Hierarchical porous metal organic framework compound and preparation method and application thereof
阅读说明：本技术 一种分级多孔金属有机框架化合物及其制备方法与应用 (Hierarchical porous metal organic framework compound and preparation method and application thereof ) 是由 郭瑞丽 陈娜娜 付巧鸽 石超逸 于 2021-10-27 设计创作，主要内容包括：本发明属于分离纯化领域,具体涉及一种分级多孔金属有机框架化合物及其制备方法与应用。本发明通过金属离子与过量调节剂首先形成金属-氧簇合物,之后少量低pKa的有机配体的加入,可以不完全替换调节剂与金属配位,因此形成可调的缺陷孔。通过改变调节剂的种类和相对含量,系统性探究了孔径分布和比表面积等孔隙参数的变化。在不引入特异性基团的情况下,通过孔径筛分作用,选择性地吸附分子量较小的STV,从而实现RA的提纯。本发明所制备的HP-NH-(2)-MIL-53不仅为甜菊糖苷分离纯化提供了新材料,还有望为其他相似分子量物质的吸附提供参考,在吸附分离领域具有广阔的应用前景。(The invention belongs to the field of separation and purification, and particularly relates to a hierarchical porous metal organic framework compound, and a preparation method and application thereof. According to the invention, metal-oxygen cluster compounds are firstly formed by metal ions and excessive regulator, and then a small amount of organic ligand with low pKa is added, so that the regulator and the metal can be incompletely replaced for coordination, and adjustable defect holes are formed. By changing the types and relative contents of the regulators, the change of pore parameters such as pore size distribution and specific surface area is systematically explored. Under the condition of not introducing specific groups, selectively adsorbing the STV with smaller molecular weight by the pore size sieving effect, thereby realizing the purification of RA. HP-NH prepared by the invention 2 ‑MIL-53 not only provides a new material for the separation and purification of stevioside, but also is expected to provide a reference for the adsorption of other substances with similar molecular weights, and has wide application prospects in the field of adsorption separation.)
1. The hierarchical porous metal organic framework compound is characterized by having adjustable defect pores and specific surface area of 175.04-2293.98 m2The pore volume is adjustable between 0.45cm and 2.16cm3The pore diameter is adjustable between 0.38 nm and 26.75 nm.
2. The preparation method of the hierarchical porous metal organic framework compound is characterized by comprising the following steps:
(1) weighing a certain amount of AlCl3·6H2Dissolving O in a proper amount of solvent, adding a certain amount of regulator, stirring and adding a proper amount of 2-amino terephthalic acid, magnetically stirring, pouring into a high-pressure reaction kettle with a polytetrafluoroethylene lining, reacting under a certain condition, and centrifugally cleaning a precipitate by using DMF after the reaction is finished;
(2) fully activating the precipitate obtained in the step (1) under a certain condition, then sequentially washing with DMF and methanol, and drying in vacuum to obtain a hierarchical porous metal organic framework compound HP-NH2-MIL-53。
3. The method according to claim 1, wherein the modifier in the step (1) comprises: one of caproic acid, caprylic acid, capric acid, lauric acid or myristic acid.
4. The method according to claim 1, wherein the solvent in step (1) is DMF; AlCl3·6H2The dosage ratio of the O, the solvent and the regulator is 1 mmoL: 8-20 mL: 5-15 mmoL.
5. The method of claim 1, wherein the AlCl in step (1) is3·6H2The molar ratio of O to 2-amino terephthalic acid is 1: 0.4-2.
6. The method according to claim 1, wherein the reaction conditions of the reaction under certain conditions in step (1) include: the reaction temperature is 120-150 ℃, and the reaction time is 20-30 h.
7. The preparation method according to claim 1, wherein the activation in step (2) is carried out by putting the precipitate into a DMF solution containing HCl with a certain concentration, and the volume ratio of HCl to DMF in the DMF solution is 1: 100-300.
8. The preparation method according to claim 1, wherein the activation in the step (2) is carried out under stirring at 60-100 ℃ for 8-12 hours.
9. The preparation method according to claim 1, wherein the temperature of the vacuum drying in the step (2) is 150 to 200 ℃ and the time is 12 to 15 hours.
10. Use of the hierarchical porous metal organic framework compound according to claim 1 for the separation and purification of steviol glycosides.
