A layered manganese dioxide-coated gold nanoparticle photocatalyst and its preparation method

Abstract

This invention discloses a layered manganese dioxide-coated gold nanoparticle photocatalyst and its preparation method, belonging to the field of photocatalytic nanomaterials technology. The preparation method is as follows: S1, tetrachloroauric acid and a quaternary ammonium salt are added to a sodium borohydride solution and stirred at 25-120℃ for 1-3 hours to obtain solution A; solution B containing the quaternary ammonium salt, tetrachloroauric acid, and ascorbic acid is prepared; solutions A and B are mixed and stirred at 25-50℃ for 1-15 hours to obtain Au nanoparticles; S2, after centrifuging the Au nanoparticle dispersion to remove the supernatant, it is added to solution C, which is composed of methoxy polyethylene glycol carboxyl groups, potassium permanganate, a reducing agent, and polyethylene glycol, and stirred at 25-50℃ for 1-5 hours to obtain layered manganese dioxide-coated gold nanoparticles. This invention, by introducing methoxy polyethylene glycol carboxyl groups, prepares a catalyst with unique layered manganese dioxide-coated gold nanoparticles for the photocatalytic conversion of 5-hydroxymethylfurfural.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic nanomaterials technology, and in particular to a layered manganese dioxide-coated gold nanoparticle photocatalyst and its preparation method. Background Technology

[0002] Photocatalytic nanomaterials are a class of nanoscale functional materials that can use light energy to drive chemical reactions, and have broad application prospects in energy conversion, environmental governance and chemical synthesis. Among the many photocatalytic nanomaterials, noble metal nanoparticles have attracted much attention due to their unique local surface plasmon resonance (LSPR) characteristics. Noble metal nanoparticles (such as Au, Ag, Pt, etc.) have a large number of free electrons, which undergo collective oscillation under the action of incident light field, forming local surface plasmon resonance (LSPR). This effect brings three key advantages: (1) LSPR extends the light response from ultraviolet to the visible and near-infrared regions, enhances visible light absorption, and breaks through the traditional wide bandgap limitation of semiconductors; (2) a strong electromagnetic field is generated on the surface of the nanoparticles during resonance, which increases the photogenerated charge production of adjacent semiconductors; (3) SPR decay generates high-energy hot electrons / hot holes, which directly drive redox reactions or inject into the semiconductor conduction band.

[0003] Gold (Au) nanoparticles are the most mature plasma photocatalysts, exhibiting excellent chemical stability, a working function of 5.1 eV, and a tendency to form Schottky barriers with semiconductors. The LSPR peak positions can be controlled by size and morphology, and hot electrons can directly participate in electrochemical reactions or be transferred to external circuits. However, some limitations still restrict the application of Au nanoparticles in photocatalysis. First, the hot carrier lifetime is short, and the quantum efficiency needs further improvement. Second, Au is a precious metal, resulting in high usage costs; therefore, it is necessary to develop high-efficiency catalysts with low Au loading to reduce the amount of Au used without compromising catalytic efficiency. Summary of the Invention

[0004] To address the problems of short hot carrier lifetime, low quantum efficiency, and high cost associated with current Au nanoparticle photocatalysts, this invention provides a layered manganese dioxide-coated gold nanoparticle photocatalyst. The manganese dioxide has a layered structure and is coated on the surface of the gold nanoparticles.

[0005] The layered manganese dioxide-coated gold nanoparticle photocatalyst provided by this invention is prepared by the following method: S1. Add tetrachloroauric acid and quaternary ammonium salt to sodium borohydride solution and stir at 25-120℃ for 1-3 hours to obtain solution A; prepare solution B containing quaternary ammonium salt, tetrachloroauric acid and ascorbic acid; mix solution A and solution B and stir at 25-50℃ for 1-15 hours, then centrifuge to obtain Au nanoparticles, disperse the Au nanoparticles in water to obtain Au nanoparticle dispersion.

[0006] The quaternary ammonium salt is a long-chain alkyl cationic quaternary ammonium salt, preferably hexadecyltrimethylammonium chloride or hexadecyltrimethylammonium bromide.

[0007] In solution A, the molar ratio of tetrachloroauric acid, quaternary ammonium salt, and sodium borohydride is (2-3):(950-1000):(5-8).

[0008] In solution B, the molar ratio of tetrachloroauric acid, quaternary ammonium salt, and ascorbic acid is (3-5):(95-100):(140-160).

