Tartaric acid-functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI), preparation method thereof, and antibacterial application thereof

Abstract

The invention discloses a tartaric acid functionalized fluorescent carbon quantum dot for Cr (VI) dual-channel detection and oxidation removal and its preparation method and antibacterial application, which belongs to the field of chromium metal detection technology; by mixing tartaric acid and tryptophan and dissolving them in ultrapure water, transferring them to an autoclave after uniform dispersion and heating to obtain a reaction mixture; after the reaction mixture is cooled to room temperature, the supernatant in the mixture is transferred to a centrifuge tube for balancing and centrifuging, and the supernatant after centrifugation is filtered; the filtered filtrate is continuously stirred and dialyzed in ultrapure water, and then tartaric acid functionalized fluorescent carbon quantum dots are prepared by freeze drying. The tartaric acid functionalized fluorescent carbon quantum dots (TA-CQDs) prepared by the present invention show excellent water solubility, strong anti-interference ability and excellent photostability, and have potential application value in Cr (VI) detection and antibacterial.

Description

Technical Field

[0001] The present invention belongs to the technical field of chromium metal detection, and relates to tartaric acid functionalized fluorescent carbon quantum dots for Cr(VI) dual-channel detection and oxidation removal, as well as a preparation method and antibacterial application thereof. Background Art

[0002] Chromium is one of the most common heavy metal pollutants in industrial wastewater. It exists in two main oxidation states: trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). Cr(III) is a trace element essential for biological processes due to its low toxicity, while Cr(VI) exists in the body's cellular environment mainly as chromate oxyanions (CrO4 - ) exists in the form of sulfate oxyanion (SO4) - Because Cr(VI) is very similar to Cr(VI), it can enter cells via general sulfate transporters on the cell surface. Once inside the cell, Cr(VI) exerts its toxic effects after being reduced by ascorbate and biothiols, such as glutathione (GSH) or cysteine ​​amino acid residues. The stepwise two-electron reduction of ascorbate produces a Cr(IV) intermediate that is ultimately converted to Cr(III). During this step, particularly during GSH reduction, quantitative hydrogen peroxide and other free radical species are generated, resulting in high levels of oxidative stress and damage to cellular lipids, proteins, and DNA. Furthermore, adding ascorbate to the cell culture medium to increase the intercellular concentration reduces overall oxidative stress but induces DNA double-strand breaks following the formation of ternary DNA complexes containing Cr(III) cross-linked to histidine, cysteine, ascorbate, or GSH. These various bulky chromium-containing DNA complexes are difficult to repair and are the primary cause of chromium-induced malignant cell transformation.

[0003] Therefore, the World Health Organization (WHO) recommends that the maximum allowable limit for Cr(VI) discharge into inland surface waters is 0.1 mg / L (100 ppb), while the maximum limit for discharge into drinking water is 0.05 mg / L (50 ppb). Similarly, the U.S. Environmental Protection Agency recommends that the concentration of Cr(VI) in drinking water should be lower than 0.1 mg / L (100 ppb). Therefore, it is very important to detect the migration characteristics and cumulative effects of Cr(VI) in water samples to avoid the harmful effects of Cr(VI) on human health.

[0004] At present, there are many relatively mature methods for the accurate detection of Cr(VI), such as electrochemical method, atomic absorption spectrometry, high performance liquid chromatography-inductively coupled plasma mass spectrometry, and ion chromatography-inductively coupled plasma mass spectrometry. However, due to the expensiveness of the instruments, these methods are very limited in practical applications. Therefore, it is urgent to develop a material and method that is low-cost, stable, and capable of accurately detecting Cr(VI). Summary of the Invention

[0005] The purpose of the present invention is to provide a tartaric acid functionalized fluorescent carbon quantum dot for dual-channel detection and oxidation removal of Cr(VI) and its preparation method and antibacterial application, so as to solve the technical problems of high cost and poor stability of the existing detection methods.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention discloses a method for preparing tartaric acid-functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI), comprising the following steps:

[0008] The organic acid and amino acid solid powders are mixed uniformly, heated to perform a melting reaction, and after the reaction is completed, they are added to ultrapure water, dispersed uniformly, and transferred to a high-pressure reactor, heated, and reacted to obtain a reaction mixture;

[0009] After the reaction mixture is cooled to room temperature, the supernatant in the mixture is transferred to a centrifuge tube, balanced and centrifuged, and the supernatant after centrifugation is filtered;

[0010] The filtered filtrate was frozen and placed in a vacuum freeze dryer for drying. The dried solid was dissolved in methanol and eluted through a Sephadex LH-20 column with a ratio of chloroform to methanol of 1:2. The eluate was vacuum-dried to obtain an oily substance. The oily substance was continuously stirred and dialyzed in ultrapure water, and then freeze-dried to prepare tartaric acid-functionalized fluorescent carbon quantum dots.

