Monodisperse PbS quantum dot as well as one-step synthesis method and application thereof

Abstract

The invention discloses a one-step synthesis method of monodisperse PbS quantum dots, which comprises the following steps: providing a sulfur precursor, the sulfur precursor being disubstituted thiourea, the disubstituted thiourea being configured in such a way that two H atoms in the molecular formula of thiourea are respectively substituted by an oil group and phenyl N, N '; providing a lead precursor, wherein the lead precursor is lead oleate prepared from octadecene, lead oxide and oleic acid in a molar ratio of (20: 1: 1)-(20: 1: 5); the sulfur precursor is injected into the lead precursor at the preset temperature, a reaction mixed solution of PbS CQDs is obtained after reaction is conducted for the preset time, and the lead-sulfur ratio (Pb / S) in the reaction mixed solution is 7: 1; and carrying out purification operation on the reaction mixed solution to obtain the required PbS CQDs. The controllable synthesis of the large-size monodisperse PbS quantum dots with the absorption wavelength of about 2000nm can be realized through the method disclosed by the invention. Furthermore, the invention also discloses the monodisperse PbS quantum dot prepared by the one-step synthesis method and application of the monodisperse PbS quantum dot.

Description

Technical Field

[0001] The invention relates to the field of semiconductor quantum dot synthesis, in particular to a one-step synthesis method of monodisperse PbS quantum dots with an absorption peak exceeding 2000nm and monodisperse PbS quantum dots prepared by the method. Background Art

[0002] PbS quantum dots (lead sulfide quantum dots) stand out as excellent candidates for narrow-bandgap optoelectronic functional materials, which have a wide range of tunable bandgaps (0.6-1.6 eV) and also exhibit high molar broadband absorption coefficients (≈10 6 M -1 cm -1 ), large Bohr exciton radius (≈18nm) and low-cost advantages of solution processing, it has great application potential in the field of infrared photoelectric detection and infrared luminescence. However, large-sized PbS quantum dots with absorption peaks exceeding 2000nm are relatively difficult to prepare due to the problems of Oswald ripening and regrowth during the synthesis process. There are also few PbS quantum dots with absorption peaks exceeding 2000nm reported previously. In order to obtain PbS quantum dot short-wave infrared optoelectronic devices with longer wavelengths, it is necessary to explore and optimize the preparation method of large-sized PbS quantum dots to achieve controllable large-size, monodisperse, high-quality PbS quantum dots.

[0003] At present, the synthesis methods of PbS quantum dots include classical hot injection method, multiple hot injection method, cation exchange method, etc. Among these methods, the most widely used sulfide precursors include hexamethyldisilathione, phosphine sulfide (R3P=S, where R represents alkyl or aryl), and hydrogen sulfide produced by heating elemental sulfur in alkane or amine solvents. The selection of suitable precursors is crucial to provide the necessary monomer supply rate, which directly affects the crystallization conditions of quantum dots. Existing synthesis methods have successfully synthesized highly monodisperse PbS nanocrystals, but the diameters of the obtained quantum dots are far lower than the 18nm exciton Bohr radius of PbS, which shows that although these methods can effectively synthesize nanocrystals, there is still room for improvement in size control. Summary of the invention

[0004] The present invention aims to solve the problem that it is difficult to synthesize large-sized, monodisperse PbS quantum dots in the prior art, and proposes a one-step synthesis method for monodisperse PbS quantum dots. By regulating the amount of oleic acid and coordinating the action of disubstituted thiourea, controllable synthesis of large-sized, monodisperse PbS quantum dots with an absorption wavelength of about 2000 nm can be achieved. Furthermore, the monodisperse PbS quantum dots prepared by the one-step synthesis method and their applications are also disclosed.

[0005] The first aspect of the present invention discloses a one-step synthesis method of monodisperse PbS quantum dots, comprising:

[0006] Providing a sulfur precursor, wherein the sulfur precursor is a disubstituted thiourea, wherein two H atoms in the molecular formula of the thiourea are substituted by an oil group and a phenyl group N,N′ respectively;

[0007] Providing a lead precursor, wherein the lead precursor is lead oleate prepared from octadecene, lead oxide and oleic acid in a molar ratio of 20:1:1 to 20:1:5;

[0008] At a preset temperature, a sulfur precursor is injected into a lead precursor, and after a preset reaction time, a reaction mixture solution of PbS CQDs is obtained, wherein the lead-sulfur ratio (Pb / S) in the reaction mixture solution is 7:1;

[0009] The reaction mixture solution is purified to obtain the desired PbS CQDs.

