boiling points can be chosen. The solvothermal method normally has better con-trol than hydrothermal methods of the size, shape distribu-tions, and the crystallinity of TiO2 nanoparticles. For exam-ple, by hydrothermal treatment of a titanium trichloride aqueous solution supersaturated with NaCl at 160 oC for 2 h, TiO2 nanorods could be prepared [57]. Different surfac-tants or compositions can be used to tune the morphology of the resulting nanorods [58,59].When TiO2 powders are put into a 2.5–20 mol/L NaOH aqueous solution and held at 20–110 °C for 20 h in an autoclave, TiO2 nanotubes are obtained [62,63]. With/without the aid of surfactants, the solvothermal method has been employed to synthesize high-quality TiO2 nanoparticles and nanorods [64–67]. For example, narrow-dispersed TiO2 nanorods could be obtained by keeping TTIP dissolved in anhydrous toluene with OA as
a surfactant at 250 oC for 20 h in an autoclave [66].
1.3 Oxidation methods
By oxidation of titanium metal using oxidants or under anodization, TiO2 nanomaterials can be obtained. TiO2 nanotubes by electrochemical oxidation of titanium foil has been extensively studied [68–73]. For example, by anodiz-ing titanium sheet under 10–20 V in a 0.5% hydrogen fluo-ride electrolyte solution for 10–30 min, aligned TiO2 nano-tube arrays can be obtained. The length and diameter of the TiO2 nanotubes could be controlled over a wide range (di-ameter, 15–120 nm; length, 20 nm to 10 μm) with the ap-plied potential between 1 and 25 V in optimized phos-phate/HF electrolytes. Crystallized TiO2 nanotubes were obtained after the anodized titanium plate was annealed at 500 °C for 6 h in oxygen [70]. This method normally pro-duces large TiO2 nanotubes with diameters over 50 nm. Figure 1 shows typicl SEM and TEM images of TiO2 nano-tubes we fabricated by this method with HCl as etching acid [73].
842 催化学报第30卷
Direct oxidation of a titanium metal plate with hydrogen peroxide can lead to the formation of TiO2 nanorods [74,75]. By the addition of inorganic salts of NaX (X = F?, Cl?, and SO42?), the crystalline phase of TiO2 nanorods were controlled. The addition of F? and SO42? helped the forma-tion of pure anatase, while the addition of Cl? favored the formation of rutile. The anions affected the precipitation rate [74].
Aligned TiO2 nanorod arrays were obtained by oxidizing titanium substrate using acetone as the oxygen source at 850 oC for 90 min [76]. The oxygen source was found to play an important role. Highly dense and well-aligned TiO2 nanorod arrays were formed when acetone was used as the oxygen source. Crystal-grain films were obtained with pure oxygen, and random nanofibers growing from the ledges of the TiO2 grains were produced with argon mixed with a low concen-tration of oxygen. Large polycrystalline TiO2 grains were formed with pure oxygen, since oxygen diffusion predomi-nated because of the high oxygen concentration and the oxidation occurred at the Ti metal and the TiO2 interface. When acetone was used as the oxygen source, well aligned TiO2 nanorod arrays were formed when Ti cations diffused to the oxide surface and reacted with the adsorbed acetone species.
1.4 Deposition methods
Vapor deposition refers to any process in which materials in a vapor state are condensed to form a solid phase mate-rial. Vapor deposition processes usually take place within a vacuum chamber. If no chemical reaction occurs, this proc-ess is called physical vapor deposition (PVD), otherwise it is called chemical vapor deposition (CVD). In CVD proc-esses, thermal energy heats the gases in the coating chamber and drives the deposition reaction. Other CVD approaches include electrostatic spray hydrolysis, diffusion flame pyro-lysis, thermal plasma pyrolysis, ultrasonic spray pyrolysis, laser-induced pyrolysis, and ultronsic-assisted hydrolysis. In PVD, materials are first evaporated and then condensed to form a solid material. The primary PVD methods include thermal deposition, ion plating, ion implantation, sputtering, laser vaporization, and laser surface alloying.
Thick crystalline TiO2 films with grain sizes below 30 nm as well as TiO2 nanoparticles with sizes below 10 nm were prepared by pyrolysis of TTIP in a mixed helium/oxygen atmosphere, using liquid precursor delivery [77]. In another example, TiO2 nanorods were developed grown on fused silica substrates with a template- and catalyst-free metalor-ganic CVD (MOCVD) method [78]. Titanium acetylaceto-nate (Ti(C10H14O5)) placed on a Pyrex glass container was used as the precursor. The precursor was loaded into the low-temperature zone of a furnace at 200–230 °C to vapor-ize. The vapor was carried by a N2/O2 flow into the high- temperature zone of the furnace, and TiO2 nanostructures were grown directly on bare fused silica or silicon substrates at 500–700 °C. The final crystalline phase and morphology were dependent on the reaction conditions. At 630 and 560 °C under a pressure of 5 Torr, single-crystalline rutile and anatase TiO2 nanorods were formed respectively; while at 535 °C under 3.6 Torr, anatase TiO2 nanowalls composed of well-aligned nanorods were formed.
TiO2 nanowire arrays have been fabricated by a simple PVD method or thermal deposition [79–81]. Typically, pure Ti metal powder was loaded as the titanium source on a quartz boat in a tube furnace. The substrate was kept ~0.5 mm away from the source. The temperature was increased to 850 °C under an argon gas flow protection. Then the fur-nace chamber was pumped down to ~300 Torr and the flow rate of the argon gas was set at 100 sccm (standard cubic centimeter per minute) and held for 3 h. After the reaction, a layer of TiO2 nanowires was obtained [79]. Alternatively, a layer of Ti nanopowders can be deposited on the substrate before the growth of TiO2 nanowires [80,81], and Au can be employed as catalyst [80].
1.5 Sonochemical and microwave-assisted methods The sonochemical method has been applied to prepare various TiO2 nanomaterials by different groups [41,82–85]. Sonochemistry arises from acoustic cavitation: the forma-tion, growth, and implosive collapse of bubbles in a liquid. Cavitational collapse produces intense
local heating (~5 000 Fig. 1. SEM (A) and TEM (B) images of TiO2 nanotubes fabricated by the electroxidation method [73].
第8期陈晓波等: 二氧化钛纳米材料及其能源应用 843
K), high pressures (~1 000 atm), and enormous heating and cooling rates (>109 K/s). Highly photoactive TiO2 nanopar-ticle photocatalysts with anatase and brookite phases can be obtained using the hydrolysis of titanium tetraisoproproxide in pure water or in a 1:1 EtOH-H2O solution under ultra-sonic radiation [41]. Arrays of TiO2 nanowhiskers with a diameter of 5 nm and nanotubes with a diameter of ~5 nm, and a length of 200–300 nm could be obtained by sonicating TiO2 particles in NaOH aqueous solution followed by washing with deionized water and dilute HNO3 aqueous solution [85].
Microwave radiation is applied to prepare various TiO2 nanomaterials [86–88]. A dielectric material can be proc-essed with energy in the form of high-frequency electro-magnetic waves. The principal frequencies of microwave heating are between 900 and 2 450 MHz. At lower micro-wave frequencies, conductive currents flowing within the material due to the movement of ionic constituents can transfer energy from the microwave field to the material. At higher frequencies, the energy absorption is primarily due to molecules with permanent dipole, which tend to re-orientate under the influence of a microwave electric field. This re-orientation loss mechanism originates from the inability of the polarisation to follow extremely rapid reversals of the electric field, so the polarisation phasor lags the applied electric field. This ensures that the resulting current density has a component in phase with the field, and therefore power is dissipated in the dielectric material. The major advantages of using microwaves for industrial processing are rapid heat transfer and volumetric and selective heating. Colloidal titania nanoparticle suspensions could be prepared within 5 to 60 min with microwave radiation, while 1 to 32 h was needed for the conventional synthesis method of forced hydrolysis at 195 °C [86]. TiO2 nanotubes can be synthesized with microwave radiation via the reaction of TiO2 crystals of anatase, rutile, or mixed phase and NaOH aqueous solution under certain microwave power [88]. Normally, the TiO2 nanotubes had the central hollow, open-ended and multi-wall structure with diameters of 8–12 nm and lengths up to 200–1000 nm [88].
2 Properties
2.1 Structural and thermodynamic properties
TiO2 has three phases of crystal structures, namely ana-tase, rutile, and brookite. The most commonly seen phases are anatase and rutile. For the bulk TiO2 material, rutile is the stable phase at high temperatures, but anatase and brookite are common in fine grained (nano-scale) natural and synthetic samples. On heating concomitant with coars-ening, the following transformations are all seen: anatase to brookite to rutile, brookite to anatase to rutile, anatase to rutile, and brookite to rutile. These transformation se-quences imply very closely balanced energetics as a func-tion of particle size. The surface enthalpies of the three polymorphs are sufficiently different that crossover in thermodynamic stability can occur under conditions that preclude coarsening, with anatase and/or brookite stable at small particle size [89,90]. In reality, the crystal structure of TiO2 nanoparticles depended largely on the preparation method [91]. For small TiO2 nanoparticles (< 50 nm), ana-tase seemed more stable and transformed to rutile at > 973 K. In another study, the prepared TiO2 nanoparticles had anatase and/or brookite structures, which transformed to rutile after reaching a certain particle size [89,92]. Once rutile was formed, it grew much faster than anatase. When the particle size was larger than 14 nm, rutile became more stable than anatase. A slow phase transition was observed from brookite to anatase below 1 053 K along with grain growth, a rapid brookite to anatase and anatase to rutile transformations between 1 053 K and 1 123 K, and rapid grain growth of rutile above 1 123 K as the dominant phase [93].
