CN107794040B

CN107794040B - Molecular sieve-carbon quantum dot probe, preparation method thereof and application thereof in heavy metal ion detection

Info

Publication number: CN107794040B
Application number: CN201711079410.XA
Authority: CN
Inventors: 夏伊宁; 邱静; 钱永忠; 王梦瑶
Original assignee: Institute of Agricultural Quality Standards and Testing Technology for Agro Products of CAAS
Current assignee: Institute of Agricultural Quality Standards and Testing Technology for Agro Products of CAAS
Priority date: 2017-11-06
Filing date: 2017-11-06
Publication date: 2020-04-28
Anticipated expiration: 2037-11-06
Also published as: CN107794040A

Abstract

The invention discloses a molecular sieve-carbon quantum dot probe, a preparation method thereof and application thereof in heavy metal ion detection. The molecular sieve-carbon quantum dot probe is prepared by a method comprising the following steps: preparing aqueous dispersion of citric acid, diethylenetriamine and a molecular sieve; placing the aqueous dispersion in a hydrothermal reaction kettle for hydrothermal reaction to obtain a molecular sieve-carbon quantum dot probe; the feeding ratio of the citric acid to the diethylenetriamine to the molecular sieve is 1 g: 0.1-0.8 mL: 0.25 g. The invention adopts a hydrothermal method, directly combines the mesoporous molecular sieve with the carbon quantum dots through one-step reaction, and has simpler operation and more time saving. By adjusting the feeding ratio of the carbon source and the nitrogen source, the response capability of the probe to different heavy metal ions can be changed. Under specific conditions, strong response to single heavy metal ions (mercury ions) can be realized, and no obvious response to other heavy metal ions is realized, so that the specific detection of the heavy metal ions is realized.

Description

Molecular sieve-carbon quantum dot probe, preparation method thereof and application thereof in heavy metal ion detection

Technical Field

The invention relates to a molecular sieve-carbon quantum dot probe, a preparation method thereof and application thereof in heavy metal ion detection.

Background

Heavy metals generally refer to densities greater than 4.5g/cm³Becomes a heavy metal ion when surface electrons are lost. Heavy metal ions are mainly generated by industrial production activities, can cause pollution to water environment and soil environment after entering the natural world without treatment, and finally can cause pollution to water environment and soil environment through migration effect and foodThe chain enters the human body. In addition, Heavy Metals are extremely difficult to decompose and accumulate in the natural environment and in organisms, causing chronic and long-term effects (Savic-Gajic I, Savic I, Gajic D. the roll and Health risk of Heavy Metals in human organization, in Heavy Metals and Health, editor: Castillo L. nova Science Publishers,2016, pp.47-89.). Research has shown that Heavy metal ions can cause harm to human body (Lal V F. (2016.) sensitivity of Heavy metals. LAP LAMBERT academic publishing, 2016.). For example, mercury affects the enzymatic and metabolic processes of an organism through chemical or biochemical reactions such as combination, complexation, displacement, synergy, redox and antagonism, and the toxicity is related to the valence state of mercury ions, and divalent mercury ions are larger than monovalent mercury ions. Lead and its compounds can cause damage to various systems such as nerves, hematopoiesis, digestion, kidneys, cardiovascular system and the like after entering into organisms. Cadmium and its compounds can enter human body through respiration, acute poisoning is manifested by acute pneumonia and pulmonary edema, and chronic poisoning can cause damage to liver and kidney. China is a large country for industrial production, and long-term production activities cause the discharge of a large amount of heavy metals, thereby seriously affecting the safety of an ecosystem and the health of human bodies. Therefore, it is necessary to detect heavy metal ions in different environments to ensure the safety of the ecosystem and the health of the human body.

The heavy metal detection means are various, and the traditional methods mainly comprise atomic absorption/emission spectrometry, inductively coupled ion plasma tandem mass spectrometry, X-ray fluorescence spectrometry and the like. These methods are typically time consuming, require expensive instrumentation, require specialized technicians to operate, and are not suitable for on-site screening and rapid detection. Therefore, it is necessary to develop a rapid and simple method for detecting heavy metals with high sensitivity. In recent years, the construction of a nanosensor by utilizing nanomaterials and technologies becomes a research hotspot in the field of rapid detection. Among them, the novel nano-materials represented by quantum dot probes play a great role in the rapid and efficient detection of small molecular substances, and are widely regarded.

