Method for regulating nonlinear optical properties of reduced graphene oxide by au@cds and rgo-au@cds composite material

Abstract

The application discloses a method for regulating nonlinear optical properties of reduced graphene oxide by Au@CdS and an rGO-Au@CdS composite material, the Au@CdS core-shell structure is uniformly grown on the surface of the reduced graphene oxide, the core-shell structure is closely connected with the reduced graphene oxide, the rGO-Au@CdS composite material is successfully synthesized by using a solvothermal method, the nonlinear absorption of the composite material has the characteristic of transition from saturated absorption to reverse saturation, and the characteristic is more and more obvious with the increase of light intensity. With the increase of the size of the Au@CdS composite structure, the intensity of the reverse saturation absorption is also improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new nanomaterials, and particularly relates to a method for regulating nonlinear optical properties of reduced graphene oxide (rGO) by Au@CdS and rGO-Au@CdS composite material.

[0002] The application belongs to the 3.3 high-performance composite material industry key direction under the 3 high-tech material industry in the strategic new industry catalogue, and belongs to the 3.3.2 metal-based composite material and ceramic-based composite material intermetallic compound-based composite material. BACKGROUND

[0003] In the past decade, since A. Geim and K. Novoselov of Manchester University successfully exfoliated graphene, the synthesis, nonlinear optical properties and device applications of two-dimensional layered materials have attracted widespread attention. Under the successful stimulation of graphene, other two-dimensional materials such as graphite carbon nitride, black phosphorus, transition metal dichalcogenides and metal organic frameworks have also developed rapidly. Due to the excellent nonlinear optical properties of two-dimensional materials, their application in photonics has become one of the most attractive fields. Due to the needs of practical applications, finding the nonlinear optical properties of suitable materials has always been an eternal topic in the field of nonlinear photonics. Therefore, it is very necessary to regulate the nonlinear optical (NLO) performance of two-dimensional materials. Graphene is the most typical representative of these two-dimensional materials, and in addition to its unique properties, the large number of chemical groups on the surface of graphene such as -OH and -C = O also make it an ideal substrate for depositing other functional materials. So far, graphene has always been an important component of functional composites, and has been combined with various organic and inorganic components. Previous studies have shown that the combination of quantum dots on the surface of graphene will affect its NLO performance. For example, Liu et al. obtained enhanced NLO performance of Bi2S3 / rGO composite materials. Zhang et al. observed the enhanced optical nonlinearity of graphene-gamma MnS, Khanzadeh et al. improved the NLO performance of graphene oxide after mixing with Ag2S@ZnS core-shell, and He et al. studied the superior optical confinement mechanism of upconversion NaYF4:Yb3+ / Er3+ nanoparticles covalently functionalized graphene oxide. These results show that functionalizing graphene with quantum dots will be a method to regulate its nonlinear optical properties.

[0004] Metal-based composite nanocrystals have attracted attention due to their excellent performance in optical, electronic and catalytic functions. Among them, the core-shell structure with metal as the core and semiconductor as the shell as a new material structure, taking the metal core as the conductive support, the surface plasmon resonance of the nanostructure greatly enhances the local electric field, which not only can improve the photocatalytic efficiency and luminescent efficiency, but also can change the optical response and nonlinear behavior. SUMMARY

[0005] The demand for regulating the nonlinear optical (NLO) performance of a two-dimensional material graphene and the core-shell structure with a metal as a core and a semiconductor as a shell can change the optical response and nonlinear behavior, and the application provides a method for regulating the nonlinear optical properties of reduced graphene oxide by Au@CdS and a rGO-Au@CdS composite material.