Surface passivation had an important impact on nanocrystal morphology and phase stability [94–96]. The surface hydrogenation induced significant changes in the shape of rutile nanocrystals, but not in anatase, and that the size at which the phase transition might be expected in-creased dramatically when the under-coordinated surface titanium atoms were H-terminated. For example, for spherical particles, the cross-over point was about 2.6 nm. For clean and faceted surface, at low temperatures, a phase transition pointed at an average diameter of approximately 9.3–9.4 nm for anatase nanocrystals, the transition size de-creased slightly to 8.9 nm when the surface bridging oxy-gens were H-terminated, and increased significantly to 23.1 nm when both the bridging oxygens and under-coordinated titanium atoms of the surface trilayer were H-terminated. Below the cross point, anatase phase was more stable than rutile phase [94].
2.2 Electronic and optical properties
The electronic structure of TiO2 has been studied by various experimental techniques, i.e. X-ray photoelectron, X-ray absorption and emission spectroscopies [91,97,98]. It is well known that for nanoparticles the bandgap energy increases and the energy band becomes more discrete with decreasing size [99,100]. As the size of a semiconductor nanoparticle falls below the Bohr radius of the first excita-tion state or comparable to the DeBroglie wavelength of the charge carriers, the charge carriers begin to behave quantum mechanically and the charge confinement leads to a series
844 催化学报第30卷of discrete electronic states [101]. However, there is dis-
crepancy on this critical size, below which quantization
effects are observed for TiO2 nanomaterials with indirect
bandgaps. The estimated critical diameter depends critically
on the effective masses of the charge carriers [102]. The
excitation radii for titania particles was found between 0.75
and 1.9 nm in two studies [103,104].
The main mechanism of light absorption in pure semi-
conductors is direct interband electron transitions. This ab-
sorption is especially small in indirect semiconductors, e.g.
TiO2, where the direct electron transitions between the band
centers are prohibited by the crystal symmetry. Indirect
electron transitions with momentum nonconservation at the
interface can enhance the light absorption in small TiO2
crystallites [105]. This effect increases at a rough interface
when the share of the interface atoms is larger. The indirect
transitions are allowed due to a large dipole matrix element and a large density of states for the electron in the valence band. Considerable enhancement of the absorption is ex-pected in small TiO2 nanocrystals, as well as in porous and microcrystalline semiconductors, when the share of the in-terface atoms is sufficiently large. A rapid increase in the absorption takes place at low (hν < E g + W c, W c: width of conduction band) photon energies. Electron transitions to any point in the conduction band become possible when hν= E g + W c. Further enhancement of the absorption occurs due to an increase of the electron density of states in only the valence band. The interface absorption becomes the main mechanism of light absorption for the crystallites that are smaller than 20 nm [105]. Due to lower dimensionality, the band gap of TiO2 nanomaterials was larger than the band gap of bulk TiO2 [106,107].
3 Modifications
Many applications of TiO2 nanomaterials are closely re-lated to their optical properties. However, the highly effi-cient use of TiO2 nanomaterials is sometimes prevented by the wide bandgap of TiO2. The bandgap of bulk TiO2 lies in the UV regime (3.0 eV for rutile phase and 3.2 eV for ana-tase phase), which is only a small fraction of the sun’s en-ergy (< 10%) [24]. Thus, one of the goals for improvement of the performance of TiO2 nanomaterials is to increase their optical activity by shifting the onset of the response from the UV to the visible region [9]. There are several ways to achieve this goal. First, doping TiO2 nanomaterials with other elements can narrow the electronic properties and thus alter the optical properties of TiO2 nanomaterials. Second, sensitizing TiO2 with other colorful inorganic or organic compounds can improve its optical activity in the visible light region. Third, coupling collective oscillations of the electrons in the conduction band of metal nanoparticle sur-faces to those in the conduction band of TiO2 nanomaterials in metal-TiO2 nanocomposites can improve the perform-ance. In addition, the modification of TiO2 nanomaterials surface with other semiconductors can alter the charge transfer properties between TiO2 and the surrounding envi-ronment, thus improving the performance of TiO2 nanoma-terials based devices. Figure 2 illustrates the modification paths in improving the properties (mainly the optical prop-erties) of TiO2 nanomaterials.
3.1 Doping
A variety of metal and nonmetal elements have been doped into TiO2 nanomaterials [108–132]. The preparation methods of doped TiO2 nanomaterials can be divided into three types: wet chemistry, high temperature treatment, and ion implantation on TiO2 nanomaterials. The wet chemistry method usually involves hydrolysis of a titanium precursor in a mixture of water and other reagents, followed by heat-ing. TiO2 nanoparticles were doped with 21 metal ions by the sol-gel method, and the presence of metal ion dopants significantly influenced the photoreactivity, charge carrier recombination rates, and interfacial electron-transfer rates [112]. C-doped TiO2 nanomateirals have been obtained by heating titanium carbide [114], or by annealing TiO2 under CO gas flow at high temperatures (500–800 °C) [115], or by direct burning of a titanium metal sheet in a natural gas flame [116]. N-doped TiO2 nanomaterials have been synthe-sized by hydrolysis of TTIP in a water/amine mixture and the post-treatment of the TiO2 sol with amines [108] or di-rectly from a Ti-bipyridine complex [122].
A red shift in the band gap transition or visible-light ab-sorption was observed in metal-doped TiO2 [112,133,134]. For V-, Mn-, or Fe-doped TiO2, the absorption spectra shifted to a lower energy region with an increase in the
dopant concentration [112,133,134]. This red shift was at-Fig. 2. Illustration of the modification paths for TiO2 nanomaterials.
第8期 陈晓波 等: 二氧化钛纳米材料及其能源应用 845
tributed to the charge-transfer transition between the d -electrons of the dopant and the conduction band (or val-ance band) of TiO 2. Our recent study on the electronic properties of C-, N-, and S-doped TiO 2 has revealed that compared to pure TiO 2, there are more electronic states above the valence band edge of TiO 2 in these doped TiO 2 materials (Fig. 3) using X-ray absorption, emission, and photoelectron spectroscopies [135,136]. This can explain the visible-light absorption properties of the doped TiO 2 materials.
Nonmetal doped TiO 2 normally has color from white to yellow or even light gray, and the onset of absorption spec-tra red-shifted to longer wavelength [108,110,118,122,125]. In N-doped TiO 2 nanomaterials, the band gap absorption onset shifted 600 nm from 380 nm of the undoped TiO 2, extending the absorption up to 600 nm (Fig. 4). The optical absorption of N-doped TiO 2 in the visible light region was primarily located between 400 and 500 nm, while that of oxygen-deficient TiO 2 was mainly above 500 nm from their density-functional theory study [137]. The red-shift in the absorption spectra of doped TiO 2 is due to the narrowing of the band gap in the electronic structure after doping. This could increase photosensitivity of the materials, i.e. photo-catalytic, photochemical, and photoelectrochemical activi-ties, in the visible region. 3.2 Sensitizing
Narrow bandgap semiconductors have been used as sen-sitizers to improve the optical absorption properties of TiO 2 nanomaterials in the visible light region by various groups [138–140]. In the sensitization of a nanocrystalline TiO 2 matrix by small PbS nanoparticles (< 2.5 nm), the photo-generated excess electrons could be directly injected from the PbS to the TiO 2, resulting in strong photoconductance in
the visible region [139]. Excitation of the sensitizer AgI on TiO 2 nanoparticles resulted in a stabilization of elec-tron-hole pairs with a lifetime well beyond 100 μs and in electron migration from AgI to TiO 2 [138]. In the sensitiza-tion of nanoporous TiO 2 by CdS, PbS, Ag 2S, Sb 2S 3, and Bi 2S 3, the relative positions of the energetic levels at the interface between the quantum size particles and TiO 2 could be optimized for efficient charge separation by using the size quantization effect, and the photostability of the elec-trodes could be significantly enhanced by surface modifica-tion of the TiO 2 nanoparticles with CdS nanoparticles [140]. When the TiO 2 nanoparticle films were sensitized with Ag nanoparticles, the color of the film could be reversely switched back and forth between brownish-gray under UV light and the color of illuminating visible light due to the oxidation of Ag by O 2 under visible light and reduction of Ag + under UV light [141]. The color of the film under visi-ble light could be tuned from green to red and white by changing the size of the Ag nanoparticles due to the plas-mon-based absorption of Ag and the dielectric confinement of the TiO 2 nanoparticle film matrix. The chromogenic properties of the Ag-TiO 2 films could be improved by si-multaneous irradiation during Ag deposition with UV and blue lights to suppress the formation of anisotropic Ag par-ticles, and nonvolatilization of a color image could be achieved by removing Ag + that was generated during the irradiation with a colored light [142].
Organic dyes have been widely employed as sensitizers for TiO 2 nanomaterials to improve their optical properties. Organic dyes are usually transition metal complexes with low lying excited states, such as polypyridine complexes, phthalocyanine, and metalloporphyrins. The metal centers for the dyes include Ru(II), Zn(II), Mg(II), Fe(II), and Al(III), while the ligands include nitrogen heterocyclics with a delocalized π or aromatic ring system [143–146].
250
300
350
400450500550
600
650
TiO 2 nanomaterial
N-TiO 2 nanomaterial
A b s o r b a n c e
Wavelength (nm)
Fig. 4. Absorbance spectra of N-doped TiO 2 nanoparticles and pure TiO 2 nanoparticles.
