CN109187462B

CN109187462B - Solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions and preparation and application thereof

Info

Publication number: CN109187462B
Application number: CN201811012657.4A
Authority: CN
Inventors: 陶劲松; 刘锦斌; 付俊俊; 朱佳仪
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2018-08-31
Filing date: 2018-08-31
Publication date: 2020-01-10
Anticipated expiration: 2038-08-31
Also published as: CN109187462A

Abstract

The invention belongs to the field of heavy metal detection, and discloses a portable visual detection method for heavy metal Hg ions (Hg) on site²⁺) The solid-phase nano composite membrane and the preparation and the application thereof. The invention mixes NFC suspension and GS-AuNPs solution in a mould andand naturally airing to form a film, thus obtaining the solid-phase nano composite film for visually detecting the heavy metal Hg ions in a field portable manner. The NFC suspension solvent is also water, a large number of hydrophilic hydroxyl groups exist on the surface of NFC, the dispersion is better in water, the two liquids are mixed with each other, the acting force of physical adsorption exists between the nano particles, a uniformly dispersed mixture solution can be prepared, and finally an ultraclear and transparent composite film sample can be prepared. The transparency of the membrane ensures that the fluorescence of the gold nanoparticles cannot be lost, the membrane has good fluorescence performance, and has good sensitivity and selectivity for detecting heavy metal Hg ions, so that the membrane is a novel material which is very portable and stable and is used for detecting the heavy metal Hg ions on site.

Description

Solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions and preparation and application thereof

Technical Field

The invention belongs to the field of heavy metal detection, and particularly relates to a field-portable solid-phase nano composite membrane for visually detecting heavy metal Hg ions, and preparation and application thereof.

Background

Water plays a crucial role in human life as an essential substance in life. However, water quality is increasingly contaminated with toxic metals. Among the numerous factors of water pollution, the threat to human beings caused by water pollution due to heavy metal use is the most serious. For example, mercury, which is a heavy metal, is the most important factor affecting human health, and is a concentration of one part per million, which causes serious damage to the human nervous system. After a lot of research and investigation, the European Union issued relevant regulations requiring mercury ions (Hg) in drinking water²⁺) The content cannot exceed 1ppb, and national regulations are established by the U.S. environmental protection agency (US EPA), which requires that the maximum mercury content of drinking water should not exceed 2ppb, otherwise adverse effects on health will be caused. Therefore, the conventional detection of the heavy metal mercury ions in the aquatic ecological environment system is extremely important, and a rapid, economic, sensitive and high-selectivity detection method for the heavy metal mercury ions is urgently needed.

The existing analysis method for heavy metal detection comprises the following steps: atomic absorption spectroscopy, cold vapor atomic fluorescence spectroscopy, inductively coupled plasma mass spectrometry, electrochemical methods, gas chromatography, and high performance liquid chromatography. These methods provide lower detection limits for heavy metal ions, however, most of them have some disadvantages, such as the need for expensive instruments and complicated sample preparation, are time consuming and are not suitable for on-site detection.

With the development of science and technology, the way of designing nano materials into optical sensors for detecting mercury ions is receiving much attention and research, mainly because the method is low in cost, simple in preparation and detection method, rapid and efficient. According to the source of optical signal generation, these optical sensors can be classified into colorimetric method, fluorescence method, Surface Enhanced Raman Scattering (SERS) method sensors, and the trace concentration of heavy metal ions can be quantitatively detected by the spectral transmittance, fluorescence intensity and surface enhanced raman spectrum signal.

In recent years, attention is paid to nano gold in detection of heavy metal Hg ions, and the nano gold is simple in preparation method, cost-effective, easy to visualize and high in sensitivity. However, most of the related applications are based on liquid phase substrates (or substrates), namely, the liquid phase substrates are carried out in solution, and the visualization degree is poor, so that the application of the liquid phase substrates in the field detection of mercury ions is limited. In order to improve the visual application of detection, methods of solid substrates are reported, mainly including DNA substrates, polymer substrates, electrospinning substrates, raw wood substrates, glass substrates, and the like, but all of the methods have some non-negligible disadvantages, such as the need for complicated preparation processes such as surface modification processes, low sensitivity, high price, toxic substances, and the like. These disadvantages can be overcome if a solid substrate with a high specific surface area, softness and transparency can be provided.

