Method for increasing content of electrophilic oxygen on surfaces of precious metal nanoparticles

Abstract

The invention belongs to the technical field of nano material surface modification, and discloses a method for increasing the content of electrophilic oxygen on the surface of noble metal nanoparticles, which comprises the following steps: preparing noble metal nanoparticles on a clean substrate, putting into a vacuum chamber, exciting glow discharge by using a radio frequency power supply to form oxygen plasma, and irradiating the surface of the noble metal nanoparticles. According to the method, the content of electrophilic oxygen on the surfaces of the precious metal nanoparticles can be remarkably increased within an extremely short time, and the method has the advantages of being simple in process, short in treatment time, remarkable in improvement effect, small in damage to the nanostructure and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterial surface modification, and particularly relates to a method for increasing the electrophilic oxygen content on the surface of noble metal nanoparticles. Background Art

[0002] In the application fields of catalysis, gas sensing, etc., oxygen species (especially electrophilic oxygen) loaded on the metal surface have a key regulatory effect on the functional properties of the material. As a highly active surface oxygen ion, electrophilic oxygen plays an irreplaceable role in key reaction steps such as kinetic regulation of catalytic oxidation reactions and selective adsorption and activation of gas molecules. However, the existing metal nanomaterials have limited surface electrophilic oxygen content during conventional preparation or simple heat treatment, which makes it difficult to meet the needs of high-performance applications. Although traditional chemical methods (such as concentrated nitric acid and persulfate treatment) can introduce oxygen species, they are prone to residual byproducts on the surface and introduce impurities, resulting in obstruction of active sites. Although high-temperature thermal oxidation can promote oxygen adsorption, the high temperature environment will cause nanoparticles to agglomerate, grain growth, and cracks due to thermal stress of the substrate, making it difficult to maintain the integrity of the nanostructure. Although electrochemical methods operate at low temperatures, they have problems such as complex equipment, risk of electrical corrosion, and uneven oxide layer, making them difficult to apply on a large scale. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides a method for increasing the electrophilic oxygen content on the surface of noble metal nanoparticles, aiming to increase the electrophilic oxygen content on the surface of noble metal nanoparticles through second-level oxygen plasma irradiation treatment, while ensuring the integrity of the nanoparticle structure and process stability.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for increasing the electrophilic oxygen content on the surface of noble metal nanoparticles is characterized by comprising the following steps:

[0006] Step 1: Preparing noble metal nanoparticles on a clean substrate;

[0007] Step 2: Using oxygen plasma to perform second-level irradiation treatment on the surface of the noble metal nanoparticle sample obtained in step 1.

[0008] Furthermore, the preparation method of the noble metal nanoparticles includes but is not limited to vacuum coating.

[0009] Furthermore, the plasma is provided by a plasma generator. Furthermore, the oxygen plasma is generated by excitation from a radio frequency power source. Under excitation from the radio frequency power source, oxygen molecules form a variety of reactive oxygen species, including molecular oxygen, atomic oxygen, oxygen anions, and oxygen cations. Some of these reactive oxygen species bombard the surface of the noble metal nanoparticles, altering their surface composition and thereby increasing the electrophilic oxygen content on the surface of the noble metal nanoparticles.

[0010] Furthermore, the method of increasing the electrophilic oxygen content on the surface of noble metal nanoparticles of the present invention can be carried out as follows: the noble metal nanoparticles are placed in a plasma generating device, and the pressure in the device is pumped down to 1×10 -3 Pa, and then introduce working gas oxygen to maintain the pressure in the device at 5-20 Pa, and use radio frequency power to excite the generated oxygen plasma to irradiate the sample surface.

[0011] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0012] 1. The method of the present invention uses a radio frequency power supply to generate glow discharge to form oxygen plasma to irradiate the surface of noble metal nanoparticles, which can significantly increase the electrophilic oxygen content on the surface of noble metal nanoparticles in a very short time, and the effect is significantly better than traditional surface modification methods.

[0013] 2. The method of the present invention is simple and easy to implement, does not require complex chemical reagents or expensive electrochemical devices, and does not introduce other impurities. It has the advantages of simple process, short processing time, and significant improvement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the process flow of Example 2.

[0015] Figure 2 This is the XPS spectrum fitting result of O1s in the sample after annealing in Example 1.

[0016] Figure 3 This is the XPS spectrum fitting result of O1s in the sample after 2 seconds of oxygen plasma treatment in Example 2.

[0017] Figure 4 (a) and (b) are high-resolution TEM images of the samples in Example 1 and Example 2, respectively. DETAILED DESCRIPTION

[0018] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the accompanying drawings and examples. The following is merely an example and illustration of the concept of the present invention. Those skilled in the art may make various modifications, supplements, or replace the specific embodiments described in the description with similar methods. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0019] The plasma generating device used in the following examples is a JGP450C ultra-high vacuum magnetron sputtering device, which is an integrated device of a magnetron sputtering device and a radio frequency sputtering device.

