CN102000577B - A kind of magnetic nanocomposite fiber and its preparation method and application - Google Patents

Abstract

The invention discloses a magnetic nanocomposite fiber and a preparation method and application thereof, and relates to the technical field of inorganic nonmetallic materials and preparation thereof. The preparation method comprises the following steps of: performing chemical reaction on citric acid and metal salt of calcium and iron serving as raw materials to prepare a precursor sol; dehydrating under reduced pressure to obtain a precursor gel; spinning to obtain gel cellulose silk; and calcining the gel cellulose silk under the protection of reducing atmosphere (hydrogen and nitrogen) at aproper temperature to obtain a target product, namely a CaO/alpha-Fe nanocomposite fiber. The fiber has uniform diameter, large length-diameter ratio, high magnetism and a special hollow structure. The method has the advantages of simple process, low equipment requirement, low cost, short operating period and the like. Meanwhile, the magnetic nanocomposite fiber prepared by the method can be usedin transesterification as a solid alkaline catalyst and has high catalytic activity and long catalytic life. The existence of the alpha-Fe component makes the simplification of the separation and recovery of the catalyst possible.

Description

A kind of magnetic nanocomposite fiber and its preparation method and application

technical field

The invention relates to the field of inorganic non-metallic materials, in particular to a magnetic nanocomposite fiber, its preparation method and its use in transesterification.

Background technique

Solid catalysts have incomparable advantages over traditional homogeneous catalysts due to their non-volatile, non-polluting, non-corrosive equipment, easy recycling, reusable, mild reaction conditions, high yield and selectivity, and easy post-treatment. , excellent and increasingly attracting widespread attention, but the solid catalyst also has the disadvantage of small specific surface area, which makes it difficult to fully contact the reactants, which in turn affects its catalytic effect.

In recent years, with the deepening of nanoscience research, nanotechnology has been more and more used in the field of catalysts. Nanoscale solid catalysts have a large specific surface area, which can effectively improve the catalytic effect.

As one of the most common solid alkaline catalysts, CaO is widely used in various industries; previous research on nano-CaO catalysts focused on the preparation of nanoparticles, and there were few studies on nanofiber catalysts; the CaO proposed by the present invention /α-Fe nanocomposite hollow fiber material combines the advantages of high catalytic activity in homogeneous catalysis, avoids the characteristics of diffusion limitation in heterogeneous catalysis, and has a larger specific surface area than nanoparticles, and α-Fe The good magnetic properties of the catalyst will endow the catalyst with unique magnetic separation characteristics, simplify the operation process, reduce the operation cost, and have an adjustable nano-hollow tube structure similar to carbon nanotubes, large aspect ratio, surface energy and surface binding energy And other excellent properties, as a new type of catalyst may have a good application prospect.

At present, the main preparation methods of nanofibers include hydrothermal method, carbon fiber grouting replacement method, chemical vapor deposition method (CVD method), sol-gel method, and organogel precursor conversion method, etc. The preparation technology of CaO-iron fiber The program has not yet been reported.

Contents of the invention

One of the purposes of the present invention is to provide a magnetic nanocomposite fiber, characterized in that: the magnetic nanocomposite fiber is composed of a mixture of CaO and α-Fe, has a hollow structure, and the diameter of the magnetic nanocomposite fiber is 0.2 ~5μm, fiber length 5μm ~2m.

The second object of the present invention is to provide a method for preparing the magnetic nanocomposite fiber.

In order to prepare CaO/α-Fe hollow nanofibers with small diameter, large aspect ratio and excellent performance, on the basis of sol-gel method, organic gel precursor conversion method was adopted to convert organic or inorganic metal salts Soluble in an appropriate solvent, configure it into a uniform and transparent solution, and achieve the mixing at the approximate molecular level; in order to cause the precursor to undergo hydrolysis-polycondensation reaction in the solvent, the amount of water, the reaction time or an appropriate catalyst should be added; after full stirring The sol is formed, and the viscosity of the sol is gradually increased by drying and other measures. Under appropriate viscosity conditions, it is drawn into a gel cellulose filament, and then dried and heat-treated to obtain the target product CaO/α-Fe nanocomposite hollow fiber .