The nanofibrillar Cellulose (NFC) is derived from natural Cellulose, is an environment-friendly high polymer material, has various excellent performances such as excellent optical performance, mechanical performance, high specific surface area, chemical modification, biocompatibility, biodegradability and the like, is a potential material which is expected to overcome the defects and becomes an ideal substrate.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention mainly aims to provide a preparation method of a solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions.

The invention also aims to provide the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions, which is prepared by the method.

The invention further aims to provide the application of the solid-phase nano composite membrane for the field portable visual detection of the heavy metal Hg ions in the field detection of the heavy metal Hg ions.

The purpose of the invention is realized by the following scheme:

a preparation method of a solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions mainly comprises the following steps:

(1) preparation of nanofibrillar cellulose NFC suspension: crushing the slurry, adding the crushed slurry into a buffer solution, stirring and dispersing to obtain slurry, adding TEMPO (2,2,6, 6-tetramethyl piperidine nitroxide free radical), NaBr and NaClO, starting reaction, simultaneously adjusting the pH value of the slurry to 10 by using alkali, after the reaction is finished, performing suction filtration and washing by using water until the pH value is 7, preparing a nano-cellulose suspension after high-pressure nano homogenization, and adjusting the pH value of the suspension to 9.5 to obtain an NFC suspension;

(2) preparing luminescent gold nanoparticle GS-AuNPs solution: adding HAuCl into L-glutathione aqueous solution₄Uniformly mixing the aqueous solution, heating for reaction, and purifying the obtained reaction solution after the reaction is finished to obtain a GS-AuNPs solution;

(3) preparing a composite membrane: and (3) adding the NFC suspension prepared in the step (1) and the GS-AuNPs solution prepared in the step (2) into a mold, then ultrasonically mixing, placing the mold in a constant-temperature and constant-humidity environment after mixing is finished, naturally evaporating to dryness to form a film, and thus obtaining the target product solid-phase nano composite film for on-site portable visual detection of heavy metal Hg ions.

The pulp in the step (1) is at least one of softwood pulp, hardwood pulp and cotton pulp; the step (1) of crushing the slurry refers to crushing the slurry into loose floccules by a crusher;

the buffer solution in the step (1) is a mixed solution of 0.1mol/L sodium carbonate aqueous solution and 0.1mol/L sodium bicarbonate aqueous solution in a volume ratio of 3: 2;

the dosage of the buffer solution in the step (1) meets the requirement that 60mL of buffer solution is added to every 1g of slurry; the TEMPO, NaBr and NaClO (available chlorine > 9%) in the step (1) are used in an amount which meets the mass ratio of TEMPO, NaBr and solute NaClO of 0.08:0.5: 0.04; the consumption of TEMPO and the sizing agent in the step (1) meets the mass ratio of the sizing agent to TEMPO of 1: 0.016;

the pH value of the slurry adjusted by adding the alkali in the step (1) is adjusted by using 0.1mol/L sodium hydroxide aqueous solution;

the reaction in the step (1) is carried out at room temperature for 16-20 h, preferably at room temperature for 18 h;

the high-pressure homogenizer treatment in the step (1) refers to homogenizing for 8 times under the pressure of 90 bar;

the suspension of the nano-cellulose in the step (1) refers to that each 100mL of the suspension contains 1.667g of nano-cellulose;

the concentration of the L-glutathione aqueous solution in the step (2) is 2.4-4.8 mmol/L, preferably 4.8 mmol/L; HAuCl described in step (2)₄The concentration of the aqueous solution is 1.0-5.0 mol/L, preferably 1.0 mol/L; the L-glutathione aqueous solution and HAuCl in the step (2)₄The dosage of the aqueous solution satisfies L-glutathione and HAuCl₄The molar ratio of (0.8-1.6): 1, preferably 1.6: 1;

the heating reaction in the step (2) is a reaction at 95 ℃ for 12 hours;

