Time resolution detection system for in-situ capture of dynamic evolution behavior of nanoparticles in nucleation reactor

Abstract

The invention provides a time-resolved detection system for capturing dynamic evolution behaviors of nanoparticles in a nucleation reactor in situ. The time-resolved detection system comprises the nucleation reactor, a light source, an in-situ flow cell, an optical fiber, a sampler, an optical fiber spectrometer and a signal control and acquisition device. According to the invention, nucleation particles are captured in a high-speed shear field through a sampler, a flow cell is connected, and a time-resolved detection system for in-situ coupling of a nucleation reactor and acquisition of a hundred microsecond (less than 500 microseconds)-level full spectrum (200-1200 nm) is established by using a large-core-diameter optical fiber, a high-power light source, a CMOS detector with a high acquisition rate and an optical fiber spectrometer with low integral time. Therefore, evolution behaviors of nanoparticle size, coordination structure and intermediate transition state can be rapidly captured in situ in real time in the nucleation process. The problem that phase transformation, structural evolution and the nucleation instantaneous process in the nucleation process cannot be observed is solved, and support is provided for revealing a mechanism that the nucleation reactor can prepare nano materials with small particle sizes and uniform distribution.

Description

Technical Field

[0001] The invention relates to a time-resolved detection system for in-situ capturing of the dynamic evolution behavior of nanoparticle coordination structures and intermediate species in a nucleation reactor. Background Art

[0002] The application performance of nanomaterials depends largely on the initial nucleation process, which determines key parameters such as nanoparticle size, morphology, structure and composition. However, due to the poor structure and micro-mixing effect of traditional stirred tank reactors, nucleation and crystal growth are not synchronized, resulting in large precipitate particle size and wide distribution range, affecting product quality. In 2002, the team of Academician Duan Xue of Beijing University of Chemical Technology first constructed a rotating liquid film reactor (Chem. Mater., 2002, 14, 4286-4291), which effectively promoted micro-mixing and mass transfer, promoted the formation of a large number of crystal nuclei and quickly left the reactor, and achieved the separation of nucleation and crystallization processes, thereby preparing nanomaterials with uniform particle size distribution, but the nucleation mechanism is still unclear.

[0003] The nucleation process of nanomaterials usually occurs on an extremely short time scale and involves complex chemical changes. At the same time, the precipitation process for preparing nanomaterials is usually carried out in a closed container, which makes it difficult to quickly and accurately capture transient processes such as phase transitions and crystallization during the precipitation process and obtain effective key information on nucleation. UV-visible absorption spectroscopy can obtain information such as the size and coordination structure of the material by utilizing the transition of the molecular or ionic valence electrons of the material to absorb ultraviolet and visible light to varying degrees. However, on the time scale, the time resolution of existing instruments for collecting the full spectrum within a certain wavelength range can only reach the second level. Therefore, upgrading the time resolution of the structural characterization method to the microsecond level is crucial to obtaining the evolution of coordination structures and intermediate species, and to deeply analyze and reveal the mechanism of action of ultrafast reaction processes. Summary of the invention

[0004] The purpose of the present invention is to provide a time-resolved detection system for in-situ capturing the dynamic evolution behavior of nanoparticles in a rotating liquid film nucleation reactor, so as to solve the problem in the prior art that it is impossible to monitor the dynamic evolution behavior of nanoparticles in a rotating liquid film reactor in real time and in-situ, and to achieve high time resolution observation of nanoparticle nucleation, growth, agglomeration and other processes, providing more comprehensive and accurate data support for the research and development of nanomaterials.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The time-resolved detection system for in-situ capturing of the dynamic evolution behavior of nanoparticles in a rotating liquid film reactor of the present invention comprises: a rotating liquid film reactor, a light source, an in-situ circulation pool, an optical fiber, a vacuum sampler, an optical fiber spectrometer, and a signal control and collection device.

[0007] The invention is characterized in that a sampling port is axially arranged on the "rotor-stator group" of the rotating liquid film nucleation reactor, and is in-situ connected to an in-situ circulation pool. The upper end of the in-situ circulation pool is connected to a light source through an optical fiber, and the lower end is connected to a fiber optic spectrometer, so as to realize the construction of an in-situ spectrum with a time resolution of hundreds of microseconds (<500μs). A metal salt solution and an alkaline solution are added to the rotating liquid film reactor for rapid nucleation, and the nucleation slurry is captured by a vacuum sampler at different stages in the high-speed shear zone to enter the in-situ circulation pool, and a spectrum with a time resolution of hundreds of microseconds (<500μs) is obtained by high-speed acquisition, thereby capturing the information on the changes in the coordination structure of the nanoparticles during the nucleation process.

