Preparation method and application of hollow porous rod-shaped Mn3O4-Co nanomaterial

Abstract

The present invention discloses a preparation method and application of a hollow porous rod-shaped Mn3O4‑Co nanomaterial. A rod-shaped Mn‑BTC MOF precursor is prepared by a simple coprecipitation method, cobalt is loaded on the MOF surface by an impregnation method, and then the hollow porous rod-shaped Mn3O4‑Co nanomaterial is obtained by centrifugation, washing, drying and calcination. The hollow porous rod-shaped Mn3O4‑Co nanomaterial prepared by the present invention has more oxygen vacancies and stronger surface lattice oxygen activity, can efficiently selectively oxidize HMF to FDCA, and the FDCA selectivity reaches 85.49% in 2 hours, and has good stability. The present invention prepares a hollow porous rod-shaped Mn3O4‑Co nanomaterial using Mn‑BTC MOF as a precursor, which has the characteristics of high economic benefit, simple preparation process, and large-scale industrial production, and has good economic and environmental benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of materials, and in particular relates to a preparation method and application of a hollow porous rod-shaped Mn3O4-Co nanomaterial. Background Art

[0002] HMF is considered to be one of the most important platform chemicals from biomass and is crucial in achieving comprehensive utilization of biomass resources. In the reaction of HMF selective oxidation to FDCA, the catalyst often chooses MnO2 or Mn2O3 with a higher valence state. Mn3O4 has a lower valence state, less lattice oxygen content and is relatively stable, which makes it difficult to overflow and has relatively weak oxidation ability, resulting in poor selectivity for FDCA. However, there is little research on Mn3O4. Therefore, improving the oxidation ability of Mn3O4 is a challenging and meaningful task.

[0003] To solve this bottleneck problem, the present invention prepares a rod-shaped Mn-BTC MOF precursor by a simple coprecipitation method, loads cobalt on the MOF surface by an impregnation method, and then centrifuges, washes, dries, and calcines to obtain a hollow porous rod-shaped Mn3O4-Co nanomaterial. The prepared hollow porous rod-shaped Mn3O4-Co nanomaterial has more oxygen vacancies and stronger surface lattice oxygen activity, and can efficiently and selectively oxidize HMF to FDCA. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a hollow porous rod-shaped Mn3O4-Co nanomaterial for high efficiency and high selectivity oxidation of HMF in view of the shortcomings of the prior art. 2+ Ions are loaded on the surface of Mn-BTC MOF, and after calcination, a hollow porous rod-shaped Mn3O4-Co nanomaterial is obtained. Co(NO3)2·6H2O is stirred and dissolved in anhydrous ethanol, and Mn-BTC MOF is added for stirring, centrifugation, drying and calcination to obtain a hollow porous rod-shaped Mn3O4-Co nanomaterial. The present invention provides a green synthesis method for a hollow porous rod-shaped Mn3O4-Co nanomaterial with simple preparation, versatility and applicability. Moreover, the prepared hollow porous rod-shaped Mn3O4-Co nanomaterial has a high efficiency oxidation activity for HMF, the method is simple, the cost is low, it has good economic and environmental benefits, and it can also be mass-produced and applied.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A preparation method and application of a hollow porous rod-shaped Mn3O4-Co nanomaterial, comprising the following raw materials: cobalt nitrate hexahydrate (Co(NO3)2·6H2O), 1,3,5-benzenetricarboxylic acid (H3BTC), manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), polyvinylpyrrolidone (PVP, Mw=58000), and ethanol (C2H5OH).

[0007] A method for preparing a hollow porous rod-shaped Mn3O4-Co nanomaterial: tetrahydrated manganese acetate, polyvinyl pyrrolidone and 1,3,5-benzenetricarboxylic acid are added to a mixed solution of ethanol and water respectively, and the precursor Mn-BTCMOF is obtained by sufficient reaction; then, hexahydrated cobalt nitrate is added to ethanol and fully dissolved to form a homogeneous solution. The precursor Mn-BTCMOF is then added to the homogeneous solution, and the hollow porous rod-shaped Mn3O4-Co nanomaterial is obtained by stirring, centrifuging, washing, drying and calcining.

