CN114318369A - Preparation method and application of MXene quantum dot supported phthalocyanine molecule composite catalyst - Google Patents

Abstract

The invention relates to a preparation method and application of a phthalocyanine molecular composite catalyst supported by MXene quantum dots. In this method, a new two-dimensional material Ti ₃ C ₂ MXene is used as the precursor to synthesize MXene quantum dots. The end groups of MXene quantum dots are regulated by changing the non-metallic source used for grafting functional groups, namely fluorine source, nitrogen source and oxygen source. Then, the metal phthalocyanine and MXene quantum dots complete the secondary coordination to form a composite molecular catalyst using controllable synthesis steps at room temperature. This MXene quantum dot-supported phthalocyanine molecular composite catalyst with adjustable catalytic activity is the first. The invention prepares a series of catalysts containing secondary coordination effect and applies them to the field of electrocatalytic reduction of carbon dioxide as a catalytic main body to realize efficient and directional conversion of carbon dioxide.

Description

Preparation method and application of a MXene quantum dot-supported phthalocyanine molecular composite catalyst

technical field

The invention relates to a preparation method of a metal phthalocyanine molecule and an MXene quantum dot composite material and its application in the field of electrocatalysis. Specifically, the method for adjusting the catalytic activity of the supported phthalocyanine molecular composite catalyst and its application in the field of electrocatalytic reduction of carbon dioxide by changing the type or number of functional groups grafted on MXene quantum dots.

Background technique

Electrocatalytic processes are very important in the transition from fossil fuels to renewable energy. Therefore, it is necessary to design electrocatalysts with high activity, high selectivity, and high stability for specific reaction pathways under the guidance of theory. Early research has focused on polycrystalline single-metal catalysts because of their simple structure, ease of manipulation, and ease of research. [Chem.Eng.J.2021,427,130980] In addition, nanostructured monometallic, ion-modified metallic, bimetallic and nonmetallic materials have been widely used in the field of electrocatalysis. Compared with traditional materials, nanomaterials usually have more low-coordination sites and larger active surface area on the surface, thus exhibiting different catalytic properties from traditional materials. [NatCommun.2021,12,3264]

Phthalocyanine is a macrocyclic conjugated complex with 18 π electrons. The π-electron conjugated macrocyclic system conforms to Huetel's rule and thus has aromaticity. Its structure is very similar to porphyrins that widely exist in nature. However, unlike porphyrins, which play an important role in living organisms, phthalocyanines are completely synthetic compounds. There is a hole in the phthalocyanine ring, which can accommodate metal elements such as iron, copper, cobalt, tin, nickel, etc., and combine to form metal phthalocyanine molecules. Monodisperse homogeneous molecular catalysts such as metal phthalocyanines themselves have a typical MN ₄ atomic structure, with well-defined active sites, which are easy to study the mechanism; in addition, their central metal structure is highly tunable. However, the single metal phthalocyanine molecule used as the catalytic host in the field of electrocatalysis still suffers from the disadvantages of poor selectivity and low stability, which limit its widespread use. [Energy Environ. Sci., 2021, 14, 2349]

Similar to homogeneous catalysts, single-atom catalysts (SACs) have attracted extensive attention of researchers due to their high atom utilization, excellent activity and selectivity for various catalytic reactions. The strong interaction between individual metal atoms and supports and the unsaturated coordination environment of SACs can significantly enhance the electrocatalytic performance. However, the vast majority of SACs are prepared by high-temperature pyrolysis, resulting in an uncontrollable coordination environment; in addition, the high surface free energy of single atoms makes them easy to aggregate to form clusters, which complicates the analysis of catalytic reaction pathways and mechanisms. [Small.2021,17,2103705]

