CN114769612B - Oil-soluble nickel nanoparticles and in-situ synthesis method thereof in vegetable oil and application thereof as vegetable oil anti-wear additive - Google Patents

Abstract

The invention discloses a method for in-situ synthesis of oil-soluble nickel nanoparticles in vegetable oil, which comprises the steps of uniformly mixing vegetable oil and nickel salt; then heating to 190-290 ℃ under the inert gas atmosphere, and reacting for 15-180 min at the temperature of the mixture; cooling to room temperature after the reaction is finished, and performing solid-liquid separation, washing and drying to obtain the catalyst. In the method, vegetable oil is used as a solvent to dissolve or disperse nickel salt; on the other hand, the modified nano-particle is used as a modifier to be modified on the surface of the nickel nano-particle, so that the nano-particle is ensured to have good oil solubility. Other reducing agents and solvents are not needed to be introduced in the reaction process, and the used vegetable oil is biodegradable and environment-friendly; the prepared nickel nano particles have controllable particle size and uniform particle size distribution, and have good oil solubility and stability; can effectively improve the tribological performance of the vegetable oil, is hopeful to be used as a novel green antiwear additive for the vegetable oil, and can be widely applied.

Description

Oil-soluble nickel nanoparticles and in-situ synthesis method thereof in vegetable oil and application thereof as vegetable oil anti-wear additive

Technical Field

The invention belongs to the technical field of preparation of novel functional nanomaterials, and specifically relates to an oil-soluble nickel nanoparticle and an in-situ synthesis method thereof in vegetable oil and an application thereof as an anti-wear additive for vegetable oil.

Background technique

As human society pays more and more attention to environmental protection, resource conservation and sustainable development, people generally realize that the development of bio-based lubricants is not only a necessary measure to protect the environment, but also an important way to alleviate the oil crisis and make full use of solar energy. Vegetable oil as a base oil has the advantages of being non-toxic, aromatic-free, low-priced, completely biodegradable, high flash point, renewable, directly dischargeable, extremely low waste treatment cost, and high comprehensive benefits. It has attracted widespread attention. Vegetable oil lubricants can solve current and future technical and environmental challenges, have the potential and trend to replace traditional petroleum-based lubricants, and have already emerged in the application fields of automotive engine oil, metalworking cutting fluid, gear bearing lubricant, etc.

Additives used in mineral oil and synthetic oil cannot be directly applied to vegetable oil lubricants, as vegetable oil has a certain selectivity for additives. In order to obtain additives with good performance, it is necessary to prepare suitable treatment agents for vegetable oil. When vegetable oil is used in the field of tribology, its inherent chemical structure and physicochemical properties will affect its tribological properties. Compared with traditional mineral oil, vegetable oil contains polar groups that will be arranged in a directional manner on the surface of the friction pair to form a friction film, which is beneficial to improving the friction reduction performance of vegetable oil; however, due to competitive adsorption, the highly polar vegetable oil is not conducive to the film formation of other additives on the friction surface. The magnetic properties of nickel nanoparticles are used to adsorb on the surface of iron-based metal friction pairs to solve the problem of competitive adsorption between vegetable oil and additives on the surface of metal friction pairs, and it is expected to achieve friction reduction and anti-wear effects on the friction pair.

The preparation methods of nickel nanoparticles are mainly divided into physical and chemical methods. However, since nickel nanoparticles are magnetic and prone to agglomeration, their dispersibility in base oil is affected. In situ synthesis of nickel nanoparticles in vegetable oil and using vegetable oil as a modifier enhances the compatibility of nickel nanoparticles with vegetable oil. On the other hand, the preparation process does not use reducing agents and organic solvents, which is highly safe. Vegetable oil lubricants have excellent environmental performance and are widely available. For China, a major agricultural country, there is a solid raw material foundation for the development and application of plant-based lubricants.

Summary of the invention

The purpose of the present invention is to overcome the defects of the prior art and provide an oil-soluble nickel nanoparticle, which has controllable particle size and uniform distribution, good tribological properties, recyclable vegetable oil, high degradability, high flash point, ignition point and good high-temperature stability, and direct discharge will not cause adverse effects on the environment.

