Methods and applications for preparing ultrasmall selenium nanomaterials using physical vapor deposition

Abstract

This invention belongs to the field of nanomaterial preparation technology, specifically disclosing a method for preparing ultrasmall selenium nanomaterials using physical vapor deposition (PVD) and its applications. This method involves placing selenium powder and sodium chloride in a tube furnace and performing gradient temperature-controlled vapor deposition under an inert gas environment to prepare ultrasmall selenium nanomaterials with a particle size of 2-5 nm. Compared to traditional solution methods, this process avoids the use of organic solvents, and post-processing only requires dissolution and centrifugation purification. It has advantages such as large-scale production capability, high product purity, and short preparation time (30 min), making it suitable for large-scale production. The ultrasmall selenium nanomaterials prepared by this invention have significant application potential in sodium-ion batteries, optoelectronic devices, immunotherapy, and selenium fertilizers (quantum dot selenium bio-fortifiers).

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a method for preparing ultrasmall selenium nanomaterials using physical vapor deposition and its application. Background Technology

[0002] Selenium nanoparticles (Se NPs) exhibit great application potential in new energy fields, such as sodium-ion battery anode materials, due to their unique quantum size and surface effects. Studies have shown that the physicochemical properties of selenium nanoparticles (such as electrochemical activity and biocompatibility) are closely related to their particle size, dispersion, and purity. However, how to prepare high-purity, ultra-small (<5 nm) selenium nanoparticles with excellent dispersion in a low-cost, environmentally friendly, and efficient manner remains a major technical challenge in the field of nanomaterial preparation.

[0003] Currently, the mainstream method for preparing selenium nanoparticles is the chemical solution method (chemical reduction method). Although this method is widely used, the process is cumbersome, typically requiring reducing agents such as sodium borohydride (NaBH4) and ascorbic acid, and relying on toxic organic solvents such as trioctylphosphine (TOP) to control particle size. This not only leads to high raw material costs but also generates a large amount of organic waste liquid, causing serious environmental pollution. In addition, particles prepared by chemical methods are usually large in size (5-12 nm), with poor dispersibility (>15%), and the products are prone to residual organic impurities or reducing agents, requiring complex multi-step ligand exchange and dialysis purification processes, which severely limits its application in biological systems and high-performance batteries.

[0004] Besides chemical solution methods, traditional chemical vapor deposition (CVD) and bio-preparation methods are also common preparation methods, but all have insurmountable industrialization bottlenecks. Traditional CVD technology is expensive, and the preparation process requires precise control of more than 20 process parameters, making process debugging cumbersome. Most studies can only achieve small-scale preparation in the laboratory (single batch yield is generally <100 mg), making it difficult to achieve mass production through simple scale-up furnaces. For example, in the gas-phase synthesis of selenium nanomaterials reported in existing literature, when the reactor tube volume is scaled up to 10 L, the product uniformity decreases by more than 40%. In addition, the process often relies on noble metal catalysts or complex substrate pretreatment (such as silicon wafer surface hydroxylation), which increases production costs and further prolongs the process, restricting the practical application of gas-phase methods in the industrialization of nanomaterials.

[0005] In summary, existing technologies generally suffer from problems such as the use of toxic reagents, complex processes, low product purity, uneven particle size distribution, and low production efficiency. Therefore, there is a need to develop a green and environmentally friendly new technology that is simple to implement, requires no complex post-processing, and can achieve high yields (at the gram level and above) for the preparation of ultra-small, high-purity selenium nanoparticles to solve the aforementioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned shortcomings of the prior art by providing a method and application for preparing ultra-small selenium nanomaterials using physical vapor deposition. This method can eliminate toxic organic solvents, simplify the process, reduce costs, significantly improve production efficiency, and obtain selenium nanoparticles with smaller particle size, higher purity, and better dispersibility.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for preparing ultrasmall selenium nanomaterials using physical vapor deposition (PVD). The method involves using selenium powder as the source material and sodium chloride as the growth substrate. Under vacuum or inert gas protection, the selenium powder is heated at 350–600 °C to evaporate into a gaseous state. The gaseous selenium is deposited on the surface of the sodium chloride substrate to form a sodium chloride composite loaded with selenium nanoparticles. The composite is then dispersed in an aqueous phase to dissolve the sodium chloride substrate, thereby obtaining dispersed ultrasmall selenium nanomaterials.