[0009] S2. After centrifuging the Au nanoparticle dispersion to remove the supernatant, add it to solution C, which is made of methoxy polyethylene glycol carboxyl group, potassium permanganate, reducing agent and polyethylene glycol. After mixing evenly, stir and react at 25-50℃ for 1-5 h to obtain layered manganese dioxide coated gold nanoparticles.

[0010] The preferred molar ratio of Au nanoparticles, methoxy polyethylene glycol carboxyl groups, and potassium permanganate is (5.6 × 10⁻⁶). -9 ):1:(2 × 10 -3 ) The reducing agent is sodium citrate or polyallylamine hydrochloride, and its amount is 1.5-2 times the molar amount of potassium permanganate.

[0011] This invention also provides an application of layered manganese dioxide-coated gold nanoparticles: used as a photocatalyst to photocatalyze the conversion reaction of 5-hydroxymethylfurfural under ultraviolet-visible light irradiation. Specifically, the furan ring of 5-hydroxymethylfurfural undergoes a ring-opening reaction to convert it into 2,5-hexanediol.

[0012] Compared with the prior art, the advantages of the present invention are: (1) This invention prepares a photocatalyst with a unique core-shell structure of layered manganese dioxide-coated gold nanoparticles by introducing methoxy polyethylene glycol carboxyl groups. This photocatalyst photocatalyzes the conversion reaction of 5-hydroxymethylfurfural under ultraviolet-visible light irradiation.

[0013] (2) The methoxy polyethylene glycol carboxyl groups used in this invention are adsorbed on the surface of gold nanoparticles through interaction with the surface of gold nanoparticles to achieve stable growth. The methoxy polyethylene glycol carboxyl groups provide anchoring points for the in-situ growth of manganese dioxide by chelating manganese ions with carboxyl groups, thereby forming a unique layered structure. (3) The layered manganese dioxide coated gold nanoparticles prepared in this invention utilize photon energy by taking advantage of the local surface plasmon resonance (LSPR) effect when the gold nanoparticles are triggered by light. At the same time, since manganese ions have multiple mixed valence states, they provide efficient and low-barrier electron transport pathways, have strong redox capabilities, and provide abundant oxygen active sites, thereby enhancing catalytic reaction activity.

[0014] (4) The catalyst preparation method of the present invention has a wide range of applications and can be extended to more nanoscale and different morphologies of gold nanoparticles to form layered manganese dioxide coated gold nanoparticles.

[0015] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope image of the gold nanoparticles obtained in step (1) of Example 1.

[0017] Figure 2 This is a scanning electron microscope image of the layered manganese dioxide-coated gold nanoparticles obtained in step (2) of Example 1.

[0018] Figure 3 This is a scanning electron microscope image of the product prepared in Comparative Example 1.

[0019] Figure 4 This is a scanning electron microscope image of the layered manganese dioxide-coated gold nanoparticles obtained in step (2) of Example 2.

[0020] Figure 5 This is a scanning electron microscope image of the product prepared in Comparative Example 2.

[0021] Figure 6 This is the UV-Vis absorption spectrum of the photocatalytic conversion of 5-hydroxymethylfurfural by the photocatalyst in Example 1. Detailed Implementation

[0022] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] Example 1 A layered manganese dioxide-coated gold nanoparticle photocatalyst is prepared as follows: (1) 0.25 mL of 10 mM tetrachloroauric acid solution and 9.75 mL of 0.1 M hexadecyltrimethylammonium bromide solution were added to 0.60 mL of 10 mM sodium borohydride solution and stirred at 30 °C for 3 h to obtain solution A. 0.20 mL of solution A was added to solution B, which was prepared by mixing 9.75 mL of 0.1 M hexadecyltrimethylammonium bromide solution, 4 mL of 10 mM tetrachloroauric acid solution, and 15 mL of 0.1 M ascorbic acid solution. The mixture was stirred at 30 °C for 12 h. After centrifugation, gold nanoparticles were obtained and dispersed in 10 mL of deionized water to obtain a gold nanoparticle dispersion.

[0024] (2) Take 1 mL of gold nanoparticle dispersion, centrifuge to remove the supernatant, and add it to solution C, which is prepared by mixing 1 mL of methoxy polyethylene glycol carboxyl (molecular weight 2000 g / mol, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), 0.2 mL of 10 mM potassium permanganate solution, 0.38 mL of 10 mM sodium citrate, and 0.1 mL of 1 mg / mL polyethylene glycol (molecular weight 4000 g / mol). After mixing evenly, stir and react at 35℃ for 4 h; then centrifuge (5000 rpm for 10 min) to obtain layered manganese dioxide coated gold nanoparticles and disperse them in 1 mL of deionized water.