[0008] The structure of the rotating liquid film reactor is cited from patent: CN202411657126.6. The rotating liquid film reactor is composed of a closed casing as a stator, and the upper end of the stator can be added with materials according to the stoichiometric ratio. The cavity inside the stator is a truncated cone with a narrow upper and wide lower structure, with a top diameter of 42.3mm, a bottom diameter of 51.5mm, a height of 75mm, a trapezoidal cross section, and a trapezoidal bottom angle designed to be 85°. There is a rotatable truncated cone rotor inside the stator, forming a slit with the stator, and the slit adjustment range is 10-500μm; a motor is connected under the rotor to drive the rotor to rotate, and the speed adjustment range is 500-5000rpm; at a certain speed and slit width, a strong shear field is formed between the rotor and the stator; because the rotor is a truncated cone with a small top and a large bottom, the centrifugal force gradually increases from top to bottom. As the centrifugal force increases, the instability of the fluid increases, and Taylor vortices are more likely to form, increasing the chances of mutual collision and mixing between fluid microelements, and enabling reactants to contact and mix more fully, so sampling ports are set at intervals of 6mm at an axial distance of 30mm from the top of the stator in the "rotor-stator group", and a total of 8 sampling ports are set to cover the entire flow field.

[0009] The dynamic evolution behavior of the nucleation process of the nanoparticles ends in the area below the position of sampling port No. 8.

[0010] The inlet of the in-situ flow cell is located at the top of the in-situ flow cell, and the outlet is located at the bottom of the in-situ flow cell, which can make the nucleation slurry flow stably and reduce the interference of bubbles. The material transmittance of the in-situ flow cell is greater than 92%, and it is one of borosilicate glass, quartz glass, and polymethyl methacrylate; a convex lens is provided at each end of the in-situ flow cell, and the focal length of the two convex lenses is 20mm, and the aperture is 10mm, forming a symmetrical light path, the light input end has a collimating effect, and the light output end converges and couples.

[0011] The core diameter of the connecting optical fiber is 400-600 μm, and the transmission band is 200-1200 nm; the light source is one of a xenon lamp, a deuterium lamp, a deuterium halogen lamp, and a halogen lamp, and the power is 40-400W.

[0012] The fiber optic spectrometer has a CMOS detector with an integration time of less than 300 μs. At the same time, a high-speed random access memory is used as a storage medium inside the fiber optic spectrometer, which allows 50,000 spectra to be stored at one time. It has the characteristics of fast reading and writing speed, allowing the fiber optic spectrometer to collect data at its maximum collection speed, thereby improving the collection efficiency of the fiber optic spectrometer, thereby realizing the collection of time-resolved spectra at the hundred-microsecond (<500 μs) level.

[0013] The molar concentration ratio of the metal salt solution and the alkaline solution is 1 / 1-3, and the concentration of the nucleation slurry is 0.005-0.01 mol / L to avoid affecting signal detection; the flow rate of the nucleation slurry captured at different stages of the high-speed shear field into the in-situ circulation pool is 50-80 mL / min, thereby avoiding the appearance of bubbles in the circulation pool to interfere with the detection signal.

[0014] The application of the time-resolved detection system is characterized by in-situ capturing of the dynamic evolution of the coordination structure, particle size, and reaction intermediates of nanoparticles in a rotating liquid film reactor, wherein the nanoparticles include but are not limited to hydrotalcite, oxides, hydroxides, pseudo-boehmite, barium sulfate, and the like.

[0015] The beneficial effects of the present invention are as follows: the present invention improves the spectral acquisition speed by constructing a time-resolved detection system and using a fiber spectrometer with a CMOS detector, and improves the time resolution of full spectrum acquisition in the acquisition band of 200-1200nm to the level of hundreds of microseconds (<500μs). Subsequently, the constructed time-resolved detection system is coupled with a rotating liquid film reactor, and the dynamic change process of the rapid nucleation process of hydrotalcite in the rotating liquid film reactor is captured in situ at a time resolution of hundreds of microseconds (<500μs), thereby analyzing the evolution trend of the reactant coordination structure and intermediate species in the nucleation process of hydrotalcite in different shear zones in the rotating liquid film reactor, laying a foundation for in-depth understanding of the nucleation mechanism of nanoparticles and deducing the nucleation mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a time-resolved spectroscopy detection system for a rotating liquid film reactor for monitoring the nucleation process of nanomaterials.

