A method for preparing two-dimensional SnO nanosheet based on water-assisted crystallization synthesis regulation strategy

Abstract

The application provides a two-dimensional SnO nanosheet preparation method based on a water-assisted crystallization synthesis regulation strategy. The core of the strategy is to introduce a specific crystal face inducing agent as a surface regulation medium, and through deep optimization of the crystallization process parameters, the thickness of the nanosheet is accurately measured and the highly crystalline state is directionally synthesized. Compared with the traditional solid phase or hydrothermal synthesis scheme, the process avoids the extreme reaction environment of high temperature and high pressure, significantly reduces the energy consumption and preparation cost, and effectively solves the stability bottleneck of batch production of materials. The SnO nanosheet prepared by the process has excellent p-type semiconductor electrical properties and high specific surface area advantages, and provides potential key material support for the industrial application of high-performance transparent thin film transistors, optoelectronic devices, gas sensitive sensors and new type of electrical contact materials.

Description

Technical Field

[0001] This invention relates to the preparation of nanosheet powders, and in particular to a water-assisted crystallization method for preparing novel layered SnO composite oxide nanosheets applicable to optoelectronic devices, gas sensors, electrical contact materials, and other fields. Background Technology

[0002] As fundamental functional materials, binary metal oxides, with their unique physicochemical properties, have established broad application prospects in semiconductors, catalysis, and energy storage. Among them, tin oxide (SnO), a highly representative p-type semiconductor, possesses excellent hole transport capabilities due to its valence band top (VBM) being a hybrid of Sn 5s and O 2p orbitals. This breaks through the bottleneck of traditional n-type oxides in hole performance, making it a cutting-edge hot topic in transparent electronics. From a structural perspective, SnO belongs to the layered tetragonal crystal system. The alternating stacking of Sn-O-Sn atomic layers endows the material with significant charge migration anisotropy, making the preparation of high-purity, high-crystallinity samples crucial for realizing high-performance devices. SnO shows great promise in CMOS circuits, TFTs, and high-performance anode materials.

[0003] Compared to common SnO2, divalent tin oxide SnO exhibits significant complementary advantages in band structure and electrical properties: its indirect band gap is approximately 0.7–2.0 eV, and its intrinsic hole mobility ranks among the highest of p-type oxides. Furthermore, SnO's unique thermal stability boundary and its disproportionation reaction under specific conditions provide a unique process pathway for the in-situ synthesis of composite materials and sensor development. However, achieving controlled morphology and phase purification remains a core challenge for materials engineering.

[0004] Currently, the mainstream technical routes for synthesizing SnO powder include chemical precipitation, solid-state reaction, and hydrothermal synthesis. However, these traditional processes have bottlenecks in practical applications: solid-state reaction is limited by reaction kinetics, often resulting in residual elemental tin or tin dioxide impurities in the product, and it is extremely demanding in terms of vacuum environment and temperature gradient control; while hydrothermal synthesis performs well in terms of crystallinity, it relies excessively on high-pressure reactors, and its long reaction cycle makes it difficult to achieve large-scale continuous production. In summary, while pursuing high purity and specific morphology, traditional preparation methods generally suffer from low energy efficiency, heavy environmental impact, and high manufacturing costs, making it difficult to meet the modern industrial demand for green and efficient synthesis of high-quality SnO materials. Summary of the Invention

[0005] To address the problems of prominent disproportionation side reactions, difficulty in controlling crystal orientation, strong equipment dependence, poor batch stability, and high manufacturing costs in existing SnO powder preparation technologies, this invention provides a method for preparing two-dimensional SnO nanosheets based on a water-assisted crystallization synthesis control strategy. This invention aims to achieve the directional synthesis of two-dimensional SnO nanosheets with preferential exposure of (001) crystal faces, controllable sheet thickness, high phase purity, and good batch stability through the synergistic effect of a low-temperature aqueous in-situ crystallization path and a surface control mechanism using crystal facet inducers, while significantly reducing equipment investment and production energy consumption.