[0025] Figure 1 This is a scanning electron microscope image of the gold nanoparticles obtained in step (1). It can be seen that the gold nanoparticles are spherical with an average diameter of about 55 nm.

[0026] Figure 2 This is a scanning electron microscope image of the layered manganese dioxide-coated gold nanoparticles obtained in step (2). It can be seen that the manganese dioxide has obvious layered structure characteristics and is coated on the surface of the gold nanoparticles.

[0027] Comparative Example 1 Following the same preparation method as in Example 1, except that the methoxy polyethylene glycol carboxyl group was replaced with an equal amount of methoxy polyethylene glycol thiol (molecular weight 2000 g / mol, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), the final product was obtained.

[0028] Figure 3 This is a scanning electron microscope image of the product prepared in Comparative Example 1. It can be seen that the obtained product is manganese dioxide-coated gold nanoparticles, but no layered manganese dioxide structure is formed, and layered manganese dioxide-coated gold nanoparticles are not present.

[0029] Example 2 A layered manganese dioxide-coated gold nanoparticle photocatalyst is prepared as follows: (1) 0.25 mL of 10 mM tetrachloroauric acid solution and 9.75 mL of 0.1 M hexadecyltrimethylammonium bromide solution were added to 0.60 mL of 10 mM sodium borohydride solution and stirred at 120 °C for 1 h to obtain solution A. 0.20 mL of solution A was added to solution B, which was prepared by mixing 9.75 mL of 0.1 M hexadecyltrimethylammonium bromide solution, 4 mL of 10 mM tetrachloroauric acid solution, and 15 mL of 0.1 M ascorbic acid solution. The mixture was stirred at 50 °C for 1 h. After centrifugation, gold nanoparticles were obtained and dispersed in 10 mL of deionized water to obtain a gold nanoparticle dispersion.

[0030] (2) Take 1 mL of gold nanoparticle dispersion, centrifuge to remove the supernatant, and add it to solution C, which is prepared by mixing 1 mL of 1 mg / mL methoxy polyethylene glycol carboxyl (molecular weight 2000 g / mol, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), 0.2 mL of 10 mM potassium permanganate solution, 0.38 mL of 10 mM polyallylamine hydrochloride solution, and 0.1 mL of 1 mg / mL polyethylene glycol (molecular weight 4000 g / mol). After mixing evenly, stir and react at 50℃ for 1 h; then centrifuge (5000 rpm for 10 min) to obtain layered manganese dioxide coated gold nanoparticles and disperse them in 1 mL of deionized water.

[0031] Figure 4 This is a scanning electron microscope image of the layered manganese dioxide-coated gold nanoparticles obtained in step (2). It can be seen that the manganese dioxide has obvious layered structure characteristics and is coated on the surface of the gold nanoparticles.

[0032] Comparative Example 2 Following the same preparation method as in Example 2, except that the methoxy polyethylene glycol carboxyl group was replaced with an equal amount of methoxy polyethylene glycol thiol (molecular weight 2000 g / mol, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), the product was obtained.

[0033] Figure 5 This is a scanning electron microscope image of the product prepared in Comparative Example 2. It can be seen that the obtained product is manganese dioxide-coated gold nanoparticles, but no layered manganese dioxide structure is formed.

[0034] Comparative Example 3 Following the same preparation method as in Example 2, only the methoxy polyethylene glycol carboxyl groups were replaced with an equal amount of amino polyethylene glycol amino groups (molecular weight 2000 g / mol, purchased from Pengshuo Biotechnology Co., Ltd.). During the preparation process, it was found that the gold nanoparticles were unstable in solution C containing methoxy polyethylene glycol amino groups and agglomerated, thus preventing the preparation of a manganese dioxide-coated gold nanoparticle product.

