Preparation method of hydrophobic multi-emitting red light carbon dots / MOF composite

Abstract

The application discloses a preparation method of a hydrophobic multi-emission red light carbon dot / MOF composite, characterized by using a single precursor to directly synthesize hydrophobic red light carbon dots (600-760 nm) with multiple emission peaks without adding any acidic reagent, loading the red light carbon dots in metal organic frameworks (MOF) with different ligand lengths to make the red light carbon dots maintain a fluorescence quantum yield of up to 33.5% and an emission peak red shift of 64.3 nm in a solid phase. The red light carbon dot / MOF composite is soaked in water for 240 days, and the fluorescence intensity can still maintain more than 91% of the initial intensity. Compared with the prior art, the application has the advantages of simplicity and high efficiency, and loading the carbon dots in the organic metal framework to solve the problems of the carbon dots, such as incapability of emitting light in a solid phase and poor stability, thereby providing a new method and a new idea for realizing efficient and simple preparation of the red light carbon dots, solid state light emission, high stability and light emission adjustment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer luminescent material, in particular to a preparation method of hydrophobic multi-emission red light carbon dots / MOF composite. BACKGROUND

[0002] Carbon dots are generally considered as spherical photoluminescent nanoparticles with a diameter less than 10 nm, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), carbon nanodots (CNDs) and polymer dots (CPDs). In recent years, carbon dots have been rapidly developed due to their simple synthesis, good biocompatibility, low cost, adjustable optical properties and other advantages. At present, most of the carbon dots synthesized from precursors only show strong emission in the blue and green ranges, and the types of precursor materials for synthesizing red light carbon dots are relatively few, and the fluorescence quantum yield is low. Red light has a deeper tissue penetration, is not easy to excite biological autofluorescence, and has little light damage to biological samples, and has obvious advantages in the field of biological imaging compared with short-wavelength fluorescence. Therefore, the synthesis of carbon dots with strong red / near-infrared emission is considered to be a key requirement for promoting the practical application of carbon dots in most fields.

[0003] In addition, due to the lack of effective purification means, many synthesized red light carbon dots are accompanied by blue light emission, and have excitation dependence. When the carbon dots are dried into powder, they cannot emit light due to the aggregation quenching effect. Although solid-phase red light carbon dots are synthesized by introducing organic polymers, metal oxides and non-metal oxides as protective media, their water stability is poor and the fluorescence quantum yield is always less than 30%. SUMMARY

[0004] The present application aims to provide a preparation method of hydrophobic multi-emission red light carbon dots / MOF composite to solve the problems in the prior art. The method uses a single precursor to synthesize red light carbon dots with high quantum yield, and uses intermolecular forces to load the carbon dots on MOF. A single precursor is used to directly synthesize hydrophobic red light carbon dots (600-760 nm) with multiple emission peaks without adding any acidic reagents. Metal organic frameworks (MOF) with different ligand lengths are used to load red light carbon dots, so that the carbon dots can maintain a fluorescence quantum yield of up to 33.5% and a red shift of the emission peak of 64.3 nm in solid phase. The red light carbon dots / MOF composite is soaked in water for 240 days, and the fluorescence intensity can still maintain more than 91% of the initial intensity. It is the most stable among the reported carbon dot composite luminescent materials. The method is simple and efficient, and uses organic metal frameworks to load carbon dots to solve the problems of no emission in solid phase and poor stability. It provides a new method and idea for the efficient and simple preparation of red light carbon dots, solid-state emission, high stability and emission adjustment.

[0005] The object of the present invention is achieved as follows: a method for preparing a hydrophobic multi-emitting red light carbon dot / MOF composite, which is characterized by using 2,3-diaminobenzoic acid or 3,4-diaminobenzoic acid as a precursor, utilizing a metal organic framework with different ligand lengths to load red light carbon dots, synthesizing hydrophobic red light carbon dots with multiple emission peaks, achieving solid-state luminescence of the red light carbon dots while adjusting the emission peak position, and the specific preparation comprises the following steps:

[0006] Step 1: Dissolve a single precursor (2,3-diaminobenzoic acid or 3,4-diaminobenzoic acid) in ethanol solution and add it into a high-temperature reactor and react at 180-260°C for 10-18 hours to generate a red-light carbon dot mixed solution.

[0007] Step 2: centrifuge the red fluorescent carbon dot mixed solution obtained in step 1 to obtain a reddish-brown supernatant, add 120-200 ml of deionized water and mix thoroughly, centrifuge again, and pour off the supernatant to obtain a non-luminescent black powder of red carbon dots.

[0008] In step 3, 0.2-2 g of two MOFs (DUT-66 or MIL-53) with different ligand lengths are dispersed in an ethanol solution (0.01 g / L) of the red-emitting carbon dots obtained in step 2. The mixture is rapidly magnetically stirred at 1000-2000 rpm at room temperature for 12-48 hours. The ligand for DUT-66 is biphenyldicarboxylic acid, while the ligand for MIL-53 is terephthalic acid. The solution is centrifuged, the supernatant is decanted, and the red precipitate is vacuum-dried for 12-48 hours. This yields a hydrophobic, multi-emissive red-emitting carbon dot / MOF composite capable of solid-phase luminescence.