[0011] Furthermore, the ratio of the added amounts of the organic acid, amino acid and ultrapure water is: (0.1g~0.4g): (0.1g~0.4g): (20ml~80ml); the organic acid is tartaric acid, succinic acid, salicylic acid or gallic acid; and the amino acid is tryptophan or 5-methyltryptophan.

[0012] Furthermore, the reaction temperature of the melt reaction is 145° C. to 155° C., and the reaction time is 2 h to 6 h; the dispersion method is ultrasonic dispersion; and the high-pressure reactor is a 50 mL Teflon-lined high-pressure reactor.

[0013] Furthermore, the reaction temperature is 140° C. to 190° C., and the reaction time is 4 h to 12 h.

[0014] Furthermore, the centrifugal speed is 8000 r / min and the centrifugal time is 10 min.

[0015] Furthermore, the filtering step is performed using a 0.22 μm microporous membrane; the step of freezing the filtered filtrate and then placing it in a vacuum freeze dryer for drying is specifically as follows: placing the filtrate in a -80°C refrigerator for 2 hours, and then placing it in a vacuum freeze dryer for 48 hours for drying.

[0016] Furthermore, the ultrapure water used in the dialysis process has a MWCO of 500 Da.

[0017] Furthermore, the dialysis duration is 8 hours, and the water is changed every 2 hours during the dialysis process.

[0018] In the second aspect, the present invention discloses a tartaric acid functionalized fluorescent carbon quantum dot for dual-channel detection and oxidation removal of Cr(VI), which is prepared by the above-mentioned preparation method of tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI).

[0019] In a third aspect, the present invention discloses an application of the above-mentioned tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) in Cr(VI) detection and antibacterial.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention discloses a tartaric acid functionalized fluorescent carbon quantum dot for dual-channel detection and oxidation removal of Cr(VI), its preparation method and antibacterial application. Tartaric acid functionalized fluorescent carbon quantum dots (TA-CQDs) were successfully prepared by a hydrothermal method using organic acid and amino acid reaction precursors. They exhibit excellent water solubility, strong anti-interference ability and excellent photostability. The functionalized groups present on the surface of the TA-CQDs of the present invention can react specifically with Cr(VI), thereby achieving high selectivity and high sensitivity detection of Cr(VI). TA-CQDs show excellent linearity in the detection of Cr(VI), with a linear range of 0.5-200μM and a detection limit of 0.51μM (S / N=3). In addition, TA-CQDs have the ability to achieve high-precision determination of Cr(VI) in tap water. TA-CQDs provide a new tool for the quantitative detection of Cr(VI) and have potential application value for the detection of Cr(VI) in tap water and industrial wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 The effect of the embodiment of the present invention on the QY of the TA-CQDs system is shown in FIG. Figure 1 A is the effect of reaction time on the QY of TA-CQDs system, Figure 1 B is the effect of reaction temperature on the QY of TA-CQDs system, Figure 1 C is the effect of the reactant ratio on the QY of the TA-CQDs system;

[0024] Figure 2 This is a microscopic image of TA-CQDs in an embodiment of the present invention. Figure 2 A is the TEM image of TA-CQDs with a magnification of 50000x and a scale bar of 100 nm. Figure 2 B is the TEM image of TA-CQDs with a magnification of 200000x and a scale bar of 20 nm. Figure 2 C is the HRTEM image of TA-CQDs with a magnification of 800000x and a scale bar of 5 nm (inset: lattice spacing annotation). Figure 2 D is the particle size distribution;

[0025] Figure 3 FT-IR spectra of TA, L-Try, and TA-CQDs of the embodiments of the present invention;

[0026] Figure 4 A is the full XPS spectrum of TA-CQDs in the embodiment of the present invention, Figure 4 B is the high-resolution C1s spectrum. Figure 4 C is the high-resolution N1s spectrum. Figure 4 D is the high-resolution O1s spectrum;

[0027] Figure 5 A is the UV-visible absorption, fluorescence excitation and emission spectra of TA-CQD in the embodiment of the present invention, Figure 5 B is the CIE coordinate diagram of TA-CQDs, Figure 5 C is the fluorescence spectra of TA-CQDs at different excitation wavelengths;

[0028] Figure 6 A is the fluorescence intensity of TA-CQDs under continuous irradiation of a xenon lamp in an embodiment of the present invention, Figure 6 B is the effect of pH on the fluorescence intensity of TA-CQDs, Figure 6C is the effect of ionic strength on the fluorescence intensity of TA-CQDs;

[0029] Figure 7 The relative fluorescence intensity F / F0 of the selectivity and anti-interference of TA-CQDs to inorganic salt ions (700 μM) in the embodiment of the present invention;

[0030] Figure 8 A is the fluorescence spectrum of TA-CQDs with different concentrations of Cr(VI) added to the samples of the present invention. Figure 8 B is the regression fitting between F0-F and 0-700 μM concentration of Cr(VI), Figure 8 C is the regression fit between F0-F and 0-200 μM concentration of Cr(VI);