The present invention also provides an in-situ synthesis method of the oil-soluble nickel nanoparticles in vegetable oil and the application thereof in vegetable oil. The preparation method of the nickel nanoparticles is green and environmentally friendly, does not introduce other reducing agents and solvents, and the vegetable oil used is biodegradable and environmentally friendly. The vegetable oil is used as both a solvent and a modifier in the reaction, thereby ensuring the compatibility of the nickel nanoparticles with the vegetable oil. The prepared nickel nanoparticles and the vegetable oil can form a matching additive, and this environmentally friendly vegetable oil lubricant has a good application prospect.

In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

A method for in-situ synthesis of oil-soluble nickel nanoparticles in vegetable oil comprises the following steps:

1) Mix the vegetable oil and nickel salt; then, in an inert gas (such as nitrogen, argon, etc.) atmosphere, heat to 190-290 °C and keep the temperature for 15-180 min;

2) After the reaction is completed, cool to room temperature, separate the solid from the liquid (such as by centrifugation), wash, and dry to obtain the product.

Specifically, the vegetable oil includes any one or more of rapeseed oil, olive oil, peanut oil, soybean oil, castor oil, palm oil, etc.

Specifically, the nickel salt includes any one or more of nickel acetylacetonate, nickel acetate, nickel formate, and the like.

Furthermore, in step 1), 30 mL of vegetable oil and 0.1-0.8 g of nickel salt can be added into a three-necked flask and stirred electrically to mix.

Further preferably, in step 1), the reaction temperature is 190, 200, 210, 220, 230, 250 or 270°C; and the reaction time is 15, 30, 60, 90, 120, 150 or 180 min.

Furthermore, in step 1), the heating rate is 5-10 °C/min.

Further preferably, in step 2), the washing is performed with n-hexane, or a mixed solution of ethanol and n-hexane (preferably with a volume ratio of 5:1); and the drying is performed in a vacuum drying oven at 50-80° C. overnight.

The invention provides oil-soluble nickel nanoparticles synthesized by the method.

The present invention also provides the use of the above-mentioned oil-soluble nickel nanoparticles as a vegetable oil anti-wear additive. Further, when used, the mass addition concentration of the oil-soluble nickel nanoparticles is 0.02%-1.0%. The present invention also tests the tribological properties of the oil-soluble nickel nanoparticles when used as a vegetable oil anti-wear additive. For example, when the oil-soluble nickel nanoparticles are used as a rapeseed oil anti-wear additive and the mass addition concentration is 0.3%, the rapeseed oil anti-wear property is improved by 36%. When the oil-soluble nickel nanoparticles are used as an olive oil anti-wear additive and the mass addition concentration is 0.3%, the olive oil anti-wear property is improved by 30%.

In the method of the present invention, vegetable oil is used as a solvent to dissolve or disperse nickel salts on the one hand; on the other hand, it is used as a modifier to modify the surface of nickel nanoparticles to ensure that the nanoparticles have good oil solubility. No other reducing agents and solvents need to be introduced during the reaction, and the vegetable oil used is biodegradable and environmentally friendly; the method for preparing nickel nanoparticles is simple, convenient, and has abundant sources of raw materials, which is suitable for large-scale industrial production. The prepared nickel nanoparticles have controllable particle size, uniform particle size distribution, good oil solubility and stability. Compared with the prior art, the significant advantages of the present invention are as follows:

(1) The present invention uses vegetable oil as a solvent, which is widely available, non-toxic, low-priced, and completely biodegradable.

(2) In the preparation process of the oil-soluble nickel nanoparticles of the present invention, the vegetable oil is used not only as a solution but also as a modifier of the target product. No reducing agent or toxic solvent is introduced into the reaction, thereby reducing impurities in the system and environmental pollution. In addition, in the process of generating the nickel nanoparticles, oleic acid and other components in the vegetable oil are modified onto the surface of the nickel nanoparticles to inhibit their growth. The lipophilic groups on the surface of the modifier provide the prepared nickel nanoparticles with good oil solubility so that they can be stably dispersed in the vegetable oil.