[0006] To achieve the above technical objectives, the specific solutions adopted by the present invention are as follows: (1) Dissolve the stannous source (specifically, one of stannous chloride, stannous sulfate, or stannous acetate) in deionized water, anhydrous ethanol, or a mixture of both to prepare a solution A with a molar concentration of 0.2 ~ 0.8 mol / L; (2) Prepare an alkaline solution with a mass concentration of 0.5 ~ 1.5 g / mL; (3) Under continuous stirring, the alkaline solution is added dropwise to solution A to adjust the pH of the system to 10-12, so that Sn 2+ The Sn(OH)2 precipitate precursor is fully neutralized, forming turbid liquid B; (4) Add a crystal plane inducing agent to the turbid liquid B, the amount of which accounts for Sn 2+ Add 1 to 5% of the total molar ratio of ions and stir continuously for 30 to 60 minutes to allow the crystal plane inducer to be directionally adsorbed on the surface of Sn(OH)2 primary particles, thus obtaining a uniform sol-gel reaction precursor. (5) The sol-gel reaction precursor was placed in a reaction vessel and subjected to a water-assisted crystallization reaction for 6 to 24 h under normal pressure or autogenous pressure (≤ 1.0 MPa) and temperature of 60 ~ 180 ℃, so that Sn(OH)2 crystallized and precipitated two-dimensional SnO nanosheets through in-situ dehydration-rearrangement-self-assembly process; after the reaction, the product was washed sequentially with deionized water and anhydrous ethanol to remove residual K + Na + and Cl - Soluble impurity ions were removed, and then the mixture was vacuum dried at 60-80 °C. (6) Place the product obtained in step (5) in an inert atmosphere (Ar or N2) and heat-treat it at 200 ~ 500 ℃ for 1 ~ 3 h to further improve crystallinity and avoid Sn 2+ Oxidized to Sn 4+This yields two-dimensional SnO nanosheets with controllable sheet thickness, preferential exposure of (001) crystal planes, and adjustable crystallinity.

[0007] In the above technical solution, further, in step (2), the alkaline solution is selected from sodium hydroxide, potassium hydroxide or ammonia water.

[0008] Further, in step (4), the crystal plane inducer is selected from one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate or ethylenediamine.

[0009] Furthermore, in step (5), the number of washing cycles is no less than 3; in step (6), the inert atmosphere is Ar or N2, and the heat treatment holding time is 1 to 3 hours.

[0010] Further, in step (4), the crystal plane inducer accounts for Sn 2+ The total molar ratio of ions is preferably 2 to 3 mol%, more preferably 2.5 mol%; in step (5), the crystallization temperature is preferably 80 to 160 ℃, more preferably 120 ℃; the crystallization time is preferably 10 to 18 h, more preferably 12 h; in step (6), the heat treatment temperature is preferably 300 to 400 ℃, more preferably 350 ℃.

[0011] The present invention also provides a two-dimensional SnO nanosheet prepared by the above method, wherein the two-dimensional SnO nanosheet has (001) crystal plane as the dominant exposed surface, the relative exposure rate of (001) crystal plane is not less than 80%, the sheet thickness is 3 ~ 30 nm, the lateral dimension is 0.5 ~ 10 μm, and the product phase purity is higher than 99%.

[0012] The inventive principle of this invention is as follows: This invention, based on low-dimensional structural engineering and green chemical synthesis design, aims to construct a novel layered SnO nanopowder with highly active exposed crystal faces. Adhering to the principles of green chemistry and economic feasibility, this study utilizes a water-assisted crystallization strategy. Through precise control of the pH buffer system and crystallization kinetic parameters, it successfully prepared novel stannous oxide nanosheets with uniform particle size distribution, excellent crystal quality, and significant layered characteristics. This process significantly reduces synthesis energy consumption while effectively achieving microscopic control over the orientation of SnO crystal growth, providing a novel technical pathway for the preparation of high-quality, high-performance semiconductor building blocks.