the purification in the step (2) is to cool the obtained reaction liquid to room temperature, adjust the pH value to 3-4, add ethanol with the volume of 1/3 in the reaction liquid for precipitation, and then centrifuge for 10min at 4000g to remove supernatant liquid to obtain precipitate; washing the obtained precipitate, dispersing the precipitate in water, adjusting the pH value to 7-8, centrifuging 21000g to remove large particles, and separating and purifying the obtained suspension by using a 10k ultrafiltration centrifugal tube to remove unreacted raw materials and redundant impurities to obtain a purified GS-AuNPs solution;

the concentration of the GS-AuNPs solution in the step (2) is 5 mg/mL;

the mould in the step (3) is preferably made of polypropylene, the interior of the mould is flat and smooth, and the mixed liquid can be directly taken out after forming a film.

The dosage of the NFC suspension and the GS-AuNPs solution in the step (3) meets the condition that the volume ratio of the NFC suspension to the GS-AuNPs solution is 1 mL: (0-50) mu L, wherein the volume of the GS-AuNPs solution is not 0; preferably, the volume ratio of the NFC suspension to the GS-AuNPs solution is 1 mL: (10-50) mu L.

The ultrasonic mixing in the step (3) refers to ultrasonic dispersion for 20-50 min under the conditions that the output power is 100% and 300 Hz;

the constant temperature and humidity environment in the step (3) refers to an environment with a relative humidity of 50-70% and a temperature of 20 +/-5 ℃;

the glassware used in step (2) is required to be aqua regia (HCl: HNO) before use₃Soaking for 12h in 3:1), and repeatedly cleaning with absolute ethyl alcohol and ultrapure water for later use;

the step (1) to the step (3) are carried out at room temperature which is 20-30 ℃;

the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions is prepared by the method.

The solid-phase nano composite membrane for the on-site portable visual detection of the heavy metal Hg ions is applied to the on-site detection of the heavy metal Hg ions.

The mechanism of the invention is as follows:

the mechanism of the present invention is shown in FIG. 1.

The nano-fibril cellulose NFC is a nano material extracted from plant cellulose and having high length-diameter ratio and high specific surface area, the surface of the nano-fibril cellulose NFC has a large number of hydroxyl and carboxyl groups, and the nano-fibril cellulose NFC can be interwoven into a net to prepare an ultra-high-definition transparent flexible film material, has low density, very good mechanical property and softness, and is biodegradable and low in cost. Thus, NFC is a good substrate loading material for GS-AuNPs.

Meanwhile, the GS-AuNPs hydrosol has good water solubility, the particle size of the nanogold is very small and is about 2-4 nm, and the strong hair is obtainedLight efficiency and higher fluorescence quantum efficiency. As shown in FIG. 1(a), Au exists on the surface of the gold nanoparticles in a certain proportion⁺These Au⁺(4f¹⁴5d¹⁰) Track and Hg²⁺(4f¹⁴5d¹⁰) The orbitals have high affinity and selectivity, and strong specific binding (Hg) can be generated after the orbitals are contacted²⁺-Au⁺Metallophilic reaction) when the two are combined, the fluorescence quenching of the gold nanoparticles is directly and rapidly initiated, as shown in fig. 1 (c). The NFC suspension solvent is also water, a large number of hydrophilic hydroxyl groups exist on the surface of NFC, the dispersion is better in water, the two liquids are mixed with each other, the acting force of physical adsorption exists between the nano particles, a uniformly dispersed mixture solution can be prepared, and finally an ultraclear and transparent composite film sample can be prepared. The fluorescence of the gold nanoparticles cannot be lost due to the transparency of the film, and the dispersion uniformity of GS-AuNPs in the film can be detected by detecting ultraviolet absorption light at different positions on the transparent composite film. The composite film emits strong red fluorescence under 365nm ultraviolet lamp, as shown in FIG. 1(b), when contacted with Hg-containing solution²⁺The mercury ions slowly permeate into the membrane from the surface of the membrane, react with GS-AuNPs in the membrane, and the fluorescence is weakened or even completely quenched according to the amount of the contacted mercury ions, so that no fluorescence phenomenon is observed under an ultraviolet lamp, as shown in FIG. 1 (d). Due to Hg²⁺-Au⁺The metallophilic reaction is highly selective, and most heavy metals do not cause quenching of GS-AuNPs. In sum, the composite membrane of the NFC loaded GS-AuNPs can realize high selectivity and sensitivity of mercury ion visual detection.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the raw material NFC is sufficient and degradable on the earth;

(2) the specific surface area of the NFC substrate is large, and the quantity of loaded nanogold is large;

(3) the NFC substrate has good light transmission, and can effectively prevent the attenuation of nanogold fluorescence due to blocking;

(4) the nano-composite substrate is a solid phase and has good stability.