(3) The oil-soluble nickel nanoparticles prepared in the present invention are generated in situ in vegetable oil and have good compatibility with the vegetable oil, which is conducive to application in the vegetable oil.

(4) The oil-soluble nickel nanoparticles prepared by the present invention have controllable particle size and uniform distribution, and the particle size is between 8-50 nm; and the preparation process is simple and the raw material source is abundant, which is conducive to industrial-scale production.

(5) When the oil-soluble nickel nanoparticles prepared by the present invention are added to vegetable oil at a concentration of only 0.3%, the wear resistance of rapeseed oil is improved by 36%, and that of olive oil is improved by 30%. The vegetable oil has good tribological properties. The vegetable oil can be recycled and has high degradability. It also has a high flash point, a high ignition point, and good high-temperature stability. Direct discharge will not cause adverse effects on the environment. The nickel nanoparticles and vegetable oil can form a matching additive. This environmentally friendly vegetable oil lubricant has broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the synthesis process of the oil-soluble nickel nanoparticles of the present invention;

FIG2 is a graph showing the morphology and particle size distribution of nickel nanoparticles synthesized in situ in rapeseed oil at different reaction temperatures in Example 1; in the graph, (a) 190°C, (b) 200°C, (c) 210°C, (d) 220°C;

FIG3 is a TEM image of in situ synthesis of nickel nanoparticles in rapeseed oil at 190° C. at different reaction times in Example 2; in the figure, (a) 30 min, (b) 60 min, (c) 90 min, (d) 120 min, (e) 150 min and (f) 180 min;

FIG4 is an XRD diagram of oil-soluble nickel nanoparticles synthesized in situ in rapeseed oil in Example 5;

FIG5 is a TEM image and particle size distribution diagram of oil-soluble nickel nanoparticles synthesized in situ in rapeseed oil in Example 5; in the figure, (a) 200° C., (b) 210° C.;

FIG6 is a TEM image and a particle size distribution diagram of the oil-soluble nickel nanoparticles synthesized at different heating rates in Example 6; in the figure, (a) the heating rate is 10°C/min, (b) the heating rate is 10°C/min;

FIG7 is a TEM image and a particle size distribution diagram of nickel nanoparticles prepared by reacting nickel acetylacetonate in olive oil at 200° C. for 120 min (a) and 150 min (b) in Example 7;

FIG8 is the tribological performance evaluation results of in-situ synthesized nickel nanoparticles in rapeseed oil at 200 and 210° C. in Example 5;

FIG. 9 shows the tribological evaluation results of the nickel nanoparticles synthesized in situ in olive oil at reaction times of 120 and 150 min in Example 7.

Detailed ways

The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

In the examples, the raw materials used are all common commercial products that can be directly purchased. Room temperature refers to 25±5°C.

Example 1

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil (as shown in FIG1 ) specifically comprises the following steps:

(1) Add 30 mL of rapeseed oil and 0.39 g of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle at a heating rate of 5 °C/min to different temperatures, such as 190, 200, 210, 220, 230, 250, 270 and 290 °C, wherein the color of the solution changes from green to black during the reaction, and the reaction time is 30 min;

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in the air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min. Wash it three times with a mixed solvent of ethanol and n-hexane in a volume ratio of 5:1, and dry it in a vacuum oven at 60°C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

The morphology of the nickel nanoparticles synthesized in situ in rapeseed oil at the above different temperatures is spherical particles, and the particle size tends to increase with the increase of temperature. As shown in Figure 2, the TEM images and particle size distribution of the nickel nanoparticles generated in situ in rapeseed oil at reaction temperatures of 190, 200, 210 and 220 ° C are shown. When the reaction temperature is 190 ° C and the reaction time is 30 min, the crystal nucleus of the nickel nanoparticles has not been generated, and the grains are in a growing state. When the temperature is 200 ° C, the crystal nucleus of the nickel nanoparticles has been generated, with good dispersibility, an average particle size of 12.2 nm, and a narrow particle size distribution; when the temperature is increased to 210 ° C, the particles begin to show obvious agglomeration, the dispersibility becomes worse, and the average particle size is about 13.4 nm; when the temperature is increased to 220 ° C for reaction, the degree of particle agglomeration is more obvious, the average particle size increases to 22.5 nm, and the particle size distribution becomes wider.

