Application of a Polymer Carbon Dots in Visual Response to Lead Ions

Abstract

The present invention discloses an application of polymer carbon dots in the visual response to lead ions. The polymer carbon dots are synthesized in one step by a hydrothermal reaction method using natural polymer sodium alginate (SA) and o-phenylenediamine (oPDA) as carbon sources. The operation is simple and the repeatability is good. The synthesized polymer carbon dots can achieve an obvious visual response to lead ions at a certain concentration.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorescent carbon nanomaterials, and specifically relates to an application of polymer carbon dots in the visual response of lead ions. Background Art

[0002] Since lead ions are common pollutants in the industrial production process, and lead ions are likely to accumulate and cause poisoning in the body, leading to serious physical harm, the detection of lead ions has always been the research focus of heavy metal ion monitoring. In recent years, some new analytical technologies with high selectivity and sensitivity have been used for the detection of lead ions, such as nuclear magnetic resonance, electrochemical sensing, and chemiluminescence. The newly developed nanomaterials are also combined with nucleic acid localization technology to improve the detection sensitivity. However, these technologies often require complex operations and expensive instruments, which hinder their practical applications in the detection of lead ions.

[0003] Fluorescent carbon dots (CDs) are a new type of carbon nanomaterial. Compared with toxic organic fluorescent dyes and expensive metal-based quantum dots, CDs have received increasing attention due to their wide sources, easy synthesis, low toxicity, and excellent optical properties. Although some reported CDs have good detection potential as nanosensing materials and can be effectively used for the detection of heavy metal lead ions, they all have some limitations. The concept and formation mechanism of polymer carbon dots (CPDs) were first proposed by Yang et al. (Tao S, Feng T, Zheng C, et al. Carbonized polymer dots: a brand new perspective to recognize luminescent carbon-based nanomaterials[J]. The Journal of Physical Chemistry Letters, 2019, 10(17): 5182 - 5188.). Such polymer carbon dots not only inherit the excellent chemical stability and high luminescence performance of traditional carbon dots, but also form a polymer chain outer structure, making them have good biocompatibility and adsorption. The excellent properties of polymer carbon dots are mainly due to the polymer carbon sources and additives with different structures. Among various organic nitrogen sources that can be used to prepare nitrogen-doped CPDs, disubstituted aniline compounds have unique structural advantages. First, due to the two substituted amine groups on the benzene ring in the carbonized cross-linked structure, they can play a role in connecting flexible polymer chains and form a charge transfer interface between the phenyl group and the carbon heteroatom bond, which is beneficial to the generation of new energy levels and thus helps the tunable luminescence behavior of CPDs. On the other hand, the presence of hydrophilic groups such as amino and hydroxyl groups makes CPDs have good complexing ability and biocompatibility, and can produce strong interfacial interactions with metal ions, thus greatly expanding the application fields of CPDs.

[0004] Alginate is a natural polysaccharide polymer rich in functional groups such as -COOH and -OH on its surface, and is mostly used in the development of nano-composites and drug-loaded particles with excellent performance. Zhao et al. (Sun J, Yu J, Jiang Z, et al. Fluorescent carbonized polymer dots prepared from sodium alginate based on the CEE effect [J]. ACS omega, 2020, 5(42): 27514-27521) synthesized fluorescent CPDs by chemically cross-linking sodium alginate with glutaraldehyde, and successfully prepared an SG-CPD film with stable anti-ultraviolet aging performance (SG represents the abbreviation of sodium alginate SA and glutaraldehyde). However, there is no report on directly using alginate as a polymer carbon source to obtain luminescent carbonized polymer dots with special luminescent properties for the visual identification of lead ions. Summary of the Invention

[0005] The purpose of the present invention is to provide an application of polymer carbon dots in the visual response to lead ions. The polymer carbon dots are prepared by a one-step hydrothermal reaction method using natural polymer sodium alginate (SA) and o-phenylenediamine (oPDA) as carbon sources. The operation is simple, the repeatability is good, and the synthesized polymer carbon dots can achieve an obvious visual response to lead ions at a certain concentration.

