Carbon quantum dots using orange peel as carbon source, preparation method and application thereof

Abstract

The present invention provides a carbon quantum dot with orange peel as a carbon source, and a preparation method and application thereof, which belongs to the technical field of testing or analyzing materials by means of measuring the chemical or physical properties of the material. The orange peel is washed and dried to make orange peel powder, the orange peel powder is mixed with distilled water, subjected to hydrothermal reaction, cooled to room temperature, and filtered to obtain carbon quantum dots; the ratio of the orange peel powder to distilled water is 0.5g:20~30ml; the temperature of the hydrothermal reaction is 190~210℃, and the insulation time is 5~7h. The preparation method of the carbon quantum dots is simple, green, environmentally friendly and non-toxic. The carbon quantum dot fluorescent probe can not only detect Fe with high selectivity 3+ , and Fe 3+ Based on the continuous and highly selective detection of L-AA.

Description

Technical Field

[0001] The present invention relates to a carbon quantum dot using orange peel as a carbon source and a preparation method and application thereof, belonging to the technical field of testing or analyzing materials by measuring the chemical or physical properties of the materials, in particular to detecting Fe 3+ And the technical field of preparation of carbon quantum of L-AA. Background Art

[0002] Iron is an indispensable trace element in living organisms. 3+ It plays a vital role in maintaining the balance of cell systems. 3+ Imbalances can damage cellular systems and lead to a range of diseases, including Alzheimer's disease, heart failure, metabolic disorders, and Parkinson's disease. L-Ascorbic acid (L-AA), commonly known as vitamin C, is an essential food-derived nutrient with antioxidant properties that plays a vital role in metabolism and immune system function.

[0003] L-AA is the abbreviation for L-Ascorbic acid, also known as L-ascorbic acid or vitamin C. It is a water-soluble compound widely found in fresh vegetables and fruits, especially citrus fruits. L-AA plays important roles in the human body, including acting as an antioxidant, promoting collagen deposition, inhibiting elasticity production, having anti-cancer effects, and stimulating immune responses. Since the human body cannot synthesize L-AA on its own, it must be met through dietary intake. L-AA deficiency can lead to scurvy, which manifests as brown spots on the skin, spongy gums, and mucous membrane bleeding. In the cosmetics industry, L-AA is also used as an antioxidant and pH adjuster. In addition, L-AA is used as a food additive, providing preservatives and nutritional supplements.

[0004] Currently, Fe 3+ The main methods for detecting L-AA include electrochemical analysis, chromatography, colorimetry, mass spectrometry and fluorescence analysis. Large-scale instrument testing has problems such as high cost and complicated sample pretreatment procedures, while fluorescence analysis has good application prospects due to its simple operation, high detection sensitivity and low time consumption. 3+ Given the important roles of L-AA and L-AA in human health, it is of great significance to develop a fluorescent sensor that can detect these two substances simply, quickly and accurately.

[0005] Carbon quantum dots (CQDs) are a class of carbon nanomaterials with remarkable fluorescent properties. They are composed of nearly spherical, dispersed carbon nanoparticles with diameters less than 10 nm. CQDs have a large surface area and abundant functional groups, which facilitate interactions with other substances. They exhibit excellent fluorescence properties, good water solubility, low toxicity, biocompatibility, and chemical stability, making them excellent fluorescent probes. As fluorescent probes, CQDs offer advantages such as rapidity, simplicity, good selectivity, high sensitivity, and a broad and continuous excitation spectrum. They have been widely used in fields such as food safety, metal ion detection, environmental monitoring, and cell imaging.

[0006] However, there is no Fe that can be detected in the prior art. 3+ and L-AA carbon quantum dots. Summary of the Invention

[0007] The present invention provides carbon quantum dots using orange peel as a carbon source, as well as a preparation method and application thereof, which can effectively solve the above problems.

