Abstract:
The present invention disclosed use of lactam as a solvent in the preparation of nanomaterials by precipitation method, sol-gel method or high temperature pyrolysis. These methods are able to recycle lactam solvent, which meet requirements of environmental protection.

Description:
TECHNICAL FIELD 
     This invention belongs to the technical field of nanomaterials, which relates to use of lactam as a solvent in preparation of nanomaterials. 
     BACKGROUND ART 
     Nanomaterials refer to those with at least one dimension in three-dimensional space within the nanoscale range (1-100 nm) or materials constituted by them as basic units. Nano-size effects often exhibit melting points and magnetic, optical, thermal conduction and electrical conduction characteristics which are different from bulk materials, so they can be widely used in optoelectronic materials, ceramic materials, sensors, semiconductor materials, catalytic materials, medical treatment and other fields. 
     Currently, the methods for synthesis of nanomaterials mainly include three categories: solid phase method, liquid phase method and gas phase method. Since nanomaterials have high surface energy, it is hard for nanomaterials obtained by various solid-phase synthesis methods, including high-temperature calcination and mechanical milling, to reach the characteristics of ultrafine size, narrow size distribution and high dispersibility. Gas phase method is an important method for synthesis of ultrafine nanopowder, for example, vapor deposition method is the technology most widely used in semiconductor industry to deposit a variety of nanomaterials, but this process has higher equipment requirements, and deposition of nanoparticles in matrix is often accompanied with permanent agglomeration of the nanoparticles, so it is difficult to ensure their monodispersity. Compared to the former two methods, liquid phase method can prepare nanomaterials of various morphologies and sizes by selecting appropriate solvents and additives. Currently, due to low cost and wide sources, water is the most commonly used solvent in liquid phase method. However, water has high polarity, the raw materials for synthesis of nanomaterials react fast in this medium, and it is very difficult to simply use water as the solvent for controlled synthesis of ideal nanomaterials, so improvement is generally made by adding surfactants and changing synthesis process. In almost all the methods currently reported in literatures and patents for synthesis of nanomaterials of monodispersity, small size and narrow distribution with water solvent system, surfactants or surfactant-like additives are used. These surfactants or additives not only increase the cost for preparation of nanomaterials, but also inevitably remain on the surface of nanomaterials, thus affecting their subsequent use, for example, residues may intoxicate some catalytic nanomaterials, affect biocompatibility of medical nanomaterials, etc. 
     Recently, a literature has reported use of organics as the solvents for synthesis of nanomaterials, such as the “alcohol-thermal method” using ethanol, ethylene glycol, propylene glycol, polyethylene glycol, etc. as the solvents and high-temperature pyrolysis, with oleic acid as the solvent, of metal oleate, carbonyl salts or acetylacetone to prepare oxides, but these methods still require to use surfactants or expensive organic metal salts, and even some synthetic routes need to consume organic solvents to provide oxygen required to produce oxides, which is not conducive to application of these methods [see specific literature: Magnetite Nanocrystals: Nonaqueous Synthesis, Characterization, and Solubility, Chem. Mater 2005, 17, 3044-3049]. 
     Lactam is an organic compound containing amide groups in cycles, for its derivatives, some nitrogen atoms and hydrogen on carbon can be substituted by other groups, among which, butyrolactam (also called α-pyrrolidone) containing four carbon atoms is liquid at room temperature and a commonly used high-boiling-point polar solvent in organic systhesis. Recently, Gao, et al, has synthesized super paramagnetic ferroferric oxide &lt;20 nm in size with carbonyl iron and ferric trichloride in butyrolactam solvent [see specific literature: One-Pot Reaction to Synthesize Water-Soluble Magnetite Nanocrystals, Chem. Mater., Vol. 16, No. 8, 2004; Preparation of Water-Soluble Magnetite Nanocrystals from Hydrated Ferric Salts in 2-Pyrrolidone: Mechanism Leading to Fe 3 O 4 , Angew. Chem. Int. Ed. 2005, 44, 123-126]. Butyrolactam used in this method itself is a highly toxic solvent, which brings great threat to production safety and environmental protection. More importantly, butyrolactam has a strong coordination effect and can be firmly adsorbed on the surface of nanomaterials, which will certainly affect the subsequent use of nanomaterials containing toxic components, especially in medical treatment, health, food and other fields. In addition, other literatures were restricted to synthesis of nano ferroferric oxide with butyrolactam as the solvent, but not investigated other oxides, hydroxides and metal nanomaterials. 
     Among lactams, except butyrolactam, cyclic lactams containing 5 or more carbon atoms in cycles are solid at room temperature, and the melting point increases with the number of carbon atoms, for example, the melting point was 39° C. for valerolactam, 68° C. for caprolactam and up to 153° C. for laurolactam, so it is difficult to think about through butyrolactam that lactams containing 5 or more carbon atoms should be used as the solvents for organic synthesis, and moreover, there is no report on use of them alone as the solvents for synthesis of nanomaterials. Such substances have the structures similar to that of butyrolactam, and at temperature higher than their melting points, they have relatively strong polarity, but weaker than the polarity of water, so they can not only guarantee certain solubility of raw materials for synthesis of nanomaterials in the solvents, but also slow down the reactions, thus they are a kind of ideal solvents for synthesis of nanomaterials. Most importantly, lactam&#39;s amide groups have a coordination effect and can play a role similar to surfactant, so no other surfactants are required for synthesis of nanomaterials when using this solvent. Furthermore, lactam derivatives contains two amide groups in the cycles, for example, succinimide, glutarimide, adipimide also have similar characteristics. Therefore, lactams containing 5 or more carbon atoms, above their melting points, can substitute other common solvents for preparation of nanomaterials. 