Quantum Dots (QDs) are a class of nano semiconductor materials with fluorescence emission capability, and the performance of the quantum dots is influenced by quantum confinement effect, surface effect and doping effectInfluence (Smith A M, Gao X H, Nie S M. Quantum dotnanocrystals for in vivo molecular and cellular imaging. Photochemical and Photobiology 2004,80, 377-385.). The quantum dots generally have three dimensions smaller than the exciton Bohr size of the corresponding semiconductor material, with a size distribution from a few nanometers to tens of nanometers. The materials composing the quantum dots are various, and the common materials include IIB-VIA group elements (such as CdSe and CdTe) and IIIA-VA group elements (such as InP and InAs). Quantum dots can also be made from carbon-containing organic materials, and such quantum dots are referred to as Carbon Quantum Dots (CQDs). Carbon quantum dots are new members of the quantum dot family, have approximately spherical shapes, are smaller than 10nm in size, usually contain a large number of hydrophilic functional groups (hydroxyl, carboxyl and the like) on the surface, and can be stably dispersed in aqueous solution (Baker S N, Baker G A. luminescent carbon nanoparticles: Emergent Nanolight. Angewandte chemical International Edition 2010,49, 6726-. Compared with the traditional semiconductor quantum dots, the carbon quantum dots have the advantages of up-conversion fluorescence property, low biological toxicity, good biocompatibility and the like, and are widely applied to the fields of biological imaging, optical devices, fluorescence detection and the like (Li H T, Kang ZH, Liu Y, Lee S T. carbon nano-dots: synthesis, properties and applications. journal of Material Chemistry 2012,22, 24230-. In the aspect of fluorescence detection, the carbon quantum dot has the advantages of quick response, high sensitivity and the like, and detection objects comprise organic small molecular substances (Chang M F, Ginjom I R, Ng SM, Single-shot 'turn-off' optical probes for segmented detection of paraoxide-ethyl peptide on fluorescent molecules)&ActuatorsB Chemical 2017,242, 1050-²⁺,and Fe³⁺.Sensors&Actors B Chemical 2015,214, 29-35.) and the like. The detection of the quantum dots on the heavy metal ions is established on the interaction between the quantum dots and the heavy metal ions, including an internal rate effect, a non-radiative combination channel, electron transmission and an ion binding reaction, so that the fluorescence intensity of the quantum dots is changed.

In recent years, the quantum dots are loaded on functional nano or micro particles to prepare novel fluorescent composite materials, so that the application range of the quantum dots can be greatly expanded, and the quantum dots become one of the hot spots in the research field of the quantum dots. For example, a fluorescent composite material obtained by loading quantum dots on a mesoporous material (such as a mesoporous molecular sieve) combines the porous characteristic of the mesoporous material and the fluorescent characteristic of the quantum dots, and has some applications in the aspects of small molecular organic matter enrichment and detection, drug release tracking and the like, but reports on the aspect of heavy metal ion detection are few. Therefore, further research in this regard is necessary.

Disclosure of Invention

The invention aims to provide a molecular sieve-carbon quantum dot probe and a preparation method thereof. The molecular sieve-carbon quantum dot probe can eliminate the interference of other heavy metal ions and selectively detect mercury ions (Hg) in an aqueous solution²⁺) According to the different types of heavy metal ions, the concentration range of the anti-interference is 10-100 mu mol/L. The fluorescence intensity of the molecular sieve-carbon quantum dot probe is reduced along with the increase of the concentration of mercury ions (0-100 mu mol/L), and reaches a minimum value at about 50 mu mol/L. The invention combines the ion exchange capacity of the molecular sieve and the fluorescence characteristic of the carbon quantum dots to obtain a novel molecular sieve-carbon quantum dot system, can enrich harmful heavy metal ions in an aqueous solution and monitor the enrichment degree in real time, and has certain practical application value.

The preparation method of the molecular sieve-carbon quantum dot (MCM-CQDs) probe provided by the invention comprises the following steps:

preparing aqueous dispersion of citric acid, diethylenetriamine and a molecular sieve; and (3) placing the aqueous dispersion in a hydrothermal reaction kettle for hydrothermal reaction to obtain the molecular sieve-carbon quantum dot probe.

The preparation method of the invention generates carbon quantum dots in the pore channels of the molecular sieve.

In the above preparation method, the molecular sieve may be an MCM-41 type molecular sieve.

In the preparation method, the feeding ratio of the citric acid, the diethylenetriamine and the molecular sieve can be 1 g: 0.1-0.8 mL: 0.25g, preferably 1 g: 0.4 mL: 0.25 g.

In the above preparation method, the citric acid has a mass volume concentration of 0.1g/mL in the aqueous dispersion.

In the preparation method, the temperature of the hydrothermal reaction is 200 ℃, and the time can be 0.25, 1 or 2 hours, and preferably 1 hour.

In the above preparation method, after the hydrothermal reaction is finished, the method further comprises the steps of cooling, centrifuging and drying the system after the hydrothermal reaction.

In the above preparation method, before the hydrothermal reaction, the step of ultrasonically oscillating the aqueous dispersion is further included.