Technical Field
The invention belongs to the field of separation and purification, and particularly relates to a hierarchical porous metal organic framework compound, and a preparation method and application thereof.
Background
Steviol Glycosides (SGs) are natural sweeteners with high sweetness and low calorie, extracted from stevia rebaudiana leaves, and are mainly used as food additives and pharmaceutical preparations. The most abundant, most sweet components of SGs are Rebaudioside A (RA) and Stevioside (STV), accounting for about 50-60% and 20-30%, respectively, with RA having a sweet taste and STV having an undesirable aftertaste.
In recent years, many studies have been made at home and abroad on the separation and purification of steviol glycosides in order to obtain high-purity RA by removing STV which is a bad taste in SGs. The methods mainly used at present are recrystallization, high-speed countercurrent chromatography, membrane separation and adsorption. Among them, the adsorption method is the most commonly used method for separating and purifying SGs due to its advantages of simple operation, high efficiency, low cost, etc. However, most of the adsorbents at present are physical/chemical adsorbents that do not involve structure-property relationships.
The metal organic framework compound (MOF) is a novel porous material formed by combining metal ions and organic ligands through coordination bonds, has the characteristics of high specific surface area, high porosity, easiness in modification and the like, and can be used for adsorption and separation of natural products. Most of the traditional MOFs are of microporous structures, and only small molecular substances with low molecular weight can be transmitted, and the small molecular substances with the molecular weight of 800-1000, such as STV and RA, cannot enter MOF pore channels. In order to solve the problem, research and development of hierarchical porous MOF (HP-MOF) broadens the application field of MOF materials, and HP-MOF refers to in-situ construction of mesopores on the basis of MOF microporous structures and adopts different means to form pores with different properties. However, there are no reports on HP-MOF materials suitable for STV and RA isolation.
Disclosure of Invention
In view of the above, the present invention aims to provide a hierarchical porous metal organic framework compound HP-NH2-MIL-53 and a preparation method and application thereof. According to the invention, a micro-mesoporous hierarchical porous structure is constructed by a regulator induced defect method, so that the adsorption capacity and the adsorption selectivity are simultaneously improved, and the pore structure parameters suitable for stevioside separation are determined on the basis of a large number of creative experiments, so that the method can be used for selective separation of RA and STV in stevioside.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a hierarchical porous metal organic framework compound HP-NH2MIL-53, said compound having adjustable defect pores and a specific surface area of 175.04-2293.98 m2The pore volume is adjustable between 0.45cm and 2.16cm3The pore diameter is adjustable between 0.38 nm and 26.75 nm.
The invention also provides a preparation method of the hierarchical porous metal organic framework compound, which comprises the following steps:
(1) weighing a certain amount of AlCl3·6H2Dissolving O in a proper amount of solvent, adding a certain amount of regulator, stirring and adding a proper amount of 2-amino terephthalic acid, magnetically stirring, pouring into a high-pressure reaction kettle with a polytetrafluoroethylene lining, reacting under a certain condition, and centrifugally cleaning a precipitate by using DMF after the reaction is finished;
(2) activating the precipitate obtained in the step (1) under a certain condition, then sequentially washing with DMF and methanol, and drying in vacuum to obtain a hierarchical porous metal organic framework compound HP-NH2-MIL-53。
Further, the regulator in step (1) comprises: one of caproic acid, caprylic acid, capric acid, lauric acid or myristic acid.
Further, the solvent in the step (1) is DMF; AlCl3·6H2The dosage ratio of the O, the solvent and the regulator is 1 mmoL: 8-20 mL: 5-15 mmoL.
AlCl described in step (1)3·6H2The molar ratio of O to 2-amino terephthalic acid is 1: 0.4-2.
The reaction conditions of the reaction under certain conditions in the step (1) include: the reaction temperature is 120-150 ℃, and the reaction time is 20-30 h.
And (3) activating in the step (2) by putting the precipitate into a DMF (dimethyl formamide) solution containing HCl with a certain concentration, wherein the volume ratio of HCl to DMF in the DMF solution is 1: 100-300.
The activation condition in the step (2) is that the mixture is stirred for 8-12 h at the temperature of 60-100 ℃, and is preferably stirred for 10h at the temperature of 90 ℃.