     SUMMARY OF THE INVENTION 
     For shortages of solid phase method, gas phase method and liquid phase method in existing techniques that are not conducive to preparation of nanomaterials with ultrafine size, narrow size distribution and high dispersibility, especially for the high toxicity of butyrolactam, which affects subsequent use of the synthetic nanoparticles, the present invention is to provide use of lactams as the solvents for preparation of nanomaterials. 
     The technical solutions of this invention are as follows: 
     This invention provides use of lactams as solvent in the synthesis of nanomaterials. 
     The lactam is one or more of substances selected from cyclic amides or cyclic amide derivatives. 
     The general structural formula of the mentioned cyclic amides is: 
     
       
                 
         
             
             
         
      
     
     From valerolactam, caprolactam, oenantholactam, 2-azacyclononanone, nonanoylamide, caprinlactam, undecanoylamide, laurolactam, glutarimide or adipimide, in which caprolactam, laurolactam, glutarimide or adipimide are preferred, and caprolactam is more preferred. 
     The general structural formula of the mentioned cyclic amide derivatives is: 
     
       
                 
         
             
             
         
      
     
     R is a substance selected from hydrogen, halogen, alkyl, hydroxy, alkoxy or acyl, wherein: halogen is selected from fluorine, chlorine, bromine or iodine; alkyl is selected from methyl, ethyl or propyl; alkoxy is selected from methoxy, ethoxy or propoxy; acyl is selected from acetyl or propionyl. 
     The cyclic amide derivatives are selected from N-methylvalerolactam, N-methylcaprolactam, N-vinylcaprolactam or N-methoxycaprolactam, and N-methylcaprolactam is preferred. 
     The nanomaterials refer to substances containing inorganic particles with 1 nm&lt;particle size≦100 nm; the content of the inorganic particles is no less than 0.01%; the inorganic particles are mixtures composed of one or more of substances selected from hydroxides, oxides, sulfides, metals or inorganic salts. 
     The hydroxides refer to water-insoluble or slightly water-soluble inorganic compounds formed by one or more than one metal elements and hydroxyl, preferably mixtures composed of one or more of substances further selected from Ni(OH) 2 , Mg(OH) 2 , Al(OH) 3 , Nd(OH) 3 , Y(OH) 3 , Mg—Al hydrotalcite or Zn—Al hydrotalcite. 
     The oxides refer to water insoluble or slightly soluble inorganic compounds formed by one or more metal elements or metalloid elements and oxygen, preferably mixtures composed of one or more of substances further selected from Ag 2 O, ZnO, Cu 2 O, Fe 3 O 4 , SiO 2 , MgAl 2 O 4  or CaTiO 3 , preferably from Ag 2 O, ZnO, Cu 2 O or Fe 3 O 4 . 
     The sulfides are the water insoluble or slightly soluble inorganic compounds formed by binding metal elements or metalloid elements with sulfur, selenium, tellurium, arsenic or antimony, preferably mixtures composed of one or more of substances further selected from CuS, ZnS, CdS, CdSe, CdTe, WSe 2 , CuTe, CoAs 2  or GaAs, preferably ZnS, CdS, CdSe or CdTe. 
     The metals are water insoluble or slightly soluble substances composed of one or more of metal elements selected from Group IIIA, IVA, IB, IIB or VIII in the periodic table of elements, preferably are alloys or mixtures composed of one or more of substances selected from Fe, Ni, Cu, Ag, Pd, Pt, Au or Ru, preferably from Cu, Ag, Au, Pd or Cu—Ag alloy. 
     The inorganic salts refer to water insoluble or slightly soluble inorganic compounds formed by binding positive ions of metal elements with carbonate, sulfate, silicate or halogen negative ions, preferably mixtures composed of one or more of substances selected from CaCO 3 , MgCO 3 , BaSO 4 , CaSiO 3 , AgCl, AgBr or CaF 2 , preferably from MgCO 3 , BaSO 4 , AgCl or CaF 2 . 
     This invention also provides a method of using lactams as the solvents for preparation of nanomaterials. Lactams can partly or completely substitute currently commonly used solvents, including water, alcohol, polyhydric alcohols with molecular weight no higher than 5000, oleic acid and α-pyrrolidone, for preparation of various nanomaterials. 
     The methods for the lactam as a solvent for synthesis of nanomaterials include precipitation method, sol-gel method or high temperature pyrolysis. 
     The precipitation method for synthesis of nanomaterials includes the following steps: add 0.01-100 weight parts of precursor and 100 weight parts of lactam into the reactor and stir at 80-200° C. for 0.1-2 hr to make the precursor fully dissolved or dispersed in the molten lactam solvent, when stirring, add 0.05-50 weight parts of precipitant for sufficient precipitation reaction, with the reaction temperature of 80-250° C. and the reaction time of 0.1-200 hr, and obtain the nanomaterials after washing with water, separation and drying. 
     The lactam solvent has a purity ≧60% and moisture ≦30%. 
     The precursor is selected from soluble inorganic salts formed by binding metal cations with halogen, nitrate, nitrite, sulfate, sulfite or carbonate anions, further from MgCl 2 .6H 2 O, Nd(NO 3 ) 3 .6H 2 O, Y(NO 3 ) 3 .6H 2 O, AlCl 3 .9H 2 O, Al 2 (SO 4 ) 3 .18H 2 O, ZnCl 2 , AgNO 3 , CuSO 4 .5H 2 O, FeCl 2 .4H 2 O, FeCl 3 .6H 2 O, Cd(NO 3 ) 2 .2H 2 O, BaCl 2  or PdCl 2 ; or from organic compounds containing metals or metalloids, further from zinc acetate, carbonyl iron, iron acetylacetonate, iron oleate, butyl titanate or tetraethyl orthosilicate. 