[0009] The present invention uses a single precursor to directly synthesize hydrophobic red fluorescent carbon dots without adding other acidic reagents, and uses MOFs with different ligand lengths to load the red light carbon dots, realizing solid-state luminescence of the red light carbon dots while adjusting the emission peak position. The quantum yield of the hydrophobic red light carbon dot / MOF complex is as high as 31.1-33.5%. After the sample is immersed in water for 240 days, its emission intensity is still 91%-92% of the initial value.

[0010] Compared with the prior art, the present invention has the following significant technical effects and beneficial improvements:

[0011] 1) The present invention uses only a single precursor for synthesis without adding an acidic reagent, thereby avoiding the generation of excessive by-products during the reaction.

[0012] 2) Unlike the previous silica gel column chromatography and dialysis methods, the hydrophobicity of the synthesized red-light carbon dots can be simply and efficiently purified by water washing. The operation is simple, the repetition rate is high, and large-scale production can be achieved.

[0013] 3) The application not only solves the problem of solid-state luminescence quenching of red carbon dots, but also basically maintains the luminescence intensity in solution state, and the water stability is greatly improved, and it can be stored stably in air environment.

[0014] 4) The ligand length of MOF has obvious effect on the emission peak position of the complex, and a new idea is proposed for the luminescence adjustment of carbon dots. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A luminescence actuality diagram of the multi-emission red carbon dots prepared in Example 1 dispersed in an ethanol solution under an ultraviolet lamp;

[0016] Figure 2 A TEM diagram of the multi-emission red carbon dots prepared in Example 1;

[0017] Figure 3 An absorption spectrum diagram and an emission spectrum diagram of the multi-emission red carbon dots prepared in Example 1;

[0018] Figure 4 A luminescence actuality diagram of the hydrophobic multi-emission red carbon dots / MOF complex prepared in Examples 1 and 2 under natural light and an ultraviolet lamp;

[0019] Figure 5 A TEM diagram of the hydrophobic multi-emission red carbon dots / MOF complex in Examples 1 and 2;

[0020] Figure 6 An absorption spectrum diagram and an emission spectrum diagram of the hydrophobic multi-emission red carbon dots / MOF complex in Examples 1 and 2;

[0021] Figure 7 Water resistance results of the hydrophobic multi-emission red carbon dots / MOF complex in Example 3. IMPLEMENTATION

[0022] The application will be further described in conjunction with the embodiments and the drawings, but the scope of the application claimed is not limited to the scope indicated by the embodiments. EMBODIMENT

[0023] 0.3 g of 2,3-diaminobenzoic acid was weighed accurately and added into a 50 ml reagent bottle, 30 ml of ethanol solution was added and ultrasonic treatment was performed for 15 min, the solution was transferred into a stainless steel high-pressure reaction kettle, the reaction temperature was 220°C, and the reaction time was 14 h. After the reaction was completed, the oven was turned off and cooled to room temperature. The liquid obtained after the reaction was subjected to centrifugal treatment to obtain a red-brown supernatant, and the centrifugal treatment conditions were 13000 r / min for 15 min. The red-brown supernatant was divided into four portions and added into 50 ml centrifuge tubes, and 35 ml of deionized water was added respectively. The red-brown solution gradually changed into a brown solution, and centrifugal treatment was continued, and the treatment conditions were 13000 r / min for 10 min. The black precipitate obtained after centrifugation was added into 35 ml of deionized water again and subjected to centrifugal treatment, and finally black powder of multi-emission red light carbon dots (R-CDs1) was obtained.

[0024] Referring to Figure 1 , the black powder can be completely dissolved in an ethanol solution, and emits bright red light under an ultraviolet lamp.

[0025] Referring to Figure 2 , the particle morphology of R-CDs1 was observed by transmission electron microscopy, and it can be seen that R-CDs1 is uniformly distributed, and the particle size ranges from 2 to 8 nm, and the average size is 4.2 nm.

[0026] Referring to Figure 3 , the excitation light is 540 nm, R-CDs1 has strong absorption in the ultraviolet and visible light regions, and has three emission peaks between 600 and 800 nm, and the main peak is located at 601.2 nm. 0.1 mg of R-CDs1 powder was dispersed in 100 ml of ethanol solution, 1 g of MIL-53 was added, and magnetic stirring was performed at a speed of 2000 r / min at room temperature for 24 h. The obtained solution was subjected to centrifugal treatment at 13000 r / min for 15 min, the upper liquid was poured, and the red precipitate was vacuum dried for 24 h.

[0027] Referring to Figure 4 , the synthesized multi-emission red light carbon dot / MOF composite (MR-CDs1) is a light orange powder under natural light, and emits bright orange under an ultraviolet lamp.

[0028] Referring to Figure 5 , the particle morphology of the synthesized MR-CDs1 was observed by transmission electron microscopy, and it can be found that the carbon dots are uniformly distributed on the surface of MIL-53.