14
12
10
8
6
4
2
-2
I n t e n s i t y
Binding energy (eV)
TiO 2
N-TiO 2
C-TiO 2
S-TiO 2
Fig. 3. Valence band (VB) X-ray photoelectron spectroscopy (XPS)spectra of pure rutile TiO 2, N-, C-, and S-doped TiO 2 [136].
846 催化学报第30卷
4 Applications
4.1 Photocatalysis
TiO2 is regarded as the most efficient and environmen-tally benign photocatalyst and has been most widely used for photodegradation of various pollutants [6,7,15,33]. TiO2 photocatalysts can also be used to kill bacteria, as has been carried out with E. coli suspensions [147]. The strong oxi-dizing power of illuminated TiO2 can be used to kill tumor cells in cancer treatment [148]. The photocatalytic reaction mechanisms are widely studied [6,7,15,33,149]. The princi-ple of semiconductor photocatalytic reaction is straightfor-ward. Upon absorption of photons with energy larger than the band gap of TiO2, electrons are excited from the valence band to the conduction band, creating electron-hole pairs. These charge carriers migrate to the surface and react with the chemicals adsorbed on the surface to decompose these chemicals. This photodecomposition process usually in-volves one or more radicals or intermediate species such as ?OH, O2?, H2O2, and O2,which play important roles in the photocatalytic reaction mechanisms. The photocatalytic activity of a semiconductor is largely controlled by: (i) the light absorption properties, e.g., light absorption spectrum and coefficient, (ii) reduction and oxidation rates on the surface by the electron and hole, and (iii) the electron-hole recombination rate. Large surface area with constant surface density of adsorbents leads to faster surface photocatalytic reaction rates. In this sense, the larger the specific surface area, the higher the photocatalytic activity is. On the other hand, the surface is a defective site, therefore the larger the surface area, the faster the recombination. The higher the crystallinity, the fewer the bulk defects, and the higher the photocatalytic activity is. High temperature treatment usu-ally improves the crystallinity of TiO2 nanomaterials, which in return can induce the aggregation of small nanoparticles and decrease of the surface area. Judging from the above general conclusions, the relation between the physical prop-erties and the photocatalytic activities is complicated. Op-timal conditions are sought by taking these considerations into account and may vary from case to case [149].
4.1.1 First generation: pure TiO2 nanomaterials
As the size of TiO2 particle decreases, the fraction of at-oms located at the surface increases with higher surface area to volume ratios, which can further enhance the catalytic activity. The increase in the bandgap energy with decreasing nanoparticle size can potentially enhance the redox potential of the valence-band holes and the conduction band elec-trons, allowing photoredox reactions, which might not oth-erwise proceed in bulk materials, to occur readily. One dis-advantage of TiO2 nanoparticles is that they can only use a small percentage of sun light for photocatalysis. Practically, there exists an optimal size for a specific photocatalytic reaction. The photocatalytic activity of TiO2 nanoparticles on hydrogenation reactions of CH3CCH with H2O increased as the diameter of the TiO2 particles decreased, especially below 10 nm [99]. The dependence of the yields on the par-ticle size arose from the differences in the chemical reactiv-ity and not from the physical properties of these catalysts. There was an optimal size for TiO2 nanoparticles for maxi-mum photocatalytic efficiency in the decomposition of chloroform [150]. For example, there was an improvement in activity when the particle size was decreased from 21 to 11 nm, but the activity decreased when the size was reduced further to 6 nm. For this particular reaction the optimum particle size was about 10 nm. In large TiO2 nanoparticles, bulk recombination of the charge carriers was the dominant process, which could be reduced by a decrease in particle size; as the particle size was lowered below a certain limit, surface recombination processes became dominant since most of the electrons and holes were generated close to the surface and surface recombination was faster than interfa-cial charge carrier transfer processes [151].
4.1.2 Second generation: doped TiO2 nanomaterials
A systematic study on the photocatalytic activity of TiO2 nanoparticles doped with 21 transition metal elements for the oxidation of CHCl3 and the reduction of CCl4 showed that the photocatalytic activity was related to the electron configuration of the dopant ion in that dopant ions with closed electron shells had little or no effect on the activity [112,113]. Non-metal-doped TiO2 nanomaterials have been demonstrated with improved photocatalytic activities com-pared to pure TiO2 nanomaterials, especially in the visi-ble-light region [108–110,124,125]. In the study of the de-composition of methylene blue using N-doped TiO2 as measured by Asahi and co-workers [125], N-doped TiO2 had much higher photocatalytic activity than pure TiO2 in the visible-light region, while displaying lower activity in the UV-light region. A nitrogen concentration dependent performance of the photocatalytic activity of the N-doped TiO2 was found in the visible region [125]. The concentra-tion dependent photocatalytic activity of the N-doped TiO2 was attributed to that the band structure of the N-doped TiO2 with lower nitrogen concentration (< 2%) was differ-ent from that with higher concentration [122]. The signifi-cant increase in photocatalytic activity in N-doped TiO2 nanoparticles was due to the O–Ti–N bond formation as oxynitride during the substitutional doping process [110]. Figure 5 shows a photocatalytic decomposition of methyl-ene blue on N-doped TiO2 nanoparticles and pure TiO2
第8期 陈晓波 等: 二氧化钛纳米材料及其能源应用 847
(Degussa P25). The experiment was monitored by the de-crease in optical density at 650 nm following 790, 540, and 390 nm laser excitation after excitation of a 5 nl volume of a 2 mmol aqueous methylene blue solution. N-doped TiO 2 nanocatalysts displayed a much higher photocatalytic activ-ity from UV to visible-light region [108,110]. 4.2 Photovoltaics
Photovoltaics based on TiO 2 nanocrystalline electrodes have been widely studied on the so-called dye-sensitized nanocrystalline solar cell (DSSC) [14,15]. The structure of a DSSC cell is illustrated in Fig. 6. At the heart of the system is a nanocrystalline mesoporous TiO 2 film with a monolayer of the charge transfer dye attached to its surface. The film is placed in contact with a redox electrolyte or an organic hole conductor. Photoexcitation of the dye injects an electron into the conduction band of TiO 2. The electron can be con-ducted to the outer circuit to drive the load and make elec-tric power. The original state of the dye is subsequently restored by electron donation from the electrolyte, usually an organic solvent containing a redox system, such as the iodide/triiodide couple. The regeneration of the sensitizer by
iodide prevents the recapture of the conduction band elec-tron by the oxidized dye. The iodide is regenerated in turn by the reduction of triiodide at the counter-electrode, the circuit being completed via electron migration through the external load.
The structure and properties of the TiO 2 electrodes play an important role in the performance of the DSSC. The mesoporosity and nanocrystallinity of the semiconductor are important not only because of the large amount of dye that can be adsorbed on the very large surface, but also for two additional reasons: (a) they allow the semiconductor small particles to become almost totally depleted upon immersion in the electrolyte (allowing for large photovoltages), and (b) the proximity of the electrolyte to all particles makes screening of injected electrons, and thus their transport, possible [152]. Ordered mesoporous TiO 2 nanocrystalline films showed enhanced solar conversion efficiency by about 50% compared to traditional films of the same thickness made from randomly oriented anatase nanocrystals [153]. Higher efficiencies of solar cells were achieved with TiO 2 nanotube-based electrodes due to the increase in electron density in nanotube electrodes compared to P25 electrodes [154]. Nanoporous electrodes in a core-shell configuration, usually a TiO 2 core coated with Al 2O 3 [155], MgO [156], SiO 2 [157], ZrO 2 [157], or Nb 2O 5 [158], could improve the performance of dye-sensitized solar cells. Doped TiO 2 nanomaterials also show a good promise in the application of DSSCs. For the best N-doped TiO 2 electrodes, the photoinduced current due to visible light and at moderate bias increased around 200 times compared to the behavior of pure TiO 2 electrodes [159]. 4.3 Solar water splitting
An enormous research effort has been dedicated to the study of the properties and applications of TiO 2 under light illumination since the discovery of photocatalytic splitting of water on a TiO 2 electrode in 1972 [5–7]. Photocatalytic splitting of water into H 2 and O 2 using TiO 2 nanomaterials continues to be a dream for clean and sustainable energy sources. The principle of water splitting using a TiO 2 photocatalyst can be summarized as follows [160]. When TiO 2 absorbs light with energy larger than the band gap, electrons and holes are generated in the conduction and valence bands, respectively. The photogenerated electrons and holes cause redox reactions. Water molecules are re-duced by the electrons to form H 2 and oxidized by the holes to form O 2, leading to overall water splitting. The width of the band gap and the potentials of the conduction and va-lence bands are important. The bottom level of the conduc-tion band has to be more negative than the reduction poten-tial of H +/H 2 (0 V vs. NHE), while the top level of the va-
Time (h)
O p t i c a l d e n s i t y (a .u .)
Time (h)
Fig. 5. Photocatalytic decomposition of methylene blue on N-doped TiO 2 nanocolloid and pure TiO 2 (Degussa P25) as monitored by the decrease in optical density at 650 nm following 790, 540, and 390 nm laser excitation after excitation of a 5 nl volume of a 2 mmol/L aque-ous methylene blue solution [110].
Fig. 6. Schematic illustration of the structure of a DSSC solar cell.