     The precipitant is selected from alkali metals, alkali metal oxides, alkali metal hydroxides, alkali metal organic salts, ammonia and compounds able to release ammonia by pyrolysis, soluble inorganic salts formed by metal elements and halogen elements, soluble inorganic salts formed by metal elements and chalcogens, soluble inorganic salts formed by metal elements and carbonate, or soluble inorganic salts formed by metal elements and sulfate; in which, alkali metals are further selected from Li, Na or K; alkali metal oxides are further selected from Na 2 O, K 2 O, Na 2 O 2  or K 2 O 2 ; alkali metal hydroxides are further selected from NaOH or KOH; alkali metal organic salts are further selected from sodium methoxide, sodium ethoxide, sodium phenoxide, potassium oleate, sodium lactam or potassium caprolactam; ammonia and compounds able to release ammonia by pyrolysis are further selected from ammonia gas, ammonia water, urea, ammonium carbonate or ammonium bicarbonate, preferably ammonia water; soluble inorganic salts formed by metal elements and halogen elements are further selected from NaCl, KCl, MgCl 2 , CaCl 2 , AlCl 3 .6H 2 O, FeCl 2 .4H 2 O or FeCl 3 .6H 2 O, preferably NaCl or KCl; soluble inorganic salts formed by metal elements and chalcogens are further selected from Na 2 S, K 2 S, Na 2 S.9H 2 O, Na 2 Se or NaHTe; soluble inorganic salts formed by metal elements and carbonate are further selected from Na 2 CO 3  or K 2 CO 3 ; soluble inorganic salts formed by metal elements and sulfate are further selected from Na 2 SO 4  or K 2 SO 4 . 
     During synthesis of nanomaterials by the precipitation method, after adding precipitant, further add 0.05-50 weight parts of reductant. 
     The sol-gel method for synthesis of nanomaterials with lactam as the solvent includes the following steps: add 0.01-100 weight parts of hydrolyzable precursor and 100 weight parts of lactam into the reactor and stir at 80-150° C. for 0.1-2 h to make the precursor fully dissolved or dispersed in the molten lactam solvent, and add 0.01-50 weight parts of water for hydrolysis to obtain sol, with the hydrolysis temperature of 80˜250° C. and hydrolysis time of 0.01˜48 hr; perform gelatinization at 80˜270° C. for 0.01˜96 hr, and obtain the nanomaterials after washing with water, separation and drying. 
     The hydrolyzable precursor is selected from hydrolyzable inorganic salts formed by binding metal cations with halogen, nitrate, sulfate or acetate anions or from metal organics; wherein: hydrolyzable inorganic salts formed by binding metal cations with halogen, nitrate, sulfate or acetate anions are further selected from FeCl 2 .4H 2 O, FeCl 3 , FeCl 3 .6H 2 O, Fe(NO 3 ) 3 .6H 2 O, Fe 2 (SO 4 ) 3 , AlCl 3 , AlCl 3 .6H 2 O, CuSO 4 .5H 2 O, CuCl 2 , CuCl 2 -2H 2 O, TiCl 3 , TiCl 4  or Zn(OAc) 2 .2H 2 O, preferably FeCl 3 .6H 2 O or AlCl 3 ; metal organics are further selected from diethyl aluminium chloride, aluminum isopropoxide, diethyl zinc, tetraethyl orthosilicate, butyl titanate or tetraethyl titanate, preferably tetraethyl orthosilicate or butyl titanate. 
     The lactam solvent has a purity ≧60% and moisture ≦30%. 
     During systhesis of nanomaterials by the sol-gel method, after hydrolysis, further add 0.05-50 weight parts of reductant. 
     The high temperature pyrolysis method for synthesis of nanomaterials with lactam as the solvent includes the following steps: add 0.01-100 weight parts of pyrolyzable precursor and 100 weight parts of lactam into the reactor and stir at 80-150° C. for 0.1-2 hr to make the precursor fully dissolved or dispersed in the molten lactam solvent, perform pyrolysis at 100-270° C. for 0.1-20 hr, and obtain the nanomaterials after washing with water, separation and drying. 
     The pyrolyzable precursor is selected from soluble inorganic salts pyrolyzable in solvent no higher than 280° C. or from metal organics pyrolyzable in solvent no higher than 280° C.; in which, soluble inorganic salts pyrolyzable in solvent no higher than 280° C. are further selected from AgNO 3 , FeCl 3 , Zn(OAc) 2  or TiCl 4 ; metal organics pyrolyzable in solvent no higher than 280° C. are further selected from oleate, levulinate or carbonyl salts, preferably ferric oleate, acetylacetone or carbonyl iron (Fe(CO) 5 ). 
     During systhesis of nanomaterials by the high temperature pyrolysis, after adding lactam, further add 0.05-50 weight parts of anion donors. 
     The anion donors are selected from compounds pyrolyzable at the temperature of ≦280° C. and able to produce anions required for synthesis of nanomaterials, further selected from benzyl alcohol, trioctylphosphine oxide (provide O 2−  required for synthesis of oxides) or tetramethyl thiuram disulfide (provide S 2−  required for synthesis of sulfides). 
     During systhesis of mixtures including nanoparticles/lactam by the high temperature pyrolysis, before pyrolysis at 100-270° C., further add 0.05-50 weight parts of reductant. 
     The reductant is selected from ascorbic acid, potassium borohydride, sodium borohydride, hydrazine, hydrazine hydrate, hydroxylamine or aldehyde group-containing organics; in which: aldehyde group-containing organics are further selected from formaldehyde, acetaldehyde, glyoxal, benzaldehyde or glucose. 
     During systhesis of nanomaterials by the precipitation method, sol-gel method or high temperature pyrolysis, after adding lactam, further add 0.01-20 weight parts of stabilizer or 0.1-80 weight parts of insoluble inorganics. 