And (3) drying in vacuum in the step (2) at the temperature of 150-200 ℃ for 12-15 h.
The invention also provides the hierarchical porous metal organic framework compound HP-NH2Application of MIL-53 in separation and purification of stevioside.
Preferably, the application comprises: weighing a certain amount of HP-NH in a conical flask2MIL-53, adding a stevioside aqueous solution with a certain concentration, adsorbing stevioside under constant temperature oscillation under a certain condition, and measuring the STV and RA contents by HPLC.
Further preferably, said HP-NH2The dosage ratio of MIL-53 to the stevioside aqueous solution is 30-100 mg: 25-100 mL; the concentration of the steviol glycoside aqueous solution was 6mg/mL (STV: RA ═ 1: 1).
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, metal-oxygen cluster compounds are firstly formed by metal ions and excessive regulator, and then a small amount of organic ligand with low pKa is added, so that the regulator and the metal can be incompletely replaced for coordination, and adjustable defect holes are formed. By changing the types and relative contents of the regulators, the change of pore parameters such as pore size distribution and specific surface area is systematically explored. HP-NH prepared by the invention2-MIL-53 can realize NH2The specific surface area of the MIL-53 is 175.04-2293.98 m2Adjustable in the range of/g, and the pore volume is 0.45-2.16 cm3The/g is adjustable, and the aperture is adjustable within 0.38-26.75 nm; screening out the best Material ratio HP-MOF-1:10:0.6 with 591.31m2Specific surface area per gram, 0.48cm3Pore volume/g and pore diameter of 3.80 nm. According to the invention, under the condition of not introducing specific groups, STV with small molecular weight is selectively adsorbed through the pore size sieving effect, so that RA purification is realized. Furthermore, the compound provided by the invention has good cyclic regeneration capacity, and HP-NH saturated in adsorption can be adsorbed by adding desorption liquid and oscillating at constant temperature2And the MIL-53 is separated by filtration, so that the separation cost is reduced. HP-NH prepared by the invention2MIL-53 not only provides a new material for the separation and purification of stevioside, but also is expected to provide a reference for the adsorption of other substances with similar molecular weights,has wide application prospect in the field of adsorption separation.
Drawings
FIG. 1 shows HP-NH prepared in example 12-MIL-53 and NH2N of-MIL-532Adsorption and desorption curve graphs;
FIG. 2 depicts HP-NH prepared in example 12-MIL-53 and NH2-pore size distribution profile of MIL-53;
FIG. 3 is the HP-NH prepared in example 22N of-MIL-532Adsorption and desorption curve graphs;
FIG. 4 is the HP-NH prepared in example 22-Pore size distribution plot of MIL-53;
FIG. 5 is the HP-NH prepared in example 32N of-MIL-532Adsorption and desorption curve graphs;
FIG. 6 is the HP-NH prepared in example 32-pore size distribution profile of MIL-53;
FIG. 7 is the HP-NH prepared in example 52N of-MIL-532Adsorption and desorption curve graphs;
FIG. 8 is the HP-NH prepared in example 52-pore size distribution profile of MIL-53;
FIG. 9 shows HP-NH prepared in example 62N of-MIL-532Adsorption and desorption curve graphs;
FIG. 10 is the HP-NH prepared in example 62Pore size distribution plot of MIL-53.
Detailed Description
The present invention will be further described by the following examples, however, the scope of the present invention is not limited to the following examples. The present invention has been described generally and/or specifically with respect to materials used in testing and testing methods. The following examples are examples of experimental methods not indicating specific conditions, and the detection is usually carried out according to conventional conditions or according to the conditions recommended by the manufacturers. Reagents, biomaterials, etc. used in the following examples are commercially available unless otherwise specified.
Example 1
In this example, the preparation method of the hierarchical porous metal organic framework compounds of different types of modulators includes the following steps:
(1) 5 parts of 5mmoL (1.21g) AlCl are weighed out3·6H2O, dissolved in 40mL of N, N-Dimethylformamide (DMF) with stirring, 50mmoL of caproic acid (C6, 5.81g), caprylic acid (C8, 7.21g), capric acid (C10, 8.61g), lauric acid (C12, 10.02g) and myristic acid (C14, 11.42g) were added, and 5mmoL (0.91g) of 2-aminoterephthalic acid (NH) was added after stirring and mixing2-BDC), stirring the mixture for 30min, pouring the mixture into a polytetrafluoroethylene-lined autoclave, reacting for 24h at 130 ℃, and centrifugally washing each precipitate with DMF three times after the reaction is finished.
