Method for in-situ synthesis of p-n type silicon quantum dots with adjustable hydrophilicity and hydrophobicity

Abstract

The invention belongs to the field of preparation of semiconductor nanomaterials, and provides a method for in-situ synthesis of hydrophilic-hydrophobic adjustable p-n type silicon quantum dots, which comprises the following steps: S1, slowly dropwise adding a mixed solution of tetraethoxysilane and a p type doped-hydrophilic regulating agent into a basic reaction solution in an alkaline hydrolysis environment, and stirring to obtain a mixed solution; stirring and reacting in an oil bath at a first temperature for more than 1 hour to form a boron-doped p-type silicon quantum dot core layer; s2, heating to a second temperature, adding a mixed regulating agent of an n-type doped-hydrophobic regulating agent and dodecyltrimethoxysilane, and continuing to react for 2-4 hours; and S3, after the reaction in the step 2 is finished, adding isopropanol accounting for 1 / 3 of the volume of the residual reaction liquid, centrifugally collecting the precipitate, and purifying the precipitate by adopting a biphase purification method to obtain the p-n type silicon quantum dots. By adjusting the molar ratio of B-TEOS / P-TEOS and the addition amount of DTMS, gradient regulation and control of p-n type doping concentration and contact angle can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor nanomaterial preparation, and particularly relates to a method for preparing silicon quantum dots that simultaneously realizes pn-type doping and hydrophilicity regulation during an in-situ synthesis process. Background Art

[0002] Due to their built-in electric field characteristics, pn-type silicon quantum dots (pn SiQDs) have unique advantages in optoelectronic devices (such as solar cells and light-emitting diodes), catalytic reactions and carrier separation.

[0003] Existing pn-type silicon quantum dots are often prepared using a step-by-step doping method: p-type or n-type silicon quantum dots are first prepared, and then the other type of dopant is introduced through physical mixing or secondary modification. This method suffers from problems such as poor doping uniformity and numerous interface defects. Furthermore, conventional hydrophilicity and hydrophobicity control relies on post-process surface modification, which is difficult to coordinate with the pn-type doping process, resulting in poor performance matching in material applications.

[0004] At present, there is no technical solution to achieve in-situ regulation of pn-type doping and hydrophilicity in the same synthetic system. Therefore, it is of great significance to develop a preparation method that can coordinate the regulation of electrical properties and interface properties. Summary of the Invention

[0005] The present invention aims to provide a method for in situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity. Through an innovative dual-doping-interface control system, the construction of p-type / n-type doping regions and the control of hydrophilic / hydrophobic surface properties are simultaneously achieved during the nanocrystal growth process, solving the performance mismatch problem caused by step-by-step operations in the existing technology and improving the material's application adaptability in optoelectronic devices and biomedical fields.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity comprises the following steps:

[0008] S1. Implant hydrophilic elements to construct p-type core layer

[0009] A mixture of tetraethyl orthosilicate (TEOS) and a p-type doping-hydrophilicity modifier is slowly dripped into the base reaction solution in an alkaline hydrolysis environment, and stirred in an oil bath at a first temperature for 1 hour to form a boron-doped p-type silicon quantum dot core layer. At this time, the surface is hydrophilic (contact angle <40°) due to the hydrolysis of trimethoxysilyl groups to form Si-OH.

[0010] S2, n-type shell coating and hydrophobicity regulation

[0011] The temperature is raised to a second temperature, and a mixed regulator of an n-type doping-hydrophobicity regulator and dodecyltrimethoxysilane (DTMS) is added, and the reaction is continued for 2-4 hours. By adjusting the ratio of DTMS, synergistic regulation of shell n-type doping and surface hydrophobicity is achieved: the higher the DTMS ratio, the higher the surface methyl coverage and the stronger the hydrophobicity (the contact angle can reach 50°-70°).

[0012] S3. Phase transfer regulation and purification

[0013] After the reaction in step 2 is completed, isopropanol is added to 1 / 3 of the remaining reaction solution volume, and the mixture is centrifuged at 7000-9000 rpm for more than 15 minutes. The precipitate is collected and purified by a two-phase purification method to obtain pn-type silicon quantum dots.

[0014] Preferably, in step S1, the molar ratio of TEOS to the p-type doping-hydrophilicity regulating agent in the mixed solution is 5:1, and the dropping speed of the mixed solution is 1-2 drops / second.

[0015] Preferably, the p-type doping-hydrophilicity regulating agent is a boron-containing silane compound, and the mass fraction of boron element is 8-12%.

[0016] Preferably, the p-type doping-hydrophilicity regulating agent is tris(3-trimethoxysilylpropyl) borate (B-TEOS).