     The stabilizer is selected from anionic surfactant, cationic surfactant, amphoteric surfactant or nonionic surfactant that adjusts the morphology of synthetic nanomaterials, in which: anionic surfactant is further selected from sodium dodecyl sulfate, sodium alkyl benzene sulfonate or sodium oleate, cationic surfactant is further selected from tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride or dodecyltrimethylammonium bromide, amphoteric surfactant is further selected from dodecyl ethoxy sulfobetaine, octadecyl 2 hydroxyethyl amine oxide or octadecanamide dimethylamine oxide, and nonionic surfactant is further selected from triblock copolymer (P123, PEO-PPO-PEO), polyethylene glycol, polyvinyl pyridine, glycerol or 2-mercaptopropionic acid. 
     The insoluble inorganics are selected from the substances as the carrier or attachment point for synthesis of nanomaterials, further from activated carbon, graphene, carbon fibers, carbon nanotubes, molecular sieves, smectite clay, diatomaceous earth, glass fibers or glass microspheres. 
     The methods applicable to synthesis of nanomaterials with lactams as solvents also include cooperative use of precipitation method, sol-gel method, or high-temperature pyrolysis. 
     As the fact that presently lactams are only used as medical and pharmaceutical raw materials, polymer monomers and chemical intermediates, this invention has developed a new use of lactams as solvents for synthesis of nanomaterials. 
     Compared to existing techniques, this invention has the following advantages and beneficial effects: 
     1. Compared to other traditional uses, lactams, as the solvents for preparation of nanomaterials, have the following advantages: 1) nanomaterials belong to an emerging technology field and have added value higher than that of traditional polymers and pharmaceutical intermediates; 2) as solvents, if recovery conditions are appropriate, they can be recycled, which complies with environmental protection requirements.
 
2. In the field of synthesis of nanomaterials with liquid phase method, compared to water or other organic solvents, lactam solvents have the following advantages: 1) nanoparticles with the size of no larger than 100 nm can be synthesized with or without adding surfactant; 2) lactam solvents can well dissolve common water-soluble salts and organic metals, and under the premise of ensuring small size, high dispersibility and high crystallinity, the yield of nanoparticles per unit mass is high; 3) the synthesized oxide nanoparticles have narrow size distribution and high dispersibility and no residual surfactant; 4) lactam solvents have high boiling point and have no pressure-resistant requirements to reaction equipments at high-temperature synthesis; 5) lactam solvents do not participate in chemical reactions throughout the preparation and can be recycled, and are suitable for large scale industrial production; 6) compared to butyrolactam with hightoxicity, tactam solvents used in this invention have low toxicity.
 
3. The raw materials used for this method are at low cost, production equipments are simple, and synthetic routes are environmentally friendly, and this method is suitable for large-scale industrial production.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  ( 13 C-NMR) before and after use of caprolactam solvent for synthesis of nano-Mg(OH) 2  powder with the method in Embodiment 1. 
         FIG. 2  X-ray diffraction diagram of synthetic nano-Mg(OH) 2  powder with the method in Embodiment 1. 
         FIG. 3  Scanning electron microscopy image of synthetic nano-Mg(OH) 2  powder with the method in Embodiment 1. 
         FIG. 4  Transmission electron microscopy image of synthetic nano-Nd(OH) 3  powder with the method in Embodiment 2. 
         FIG. 5  Transmission electron microscopy image of synthetic nano-Al(OH) 3 /Y(OH) 3  powder with the method in Embodiment 3. 
         FIG. 6  X-ray diffraction diagram of synthetic nano-Ag 2 O powder with the method in Embodiment 5. 
         FIG. 7  Transmission electron microscopy image of synthetic nano-Ag 2 O powder with the method in Embodiment 5. 
         FIG. 8  X-ray diffraction diagram of synthetic nano-ZnO powder with the method in Embodiment 6. 
         FIG. 9  Scanning electron microscopy image of synthetic nano-ZnO powder with the method in Embodiment 6. 
         FIG. 10  Scanning electron microscopy image of synthetic nano-ZnO powder with the method in Embodiment 7. 
         FIG. 11  Scanning electron microscopy image of synthetic nano-ZnO powder with the method in Embodiment 8. 
         FIG. 12  X-ray diffraction diagram of synthetic nano-CuO powder with the method in Embodiment 14. 
         FIG. 13  Transmission electron microscopy image of synthetic nano-CuO powder with the method in Embodiment 14. 
         FIG. 14  X-ray diffraction diagram of synthetic nano-Fe 3 O 4  powder with the method in Embodiment 15. 
         FIG. 15  Transmission electron microscopy image of synthetic nano-Fe 3 O 4  powder with the method in Embodiment 15. 
         FIG. 16  Magnetization curve measured by Superconductivity Quantum Interference Device (SQUID) of synthetic nano-Fe 3 O 4  powder with the method in Embodiment 15. 
         FIG. 17  Transmission electron microscopy image of synthetic nano-ZnS powder with the method in Embodiment 19. 
         FIG. 18  Transmission electron microscopy image of synthetic nano-CdTe powder with the method in Embodiment 21. 
         FIG. 19  Transmission electron microscopy image of synthetic nano-Ag powder with the method in Embodiment 22. 
         FIG. 20  Transmission electron microscopy image of synthetic nano-Ag powder with the method in Embodiment 23. 
         FIG. 21  Transmission electron microscopy image of synthetic nano-Cu powder with the method in Embodiment 25. 
         FIG. 22  Transmission electron microscopy image of synthetic nano-Fe 2 O 3  powder with the method in Embodiment 27. 
         FIG. 23  Transmission electron microscopy image of synthetic nano-TiO 2  powder with the method in Embodiment 32. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Further explanations are made to this invention in combination with the embodiments shown in the following diagrams. 
     Embodiment 1 
     Use of Caprolactam as Solvent for Synthesis of Nano-Mg(OH) 2  by Precipitation Method 
     Add 20.3 g MgCl 2 .6H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make MgCl 2  fully dissolved. When stirring, rapidly add 10 g ammonia water (containing ammonia: 26%) and keep at constant temperature of 100° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Mg(OH) 2  powder after intensive drying and crushing. 
