A method for removing halogen ions adsorbed on the surface of metal nanocrystals

Abstract

A method for removing halogen ions adsorbed on the surface of metal nanocrystals, the method releases [BH4] ‑ and H ‑ from borohydride The strong adsorption of the metal removes the halogen ions adsorbed on the surface of the metal, and the surface modification and effective dispersion of the metal nanocrystals are achieved by introducing suitable surface-adsorbed molecules (or groups), thereby achieving the removal of halogen ions on the surface of the metal, the adsorption of specific molecules (or groups), and the dispersion of the metal nanocrystals. This method can achieve the removal and replacement of halogen ions on the surface of the metal, and then achieve the characteristic modification and effective dispersion of the surface of the metal nanocrystals.

Description

TECHNICAL FIELD

[0001] The present application relates to a surface treatment method of metal nanocrystals, and belongs to the field of nanomaterials. BACKGROUND

[0002] The surface properties of nanoparticles have important influence on their performance in practical applications. For nanoparticles synthesized by wet chemical methods, their surfaces are usually covered with adsorbed surface capping agents or colloidal stabilizers, or ligands. These adsorbed molecules or groups can help the particles to grow directionally and avoid agglomeration, but these adsorbed ligands can affect the final performance. Therefore, it is necessary to post-treat the synthesized nanoparticles to obtain ideal surface states to meet different use requirements.

[0003] Metal nanocrystals, such as Au, Ag, Ru, Rh, Pd, Ir, Pt, etc., have good physical and chemical properties and have great application prospects in the fields of optics and catalysis. The physical and chemical properties of metal nanocrystals are affected by their size and morphology. It has been reported that sharp edges and corners or high-index crystal faces are beneficial to improve the catalytic performance of metal nanocrystals. Therefore, it is very important to precisely control the size and morphology to obtain metal nanocrystals with excellent performance.

[0004] In the process of synthesizing metal nanocrystals, cationic surfactants, such as cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB), etc., are often used to control the morphology of nanocrystals due to their strong binding with metal nanocrystals. It is generally believed that the cationic surfactants form a bilayer structure with counterions (Cl - , Br - ) on the surface of metal nanocrystals. However, it is difficult to completely replace and remove the halogen ions on the surface of metal nanocrystals by the commonly used direct ligand exchange method due to their strong binding. The two-step method is another method for removing surface ligands other than the direct ligand exchange method, which first removes the original surface ligands through surface acid treatment and ultrasonic treatment, and then adjusts the surface chemical properties of the nanoparticles by depositing a second ligand or heat treatment. The second step in this method also depends on the direct ligand exchange process, and faces the problems of incomplete replacement and easy agglomeration caused by the binding strength of the ligand and the charge properties of the ligand. In addition, there are studies that use the method of depositing a metal coating on the surface of metal nanocrystals to help remove the surface active agent, but this method is technically complex and has a long cycle. SUMMARY

[0005] The technical scheme of the present application is to provide a method for removing halogen ions adsorbed on the surface of metal nanocrystals, and to solve the problem of the influence of halogen-containing surfactants on the surface properties thereof. The halogen ions adsorbed on the surface are removed by using borohydride, and then the surface adsorption groups are removed by centrifugation, and finally the surface properties of the metal nanocrystals are changed by adsorption of other ligand groups.

[0006] The present application is a method for removing halogen ions adsorbed on the surface of metal nanocrystals, which is carried out according to the following steps:

[0007] (1) The synthesized metal nanocrystals are dispersed in deionized water, and then centrifuged and the supernatant is removed, and this cleaning is repeated 1-10 times to remove weakly bound and unadsorbed surface groups, and finally the nanocrystals are redispersed in deionized water for use;

[0008] (2) A certain amount of freshly prepared borohydride aqueous solution is uniformly mixed with the dispersion of metal nanocrystals, and then left to stand for a certain period of time; then the metal nanocrystals are separated from the solution by centrifugation, and the supernatant is removed; this step is repeated 1-50 times to remove the halogen-containing surfactants adsorbed on the surface of the metal nanocrystals;

[0009] (3) The borohydride aqueous solution, the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals, and the dispersion of the centrifuged metal nanocrystals are mixed and dispersed by ultrasonic dispersion 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 no more is added; finally, the halogen-containing surfactants are completely removed and the metal nanocrystals with specific groups adsorbed on the surface are obtained.