[0006] The purpose of the application is achieved in the following manner:

[0007] The method for regulating the nonlinear optical properties of reduced graphene oxide by Au@CdS comprises the following steps,

[0008] Firstly, graphene oxide (GO) is prepared by using an improved Hummers method;

[0009] Secondly, a reduced graphene oxide gold nanoparticle sol (rGO-Au) solution is prepared;

[0010] 50 mL of a 0.1 mg / mL graphene oxide suspension is mixed with 0.5 mL of 0.25 mmol chloroauric acid; 1.5±0.1 g of trisodium citrate and 0.0037±0.0001 g of sodium borohydride are added to 50 mL±2 ml of ultrapure water, and the solution is stirred uniformly, 2 mL of the solution is extracted, and the mixed solution of graphene oxide and chloroauric acid is added, and ultrasonic stirring is performed at room temperature for 30±0.6 min, and then it is left to stand for 120±2.4 min, and after the solution is wine red, 0.01±0.001 mL of hydrazine hydrate is added, and the solution is continuously stirred at 90±2 ℃ for 60±1.2 min, and finally, after the solution is cooled, a reduced graphene oxide gold nanoparticle sol solution is obtained;

[0011] Finally, the rGO-Au@CdS composite material is synthesized;

[0012] A Cys / Cd mixture with a molar concentration of 10 mmol is prepared by using cadmium nitrate and cysteine, the molar concentration ratio of Cys to Cd is kept at 2:1, and the acid-base property of the two mixtures is adjusted by adding ammonia, then 5 mL of the Cys / Cd2 mixture is added to 10 mL of the reduced graphene oxide gold nanoparticle sol solution prepared in the previous step, and 15 mL of ultrapure water is added to dilute the mixture, and after ultrasonic stirring, the obtained mixture is transferred to a polytetrafluoroethylene liner in a stainless steel reaction kettle with a capacity of 50 mL, and finally, the reaction kettle is placed in a constant-temperature drying box, and kept at a reaction environment temperature of 130±2.5 ℃ for 5-7 hours, and after natural cooling, the reduced graphene oxide and Au@CdS composite material (rGO-Au@CdS composite material) is obtained by repeatedly washing with ultrapure water and anhydrous ethanol.

[0013] The rGO-Au@CdS composite material is prepared by the method.

[0014] Compared with the prior art, the Au@CdS core-shell structure is used to regulate the nonlinear optical properties of reduced graphene oxide, the Au@CdS core-shell structure is uniformly grown on the surface of the reduced graphene oxide, the core-shell structure is closely connected with the reduced graphene oxide, the rGO-Au@CdS composite material is successfully synthesized by using a solvothermal method, the nonlinear absorption of the composite material appears the characteristics of the transition from saturated absorption to reverse saturation, and the characteristics become more and more obvious with the increase of light intensity. With the increase of the size of the Au@CdS composite structure, the intensity of the reverse saturation absorption is also improved.

[0015] The application provides a train of thought and a method for promoting the further development of graphene composite materials in the field of photonic device applications. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a synthesis process diagram of the rGO-Au@CdS core-shell structure composite material.

[0017] Figure 2 is a TEM image of the rGO-Au@CdS composite material, wherein a is a morphology image of an Au@CdS core-shell structure monomer, b, c and d are morphology images of S1, S2 and S3 of the composite material with different sizes, respectively.

[0018] Figure 3 A is an open aperture Z-scan normalized transmittance diagram of reduced graphene oxide, reduced graphene oxide gold nanoparticle sol and Au@CdS core-shell structure;

[0019] Figure 3 B is an open aperture Z-scan normalized transmittance diagram of the rGO-Au@CdS composite material with three different sizes;

[0020] Figure 3 C is a normalized transmittance diagram of closed aperture divided by open aperture Z-scan of reduced graphene oxide, reduced graphene oxide gold nanoparticle sol and Au@CdS core-shell structure;

[0021] Figure 3 D is a normalized transmittance diagram of closed aperture divided by open aperture Z-scan of the rGO-Au@CdS composite material with three different sizes. DETAILED DESCRIPTION

[0022] The method for regulating the nonlinear optical properties of reduced graphene oxide by the Au@CdS core-shell structure is shown in the overall synthesis train of thought flow as Figure 1 , and specifically includes the following steps:

[0023] First, the improved Hummers method was used to prepare graphene oxide (GO). The specific process of preparing graphene oxide (GO) by the improved Hummers method can refer to the literature Hummers W. S., Offeman R. E., Preparation of Graphitic Oxide. [J]. Am. Chem. Soc, 1958, 25(80): 1334-1339.