[0008] Furthermore, the mass ratio of selenium powder to sodium chloride is 1:(8~12).

[0009] Furthermore, the inert gas is argon.

[0010] Furthermore, the inert gas flow rate is 1~10 L / min.

[0011] Furthermore, the reaction time for the deposition is 0.5 h to 4 h.

[0012] Furthermore, the heating temperature is 600~650℃, and the deposition reaction time is 30~60 min.

[0013] A second objective of this invention is to provide ultrasmall selenium nanomaterials prepared using the method described above.

[0014] Furthermore, the average particle size of the ultrasmall selenium nanomaterial is 2~5nm.

[0015] Furthermore, the zeta potential of the ultrasmall selenium nanomaterial is -22.1 mV to -25.7 mV.

[0016] A third objective of this invention is to provide the application of the ultrasmall selenium nanomaterials prepared by the above method in the preparation of electrochemical energy storage devices and electrode materials.

[0017] Furthermore, the electrochemical energy storage device is a sodium-ion battery, and the ultra-small selenium nanomaterial is used as the negative electrode material of the sodium-ion battery.

[0018] Furthermore, when the ultra-small selenium nanomaterial is used as the negative electrode material of a sodium-ion battery, its initial discharge specific capacity reaches at least 194 mAh / g.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention provides a method for preparing ultra-small selenium nanomaterials using physical vapor deposition. This method involves placing selenium powder and sodium chloride in a tube furnace and performing gradient temperature-controlled vapor deposition in an inert gas environment to prepare ultra-small selenium nanomaterials. Compared with the traditional solution method, this process avoids the use of organic solvents, and the post-processing only requires dissolution, purification with ethanol, and centrifugation. It has advantages such as large-scale production capability, high product purity, and short preparation time (30 min), and is suitable for large-scale production.

[0020] (2) By introducing a sodium chloride substrate, this invention achieves the preparation of ultra-small particles with extremely narrow particle size distribution (<8%) without the need for any organic dispersant, breaking the technical understanding that only chemical liquid phase method can prepare highly dispersed quantum dots.

[0021] (3) The ultra-small selenium nanomaterials prepared by this invention have small particle size (2-5 nm), low dispersion (<8%), purity close to 100%, and excellent stability (Zeta potential about -23.6 mV), so as to improve their permeability in biological bodies and electrochemical performance in battery materials.

[0022] (4) Selenium nanoparticles prepared by existing chemical methods inevitably have long-chain organic ligands adsorbed on their surface (for particle stabilization). This "insulating layer" severely hinders electron transport and the exposure of active sites. The particles prepared by this invention have a unique "ligand-free pure surface" characteristic. Experimental data show that, at the same particle size, the sodium-ion battery prepared with the product of this invention has a first-efficiency discharge specific capacity of 194 mAh / g (significantly higher than conventional selenium materials).

[0023] (5) The method provided by this invention simplifies the process, eliminating the need for complex dialysis purification and ligand exchange. It only requires the adjustment of a few parameters such as temperature and gas flow to achieve a high yield, meeting the needs of industrial applications. This combination of high yield and ultra-small particle size resolves the contradiction that traditional gas-phase methods cannot meet industrial requirements.