In general, carbon quantum dots can bind to a variety of heavy metals and undergo fluorescence quenching or enhancement. According to the invention, the carbon quantum dots are generated in the pore channels by virtue of the porous structure and the pore diameter adjustable characteristic of the molecular sieve, and the structure of the carbon quantum dots is different from that of the carbon quantum dots directly generated in water by the traditional hydrothermal method, so that different fluorescence characteristics are shown. By adjusting the chemical reaction conditions, the response of the molecular sieve-carbon quantum dot probe to different heavy metal ions can be adjusted. When the reaction conditions are optimized (the reaction temperature is 200 ℃, the reaction time is 1h, and the feeding ratio is 1 g: 0.4 mL: 0.25g), the obtained molecular sieve-carbon quantum dot probe has specific response to mercury ions and has no obvious response to other heavy metal ions. The fluorescence intensity of the molecular sieve-carbon quantum dot probe is weakened along with the increase of the concentration of mercury ions, the balance is finally achieved, and the concentration of the mercury ions corresponding to the minimum fluorescence intensity is about 50 mu mol/L.

The molecular sieve-carbon quantum dot probe of the invention adopts the molecular sieve as a template, and can obtain the following effects: the molecular sieve has a porous structure and adjustable pore diameter, carbon quantum dots are generated in pore channels of the molecular sieve, and the structure of the molecular sieve is different from that of quantum dots freely generated in water due to the restriction of the pore channels, so that different fluorescence characteristics are shown. Meanwhile, the preparation conditions of the molecular sieve-carbon quantum dots can have certain influence on the structure of the molecular sieve, so that the formation and the fluorescence characteristics of the carbon quantum dots in the molecular sieve are influenced. The crystal structure and porous conformation of the molecular sieve allow it to concentrate heavy metal ions in water by cation exchange. The enrichment process is a dynamic process, the enrichment amount increases along with the increase of time, and the fluorescence intensity of carbon quantum dots in the molecular sieve is changed, so that the dynamic monitoring of the enrichment of heavy metal ions is realized.

According to the invention, citric acid is used as a carbon source, diethylenetriamine is used as a nitrogen source, and a one-step hydrothermal method is adopted to prepare the molecular sieve-carbon quantum dot probe. The molecular sieve-carbon quantum dot probe of the invention shows different responses to different heavy metal ions, and shows specific response to mercury ions under specific reaction conditions without obvious response to other heavy metal ions. The fluorescence intensity of the molecular sieve-carbon quantum dots is weakened along with the increase of the concentration of mercury ions, the balance is finally achieved, and the concentration of the mercury ions corresponding to the minimum fluorescence intensity is about 50 mu mol/L. While carbon quantum dots freely generated in water under the same reaction conditions respond to various heavy metal ions, specific response to single heavy metal ions cannot be realized. In addition, the invention endows the molecular sieve-carbon quantum dot probe with the heavy metal ion enrichment capability by virtue of the cation exchange capability of the molecular sieve, and realizes dynamic monitoring of the enriched heavy metal ions through the carbon quantum dots in the molecular sieve. These functions are not possessed by the carbon quantum dots themselves generated in water.

The mercury ions can be specifically detected according to the following steps:

respectively dispersing the molecular sieve-carbon quantum dot probes with the same mass in water with the same volume and aqueous solution of a heavy metal sample to be detected (the concentration range is 10-100 mu mol/L), measuring the fluorescence intensity of the obtained system, and respectively marking as F₁And F₂；

When F is present₂Is compared with F₁When the reduction is not less than 40%, the sample to be detected contains mercury ions;

the sample to be detected is preferably a water body sample.

Experiments of the invention show that the fluorescence intensity of a mercury ion (solution) containing sample is reduced by 40-60% compared with that of water with the same volume, and the fluorescence intensity of a mercury ion containing solution is reduced within 10% or even 5% in other heavy metal ion containing solutions, so that the fluorescence reduction amplitude of the mercury ion containing solution is far larger than that of the mercury ion containing solutions. The molecular sieve-carbon quantum dot probe can effectively eliminate the interference of other heavy metal ions when detecting the mercury ions in the aqueous solution, and can realize the specific detection of the mercury ions.

The invention has the following advantages:

1. the invention uses the mesoporous molecular sieve as a carrier, verifies the feasibility of generating carbon quantum dots in the molecular sieve by using a hydrothermal method, and can generate new molecular sieve-carbon quantum dot probes with different fluorescence characteristics by changing a carbon source and a nitrogen source and even introducing a new element source (such as a sulfur source). Therefore, the invention can provide certain guiding significance for subsequent similar research.

2. The molecular sieve-carbon quantum dot probe constructed by the invention combines the cation exchange capacity of the molecular sieve with the fluorescence detection capacity of the quantum dot, and realizes dynamic monitoring of enrichment conditions while enriching heavy metal ions.