The preparation method of the CaO/α-Fe nanocomposite hollow fiber includes the steps of preparing a precursor solution, dissolving the prepared precursor into a gel cellulose filament, and roasting the gel cellulose filament, It is characterized in that: in the step of calcining the gel cellulose filaments, the gel cellulose filaments are calcined under a reducing atmosphere of _H2 and _N2 .

，搅拌至均匀，室温下磁力搅拌8~30小时。 In the above-mentioned preparation method, the preparation steps of the precursor solution are: first, ferric nitrate is used as the iron source, the nitrate of calcium is used as the calcium source, and citric acid (CA) is dissolved in deionized water, M(Fe ³⁺ ):M (Ca ²⁺ )=1~2:1, M(CA)=

, stirred until uniform, and magnetically stirred at room temperature for 8 to 30 hours.

In the above preparation method, the step of dissolving the prepared precursor into gel cellulose filaments is as follows: dehydrating the prepared precursor solution under vacuum and reduced pressure under the condition of 50°C~70°C to obtain a gel, after The gelled cellulose filaments are obtained by picking, drawing, spinning or drawing, and then drying the gelled cellulose filaments.

In the above-mentioned preparation method, the step of roasting the gelled cellulose filaments is: roasting the gelled cellulose filaments in a reducing atmosphere of _H2 and _N2 in the temperature range of 900-1100°C, and the ratio of the flow rates of hydrogen and nitrogen is 1:4, keep warm for 1~6 hours, and finally cool down to room temperature naturally to obtain CaO/α-Fe fibers.

The concentration of Ca ²⁺ in the precursor solution is 0.1-0.3 mol/L, and the concentration of Fe ³⁺ is 0.1-0.3 mol/L.

The drying of the gelled cellulose filaments refers to drying the gelled cellulose filaments at 60-100°C.

The third object of the present invention is to provide the use of the magnetic nanocomposite fiber in catalyzing transesterification.

Using secondary rapeseed oil, methanol (analytical pure) as reactants, reaction temperature 60°C, reaction time 60min, alcohol to oil molar ratio 12:1, adding different catalysts, wherein the active ingredient CaO content is 5% by mass fraction of rapeseed oil % (in the three examples, the CaO mass accounts for 50%, 40%, and 33% of the mass fraction of the entire fiber), and at the same time, in order to detect the service life of the catalyst, the catalyst is reclaimed and reused, and the fatty acid methyl ester yield is measured respectively. The results As shown in Table 1 below:

Table 1 Comparison of yields (%) of fatty acid methyl esters catalyzed by several catalysts for transesterification

。

.

It can be seen from Table 1 that the CaO/α-Fe nanocomposite hollow fiber catalysts prepared under the conditions described in the three examples have higher catalytic activity and better performance than ordinary CaO catalysts in catalyzing transesterification reactions. Long service life, fatty acid methyl ester can still achieve high conversion rate after repeated use 10 times.

In addition, since CaO is used as a catalytically active component in the present invention, the addition of α-Fe is to simplify the separation and recovery process of the catalyst, and CaO, as a solid basic catalyst with excellent performance, can be used to catalyze various reactions, so the present invention It can be extended to all chemical reactions where CaO can be used as a catalyst.

The present invention adopts organic gel precursor transformation method to prepare magnetic CaO/α-Fe nanocomposite hollow fiber for the first time. Its advantage is that raw materials are extensive, and metal organic salts and inorganic salts are used as raw materials to prepare precursors mixed at molecular or atomic level. The solution is dehydrated under vacuum to obtain a gel, and then the gel cellulose filament is obtained by drawing, spinning or spinning, and then roasted at a suitable temperature and a reducing protective atmosphere to obtain a CaO/α-Fe nanocomposite hollow fiber ; The present invention has the advantages of cheap raw materials, short cycle, simple process, easy scale and little impact on the environment in the operation process. The method can also be applied to the preparation of other various types of alkali metal oxide iron fibers.