Example 2

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of rapeseed oil and 0.39 g of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle to 190°C at a heating rate of 5°C/min, wherein the color of the solution changes from green to black during the reaction, and the reaction times are 30, 60, 90, 120, 150 and 180 min, respectively;

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min, wash three times with a mixed solvent of ethanol and n-hexane in a volume ratio of 5:1, and dry in a vacuum drying oven at 60°C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

The reaction temperature is 190 °C. The nickel nanoparticles prepared at different reaction times (as shown in Figure 3) have no nickel nuclei formed when the reaction time is 30 min, and the reaction is not complete; when the reaction is carried out for 60-90 min, nickel nuclei have been formed, but there are still some agglomerations and poor dispersion, with an average particle size of about 31.5 nm; when the reaction time is from 120 min to 180 min, the nickel nanoparticles have better dispersion and smaller particle size, and the particle size decreases from 35.1 nm to 22.2 nm.

Example 3

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of rapeseed oil and 0.39 g of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle to 200° C. at a heating rate of 5° C./min. During the reaction, the color of the solution changed from green to black. The reaction times were 30, 60, 90, 120, 150 and 180 min, respectively.

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in the air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min. Wash it three times with a mixed solvent of ethanol and n-hexane in a volume ratio of 5:1, and dry it in a vacuum oven at 80°C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

When the nickel nanoparticles were prepared at a higher temperature of 200 °C and the reaction time was 30 min, the in-situ synthesized nickel nanoparticles in rapeseed oil had good dispersibility, no obvious agglomeration, and an average particle size of about 12.2 nm. As the reaction time increased, the agglomeration degree of the nickel nanoparticles increased, the dispersibility became worse, and due to the Oswald ripening phenomenon, the particle size gradually increased. When the reaction time was extended to 180 min, the average particle size increased to 24.8 nm.

Example 4

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of rapeseed oil and 0.19 g (or 0.78 g) of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle to 200°C at a heating rate of 5°C/min. During the reaction, the color of the solution changed from green to black. The reaction time was 30 min.

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min, wash three times with a mixed solvent of ethanol and n-hexane in a volume ratio of 5:1, and dry in a vacuum drying oven at 60°C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

When the concentration of the above-mentioned reactant nickel acetylacetonate is 0.025 mol/L, the obtained nickel nanoparticles have good particle size dispersibility, and the average particle size is about 15 nm. When the concentration is 0.05 mol/L, the nickel nanoparticles have good dispersibility, no obvious agglomeration phenomenon, and the average particle size is about 12.2 nm. When the concentration increases to 0.1 mol/L, the average particle size of the prepared oil-soluble nickel nanoparticles increases to 45 nm, the particles agglomerate into blocks, and the dispersibility is poor.

Example 5

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of rapeseed oil and 0.39 g of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle at a heating rate of 5 °C/min to 200 °C and 210 °C, respectively. During the reaction, the color of the solution changes from green to black. The reaction time is 15 min.

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min, wash three times with a mixed solvent of ethanol and n-hexane in a volume ratio of 5:1, and dry in a vacuum drying oven at 60°C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

In the above-mentioned in-situ preparation of nickel nanoparticles in rapeseed oil using nickel acetylacetonate as the nickel source, the reaction temperatures were 200°C and 210°C, respectively, and the reaction time was shortened to 15 min. The XRD pattern of the obtained oil-soluble nickel nanoparticles is shown in Figure 4, which is consistent with the standard card (JCDPS04-0859). The diffraction peaks at 44.51°, 51.85° and 76.37° correspond to the (111), (200) and (220) crystal planes of face-centered cubic nickel, respectively, and no other diffraction peaks such as nickel oxide were found, indicating that nickel nanoparticles with higher purity were synthesized.

The TEM image of the oil-soluble nickel nanoparticles prepared above is shown in Figure 5. As shown in Figure 5, the nickel nanoparticles have a small particle size, are evenly distributed, and are spherical particles. With the increase of the reaction temperature, the average particle size increases slightly. The average particle sizes at reaction temperatures of 200°C and 210°C are 12.66 nm and 14.34 nm, respectively.