[0031] Figure 9 A is the UV-vis spectrum of Cr(VI) and the fluorescence absorption and emission spectra of TA-CQDs in the embodiment of the present invention, Figure 9 B is the fluorescence absorption-emission three-dimensional spectrum of TA-CQDs, Figure 9 C is the UV absorption spectra of TA-CQDs and TA-CQDs@Cr(VI) (D) fluorescence decay curves of TA-CQDs and TA-CQDs@Cr(VI);

[0032] Figure 10 This is a schematic diagram of the photodynamic antibacterial activity of TA CQDs in an embodiment of the present invention. Figure 10 A is the AGAR plate image of Staphylococcus aureus and Escherichia coli colonies under different conditions. Figure 10 B is the relative survival rate of Escherichia coli and Staphylococcus aureus, Figure 10 C is the SEM image of Escherichia coli and Staphylococcus aureus. DETAILED DESCRIPTION

[0033] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0034] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0035] Herein, all features such as values, amounts, amounts, and concentrations defined in numerical ranges or percentage ranges are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0036] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0037] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0038] The present invention is described in further detail below with reference to the accompanying drawings:

[0039] The present invention discloses a method for preparing tartaric acid-functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI), comprising the following steps:

[0040] S1, mixing organic acid and amino acid solid powders uniformly, heating to perform a melting reaction, adding the mixture to ultrapure water after the reaction is completed, dispersing the mixture uniformly, transferring the mixture to a high-pressure reactor, heating and reacting to obtain a reaction mixture; after the reaction mixture is cooled to room temperature, transferring the supernatant in the mixture to a centrifuge tube, balancing the mixture, and centrifuging the mixture, and filtering the supernatant after centrifugation;

[0041] In this step, the ratio of the organic acid, amino acid, and ultrapure water added is: (0.1g-0.4g): (0.1g-0.4g): (20ml-80ml). The organic acid is tartaric acid, succinic acid, salicylic acid, or gallic acid; the amino acid is tryptophan or 5-methyltryptophan. The melt reaction is performed at a temperature of 145-155°C and for a time of 2-6 hours. Ultrasonic dispersion is preferred. The autoclave is a 50mL Teflon-lined autoclave. The reaction temperature within the autoclave is 140-190°C and the reaction time is 4-12 hours.

[0042] S2, after the reaction mixture is cooled to room temperature, the supernatant in the mixture is transferred to a centrifuge tube, balanced and centrifuged, and the supernatant after centrifugation is filtered;

[0043] In this step, the centrifugal speed is 8000 r / min and the centrifugal time is 10 min. Filtering the supernatant after centrifugation specifically includes: filtering with a 0.22 μm microporous membrane.

[0044] S3, the filtered filtrate is frozen and placed in a vacuum freeze dryer for drying, the dried solid is dissolved in methanol, and eluted through a Sephadex LH-20 column with chloroform: methanol = 1:2. The eluate is vacuum-dried to obtain an oily substance; the oily substance is continuously stirred and dialyzed in ultrapure water, and then freeze-dried to prepare tartaric acid-functionalized fluorescent carbon quantum dots.

[0045] In this step, the step of freezing the filtered filtrate and then placing it in a vacuum freeze dryer for drying is specifically: freezing the filtrate in a -80°C refrigerator for 2 hours, and then placing it in a vacuum freeze dryer for 48 hours for drying. The step of continuously stirring and dialyzing the filtered filtrate in ultrapure water is specifically: continuously stirring and dialyzing the filtrate in ultrapure water with a MWCO of 500Da for 8 hours, changing the water every 2 hours.

[0046] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0047] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0048] Example 1:

[0049] Tartaric acid (0.1 g, 0.67 mmol) and tryptophan (0.1 g, 0.49 mmol) were mixed uniformly, heated to 145°C for a 2-hour melt reaction, cooled to room temperature, added to 20 mL of ultrapure water, and ultrasonically dispersed. The mixture was then transferred to a 50 mL Teflon-lined autoclave and heated in an oven to 160°C before a 10-hour timer reaction. After heating, the mixture was cooled to room temperature. The supernatant was transferred to a centrifuge tube, balanced, and centrifuged at 8000 rpm for 10 minutes. The supernatant was filtered through a 0.22 μm microporous membrane. For further purification, the filtrate was frozen at -80°C for 2 hours and placed in a vacuum freeze dryer for 48 hours to obtain a solid. The solid was dissolved in methanol and eluted with 800 ml of chloroform and methanol using a Sephadex LH-20 column in a ratio of 1:2. The eluate was vacuum-dried to obtain an oily substance, which was then dispersed and dissolved by ultrasonication at 20°C. The oil was then dialyzed in ultrapure water with a MWCO of 500 Da for 8 hours with continuous stirring, changing the water every 2 hours. Finally, a solid powder of TA-CQDs was prepared by freeze drying and stored under low-temperature dry conditions for future use.

