Method for removing halogen ions adsorbed on surface of metal nanocrystal

Abstract

A method for removing halogen ions adsorbed on the surface of a metal nanocrystal is characterized in that the halogen ions adsorbed on the surface of the metal are removed through strong adsorption of [BH4] <-> and H <-> released by hydroboron and the metal, and surface modification and effective dispersion of the metal nanocrystal are realized by introducing proper molecules (or groups) to be adsorbed on the surface. Therefore, removal of halogen ions on the metal surface, adsorption of specific molecules (or groups) and dispersion of metal nanocrystals are realized. According to the method, halogen ions on the metal surface can be removed and replaced, and then characteristic modification and effective dispersion on the surface of the metal nanocrystal are achieved.

Description

Technical Field

[0001] The invention relates to a surface treatment method for metal nanocrystals and belongs to the field of nano materials. Background Art

[0002] The surface properties of nanoparticles significantly influence their performance in practical applications. Nanoparticles synthesized using wet chemical methods often have adsorbed surface capping agents or colloidal stabilizers, also known as ligands. These adsorbed molecules or groups help particles grow in a directional manner and prevent aggregation, but these adsorbed ligands can also affect their ultimate performance. Therefore, post-processing of the synthesized nanoparticles is necessary to achieve the ideal surface condition to meet different application requirements.

[0003] Metal nanocrystals, such as Au, Ag, Ru, Rh, Pd, Ir, and Pt, possess excellent physicochemical properties and hold great promise for applications in optics and catalysis. The physicochemical properties of metal nanocrystals are influenced by their size and morphology. Sharp edges and corners, or high-index facets, have been reported to enhance the catalytic performance of metal nanocrystals. Therefore, precise control of size and morphology is crucial for achieving superior performance in metal nanocrystals.

[0004] In the process of synthesizing metal nanocrystals, cationic surfactants such as cetyltrimethylammonium chloride (CTAC) and cetyltrimethylammonium bromide (CTAB) are often used to control the morphology of metal nanocrystals because of their strong binding with metal nanocrystals. It is generally believed that cationic surfactants bind to the counter ions (Cl - Br - ) forms a double-layer structure. If the surface active agent is to be removed, the halide ions on the surface of the metal nanoparticles need to be removed. However, due to the strong binding of halide ions on the surface of metal nanocrystals, the commonly used direct ligand exchange method is difficult to completely replace and remove the halide ions. The two-step method is another method to remove surface ligands besides the direct ligand exchange method. It first removes the original ligands on the surface through surface acid treatment and ultrasound, and then adjusts the surface chemical properties of the nanoparticles through the deposition or heat treatment of a second ligand. The second step in this method also depends on the direct ligand exchange process, facing the problems of difficulty in complete replacement and easy agglomeration due to the ligand binding strength and ligand charge properties. In addition, there are studies that use the method of depositing metal coatings on the surface of metal nanocrystals to help remove surfactants, but this method is technically complex and has a long cycle. Summary of the Invention

[0005] The technical solution of the present invention aims to provide a method for removing halogen ions adsorbed on the surface of metal nanocrystals, addressing the problem of halogen-containing surfactants affecting their surface properties. The method utilizes borohydride to remove surface-adsorbed halogen ions, then centrifuges to remove surface adsorbed groups. Finally, the surface properties of the metal nanocrystals are modified by adsorption of other ligand groups.

[0006] The present invention provides a method for removing halogen ions adsorbed on the surface of metal nanocrystals, wherein the method is carried out according to the following steps: (1) Dispersing the synthesized metal nanocrystals in deionized water, centrifuging and removing the supernatant, washing 1 to 10 times to remove weakly bound and non-adsorbed groups, and finally redispersing the nanocrystals in deionized water for later use; (2) uniformly mixing a certain amount of a freshly prepared aqueous borohydride solution with a dispersion of metal nanocrystals and allowing the mixture to stand for a certain period of time; then separating the metal nanocrystals from the solution using a centrifuge and removing the supernatant; repeating this step 1 to 50 times to remove the halogen ion-containing surfactant adsorbed on the surface of the metal nanocrystals; (3) The borohydride aqueous solution, the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals, and the centrifuged metal nanocrystal dispersion are mixed and dispersed by ultrasonication to make them uniformly mixed and fully adsorbed on the surface of the metal nanocrystals; this step is repeated, and the amount of borohydride added is gradually reduced until it is no longer added; finally, metal nanocrystals are obtained in which the surfactant containing halogen ions is completely removed and specific groups are adsorbed on the surface.