[0020] Example 1

[0021] In this embodiment, vacuum magnetron sputtering technology combined with nitrogen annealing is used to prepare silver nanoparticles on a glass substrate. The specific preparation process includes the following steps:

[0022] Step 1: Clean the glass substrate with acetone and alcohol ultrasonically in sequence and blow dry. Then place the glass substrate on the substrate holder of the vacuum chamber of the magnetron sputtering equipment and use the mechanical pump and molecular pump unit to pump the vacuum chamber to 4×10 - 4 Argon gas with a flow rate of 20 sccm was introduced into the vacuum chamber. After 5 min, the high vacuum valve was adjusted to stabilize the pressure at 6.5 Pa. Then, a Ag film with an average thickness of 2 nm was deposited on the glass substrate using a magnetron sputtering device.

[0023] Step 2: Take out the sample and quickly put it into a tubular annealing furnace for annealing. The annealing atmosphere is nitrogen (flow rate 1600 sccm), the annealing temperature is 200° C., and the annealing time is 10 min.

[0024] Figure 2 This is the X-ray photoelectron spectrum of the silver nanoparticles prepared in Example 1 after annealing. By performing peak fitting on the O1s spectrum line, it can be seen that the relative content of electrophilic oxygen accounts for 7.2%.

[0025] Example 2

[0026] In this embodiment, silver nanoparticles were prepared on a glass substrate using vacuum magnetron sputtering technology combined with nitrogen annealing, and then the sample surface was irradiated with oxygen plasma. The specific preparation process includes the following steps:

[0027] Step 1: Clean the glass substrate with acetone and alcohol ultrasonically in sequence and blow dry. Then place the glass substrate on the substrate holder of the vacuum chamber of the magnetron sputtering equipment and use the mechanical pump and molecular pump unit to pump the vacuum chamber to 4×10 - 4Argon gas with a flow rate of 20 sccm was introduced into the vacuum chamber. After 5 min, the high vacuum valve was adjusted to stabilize the pressure at 6.5 Pa. Then, a Ag film with an average thickness of 2 nm was deposited on the glass substrate using a magnetron sputtering device.

[0028] Step 2: Take out the sample and quickly put it into a tubular annealing furnace for annealing. The annealing atmosphere is nitrogen (flow rate 1600 sccm), the annealing temperature is 200° C., and the annealing time is 10 min.

[0029] Step 3: The annealed sample is quickly placed in the RF sputtering vacuum chamber, and the vacuum chamber pressure is pumped to 4×10 -4 Oxygen gas at a flow rate of 20 sccm was introduced into the vacuum chamber. After 5 minutes, the high vacuum valve was adjusted to stabilize the pressure at 6.5 Pa. Then, an RF power supply was used to excite oxygen plasma (RF power of 7 W) and irradiate the nitrogen annealed silver nanoparticles for 2 seconds.

[0030] Figure 3 The X-ray photoelectron spectrum of the silver nanoparticles prepared in Example 2 after annealing and 2 seconds of oxygen plasma treatment shows that the relative content of electrophilic oxygen is 59.3% by peak fitting of the O1s spectrum line.

[0031] Figure 4 (a) is a TEM image of the silver nanoparticles prepared in Example 1 after annealing, and (b) is a TEM image of the silver nanoparticles prepared in Example 2 after annealing and subjected to 2-second oxygen plasma treatment. The TEM results show that the structures of the silver nanoparticles without OPI and after 2s OPI treatment remain intact.

[0032] Comparing Example 1 with Example 2, it can be seen that the method of the present invention can significantly increase the electrophilic oxygen content on the surface of metallic silver nanoparticles from 7.2% after annealing to 59.3%. During oxygen plasma irradiation, oxygen molecules form a variety of active oxygen species such as oxygen molecules, atomic oxygen, oxygen anions and oxygen cations under the excitation of a radio frequency power supply, and some oxygen species bombard the surface of precious metal nanoparticles. Since the oxidation potential of precious metals is usually higher than their adsorption energy, for example, the adsorption energy of silver is about 0.68eV and the oxidation potential is about 0.80eV, the surface of precious metal nanoparticles is more inclined to form adsorbed oxygen than direct oxidation to form oxides, that is, electrophilic oxygen is more easily adsorbed on the surface of precious metal nanoparticles. The present invention significantly increases the electrophilic oxygen content on the surface of precious metal silver nanoparticles through second-level oxygen plasma irradiation.

[0033] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for increasing the electrophilic oxygen content on the surface of noble metal nanoparticles, characterized in that: The following steps are involved: Step 1: Preparing noble metal nanoparticles on a clean substrate; Step 2: Using oxygen plasma to perform second-level irradiation treatment on the surface of the noble metal nanoparticle sample obtained in step 1.

2. The method for increasing the electrophilic oxygen content on the surface of noble metal nanoparticles according to claim 1, wherein: The oxygen plasma is generated by exciting a radio frequency power supply of a plasma generating device.

3. The method for increasing the electrophilic oxygen content on the surface of noble metal nanoparticles according to claim 2, wherein: The working pressure of the oxygen plasma treatment is 5-20 Pa.

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