Ag-sensitized core-shell Ag (at) CdS (at) ZnS quantum dot and preparation and application thereof

Abstract

The invention discloses an Ag-sensitized core-shell Ag (at) CdS (at) ZnS quantum dot as well as preparation and application thereof. The quantum dot comprises a silver nanoparticle inner core, a cadmium sulfide middle layer coating the silver nanoparticle inner core, and a zinc sulfide outer layer coating the cadmium sulfide middle layer, a core-shell structure of silver nanoparticle inner core-cadmium sulfide middle layer-zinc sulfide outer layer is constructed, CdS and ZnS shell layers are coated step by step, lattice defects can be reduced, meanwhile, Ag is introduced, the plasma resonance effect can be improved, and the quantum yield and the detection sensitivity to nitro explosives are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to Ag-sensitized core-shell Ag@CdS@ZnS quantum dots and their preparation and application. Background Art

[0002] Nitrobenzene explosives pose a serious threat to public safety and the ecological environment due to their high explosiveness, persistent environmental residues, and biotoxicity. Traditional detection methods (such as gas chromatography and mass spectrometry), while highly accurate, are subject to costly equipment, complex operation, and difficulty in rapid on-site screening. In recent years, fluorescence-based detection technologies have attracted considerable attention due to their high sensitivity, real-time response, and low cost. However, their core probe materials (such as organic dyes and carbon dots) generally suffer from low quantum yields and poor photostability, making them inadequate for trace explosive detection.

[0003] Quantum dots (QDs), as semiconductor nanomaterials, are considered ideal probes for fluorescence sensing due to their size-tunable luminescence properties, high photostability, and ease of surface modification. However, traditional QDs (such as CdS and CdSe) face two major bottlenecks in the detection of nitrobenzene explosives. First, surface defects in QDs lead to severe non-radiative recombination, resulting in quantum yields (QY) generally below 50%, limiting the detection signal strength. Second, the electron transfer efficiency between the strong electron-withdrawing groups of nitro explosives and the QDs is insufficient, resulting in low fluorescence quenching sensitivity.

[0004] Therefore, it is very necessary to provide a quantum dot for highly sensitive detection of nitrobenzene explosives. Summary of the Invention

[0005] In view of this, the present application provides an Ag-sensitized core-shell Ag@CdS@ZnS quantum dot and its preparation and application, which are used to solve the problem of how to improve the sensitivity of quantum dots to nitrobenzene explosives detection.

[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present application provides an Ag-sensitized core-shell Ag@CdS@ZnS quantum dot, comprising a silver nanoparticle core, a cadmium sulfide intermediate layer coated on the silver nanoparticle core, and a zinc sulfide outer layer coated on the cadmium sulfide intermediate layer.

[0007] In a second aspect, the present application provides a method for preparing Ag-sensitized core-shell Ag@CdS@ZnS quantum dots, comprising the following steps: S1. Mixing a silver source with a reducing agent solution and heating the reaction to obtain a colloidal solution of silver nanoparticles; S2. Adding a colloidal solution of silver nanoparticles and a sulfur source to a mixed solution of a cadmium salt and a surface modifier, adjusting the pH to alkaline and performing a reflux reaction to obtain an Ag@CdS dispersion; S3. Zinc salt is added to the Ag@CdS dispersion in batches. After the reaction is completed, the dispersion is washed and dried to obtain Ag-sensitized core-shell Ag@CdS@ZnS quantum dots.

[0008] Preferably, the silver source is silver nitrate, the reducing agent is sodium citrate, and the heating reaction temperature is 90-100°C.

[0009] Preferably, the cadmium salt includes one or more of cadmium acetate, cadmium sulfate, cadmium oleate, cadmium carbonate, cadmium oxalate, cadmium phosphate, cadmium chloride, cadmium nitrate, and cadmium bromide; the surface modifier includes one or more of l-cysteine, thioglycolic acid, mercaptoethylamine, ethanedithiol, butanedithiol, p-aminobenzenethiol, glutathione, polyethylene glycol, and polyethyleneimine; and the sulfur source is thiourea.

[0010] Preferably, the molar ratio of the cadmium salt to the sulfur source is 1:1-3.

[0011] Preferably, the pH value is in the range of 8-11, and the reflux reaction is condensation reflux.

[0012] Preferably, the zinc salt is zinc acetate; and the molar ratio of the zinc salt to the cadmium salt is 1:1-2.

