CN112485311A

CN112485311A - Photoelectrochemical method for quantitatively detecting monovalent thallium

Info

Publication number: CN112485311A
Application number: CN202011261364.7A
Authority: CN
Inventors: 秦冬冬; 韦秋钰; 陶春兰; 牛利; 韩冬雪; 王伟; 李春凤; 韩东方
Original assignee: Guangzhou University
Current assignee: Guangzhou University
Priority date: 2020-11-12
Filing date: 2020-11-12
Publication date: 2021-03-12

Abstract

The invention belongs to the technical field of semiconductor nano material photoelectrochemical sensors, and discloses a photoelectrochemical method for quantitatively detecting univalent thallium. The invention takes indium sulfide with rich sulfur on the surface as a photoelectrode, and the photoelectrode generates strong sulfur surface state oxidation current under-0.6V. After the photoelectrode is contacted with monovalent thallium ions, the specific atomic level combination of the monovalent thallium and the sulfur reduces the sulfur surface state concentration, thereby triggering the quenching of the photocurrent signal. The magnitude of quenching is directly proportional to the thallium ion concentration, and the reaction can occur at solution pH 2 and 6. The method artificially synthesizes a surface state with a specific function on the surface of a crystal material, and utilizes the surface state to induce a target detection object monovalent thallium to generate an atomic-scale specific reaction on a crystal interface. The photoelectrochemical quantitative analysis of the toxic metal monovalent thallium is realized by utilizing the obvious change of a photoelectric conversion current signal triggered by the change of the interface charge transfer kinetic rate before and after the reaction.

Description

Photoelectrochemical method for quantitatively detecting monovalent thallium

Technical Field

The invention belongs to the technical field of semiconductor nano material photoelectrochemical sensors, and particularly relates to a photoelectrochemical method for quantitatively detecting univalent thallium.

Background

In recent years, researches show that the thallium compound and the elemental substance have some unique advanced functions, and have key and irreplaceable functions in important industrial and military fields such as special alloys, high-temperature superconductivity, atomic energy industry, optical communication and the like. Therefore, thallium is the same as most of rare metals and becomes a strategic resource in China. The fact that the problem of high toxicity of thallium cannot be avoided while people enjoy the rich thallium resources and the ultrahigh industrial value of China is satisfied. Thallium is an unnecessary element for human body, and has toxicity even higher than heavy metals such As Cd, Pd, As, Hg, etc. which are widely concerned. Thallium pollution in the environment mainly comes from industrial application of thallium, mining and smelting processes of thallium-containing minerals, industrial wastewater discharge and sedimentation processes of cement plant smoke dust. Along with the development and utilization of thallium resources in recent years in China, pollution events sometimes occur. The content of thallium in underground water of certain mining areas far exceeds the total thallium concentration specified by drinking water standards in China. Thallium, a heavy metal, is an unnatural, degradable pollutant that enters the body mainly through drinking water, food intake, skin contact and the food chain. Strong cumulative toxicities can severely damage nerve fibers, the cardiovascular system, nucleic acid synthesis and protein activity, leading to significant disease and serious health problems. However, thallium is long in environmental cycle and toxicity enrichment time (20-30 years), so thallium pollution is often neglected easily by people.

The analysis and detection are the prerequisite and the core for thallium pollution prevention and control of the whole chain. Currently, thallium detection at home and abroad mainly depends on instrument analysis methods such as Atomic Absorption Spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma emission spectroscopy (ICP-AES). The instrument analysis methods have good selectivity in the aspect of metal detection, but have the defects of complex and complicated operation process, expensive equipment, high maintenance cost and the like. Therefore, it is necessary to develop a feasible and efficient monovalent thallium chemical analysis method, and it is also a direction in which our analytical chemists need to make active efforts and responses. However, thallium mainly exists in the form of monovalent thallium in the environment, and the chemical property of the monovalent thallium is similar to that of sodium and potassium ions of alkali metals, so that the monovalent thallium is stable in chemical property, difficult to form a coordinate bond with Lewis base and difficult to generate redox reaction. These physicochemical properties of thallium create difficulties for the establishment of chemical analysis methods.

A Photoelectrochemical (PEC) sensor is a novel analysis method which is established on the basis of electrochemical sensing and utilizes the photoelectric conversion characteristic of a substance to enhance the electrochemical response of a specific substance to be detected. The photoelectrochemical sensor has the advantages of both an optical sensor and an electrochemical sensor, and separation of an excitation signal and a detection signal is realized through the coordinated design of the optical sensor and the electrochemical sensor. The unique sensing mode endows the sensor with the advantages of high sensitivity, good selectivity, low cost, simple and convenient operation, high accuracy and the like. Therefore, the photoelectrochemical sensing analysis method becomes an important component of the science of analysis and measurement, and is a hotspot and a leading direction of the current domestic and foreign research. The existing published documents do not disclose a photoelectrochemical method for quantitative detection of monovalent thallium by using a crystal surface state-induced specific reaction.

