Controllable preparation method of high-purity cadmium telluride nanocrystals
By introducing ammonia into the aqueous reaction system to construct a buffer system, controlling the pH value and utilizing its transient stabilizing effect, the problems of cadmium telluride nanocrystal aggregation and purity in the aqueous method were solved, achieving high-purity and controllable preparation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- LUXI LANTIAN HIGH TECH CO LTD
- Filing Date
- 2026-03-19
- Publication Date
- 2026-06-09
AI Technical Summary
Existing technologies make it difficult to controllably prepare high-purity cadmium telluride nanocrystals in an aqueous inorganic process, avoiding both organic residues and preventing the agglomeration and uneven particle size of the nanocrystals.
Ammonia was introduced into the aqueous reaction system as an inorganic gaseous ligand to construct an in-situ buffer system. By controlling the pH value within the range of 8.5 to 10, the transient stabilizing effect of ammonia was used to inhibit aggregation. Residues after the reaction were removed by physical means, thereby achieving controllability and purity of nanocrystal growth.
It achieves a balance between high purity and controllability in the preparation of inorganic compounds, avoids the generation of organic residues, and ensures the monodispersity and particle size uniformity of nanocrystals.
Smart Images
Figure CN121849860B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a controllable preparation method for high-purity cadmium telluride nanocrystals, belonging to the field of high-purity inorganic nanomaterial preparation technology. Background Technology
[0002] The current mainstream technical approaches are mainly divided into high-temperature organic phase methods and low-temperature aqueous phase inorganic methods. High-temperature organic phase methods, such as reacting cadmium and tellurium sources in the presence of organic ligands like oleic acid, can utilize the strong coating and coordination effects of organic ligands to achieve precise control over the morphology and size of nanocrystals. However, this approach introduces inherent technical problems within the scope of inorganic compound preparation: the organic ligands used for control degrade, carbonize, or strongly adsorb onto the product surface at high temperatures, forming difficult-to-remove organic residues, making the product highly polluting at the inorganic level, which violates... The original intention was to pursue high-purity inorganic products. As an alternative, the low-temperature aqueous inorganic method, such as the reaction of cadmium chloride and sodium telluride, is considered one of the ways to achieve high-purity preparation because the raw materials are readily available, the process is simple, and the product does not contain organic residues. However, this route has inherent technical problems: in the strongly polar solvent of the aqueous phase, the surface of the newly formed inorganic nanocrystals lacks any effective stabilization mechanism. Once the crystal nucleus is formed, it will immediately undergo uncontrollable agglomeration and ripening, resulting in uncontrolled product morphology and severely uneven particle size, making it difficult to achieve controllable preparation.
[0003] This has long presented the field with a dilemma in technology selection: choosing an organic phase method to obtain controllability sacrifices purity; choosing an inorganic phase method to obtain purity results in a loss of controllability. Those skilled in the art have attempted to add water-soluble organic ligands to the aqueous phase, but this reintroduces the problem of organic residues. This approach, which attempts to achieve control in the aqueous phase using organic matter but ultimately cannot eliminate organic residues, is already evident in existing technologies. For example, Chinese invention patent CN105219392A discloses an organic phase cadmium sulfide / cadmium telluride nanocrystalline superstructure, its preparation method, and its application. The technical approach of this scheme is to first synthesize it in the aqueous phase using mercaptoacetic acid, and then transfer it to an organic solvent using an organic phase transfer agent. The final product of this method inevitably has difficult-to-remove organic ligands and phase transfer agent residues adsorbed on its surface. Essentially, it still serves the application of the organic phase and fails to solve the fundamental problem of the inability to achieve both controllability and high purity in the inorganic aqueous phase method.
[0004] Therefore, the technical problem to be solved by this invention is how to provide a preparation method that can maintain the high purity inherent in aqueous inorganic methods, and achieve precise control during the growth of nanocrystals to avoid the aggregation and runaway of the final product. Summary of the Invention
[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A controllable preparation method for high-purity cadmium telluride nanocrystals, the method comprising:
[0006] In the aqueous reaction system, a conjugate acid salt selected from ammonium salts is pre-dissolved;
[0007] In an aqueous reaction system, a soluble cadmium salt precursor reacts with a tellurium source precursor to generate cadmium telluride nanocrystals.
[0008] During the reaction, ammonia gas is introduced as an inorganic gaseous ligand into the aqueous reaction system pre-dissolved with conjugate acid salts.
[0009] Construction of ammonia gas and conjugate acid salt in an aqueous reaction system Buffer system;
[0010] The buffer system keeps the pH of the aqueous reaction system within a preset alkaline range;
[0011] The preset alkalinity range is lower than the pH threshold for the hydrolysis of soluble cadmium salt precursors to form cadmium hydroxide impurity phases, and the preset alkalinity range is the pH condition under which ammonia, as an inorganic gaseous ligand, exerts a transient stabilizing effect on the generated cadmium telluride nanocrystals.
[0012] After the reaction is complete, ammonia and conjugate salts are removed from the aqueous reaction system by physical removal methods.