       FIG. 1  shows  13 C-NMR before and after use of caprolactam solvent, deuterated chloroform is used as a solvent, and the spectrum keeps unchanged before and after use of caprolactam solvent, indicating that caprolactam solvent can be recycled.  FIG. 2  is the X-ray diffraction diagram of synthetic nano-Mg(OH) 2  powder with the method in this Embodiment, and at the double diffraction angles 2θ=18.7°, 38.0°, 50.8° and 58.8°, the number of JCPDS card corresponding to the diffraction peak in comparison database is 44-1482, belonging to typical brucite crystal form, indicating that the product is high-purity Mg(OH) 2 . Moreover, diffraction peak broadening is generally due to particle size refinement, indicating that the synthetic Mg(OH) 2  is small in particle size. However, diffraction peak intensity is still high, indicating that the synthetic material has high degree of crystallinity.  FIG. 3  is the scanning electron microscopy (SEM) image of synthetic nano-Mg(OH) 2  powder with the method in this Embodiment, and the observation results show that Mg(OH) 2  powder is composed of regular hexagonal flaky nanoparticles of about 10 nm in thickness and about 80 nm in long diameter. Mg(OH) 2 /PA6 nanocomposite can be obtained by mixing this Mg(OH) 2  powder as the filler, when the adding amount reaches 80 weight parts, Mg(OH) 2 /PA6 nanocomposite can reach level V-0 inflaming retarding effect, and the tensile strength and notched impact strength still remain at 69.5 and 11.2 kJ/m 2  (the results are tested respectively according to ASTM-D638 and D6110 standard). 
     Embodiment 2 
     Use of Caprolactam as Solvent for Synthesis of Nano-Nd(OH) 3  by Precipitation Method 
     Add 10.96 g Nd(NO 3 ) 3 .6H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 200° C. for 30 min to make Nd(NO 3 ) 3 .6H 2 O fully dissolved. When stirring, rapidly add 3 g NaOH and keep at constant temperature of 200° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Nd(OH) 3  powder after intensive drying and crushing.  FIG. 4  is transmission electron microscopy (TEM) image of synthetic nano-Nd(OH) 3  powder with the method in this Embodiment, and the observation results show that Nd(OH) 3  powder is composed of evenly dispersed rodlike nanoparticles of about 40 nm is mean length and about 7 nm in mean diameter. 
     Embodiment 3 
     Use of Caprolactam as Solvent for Synthesis of Nano-Al(OH) 3 /Y(OH) 3  Compound by Precipitation 
     Add 3.83 g Y(NO 3 ) 3 .6H 2 O and 4.02 g AlCl 3 .9H 2 O (molar ratio: [Y 3+ ]/[Al 3+ ]=3/5) into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 200° C. for 30 min to make Y(NO 3 ) 3 .6H 2 O and AlCl 3 .9H 2 O fully dissolved. When stirring, rapidly add 8 g NaOH and keep at constant temperature of 200° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Al(OH) 3 /Y(OH) 3  powder after intensive drying and crushing.  FIG. 5  is TEM image of synthetic nano-Al(OH) 3 /Y(OH) 3  powder with the method in this Embodiment, and the observation results show that the product is aggregated by small particles of about 5 nm in diameter. 
     Embodiment 4 
     Use of Valerolactam as Solvent for Synthesis of Nano-Mg—Al Hydrotalcite by Precipitation Method 
     Add 2.03 g MgCl 2 .6H 2 O and 3.33 g Al 2 (SO 4 ) 3 .18H 2 O into 100 g molten valerolactam (purity of valerolactam &gt;80%, moisture ≦20%) and stir at 120° C. for 30 min to make the raw materials fully dissolved, and add 1.4 g NaOH and 1.86 g Na 2 CO 3  and keep at constant temperature of 150° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Mg—Al hydrotalcite powder after intensive drying and crushing. 
     Embodiment 5 
     Use of Caprolactam as Solvent for Synthesis of Nano-Ag 2 O by Precipitation Method 
     Add 4.24 g AgNO 3  into 100 g molten caprolactam (purity of caprolactam ≧60%, moisture ≦30%) and stir at 80° C. for 30 min to make AgNO 3  fully dissolved. When stirring, rapidly add 1 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Ag 2 O powder after intensive drying and crushing.  FIG. 6  is the X-ray diffraction diagram (XRD) of synthetic nano-Ag 2 O powder with the method in this Embodiment, and positions and intensity of all the diffraction peaks perfectly match the JCPDS card 65-6811 of Ag 2 O in the database, indicating that the product is high-purity Ag 2 O. Moreover, diffraction peak broadening is generally due to particle size refinement, indicating that the synthetic Ag 2 O is small in particle size. However, diffraction peak intensity is still high, indicating that the synthetic material has high degree of crystallinity.  FIG. 7  is TEM image of synthetic nano-Ag 2 O powder with the method in this Embodiment, and the observation results show that Ag 2 O powder is composed of monodisperse spherical particles of about 5 nm in diameter. 
     Embodiment 6 
     Use of Caprolactam as Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 150° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing.  FIG. 8  is the X-ray diffraction diagram (XRD) of synthetic nano-ZnO powder with the method in this Embodiment, and positions and intensity of all the diffraction peaks perfectly match the JCPDS card 36-1451 of zincite ZnO in the database, indicating that the product is high-purity ZnO. Moreover, diffraction peak broadening is generally due to particle size refinement, indicating that the synthetic ZnO is small in particle size. However, diffraction peak intensity is still high, indicating that the synthetic material has high degree of crystallinity and is very applicable to luminescent materials.  FIG. 9  is SEM image of synthetic nano-ZnO powder with the method in this Embodiment, and the observation results show that ZnO powder is composed of spherical particles of about 8 nm in diameter and can be used for semiconductor luminescent quantum dots. 