Disclosure of Invention

In order to overcome the shortcomings and drawbacks of the prior art, the present invention provides a photoelectrochemical method for quantitatively detecting thallium through artificially synthesizing a surface state with a specific function on the surface of a crystal material, and inducing the target detection object thallium to perform an atomic-level specific reaction on the crystal interface by using the surface state. The photoelectrochemical quantitative analysis of the toxic metal monovalent thallium is realized by utilizing the obvious change of a photoelectric conversion current signal triggered by the change of the interface charge transfer kinetic rate before and after the reaction.

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

a photoelectrochemical method of quantitatively detecting monovalent thallium comprising the steps of:

(1) taking two fluorine-doped tin oxide (FTO) electrodes, placing the two FTO electrodes into a polyvinyl fluoride reaction kettle with the conductive surfaces facing downwards; adding indium trichloride tetrahydrate into absolute ethyl alcohol, stirring and dissolving uniformly, adding Thioacetamide (TAA), stirring until the solution is light yellow, pouring the light yellow solution into a polyethylene fluoride reaction kettle with an FTO glass sheet with a conductive surface facing downwards for reaction, taking out after the reaction, washing substances with a non-conductive surface with ethyl alcohol, and drying with nitrogen to obtain the indium sulfide thin film electrode In₂S₃；

(2) An indium sulfide thin film electrode In prepared In the step (1)₂S₃Putting the mixture into a prepared thallium nitrate solution for reaction, and recording the obtained product as In₂S₃-Tl；

(3) Platinum sheet as counter electrode, Ag/AgCl as reference electrode, 0.5mol L^-1Na₂SO₄As an electrolyte, another blank sample In was used₂S₃And In₂S₃Tl is used as a working electrode to form a three-electrode system, under the irradiation of visible light, a linear cyclic voltammetry method is used, the scanning voltage range is-0.8-0.4V, the illumination and non-illumination cyclic switching is carried out, and a blank sample In is collected₂S₃And In₂S₃Reading the current value at-0.6V, respectively marked as I, of the photocurrent signal of-Tl₀And I, the signal intensity difference Δ I ═ I₀-I；

(4) Changing the concentration of the thallium nitrate solution in the step (2) only, keeping the rest unchanged, then repeating the operations of the steps (1) to (3) to obtain a plurality of groups of delta I corresponding to the thallium concentration, and plotting the delta I to the thallium concentration to obtain a linear relation of the delta I to the thallium concentration, namely a working curve;

(5) detecting Fe in solution to be detected³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu² ⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The concentration of the 17 interfering ions is determined as Pb in the solution to be measured²⁺,Cd²⁺,Hg⁺When the sum of the concentrations of the other 14 ions is less than 10 mu M and the sum of the concentrations of the other 14 ions is less than 100 mu M, replacing the thallium nitrate solution prepared in the step (2) with a solution to be detected with the same volume and the same pH value, then repeating the operations in the steps (1) to (3), substituting the obtained photocurrent signal intensity difference Delta I into the working curve in the step (4), wherein the obtained thallium concentration is the thallium concentration of the solution containing thallium to be detected;

(6) detecting Fe in solution to be detected³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu² ⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The concentration of the 17 interfering ions is determined when at least one of the following two conditions occurs in the solution to be measured, namely Pb²⁺,Cd²⁺,Hg⁺The sum of the concentrations of (1) and (4) other ions is higher than 10. mu.M, and the sum of the concentrations of (14) other ions is higher than 100. mu.M, the specific operation is as follows:

(6.1) repeating the step (1) to obtain two indium sulfide thin film electrodes In₂S₃Then one of the indium sulfide thin film electrodes In₂S₃Adding the mixture into EDTA aqueous solution for reaction, and obtaining a product named as EDTA-In₂S₃；

(6.2) adding EDTA into the solution to be detected with the volume consistent with that of the thallium nitrate solution prepared In the step (2) for reaction, then adjusting the pH value of the solution to be detected to be consistent with that of the thallium nitrate solution prepared In the step (2), and then putting another indium sulfide thin film electrode In the step (6.1)₂S₃Adding the mixture into a solution to be detected for reaction, and marking the obtained product as EDTA-In₂S₃-M；

(6.3) EDTA-In obtained In step (6.1)₂S₃And EDTA-In obtained In step (6.2)₂S₃-M replaces In step (3) respectively₂S₃And In₂S₃Tl, then repeating the step (3), and substituting the obtained photocurrent signal intensity difference Delta I into the work in the step (4)And in the curve drawing, the obtained thallium concentration is the thallium concentration of the thallium-containing solution to be detected.