[0008] The present invention is achieved in that:

[0009] A method for preparing carbon quantum dots using orange peel as a carbon source comprises the following steps: washing and drying the orange peel to prepare orange peel powder, mixing the orange peel powder with distilled water, performing a hydrothermal reaction, cooling to room temperature, and filtering to obtain the carbon quantum dots; the ratio of the orange peel powder to distilled water is 0.5 g: 20-30 ml; the hydrothermal reaction temperature is 190-210° C., and the holding time is 5-7 hours.

[0010] In some embodiments, the drying temperature is 80-100° C. and the drying time is 2-3 days.

[0011] In some embodiments, the filtration is performed through a 0.22 μm microporous membrane.

[0012] The invention relates to carbon quantum dots prepared by the method using orange peel as a carbon source.

[0013] In some embodiments, the particle size of the carbon quantum dots is 2.2-6.2 nm.

[0014] A method for detecting iron ions comprises mixing the carbon quantum dots with a solution containing iron ions, fully reacting the mixture, measuring the fluorescence spectrum intensity, and calculating the concentration of the iron ions according to the change in the fluorescence spectrum intensity.

[0015] In some embodiments, the excitation wavelength of the fluorescence spectrum is 355-365 nm.

[0016] In some embodiments, the detection range of iron ions is 0~90μmol·L -1

[0017] A method for detecting L-ascorbic acid comprises mixing the carbon quantum dots with a solution containing iron ions, allowing the mixture to react fully, and then measuring the fluorescence spectrum. When the fluorescence is quenched, a solution containing L-ascorbic acid is added, and the fluorescence spectrum is measured again. The concentration of the L-ascorbic acid is calculated based on the degree of recovery of the fluorescence intensity.

[0018] In some embodiments, the detection range of L-ascorbic acid is 0~2000 μmol·L -1 .

[0019] The beneficial effects of the present invention are:

[0020] The present invention relates to a method for preparing carbon quantum dots using orange peel as a carbon source. This method is not only simple and easy to implement, but also environmentally friendly and non-toxic. The prepared carbon quantum dots have good solubility in water and exhibit strong fluorescence properties. In addition, these carbon quantum dots show excellent performance stability within the physiological pH range. More importantly, these carbon quantum dots can be used as fluorescent probes, not only capable of highly selectively detecting Fe 3+ ions, and in completing Fe 3+ In addition to the detection of L-ascorbic acid (L-AA), it can also continuously and highly selectively detect L-ascorbic acid (L-AA). This dual detection capability makes this carbon quantum dot fluorescent probe have broad application prospects in fields such as biochemical analysis and environmental monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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.

[0022] Figure 1 This is the morphological structure characterization of the OP-CQDs of Example 2, where a is the TEM image of OP-CQDs; b is the particle size distribution diagram of OP-CQDs.

[0023] Figure 2 Fluorescence excitation and emission spectra of OP-CQDs.

[0024] Figure 3 The selectivity of OP-CQDs in detecting metal ions, where a is the fluorescence spectrum of OP-CQDs under the same concentration of different metal ions; b is the fluorescence response diagram of OP-CQDs at the emission wavelength of 445 nm under the same concentration of different metal ions.

[0025] Figure 4Fe 3+ Detection specificity, where a is the concentration of Fe 3+ Fluorescence spectra of OP-CQDs under the condition of Fe 3+ The concentration is between 10 and 60 μmol·L -1 The fluorescence intensity changes in the range are linearly related to the concentration (emission wavelength is 445 nm).

[0026] Figure 5 The detection of L-AA by OP-CQDs, where a is the OP-CQDs-Fe 3+ Fluorescence spectra of the solution; b is the fluorescence spectrum of L-AA concentration in the range of 0~2000μmol·L -1 The fluorescence intensity changes with the concentration in the range of c is the concentration of L-AA in the range of 5~300μmol·L -1 The fluorescence intensity changes in the range of 1:1 are linearly related to the concentration. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Embodiments of the present invention relate to an innovative preparation method for synthesizing carbon quantum dots using orange peel as a carbon source. Specifically, the present invention provides a simple and efficient technique for obtaining carbon quantum dots (OP-CQDs) with specific properties by subjecting orange peels to a series of processing steps. First, the orange peels are thoroughly cleaned and then dried to remove excess moisture and impurities. The dried orange peels are then ground into a powder, forming orange peel powder.