[0006] To achieve the above purpose, the solution of the present invention is as follows:

[0007] An application of polymer carbon dots in the visual response to lead ions, wherein the polymer carbon dots are alginate-based polymer carbon dots (SA-oPDA CPDs) prepared by a one-step hydrothermal reaction method using sodium alginate and o-phenylenediamine as carbon sources. The polymer carbon dots have a visual response to lead ions at a micromolar concentration in a solution environment with a pH of 6-8. When the solution of the polymer carbon dots is excited at a wavelength of 352 nm, the fluorescence emitted by the solution changes from blue to blue-green before and after binding to lead ions.

[0008] An application of polymer carbon dots in the visual response to lead ions, wherein the method for the visual response to lead ions includes the following steps:

[0009] Step 1, prepare the polymer carbon dots;

[0010] Step 2, prepare a solution of the polymer carbon dots with ultrapure water, and then add a B-R buffer solution to the solution of the polymer carbon dots to control the pH environment of the solution to 1-12;

[0011] Step 3: Then, add aqueous solutions of lead ions with different concentrations to the solution of the polymer carbon dots obtained in Step 2, and make up the volume to 10 mL with ultrapure water to obtain the test solution.

[0012] Step 4: Measure the fluorescence spectra of the solution of the polymer carbon dots and the test solution, as well as the fluorescence phenomenon under ultraviolet lamp irradiation, before and after adding the aqueous solution of lead ions, respectively.

[0013] In Step 1, the preparation method of the polymer carbon dots is as follows: Mix sodium alginate and o-phenylenediamine in a certain proportion, place them in an ultrasonic oscillator until completely dissolved, then adjust the pH value of the solution to 3 - 12 with hydrochloric acid and sodium hydroxide solution, make up the volume to 15 mL, seal it in the PTFE inner lining of the reaction kettle, and place it in an oven at 140 - 220 °C for reaction for 2 - 12 h to obtain the crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder is obtained, which is the polymer carbon dots.

[0014] In Step 1, the mixing ratio of sodium alginate and o-phenylenediamine is 1:2 - 4:1.

[0015] In Step 1, the best mixing ratio of sodium alginate and o-phenylenediamine is 2:1.

[0016] In Step 1, the pH value of the solution is 4.

[0017] In Step 1, the reaction temperature of the oven is 160 °C.

[0018] In Step 1, the reaction time is 10 h.

[0019] In Step 2, the solution of the polymer carbon dots is 1 g / L.

[0020] In Step 3, the concentration of lead ions in the test solution is 3.0×10 -6 ~7.5×10 -5 mol / L, and the aqueous solution of lead ions is prepared by diluting the national standard lead solution purchased from the National Testing Center for Steel Materials, Central Iron and Steel Research Institute.

[0021] After adopting the above technical solution, for the application of a polymer carbon dot in the visual response of lead ions in the present invention, the polymer carbon dot is an alginate-based polymer carbon dot prepared by a hydrothermal reaction method using sodium alginate and o-phenylenediamine as carbon sources, and has the following advantages:

[0022] 1. The obtained polymer carbon dots have excitation wavelength independence and stable luminescence performance. The Stokes shift can reach 110 nm, and they have stronger luminescence performance than the carbon dots synthesized from a single carbon source. The fluorescence quantum yield is 16.9%.

[0023] 2. The obtained polymer carbon dots show tunable positive and negative charge conversion on the particle surface with the change of pH in the solution environment. When the fluorescence emission peak of the corresponding solution changes from acidic to alkaline, a blue shift of about 40 nm occurs.