[0013] Preferably, the conjugate acid salt is ammonium chloride; The buffer system is constructed using ammonia and ammonium chloride, with a preset alkalinity range of pH 8.5 to 10; the soluble cadmium salt precursor is cadmium chloride, and the tellurium source precursor is sodium telluride.
[0014] Preferably, the method further includes controlling the final particle size of cadmium telluride nanocrystals by regulating the ammonia introduction rate; The buffer system maintains the pH value of the aqueous reaction system within a preset alkaline range when the ammonia introduction rate changes.
[0015] Preferably, the step of introducing ammonia into the aqueous reaction system is specifically an in-situ chemical generation step, which includes: pre-dissolving an inert ammonia source precursor in the aqueous reaction system; and heating the aqueous reaction system to thermally decompose or hydrolyze the inert ammonia source precursor, thereby uniformly generating ammonia in the aqueous reaction system.
[0016] Preferably, the inert ammonia source precursor is urea. The step of heating the aqueous reaction system is used to drive the reaction between the soluble cadmium salt precursor and the tellurium source precursor, and to trigger the hydrolysis of urea to generate ammonia.
[0017] Preferably, the method further includes: applying an ultrasonic energy field to the aqueous reaction system during the reaction process, the ultrasonic energy field having a frequency range of 19.5 kHz to 42.0 kHz. to The power density.
[0018] Preferably, the steps of reacting the soluble cadmium salt precursor with the tellurium source precursor and introducing ammonia into the aqueous reaction system are sequentially comprised of: injecting the tellurium source precursor into the aqueous reaction system under conditions where ammonia is absent or its concentration is below the concentration required for transient stabilization to induce explosive nucleation and form crystal nuclei; and after explosive nucleation occurs, performing the step of introducing ammonia into the aqueous reaction system, which terminates the generation of new crystal nuclei and stabilizes the generated crystal nuclei.
[0019] Preferably, the method further includes: continuously monitoring the concentration of ammonia in the exhaust pipe of the aqueous reaction system; and identifying the transition point between the nucleation and growth stages of cadmium telluride nanocrystals based on the characteristics of ammonia concentration changes, wherein the characteristics of changes include the concentration of ammonia in the exhaust gas. satisfy The inflection point of recovery; based on the conversion point, adjust the subsequent reaction process parameters.
[0020] Preferably, the physical removal method is limited to spray drying; the spray drying operation atomizes the aqueous reaction system after the reaction is completed into droplets, and the aqueous reaction system contains ammonia-stabilized cadmium telluride nanocrystals; the spray drying operation removes ammonia and aqueous solvent from the droplets at the same instant, and at the instant of ammonia dissociation, the phase transition of cadmium telluride nanocrystals from the liquid phase to solid dry powder is completed simultaneously.
[0021] Preferably, physical removal methods include heating the aqueous reaction system to 50°C. Up to 80 .
[0022] Compared with the prior art, the beneficial effects of the present invention are:
[0023] 1. By introducing inorganic gaseous ligands into the aqueous reaction system, their dynamic coordination during the nanocrystal growth stage provides transient stability and suppresses the inherent aggregation phenomenon in the aqueous reaction. After the reaction, the ligands are completely removed by physical means such as heating or applying vacuum, taking advantage of their high volatility. The controllability requirements of the preparation process and the high purity requirements of the product are separated in the process, so that within the scope of inorganic compound preparation, the growth of nanocrystals can be controlled and adjusted without the introduction of organic residues.
[0024] 2. By pre-dissolving the conjugate acid salt of the inorganic gaseous ligand in the aqueous system, and using the conjugate acid salt and subsequently introduced ammonia to construct an in-situ pH buffer system, and utilizing ammonia itself as the alkaline component of the system as a buffer pair, the alkalinity is restrained by the pre-placed conjugate acid during the reaction, and the pH value of the system is spontaneously stabilized within a range that is insufficient to precipitate the cadmium hydroxide impurity phase. This allows the stabilizing function of ammonia as a transient ligand to be exerted, while the chemical side reaction as an alkaline is effectively suppressed. This decouples the ligand function from pH regulation, ensuring the purity and stability of the inorganic compound preparation process.
[0025] 3. The introduction of inorganic gaseous ligands is placed after the critical physicochemical stage, that is, under ligand-free or undercoordinated conditions, a concentrated burst of nucleation is induced by rapid mixing of precursors; after the nucleation burst, inorganic gaseous ligands are immediately introduced; in this mechanism, the absence of ligands at the beginning of the reaction ensures the instantaneous nature of nucleation, and their presence after nucleation immediately terminates the generation of new nuclei and turns to stable growth. This transforms the function of ligands from a single stabilizing effect to dynamic gating of the two physical stages of nucleation and growth in the preparation of inorganic compounds, achieving effective separation of the two stages and providing a reliable process route for the preparation of highly monodisperse inorganic nanocrystals. Attached Figure Description
[0026] Fig. 1 This is a flowchart of the controllable preparation method based on the in-situ buffer system of the present invention;
[0027] Fig. 2 This is a comparison diagram of the effects of ultrasonic frequency and power density on the nanocrystalline dispersion PDI of the present invention.
