1. A method for preparing a rare earth metal material, comprising the steps of:

mixing nitrate, nitrilotriacetic acid and a solvent, and then carrying out coordination reaction to obtain the rare earth metal material.

2. The method according to claim 1, wherein the nitrate is neodymium nitrate hexahydrate, terbium nitrate hexahydrate, or europium nitrate hexahydrate;

the molar ratio of the nitrate to the nitrilotriacetic acid is 1-2: 1 to 2.

3. The production method according to claim 1 or 2, wherein the solvent comprises water and N, N-dimethylformamide;

the volume ratio of the water to the N, N-dimethylformamide is 1-2: 1 to 2.

4. The method according to claim 3, wherein the nitrate and the solvent are used in a ratio of 1 mol: 90-110L.

5. The method of claim 1, 2 or 4, wherein the mixing is by sonication;

the frequency of the ultrasonic wave is 30-50 KHz, and the time of the ultrasonic wave is 20-40 min; the temperature of the ultrasound is 20-30 ℃.

6. The method according to claim 5, wherein the temperature of the coordination reaction is 80 to 140 ℃.

7. The method according to claim 1 or 6, wherein the time of the coordination reaction is 70 to 74 hours.

8. The method according to claim 7, wherein the cooling, filtration and drying are sequentially carried out after the completion of the coordination reaction;

the drying temperature is 20-30 ℃, and the drying time is 40-56 h.

9. A rare earth metal material obtained by the production method according to any one of claims 1 to 8.

10. Use of the rare earth metal material of claim 9 in ferric ion detection.

Background

As the most common metal iron among transition metals, Fe is mainly used³⁺The ionic form is free in all corners of production life, such as the discharge amount of iron element in wastewater pollution detection in industrial productionIs an important metric; iron ions can be competent for combining with hemoglobin, combining with transport enzyme, acting as signal molecules, regulating ion balance and other action functions for maintaining homeostasis in organisms, so that the iron ions are indispensable essential trace elements; however once intracellular Fe³⁺Sharp increases in ionic content can also cause irreversible disease damage such as alzheimer's disease, huntington's disease, and parkinson's disease. Therefore, when these functions are disturbed, it is urgently necessary to detect a trace amount of Fe inside and outside the body³⁺Whether the ion content is seriously unbalanced can quickly and effectively eliminate the cause of the symptom and find a remedy for the treatment in time.

Since the twenty-first century, the appearance of various large, medium, small and medium-sized instruments led to the development of detection means aiming at metal cations. Atomic absorption, voltammetry, inductively coupled plasma atomic emission spectrometry and chromatography are frequently used. Although these methods have created the beginning of the testing field, they still have various disadvantages, such as some methods are demanding on the test sample, some methods have fixed testing place and duration, some methods have cross interference factors, which obviously cause low sensitivity and accuracy of the result, and high equipment purchasing and maintaining cost.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a rare earth metal material and a preparation method and application thereof.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of a rare earth metal material, which comprises the following steps:

mixing nitrate, nitrilotriacetic acid and a solvent, and then carrying out coordination reaction to obtain the rare earth metal material.

Preferably, the nitrate is neodymium nitrate hexahydrate, terbium nitrate hexahydrate or europium nitrate hexahydrate;

the molar ratio of the nitrate to the nitrilotriacetic acid is 1-2: 1 to 2.

Preferably, the solvent comprises water and N, N-dimethylformamide;

the volume ratio of the water to the N, N-dimethylformamide is 1-2: 1 to 2.

Preferably, the dosage ratio of the nitrate to the solvent is 1 mol: 90-110L.

Preferably, the mixing mode is ultrasonic;

the frequency of the ultrasonic wave is 30-50 KHz, and the time of the ultrasonic wave is 20-40 min; the temperature of the ultrasound is 20-30 ℃.

Preferably, the temperature of the coordination reaction is 80-140 ℃.

Preferably, the time of the coordination reaction is 70-74 h.

Preferably, after the coordination reaction is finished, cooling, filtering and drying are sequentially carried out;

the drying temperature is 20-30 ℃, and the drying time is 40-56 h.

The invention also provides the rare earth metal material obtained by the preparation method.

The invention also provides application of the rare earth metal material in ferric ion detection.