[0024] 3. After the obtained polymer carbon dots bind to lead ions at a micromolar concentration in a solution environment with pH = 6 - 8, under the irradiation of an ultraviolet lamp, the fluorescence emitted by the solution changes from blue to blue - green, enabling an obvious visual response to lead ions at a certain concentration. Brief Description of the Drawings

[0025] Figure 1 This is the optical property characterization diagram of the polymer carbon dots of the present invention. Among them, (a) is the spectral characteristic diagram of SA CPDs and SA - oPDA CPDs (the inset is the solution image of the polymer carbon dots before and after irradiation with an ultraviolet lamp), and (b) is the FT - IR spectral characterization diagram of oPD - CDs, SA CPDs, and SA - oPDA CPDs;

[0026] Figure 2 This is the transmission electron microscopy result diagram of the polymer carbon dots of the present invention. Among them, (a) is the transmission electron microscopy image, and (b) is the particle size distribution histogram;

[0027] Figure 3 This is the XPS spectrum diagram of the polymer carbon dots of the present invention;

[0028] Figure 4 This is the fluorescence spectrum diagram of SA - oPDA CPDs in B - R buffer solutions with different pH values

[0029] Figure 5 This is the response trend diagram of the fluorescence signal of the polymer carbon dots with different concentrations of lead ions in B - R buffer solutions with different pH values;

[0030] Figure 6 This is the fluorescence spectrum diagram of SA - oPDA CPDs with different concentrations of lead ions in a B - R buffer solution with pH = 6.80. Among them, (a) is the fluorescence spectrum diagram, (b) is the relative fluorescence intensity change trend diagram, and (c) is the change trend diagram of the fluorescence emission wavelength with the concentration of Pb 2+ concentration. Detailed Embodiments

[0031] In order to further explain the technical solution of the present invention, the present invention will be elaborated in detail through specific embodiments below.

[0032] I. Optimization of the Preparation of Polymer Carbon Dots

[0033] 1.1 Ratio of Reactants

[0034] Sodium alginate and o-phenylenediamine were mixed in the proportions shown in Table 1. After being placed in an ultrasonic bath until completely dissolved, the pH value of the solution was adjusted to 4 with hydrochloric acid and sodium hydroxide solution, made up to 15 mL in volume, sealed in the PTFE liner of a reaction kettle, and placed in an oven at 160 °C for reaction for 10 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder was obtained, which was the polymer carbon dots.

[0035] 1.2 Dosage of reactants

[0036] Sodium alginate and o-phenylenediamine were mixed in a ratio of 2:1. The specific dosages are shown in Table 1. After being placed in an ultrasonic bath until completely dissolved, the pH value of the solution was adjusted to 4 with hydrochloric acid and sodium hydroxide solution, made up to 15 mL in volume, sealed in the PTFE liner of a reaction kettle, and placed in an oven at 160 °C for reaction for 10 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder was obtained, which was the polymer carbon dots.

[0037] 1.3 Reaction temperature

[0038] 0.1 g of sodium alginate and 0.05 g of o-phenylenediamine were mixed. After being placed in an ultrasonic bath until completely dissolved, the pH value of the solution was adjusted to 4 with hydrochloric acid and sodium hydroxide solution, made up to 15 mL in volume, sealed in the PTFE liner of a reaction kettle, and placed in an oven at 140 - 220 °C for reaction for 10 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder was obtained, which was the polymer carbon dots.

[0039] 1.4 Reaction time

[0040] 0.1 g of sodium alginate and 0.05 g of o-phenylenediamine were mixed. After being placed in an ultrasonic bath until completely dissolved, the pH value of the solution was adjusted to 4 with hydrochloric acid and sodium hydroxide solution, made up to 15 mL in volume, sealed in the PTFE liner of a reaction kettle, and placed in an oven at 160 °C for reaction for 2 - 12 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder was obtained, which was the polymer carbon dots.