[0010] As an optional scheme, the preparation method of the disubstituted thiourea is: firstly mix octadecene and phenyl isothiocyanate at room temperature, then drop oleylamine into the mixed solution at room temperature and nitrogen environment, stir and leave to obtain the disubstituted thiourea.

[0011] As an optional solution, the molar ratio of octadecene / phenyl isothiocyanate / oleylamine is 6:3:8.

[0012] As an optional solution, the molar ratio of octadecene / lead oxide / oleic acid is 20:1:2.5 to 20:1:4.

[0013] As an optional scheme, the preparation method of the lead precursor is: octadecene, lead oxide and oleic acid are placed in a reaction container; the obtained mixture is placed in a vacuum environment at 120±5°C for 60±5 minutes to obtain a dry lead precursor.

[0014] As an optional solution, the preset temperature is 135±5° C., and the preset time is 20±5 minutes.

[0015] As an optional scheme, the purification operation includes: loading the reaction mixture solution and the anti-solvent into a centrifuge together, and after centrifugal precipitation, removing the supernatant to obtain the desired PbS CQDs; the anti-solvent uses n-butanol and anhydrous methanol in a volume ratio of 2:1.

[0016] As an optional solution, when the ratio of octadecene / lead oxide / oleic acid is less than or equal to 20:1:2, ethanol is also added to the centrifuge during the purification operation to promote flocculation.

[0017] The second aspect of the present invention discloses a monodisperse PbS quantum dot, characterized in that it is synthesized using the one-step synthesis method of the monodisperse PbS quantum dots described in the first aspect of the present invention or any one of its optional schemes; the size of the PbS CQDs is related to the amount of oleic acid used in the preparation process of lead oleate.

[0018] The third aspect of the present invention is to apply the monodisperse PbS quantum dots disclosed in the second aspect of the present invention to the fields of short-wave infrared photoelectric detection and solar cells.

[0019] The present invention has the following beneficial effects:

[0020] (1) The present application selects a disubstituted thiourea compound as a sulfur precursor and uses an excess of oleic acid ligand to achieve effective control of the average characteristic size of quantum dots in the range of 6 to 20 nm and the absorption peak in the controllable short-wave infrared range of 1700-2300 nm. In particular, a one-step synthesis of large-sized, monodisperse Pbs quantum dots with an average characteristic size exceeding 10 nm and an absorption peak exceeding 2000 nm is achieved.

[0021] (2) The PbS quantum dot synthesis method disclosed in the present invention has a simple process and good repeatability, uses a relatively cheap precursor, and the synthesized PbS quantum dots have a long-term stable Tyndall effect.

[0022] (3) The large-sized, monodisperse PbS quantum dots prepared by the present invention have an absorption peak exceeding 2000 nm and can be applied to short-wave infrared photoelectric detection, solar cells and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD pattern of the PbS quantum dots synthesized in Example 1;

[0024] Figure 2 is a TEM image of the PbS quantum dots synthesized in Example 1;

[0025] Figure 3 is a HRTEM image of the PbS quantum dots synthesized in Example 1;

[0026] Figure 4 is the normalized absorption spectrum of the PbS quantum dots synthesized in Example 1;

[0027] Figure 5 It is a physical picture of the PbS quantum dot sol synthesized in Example 1 and the Tyndall effect;

[0028] Figure 6 is a particle size diagram of the PbS quantum dots synthesized in Example 1;

[0029] Figure 7is the normalized absorption spectrum of the PbS quantum dots synthesized in Examples 1, 2, and 3;

[0030] Figure 8 is a HRTEM image of the PbS quantum dots synthesized in Example 2;

[0031] Fig. 9 This is the HRTEM image of the PbS quantum dots synthesized in Example 3. DETAILED DESCRIPTION

[0032] The present invention discloses a one-step synthesis method for monodisperse PbS quantum dots, which adopts a combination of a disubstituted thiourea compound as a sulfur precursor and lead oleate as a lead precursor, and can prepare high-quality, large-size, monodisperse PbS CQDs (i.e., PbS quantum dots) with an absorption peak exceeding 2000nm.

[0033] It can be understood that the absorption peak refers to the peak value of the wavelength at which the light absorption coefficient of the material is the largest in the absorption spectrum. The absorption wavelength refers to the wavelength corresponding to the absorption peak of the material within the test range. As the size of the quantum dots decreases, its band gap increases, causing the absorption peak to blue shift (i.e. move to the shorter wavelength direction); conversely, it will red shift (i.e. move to the longer wavelength direction).