[0029] Next, the prepared orange peel powder is mixed with distilled water in a specific ratio. In this invention, the ratio is designed to be 0.5 grams of orange peel powder to 20 to 30 milliliters of distilled water. This ratio is chosen to ensure that the orange peel powder fully dissolves and reacts during the subsequent hydrothermal reaction, effectively producing the desired carbon quantum dots.

[0030] The mixed solution is then placed in a sealed reaction vessel for a hydrothermal reaction. A hydrothermal reaction is a chemical reaction carried out under high temperature and high pressure conditions that promotes the transformation of substances and the generation of new substances. In the present invention, the temperature of the hydrothermal reaction is set between 190 and 210 degrees Celsius. This temperature range ensures the smooth progress of the reaction while avoiding side reactions or decomposition of carbon quantum dots caused by excessively high temperatures. In addition, the holding time of the hydrothermal reaction is set to 5 to 7 hours. This time length is to ensure that the carbon source in the orange peel powder can fully react to generate high-quality carbon quantum dots.

[0031] After the hydrothermal reaction, the reaction mixture needs to be cooled to room temperature. The cooling process is carried out slowly to prevent the carbon quantum dots from aggregating or structurally damaging due to a sudden drop in temperature. After cooling is completed, unreacted solid impurities are removed by filtration to obtain a pure carbon quantum dot solution. Finally, through appropriate post-processing steps such as centrifugation, washing, and drying, a pure carbon quantum dot product, namely OP-CQDs, can be obtained.

[0032] In summary, the present invention provides a method for preparing carbon quantum dots using orange peel as a carbon source. This method is not only environmentally friendly and low-cost, but also has high practical value and application prospects. The carbon quantum dots prepared by this method have broad application potential in optoelectronics, bioimaging, sensors and other fields.

[0033] In some embodiments, the drying temperature is 80-100° C. and the drying time is 2-3 days.

[0034] In certain specific embodiments, the filtration process is performed by using a 0.22 micron microporous membrane to ensure that impurities and particles in the solution are effectively removed.

[0035] The present invention provides carbon quantum dots prepared by the aforementioned specific method, wherein the carbon source is primarily derived from orange peel. In this process, the orange peel undergoes a series of chemical reactions and processing steps, ultimately transforming it into carbon quantum dots with unique properties. In certain embodiments, these carbon quantum dots exhibit excellent performance and characteristics.

[0036] In these embodiments, the prepared carbon quantum dots have a specific particle size range, ranging from 2.2 nanometers to 6.2 nanometers. This particle size range enables these carbon quantum dots to perform well in optical, electronic and chemical applications. Due to their tiny size, these carbon quantum dots have a high surface area to volume ratio, thus having broad application prospects in fields such as catalysis, sensors and bioimaging. In addition, carbon quantum dots made from orange peels are not only environmentally friendly but also cost-effective, providing new ideas for sustainable development.

[0037] Embodiments of the present invention provide a method for detecting iron ion concentration. Specifically, the method involves mixing carbon quantum dots with a solution containing iron ions. After mixing, the mixture is allowed to react for a period of time to ensure complete reaction. After the reaction is complete, further analysis is performed by measuring the fluorescence spectrum intensity of the mixed solution. By analyzing the changes in the fluorescence spectrum intensity, the specific concentration of iron ions in the solution can be calculated.

[0038] The detailed explanation of the detection mechanism of iron ion concentration is as follows: On the surface of OP-CQDs, there are a large number of active groups such as hydroxyl, amino and carboxyl groups. These groups play a key role on the surface of OP-CQDs. Specifically, these groups may interact with Fe through electronic transitions. 3+ The d orbitals of ions interact with each other. This interaction leads to the interaction between OP-CQDs and Fe 3+ Chelation between ions. Chelation is a special chemical reaction in which a molecule or ion binds to a central metal ion through multiple coordination bonds to form a ring structure. In this process, the fluorescence properties of OP-CQDs may be suppressed. In other words, when Fe 3+ When ions chelate with the active groups on the surface of OP-CQDs, this combination interferes with the electronic transition process of OP-CQDs, causing its fluorescence intensity to weaken or disappear. This phenomenon can be used to detect Fe 3+ The presence and concentration of ions.

