CN114950410B - Synthetic method of zirconium-manganese composite material - Google Patents

Abstract

The invention belongs to the technical field of preparation of nanometer materials, and discloses a method for synthesizing zirconium-manganese composite materials, which uses a hydrothermal method to prepare ultra-thin two-dimensional sheet-like δ-MnO ₂ formed on the surface of UiO-66; Potassium Oxide and UiO-66 as raw materials, deionized water as solvent, constant temperature reaction under specific temperature conditions, and after centrifugation, sample washing, and drying, a uniformly dispersed surface with ultra-thin two-dimensional sheet-like δ _‑MnO2 zirconium manganese composites. The zirconium-manganese composite material prepared by the invention can efficiently catalyze and oxidize 5-hydroxymethylfurfural (HMF) to generate 2,5-furandicarboxylic acid (FDCA). The preparation process of the invention is simple, the cycle is short, the cost is low, large-scale industrial production is possible, and the invention has good economic and environmental benefits.

Description

A kind of synthetic method of zirconium manganese composite material

technical field

The invention belongs to the technical field of nano-material preparation, and in particular relates to a synthesis method and application of a zirconium-manganese composite material.

Background technique

Ultrathin two-dimensional (2D) nanomaterials are only one or a few atoms thick (typically 5 nm). Displaying unusual mechanical, optical and electronic properties, they are both ideal low-dimensional materials for fundamental research and fundamental building blocks for designed assemblies. However, it is still a great challenge to achieve good dispersion of two-dimensional (2D) nanomaterials and avoid their agglomeration, which also limits the practical application of two-dimensional (2D) nanomaterials in the field of catalysis.

MOFs are materials with well-defined active sites and functional structures, which have shown good catalytic oxidation performance, but low permeability and stability limit their development.

At present, the commonly used MnO ₂ catalytic materials include 0D MnO ₂ , 1D MnO ₂ , and 2D MnO ₂ . Among them, 0D and 1D MnO ₂ have fewer exposed active sites, and their catalytic performance is poorer than that of 2D MnO ₂ . Common methods for preparing two-dimensional MnO ₂ include co-precipitation method, hydrothermal method, sol-gel method, etc. Among them, the co-precipitation method is uncontrollable due to its rapid reaction, which affects the uniformity of the prepared catalyst, and the prepared monolayer The thickness of _MnO2 flakes is generally between 3-7 nm; while the samples produced by the sol-gel method are more uniform than the co-precipitation method, but the production cycle is generally longer and the process is troublesome, which limits its large-scale production. The thickness of a single-layer MnO ₂ sheet is generally between 0.5-5 nm; therefore, the present invention adopts a relatively convenient hydrothermal synthesis method with uniform growth. However, the traditional hydrothermal method generally uses direct hydrothermal KMnO ₄ . The two-dimensional MnO ₂ prepared in this way has poor dispersion and is easy to agglomerate. The thickness of the prepared single-layer MnO ₂ sheet is generally between 2-6 nm.

Therefore, in order to design highly efficient thermal catalysts, the co-construction of a catalyst with a 3D self-supporting structure and a 2D catalytic surface by the present invention using 2D _MnO2 nanosheets and MOF matrix may be a suitable strategy.

Based on this, the present invention provides a method for preparing a zirconium-manganese composite material, using the classic MOF material UiO-66 as a matrix, and using a certain method to make KMnO ₄ and UiO-66 react, in this process, KMnO ₄ As an oxidant, The organic functional group on UiO-66 acts as a reducing agent, and a redox reaction occurs, and δ-MnO ₂ grows on the surface of UiO-66 in situ, and the growth time is controlled to adjust the morphology of MnO ₂ and increase its specific surface area to increase the catalytic performance of the material. Active sites, designed and prepared zirconium manganese composites with regular morphology.

Contents of the invention

The object of the present invention is to provide a zirconium-manganese composite material with ultra-thin two-dimensional sheet-like δ-MnO ₂ grown on the surface and a preparation method thereof.

To achieve the above object, the present invention adopts the following technical solutions:

A method for synthesizing a zirconium-manganese composite material, comprising the following raw materials: potassium permanganate (KMnO ₄ ), UiO-66 (C ₄₈ H ₂₈ O ₃₂ Zr ₆ ).

A method for synthesizing zirconium-manganese composite materials: mixing and dissolving potassium permanganate in deionized water to make a uniformly dispersed reaction precursor; then adding UiO-66 to the reaction precursor, performing ultrasonic stirring treatment, and transferring to The polytetrafluoroethylene lining in the stainless steel autoclave, and the constant temperature reaction is carried out in the drying oven; after the reaction is completed, it is cooled, centrifuged, washed, and dried until the water is completely volatilized, and the black solid powder with uniform size and highly dispersed zirconium manganese is obtained composite material.