[0034] In addition, it should be noted that, unless otherwise specified, the numerical range A to B in the present invention includes the endpoint value A and the endpoint value B.

[0035] The technical solution of the present invention is further described below in conjunction with the embodiments and drawings.

[0036] The embodiment of the present invention discloses a method for synthesizing PbS quantum dots, which mainly includes the following steps:

[0037] S1, Preparation of sulfur precursor (disubstituted thiourea)

[0038] Before preparing the sulfur precursor, water and oxygen in the three-necked flask can be removed through a double-row tube, and the flask is filled with nitrogen, and then the sulfur precursor is prepared according to the molar ratio of octadecene / phenyl isothiocyanate / oleylamine of 6:3:8. The preparation process is as follows: first, octadecene and phenyl isothiocyanate are mixed at room temperature; then, oleylamine is slowly added dropwise to the mixed solution of octadecene and phenyl isothiocyanate at room temperature and nitrogen environment, stirred and left overnight to obtain a uniform and transparent solution, that is, disubstituted thiourea as a sulfur precursor.

[0039] It is worth noting that the present invention can prepare large-sized quantum dots by using disubstituted thiourea as a sulfur precursor, and achieve good size regulation through the synergistic effect of disubstituted thiourea and oleic acid. This sulfur precursor uses oleyl and phenyl N,N' to replace the two H atoms in the thiourea molecular formula, where the strong electron-donating groups of phenyl N,N' reduce the pathway to the reaction center of the thiourea molecule; the oleyl (C 18 H 36 The ) (relative molecular weight of 252) group is much larger than other substituent groups, such as amino (-NH2) (relative molecular weight of 16) and propyl (-C3H7) (relative molecular weight of 43), which ensures low reactivity and slows down the growth rate of the monomer, thereby reducing the nucleation rate of PbS quantum dots, which is beneficial to controlling its growth shape. In addition, the raw material price of the disubstituted thiourea prepared by the above method is relatively low, and the preparation process is simple and easy to operate.

[0040] S2. Preparation of lead precursor

[0041] The lead precursor is lead oleate prepared from octadecene, lead oxide and oleic acid. The preparation process includes: octadecene, lead oxide and oleic acid are respectively placed in a three-necked round-bottom flask, and the molar ratio thereof is 20:1:1 to 20:1:5; the obtained mixture is placed in a 120±5°C environment and evacuated for 60±5 minutes to obtain a relatively dry lead precursor. Among them, oleic acid is used as an adjustment knob for size control. Under the action of oleic acid, the average size of the characteristic size of PbS quantum dots can be effectively changed from 6 to 20nm. Among them, vacuum degassing is to remove impurity gases such as oxygen and water vapor in the system to prevent oxidation of lead oleate, optimize reaction conditions and enhance the stability of the reaction system.

[0042] It is understandable that there is no strict order between step S1 and step S2, but considering that the sulfur precursor preparation needs to stand for a period of time, the sulfur precursor is usually prepared first and then the lead precursor.

[0043] S3, Synthesis of PbS quantum dots

[0044] The ambient temperature is raised to 130°C to 135°C, and the sulfur precursor obtained in step S1 is added to the lead precursor prepared in step 2, and the Pb / S molar ratio is ensured to be 7:1. The lead precursor solution turns black within a few minutes after the sulfur precursor is injected, indicating that quantum dots are generated. The temperature is maintained within the range of 135±5°C for 20±5 minutes to promote the reaction, and the reaction is completed when the timing ends. After the reaction is completed, the resulting solution is naturally cooled to room temperature to obtain a reaction mixed solution of PbS quantum dots.

[0045] S4. PbS quantum dot purification

[0046] The reaction mixture obtained in step S3 and the anti-solvent are placed in a centrifuge together and rotated at 6000 rpm to remove impurities therein. After the rotation is completed, precipitated nanocrystals, i.e., PbS quantum dots, are obtained; the nanocrystals are then dispersed in hexane and dissolved to repeat the above centrifugation process; after the centrifugation operation is completed, the supernatant is removed to obtain a clean, impurity-free black powder of PbS quantum dots. In this process, the color of the supernatant in the mixed solution can be used to determine whether the purification is completed. The more centrifugation times, the clearer the supernatant, the purer the quantum dots, and the operation is completed when the color of the supernatant is almost transparent. The above centrifugation process is usually repeated 1 to 3 times. The anti-solvent can be n-butanol and anhydrous methanol in a volume ratio of 2:1. The anti-solvent is mainly used to promote the precipitation of quantum dots in the reaction mixture so as to separate them from other impurities.