848 催化学报第30卷
lence band has to be more positive than the oxidation poten-tial of O2/H2O (1.23 V). The potential of the band structure of TiO2 is just the thermodynamical requirement. Other factors such as charge separation, mobility, and lifetime of photogenerated electrons and holes also affect the photo-catalytic properties of TiO2. These factors are strongly af-fected by bulk properties of the material such as crystallin-ity. Surface properties such as surface states, surface chemical groups, surface area, and active reaction sites are also important. The water splitting process in return affects the local pH environment and surface structures of the TiO2 electrode [161]. A thermodynamic and kinetic study of wa-ter splitting and competitive reactions in the photoelectro-chemical cell showed that the overvoltage for evolution of O must be minimized, which was on the order of 0.6 eV for n-TiO2 electrodes loaded with RuO2 [162].Co-catalysts such as Pt and NiO are often loaded on the surface in order to introduce active sites for H2 evolution. Addition of car-bonate salts to Pt-loaded TiO2 suspensions led to highly efficient water splitting [163].
Suitable bulk and surface properties and energy structure are demanded for photocatalysts. Figure 7 illustrates the ideal conditions for a semiconductor to perform solar photocatalytic water splitting. In this figure, it is assumed that the valence band edge (E v) at the interface is far enough below the redox Fermi level for water oxidation (E F(H2O/O2)) and the conduction band edge (E c) is above the redox Fermi level for water reduction (E F(H2/H2O)). The light splits the quasi-Fermi levels of electrons and holes so far that they exceed the energy difference for water splitting (1.23 eV) plus the additional overpotentials (η), which are assumed small for hydrogen evolution but large for oxygen evolution. The quasi-Fermi levels (E*F) under light at the interface between the semiconductor and the electrolyte must be at the right position for water oxidation and reduc-tion. Including the energy losses in the electron-hole separa-tion process and the internal resistance of the cell, a band gap (E g) of 2.1 eV is the minimum for a semiconductor ca-pable of solar water splitting. In reality, the band gap nor-mally is wider, around 2.3 or 2.4 eV.
Pure TiO2 cannot easily split water into H2 and O2 in the simple aqueous suspension system due to the fast, undesired electron-hole recombination reaction [107,164,165].There-fore, it is important to prevent the electron-hole recombina-tion process. A sacrificial reagent helps to control the elec-tron-hole recombination process. Photoefficiency of the process can be improved by the addition of sacrificial re-agents [164,165]. The sacrificial reagents help separation of the photoexcited electrons and holes. Various compounds such as methanol, ethanol, EDTA (an ethylenediamine-tetraacetic derivative), Na2S, Na2SO4, or ions such as I?, IO3?, CN?, and Fe3+ have been used as sacrificial reagents [164,166–168].
Highly ordered TiO2 nanotube arrays efficiently decom-posed water under UV radiation [169]. The nanotube wall thickness was a key parameter influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For TiO2 nanotubes with 22 nm pore diameter and 34 nm wall thickness, upon 320–400 nm illumination at an intensity of 100 mW/cm2, hydrogen gas was generated at the power-time normalized rate of 960 μmol/(h·W) (24 ml/(h·W)) at an overall conversion effi-ciency of 6.8% [169,170]. When doped with carbon, TiO2-x C x nanotube arrays showed more efficient water split-ting under UV and visible-light illumination (> 420 nm) than pure TiO2 nanotube arrays [115].
Water cleavage could be induced with visible light in colloidal solutions of Cr-doped TiO2 nanoparticles deposited with ultrafine Pt or RuO2 [171]. A pronounced synergistic effect in catalytic activity was noted when both RuO2 and Pt were codeposited onto the particle. Jin et al. [172] found that Pt/B-doped TiO2 was a good system for water splitting under B4O72– environment without sacrificial electron donor reagents. Ni-doped mesoporous TiO2 photocatalyst with 0.2% Pt accomplished hydrogen evolution at nearly 125.6 μmol/h compared to 81.2 μmol/h for TiO2 P25 [173]. N- and B-doped TiO2 nanomaterials have displayed higher activity than pure TiO2 in water splitting, i.e. under visible light illumination [165,174]. C-doped TiO2 nanocrystalline film with visible light response obtained by controlled combus-tion of Ti metal in a natural gas flame had a high water splitting performance with a total conversion efficiency of 11% and a maximum photoconversion efficiency of 8.35% when illuminated at 40 mW/cm2 [116], although there were questions about its solar-to-hydrogen conversion efficiency by other researchers [175–177].
