阅读说明：本技术 一种稀土二聚体配位聚合物低温磁制冷材料及制备方法 (Rare earth dimer coordination polymer low-temperature magnetic refrigeration material and preparation method thereof ) 是由 李领伟 吴玉维 张振乾 张晓飞 于 2020-12-18 设计创作，主要内容包括：本发明属于低温磁制冷材料技术领域,涉及一种稀土二聚体配位聚合物低温磁制冷材料及制备方法。其组成式为Ln-2(L)-2(DMF)-4；其中,Ln为镧系稀土金属Gd,Tb,Dy,Ho中的一种或两种,L为脱质子后的5-(4-羧基苯甲氧基)间苯二甲酸,DMF为N,N-二甲基甲酰胺。该聚合物属单斜晶系、C2/c空间群,具有三维层堆积状结构,其最小不对称单元由两个稀土金属阳离子,两个配体阴离子和两个DNF分子组成。材料在0～5T的磁场变化下,等温磁熵变为7.2-26.4J/kg K。其化学稳定性好,该类稀土二聚体配位聚合物制备方法简单,磁热性能大,重复性好,可用于工业化生产。(The invention belongs to the technical field of low-temperature magnetic refrigeration materials, and relates to a rare earth dimer coordination polymer low-temperature magnetic refrigeration material and a preparation method thereof. The composition formula is Ln 2 (L) 2 (DMF) 4 (ii) a Wherein Ln is one or two of lanthanide rare earth metals Gd, Tb, Dy and Ho, L is deprotonated 5- (4-carboxyl benzyloxy) isophthalic acid, and DMF is N, N-dimethylformamide. The polymer belongs to a monoclinic system and a C2/C space group, has a three-dimensional layer stacking structure, and the minimum asymmetric unit of the polymer consists of two rare earth metal cations, two ligand anions and two DNF molecules. Under the change of a magnetic field of 0-5T, the isothermal magnetic entropy of the material is changed to 7.2-26.4J/kg K. The chemical stability is good, the preparation method of the rare earth dimer coordination polymer is simple, the magnetic thermal performance is large, the repeatability is good,can be used for industrial production.)

1. A rare earth dimer coordination polymer low-temperature magnetic refrigeration material is characterized in that the composition formula is Ln₂(L)₂(DMF)₄(ii) a Wherein Ln is one or two of rare earth metals Gd, Tb, Dy and Ho, L is deprotonated 5- (4-carboxyl benzyloxy) isophthalic acid, and DMF is N, N-dimethylformamide; the rare earth dimer coordination polymer material has a monoclinic system, belongs to a C2/C space group, and has a three-dimensional layer accumulation-shaped structure, wherein the minimum asymmetric unit of the rare earth dimer coordination polymer material consists of two rare earth metal cations, two ligand anions and two DMF molecules; under the condition of 0-5T magnetic field change, isothermal magnetic entropy of the rare earth dimer coordination polymer material is changed into isothermal magnetic entropy7.4-26.4J/kg K。

2. A preparation method of a rare earth dimer coordination polymer low-temperature magnetic refrigeration material comprises the following steps:

step 1: dissolving rare earth nitrate and organic ligand in an organic solvent, stirring for 30-60 minutes until the rare earth nitrate and the organic ligand are dissolved and uniformly mixed to form a solution;

step 2: putting the mixed solution prepared in the step 1 into a polytetrafluoroethylene lining hydro-thermal synthesis reaction kettle, preserving the heat for 3-5 days at the temperature of 80-180 ℃, and then cooling to room temperature at the speed of 3-5 ℃/h to form a solution;

and step 3: uniformly stirring the solution prepared in the step 2, and then placing the solution in a centrifugal tube for centrifugal separation at the rotating speed of 4800-;

and 4, step 4: and (4) washing the solid product obtained in the step (3) with DMF and ethanol for 3-5 times, performing suction filtration, and naturally drying to obtain the low-temperature magnetic refrigeration material applied to the rare earth dimer coordination polymer.

3. The method for preparing the rare earth dimer coordination polymer low-temperature magnetic refrigeration material according to claim 2, characterized in that the rare earth nitrate is one or two of gadolinium nitrate, terbium nitrate, dysprosium nitrate and holmium nitrate; the organic ligand is 5- (4-carboxyl benzyloxy) isophthalic acid.

4. The method for preparing a rare earth dimer coordination polymer low-temperature magnetic refrigeration material according to claim 2 or 3, characterized in that the molar ratio of rare earth nitrate to organic ligand is 1: (0.7-1.2).