[0050] Example 2:

[0051] Salicylic acid (0.1 g) and tryptophan (0.2 g) were mixed uniformly, heated to 150°C for a 5-hour melt reaction, cooled to room temperature, added to 30 mL of ultrapure water, and ultrasonically dispersed. The mixture was then transferred to a 50 mL Teflon-lined autoclave and heated in an oven to 150°C before a 6-hour timer reaction. After heating, the mixture was cooled to room temperature. The supernatant was transferred to a centrifuge tube, balanced, and centrifuged at 8000 rpm for 10 minutes. The supernatant was filtered through a 0.22 μm microporous membrane. For further purification, the filtrate was frozen at -80°C for 2 hours and placed in a vacuum freeze dryer for 48 hours to obtain a solid. The solid was dissolved in methanol and eluted with 800 ml of chloroform and methanol using a Sephadex LH-20 column in a ratio of 1:2. The eluate was vacuum-dried to obtain an oily substance, which was then dispersed and dissolved by ultrasonication at 20°C. The oil was then dialyzed in ultrapure water with a MWCO of 500 Da for 8 hours with continuous stirring, changing the water every 2 hours. Finally, a solid powder of TA-CQDs was prepared by freeze drying and stored under low-temperature dry conditions for future use.

[0052] Example 3:

[0053] Tartaric acid (0.1 g) and 5-methyltryptophan (0.4 g) were mixed uniformly, heated to 145°C for a 4-hour melt reaction, cooled to room temperature, added to 50 mL of ultrapure water, and ultrasonically dispersed. The mixture was then transferred to a 50 mL Teflon-lined autoclave and heated in an oven to 170°C before a timed reaction of 8 hours. After heating, the mixture was cooled to room temperature. The supernatant was transferred to a centrifuge tube, balanced, and centrifuged at 8000 rpm for 10 minutes. The supernatant was filtered through a 0.22 μm microporous membrane. For further purification, the filtrate was frozen at -80°C for 2 hours and placed in a vacuum freeze dryer for 48 hours to obtain a solid. The solid was dissolved in methanol and eluted with 800 ml of chloroform and methanol using a Sephadex LH-20 column in a ratio of 1:2. The eluate was vacuum-dried to obtain an oily substance, which was then dispersed and dissolved by ultrasonication at 20°C. The oil was then dialyzed in ultrapure water with a MWCO of 500 Da for 8 hours with continuous stirring, changing the water every 2 hours. Finally, a solid powder of TA-CQDs was prepared by freeze drying and stored under low-temperature dry conditions for future use.

[0054] Example 4:

[0055] Tartaric acid (0.2 g) and tryptophan (0.1 g) were mixed uniformly, heated to 155°C for a 6-hour melt reaction, cooled to room temperature, added to 30 mL of ultrapure water, and ultrasonically dispersed. The mixture was then transferred to a 50 mL Teflon-lined autoclave and heated in an oven to 180°C before a 12-hour timer reaction. After heating, the mixture was cooled to room temperature. The supernatant was transferred to a centrifuge tube, balanced, and centrifuged at 8000 rpm for 10 minutes. The supernatant was filtered through a 0.22 μm microporous membrane. For further purification, the filtrate was frozen at -80°C for 2 hours and placed in a vacuum freeze dryer for 48 hours to obtain a solid. The solid was dissolved in methanol and eluted with 800 ml of chloroform and methanol using a Sephadex LH-20 column in a ratio of 1:2. The eluate was vacuum-dried to obtain an oily substance, which was then dispersed and dissolved by ultrasonication at 20°C. The oil was then dialyzed in ultrapure water with a MWCO of 500 Da for 8 hours with continuous stirring, changing the water every 2 hours. Finally, a solid powder of TA-CQDs was prepared by freeze drying and stored under low-temperature dry conditions for future use.

[0056] Determination of fluorescence quantum yield by reference method:

[0057] A substance with similar absorption and emission wavelengths to the analyte and a known fluorescence quantum yield was selected. Quinine sulfate was used as a reference. The integrated fluorescence intensity of quinine sulfate and TA-CQDs and the absorbance at the same excitation wavelength were measured at the same excitation wavelength. The fluorescence quantum yield (QY) of TA-CQDs can be calculated by substituting the following formula:

[0058]

[0059] Where, represents the QY of the sample to be tested, the subscripts "1" and "2" represent quinine sulfate and TA-CQDs, respectively, "A" is the absorbance of the sample to be tested, "F" is the integrated fluorescence intensity of the sample to be tested, and "n" is the refractive index of the sample to be tested. According to the literature, the quantum yield of quinine sulfate is 54% at an excitation wavelength of 365 nm.