[0035] Application examples Take 1 mL of the aqueous dispersion of manganese dioxide-coated gold nanoparticles obtained in Examples 1 and 2 and Comparative Examples 1 and 2, centrifuge at 5000 rpm for 10 min to remove the supernatant, and then disperse it in 1.5 mL of acetonitrile solution containing 5 mg of 5-hydroxymethylfurfural. Irradiate the solution under a 300 W xenon lamp for 6 h, with the xenon lamp 15 cm away from the sample. Measure the UV-Vis absorption spectrum of the solution every 1 h. Figure 6 The image shows the UV-Vis absorption spectra of the photocatalyst for 5-hydroxymethylfurfural at different conversion times in Example 1. It can be seen that the two characteristic absorption peaks of 5-hydroxymethylfurfural gradually weaken with increasing illumination time. The absorption peak at 250-300 nm, a characteristic peak of the furan ring, significantly weakens and eventually disappears, indicating that the furan ring has undergone a ring-opening reaction. This proves that manganese dioxide-coated gold nanoparticles can achieve the conversion of 5-hydroxymethylfurfural at room temperature and atmospheric pressure using a photocatalyst. Analysis revealed that the main product of the conversion reaction is 2,5-hexanediol. The photocatalytic conversion rates of various catalysts for 5-hydroxymethylfurfural after 6 hours were calculated, and the results are shown in Table 1.

[0036] Table 1 shows the photocatalytic conversion rates of 5-hydroxymethylfurfural by the products obtained in Examples 1 and 2 and Comparative Examples 1 and 2.

[0037] As shown in Table 1, the manganese dioxide-coated gold nanoparticles with a distinct layered structure prepared in Examples 1 and 2 of this invention exhibit excellent photocatalytic conversion performance of 5-hydroxymethylfurfural, with a conversion rate exceeding 85%. In contrast, the manganese dioxide-coated gold nanoparticles without a layered structure prepared in Comparative Examples 1 and 2 show a lower photocatalytic conversion rate of 5-hydroxymethylfurfural, below 30%. This indicates that the layered manganese dioxide-coated gold nanoparticles prepared in this invention demonstrate significantly better photocatalytic conversion performance of 5-hydroxymethylfurfural than those without a layered structure. Therefore, this invention provides a photocatalyst for the photocatalytic conversion of 5-hydroxymethylfurfural.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a layered manganese dioxide-coated gold nanoparticle photocatalyst, characterized in that, Includes the following steps: S1. Add tetrachloroauric acid and quaternary ammonium salt to sodium borohydride solution and stir at 25-120℃ for 1-3 hours to obtain solution A; Prepare solution B containing quaternary ammonium salt, tetrachloroauric acid and ascorbic acid; mix solution A and solution B, stir and react at 25-50℃ for 1-15h, then centrifuge to obtain Au nanoparticles, disperse the Au nanoparticles in water to obtain Au nanoparticle dispersion; S2. After centrifuging the Au nanoparticle dispersion to remove the supernatant, add it to solution C, which is made of methoxy polyethylene glycol carboxyl group, potassium permanganate, reducing agent and polyethylene glycol. After mixing evenly, stir and react at 25-50℃ for 1-5 h to obtain layered manganese dioxide coated gold nanoparticles.

2. The preparation method of the layered manganese dioxide-coated gold nanoparticle photocatalyst as described in claim 1, characterized in that, The quaternary ammonium salt is hexadecyltrimethylammonium chloride or hexadecyltrimethylammonium bromide.

3. The preparation method of the layered manganese dioxide-coated gold nanoparticle photocatalyst as described in claim 2, characterized in that, In solution A, the molar ratio of tetrachloroauric acid, quaternary ammonium salt, and sodium borohydride is (2-3):(950-1000):(5-8).

4. The preparation method of the layered manganese dioxide-coated gold nanoparticle photocatalyst as described in claim 2, characterized in that, In solution B, the molar ratio of tetrachloroauric acid, quaternary ammonium salt, and ascorbic acid is (3-5):(95-100):(140-160).

5. The preparation method of the layered manganese dioxide-coated gold nanoparticle photocatalyst as described in claim 1, characterized in that, The reducing agent is sodium citrate or polyallylamine hydrochloride.

6. The method for preparing the layered manganese dioxide-coated gold nanoparticle photocatalyst as described in claim 5, characterized in that, The amount of reducing agent used is 1.5-2 times the molar amount of potassium permanganate.

7. A photocatalyst prepared by the method according to any one of claims 1-6, characterized in that, The catalyst has a core-shell structure formed by layered manganese dioxide-coated gold nanoparticles.

8. An application of the photocatalyst as described in claim 7, characterized in that, Used for photocatalytic conversion of 5-hydroxymethylfurfural.

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