[0039] In certain specific embodiments, to achieve optimal detection results, the excitation wavelength of the fluorescence spectrum is set between 355 and 365 nanometers. By selecting this specific wavelength range, the intensity and stability of the fluorescence signal can be ensured, thereby improving the accuracy and reliability of the detection.

[0040] In addition, in some embodiments, the detection method can cover the iron ion concentration range of 0 to 90 μmol·L -1This means that this method can detect not only low concentrations of iron ions but also iron ions in a higher concentration range, thus having a wide range of applications and high practicality. This method can conveniently and accurately quantify iron ions at different concentrations.

[0041] Embodiments of the present invention provide a method for detecting L-ascorbic acid (vitamin C) content. This method involves mixing carbon quantum dots with a solution containing iron ions and ensuring a sufficient chemical reaction occurs between the two. After the reaction is complete, the fluorescence spectrum of the mixed solution is measured to assess the reaction. Specifically, a significant decrease or quenching of the fluorescence intensity indicates that a complex has formed between the carbon quantum dots and the iron ions.

[0042] Next, a sample solution containing L-ascorbic acid is added to the mixed solution. L-ascorbic acid reacts with iron ions, thereby affecting the stability of the carbon quantum dot-iron ion complex. By measuring the fluorescence spectrum again, changes in fluorescence intensity can be observed. If the fluorescence intensity recovers, it indicates that the presence of L-ascorbic acid has caused the iron ions to be released from the complex.

[0043] According to the degree of fluorescence intensity recovery, the concentration of L-ascorbic acid can be quantitatively calculated. In some specific embodiments, the detection method can cover the range from 0 to 2000 μmol·L -1 This method can accurately determine the L-ascorbic acid content in samples, providing an effective detection method for food, pharmaceutical, and biological sample analysis.

[0044] The detailed description of the detection mechanism of L-ascorbic acid (vitamin C) content is as follows: 3+ In the system, when L-AA (L-ascorbic acid) is added, L-AA will react with Fe 3+ Oxidation-reduction reaction occurs. In this process, L-AA acts as a reducing agent to reduce Fe 3+ Reduction to Fe 2+ , and L-AA itself is oxidized. 3+ The decrease in the amount of L-AA leads to the destruction of the interaction between OP-CQDs (graphene oxide quantum dots) that originally interacted with it. The destruction of this interaction leads to the recovery of some of the suppressed fluorescence signals in the system. Therefore, by monitoring the changes in the fluorescence intensity of the system, the concentration of L-AA can be indirectly reflected, thereby achieving the quantitative detection of L-AA. This process not only reveals the interaction between OP-CQDs and Fe 3+ The interaction mechanism between them is also studied, and the potential of using this interaction change to detect specific substances is demonstrated.

[0045] Example 1: A method for preparing carbon quantum dots using orange peel as a carbon source

[0046] First, fresh Gannan navel orange peels were placed in a beaker and thoroughly washed with distilled water. After washing, the peels were torn into small pieces and dried in a 90°C oven for 2.5 days. After drying, the peels were ground into a fine powder in a mortar.

[0047] Next, 0.5 g of the orange peel powder was weighed and mixed with 30 ml of distilled water to ensure uniform mixing. The mixture was placed in an electric heated air drying oven at 200°C for 6 hours.

[0048] After the reaction is complete, the reactor is cooled to room temperature. The residue is first removed by room-temperature filtration, followed by a secondary filtration using a 0.22-μm microporous membrane to obtain a clear orange-yellow OP-CQDs stock solution. Finally, this stock solution is diluted 20-fold and used as the working solution for subsequent experiments.

