CN112034027B - Electrochemical sensing electrode for measuring ammonia nitrogen ions in wastewater and preparation method thereof - Google Patents
Electrochemical sensing electrode for measuring ammonia nitrogen ions in wastewater and preparation method thereof Download PDFInfo
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- -1 ammonia nitrogen ions Chemical class 0.000 title claims abstract description 25
- 238000002360 preparation method Methods 0.000 title claims abstract description 11
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- 238000000034 method Methods 0.000 claims abstract description 26
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- SOIFLUNRINLCBN-UHFFFAOYSA-N ammonium thiocyanate Chemical compound [NH4+].[S-]C#N SOIFLUNRINLCBN-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y15/00—Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
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- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/333—Ion-selective electrodes or membranes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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Abstract
The invention discloses a sensing electrode for detecting the content of ammonia nitrogen ions in wastewater and a preparation method thereof, wherein the sensing electrode comprises the following steps: (1) ultrasonically dispersing a porous nano flaky CZTS powder sample in a chitosan-acetic acid solution to obtain a CZTS-chitosan-acetic acid mixed solution; (2) dripping the CZTS-chitosan-acetic acid mixed liquid on the surface of a glassy carbon electrode; (3) and drying the glassy carbon electrode. The lowest detection limit of this electrode was 30.0 μmol/L (S/N ═ 10). Thus, the process was at 0.5mmol/L H2SO4The determination of the content of ammonia nitrogen ions in the base solution is successful.
Description
Technical Field
The invention relates to an electrochemical sensing electrode and a preparation method thereof, belonging to the technical field of electrochemical environment detection.
Background
The discharge of industrial wastewater containing ammonia into the water environment causes water eutrophication and fish toxicity. Determination of ammonia nitrogen ion (NH) in wastewater3-NH4 +) There are various methods for concentration, including spectrophotometry, ion chromatography, and electrochemical methods. The spectrophotometry is used as a national standard method for measuring the content of ammonia nitrogen ions, has high sensitivity, but has the defects of more complex operation process and higher purity of required reagents. The ion chromatography based on the ion exchange reaction has the advantages of strong separation capability and high sensitivity, but has the defects of narrow detection range and high cost by using a special ion spectrometer. Electrochemical ammonia removal has proven to be a very promising method of degrading ammonia nitrogen ions in wastewater. In fact, it only consumes electric energy to eliminate pollutants, and does not need chemical substances or bacteria, and in the process, the loss and secondary pollution are reduced as much as possible, so that the aim of optimizing energy consumption is fulfilled. Therefore, study was madeThe electrochemical method which is simple and convenient to operate, high in sensitivity and capable of accurately detecting the content of the ammonia nitrogen ions has important significance on human health and environmental safety.
At present, the electrochemical method adopted at home and abroad for detecting the content of ammonia nitrogen ions in an aqueous solution mainly focuses on the research on all-solid-state Ion Selective Electrodes (ISEs), and a sensitive membrane is utilized to convert the specific ion activity into a potential signal. Compared with the traditional internal liquid-filled ion selective electrode, the ISEs have the advantages of durability, easiness in miniaturization, capability of placing the electrode at any position during measurement, no need of considering the problem of internal liquid filling leakage and the like. The ISEs are that sensitive films are directly and uniformly coated on electronic conductors, and the interface potential is unstable and becomes a fatal problem because charge transfer substances are lacked between the ion selective films and the solid conductive substrates. Research shows that a water layer exists between the sensitive membrane and the solid conducting layer, and a half-cell reaction can occur in the water layer to generate oxygen, so that the potential response is interfered, and the detection accuracy of the electrode is influenced. In addition, ISEs are influenced by electrode conductor materials, the potential signal response is limited, the detection linear width is only 2-3 orders of magnitude, the detection range is not suitable for environmental monitoring concentration in national emission standards, and the practical applicability of the ISEs to real-time monitoring of the concentration of ammonia nitrogen ions is poor.
The electrode is the site of electrochemical reaction, and the electrode material is an important determinant factor of electrochemical analysis, so the key for determining the content of ammonia nitrogen ions in wastewater by adopting an electrochemical method is how to select the electrode and a proper electrochemical system. The nanometer material is in the transition region of microscopic world and macroscopic object with atomic molecules as the first part in size, has larger specific surface area, can provide more active sites, improves the chemical reaction rate, effectively accelerates the electron transfer speed, and can be used as a bridge for connecting a substance to be detected and an electrochemical signal. In recent years, polymetallic sulfides have wide application prospects in the fields of catalysis, photoelectric devices, solar cells, sensing and the like due to unique physical and chemical properties of the polymetallic sulfides. The ternary and quaternary transition metal sulfide has narrower optical band gap and excellent conductivity, and the electronegativity of sulfur is lower than that of oxygen, so that the structure of the sulfide can be prevented from being decomposed due to interlayer elongation, and electrons can be more easily separated in the structureAnd (5) transmitting in the structure. In addition, the structure of the polymetallic sulfide has a plurality of intrinsic vacancy defects which can be used as active sites in an electrocatalytic reaction to accelerate the progress of a redox reaction. At present, quaternary transition metal sulfides Cu2ZnSnS4The application of (CZTS) on the electrochemical sensing electrode is not reported.