[0047] It is worth noting that during the preparation of the lead precursor, when the ratio of octadecene / lead oxide / oleic acid is less than or equal to 20:1:2, that is, when small-sized quantum dots need to be formed, a small amount of ethanol can be added to the anti-solvent in the purification process to promote flocculation.

[0048] Based on the above method, in a specific embodiment 1, when preparing a sulfur precursor (disubstituted thiourea) in step S1, 3.21 g of octadecene, 2.28 g of phenyl isothiocyanate, and 4.51 g of oleylamine are used; when preparing a lead precursor in step S2, 15 ml of octadecene, 0.45 g of lead oxide, and 2.5 ml of oleic acid are used, and the corresponding octadecene / lead oxide / oleic acid ratio is 20:1:3; in step S3, 0.8 g of the sulfur precursor prepared in step S1 is quickly injected into the lead precursor prepared in step 2, and the Pb / S ratio in the mixture is 7:1; after mixing, vacuum is first evacuated at 120°C for 1h, and then the temperature is raised to 135°C and maintained for 20 minutes before injecting thiourea, and the reaction is carried out for 20 minutes to prepare a PbS quantum dot mixed solution; and the purification in step S4 is carried out as described above. After the synthesis of PbS quantum dots is completed, the PbS quantum dots are placed in an oven and dried at 100°C for 20 minutes, and then the PbS quantum dot powder can be subjected to X-ray diffraction (XRD) analysis.

[0049] It can be seen Figure 1There are 9 obvious diffraction peaks, respectively at 25.901°, 29.970°, 42.930°, 50.798°, 53.272°, 62.449°, 68.705°, 70.748° and 78.903°. By comparing with the standard diffraction peak card of PbS (JCPDS No: 02-0699), it can be known that the crystal plane diffraction peaks of the synthesized PbS quantum dots correspond to the diffraction peaks of the (111), (200), (220), (311), (222), (400), (331), (420) and (422) crystal planes of PbS cubic crystals. It is consistent with the international standard PDF card. This shows that Example 1 synthesized high-quality PbS quantum dots, and its absorption peak exceeds 2000nm.

[0050] like Figure 2 As shown, from the transmission electron microscopy (TEM) image of the PbS quantum dots synthesized at a concentration of 2.5 ml of oleic acid in Example 1, it can be seen that the quantum dots are relatively uniform in size and have good monodispersity. The size of the quantum dots synthesized with 2.5 ml of oleic acid is 13.89±1.74 nm.

[0051] like Figure 3 As shown, from the high-resolution transmission electron microscopy (HRTEM) image of the PbS quantum dots synthesized in Example 1 and the interplanar spacing measurement results, it can be seen that the quantum dot lattice fringes have clear boundaries, and the interplanar spacing measurement result is 0.169nm, which belongs to the (222) crystal plane of the PbS cubic structure.

[0052] like Figure 4 As shown, from the normalized absorption spectrum of PbS quantum dots, it can be seen that the first exciton absorption peak of the PbS quantum dots synthesized in Example 1 is at 2200nm, indicating that it has potential application value in the fields of short-wave infrared photoelectric detectors and the like.

[0053] like Figure 5 As shown, it can be seen from the actual photos of the PbS quantum dot sol that the PbS quantum dot sol synthesized in Example 1 has an obvious Tyndall effect, and no sedimentation occurs after being stored in the air for one week.

[0054] like Figure 6 As shown in the particle size diagram of the PbS quantum dots synthesized in Example 1, it can be seen that the particle size is mainly concentrated around 17 nm, which indirectly proves that the synthesized PbS quantum dots have uniform size.

[0055] Further, the present invention provides another specific embodiment 2, which is different from embodiment 1 only in the amount of oleic acid added during the synthesis. In embodiment 2, the amount of oleic acid added during the preparation of the lead precursor is 1.5 ml, and the corresponding octadecene / lead oxide / oleic acid ratio is 20:1:2.

[0056] Further, the present invention provides another embodiment 3, which is also different from embodiment 1 only in the amount of oleic acid added during the synthesis. In embodiment 3, the amount of oleic acid added during the preparation of the lead precursor is 2 ml, and the corresponding octadecene / lead oxide / oleic acid ratio is 20:1:2.5.