Before use, the fluorine-doped tin oxide (FTO) electrode in the step (1) is preferably ultrasonically cleaned for 10-20min by sequentially using cleaning powder, ethanol and water respectively, and is used after being naturally dried;

the relative dosage ratio of the absolute ethyl alcohol, the indium trichloride tetrahydrate and the thioacetamide in the step (1) is 30-60 mL: 0.4399-0.8798 g: 0.2255-0.4510g, preferably 30 mL: 0.4399 g: 0.2255 g.

The reaction in the step (1) refers to moving the reaction kettle to an oven with the temperature of 80-100 ℃ for reaction for 4-6 h.

The usage amount of the FTO glass and the light yellow solution in the step (1) meets the following requirements: two pieces of 1.5X2.5cm electrodes were used corresponding to 8-12mL of light yellow solution.

The concentration of the thallium nitrate solution in the step (2) is 0.625-10 μ M, the pH value of the thallium nitrate solution is 2 or 6, and the pH value is preferably 2; the thallium nitrate solution in the step (2) is used in an amount such that 8 to 12mL of the thallium nitrate solution is used for each electrode of 1.5X2.5cm, preferably 10mL of the thallium nitrate solution is used for each electrode of 1.5X2.5 cm.

The reaction in the step (2) is carried out for 10-20min at the temperature of 50-60 ℃.

The illumination and non-illumination cyclic switching in the step (3) is realized through manual switching, namely light blocking and non-light blocking in the traditional sense are realized, light is blocked at intervals by using a hard board, and the interval or switching time is about 1 second (due to manual operation, the time interval is only roughly estimated). In the process of linear cyclic voltammetry scanning, a method for continuously switching illumination and non-illumination is a common method for researching photoelectric response of semiconductor materials in the field of photoelectrochemistry, and a large number of documents are reported, so that detailed description is not needed.

The plurality of groups in step (4) means 5 or more groups, preferably 5 groups.

The dosage of the EDTA aqueous solution in the step (6.1) meets the following requirements: the use amount of EDTA in the EDTA aqueous solution meets the condition that the molar weight of EDTA is Fe in the solution to be detected³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The sum of the molar amounts of these 17 interfering ions; the reaction in the step (6.1) is carried out for 10-20min at the temperature of 50-60 ℃.

The dosage of the EDTA added in the step (6.2) meets the condition that the molar weight of the EDTA is Fe in the solution to be detected³⁺,Ni²⁺，Cr³ ⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The sum of the molar amounts of these 17 interfering ions; the reaction in the step (6.2) is carried out for 10-20min at the temperature of 50-60 ℃.

The mechanism of the invention is as follows:

the invention takes indium sulfide with rich sulfur on the surface as a photoelectrode, and the photoelectrode generates strong sulfur surface state oxidation current under-0.6V (vs. Ag/AgCl). After the photoelectrode is contacted with monovalent thallium ions, the specific atomic level combination of the monovalent thallium and the sulfur reduces the sulfur surface state concentration, thereby triggering the quenching of the photocurrent signal. The magnitude of quenching is directly proportional to the thallium ion concentration, and the reaction can occur at

solution pH

2 and 6. The experiment utilizes the thiophilic property of monovalent thallium, and realizes the purpose of quantitatively analyzing and detecting the monovalent thallium by promoting the quenching phenomenon of an oxidation current signal through the specific combination of thallium ions and an indium sulfide photoelectrode containing a sulfur-rich surface state.

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

(1) the sulfur-rich indium sulfide grown in situ is used as a semiconductor optical active electrode, the indium sulfide has strong adhesive force with a substrate, the material has high mechanical strength and long operation life, and is not easy to dissolve and fall off in the operation process of the sensor.

(2) The sheet structure of the indium sulfide has a huge specific surface area, and the large specific surface area can maximize the sulfur-rich active surface state density of the material surface; meanwhile, the sheet structure has excellent charge separation and transport efficiency. The advantages can amplify the detection current signal, reduce background interference and widen the detection range.

(3) Compared with a composite electrode commonly used in other photoelectric sensing systems, the method has the advantages that the monovalent thallium is detected by using the single indium sulfide photosensitive material synthesized by one-step reaction, so that the process flow can be effectively simplified, the cost is reduced, and the detection efficiency is improved.

(4) The sensor has good detection performance on the monovalent thallium, the detection limit can reach 0.625 mu M, and the sensor has the advantages of wide pH detection influence range and high selectivity, and can be used for quantitatively analyzing and detecting the monovalent thallium from a complex system with a plurality of metal ions.

(5) A photoelectrochemical method for quantitative detection of monovalent thallium is established for the first time, and analytical scientific methods and technologies are enriched and developed.