[0028] Fig. 3 This is an interaction timing diagram of the key roles in the preparation process of this invention. Detailed Implementation
[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0030] This invention discloses a controllable preparation method for high-purity cadmium telluride nanocrystals, which involves constructing an in-situ dynamic [method / process] in an aqueous reaction system. A buffer system that, while suppressing the precipitation of key inorganic impurities, utilizes ammonia gas in the system ( The component, as a purely inorganic, highly volatile transient ligand, enables controllable and stable growth of cadmium telluride nanocrystals. After the reaction, the ligand and buffer salt are removed using their physical properties, thus solving the technical problem of uncontrolled nanocrystal aggregation while maintaining the high purity of the inorganic phase method. In the field of inorganic compound preparation, if ammonia is used in the aqueous phase... Using ligands to stabilize nanocrystals would immediately face technical obstacles: It dissolves in water to form a strong alkaline solution, which can lead to the hydrolysis and precipitation of soluble cadmium salts, such as cadmium chloride, which are precursors. This inorganic impurity phase; to avoid this problem, the present invention pre-dissolves a conjugate acid salt selected from ammonium salts in the aqueous reaction system, wherein the conjugate acid salt is ammonium chloride ( ); soluble cadmium salt precursor, in the form of cadmium chloride ( For example, dissolve in a solution containing ammonium chloride ( In an aqueous system; subsequently, cadmium chloride is reacted with a tellurium source precursor, such as sodium telluride ( During the reaction, ammonia gas is introduced into the system; at this time, the newly introduced ammonia gas ( As an alkaline component, it reacts with pre-dissolved ammonium chloride ( As an acidic component, it is immediately constructed in the aqueous phase. The buffer system, based on the principle of chemical equilibrium, will spontaneously maintain the pH value of the aqueous system within a preset alkaline range, which is defined as pH 8.5 to 10. This pH range is determined to simultaneously meet two technical conditions: firstly, the pH value is lower than that of the soluble cadmium salt precursor (…). Hydrolysis forms cadmium hydroxide ( The pH threshold of the impurity phase is thus thermodynamically suppressed. The formation of impurities; secondly, within this pH range, there is still a sufficient concentration of free [unspecified substance] in the system. Molecules, these As a purely inorganic Lewis base ligand, the molecule can undergo dynamic and reversible coordination with the surface of growing cadmium telluride nanocrystals, providing transient stabilization.
[0031] In the implementation, The buffer capacity of the buffer system is sufficient to regulate ammonia gas ( When the introduction rate of ) changes, the pH value of the aqueous reaction system is maintained within a preset alkaline range, i.e., pH 8.5 to 10, to remain stable; given that The introduction rate or its steady-state concentration in the system is directly related to the degree of passivation of the nanocrystal surface, which can be actively controlled by those skilled in the art. The introduction rate is used to achieve precise control over the final particle size of cadmium telluride nanocrystals, for example, a higher introduction rate. A higher introduction rate corresponds to a higher steady-state ligand concentration, leading to stronger surface passivation and a slower growth rate, thereby obtaining cadmium telluride nanocrystals with smaller particle sizes. This controlled process does not sacrifice pH stability or product purity. To further optimize the uniformity of ammonia introduction and avoid localized concentration unevenness that may result from physical bubbling, the ammonia introduction step in the aqueous reaction system can be specifically a form of in-situ chemical generation. This step includes: in the aqueous reaction system, the system already contains... and An inert ammonia source precursor is pre-dissolved; in a preferred implementation, the inert ammonia source precursor is urea, i.e. By heating the aqueous reaction system to 60°C Up to 90 For example, this heating step is used simultaneously to drive the reaction between the soluble cadmium salt precursor and the tellurium source precursor, and to trigger the slow, uniform hydrolysis of urea in the aqueous phase, thereby homogeneously generating ammonia gas throughout the liquid phase. ), generated Immediately connect with the pre-set system Constructing a buffer system; to obtain cadmium telluride nanocrystals with a narrower particle size distribution, i.e., high monodispersity, the method of this invention can strictly limit the timing of reactant introduction to achieve separation of the nucleation and growth stages; this timing step includes: in ammonia ( Under conditions where the tellurium source precursor is absent or its concentration is below the concentration required for transient stabilization, i.e., in an undercoordinated system, the tellurium source precursor, i.e. The solution is introduced in a rapid, single-injection manner, containing... and In aqueous reaction systems, due to the lack of ligand stabilization, the supersaturation of the system increases instantaneously and dramatically, inducing a concentrated burst of nucleation to form crystal nuclei. Following this burst of nucleation, with a delay of 0.1 to 1 second, an immediate process is performed to introduce [a specific substance] into the aqueous reaction system. The process involves high-flow-rate bubbling or triggered urea hydrolysis, resulting in high concentrations. It rapidly coordinates to the surface of all the generated crystal nuclei, immediately terminating the generation of new crystal nuclei and stabilizing the generated crystal nuclei, allowing the reaction to enter the growth stage.