     Embodiment 7 
     Use of Valerolactam as Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into 100 g molten valerolactam (purity of valerolactam ≧80%, moisture ≦20%) and stir at 150° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing  FIG. 10  is SEM image of synthetic nano-ZnO powder with the method in this Embodiment, and the observation results show that the product is composed of monodisperse spherical particles of about 5 nm in diameter. 
     Embodiment 8 
     Use of Laurolactam as Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into 100 g molten laurolactam (purity of laurolactam ≧90%, moisture ≦5%) and stir at 160° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing.  FIG. 11  is SEM image of synthetic nano-ZnO powder with the method in this Embodiment, and the observation results show that the product is composed of monodisperse spherical particles of about 20 nm in diameter. 
     Embodiment 9 
     Use of Caprolactam/Laurolactam as Mixed Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into mixed lactam solvent composed of 80 g caprolactam and 20 g laurolactam (purity of caprolactam and laurolactam ≧90%, moisture ≦5%) and stir at 160° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing, with the size of about 12 nm. 
     Embodiment 10 
     Use of Caprolactam/N-Methylcaprolactam as Mixed Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into mixed lactam solvent composed of 80 g caprolactam and 20 g N-methylcaprolactam (purity of caprolactam and N-methylcaprolactam ≧90%, moisture ≦5%) and stir at 160° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing, with the size of about 10 nm. 
     Embodiment 11 
     Use of Valerolactam/Caprolactam/Laurolactam as Mixed Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into mixed lactam solvent composed of 20 g valerolactam, 60 g caprolactam and 20 g laurolactam (purity of caprolactam ≧90%, moisture ≦5%; purity of valerolactam and laurolactam ≧80%, moisture ≦20%) and stir at 160° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing, with the size of about 10 nm, indicating that the size of synthetic nanomaterials can be effectively adjusted by changing the components of lactam solvent. 
     Embodiment 12 
     Use of Adipimide as Mixed Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into 100 g molten adipimide (purity of adipimide ≧90%, moisture ≦5%) and stir at 160° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing. 
     Embodiment 13 
     Use of N-Methylcaprolactam as Solvent for Synthesis of Nano-ZnO by Precipitation Method 
     Add 3.41 g ZnCl 2  into 100 g molten N-methylcaprolactam (purity of N-methylcaprolactam ≧99%, moisture &lt;0.2%) and stir at 160° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 8 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnO powder after intensive drying and crushing. 
     Embodiment 14 
     Use of Caprolactam as Solvent for Synthesis of Nano-CuO by Precipitation Method 
     Add 6.242 g CuSO 4 .5H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make CuSO 4 .5H 2 O fully dissolved. When stirring, rapidly add 2 g NaOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-CuO powder after intensive drying and crushing.  FIG. 12  is the X-ray diffraction diagram (XRD) of synthetic nano-CuO powder with the method in this Embodiment, and positions and intensity of all the diffraction peaks perfectly match the JCPDS card 44-0706 of CuO in the database, indicating that the product is high-purity CuO. Moreover, diffraction peak broadening is generally due to particle size refinement, indicating that the synthetic CuO is small in particle size.  FIG. 13  is TEM image of synthetic nano-CuO powder with the method in this Embodiment, and the observation results show that the product is composed of monodisperse and narrow-distributed spherical particles of about 3.5 nm in diameter. 
     Embodiment 15 
     Use of Caprolactam as Solvent for Synthesis of Nano-Fe 3 O 4  by Precipitation Method 
     Add 4.1 g FeCl 2 .4H 2 O and 8.2 g FeCl 3 .6H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 150° C. for 30 min to make them fully dissolved. When stirring, rapidly add 9.8 g KOH and keep at constant temperature of 100° C. for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Fe 3 O 4  powder after intensive drying and crushing.  FIG. 14  is the X-ray diffraction diagram (XRD) of synthetic nano-Fe 3 O 4  powder with the method in this Embodiment, and positions and intensity of all the diffraction peaks perfectly match magnetite Fe 3 O 4  in the database, indicating that the product is high-purity Fe 3 O 4 . Moreover, diffraction peak broadening is generally due to particle size refinement, indicating that the synthetic Fe 3 O 4  is small in particle size.  FIG. 15  is TEM image of synthetic nano-Fe 3 O 4  powder with the method in this Embodiment, and the observation results show that the product is composed of spherical particles of about 5 nm in diameter.  FIG. 16  is magnetization curve measured by Superconductivity Quantum Interference Device (SQUID), and the results show that Fe 3 O 4  powder is a super-paramagnetic material, with the saturation magnetization of 40 emu/g, and is very applicable to magnetic separation and MRI. 
     Embodiment 16 
     Use of Caprolactam as Solvent for Synthesis of Nano-MgCO 3  by Precipitation Method 
     Add 20.3 g MgCl 2 .6H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make MgCl 2  fully dissolved. When stirring, rapidly add 15 g Na 2 CO 3  and keep at constant temperature of 100° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-MgCO 3  powder after intensive drying and crushing. The product is in flake structure, with the thickness of about 5 nm and long diameter of 60 nm. 
     Embodiment 17 
     Use of Caprolactam as Solvent for Synthesis of Nano-BaSO 4  by Precipitation Method 
     Add 5.6 g BaCl 2  into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make MgCl 2  fully dissolved. When stirring, rapidly add 3.0 g Na 2 SO 4  and keep at constant temperature of 100° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-BaSO 4  powder after intensive drying and crushing. The product is in flake structure, with the thickness of about 4 nm and long diameter of 90 nm. 
     Embodiment 18 
     Use of Caprolactam as Solvent for Synthesis of Nano-AgCl by Precipitation Method 
     Add 2.1 g AgNO 3  into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make AgNO 3  fully dissolved. When stirring, rapidly add 1.5 g NaCl and keep at constant temperature of 100° C. for 24 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-AgCl powder after intensive drying and crushing. The product is composed of spherical particles, with the size of about 3 nm. 