[0010] Further, in step (1), the metal nanocrystals are Au, Ag, Ru, Rh, Pd, Ir, Pt nanocrystals, and the concentration of the metal nanocrystal dispersion is 1 μmol / L-100 mol / L.

[0011] Further, in step (2), the concentration of the borohydride aqueous solution is 1 μmol / L-100 mol / L, the concentration of the dispersion of the metal nanocrystals is 1 μmol / L-100 mol / L, and the volume ratio of the borohydride aqueous solution to the dispersion of the metal nanocrystals is 1000:1-1:1000.

[0012] Further, 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), (C2H5)4N(BH4).

[0013] Further, the molecules (or groups) to be adsorbed on the surface of the metal nanocrystals in step (3) can be one or more of 1,4-diisocyanatobenzene (PDI), polyvinylpyrrolidone (PVP), Pluronic F127, cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB), behenyltrimethylammonium chloride (C 22 TAC), dimethyldioctadecylammonium chloride (DDAC), dimethyldioctadecylammonium bromide (DDAB), hexadecyl dimethyl benzyl ammonium chloride (HDBAC), stearyltrimethylammonium chloride (STAC), dodecyltrimethylammonium chloride (DTAC), sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecylsulfonate (SLS).

[0014] Further, the concentration of the aqueous borohydride solution in step (3) is 1 μmol / L-100 mol / L, the concentration of the dispersion of the metal nanocrystals 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 among the three is aqueous borohydride solution: volume of the dispersion of the metal nanocrystals: volume of the molecules (or groups) to be adsorbed on the surface of the Au nanocrystals = 1-1000: 1-1000: 1-1000.

[0015] Advantages of the present application: the present application uses borohydride as a surface treatment agent, and the borohydride can form [BH4] - and H - on the surface of water, and [BH4] - and H - have a high binding energy with metal nanocrystals, and can replace other groups adsorbed on the surface of the metal nanocrystals; the borohydride used in the present application utilizes the adsorption of [BH4] - and H - in the process of replacing the groups adsorbed on the surface of the metal nanocrystals, mainly the adsorption of [BH4] - , and [BH4] - will further decompose and be depleted, which is conducive to the re-adsorption of other groups on the surface of the metal nanocrystals; H - has a small size and does not affect the adsorption of other groups. Since [BH4] - will decompose and be depleted by itself, [BH4] -In the present application, the desorption, removal and re-adsorption of surface groups can be controlled by controlling the treatment time of borohydride on metal nanocrystals and the adsorption time of target groups; and the adsorption of target groups can be realized by the co-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 DRAWINGS

[0016] Figure 1 Au nanocrystals cleaned by 20 mmol / L NaBH4 aqueous solution and adsorbed by 20 mmol / L polyvinylpyrrolidone (PVP) on the surface. DETAILED DESCRIPTION

[0017] The present application will be further described below in conjunction with examples. However, the scope of the present application is not limited to the following examples. Those skilled in the art can understand that various changes and modifications can be made to the present application without departing from the spirit and scope of the present application.

[0018] The instruments, reagents and materials involved in the following examples are conventional instruments, reagents and materials existing in the prior art, and can be obtained through regular commercial channels, unless otherwise specified. The experimental methods and detection methods involved in the following examples are conventional experimental methods and detection methods existing in the prior art, unless otherwise specified.

[0019] Example:

[0020] Example 1: A method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps:

[0021] (1) Au nanocrystals adsorbed with halogen ions on the surface were dispersed in ionized water, and the concentration was adjusted to 1 μmol / L. Then, the supernatant was removed after centrifugation at a speed of 12000 rpm for 10 min, and this washing was repeated twice. Finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water for use;

[0022] (2) 0.5 mL of freshly prepared 20 mmol / L NaBH4 aqueous solution was uniformly mixed with the dispersion of Au nanocrystals, and then left to stand for 10 min. Then, the Au nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed. This step was repeated twice to remove the halogen ion-containing surfactants adsorbed on the surface of Au nanocrystals during synthesis;