[0013] The innovative points and beneficial effects of this invention are as follows: This invention, based on the water-assisted crystallization self-assembly (WASI) evolution mechanism, innovatively proposes a green and low-cost complete process for synthesizing two-dimensional SnO nanosheets. By precisely controlling the concentration of crystal facet inducers and crystallization kinetic parameters, it achieves precise measurement of nanosheet layer thickness and directional construction of highly crystalline layered structures. Compared to traditional solid-state or hydrothermal methods, this process avoids the harsh reaction conditions of high temperature and high pressure, significantly reducing energy consumption and manufacturing costs while ensuring the stability of mass production. These two-dimensional SnO nanosheets with excellent properties show great potential in cutting-edge applications such as optoelectronic devices, high-performance gas sensors, and electrical contact materials. Attached Figure Description

[0014] Figure 1 shows (a), (b), and (c) scanning electron microscope (SEM) images of the two-dimensional SnO nanosheets prepared in Examples 1, 2, and 3 of this invention. Figures 2 and 3 are X-ray diffraction (XRD) spectra of the two-dimensional SnO nanosheets prepared in Examples 1-3 and 4-9 of the present invention, respectively. The diffraction peaks are completely matched with the tetragonal SnO (JCPDS No. 06-0395), with no Sn elemental or SnO2 impurity diffraction peaks. Moreover, the intensity of the (001) plane diffraction peak is significant, indicating that the crystal plane is preferentially exposed. Detailed Implementation

[0015] The implementation of the present invention will be described in detail below through specific embodiments.

[0016] Example 1: (1) Weigh 0.08 mol of stannous chloride (SnCl2·2H2O) and dissolve it in deionized water to prepare a solution A with a molar concentration of 0.2 mol / L; (2) Prepare a potassium hydroxide (KOH) aqueous solution with a mass concentration of 0.5 g / mL; (3) Under continuous stirring, the above KOH solution was added dropwise to solution A to adjust the pH of the system to 10, so that Sn 2+ The Sn(OH)2 precipitate precursor is fully neutralized, forming turbid liquid B; (4) Ethylenediamine is added to the turbid solution B as a crystal plane inducing agent, and the amount added accounts for Sn 2+ Add 1% of the total molar ratio and stir continuously for 30 min to obtain a homogeneous sol-gel reaction precursor. (5) The obtained sol-gel reaction precursor was placed in an open reflux condenser and subjected to water-assisted crystallization reaction at atmospheric pressure and 60 °C for 6 h. After the reaction was completed, it was washed three times with deionized water and anhydrous ethanol, and then dried under vacuum at 60 °C. (6) The obtained powder was placed in a tube furnace and heat-treated at 200 °C for 2 h in an Ar atmosphere to obtain two-dimensional SnO nanosheets.

[0017] Characterization revealed that the SnO nanosheets obtained in this embodiment are regular two-dimensional sheet structures with a lateral dimension of approximately 0.5 ~ 1.5 μm and a sheet thickness of approximately 3 ~ 6 nm (e.g., ...). Figure 1 As shown in (a)); the XRD pattern confirms that the product is a pure tetragonal SnO (JCPDS No. 06-0395), with no Sn elemental or SnO2 impurity diffraction peaks; due to the thin sheet, the material obtained in this embodiment is particularly suitable for gas sensing and photocatalysis applications.

[0018] Example 2: (1) Weigh 0.08 mol of stannous sulfate (SnSO4) and dissolve it in a mixed solvent of deionized water and anhydrous ethanol in a volume ratio of 1:1 to prepare a solution A with a molar concentration of 0.8 mol / L; (2) Prepare an aqueous solution of sodium hydroxide (NaOH) with a mass concentration of 1.5 g / mL; (3) Under continuous stirring, the above NaOH solution was added dropwise to solution A to adjust the pH value of the system to 12, forming turbid solution B; (4) Polyvinylpyrrolidone (PVP, K-30) was added to the turbid solution B as a crystal plane inducer, the amount of which accounted for Sn 2+ Add 5% of the total molar ratio and stir continuously for 60 min to obtain a homogeneous sol-gel reaction precursor. (5) The obtained sol-gel reaction precursor was loaded into a polytetrafluoroethylene-lined reactor and subjected to water-assisted crystallization reaction at autogenous pressure (approximately 0.8 ~ 1.0 MPa) and 180 °C for 24 h. After the reaction was completed, it was washed three times with deionized water and anhydrous ethanol, and then dried under vacuum at 80 °C. (6) The obtained powder was placed in a tube furnace and heat-treated at 500 °C for 2 h in N2 atmosphere to obtain two-dimensional SnO nanosheets.