[0060] Optimization of reaction conditions:

[0061] In order to obtain the best performance of the TA-CQDs system, the reactant ratio, reaction temperature, reaction time and QY yield were optimized. First, the reactant ratio was optimized. Considering the TA:L-Try mass ratio, the feed ratios were 4:1, 2:1, 1:1, 1:2 and 1:4, respectively. Figure 1 As shown in C, when the feed ratio is 1:1, QY reaches the maximum value. Therefore, this experiment uses TA:L-Try1:1 feed. The effect of TA-CQDs reaction time on QY is studied. Figure 1 It can be seen from A that QY reaches a high value when the reaction time is 4 h and then decreases. It reaches a peak when the reaction time reaches 10 h and then decays. Therefore, 10 h is selected for the reaction. In addition, the effect of the reaction temperature of TA-CQDs is also studied. Figure 1 As shown in B, the subsequent experiments selected 160°C for reaction.

[0062] Characterization of TA-CQDs:

[0063] TA-CQDs were prepared in deionized water at a concentration of 6 mg / mL as a stock solution for subsequent use.

[0064] Three-dimensional scanning was performed using an F-970 fluorescence spectrophotometer (Shanghai, China). A UV-2310 UV-visible spectrophotometer from Shimadzu Corporation (Japan) was used with a scanning range of 400 nm to 800 nm, a slit width of 1.5 mm, and a scanning rate of 800 nm min. -1Fourier transform infrared spectroscopy (FT-IR) was performed by placing the TA-CQDs powder on a Frontier PerkinElmer FT-IR spectrometer with a scanning wavenumber range of 4000 to 400 cm-1. For transmission electron microscopy (TEM), TA-CQDs were sonicated in ultrapure water and then drop-coated on a copper grid coated with a carbon film, and then photographed using a Japan-JEOL-JEM 2100 at an accelerating voltage of 200 kV. TA-CQDs powder was deposited on a Thermo Scientific ESCALAB 250Xi using an alα excitation x-ray source (1487.2 eV) with an analysis chamber of 8×10 -8 X-ray photoelectron spectroscopy was performed at mbar with an X-ray spot size of 650 μm. Fluorescence lifetime measurements were performed on a Horiba Fluorologic-QM using an EPL laser (LED, 445 nm).

[0065] In order to observe its TEM surface morphology, TEM was used to characterize the surface morphology and size of TA-CQDs. Figure 2 A. Figure 2 B and Figure 2 As shown in Figure C, TEM images reveal that the TA-CQDs exhibit a quasi-spherical structure and good monodispersity. HRTEM measurements show a lattice spacing of 0.23 nm for the TA-CQDs, with a size distribution between 1.2 nm and 2.6 nm, and an average particle size of 1.74 nm.

[0066] like Figure 3 3300cm shown -1 The overtone peaks are OH stretching vibration, NH bending vibration, 3381cm -1 NH stretching vibration can be inferred that the prepared TA-CQDs contain hydroxyl and amino groups; 3080 cm -1 is the CH stretching vibration on the benzene ring, and 1631 cm -1 The stretching vibration of the CC skeleton of the benzene ring is 1456 cm -1 、1415cm -1 The benzene ring carbon CH plane is bent, 1355cm -1 The C—C stretching vibration and the C—H bending vibration of the benzene ring carbon can prove that TA-CQDs contain the benzene ring group in L-Try; 1720 cm -1 The carboxyl stretching vibration can be inferred to be contained in TA-CQDs; by querying the fingerprint peak spectrum at 1132 cm -1 and 1067cm -1 Mainly CH, OH, NH bending vibration, 744cm -1The CC skeleton vibration of the benzene ring can be used to determine the substitution structure on the benzene ring, 676cm -1 The OH bending vibration next to the carboxyl group can further infer that the TA-CQDs contain the involved structure and the indole structure is not destroyed.

[0067] From the XPS spectrum Figure 4 A shows that TA-CQD is mainly composed of C, N, and O elements, with atomic ratios of 58.2%, 2.44%, and 39.33%, respectively. High-resolution C1s spectrum Figure 4 B exhibits four peaks at 284.35 eV, 285.00 eV, 286.20 eV, and 288.485 eV, primarily representative of CC, CN, CO, and C=O functional groups. High-resolution N1s spectrum 4C illustrates the presence of three nitrogen dopants: graphitic N (399.70 eV), amino N (400.95 eV), and indolic N (401.60 eV). High-resolution O1s spectrum 4D exhibits three peaks at 531.10 eV, 532.15 eV, and 533.50 eV, corresponding to CO, COC=O, C=O, C-OH, and COC bonds, respectively.

[0068] In summary, XPS spectra show that TA-CQDs have abundant functional groups such as –NH2, –OH, and –COOH. Analysis of these functional groups shows that TA-CQDs have high polarity, are easy to form hydrogen bonds, have good water solubility, and are easily oxidized by Cr(VI).