[0032] The method may also include applying an ultrasonic energy field to the aqueous reaction system during the reaction process. The ultrasonic energy field has a frequency range of 19.5 kHz to 42.0 kHz and a power density of 0.15 W / cm² to 4.8 W / cm². Its function is not to drive the chemical reaction, but rather to physically disperse micro-aggregates that may form during the reaction through micro-shear forces generated by cavitation effects, and to accelerate the reaction. Mass transfer and homogenization coordination of ligands in the liquid phase improve the dispersion uniformity of the final product; to achieve accurate determination of the transition point between explosive nucleation and growth stages, the method may further include: setting up a [missing information - likely a device or mechanism] in the exhaust pipe of the reactor. A gas concentration sensor continuously monitors the concentration of ammonia in the exhaust pipe of the aqueous reaction system, and records it as follows: ;based on The concentration variation characteristics were analyzed to identify the transition point between the nucleation and growth stages of cadmium telluride nanocrystals; specifically, when explosive nucleation occurs, the total surface area of the nanocrystals increases dramatically, leading to a significant change in the system's response to... The rate of ligand consumption surges, in exhaust gas Concentration, i.e. A momentary drop occurs; when nucleation ends and the total surface area no longer increases, Consumption rate is stable. The decline stopped and began to rise; this change is characterized by the concentration of ammonia in the exhaust gas. satisfy The inflection point of the reaction is identified as an objective signal that the nucleation stage has ended. Based on the conversion point, the system can automatically adjust subsequent reaction process parameters, such as reducing the ammonia gas flow rate or starting to cool down. After the reaction is completed, i.e., after obtaining cadmium telluride nanocrystal colloids of the target particle size, ammonia is removed from the aqueous reaction system by physical removal methods. ) and conjugate acid salts ( To achieve high purity of the final product; in the implementation method, physical removal means include heating the aqueous reaction system to 50°C. Up to 80 Or apply a vacuum, using High volatility and Due to their tendency to sublimate and decompose upon heating, both are dissociated from the solution and removed from the nanocrystal surface. In another preferred embodiment, to avoid the risk of secondary agglomeration that may occur when the nanocrystals are exposed in the liquid phase during ligand removal, the physical removal method is limited to spray drying. This operation removes the nanocrystals after the reaction is complete. The system is stable, remaining a monodisperse aqueous reaction system, i.e., a colloidal solution, atomized into micron-sized droplets; within the spray drying tower, the droplets react with a high-temperature heat medium, such as 100... Up to 150 Contact with hot air, within a sub-second timescale, the highly volatile components in the droplet, namely... Both the aqueous and aqueous solvents are removed at the same instant; At the instant the ligands dissociate from the surface of the nanocrystals, the aqueous solvent, which serves as the aggregation medium, also vaporizes simultaneously. Before the nanocrystals have a chance to undergo liquid-phase aggregation, the phase transition of cadmium telluride nanocrystals from the liquid phase to the solid phase dry powder is completed simultaneously, thereby obtaining high-purity T-ehua cadmium nanocrystal dry powder with a clean surface, no ligand residue, and good dispersion.
[0033] Example 1: In the specific application of the aqueous phase method for preparing cadmium telluride nanocrystals, the operator faces a technical conflict: to inhibit the uncontrollable aggregation of crystal nuclei in the aqueous phase, a stabilizer needs to be introduced. However, if conventional ammonia is introduced as an inorganic ligand, its alkalinity will immediately cause the pH value to rise, causing the cadmium salt precursor to hydrolyze and release cadmium hydroxide. In cases where a heterogeneous phase exists, controllability and high purity cannot be simultaneously achieved. Therefore, in the aqueous reaction system, ammonium chloride, acting as a conjugate acid salt, is pre-dissolved. ), and added the soluble cadmium salt precursor cadmium chloride ( ) and urea as an inert ammonia source precursor ( At this point, the system's pH is weakly acidic, lacking the ability to stabilize nanocrystals, and there is no cadmium hydroxide ( Risk of impurities; heating the aqueous reaction system to 80°C Under these undercoordinated conditions, sodium telluride, a tellurium source precursor, was rapidly injected in a single injection. This injection induces explosive nucleation in an environment lacking ligand stability, instantly forming a large number of exposed crystal nuclei; almost simultaneously with the nucleation explosion, 80 The temperature triggers the hydrolysis of the pre-placed urea, uniformly generating ammonia gas in situ throughout the liquid phase. ), generated in situ here As an alkaline component, it reacts with ammonium chloride (which is pre-existing in the system) As an acidic component, it works synergistically to jointly construct the structure described in the aforementioned specific embodiments. A buffer system that spontaneously clamps the pH value at 9.0; this pH value is below the precipitation threshold of cadmium hydroxide, thereby inhibiting the formation of impurity phases. Simultaneously, free ammonia gas under this pH 9.0 condition (…) It also acts as a transient ligand, immediately coordinating to the surface of all newly formed crystal nuclei, terminating the generation of new nuclei and providing transient stability, thus preventing aggregation; the reaction occurs at 80°C. The process continues and enters the pure growth stage. Because the nucleation and growth stages are effectively separated by the aforementioned timing operations, and the growth process is influenced by ammonia (… The continued stabilization of the ligands ultimately yielded cadmium telluride nanocrystal colloids with extremely narrow particle size distribution. After the reaction, the still monodisperse colloidal solution was directly fed into a spray dryer for sub-second drying. ligands The buffer salt and aqueous solvent are simultaneously and instantaneously removed, allowing the nanocrystals to complete the phase transition from liquid to solid dry powder before liquid-phase aggregation occurs, ultimately yielding a powder free of any organic residue and free of pollutants. High-purity cadmium telluride nanocrystalline dry powder that is mixed with impurities and maintains a highly monodisperse state.