[0023] (3) 0.5 mL of 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 solution was mixed uniformly and then left to stand for 1 h, and then the Au nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; 1 mL of 20 mmol / L PVP aqueous solution was added to the Au nanocrystals obtained after centrifugation, and after ultrasonic dispersion, it was left to stand for 30 min; then the Au nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; this step was repeated 3 times, and finally the Au nanocrystals were dispersed in deionized water; finally, the halogen ion-containing surfactant adsorbed on the surface was completely removed, and PVP was adsorbed on the surface of the Au nanocrystal dispersion, as shown in FIG. 2B. Figure 1

[0024] Example 2, a method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps:

[0025] (1) Au nanocrystals with halogen ions adsorbed on the surface were dispersed in deionized water, and the concentration was adjusted to 100 mol / L, and then the supernatant was removed after centrifugation at 15000 rpm for 20 min, and this washing was repeated 5 times; finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water for use;

[0026] (2) 1 mL of freshly prepared 1 mmol / L NaBH4 aqueous solution was uniformly mixed with the Au nanocrystal dispersion, and then left to stand for 20 min; then the Au nanocrystals were separated from the solution by centrifugation at 15000 rpm for 20 min, and the supernatant was removed; this step was repeated 5 times to remove the halogen ion-containing surfactant adsorbed on the surface of the Au nanocrystals during synthesis;

[0027] ​(3) 0.5 mL of freshly prepared 1 mmol / L aqueous NaBH4 solution and 1 mL of 20 mmol / L 1,4-diisocyanatobenzene (PDI) were sequentially added to the NaBH4 treated Au nanocrystal suspension; the above solution was mixed well and then left to stand for 0.5 h, after which the supernatant was removed by centrifugation at 15000 rpm for 20 min; 1 mL of 2 mmol / L aqueous PDI was added to the Au nanocrystals obtained after centrifugation, which were ultrasonically dispersed and then left to stand for 30 min; the Au nanocrystals were then separated from the solution by centrifugation at 15000 rpm for 20 min, and the supernatant was removed; this step was repeated 5 times, and finally the Au nanocrystals were dispersed in deionized water; the halide ion-containing surfactant adsorbed on the surface was completely removed, and PDI was adsorbed on the surface of the Au nanocrystal dispersion.

[0028] Example Three, a method for removing halide ions adsorbed on the surface of metal nanocrystals, comprising the following steps:

[0029] (1) Au nanocrystals having halide ions adsorbed on the surface were dispersed in 1 mL of deionized water, which was then centrifuged at 10000 rpm for 30 min to remove the supernatant, and this washing step was repeated 10 times; finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water and left to stand;

[0030] (2) 1 mL of freshly prepared 0.01 mmol / L aqueous Mg[BH4]2 solution was mixed well with the Au nanocrystal dispersion, which was then left to stand for 20 min; the Au nanocrystals were then separated from the solution by centrifugation at 10000 rpm for 10 min, and the supernatant was removed; this step was repeated 10 times to remove the halide ion-containing surfactant adsorbed on the surface of the Au nanocrystals during synthesis;

[0031] (3) 1 mL of freshly prepared 0.01 mmol / L aqueous Mg[BH4]2solution and 1 mL of 1 mmol / L aqueous sodium dodecylbenzenesulfonate (SDBS) were sequentially added to the Mg[BH4]2treated Au nanocrystal suspension; the above solution was mixed well and then left to stand for 1 h, after which the supernatant was removed using a centrifuge at 10,000 rpm for 10 min; 1 mL of 1 mmol / L aqueous sodium dodecylbenzenesulfonate (SDBS) was added to the Au nanocrystals obtained after centrifugation, and after ultrasonic dispersion, the solution was left to stand for 1 h; the Au nanocrystals were then separated from the solution using a centrifuge at 10,000 rpm for 10 min, and the supernatant was removed; this step was repeated 5 times, and finally the Au nanocrystals were dispersed in deionized water; the halide ion-containing surfactant adsorbed on the surface was completely removed, and sodium dodecylbenzenesulfonate (SDBS) was adsorbed on the surface of the Au nanocrystal dispersion.