[0069] The present invention studies the optical properties of TA-CQDs by UV-visible detection method. Figure 5 As shown in A, TA-CQDs exhibit two absorption peaks at around 220nm and 277nm, originating from the π-π* transition in the sp2 structure of the aromatic ring skeleton. At the same time, a broad peak is found near 351nm, corresponding to the n-π* transition of C=O / CN. Figure 5 From the fluorescence spectrum in A, we can see that the optimal excitation and emission wavelengths of TA-CQDs are 375nm and 445nm. At the same time, the fluorescence emission spectrum data of TA-CQDs are input into the CIE diagram. Figure 5 In the BCIE chromaticity diagram, the coordinates of the maximum emission intensity are (0.1495, 0.0617), further indicating the blue fluorescence of GCQD. In addition, when the excitation wavelength is shifted from 330nm to 400nm, the fluorescence intensity first increases and then decreases, while the emission wavelength remains almost unchanged ( Figure 5 C).

[0070] Stability of TA-CQDs:

[0071] Photobleaching resistance: 4 mL of 150 μg / mL TA-CQDs aqueous solution was prepared for the photobleaching resistance experiment and irradiated continuously for 60 min using a 150 W xenon lamp (Ex = 400 nm). The fluorescence spectrum was continuously monitored.

[0072] Salt resistance: Prepare a series of 4 mL TA-CQDs aqueous solutions with a concentration of 150 μg / mL and NaCl concentrations of 0, 10 -4 mol / L, 10 -3 mol / L, 10 -2 mol / L, 10 -1 mol / L, 1mol / L aqueous solution, and measured their fluorescence spectra respectively.

[0073] Acid and alkali resistance: A series of 4 mL aqueous solutions of TA-CQDs with a concentration of 150 μg / mL were prepared. The pH of the solutions was adjusted to 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 using NaOH and HCl, and their fluorescence spectra were measured.

[0074] Excitation wavelength dependence: A series of 4 mL aqueous solutions of TA-CQDs with a concentration of 150 μg / mL were prepared. Fluorescence spectrophotometry and three-dimensional fluorescence spectrum scanning were performed to obtain spectra of their excitation wavelength, emission wavelength, and fluorescence intensity.

[0075] Photobleaching experiments were performed on TA-CQDs. Figure 6 A shows that when the fluorescence intensity of the TA-CQDs solution was continuously irradiated for 60 minutes with a xenon lamp at Ex = 400nm and a power of 150w, it was found that the fluorescence intensity was very stable, and the fluorescence intensity at 60 minutes remained at 100.56% of the original intensity. The experiment shows that TA-CQDs have strong resistance to photobleaching and photostability. At the same time, the effect of pH on the fluorescence intensity of TA-CQDs was explored. Figure 6 B shows that the fluorescence intensity gradually decreases from 2 to 10, which may be caused by the deprotonation of the carboxyl group. However, the effect of pH on the fluorescence intensity is not significant, and the pH stability of TA-CQDs is relatively strong. The present invention also studies the ability of TA-CQDs to resist inorganic salts, such as Figure 6 As shown in Figure C, TA-CQDs can still maintain more than 87.7% of their initial fluorescence intensity in a high-salt environment, indicating that the fluorescence stability of TA-CQDs is strong.

[0076] Evaluation of selectivity and interference of TA-CQDs:

[0077] Mother solutions of common metal ions (NaCl, AgCl, ZnCl2, PbCl2, MgCl2, CuCl2, CaCl2, MnCl2, CrCl3, CrCl6) were prepared respectively, and the TA-CQDs content in the test solution was adjusted to 150 μg / mL and the cation concentration to 700 μmol / L. After ultrasonic mixing of the above solutions, their fluorescence spectra were measured respectively.

[0078] At the same time, after introducing different 100 μL of the above metal ion mother liquors into a 5 mL centrifuge tube, 100 μL of CrCl(VI) solution was added to a series of solutions except the Cr6+ solution, and then 3.7 ml of distilled water and 100 μL of TA-CQDs solution (6 mg / mL) were added to the centrifuge tube. At this time, the TA-CQDs content in the test solution was 150 μg / mL, except for Cr6+, the concentration of other cations was 700 μmol / L, and the Cr(VI) concentration was 700 μmol / L. After ultrasonic mixing of the above solutions, their fluorescence spectra were measured respectively.

[0079] The selectivity and anti-interference properties of TA-CQDs are also important factors in evaluating the sensing system. Figure 7 The present invention evaluates 10 inorganic salt ions (Na + 、Ag + 、Zn 2+ , Pb 2+ Mg 2+ 、Cu 2+ , Ca 2+ 、Mn 2+ Cr 3+ Cr 6+ ) on the optical properties of TA-CQDs. The results showed that only Cr(VI) could significantly quench the fluorescence of TA-CQDs. At the same time, when interfering ions were added to the mixture of TA-CQDs and Cr(VI), the fluorescence sensing system of TA-CQDs was also negligible. Therefore, it can be concluded that TA-CQDs show potential practicality and are fluorescent probes that can be used to detect Cr(VI) in complex real samples.

[0080] Quantitative response of TA-CQDs to Cr(VI):

[0081] A series of test solutions were prepared in 5 mL centrifuge tubes using deionized water, where the TA-CQDs concentration was 150 μg / mL and the Cr(VI) concentration was 0-700 μmol / L. The fluorescence spectra were measured and recorded.