The zirconium-manganese composite material with uniform and highly dispersed sizes specifically comprises the following steps:

(1) Add heptavalent manganese salt into deionized water, fully mix and dissolve to make a uniformly dispersed reaction precursor;

(2) Then UiO-66 was added to the reaction precursor solution for a certain ultrasonic stirring treatment, and then transferred to multiple polytetrafluoroethylene-lined stainless steel autoclaves, and the constant temperature reaction was carried out in a dry box;

(3) After the reaction is completed, the two-dimensional zirconium-manganese composite material in the form of black solid powder is obtained through cooling, centrifugal separation, washing, and drying until the water is completely evaporated.

Further, the heptavalent manganese salt in step (1) is non-toxic potassium permanganate (KMnO ₄ );

Further, in step (2), the molar ratio of UiO-66 (C ₄₈ H ₂₈ O ₃₂ Zr ₆ ) and the element Zr:Mn in KMnO ₄ is 1:1-1:4, and the amount of deionized water is 250 mL.

Further, the mixing and dissolving described in step (2) specifically includes: ultrasonic dispersion and magnetic stirring, the ultrasonic dispersion time is 10-30 min; the magnetic stirring speed is 500 rpm; the magnetic stirring time is 20-30 min.

Further, the specification of the polytetrafluoroethylene lining in step (2) is 25 mL.

Further, the constant temperature reaction described in step (2) specifically includes: constant temperature reaction at 180° C. for 30 min-4 h.

Further, the cooling described in step (3) specifically includes: cooling to room temperature with the furnace.

Further, the washing solvent in step (3) is deionized water, and the washing times are 3 times.

Further, the drying method described in step (3) is vacuum freeze-drying at -53 °C, and the drying time is 12 h.

Significant advantage of the present invention is:

(1) The present invention utilizes cheap and easily available raw materials, adopts a simple and easy-to-operate hydrothermal method, and synthesizes zirconium-manganese composite oxide step by step, and its size distribution is 200-500 nm. The preparation process of the invention is economical, convenient and efficient, and does not need to add any surfactant.

(2) The zirconium-manganese composite oxide obtained in the present invention can not only maintain the basic structure of the matrix MOF, but also improve its catalytic oxidation performance by combining with the MOF structure.

(3) The equipment and materials required by the preparation method of the present invention are easy to obtain, the process operation is simple, the process conditions are simple, and it has the advantages of low cost, safety and high efficiency; what the present invention obtains is an eco-friendly material, which has Very good promotion and application value.

(4) The present invention utilizes the hydrothermal method to form ultra-thin two-dimensional sheet-like δ-MnO ₂ on the surface of UiO-66, with a thickness distribution between 0.9-1.5 nm; using potassium permanganate and UiO-66 as raw materials, removing Ionized water is used as a solvent, and a constant temperature reaction is carried out under a specific temperature condition. After centrifugation, sample washing, and drying, a uniformly dispersed zirconium-manganese composite material with ultrathin two-dimensional sheet-like δ-MnO ₂ grown on the surface is obtained. The zirconium-manganese composite material prepared by the invention can efficiently catalyze and oxidize 5-hydroxymethylfurfural (HMF) to generate 2,5-furandicarboxylic acid (FDCA).

(5) UiO-66 is a MOF formed by the coordination of Zr and terephthalic acid, in which terephthalic acid undergoes a redox reaction with KMnO ₄ to generate layered δ-MnO _{2 in situ, and layered δ-MnO 2} -MnO ₂ grows up gradually, and finally forms δ-MnO ₂ with a three-dimensional self-supporting structure. UiO-66 provides a supporting role to avoid the agglomeration of layered structure δ-MnO ₂ . However, MOF materials are usually unstable in water, and the structure will collapse or be destroyed during the hydrothermal synthesis process. UiO-66 is relatively stable and can be used as a stable support structure. Zirconium is acidic and basic, and has a certain activation effect on the substrate, but because its own lattice oxygen is relatively stable and lacks certain oxidation ability, it is used as a matrix to composite with _MnO2 , which is beneficial to the catalytic oxidation of HMF. Manganese oxide has a strong selective oxidation ability, and can selectively oxidize HMF to FDCA. The layered structure of manganese dioxide has more exposed surfaces and more catalytic active sites, which is conducive to the rapid progress of the reaction. , due to the supporting effect of the three-dimensional matrix, the agglomeration of layered manganese dioxide is avoided, and the high-efficiency activity of the catalyst is maintained.