Disclosure of Invention
In order to solve the limitation of narrow linear width of the existing electrochemical potential detection and widen the application of nano materials on electrochemical sensing electrodes, the research result can be used for treating ammonia nitrogen ions (NH) in wastewater on the premise of optimizing energy consumption3-NH4 +) The content can be monitored in real time, accurately and rapidly.
The invention provides a preparation method of a sensing electrode for detecting the content of ammonia nitrogen ions in wastewater, which comprises the following steps:
(1) ultrasonically dispersing a porous nano flaky Cu2ZnSnS4(CZTS) powder sample in a chitosan (more than or equal to 100cps) -acetic acid solution to obtain a CZTS-chitosan-acetic acid mixed solution;
(2) dripping the CZTS-chitosan-acetic acid mixed liquid on the surface of a glassy carbon electrode;
(3) and drying the glassy carbon electrode.
Preferably, the chitosan-acetic acid solution is that the concentration of chitosan in the acetic acid solution is 0.2-1.0 wt%.
Preferably, the concentration of the CZTS powder sample in the chitosan-acetic acid solution is 0.5-2.0 mg/mL.
Preferably, the glassy carbon electrode is pretreated by polishing with alumina powder before dispensing.
Preferably, the CZTS-chitosan-acetic acid mixed liquid is dripped on the surface of a glassy carbon electrode, and the dripping amount is 0.084-0.14 mg/cm2。
The invention also provides the sensing electrode for detecting the content of ammonia nitrogen ions in wastewater, which is obtained by the preparation method.
NH in aqueous solution of sensing electrode3-NH4 +The lowest detection limit of (2) was 30.0. mu. mol/L (S/N10).
The sensing electrode is coupled to NH3-NH4 +The concentration is in the range of 1.0-600.0 mmol/L, and the sensitivity is 8.29 muA/(mmol/L cm)2) (ii) a At NH3-NH4 +The concentration is in the range of 0.1-1.0 mmol/L, and the sensitivity is 96.14 muA/(mmol/L cm)2)。
Advantageous effects
The invention successfully prepares the Cu based on the porous nano sheet2ZnSnS4(CZTS) high performance electrochemical sensing electrode. Wherein, the porous structure of CZTS can change the diffusion region from plane diffusion to effective thin layer diffusion, so that the sensing electrode pair NH based on the structure3-NH4 +Has a wider linear range in NH3-NH4 +The concentration is in the range of 1.0-600.0 mmol/L, and the linear regression equation is IP(μA)＝0.58C(mmol/L)+12.32(R20.9989), the sensitivity was 8.29 μ a/(mmol/L cm)2) (ii) a At NH3-NH4 +The concentration is in the range of 0.1-1.0 mmol/L, and the linear regression equation is IP(μA)＝6.73C(mmol/L)+1.52(R20.9990), and the sensitivity was 96.14. mu.A/(mmol/L cm)2). The lowest detection limit was 30.0 μmol/L (S/N ═ 10). Thus, the process was at 0.5mmol/L H2SO4To NH in the base liquid3-NH4 +The determination of the content was successful.
Drawings
In order that those skilled in the art will better understand the disclosure, the invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The invention is illustrated in figure 10.
FIG. 1 is an X-ray diffraction pattern of porous nanosheet-like CZTS prepared in example 1.
FIG. 2 is a Raman spectrum of porous nanosheet CZTS prepared in example 1.
FIG. 3 is a scanning electron micrograph of porous nanosheet-like CZTS prepared in example 1 ((a): 5 min; (b): 15 min; (c): 30 min; (d): 90 min;).
FIG. 4 shows the GCE, CHIT/GCE, CZTS/CHIT/GCE electrodes prepared in example 2Cyclic voltammograms. In the graph (a), the curves a, b and c are NH at the GCE, CHIT/GCE, CZTS/CHIT/GCE electrodes3-NH4 +Cyclic voltammetry of an aqueous solution at a concentration of 60.0 mmol/L; curve d is the electrode NH at CZTS/CHIT/GCE3-NH4 +0.5mmol/L H at a concentration of 60.0mmol/L2SO4Cyclic voltammograms in solution; curves e, f, g and h in the graph (b) are respectively used for preparing porous nano flaky CZTS under different microwave irradiation time (5min, 15min, 30min and 90min) conditions to obtain different CZTS/CHIT/GCE electrodes on NH3-NH4 +0.5mmol/L H at a concentration of 60.0mmol/L2SO4Cyclic voltammogram in solution.
FIG. 5 is an AC impedance profile of the GCE, CHIT/GCE, CZTS/CHIT/GCE electrodes prepared in example 2. (a) The electrode of GCE, CHIT/GCE, CZTS/CHIT/GCE has a K concentration of 5.0mmol/L3[Fe(CN)6]/K4[Fe(CN)6]An alternating current impedance profile in an aqueous solution; (b) is an equivalent circuit diagram of the electrode CZTS/CHIT/GCE.