[0082] The present invention studies the quantitative response performance of TA-CQDs to Cr(VI). Figure 8As shown in A, the fluorescence signal of TA-CQDs decreases with the increase of Cr(VI) concentration. Figure 8 B shows that the fluorescence intensity decreases linearly in the concentration range of 0-700 μM. After linear regression, the regression equation is F0-F=15.95[Cr 6+ ]+862.8(R 2 =0.9613). However, when the concentration was within the range of 0-200 μM, the linearity was significantly improved, and the regression equation was F0-F=24.53[Cr 6+ ]+21.13(R 2 =0.9982)( Figure 8 C), and its detection limit calculated based on 3δ / k was 0.51 μM (S / N=3).

[0083] Detection mechanism of TA-CQDs:

[0084] A 1.5 mg / mL TA-CQDs aqueous solution and a 28 mmol / L Cr(VI) solution were prepared.

[0085] (1) The fluorescence absorption and emission spectra of TA-CQDs diluted to 150 μg / mL were measured, and the UV absorption spectrum of Cr(VI) diluted to 700 μmol / L was measured.

[0086] (2) Measure the three-dimensional fluorescence spectrum of TA-CQDs diluted to 150 μg / mL.

[0087] (3) TA-CQDs were diluted to a final concentration of 150 μg / mL and prepared to a final concentration of 0 and 10 μg / mL of Cr(VI). -1 , 10 -3 , 10 -5 mol / L, UV absorption spectrum.

[0088] (4) Measure the fluorescence decay curve of TA-CQDs diluted to 150 μg / mL.

[0089] Test results such as Figure 9 As shown in Figure A, Cr(VI) exhibits an absorption peak at 365 nm, which overlaps with the absorption peak of TA-CQDs. Therefore, the excitation wavelength of TA-CQDs can be absorbed by Cr(VI), resulting in the fluorescence of TA-CQDs being quenched by Cr(VI) absorption. This significant spectral overlap may be caused by fluorescence resonance energy transfer (FRET) or the strong internal filtering effect (IFE) between TA-CQDs and Cr(VI).

[0090] The absorption spectra of CDs before and after adding Cr(VI) were measured, and the results are as follows: Figure 9As shown in Figure B, only the absorption peak of TA-CQDs overlapping with Cr(VI) changes significantly, and no other peaks are generated or changed, indicating that no ground state complex is formed, that is, there is no static quenching.

[0091] In order to further verify the quenching mechanism of TA-CQDs on Cr(VI), the lifetimes of TA-CQDs without Cr(VI) and with Cr(VI) were measured. The results are shown in Figure 2. Figure 9 As shown in C. Although there is almost no change between TA-CQDs and TA-CQDs-Cr(VI), dynamic quenching and FRET can be excluded. In summary, the fluorescence quenching of TA-CQDs by Cr(VI) is attributed to IFE.

[0092] Application in actual sample testing:

[0093] It is used to detect Cr(VI) in tap water samples. A 4mmol / L Cr(VI) standard solution was prepared, and 160μL and 320μL of the standard concentration were pipetted into 5ml centrifuge tubes, 400μL of TA-CQDs solution (1.5mg / mL) was pipetted, and the volume was filled to 4.0ml with tap water. In the resulting series of test solutions, the concentration of TA-CQDs was 150μg / mL and the concentration of Cr(VI) was 80 and 160μmol / L. The PL spectra were measured, and the recovery rate and RSD were calculated.

[0094] To further evaluate the accuracy of TA-CQDs as a fluorescent sensor in complex environments, they were used to detect Cr(VI) in tap water samples. The tap water was centrifuged (8000 rpm, 10 min) and then filtered through a 0.22 μM membrane to obtain the supernatant. Cr(VI) solutions at standard concentrations (80 and 160 μmol / L) were added to the actual samples to evaluate recovery and accuracy (n = 3).

[0095] Table 1 Detection of Cr(VI) in actual samples

[0096]

[0097] As shown in Table 1, sample recoveries ranged from 98.2% to 104.9%, with relative standard deviations (RSDs) below 5%, demonstrating that TA-CQDs exhibited high recovery and accuracy for Cr(VI) detection. This provides a potential new method for the detection of Cr(VI) in complex samples and offers potential guidance for wastewater testing and disease prevention in the environment.