[0019] Characterization showed that the SnO nanosheets obtained in this embodiment are regular two-dimensional sheet structures with a lateral dimension of approximately 5-10 μm and a sheet thickness of approximately 20-30 nm (e.g., ...). Figure 1As shown in (b)); the relative intensity of the diffraction peak of the (001) plane in the XRD pattern is 3.2 times that of the (101) plane, and the half-width at half-maximum (FWHM) is 0.15°, confirming that the (001) crystal plane is preferentially exposed and has high crystallinity; the product is pure tetragonal SnO (JCPDS No. 06-0395) with a phase purity > 99.5%; the material obtained in this embodiment has high crystallinity and low defect density, and is especially suitable for p-type transparent thin film transistors, transparent electrodes and silver-based electrical contact composite materials.

[0020] Example 3: (1) Weigh 0.08 mol of stannous acetate (Sn(CH3COO)2) and dissolve it in anhydrous ethanol to prepare a solution A with a molar concentration of 0.5 mol / L; (2) Prepare an ammonia solution with a mass concentration of 1.0 g / mL; (3) Under continuous stirring, the above ammonia water is added dropwise to solution A to adjust the pH value of the system to 9, forming turbid solution B; (4) Sodium dodecylbenzenesulfonate (SDBS) was added to the turbid solution B as a crystal plane inducer, the amount of which accounted for Sn 2+ Add 3% of the total molar ratio and stir continuously for 45 min to obtain a homogeneous sol-gel reaction precursor. (5) The obtained sol-gel reaction precursor was loaded into a polytetrafluoroethylene-lined reactor and subjected to water-assisted crystallization reaction at autogenous pressure (approximately 0.3 ~ 0.5 MPa) and 120 °C for 15 h. After the reaction was completed, it was washed three times with deionized water and anhydrous ethanol, and then dried under vacuum at 70 °C. (6) The obtained powder was placed in a tube furnace and heat-treated at 350 °C for 2 h in an Ar atmosphere to obtain two-dimensional SnO nanosheets.

[0021] Characterization revealed that the SnO nanosheets obtained in this embodiment are regular two-dimensional sheet structures with a lateral dimension of approximately 2–5 μm and a sheet thickness of approximately 10–18 nm (e.g., ...). Figure 1 As shown in (c)); the relative intensity of the (001) plane diffraction peak in the XRD pattern is 2.6 times that of the (101) plane, and the full width at half maximum (FWHM) is 0.18°, confirming that the (001) crystal plane is preferentially exposed and has high crystallinity; the product phase purity is >99%, with no Sn elemental or SnO2 impurity phase residues. This embodiment represents the optimal process with the best overall performance. The obtained SnO nanosheets have both high crystallinity and high specific surface area, and can exhibit excellent comprehensive performance in various application scenarios such as p-type thin film transistors, optoelectronic devices, gas sensors, and electrical contact materials.