Based on the above studies, a few literatures reported that metal phthalocyanine molecules were supported on carbon-based nanomaterials to explore the interaction between carbon substrates and metal phthalocyanine molecules. Wang group studied the effect of cobalt phthalocyanine and carbon nanotube composites on the electrocatalytic reduction of CO ₂ to CH ₃ OH. The cobalt phthalocyanine/carbon nanotube composite catalyzed CO ₂ to generate a large amount of CO, resulting in the loss of metal phthalocyanine central atoms. The activity of the catalyst decreased sharply and the amount of CH ₃ OH was reduced. In addition, the reduction of _H2 in the composite catalyst at a higher overpotential cannot be ignored. Due to the reduction of _H2 , the electron cloud density on the phthalocyanine decreases rapidly, which makes the overall structure of the phthalocyanine change and fails, which eventually leads to the catalytic effect. Activity decreased with time. [Nature 2019, 575, 639] The Shui group studied the effect of cobalt phthalocyanine and acetylene black composites on the electrocatalytic reduction of _CO to CO. The lack of the interaction between the anchored CoPc and the matrix limits the further improvement of the catalytic activity. [ACSAppl.Energy Mater.2021,4,1442]

Therefore, how to develop a method with a controllable preparation method and a simple process can realize the precise control of the coordination environment of the metal phthalocyanine molecule and the clear positioning of the active site of the composite catalyst, and further optimize the active center metal atom and the reaction intermediate. It is an urgent problem to realize the directional and efficient transformation of reactants.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for regulating the catalytic activity of the supported phthalocyanine molecular composite catalyst by the type or quantity of functional groups grafted on the substrate, and its application in the field of electrocatalytic reduction of carbon dioxide, aiming at the deficiencies in the current technology. In this method, a new two-dimensional material Ti ₃ C ₂ MXene is used as the precursor to synthesize MXene quantum dots. The end groups of MXene quantum dots are regulated by changing the non-metallic source used for grafting functional groups, namely fluorine source, nitrogen source and oxygen source. source. Then, the metal phthalocyanine and MXene quantum dots complete the secondary coordination to form a composite molecular catalyst by using controllable synthesis steps at room temperature. This MXene quantum dot-supported phthalocyanine molecular composite catalyst with adjustable catalytic activity is the first. The invention prepares a series of catalysts containing secondary coordination effect and applies them to the field of electrocatalytic reduction of carbon dioxide as a catalytic main body to realize efficient and directional conversion of carbon dioxide.

Technical scheme of the present invention:

A preparation method of MXene quantum dot-supported phthalocyanine molecular composite catalyst, the method comprises the following steps:

(1) Immerse Ti ₃ AlC ₂ in hydrofluoric acid for 20-48 h, take it out, centrifuge and freeze-dry to obtain Ti ₃ C ₂ -MXene; then add it to the surface termination source solution, ultrasonically disperse 3- After 6 hours, the mixture was stirred at room temperature for 2-48 hours, and then centrifuged to obtain the supernatant; the supernatant was dialyzed for 3-6 hours, and the dialysate was collected to obtain a Ti ₃ C ₂ -A-MXene quantum dot solution.

Wherein, the concentration of the hydrofluoric acid is 35-45wt%; the surface termination source is F source, O source or N source, and the concentration range is 0.2-0.5mol/L; every 50mL of the surface termination source solution is added with 0.1 ~1.0 g of _{Ti3C2 - MXene} ; add 1-4 g of Ti3AlC2 per 50-100 mL of hydrofluoric _acid .

The concentration of the Ti ₃ C ₂ -A-MXene quantum dot solution is 1.0-1.2 mg/mL.

The ultrasonic power is 100W-500W; the molecular weight cut-off of the dialysis bag is 500Da-3000Da.

The inert gas is argon or nitrogen.

In the Ti ₃ C ₂ -A-MXene quantum dots, A is a surface termination group, specifically -F, -OH or -NH ₂ .