Example 6

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of rapeseed oil and 0.39 g of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle to 210° C. at heating rates of 5° C./min and 10° C./min, respectively. During the reaction, the color of the solution changes from green to black. The reaction time is 30 min.

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in the air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min. Wash with ethanol three times and dry in a vacuum oven at 60 °C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

When the oil-soluble nickel nanoparticles were prepared as described above, when the heating rate was increased from 5°C/min to 10°C/min, as shown in FIG6 , the particle size of the nickel nanoparticles increased from 13.4 nm to 21.7 nm, with slight agglomeration and poor dispersibility.

Example 7

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of olive oil and 0.39 g of nickel acetylacetonate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle to 200°C at a heating rate of 5°C/min. During the reaction, the color of the solution changed from green to black. The reaction times were 60, 90, 120 and 150 min, respectively.

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min. Wash with n-hexane three times and dry in a vacuum oven at 60°C overnight to obtain surface-modified oil-soluble nickel nanoparticles.

The TEM images and particle size distribution diagram of nickel nanoparticles prepared by reacting nickel acetylacetonate in olive oil for 120 min and 150 min at a reaction temperature of 200 °C are shown in Figure 7. When the reaction time is 120 min, the average particle size of the prepared nickel nanoparticles is about 11.9 nm; when the reaction time is 150 min, the particle size of the prepared nickel nanoparticles increases, and the average particle size is about 15.6 nm. Under the same conditions, the nickel nanoparticles prepared in olive oil have smaller particle sizes and better dispersibility than those prepared in rapeseed oil.

Example 8

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL soybean oil and 0.27 g nickel acetate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle to 230°C at a heating rate of 5°C/min. During the reaction, the color of the solution changed from green to yellow. After heating at 260°C for 20 min, the color of the solution completely turned black.

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in the air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min. Wash it three times with a mixed solvent of ethanol and n-hexane in a volume ratio of 5:1, and dry it in a vacuum drying oven at 60 °C overnight to obtain surface-modified oil-soluble nickel nanoparticles. The average particle size of the nickel nanoparticles is about 29 nm, with slight agglomeration and a wide particle size distribution.

Example 9

A method for in-situ preparation of oil-soluble nickel nanoparticles in vegetable oil specifically comprises the following steps:

(1) Add 30 mL of castor oil and 0.23 g of nickel formate into a 50 mL three-necked flask in sequence and stir evenly under electric stirring;

(2) continuously introducing inert protective gas nitrogen into the reaction solution obtained in step (1) at a flow rate of about 0.5 L/min;

(3) heating the reaction solution obtained in step (2) in a heating mantle at a heating rate of 5 °C/min until the color of the solution changes from green to black, and continuing the reaction for 30 min;

(4) After the reaction is completed, stop heating, cool the reaction solution in the three-necked flask to room temperature in the air, stop introducing nitrogen, and then centrifuge the reaction solution in a centrifuge at 10,000 rev/min for 15 min. Wash with anhydrous ethanol three times and dry in a 60°C vacuum oven overnight to obtain black oil-soluble nickel nanoparticles. The average particle size of the nickel nanoparticles is about 50 nm, with obvious agglomeration and uneven particle size.

Tribology test 1

The oil-soluble nickel nanoparticles prepared in Example 5 were added to rapeseed oil at a mass fraction of 0.3 wt%, and tribological tests were carried out on a four-ball friction and wear tester under the conditions of a load of 392 N, a rotation speed of 1200 rev/min, a temperature of 75 °C, and a time of 60 min. The experimental results are shown in FIG8 .