     Embodiment 19 
     Use of Caprolactam as Solvent for Synthesis of Nano-ZnS by Precipitation Method 
     Add 10.0 g ZnCl 2  into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make ZnCl 2  fully dissolved. When stirring, rapidly add 12.0 g Na 2 S.9H 2 O and keep at constant temperature of 150° C. for 12 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-ZnS powder after intensive drying and crushing.  FIG. 17  is TEM image of synthetic nano-ZnS powder with the method in this Embodiment, and the observation results show that the product is composed of spherical particles of about 20 nm in diameter. 
     Embodiment 20 
     Use of Caprolactam as Solvent for Synthesis of Nano-CdSe by Precipitation Method 
     Add 7.71 g Cd(NO 3 ) 2 .2H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make Cd(NO 3 ) 2 .2H 2 O fully dissolved. When stirring, rapidly add 3 g Na 2 Se and keep at constant temperature of 150° C. for 12 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-CdSe powder after intensive drying and crushing. 
     Embodiment 21 
     Use of Caprolactam as Solvent for Synthesis of Nano-CdTe by Precipitation Method 
     Add 0.82 g Cd(NO 3 ) 2 .2H 2 O and 0.54 ml 2-mercaptopropionic acid (stabilizer) into 100 g molten caprolactam (purity of caprolactam ≧90%, moisture ≦1%) and stir at 80° C. for 30 min to make Cd(NO 3 ) 2 .2H 2 O and 2-mercaptopropionic acid fully dissolved. Under the protection of nitrogen, rapidly add 0.5 g NaHTe and keep at constant temperature of 90° C. for 14 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-CdTe powder after intensive drying and crushing  FIG. 18  is TEM image of synthetic nano-CdTe powder with the method in this Embodiment, and the observation results show that the product is composed of monodisperse spherical particles of about 5 nm in diameter and is very applicable to luminescent devices as semiconductor quantum dots. 
     Embodiment 22 
     Use of Caprolactam as Solvent for Synthesis of Nano-Ag by Precipitation Method 
     Add 4.24 g AgNO 3  into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make AgNO 3  fully dissolved. When stirring, rapidly add 1 g NaOH and keep at constant temperature of 100° C. for 2 hr, and then add 2 g NaBH for continued reaction for 1 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Ag powder after intensive drying and crushing.  FIG. 19  is TEM image of synthetic nano-Ag powder with the method in this Embodiment, and the observation results show that the product is composed of spherical particles of about 6 nm in diameter. This nano-Ag powder can be stably dispersed in water, alcohol and other solvents, and the dispersion liquid can be directly used as conductive adhesive and antibacterial agent. 
     Embodiment 23 
     Use of Caprolactam as Solvent for Synthesis of Nano-Ag by Precipitation Method 
     Add 4.24 g AgNO 3  and 10 g cetyltrimethylammonium bromide into 100 g molten caprolactam (purity of caprolactam ≧95%, moisture ≦1%) and stir at 100° C. for 30 min to make AgNO 3  and cetyltrimethylammonium bromide fully dissolved. When stirring, rapidly add 1 g NaOH and keep at constant temperature of 100° C. for 2 hr, and then add 2 g NaBH for continued reaction for 1 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Ag powder after intensive drying and crushing.  FIG. 20  is TEM image of synthetic nano-Ag powder with the method in this Embodiment, and the observation results show that the product is composed of rodlike particles of about 15 nm in diameter and about 200 nm in length. 
     Embodiment 24 
     Use of Caprolactam as Solvent for Synthesis of Nano-Ag Plated Glass Microspheres by Precipitation Method 
     Add 4.24 g AgNO 3  and 10 g glass microspheres (mean diameter is about 15 um) into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 1 hr to make glass microspheres fully dispersed. When stirring, rapidly add 1 g NaOH and keep at constant temperature of 100° C. for 30 min, and then add 2 g glucose for continued reaction for 12 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Ag plated glass microspheres after intensive drying and crushing. The nano-Ag plated glass microspheres can be used as an antibacterial component to be added in polymers and metals and as an electricity and heat conductive filler to be added in plastic and rubber. 
     Embodiment 25 
     Use of Caprolactam as Solvent for Synthesis of Nano-Cu by Co-Precipitation Method 
     Add 6.242 g CuSO 4 .5H 2 O into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make CuSO 4 .5H 2 O fully dissolved. When stirring, rapidly add 1 g NaOH and keep at constant temperature of 120° C. for 2 hr, and then add 4 g ascorbic acid for reaction for 12 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain nano-Cu powder after intensive drying and crushing.  FIG. 21  is TEM image of synthetic nano-Cu powder with the method in this Embodiment, and the observation results show that the product is composed of rodlike particles of about 300×30 nm in diameter. 
     Embodiment 26 
     Use of Caprolactam as Solvent for Preparation Activated Carbon Loaded Nano-Pd by Precipitation Method 
     Add 5.0 g PdCl 2  and 10 g activated carbon (carrier) into 100 g molten caprolactam (purity of caprolactam ≧80%, moisture ≦20%) and stir at 100° C. for 30 min to make PdCl 2  fully dissolved. When stirring, rapidly add 1 g NaOH and keep at constant temperature of 100° C. for 2 hr, and then add 2 g KBH 4  for continued reaction for 2 hr. Wash the obtained mixture with 200 g deionized water by centrifugation for three times, and obtain activated carbon loaded nano-Pd after intensive drying and crushing. This activated carbon loaded nano-Pd has high catalytic activity in hydrogenation reduction of nitrobenzene-containing compounds to aminobenzene compound, and in catalytic hydrogenation of paranitrotoluene to produce 4-methylaniline, the conversion rate is 90% and the selectivity is 98%. 