FIG. 6 depicts CZTS/CHIT/GCE electrodes prepared in example 2 at different NH levels3-NH4 +Cyclic voltammograms in concentration solution. Graph (a) shows the potential scan rate of the CZTS/CHIT/GCE electrode at 20mV/s in NH3-NH4 +0.5mmol/L H at concentrations of 2.0, 8.0, 16.0, 30.0, 60.0, 90.0, 120.0, 150.0 and 165.0mmol/L, respectively2SO4Cyclic voltammograms in solution; graph (b) shows the response current of CZTS/CHIT/GCE electrode versus NH3-NH4 +A linear fit curve of concentration.
FIG. 7 is a cyclic voltammogram of the CZTS/CHIT/GCE electrode prepared in example 2 at different potential scan rates. Graph (a) CZTS/CHIT/GCE electrode at NH3-NH4 +0.5mmol/L H at a concentration of 2.0mmol/L2SO4Cyclic voltammograms in solution at potential scan rates of 10, 20, 40, 60, 80, 100, 120, 140, 160 and 200mV/s, respectively; FIG. b is a linear fit of the response current to the square root of the potential sweep rate for a CZTS/CHIT/GCE electrode.
FIG. 8The i-t curves for the CZTS/CHIT/GCE electrode prepared in example 2. FIG. a shows the electrode thickness of CZTS/CHIT/GCE at 0.5mmol/L H2SO4Continuous variation of NH in solution3-NH4 +Under the concentration, response current changes along with the time curve; graph (b) response current versus NH of CZTS/CHIT/GCE electrodes in different linear ranges3-NH4 +A linear fit curve of concentration.
FIG. 9 shows the stability and reproducibility of the CZTS/CHIT/GCE electrode prepared in example 2. FIG. a shows a CZTS/CHIT/GCE electrode at NH3-NH4 +0.5mmol/L H at a concentration of 50.0mmol/L2SO4Cyclic voltammograms measured at 4, 8, 12, 16, 20 and 24 days in solution at a potential sweep rate of 20mV/s, with internal plots of the response current of the CZTS/CHIT/GCE electrode versus the number of days measured; FIG. b shows the electrode of CZTS/CHIT/GCE at NH3-NH4 +0.5mmol/L H at a concentration of 50.0mmol/L2SO4In solution, the cyclic voltammograms were measured 5 times repeatedly at a potential sweep rate of 20mV/s, with the internal plot being the response current of the CZTS/CHIT/GCE electrode versus the number of repetitions.
FIG. 10 shows the interference resistance of the CZTS/CHIT/GCE electrode prepared in example 2. At 0.5mmol/L H for CZTS/CHIT/GCE electrode2SO4Adding NH into the solution3-NH4 +After the concentration of 1.0mmol/L, 1.0mmol/L of interferent (Pb) was added at response times of 180, 210, 240 and 270s, respectively2+、Cr3+/Cr6+、Hg2+And formaldehyde) under the conditions of i-t curve.
Detailed Description
The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way. The chemicals and reagents used in the scheme of the invention are as follows:
Cu(NO3)2·3H2O、Zn(CH3COO)2·2H2O、SnCl2·2H2O、CH4N2s, polyethylene glycol 400, potassium ferricyanide, potassium ferrocyanide, chitosan and methylThe aldehyde, sulfuric acid and acetic acid are all from alatin (shanghai, china) limited. The metal element solution is from China institute of metrology. All other chemicals and reagents were of analytical grade and used without further purification. All solutions were prepared with ultra pure water.
The CZTS is a p-type semiconductor material with a direct band gap, the optical band gap of the CZTS is 1.54eV, and the absorption coefficient of the CZTS on an ultraviolet-visible light wave band reaches 105cm-1The method is mainly applied to the field of solar thin film batteries. The intrinsic CZTS has rich oxidation/reduction valence and structural defects, can provide a large number of carriers, and effectively improves the photoelectric conversion rate. In the field of catalysis, as an ion sensitive substance, a carrier generated in a semiconductor often has very high chemical activity, the electrochemical reaction rate of a sensing electrode interface can be accelerated, a CZTS structure defect can provide holes and electrons, wherein a Cu hole is the most main defect for providing the hole carrier, and a main active site can be provided for an ammonia nitrogen ion oxidation reaction. Therefore, the electrochemical method for converting the ion concentration into the current signal is expected to become a new method for detecting the concentration of the ammonia nitrogen ions in the water body.
EXAMPLE 1 preparation of porous Nanoplastic CZTS
Preparation of porous nano flaky Cu by microwave and ultrasonic synergetic chemical reaction system2ZnSnS4(CZTS) Material: the method is to add 2.0mmol of Cu (NO)3)2·3H2O, 1.0mmol of Zn (CH)3COO)2·2H2O, 1.0mmol of SnCl2·2H2O, 8.0mmol of CH4N2S and 60mL of polyethylene glycol 400 are mixed and placed into a beaker, the beaker is placed into a reaction system after being completely dissolved under magnetic stirring, the total power is 800w, the reaction system is irradiated in a microwave oven for 5-90 min, and then the reaction system is cooled to room temperature in the air. And (3) separating precipitates from the solution by centrifuging at 8000rpm for 10min, washing with deionized water and ethanol for a plurality of times, and drying in vacuum at 70 ℃ for 6h to obtain the target product, namely the porous nano flaky CZTS material.