[0017] Figure 2 This is the cross-sectional design diagram of the stator of the rotating liquid film reactor, where the bottom angle is 85°.

[0018] Figure 3 Schematic diagram of the rotor-stator slit gap in a rotating liquid film reactor.

[0019] Figure 4 This is a schematic diagram of 8 sampling ports set at intervals of 6 mm on the side of the rotating liquid film reactor, 30 mm away from the top of the stator.

[0020] Figure 5 Microsecond time-resolved UV-visible spectra obtained from testing at different sampling ports.

[0021] Figure 6 This is the UV-visible spectrum of sampling port No. 1 obtained by testing the halogen light source with a trial power of 400 W as described in Example 8.

[0022] Figure 7 This is the UV-visible spectrum of sampling port No. 1 obtained by testing an optical fiber with a core diameter of 50 μm as described in Comparative Example 1.

[0023] Figure 8 This is the UV-visible spectrum of sampling port No. 1 obtained by testing when the flow rate of the nucleation slurry entering the circulation pool is increased to 80 mL / min as described in Comparative Example 2.

[0024] List of parts and illustrations:

[0025] 1. Halogen light source; 2. In-situ flow cell; 3. Convex lens; 4. Vacuum sampler; 5. Sampling port; 6. Fiber optic spectrometer; 7. Rotating liquid film reactor; 8. Computer. DETAILED DESCRIPTION

[0026] Example 1

[0027] like Figure 1 The invention discloses a time-resolved detection system for in-situ capturing the dynamic evolution behavior of nanoparticles in a nucleation reactor, wherein the nucleation reactor has a closed housing, the cavity in the stator is a truncated cone with a narrow upper and wide lower structure, the cross section of which is a trapezoidal shape, and the bottom angle of the trapezoid is designed to be 85°. Materials can be added to the upper end of the stator according to a stoichiometric ratio, a rotatable truncated cone rotor is arranged in the stator, and a motor is connected below the rotor; a strong shear field is formed between the rotor and the stator, and a sampling port is arranged at an interval of 6 mm at a distance of 30 mm from the top of the stator in the axial direction of the "rotor-stator group", and a total of 8 sampling ports are arranged, and an in-situ flow cell made of quartz glass is in-situ connected. The upper end of the in-situ flow cell is connected to a halogen light source with a power of 40W through an optical fiber with a core diameter of 600μm and a transmission band of 200-1200nm, and the lower end is connected to a fiber optic spectrometer with a CMOS detector with an integration time of 220μs.

[0028] The above-mentioned rotating liquid film reactor time-resolved spectroscopy detection system for monitoring the nucleation process of nanomaterials was applied to the preparation of cobalt-based hydrotalcite, and the specific operation was as follows:

[0029] Co(Cl)2 and Al(Cl)3 were separated according to Co 2+ / Al 3+ The molar ratio is 2, and a chloride salt mixed solution is prepared, wherein [Co 2+ ]=0.02mol / L;According to [n(Co 2+)+n(Al 3+ )] / n(NaOH)=1 / 2 to prepare NaOH solution. The mixed salt solution and the alkaline solution were simultaneously injected into the rotating liquid film reactor for rapid nucleation. The nucleation speed was 1000rpm, the slit width between the rotor and the stator was 200μm, the nucleation slurry concentration was 0.005mol / L, and the nucleation slurry was obtained through the vacuum sampler at the sampling port No. 1 in the high-speed shear zone and entered the in-situ flow cell at a flow rate of 50mL / min. The ultraviolet-visible spectrum with a time resolution of 435μs was obtained by high-speed acquisition.

[0030] from Figure 5 It can be seen that the nucleation slurry obtained from sampling port 1 only observed the wavelength at 490-530nm. 4 T 1g (P) → 4 T 1g (F), 4 T2g→ 4 T 1g (F) Transformed v3(O h ) characteristic vibration peak, but the typical layered structure characteristic peak (460nm) of LDH has not yet appeared, indicating that Co 2+ Initial and OH - Coordination to form [Co(OH)6] 4- Octahedral structure, but not with [Al(OH)6] 3- The stacking forms hydrotalcite lamellae.

[0031] Example 2

[0032] The experiment was carried out under the same conditions and parameters as in Example 1, and the nucleation slurry was obtained at sampling port No. 2 in the high-speed shear zone through a vacuum sampler and entered into the in-situ circulation pool.