[0024] Second, the reduced graphene oxide gold nanoparticle sol (rGO-Au) solution was prepared.

[0025] 50 mL of graphene oxide suspension (0.1 mg / mL) was mixed with 0.5 mL of chloroauric acid (0.25 mmol); 1.5 g of trisodium citrate and 0.0037 g of sodium borohydride were added to 50 mL of ultrapure water, stirred uniformly, and 2 mL of the solution was extracted and added to the mixed solution of graphene oxide and chloroauric acid, and ultrasonic stirring was carried out at room temperature for 30 minutes, and then it was left to stand for 2 hours; after the solution turned wine red, 0.01 mL of hydrazine hydrate was added, and continuous stirring was carried out at 90 ℃ for 1 hour; finally, after the solution was cooled, the reduced graphene oxide gold nanoparticle sol solution was obtained.

[0026] Finally, the reduced graphene oxide and Au@CdS composite material (rGO-Au@CdS composite material) was synthesized.

[0027] A Cys / Cd mixture with a molar concentration of 10 mmol was prepared using cadmium nitrate and cysteine, and the molar concentration ratio of Cys to Cd was kept at 2:1; the acid-base properties of the two mixtures were adjusted by adding ammonia; then, 5 mL of the Cys / Cd2 mixture was added to 10 mL of the reduced graphene oxide gold nanoparticle sol solution prepared in the previous step, and 15 mL of ultrapure water was added to dilute the mixture; after ultrasonic stirring, the obtained mixture was transferred to a polytetrafluoroethylene liner in a stainless steel reaction kettle with a capacity of 50 mL; finally, the reaction kettle was placed in a constant temperature drying box, and the reaction was carried out at 130 ℃ for 5-7 hours; as the time increased, the size of the core-shell structure gradually increased; after natural cooling, the reduced graphene oxide and Au@CdS composite material (rGO-Au@CdS composite material) was obtained by repeated washing with ultrapure water and anhydrous ethanol.

[0028] Figure 2TEM images of rGO-Au@CdS composite material, wherein, a figure is the morphology image of Au@CdS core-shell structure monomer, b, c, d figure corresponds to the morphology image of different size of reduced graphene oxide and Au@CdS composite material S1, S2, S3 formed in preparation reaction for 5, 6, 7 hours.

[0029] As shown in Figure 2 The composite of Au@CdS core-shell structure and reduced graphene oxide improves the agglomeration phenomenon of the core-shell structure. In the image, the yarn structure of reduced graphene oxide is obvious and the surface is smooth. The Au@CdS core-shell structure grows uniformly on the surface of reduced graphene oxide. With the increase of reaction time, the size of the core-shell structure gradually increases from about 30 nm at 5 hours to about 45 nm at 6 hours, and to about 60 nm at 7 hours. It shows that the composite of core-shell structure and graphene does not affect the original growth process and structure morphology of Au@CdS core-shell structure. From the wrinkles on the surface of reduced graphene oxide, it can be seen that the connection between the core-shell structure and graphene is tight. It is judged that the preparation scheme of coupling Au@CdS core-shell structure on the surface of reduced graphene oxide is feasible, and the result is successful.