3. The invention adopts a hydrothermal method, directly combines the mesoporous molecular sieve with the carbon quantum dots through one-step reaction, and has simpler operation and more time saving. By adjusting the feeding ratio of the carbon source and the nitrogen source, the response capability of the probe to different heavy metal ions can be changed. Under specific conditions, the method can realize the response to single heavy metal ions and no response to other heavy metal ions, thereby realizing the specific detection of the heavy metal ions.

Drawings

FIG. 1 is a graph showing the change of fluorescence intensity of MCM-CQDs sample according to the amount of DETA added at 200 ℃ without reaction time in example 1 of the present invention.

FIG. 2 is a graph showing the response of MCM-CQDs samples obtained at 200 ℃ with different reaction times in example 1 of the present invention to 8 heavy metals (100. mu. mol/L) as a function of the DETA addition, wherein the reaction time shown in FIG. 2(a) is 0.25h, the reaction time shown in FIG. 2(b) is 1h, and the reaction time shown in FIG. 2(a) is 2 h.

FIG. 3 is a fluorescence spectrum of MCM-CQDs prepared in example 2 of the present invention.

FIG. 4 is a UV-Vis spectrum of MCM-CQDs prepared in example 2 of the present invention.

FIG. 5 is an IR spectrum of MCM-CQDs prepared in example 2 of the present invention.

FIG. 6 is a SEM-EDS spectrum of MCM-CQDs prepared in example 2 of the present invention.

FIG. 7 is a TEM map of MCM-CQDs prepared in example 2 of the present invention, wherein FIG. 7(a) is a TEM map of MCM-41, FIG. 7(b) is a TEM map of CQDs, and FIGS. 7(c) to (d) are TEM maps of MCM-CQDs.

FIG. 8 is the response of MCM-CQDs prepared in example 2 of the present invention to 8 heavy metal ions at different concentrations, wherein FIG. 8(a) is the response of CQDs to 8 heavy metal ions at 100. mu. mol/L, and FIGS. 8(b) to (d) are the response of MCM-CQDs to 8 heavy metal ions at 100, 50 and 10. mu. mol/L, respectively.

FIG. 9 is a graph showing the change of fluorescence intensity of MCM-CQDs prepared in example 2 of the present invention with the concentration of mercury ions.

FIG. 10 is a graph showing the change of fluorescence intensity with time of MCM-CQDs prepared in example 2 of the present invention in a 1. mu. mol/L mercury ion solution.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

The MCM-41 type molecular sieve used in the following examples has an average pore diameter of about 3.4 to 3.7nm, a particle diameter of 1 to 2 μm, and a surface area>850m²/g。

Example 1 investigation of the amount of Diethylenetriamine (DETA) added and reaction time in the preparation of molecular Sieve-carbon dots (MCM-CQDs)

1g of citric acid (citric acid) and 0.1mL, 0.2mL, 0.3mL, 0.4mL, 0.5mL, 0.6mL, 0.8mL of Diethylenetriamine (DETA) were weighed out and dissolved in 10mL of water, and 0.25g of MCM-41 type molecular sieve was added thereto and subjected to ultrasonic oscillation for 10 minutes. The solution was transferred to a 50mL hydrothermal reaction kettle (PPL material), placed in an oven and heated to 200 ℃ for 0.25, 1, 2 hours, then the oven was closed, the hydrothermal reaction kettle was taken out and placed in a fume hood to cool to room temperature. Pouring the solution in the hydrothermal reaction kettle into a 50mL centrifuge tube, centrifuging (5000rpm, 5min), washing with water (vortex for 30s), repeating for at least 6 times, finally taking out the lower precipitate, drying in an oven (50 ℃) for 16h, grinding the powder, and storing (at room temperature and in a dark place) for later use.

The fluorescence intensity of MCM-CQDs prepared under different DETA adding amounts and different reaction times and the fluorescence response of each sample to 8 heavy metal ions (the concentration is 100 mu mol/L) are considered, and the experimental operation steps are as follows:

5mg of MCM-CQDs powder was weighed, dispersed in 5ml of water, vortexed for 20s, and a portion of the solution was transferred to a quartz cuvette and placed in a fluorometer to measure the fluorescence intensity (fluorometer parameters, excitation wavelength 350nm, voltage 400V, slit width 10 nm). In another parallel control group, 8 heavy metal ion solutions (Fe) with the concentration of 100 mu mol/L are prepared³⁺、Co²⁺、Cu²⁺、Zn²⁺、Ag⁺、Cd²⁺、Hg²⁺、Pb²⁺) Weighing 5mg of MCM-CQDs powder, dispersing in 5ml of the prepared heavy metal ion solution, carrying out vortex rotation for 30s, transferring part of the solution into a quartz cuvette, and placing the cuvette in a fluorimeter to measure the fluorescence intensity (the parameters of the fluorimeter, the excitation wavelength is 350nm, the voltage is 400V, and the slit width is 10 nm).