[0017] Preferably, in step S2, the molar ratio of the n-type doping-hydrophobic regulating agent to dodecyltrimethoxysilane (DTMS) in the mixed regulating agent is 1:0.5-2.

[0018] Preferably, the molar ratio of the n-type doping-hydrophobicity regulating agent to tetraethyl orthosilicate is 1:3-5.

[0019] Preferably, the n-type doping-hydrophobicity regulating agent is a phosphorus-containing silane compound, and the mass fraction of phosphorus element is 5-8%.

[0020] Preferably, the n-type doping-hydrophobicity regulating agent is tris(trimethoxysilylpropyl)phosphate (P-TEOS).

[0021] Preferably, the first temperature is about 40°C and the second temperature is about 60°C; the configuration of the basic reaction liquid is as follows: in a nitrogen-protected three-necked flask, a mixture of analytical pure ethanol and deionized water with a volume ratio of 5:1 is added, and 25% volume fraction of ammonia water is added under stirring to adjust the pH to 9.5-10.5 to form an alkaline hydrolysis environment.

[0022] Preferably, the two-phase purification method is specifically to dissolve the precipitate in the hydrophobic phase toluene, then add the hydrophilic phase containing 3-mercaptopropionic acid (MPA) aqueous solution for phase transfer, adjust the pH of the aqueous phase to 6-7, transfer the quantum dots from the organic phase to the aqueous phase, and finally dialyze through a 2500-3500Da dialysis bag for more than 24 hours.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention provides a method for in-situ synthesis of pn-type silicon quantum dots with adjustable hydrophilicity and hydrophobicity. Through an innovative dual-doping-interface control system, the method simultaneously achieves the construction of p-type / n-type doping regions and the control of hydrophilic / hydrophobic surface properties during nanocrystal growth. Experimental results show that the gradient control range of the pn-type doping concentration is: boron content 0.5-2at.%, phosphorus content 0.3-1.5at.%, and the contact angle gradient control range is: 30°-65°. When B-TEOS / P-TEOS = 1:2 and DTMS accounts for 40% of the shell modulator, a pn junction photocurrent response of 0.023mA / cm 2 , the optimal performance combination of contact angle 46.4°±3°.

[0025] 2. The method provided by the present invention is simple to operate and has rich control dimensions. It provides a new technical path for the multifunctional preparation of semiconductor nanomaterials, which can solve the performance mismatch problem caused by step-by-step operation in the existing technology and improve the application adaptability of materials in optoelectronic devices and biomedical fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : This is the X-ray diffraction pattern of the moderately hydrophilic pn-type silicon quantum dots before and after doping in Example 1 of the present invention;

[0027] Figure 2 This is the X-ray photoelectron spectroscopy analysis of the moderately hydrophilic pn-type in Example 1 of the present invention (A is the boron element XPS after pn-type silicon quantum dots are doped, B is the phosphorus element XPS after pn-type silicon quantum dots are doped, and C is the silicon element XPS after pn-type silicon quantum dots are doped);

[0028] Figure 3 This is the photocurrent response analysis before and after doping of the moderately hydrophilic pn-type quantum dots in Example 1 of the present invention;

[0029] Figure 4 This is the electron lifetime analysis before and after doping of the moderately hydrophilic pn-type quantum dots in Example 1 of the present invention;

[0030] Figure 5 This is the effect of the DTMS addition amount on the contact angle of pn-type quantum dots in the present invention. DETAILED DESCRIPTION

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0032] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific 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.

[0034] like Figure 1 As shown, a method for in situ synthesis of pn-type silicon quantum dots with adjustable hydrophilicity and hydrophobicity comprises the following steps:

[0035] Step 1: Raw material pretreatment and reaction system construction

[0036] 1) Prepare bifunctional doping regulator:

[0037] P-type doping-hydrophilicity modifier: boron-containing silane compound, tris(3-trimethoxysilylpropyl) borate (B-TEOS) is selected, wherein the mass fraction of boron element is 8-12%, and the trimethoxysilyl group provides hydrophilic anchoring sites.

[0038] N-type doping-hydrophobicity control agent: phosphorus-containing silane compound, tris(trimethoxysilylpropyl) phosphate (P-TEOS), with a phosphorus mass fraction of 5-8%, and long-chain alkyl groups forming a hydrophobic layer through subsequent hydrolysis and condensation.

[0039] 2) Basic reaction solution preparation: In a nitrogen-protected three-necked flask, add a mixture of ethanol (analytical grade) and deionized water in a volume ratio of 5:1. While stirring, add 25% by volume ammonia water to adjust the pH to 9.5-10.5 to form an alkaline hydrolysis environment.