[0022] Example 4: The difference between this example and Example 1 is that the crystal plane inducer mentioned in step (4) accounts for Sn 2+ The total molar ratio of ions is specifically 2%. Characterization showed that the SnO nanosheets obtained in this example are regular two-dimensional sheet structures with a lateral dimension of approximately 1-3 μm and a sheet thickness of approximately 6-10 nm; the relative intensity of the (001) plane diffraction peak in the XRD pattern is 2.3 times that of the (101) plane, confirming that the (001) crystal plane has achieved preferential exposure; the product is pure tetragonal SnO (JCPDS No. 06-0395), with a phase purity > 99%, and no Sn elemental or SnO2 impurity phases. Example 5: The difference between this example and Example 1 is that the crystal plane inducer mentioned in step (4) accounts for a larger proportion of the Sn... 2+ The total molar ratio of ions is specifically 2.5%. Characterization shows that the SnO nanosheets obtained in this example are regular two-dimensional sheet structures with a lateral dimension of about 1.5 ~ 3.5 μm and a sheet thickness of about 5 ~ 8 nm; the relative intensity of the (001) plane diffraction peak in the XRD spectrum is 3.5 times that of the (101) plane, the half-width at half-maximum (FWHM) is 0.14°, and the relative exposure rate of the (001) crystal plane reaches 88%; the product phase purity is > 99.5%. This proves that the overall performance of the product is best when the molar ratio of the crystal plane inducer is 2.5%. Example 6: The difference between this example and Example 5 is that the crystallization temperature in step (5) is specifically 80 ℃, the crystallization time is specifically 10 h, and the heat treatment temperature in step (6) is specifically 300 ℃. Characterization showed that the SnO nanosheets obtained in this embodiment were regular two-dimensional sheet structures with a lateral dimension of about 0.8 ~ 2 μm and a sheet thickness of about 4 ~ 7 nm; the relative intensity of the (001) plane diffraction peak in the XRD pattern was 2.8 times that of the (101) plane, confirming the preferential exposure of the (001) crystal plane; the product phase purity was > 99%.

[0023] Example 7: The difference between this example and Example 5 is that the crystallization temperature in step (5) is specifically 160 ℃, the crystallization time is specifically 18 h, and the heat treatment temperature in step (6) is specifically 400 ℃. Characterization shows that the SnO nanosheets obtained in this example are regular two-dimensional sheet structures with a lateral dimension of about 3 ~ 6 μm and a sheet thickness of about 12 ~ 20 nm; the relative intensity of the (001) plane diffraction peak in the XRD spectrum is 3.0 times that of the (101) plane, the half-width at half-maximum (FWHM) is 0.16°, and the (001) crystal plane is preferentially exposed significantly; the product phase purity is > 99.3%. Example 8: The difference between this example and Example 5 is that the crystallization temperature in step (5) is specifically 120 ℃, the crystallization time is specifically 12 h, and the heat treatment temperature in step (6) is specifically 350 ℃. Characterization revealed that the SnO nanosheets obtained in this embodiment exhibited a regular two-dimensional sheet structure with a lateral dimension of approximately 2–4 μm and a sheet thickness of approximately 8–12 nm. In the XRD pattern, the relative intensity of the (001) plane diffraction peak was 3.6 times that of the (101) plane, with a full width at half maximum (FWHM) of 0.13°. The relative exposure rate of the (001) crystal plane reached 90%, indicating the highest crystallinity (due to…). Figure 2 and Figure 3 It can be seen that the product phase purity is > 99.6%, with no Sn elemental or SnO2 impurity phase residues. This embodiment is a preferred embodiment under the synergistic effect of various optimal process parameters (2.5% crystal plane inducer, crystallization temperature 120 ℃, crystallization time 12 h, heat treatment temperature 350 ℃). The obtained SnO nanosheets exhibit the best comprehensive performance in p-type transparent thin film transistors, gas-sensitive sensors, and silver-based composite electrical contact materials.

[0024] Example 9: The difference between this embodiment and Embodiment 1 is that the crystal plane inducer mentioned in step (4) accounts for Sn 2+The total molar ratio of ions is 2.5%, the crystallization temperature in step (5) is 120 °C, the crystallization time is 12 h, and the heat treatment temperature in step (6) is 350 °C and the heat treatment time is 1 h. Characterization shows that the SnO nanosheets obtained in this embodiment are regular two-dimensional sheet structures with a lateral dimension of about 2 ~ 4 μm and a sheet thickness of about 8 ~ 12 nm; the relative intensity of the (001) plane diffraction peak in the XRD spectrum is 3.3 times that of the (101) plane, the half-width at half-maximum (FWHM) is 0.15°, the relative exposure rate of the (001) crystal plane reaches 85%, and the crystallinity is good; the product is pure tetragonal SnO (JCPDS No. 06-0395), the phase purity is >99.3%, and there is no Sn element or SnO2 impurity phase residue. This embodiment verifies the feasibility of step (6) of claim 1 and the 1-hour heat treatment time endpoint in claim 5, showing that under the synergistic effect of other optimal process parameters, a short heat treatment of only 1 hour can obtain two-dimensional SnO nanosheets with high crystallinity and preferential exposure of (001) crystal planes, further highlighting the process advantages of this invention in low energy consumption and green preparation.