The invention provides a rare earth metal material, which is obtained by carrying out coordination reaction on nitrate and nitrilotriacetic acid in a solvent. The material provided by the application takes rare earth metal as a bridging atom of an organic framework, and achieves that the whole complex can specifically recognize Fe by utilizing the special luminescence of the rare earth metal³⁺The purpose of the ions shows that the ferric ions have obvious fluorescence quenching phenomenon on the rare earth metal material solution. The rare earth metal material provided by the invention not only can be used for accurately, qualitatively and quantitatively determining ferric ions, but also is simple in detection process, and the complicated and strict test steps are greatly reduced.

Drawings

FIG. 1 is a three-dimensional crystal structure diagram of a complex 1;

FIG. 2 is a two-dimensional chain structure diagram of complex 1;

FIG. 3 is a three-dimensional stacking diagram of complex 1;

FIG. 4 is a graph showing the fluorescence excitation spectrum of complex 1;

FIG. 5 is a graph of the emission spectrum of complex 1;

FIG. 6 is a graph of fluorescence intensity of complex 1 in different metal solutions;

FIG. 7 is a fluorescence quenching diagram of complex 1;

FIG. 8 shows the ratio of Fe equivalent to complex 1³⁺Fluorescence intensity profile in solution;

FIG. 9 shows the coordination compound 1 at different equivalent weights of Fe³⁺Linear quenching profile of the ion;

FIG. 10 shows Fe of Complex 1³⁺A detection limit map of the ions;

FIG. 11 is a three-dimensional crystal structure diagram of complex 2;

FIG. 12 is a two-dimensional chain structure diagram of complex 2;

FIG. 13 is a three-dimensional stacking diagram of complex 2;

FIG. 14 is a graph showing the fluorescence excitation spectrum of complex 2;

FIG. 15 is a graph of the emission spectrum of complex 2;

FIG. 16 is a graph of fluorescence intensity of complex 2 in different metal solutions;

FIG. 17 is a fluorescence quenching diagram of complex 2;

FIG. 18 shows the coordination compound 2 at different equivalent weights of Fe³⁺Fluorescence intensity profile in solution;

FIG. 19 shows the amounts of Fe in different equivalents of complex 2³⁺Linear quenching profile of the ion;

FIG. 20 is Fe of Complex 2³⁺A detection limit map of the ions;

FIG. 21 is a three-dimensional crystal structure diagram of complex 3;

FIG. 22 is a two-dimensional chain structure diagram of complex 3;

FIG. 23 is a three-dimensional stacking diagram of complex 3;

FIG. 24 is a graph showing the fluorescence excitation spectrum of complex 3;

FIG. 25 is a graph of the emission spectrum of complex 3;

FIG. 26 is a graph of fluorescence intensity of complex 3 in different metal solutions;

FIG. 27 is a fluorescence quenching diagram of complex 3;

FIG. 28 shows the amounts of Fe in different equivalents of complex 3³⁺Fluorescence intensity profile in solution;

FIG. 29 shows the coordination compound 3 at different equivalent weights of Fe³⁺Linear quenching profile of the ion;

FIG. 30 shows Fe of Complex 3³⁺Limit of detection of ions.

Detailed Description

The invention provides a preparation method of a rare earth metal material, which comprises the following steps:

mixing nitrate, nitrilotriacetic acid and a solvent, and then carrying out coordination reaction to obtain the rare earth metal material.

In the present invention, the nitrate is preferably neodymium nitrate hexahydrate, terbium nitrate hexahydrate, or europium nitrate hexahydrate.

In the invention, the molar ratio of the nitrate to the nitrilotriacetic acid is preferably 1-2: 1 to 2, and more preferably 1.2 to 1.8: 1.2 to 1.8, more preferably 1.4 to 1.6: 1.4 to 1.6.

In the present invention, the solvent preferably comprises water and N, N-dimethylformamide.

In the invention, the volume ratio of the water to the N, N-dimethylformamide is preferably 1-2: 1 to 2, and more preferably 1.2 to 1.8: 1.2 to 1.8, more preferably 1.4 to 1.6: 1.4 to 1.6.

In the present invention, N-dimethylformamide is mixed with water to give a specific polarity in proportion, which contributes to the progress of the complexation reaction.