The results of the initial fluorescence intensity measurements for each sample at different reaction times and different DETA addition levels are shown in FIG. 1, when the reaction temperature is 200 ℃. As can be seen from FIG. 1, the fluorescence intensity of MCM-CQDs increases with the addition amount of DETA regardless of the reaction time (0.25, 1 or 2h), i.e., the fluorescence intensity of MCM-CQDs is higher when the addition amount of DETA is higher. In addition, when DETA is added in a large amount (>0.6mL), the fluorescence intensity of MCM-CQDs formed in a large reaction time is also high.

The results of the measurement of the change in fluorescence intensity after addition of heavy metal ions for various samples at different reaction times and different DETA addition amounts when the reaction temperature was 200 ℃ are shown in FIG. 2, in which the reaction times shown in FIGS. 2(a) -2 (c) were 0.25, 1 and 2 hours in this order. As can be seen from FIG. 2, at different reaction times and different DETA addition levels, MCM-CQDs can respond positively (fluorescence enhancement) to heavy metal ions and also respond negatively (fluorescence reduction) to heavy metal ions, and the response of the MCM-CQDs to each heavy metal ion is changed randomly along with the DETA addition level. In most cases, the addition of mercury ions reduces the fluorescence intensity of MCM-CQDs, and the reduction amplitude of partial conditions (200 ℃, 0.25 or 1h, DETA addition amount of 0.3 or 0.4mL) reaches about 60 percent, which is greatly higher than that of the MCM-CQDs under other heavy metal exposure conditions. The reduction of the fluorescence intensity of MCM-CQDs by the ferric ions (trivalent) is discharged after the mercury ions, and the reduction of the fluorescence intensity is about 40% under partial conditions (200 ℃, 0.25h, 0.2 or 0.3mL of DETA addition, 200 ℃, 1h, 0.1 or 0.2mL of DETA addition). Besides mercury ions, MCM-CQDs can show stronger positive response to other 7 heavy metal ions under certain conditions, and the fluorescence intensity is increased by over 10 percent. Moreover, the trend of the heavy metal ions to increase the fluorescence of MCM-CQDs is more obvious along with the increase of the reaction time. When the reaction temperature is 200 ℃, the reaction time is 1h, and the DETA addition amount is 0.3 or 0.4mL (FIG. 2(b)), the MCM-CQDs have stronger negative response (-about 60%) to mercury ions, and have weaker response (mostly within +/-10%) to other heavy metals. The MCM-CQDs obtained by the method with the reaction temperature of 200 ℃, the reaction time of 1h and the DETA addition of 0.4mL have the optimal effect, show moderate fluorescence intensity, show specific response to mercury ions and have high response degree (reduced by about 60%), and have the lowest response degree to other heavy metal ions (within +/-10% or even 5% in most cases). Therefore, the following experiment was conducted using MCM-CQDs prepared under this condition as a sample, and Carbon Quantum Dots (CQDs) freely generated in water at the time of preparing MCM-CQDs (reaction temperature of 200 ℃, reaction time of 1 hour, DETA addition amount of 0.4mL) were used as a control group.

Example 2 preparation of molecular Sieve-carbon Quantum dots (MCM-CQDs)

1g of citric acid (citric acid) and 0.4mL of Diethylenetriamine (DETA) are weighed and dissolved in 10mL of water, 0.25g of MCM-41 type molecular sieve is added, and ultrasonic oscillation is carried out for 10 min. The solution was transferred to a 50mL hydrothermal reaction kettle (PPL material), placed in an oven and heated to 200 ℃ and held for 1h, then the oven was closed, the hydrothermal reaction kettle was taken out and placed in a fume hood to cool to room temperature. Pouring the solution in the hydrothermal reaction kettle into a 50mL centrifuge tube, centrifuging (5000rpm, 5min), washing (spiral for 30s), repeating for at least 6 times, finally taking out the lower precipitate, drying in an oven (50 ℃) for 16h, grinding the powder, and storing (normal temperature and light shielding) for later use.

Characterization of MCM-CQDs:

(1) fluorescence Spectroscopy (fluorescence spectrometer, used to characterize the fluorescence intensity of MCM-CQDs)

Weighing 5mg MCM-CQDs powder, dispersing in 5ml water, spirally rotating for 20s, transferring part of the solution into a quartz sample cell, and placing in a fluorimeter to measure the emission wavelength and the fluorescence intensity (the parameters of the fluorimeter, the excitation wavelength is 350nm, the voltage is 400V, and the slit width is 10 nm). In another set of parallel experiments, CQDs was selected as a control group, diluted with water by a suitable factor, and a portion of the solution was transferred to a quartz sample cell and placed in a fluorometer to measure fluorescence intensity and emission wavelength (fluorometer parameters, excitation wavelength 350nm, voltage 400V, slit width 10 nm). The measurement results are shown in FIG. 3.