[0049] Example 2: Characterization and Analysis of OP-CQDs

[0050] The morphological characteristics of carbon quantum dots using orange peel as the carbon source were carefully characterized by transmission electron microscopy (TEM). Figure 1 Figure (a) shows a TEM image of the OP-CQDs prepared in Example 1. The OP-CQDs exhibit good dispersion and a regular spherical structure. The inset shows a lattice spacing of 0.27 nm, which is highly consistent with the (002) plane of graphite, further confirming that the synthesized OP-CQDs fall within the category of carbon quantum dots (CQDs).

[0051] Figure 2 The fluorescence excitation and emission spectra of OP-CQDs are shown. It can be clearly seen from the figure that when the excitation wavelength is 360 nanometers, OP-CQDs exhibit the strongest fluorescence intensity at the maximum emission wavelength of about 445 nanometers.

[0052] Example 3 Application of OP-CQDs as a fluorescent probe in detecting iron ions

[0053] Add 2 mL of OP-CQDs working solution to the cuvette, and add 1 mL of 10 mmol·L -1 14 different metal ion aqueous solutions (Mn 2+ 、Cd 2+ 、Co 2+ 、Ce 2+ 、Zn 2+ 、Cu 2+ Mg2+ 、Fe 2+ 、Fe 3+ 、Ag+、Ni 2+ , Pb 2+ 、Ba 2+ and Ca 2 + ), after fully reacting for about 15 minutes, the fluorescence spectrum of each solution was measured (excitation wavelength was 360 nm).

[0054] Selectivity is an important indicator for evaluating the performance of fluorescent probes. 14 metal ions were selected as interfering ions and added to the OP-CQDs working solution to investigate the changes in the fluorescence properties of OP-CQDs. Figure 3 As shown in the figure, after adding equal amounts of different metal ions into OP-CQDs, the peak shape of the fluorescence spectrum did not change significantly, and the intensity changed slightly. 3+ When the fluorescence of OP-CQDs is almost completely quenched, it indicates that OP-CQDs have a strong affinity for Fe 3+ Has good selectivity.

[0055] 3 mL of OP-CQDs working solution was mixed with different volumes of 2 mmol·L -1 Fe 3+ Mixing, making Fe 3+ The concentration range is 0~90μmol·L -1 , and investigate the changes in its fluorescence spectrum.

[0056] Figure 4 OP-CQDs were shown to be effective for Fe 3+ Sensitivity test results. Figure 4 It can be observed that in Fe 3+ Concentration ranged from 0 to 90 μmol·L -1 In the range of Fe 3+ With the gradual increase of concentration, the fluorescence intensity of OP-CQDs showed a trend of gradually weakening. Figure 4 In b, we found that the change in fluorescence intensity (F0-F) at an emission wavelength of 445 nm was related to the Fe 3+ Concentrations range from 10 to 60 μmol·L -1 There is a significant linear correlation within the range.

[0057] According to the calculation formula of detection limit LOD=3σ / k (where σ represents the standard deviation of the blank sample and k is the slope of the linear equation), we can get Fe 3+ The detection limit was 1.1 μmol·L -1 This value is significantly lower than the Fe content in drinking water set by the World Health Organization. 3+The maximum limit standard (5.36 μmol·L -1 ), thus proving that the synthesized OP-CQDs 3+ Excellent sensitivity in detection.

[0058] Example 4 Application of OP-CQDs as a fluorescent probe in the detection of iron ions and L-ascorbic acid

[0059] 2 mL of OP-CQDs working solution was mixed with 10 μL of 1 mol·L -1 Fe 3+ Aqueous solution was mixed to prepare OP-CQDs-Fe 3+ Add 10 mL of solution and mix thoroughly.

[0060] Take out 2mL OP-CQDs-Fe 3+ The solution was placed in a cuvette and different volumes of 1, 10 and 50 mmol·L - 1 L-AA, so that the concentration of L-AA ranges from 0 to 2000 μmol·L -1 , investigate OP-CQDs-Fe 3+ Changes in fluorescence spectra.