[0041] 1.5 pH of the reaction solution

[0042] Ten portions of 0.1 g of sodium alginate and 0.05 g of o-phenylenediamine were weighed in parallel. After being placed in an ultrasonic bath until completely dissolved, the pH values of the reaction solutions were adjusted to 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 respectively with 1 mol / L HCl and 1 mol / L NaOH solutions, made up to 15 mL in volume, sealed in the PTFE liner of a reaction kettle, and placed in an oven at 160 °C for reaction for 10 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder was obtained, which was the polymer carbon dots.

[0043] 1.6 Experimental Results

[0044] The prepared polymer carbon dots were dissolved in pure water to prepare a carbon dot solution, and the fluorescence spectra were measured respectively with slit (Ex / Em) being 5.0 nm / 5.0 nm. The results are shown in Table 1:

[0045] ① As the amount of o-phenylenediamine (oPDA) increased, the fluorescence intensity of the prepared carbon dot solution first increased and then decreased. When the mass ratio of sodium alginate (SA) to oPDA was 2:1, the fluorescence intensity of the prepared carbon dots was the strongest. Therefore, the optimal mass ratio of SA to oPDA was selected as 2:1.

[0046] ② When the amount of SA reached 0.05 g and the amount of oPDA reached 0.025 g, the emission peak position and fluorescence intensity tended to level off. When the amount of SA was 0.1 g and the amount of oPDA was 0.05 g, the fluorescence of the prepared polymer carbon dots was the strongest.

[0047] ③ As the synthesis temperature increased, the fluorescence intensity of the synthesized polymer carbon dots gradually increased and leveled off above 160 °C. Therefore, 160 °C was selected as the optimal reaction temperature for synthesis.

[0048] ④ When the reaction time was 10 h, the fluorescence intensity of the polymer carbon dots reached the highest. Therefore, 10 h was selected as the optimal reaction time.

[0049] ⑤ As the pH value of the reaction solution changed, when the reaction was carried out under the condition of pH = 4, the fluorescence intensity of the polymer carbon dot solution was the highest. After the pH value increased to 5, the fluorescence intensity decreased sharply. Along with the transition from pH = 4 to pH = 5, the fluorescence emission peak position of the carbon dots changed significantly from 468 nm to 424 nm, with a blue shift of up to 40 nm. Therefore, in order to obtain SA-oPDA CPDs with high and stable fluorescence intensity, pH = 4 was selected as the optimal reaction pH value.

[0050] Table 1 Influence of reaction conditions on the fluorescence properties of carbon dot solution

[0051]

[0052]

[0053] II. Optical Property Characterization of Polymer Carbon Dots

[0054] The spectral characteristics of the polymer carbon dots prepared under the condition of pH = 4 were investigated, as Figure 1 shown, where SA CPDs are carbon dots synthesized with sodium alginate as the single carbon source, oPD-CDs are carbon dots synthesized with o-phenylenediamine as the single carbon source, and SA-oPDACPDs are the polymer carbon dots of the present invention, as Figure 1As shown in (a), when excited at a wavelength of 352 nm, SA-oPDA CPDs have the strongest fluorescence emission peak at 462 nm, and the Stokes shift can reach 110 nm. The luminescence intensity of this polymer carbon dots is about 4 times stronger than that of SA-CPDs synthesized with sodium alginate as the single carbon source under the same conditions. Using quinine sulfate as a reference, the fluorescence quantum yield of SA-oPDA CPDs was measured to be 16.9%. The infrared spectrum of the SA-oPDA CPDs solution ( Figure 1 (b)) shows that the CPDs formed during the carbonization process have a structure similar to aniline.