(2) Respectively placing the precipitate obtained in step (1) in 40mL of DMF solution containing 0.2mL of HCl, stirring at 80 deg.C for 12h to complete the activation process, sequentially washing with DMF and methanol three times, and drying in a vacuum drying oven at 150 deg.C for 12h to obtain HP-NH corresponding to different types of regulator2-MIL-53. Respectively designated as HP-MOF-C6, HP-MOF-C8, HP-MOF-C10, HP-MOF-C12, and HP-MOF-C14. Respectively for the obtained HP-NH2MIL-53 was subjected to a specific surface area test (BET), the BET characterization results indicated that the specific surface areas of HP-MOF-C6, HP-MOF-C8, HP-MOF-C10, HP-MOF-C12, and HP-MOF-C14 were: 922.14m2/g、1104.39m2/g、1178.14m2/g、706.22m2G and 597.02m2(ii)/g; the pore volumes are respectively: 1.05cm3/g、0.92cm3/g、1.15cm3/g、1.22cm3G and 0.93cm3(ii)/g; the pore diameters are respectively 0.63-15.67nm, 0.64-17.39nm, 0.64-21.73nm, 1.24-20.20nm and 0.63-26.75 nm.
Testing HP-NH corresponding to different types of regulators prepared above2-MIL-53 adsorption at 30 ℃. 30mg of HP-MOF-C6, HP-MOF-C8, HP-MOF-C10, HP-MOF-C12 and HP-MOF-C14 are weighed in conical flasks, 25mL of stevioside aqueous solution with the concentration of 6mg/mL (STV: RA ═ 1:1) is added respectively, the stevioside is adsorbed by constant temperature oscillation for 24h at the conditions of 150rpm and 30 ℃, the contents of STV and RA are determined by HPLC, and each HP-NH is measured2MIL-53 three replicates were tested, all taking the value of the sum and mean of the replicates. Tested HP-MOF-C6, HP-MOF-C8, HP-MOF-C10, HP-MOFThe total adsorption amounts of STV and RA for-C12, HP-MOF-C14 were: 166.83mg/g, 253.89mg/g, 155.32mg/g, 106.40mg/g, 58.80 mg/g. The adsorption selectivity of the corresponding STV versus RA was: 1.34, 1.69, 1.81 and 2.58.
In this example, by way of comparison, a graded porous metal organic framework compound (NH) without added conditioning agent was also prepared2MIL-53), preparation procedure and HP-NH2MIL-53 with the difference that caproic acid, caprylic acid, capric acid, lauric acid and myristic acid are not added as regulators, and the final product obtained is noted NH2-MIL-53. BET results show NH2MIL-53 having 175.04m2Specific surface area per gram, 0.45cm3Pore volume in g and pore size range of 1.09-1.73 nm. By reaction with HP-NH2NH obtained by the same test method as for-MIL-532-MIL-53 adsorption at 30 ℃. The adsorption amount of the test result on STV is 4.20mg/g, and no adsorption on RA exists. FIG. 1 and FIG. 2 show HP-NH prepared in this example2-MIL-53 and NH2N of-MIL-532Adsorption-desorption curve diagram and aperture distribution diagram; as can be seen from FIGS. 1 and 2, the size of the defective pores can be influenced by the modifier, and framework compounds with different pore sizes can be prepared by adding different types of modifiers.
Example 2
In this example, the preparation method of the hierarchical porous metal organic framework compounds with different regulator contents includes the following steps:
(1) weighing 4 parts of 5mmoL (1.21g) AlCl3·6H2O, dissolved in 40mL of DMF under stirring, 25mmoL (4.31g), 40mmoL (6.89g), 50mmoL (8.61g) and 60mmoL (10.34g) of capric acid were added to each portion under stirring, and 5mmoL (0.91g) of NH was added to each portion under stirring2-BDC, stirring the mixture for 30min, pouring the mixture into a polytetrafluoroethylene-lined high-pressure reaction kettle, reacting for 24h at the temperature of 130 ℃, and centrifugally washing the precipitate with DMF three times after the reaction is finished.