[0024] (6) The ultra-small selenium nanomaterials prepared by this invention have significant application potential in sodium-ion batteries, optoelectronic devices, photocatalysis, selenium fertilizers, and other fields. This invention can increase the first-effect discharge specific capacity of sodium-ion batteries to 194 mAh / g. Attached Figure Description

[0025] Figure 1 A diagram of the experimental setup for implementing selenium nanomaterials; Figure 2 shows a digital photograph (left) and a corresponding transmission electron microscope image (right, particle size 2-5 nm) of ultra-small selenium nanomaterials prepared by the high temperature short time method dispersed in water. Figure 3 The XRD absorption spectrum of the ultrasmall selenium nanomaterials is shown. Figure 4 The full element XPS spectrum of ultrasmall selenium nanomaterials; Figure 5 This is a high-resolution scan spectrum of Se3d. Figure 6 The CV curves for sodium-ion batteries using ultra-small selenium nanomaterials are shown. Figure 7 Sodium electrocycle diagram for Example 1 of selenium nanomaterials; Figure 8 Sodium electrocycle diagram for Example 2 of selenium nanomaterials; Figure 9 Sodium electrocycle diagram for Example 3 of selenium nanomaterials; Figure 10 Sodium electrocycle diagram for Example 4 of selenium nanomaterials; Figure 11 Sodium electrocycle diagram for Example 5 of selenium nanomaterials; Figure 12 The sodium electrocycle diagram is shown for Example 6 of selenium nanomaterials. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0027] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0028] Device Design refer to Figure 1The device employs a high-frequency gradient temperature-controlled quartz furnace tube (200-1000 ℃, error ±1 ℃). The furnace tube incorporates multiple independent temperature control zones and a spiral airflow guide plate. The high-temperature zone is set at 350-650 ℃, while the low-temperature zone temperature is set according to actual conditions. The distance between the high-temperature and low-temperature zones is 5 cm, allowing for precise control of the axial temperature gradient. A micro-pump stabilizes the airflow, with the airflow velocity optimized within the range of 1-10 L / min. Experiments determined the optimal airflow velocity to be 1 L / min, ensuring uniform distribution of the reaction gas and resulting in a film thickness fluctuation of <3%. The device integrates a 3-chamber series reaction module (made of quartz, each chamber with independent temperature control). Material channels are switched via pneumatic valves, enabling continuous deposition of ultra-small selenium nanomaterials with functional layers such as metal oxides and sulfides. For the placement of selenium powder and sodium chloride, half the volume of NaCl is placed at one end of the quartz tube, while the other end is loaded with Se powder using a quartz boat. A long iron rod pushes the quartz boat into the tube, ensuring the front end of the boat contacts the NaCl.

[0029] Although this invention adopts the basic process of physical vapor deposition (PVD), its core lies in the discovery and utilization of the special heterogeneous nucleation and growth kinetics mechanism of gaseous selenium atoms on the surface of ionic crystals (sodium chloride). Therefore, even in high-temperature environments that are conducive to crystal growth, the growth of selenium particles is "locked" in the ultra-small size range of 2-5 nm, rather than forming continuous thin films or large particle aggregates. Unlike chemical reduction methods, which rely on organic ligands (such as surfactants) to prevent particle aggregation, this invention utilizes the aforementioned physical vapor deposition method to achieve surfactant-free dispersion. This means that the resulting selenium nanoparticles have a "naked" surface rich in highly active defect sites. This pristine surface, unpassivated by organic molecules, retains the quantum dot surface effects that were originally shielded by the ligand layer in the selenium material, which may explain the improved electrochemical performance of the product.

[0030] Example 1 This embodiment provides a method for preparing ultrasmall selenium nanomaterials using physical vapor deposition.

[0031] Ultrasmall selenium nanomaterials were prepared using physical vapor deposition (PVD). 50 g of NaCl particles were packed into one end of a quartz tube (occupying half the tube's volume). 5 g of selenium powder was placed in a quartz boat and pushed into the other end of the tube, ensuring it contacted the edge of the NaCl-filled section (distance < 0.5 cm). Both ends of the tube were sealed and connected to gas lines (Ar2 inlet and exhaust gas outlet). The initial temperature was 25 °C, then increased to 600 °C at a rate of 5 °C / min (Ar flow rate 1 L / min). After holding at this temperature for 30 min, the temperature was naturally cooled to below 100 °C while maintaining an Ar flow rate of 1 L / min. After cooling to room temperature, the NaCl particles with a dark red solid film were removed, and 200 mL of deionized water was added and stirred for 30 min until dissolved. 100 mL of the suspension was centrifuged at 10000 r / min for 10 min, and the filtrate was collected to obtain the ultrasmall selenium nanomaterial solution. After purification by dissolution in ethanol, freeze-drying, and weighing, 0.416 g of ultra-small selenium nanomaterials can be prepared from 5 g of selenium powder in this example. The resulting solution was tested for Zeta potential and PDI. The Zeta potential was -23.6 mV and the PDI was 0.381, indicating that the solution has good stability.

