1.什么是微波?
    微波是指频率在300MHz~300GHz 即波长在1m~1mm 范围内的电磁波，位于电磁波谱的红外辐射和无线电波之间[1]. 微波分米波、厘米波和毫米波。米波的频率范围在300~3000MHz,主要用于通讯和电视广播。厘米波的频率范围在3000~30000MHz 主要用于雷达、卫星通讯，无线电导航。毫米波的频率范围在30000~300000MHz 用于卫星通讯。目前国际上广泛使用的微波加热频率为915MHz和2450MHz。加热频率为915MHz（波长约32.97cm）的微波炉（也称为微波灶）主要在产业和工业部作烘烤、干燥、消毒用；加热频率为2450MHz（波长约12.24cm）的微波炉主要作家庭烹调用。
     2.微波加热的特点?
    微波加热是通过微波与物质相互作用而转变的。在电磁场的作用下，物质中微观粒子能产生极化，即电子极化(原子核周围电子的重新排布)、原子极化(分子内原子的重新排布)、取向极化(分子永久偶极的重新取向)和空间电荷极化(自由电荷的重新排布)。与传统的外部加热方式相比，微波加热是使被加热物体本身成为发热物体，称之为整体加热方式，不需要热传导的过程，因此能在短时间内过到均匀加热。物料介质由极性分子和非极性分子组织，在电磁场作用下，这些极性分子从随机分布状态转为依电场方向进行取向排列。而在微波电磁场作用下，这些取向运动以每秒数十亿次的频率不断变化，造成分子的剧烈运动与碰撞摩擦，从而产生热量，达到电能直接转化为介质内的热能[2]。可见，微波加热是介质材料自身损耗电场能量而发热。而不同介质材料的介电常数εr和介质损耗角正切值tgδ是不同的，故微波电磁场作用下的热效应也不一样。由极性分子所组织的物质，能较好地吸收微波能。水分子呈极强的极性，是吸收微波的最好介质，所以凡含水分子的物资必定吸收微波。另一类由非极性分子组成,它们基本上不吸收或很少吸收微波，这类物质有聚四氟乙烯、聚丙烯、聚乙烯、聚砜等、塑料制品和玻璃、陶瓷等，它们能透过微波，而不吸收微波。这类材料可作为微波加热用的容器或支承物，或做密封材料。微波对不同物质有不同的作用，含有极性的物质容易吸收微波能量而发热。不含极性则很少吸收微波加热。微波对不同介质特性的物料有不同的作用。因为水分子对微波和吸收最好，所以含水量高的部位吸收微波功率多于含水量较低的部位，这就是微波选择性加热的特点。微波加热被认为是很有前途的体加热方法，它具有加热速度快，节能高效，易于控制，清洁卫生，选择性加热、安全无害的优点。它能够提高反应速率，缩短反应时间。微波技术在材料制备中被认为是高效、简便的手段，它为短时间内快速合成纳米材料提供了可能性。
     1946年，美国雷声公司的研究员斯潘瑟发现微波溶化了糖果。事实证明，微波辐射能引起食物内部的分子振动，从而产生热量。1947年，第一台微波炉问世。
      3.微波在材料合成尤其是纳米材料合成中的应用      
      自从1986年微波技术首次在液相有机合成中应用以来[3-4]，微波加热技术在有机合成中的应用迅速增加[5-8]。相比之下，微波在无机纳米材料合成中的应用研究却较少，因此急需更进一步的研究。目前已经用微波加热法制备了多种形态的金属单质，氧化物，复合氧化物，硫族半导体以及有机无机复合材料[9-25]。
     S. Komarneni[26]等利用一步微波辅助溶剂热法在160~170度反应3小时制备了均一尺寸单分散的银纳米颗粒。乙二醇和dodecylthiol的相对比率显著的影响颗粒的成核，生长、尺寸、形态和排列。控制它们的比率还可以形成Ag2S超晶格。Zhu[27-29]等结合室温离子液体和微波辅助加热的优点，还原TeO2合成出了单质Te的纳米棒，实验发现微波和室温离子液体对棒的形成有重要的影响；在离子液体中利用MnCl2•4H2O 和KMnO4在90度反应1个小时就获得了Cryptomelane的纳米针；而在离子液体中利用Co(CH3COO)2•4H2O和H2C2O4 、NaOH在90度反应10分钟得到草酸钴的纳米棒，高温煅烧，草酸钴分解得到形貌保持Co3O4的纳米棒。A.Gedanken[30]等利用硝酸Ln(III) (Ln = La, Ce, Nd, Sm, Eu, Gd 和Tb)和NH4H2PO4 在pH为1.8–2.2的条件下微波辅助加热20分钟，得到了Ln(III) PO4•nH2O的纳米棒和纳米线。微波反应环境有利于产物各向异性的生长形成一维的纳米结构。
      M. S. El-Shall[31]等报道了利用微波辅助的方法合成出了尺寸分布特别窄，形态均一，晶化度高，并且排列成超晶格结构的ZnS,ZnSe, CdS,和 CdSe的纳米棒纳米线，获得的一维纳米结构只有几个纳米宽，长度达到几百个纳米。通过调节反应时间从30秒到60秒，一分钟到两分钟不等，可以观察到纳米线是从小的球形晶核到短的排列的棒再到长的纳米线的自组装。一维纳米结构的量子尺寸效应被观察到。而且均一的纳米棒和线自发的组装成二维的超晶格。Zhu[32-33]等在乙二醇中体系中，以微波辅助加热的手段，通过金属粒子或金属硫化物的合成与丙烯酰胺单体的聚合同时进行，得到了在聚丙烯酰胺中均匀分散的Pt，Cu，Ag，Ag2S等纳米复合物。
     国内做微波辅助合成的比较少.很多都采用普通的家用微波加热器.家用微波炉不能控制温度是最大的缺点.
      4.总结      
       微波以体加热的方式进行,升温速度快,可以加快反应速率,缩短反应时间,提高反应选择性和产率,节省能源.
      利用微波辅助合成纳米材料,一般可以在30秒到10分钟内完成整个反应过程.利用微波结合溶剂热,微乳液等其他合成方法,往往可以得到一些新奇的结果.而且,利用微波辅助合成,比较容易得到一维的纳米结构.
      微波只对少数能够与微波产生作用的溶剂和物质有特别的作用.但是作为一种加热的方法,的确有其存在的价值.只要反应中间存在热效应,就可以采用微波加热.普通水热反应或油浴加热,几个小时或者十几个小时才能完成的反应,利用微波可以在几分钟到几十分钟内完成.
      不足之处在于需要特别的实验设备,反应机理的研究不深入.也很难深入研究反应机理.
      材料的最终目的在于性能在于应用.所以无论那种合成方法那种合成手段只是一种选择,只能是一种方法,一种手段而不是其它.为了达到合成出高质量产物的目的,应该综合应用多种方法.