Drawings

FIG. 1 is In example 1, prepared at a TI concentration of 10. mu.M₂S₃And In₂S₃Profile of Tl, where a is In₂S₃SEM picture of (1); b is In₂S₃SEM picture of Tl; c is In₂S₃A TEM image of (B); d is In₂S₃TEM image of Tl.

FIG. 2 is In prepared at a TI concentration of 10. mu.M In example 1₂S₃And In₂S₃-X-ray powder diffraction pattern of Tl.

FIG. 3 is In prepared at a TI concentration of 10. mu.M In example 1₂S₃And In₂S₃X-ray photoelectron spectroscopy (XPS) of Tl, where a is In₂S₃And In₂S₃-S2 p high resolution energy spectrum of Tl; b is In₂S₃And In₂S₃-In 3d high resolution energy spectrum of Tl; c is In₂S₃Tl 4f high resolution energy spectrum of Tl.

FIG. 4 shows In prepared at a pH of 2 and a Tl concentration of 0.625. mu.M In example 1₂S₃And In₂S₃Tl at 0.5mol L^- ¹Na₂SO₄Linear cyclic voltammetry in solution scans the curve.

Fig. 5 is a plot of Δ I at-0.6V (Ag/AgCl) potential versus thallium ion concentration for

pH

2 or 6 prepared in examples 1 and 2.

FIG. 6 shows Tl in example 4⁺Δ I value response versus other metal ions plot: wherein Fe³⁺、Ni²⁺、Cr³⁺、Mg² ⁺、Ag⁺、K⁺、Co²⁺、La³⁺、Al³⁺、Na⁺、Ca²⁺、Zr⁴⁺、Cu²⁺、Zn²⁺The concentration of (D) is 100. mu.M; pb²⁺、Cd²⁺、Hg⁺、Tl⁺The concentration of (D) is 10. mu.M;

FIG. 7 shows Tl in the absence of EDTA in example 4⁺Co was compared at a solution concentration of 10. mu.M²⁺、La³⁺、Cu²⁺Response plots for Δ I values at concentrations of 100 μ M and 300 μ M.

FIG. 8 shows Tl in the absence of EDTA in example 4⁺Solution concentration of 10. mu.M for respective comparison with Pb²⁺、Hg²⁺、Cd²⁺Response plots for Δ I values at concentrations of 10 μ M and 100 μ M.

FIG. 9 shows Tl in the presence of EDTA in example 5⁺The concentration is 0 μ M or 10 μ M, and other ions are Co²⁺、La³⁺、Cu²⁺A.DELTA.I value response at a concentration of 300. mu.M is plotted.

FIG. 10 shows Tl in the presence of EDTA in example 5⁺The concentration is 0. mu.M or 10. mu.M, other ion Pb²⁺、Hg²⁺、Cd² ⁺Δ I values at concentrations of 100 μ M are response plots.

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. The drugs used were: indium trichloride tetrahydrate, absolute ethyl alcohol, Thioacetamide (TAA), thallium nitrate, ferric nitrate, nickel nitrate, chromium nitrate, magnesium nitrate, silver nitrate, potassium nitrate, cobalt nitrate, lanthanum nitrate, sodium nitrate, calcium nitrate, zirconium nitrate, copper nitrate, zinc nitrate, mercury nitrate, lead nitrate, cadmium nitrate, concentrated nitric acid, and sodium sulfate.

The instrumentation used in the examples: and (3) obtaining the crystal structures of the nano material before and after detection by using a PW 3040/60X-ray powder diffractometer. The elemental composition and surface chemical valence states of the samples were analyzed using VG ESCALABMK II X-ray photoelectron spectroscopy. And (3) using a JSM-7001F field emission scanning electron microscope to characterize the material morphology. And obtaining the microscopic appearance and the element composition of the sample by using a JEOL JEM-2100F high-resolution transmission electron microscope. And (3) acquiring an absorption spectrum of the material by using a Hitachi U-3900 ultraviolet-visible spectrophotometer. Under the irradiation of visible light (the wavelength is more than 420nm) generated by a PLS-SXE300 xenon lamp, an electrochemical workstation CHI660E of Shanghai Chenghua apparatus Limited company is used for detecting the sensing performance and representing the characteristics of a material semiconductor.