[0032] from Figure 2 It can be clearly seen that the prepared ultra-small selenium nanomaterials are relatively uniformly dispersed. Figure 3 The XRD absorption spectrum shows that this ultrasmall selenium nanomaterial has specific crystal structure characteristics. Figure 4-5 XPS spectra and other data further verified the composition and purity of the material, indicating that the purity of the product is close to 100%.

[0033] Example 2 The difference between this embodiment and Example 1 is the low-temperature, long-time process: temperature 350 ℃, holding time 4 h, and carrier gas flow rate 1 L / min. Because the reaction is slower at low temperatures, the ordered stacking of Se atoms reduces vacancies; the stable gas flow results in a smooth and regular surface; and low residual impurities reduce defect density. After the reaction, the product was tested, purified by dissolving in ethanol, freeze-dried, and weighed. 0.326 g of ultra-small selenium nanomaterials could be prepared from 5 g of selenium powder. The zeta potential was -24.5 mV, and the PDI was 0.151.

[0034] Example 3 The difference between this embodiment and Example 1 is that the reaction temperature is 500℃, while all other conditions are the same. After the reaction, the product was tested, purified by dissolving in ethanol, freeze-dried, and weighed. 0.365 g of ultra-small selenium nanomaterials could be prepared from 5 g of selenium powder. The zeta potential was -28.5 mV, and the PDI was 0.16.

[0035] Example 4 The difference between this embodiment and Example 1 is that the reaction temperature is 650 ℃, while all other conditions are the same. After the reaction, the product was tested, and 0.387 g of ultrasmall selenium nanomaterials could be prepared from 5 g of selenium powder. The zeta potential was -22.3 mV, and the PDI was 0.12.

[0036] Example 5 The difference between this embodiment and Example 1 is that the mass ratio of selenium powder to sodium chloride is 1:8 (the amount of sodium chloride is reduced), while all other conditions are the same. After the reaction is complete, the product is tested; after being purified by dissolving in ethanol, freeze-dried, and weighed, 0.316 g of ultra-small selenium nanomaterials can be prepared from 5 g of selenium powder. The zeta potential is -22.1 mV, and the PDI is 0.28.

[0037] Example 6 The difference between this embodiment and Example 1 is that the mass ratio of selenium powder to sodium chloride is 1:12 (the amount of sodium chloride is increased), while all other conditions are the same. After the reaction is complete, the product is tested, purified by dissolution with ethanol, freeze-dried, and weighed. 0.211 g of ultra-small selenium nanomaterials can be prepared from 5 g of selenium powder. The zeta potential is -25.7 mV, and the PDI is 0.09.

[0038] Comparing the above examples, it can be seen that when the reaction temperature is 600 ℃, the mass ratio of selenium powder to sodium chloride is 1:10, and the reaction time is 30 min, the prepared ultra-small selenium nanomaterials exhibit the best performance in terms of particle size distribution, yield, and stability, making it the optimal solution of this invention. This high-temperature, short-time process is suitable for the synthesis of ultra-small selenium nanomaterials because the reaction is rapid at high temperatures, the disordered stacking of Se atoms leads to vacancies, uneven local airflow causes surface irregularities, and the adhesion of residual impurities exacerbates defects.

[0039] Example 7 The electrochemical activity of the prepared ultrasmall selenium nanomaterials was studied.