[0008] The hollow porous rod-shaped Mn3O4-Co nanomaterial specifically comprises the following steps:

[0009] (1) dissolving manganese acetate tetrahydrate and polyvinyl pyrrolidone in a mixed solvent to prepare liquid A;

[0010] (2) Stir and dissolve 1,3,5-benzenetricarboxylic acid in a mixed solvent as liquid B.

[0011] (3) Dropping liquid B into liquid A. Stirring, aging, washing, and drying overnight to obtain Mn-BTC MOF precursor;

[0012] (4) Cobalt nitrate hexahydrate and Mn-BTC MOF precursor are added to an alcohol solvent and stirred thoroughly to prepare solution C. Solution C is centrifuged, washed, and dried to obtain MnBTC-Co, which is then calcined to obtain a hollow porous rod-shaped Mn3O4-Co nanomaterial.

[0013] Furthermore, the mixed solvent in step (1) is a mixed solution of ethanol and deionized water, and the volume ratio of ethanol to deionized water is 2:1.

[0014] Furthermore, in step (1), the amount of manganese acetate tetrahydrate is 0.1-5.0 g, the amount of polyvinyl pyrrolidone is 1-5 g, and the amount of the mixed solution of ethanol and deionized water is 50-400 mL.

[0015] Furthermore, the mixed solvent in step (2) is a mixed solution of ethanol and deionized water, and the volume ratio of ethanol to deionized water is 2:1.

[0016] Furthermore, in step (2), the amount of 1,3,5-benzenetricarboxylic acid used is 0.5-4.0 g, and the amount of the mixed solution of ethanol and deionized water used is 50-400 mL.

[0017] Furthermore, the sufficient stirring in step (3) specifically includes: magnetic stirring; a stirring speed of 500-1000 rpm; and a stirring time of 20-30 min.

[0018] Furthermore, the aging time in step (3) is 12-24 h.

[0019] Furthermore, the washing in step (3) is specifically: washing with ethanol 3 times.

[0020] Furthermore, the drying in step (3) is specifically as follows: the drying method is drying at 60° C. and the drying time is 12-24 hours.

[0021] Furthermore, in step (4), the amount of cobalt nitrate hexahydrate used is 0.1-5.0 g, and the amount of ethanol used is 50-300 ml.

[0022] Furthermore, the sufficient stirring in step (4) specifically includes: magnetic stirring; a stirring speed of 500-1000 rpm; and a stirring time of 8-24 h.

[0023] Furthermore, the centrifugation in step (4) is specifically: centrifuging in a centrifuge at a speed of 8000 rpm for 3-5 min.

[0024] Furthermore, the drying in step (4) is specifically as follows: the drying method is vacuum drying at 60° C., and the drying time is 6-12 h.

[0025] Furthermore, the calcination in step (4) is specifically as follows: heating rate: 5-20°C / min, calcination temperature: 350-500°C, calcination time: 240-360min.

[0026] The beneficial effects of the present invention are:

[0027] (1) The present invention adopts a simple co-precipitation method to prepare a rod-shaped Mn-BTC MOF precursor. The Co element is loaded on the MOF surface by an impregnation method, and a hollow porous rod-shaped Mn3O4-Co nanomaterial is obtained by simple calcination, providing a new method for synthesizing porous rod-shaped catalysts and a new idea for the preparation of catalysts for efficient HMF conversion.

[0028] (2) The hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in the present invention is a hollow porous rod-shaped structure formed by interweaving and linking flaky particles, and the size of a single particle is about 4 μm.

[0029] (3) The raw materials and equipment required for the preparation method of the present invention are simple and easy to obtain, the process is simple, easy to operate and safe, the cost is relatively low, and large-scale industrial production is possible; compared with the products prepared by other traditional methods, it has high efficiency in oxidizing HMF activity and high selectivity, is an environmentally friendly new material, and has great promotion and application value and use prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is an X-ray diffraction (XRD) diagram of the hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention, the porous nano-spherical Mn3O4 nanomaterial prepared in Comparative Example 1, and the MnBTC-Co nanomaterial prepared in Example 1;

[0031] Figure 2 It is a schematic diagram of the 2 h FDCA yield and HMF conversion rate of the hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention, the porous nano-spherical Mn3O4 nanomaterial prepared in Comparative Example 1, and the commercial Mn3O4 material prepared in Comparative Example 2;