[0030] Nonlinear property test experiment of reduced graphene oxide and Au@CdS composite material ((rGO-Au@CdS composite material)):

[0031] The nonlinear optical properties of the composite were systematically studied by Z-scan test using a Nd:YAG mode-locked laser (EKSPLA, PL2251) to generate 532 nm wavelength, 30 ps pulse width, and 10 Hz repetition frequency pulsed laser. The concentration of all samples was 0.1 mg / mL. The nonlinear properties of reduced graphene oxide and Au@CdS composite material can be inferred from the Z-scan test results. Figure 3 A is the open aperture Z-scan normalized transmittance data of reduced graphene oxide, reduced graphene oxide gold nanoparticle sol, and Au@CdS core-shell structure; Figure 3 B is the open aperture Z-scan normalized transmittance data of reduced graphene oxide and Au@CdS composite material with three different sizes; Figure 3 C is the normalized transmittance data of closed aperture divided by open aperture Z-scan of reduced graphene oxide, reduced graphene oxide gold nanoparticle sol, and Au@CdS core-shell structure; Figure 3 D is the normalized transmittance data of closed aperture divided by open aperture Z-scan of reduced graphene oxide and Au@CdS composite material (rGO-Au@CdS composite material) with three different sizes, wherein S1, S2, S3 are the composite materials maintained for 5 hours, 6 hours, and 7 hours at 130℃ reaction environment temperature, respectively.

[0032] From Figure 3 It can be found in A that both reduced graphene oxide (rGO) and reduced graphene oxide gold colloid (rGO-Au) exhibit nonlinear optical saturable absorption characteristics, but the latter is weaker than the former, while the Au@CdS core-shell structure exhibits obvious nonlinear optical anti-saturable absorption characteristics; in Figure 3 In B, it can be seen that the Z-scan curves of rGO-Au@CdS (S1, S2, S3) as a composite material mainly present a symmetrical valley, and each valley has two shoulder peaks, indicating that the nonlinear optical absorption process changes from saturable absorption to anti-saturable absorption and then returns to saturable absorption with the change of irradiance near the focus. This phenomenon may be caused by the synergistic effect of the coexistence of saturable absorption of reduced graphene oxide and saturable absorption and anti-saturable absorption of Au-CdS. With the increase of growth time, the valley peak becomes deeper and the shoulder peak becomes lower, indicating that with the increase of growth time, the nonlinear optical absorption process of rGO-Au@CdS composite material finally transitions from saturable absorption to anti-saturable absorption. When the shoulder peak is negligible compared with the valley peak, the overall performance of nonlinear optical absorption can be effectively regarded as anti-saturable absorption. Different nonlinear optical absorption characteristics can be used in different practical application fields. Samples with saturable absorption characteristics can be used for Q-switching and mode-locking in pulse lasers, while samples with anti-saturable absorption characteristics can be used for optical switching and optical limiting.

[0033] Figure 3 C and Figure 3 D are the closed aperture Z-scan divided by the open aperture Z-scan results of all samples, reflecting the changes in the nonlinear refractive properties of the samples. All sample data curves show a valley-peak shape, which indicates that all samples have self-focusing properties and their nonlinear refractive indices are positive. The composite material is affected by the synergistic effect from reduced graphene oxide and core-shell structure, and the material's Kerr effect is significantly stronger than that of reduced graphene oxide itself. With the continuous increase of the size of metal-semiconductor composite structure, its coupling with reduced graphene oxide also increases, and the synergistic effect also increases, making the nonlinear refractive index of the composite material continuously increase.