[0040] A sodium-ion battery was constructed using ultra-small selenium nanomaterials as electrode materials. The ultra-small selenium nanomaterial solution, prepared by physical vapor deposition, was freeze-dried into powder. Conductive carbon black and binder (polyvinylidene fluoride PVDF) were mixed at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added to form a slurry. This slurry was coated onto a 12 μm copper foil (1 cm × 1 cm area, 100 μm wet film thickness). After vacuum drying at 80 ℃ for 12 hours, the foil was rolled twice under 5 MPa pressure and cut into 12 mm diameter electrode sheets. In an argon glove box (O2, H2O < 0.1 ppm), a CR2032 (button cell casing for the experimental battery, 20 mm diameter, 3.2 mm thickness) positive electrode shell was taken, and a spring clip and a gasket were placed in sequence. The ultra-small selenium nanomaterial electrode sheet (active side up) was then placed on top and covered with a pre-impregnated electrolyte (1 mol / L NaPF6 in ethylene carbonate / dimethyl carbonate 1:1). For the mixture, after 30 minutes, place a 16 mm diameter glass fiber diaphragm, add 100 μL of electrolyte, quickly place a 14 mm diameter sodium foil disc (metal side down), cover with the negative electrode shell, and seal with 10 MPa pressure; after sealing, transfer to a 25 ℃ environment and place for 12 hours before electrochemical testing.

[0041] like Figure 6 As shown in the CV curve, this is a cyclic voltammetry curve measured at a scan rate of 0.08 mV / s. Within the potential range of 2.4 V to 4.2 V, the curve exhibits a pair of distinct redox peaks: the oxidation peak appearing during the forward scan (potential increase) corresponds to the oxidation process of selenium quantum dots losing electrons, while the reduction peak appearing during the reverse scan (potential decrease) corresponds to the reduction process of the oxidation products regaining electrons. This result not only confirms the good electrochemical activity of selenium quantum dots within this potential range but also demonstrates the reversibility of their redox reactions, providing important experimental evidence for their application in fields such as sodium-ion batteries.

[0042] like Figure 7 As shown in the figure, corresponding to the optimal process parameters (600 ℃, selenium powder to sodium chloride mass ratio 1:10, reaction time 30 min), this figure clearly demonstrates the excellent cycle performance of the ultra-small selenium nanomaterials as the anode of sodium-ion batteries. The material achieves a core indicator of 194 mAh / g specific capacity during the first discharge, retains over 85% of its capacity after 20 cycles, and maintains a coulombic efficiency of over 90% after 3 cycles. This outstanding performance stems from the structural advantages of the optimal process: the ultra-small particle size of 2-5 nm significantly shortens the sodium ion transport path, the low dispersion of <8% avoids particle agglomeration, and the quantum size effect further suppresses electrode structure degradation, comprehensively ensuring high capacity and long-term cycle stability.

[0043] like Figure 8 As shown in the figure, using a low-temperature, long-time process (350 ℃, reaction time 4 h, mass ratio 1:10), the material's initial discharge capacity is approximately 141.1 mAh / g. After 20 cycles, the coulombic efficiency exceeds 85%, and stabilizes above 90% after 3 cycles. The low-temperature environment allows selenium atoms to stack in an orderly manner, reducing crystal vacancies. Stable airflow results in a smooth and regular material surface with low defect density and excellent structural integrity. Therefore, there is no significant structural collapse or active material shedding during cycling, demonstrating outstanding cycle stability and suitability for applications with high cycle life requirements.

[0044] like Figure 9 As shown, the corresponding process is 500 ℃, and the mass ratio of selenium powder to sodium chloride is 1:10. The figure shows that the initial discharge capacity of the material is about 146 mAh / g. After 20 cycles, the coulombic efficiency reaches more than 85%. After the second cycle, the coulombic efficiency drops to below 90%, but in subsequent cycles, the coulombic efficiency rapidly increases and stabilizes at 90%.