(5) The nano-composite substrate is soft and bendable, and has good subsequent processability;

(6) the method has good sensitivity and high selectivity for detecting the heavy metal Hg ions.

Drawings

FIG. 1 is a mechanism diagram of the present invention;

FIG. 2 is a microscopic topography observation of the material in example 1, wherein FIG. 2(a) is an atomic force microscope image of the NFC fiber; FIG. 2(b) is a high resolution FES scanning electron microscope image of the NFC blank film; FIG. 2(c) is a transmission electron microscope photograph of GS-AuNPs; FIG. 2(d) is a high-resolution field emission scanning electron microscope photograph of the composite film prepared at the addition amount of 40. mu.L of the GS-AuNPs solution in example 1.

FIG. 3 is a graph showing optical property detection patterns of the composite film and the NFC blank film prepared in example 1 when the GS-AuNPs solution is added in an amount of 40. mu.L, wherein FIG. 3(a) is a real object graph of the composite film and the NFC blank film; FIG. 3(b) is a graph of light transmittance at different wavelengths of a composite film; fig. 3(c) is a graph of absorbance at different wavelengths for eight arbitrary points on the NFC blank film; fig. 3(d) is a graph showing absorbance curves of ten arbitrary points of the NFC/GS-AuNPs composite film prepared in example 1 at different wavelengths.

FIG. 4 is a photograph of naked eye fluorescence of the composite membrane prepared in example 1 with the addition amounts of GS-AuNPs solution of 10. mu.L, 20. mu.L, 30. mu.L, 40. mu.L and 50. mu.L, respectively, under the irradiation of 365nm ultraviolet light;

FIG. 5 is a graph showing the sensitivity detection result of the composite membrane prepared when the amount of the GS-AuNPs solution added in example 1 is 50 μ L to Hg ions, wherein FIG. 5(a) and FIG. 5(b) are a quenching effect graph and a fluorescence intensity histogram of the composite membrane under the action of different mercury ion concentrations under a 365nm ultraviolet lamp, respectively;

FIG. 6 is a graph showing selective detection results of the composite membrane prepared when the amount of the GS-AuNPs solution added in example 1 is 40. mu.L, and FIG. 6(a) and FIG. 6(b) are a graph showing response effects and fluorescence intensity bar graphs of the composite membrane under the action of different heavy metal ions of the same concentration and volume under a 365nm ultraviolet lamp, respectively.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

The reagents used in the examples are commercially available without specific reference.

Example 1

(1) Preparation of NFC suspensions

Firstly, 0.1mol/L Na is used₂CO₃Solution and 0.1mol/L NaHCO₃Preparing a buffer solution with the pH value of 400mL and the pH value of about 10 by the volume ratio of 3:2, and putting 300mL into a 500mL beaker; 5g of the slurry (softwood pulp) was pulverized into a loose cotton-like shape by a pulverizer, and then added to a flask and sufficiently stirred by a magnetic stirrer. Respectively weighing 0.08g TEMPO and 0.5g NaBr, and measuring 35mL NaClO (effective rate)>9%) of the mixture is added into the mixed solution to start reaction; during the reaction period, adjusting the pH of the reaction solution to about 10.0 by using 0.1mol/L sodium hydroxide standard solution; the total reaction time was 18 hours. After the reaction is finished, fully washing the reaction mixed solution by using deionized water in a suction filtration bottle, transferring the washed sample into a clean beaker, and adding deionized water to ensure that the concentration of the nano-cellulose is 0.01667 g/mL; and finally, processing a suspension sample by using a high-pressure homogenizer, dispersing for 8 times under the pressure of 90bar to finally obtain the nanofibrillar cellulose suspension, and after the preparation is finished, adjusting the pH of the suspension to be about 9.5.