Description of drawings

Figure 1: Flow chart of the preparation of ferrite fibers;

Figure 2: XRD diffraction pattern of CaO/α-Fe nanocomposite hollow fiber;

Figure 3: SEM scanning photo of CaO/α-Fe nanocomposite hollow fiber;

Figure 4: SEM scanning electron micrograph (a) and TEM transmission electron micrograph (b) of CaO/α-Fe nanocomposite hollow fiber hollow structure.

Detailed ways

Example 1 ( CaO/α-Fe fiber M(CaO):M (α-Fe)=1:1 ):

Step 1: Take 5.618g calcium nitrate (Ca(NO ₃ ) ₂ 4H ₂ O), 9.612g iron nitrate (Fe(NO ₃ ) ₃ .9H ₂ O), 15g citric acid (CA:C ₆ H ₈ O ₇ H ₂ O), mixed in 150ml deionized water, the molar concentration of Ca ²⁺ is 0.159mol/L, the molar concentration of Fe ³⁺ is 0.159mol/L, the molar ratio of raw materials is: CA: Fe ³⁺ :Ca ^{2 +} =3:1:1, then carry out magnetic stirring for 20 hours;

Step 2: Then put the precursor solution into a vacuum rotary evaporator, depressurize at 60°C, the pressure is less than 0.1Mpa, dehydrate for about 30 minutes, and obtain a gel-like colloidal substance;

Step 3: Put the gel obtained in step 2 into an oven, dry and dehydrate at 60°C, and place it in the oven for about 1 hour, then pull the gel into gel cellulose filaments, and the cellulose filaments Dry in a crucible at 100°C.

Step 4: Heat the fiber precursor to 900°C at a heating rate of 3°C/min in an H ₂ , N ₂ atmosphere furnace, and keep it for 2 hours; cool naturally to obtain the target product CaO/α-Fe fibers with a diameter of micron.

Example 2 ( CaO/α-Fe fiber M(CaO):M (α-Fe)=1:1.5 ):

Step 1: Take 4.214g calcium nitrate (Ca(NO ₃ ) ₂ 4H ₂ O), 10.814g iron nitrate (Fe(NO ₃ ) ₃ 9H ₂ O), 15g citric acid (CA:C ₆ H ₈ O ₇ H ₂ O), mixed in 150ml deionized water, the molar concentration of Ca ²⁺ is 0.119mol/L, the molar concentration of Fe ³⁺ is 0.178mol/L, the molar ratio of raw materials is: CA: Fe ³⁺ :Ca ^{2 +} =3:1.5:1, then carry out magnetic stirring for 20 hours;

Step 2: Then put the precursor solution into a vacuum rotary evaporator, depressurize at 60°C, the pressure is less than 0.1Mpa, dehydrate for about 30 minutes, and obtain a gel-like colloidal substance;

Step 3: Put the gel obtained in step 2 into an oven, dry and dehydrate at 60°C, and place it in the oven for about 1 hour, then pull the gel into gel cellulose filaments, and the cellulose filaments Place in a crucible and dry at 100°C;

Step 4: Heat the fiber precursor to 1000°C at a heating rate of 3°C/min in an H ₂ , N ₂ atmosphere furnace, and keep it for 2 hours; cool naturally to obtain the target product CaO/α-Fe fibers with a diameter of micron.

Example 3 ( CaO/α-Fe fiber M(CaO):M (α-Fe)=1:2 ):

Step 1: Take 3.746g calcium nitrate (Ca(NO ₃ ) ₂ 4H ₂ O), 12.817g iron nitrate (Fe(NO ₃ ) ₃ .9H ₂ O), 15g citric acid (CA:C ₆ H ₈ O ₇ H ₂ O), mixed in 150ml deionized water, the molar concentration of Ca ²⁺ is 0.106mol/L, the molar concentration of Fe ³⁺ is 0.212mol/L, the molar ratio of raw materials is: CA: Fe ³⁺ :Ca ^{2 +} =4.5:2:1, then carry out magnetic stirring for 20 hours;