The CZTS is used as a quaternary transition metal sulfide, and is a catalytic material with rich properties, no toxicity and high environmental stability. Intrinsic CZTS has rich redox states, structural defects, and a large number of carriers. The carrier generated in the semiconductor is used as an ion sensitive material for electrocatalysis, generally has high chemical activity, and can accelerate the electrochemical reaction speed of the sensing electrode interface. And the CZTS structural defects can provide holes and electrons, wherein Cu holes are the most important defects for providing hole carriers and provide a main active center for ammonia nitrogen ion oxidation.
EXAMPLE 2 preparation of sensing electrodes
(1) Sensor electrode preconditioning
The modified Glassy Carbon Electrode (GCE) is prepared by a simple coating method.
The GCE electrode was polished with 1.0 μm and 0.05 μm alumina powders in this order to obtain a mirror-like surface, and rinsed thoroughly with distilled water between the two polishing steps as a backup electrode.
(2) Construction of CZTS/CHIT/GCE sensing electrode
A sample of 1.0mg of the CZTS powder prepared in example 1 was dispersed in 1.0mL of 0.5 wt% chitosan-acetic acid solution (CHIT) by sonication for 30min to give a CZTS-chitosan-acetic acid mixture (CZTS-CHIT).
0.010mg of chitosan-acetic acid solution (CHIT) is dripped on the surface of the GCE electrode with the diameter of 3mm, and the GCE electrode is dried at room temperature to obtain the modified CHIT/GCE electrode.
And (3) dropwise coating a 0.010mg volume of CZTS-chitosan-acetic acid mixed solution (CZTS-CHIT) on the surface of a GCE electrode with the diameter of 3mm, and drying at room temperature to obtain the modified CZTS/CHIT/GCE electrode.
Test example 1 characterization test on porous nanosheet CZTS material
The morphology of the porous nanosheets CZTS made in example 1 was characterized by scanning electron microscopy (SEM, TESCAN, LYRA 3). The composition and phase of the porous nanosheet-shaped CZTS obtained in example 1 were investigated using an energy spectrometer (EDS) and an X-ray diffractometer (XRD, Rigaku-Ultima-IV). The specific surface area of Brunauere-Emmette-Teller (BET, Quantachrome, Quadrasorb-SI) was measured.
Adsorption refers to the process of attaching atoms or molecules of one substance to the surface of another substance, and the concentration of the substance caused by the difference in the forces exerted on the molecules at the interface and the molecules in the phase. According to a multi-molecular layer adsorption model proposed by Brunauer, Emmett and Teller, an adsorption isotherm equation is established, and a BET adsorption isotherm equation is obtained:
wherein, P0-the saturated vapour pressure of the adsorbate at the adsorption temperature, Pa; p-the pressure in the adsorption process, Pa; vmSaturated adsorption capacity of the monolayer, mL/g.
By using N2The specific surface area of the porous nanosheet-shaped CZTS as an adsorbed molecule is calculated by the equation:
wherein A ism-N2Average cross-sectional area of adsorbed molecules, 0.162nm2；NA-an avogalois constant; sgSpecific surface, m2/g，SgIs proportional to Vm。
And deducing a C constant equation from the adsorption-desorption equilibrium relation of the multilayer adsorption model as follows:
wherein, C-constant; eAdsorption-heat of adsorption, cal/mol, of the first adsorption layer; eEvaporation ofHeat of vaporization, cal/mol, of the other adsorption layers. The C constant is related to the strength of an acting force field between the adsorbate and the surface, and weak adsorption is realized when the C constant is a low value; 2-50% of C, organic matter, polymer and metal; 50-200% of C, oxide and silicon oxide; c > 200, active carbon and molecular sieve. When the C constant is more than 20, the adsorbate has strong interaction with the surface of the material.