[0034] Example 2: To verify the successful construction To achieve both high purity and controllability in the buffer system, the following comparative experiments were conducted. All experiments were carried out in a 1000mL isothermal stirred glass reactor equipped with an accuracy of ±0.1... The equipment included a temperature probe, an online pH electrode with an accuracy of ±0.02 pH units, a gas mass flow controller, and a mechanical stirrer (fixed speed 300 rpm); the raw material used was 0.1M... Aqueous solution, 0.1M Aqueous solution (prepared fresh before use), analytical grade Solids, and high purity Gas; Product characterization: X-ray diffraction (XRD) was used to analyze the presence of gas in the final product dry powder. Impurities; the average particle size and polydispersity index (PDI) of nanocrystals in the aqueous colloid were determined using dynamic light scattering (DLS). A PDI value closer to 0 indicates a more uniform particle size distribution, while a PDI value greater than 0.3 typically indicates severe agglomeration in the system. Control group A (no stabilization measures): 0.1 M... 500 mL of aqueous solution was rapidly injected into a 0.1 M solution while stirring at 300 rpm. 500 mL of aqueous solution was stirred continuously for 1 hour; control group B (only...) (Unbuffered): Add 0.1M to the reactor. 500 mL of aqueous solution was introduced into the solution while stirring at 300 rpm. The gas was used to attempt to adjust the pH value to 9.0; Sample 1 of the present invention ( Buffer system): Add 0.1M to the reactor. 500 mL of aqueous solution, and dissolve Solids in the reaction system The initial concentration reached 0.5M; under stirring at 300 rpm, the solution was introduced... Gas (flow rate controlled at 50 sccm) was used to stabilize the pH of the system at 9.0; after confirming pH stability, 0.1 M was rapidly injected. 500 mL of aqueous solution, maintained at pH 9.0 and stirred continuously for 1 hour; Boundary test group A (beyond the lower pH limit): The operation is the same as sample group 1 of this invention, but with the addition of... At that time, the system was injected only after the pH value was stabilized at 8.0. Solution; Boundary test group B (beyond the upper pH limit): The operation is the same as that of sample group 1 of this invention, but the solution is introduced... Once the pH of the system is stabilized at 10.5, it is then injected. Solution; for further verification To introduce the effect of rate on particle size control, sample group 2 and sample group 3 of the present invention were set up, and their operation was completely consistent with that of sample group 1 of the present invention, except that... The gas introduction rate was adjusted to 10 sccm and 100 sccm, respectively, and the pH was maintained at 9.0 throughout the reaction. The key results of each group of experiments are summarized in Table 1.
[0035]
[0036] Table 1 data objectively confirms the synergistic effect and boundary conditions of the technical solution of the present invention: Control group A shows that in an aqueous phase without any stabilization measures, although no synergistic effect is produced... The impure phase, however, immediately exhibited severe agglomeration of the newly formed nanocrystals (average particle size 850.5 nm, PDI as high as 0.58), completely losing controllability; control group B showed that if attempted to use alone... As a ligand (none) (buffer), strong alkalinity immediately leads to Precursor hydrolysis generates a large amount of Impure phases led to the failure of CdTe synthesis, confirming the necessity of impure phase suppression; a comparison of samples 1 (and 2, 3) with control groups A and B showed a key synergistic effect: (ligands) and The combination of (conjugate acids) at pH 9.0, through... The transient stabilizing effect of the ligand keeps the PDI at a low level below 0.17 (solving the aggregation problem), and also through... The pH clamping effect of the buffer system effectively avoids The formation of impurity phases (solving purity issues); data from boundary test groups A (pH 8.0) and B (pH 10.5) empirically verify the rationality of the preset alkaline range of pH 8.5 to 10; when pH is below 8.5 (e.g., 8.0), free phases in the system... Insufficient concentration to provide effective transient stability leads to a deterioration of the PDI to 0.49, approaching a state of aggregation. When the pH is above 10 (e.g., 10.5), although the stabilizing effect is still acceptable, the buffer system begins to fail or the alkalinity becomes too strong, resulting in trace amounts being detected by XRD. Impurities sacrifice purity.