Example 1: acquisition of working curve at pH 2 of thallium nitrate solution

(1) Preparing an indium sulfide thin film electrode: cutting a fluorine-doped tin oxide (FTO) electrode into 1.5x2.5cm, then ultrasonically cleaning for 30min by using cleaning powder, ethanol and deionized water in sequence, and naturally drying. Taking two pieces of cleaned and dried FTO, placing the FTO into a polyvinyl fluoride reaction kettle with the conductive surface facing downwards oppositely. 30mL of absolute ethanol is taken from a 50mL beaker, 0.4399g of indium trichloride tetrahydrate is added while stirring and the mixture is completely dissolved, 0.2255g of Thioacetamide (TAA) is added, magnetic stirring is carried out at room temperature until the solution is light yellow, 10mL of light yellow solution is taken from a measuring cylinder, and the solution is poured into a polyvinyl fluoride reaction kettle prepared with an FTO glass sheet with a downward conductive surface. The reaction kettle is moved to an oven with the temperature of 80 ℃ for reaction for 4 hours. And taking out the indium sulfide electrode after reaction, washing substances on the non-conducting surface with ethanol, and drying with nitrogen.

(2) Putting the prepared sulfur-rich indium sulfide electrode In₂S₃Reacting for 20min In 10mL of 10 mu M thallium nitrate solution at the pH value of 2 and the temperature of 50 ℃, and recording as In₂S₃-Tl。

In obtained when the concentration of thallium nitrate solution was 10. mu.M₂S₃And In₂S₃The topographic characterization of-Tl is shown In FIG. 1, where a is In₂S₃SEM picture of (1); b is In₂S₃SEM picture of Tl; c is In₂S₃A TEM image of (B); d is In₂S₃TEM image of Tl. In₂S₃And In₂S₃Results of Scanning Electron Microscope (SEM) tests of Tl show that the indium sulfide electrode with no thallium and thallium on the surface consists of a lamellar structure. The thickness of the nanoplatelets is about 10nm and the thickness of the entire film is 2.8 and 2.6 μm, respectively. The Transmission Electron Microscope (TEM) results further demonstrate the lamellar structure of the material, with the apparent clear lattice fringes indicating a higher crystallinity of the material.

In obtained when the concentration of thallium nitrate solution was 10. mu.M₂S₃And In₂S₃The X-ray powder diffraction pattern of-Tl is shown In FIG. 2, and In can be seen from FIG. 2₂S₃And In₂S₃Diffraction peaks of Tl samples are similar, and signals of (311) (400) (440) (533)4 crystal planes are all generated. Indicating that the indium sulfide exists in a cubic phase before and after the reaction, and the crystallinity and the crystal phase are not changed. This result also indicates that thallium binding to indium sulfide occurs primarily at the crystal surface, as is thallium binding to sulfur-rich surface states, with thallium not being incorporated into the indium sulfide lattice.

In obtained when the concentration of thallium nitrate solution was 10. mu.M₂S₃And In₂S₃An X-ray photoelectron spectroscopy (XPS) pattern of-Tl, wherein a is In, is shown In FIG. 3₂S₃And In₂S₃-S2 p high resolution energy spectrum of Tl; b is In₂S₃And In₂S₃-In 3d high resolution energy spectrum of Tl; c is In₂S₃Tl 4f high resolution energy spectrum of Tl. As can be seen In FIG. 3, the indium sulfide (i.e., In) after photoelectrochemical detection₂S₃Tl) the surface has thallium element, which indicates that the detection mechanism is the chemical bond combination of thallium and the indium sulfide surface. Before and after the reaction, the XPS signal of In indium sulfide does not change obviously, which indicates that the chemical environment of In is not changed In the thallium binding process. However, the shift of the S signal before and after the reaction is obvious,indicating that a new sulfur-thallium chemical bond is generated during the detection process, thereby changing the chemical environment of S in the original sulfur-rich surface state.

(3) Photoelectrochemical testing: platinum sheet as counter electrode, Ag/AgCl as reference electrode, 0.5mol L^-1Na₂SO₄In as the electrolytic solutions, respectively₂S₃And In₂S₃Tl is used as a working electrode to form a three-electrode system, under the irradiation of visible light, a linear cyclic voltammetry method is used, the scanning voltage range is-0.8-0.4V, illumination and non-illumination cyclic switching is carried out, and a blank sample In is collected₂S₃And In₂S₃Reading the current value at-0.6V by using the photocurrent signal of-Tl, and respectively recording the intensity of the current signal as I₀And I, the signal intensity difference Δ I ═ I₀-I。

(4) And (3) modifying the concentration of the thallium nitrate solution in the step (2) from 10 mu M to any four concentrations of 0.625-10 mu M (wherein one concentration is 0.625 mu M and does not comprise 10 mu M), and keeping the rest unchanged, and then repeating the operations of the steps (1) - (3) to obtain delta I corresponding to other four concentrations. In prepared at a concentration of 0.625 μ M, pH ═ 2 In₂S₃And In₂S₃Tl at 0.5mol L^-1Na₂SO₄The linear cyclic voltammetry scan in solution is shown in FIG. 4, and plotting Δ I against thallium concentration at-0.6V (Ag/AgCl) potential yields a linear relationship of Δ I against thallium concentration, i.e., the working curve, as shown in FIG. 5.