Fig. 7. Ideal conditions for a semiconductor to perform solar photo-catalytic water splitting.
第8期陈晓波等: 二氧化钛纳米材料及其能源应用 849
5 Summary
The tremendous effort put into TiO2 nanomaterials has resulted in a rich database for their synthesis, properties, modifications, and applications. New properties and new applications with improved performance have been seen along with the continuing breakthroughs in the synthesis and modifications of TiO2 nanomaterials. These new nano-materials demonstrate the size-dependent as well as shape- and structure-dependent optical, electronic, thermal, and structural properties and have continued to be highly active in photocatalytic and photovoltaic applications, an impor-tant role in the search for renewable and clean energy tech-nologies.
Acknowledgements
We acknowledge the financial support from the U.S. De-partment of Energy.
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材料学《第二课堂》课程论文题目：TiO2半导体纳米材料姓名： 学号：
目录 1. 课程设计的目的 (1) 2. 课程设计题目描述和要求 (1) 3. 课程设计报告内容 (1) 3.1 TiO2半导体纳米材料的特性 (1) 3.2 TiO2半导体纳米材料的制备方法 (3) 3.3 TiO2半导体纳米材料的表征手段 (3) 3.4 TiO2半导体纳米材料的发展现状与趋势 (4) 4. 结论 (5)
1.课程设计的目的 本课程论文的主要目的是论述TiO2半导体纳米材料，通过简要概述TiO2半导体纳米材料的特性、制备方法、表征手段及发展现状与趋势等相关方面的内容。通过这次课设，了解TiO2半导体纳米材料，巩固课堂上所学的有关纳米材料的有关知识，提高自己应用所学知识和技能解决实际问题的能力。 2．课程设计的题目描述及要求 课程设计的题目：TiO2半导体纳米材料 TiO2半导体纳米材料由于它具有不同于体材料的光学非线性和发光性质,在未来光开关、光存储、光快速转换和超高速处理等方面具有巨大的应用前景。本文就TiO2半导体纳米材料的主要制备方法与表征手段做一全面总结。 3.课程设计报告内容 3．1 TiO2半导体纳米材料的特性 1、光学特性 TiO2半导体纳米粒子(1～ 100 nm ) [2]由于存在着显著的量子尺寸效应, 因此它们的光物理和光化学性质迅速成为目前最活跃的研究领域之一, 其中TiO2半导体纳米粒子所具有的超快速的光学非线性响应及(室温) 光致发光等特性倍受世人瞩目。通常当半导体粒子尺寸与其激子玻尔半径相近时, 随着粒子尺寸的减小, 半导体粒子的有效带隙增加, 其相应的吸收光谱和荧光光谱发生蓝移, 从而在能带中形成一系列分立的能级[1]。 2、光电催化特性 1）TiO2半导体纳米粒子优异的光电催化活性 近年来, 对纳米TiO2半导体粒子研究表明: 纳米粒子的光催化活性均明显优于相应的体相材料。我们认为这主要由以下原因所致: ①TiO2半导体纳米粒子所具有的量子尺寸效应使其导带和价带能级变成分立的能级, 能隙变宽, 导带电位变得更负, 而价带电位变得更正。[1]这意味着TiO2半导体纳米粒子获得了更强的还原及氧化能力, 从而催化活性随尺寸量子化程度的提高而提高[5]。 ②对于TiO2半导体纳米粒子而言, 其粒径通常小于空间电荷层的厚度, 在离开粒子中心L距离处的势垒高度可以表述为[1]: 公式（1） 这里LD是半导体的Debye 长度, 在此情况下, 空间电荷层的任何影响都可忽略, 光生载流子可通过简单的扩散从粒子内部迁移到粒子表面而与电子给体或受体发生还原或氧化反应。计算表明: 在粒径为1Lm 的T iO 2 粒子中, 电子从体内扩散到表面的时间约为100n s, 而在粒径为10 nm 的微粒中只有10 p s。因此粒
纳米材料导论复习题(2016) 一、填空： 1.纳米尺度是指 2.纳米科学是研究纳米尺度内原子、分子和其他类型物质的科学 3.纳米技术是在纳米尺度范围内对原子、分子等进行的技术 4.当材料的某一维、二维或三维方向上的尺度达到纳米范围尺寸时，可将此类材料称为 5.一维纳米材料中电子在个方向受到约束，仅能在个方向自由运动，即电子在 个方向的能量已量子化一维纳米材料是在纳米碳管发现后才得到广泛关注的，又称为 6.1997年以前关于Au、Cu、Pd纳米晶样品的弹性模量值明显偏低，其主要原因是 7.纳米材料热力学上的不稳定性表现在和两个方面 8.纳米材料具有高比例的内界面，包括、等 9.根据原料的不同，溶胶-凝胶法可分为： 10.隧穿过程发生的条件为. 11.磁性液体由三部分组成：、和 12.随着半导体粒子尺寸的减小，其带隙增加，相应的吸收光谱和荧光光谱将向方向移动，即 13.光致发光指在照射下被激发到高能级激发态的电子重新跃入低能级被空穴捕获而发光的微观过程仅在激发过程中发射的光为在激发停止后还继续发射一定时间的光为 14.根据碳纳米管中碳六边形沿轴向的不同取向，可将其分成三种结构：、和 15.STM成像的两种模式是和. 二、简答题：（每题5分，总共45分） 1、简述纳米材料科技的研究方法有哪些？ 2、纳米材料的分类？ 3、纳米颗粒与微细颗粒及原子团簇的区别？ 4、简述PVD制粉原理 5、纳米材料的电导（电阻）有什么不同于粗晶材料电导的特点？ 6、请分别从能带变化和晶体结构来说明蓝移现象
7、在化妆品中加入纳米微粒能起到防晒作用的基本原理是什么？ 8、解释纳米材料熔点降低现象 9、AFM针尖状况对图像有何影响？画简图说明 1. 纳米科学技术 (Nano-ST):20世纪80年代末期刚刚诞生并正在崛起的新科技，是研究在千万分之一米10–7)到十亿分之一米(10–9米)内，原子、分子和其它类型物质的运动和变化的科学；同时在这一尺度范围内对原子、分子等进行操纵和加工的技术，又称为纳米技术 2、什么是纳米材料、纳米结构？ 答：纳米材料：把组成相或晶粒结构的尺寸控制在100纳米以下的具有特殊功能的材料称为纳米材料，即三维空间中至少有一维尺寸小于100nm的材料或由它们作为基本单元构成的具有特殊功能的材料，大致可分为纳米粉末、纳米纤维、纳米膜、纳米块体等四类；纳米材料有两层含义： 其一，至少在某一维方向，尺度小于100nm，如纳米颗粒、纳米线和纳米薄膜，或构成整体材料的结构单元的尺度小于100nm，如纳米晶合金中的晶粒;其二，尺度效应：即当尺度减小到纳米范围，材料某种性质发生神奇的突变，具有不同于常规材料的、优异的特性量子尺寸效应。 纳米结构：以纳米尺度的物质为单元按一定规律组成的一种体系 3、什么是纳米科技？ 答：纳米科技是研究在千万分之一米(10-8)到亿分之一米(10-9米)内，原子、分子和其它类型物质的运动和变化的学问；同时在这一尺度范围内对原子、分子进行操纵和加工 4、什么是纳米技术的科学意义？ 答：纳米尺度下的物质世界及其特性，是人类较为陌生的领域，也是一片新的研究疆土在宏观和微观的理论充分完善之后，再介观尺度上有许多新现象、新规律有待发现，这也是新技术发展的源头；纳米科技是多学科交叉融合性质的集中体现，我们已不能将纳米科技归为任何一门传统的学科领域而现代科技的发展几乎都是在交叉和边缘领域取得创新性的突破的，在这一尺度下，充满了原始创新的机会因此，对于还比较陌生的纳米世界中尚待解释的科学问题，科学家有着极大的好奇心和探索欲望 5、纳米材料有哪4种维度？举例说明 答：零维：团簇、量子点、纳米粒子 一维：纳米线、量子线、纳米管、纳米棒 二维：纳米带、二维电子器件、超薄膜、多层膜、晶体格 三维：纳米块体 6、请叙述什么是小尺寸效应、表面效应、量子效应和宏观量子隧道效应、库仑堵塞效应 答：小尺寸效应：当颗粒的尺寸与光波波长、德布罗意波长以及超导态的相干长度或透射深度等物理特征尺寸相当或更小时，晶体周期性的边界条件将被破坏，非晶态纳米粒子的颗粒表面层附近的原子密度减少，导致声、光、电、磁、热、力学等特性呈现新的物理性质的变化称为小尺寸效应 表面效应：球形颗粒的表面积与直径的平方成正比，其体积与直径的立方成正比，故其比表面积（表面积/体积）与直径成反比随着颗粒直径的变小，比表面积将会显著地增加，颗粒表面原子数相对增多，从而使这些表面原子具有很高的活性且极不稳定，致使颗粒表现出不一样的特性，这就是表面效应 量子尺寸效应：当粒子的尺寸达到纳米量级时，费米能级附近的电子能级由连续态分裂成分立能级当能级间距大于热能、磁能、静电能、静磁能、光子能或超导态的凝聚能时，会出现纳米材料
聚合物基纳米复合材料的研究进展 摘要:本文总结了聚合物基纳米复合材料的研究进展，主要涉及纳米复合材料的制备方法、性能介绍和应用情况等方面，对聚合物基纳米复合材料的合成技术方法、不同的类型和相应性能特点进行了重点分析。对于聚合物基纳米复合材料，纳米填料的分散性、与聚合物基体的界面性能以及基体的性质都是影响其物理、热性能、机械等性能的重要参数。最后，简要介绍了目前在聚合物基纳米复合材料研究领域存在的问题，并对中国在该领域的未来发展以及纳米复材的产业化应用提出了相关建议。 关键词：纳米复合材料；聚合物；进展 Progress in Polymer Nanocomposites Development Abstract：This article summarizes some of the highlights of newest development in polymer nanocomposites research. It focuses on the preparation, properties and applications of polymer nanocomposites. The various manufacturing techniques, analysis of kinds of polymer nanocomposites and their applications have been described in detail. In the case of polymer nanocomposites, filler dispersion, intercalation/exfoliation, orientation and filler-matrix interaction are the main parameters that determine the physical, thermal, transport, mechanical and rheological properties of the nanocomposites. Finally, the recent situation of research in polymer nanocomposites was introduced and some constructive suggestions were proposed about the industrialization of polymer nanocomposites in China. Keywords：nanocomposites; polymer; progress