Table 1 shows the results of the microwave irradiation at different microwave irradiation timesBET and EDS test results of porous nanosheet shaped CZTS material prepared with thiourea (CS) as a sulfur source. Under the microwave irradiation effect of 5min, the specific surface area of the prepared material is only 20.6m2(ii)/g, Cu/Sn is greater than 3: 1. After the microwave irradiation reaction is carried out for 15min, the specific surface area of the prepared material is increased to 45.1m2The element ratio Cu/(Zn + Sn) is 0.967, close to 1: 1, but the metal/sulphur ratio is 1.427, greater than 1: 1. When the microwave irradiation time is 30min, the specific surface area of the material is increased to 51.3m2The C constant reaches a maximum of 114.6 per g, which is closest to the elemental ratio of the quaternary sulfide CZTS, where the ratio of the metal elements (Cu: Zn: Sn) is about 2: 1 and the metal/sulfur ratio is 1.097, close to 1: 1. The specific surface area of CZTS nano-particles synthesized by adopting a one-step sonification method in the literature is only 2.016m2(ii) in terms of/g. Therefore, the intermediate phase disappears under the microwave irradiation for 15-30 min, and the CZTS phase with the porous structure is formed. When the microwave irradiation time is longer than 15min, the longer the irradiation time is, the lower the relative content of Cu or Zn in the nanosheet is. When the microwave irradiation time is more than 30min, although the proportion of Cu and Zn elements in the metal is reduced, the proportion of the Cu element relative to the Zn element is increased from 1.98 to 2.09. This is probably due to the presence of Cu vacancies in the CZTS phase, and as the irradiation time increases, the Cu vacancies are continually filled, while the Zn sites are replaced by Sn. When the microwave irradiation time reaches 90min, the specific surface area of the nanosheet is still increased, and the C constant is reduced, which indicates that the adsorption heat on the surface of the material is reduced. The nano-sheet is not aggregated due to the increase of the specific surface area, the change of the metal/sulfur in the nano-sheet is not much about 1.019, the crystal phase is basically unchanged, but the decrease of the surface adsorption heat is probably due to the change of the lattice spacing.
TABLE 1 BET and EDS testing of porous Nanoplash CZTS materials
FIG. 1 shows XRD spectra of porous nanosheet-like CZTS prepared with CS as a sulfur source under different microwave irradiation times. Diffraction peaks of all samples were sharp angles, diffractingPeaks 28.53 °, 32.80 °, 47.33 °, 56.18 °, and 76.61 ° correspond to (112), (200), (220), (312), and (332), respectively, of CZTS (JCPDS card numbers 01-089-4714). XRD analysis shows that Cu possibly exists in the prepared material in a short reaction time2-xS phase, Cu10Sn3Phase, ZnS phase and CZTS phase. After the microwave irradiation treatment for 15min, the CZTS phase in the XRD spectrum shows obvious peaks, and weaker CZTS phase (200) and (332) crystal face diffraction peaks appear at diffraction angles of 32.80 degrees and 76.61 degrees, and in addition, Cu still exists10Sn3In addition to the phase diffraction peak, Cu appears2Sn3Phase diffraction peak, Cu2-xThe S phase and ZnS phase diffraction peaks disappeared. Weak Cu still exists in the material prepared after the reaction for 30min2Sn3Phase diffraction peak, Cu10Sn3The phase diffraction peak disappeared. The longer the reaction time, the sharper the CZTS phase diffraction peak in the sample. After a reaction time of 90min, Cu2SnS3The phases disappear in the CZTS phase.
As shown in fig. 2, the structural properties of porous nanosheets CZTS were further investigated using raman spectroscopy. The Raman spectrum results show that 333cm is observed in four samples-1There appeared a CZTS Raman peak, which coincided with the zincite structure of CZTS. In the sample at 289cm under the action of microwave irradiation for 5min and 15min-1All have Cu appeared2SnS3Raman peak. In addition, the sample irradiated for 5min was 351cm-1Has ZnS Raman peak at 475cm-1In the presence of Cu2-xS raman peak.
The experimental results show that the reaction process for preparing the porous nano flaky CZTS under different microwave irradiation times by using CS as a sulfur source and using polyethylene glycol 400 as a solvent is deduced as follows: when the temperature of the reaction solution is 170 ℃, CS is irradiated and then converted into ammonium thiocyanate, the ammonium thiocyanate is finally decomposed into ammonia and thiocyanate, and the thiocyanate is further decomposed into hydrogen sulfide, carbon disulfide, nitrogen and acetonitrile. Cu having reducing property when metal ion is dissolved in polyethylene glycol 4002+And Sn having oxidizing property2+Cu which is firstly combined with Cu which is unstable in the initial stage of microwave irradiation heating10Sn3Therefore, characterization of sodium by EDSThe Cu/Sn ratio in the rice grains was about 3: 1. After the formation of hydrogen sulfide from thiocyanic acid, Zn2+Reacting with hydrogen sulfide to generate stable ZnS, and observing by XRD and Raman to obtain Cu2+，Sn2+With hydrogen sulfide to form Cu2SnS3Cu as intermediate product in phase process2-xAnd (5) generating S. Continuing microwave irradiation, and allowing ZnS phase to enter Cu2SnS3Phase, finally obtaining Cu2ZnSnS4And (4) phase(s). The reaction formula is shown as follows:
FIG. 3 is a scanning electron microscope used to characterize the sample morphology at different reaction times. The reaction time is 5min, and the prepared granule has a diameter of about 40nm and is in the shape of ball cactus. When the reaction time was increased to 15min, fine nanoplatelets with a diameter of about 100nm were formed on the surface of the spherical particles. With further increase in reaction time to 30min, nanosheet-like CZTS with a uniform diameter of about 150nm was prepared. As the microwave irradiation time was extended, when the microwave irradiation time was 90min, the size of the nanosheets gradually increased with a small number of particles, as shown by the black box in fig. 3 (d).