[0040] Step 2: Gradient doping-interface coordinated regulation

[0041] Step 1: p-type core layer growth (hydrophilic element implantation)

[0042] A mixture of tetraethyl orthosilicate (TEOS) and B-TEOS at a molar ratio of 5:1 was slowly added to the base reaction solution at a rate of 1-2 drops / second. The mixture was stirred in a 40°C oil bath for 1 hour to form a boron-doped p-type silicon quantum dot core layer. At this time, the surface was hydrophilic (contact angle <40°) due to the hydrolysis of trimethoxysilyl groups to form Si-OH.

[0043] Step 2: n-type shell coating and hydrophobicity control

[0044] After the core layer growth in the first step is completed, the temperature is raised to 60°C, and a mixed control agent of P-TEOS and dodecyltrimethoxysilane (DTMS) with a molar ratio of 1:0.5-2 is added, where the molar ratio of P-TEOS to TEOS is controlled at 1:3-1:5, and the reaction is continued for 2-4 hours; by adjusting the proportion of DTMS, the coordinated regulation of shell n-type doping and surface hydrophobicity is achieved: the higher the DTMS proportion, the higher the surface methyl coverage and the stronger the hydrophobicity (the contact angle can reach 90-120°).

[0045] Step 3: Phase transfer control and purification

[0046] After the reaction in step 2 is completed, isopropanol is added to a volume of 1 / 3 of the remaining reaction solution to reduce polarity and promote quantum dot aggregation; the mixture is centrifuged at 7000-9000 rpm for more than 15 minutes to collect the precipitate.

[0047] The precipitate was purified by a two-phase purification method: the precipitate was first dissolved in toluene (hydrophobic phase), and then an aqueous solution containing 3-mercaptopropionic acid (MPA) (hydrophilic phase) was added for phase transfer, and the pH of the aqueous phase was adjusted to 6-7 to transfer the quantum dots from the organic phase to the aqueous phase. Finally, the precipitate was dialyzed through a 2500-3500Da dialysis bag for more than 24 hours to obtain pn-type silicon quantum dots.

[0048] The following is a further detailed description of a method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to the present invention, in conjunction with examples.

[0049] Example 1: Preparation of pn-type silicon quantum dots with moderate hydrophilicity

[0050] Basic reaction solution: 200 mL ethanol + 40 mL deionized water, add 10 mL ammonia water to adjust the pH to 10.0.

[0051] Mixed solution containing p-type regulator: 5mmol of TEOS and 1mmol of B-TEOS are mixed.

[0052] Mixture containing n-type modulator: P-TEOS 2mmol and DTMS 2mmol. Core layer growth: Add the mixture containing p-type modulator dropwise to the base reaction solution and stir at 40℃ for 1 hour. The system will turn transparent and light blue.

[0053] Shell coating: Heat to 60°C, add a mixture containing n-type regulator, react for 3 hours, and the solution turns dark blue.

[0054] Purification treatment: add 60 mL of isopropanol and centrifuge at 8000 rpm for 15 minutes. Collect the precipitate and dissolve it in 50 mL of toluene. Then add 20 mL of aqueous solution containing 5 mmol of MPA (pH = 6.5). After shaking, separate the liquids and dialyze the aqueous phase for 24 hours to obtain a pn-type silicon quantum dot solution.

[0055] Performance parameters: Boron content 1.2at.%, Phosphorus content 0.8at.%, Contact angle 46.4°±3°, Photocurrent response of pn junction 0.023mA / cm 2 .

[0056] The moderately hydrophilic pn-type silicon quantum dots obtained in this example were subjected to X-ray diffraction patterns before and after doping, X-ray photoelectron spectroscopy analysis, photocurrent response analysis before and after doping, and electron lifetime analysis before and after doping. The results are shown in Tables 1 and Figure 1-4 .

[0057] Table 1. Boron and phosphorus content determined by XPS

[0058]

[0059] Example 2: Preparation of hydrophobic pn-type silicon quantum dots

[0060] The DTMS content in the mixed solution containing the n-type control agent was increased to 4 mmol (P-TEOS / DTMS=1:2). The remaining steps and parameters were the same as those in Example 1.

[0061] Performance parameters: contact angle 63.37°±3°, dispersion concentration in toluene 15 mg / mL, suitable for oil-phase optoelectronic device assembly.

[0062] Example 3: Preparation of hydrophilic pn-type silicon quantum dots

[0063] The DTMS content in the mixed solution containing the n-type regulator was reduced to 1 mmol (P-TEOS / DTMS=2:1), and 1 mmol APTES (aminosilane) was added during the shell reaction to enhance the hydrophilicity.

[0064] Performance parameters: contact angle 31.62°±2°, dispersibility PDI in water = 0.15, suitable for the field of biological imaging.