(2) Preparation of GS-AuNPs solution

All glassware was washed with aqua regia (HCl: HNO)₃Soaking for 12h at a ratio of 3:1), repeatedly cleaning with absolute ethanol and ultrapure water, and drying for later use. 50mL of 4.8mmol/L aqueous L-glutathione (reduced form) solution was first added to an Erlenmeyer flask, and 150. mu.L of 1mol/L HAuCl was added to the solution₄Magnetic stirring the aqueous solution uniformly, heating the mixed solution in an oil bath kettle at 95 ℃ for 12h to obtain GS-AuNPs, cooling to room temperature, adjusting the pH of the obtained solution to 3-4, adding 1/3 volumes of ethanol, centrifuging for 10 minutes at 4000g to obtain a precipitate, removing the supernatant, washing the obtained precipitate with ultrapure water for several times, adding 1mL of ultrapure water to adjust the pH value to 7 ^ EAnd 8, completely dissolving the gold nanoparticles, centrifuging 21000g to remove large particles generated in the reaction process, purifying the obtained gold nanoparticles by using a 10k ultrafiltration tube, and finally preparing 5mg/mL for later use.

(3) Preparation of composite membranes

The mould for preparing the membrane is made of polypropylene, the interior of the mould is flat and smooth, and the mixed liquid can be conveniently and directly taken out after the membrane is formed. In order to investigate the influence of different dosages of GS-AuNPs on the fluorescence intensity of a membrane, 6 identical molds (2X 2cm) are taken, 1mL of NFC suspension (0.01667g/mL) is added into each mold, GS-AuNPs solutions with different volumes are sequentially added into each mold, the adding amount is 0 muL, 10 muL, 20 muL, 30 muL, 40 muL and 50 muL, and in order to enable the GS-AuNPs solutions to be fully and uniformly mixed with the NFC suspension, the molds are placed into an ultrasonic cleaning machine to be subjected to ultrasonic treatment for 20min, the output power is 100% and 300 Hz; after the ultrasonic treatment is finished, the die is placed into a constant-temperature and constant-humidity laboratory (the relative humidity is 50-70%, and the temperature is 20 +/-5 ℃) and is naturally evaporated to dryness to form a film.

And (3) performance detection:

1. microscopic topography Observation of materials

The microscopic morphology observation image of the material in the embodiment 1 is shown in fig. 2, wherein fig. 2(a) is an atomic force microscope image of the NFC fiber, and the shape of a single NFC fiber can be visually observed from the image, the diameter is about 8-10 nm, the length-diameter ratio is large, and the size distribution is uniform; the microscopic morphology of the surface of the NFC blank film (i.e., the film prepared when the addition amount of the GS-AuNPs solution is 0 μ L) observed with a high-resolution field emission scanning electron microscope is shown in fig. 2(b), and it can be seen that the film surface is dense and very flat at a magnification of 50K. FIG. 2(c) is a transmission electron microscope image of GS-AuNPs (sample preparation reference scanning/transmission electron microscope sample preparation process: the conductive adhesive is pasted on an objective table, the suspension is dripped on the conductive adhesive, and the suspension is naturally dried by distillation or blow-drying by a blower or drying by a low-temperature oven, and then gold spraying is carried out), and the particle size of the Au NPs is uniform and well dispersed, and the diameter is about 2-3 nm. The composite film is characterized in fig. 2(d), and it can be seen that the surface of the film is relatively flat, and the GS-AuNPs are relatively uniformly dispersed.

When the addition amounts of the GS-AuNPs solution are 10 muL, 20 muL, 30 muL and 50 muL, the image obtained by observing the surface micro-topography of the GS-AuNPs solution by using a high-resolution field emission scanning electron microscope is similar to that of FIG. 2(d), which shows that when the addition amounts of the GS-AuNPs solution are 10 muL, 20 muL, 30 muL and 50 muL, the composite film which is relatively flat and has relatively uniform GS-AuNPs dispersion can be obtained.