In the present invention, the amount ratio of the nitrate to the solvent is preferably 1 mol: 90-110L, more preferably 1 mol: 95-105L, more preferably 1 mol: 98-102L.

In the present invention, the means of mixing is preferably ultrasound.

In the invention, the frequency of the ultrasonic wave is preferably 30-50 KHz, more preferably 35-45 KHz, and more preferably 38-42 KHz; the ultrasonic treatment time is preferably 20-40 min, more preferably 25-35 min, and even more preferably 28-32 min; the temperature of the ultrasonic wave is preferably 20-30 ℃, more preferably 22-28 ℃, and even more preferably 24-26 ℃.

In the invention, the temperature of the coordination reaction is preferably 80-140 ℃, more preferably 90-130 ℃, and even more preferably 100-120 ℃.

In the present invention, the time of the coordination reaction is preferably 70 to 74 hours, more preferably 71 to 73 hours, and still more preferably 71.5 to 72.5 hours.

In the present invention, it is preferable to perform cooling, filtration and drying in this order after the completion of the coordination reaction.

In the present invention, the cooling is preferably natural cooling to room temperature.

In the invention, the filtration is solid-liquid separation, and impurities are filtered to obtain the product.

In the invention, the drying temperature is preferably 20-30 ℃, more preferably 22-28 ℃, and more preferably 24-26 ℃; the drying time is preferably 40-56 h, more preferably 44-52 h, and even more preferably 46-50 h.

The invention also provides the rare earth metal material obtained by the preparation method.

The invention also provides application of the rare earth metal material in ferric ion detection.

The technical solutions provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.

Example 1

Taking 0.2mmol of neodymium nitrate hexahydrate, 0.2mmol of nitrilotriacetic acid and 20mL of solvent; the volume ratio of water to N, N-dimethylformamide in the solvent is 1: 1;

the rare earth metal material was prepared as follows: and (2) carrying out ultrasonic treatment on neodymium nitrate hexahydrate, nitrilotriacetic acid and a solvent at the temperature of 40KHz and 25 ℃ for 30min to complete mixing, then carrying out coordination reaction on the mixed system at the temperature of 90 ℃ for 72h, naturally cooling the reaction solution to room temperature after the coordination reaction is finished, filtering impurities, and drying at the temperature of 25 ℃ for 48h to obtain a light purple rod-shaped crystal, namely the rare earth metal material, which is marked as a complex 1.

The three-dimensional crystal structure of the complex 1 is shown in FIG. 1, and as can be seen from FIG. 1, two metal neodymium in the complex are connected by four acetoxy groups sharing ligand nitrilotriacetic acid to form an assembly unit. Three acetate groups on the ligand are bridged with a central nitrogen atom and rare earth metal neodymium like arms to form three common-edge five-membered ring stable structures, and the two metal neodymium are connected by a hydroxyl oxygen atom of carboxylic acid.

The structure diagram of the two-dimensional chain of the complex 1 is shown in fig. 2, each assembly unit continuously extends through two common acetate groups to form a two-dimensional long chain, five-membered rings in the same bonding direction between the units are stacked in the same direction, and gaps in the long chain are enlarged to form a porous structure.

The three-dimensional stacking diagram of the complex 1 is shown in FIG. 3, the complex long chains are stacked and extended transversely again to assemble a three-dimensional solvent channel structure, the solvent channel is formed by connecting tail long chains of four assembly units when viewed from the a-axis direction, and free water molecules can freely shuttle among the tail long chains, so that the pore diameter of the solvent channel is larger and the functional ions are accommodated most.

And (3) performing a fluorescent probe performance test on the complex 1.

30mg of complex 1 crystal is weighed, ground into powder, dispersed in different solvents and placed in a fluorescence spectrometer, and a fluorescence excitation spectrum is shown in figure 4, and as can be seen from the figure, a strong emission peak at 305nm in an ethanol solution is most obvious. Therefore, an ethanol solution was selected as a dispersion system at room temperature under an ambient condition of ph 7.

As shown in FIG. 5, it can be seen that the excitation wavelength was 241nm and four characteristic emission peaks were shown at 305, 584, 617 and 736nm in the case of using an ethanol solution as a dispersion, and they respectively belong to Nd³⁺In ion 5D₀→7F_J＝0The transition of-5, the peak height of the emission peak in the 305nm region is sharp, and can be used as the reference peak of the subsequent exploration experiment.