(2) The Ti ₃ C ₂ -A-MXene quantum dot solution and the metal phthalocyanine were added to the organic solvent, respectively, and ultrasonically treated for 1-4 hours, then the two solutions were mixed, and ultrasonic dispersion was continued for 0.2 to 1.0 hours; Stir at room temperature for 20-24 hours, and finally centrifuge, wash and freeze-dry to obtain a supported composite molecular catalyst CoPc-Ti ₃ C ₂ A QDs, that is, an MXene quantum dot-supported phthalocyanine molecular composite catalyst.

Among them, every 30 mL of metal phthalocyanine solution contains 0.5-3 mg of metal phthalocyanine; every 10 mL of organic solvent is added with 1-8 mL of Ti ₃ C ₂ -A-MXene quantum dot solution; Ti ₃ C ₂ -A-MXene quantum dots and metal phthalocyanine The mass ratio of feeding materials is 1 to 20:1.

The freeze-drying temperature is -40°C--60°C; the vacuum degree is 15-20kPa.

The F source is sodium fluoride, lithium fluoride or ammonium fluoride; the O source is sodium hydroxide, potassium hydroxide or sodium carbonate; the N source is ammonia water or hydrazine hydrate.

The metal phthalocyanine is iron phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, copper phthalocyanine or tin phthalocyanine.

The solvent added to the metal phthalocyanine solution and the Ti ₃ C ₂ -A-MXene quantum dot solution is the same, and both are organic solvents, specifically NN, dimethylformamide (DMF) or absolute ethanol.

The use of the MXene quantum dot-supported phthalocyanine molecular composite catalyst prepared by the method is as a catalytic material for electrocatalytic reduction of CO ₂ .

The essential features of the present invention are:

The supported molecular catalyst prepared by the invention is synthesized at room temperature, which avoids the complex and uncontrollable coordination effect between the metal and the carrier caused by high temperature carbonization; the coordination environment between the MXene quantum dot and the central metal can be changed by changing the edge of the carrier. Different functional groups will form different secondary coordination, which is beneficial to the mechanism analysis of the electrocatalytic _CO reduction reaction. Metal phthalocyanine molecules can be adjusted, such as iron phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, copper phthalocyanine, tin phthalocyanine, etc.; MXene quantum dot end-group functional groups can be adjusted, such as fluorine end-group, hydroxyl, amino, etc.; the number of functional groups It is obtained by preparing MXene quantum dots of different sizes. This MXene quantum dot-supported phthalocyanine molecular composite catalyst with tunable catalytic activity is the first of its kind. Therefore, the supported composite molecular catalyst prepared by the present invention is a good catalyst host.

Beneficial effects of the present invention:

(1) The present invention provides a preparation method for regulating the catalytic activity of a composite molecular catalyst by changing the type or quantity of grafted functional groups on MXene quantum dots;

(2) The supported phthalocyanine molecule composite catalyst obtained in the present invention exhibits excellent electrochemical performance in the field of electrocatalytic reduction of carbon dioxide. The traditional electrochemical reduction of CO by cobalt phthalocyanine produces mainly _CO with a Faradaic efficiency of only 76%. The composite catalyst obtained by the invention changes the adsorption of intermediates in the electroreduction process, greatly improves the selectivity of the catalyst, and the Faradaic efficiency of CO can reach 100%. In addition, the composite molecular catalyst obtained in the present invention has a secondary coordination effect, and the active site is clear, namely MN ₄ O ₁ (M is the central metal of the metal phthalocyanine molecule). It exhibits excellent electrochemical performance in the field of electrocatalytic reduction of carbon dioxide.

Description of drawings

1 is a transmission electron microscope image of the hydroxyl-rich MXene quantum dots prepared in Example 1.

2 is an X-ray photoelectron spectrogram of the cobalt phthalocyanine supported hydroxyl-rich MXene quantum dot composite molecular catalyst prepared in Example 4.

3 is a test diagram of the electrocatalytic performance of the cobalt phthalocyanine-supported hydroxyl-rich MXene quantum dot composite molecular catalyst prepared in Example 4 for electrocatalytic reduction of carbon dioxide.