(2) The precipitate washed in step (1) is placed in 40mL of DMF solution containing 0.2mL of HCl, stirred at 80 ℃ for 12h to complete the activation process, and finally washed with DMF and methanol three times in sequence at 1Drying in a vacuum drying oven at 50 ℃ for 12h to obtain HP-NH with different regulator contents2MIL-53, noted as HP-MOF-1:5:1, HP-MOF-1:8:1, HP-MOF-1:10:1(HP-MOF-C10), HP-MOF-1:12:1, respectively. The BET characterization results showed that HP-MOF-1:5:1, HP-MOF-1:8:1, HP-MOF-1:10:1, and HP-MOF-1:12:1 have 1998.32m, respectively2/g、1900.24m2/g、1178.14m2G and 632.71m2Specific surface area per gram, 1.59cm3/g、2.16cm3/g、1.15cm3G and 0.62cm3Pore volume per gram, and pore size ranges of 0.64-2.95nm, 0.64-3.18nm, 1.39-7.69nm, and 1.39-12.91 nm.
The four HP-NH compounds prepared as described above were tested using the test method of example 12-MIL-53 adsorption performance at 30 ℃, corresponding to total adsorption amounts of HP-MOF-1:5:1, HP-MOF-1:8:1, HP-MOF-1:10:1, HP-MOF-1:12:1 on STV and RA: 161.61mg/g, 155.18mg/g, 168.39mg/g, 159.03 mg/g. The adsorption selectivity for STV versus RA was: 1.49, 1.50, 1.70, 1.63.
FIG. 3 and FIG. 4 are HP-NH prepared in this example, respectively2N of-MIL-532Adsorption and desorption curve diagram and aperture distribution diagram. As can be seen from fig. 3 and 4, the amount of the added regulator affects the number of defective pores, and thus the pore size distribution range.
Example 3
In this example, the preparation method of the hierarchical porous metal organic framework compounds with different ligand contents includes the following steps:
(1) weighing 4 parts of 5mmoL (1.21g) AlCl3·6H2O, dissolved in 40mL of DMF under stirring, 50mmoL (8.61g) of capric acid (C10) was added to each portion under stirring, and 5mmoL (0.91g), 4mmoL (0.73g), 3mmoL (0.54g) and 2mmoL (0.36g) of NH were added thereto respectively2-BDC, stirring the mixture for 30min, pouring the mixture into a polytetrafluoroethylene-lined high-pressure reaction kettle, reacting for 24h at the temperature of 130 ℃, and centrifugally washing the precipitate with DMF three times after the reaction is finished.
(2) The precipitate washed in step (1) is placed in 40mL of DMF solution containing 0.2mL of HCl, stirred at 80 ℃ for 12h to complete the activation process, and finally usedSequentially washing DMF and methanol for three times, and drying in a vacuum drying oven at 150 ℃ for 12h to obtain HP-NH with different ligand contents2MIL-53, noted as HP-MOF-1:10:1, HP-MOF-1:10:0.8, HP-MOF-1:10:0.6, HP-MOF-1:10:0.4, respectively. BET characterization results indicated that HP-MOF-1:10:1, HP-MOF-1:10:0.8, HP-MOF-1:10:0.6, HP-MOF-1:10:0.4 had 1178.14m2/g、886.60m2/g、591.31m2G and 552.48m2Specific surface area per gram, 1.15cm3/g、1.10cm3/g、0.48cm3G and 0.60cm3Pore volume per gram, and pore size distribution ranges of 1.48 to 7.69nm, 1.48 to 7.73nm, 1.48 to 6.46nm, and 2.63 to 6.46nm, with a peak at 3.80 nm.
The four HP-NH compounds prepared as described above were tested using the test method of example 12The adsorption performance of MIL-53 at 30 ℃ corresponding to the total adsorption amounts of HP-MOF-1:10:1, HP-MOF-1:10:0.8, HP-MOF-1:10:0.6, and HP-MOF-1:10:0.4 for STV and RA, respectively: 168.39mg/g, 149.89mg/g, 125.39mg/g, 38.58 mg/g. The adsorption selectivity for STV versus RA was: 1.70, 1.76, 2.11, 4.13.