[0037] Example 3: This example combines Figs. 1 to 3 A controllable preparation method for high-purity cadmium telluride nanocrystals is described, such as... Fig. 1 As shown, the process begins with the input of the system precursor, including the aqueous phase, , Urea, etc., are hydrolyzed by heating to 60-90℃, and the in-situ generation mechanism of the inert ammonia source precursor in the key module is utilized to hydrolyze urea under heat and produce homogeneous products. The generated and jointly build A buffer system that, on the one hand, maintains the pH within the range of 8.5-10 to inhibit... Impurities, on the other hand, utilize As a transient ligand to prevent aggregation, in the main pathway, after the injection of a tellurium source precursor such as NaHTe, explosive nucleation is instantaneously induced at the undercoordinated sites. Under transient stability, the crystal nucleation stage begins. During this stage, the concentration of exhaust ammonia from key modules is controlled. Monitoring to continuously monitor exhaust Concentration changes, and by identification The turning point is identified by the rebound inflection point, which in turn allows for the adjustment of subsequent process parameters, such as... Flow rate, cooling, etc., ultimately, physical removal such as spray drying for instantaneous removal. , High-purity CdTe nanocrystal dry powder was obtained by mixing with solvents.
[0038] like Fig. 2 As shown in the figure, the ultrasonic power density Plotting the multidispersion index (PDI) on the x-axis and the polydispersion index (PDI) on the y-axis, this compares the PDI value with power density at 20kHz and 40kHz frequencies. The data shows that at 40kHz, the PDI value is around 3... The PDI value reaches a minimum of 0.14 near the 20kHz frequency, while at 20kHz, the PDI value is consistently higher than the corresponding value at 40kHz; for example... Fig. 3 As shown in the timeline diagram, the interactions between four key components—the operator, the reaction system, the buffer system, and the nanocrystals—are illustrated. The process begins with the operator sequentially adding pre-dissolved conjugate acid salts to the reaction system, such as… Adding cadmium salt precursors such as The process of introducing ammonia as an inorganic gaseous ligand followed by interaction between the reaction system and a buffer system to construct... A buffer system is used to maintain the pH within the range of 8.5-10. The operator injects a tellurium source precursor such as NaHTe, and the reaction system begins to generate cadmium telluride nanocrystals. At the same time, the buffer system provides transient stabilization for the nanocrystals. Finally, the operator performs a physical removal operation on the reaction system to remove ammonia and its conjugate acid salts, so that the nanocrystals are finally obtained in the form of high-purity cadmium telluride nanocrystals.
[0039] Example 4: This example illustrates the specific procedure for performing physical removal using a gentle heating method; 500 mL of the cadmium telluride nanocrystalline colloid obtained from sample group 1 of the present invention prepared in Example 2 was taken. After preparation, the colloid had a PDI value of 0.16, and the system contained 0.5 M ammonium chloride as a buffer system component. The 500 mL colloidal solution was transferred to a 1 L rotary evaporator flask and the water bath temperature was set to 60 °C. (The temperature is 50) Up to 80 Within the specified range (and under a vacuum of -0.08 MPa), rotary evaporation removes the solvent and volatile components; during this process, highly volatile... The ligands dissociate from and are removed from the nanocrystal surface, causing the steric stabilization mechanism they provide to fail; however, given the high concentration of [unclear - possibly a specific substance or component] in the system, [the situation remains unresolved]. The conjugate acid salt of the buffer system, namely ammonium chloride ( At this time, ammonium chloride acts as an inert inorganic salt electrolyte. and Ions in The dissociated nanocrystal surface instantaneously establishes an electric double layer (EDL), providing electrostatic repulsion stability. This electrostatic repulsion relays the steric stabilization mechanism, effectively preventing the nanocrystals from... Secondary agglomeration during the slow removal process; after the solvent is evaporated, the resulting solid contains CdTe nanocrystals and Wash three times with high-purity water and centrifuge to remove residual substances. Or through 150 Vacuum sublimation removal The final obtained cadmium telluride nanocrystal dry powder was redispersed in water, and its PDI value was measured to be 0.19, indicating that even with the removal method of gentle heating, the product still maintained a good dispersion state and no serious agglomeration occurred.