Description of drawings

Figure 1 is an X-ray diffraction (XRD) diagram of a zirconium-manganese composite material of Zr:Mn=1:1-1:4 prepared in Example 1 of the present invention with a hydrothermal time of 3 h;

Fig. 2 is a comparison diagram of the microscopic morphology of the zirconium-manganese composite material prepared from Zr:Mn=1:2 in Example 1 of the present invention, and the hydrothermal time is from 30 min to 12 h, and the Zr:Mn=1:2, hydrothermal EDS energy spectrum of zirconium manganese composite material prepared in 3 h;

Fig. 3 is the microscopic appearance of the UiO-66 that comparative example 1 of the present invention makes;

Fig. 4 is Zr:Mn=1:2 in the embodiment of the present invention 1, the transmission electron microscope figure of the zirconium manganese composite material that hydrothermal time 3 h makes;

Fig. 5 is Zr:Mn=1:2 in the embodiment 1 of the present invention, the zirconium manganese composite material that hydrothermal time 3 h makes;

Fig. 6 is the transmission electron microscope figure of the UiO-66 that comparative example 1 of the present invention makes;

Figure 7 shows the zirconium-manganese composite material prepared in Example 1 of the present invention with Zr:Mn=1:2, and the hydrothermal time is 30 min, 3 h, and 12 h. HMF is catalyzed at 130 °C, 1.5 MPa, and reacted for 18 h. performance comparison chart;

Figure 8 shows the Zr:Mn=1:2 in Example 1 of the present invention, the zirconium-manganese composite material prepared by hydrothermal treatment for 3 h, the UiO-66 prepared in Comparative Example 1, and the UiO-66 and MnO prepared in Comparative Example 2 ₂ Performance comparison chart of mechanically mixed materials;

Fig. 9 is a cycle performance graph of the zirconium-manganese composite material prepared in Example 1 of the present invention with Zr:Mn=1:2 and hydrothermal for 3 h.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings, that is, embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined as long as there is no conflict with each other.

Example 1

Preparation of zirconium manganese composite materials:

(1) Weigh 0.22-0.88 g of potassium permanganate (KMnO ₄ ) with an electronic balance, add it into 250 mL of deionized water, and disperse it ultrasonically for 10 min, then magnetically stir for 30 min at a stirring speed of 500 rpm to obtain solution A , the solution A is placed in the polytetrafluoroethylene liner by 14mL each;

(2) Weigh 0.02 g of UiO-66 (Zr:Mn=1:1-1:4) with an electronic balance, add it to the above-mentioned polytetrafluoroethylene lining, stir it magnetically for 10 min at a stirring speed of 500 rpm, and prepare Obtain uniformly dispersed solution B;

(3) Then transfer the polytetrafluoroethylene lining to a stainless steel autoclave, and react in a drying oven at a constant temperature of 180 °C for 3 h (30 min, 1 h, 2 h, 4 h, 12 h). Cool to room temperature;

(4) Centrifuge the sample with a centrifuge to obtain a black solid powder at a rotational speed of 9000 rpm; wash with deionized water three times;

(5) Zirconium-manganese composites were obtained by freeze-drying overnight until the water evaporated completely.