[0033] from Figure 5 It can be seen that the nucleation slurry obtained from sampling port No. 2 has a v3(O h ) characteristic vibration peak is significantly enhanced, indicating that [Co(OH)6] 4- The number of octahedral unit cells gradually increases.

[0034] Example 3

[0035] The experiment was carried out under the same conditions and parameters as in Example 1, and the nucleation slurry was obtained at sampling port No. 3 in the high-speed shear zone through a vacuum sampler and entered into the in-situ circulation pool.

[0036] from Figure 5 It can be seen that the nucleation slurry obtained from sampling port 3 has a v3(O h) characteristic vibration peaks continue to strengthen, and new characteristic peaks appear at 580nm and 640nm, respectively, which are attributed to Co[(OH) x (H2O) δ ] |x-2| The intermediate transition state and 4 A 2g (F) → 4 T 1g (F) Transformed ν3(T d ), which is due to the instability of the intermediate transition state, which is easy to dehydrogenate to form a tetrahedral coordinated [Co(OH)4] 2- In addition, a shoulder peak appeared at 460 nm, indicating that [Co(OH)6] 4- Octahedron and [Al(OH)6] 3- The octahedral unit cells begin to stack.

[0037] Example 4

[0038] The experiment was carried out under the same condition parameters as in Example 1, and the nucleation slurry was obtained at sampling port No. 4 in the high-speed shear zone through a vacuum sampler and entered into the in-situ circulation pool.

[0039] from Figure 5 It can be seen that the characteristic peak intensities of the nucleation slurry obtained from sampling port No. 4 at 490-530nm, 580nm, 640nm and 460nm slowly increase.

[0040] Example 5

[0041] The experiment was carried out under the same condition parameters as in Example 1, and the nucleation slurry was obtained at sampling port No. 6 in the high-speed shear zone through a vacuum sampler and entered into the in-situ circulation pool.

[0042] from Figure 5 It can be seen that the characteristic peak intensities of the nucleation slurry obtained from sampling port No. 6 at 490-530nm, 580nm, 640nm and 460nm are significantly enhanced.

[0043] Example 6

[0044] The experiment was carried out under the same condition parameters as in Example 1, and the nucleation slurry was obtained at sampling port No. 8 in the high-speed shear zone through a vacuum sampler and entered into the in-situ circulation pool.

[0045] from Figure 5 It can be seen that the characteristic peak intensity of the intermediate transition state of the nucleation slurry obtained from sampling port 8 at 580nm and 640nm decreases, and the characteristic peak intensity at 490-530nm and 460nm continues to increase, indicating that the intermediate transition state gradually changes at this time to form an LDH layer plate stacked with Co-Al octahedral unit cells.

[0046] Example 7

[0047] The experiment was carried out under the same conditions and parameters as in Example 1, and the nucleation slurry was obtained at the bottom liquid outlet through a vacuum sampler and entered into the in-situ circulation pool.

[0048] from Figure 5 It can be seen that the characteristic peaks of the intermediate transition state of the nucleation slurry obtained at the bottom mouth at 580nm and 640nm completely disappeared, and the characteristic peak intensities at 490-530nm and 460nm reached the highest, indicating that the characteristic layered structure of CoAl-LDH was formed.

[0049] Example 8

[0050] The experiment was carried out under the same conditions and parameters as in Example 1. A halogen light source with a power of 400 W was connected to an optical fiber with a core diameter of 600 μm and a transmission band of 200-1200 nm to improve the detection sensitivity. The lower end was connected to a fiber optic spectrometer with a CMOS detector with an integration time of 220 μs.

[0051] The above-mentioned rotating liquid film reactor time-resolved spectroscopy detection system for monitoring the nucleation process of nanomaterials was applied to the preparation of cobalt-based hydrotalcite, and the specific operation was the same as that in Example 1.

[0052] Compared to Figure 5 The spectrum obtained from port 1 in the middle, the spectrum obtained using a 400W halogen light source ( Figure 6 ) was significantly improved, and the peak positions were the same, with only the peaks at 490-530nm belonging to 4 T 1g (P) → 4 T 1g (F), 4 T 2g → 4 T 1g (F) Transformed ν3(O h ) characteristic vibration peak, indicating that Co 2+ First with OH - Growth unit [Co(OH)6] coordinated to form an octahedral structure 4- , and did not react with [Al(OH)6] 3- The stacking forms a laminate.