纳米二氧化钛的应用 纳米二氧化钛作为一种高效、无毒的光催化剂，在环保领域的应用越来越 受到人们的广泛关注和重视。抗菌材料纳米TiO2以其优异的抗菌性能成为开发研 究的热点之一，以期应用于水处理装置、医疗设备、食品包装、建材（如抗菌地砖、抗菌陶瓷卫生设施、抗菌砂浆、抗菌涂料等）、化妆品、纺织品、日用品以及家用电器等各个领域。1、气体净化环境有害气体可分为室内有害气体和大气污染气体。室内有害气体主要有装饰材料等放出的甲醛及生活环境中产生的甲硫醇、硫化氢及氨气等。TiO2通过光催化作用可将吸附于其表面的这些物质分解氧化，从而使空气中这些物质的浓度降低，减轻或消除环境不适感。大气污染气体，主要是由汽车尾气与工业废气等带来的氮氧化物和硫氧化合物。利用纳米TiO2的催化作用将这些气体氧化成蒸汽压低的硫酸和硝酸，在降雨过程中除去，从而达到降低大气污染的目的。在居室、办公室窗玻璃、陶瓷等建材表面涂敷TiO2光催化薄膜或在房间内安放TiO2光催化设备，均可有效地降解污染物，净化室内空气。利用纳米TiO2开发出来的一种抗剥离光催化薄板，可利用太阳光有效去除空气中的NOx气体，而且薄板表面生成的HN03可由雨水冲洗掉，保证了催化剂活性的稳定。2、抗菌除臭抗菌是指纳米TiO2在光照下对环境中微生物的抑制或杀灭作用。TiO2光催化剂对绿脓杆菌、大肠杆菌、金黄色葡萄球菌等具有很强的杀能力。当细菌吸附于由纳米二氧化钛涂敷的光催化陶瓷表面时，2被紫外光激发后产生的活性超氧离子自由基(·O2-)和羟基自由基(·OH)能穿透细菌的细胞壁，破坏细胞膜质，进入菌体，阻止成膜物质的传输，阻断其呼吸系统和电子传输系统，从而有效地杀灭细菌，并抑制细菌分解有机物产生臭味物质(如H2S、SO2、硫醇等)。因此，纳米TiO2能净化空气，具有除臭功能。3、处理有机污水工业污水和生活污水中含有大量的有机污染物，尤其是工业污水中含有大量的有毒、有害的有机物质，这些污染物用生物处理技术很难消除。许多学者对水中有机污染物光催化分解进行了系统的研究，结果表明以TiO2为光催化剂，在光照的条件下，可使水中的烃类、卤代物、羧酸等发生氧化还原反应，并逐步降解，最终完全氧化为环境友好的CO2和H2O等无害物质。4、处理无机污水除有机物外，许多无机物在TiO2表面也具有光学活性，例如无机污水中的Cr6+接触到TiO2催化剂表面时，能够捕获表面的光生电子而发生还原反应，使高价有毒的Cr6+降解为毒性较低或无毒的Cr3+，从而起到净化污水的作用；一些重金属离子如Pt4+，Hg2+，Au3+等，在催化剂表面也能够捕获电子而发生还原沉淀反应，可回收污水的无机重金属离子。5、防雾、自清洁功能TiO2薄膜在光照下具有超亲水性和超永久性，因此其具有防雾功能。如在汽车后视镜上涂覆一层氧化钛薄膜，即使空气中的水分或者水蒸气凝结，冷凝水也不会形成单个水滴，而是形成水膜均匀地铺展在表面，所以表面不会发生光散射的雾。当有雨水冲过，在表面附着的雨水也会迅速扩散成为均匀的水膜，这样就不会形成分散视线的水滴，使得后视镜表面保持原有的光亮，提高行车的安全性。阅读会员限时特惠 7大会员特权立即尝鲜 如果把高层建筑的窗玻璃、陶瓷等这些建材表面涂覆一层氧化钛薄膜，利用氧化钛的光催化反应就可以把吸附在氧化钛表面的有机污染物分解为CO2和O2，同剩余的无机物一起可被雨水冲刷干净，从而实现自清洁功能。 6、抗菌塑料 在日常生活中人们是离不开塑料制品的，如卫生间设施、桌面、垃圾箱、厨房用具、家用电器的塑料外壳、食品包装袋等等，由于温度、湿度合适，非常容易滋生感染细菌。因此!，对此类材料进行抗菌处理是极其必要的。 徐瑞芬等【2】 利用纳米TiO2作为无机抗菌剂，研制抗菌广谱长效的功能塑料。结果表明：采用锐钛矿
碳纳米材料简介 第一章碳纳米材料简介 碳元素 碳在元素周期表中排第六位，是自然界分布非常广泛的元素，也是目前最重要、最使人着迷的元素之一。尽管它在地壳中含量仅为0.027%，但是对一切 生物体而言，它是最重要且含量最多的元素，人体中碳元素约占总质量的18%碳元素是元素周期表中IV A族中最轻的元素。它存在三种同位素：12C、13C、14c。 碳单质有多重同素异形体，他是迄今为止人类发现的唯一一种可以从零围到三维都稳定存在的物质。如零维的富勒烯( fullerenes )，一维的碳纳米管(carb on nano tubes )，二维的石墨烯(graphe ne)，三维的金冈寸石(diam ond) 和石墨(graphite )等。 碳纳米材料 富勒烯 富勒烯是指完全由碳原子组成的具有空心球状或管状结构的分子。1985年, Kroto，Smalley和Curl在美国莱斯大学发现了第一个富勒烯分子一一C6。。这一发现使得他们赢得了1996年的诺贝尔化学奖。G。由60个原子组成，包含20个六元环和12个五元环。这些环平面堆积在一起的方式和足球的表面结构一样，因此也也被称为足球烯。从那以后，不同分子质量和尺寸的富勒烯纷纷被制备出来。G。的发现和研究开启了对碳元素和碳纳米材料广泛、深入研究的新时代，对纳米材料科学和技术的发展起到了极大的推动作用。 由于其独特的结构，富勒烯同时具有芳香化合物和缺电子烯烃的性质，表现出很多
优良的物理和化学性质(表1-1 ) 表 60的一些基本物理和化学性质 碳纳米管（carbon nano tubes ）是由碳原子形成的管状结构分子，包括单壁碳纳米管（single-walled carbon nanotubes,SWNTs）和多壁碳纳米管（multi-walled carbon nano tubes ，MWNTs其直径从几百皮米到几十纳米， 而长径比可以上万。碳纳米管是前最重要的一维纳米材料之一。 虽然对碳纳米管发现的确切时间存在争议，但公认碳纳米管从1991年才引 起了科学界的广泛兴趣。1991年日本的Iijima 在研究富勒烯的制备过程中由于电弧产物中发现了多壁碳纳米管，并利用透射电镜证实了它的存在。随后在1993 年，他又发现了单壁碳纳米管，与此同时，Bethune等也独立观察到了单壁碳纳米管。 单壁碳纳米管可看成是由一层石墨烯沿一定角度卷曲而成的管状结构（图 1-1 ）。根据卷曲角度的不同，可以形成具有不同手性和直径的碳纳米管，因此常用两个整数（n,m）表征单壁碳纳米管的结构。当m=0时，该类单壁碳纳米管 被称为锯齿形（zigzag ）单壁碳纳米管；当n=m时，该类单壁碳纳米管被称为扶手椅形 （armchair ）单壁碳纳米管；其他的均被称为手性（chiral ）碳纳米管。单壁碳纳米管 的直径可以通过两个指数算出来。
纳米材料的制备技术及其特点 一纳米材料的性能 广义地说,纳米材料是指其中任意一维的尺度小于100nm的晶体、非晶体、准晶体以及界面层结构的材料。当小粒子尺寸加入纳米量级时,其本身具有体积效应、表面效应、量子尺寸效应和宏观量子隧道效应等。从而使其具有奇异的力学、电学、光学、热学、化学活性、催化和超导特性,使纳米材料在各种领域具有重要的应用价值。通常材料的性能与其颗粒尺寸的关系极为密切。当晶粒尺寸减小时, 晶界相的相对体积将增加,其占整个晶体的体积比例增大,这时,晶界相对晶体整体性能的影响作用就非常显著。此外,由于界面原子排列的无序状态,界面原子键合的不饱和性能都将引起材料物理性能上的变化。研究证实,当材料晶粒尺寸小到纳米级时,表现出许多与一般材料截然不同的性能,如高硬度、高强度和陶瓷超塑性以及特殊的比热、扩散、光学、电学、磁学、力学、烧结等性能。而这些特性主要是由其表面效应、体积效应、久保效应等引起的。由于纳米粒子有极高的表面能和扩散率,粒子间能充分接近,从而范德华力得以充分发挥,使得纳米粒子之间、纳米粒子与其他粒子之间的相互作用异常激烈,这种作用提供了一系列特殊的吸附、催化、螯合、烧结等性能。 二纳米材料的制备方法
纳米材料从制备手段来分,一般可归纳为物理方法和化学方法。 1 物理制备方法 物理制备纳米材料的方法有: 粉碎法、高能球磨法[4]、惰性气体蒸发法、溅射法、等离子体法等。 粉碎法是通过机械粉碎或电火花爆炸而得到纳米级颗粒。 高能球磨法是利用球磨机的转动或振动,使硬球对原料进行强烈的撞击,研磨和搅拌,将金属或合金粉碎为纳米级颗粒。高能球磨法可以将相图上几乎不互溶的几种元素制成纳米固溶体,为发展新材料开辟了新途径。 惰性气体凝聚- 蒸发法是在一充满惰性气体的超高真空室中,将蒸发源加热蒸发,产生原子雾,原子雾再与惰性气体原子碰撞失去能量,骤冷后形成纳米颗粒。由于颗粒的形成是在很高的温度下完成的,因此可以得到的颗粒很细(可以小于10nm) ,而且颗粒的团、凝聚等形态特征可以得到良好的控制。 溅射技术是采用高能粒子撞击靶材料表面的原子或分子交换能量或动量,使得靶材表面的原子或分子从靶材表面飞出后沉积到基片上形成纳米材料。常用的有阴极溅射、直流磁控溅射、射频磁控溅射、离子束溅射以及电子回旋共振辅助反应磁控溅射等技术。 等离子体法的基本原理是利用在惰性气氛或反应性气氛中