Fig. 1 is the X-ray diffraction (XRD) figure of the zirconium-manganese composite material of Zr:Mn=1:1-1:4 prepared in the hydrothermal time of 3 h in Example 1 of the present invention, as can be seen from the figure With Zr:Mn=1:1-1:4, UiO-66 in the synthesized zirconium-manganese composite material is transformed into monoclinic phase ZrO ₂ (m-ZrO ₂ ) and then into tetragonal phase ZrO ₂ (t-ZrO ₂ ), At the same time, the existing phase of Mn is δ-MnO ₂ , and it can be seen from the energy spectrum that the three elements of Mn, Zr and O are evenly distributed. Fig. 2 is Zr:Mn=1:2 in the embodiment 1 of the present invention, the microcosmic morphology comparison figure of the zirconium-manganese composite material that hydrothermal time is made from 30min-12 h and Zr:Mn=1:2, hydrothermal 3 The EDS energy spectrum of the zirconium-manganese composite material prepared in h, it can be seen from the figure that as the hydrothermal time is extended from 30 min to 3 h, the MnO ₂ on the surface of UiO-66 gradually transforms from filaments attached to the surface to obvious The two-dimensional sheets gradually transformed into one-dimensional lines at 4 h. Fig. 3 and Fig. 6 are the microcosmic topography diagram and transmission electron microscope diagram of the UiO-66 that the comparative example 1 of the present invention makes, can find out from the figure that the prepared UiO-66 has regular and uniform appearance, and the size distribution is in the range of 0.5-2 between μm. Fig. 4 is the transmission electron microscope picture of the zirconium-manganese composite material prepared by Zr:Mn=1:2 in Example 1 of the present invention, and the hydrothermal time is 3 h. It can be seen from the figure that the particle size of the zirconium-manganese composite material synthesized by hydrothermal The distribution is slightly larger than the original UiO-66 size, distributed between 0.6-2.1 μm, while the edge flake _MnO2 is clearly visible. Figure 5 is an atomic force microscope image of the zirconium-manganese composite material prepared in Example 1 of the present invention with Zr:Mn=1:2 and a hydrothermal time of 3 h. It can be seen from the figure that the ultra-thin two-dimensional δ-MnO ₂ on the surface The thickness of the nanosheets is distributed between 0.9-1.5nm. Figure 7 is a comparison chart of the performance of the zirconium-manganese composite material prepared in Example 1 of the present invention with Zr:Mn=1:2, and the hydrothermal time is 30 min, 3 h, and 12 h for catalytic HMF. It can be seen from the figure The HMF conversion rate of the three can reach 100%, and the yield of FDCA of the sample heated for 3 hours is the highest, reaching 99.2%, which is higher than 62.8% for 30 minutes and 74.2% for 12 hours. The performance is better than the hydrothermal 30 min sample because the MnO ₂ gradually grows with the hydrothermal time extending from 30 min to 3 h, and the growth is not complete at 30 min, but as the hydrothermal time is further extended to 12 h, the layered δ- _MnO2 on the surface transforms into a linear

α-MnO ₂ , the active sites that play a catalytic role are reduced, and the performance is reduced to a certain extent.

Comparative example 1

Preparation of UiO-66:

(1) Weigh 0.0469 g of zirconium chloride (AlCl ₃ 6H ₂ O) and 0.0.0348 g of terephthalic acid (PTA) with an electronic balance, add them to 40 ml of DMF, stir for 30 min, then add 5 mL of acetic acid, Stir again for 30 min to make a reaction precursor;

(2) Then the reaction precursor solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave, and reacted at a constant temperature of 120 °C in a dry box for 24 h, and cooled to room temperature with the furnace after the reaction;

(3) Centrifuge the sample with a centrifuge to obtain a white solid powder at a rotational speed of 9000 rpm; wash with DMF and formic acid three times respectively;

(4) UiO-66 with uniform size and high dispersion was obtained by vacuum drying overnight until the water evaporated completely.

Comparative example 2

Preparation of mechanically mixed samples of UiO-66 and _MnO :

(1) Weigh 0.1 g of UiO-66 (C ₄₈ H ₂₈ O ₃₂ Zr ₆ ) and 0.062 g of δ-MnO ₂ with an electronic balance and mix them evenly. The element Zr:Mn in UiO-66 and δ-MnO ₂ The molar ratio is 1:2;

(2) The sample after the two are evenly mixed is ground with a mortar for 20 min and then sieved with a sieve for 3 times.

HMF catalytic oxidation experiment

Application Example 1

The zirconium-manganese composite material obtained in Example 1 is used for the catalytic oxidation of 5-hydroxymethylfurfural (HMF), and the specific steps are as follows:

(1) Take 10 mL of ultra-pure water and place it in the liner of the autoclave, add 50 mg of HMF, then add 50 mg of sodium bicarbonate, add 100 mg of zirconium-manganese composite catalyst, and perform ultrasonic treatment;

(2) Introduce oxygen, keep the pressure at 1.5 MPa, and start timing after the temperature rises to 130 °C;

(3) After 18 hours of reaction, take out the reaction solution and quantify it into a 10 mL volumetric flask, pour it into a 50 mL centrifuge tube, take 1 mL of the supernatant after centrifugation, drop it into a 100 mL volumetric flask, and quantify it to 100 mL, after ultrasonication for five minutes Take an appropriate amount of the solution and place it in the liquid chromatography test.