[0007] Furthermore, in step (1), the metal nanocrystals are nanocrystals of Au, Ag, Ru, Rh, Pd, Ir, or Pt, and the concentration of the metal nanocrystal dispersion is 1 μmol / L-100 mol / L.

[0008] Furthermore, in step (2), the concentration of the borohydride aqueous solution is 1 μmol / L-100 mol / L, the concentration of the metal nanocrystal dispersion is 1 μmol / L-100 mol / L, and the volume ratio of the borohydride aqueous solution to the metal nanocrystal dispersion is 1000:1~1:1000.

[0009] Furthermore, in step (2), the borohydride is one or more of LiBH4, NaBH4, KBH4, Mg[BH4]2, Zn[BH4]2, Ca[BH4]2, (CH3)4N(BH4), and (C2H5)4N(BH4).

[0010] Furthermore, the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals in step (3) can be 1,4-diisocyanatobenzene (PDI), polyvinylpyrrolidone (PVP), Pluronic F127, hexadecyltrimethylammonium chloride (CTAC), hexadecyltrimethylammonium bromide (CTAB), behenyltrimethylammonium chloride (C 22 One or more of dioctadecyl ammonium chloride (TAC), dimethyldioctadecyl ammonium chloride (DDAC), dimethyldioctadecyl ammonium bromide (DDAB), hexadecyldimethylbenzylammonium chloride (HDBAC), octadecyltrimethylammonium chloride (STAC), dodecyltrimethylammonium chloride (DTAC), sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecyl sulfonate (SLS).

[0011] Furthermore, in step (3), the concentration of the borohydride aqueous solution is 1 μmol / L-100 mol / L, the concentration of the metal nanocrystal dispersion is 1 μmol / L-100 mol / L, and the concentration of the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals is 1 μmol / L-100 mol / L, and the volume ratio between the three is the volume of the borohydride aqueous solution: the volume of the metal nanocrystal dispersion: the volume of the molecules (or groups) to be adsorbed on the surface of the Au nanocrystals = 1~1000:1~1000:1~1000.

[0012] Advantages of the present invention: The present invention uses borohydride as a surface treatment agent, and borohydride will form [BH4] in water. - and H - , [BH4] - and H - It has a high binding energy with metal nanocrystals and can replace most other groups adsorbed on the surface of metal nanocrystals. The borohydride used in the present invention utilizes [BH4] - and H - The adsorption is mainly [BH4] - Adsorption of [BH4] - It will further decompose and be exhausted, which is conducive to the re-adsorption of other groups on the surface of metal nanocrystals; H - The size of [BH4] is small and does not affect the adsorption of other groups. - It will decompose and consume by itself, and does not need to be removed by group replacement [BH4] -; In the present invention, the desorption and removal of surface groups and the re-adsorption of target groups can be controlled by controlling the treatment time of borohydride on metal nanocrystals and the adsorption time of target groups; In the present invention, the adsorption of target groups can be achieved by the joint introduction of borohydride and target group molecules, and the agglomeration of nanocrystals caused by the removal of initial adsorption groups can be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The Au nanocrystals were washed with 20 mmol / L NaBH4 aqueous solution and adsorbed on the surface of 20 mmol / L polyvinylpyrrolidone (PVP). DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with the embodiments. However, the scope of the present invention is not limited to the following embodiments. Those skilled in the art will appreciate that various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention.

[0015] Unless otherwise specified, the instruments, reagents, and materials used in the following examples are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods and detection methods used in the following examples are all conventional experimental methods and detection methods available in the prior art, unless otherwise specified.