[0029] Referring to Figure 6 , the excitation light is 540 nm, and it can be seen that MR-CDs1 has obvious absorption between 500 and 600 nm, which is derived from the red light carbon dots carried on the MOF. MR-CDs1 retains the original three emission peaks of carbon dots, but the main emission peak has a blue shift of 16.2 nm compared with the pure carbon dot solution. Embodiment

[0030] Embodiment 2 is similar to embodiment 1, using 3,4-diaminobenzoic acid to substitute 2,3-diaminobenzoic acid. Red fluorescent carbon dots (R-CDs2) are obtained by repeating the steps of embodiment 1. Take 0.1 mg of R-CDs2 powder and disperse it in 100 ml of ethanol solution, add 1.5 g of DUT-66, and stir at room temperature at a speed of 1000 r / min for 24 h. Centrifuge the obtained solution at 12000 r / min for 10 min, pour the supernatant, and vacuum dry the red precipitate for 24 h.

[0031] Referring to Figure 4 , the synthesized multi-emission red light carbon dots / MOF composite (DR-CDs1) is a pink powder under natural light and emits bright red light under ultraviolet light.

[0032] Referring to Figure 5 , the particle morphology of the synthesized DR-CDs1 is observed by transmission electron microscopy, and it can be found that the carbon dots are uniformly distributed on the surface of DUT-66.

[0033] Referring to Figure 6 , it can be seen that the DR-CDs1 has a significant absorption between 500 and 600 nm, which is derived from the red light carbon dots carried on the MOF. The DR-CDs1 still retains the original three emission peaks of the carbon dots, but the main emission peak has a red shift of 64.3 nm compared to the carbon dot solution.

[0034] The hydrophobic red light carbon dots / MOF composite of the above embodiments has a quantum yield as high as 31.1-33.5%. Embodiment

[0035] In order to test the water resistance of the prepared multi-emission red light carbon dots / MOF composite, take 0.5 g of MR-CDs1 and DR-CDs1 prepared in embodiments 1 and 2, respectively, and immerse them in 20 mL of room temperature deionized water. Use a fluorescence spectrometer to detect the fluorescence intensity of the powder after immersion for different times under 540 nm excitation, and compare it with the original fluorescence intensity of the composite material.

[0036] Referring to Figure 7 From the change in luminescence intensity of the multi-emission red light carbon dots / MOF composite after immersion in water for 1-240 days, it can be seen that the water resistance of the multi-emission red light carbon dots / MOF composite is greatly improved, making it can be stored stably in air environment. After immersion in water for 240 days, its fluorescence intensity can still remain above 91% of the initial intensity.

[0037] The present application provides a new idea for adjusting luminescence of carbon dots, and has great potential application value in the field of photoelectric devices. The above is only for further illustrating the present application, and is not used to limit the present application patent. Any equivalent implementation of the present application should be included in the scope of the claims of the present application patent.

Claims

1. A method for preparing a hydrophobic multi-emitting red light carbon dot / MOF composite, characterized in that: Using 2,3-diaminobenzoic acid or 3,4-diaminobenzoic acid as a precursor, and utilizing metal organic frameworks with different ligand lengths to load red light-emitting carbon dots, hydrophobic red light-emitting carbon dots with multiple emission peaks are synthesized. The solid-state luminescence of the red light-emitting carbon dots is achieved while adjusting the emission peak position. The specific preparation includes the following steps: Step 1: dissolving 2,3-diaminobenzoic acid or 3,4-diaminobenzoic acid in an ethanol solution and reacting at a temperature of 180-260° C. for 10-18 hours to generate a mixed solution of red-emitting carbon dots, wherein the weight-to-volume ratio of the 2,3-diaminobenzoic acid or 3,4-diaminobenzoic acid to ethanol is 1 g: 0.05-0.5 L; Step 2, centrifuging the mixed solution of red carbon dots at 12000-13000 r / min for 10-15 min to obtain a reddish-brown supernatant; Step 3: Mix the reddish-brown supernatant with deionized water at a ratio of 1:120 to 200 ml, centrifuge at 12,000 to 13,000 r / min for 10 to 15 minutes, pour off the upper layer to obtain a non-luminescent black powder of red-light carbon dots, and mix it with an ethanol solution at a weight-to-volume ratio of 0.01 g: 0.1 to 1 L to prepare a red-light carbon dot solution, which is sealed for later use; Step 4: DUT-66 or MIL-53 is taken as a metal organic framework and mixed with a red light carbon dot solution in a weight volume ratio of 0.2 to 2 g: 1 L. The mixture is magnetically stirred at a speed of 1000 to 2000 r / min at room temperature for 12 to 48 hours. The reacted solution is centrifuged at 12000 to 13000 r / min for 10 to 15 minutes. The upper layer liquid is poured off and the red precipitate is vacuum dried for 12 to 48 hours to obtain a hydrophobic multi-emitting red light carbon dot / MOF complex.

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