4 is a schematic structural diagram of the cobalt phthalocyanine-supported hydroxyl-rich MXene quantum dot molecular catalysts prepared in Examples 4-6 of the present invention with secondary coordination effect. Among them, cobalt phthalocyanine can be replaced by iron phthalocyanine, nickel phthalocyanine, copper phthalocyanine, tin phthalocyanine and other molecules, and hydroxyl-rich titanium carbide quantum dots can be replaced by titanium carbide quantum dot carriers with different functional groups.

Detailed ways

The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

Example 1

2 g of Ti ₃ AlC ₂ was weighed, slowly added to 70 ml of HF (40 wt %) within 15 min, and stirred at 35° C. for 24 h to etch the Al layer. After removal and centrifugation, the product was washed with deionized water until pH ≥ 6. The precipitate was collected, freeze-dried for 24 hours (freeze-drying temperature -55° C., vacuum degree 15 kPa) to obtain a sample Ti ₃ C ₂ MXene.

Weigh 500 mg of Ti ₃ C ₂ MXene, disperse it into a flask containing 50 mL of 0.5M NaOH solution, perform ultrasonic treatment for 3 h under argon protection, transfer the flask to a water bath, and stir at room temperature for 48 h under argon protection. Centrifuge the solution, collect the supernatant and dialyze it to neutrality for 3 hours (dialysis bag parameter is 1000Da), collect the dialysate, and obtain a hydroxyl-rich MXene quantum dot solution (Ti ₃ C ₂ -OH-MXene QDs) with a concentration of 1.0 mg/mL .

1 is a transmission electron microscope image of the hydroxyl-rich MXene quantum dots obtained in Example 1. It can be seen from the figure that the average size of the prepared hydroxyl-rich MXene quantum dots is around 10 nm, and no agglomeration is observed.

Example 2-3

Other steps are the same as in Example 1, except that NaOH is replaced with NaF, NH ₃ ·H ₂ O respectively, and the subsequent steps are the same to obtain MXene quantum dots (Ti ₃ C ₂ -F with end groups -F, -NH ₂ ) -MXene QDs, Ti3C2 _{- NH2 -} MXene QDs).

Example 4

Weigh 4 mL of the hydroxyl-rich titanium carbide quantum dot solution obtained in Example 1 (that is, containing 4 mg of quantum dots) and dissolve it in 10 mL of DMF, and weigh 4 mg of cobalt phthalocyanine and dissolve it in 60 mL of DMF. Mix and sonicate for 0.5h. The obtained solution was transferred to a flask and stirred at room temperature for 20 h. The solution was collected in a centrifuge tube, washed 3-5 times with DMF and 3-5 times with absolute ethanol, and freeze-dried (freeze-drying temperature -55°C, vacuum degree 15kPa ) to obtain the supported molecular catalyst CoPc-Ti ₃ C ₂ OH QDs.

2 is an X-ray photoelectron spectrogram of the cobalt phthalocyanine-supported hydroxyl-rich MXene quantum dot composite molecular catalyst obtained in Example 4. From the O1s energy spectrum, it can be seen that in addition to TiO ₂ , C-Ti-O _x , C-Ti-(OH) _x and Al ₂ O ₃ , Co-O coordination is also observed.

3 is a test diagram of the electrocatalytic reduction of carbon dioxide performance of the cobalt phthalocyanine-supported hydroxyl-rich MXene quantum dot composite molecular catalyst obtained in Example 4. The composite catalyst has excellent electrocatalytic _CO reduction performance, high selectivity to CO, and the Faradaic efficiency for CO generation is maintained above 90% in a wide potential range (600 mV), and can reach up to 100%.

Weigh 5 mg of CoPc-Ti ₃ C ₂ OH QDs, add 475 μL of absolute ethanol, 475 μL of deionized water and 50 μL of 0.5 wt.% Nafion solution, and ultrasonically disperse for 1 h to form a uniform dispersion. 50 μL of the obtained dispersion was dropped on carbon paper (0.1 cm ⁻² ) and dried naturally at room temperature.