Example 2: acquisition of working curve at pH 6 of thallium nitrate solution

The thallium nitrate solution of the step (2) in example 1 was adjusted to pH 6, and the remainder was kept unchanged, example 1 was repeated, and Δ I was plotted against the thallium concentration at a potential of-0.6V (Ag/AgCl) to obtain a linear relationship between Δ I and the thallium concentration, i.e., a working curve at pH 6, as shown in fig. 5.

As can be seen from FIG. 5, the Tl concentrations we can measure were all 0.625. mu.M, i.e., the detection limit was 0.625. mu.M. However, under the condition of pH 2, the Δ I value is larger than that at pH 6 for the same Tl concentration, and the detection current becomes more significant. That is, the phenomenon is more obvious under the condition of high acidity by the proposed photoelectric detection method for monovalent thallium induced by the surface state of the crystalline material. Therefore, the following selective test, the anti-interference test and the actual sample test were performed under the condition of pH 2.

Example 3: detection of thallium concentration in actual aqueous solution and accuracy characterization thereof

(1) 100mL of tap water (school district of Guangzhou university City) and Zhujiang water (Zhujiang river system of Guangzhou university City) were each centrifuged for 5 minutes (10000 rpm), and the supernatant was filtered through a microfiltration membrane (0.22. mu.m). The thallium content of these two actual samples was determined by analytical chemistry spiking recovery at a pH of 2. The results showed that no monovalent thallium was detected in both water samples. Respectively adding 2, 5 and 8 mu M of univalent thallium into the two water samples to obtain six water samples to be detected;

(2) step (1) of example 1 was repeated to obtain a sulfur-rich indium sulfide electrode In₂S₃In the prepared sulfur-rich indium sulfide electrode₂S₃Reacting for 20min In a water sample to be detected with the pH value of 2 and the volume of 10mL at the temperature of 50 ℃, and recording as In₂S₃-Tl；

(3) Platinum sheet as counter electrode, Ag/AgCl as reference electrode, 0.5mol L^-1Na₂SO₄In as the electrolytic solutions, respectively₂S₃And In₂S₃Tl is used as a working electrode to form a three-electrode system, under the irradiation of visible light, a linear cyclic voltammetry method is used, the scanning voltage range is-0.8-0.4V, illumination and non-illumination cyclic switching is carried out, and a blank sample In is collected₂S₃And In₂S₃The photocurrent signals of Tl, the current signal intensities being respectively denoted as I₀And I, the signal intensity difference Δ I ═ I₀And (4) reading the thallium concentration corresponding to delta I under the potential of-0.6V (Ag/AgCl) in the working curve obtained in the example 1, namely the thallium solution concentration in the water sample to be detected. And comparing the experimental value with the added standard value, and calculating to obtain the standard recovery rate. The measured standard recovery rate of tap water is 96.5-103.4%, the standard recovery rate of Zhujiang water is 95.2-106%, and the precision between parallel samples is higher. These resultsThe method has higher accuracy in the analysis and detection of actual samples. Specific results are shown in table 1.

TABLE 1 results of detection of thallium ion in actual samples

Example 4: selectivity test

Thallium replacement by Fe in step (2) of example 1³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺，Zn²⁺,Pb²⁺,Cd²⁺,Hg⁺And Tl⁺Wherein Fe is³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co² ⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺And Zn²⁺At a concentration of 100. mu.M, Pb²⁺,Cd²⁺,Hg⁺,Tl⁺The concentration of (2) was 10. mu.M. The remaining steps (1) to (3) of example 1 were repeated, with the remainder unchanged, to obtain values of Δ I at-0.6V (Ag/AgCl) potential for various metal ions, and the results are shown in fig. 6. FIG. 6 shows that even Fe³⁺To Zn²⁺The concentration of the 14 metal ions is Tl⁺The photocurrent response (Δ I) was also very weak at 10 times the concentration. When it is Pb²⁺,Cd²⁺,Hg⁺Concentration maintenance and Tl of these 3 common heavy metal contaminants⁺At the same concentration (all 10. mu.M), with Tl⁺Their response is also small compared to Δ I. These results show that the photoelectrochemical system designed by the invention has high selectivity to thallium.