[0016] Example: Example 1, a method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps: (1) Disperse Au nanocrystals with halogen ions adsorbed on their surfaces in deionized water, adjust the concentration to 1 μmol / L, and then centrifuge at 12,000 rpm for 10 min, remove the supernatant, and repeat this process twice. Finally, ultrasonically disperse the nanocrystals in 1 mL of deionized water for later use. (2) After 0.5 mL of a freshly prepared 20 mmol / L NaBH4 aqueous solution was evenly mixed with the Au nanocrystal dispersion, the mixture was allowed to stand for 10 min. The Au nanocrystals were then centrifuged at 12,000 rpm for 10 min to separate the Au nanocrystals from the solution, and the supernatant was removed. This step was repeated twice to remove the halogen-containing surfactant adsorbed on the surface of the Au nanocrystals during the synthesis process. (3) 0.5 mL of a freshly prepared 20 mmol / L NaBH4 aqueous solution and 1 mL of 20 mmol / L polyvinylpyrrolidone (PVP) were added to the NaBH4-treated Au nanocrystal suspension in sequence; the above solutions were mixed evenly and allowed to stand for 1 hour, and then centrifuged at 12,000 rpm for 10 minutes to separate the Au nanocrystals from the solution, and the supernatant was removed; 1 mL of a 20 mmol / L PVP aqueous solution was added to the Au nanocrystals obtained after centrifugation, ultrasonically dispersed and allowed to stand for 30 minutes; then centrifuged at 12,000 rpm for 10 minutes to separate the Au nanocrystals from the solution, and the supernatant was removed; this step was repeated 3 times, and finally the Au nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halogen-containing surfactant was completely removed, and the Au nanocrystal dispersion with PVP adsorbed on the surface was obtained, as shown in FIG. Figure 1 shown.

[0017] Example 2, a method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps: (1) Disperse Au nanocrystals with halogen ions adsorbed on their surfaces in deionized water, adjust the concentration to 100 mol / L, and then centrifuge at 15,000 rpm for 20 min, remove the supernatant, and repeat this process five times. Finally, ultrasonically disperse the nanocrystals in 1 mL of deionized water for later use. (2) After 1 mL of freshly prepared 1 mmol / L NaBH4 aqueous solution was evenly mixed with the Au nanocrystal dispersion, the mixture was allowed to stand for 20 min. The Au nanocrystals were then centrifuged at 15,000 rpm for 20 min to separate the Au nanocrystals from the solution, and the supernatant was removed. This step was repeated 5 times to remove the surfactant containing halogen ions adsorbed on the surface of the Au nanocrystals during the synthesis process. (3) 0.5 mL of freshly prepared 1 mmol / L NaBH4 aqueous solution and 1 mL of 20 mmol / L 1,4-diisocyanatobenzene (PDI) were added to the NaBH4-treated Au nanocrystal suspension in sequence; the above solutions were mixed evenly and allowed to stand for 0.5 h, then centrifuged at 15,000 rpm for 20 min and the supernatant was removed; 1 mL of 2 mmol / L PDI aqueous solution was added to the Au nanocrystals obtained after centrifugation, ultrasonically dispersed and allowed to stand for 30 min; then centrifuged at 15,000 rpm for 20 min to separate the Au nanocrystals from the solution and remove the supernatant; this step was repeated 5 times, and finally the Au nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halogen-containing surfactant was completely removed, and an Au nanocrystal dispersion with PDI adsorbed on the surface was obtained.

[0018] Example 3, a method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps: (1) Disperse Au nanocrystals with halogen ions adsorbed on their surfaces in 1 mL of deionized water, then centrifuge at 10,000 rpm for 30 min and remove the supernatant. Repeat this process for 10 washes. Finally, ultrasonically disperse the nanocrystals in 1 mL of deionized water for later use. (2) 1 mL of freshly prepared 0.01 mmol / L Mg[BH4]2 aqueous solution was uniformly mixed with the Au nanocrystal dispersion and allowed to stand for 20 min. The Au nanocrystals were then centrifuged at 10,000 rpm for 10 min to separate the Au nanocrystals from the solution and the supernatant was removed. This step was repeated 10 times to remove the halogen-containing surfactant adsorbed on the surface of the Au nanocrystals during the synthesis process. (3) 1 mL of freshly prepared 0.01 mmol / L Mg[BH4]2 aqueous solution and 1 mL of 1 mmol / L sodium dodecylbenzenesulfonate (SDBS) were added to the Mg[BH4]2-treated Au nanocrystal suspension in sequence; the above solutions were mixed evenly and allowed to stand for 1 h, then centrifuged at 10,000 rpm for 10 min and the supernatant was removed; 1 mL of 1 mmol / L sodium dodecylbenzenesulfonate (SDBS) aqueous solution was added to the Au nanocrystals obtained after centrifugation, ultrasonically dispersed and allowed to stand for 1 h; then centrifuged at 10,000 rpm for 10 min to separate the Au nanocrystals from the solution and remove the supernatant; this step was repeated 5 times, and finally the Au nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halogen-containing surfactant was completely removed, and a Au nanocrystal dispersion with sodium dodecylbenzenesulfonate (SDBS) adsorbed on the surface was obtained.