FIG. 5 and FIG. 6 show HP-NH prepared in this example2N of-MIL-532Adsorption and desorption curve diagram and aperture distribution diagram. As can be seen from fig. 5 and 6, the amount of ligand influences the number of defect pores.
Example 4
The HP-MOF-1:10:0.6 adsorbent obtained in example 3 was tested for its adsorption performance on a crude sugar solution having a concentration of 5mg/mL at 30 ℃ and 150rpm, where CSTV1.32mg/mL, CRAUnder the adsorption condition of 3.02mg/mL, the total adsorption quantity of the adsorbent to STV and RA is 153.24 mg/g. The adsorption selectivity for STV versus RA was 2.26.
Adding 80% ethanol-water solution into the HP-MOF-1:10:0.6 with saturated adsorption to serve as desorption solution, oscillating at constant temperature of 150rpm and 30 ℃ for 24h, and desorbing the adsorbed stevioside. Through measurement, the desorption rates of STV and RA can reach 91.63% and 97.58% respectively. It can be seen that the HP-NH prepared according to the invention2MIL-53 has good effect on the separation and purification of steviosideCyclic regeneration capability and application capability.
Example 5
(1) Weighing 2mmoL (0.48g) AlCl3·6H2O, dissolved in 40mL of DMF under stirring, 20mmoL of capric acid (3.45g) was added thereto, and after mixing under stirring, 4mmoL (0.72g) of NH was added thereto2-BDC, stirring the mixture for 30min, pouring the mixture into a polytetrafluoroethylene-lined high-pressure reaction kettle, reacting for 30h at 120 ℃, and centrifugally cleaning the precipitate with DMF for three times after the reaction is finished;
(2) and (3) placing the precipitate obtained in the step (1) in 40mL of DMF solution containing 0.2mL of HCl, stirring for 8h at 100 ℃ to complete the activation process, sequentially washing with DMF and methanol three times, and drying in a vacuum drying oven at 150 ℃ for 15h to obtain the product, wherein the product is recorded as HP-MOF-1:10: 2. BET characterization showed that HP-MOF-1:10:2 has 730.11m2Specific surface area per gram, 1.07cm3A pore volume of/g and a pore size distribution range of 0.64 to 3.67 nm.
The adsorption performance of HP-MOF-1:10:2 prepared as described above at 30 ℃ was tested using the test method in example 1, and the results showed that the total adsorption amount was 88.74mg/g, and the adsorption selectivity of STV to RA was 1.99. FIG. 7 and FIG. 8 show HP-NH prepared in this example2N of-MIL-532Adsorption and desorption curve diagram and aperture distribution diagram.
Example 6
(1) Weighing 2mmoL (0.48g) AlCl3·6H2O, dissolved in 40mL of DMF under stirring, 30mmoL of capric acid (5.17g) was added thereto, and after mixing under stirring, 4mmoL (0.72g) of NH was added thereto2-BDC, stirring the mixture for 30min, pouring the mixture into a polytetrafluoroethylene-lined high-pressure reaction kettle, reacting for 20h at the temperature of 150 ℃, and centrifugally cleaning the precipitate with DMF for three times after the reaction is finished;
(2) placing the precipitate obtained in the step (1) in 40mL of DMF solution containing 0.4mL of HCl, stirring at 60 ℃ for 12h to complete the activation process, washing with DMF and methanol three times in sequence, and drying in a vacuum drying oven at 200 ℃ for 12h to obtain the product, which is recorded as HP-MOF-1:15: 2. The BET characterization showed that HP-MOF-1:15:2 has 2293.98m2Specific surface area per gram, 1.36cm3Pore volume in g and pore size distribution range of 0.64-2.95nm。
The adsorption performance of HP-MOF-1:15:2 prepared as described above at 30 ℃ was tested using the test method in example 1, and the results showed that the total adsorption amount was 282.52mg/g, and the adsorption selectivity for STV versus RA was 1.35. FIG. 9 and FIG. 10 show HP-NH prepared in this example2N of-MIL-532Adsorption and desorption curve diagram and aperture distribution diagram.
While embodiments of the invention have been shown and described above, it is to be understood that the above embodiments are exemplary and not to be construed as limiting the invention, and that various embodiments or examples and features of various embodiments or examples described in this specification are capable of being combined and brought together by those skilled in the art without thereby conflicting with each other.