Figure 1. 微波
Figure 2. TEM of (a)Silver Nanocrystals; (b) silver sulfide superstructures (c) Te nanorods;.(d,e) Cryptomelane; (f) cobalt oxalate.
Figure 3. TEM of ZnS (a) rods, (b) wires, (c) ZnSe wires, (d) CdSe rods; (e) PAM-Pt nanocomposite , (f) PAM-Cu nanocomposite, (g) PAM-Ag nanocomposite, (h)PAM-Ag2S nanocomposite. Higher resolution images are shown in the insets.

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There are three main uses of zeolites in industry: catalysis, gas separation and ion exchange.
 

• Catalysis: Zeolites are extremely useful as catalysts for several important reactions involving organic molecules. The most important are cracking, isomerisation and hydrocarbon synthesis. Zeolites can promote a diverse range of catalytic reactions including acid-base and metal induced reactions. Zeolites can also be acid catalysts and can be used as supports for active metals or reagents.
  Zeolites can be shape-selective catalysts either by transition state selectivity or by exclusion of competing reactants on the basis of molecular diameter. They have also been used as oxidation catalysts. The reactions can take place within the pores of the zeolite, which allows a greater degree of product control.
  The main industrial application areas are: petroleum refining, synfuels production, and petrochemical production. Synthetic zeolites are the most important catalysts in petrochemical refineries.
   