The specific metal cation recognition of this fluorescent probe was then initially investigated after the fluorescent representation of the blank sample was determined. Weighing 20mg of solid powder of the complex 1, dispersing the solid powder in an ethanol solution, and mixing 2ml of solution to be detected with Zn with the same equivalent weight²⁺、Cd²⁺、Ni²⁺、Co²⁺、Cu²⁺、Fe³⁺2ml of nitrate solution is placed in a fluorescence spectrometer, and the results are shown in FIGS. 6 and 7, wherein FIG. 6 is a fluorescence intensity graph of different metal solutions, and FIG. 7 is a fluorescence quenching graph; as can be seen from FIGS. 6 and 7, comparing the blank set results shows Ni²⁺、Zn²⁺、Cd²⁺、Cu²⁺、Co²⁺The five metal ions have little influence on the fluorescence intensity of the sample, but Fe³⁺The ion can completely quench all emission characteristic peaks. So that it is concluded that Fe³⁺The fluorescence behavior of the ion-specific quenching complex 1.

Measuring 4ml of sample solution to be tested, putting the sample solution into a standard cuvette, putting the cuvette into a fluorescence spectrometer, and testing a group of blank data. Subsequently with Fe³⁺Titration is carried out step by step, and the equivalent weight of the metal cation is increased in turn. The results are shown in FIGS. 8 and 9, where FIG. 8 shows different equivalent weights of Fe³⁺Fluorescence intensity in solution, FIG. 9 is Fe³⁺Linear quenching profile of the ion; as can be seen from FIGS. 8 and 9, Fe³⁺The fluorescence emission intensity of the complex 1 at four characteristic peaks tends to decrease linearly in the process that the equivalent of the ion is increased from 0 to 0.60, and the fluorescence of the sample shows complete and smooth quenching after 0.60 equivalent.

According to the above Fe³⁺Ion titration experimental study, which is to draw a conclusion by testing a plurality of groups of fluorescence intensity curves, calculate the standard deviation and calculate the standard deviation for detecting Fe by using the formula LOD (3 sigma/s)³⁺The limit of detection (LOD) of the ionic complex 1 was 3.76X 10^-7M, the results are shown in FIG. 10.

Example 2

Taking 2mol of terbium nitrate hexahydrate, 2mol of nitrilotriacetic acid and 200L of solvent; the volume ratio of water to N, N-dimethylformamide in the solvent is 1: 1;

the rare earth metal material was prepared as follows: and (2) ultrasonically mixing terbium nitrate hexahydrate, nitrilotriacetic acid and a solvent for 40min at the temperature of 30KHz and 28 ℃, then carrying out coordination reaction on the mixed system for 72h at the temperature of 130 ℃, naturally cooling the reaction solution to room temperature after the coordination reaction is finished, filtering impurities, and drying at the temperature of 20 ℃ for 56h to obtain transparent blocky particles, namely the rare earth metal material, which is marked as a complex 2.

The three-dimensional crystal structure of the complex 2 is shown in FIG. 11, and it can be seen from FIG. 11 that two metal terbium in the complex are connected by the acetoxy groups of four common ligands, nitrilotriacetic acid, to form an assembly unit. Three acetate groups on the ligand are bridged with a central nitrogen atom and a rare earth metal terbium like arms to form three coterminous five-membered ring stable structures, and the two metal terbium are connected by a hydroxyl oxygen atom of carboxylic acid.

The two-dimensional chain structure diagram of the complex 2 is shown in fig. 12, each assembly unit continuously extends through two common acetate groups to form a two-dimensional long chain, five-membered rings in the same bonding direction between the units are stacked in the same direction, and gaps in the long chain are enlarged to form a porous structure.

The three-dimensional stacking diagram of the complex 2 is shown in FIG. 13, the complex long chains are stacked and extended transversely again to assemble a three-dimensional solvent channel structure, the solvent channel is formed by connecting tail long chains of four assembly units when viewed from the a-axis direction, and free water molecules can freely shuttle among the tail long chains, so that the pore diameter of the solvent channel is larger and the functional ions are accommodated most.