[0053] Comparative Example 1

[0054] The experiment was carried out under the same conditions and parameters as in Example 1, and a halogen light source with a power of 40 W was connected to an optical fiber with a core diameter of 50 μm and a transmission band of 200-1200 nm. The nucleation slurry was obtained at port 1 of the high-speed shear zone through a vacuum sampler and entered into an in-situ circulation pool.

[0055] from Figure 7It can be seen that the spectrum obtained using an optical fiber with a core diameter of 50μm does not show obvious characteristic peaks due to the small light flux.

[0056] Comparative Example 2

[0057] The experiment was carried out under the same conditions and parameters as in Example 1, and the nucleation slurry was obtained through the vacuum sampler at sampling port No. 1 and entered into the in-situ circulation pool at a flow rate of 80 mL / min.

[0058] from Figure 8 It can be seen that when the flow rate of the nucleation slurry entering the in-situ flow cell is increased to 80 mL / min, no obvious characteristic peak appears due to obvious bubble interference.

Claims

1. A time-resolved detection system for in-situ capture of the dynamic evolution of nanoparticles in a nucleation reactor, characterized in that include: Rotating liquid film reactor, light source, in-situ flow cell, optical fiber, vacuum sampler, fiber optic spectrometer, signal control and acquisition device; A sampling port is provided in the rotating liquid film reactor, and the in-situ flow cell is connected in-situ; the upper end of the in-situ flow cell is connected to a light source through an optical fiber, and the lower end is connected to a fiber optic spectrometer, so as to realize the construction of an in-situ spectrum with a time resolution of less than 500 μs; a metal salt solution and an alkaline solution are added to the rotating liquid film reactor for nucleation, and the nucleation slurry is captured by a vacuum sampler and enters the in-situ flow cell, and a time resolution spectrum of less than 500 μs is obtained by acquisition, so as to capture the coordination structure change information of the nanoparticles during the nucleation process; a convex lens is provided at each end of the in-situ flow cell to form a symmetrical light path; The rotating liquid film reactor is composed of a closed casing as a stator, the upper end of the stator can be charged with materials according to a stoichiometric ratio, the inner cavity of the stator is a truncated and hollow cone with a narrow upper and wide lower structure, the top diameter is 42.3 mm, the bottom diameter is 51.5 mm, the height is 75 mm, the cross section is trapezoidal, and the trapezoidal bottom angle is designed to be 85°; there is a rotatable truncated cone rotor inside the stator, forming a slit with the stator, and the slit adjustment range is 10-500 μm; a motor is connected under the rotor to drive the rotor to rotate, and the speed adjustment range is 500-5000 rpm; sampling ports are set at intervals of 6 mm at a distance of 30 mm from the top of the stator, and a total of 8 sampling ports are set to cover the entire flow field; The dynamic evolution behavior of the nucleation process of the nanoparticles ends in the area below the position of sampling port No.

8.

2. The system according to claim 1, characterized in that: The inlet of the in-situ flow cell is located at the top of the in-situ flow cell, and the outlet is located at the bottom of the in-situ flow cell.

3. The system according to claim 1, characterized in that: The material transmittance of the in-situ flow cell is greater than 92%, and is one of borosilicate glass, quartz glass, and polymethyl methacrylate.

4. The system according to claim 1, characterized in that: The focal length of the convex lens is set to 20mm, and the aperture is 10mm.

5. The system according to claim 1, characterized in that: The core diameter of the connecting optical fiber is 400-600 μm, and the transmission band is 200-1200 nm; the light source is one of a xenon lamp, a deuterium lamp, a deuterium halogen lamp, and a halogen lamp, and the power is 40-400W.

6. The system according to claim 1, characterized in that: The fiber optic spectrometer has a CMOS detector with an integration time of <300 μs.

7. The system according to claim 1, characterized in that: The fiber optic spectrometer uses high-speed random access memory as the storage medium, which allows more than 50,000 spectra to be stored at one time.

8. The system according to claim 1, characterized in that: The molar concentration ratio of the metal salt solution and the alkali solution is 1 / 1-3, the concentration of the nucleation slurry is 0.005-0.01 mol / L, and the flow rate of the nucleation slurry entering the in-situ circulation pool is 50-80 mL / min.

9. The system according to claim 1, characterized in that: The application of the time-resolved detection system is characterized by in-situ capturing of the dynamic evolution of the coordination structure, particle size, and reaction intermediates of nanoparticles in a rotating liquid film reactor, wherein the nanoparticles include hydrotalcite, oxides, hydroxides, pseudo-boehmite, barium sulfate, and the like.

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