• Adsorption: Zeolites are used to adsorb a variety of materials. This includes applications in drying, purification, and separation. They can remove water to very low partial pressures and are very effective desiccants, with a capacity of up to more than 25% of their weight in water. They can remove volatile organic chemicals from air streams, separate isomers and mixtures of gases. A widely used property of zeolites is that of gas separation. The porous structure of zeolites can be used to "sieve" molecules having certain dimensions and allow them to enter the pores. This property can be fine tuned by variating the structure by changing the size and number of cations around the pores.  Other applications that can take place within the pore include polymerisation of semi conducting materials and conducting polymers to produce materials having unusual physical and electrical attributes.
   
• Ion exchange: Hydrated cations within the zeolite pores are bound loosely to the zeolite framework, and can readily exchange with other cations when in aqueous media. Applications of this can be seen in water softening devices, and the use of zeolites in detergents and soaps. The largest volume use for zeolites is in detergent formulations where they have replaced phosphates as water-softening agents. They do this by exchanging the sodium in the zeolite for the calcium and magnesium present in the water. It is even possible to remove radioactive ions from contaminated water.

For more information about the removal of substances by zeolites click here.

From a practical point of view, zeolite can be adapted for a variety of uses:
 

Agriculture:

• Odour control
• Confined animal environmental control
• Livestock feed additives

In Eastern Europe, Japan and Cuba zeolites have been traditionally used in agriculture. About a 5% addition to livestock rations reduces ammonia and odour emissions, improves feed utilisation, assists with mycotoxin absorption and may contribute trace elements. Several years ago NASA used nutrient loaded zeolites as slow release fertilisers.

Horticulture:

• Nurseries, Greenhouses
• Floriculture
• Vegetables/herbs
• Foliage
• Tree and shrub transplanting
• Turf grass soil amendment 
• Reclamation, revegetation, landscaping
• Silviculture (forestry, tree plantations)
• Medium for hydroponics growing
   

• Ammonia filtration in fish hatcheries
• Biofilter media

In a fish farm the load of the water with fish can be very high. This results in quick pollution of the water and as a result the concentrations of toxic substances can increase rapidly. Therefore extensive water purification is necessary. The zeolites can be used in various steps of the purification process: as a secondary filtration unit after biological purification and/or aeration; as a support material for bacteria; as a filter medium for the removal of solid and suspended particles and removal of unwanted ions at the same time.

Household products:

• Household odour control
• Pet odour control

Domestic uses relate primarily to the odour and liquid adsorbing characteristics of zeolite. A range of gases including formaldehyde, hydrogen sulphide has been shown to be adsorbed by zeolite.
In the USA, zeolite is routinely added to small air filters to adsorb such gases and reduce allergy problems. It can be used to dry sports shoes, reduce moisture in wardrobes and is commonly used to adsorb cigarette odours. A very useful carpet cleaner had zeolite as its base material.
The most common use for zeolite around the home is as kitty litter and as a fat absorber for barbecues. It is also used in fish tanks to adsorb ammonia. When fully utilised the spent product makes an ideal addition to composts where it will assist in conditioning and eventually contribute to soil moisture and nutrient holding capacity.

• Absorbents for oil and spills
• Gas separations

Industrial uses focus on the liquid and vapour absorbing characteristics of zeolite. It can be an ideal granular oil/chemical spill cleanup; it is inert and safe to use.

Radioactive Waste:

• Site remediation/decontamination

Water treatment:

• Water filtration
• Heavy metal removal
• Swimming pools

Wastewater treatment:

• Ammonia/ammonium removal in municipal sludge/wastewater
• Heavy metal removal
• Septic leach fields

International Zeolite Association

Federation of European Zeolite Assocations

British Zeolite Association

Czech Zeolite Association

French Zeolite Association

Italian Zeolite Association

Dutch Zeolite Association

Atlas of Zeolite Structures

Verified Synthesis of Zeolitic Materials

X-Ray Diffraction Patterns