[0098] Application of light-induced antibacterial

[0099] The present invention studies the photodynamic antibacterial activity of TA CQDs. Figure 10As shown, (I) blank control, (II) UV / 4 min, (III) TA CQD, (IV) TA CQD+UV / 2 min, (V) TA CQDs+UV / 4 min; As we all know, reactive oxygen species (ROS), such as H2O2,·OH, and 1 O2, has strong oxidative properties and can cause oxidative damage to bacterial organelles or directly kill bacteria, thereby achieving a rapid bactericidal effect. Studies have shown that TA-CQDs exhibit oxidase-like activity and can produce a large amount of Therefore, it has significant advantages as an antibacterial material. First, the cytotoxicity of TA CQDs was evaluated by CCK-8 assay. The results showed that even at a concentration of 200 μg / mL, the cell viability remained at around 97.33%, indicating that TA CQDs are environmentally friendly and have excellent biocompatibility. In addition, the antibacterial effect of TA CQDs against Escherichia coli and Staphylococcus aureus was studied by agar plate counting method. Figure 10 As shown in Figure A. The experimental results showed that the use of TA CQDs (150 μg / mL) or 4 minutes of low-power UV LED alone had no significant antibacterial effect on the two bacteria. However, when TA CQDs and low-power light sources were combined, the viability of Escherichia coli and Staphylococcus aureus decreased significantly by 97.33% and 82.67%, respectively. Figure 10 As shown in Figure B; To further evaluate the antibacterial properties of TA CQDs, we used scanning electron microscopy (SEM) to observe the microstructural changes of Escherichia coli and Staphylococcus aureus under different conditions, as shown in Figure 2. Figure 10 C. Notably, compared to the blank control, under the photocatalytic action of TA-CQDs, the bacteria exhibited significant cell morphology collapse and deformation, as well as leakage and accumulation of intracellular substances. In summary, TA-CQDs with oxidase-like activity exhibit excellent broad-spectrum antibacterial properties through photocatalytic generation of ROS, and have broad research and application prospects in antibacterial fields such as food, environment, and biology.

[0100] The present invention uses tartaric acid and L-tryptophan as reaction precursors and successfully prepares tartaric acid functionalized fluorescent carbon quantum dots (TA-CQDs) by a hydrothermal method. It exhibits excellent water solubility, strong anti-interference ability and excellent photostability. Studies have confirmed that the functional groups present on the surface of TA-CQDs can react specifically with Cr(VI), thereby achieving highly selective and highly sensitive detection of Cr(VI), and further speculated its fluorescence detection and quenching principles. TA-CQDs show excellent linearity in the detection of Cr(VI), with a linear range of 0.5-200μM and a detection limit of 0.51μM (S / N=3). In addition, TA-CQDs have the ability to achieve high-precision determination of Cr(VI) in tap water. TA-CQDs provide a new tool for the quantitative detection of Cr(VI) and have potential application value in the detection of Cr(VI) in tap water and industrial wastewater.

[0101] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI), characterized in that: The following steps are involved: The organic acid and amino acid solid powders are mixed uniformly, heated to perform a melting reaction, and after the reaction is completed, added to ultrapure water, uniformly dispersed, transferred to a high-pressure reactor, heated and reacted to obtain a reaction mixture, the reaction temperature is 160° C. to 190° C., and the reaction time is 4 h to 12 h. The addition ratio of the organic acid, amino acid and ultrapure water is: (0.1 g to 0.4 g): (0.1 g to 0.4 g): (20 ml to 80 ml); the organic acid is tartaric acid; and the amino acid is tryptophan or 5-methyltryptophan. After the reaction mixture is cooled to room temperature, the supernatant in the mixture is transferred to a centrifuge tube, balanced and centrifuged, and the supernatant after centrifugation is filtered; The filtered filtrate was frozen and placed in a vacuum freeze dryer for drying. The dried solid was dissolved in methanol and eluted through a Sephadex LH-20 column with a chloroform: methanol ratio of 1:

2. The eluate was vacuum-dried to obtain an oily substance. The oily substance was continuously stirred and dialyzed in ultrapure water, and then freeze-dried to prepare tartaric acid-functionalized fluorescent carbon quantum dots.

2. The method for preparing tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to claim 1, wherein: The reaction temperature of the melt reaction is 145° C. to 155° C., and the reaction time is 2 h to 6 h. The dispersion method is ultrasonic dispersion. The high-pressure reactor is a 50 mL Teflon-lined high-pressure reactor.

3. The method for preparing tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to claim 1, wherein: The centrifugal speed is 8000 r / min and the centrifugal time is 10 min.

4. The method for preparing tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to claim 1, wherein: The filtering step uses a 0.22 μm microporous membrane for filtration; the step of freezing the filtered filtrate and then placing it in a vacuum freeze dryer for drying is specifically: placing the filtrate in a refrigerator at -80°C for 2 hours, and then placing it in a vacuum freeze dryer for 48 hours for drying.

5. The method for preparing tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to claim 1, wherein: The ultrapure water used in the dialysis process had a MWCO of 500 Da.

6. The method for preparing tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to claim 1, wherein: The dialysis time was 8 h, and the water was changed every 2 h during the dialysis process.

7. A tartaric acid functionalized fluorescent carbon quantum dot for dual-channel detection and oxidation removal of Cr(VI), characterized in that: The method for preparing tartaric acid-functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to any one of claims 1 to 6 is adopted.

8. Use of the tartaric acid functionalized fluorescent carbon quantum dots for dual-channel detection and oxidation removal of Cr(VI) according to claim 7 in Cr(VI) detection and antibacterial treatment.

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