Test example 2 test of sensor electrode
All electrochemical experiments were performed in a conventional three-electrode electroanalytical system controlled by CHI760D electrochemical workstation (Shanghai Huachen instruments, Inc., China), a glassy carbon electrode GCE (diameter 3mm) or a modified GCE electrode as a working electrode, an Ag/AgCl electrode as a reference electrode, and a platinum wire as a counter electrode. All experiments were performed at room temperature. The physicochemical properties of the spiked samples were studied using an acidimeter (PHS-3C, Rex instruments and factories, Shanghai, China) and a spectrophotometer (Shimadzu UV 3600).
(1) Electrolyte solution contrast and contrast of sensing material
In FIG. 4(a), the curves a, b and c are respectively the potential scan rate at 20mV/s for an unmodified GCE electrode, a GCE electrode modified with chitosan-acetic acid solution (CHIT) and a GCE electrode modified with CZTS-chitosan-acetic acid mixture (CZTS-CHIT) (prepared in example 2) at NH3-NH4 +Cyclic voltammogram in an aqueous solution at a concentration of 60.0 mmol/L.
a. b no NH appeared in cyclic voltammogram3-NH4 +Shows that the surfaces of the two electrodes do not have NH pairs3-NH4 +The electroactive substance of (1).
The cyclic voltammogram at a potential of-0.089V (vs. Ag/AgCl) had significant NH3-NH4 +Oxidation peak, response current intensity is 16.84 muA, this is because the porous nano flaky CZTS material with higher specific surface area is an electroactive substance, NH3-NH4 +Provides a channel for redox and electron conduction.
FIG. 4(a) shows the cyclic voltammetry curve of the electrode of GCE modified with CZTS-Chitosan-acetic acid mixture (CZTS-CHIT) (prepared in example 2) in NH3-NH4 +0.5mmol/L H at a concentration of 60.0mmol/L2SO4Cyclic voltammogram in solution, the potential for NH at-0.047V (vs. Ag/AgCl)3-NH4 +The oxidation peak, response current intensity is 46.70 μ A, the oxidation peak of d cyclic voltammogram is slightly shifted in positive potential compared with the oxidation peak of c cyclic voltammogram, but the response current intensity is obviously improved, therefore, the response current intensity is 0.5mmol/L H2SO4Under the environment of base liquid, the oxidation reduction of ammonia nitrogen ions can generate higher response current.
CS is used as a sulfur source, and the GCE electrodes are respectively modified by CZTS materials prepared under different microwave irradiation times, for example, in the figure 4(b), the GCE electrodes modified by the CZTS materials are prepared under the conditions that the microwave irradiation time is 5min, 15min, 30min and 90min respectively for e, g, h and f curves, and the potential scanning rate is 20mV/s, and NH is generated3-NH4 +0.5mmol/L H at a concentration of 60.0mmol/L2SO4Cyclic voltammogram in solution. The e-cyclic voltammogram does not have an oxidation peak, which indicates that no NH exists on the surface of the electrode3-NH4 +The electroactive substance of (1). g. h and f cyclic voltammetry curves show that the potential has obvious oxidation peaks at-0.047V (vs. Ag/AgCl), which indicates that the porous nano flaky CZTS material with the kesterite structure synthesized by microwave irradiation time of more than or equal to 15min can react with NH3-NH4 +Has an electrochemical response. In addition, the response currents of the g, h and f cyclic voltammograms increase with the increase of the microwave irradiation time when the material is prepared, because the content of the porous nanosheet-shaped CZTS in the synthesized material increases with the increase of the microwave irradiation time. However, the oxidation peak-to-peak current of the f cyclic voltammogram at a potential of-0.047V (vs. Ag/AgCl) is too low relative to that of the g cyclic voltammogram, and higher sensitivity cannot be obtained; the higher polarization current of the h-cycle voltammogram with the increase of the potential may be caused by the generation of some intermediate products in the electrochemical reaction process due to the existence of some particulate structure substances in the modified nanosheet material.
Based on a porous nanosheet structure and high specific surface area CZTS, a CZTS/CHIT/GCE electrode for detecting the content of ammonia nitrogen ions is constructed, and the sensing electrode is coupled with NH3-NH4 +The oxidation reaction of (a) has a good voltammetric response with a linear range of: high concentration of 1.0 to 600.0mmol/L (R)20.9989), sensitiveThe degree is 8.29 muA/(mmol/L cm)2) (ii) a Low concentration of 0.1-1.0 mmol/L (R)20.9990), and the sensitivity was 96.14. mu.A/(mmol/L cm)2) (ii) a The minimum detection limit is 30.0 μmol/L (signal-to-noise ratio S/N10). The content of ammonia nitrogen ions in the solution sample is measured by adopting a standard addition method. The relative standard deviation of 5 times of parallel measurement is 1.00-2.75%, and the recovery rate is 92.1-101.7%. CZTS/CHIT/GCE electrode for electrochemical detection of NH3-NH4 +The new platform of (1).