Step 2: Then put the precursor solution into a vacuum rotary evaporator, depressurize at 60°C, the pressure is less than 0.1Mpa, dehydrate for about 30 minutes, and obtain a gel-like colloidal substance;

Step 3: Put the gel obtained in step 2 into an oven, dry and dehydrate at 60°C, and place it in the oven for about 1 hour, then pull the gel into gel cellulose filaments, and the cellulose filaments Place in a crucible and dry at 100°C;

Step 4: Heat the fiber precursor to 1100°C at a heating rate of 3°C/min in an H ₂ , N ₂ atmosphere furnace, and keep it for 2 hours; cool naturally to obtain the target product CaO/α-Fe fibers with a diameter of micron.

Claims (5)

1. A magnetic nanocomposite fiber, characterized in that: the component of the magnetic nanocomposite fiber is a mixture of CaO and α-Fe, with a hollow structure, the diameter of the magnetic nanocomposite fiber is 0.2 ~ 5 μm, and the fiber length is 5 μm ~2m; the magnetic nanocomposite fiber is prepared by the following method: the method includes the steps of preparing a precursor solution, preparing the prepared precursor solution into a gel cellulose filament, and roasting the gel cellulose filament. Step, it is characterized in that: the preparation step of described precursor solution is: at first ferric nitrate is used as iron source, the nitrate of calcium is used as calcium source, and citric acid (CA) is dissolved in deionized water, M(Fe ³⁺ ) : M(Ca ²⁺ )=1~2:1, M(citric acid)=

, stirred until uniform, and magnetically stirred at room temperature for 8 to 30 hours; the step of preparing the prepared precursor solution into gel cellulose filaments is: putting the prepared precursor solution at 50°C to 70°C Vacuum dehydration under reduced pressure to obtain a gel, and gel cellulose filaments are obtained by picking, drawing, spinning or drawing, and then drying the gel cellulose filaments; the step of roasting the gel cellulose filaments is as follows: : Gel cellulose filaments are calcined in a reducing atmosphere of H ₂ and N ₂ in the temperature range of 900~1100°C, the ratio of hydrogen to nitrogen gas flow is 1:4, heat preservation for 1~6 hours, and finally naturally cool to room temperature, CaO/α-Fe fibers are obtained. 2. The preparation method of a kind of magnetic nanocomposite fiber as claimed in claim 1, comprises the preparation step of precursor solution, the step of preparing precursor solution into gel cellulose silk, gel cellulose silk The step of roasting is characterized in that: the preparation step of the precursor solution is: first, ferric nitrate is used as iron source, calcium nitrate is used as calcium source, and citric acid (CA) is dissolved in deionized water, M(Fe ^{3 +} ): M(Ca ²⁺ )=1~2:1, M(citric acid)=

, stir until uniform, and stir magnetically at room temperature for 8 to 30 hours; the step of preparing the prepared precursor solution into gel cellulose filaments is: put the prepared precursor solution at 50°C to 70°C Vacuum dehydration under reduced pressure to obtain a gel, and gel cellulose filaments are obtained by picking, drawing, spinning or drawing, and then drying the gel cellulose filaments; the step of roasting the gel cellulose filaments is as follows: : Gel cellulose filaments are roasted in a reducing atmosphere of H ₂ and N ₂ in the temperature range of 900~1100°C, the ratio of hydrogen gas to nitrogen gas flow is 1:4, keep it warm for 1~6 hours, and finally cool naturally to room temperature. CaO/α-Fe fibers are obtained. 3. The preparation method of a kind of magnetic nanocomposite fiber as claimed in claim 2, it is characterized in that: the concentration of Ca in the precursor solution is ^0.1 ～0.3 mol/L, the concentration of Fe ³⁺ is 0.1～0.3 mol/L. 4. The preparation method of a magnetic nanocomposite fiber as claimed in claim 2, characterized in that: said drying the gel cellulose filaments refers to drying the gel cellulose filaments at 60-100°C Dry. 5. The use of the magnetic nanocomposite fiber as claimed in claim 1 in catalyzing transesterification.

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