[0040] Example 5: In the process aimed at preparing highly monodisperse cadmium telluride nanocrystals, a key engineering challenge lies in how to accurately capture the endpoint of the explosive nucleation stage and immediately switch to the growth stage; if the switch is too early, nucleation is insufficient; if the switch is too late, nucleation and growth overlap, both leading to a deterioration in the PDI value of the final product; the concentration of ammonia in the exhaust pipe, i.e. The signal provides objective evidence for this, but the original... The signal contains measurement noise, and its derivative is... The noise fluctuates wildly around 0, making it unsuitable for direct trigger control. To eliminate this noise and reliably identify the inflection point, the method includes a step for identifying the transition point, specifically digital signal processing and state judgment logic. This logic is used when equipped with an exhaust system. The concentration sensor operates on the reactor control system, and the sensor's raw concentration readings are... Samples are taken every 0.5 seconds and fed into a 10-point window Savitzky-Golay smoothing filter to generate a smoothed concentration signal. Real-time calculation of the control system first derivative The control logic is set as follows: State 1 (Waiting for core formation): System initialization, at this time... Fluctuating around 0 values between -0.1 ppm / sec and +0.1 ppm / sec; State 2 (nucleation confirmation): When the system detects... When the sampling rate is less than -0.5 ppm / sec for three consecutive sampling points (1.5 seconds), the system confirms that explosive nucleation has begun and switches to the monitoring inflection point state; State 3 (Inflection Point Identification): In the monitoring inflection point state, the system continues to calculate And find the point where it changes from negative to positive; State 4 (trigger action): when the system detects When two consecutive sampling points, each lasting 1.0 second, are both greater than +0.05 ppm / sec, the system determines that the inflection point of recovery has been reliably passed, meaning the transition point between the nucleation and growth stages has been identified. At the instant state 4 is triggered, the control system immediately executes a preset step to adjust subsequent reaction process parameters. In this embodiment, this step is specifically defined as: simultaneously adjusting the temperature setpoint of the heating jacket of the reactor from 80... Reduced to 60 and will The introduction rate was reduced from 100 sccm for stable nucleation to 20 sccm for maintaining growth; this is based on the smoothed derivative signal. right The process switching, which objectively identifies the inflection point, ensures that the nucleation process is terminated immediately, and the reaction enters a pure growth stage. The final cadmium telluride nanocrystal product, measured by DLS, has a PDI value that can be stably controlled below 0.15.
[0041] Example 6: In large-scale preparation, the tellurium source precursor is sodium telluride (Sodium telluride) For example, because it is easily oxidized in aqueous solution, its actual concentration may deviate from the nominal value with storage time. If it is used in the reaction without calibration, it will lead to inaccurate stoichiometry in the subsequent explosive nucleation stage, thus affecting the uniformity of the final nanocrystal size. To eliminate this uncertainty, this method includes a pre-calibration procedure for the tellurium source precursor before performing the step of reacting the soluble cadmium salt precursor with the tellurium source precursor. Specifically, under the protection of an inert atmosphere, take a 10.0 mL sample of the precursor to be used. Aqueous precursor solution, with standardized 0.05M iodine ( The solution was used as a titrant, and redox titration was performed to determine its composition. The accurate molar concentration; in a specific calibration batch, if measured... The actual concentration of the solution was 0.092 M instead of the nominal 0.1 M. Therefore, during the subsequent explosive nucleation injection step, the injection volume was adjusted from the nominal 500 mL (calculated based on 0.1 M) to 543.5 mL. This procedure ensures that the injected tellurium source and the soluble cadmium salt precursor in the system, i.e. Maintaining precise stoichiometry is a prerequisite for achieving repeatable and controllable preparation; correspondingly, to objectively verify physical removal methods, spray drying is used as an example to treat ammonia and its conjugate acid salts, i.e. To assess the removal effect, this method, after the physical removal step, also includes a procedure for verifying the purity of the final product. Specifically, this procedure involves accurately weighing 1.0 g of cadmium telluride nanocrystal powder obtained after spray drying, placing it in 100 mL of high-purity water, applying ultrasound to fully disperse it, filtering through a 0.22 μm filter membrane to obtain the supernatant, and using ion chromatography (IC) based on a standard curve to analyze the residues in the supernatant. Ions and Quantitative analysis of ion concentrations was performed; the results showed... and The concentrations were all below the instrument detection limit of 0.1 ppm, which objectively confirms... The components of the buffer system have been removed by physical removal methods, and the final product meets the required high purity standard.
[0042] Example 7: This example provides a standardized engineering calibration procedure for determining key process parameters for applying an ultrasonic energy field in a specific production environment. This addresses localized micro-agglomeration caused by uneven stirring during process scale-up, thereby ensuring the batch-to-batch stability of the PDI value of the final cadmium telluride nanocrystals. This procedure is performed in a 5L jacketed stainless steel reactor equipped with a bottom piezoelectric ceramic transducer array for applying the ultrasonic energy field. The reactor's control system allows independent adjustment of the ultrasonic frequency (kHz) and ultrasonic power density (W / cm²). The calibration objective is to achieve the desired results in the process described in the preceding examples. Buffer system, i.e., 0.5M pH 9.0, and precursor concentration, i.e., 0.05M. Under the baseline conditions, an optimized operating parameter window was found that could stably suppress the PDI value of the final product below 0.20 while avoiding local overheating or cavitation corrosion caused by excessive power. The calibration procedure includes the following steps: fixing the ultrasonic frequency as the lower limit of the range, i.e., 20 kHz, and performing the complete nanocrystal preparation process at power densities of 0.1, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 W / cm² while keeping other chemical parameters constant, and collecting the PDI value of the final product; secondly, fixing the ultrasonic frequency as the upper limit of the range, i.e., 40 kHz, and repeating the above gradient test at power densities from 0.1 to 5.0 W / cm²; in all tests, the solution temperature change near the transducer was monitored.