     Embodiment 27 
     Use of Caprolactam as Solvent for Synthesis of Nano-Fe 2 O 3  by Sol-Gel Method 
     Add 8.2 g FeCl 3 .6H 2 O into 100 g molten caprolactam (purity of caprolactam ≧95%, moisture ≦1%) and stir at 80° C. for 30 min, add 5 g deionized water for hydrolysis reaction at 100° C. for 24 hr, and then vacuumize to remove water and shift to crystallization at 180° C. for 8 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-Fe 2 O 3  powder after intensive drying and crushing.  FIG. 22  is TEM image of synthetic nano-Fe 2 O 3  powder with the method in this Embodiment, and the observation results show that the product is composed of particles of about 3 nm in diameter. 
     Embodiment 28 
     Use of Caprolactam as Solvent for Synthesis of Nano-Al(OH) 3  by Sol-Gel Method 
     Add 6.4 g AlCl 3  into 100 g molten caprolactam (purity of caprolactam ≧99.5%, moisture ≦0.1%) and stir at 80° C. for 30 min, slowly add 10 g deionized water for hydrolysis reaction at 100° C. for 24 hr, and then vacuumize to remove water and shift to crystallization at 150° C. for 24 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-Al(OH) 3  powder after intensive drying and crushing. The powder is composed of irregular flaky particles of 2 nm in thickness. 
     Embodiment 29 
     Use of Caprolactam as Solvent for Synthesis of Nano-SiO 2  by Sol-Gel Method 
     Add 6 g tetraethyl orthosilicate into 100 g molten caprolactam (purity of caprolactam ≧60%, moisture ≦30%) and stir at 150° C. for 30 min, add 20 g deionized water for hydrolysis reaction at 120° C. for 15 hr, and then vacuumize to remove water and shift to crystallization at 200° C. for 24 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-SiO 2  powder after intensive drying and crushing, with the size of 50 nm. 
     Embodiment 30 
     Use of Caprolactam as Solvent for Synthesis of Nano-SiO 2  by Sol-Gel Method 
     Add 6 g tetraethyl orthosilicate into 100 g molten caprolactam (purity of caprolactam ≧60%, moisture ≦30%) and stir at 150° C. for 30 min, add 0.1 g deionized water for hydrolysis reaction at 120° C. for 15 hr, and then vacuumize to remove water and shift to crystallization at 200° C. for 24 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-SiO 2  powder after intensive drying and crushing, with the size of 12 nm. 
     Embodiment 31 
     Use of Caprolactam as Solvent for Synthesis of Nano-SiO 2  by Sol-Gel Method 
     Add 6 g tetraethyl orthosilicate into 100 g molten caprolactam (purity of caprolactam ≧60%, moisture ≦30%) and stir at 150° C. for 30 min, add 40 g deionized water for hydrolysis reaction at 120° C. for 5 hr, and then vacuumize to remove water and shift to crystallization at 200° C. for 24 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-SiO 2  powder after intensive drying and crushing, with the size of 80 nm. 
     Embodiment 32 
     Use of Caprolactam as Solvent for Synthesis of Nano-TiO 2  by Sol-Gel Method 
     Add 5 ml butyl titanate into 100 g molten caprolactam (purity of caprolactam ≧99.5%, moisture ≦0.1%) and stir at 80° C. for 30 min, add 5 g deionized water for hydrolysis reaction at 100° C. for 24 hr, and then vacuumize to remove water and shift to crystallization at 200° C. for 18 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-TiO 2  powder after intensive drying and crushing  FIG. 23  is TEM image of synthetic nano-TiO 2  powder with the method in this Embodiment, and the observation results show that the product is composed of particles of about 7 nm in diameter. 
     Embodiment 33 
     Use of Caprolactam as Solvent for Synthesis of Nano-Fe 3 O 4  by High-Temperature Pyrolysis 
     Add 3.2 g carbonyl iron into 100 g molten caprolactam (purity of caprolactam ≧99.5%, moisture ≦0.1%) and stir at 150° C. for 30 min to make it fully dissolved, add 5 g glucose, and increase the temperature to 270° C. for reflux reaction for 2 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-Fe 3 O 4  powder after intensive drying and crushing, with the size of 4 nm and the saturation magnetization of 65 emu/g. 
     Embodiment 34 
     Use of Caprolactam as Solvent for Synthesis of Nano-ZnS by High-Temperature Pyrolysis 
     Add 2.2 g zinc acetate and 2.4 g tetramethylthiuram disulfide (donor of anion S 2− ) into 100 g molten caprolactam (purity of caprolactam ≧90%, moisture ≦1%) and stir at 150° C. for 30 min to make it fully dissolved, and increase the temperature to 270° C. for reflux reaction for 2 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-ZnS powder after intensive drying and crushing. 
     Embodiment 35 
     Use of Caprolactam as Solvent for Synthesis of Nano-TiO 2  by High-Temperature Pyrolysis 
     Add 1 g TiCl 4  and 1.4 g trioctylphosphine oxide (donor of anion O 2− ) into 100 g molten caprolactam (purity of caprolactam ≧99.5%, moisture ≦0.01%) and stir at 80° C. for 30 min to make them fully dissolved, and increase the temperature to 270° C. for reflux reaction for 2 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-TiO 2  powder after intensive drying and crushing. 
     Embodiment 36 
     Use of Caprolactam as Solvent for Synthesis of Nano-Ag by High-Temperature Pyrolysis 
     Add 4.24 g AgNO 3  into 100 g molten caprolactam (purity of caprolactam ≧99.5%, moisture ≦0.01%) and stir at 80° C. for 30 min to make AgNO 3  fully dissolved, add 5 g glucose, and increase the temperature to 200° C. for reaction for 12 hr. Wash the obtained mixture with 200 g absolute alcohol by centrifugation for three times, and obtain nano-Ag powder after intensive drying and crushing. 
     The above descriptions of the embodiments are to help ordinary technicians in this technical field understand and apply this invention. The technicians skilled in the field can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the embodiments herein, and the improvement and modifications within the scope of this invention made by the technicians in this field according to the disclosure of this invention should be within the protection scope of this invention.