[0034] In the composite, the electrons in the excited state of the core-shell structure can also transfer to rGO, which can affect the carrier relaxation of rGO itself, but is conducive to the nonlinear saturable absorption. Therefore, the nonlinear absorption conversion phenomenon of saturable absorption-unsaturable absorption in the rGO-Au@CdS composite can be attributed to the competition between the absorption of the excited state electrons from the core-shell structure to rGO and the absorption of the excited state electrons of the core-shell structure itself. Under strong light excitation, rGO exhibits saturable absorption properties, and the rGO-Au@CdS composite initially exhibits saturable absorption properties and then converts to unsaturable absorption properties, that is, saturable absorption dominates the nonlinear absorption of the composite at a relatively low intensity of pulsed laser, however, with the further increase of light intensity, the absorption of the excited state becomes dominant, leading to the enhancement of the unsaturable absorption properties of the composite. With the increase of the growth time of the rGO-Au@CdS composite control sample S1, S2 and S3, the size of CdS in the Au@CdS composite structure increases, and the contact area with rGO also increases, which leads to the further increase of the unsaturable absorption intensity of the composite. A qualitative explanation can be given for the nonlinear absorption of the composite, that is, when the excitation light is at a low energy intensity, most of the electrons in the material are in the ground state, and the ground state absorption dominates, and the absorption is linear. When the excitation light is at a high energy intensity, in the rGO-Au@CdS composite, on the one hand, the number of excited state electrons in the Au@CdS core-shell structure increases, and the excited state absorption increases, leading to its obvious unsaturable absorption, on the other hand, some electrons in the excited state of the core-shell structure transfer to rGO, which destroys the relaxation of part of the electrons on the Dirac cone of rGO, further hinders the transition of electrons from the ground state to the excited state in rGO, and is conducive to the formation of saturable absorption in rGO. Because the unsaturable absorption of Au@CdS is weaker than the saturable absorption of rGO, it leads to the saturable absorption in rGO-Au@CdS. With the increase of light intensity, when the light intensity is higher, the unsaturable absorption of Au@CdS begins to exceed the saturable absorption of rGO, so the unsaturable absorption in rGO-Au@CdS dominates. However, because of the saturable absorption effect of rGO, the total unsaturable absorption in rGO-Au-CdS cannot exceed the unsaturable absorption of Au-CdS. Because the saturable absorption intensity exhibited by the composite structure is weaker than that exhibited by rGO, the composite initially exhibits saturable absorption properties, but as the size of the semiconductor material in the composite structure increases, the nonlinear absorption of the composite structure gradually dominates the overall performance of the nonlinear absorption of the composite.

[0035] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several changes and improvements can be made without departing from the overall concept of the present application, and these should also be considered as the protection scope of the present application.

Claims

1. A method for Au@CdS modulating nonlinear optical properties of reduced graphene oxide, characterized in that: The method comprises the following steps of: Firstly, graphene oxide is prepared by using an improved Hummers method; Secondly, a reduced graphene oxide gold nanoparticle sol solution is prepared; 50 mL of 0.1 mg / mL graphene oxide suspension is mixed with 0.5 mL of 0.25 mmol chloroauric acid; 1.5±0.1 g of trisodium citrate and 0.0037±0.0001 g of sodium borohydride are added to 50 mL±2 mL ultrapure water, and the solution is stirred uniformly, 2 mL of the solution is extracted, and the mixed solution of graphene oxide and chloroauric acid is added, and the solution is ultrasonically stirred at room temperature for 30±0.6 min, and then is left to stand for 120±2.4 min, and then 0.01±0.001 mL of hydrazine hydrate is added, and the solution is continuously stirred at 90±2 ℃ for 60±1.2 min, and finally, the reduced graphene oxide gold nanoparticle sol solution is obtained after the solution is cooled; Finally, a reduced graphene oxide and Au@CdS composite material is synthesized; A Cys / Cd mixture with a molar concentration of 10 mmol is prepared by using cadmium nitrate and cysteine, the molar concentration ratio of Cys to Cd is kept at 2:1, and the acid-base property of the two mixtures is adjusted by adding ammonia, then 5 mL of the Cys / Cd2 mixture is added to 10 mL of the reduced graphene oxide gold nanoparticle sol solution prepared in the previous step, and 15 mL of ultrapure water is added to dilute the mixture, and after ultrasonic stirring, the obtained mixture is transferred to a polytetrafluoroethylene liner in a stainless steel reaction kettle with a capacity of 50 mL, and finally, the reaction kettle is placed in a constant-temperature drying box, and is kept at a reaction environment temperature of 130±2.5 ℃ for 5-7 hours, and after natural cooling, the reduced graphene oxide and Au@CdS composite material is obtained by repeatedly washing with ultrapure water and anhydrous ethanol.

2. A rGO-Au@CdS composite material prepared by the method of claim 1.

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