[0025] As shown in Figure 1 (SEM morphology) and Figures 2 and 3 (XRD diffraction patterns), this invention achieves precise control over the thickness and crystallinity of SnO nanosheets by introducing specific amine compounds or surfactants as crystal facet inducers and relying on a green and low-cost water-assisted crystallization self-assembly technology. Benefiting from its excellent hole mobility, tunable band structure, and high specific surface area, the SnO nanosheets prepared by this invention will significantly enhance their industrial application value in high-performance optoelectronic devices (such as p-type transparent flexible transistors), high-sensitivity gas sensors, and silver-based composite electrical contact materials (as key second-phase reinforcing particles).

Claims

1. A method for preparing two-dimensional SnO nanosheets based on a water-assisted crystallization synthesis control strategy, characterized in that, Includes the following steps: (1) Dissolve the stannous source in deionized water, anhydrous ethanol, or a mixture of the two to prepare a solution A with a molar concentration of 0.2 ~ 0.8 mol / L; (2) Prepare an alkaline solution with a mass concentration of 0.5 ~ 1.5 g / mL; (3) Under stirring conditions, the alkaline solution is added dropwise to solution A to adjust the pH value of the system to 10-12, forming turbid solution B; (4) Add Sn to turbid liquid B 2+ A crystal facet inducer with a total ion molar ratio of 1 to 5% was added and stirred continuously for 30 to 60 minutes to obtain a homogeneous sol-gel reaction precursor. (5) The sol-gel precursor is subjected to water-assisted crystallization reaction at atmospheric pressure or autogenous pressure and temperature of 60-180 °C for 6-24 h; after the reaction is completed, it is washed with deionized water and anhydrous ethanol in sequence, and then dried under vacuum at 60-80 °C. (6) The product obtained in step (5) is heat-treated in an inert atmosphere at 200 ~ 500 °C to obtain two-dimensional SnO nanosheets.

2. The preparation method according to claim 1, characterized in that, In step (1), the stannous source is selected from one of stannous chloride, stannous sulfate or stannous acetate.

3. The preparation method according to claim 1, characterized in that, In step (2), the alkaline solution is selected from sodium hydroxide, potassium hydroxide or ammonia water.

4. The preparation method according to claim 1, characterized in that, In step (4), the crystal plane inducer is selected from one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate or ethylenediamine.

5. The preparation method according to claim 1, characterized in that, In step (5), the washing is performed at least 3 times; in step (6), the inert atmosphere is Ar or N2, and the heat treatment time is 1 to 3 hours.

6. The preparation method according to claim 1, characterized in that, In step (4), the crystal plane inducer accounts for Sn 2+ The total molar ratio of ions is 2 to 3%.

7. The preparation method according to claim 1, characterized in that, In step (5), the crystallization temperature is 80 ~ 160 ℃ and the crystallization time is 10 ~ 18 h.

8. The preparation method according to claim 1, characterized in that, In step (6), the heat treatment temperature is 300~400 ℃.

9. The preparation method according to claim 1, characterized in that, In step (4), the crystal plane inducer accounts for Sn 2+ The total molar ratio of ions is 2.5%; in step (5), the crystallization temperature is 120 °C and the crystallization time is 12 h; in step (6), the heat treatment temperature is 350 °C.

10. A two-dimensional SnO nanosheet prepared by the method according to any one of claims 1-9, characterized in that, The two-dimensional SnO nanosheets have (001) crystal planes as the dominant exposed surface, with a relative exposure rate of (001) crystal planes of not less than 80%, a sheet thickness of 3 ~ 30 nm, a lateral dimension of 0.5 ~ 10 μm, and a product phase purity of higher than 99%.

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