As can be seen from FIG. 3, the emission wavelength of MCM-CQDs is 449.2nm, and the emission wavelength of CQDs is 435.6 nm. It can be seen that the carbon quantum dots generated in MCM-41 are different from those generated in water, so that the fluorescence emission wavelengths of MCM-CQDs are red-shifted.

(2) UV-Vis (ultraviolet absorption for characterization of MCM-CQDs)

Weighing 5mg of MCM-41 or MCM-CQDs powder, dispersing in 5ml of water, spirally rotating for 20s, transferring part of the solution into a quartz sample pool, and placing the quartz sample pool in an ultraviolet-visible spectrophotometer to measure ultraviolet absorption (the scanning range is 200-600 nm, each sample is scanned for 3 times). In another set of parallel experiments, CQDs were diluted by a suitable amount, a portion of the solution was transferred to a quartz sample cell and placed in an ultraviolet-visible spectrophotometer to measure the ultraviolet absorption (scan range: 200-600 nm, each sample was scanned 3 times). The measurement results are shown in FIG. 4.

As can be seen from FIG. 4, MCM-CQDs and CQDs exhibit similar ultraviolet absorption peaks, whereas MCM-41 has no absorption peak. From this, it can be concluded that carbon quantum dots are generated in MCM-41, but unlike carbon quantum dots generated in water, there is a relatively significant difference between the strong ultraviolet absorption at 360nm of MCM-CQDs and the ultraviolet absorption peak at 351nm of CQDs corresponding to the MCM-CQDs.

(3) FT-IR (functional group for characterizing MCM-CQDs surface)

Infrared spectrograms of MCM-41 and MCM-CQDs were obtained with an infrared spectrometer in ATR (attenuated total reflection) mode. Each sample is scanned for 32 times, and the scanning range is 650-4000 cm^-1Resolution of 4cm^-1. The infrared spectra of the four samples are shown in fig. 5.

As can be seen from FIG. 5, the infrared spectrum of MCM-CQDs shows several absorption peaks more than that of MCM-41. Wherein, 2880-3000 cm^-1The two absorption peaks are the stretching vibration peaks of the alkane, which shows that the MCM-CQDs contain more carbon elements than the MCM-41, and the carbon elements are from carbon quantum dots in the MCM-CQDs. In addition, 1551cm^-1The absorption peak at position (D) corresponds to the in-plane vibration peak of amino group, 1395cm^-1The absorption peak at (a) corresponds to the in-plane vibration peak of the carboxyl group, while the amino and carboxyl groups are the main functional groups in DETA and citric acid, respectively. Therefore, the citric acid and DETA are involved in the synthesis of carbon quantum dots in MCM-CQDs, and the surfaces of the carbon quantum dots contain carboxyl and amino. However, the absorption of several characteristic peaks in MCM-CQDs is weak, which indicates that the content of the generated carbon quantum dots is not high.

(4) SEM-EDS (for characterizing the elemental composition of MCM-CQDs)

The surface morphologies of MCM-41 and MCM-CQDs were observed by an electron scanning microscope, and the elemental composition of selected regions was analyzed by EDS, the results of which are shown in FIG. 6.

As can be seen from FIG. 6, the EDS spectrum of MCM-CQDs shows a tiny peak of nitrogen at 0.42keV, while the spectrum of MCM-41 at the same position shows no peak at all. Therefore, the DETA is proved to participate in the synthesis of the carbon quantum dots in the MCM-41 as a nitrogen source, so that the carbon quantum dots are doped with nitrogen elements but have very small content.

(5) TEM (for characterizing the microstructure and morphology of MCM-CQDs)

TEM spectra of CQDs, MCM-41 and MCM-CQDs are shown in FIG. 7, in which FIG. 7(a) is a TEM image of MCM-41, FIG. 7(b) is a TEM image of CQDs, and FIGS. 7(c) to (d) are TEM images of MCM-CQDs.

As can be seen from FIG. 7(a), the surface of the MCM-41 molecular sieve is distributed with approximately circular holes, and the holes are regularly arranged. As can be seen from FIG. 7(c), part of the surface of MCM-CQDs is also distributed with approximately circular pores, but the size is increased compared with that of MCM-41, and the arrangement regularity is worse. Meanwhile, the surfaces of MCM-CQDs exhibit more tiny black spots (FIG. 7(d)), and the morphology and size are similar to those of carbon quantum dots generated in water (FIG. 7 (b)). Therefore, it is inferred that these black dots should be carbon quantum dots generated in MCM-41.