[0061] In Fe 3+ After quenching the fluorescence of the OP-CQDs system, different concentrations of L-AA were added to the system, and it was found that L-AA could make the OP-CQDs-Fe 3+ The fluorescence of the system was partially restored.

[0062] like Figure 5 As shown in (a), when the L-AA (ascorbic acid) concentration ranged from 0 to 2000 μmol·L -1 In the range of , it can be observed that with the gradual increase of L-AA concentration, the fluorescence intensity shows a trend of gradual enhancement. Figure 5 Figure b shows the relationship between the fluorescence intensity change (F-F0) and the L-AA concentration at an emission wavelength of 445 nm. 3+ The fluorescence intensity change of the system showed a significant exponential function relationship with the L-AA concentration. This phenomenon may be attributed to the effect of L-AA on Fe 3+ The reduction of Fe 3+ Converted to Fe 2+ , thereby reducing the OP-CQDs-Fe 3+ The energy transfer and electron transfer efficiency within the system lead to partial recovery of fluorescence.

[0063] Further observation Figure 5 In c, when the L-AA concentration was 50 to 600 μmol·L-1 Within the range of 445 nm, the fluorescence intensity change (F-F0) at the emission wavelength of 445 nm showed a linear relationship with the L-AA concentration. According to the calculation formula of the limit of detection LOD=3σ / k (where σ represents the standard deviation of the blank sample and k is the slope of the linear equation), it can be concluded that the detection limit of L-AA is 32 μmol·L -1 .

[0064] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for detecting iron ions, characterized in that, Carbon quantum dots are mixed with a solution containing iron ions, and after sufficient reaction, the fluorescence spectrum intensity is measured, and the concentration of iron ions is calculated based on the change in the fluorescence spectrum intensity. The excitation wavelength of the fluorescence spectrum is 355-365 nm. The preparation method of the carbon quantum dots is as follows: orange peel is washed and dried to prepare orange peel powder, the orange peel powder is mixed with distilled water, a hydrothermal reaction is carried out, the mixture is cooled to room temperature, and the carbon quantum dots are obtained by filtering. The ratio of the orange peel powder to distilled water is 0.5 g:30 ml. The hydrothermal reaction temperature is 200 ° C, and the holding time is 6 h. The drying temperature is 90 ° C, and the drying time is 2.5 d. The filtration is performed through a 0.22 μm microporous membrane. The particle size of the carbon quantum dots is 2.2-6.2 nm. The detection limit of the iron ions is 1.1 μmol·L -1 The detection range of the iron ion is 0~90μmol·L -1 .

2. A method for detecting L-ascorbic acid, characterized in that: The carbon quantum dots were mixed with a solution containing iron ions, and after sufficient reaction, the fluorescence spectrum was measured. When the fluorescence was quenched, a solution containing L-ascorbic acid was added, and the fluorescence spectrum was measured again. The concentration of L-ascorbic acid was calculated based on the degree of recovery of the fluorescence intensity. The excitation wavelength of the fluorescence spectrum was 355-365 nm. The preparation method of the carbon quantum dots was as follows: orange peel was washed and dried to prepare orange peel powder, the orange peel powder was mixed with distilled water, a hydrothermal reaction was carried out, the mixture was cooled to room temperature, and the carbon quantum dots were obtained by filtering. The ratio of the orange peel powder to distilled water was 0.5 g:30 ml. The temperature of the hydrothermal reaction was 200 ° C, and the holding time was 6 h. The drying temperature was 90 ° C, and the drying time was 2.5 d. The filtration was carried out through a 0.22 μm microporous membrane. The particle size of the carbon quantum dots was 2.2-6.2 nm. The detection limit of the iron ions was 1.1 μmol·L -1 The detection range of the iron ion is 0~90μmol·L -1 .

3. The method for detecting L-ascorbic acid according to claim 2, wherein The detection range of L-ascorbic acid is 0~2000μmol·L -1 .

Images