[0032] Figure 3 This is a performance diagram of a cycle test of a hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention;

[0033] Figure 4 This is a transmission electron microscope (SEM) image of the hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention;

[0034] Figure 5 This is a scanning electron microscope (TEM) image of the hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention;

[0035] Figure 6 is a (SEM) image of the MnBTC-Co nanomaterial prepared in Example 1 of the present invention;

[0036] Figure 7 is a (TEM) image of the MnBTC-Co nanomaterial prepared in Example 1 of the present invention;

[0037] Figure 8 This is a SEM image of the porous nano-spherical Mn3O4 nanomaterial prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings, i.e., embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined as long as they do not conflict with each other.

[0039] Example 1

[0040] Preparation of hollow porous rod-shaped Mn3O4-Co nanomaterials:

[0041] (1) Dissolve 0.49 g of manganese acetate tetrahydrate and 2 g of polyvinyl pyrrolidone in 100 mL of a mixed solution consisting of ethanol and deionized water in a volume ratio of 2:1 to prepare solution A.

[0042] (2) Dissolve 0.9 g of 1,3,5-benzenetricarboxylic acid in 80 mL of a mixed solution consisting of ethanol and deionized water in a volume ratio of 2:1 by stirring to obtain solution B.

[0043] (3) Drop liquid B into liquid A. Stir vigorously for 20 min, age for 12 h, wash 3 times, and dry at 60 °C overnight to obtain the Mn-BTC MOF reaction precursor.

[0044] (4) 2 mmol of cobalt nitrate hexahydrate and 800 mg of Mn-BTC MOF precursor were added to 100 mL of anhydrous ethanol and stirred for 8 h to prepare solution C. Solution C was centrifuged, washed, and dried to obtain MnBTC-Co. Finally, the temperature was increased from room temperature to 350 °C at a heating rate of 5 °C / min and calcined at 350 °C for 4 h to obtain a hollow porous rod-shaped Mn3O4-Co nanomaterial.

[0045] Comparative Example 1

[0046] Preparation of porous nano-spherical Mn3O4 nanomaterials:

[0047] (1) Take 1.149 g of MnCO3 and dissolve it in a single-necked flask containing 10 mL of formic acid and 75 mL of ultrapure water. Condensate and reflux at 75 °C for 3 h to obtain solution A.

[0048] (2) Place solution A in a rotary evaporator, evaporate to dryness, add 50 mL of ultrapure water, evaporate to dryness again, and freeze-dry to obtain manganese formate;

[0049] (3) Weigh 0.181 g of the manganese formate prepared above and dissolve it in 60 mL of methanol. Stir for 30 min to dissolve it to obtain solution B.

[0050] (4) Solution B was transferred to a 100 mL hydrothermal autoclave with a polytetrafluoroethylene liner and subjected to solvothermal reaction at 180 °C for 18 h. The solution was taken out for centrifugal washing and freeze-dried to obtain porous nano-spherical Mn3O4 nanomaterials.

[0051] Comparative Example 2

[0052] Preparation of commercial Mn3O4 materials:

[0053] (1) Take 1.51 g of MnSO4 and dissolve it in a single-necked flask containing 100 mL of ultrapure water to obtain solution A.

[0054] (2) Add 25 wt% ammonia water to solution A to generate Mn(OH)2 precipitate.

[0055] (3) The generated Mn(OH)2 precipitate is separated by filtration and repeatedly washed three times with deionized water. Air is introduced during stirring. Mn(OH)2 is oxidized in the air to obtain Mn3O4 precipitate.

[0056] (4) Finally, the precipitate is filtered and washed to obtain commercial Mn3O4.