[0013] Preferably, in the step of adding the zinc salt in batches, the number of batch additions is 1-5 times, and the time interval between the batch additions is 1-2 hours; and the washing liquid used in the washing step is an alcohol solution.

[0014] In a third aspect, the present application provides an application of Ag-sensitized core-shell Ag@CdS@ZnS quantum dots in the detection of nitrobenzene explosives.

[0015] Preferably, the nitrobenzene explosives include one or more of trinitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, and 2,4,6-trinitrophenol.

[0016] The beneficial effects of the present application are as follows: the present application constructs a core-shell structure of "silver nanoparticle core-cadmium sulfide intermediate layer-zinc sulfide outer layer", and step-by-step coating of CdS and ZnS shells can reduce lattice defects. At the same time, the introduction of Ag can increase the plasma resonance effect, significantly improving the quantum yield and the detection sensitivity of nitro explosives; the introduction of silver nanoparticles in the present application enhances the light absorption ability. At the same time, the electron transfer effect between the Ag core and the CdS shell accelerates the electron exchange between the nitro explosive molecules and the surface of the quantum dots, thereby amplifying the fluorescence quenching signal; the CdS shell between the Ag core and the ZnS outer layer reduces the lattice mismatch between the core-shell materials, thereby reducing the interface defect density; and ZnS as a wide-bandgap semiconductor shell can passivate the dangling bonds on the CdS surface, inhibit non-radiative recombination losses, and improve fluorescence stability. At the same time, the ZnS shell and the CdS shell can block the corrosion of the Ag core by the external environment, ensuring the stability of the quantum dots in complex detection environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the prepared Ag-sensitized quantum dots; Figure 2 TEM image of the prepared quantum dots; Figure 3 This is a fluorescence spectrum of the quantum dots prepared in Example 1 in the presence of TNP; Figure 4 This is a fluorescence spectrum of the quantum dots prepared in Comparative Example 1 in the presence of TNP; Figure 5 Fitting curves for determining TNP for the quantum dots prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the 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.

[0019] Term explanation: a@b means a is the core layer and b is the cladding layer covering a.

[0020] The present application provides an Ag-sensitized core-shell Ag@CdS@ZnS quantum dot, comprising a silver nanoparticle core, a cadmium sulfide intermediate layer coated on the silver nanoparticle core, and a zinc sulfide outer layer coated on the cadmium sulfide intermediate layer.

[0021] The schematic diagram of the structure of Ag@CdS@ZnS quantum dot particles is shown in Figure 1As shown. This application constructs a core-shell structure of "silver nanoparticle core-cadmium sulfide intermediate layer-zinc sulfide outer layer", and gradually coats CdS and ZnS shell layers, which can reduce lattice defects. At the same time, the introduction of Ag can increase the plasma resonance effect, significantly improving the quantum yield and the detection sensitivity of nitro explosives. The introduction of silver nanoparticles in this application enhances the light absorption capacity. At the same time, the electron transfer between the Ag core and the CdS shell accelerates the electron exchange between the nitro explosive molecules and the surface of the quantum dots, thereby amplifying the fluorescence quenching signal. The CdS shell between the Ag core and the ZnS outer layer reduces the lattice mismatch between the core and shell materials, thereby reducing the interface defect density. ZnS, as a wide-bandgap semiconductor shell, can passivate the dangling bonds on the CdS surface, inhibit non-radiative recombination losses, and improve fluorescence stability. At the same time, the ZnS shell and CdS shell can block the corrosion of the Ag core by the external environment, ensuring the stability of the quantum dots in complex detection environments.

[0022] The present application provides a method for preparing Ag-sensitized core-shell Ag@CdS@ZnS quantum dots, comprising the following steps: S1. Mixing a silver source with a reducing agent solution and heating the reaction to obtain a colloidal solution of silver nanoparticles; S2. Adding a colloidal solution of silver nanoparticles and a sulfur source to a mixed solution of a cadmium salt and a surface modifier, adjusting the pH to alkaline and performing a reflux reaction to obtain an Ag@CdS dispersion; S3. Zinc salt is added to the Ag@CdS dispersion in batches. After the reaction is completed, the dispersion is washed and dried to obtain Ag-sensitized core-shell Ag@CdS@ZnS quantum dots.