2. Optical Performance testing

The detection spectra of the optical properties of the composite film and the NFC blank film prepared when the addition amount of the GS-AuNPs solution in example 1 is 40 μ L are shown in fig. 3, wherein fig. 3(a) is a real diagram of the composite film and the NFC blank film, and it can be seen that both the NFC blank film and the prepared nanocomposite film have good visual transparency; FIG. 3(b) is a graph of transmittance of the composite film at different wavelengths, and from FIG. 3(b), the transmittance of the composite film is as high as 90%; fig. 3(c) is a graph of absorbance curves of eight arbitrary points on the NFC blank film at different wavelengths, eight arbitrary points are randomly selected on the NFC blank film to obtain eight groups of absorption spectrum curves, and it can be seen from the graph that the absorbance of the 8 points is completely matched; fig. 3(d) is a graph of absorbance at different wavelengths for ten arbitrary points of the NFC/GS-AuNPs composite film prepared in example 1, and it can be seen from the graph that the absorbance at each point measured at random is substantially coincident, thereby indicating that the GS-AuNPs are dispersed in the NFC film very uniformly.

When the amounts of the GS-AuNPs solutions added were 10 μ L, 20 μ L,30 μ L, and 50 μ L, the absorbance curves at different wavelengths at ten arbitrary points of the NFC/GS-AuNPs composite film prepared in example 1 also substantially coincided, indicating that the GS-AuNPs were very uniformly dispersed in the NFC film when the amounts of the GS-AuNPs solutions added were 10 μ L, 20 μ L,30 μ L, and 50 μ L.

3. Detection of fluorescent properties

The numbers of composite membranes prepared when the amounts of GS-AuNPs solution added in example 1 were 10. mu.L, 20. mu.L, 30. mu.L, 40. mu.L and 50. mu.L, respectively, were 1,2,3,4 and 5, respectively. The naked eye fluorescence photograph of the five composite films under the 365nm ultraviolet lamp is shown in FIG. 4, and it can be seen from FIG. 4 that the fluorescence is enhanced with the increase of the addition amount of GS-AuNPs.

4. Detection of composite membrane to heavy metal mercury ions

4.1 sensitivity detection

The prepared composite membrane has stronger fluorescence emission, and in order to improve the sensitivity of the detection process, the invention selects the composite membrane with the same GS-AuNPs content for Hg²⁺And (5) detection experiments. At room temperature, 2mol/L of HNO is used for mercury sulfate powder₃The solution is prepared into 0.01mol/L Hg²⁺The stock solution of (1). Subsequently, Hg is added²⁺The concentrations were 1000. mu. mol/L, 100. mu. mol/L, 10. mu. mol/L, 1. mu. mol/L, 0.1. mu. mol/L, 0.01. mu. mol/L, 0.001. mu. mol/L, 0.0001. mu. mol/L, each 1mL of each was prepared for use.

The composite membrane added with the GS-AuNPs solution in the amount of 50 mu L in example 1 is punched by a puncher to cut 9 membranes with the same size and shape, eight membranes are respectively dripped with one drop of the above eight mercury ion solutions with different concentrations, the membranes are taken out and dried, and then the membranes are placed in a fluorescence imager, a 365nm ultraviolet light source is used, and the exposure time is 1.5s, so that a fluorescence picture is obtained. The graph of the detection result of the sensitivity of the composite membrane to Hg ions is shown in fig. 5, wherein fig. 5(a) is a graph of the quenching effect of the composite membrane under the action of different mercury ion concentrations under a 365nm ultraviolet lamp; FIG. 5(b) is a bar graph of fluorescence intensity of the composite membrane under the action of different mercury ion concentrations under a 365nm ultraviolet lamp; as shown in FIG. 5(a), nine membranes cut from the same composite membrane, the first membrane was blank (not reacted with mercury ion solution), and the remaining eight membranes were sequentially dropped with 0.001. mu. mol/L, 0.01. mu. mol/L, 0.1. mu. mol/L, 1. mu. mol/L, 10. mu. mol/L²μmol/L，10³μmol/L，10⁴Mu mol/L mercury ion solution 10 mu L, then placed under 365nm wavelength ultraviolet lamp, can very visually see the quenching effect of fluorescence, with the mercury ion concentration increase, quenching effect is enhanced in turn. Quenching is very significant when the mercury ion concentration is above 0.1. mu. mol/L. A bar graph of fluorescence intensity of the composite membrane under the action of different mercury ion concentrations under a 365nm ultraviolet lamp is shown in fig. 5(b), the fig. 5(b) is a data graph formed by plotting fluorescence average density data acquired by a fluorescence imager, and when the concentration of mercury ions reaches 0.001 mu mol/L, namely 1nmol/L, a certain fluorescence quenching effect can also be observed. Maximum content of inorganic mercury ions in drinking water released by the United states Environmental Protection Agency (EPA)It should not exceed 2ppb, i.e. 10 nmol/L. The experimental result of the invention shows that the composite membrane has higher sensitivity of 1nmol/L for detecting mercury ions<2ppb, thereby completely meeting the requirements and having practical potential and value for detecting heavy metal mercury ions in daily life.