Example 3 heavy Metal ion response test of MCM-CQDs

Preparing aqueous solutions of 8 heavy metal ions, the concentration of each heavy metal ion being 10, 50 and 100. mu. mol/L, respectively, weighing 5mg of MCM-CQDs prepared in example 2, dispersing in 5mL of heavy metal ion solution (10, 50 and 100. mu. mol/L), vortexing for 20s, transferring part of the solution in a quartz sample cell, and placing in a fluorometer to measure the fluorescence intensity. CQDs was used as a control group, diluted by an appropriate factor, 50. mu.L was transferred and added to 5mL of a heavy metal ion solution (100. mu. mol/L), vortexed for 20s, and a portion of the solution was transferred to a quartz sample cell and placed in a fluorometer to measure the fluorescence intensity. The responses of CQDs and MCM-CQDs to 8 kinds of heavy metal ions are shown in FIG. 8, in which FIG. 8(a) is the response of CQDs to 8 kinds of heavy metal ions at one concentration (100. mu. mol/L), FIGS. 8(b) to (d) are the responses of MCM-CQDs to 8 kinds of heavy metal ions at three concentrations (100, 50 and 10. mu. mol/L), and control refers to the fluorescence intensity when no heavy metal ion is added.

As can be seen from FIGS. 8(a) to (b), the responses of CQDs and MCM-CQDs to 8 kinds of heavy metal ions were different at the same concentration of heavy metal ions. Fe³⁺The fluorescence weakening effect on CQDs is strongest, and the fluorescence intensity is reduced by about 80%; hg is a mercury vapor²⁺The reduction effect on MCM-CQDs is strongest, the fluorescence intensity is reduced by about 60 percent, and Fe³⁺The fluorescence reduction effect on MCM-CQDs was insignificant (about 10%). Furthermore, CQDs are on Zn²⁺And Cd²⁺The response is shown by a decrease in fluorescence, whereas MCM-CQDs respond to Zn²⁺And Cd²⁺The response of (a) is manifested as an increase in fluorescence. From these results, it was also judged that CQDs produced in MCM-41 are different from CQ produced in waterDs. As can be seen from FIGS. 8(b) to (d), when the concentration of heavy metal ions was decreased from 100. mu. mol/L to 10. mu. mol/L, MCM-CQDs were responsible for removing Hg²⁺The response degree of other 7 kinds of heavy metal ions is reduced, the fluorescence intensity of MCM-CQDs added with the heavy metal ions is gradually close to that of a control group (the fluorescence intensity of the metal ions is not emphasized), and the MCM-CQDs are used for Hg²⁺The response is still strong, and the fluorescence attenuation amplitude is 60-40%. MCM-CQDs to Hg as the concentration of heavy metal ions decreases²⁺The response of (A) is more obvious than the response of (B) to other heavy metal ions. Therefore, when the concentration of other heavy metal ions is lower, the MCM-CQDs can better eliminate the interference of the heavy metal ions and simultaneously can also play a role in Hg²⁺Has stronger response, thereby realizing the aim of treating Hg²⁺Specific detection of (3).

Example 4 detection of Mercury ions by MCM-CQDs

Preparing a series of mercury ions (Hg) with different concentrations (0-100 mu mol/L)²⁺) Aqueous solution, 5mg of MCM-CQDs prepared in example 2 were weighed out and dispersed in 5mL of Hg at various concentrations²⁺In the aqueous solution, the solution was vortexed for 20 seconds, and a portion of the solution was transferred to a quartz sample cell and placed in a fluorometer to measure the fluorescence intensity. CQDs were used as a control group, diluted by an appropriate factor, and 50. mu.L of the diluted solution was pipetted and added to 5mL of Hg at various concentrations²⁺In the aqueous solution, the solution was vortexed for 20 seconds, and a portion of the solution was transferred to a quartz sample cell and placed in a fluorometer to measure the fluorescence intensity. Fluorescence intensity of CQDs and MCM-CQDs with Hg²⁺The change in concentration is shown in FIG. 9.

As can be seen from FIG. 9, the fluorescence intensity of MCM-CQDs decreases exponentially with the increase of the mercury ion concentration, i.e., the fluorescence intensity of MCM-CQDs decreases rapidly with the increase of the mercury ion concentration in the initial stage, and then the decrease is slowed down and reaches an equilibrium around 50 μmol/L. In a lower mercury ion concentration range (0-5 mu mol/L), the fluorescence intensity of the MCM-CQDs and the concentration of mercury ions form a better linear relation (R)²>0.97), the interval can be regarded as the optimal concentration interval of the MCM-CQDs for detecting the mercury ions. CQDs respond poorly to mercury ions compared to MCM-CQDs. Mainly expressed in that the fluorescence intensity of CQDs is within a lower mercury ion concentration range (0-2 mu mol/L)There was no significant decrease, while the fluorescence intensity of MCM-CQDs was significantly decreased. Then, the fluorescence intensity of CQDs decreases with the increase of the concentration of mercury ions, and the decrease trend is similar to that of MCM-CQDs, but the decrease amplitude is obviously smaller than that of the MCM-CQDs. Therefore, the detection effect of MCM-CQDs on mercury ions is better than that of CQDs.