[0032] Example Four, a method for removing halide ions adsorbed on the surface of metal nanocrystals, comprising the following steps:

[0033] (1) Ag nanocrystals with halide ions adsorbed on the surface were dispersed in 1 mL of deionized water, and then centrifuged at 10,000 rpm for 10 min using a centrifuge to remove the supernatant, and this washing step was repeated 5 times; finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water and used as needed;

[0034] (2) 0.5 mL of freshly prepared 0.1 mmol / L aqueous KBH4solution was uniformly mixed with the dispersion of Ag nanocrystals, and then left to stand for 10 min; the Ag nanocrystals were then separated from the solution using a centrifuge at 10,000 rpm for 10 min, and the supernatant was removed; this step was repeated 2 times to remove the halide ion-containing surfactant adsorbed on the surface of the Ag nanocrystals during synthesis;

[0035] (3) 0.5 mL of freshly prepared 2 mmol / L aqueous KBH4solution and 1 mL of 20 mmol / L polyvinylpyrrolidone (PVP) were added to the KBH4treated Ag nanocrystal suspension in sequence; the above solution was mixed uniformly and then left to stand for 1 h, after which the Ag nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; 1 mL of 20 mmol / L aqueous PVP was added to the Ag nanocrystals obtained after centrifugation, and after ultrasonic dispersion the solution was left to stand for 30 min; the Ag nanocrystals were then separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; this step was repeated 3 times, and finally the Ag nanocrystals were dispersed in deionized water; the halide ion-containing surfactant adsorbed on the surface was completely removed, and PVP was adsorbed on the surface of the Ag nanocrystal dispersion.

[0036] Example Five, a method for removing halide ions adsorbed on the surface of metal nanocrystals, comprising the following steps:

[0037] (1) Pt nanocrystals with halide ions adsorbed on the surface were dispersed in 1 mL of deionized water, and then the supernatant was removed after centrifugation at 10000 rpm for 10 min using a centrifuge; this washing step was repeated 5 times; finally the nanocrystals were ultrasonically dispersed in 1 mL of deionized water and left to stand;

[0038] (2) 0.5 mL of freshly prepared 0.1 mmol / L aqueous (CH3)4N(BH4) solution was mixed uniformly with the dispersion of Pt nanocrystals, and then left to stand for 10 min; the Pt nanocrystals were then separated from the solution by centrifugation at 10000 rpm for 10 min, and the supernatant was removed; this step was repeated 2 times to remove the halide ion-containing surfactant adsorbed on the surface of the Pt nanocrystals during synthesis;

[0039] (3) 0.5 mL of freshly prepared 2 mmol / L (CH3)4N(BH4) aqueous solution and 1 mL of 20 mmol / L polyvinylpyrrolidone (PVP) were added to the (CH3)4N(BH4) treated Pt nanocrystal suspension in sequence; the above solution was mixed uniformly and then left to stand for 1 h, and then the Pt nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; 1 mL of 20 mmol / L PVP aqueous solution was added to the Pt nanocrystals obtained after centrifugation, and after ultrasonic dispersion, the solution was left to stand for 30 min; then the Pt nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; this step was repeated 3 times, and finally the Pt nanocrystals were dispersed in deionized water; finally, the halogen ion-containing surfactant adsorbed on the surface was completely removed, and PVP was adsorbed on the surface of the Pt nanocrystal dispersion.

[0040] Example Six, a method for removing halogen ions adsorbed on the surface of metal nanocrystals, comprising the following steps:

[0041] (1) Rh nanocrystals with halogen ions adsorbed on the surface were dispersed in 1 mL of deionized water, and then the supernatant was removed after centrifugation at 10000 rpm for 10 min using a centrifuge, and this washing was repeated 5 times; finally, the nanocrystals were ultrasonically dispersed in 1 mL of deionized water and used as is;

[0042] (2) 0.5 mL of freshly prepared 1 μmol / L (C2H5)4N(BH4) aqueous solution was uniformly mixed with the dispersion of Rh nanocrystals, and then left to stand for 10 min; then the Rh nanocrystals were separated from the solution by centrifugation at 10000 rpm for 10 min, and the supernatant was removed; this step was repeated 50 times to remove the halogen ion-containing surfactant adsorbed on the surface of the Rh nanocrystals during synthesis;