[0043] The calibration test results show that at a frequency of 20kHz, when the power density is below 1.0W / cm², the PDI value still fluctuates between 0.22 and 0.28, indicating that the micro-agglomeration suppression effect is not significant. When the power density increases to 3.0W / cm², the PDI value can decrease to 0.19. At a frequency of 40kHz, the power density is only 0.5W / cm², which is in the range of 0.15W / cm² to 4.8W / cm², at which point the PDI value has dropped to 0.18. When the power density increases to 2.5W / cm² to 4.8W / cm², the PDI value can decrease further. At 0 W / cm², the PDI value remained stable at a low level of 0.14 to 0.16. When the power density continued to increase to 5.0 W / cm² at 40 kHz, exceeding the upper limit of 4.8 W / cm², the PDI value no longer decreased, but instead rose slightly to 0.17, accompanied by an increase in temperature near the transducer. Based on this data, it was determined that for this 5L reactor system, the power density range of 2.5 W / cm² to 4.0 W / cm² at 40 kHz is the optimal process window for balancing the micro-agglomeration suppression effect and energy consumption.
[0044] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.
[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims
1. A controllable preparation method for high-purity cadmium telluride nanocrystals, characterized in that, The methods include: In the aqueous reaction system, a conjugate acid salt selected from ammonium salts is pre-dissolved; In an aqueous reaction system, a soluble cadmium salt precursor reacts with a tellurium source precursor to generate cadmium telluride nanocrystals. During the reaction, ammonia gas is introduced as an inorganic gaseous ligand into the aqueous reaction system pre-dissolved with conjugate acid salts. Construction of ammonia gas and conjugate acid salt in an aqueous reaction system Buffer system; The buffer system keeps the pH of the aqueous reaction system within a preset alkaline range, which is pH 8.5 to 10. The preset alkalinity range is lower than the pH threshold for the hydrolysis of soluble cadmium salt precursors to form cadmium hydroxide impurity phases, and the preset alkalinity range is the pH condition under which ammonia, as an inorganic gaseous ligand, exerts a transient stabilizing effect on the generated cadmium telluride nanocrystals. The steps of reacting a soluble cadmium salt precursor with a tellurium source precursor and introducing ammonia into the aqueous reaction system include, in sequence: injecting the tellurium source precursor into the aqueous reaction system under conditions where ammonia is absent or its concentration is lower than the concentration required for transient stabilization, in order to induce explosive nucleation and form crystal nuclei. After explosive nucleation occurs, a step of introducing ammonia into the aqueous reaction system is performed. This step terminates the generation of new crystal nuclei and stabilizes the generated crystal nuclei. After the reaction is complete, ammonia and conjugate salts are removed from the aqueous reaction system by physical removal methods.
2. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, The conjugate acid salt is ammonium chloride; The buffer system is constructed using ammonia and ammonium chloride, with cadmium chloride as the soluble cadmium salt precursor and sodium telluride as the tellurium source precursor.
3. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, The method also includes controlling the final particle size of cadmium telluride nanocrystals by regulating the ammonia introduction rate; The buffer system maintains the pH value of the aqueous reaction system within a preset alkaline range when the ammonia introduction rate changes.
4. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, The step of introducing ammonia into an aqueous reaction system is specifically an in-situ chemical generation step, which includes: pre-dissolving an inert ammonia source precursor in the aqueous reaction system; and heating the aqueous reaction system to thermally decompose or hydrolyze the inert ammonia source precursor, thereby uniformly generating ammonia in the aqueous reaction system.
5. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 4, characterized in that, The inert ammonia source precursor is urea. The step of heating the aqueous reaction system is used to drive the reaction between the soluble cadmium salt precursor and the tellurium source precursor, and to trigger the hydrolysis of urea to generate ammonia.
6. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, The method further includes: applying an ultrasonic energy field to the aqueous reaction system during the reaction process, the ultrasonic energy field having a frequency range of 19.5 kHz to 42.0 kHz. to The power density.
7. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, The method also includes: continuously monitoring the concentration of ammonia in the exhaust pipe of the aqueous reaction system; and identifying the transition point between the nucleation and growth stages of cadmium telluride nanocrystals based on the characteristics of ammonia concentration changes, wherein the characteristics of changes include the concentration of ammonia in the exhaust gas. satisfy The inflection point of recovery; based on the conversion point, adjust the subsequent reaction process parameters.
8. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, The physical removal method is limited to spray drying. The spray drying process atomizes the aqueous reaction system after the reaction is completed into droplets. The aqueous reaction system contains ammonia-stabilized cadmium telluride nanocrystals. The spray drying process removes ammonia and aqueous solvent from the droplets at the same instant. At the instant of ammonia dissociation, the phase transition of cadmium telluride nanocrystals from the liquid phase to solid dry powder is completed simultaneously.
9. The controllable preparation method of high-purity cadmium telluride nanocrystals according to claim 1, characterized in that, Physical removal methods include heating the aqueous reaction system to 50°C. Up to 80 .