[0057] Experiment on conversion of HMF to FDCA

[0058] The catalysts prepared in Example 1 and Comparative Examples 1-2 were used to oxidize HMF to FDCA, and the specific steps were as follows:

[0059] (1) In a 25 mL polytetrafluoroethylene liner, add 10 mL of ultrapure water, then add 50 mg of hydroxymethylfurfural and a certain amount of NaHCO3, and stir at 500 rpm for 1 min to obtain solution A;

[0060] (2) 105 mg of the nanomaterials prepared in Example 1, Comparative Example 1, and Comparative Example 2 were added to Solution A, respectively, and ultrasonically stirred for 1 min each;

[0061] (3) Then, the mixture was placed in an autoclave, 1.5 MPa of O2 was introduced into the autoclave, and the gas was continuously introduced and discharged three times for gas washing. The reaction mixture was stirred at a temperature of 130 °C and a stirring speed of 500 rpm for 2 hours;

[0062] (4) Collect the liquid phase after the reaction, dilute it 100 times, test the FDCA content in the solution by high performance liquid chromatography, and calculate the yield of FDCA.

[0063] Figure 2This is a schematic diagram of the FDCA yield and HMF conversion rate of the hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention, the porous nano-spherical Mn3O4 nanomaterial prepared in Comparative Example 1, and the commercial Mn3O4 material prepared in Comparative Example 2. It can be seen that the hollow porous rod-shaped Mn3O4-Co nanomaterial has the best selective oxidation activity, and its conversion rate is much faster than that of other prepared materials, and an FDCA yield of 85.49% can be achieved in 2 h. Figure 3 It is a schematic diagram of the conversion performance of the hollow porous rod-shaped Mn3O4-Co nanomaterial prepared in Example 1 of the present invention during a cyclic reaction. After 4 cycles, the performance of the hollow porous rod-shaped Mn3O4-Co nanomaterial does not decrease significantly. Figure 4 , Figure 5 They are the SEM and TEM images of the hollow porous rod-like Mn3O4-Co nanomaterials. It can be seen from the figures that the hollow porous rod-like Mn3O4-Co nanomaterials present a porous rod-like structure, and the particle size is about 4 μm, which is assembled by interweaving flaky particles. Figure 8 This is the SEM image of the porous nano-spherical Mn3O4 nanomaterial. It can be seen from the figure that the porous nano-spherical Mn3O4 nanomaterial is formed by the aggregation of tiny Mn3O4 nanoparticles to form porous nanospheres. There are also abundant pores on the surface, and the diameter is smaller than that of Mn3O4-Co, about 1.5 μm.

[0064] Those skilled in the art will easily understand that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of a hollow porous rod-shaped Mn3O4-Co nanomaterial as a catalyst in the selective oxidation of HMF to prepare FDCA, characterized in that: The method for preparing the hollow porous rod-shaped Mn3O4-Co nanomaterial comprises the following steps: (1) dissolving divalent manganese salt and polyvinyl pyrrolidone in a mixed solvent to prepare liquid A; (2) stirring and dissolving 1,3,5-benzenetricarboxylic acid in a mixed solvent to prepare liquid B; (3) Liquid B is dropped into liquid A, stirred, aged, washed, and dried overnight to obtain the reaction precursor Mn-BTC MOF; (4) adding the divalent cobalt salt and the reaction precursor into an alcohol solvent and stirring thoroughly to prepare a solution C; (5) Solution C is centrifuged and dried to obtain MnBTC-Co, and MnBTC-Co is calcined to obtain the hollow porous rod-shaped Mn3O4-Co nanomaterial.

2. The use according to claim 1, characterized in that: The mixed solvent described in steps (1) and (2) is a mixed solution of ethanol and deionized water, and the volume ratio of ethanol to deionized water is 2:

1.

3. The use according to claim 1, characterized in that: The divalent manganese salt in step (1) is specifically manganese acetate tetrahydrate.

4. The use according to claim 1, characterized in that: The aging time in step (3) is 12-24 h.

5. The use according to claim 1, characterized in that: The drying in step (3) is specifically as follows: the drying method is drying at 60° C. and the drying time is 12-24 h.

6. The use according to claim 1, characterized in that: The divalent cobalt salt described in step (4) is cobalt nitrate hexahydrate.

7. The use according to claim 1, characterized in that: The alcohol solvent in step (4) is anhydrous ethanol.

8. The use according to claim 1, characterized in that: The drying in step (5) is specifically as follows: the drying method is vacuum drying at 60°C for 6-12 h; the calcination is specifically as follows: the heating rate is 5-20°C / min, the calcination temperature is 300-500°C, and the calcination time is 240-360 min.

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