[0023] The preparation method of the present application obtains Ag-sensitized core-shell Ag@CdS@ZnS quantum dots, wherein step S1 is the AgNPs colloid preparation process, in which the silver source is reduced to Ag nanoparticles, and a well-dispersed AgNPs colloid solution is obtained, which provides a uniform core for the subsequent core-shell structure growth and avoids uneven shell coating due to core agglomeration; step S2 is the Ag@CdS dispersion preparation process, which is used to achieve uniform coating of the CdS shell on the AgNPs surface, reduce interface defects, and improve the luminescence efficiency of quantum dots; step S3 is the ZnS shell preparation process, which is used to form a continuous and dense ZnS shell, further passivate surface defects, and enhance the environmental stability of quantum dots.

[0024] In some embodiments, the silver source is silver nitrate, the reducing agent is sodium citrate, and the heating reaction temperature is 90-100°C.

[0025] In this embodiment, sodium citrate has both reducing and dispersing properties. On the one hand, it is used to reduce silver ions to elemental silver. On the other hand, its carboxylate groups adsorb on the surface of AgNPs to form a double layer, preventing particle agglomeration. High-temperature boiling at 90-100°C can promote the adsorption of citrate on the surface of nanoparticles and control the size uniformity of AgNPs.

[0026] In some embodiments, the cadmium salt includes one or more of cadmium acetate, cadmium sulfate, cadmium oleate, cadmium carbonate, cadmium oxalate, cadmium phosphate, cadmium chloride, cadmium nitrate, and cadmium bromide; the surface modifier includes one or more of l-cysteine, thioglycolic acid, mercaptoethylamine, ethanedithiol, butanedithiol, p-aminobenzenethiol, glutathione, polyethylene glycol, and polyethyleneimine; and the sulfur source is thiourea.

[0027] In this embodiment, the surface modifier forms coordination bonds with the quantum dot surface through the coordination atoms, passivating surface defects and preventing quantum dot aggregation, thereby improving the fluorescence efficiency and stability of the quantum dots. This helps to enhance the intensity and reliability of the detection signal.

[0028] In some embodiments, the molar ratio of cadmium salt to sulfur source is 1:1-3. An appropriate amount of silver source can ensure the formation of uniformly dispersed silver nanoparticle cores, providing a good foundation for subsequent CdS and ZnS shell coating. If the amount of silver source is too much or too little, it may lead to uneven size or agglomeration of silver nanoparticles, thereby affecting the integrity of the core-shell structure and detection performance. In this embodiment, the sulfur source is excessive to avoid 2- The deficiency results in an incomplete CdS shell and reserves a sulfur source for the subsequent generation of ZnS.

[0029] In some embodiments, the pH value ranges from 8 to 11, and the reflux reaction is condensation reflux.

[0030] In this embodiment, the alkaline environment is conducive to the decomposition of sulfur sources such as thiourea to generate S 2- and with Cd 2+ The reaction generates a CdS shell; too high a pH may lead to the formation of Cd(OH)2 precipitation, while too low a pH may result in incomplete decomposition of thiourea. Controlling the pH at 8-11 is beneficial to ensure uniform deposition of CdS.

[0031] In some embodiments, the zinc salt is zinc acetate; and the molar ratio of the zinc salt to the cadmium salt is 1:1-2.

[0032] In this embodiment, under the premise of reserving the sulfur source, the molar ratio of zinc salt to cadmium salt is within a limited range, which is conducive to the complete coverage of the CdS surface by the ZnS shell, while avoiding excessive Zn 2+ Initiate independent nucleation of ZnS.

[0033] In some embodiments, in the step of adding the zinc salt in batches, the number of batch additions is 1-5 times, and the time interval between the batch additions is 1-2 hours; the washing solution used in the washing step is an alcohol solution.

[0034] In this embodiment, zinc salt is added in batches to make Zn 2+ Slow release, with S 2- The reaction generates a ZnS shell; adding in batches can avoid the local excessive concentration that causes ZnS to nucleate alone, ensuring that ZnS grows preferentially on the CdS surface to form a continuous and dense ZnS shell, which is beneficial to further passivate surface defects and enhance the environmental stability of quantum dots; the washing liquid of the present application is an alcohol solution, which promotes efficient centrifugal separation of quantum dots by reducing the polarity of the solvent, thereby improving the purity of the final product.

[0035] The present application provides an application of Ag-sensitized core-shell Ag@CdS@ZnS quantum dots in the detection of nitrobenzene explosives.