[0065] The results of Example 1 show that the phase does not change before and after doping, and the crystallinity is good (see Figure 1 ); The method provided in Example 1 can realize the synthesis of boron and phosphorus doped into silicon quantum dots (see Figure 2 ), wherein the boron content is 1.2at.%, and the phosphorus content is 0.8at.% (see Table 1); the pn-type quantum dots after doping have better electron transfer performance and better separation of photogenerated electrons and holes (see Figure 3 ); the electron lifetime of the doped quantum dots is prolonged, which further indicates that the electron-hole separation efficiency is improved (see Figure 4 ).

[0066] Examples 1-3 show that when the amount of DTMS added is adjusted to 20%, 40%, and 60% of the shell modifier, the contact angles are 31.62°, 46.4°, and 63.37°, respectively, showing a positive correlation (see Figure 5 ), that is, by adjusting the molar ratio of B-TEOS / P-TEOS (1:1 to 1:3) and the amount of DTMS added in the two-step reaction in step 2, a gradient control of the pn-type doping concentration (boron content 0.5-2at.%, phosphorus content 0.3-1.5at.%) and the contact angle (30°-70°) can be achieved. When B-TEOS / P-TEOS = 1:2 and DTMS accounts for 40% of the shell modulator, a pn junction photocurrent response of 0.023mA / cm 2 , the optimal performance combination of contact angle 46.4°±3°.

[0067] In summary, the present invention achieves in situ precise control of the hydrophilicity and hydrophobicity of pn-type silicon quantum dots through the design of dual-functional regulators and gradient growth process. This method is simple to operate and has rich control dimensions, providing a new technical path for the multifunctional preparation of semiconductor nanomaterials.

[0068] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may of course make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for in situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity, characterized in that: The following steps are involved: S1. Implant hydrophilic elements to construct p-type core layer Slowly dripping a mixture of tetraethyl orthosilicate and a p-type doping-hydrophilicity regulating agent into the basic reaction solution in an alkaline hydrolysis environment, stirring and reacting in an oil bath at a first temperature for more than 1 hour to form a boron-rich p-type silicon quantum dot core layer; S2, n-type shell coating and hydrophobicity regulation Raise the temperature to a second temperature, add a mixed regulator of an n-type doping-hydrophobic regulator and dodecyltrimethoxysilane, and continue the reaction for 2-4 hours; S3. Phase transfer regulation and purification After the reaction in step 2 is completed, isopropanol is added to 1 / 3 of the remaining reaction solution volume, and the mixture is centrifuged at 7000-9000 rpm for more than 15 minutes. The precipitate is collected and purified by a two-phase purification method to obtain pn-type silicon quantum dots.

2. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 1, characterized in that: In step S1 , the molar ratio of tetraethyl orthosilicate to the p-type doping-hydrophilicity regulating agent in the mixed solution is 5:1, and the dropping speed of the mixed solution is 1-2 drops / second.

3. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 2, characterized in that: The p-type doping-hydrophilicity regulating agent is a boron-containing silane compound, and the mass fraction of the boron element is 8-12%.

4. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 3, characterized in that: The p-type doping-hydrophilicity regulating agent is tris(3-trimethoxysilylpropyl) borate.

5. The method for in-situ synthesis of pn-type silicon quantum dots with adjustable hydrophilicity and hydrophobicity according to claim 2, characterized in that: In step S2, the molar ratio of the n-type doping-hydrophobic regulating agent to dodecyltrimethoxysilane in the mixed regulating agent is 1:0.5-2.

6. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 5, characterized in that: The molar ratio of the n-type doping-hydrophobicity regulating agent to tetraethyl orthosilicate is 1:3-5.

7. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 6, characterized in that: The n-type doping-hydrophobicity regulating agent is a phosphorus-containing silane compound, and the mass fraction of phosphorus element is 5-8%.

8. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 7, characterized in that: The n-type doping-hydrophobicity regulating agent is tris(trimethoxysilylpropyl)phosphate.

9. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 1, characterized in that: The first temperature is about 40°C, and the second temperature is about 60°C; the configuration of the basic reaction liquid is as follows: a mixture of analytical pure ethanol and deionized water with a volume ratio of 5:1 is added to a three-necked flask protected by nitrogen, and 25% volume fraction of ammonia water is added while stirring to adjust the pH to 9.5-10.5 to form a reaction liquid in an alkaline hydrolysis environment.

10. The method for in-situ synthesis of pn-type silicon quantum dots with controllable hydrophilicity and hydrophobicity according to claim 1, characterized in that: The two-phase purification method specifically involves first dissolving the precipitate in the hydrophobic phase of toluene, then adding a hydrophilic phase of an aqueous solution containing 3-mercaptopropionic acid for phase transfer, adjusting the pH of the aqueous phase to 6-7, transferring the quantum dots from the organic phase to the aqueous phase, and finally dialyzing through a 2500-3500Da dialysis bag for more than 24 hours.

Images