(2) Alternating current impedance EIS
FIG. 5 shows the ratio of 5.0mmol/L K3[Fe(CN)6]/K4[Fe(CN)6]Ac impedance curve diagram of GCE electrode modified by unmodified GCE electrode, chitosan-acetic acid solution (CHIT) and CZTS-chitosan-acetic acid mixed solution (CZTS-CHIT) in aqueous solution (prepared in example 2). R of unmodified GCE electrodectThe value was 99.5Ohm/cm2The conductivity is strongest; after the surface of the GCE electrode is modified by chitosan-acetic acid solution (CHIT), the conductivity of the GCE electrode is poor, and R isctThe value was 109.0Ohm/cm2(ii) a After the mixed solution of CZTS-chitosan-acetic acid (CZTS-CHIT) is coated on the surface of the GCE electrode, the conductivity is obviously improved, and R isctThe value was 104.0Ohm/cm2. The electrocatalytic properties of the sensing electrode can be explained by the application of porous structured substances in the "mass transfer theory". The mass transfer theory considers that: the process of mass transport is complex and generally involves both thin layer diffusion and semi-limiting diffusion. When the material of the modified electrode is a conductive porous material, the diffusion at the electrode will change from the semi-limiting diffusion of the unmodified electrode to an efficient thin layer diffusion. Analyte NH3-NH4 +When contacting with the electrode surface, the nano-sheet-shaped porous CZTS material quickly reaches the surface of the porous nano-sheet-shaped CZTS material through thin-layer diffusion, is adsorbed on the large specific surface of the porous nano-sheet-shaped CZTS material to contact with an active site, and is beneficial to NH3-NH4 +Oxidizing charge transfer and accelerating electrocatalytic reaction.
TABLE 2 at 5.0mmol/L K3[Fe(CN)6]/K4[Fe(CN)6]R of different electrodes in aqueous solutionctValue determination
(3) Different NH3-NH4 +Cyclic voltammogram CV at concentration
We aimed at the electrode pair of CZTS/CHIT/GCE NH3-NH4 +The electrochemical sensitivity was studied. The electrochemical cyclic voltammetry response is influenced by concentration, FIG. 6(a) is a CZTS/CHIT/GCE electrode at a potential sweep rate of 20mV/s at 0.5mmol/L H2SO4With NH in the base liquid3-NH4 +Cyclic voltammogram with change in concentration. It shows a co-ordination with NH3-NH4 +The concentration is increased, and the oxidation peak-to-peak current is gradually increased. FIG. 6(b) shows NH3-NH4 +Concentration versus peak current, NH3-NH4 +The increase in concentration from 2.0mmol/L to 165.0mmol/L is a good linear relationship with peak current (R)2＝0.9991)。
(4) Minimum NH3-NH4 +Cyclic voltammograms CVs at different potential scan rates at concentration
The reversibility of the electrode reaction can be judged according to the oxidation peak potential difference of the cyclic voltammetry curve. The reversibility of the electrode reaction mainly depends on the magnitude of the rate constant of the electrode reaction and is also related to the potential scanning rate. When the potential scanning speed is changed, the growth of the diffusion layer on the surface of the sensing electrode is different along with the difference of the potential scanning speed. Under the slower potential scanning speed, the growth rate of the diffusion layer is prior to the scanning speed, electrons are rapidly transferred in the electrode reaction process, the dynamic electrode reaction is adopted, the peak current should appear under the same potential, the peak current is increased along with the increase of the potential scanning speed, and a good linear relation is presented between the peak current and the potential scanning speed, and the electrode reaction is a reversible electron transfer reaction; when the transfer or transfer rate of electrons is slower than the scan rate, the peak current is not at the same potential, and the electrode reaction is an irreversible electron reaction. As can be seen from FIG. 7(a), when NH is present3-NH4 +The concentration is 2.0In mmol/L, the potential scanning speed is within the range of 10-140 mV/s, peak currents are all present at the potential of-0.047V (vs. Ag/AgCl), and the electrode reaction is a reversible electron transfer reaction; when the potential scanning rate is more than 140mV/s, the potential of the peak current generates positive deviation, the electron transfer or transmission generates lag in the electrode reaction process, and the electrode reaction is irreversible electron transfer reaction.
According to the Nicholson and Shain equation (nicolson and shan equation):
Ip: oxidation or reduction current, a; a: effective area of the electrode, cm2(ii) a n: a charge transfer number; d: diffusion coefficient, cm2S; v: potential scan rate, V/s; c: reactant concentration, mol/L.
As can be seen from FIG. 7(b), the potential scan rate is in the range of 10-140 mV/s, and the peak current has a good linear relationship with the square root of the potential scan rate (R)20.9993), NH is illustrated3-NH4 +The control process at the interface is diffusion control.
(5) At the working potential, different NH3-NH4 +I-t curve of concentration, and plotting response current and NH3-NH4 +Regression curve of concentration
FIG. 8(a) shows the continuous addition of NH of different concentration gradients to a CZTS/CHIT/GCE electrode at an operating potential of-0.047V (vs. Ag/AgCl)3-NH4 +I-t diagram obtained after solution. FIG. 8(b) shows the response current and NH at this electrode3-NH4 +Linear dependence of concentration. As can be seen, the response current is related to NH3-NH4 +The concentration of (b) shows a good linear relationship in both the following two ranges: 0.1 to 1.0mmol/L and 1.0 to 600.0 mmol/L; the linear regression equation is respectively as follows: i isp(μA)＝6.73C(mmol/L)+1.52(R20.9990) and Ip(μA)＝0.58C(mmol/L)+12.32(R20.9989); the sensitivity was 96.14. mu.A/[ (mmol/L). cm2]And 8.29. mu.A/[ (mmol/L). cm2]The detection limit was calculated to be 30.0 μmol/L (signal-to-noise ratio S/N ═ 10).