[0036] The Ag@CdS@ZnS quantum dots of the present application undergo electron transfer with the strong electron-withdrawing groups of nitrobenzene explosives, resulting in fluorescence quenching, wherein the Ag sensitization effect significantly amplifies the quenching signal, realizing trace detection, and ultimately improving the detection sensitivity and specificity of quantum dots for nitrobenzene explosives, and are suitable for the rapid detection of trace explosives in aqueous phases, aerosols and solid residues.

[0037] In some embodiments, the nitrobenzene explosive includes one or more of trinitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, and 2,4,6-trinitrophenol.

[0038] The present invention is further described below through specific examples.

[0039] Example 1 The invention discloses an Ag-sensitized core-shell Ag@CdS@ZnS quantum dot, which comprises a silver nanoparticle core, a cadmium sulfide middle layer coated on the silver nanoparticle core, and a zinc sulfide outer layer coated on the cadmium sulfide middle layer.

[0040] A method for preparing Ag-sensitized core-shell Ag@CdS@ZnS quantum dots comprises the following steps: S1. Boil 40 mL of a 1 mM AgNO₃ solution to 100°C, then add 1 mL of a 0.1 M trisodium citrate solution and continue boiling. Stop heating when the solution turns dark orange. After cooling, wash with ethanol, purify, and dry. Redisperse the solution in deionized water for later use to obtain a silver nanoparticle colloidal solution (AgNPs colloidal solution). S2. 0.15 mmol of Cd(NO3)2 and 0.4 mmol of L-cysteine ​​were added to 40 mL of deionized water and magnetically stirred for half an hour. The pH was adjusted to 11 with 0.1 M NaOH solution, and 2 mL of AgNPs colloidal solution was added. Subsequently, 0.3 mmol of thiourea was added, and the mixture was condensed and refluxed for 2 h to obtain a Ag@CdS dispersion. S3. Dissolve 0.15 mmol of zinc acetate in 10 ml of deionized water, add 2 ml to the Ag@CdS dispersion every 1 h, condense and reflux, and finally add ethanol and centrifuge at 9000 rpm / min for washing. After washing, dry the mixture at 80°C in a vacuum for 14 h to obtain Ag@CdS@ZnS quantum dot particles.

[0041] The transmission electron microscope (TEM) image of the quantum dot particles obtained in this example is as follows: Figure 2 As shown, the electron microscope image shows that the average size of the synthesized Ag-sensitized quantum dots is about 20nm, with certain agglomeration properties. The Ag@CdS@ZnS quantum dot particles of this application were successfully prepared. The average size of the quantum dots has a significant impact on the detection sensitivity. A smaller size helps to increase the specific surface area and surface activity, thereby enhancing the interaction with the nitroaromatic compound molecules and improving the detection sensitivity. At the same time, the thickness of each layer also has an important influence on the detection sensitivity. The appropriate thickness of the CdS middle layer and the ZnS outer layer can effectively transfer electrons, passivate surface defects and improve environmental stability. These factors work together to ensure the high sensitivity of quantum dots to nitroaromatic compounds.

[0042] Examples 2-5 A Ag-sensitized core-shell Ag@CdS@ZnS quantum dot, the other contents are the same as those in Example 1, except that the amounts of thiourea used are 0.01 mmol, 0.15 mmol, 0.45 mmol, and 0.5 mmol, respectively.

[0043] Example 6 A Ag-sensitized core-shell Ag@CdS@ZnS quantum dot, the other contents of which are the same as those in Example 1, except that the reducing agent is sodium borohydride (without dispersing function).

[0044] Comparative Example 1 A quantum dot, the preparation method of which is the same as that of Example 1, except that step S1 is not included.

[0045] Comparative Example 2 A quantum dot, the preparation method of which is the same as that of Example 1, except that the surface modifier is not added.

[0046] Comparative Example 3 A quantum dot, the preparation method of which is the same as that of Example 1, except that in step S3, the zinc salt is added at one time.

[0047] Comparative Example 4 A quantum dot, the preparation method of which is the same as that of Example 1, except that step S2 is not included.

[0048] Comparative Example 5 A quantum dot, the preparation method of which is the same as that of Example 1, except that the Ag@CdS dispersion obtained in step S2 is directly washed and dried.

[0049] Comparative Example 6 A quantum dot, the preparation method of which is the same as that of Example 1, except that the order of the CdS layer preparation step in step S2 and the ZnS layer preparation step in step S3 are swapped.