The results in Figure 8 show that compared with pure rapeseed oil, when the nickel nanoparticles synthesized at reaction temperatures of 200 ℃ and 210 ℃ were added to rapeseed oil at 0.3wt%, the friction coefficient (COF) increased from 0.064 to 0.087 and 0.091, respectively, up 36% and 42%, respectively. The nickel nanoparticles did not reduce friction in rapeseed oil, but increased friction. However, the wear spot diameter (WSD) of 0.3wt% nickel nanoparticles in rapeseed oil was significantly reduced. Among them, the anti-wear performance of the nickel nanoparticles synthesized at 200 ℃ in rapeseed oil was more significant, and the wear spot diameter decreased from 0.77 mm in rapeseed oil to 0.49 mm, a decrease of 36%. When the reaction temperature was increased to 210 ℃, the particle size of the synthesized nickel nanoparticles increased, causing its anti-wear performance to begin to weaken. At this time, the wear spot diameter was 0.51 mm, which was 33% lower than that of rapeseed oil.

Tribology test 2

The oil-soluble nickel nanoparticles prepared in Example 7 above at 200°C in olive oil for 120 and 150 min respectively were added to pure olive oil at 0.3 wt% and the tribological properties were evaluated on a four-ball friction and wear tester under the conditions of load 392 N, speed 1200 rev/min, temperature 75°C and time 60 min. The experimental results are shown in FIG9 .

The results in Figure 9 show that the introduction of 0.3wt% nickel nanoparticles into olive oil did not reduce friction, but increased the friction coefficient (COF), which increased from 0.072 of olive oil to 0.12 and 0.11, respectively, and the friction coefficient increased by 67% and 53%, respectively; from the average wear spot diameter (WSD) size, the wear spot diameter of 0.3wt% nickel nanoparticles introduced into olive oil was smaller than that of pure olive oil. The average wear spot diameter of the in-situ synthesized nickel nanoparticles under the reaction conditions of 200 ℃ and 120 min was smaller, which was 0.45 mm, a decrease of about 30%. As the reaction time was extended to 150 min, the anti-wear performance of nickel nanoparticles also gradually weakened with the increase of particle size. At this time, the average wear spot diameter was 0.49 mm, which was 23% lower than that of pure olive oil (0.64 mm), and the decline gradually narrowed.

The oil-soluble nickel nanoparticles obtained in the above examples 1 to 9 were detected by XRD and TEM and found that the obtained products were all nickel nanoparticles, and their morphology, size and dispersibility changed with the reaction temperature, reaction time and reactant concentration. By optimizing the reaction conditions, the obtained oil-soluble nickel nanoparticles had a small particle size between 8 and 50 nm, a narrow particle size distribution and good oil solubility.

In summary, it can be found that the oil-soluble nickel nanoparticles prepared in situ in vegetable oil according to the present invention have good anti-wear properties in the vegetable oil and can be widely used as a vegetable oil additive.

Claims (6)

1. An in-situ synthesis method of oil-soluble nickel nanoparticles in vegetable oil is characterized by comprising the following steps:

1) Mixing vegetable oil and nickel salt; then heating to 190-210 ℃ under the inert gas atmosphere, and reacting for 15-180 min at the temperature of the mixture;

2) Cooling to room temperature after the reaction is finished, and performing solid-liquid separation, washing and drying to obtain the catalyst;

the vegetable oil comprises one or more of rapeseed oil, peanut oil, soybean oil, castor oil and palm oil;

the nickel salt comprises any one or more of nickel acetylacetonate, nickel acetate and nickel formate;

in the step 1), 30 mL vegetable oil and 0.1-0.39 g nickel salt are stirred and mixed uniformly.

2. The method for in situ synthesis of oil-soluble nickel nanoparticles in vegetable oil according to claim 1, wherein in step 1), the temperature rising rate is 5-10 ℃/min.

3. The method for in-situ synthesis of oil-soluble nickel nanoparticles in vegetable oil according to claim 1, wherein in step 2), n-hexane or a mixed solution of ethanol and n-hexane is selected for washing; drying in a vacuum oven at 50-80deg.C overnight.

4. The oil-soluble nickel nanoparticles obtained by synthesis using the method of any one of claims 1 to 3.

5. The use of the oil-soluble nickel nanoparticles of claim 4 as an antiwear additive for vegetable oils.

6. The use of the oil-soluble nickel nanoparticles as an antiwear additive for vegetable oils according to claim 5, wherein the mass addition concentration of the oil-soluble nickel nanoparticles is 0.02% -1.0%.