[0055] III. Structure and Morphology Characterization of Polymer Carbon Dots

[0056] The size and morphology of SA-oPDA CPDs were studied by high-resolution transmission electron microscopy (TEM). As Figure 2 shown, the results indicate that the CPDs are easily and uniformly dispersed in water, and the microscopic morphology is spherical without an obvious lattice structure. The results of X-ray photoelectron spectroscopy (XPS) (as Figure 3 shown) confirm that the surface of SAPD-CPDs is rich in carboxyl, hydroxyl, and amino groups, which is consistent with the results of FT-IR analysis. The comprehensive results show that the reactive carbon source forms polymer carbon dots with a particle size of about 3.21 nm and a large number of carboxyl and amine groups coexisting on the surface through a hydrothermal reaction at high temperature.

[0057] IV. Visual Response of Polymer Carbon Dots to Lead Ions

[0058] 4.1 Experimental Method

[0059] Step 1: Weigh 0.1 g of sodium alginate and 0.05 g of o-phenylenediamine, place them in an ultrasonic oscillator until completely dissolved, adjust the pH value of the reaction solution to 4 with 1 mol / L HCl and 1 mol / L NaOH solutions, make the volume up to 15 mL, seal it in the PTFE liner of the reaction kettle, and place it in an oven at 160 °C for 10 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder is obtained, which is the polymer carbon dots (SA-oPDA CPDs);

[0060] Step 2: Dissolve the above polymer carbon dot powder in ultrapure water to prepare a 1 g / L polymer carbon dot (SA-oPDA CPDs) solution. Pipette 200 μL of the above SA-oPDA CPDs solution, add 3 mL of B-R buffer solution with different pH values to control the solution pH to 1 - 12, specifically 1.81, 2.87, 3.78, 4.78, 5.72, 6.80, 7.96, 8.95, 9.91, 10.88, 11.82;

[0061] Step 3: Then add lead ion aqueous solutions within different concentration ranges, and make up the volume to 10 mL with ultrapure water to obtain the test solutions, where the concentration of lead ions is 3.0×10 -6 ~7.5×10 -5 mol / ;

[0062] Step 4: Measure the fluorescence spectra of the polymer carbon dot solution and the test solutions before and after adding the lead ion aqueous solutions, as well as their fluorescence phenomena under ultraviolet lamp irradiation respectively.

[0063] In Step 3, the lead ion aqueous solution is prepared by diluting the national standard lead solution purchased from the National Testing Center for Iron and Steel Materials, Central Iron and Steel Research Institute.

[0064] 4.2 Experimental Results

[0065] It is found through fluorescence phenomenon observation that under the alkaline condition of pH = 7.96, the polymer carbon dot solution shows blue under the irradiation of ultraviolet light at 352 nm, and the fluorescence emission spectrum position of the solution is about 420 nm. When Pb with a concentration of 3×10 -5 mol / L is introduced, 2+ the color of the test solution visibly changes to blue-green, and the fluorescence emission spectrum position of the solution is about 460 nm.

[0066] Therefore, the influence of different pH solution environments on the response experiment is investigated, and the results are as Figure 4 and Figure 5 shown. When performing fluorescence tests on the influence of lead ions on the carbon dot solution in an alkaline solution environment with pH = 6 - 8, there is an obvious quenching effect on the fluorescence signal. Under the condition of pH = 6.80, SA-oPDA CPDs show the most obvious response to a series of changes in the concentration of Pb 2+ concentrations.

[0067] When the concentration of lead ions is in the range of 3.0×10 -6 ~7.5×10 -5 mol / L (the specific concentrations are shown in the figure), the fluorescence spectra of the polymer carbon dot solution after the addition of lead ions are as Figure 6 shown. Under the condition of pH = 6.80, when the concentration of lead ions in the test solution changes from 4.0×10 -5 mol / L to 4.85×10 -5 mol / L, the fluorescence emission spectrum position of the solution starts to redshift from 420 nm. When the concentration of lead ions in the test solution is 7.41×10 -5When it is [[mol / L]], the fluorescence emission position redshifts to 460 nm, and the visualization of the lead ion content can be realized. As the concentration of lead ions increases, the fluorescence intensity of the carbon dots gradually decreases. Multiple model fitting analyses are performed on the change data of the relationship between the relative fluorescence intensity quenching degree and the concentration of lead ions. The change trend of the relationship between the two is most in line with the fitting result of the nonlinear DoswResp equation, and the correlation coefficient is 0.9983. This indicates that the process of the surface groups of the polymer carbon dots synthesized in the present invention binding to lead ions involves various coordinated actions such as the penetration of ions in the solution and the adsorption and complexation with carbon dots. After binding, the fluorescence signal of the carbon dots is quenched.