When we handle Co²⁺,La³⁺,Cu²⁺The concentration of Pb is increased to 100-300 mu M²⁺,Cd²⁺,Hg⁺When the concentration of (2) is increased to 100. mu.M (according to the theory of soft and hard acids and bases and the results of related researches, the binding capacity of the remaining 11 ions to sulfur is very weak compared with that of the 6 ions, and no interference is generated even if the concentration is increased, and the related experiments prove that the interference experiment that the concentration of the remaining 11 ions is increased is not supplemented), the delta I value response and the Tl under the potential of-0.6V (Ag/AgCl) of the ion are increased⁺A significant improvement occurs compared to (10 μ M), as shown in particular in figures 7 and 8. That is, when monovalent thallium and one or more of these 6 ions are present in a complex system at high concentrations at the same time, the signal generated by these ions will have some effect on thallium detection. In order to solve the problem, a corresponding anti-interference scheme is designed.

Example 5: anti-interference experimental test

(1) The experiment is divided into six groups, each group of interference ion solution contains single metal ions M with different concentrations, the volume of each group of interference ion solution is 10mL, wherein A1 group is Co ²⁺300 μ M aqueous solution, La in group A2 ³⁺300 μ M aqueous solution, Cu in group A3 ²⁺300 μ M aqueous solution, Pb in group B1²⁺Aqueous solution with concentration of 100 μ M, Cd in group B2 ²⁺100 μ M aqueous solution, Hg in group B3⁺Aqueous solution at a concentration of 100. mu.M.

(2) Step (1) of example 1 was repeated to obtain a sulfur-rich indium sulfide electrode In₂S₃Adding sulfur-rich indium sulfide electrode In₂S₃Respectively reacting with EDTA at 50 deg.C for 20min, wherein the molar amount of EDTA In each reaction is equal to that of metal ion M In six groups of interfering ion solutions, to obtain six groups of blank samples, which are marked as EDTA-In₂S₃；

(3) EDTA (ethylene diamine tetraacetic acid) with the molar weight equal to that of the metal ion M is added into the interference ion solutions of the groups A1, A2, A3, B1, B2 and B3 respectively, and the pH value of the solution is adjusted to be 2; step (1) of example 1 was repeated to obtain a sulfur-rich indium sulfide electrode In₂S₃To convert sulfur-rich indium sulfide into electricityExtremely In₂S₃Respectively placing In the 6 groups of interfering ion solution, reacting at 50 deg.C for 20min to obtain EDTA-In₂S₃-M；

(4) Platinum sheet as counter electrode, Ag/AgCl as reference electrode, 0.5mol L^-1Na₂SO₄As the electrolyte, corresponding blank EDTA-In was used₂S₃And EDTA-In₂S₃the-M is used as a working electrode to form a three-electrode system, under the irradiation of visible light, a linear cyclic voltammetry method is used, the scanning voltage range is-0.8-0.4V, illumination and non-illumination cyclic switching is carried out, and a blank sample EDTA-In is collected₂S₃And EDTA-In₂S₃The photocurrent signals of-M, the current signal strengths are respectively denoted as I₀And I_MDifference in signal intensity Δ I_M＝I₀-I_M。

In the presence of EDTA, Tl⁺The concentration is 0 μ M or 10 μ M, and other ions are Co²⁺、La³⁺、Cu²⁺A comparison of the response of the Δ I values at 300. mu.M concentration is shown in FIG. 9.

In the presence of EDTA, Tl⁺The concentration is 0. mu.M or 10. mu.M, other ion Pb²⁺、Hg²⁺、Cd²⁺A comparison of the response of the Δ I values at a concentration of 100. mu.M is shown in FIG. 10.

The results show that the ions of the six groups A1, A2, A3, B1, B2 and B3 respectively have delta I in the presence of EDTA with equal amount of substances_MThe value response is weak. Due to the strong coordination effect of EDTA and the higher stability of the corresponding complex, 6 ions in the solution exist basically in the form of EDTA complex, but not in a free state. After coordination of metal ions, the metal ions can not be combined with the sulfur-rich surface state of the indium sulfide surface, thereby obtaining lower delta I_MThe value is obtained. When the interfering ion solution of six groups A1, A2, A3, B1, B2 and B3 in the step (3) is added with 10 mu M Tl⁺When, Tl⁺The signal of Δ I of (a) will appear immediately and the strength reaches the level of the photocurrent signal of EDTA-TI without interfering ions (as shown in FIGS. 9 and 10). The experimental results show that at Tl⁺And in complex systems in which a plurality of heavy metal ions are presentIndeed, EDTA may act as a masking agent for 6 metal ions of groups a1, a2, A3, B1, B2, B3. In combination with the results of the selectivity experiments, we can conclude that: when it is Pb²⁺,Cd²⁺,Hg⁺Is less than 10 mu M, Co²⁺,La³⁺,Cu²⁺When the single concentration or the total concentration is less than 100 mu M, the photoelectric method designed by the invention can be directly used for quantitatively detecting the Tl⁺. When at least one of these conditions occurs, i.e. Pb²⁺,Cd²⁺,Hg⁺Up to 100. mu.M, Co, in single or total concentration²⁺,La³⁺,Cu²⁺When the single concentration or the total concentration of the sulfur-rich indium sulfide reaches 300 mu M, only the sulfur-rich indium sulfide electrode In needs to be added₂S₃The reaction product of ETDA with the amount of interfering ions and other substances is used as a new blank sample electrode, and EDTA with the molar amount equal to that of the interfering ions is added into the solution to be tested as a masking agent, so that the Tl can be treated⁺And (4) carrying out quantitative 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 photoelectrochemical method for quantitative detection of monovalent thallium, comprising the steps of:

(1) taking two fluorine-doped tin oxide electrodes, placing the two fluorine-doped tin oxide electrodes into a polyvinyl fluoride reaction kettle with the conductive surfaces facing downwards; adding indium trichloride tetrahydrate into absolute ethyl alcohol, stirring and dissolving uniformly, adding thioacetamide, stirring until the solution is light yellow, pouring the light yellow solution into a polyethylene fluoride reaction kettle with an FTO glass sheet with a conductive surface facing downwards for reaction, taking out after the reaction, washing substances with a non-conductive surface with ethyl alcohol, and drying with nitrogen to obtain the indium sulfide thin film electrode In₂S₃；

(5) detecting Fe in solution to be detected³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The concentration of the 17 interfering ions is determined as Pb in the solution to be measured²⁺,Cd²⁺,Hg⁺When the sum of the concentrations of the other 14 ions is less than 10 mu M and the sum of the concentrations of the other 14 ions is less than 100 mu M, replacing the thallium nitrate solution prepared in the step (2) with a solution to be detected with the same volume and the same pH value, then repeating the operations in the steps (1) to (3), substituting the obtained photocurrent signal intensity difference Delta I into the working curve in the step (4), wherein the obtained thallium concentration is the thallium concentration of the solution containing thallium to be detected;

(6) detecting Fe in solution to be detected³⁺,Ni²⁺，Cr³⁺,Mg²⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The concentration of the 17 interfering ions is determined when at least one of the following two conditions occurs in the solution to be measured, namely Pb²⁺,Cd²⁺,Hg⁺The sum of the concentrations of the above-mentioned components is higher than 10 μ M or the sum of the concentrations of other 14 ions is higher than 100 μ M, and the specific operation is as follows:

(6.3) EDTA-In obtained In step (6.1)₂S₃And EDTA-In obtained In step (6.2)₂S₃-M replaces In step (3) respectively₂S₃And In₂S₃And (4) Tl, then repeating the step (3), and substituting the obtained photocurrent signal intensity difference Delta I into the working curve in the step (4), wherein the obtained thallium concentration is the thallium concentration of the thallium-containing solution to be detected.

2. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

the relative dosage ratio of the absolute ethyl alcohol, the indium trichloride tetrahydrate and the thioacetamide in the step (1) is 30-60 mL: 0.4399-0.8798 g: 0.2255-0.4510 g;

the reaction in the step (1) is to move the reaction kettle to an oven with the temperature of 80-100 ℃ for reaction for 4-6 h;

3. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

and (2) before use, the fluorine-doped tin oxide electrode in the step (1) is sequentially subjected to ultrasonic cleaning for 10-20min by using cleaning powder, ethanol and water respectively, and is naturally dried for use.

4. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

and (3) the pH value of the thallium nitrate solution in the step (2) is 2 or 6.

5. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

and (3) the pH value of the thallium nitrate solution in the step (2) is 2.

6. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

the concentration of the thallium nitrate solution in the step (2) is 0.625-10 mu M;

the dosage of the thallium nitrate solution in the step (2) is such that 8-12mL of thallium nitrate solution is used for each electrode of 1.5 x2.5cm;

7. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

the illumination and non-illumination cyclic switching in the step (3) is realized through manual switching, namely light blocking and non-light blocking in the traditional sense are realized, light is blocked at intervals by using a hard board, and the interval or switching time is 1 second.

8. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

the plurality of groups in the step (4) means 5 or more groups.

9. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

10. The photoelectrochemical method for quantitatively detecting monovalent thallium according to claim 1, characterized in that:

the dosage of the EDTA added in the step (6.2) meets the condition that the molar weight of the EDTA is Fe in the solution to be detected³⁺,Ni²⁺，Cr³⁺,Mg² ⁺,Ag⁺,K⁺,Co²⁺,La³⁺,Al³⁺,Na⁺,Ca²⁺,Zr⁴⁺,Cu²⁺，Zn²⁺Pb²⁺,Cd²⁺,Hg⁺The sum of the molar amounts of these 17 interfering ions; the reaction in the step (6.2) is carried out for 10-20min at the temperature of 50-60 ℃.