纳米材料与技术作业 1.纳米材料按维度划分，可分为几类？ (1) 0维材料quasi-zero dimensional—三维尺寸为纳米级(100 nm)以下的颗粒状物质。 (2) 1维材料—线径为1—100 nm的纤维(管)。 (3) 2维材料—厚度为1 — 100 nm的薄膜。 (4) 体相纳米材料(由纳米材料组装而成)。 (5)纳米孔材料(孔径为纳米级) 2. 详细说明纳米材料有那几大特性？这几大特性的特点是什么？为什么纳米材料具有这些特性？ (1) 表面效应：我们知道球形颗粒的比表面积是与直径成反比的，故颗粒直径越小，比表面积就会越大，因此，纳米颗粒表面具有超高的活性，在空气中金属颗粒会迅速氧化而燃烧，也正是基于表面活性大的原因，纳米金属颗粒可以看成新一代的高效催化剂，储气材料和低熔点材料； (2) 小尺寸效应：随着颗粒尺寸的量变会引起颗粒宏观物理性质的质变。特殊的光学性质：所有的金属在超微颗粒状态都呈现为玄色。尺寸越小，颜色愈黑，银白色的铂（白金）变成铂黑，金属铬变成铬黑。由此可见，金属超微颗粒对光的反射率很低，通常可低于l％，大约几微米的厚度就能完全消光。利用这个特性可以作为高效率的光热、光电等转换材料，可以高效率地将太阳能转变为热能、电能。此外又有可能应用于红外敏感元件、红外隐身技术等；特殊的热学性质：固体颗粒在超微细化后其熔点将明显降低，当颗粒小于10纳米量级时尤为明显；特殊的磁学性质：超微的磁性颗粒可以使鸽子、海豚等生物在微弱的地磁场中辨别方向，利用磁性超微颗粒具有高矫顽力的特性，可以做成高贮存密度的磁记录磁粉，大量应用于磁带、磁盘、磁卡以及磁性钥匙等；利用超顺磁性，可以将磁性超微颗粒制成用途广泛的磁性液体；特殊的力学性质：由于纳米材料具有大的界面，界面的原子排列是相当混乱的，原子在外力变形的条件下很轻易迁移，因此表现出甚佳的韧性与一定的延展性。 (3)宏观量子隧道效应：处于分子、原子与大块的固体颗粒之间的超微纳米颗粒具有量子隧道效应，例如：在知道半导体集成电路时，当电路的尺寸接近电子的波长时，电子就会通过隧道效应溢出器件，使器件无法正常工作。 3.半导体纳米材料光催化特性产生的原因是什么？为什么一些半导体纳米材料的光催化特性要远远好于非纳米结构的半导体材料？ (1)光催化特性是半导体具有的独特性能之一，在光的照射下，半导体价带中的电子跃迁到导带，从而价带产生空穴，导带中产生电子。空穴具有很强的氧化性，电子具有很强的还原性；(2)光激发和产生的电子和空穴可经历多种变化途径，其中最主要的分离和符合这两个相互竞争的过程，因此为了提高催化效率，需要加入电子或者空穴捕获剂，纳米半导体材料相比于一般的半导体材料具有更大的比表面积，因此具有更好的催化效果。 4.详细说明零维纳米材料具有哪些优良的物理化学特性？产
纳米二氧化钛的制备综述 摘要综述了纳米二氧化钛的多种制备方法和原理，比较和评述了不同方 法的优缺点。 关键词纳米二氧化钛；制备方法；原理 纳米材料以其特殊的性能和广阔的发展前景引起众多科学家们的广泛关注。纳米材料是指微粒几何尺寸在1nm～l00nm范围内的固体材料。纳米粒子是处于微观粒子和宏观粒子之间的介观系统。纳米材料以其独特的表面效应、小尺寸效应、量子尺寸效应和宏观量子效应等性质，而呈现出许多奇异的物理、化学性质，使其在众多领域具有特别重要的应用价值和广阔的发展前景。纳米二氧化钛TiO2是当前应用前景最为广阔的一种纳米材料，它是当前众多纳米材料中的“明星”。我国对纳米二氧化钛的研究已经进入产业化开发与生产阶段，其制备手段可分为物理和化学两大类。本文就采用化学方法制备纳米二氧化钛的一些方法进行总结，并对不同方法的优缺点进行比较和评述。 一气相法 1．气相合成法 气相合成法是一种传统方法。1941年德国Degussa公司率先采用气相四氯化硅氧焰水解制备自炭黑(纳米级的二氧化硅)。在20世纪80年代中后期，气相氢氧焰水解法(Aerosil法)制备纳米级TiO2开始被应用于工业生产中。其生产过程是将精制过的氢气、空气和氯化物(TIC14 )蒸汽以一定的配比进入水解炉高温水解，温度控制在18000C以上，生成TiO2的气溶胶，经过聚集冷却器停留一段时间即形成絮状大颗粒的TiO2，再经过脱酸炉脱酸(吸附在TiO2表面的HC1)后，从而得到产品，其生产原理如下： Ti+2CI4 = TiC14 TiC14 +2H2+ O2 = TiO2 + 4HCI Aerosil法的优点是：原料TiC14获得容易，可挥发，易水解，易提纯，产品无需粉碎，物质的浓度小，生成粒子的凝聚少，气相产物TiO2的表面整洁、纯度高，易控制粒径颗粒分布集中，可得到不同比表面或不同晶型的系列产品。2．气相沉积法 化学气相沉积法可沉积金属、碳化物、氧化物、氮化物、硼化物等，能在几何形状复杂的物件表面涂敷，涂层与基底结合牢固，此方法发展非常迅速。 魏培海以1200C Ti(OC4H9) 为源物质，将一定流量的氮气通入其中进行鼓泡，并作为载气将Ti(OC4H9)带入TiO2反应器，同时将一定量的氮气通入反应器，应用金属气相沉积(MOCVD)方法沉积TiO2薄膜。当基底物质维持在4000C时，在基底表面发生下列反应：Ti(OC4H9)+24 O2=TiO2+16CO2+18 H2O TiO2分子沉积在基底表面，形成金红石型的TiO2薄膜，膜的厚度可通过调节反应时间来控制，此膜具有较强的光响应性能及稳定性，平带电位与溶液的pH值有关，是较理想的光电化学修饰材料。李文军等也以Ti(OC4H9) 为原料，氧气作反应气体，高纯氮作载体，采用低压MOCVD法在单晶硅基片上制备了TiO2薄膜。通过控制基片温度制成不同构型的TiO2。孙顺明应用自制设备及MOCVD 技术，分别在高掺杂硅片和有透明导电膜玻璃的基片上生长了TiO2薄膜。另外，
纳米材料及其应用前景 摘要:21世纪，纳米技术、纳米材料在科技领域将扮演重要角色。纳米技术是当今世界最有前途的决定性技术之一。本文简要地概述了纳米材料的基本特性以及其在力学、磁学、电学、热学等方面的主要应用，并简单展望了纳米材料的应用前景。 关键词：纳米材料；功能；应用； 一、纳米材料的基本特性 所谓纳米材料是指材料基本构成单元的尺寸在纳米范围即1~100纳米或者由他们形成的材料。由于纳米材料是由相当于分子尺寸甚至是原子尺寸的微小单元组成，也正因为这样，纳米材料具有了一些区别于相同化学元素形成的其他物质材料特殊的物理或是化学特性例如：其力学特性、电学特性、磁学特性、热学特性等，这些特性在当前飞速发展的各个科技领域内得到了应用。科学家们和工程技术人员利用纳米材料的特殊性质解决了很多技术难题，可以说纳米材料特性促进了科技进步和发展。 1、力学性质 高韧、高硬、高强是结构材料开发应用的经典主题。具有纳米结构的材料强度与粒径成反比。纳米材料的位错密度很低，位错滑移和增 殖符合Frank-Reed模型，其临界位错圈的直径比纳米晶粒粒径还要大，增殖后位错塞积的平均间距一般比晶粒大，所以纳米材料中位错滑移和 增殖不会发生，这就是纳米晶强化效应。金属陶瓷作为刀具材料已有50 多年历史，由于金属陶瓷的混合烧结和晶粒粗大的原因其力学强度一直 难以有大的提高。应用纳米技术制成超细或纳米晶粒材料时，其韧性、 强度、硬度大幅提高，使其在难以加工材料刀具等领域占据了主导地位。 使用纳米技术制成的陶瓷、纤维广泛地应用于航空、航天、航海、石油 钻探等恶劣环境下使用。 2、热学性质 纳米材料的比热和热膨胀系数都大于同类粗晶材料和非晶体材料的值，这是由于界面原子排列较为混乱、原子密度低、界面原子耦合作用 变弱的结果。因此在储热材料、纳米复合材料的机械耦合性能应用方面 有其广泛的应用前景。例如Cr-Cr2O3颗粒膜对太阳光有强烈的吸收作 用，从而有效地将太阳光能转换为热能。 3、电学性质 由于晶界面上原子体积分数增大，纳米材料的电阻高于同类粗晶材料，甚至发生尺寸诱导金属——绝缘体转变（SIMIT）。利用纳米粒子的 隧道量子效应和库仑堵塞效应制成的纳米电子器件具有超高速、超容量、超微型低能耗的特点，有可能在不久的将来全面取代目前的常规半导体 器件。2001年用碳纳米管制成的纳米晶体管，表现出很好的晶体三极管 放大特性。并根据低温下碳纳米管的三极管放大特性，成功研制出了室 温下的单电子晶体管。随着单电子晶体管研究的深入进展，已经成功研 制出由碳纳米管组成的逻辑电路。
纳米技术知识材料 一、纳米（nano meter,nm）： 一种长度单位，一纳米等于十亿分之一米，千分之一微米。大约是三、四个原子的宽度。 二、纳米科学技术（nanotechnology）： 纳米科学技术是用单个原子、分子制造物质的科学技术。纳米科学技术是以许多现代科学技术为基础的科学技术，它是现代科学（混沌物理、量子力学、介观物理、分子生物学）和现代技术（计算机技术、微电子和扫描隧道显微技术、核分析技术）结合的产物，纳米科学技术又将引发一系列新的科学技术，例如纳米电子学、纳米材料学、纳米机械学等。纳米科学技术被认为是世纪之交出现的一项高科技。 三、纳米材料（nano material）与纳米粒子（nano particle）： 纳米材料又称为超微颗粒材料，由纳米粒子组成。纳米粒子也叫超微颗粒，一般是指尺寸在1～100nm间的粒子，是处在原子簇和宏观物体交界的过渡区域，从通常的关于微观和宏观的观点看，这样的系统既非典型的微观系统亦非典型的宏观系统，它具有表面效应、小尺寸效应和宏观量子隧道效应。当人们将宏观物体细分成超微颗粒（纳米级）后，它将显示出许多奇异的特性，即它的光学、热学、电学、磁学、力学以及化学方面的性质和大块固体时相比将会有显著的不同。 四、几种典型的纳米材料： a) 纳米颗粒型材料： 应用时直接使用纳米颗粒的形态称为纳米颗粒材料。被称为第四代催化剂的超微颗粒催化剂，利用甚高的比表面与活性可以显著得提高催化效率，例如，以微径小于微米的镍和钢-锌合金的超微颗粒为主要成分制成的催化剂可使有机物氯化的效率达到传统镍催化剂的10倍；超细的铁微粒作为催化剂可以在低温将二氧化碳分解为碳和水，超细铁粉可在苯气相热分解中起成核作用，从而生成碳纤维。 录音带、录像带和磁盘等都是采用磁性粒子作为磁记录介质。随着社会的信息化，要求信息储存量大、信息处理速度高，推动着磁记录密度日益提高，促使磁记录用的磁性颗粒尺寸趋于超微化。目前用金属磁粉（20）纳米左右的超微磁性颗粒）制成的金属磁带、磁盘，国外已经商品化，其记录密度可达4’106～4’107位/厘米（107～108位/英寸），即每厘米可记录4百万至4千万的信息单元，与普通磁带相比，它具有高密度、低噪音和高信噪比等优点。
第一章 1 关键词： Nanomaterials Scanning Tunneling Microscope (STM) Zero (one, two, three)-dimension Size Effect - Kubo theory (1) Quantum size effect (2) Small size effect Surface effect Coulomb blockade and Quantum tunneling effect Dielectric confinement effect 纳米材料 扫描隧道显微镜（STM） 零（一，二，三）维 尺寸效应 - 久保理论 （1）量子尺寸效应 （2）小尺寸效应 表面效应 库仑阻塞和量子隧道效应 介电限域效应 2 名词解释： （1）Nano” –From the Greek word for “dwarf” and means for 10-9, or one billionth. In this case it refers to 10-9 meters, or 1 nanometer (nm). 1 nm is about 3 atoms long. （2）Nanomaterials – Materials having a characteristic length scale less than about a hundred nanometers. （1）纳米“ - 从希腊字为”矮“和10-9，或十亿分之一的手段。在这种情况下，它指的是10-9米，或1纳米（nm）。 1纳米是关于三原子长。 （2）纳米材料- 材料特征长度有规模比大约一百纳米以下。 这可能是一个尺度粒径，粒度，层厚，或在电子芯片导体线宽。 1. Size Effect - Kubo theory（课堂笔记）:尺寸效应：当纳米材料组成的尺寸如晶粒的尺寸，第二相离子的尺寸减小时，纳米材料的性能会发生变化，当组成相的尺寸小到于某一临界尺寸相当时，材料的性能将发生明显的变化或突变 2. snall size effect 小尺寸效应：随着颗粒尺寸的量变，在一定条件会引起颗粒性质的质变，由于颗粒尺寸变小所引起的宏观物理性质的变化就成为小尺寸效应 3. Coulomb blockade and Quantum tunneling 库伦阻塞量子隧穿效应：体系进入纳米体系是电荷量子化的，即充电和放电过程是不连续的，充入一个电子所需的能量Ec=e2/kc这个能量就成为库伦阻赛能，这就导致了一个销体系的充放电过程，电子不能集体传输，惹事一个个单电子的传输。通常把销体系这种单电子输运行为成为库伦阻赛效应。如果两个量子点通过一个结连接起来，一个量子点上的单个电子穿过能垒到另一个电子上的行为就成为量子隧穿效应。 4.Quantum size effect 量子尺寸效应：电子的能量被量子化，形成分离的电