[0068] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by those of ordinary skill in the art shall be regarded as not departing from the patent scope of the present invention.

Claims

1. Application of a polymer carbon dot in the visual response to lead ions, characterized in that: The polymer carbon dots are alginate-based polymer carbon dots prepared by a one-step hydrothermal reaction method using sodium alginate and o-phenylenediamine as carbon sources. The polymer carbon dots have a visual response to lead ions with a concentration of 3.0×10 -6 ~7.5×10 -5 mol / L in a solution environment with a pH of 6 to 8. When the solution of the polymer carbon dots is excited at a wavelength of 352 nm, the fluorescence emitted by the solution changes from blue to blue-green before and after binding to lead ions.

2. The application of a polymer carbon dot in the visual response of lead ions according to claim 1, wherein: The method for visual response to lead ions includes the following steps: Step 1: Prepare the polymer carbon dots; Step 2: Prepare a solution of the polymer carbon dots with ultrapure water, and then add a B-R buffer solution to the solution of the polymer carbon dots to control the pH environment of the solution to 1-12; Step 3: Then add aqueous solutions of lead ions with different concentrations to the solution of the polymer carbon dots obtained in Step 2, and make up the volume to 10 mL with ultrapure water to obtain a test solution; Step 4: Measure the fluorescence spectra of the solution of the polymer carbon dots and the test solution before and after adding the aqueous solution of lead ions, as well as the fluorescence phenomenon under ultraviolet lamp irradiation, respectively.

3. The application of a polymer carbon dot in the visual response of lead ions according to claim 2, wherein: In Step 1, the preparation method of the polymer carbon dots is as follows: Mix sodium alginate and o-phenylenediamine in a certain proportion, place them in an ultrasonic oscillator until completely dissolved, then adjust the pH value of the solution to 3-12 with hydrochloric acid and sodium hydroxide solution, make up the volume to 15 mL, seal it in the PTFE liner of a reaction kettle, and place it in an oven at 140-220 °C for reaction for 2-12 h to obtain a crude product. After dialysis purification, vacuum concentration, and freeze-drying in sequence, a solid powder is obtained, which is the polymer carbon dots.

4. The application of a polymer carbon dot in the visual response to lead ions according to claim 3, characterized in that: In Step 1, the mixing ratio of sodium alginate and o-phenylenediamine is 1:2-4:

1.

5. Use of a polymer carbon dot in the visual response to lead ions according to claim 3, characterized in that: In Step 1, the mixing ratio of sodium alginate and o-phenylenediamine is 2:

1.

6. The application of a polymer carbon dot in the visual response to lead ions according to claim 3, characterized in that: In Step 1, the pH value of the solution is 4.

7. Use of a polymer carbon dot in the visual response of lead ions according to claim 3, characterized in that: In Step 1, the reaction temperature of the oven is 160 °C.

8. The application of a polymer carbon dot in the visual response of lead ions according to claim 3, characterized in that: In Step 1, the reaction time is 10 h.

9. The application of a polymer carbon dot in the visual response to lead ions according to claim 2, characterized in that: In Step 2, the concentration of the solution of the polymer carbon dots is 1 g / L.

10. The application of a polymer carbon dot in the visual response of lead ions according to claim 2, wherein: In step 3, the concentration of lead ions in the solution to be measured is 3.0×10 -6 ~7.5×10 -5 mol / L.

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