[0043] (3) 0.5 mL of freshly prepared 1 μmol / L aqueous (C2H5)4N(BH4) solution and 1 mL of 1 μmol / L aqueous sodium lauryl sulfonate (SLS) solution were sequentially added to the (C2H5)4N(BH4)-treated Rh nanocrystal suspension; after the above solutions were mixed and left to stand for 1 h, the Rh nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; 1 mL of 1 mL of 1 μmol / L aqueous SLS solution was added to the Rh nanocrystals obtained after centrifugation, and the mixture was ultrasonically dispersed and left to stand for 30 min; then the Rh nanocrystals were separated from the solution by centrifugation at 12000 rpm for 10 min, and the supernatant was removed; this step was repeated once, and finally the Rh nanocrystals were dispersed in deionized water; finally, the surface-adsorbed halide ion-containing surfactant was completely removed, and SLS was achieved on the surface-adsorbed Rh nanocrystal dispersion.

Claims

1. A method for removing surface-adsorbed halogen ions from a metal nanocrystal, characterized by The method is carried out according to the following steps: (1) The synthesized metal nanocrystals are dispersed in deionized water, then centrifuged by a centrifuge and the supernatant is removed, and such washing is repeated 1-10 times to remove the weakly combined and unadsorbed groups on the surface, and finally the nanocrystals are redispersed in deionized water for standby; (2) A certain amount of freshly prepared borohydride aqueous solution is uniformly mixed with the dispersion of metal nanocrystals, and then left for a certain time; then the metal nanocrystals are separated from the solution by using a centrifuge, and the supernatant is removed; this step is repeated to remove the surfactant containing halide ions 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 dispersion of the centrifuged metal nanocrystals are mixed, and dispersed by ultrasonic dispersion, so that they are uniformly mixed and fully adsorbed on the surface of the metal nanocrystals; this step is repeated, and the amount of borohydride is gradually reduced until no more is added; finally, the metal nanocrystals with the surfactant containing halide ions completely removed and the molecules or groups adsorbed on the surface are obtained.

2. The method of removing surface-adsorbed halogen ions from metal nanocrystals of claim 1, wherein In step (1), the metal nanocrystals are Au, Ag, Ru, Rh, Pd, Ir, Pt nanocrystals, and the concentration of the dispersion of the metal nanocrystals is 1 μmol / L-100 mol / L.

3. The method of removing surface-adsorbed halogen ions from metal nanocrystals of claim 1, wherein In step (2), the concentration of the borohydride aqueous solution used is 1 μmol / L-100 mol / L, the concentration of the dispersion of the metal nanocrystals is 1 μmol / L-100 mol / L, and the volume ratio of the borohydride aqueous solution to the dispersion of the metal nanocrystals is 1000:1-1:1000.

4. The method of removing surface-adsorbed halogen ions from metal nanocrystals of claim 1, wherein 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), (C2H5)4N(BH4).

5. The method of removing surface-adsorbed halogen ions from metal nanocrystals of claim 1, wherein the metal nanocrystals are selected from the group consisting of gold, silver, copper, platinum, palladium, and combinations thereof. The number of centrifugation in step (2) varies between 1-50 times.

6. The method of removing surface-adsorbed halogen ions from metal nanocrystals of claim 1, wherein The molecules or groups to be adsorbed on the surface of the metal nanocrystals in step (3) are one or more of 1,4-diisocyanatobenzene (PDI), polyvinylpyrrolidone (PVP), Pluronic F127, cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB), behenyltrimethylammonium chloride (C 22 TAC), dimethyl dioctadecyl ammonium chloride (DDAC), dimethyl dioctadecyl ammonium bromide (DDAB), hexadecyl dimethyl benzyl ammonium chloride (HDBAC), stearyltrimethylammonium chloride (STAC), dodecyltrimethylammonium chloride (DTAC), sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), sodium dodecylsulfonate (SLS).

7. The method of removing surface-adsorbed halogen ions from metal nanocrystals of claim 1, wherein In step (3), the concentration of the borohydride aqueous solution is 1 μmol / L-100 mol / L, the concentration of the dispersion of the metal nanocrystals 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 among the three is borohydride aqueous solution: dispersion of metal nanocrystals: molecules or groups to be adsorbed on the surface of the metal nanocrystals = 1-1000:1-1000:1-1000.

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