[0019] Example 4: A method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps: (1) Disperse the Ag nanocrystals with halide ions adsorbed on their surfaces in 1 mL of deionized water, centrifuge at 10,000 rpm for 10 min, remove the supernatant, and repeat this process five times. Finally, ultrasonically disperse the nanocrystals in 1 mL of deionized water for later use. (2) After 0.5 mL of freshly prepared 0.1 mmol / L KBH4 aqueous solution was evenly mixed with the Ag nanocrystal dispersion, the mixture was allowed to stand for 10 min. The Ag nanocrystals were then centrifuged at 10,000 rpm for 10 min to separate the Ag nanocrystals from the solution, and the supernatant was removed. This step was repeated twice to remove the halogen ion-containing surfactant adsorbed on the surface of the Ag nanocrystals during the synthesis process. (3) 0.5 mL of freshly prepared 2 mmol / L KBH4 aqueous solution and 1 mL of 20 mmol / L polyvinylpyrrolidone (PVP) were added to the KBH4-treated Ag nanocrystal suspension in sequence; the above solutions were mixed evenly and allowed to stand for 1 h, then centrifuged at 12,000 rpm for 10 min to separate the Ag nanocrystals from the solution and remove the supernatant; 1 mL of 20 mmol / L PVP aqueous solution was added to the Ag nanocrystals obtained after centrifugation, ultrasonically dispersed and allowed to stand for 30 min; then centrifuged at 12,000 rpm for 10 min to separate the Ag nanocrystals from the solution and remove the supernatant; this step was repeated 3 times, and finally the Ag nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halogen-containing surfactant was completely removed, and a Ag nanocrystal dispersion with PVP adsorbed on the surface was obtained.

[0020] Example 5, a method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps: (1) Pt nanocrystals with halogen ions adsorbed on their surfaces were dispersed in 1 mL of deionized water. The mixture was then centrifuged at 10,000 rpm for 10 min and the supernatant was removed. This process was repeated five times. Finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water for later use. (2) After 0.5 mL of freshly prepared 0.1 mmol / L (CH3)4N(BH4) aqueous solution was evenly mixed with the Pt nanocrystal dispersion, the mixture was allowed to stand for 10 min. The Pt nanocrystals were then separated from the solution by centrifugation at 10,000 rpm for 10 min, and the supernatant was removed. This step was repeated twice to remove the halogen-containing surfactant adsorbed on the surface of the Pt nanocrystals during the synthesis process. (3) 0.5 mL of a freshly prepared 2 mmol / L (CH3)4N(BH4) aqueous solution and 1 mL of 20 mmol / L polyvinylpyrrolidone (PVP) were added sequentially to the (CH3)4N(BH4)-treated Pt nanocrystal suspension; the above solutions were mixed evenly and allowed to stand for 1 h, then centrifuged at 12,000 rpm for 10 min to separate the Pt nanocrystals from the solution, and the supernatant was removed; 1 mL of 20 mmol / L PVP aqueous solution was added to the Pt nanocrystals obtained after centrifugation, ultrasonically dispersed and allowed to stand for 30 min; then centrifuged at 12,000 rpm for 10 min to separate the Pt nanocrystals from the solution, and the supernatant was removed; this step was repeated 3 times, and finally the Pt nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halogen-containing surfactant was completely removed, and a Pt nanocrystal dispersion was obtained in which PVP was adsorbed on the surface.

[0021] Example 6: A method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps: (1) Rh nanocrystals with halogen ions adsorbed on their surfaces were dispersed in 1 mL of deionized water. The mixture was then centrifuged at 10,000 rpm for 10 min and the supernatant was removed. This process was repeated five times. Finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water for later use. (2) 0.5 mL of a freshly prepared 1 μmol / L (C2H5)4N(BH4) aqueous solution was uniformly mixed with the Rh nanocrystal dispersion and allowed to stand for 10 min. The Rh nanocrystals were then separated from the solution by centrifugation at 10,000 rpm for 10 min, and the supernatant was removed. This step was repeated 50 times to remove the halogen-containing surfactant adsorbed on the surface of the Rh nanocrystals during the synthesis process. (3) 0.5 mL of a freshly prepared 1 μmol / L (C2H5)4N(BH4) aqueous solution and 1 mL of 1 μmol / L sodium dodecylsulfonate (SLS) were added sequentially to the (C2H5)4N(BH4)-treated Rh nanocrystal suspension; the above solutions were mixed evenly and allowed to stand for 1 h, then centrifuged at 12,000 rpm for 10 min to separate the Rh nanocrystals from the solution, and the supernatant was removed; 1 mL of 1 μmol / L SLS aqueous solution was added to the Rh nanocrystals obtained after centrifugation, ultrasonically dispersed, and allowed to stand for 30 min; then centrifuged at 12,000 rpm for 10 min to separate the Rh nanocrystals from the solution, and the supernatant was removed; this step was repeated once, and finally the Rh nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halogen-containing surfactant was completely removed, and a Rh nanocrystal dispersion in which SLS was adsorbed on the surface was obtained.