[0045] like Figure 10 As shown, the corresponding process is 650 °C, and the mass ratio of selenium powder to sodium chloride is 1:10. The figure shows that the initial discharge capacity of the material is about 146 mAh / g, the coulombic efficiency reaches 85% after 20 cycles, the initial coulombic efficiency is about 90%, and the coulombic efficiency is stable at over 80%.

[0046] like Figure 11 As shown, the process parameters were 600 ℃ and a selenium powder to sodium chloride mass ratio of 1:8 (insufficient sodium chloride). The data in the figure shows an initial discharge capacity of 170.8 mAh / g. After the first cycle, the coulombic efficiency dropped to around 60%, but in subsequent cycles, the coulombic efficiency rapidly increased and stabilized at 80%. After 20 cycles, the coulombic efficiency stabilized above 90%. Insufficient sodium chloride weakened the substrate adsorption and anchoring effect, reduced the loading of selenium nanoparticles, and decreased the number of electrochemical active sites, thus affecting the capacity output. However, thanks to the inherent advantages of physical vapor deposition, the material did not undergo large-scale agglomeration or electrode pulverization, exhibiting good structural stability. Therefore, the coulombic efficiency did not fluctuate significantly, and the capacity decay was gradual.

[0047] like Figure 12As shown, the corresponding process is 600 ℃, with a selenium powder to sodium chloride mass ratio of 1:12 (sodium chloride in excess). The figure shows an initial discharge capacity of 155.2 mAh / g, and a coulombic efficiency of 80% after 20 cycles. The coulombic efficiency stabilizes above 85% after the second cycle. The short cycle time, high efficiency, rapid acceptance, and the excess sodium chloride enhancing substrate adsorption and anchoring, prevent particle agglomeration, and ensure excellent structural stability, guaranteeing superior cycling performance. However, excessive sodium chloride occupies reaction space, leading to a significant reduction in the loading of selenium nanoparticles (yield of only 0.211 g / 5 g selenium powder), reducing the proportion of active material in the electrode, ultimately resulting in an initial discharge capacity lower than the optimal ratio product. This confirms that a 1:10 mass ratio is the optimal mass ratio balancing capacity and dispersibility.

[0048] For any points not covered above, existing technologies shall apply.

[0049] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultrasmall selenium nanomaterials using physical vapor deposition, characterized in that, Using selenium powder as the source material and sodium chloride as the growth substrate, the selenium powder is heated at 350~650 °C under vacuum or inert gas protection to evaporate it into gaseous selenium. The gaseous selenium is deposited on the surface of the sodium chloride substrate to form a sodium chloride composite loaded with selenium nanoparticles. The composite is dispersed in an aqueous phase to dissolve the sodium chloride substrate, thereby obtaining dispersed ultrasmall selenium nanomaterials.

2. The method according to claim 1, characterized in that, The inert gas is argon, with a flow rate of 1~10 L / min.

3. The method according to claim 1, characterized in that, The mass ratio of selenium powder to sodium chloride is 1:(8~12).

4. The method according to claim 1, characterized in that, The heating temperature is 600~650 ℃, and the deposition reaction time is 30~60 min.

5. An ultra-small selenium nanomaterial prepared by any one of claims 1-4.

6. The ultra-small selenium nanomaterial according to claim 5, characterized in that, The average particle size of the ultra-small selenium nanomaterials is 2~5nm.

7. The ultrasmall selenium nanomaterial according to claim 5, characterized in that, The zeta potential of the ultrasmall selenium nanomaterial is -22.1 mV to -25.7 mV.

8. The application of the ultra-small selenium nanomaterials according to claim 5 in the preparation of electrochemical energy storage devices and electrode materials.

9. The application according to claim 8, characterized in that, The electrochemical energy storage device is a sodium-ion battery, and the ultra-small selenium nanomaterial is used as the negative electrode material of the sodium-ion battery.

10. The application according to claim 9, characterized in that, When the ultra-small selenium nanomaterial is used as the negative electrode material of a sodium-ion battery, its initial discharge specific capacity reaches at least 194 mAh / g.

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