In addition, due to the cation exchange effect of the MCM-41, the MCM-CQDs can enrich mercury ions in the solution, and meanwhile, the enrichment of the mercury ions is dynamically monitored. The specific procedure was as follows, weighing 5mg of MCM-CQDs prepared in example 2 dispersed in 5mL of Hg at a concentration of 1. mu. mol/L²⁺Among the solutions, vortex for 20 seconds, transfer 1.5mL of the solution into a quartz sample cell and seal with Paraffin film. And (3) placing the quartz sample cell under the conditions of normal temperature and light resistance, and placing the sample cell in a fluorescence instrument to measure fluorescence intensity at different time points (0-48 h). In a control experiment, 5mg of the MCM-CQDs prepared in example 2 were weighed out and dispersed in 5mL of water, vortexed for 20s, and 1.5mL of the solution was transferred to a quartz sample cell and sealed with Paraffin film. And (3) placing the quartz sample cell under the conditions of normal temperature and light resistance, and placing the sample cell in a fluorescence instrument to measure fluorescence intensity at different time points (0-48 h). MCM-CQDs in water and 1. mu. mol/L Hg²⁺The change in fluorescence intensity in the solution with time is shown in FIG. 10.

As can be seen from FIG. 10, the fluorescence intensity of MCM-CQDs in water did not change significantly with time (0-48 h), while the fluorescence intensity of MCM-CQDs was 1. mu. mol/L Hg²⁺The fluorescence intensity in the solution changes with time. When the time is 0-12 h, the Hg of the MCM-CQDs is 1 mu mol/L²⁺The fluorescence intensity in solution decreased with increasing time, with a decrease of about 15%. After that (12-48 h), the fluorescence intensity of the MCM-CQDs has no obvious change. MCM-CQDs 1 mu mol/L Hg²⁺The decrease in fluorescence intensity in solution can be attributed to molecular sieves on heavy metal ions (including Hg)²⁺) Enrichment of (Da' Na E.adsorption of heavymetals on functionalized-mesoporous silica: a review. Microporous)&Mesoporous materials 2017, 145-157.), to Hg in MCM-CQDs²⁺The concentration continued to increase, more Hg²⁺The interaction with carbon quantum dots results in further fluorescence intensity of MCM-CQDsAnd (4) descending.

Claims

1. The application of the molecular sieve-carbon quantum dot probe in heavy metal ion detection;

the molecular sieve-carbon quantum dot probe is prepared according to a method comprising the following steps:

preparing aqueous dispersion of citric acid, diethylenetriamine and a molecular sieve; placing the aqueous dispersion in a hydrothermal reaction kettle for hydrothermal reaction to obtain the molecular sieve-carbon quantum dot probe;

the molecular sieve is an MCM-41 type molecular sieve;

the feeding ratio of the citric acid to the diethylenetriamine to the molecular sieve is 1 g: 0.1-0.8 mL: 0.25 g.

2. Use according to claim 1, characterized in that: the heavy metal ions are Hg²⁺。

3. Use according to claim 1 or 2, characterized in that: in the aqueous dispersion, the mass volume concentration of the citric acid is 0.1 g/mL.

4. Use according to claim 3, characterized in that: the temperature of the hydrothermal reaction is 200 ℃, and the time is 0.25-2 h.

5. Use according to claim 4, characterized in that: after the hydrothermal reaction is finished, the method further comprises the steps of cooling, centrifuging and drying the system after the hydrothermal reaction.

6. A method of detecting mercury ions, comprising the steps of:

respectively dispersing molecular sieve-carbon quantum dot probes with the same mass in water with the same volume and aqueous solution of a heavy metal sample to be detected, measuring the fluorescence intensity of the obtained system, and respectively marking as F₁And F₂；

When F is present₂Is compared with F₁When the reduction is not less than 40%, the sample to be tested containsHas mercury ions;

the molecular sieve is an MCM-41 type molecular sieve;

7. The method of claim 6, wherein: in the aqueous dispersion, the mass volume concentration of the citric acid is 0.1 g/mL.

8. The method according to claim 6 or 7, characterized in that: the temperature of the hydrothermal reaction is 200 ℃, and the time is 0.25-2 h.

9. The method of claim 8, wherein: after the hydrothermal reaction is finished, the method further comprises the steps of cooling, centrifuging and drying the system after the hydrothermal reaction.