And (3) carrying out a fluorescent probe performance test on the complex 2.

30mg of complex 2 crystal is weighed, ground into powder and dispersed in different solvents and then placed in a fluorescence spectrometer, and a fluorescence excitation spectrum is shown in figure 14, and as can be seen from the figure, a strong emission peak at 305nm in an ethanol solution is most obvious. Therefore, an ethanol solution was selected as a dispersion system at room temperature under an ambient condition of ph 7.

As shown in FIG. 15, it can be seen that the excitation wavelength is 241nm and five characteristic emission peaks are shown at 304, 545, 582, 619 and 759nm with ethanol solution as dispersion, and belong to Tb³⁺In ion 5D₀→7F_J＝0The transition of-5, the peak height of the emission peak in the 304nm region is sharp, and can be used as the reference peak of the subsequent exploration experiment.

After the fluorescent representation of the blank sample is determined, the specific metal cation recognition of the fluorescent probe is subsequently soughtAnd (4) sex. Weighing 20mg of solid powder of the complex 2, dispersing the solid powder in an ethanol solution, and mixing 2ml of solution to be detected with Zn with the same equivalent weight²⁺、Cd²⁺、Ni²⁺、Co²⁺、Cu²⁺、Fe³⁺2ml of nitrate solution is placed in a fluorescence spectrometer, and the results are shown in FIGS. 16 and 17, wherein FIG. 16 is a fluorescence intensity graph of different metal solutions, and FIG. 17 is a fluorescence quenching graph; as can be seen from FIGS. 16 and 17, comparing the blank set results shows Ni²⁺、Zn²⁺、Cd²⁺、Cu²⁺、Co²⁺The five metal ions have little influence on the fluorescence intensity of the sample, but Fe³⁺The ion can completely quench all emission characteristic peaks. So that it is concluded that Fe³⁺The fluorescence of complex 2 was quenched ion-specifically.

Measuring 4ml of sample solution to be tested, putting the sample solution into a standard cuvette, putting the cuvette into a fluorescence spectrometer, and testing a group of blank data. Subsequently with Fe³⁺Titration is carried out step by step, and the equivalent weight of the metal cation is increased in turn. The results are shown in FIGS. 18 and 19, in which FIG. 18 shows different equivalent amounts of Fe³⁺Fluorescence intensity in solution, FIG. 19 is Fe³⁺Linear quenching profile of the ion; as can be seen from FIGS. 18 and 19, Fe³⁺The fluorescence emission intensity of the complex 2 at four characteristic peaks tends to decrease linearly in the process that the equivalent of the ion is increased from 0 to 1.00, and the fluorescence of the sample shows complete and smooth quenching after 1.00 equivalent.

According to the above Fe³⁺Ion titration experimental study, which is to draw a conclusion by testing a plurality of groups of fluorescence intensity curves, calculate the standard deviation and calculate the standard deviation for detecting Fe by using the formula LOD (3 sigma/s)³⁺The limit of detection (LOD) of the ionic complex 2 was 2.59X 10^-7M, results are shown in FIG. 20.

Example 3

Taking 0.2mol of europium nitrate hexahydrate, 0.2mol of nitrilotriacetic acid and 20L of solvent; the volume ratio of water to N, N-dimethylformamide in the solvent is 1: 1;

the rare earth metal material was prepared as follows: europium nitrate hexahydrate, nitrilotriacetic acid and a solvent are subjected to ultrasonic treatment for 28min at the temperature of 45KHz and 30 ℃ to complete mixing, then the mixed system is subjected to coordination reaction for 72h at the temperature of 130 ℃, after the coordination reaction is finished, the reaction solution is naturally cooled to room temperature, impurities are filtered, and transparent massive particles are obtained by drying for 48h at the temperature of 25 ℃, namely the rare earth metal material is marked as a complex 3.

The three-dimensional crystal structure of the complex 3 is shown in FIG. 21, and it can be seen from FIG. 21 that two metal europium in the complex are connected by four acetate groups sharing ligand nitrilotriacetic acid to form an assembly unit. Three acetic acid groups on the ligand are bridged with a central nitrogen atom and rare earth metal europium like arms to form three common-edge five-membered ring stable structures, and the two metal europium are connected by a hydroxyl oxygen atom of carboxylic acid.