Application Comparative Example 1

The UiO-66 obtained in Comparative Example 1 is used for the catalytic oxidation of HMF, and the specific steps are as follows:

(1) Take 10 mL of ultrapure water and place it in the liner of the autoclave, add 50 mg of HMF, add 50 mg of sodium bicarbonate, add 100 mg of UiO-66 catalyst, and perform ultrasonic treatment;

(2) Introduce oxygen, keep the pressure at 1.5 MPa, and start timing after the temperature rises to 130 °C;

(3) After 18 hours of reaction, take out the reaction solution and quantify it into a 10 mL volumetric flask, pour it into a 50 mL centrifuge tube, take 1 mL of the supernatant after centrifugation, drop it into a 100 mL volumetric flask, and quantify it to 100 mL, after ultrasonication for five minutes Take an appropriate amount of the solution and place it in the liquid chromatography test.

Application Comparative Example 2

The mechanically mixed sample of UiO-66 and _MnO2 obtained in Comparative Example 2 was used for the catalytic oxidation of HMF, and the specific steps were as follows:

(1) Take 10 mL of ultrapure water and place it in the inner tank of the autoclave, add 50 mg of HMF, then add 50 mg of sodium bicarbonate, add 100 mg of UiO-66 and MnO ₂ mechanically mixed catalysts, and perform ultrasonic treatment;

(2) Introduce oxygen, keep the pressure at 1.5 MPa, and start timing after the temperature rises to 130 °C;

(3) After 18 hours of reaction, take out the reaction solution and quantify it into a 10 mL volumetric flask, pour it into a 50 mL centrifuge tube, take 1 mL of the supernatant after centrifugation, drop it into a 100 mL volumetric flask, and quantify it to 100 mL, after ultrasonication for five minutes Take an appropriate amount of the solution and place it in the liquid chromatography test.

Figure 8 is a performance comparison diagram of the zirconium-manganese composite material prepared in Example 1 of the present invention, UiO-66 prepared in Comparative Example 1, and UiO-66 and MnO2 prepared in Comparative Example _2. It can be seen that the zirconium-manganese The composite material has the best catalytic performance, and the FDCA yield reaches 99.2%, which exceeds 64.8% of mechanical mixing and 3.9% of pure UiO-66. Zirconium-manganese composites can completely catalytically reduce 100% of HMF after 18h, and its performance is much better than that of UiO-66 and UiO-66 and MnO ₂ mechanically mixed samples. It can be seen from Figure 9 that the zirconium-manganese composite material prepared by the present invention has a conversion rate of 100% to HMF, while the FDCA yield reaches 99.2%, and has excellent cycle performance, and each cycle can maintain 100% HMF The conversion rate and FDCA yield are all over 90%, and the excellent catalytic oxidation performance to HMF is still maintained after 4 cycles.

It is easy for those skilled in the art to understand that the above descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be Included within the protection scope of the present invention.

Claims (6)

1. The application of a zirconium-manganese composite material, characterized in that: the zirconium-manganese composite material is used as a catalyst in catalytic oxidation of 5-hydroxymethylfurfural to generate 2,5-furandicarboxylic acid; The synthetic method of described zirconium manganese composite material comprises the following steps: (1) Add heptavalent manganese salt into deionized water and fully dissolve to form solution A; (2) Add UiO-66 to solution A to form reaction solution B, which is stirred at room temperature and then ultrasonicated; (3) Then transfer the reaction solution B to the polytetrafluoroethylene lining in the stainless steel autoclave, and carry out constant temperature reaction in the dry box; (4) After the reaction, cooling, centrifugal separation, washing, and drying until the water is completely evaporated, a zirconium-manganese composite material with ultra-thin two-dimensional sheet-like δ-MnO ₂ grown on the surface is obtained; The heptavalent manganese salt described in step (1) is potassium permanganate KMnO ₄ ; In step (2), UiO-66 is added according to the Zr:Mn molar ratio of 1:2; The constant temperature reaction described in step (3) is specifically: constant temperature reaction at 180 °C for 3 h. 2. The application according to claim 1, characterized in that: in step (1), the dosage of potassium permanganate is 0.002-0.005mol, and the dosage of deionized water is 250 mL. 3. The application according to claim 1, characterized in that: the dissolution described in step (1) is specifically: ultrasonic dispersion and magnetic stirring, the ultrasonic dispersion time is 10-30 min; the magnetic stirring speed is 500 rpm; the magnetic stirring The time is 20-30 min. 4. The application according to claim 1, characterized in that: the cooling in step (4) is specifically: cooling the room temperature with the furnace. 5. The application according to claim 1, characterized in that the washing solvent in step (4) is deionized water, and the number of washings is 3 times. 6. The application according to claim 1, characterized in that the drying method in step (4) is vacuum freeze-drying at -53°C, and the drying time is 8-12 hours.