5. The method for preparing a rare earth dimer coordination polymer low-temperature magnetic refrigeration material according to claim 2, wherein the organic solvent is a mixed solvent of DMF and ethanol, and the volume ratio of DMF to ethanol in the mixed solvent is 1: (0.8-1.3).

Technical Field

The invention belongs to the technical field of magnetic materials, and particularly relates to a rare earth dimer coordination polymer material applied to low-temperature magnetic refrigeration and a preparation method thereof.

Background

The refrigeration technology is widely applied to food processing, biological pharmacy, petrochemical industry, high-energy physics and aerospaceAnd the like, and extremely important technologies in the fields. The usage amount of refrigeration equipment in China is large, but the core technology is lacked, so the energy utilization rate is high; common low temperature refrigerant R728 (N)₂)、R732(O₂) However, helium-3 refrigerant can reach a temperature of 2K or less, but has low efficiency and high price, and experimental studies in low temperature regions are limited. In order to solve the problem of insufficient energy utilization rate and support the research of high and new technologies, the research and development of a novel low-temperature refrigeration technology are obviously urgent.

The magnetic refrigeration technology is a high and new refrigeration technology which realizes refrigeration based on the magnetocaloric effect (also called magnetic card effect) of materials and has low noise, no pollution and high efficiency. The principle of magnetic refrigeration is that the change of an external magnetic field is utilized to make the magnetic moments of magnetic working media generate orderly and unordered mutual transformation, and when the magnetic moments change, a magnet can generate heat absorption and heat release effects, so that refrigeration cycle is carried out. Compared with the traditional compressor refrigeration mode, the magnetic refrigeration takes the magnetic solid material as the magnetic refrigeration working medium, so that the instability of the refrigerator caused by the change of the volume of the material can not occur in the refrigeration process; the refrigerant such as Freon and the like is not used, so that toxic gas or greenhouse gas cannot be discharged, and the environment-friendly effect is achieved; the magnetic working medium is solid, the entropy density is far greater than that of gas, and the miniaturization of equipment is facilitated; the acting temperature span area is large, and the refrigerating device is one of novel refrigerating modes with the most potential in the future.

In recent years, rare earth ions have various and unique coordination modes, so that rare earth-based coordination polymer materials often show rich and novel structures and magnetism and the paramagnetic nature thereof, and become one of the main research objects of liquid helium region magnetic refrigeration. For the magnetic refrigeration materials, the crystal formation and structure regulation theory of the existing rare earth-based coordination polymer magnetic refrigeration materials is not mature, the oriented synthesis is difficult, the synthesis process is complicated, the cost is high, and the like.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a rare earth dimer coordination polymer low-temperature magnetic refrigeration material and a preparation method thereof.

Rare earth dimer coordination polymerA low-temperature magnetic refrigeration material with the composition formula of Ln₂(L)₂(DMF)₄(ii) a Wherein Ln is one or two of rare earth metals Gd, Tb, Dy and Ho, L is deprotonated 5- (4-carboxyl benzyloxy) isophthalic acid, and DMF is N, N-dimethylformamide. The coordination polymer material has a monoclinic system, belongs to a C2/C space group, has a three-dimensional layer stacking structure, and the minimum asymmetric unit of the coordination polymer material consists of two rare earth metal cations, two ligand anions and two DMF molecules. The isothermal magnetic entropy of the rare earth dimer coordination polymer material is 7.2-26.4J/kg K under the change of a 0-5T magnetic field.

A preparation method of a rare earth dimer coordination polymer low-temperature magnetic refrigeration material comprises the following steps:

step 1: dissolving rare earth nitrate and organic ligand in an organic solvent, stirring for 30-60 minutes until the rare earth nitrate and the organic ligand are dissolved and uniformly mixed to form a solution;

step 2: putting the mixed solution prepared in the step 1 into a Polytetrafluoroethylene (PTFE) lining hydro-thermal synthesis reaction kettle, preserving the heat for 3-5 days at the temperature of 80-180 ℃, and then cooling to room temperature at the speed of 3-5 ℃/h to form a solution;

and step 3: and (3) uniformly stirring the solution prepared in the step (2), and then placing the solution in a centrifuge tube for centrifugal separation at the rotating speed of 4800-.

And 4, step 4: and (3) washing the solid product obtained in the step (3) with DMF and ethanol for 3-5 times, performing suction filtration, and naturally drying to obtain the rare earth dimer coordination polymer material applied to low-temperature magnetic refrigeration.