Claims

1. A method for removing halogen ions adsorbed on the surface of metal nanocrystals, characterized in that The method proceeds as follows: (1) Dispersing the synthesized metal nanocrystals in deionized water, centrifuging and removing the supernatant, washing 1 to 10 times to remove weakly bound and non-adsorbed groups, and finally redispersing the nanocrystals in deionized water for later use; (2) uniformly mixing a certain amount of a newly prepared aqueous borohydride solution with a dispersion of metal nanocrystals and allowing the mixture to stand for a certain period of time; then separating the metal nanocrystals from the solution using a centrifuge and removing the supernatant; repeating this step to remove the halogen ion-containing surfactant adsorbed on the surface of the metal nanocrystals; (3) The borohydride aqueous solution, the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals, and the centrifuged metal nanocrystal dispersion are mixed and dispersed by ultrasonication to make them uniformly mixed and fully adsorbed on the surface of the metal nanocrystals; this step is repeated, and the amount of borohydride added is gradually reduced until it is no longer added; finally, metal nanocrystals are obtained in which the surfactant containing halogen ions is completely removed and specific groups are adsorbed on the surface.

2. A method for removing halogen ions adsorbed on the surface of metal nanocrystals according to claim 1, characterized in that In step (1), the metal nanocrystals are nanocrystals of Au, Ag, Ru, Rh, Pd, Ir, or Pt, and the concentration of the dispersion of the metal nanocrystals is 1 μmol / L-100 mol / L.

3. A method for removing halogen ions adsorbed on the surface of metal nanocrystals according to claim 1, characterized in that The concentration of the borohydride aqueous solution used in step (2) is 1 μmol / L-100 mol / L, the concentration of the metal nanocrystal dispersion is 1 μmol / L-100 mol / L, and the volume ratio of the borohydride aqueous solution to the metal nanocrystal dispersion is 1000:1~1:1000.

4. A method for removing halogen ions adsorbed on the surface of metal nanocrystals according to claim 1, characterized in that The borohydride used in steps (2) and (3) is one or more of LiBH4, NaBH4, KBH4, Mg[BH4]2, Zn[BH4]2, Ca[BH4]2, (CH3)4N(BH4), and (C2H5)4N(BH4).

5. A method for removing halogen ions adsorbed on the surface of metal nanocrystals according to claim 1, characterized in that The number of centrifugation steps (2) and (3) varies between 1 and 50 times.

6. The method for removing halogen ions adsorbed on the surface of metal nanocrystals according to claim 1, characterized in that The molecules (or groups) to be adsorbed on the surface of the metal nanocrystals in step (3) can be 1,4-diisocyanatobenzene (PDI), polyvinylpyrrolidone (PVP), Pluronic F127, hexadecyltrimethylammonium chloride (CTAC), hexadecyltrimethylammonium bromide (CTAB), behenyltrimethylammonium chloride (C 22 One or more of dioctadecyl ammonium chloride (TAC), dimethyldioctadecyl ammonium chloride (DDAC), dimethyldioctadecyl ammonium bromide (DDAB), hexadecyldimethylbenzylammonium chloride (HDBAC), octadecyltrimethylammonium chloride (STAC), dodecyltrimethylammonium chloride (DTAC), sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecyl sulfonate (SLS).

7. The method for removing halogen ions adsorbed on the surface of metal nanocrystals according to claim 1, characterized in that The concentration of the borohydride aqueous solution described in step (3) is 1 μmol / L-100 mol / L, the concentration of the metal nanocrystal dispersion is 1 μmol / L-100 mol / L, and the concentration of the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals is 1 μmol / L-100 mol / L. The volume ratio of the three is borohydride aqueous solution: volume of metal nanocrystal dispersion: volume of molecules (or groups) to be adsorbed on the surface of the metal nanocrystals = 1~1000:1~1000:1~1000.

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