[0050] Testing and Evaluation The quantum dots obtained in each example and comparative example were redispersed in deionized water to prepare a 1 mg / mL quantum dot solution. Different samples were taken and TNP standard solutions of different concentrations were added respectively. The fluorescence emission spectra of the Ag / CdS / ZnS quantum dot solutions after adding different concentrations of TNP were measured using a fluorescence spectrophotometer. Figure 3 The results of the detection of TNP standard samples in Example 1 are shown. In the concentration range of 0-36 μM, the fluorescence intensity of the Ag-sensitized core-shell Ag@CdS@ZnS quantum dots in Example 1 decreases with increasing TNP concentration. After mixing with 36 μM TNP solution, its quenching efficiency is close to 90%. Figure 4 This is a graph showing the changes in the fluorescence spectrum of CdS@ZnS quantum dots prepared in Comparative Example 1 after adding TNP solutions of different concentrations. In the concentration range of 0-100 μM, the fluorescence intensity of CdS@ZnS quantum dots decreases with increasing TNP concentration. After mixing with 100 μM TNP solution, its quenching efficiency is close to 80%. Figure 5 The fitting curves for determining TNP for the quantum dots prepared in Example 1 and Comparative Example 1 are shown. By comparing the two, it is found that the sensitivity of Ag@CdS@ZnS quantum dots in detecting TNP is much higher than that of CdS@ZnS quantum dots. With the increase of TNP concentration, the fluorescence quenching rate I0 / I-1 of Ag@CdS@ZnS in Example 1 reaches 0.136 / uM, while that of the non-sensitized CdS@ZnS quantum dots in the comparative example is only 0.035 / uM.

[0051] According to the above test conditions, the results of the quenching efficiency and fluorescence quenching rate of each embodiment and comparative example are shown in Table 1.

[0052] Table 1 Test results

[0053] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. An Ag-sensitized core-shell Ag@CdS@ZnS quantum dot, characterized in that: The invention comprises a silver nanoparticle core, a cadmium sulfide middle layer coated on the silver nanoparticle core, and a zinc sulfide outer layer coated on the cadmium sulfide middle layer.

2. A method for preparing Ag-sensitized core-shell Ag@CdS@ZnS quantum dots according to claim 1, characterized in that: The steps include: mixing a silver source with a reducing agent solution, heating the mixture for reaction, and obtaining a silver nanoparticle colloidal solution; Adding the silver nanoparticle colloidal solution and a sulfur source to a mixed solution of a cadmium salt and a surface modifier, adjusting the pH value to alkaline and performing a reflux reaction to obtain an Ag@CdS dispersion; Zinc salt is added to the Ag@CdS dispersion in batches, and after the reaction is completed, washing and drying are performed to obtain the Ag-sensitized core-shell Ag@CdS@ZnS quantum dots.

3. The preparation method according to claim 2, characterized in that The silver source is silver nitrate, the reducing agent is sodium citrate, and the temperature of the heating reaction is 90-100°C.

4. The preparation method according to claim 2, characterized in that The cadmium salt includes one or more of cadmium acetate, cadmium sulfate, cadmium oleate, cadmium carbonate, cadmium oxalate, cadmium phosphate, cadmium chloride, cadmium nitrate, and cadmium bromide; the surface modifier includes one or more of l-cysteine, thioglycolic acid, mercaptoethylamine, ethanedithiol, butanedithiol, p-aminobenzenethiol, glutathione, polyethylene glycol, and polyethyleneimine; and the sulfur source is thiourea.

5. The preparation method according to claim 2, characterized in that The molar ratio of the cadmium salt to the sulfur source is 1:1-3.

6. The preparation method according to claim 2, characterized in that The pH value ranges from 8 to 11, and the reflux reaction is condensation reflux.

7. The preparation method according to claim 2, characterized in that The zinc salt is zinc acetate; the molar ratio of the zinc salt to the cadmium salt is 1:1-2.

8. The preparation method according to claim 2, characterized in that In the step of adding the zinc salt in batches, the number of batch additions is 1-5 times, and the time interval between the batch additions is 1-2 hours; the washing liquid used in the washing step is an alcohol solution.

9. Use of Ag-sensitized core-shell Ag@CdS@ZnS quantum dots prepared by the method according to any one of claims 2 to 8 in detecting nitrobenzene explosives.

10. The use according to claim 9, characterized in that The nitrobenzene explosives include one or more of trinitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene and 2,4,6-trinitrophenol.

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