(6) Sensing electrode repeatability, stability and selectivity
FIG. 9(a) and (b) evaluate the stability and reproducibility of CZTS/CHIT/GCE electrodes. We treated the CZTS/CHIT/GCE sensing electrode at NH every 4 days3-NH4 +0.5mmol/L H at a concentration of 60.0mmol/L2SO4The cyclic voltammetry test was performed in solution, and as shown in FIG. 9(a), after 24 days of testing, the response current intensity was 85.1% of the initial current, indicating that the electrode pair of CZTS/CHIT/GCE was NH3-NH4 +The response has good stability. As shown in FIG. 9(b), the CZTS/CHIT/GCE electrodes were continuously aligned with NH3-NH4 +0.5mmol/L H at a concentration of 60.0mmol/L2SO4The solutions were subjected to 5 parallel cyclic voltammetry tests with a Relative Standard Deviation (RSD) of 1.15%, which showed good reproducibility. Therefore, the CZTS/CHIT/GCE electrode is a sensing electrode with good stability and repeatability for ammonia nitrogen ion response.
Researches on several common heavy metals (Pb) in industrial sewage by using CZTS/CHIT/GCE electrode pair by adopting amperometry2+、Cr3+、Cr6+Hg2+) and formaldehyde. However, the selectivity of this technique may be limited by the detection of coexisting electroactive species. Therefore, i-t tests were carried out with a CZTS/CHIT/GCE electrode at a potential of-0.047V (vs. Ag/AgCl), to which respective Pb concentrations were added2+、Cr3+、Cr6+、Hg2+And formaldehyde solution, and observing the change of response current. As shown in FIG. 10, 1.0mmol/L NH was injected for the first time3-NH4 +When obvious current step appears, 1.0mmol/L Pb is added at 180 s, 210 s, 240 s and 270s respectively2+、Cr3+/Cr6+、Hg2+And interfering substances of formaldehyde, to NH3-NH4 +The response of (c) has no effect. Thus, the working potential was-0.047V (vs. Ag/AgCl) vs. NH3-NH4 +Has good response and does not activate interfering substances. The results show that the electrode pair of CZTS/CHIT/GCE is NH3-NH4 +The detection has good selectivity.
(7) Electrochemical assay of spiked samples
To evaluate the reliability of the sensing electrode, a tap water sample was tested using standard addition methods. The tap water sample without further pretreatment had a pH of 6.88, NH3-NH4 +The concentration is less than 0.015 mmol/L. Table 3 shows that the detection result of the CZTS/CHIT/GCE electrode has good recovery rate, which means that the sensing electrode can be used for detecting NH-containing substances3-NH4 +The solution sample of (2) is analyzed.
TABLE 3 measurement of tap water samples by CZTS/CHIT/GCE electrodes Using Standard addition method
Claims (7)
1. NH for detecting ammonia nitrogen ions in wastewater3-NH4 +The preparation method of the content sensing electrode is characterized by comprising the following steps of:
(1) ultrasonically dispersing a CZTS powder sample in a chitosan-acetic acid solution to obtain a CZTS-chitosan-acetic acid mixed solution;
(2) preparing a modified glassy carbon electrode GCE by adopting a coating method, and dripping a CZTS-chitosan-acetic acid mixed solution on the surface of the glassy carbon electrode;
(3) drying the glassy carbon electrode;
the sensing electrode is at NH3-NH4 +The concentration is 1.0-600.0 mmol/L, and the sensitivity is 8.29 muA/(mmol/L cm)2) (ii) a At NH3-NH4 +The concentration is in the range of 0.1-1.0 mmol/L, and the sensitivity is 96.14 muA/(mmol/L cm)2)；
The CZTS is porous nano sheet Cu2ZnSnS4。
2. The method according to claim 1, wherein the chitosan-acetic acid solution has a concentration of 0.2-1.0 wt% in the acetic acid solution.
3. The method according to claim 2, wherein the concentration of the CZTS powder sample in the chitosan-acetic acid solution is 0.5-2.0 mg/mL.
4. The method of claim 1, wherein the glassy carbon electrode is pretreated by polishing with alumina powder before dispensing.
5. The method of claim 1, wherein the CZTS-chitosan-acetic acid mixture is applied to the surface of the glassy carbon electrode in a dropping amount of 0.084-0.14 mg/cm2。
6. A sensing electrode for detecting the content of ammonia nitrogen ions in wastewater, which is obtained by the preparation method of any one of claims 1 to 5.
7. The sensing electrode of claim 6, wherein the sensing electrode is coupled to NH in water3-NH4 +The lowest detection limit of (2) was 30.0. mu. mol/L, and S/N was 10.
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