The two-dimensional chain structure diagram of the complex 3 is shown in fig. 22, each assembly unit continuously extends through two common acetate groups to form a two-dimensional long chain, five-membered rings in the same bonding direction between the units are stacked in the same direction, and gaps in the long chain are enlarged to form a porous structure.

The three-dimensional stacking diagram of the complex 3 is shown in FIG. 23, the complex long chains are stacked and extended transversely again to assemble a three-dimensional solvent channel structure, the solvent channel is formed by connecting tail long chains of four assembly units when viewed from the a-axis direction, and free water molecules can freely shuttle among the tail long chains, so that the pore diameter of the solvent channel is larger, and the functional ions are accommodated most.

And (3) performing a fluorescent probe performance test on the complex 3.

30mg of complex 3 crystal is weighed, ground into powder, dispersed in different solvents and placed in a fluorescence spectrometer, and a fluorescence excitation spectrum is shown in figure 24, and as can be seen from the figure, a strong emission peak at 309nm in an ethanol solution is most obvious. Therefore, an ethanol solution was selected as a dispersion system at room temperature under an ambient condition of ph 7.

As shown in FIG. 25, it can be seen that the excitation wavelength is 241nm and four characteristic emission peaks are shown at 309, 587, 620 and 741nm with the ethanol solution as the dispersion, and belong to Eu respectively³⁺In ion 5D₀→7F_J＝0The transition of-5 and the peak height and sharpness of the emission peak in the 309nm region can be used for subsequent research experimentsA reference peak.

The specific metal cation recognition of this fluorescent probe was then initially investigated after the fluorescent representation of the blank sample was determined. Weighing 20mg of solid powder of the complex 3, dispersing the solid powder in an ethanol solution, and mixing 2ml of solution to be detected with Zn with the same equivalent weight²⁺、Cd²⁺、Ni²⁺、Co²⁺、Cu²⁺、Fe³⁺2ml of nitrate solution is placed in a fluorescence spectrometer, and the results are shown in FIG. 26 and FIG. 27, FIG. 26 is a fluorescence intensity graph of different metal solutions, and FIG. 27 is a fluorescence quenching graph; as can be seen from FIGS. 26 and 27, comparing the blank set results shows Ni²⁺、Zn²⁺、Cd²⁺、Cu²⁺、Co²⁺The five metal ions have little influence on the fluorescence intensity of the sample, but Fe³⁺The ion can completely quench all emission characteristic peaks. So that it is concluded that Fe³⁺The fluorescence of complex 3 was quenched ion-specifically.

Measuring 4ml of sample solution to be tested, putting the sample solution into a standard cuvette, putting the cuvette into a fluorescence spectrometer, and testing a group of blank data. Subsequently with Fe³⁺Titration is carried out step by step, and the equivalent weight of the metal cation is increased in turn. The results are shown in FIGS. 28 and 29, in which FIG. 28 shows different equivalent weights of Fe³⁺Fluorescence intensity in solution, FIG. 29 is Fe³⁺Linear quenching profile of the ion; as can be seen from FIGS. 28 and 29, Fe³⁺The fluorescence emission intensity of the complex 3 at four characteristic peaks tends to decrease linearly in the process that the equivalent of the ion is increased from 0 to 0.80, and the fluorescence of the sample shows complete and smooth quenching after 0.80 equivalent.

According to the above Fe³⁺Ion titration experimental study, which is to draw a conclusion by testing a plurality of groups of fluorescence intensity curves, calculate the standard deviation and calculate the standard deviation for detecting Fe by using the formula LOD (3 sigma/s)³⁺The detection Limit (LOD) of the ionic complex 3 was 2.79X 10^-7M, results are shown in FIG. 30.

From the above examples, it can be seen that the present invention provides a rare earth metal material obtained by a coordination reaction of nitrate and nitrilotriacetic acid. The material provided by the invention can keep the original stability of the organic framework before 350 DEG CA configuration is determined to satisfy the precondition as a luminescent material; the invention also provides the material pair Fe³⁺The fluorescent material shows characteristic identification, shows that a fluorescence reference emission peak has a fluorescence quenching phenomenon, has high sensitivity and is a very excellent optical material.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.