All electrochemical tests in the present invention were carried out in a conventional three-electrode cell using a CHI760E electrochemical workstation, and the electrolyte was a 0.1M _KHCO3 solution. With Ag/AgCl as the reference electrode, platinum wire as the counter electrode, and carbon paper coated with catalyst ink as the working electrode, the conversion formula of electrode potential and RHE is: E(vs.RHE)=E(vs.Ag/AgCl) +0.224V+0.0596×pH. The test process is to conduct electroreduction _CO2 test in _CO2 -saturated 0.1M _KHCO3 electrolyte, and the maximum Faradaic efficiency of _CO2 production by CoPc- _Ti3C2OH QDs can reach 100%.

FIG. 4 is a schematic structural diagram of the cobalt phthalocyanine-supported MXene quantum dot molecular catalyst obtained in Examples 4-6 having a secondary coordination effect. It can be seen from the figure that cobalt phthalocyanine coordinates with the hydroxyl groups on the MXene quantum dots through axial traction to form an asymmetric coordination structure.

Embodiment 5-6

Other steps are the same as in Example 4, except that the used hydroxyl-rich MXene quantum dots (Ti ₃ C ₂ -OH-MXeneQDs) are replaced with MXene quantum dots ₍ Ti ₃ C ₂ -F-MXene QDs, Ti ₃ C ₂ -NH ₂ -MXene QDs) to obtain supported molecular catalysts CoPc-Ti ₃ C ₂ F QDs and CoPc-Ti ₃ C ₂ NH ₂ QDs with end groups -F and -OH, respectively .

Examples 7-8

Other steps are the same as in Example 4, except that the mass ratio of cobalt phthalocyanine to hydroxyl-rich MXene quantum dots (Ti ₃ C ₂ -OH-MXene QDs) is replaced by 1: 1 to 1: 5, 1: 10 (phthalocyanine). The mass of cobalt is fixed at 2 mg), and subsequent steps are the same to obtain supported molecular catalysts CoPc-Ti ₃ C ₂ OH QDs-5 and CoPc-Ti ₃ C ₂ OH QDs-10. The test process is the electroreduction of CO ₂ in a 0.1M KHCO ₃ electrolyte saturated with CO ₂ . CoPc-Ti ₃ C ₂ OH QDs-5 can produce CO with a maximum Faradaic efficiency of 75.2%, and CoPc-Ti ₃ C ₂ OH can reach 75.2%. The maximum Faradaic efficiency of QDs-10 for CO production can reach 65.4%.

Examples 9-10

Other steps are the same as in Example 4, except that the metal phthalocyanine molecules are replaced by cobalt phthalocyanine with tin phthalocyanine and iron phthalocyanine, and the subsequent steps are the same to obtain supported molecular catalysts SnPc-Ti ₃ C ₂ OH QDs, FePc-Ti ₃ C ₂ OH QDs. The test procedure is the electroreduction of _CO2 in 0.1M _KHCO3 electrolyte saturated with _CO2 . The _{SnPc -} Ti3C2OH QDs produce CO2 with a maximum Faradaic efficiency close to 40%, and FePc- _Ti3C2OH QDs produce _CO2 The maximum Faradaic efficiency can reach 63.5%.

It can be seen from the above examples that the supported composite molecular catalyst CoPc-Ti ₃ C ₂ A QDs prepared by the present invention avoids the complex and uncontrollable coordination effect between metal-support caused by high temperature carbonization; The coordination environment of the central metal can be controlled by changing the functional groups of the edge positions of the MXene quantum dots, and different functional groups will form different secondary coordination; the high-density dispersion of single metal atoms on the MXene material is realized, and the metal activity is significantly improved. The number of centers; during the electroreduction of _CO2 , the CoPc _{- Ti3C2A} QDs with secondary coordination effect further optimize the binding energy of the metal atom of the active center and the reaction intermediate, and realize the efficient directional conversion of the reactants.