Preferably, the rare earth nitrate is one or two of gadolinium nitrate, terbium nitrate, dysprosium nitrate and holmium nitrate; the organic ligand is 5- (4-carboxyl benzyloxy) isophthalic acid (H)₃L)。

Preferably, the molar ratio of the rare earth nitrate to the organic ligand is 1: (0.7-1.2).

Preferably, the organic solvent is a mixed solvent of DMF and ethanol, and the volume ratio of DMF to ethanol in the mixed solvent is 1: (0.8-1.3).

Compared with the prior art, the invention has the following effects: the material has the advantages of good chemical stability, simple preparation method, large magnetic entropy and good repeatability, and can be used for industrial production.

Detailed Description

The present invention is further analyzed, but the specific embodiments do not limit the present invention.

Example 1: preparation of Dy₂(L)₂(DMF)₄Magnetic refrigeration material

Step 1: 0.5mmol of Dy (NO)₃)₃And 0.5mmol of 5- (4-carboxyphenylmethoxy) isophthalic acid are dissolved in a mixed solution of 7.5mL of dimethylformamide and 7.5mL of ethanol, and the mixture is stirred for 45 minutes until the mixture is dissolved and mixed uniformly;

step 2: putting the mixed solution prepared in the step 1 into a Polytetrafluoroethylene (PTFE) lining hydro-thermal synthesis reaction kettle, preserving the heat for 3 days at 80 ℃, and then cooling to room temperature at the rate of 3 ℃/h;

and step 3: uniformly stirring the solution e prepared in the step 2, taking out 12ml of the solution, placing the solution in a centrifuge tube, and centrifugally separating the solution for 5min at the rotating speed of 7000r/min to obtain colorless precipitate;

and 4, step 4: and (4) washing the colorless precipitate obtained in the step (3) with DMF (dimethyl formamide) for three times, washing with ethanol for three times, performing suction filtration, and naturally drying to obtain Dy₂(L)₂(DMF)₄A coordination polymer material. And measuring that the isothermal magnetic entropy of the obtained finished product is 8.1J/kg K under the magnetic field change of 0-5T.

Example 2: preparation of GdTb (L)₂(DMF)₄Magnetic refrigeration material

Step 1: 0.2mmol of Tb (NO)₃)₃0.2mmol of Gd (NO)₃)₃And 0.4mmol of 5- (4-carboxyphenylmethoxy) isophthalic acid are dissolved in a mixed solution of 7.5mL of dimethylformamide and 7.5mL of ethanol, and the mixture is stirred for 60 minutes until the mixture is dissolved and mixed uniformly;

step 2: putting the mixed solution prepared in the step 1 into a Polytetrafluoroethylene (PTFE) lining hydro-thermal synthesis reaction kettle, preserving the heat for 5 days at the temperature of 120 ℃, and then cooling to room temperature at the speed of 4 ℃/h;

and step 3: uniformly stirring the solution prepared in the step 2, taking out 10ml of the solution, placing the solution into a centrifugal tube, and centrifugally separating the solution at the rotating speed of 4800r/min for 3min to obtain colorless precipitate;

and 4, step 4: washing the colorless precipitate obtained in the step 3 with DMF for three times, washing with ethanol for three times, filtering, and naturally drying to obtain GdTb (L)₂(DMF)₄A coordination polymer material. And measuring that the isothermal magnetic entropy of the obtained finished product is 26.4J/kg K under the magnetic field change of 0-5T.

Example 3: preparation of Ho₂(L)₂(DMF)₄Magnetic refrigeration material

Step 1: 0.3mmol of Ho (NO)₃)₃And 0.36mmol of 5- (4-carboxyphenylmethoxy) isophthalic acid are dissolved in a mixed solution of 8mL of dimethylformamide and 7.5mL of ethanol, and the mixture is stirred for 30 minutes until the mixture is dissolved and mixed uniformly;

step 2: putting the mixed solution prepared in the step 1 into a Polytetrafluoroethylene (PTFE) lining hydro-thermal synthesis reaction kettle, preserving the heat for 4 days at 100 ℃, and then cooling to room temperature at the speed of 4 ℃/h;

and step 3: uniformly stirring the solution prepared in the step 2, taking out 12ml of the solution, placing the solution into a centrifugal tube, and centrifugally separating the solution for 6min at the rotating speed of 6400r/min to obtain colorless precipitate;

and 4, step 4: washing the colorless precipitate obtained in the step 3 with DMF for three times, washing with ethanol for three times, performing suction filtration, and naturally drying to obtain Ho₂(L)₂(DMF)₄A coordination polymer material. And measuring that the isothermal magnetic entropy of the obtained finished product is 7.4J/kg K under the magnetic field change of 0-5T.