When the addition amount of GS-AuNPs solution is 10 muL, 20 muL, 30 muL, 40 muL, nine membranes cut from the same composite membrane, the first one is blank membrane (not reacted with mercury ion solution), and the other eight membranes are dropped with 0.001 mumol/L, 0.01 mumol/L, 0.1 mumol/L, 1 mumol/L, 10 mumol/L²μmol/L，10³μmol/L，10⁴Mu mol/L mercury ion solution 10 mu L, then placed under 365nm wavelength ultraviolet lamp, can very visually see the quenching effect of fluorescence, with the increase of mercury ion concentration, quenching effect is enhanced in turn. When the concentration of mercury ions is higher than 0.1 mu mol/L, the quenching effect is very obvious. It is shown that when the GS-AuNPs solution is added in an amount of 10. mu.L, 20. mu.L, 30. mu.L, or 40. mu.L, the sensitivity can be satisfied with 1nmol/L<2ppb。

4.2 Selective detection

In-situ detection of composite membrane to Hg²⁺In the selective experiment, the GS-AuNPs solution is firstly added into the composite membrane with 40 mu L of composite membrane and cut into 12 pieces with the same small and large shapes, and then the Ag with the concentration of 100 mu mol/L is prepared⁺,Ca²⁺,Cr³⁺,Cu²⁺,K⁺,Co³ ⁺,Na⁺,Al³⁺,Pb²⁺,Zn²⁺,Ni²⁺An aqueous nitrate solution. The 12 films were dropped into 100. mu. mol/L Ag⁺,Ca²⁺,Cr³⁺,Cu²⁺,K⁺,Co³⁺,Na⁺,Al³⁺,Pb²⁺,Zn²⁺,Ni²⁺,Hg²⁺Taking out a drop of nitrate aqueous solution, evaporating to dryness, putting into a living body fluorescence imager for collecting fluorescence images, using a 365nm ultraviolet light source, carrying out exposure time of 1.5s, selecting the same area on each film through system software to collect pixel points, and obtaining average pixel point density data corresponding to corresponding fluorescence intensity change. The composite membrane has Hg ion selectivity detection result as shown in figureFIG. 6 is a graph showing the response effect of the composite membrane under the action of different heavy metal ions with the same concentration and volume under a 365nm ultraviolet lamp; FIG. 6(b) is a bar graph of the fluorescence intensity of the composite membrane under the action of different heavy metal ions of the same concentration and volume under a 365nm ultraviolet lamp; as can be seen from fig. 6, under the action of heavy metal ions with the same concentration and volume, most of the heavy metal ions have no obvious quenching effect on the fluorescence of the composite membrane, and the mercury ion solution has the strongest effect on quenching the fluorescence of the composite membrane.

Similarly, corresponding operations are carried out on the composite membrane obtained when the addition amount of the GS-AuNPs solution is 10 muL, 20 muL, 30 muL and 50 muL, and it can also be observed that most heavy metal ions have no obvious quenching effect on the fluorescence of the composite membrane, the effect of the mercury ion solution on the fluorescence quenching of the composite membrane is strongest, and silver ions and copper ions also have a certain fluorescence quenching effect on the composite membrane, but the effect is weaker than that of the mercury ions. The experimental results prove that the nano composite membrane prepared by the invention has high selectivity for mercury ion detection.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions is characterized by mainly comprising the following steps:

(1) preparation of nanofibrillar cellulose NFC suspension: crushing the slurry, adding the crushed slurry into a buffer solution, stirring and dispersing to obtain slurry, adding TEMPO, NaBr and NaClO, starting reaction, simultaneously adjusting the pH value of the slurry to 10 by using alkali, after the reaction is finished, carrying out suction filtration and washing by using water until the pH value is 7, preparing a nano-cellulose suspension after high-pressure nano homogenization, and adjusting the pH value of the suspension to 9.5 to obtain an NFC suspension;

2. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

the dosage of the buffer solution in the step (1) meets the requirement that 60mL of buffer solution is added to every 1g of slurry; the dosage of TEMPO, NaBr and NaClO in the step (1) meets the requirement that the mass ratio of TEMPO, NaBr and solute NaClO is 0.08:0.5: 0.04; the dosage of the TEMPO and the sizing agent in the step (1) meets the mass ratio of the sizing agent to the TEMPO of 1: 0.016.

3. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

the pH value of the slurry adjusted to 10 by using the alkali in the step (1) refers to the adjustment by using 0.1mol/L sodium hydroxide aqueous solution;

the reaction in the step (1) is carried out at room temperature for 16 ~ 20 h;

the suspension of nanocellulose described in step (1) means that 1.667g of nanocellulose was contained per 100mL of suspension.

4. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

the concentration of the L-glutathione aqueous solution in the step (2) is 2.4 ~ 4.8.8 mmol/L;

HAuCl described in step (2)₄The concentration of the aqueous solution is 1.0 ~ 5.0.0 mol/L;

the L-glutathione aqueous solution and HAuCl in the step (2)₄The dosage of the aqueous solution satisfies L-glutathione and HAuCl₄The molar ratio of (0.8 ~ 1.6.1.6) to (1).

5. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

the reaction in the step (2) is carried out at 95 ℃ for 12 h;

the purification in the step (2) is that the obtained reaction liquid is cooled to room temperature, the pH value is adjusted to 3 ~ 4, ethanol with the volume of 1/3 of the reaction liquid is added for precipitation, then the reaction liquid is centrifuged for 10min at 4000g to remove supernatant to obtain precipitate, the obtained precipitate is washed, then the precipitate is dispersed in water, the pH value is adjusted to 7 ~ 8, then 21000g of the precipitate is centrifuged to remove large particles, and the obtained suspension is centrifuged for 10 g to obtain 10kAnd (4) separating and purifying the ultrafiltration centrifugal tube to remove unreacted raw materials and redundant impurities to obtain the purified GS-AuNPs solution.

6. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

the concentration of the GS-AuNPs solution in the step (2) is 5 mg/mL.

7. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

the dosage of the NFC suspension and the GS-AuNPs solution in the step (3) meets the condition that the volume ratio of the NFC suspension to the GS-AuNPs solution is 1mL (0 ~ 50) mu L, wherein the volume of the GS-AuNPs solution is not 0;

the ultrasonic mixing in the step (3) refers to ultrasonic cleaning for 20 ~ 50min under the conditions that the output power is 100% and the frequency is 300 Hz;

the constant temperature and humidity environment in the step (3) refers to an environment with a relative humidity of 50 ~ 70% and a temperature of 20 +/-5 ℃.

8. The preparation method of the solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions according to claim 1, wherein the solid-phase nano composite membrane comprises the following steps:

soaking glassware used in the step (2) in aqua regia for 12h before use, then cleaning with absolute ethyl alcohol and ultrapure water, and drying for later use;

the reaction in the step (2) is carried out at 95 ℃ for 12h, the constant temperature and humidity environment in the step (3) is an environment with the relative humidity of 50 ~ 70% and the temperature of 20 +/-5 ℃, and the unspecified temperature in the step (1) ~ (3) is carried out at room temperature of 20 ~ 30 ℃.

9. A solid-phase nano composite membrane for on-site portable visual detection of heavy metal Hg ions prepared according to the method of any one of claims 1 ~ 8.

10. The application of the solid-phase nano composite membrane for the on-site portable visual detection of heavy metal Hg ions according to claim 9 in the on-site detection of heavy metal Hg ions.