Matters not addressed in the present invention are known in the art.

Claims (8)

1. A preparation method of an MXene quantum dot supported phthalocyanine molecule composite catalyst is characterized by comprising the following steps:

(1) mixing Ti₃AlC₂Immersing in hydrofluoric acid for 20-48h, taking out, centrifuging, and freeze drying to obtain Ti₃C₂-MXene; then adding the solution into a surface termination source solution, carrying out ultrasonic dispersion for 3-6h under an inert atmosphere, stirring for 2-48h at room temperature, and centrifuging to obtain a supernatant; dialyzing the supernatant for 3-6h, and collecting the dialysate to obtain Ti₃C₂-a-MXene quantum dot solution;

wherein the surface termination source is an F source, an O source or an N source, and the concentration range is 0.2-0.5 mol/L;

adding 0.1-1.0 g of Ti into each 50mL of surface termination source solution₃C₂-MXene; adding 1-4 g Ti to 50-100 mL hydrofluoric acid₃AlC₂；

The Ti₃C₂The concentration of the A-MXene quantum dot solution is 1.0-1.2 mg/mL;

the Ti₃C₂In the-A-MXene quantum dots, A is a surface termination group, specifically-F, -OH or-NH₂；

(2) Mixing Ti₃C₂Respectively adding the-A-MXene quantum dot solution and the metal phthalocyanine into an organic solvent for ultrasonic treatment for 1-4 hours, mixing the two solutions, and continuing to perform ultrasonic dispersion for 0.2-1.0 hour; then stirring at room temperature for 20-24 hours, finally centrifuging, washing, and freeze-drying to obtain the supported composite molecular catalyst CoPc-Ti₃C₂A QDs, i.e. MXAn ene quantum dot supported phthalocyanine molecular composite catalyst;

wherein, Ti₃C₂The feeding mass ratio of the-A-MXene quantum dots to the metal phthalocyanine is 1-20: 1.

2. The preparation method of the MXene quantum dot supported phthalocyanine molecule composite catalyst according to claim 1, wherein the concentration of the hydrofluoric acid is 35-45 wt%; the inert gas is argon or nitrogen.

3. The preparation method of MXene quantum dot supported phthalocyanine molecule composite catalyst of claim 1, wherein dialysis bag cut-off molecular weight is 500Da-3000 Da.

4. The preparation method of MXene quantum dot supported phthalocyanine molecule composite catalyst according to claim 1, wherein the ultrasonic power in step (1) or (2) is 100W-500W; the freeze drying temperature is-40 ℃ to-60 ℃; the vacuum degree is 15-20 kPa.

5. The method for preparing the MXene quantum dot supported phthalocyanine molecule composite catalyst of claim 1, wherein the F source is sodium fluoride, lithium fluoride or ammonium fluoride; the O source is sodium hydroxide, potassium hydroxide or sodium carbonate; the N source is ammonia water or hydrazine hydrate.

6. The method for preparing MXene quantum dot supported phthalocyanine molecule composite catalyst of claim 1, wherein the metal phthalocyanine is iron phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, copper phthalocyanine or tin phthalocyanine.

7. The preparation method of the MXene quantum dot supported phthalocyanine molecule composite catalyst of claim 1, wherein each 30mL of the metal phthalocyanine solution contains 0.5-3 mg of metal phthalocyanine; adding 1-8mL of Ti into each 10mL of organic solvent₃C₂-a-MXene quantum dot solution; the metal phthalocyanine solution and Ti₃C₂The solvent added into the solution of the-A-MXene quantum dots is the same as the solvent added into the solution of the-A-MXene quantum dots, and the solvent is the same as the solvent added into the solution of the-A-MXene quantum dotsThe organic solvent is N-N, Dimethylformamide (DMF) or anhydrous ethanol.

8. The use of MXene quantum dot supported phthalocyanine molecular composite catalyst prepared by the method of claim 1 as electrocatalytic reduction CO₂A catalytic material.

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