[0057] like Figure 7 As shown, through the normalized absorption spectra of PbS quantum dots in Examples 1, 2, and 3, it can be seen that as the amount of oleic acid added during the synthesis of PbS quantum dots decreases, the position of the first exciton absorption peak blue-shifts from 2200 nm in Example 1 to 1700 nm in Example 3, indicating that as the amount of oleic acid decreases, the size of the quantum dots also decreases.

[0058] like Figure 8 As shown in FIG. 1 , it can be seen from the high-resolution transmission electron microscopy (HRTEM) image of the PbS quantum dots synthesized in Example 2 that the PbS quantum dots at this size still have good monodispersity, and the lattice fringes of the quantum dots have clear boundaries. Fig. 9 As shown, from the high-resolution transmission electron microscopy (HRTEM) image of the PbS quantum dots synthesized in Example 3, it can be seen that the PbS quantum dots at this size still have good monodispersity, and the lattice fringes of the quantum dots are also clearly defined.

[0059] Furthermore, the present invention provides comparative data of the size distribution deviation, i.e., monodispersity, of the PbS quantum dots synthesized in Examples 1, 2, and 3, as shown in Table 1.

[0060] Table 1

[0061]

[0062] From the comparative data in Table 1, it can be seen that the present invention proposes a novel disubstituted thiourea precursor, by fixing the Pb / S ratio (7:1) in the mixed solution of the sulfur precursor and the lead precursor reaction, and only changing the amount of oleic acid used in the preparation of the lead precursor, the controllable synthesis of different large-sized, monodispersed PbS quantum dots can be achieved, and the absorption peak can be controlled in the short-wave infrared range. Further, considering the size of the PbS quantum dots and the uniformity of their distribution, the molar ratio of octadecene / lead oxide / oleic acid can be set at 20:1:2.5 to 20:1:4.

[0063] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A one-step synthesis method for monodisperse PbS quantum dots, characterized in that: include: Providing a sulfur precursor, wherein the sulfur precursor is a disubstituted thiourea, wherein two H atoms in the molecular formula of the thiourea are substituted by an oil group and a phenyl group N,N′ respectively; Providing a lead precursor, wherein the lead precursor is lead oleate prepared from octadecene, lead oxide and oleic acid in a molar ratio of 20:1:1 to 20:1:5; At a preset temperature, a sulfur precursor is injected into a lead precursor, and after a preset reaction time, a reaction mixture solution of PbS CQDs is obtained, wherein the lead-sulfur ratio (Pb / S) in the reaction mixture solution is 7:1; The reaction mixture solution is purified to obtain the desired PbS CQDs.

2. The one-step synthesis method according to claim 1, characterized in that The preparation method of the disubstituted thiourea is as follows: octadecene and phenyl isothiocyanate are first mixed at room temperature, and then oleylamine is added dropwise to the mixed solution at room temperature and under nitrogen, and the mixture is stirred and allowed to stand to obtain the disubstituted thiourea.

3. The one-step synthesis method according to claim 2, characterized in that: The molar ratio of octadecene / phenyl isothiocyanate / oleylamine is 6:3:

8.

4. The one-step synthesis method according to claim 1, characterized in that The molar ratio of octadecene / lead oxide / oleic acid is 20:1:2.5 to 20:1:

4.

5. The one-step synthesis method according to claim 1, characterized in that The preparation method of the lead precursor is as follows: octadecene, lead oxide and oleic acid are placed in a reaction container; the obtained mixture is placed in a 120±5° C. environment and vacuumed for 60±5 minutes to obtain a dry lead precursor.

6. The one-step synthesis method according to claim 1, characterized in that: The preset temperature is 135±5° C., and the preset time is 20±5 minutes.

7. The one-step synthesis method according to any one of claims 1 to 6, characterized in that: The purification operation includes: loading the reaction mixture solution and the anti-solvent into a centrifuge together, and after centrifugal precipitation, removing the supernatant to obtain the desired PbS CQDs; the anti-solvent is n-butanol and anhydrous methanol in a volume ratio of 2:

1.

8. The one-step synthesis method according to claim 7, characterized in that: When the ratio of octadecene / lead oxide / oleic acid is less than or equal to 20:1:2, the method further includes adding ethanol to a centrifuge during the purification operation to promote flocculation.

9. A monodisperse PbS quantum dot, characterized in that: The monodisperse PbS quantum dots are synthesized by the one-step synthesis method according to any one of claims 1 to 8; The size of the PbS CQDs is related to the amount of oleic acid used during the preparation of lead oleate.

10. The monodisperse PbS quantum dots described in claim 9 are applied in the fields of short-wave infrared photoelectric detection and solar cells.

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