深圳大学课程教学大纲 课程编号: 23200001 课程名称: 纳米科学与技术 开课院系: 材料学院 制订(修订)人: 曹培江 审核人: 批准人： 2007年9月3日制(修)订
课程名称:纳米材料与技术 英文名称: Nano science & technology 总学时: 36 其中：实验课0 学时 学分: 2 先修课程:大学物理、普通化学、材料科学基础 教材:《纳米材料和纳米结构》—张立德，牟季美著；科学出版社 参考教材:《纳米科学与技术》—白春礼著；云南科技出版社《纳米材料制备技术》—王世敏主编；化学工业出版社《纳米技术与纳米武器》—赵冬等编著；军事谊文出版社 授课对象：非材料专业大学本科生 课程性质: 综合选修（全校公选课） 教学目标: 1. 了解纳米科技的内涵、实用目的及其终极目标。 2. 简单了解用于纳米材料制备的各种仪器。纳米微粉的科学制备分类方法应该是气相法、液相法、固相法。其中气相法包括电阻加热法、高频感应加热法、等离子体加热法、电子束加热法、激光加热法、通电加热蒸发法、流动油面上真空沉积法、爆炸丝法、热管炉加热化学气相反应法、激光诱导化学气相反应法、等离子体加强化学气相反应、化学气相凝聚法、溅射法等。其中液相法包括沉淀法、水解法、喷雾法、溶剂热法(高温高压)、蒸发溶剂热解法、氧化还原法(常
压)、乳液法、辐射化学合成法、溶胶—凝胶法等。其中固相法包括热分解法、固相反应法、火花放电法、溶出法、球磨法等。 3. 了解用于纳米材料测试的各种仪器。其中了解扫描电子显微镜(SEM)、透射电子显微镜(TEM)和扫描隧道显微镜(STM)。 4. 了解纳米科技的国际环境及纳米材料的主要现实应用领域。 通过本门课程的学习，要求学生对纳米材料与技术所涉及的相关领域有初步认知。使学生开阔视野，拓宽知识面，改善知识结构，增强适应能力，激发学习兴趣，破除对高技术的神秘感，树立攀登科技高峰的信心。 课程简介: 纳米材料与技术是一门基础研究与应用研究紧密联系的新型学科。本课程紧跟当代纳米技术发展的最新成就和前沿，系统阐述纳米技术的有关概念、应用、国内外研究开发战略和中国的纳米产业，介绍国内外纳米行业研究开发的最新资料和信息，特别是当前国内外在纳米领域的新成果、新观点、新理论和产业化实例，具有最新实时的特点，为学生提供新思路和应用信息。 教学内容： 1.加深长度概念的理解。 （1）展示一组题为“无限”的图片(42张) （2）了解长度单位：光年、公里、米、毫米、微米、纳米、皮米、飞米等。 2. 碳纳米管
纳米二氧化钛 1引言 纳米微粒是指尺寸为纳米量级的超微颗粒,它的尺度大于原子簇,小于通常的微粒,粒径一般在1～100 nm之间。由于纳米微粒有小尺寸效应、量子尺寸效应、表面效应和宏观量子隧道效应等基本特性,使得纳米微粒以及纳米材料具有常规微粒和常规材料没有的独特的光、电、磁、热以及催化性能。自从1984年Gleiter 等人关于纳米材料的报道以来,纳米材料以其优异的性能引起人们的普遍关注。 纳米TiO2 是一种附加值很高的功能精细无机材料。因其具备良好的耐侯性、耐化学腐蚀性、抗紫外线能力强、透明性优异等特点,被广泛应用于汽车面漆、感光材料、光催化剂、化妆品、食品包装材料、陶瓷添加剂、气体传感器及电子材料等。但由于纳米TiO2 大的比表面及较多的表面空键,在制备和应用过程中极易发生团聚,使其优异的性能得不到充分的发挥。近年来人们关于纳米TiO2 改性方面的工作已经做了很多,达到了改性的目的,现综述纳米TiO2 的性质与改性的关系及改性的方法和机理。 2TiO2 的基本结构 TiO2 是金属钛的一种氧化物,其分子式为TiO2。根据其晶型,可分为板钛矿型、锐钛矿型和金红石型三种。其中锐钛矿型TiO2 属于四方晶系,其晶格参数a 0 = 3. 785 ! , c0 = 9. 514 ! 。图1为锐钛矿型TiO2 的单元结构,钛原子处于钛氧八面体的中心,其周围的六个氧原子都位于八面体的棱角处,有四个共棱边,也就是说，锐钛矿型的单一晶格有四个TiO2 分子。锐钛型TiO2 的八面体呈明显的斜方晶型畸变, Ti—O键距离均很小且不等长,分别为1. 937 ! 和1. 964 ! , 这种不平衡使TiO2分子极性很强,强极性使TiO2 表面易吸附水分子并使水分子极化而形成表 1
外文资料 Nanotechnology and Micro-machine 原文(一): Nanomaterial Nanomaterials and nanotechnology have become a magic word in modern society. Nanomaterials represent today’s cutting edge in the development of novel advanced materials which promise tailor-made functionality and unheard applications in all key technologies. So nanomaterials are considered as a great potential in the 21th century because of their special properties in many fields such as optics, electronics, magnetics, mechanics, and chemistry. These unique properties are attractive for various high performance applications. Examples include wear resistant surfaces, low temperature sinterable high-strength ceramics, and magnetic nanocomposites. Nanostructures materials present great promises and opportunities for a new generation of materials with improved and marvelous properties. It is appropriate to begin with a brief introduction to the history of the subject. Nanomaterials are found in both biological systems and man-made structures. Nature has been using nanomaterials for millions of years,as Disckson has noted: “Life itself could be regarded as a nanophase system”.Examples in which nanostructured elements play a vital role are magnetotactic bacteria, ferritin, and molluscan teeth. Several species of aquatic bacteria use the earth’s magnetic field to orient thenselves. They are able to do this because they contain chains of nanosized, single-domain magnetite particles. Because they have established their orientation, they are able to swim down to nutriments and away from what is lethal to them ,oxygen. Another example of nanomaterials in nature is that herbivorous mollusks use teeth attached to a tonguelike organ, the radula, to scrape their food. These teeth have a complex
纳米材料与技术 (2007-05-15 16:05:21) 转载 1959年，美国著名物理学家(1965年诺贝尔物理学奖获得者)费因曼教授(R．P．Feynman)曾指出：“如果有一天人类能够按人的意志安排一个原子和分子，那将会产生什么奇迹?”今天，这个美好的愿望已经开始走向现实。目前，人 类已经能够制备出包括有几十个到几万个原子的纳米颗粒，并把它们作为基本单元构造一维量子线、二维量子面和三 维纳米固体，创造出相同物质传统材料完全不具备的奇特 性能。这就是面向21世纪的纳米科学技术。 0．2纳米材料的研究历史 人类对物质的认识分为宏观和微观两个层次。宏观是指研究的对象尺寸很大，并且下限有限，上限无限(肉眼可见的是最小宏观，而上限是天体、星系)。到目前为止，人类对宏观物质结构及运动规律已经有相当的了解，一些学科 领域都已建立，如力学、地球物理学、天体物理学、空间 科学等。微观指原子、分子，以及原子内部的原子核和电子，微观有上限而无法定义下限。
19世纪末到20世纪初，人类对微观世界的认识已延伸到一定层次，时间上达到纳秒、皮秒和飞秒数量级。建立了相应的理论，例如原子核物理、粒子物理、量子力学等。 相对而言，在原子、分子与宏观物质的中间领域，人类的认识还相当肤浅，被誉为有待开拓的“处女地”。近20年以来，人类已经发现，在微观到宏观的中间物质出现了许多既不同于宏观物质，也不同于微观体系的奇异现象。下面对纳米材料的研究历史作简要介绍。 1 000年以前。当时，中国人利用燃烧的蜡烛形成的烟雾制成碳黑，作为墨的原料或着色染料，科学家们将其誉为最早的纳米材料。中国古代的铜镜表面防锈层是由Sn02颗粒构成的薄膜，遗憾的是当时人们并不知道这些材料是由肉眼根本无法看到的纳米尺度小颗粒构成。 1861年，随着胶体化学(colloidchemistry)的建立，科学家们开始对1—lOOnm的粒子系统进行研究。但限于当时的科学技术水平，化学家们并没有意识到在这样一个尺寸范围是人类认识世界的一个崭新层次，而仅仅是从化学角度作为宏观体系的中间环节进行研究。 20世纪初，有人开始用化学方法制备作为催化剂使用的铂超微颗粒。