CN108088814B - Method for quantitatively detecting sulfate radical by using laser flash photolysis technology - Google Patents

Method for quantitatively detecting sulfate radical by using laser flash photolysis technology Download PDF

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CN108088814B
CN108088814B CN201810001096.1A CN201810001096A CN108088814B CN 108088814 B CN108088814 B CN 108088814B CN 201810001096 A CN201810001096 A CN 201810001096A CN 108088814 B CN108088814 B CN 108088814B
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姜晓
全燮
陈景文
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Abstract

A method for quantitatively detecting sulfate radical by laser flash photolysis features that Br is added—Excess addition of S2O8 2‑In the system, S is excited by 266nm laser2O8 2‑Homolytic generation of SO4 ·—，Br—Is coated with SO4 ·—Oxidation to Br·，Br·With Br—Reaction to produce Br2 ·—Thereby obtaining Br2 ·—And absorbance values at 360 nm. Obtaining Br according to Lambert-Beer law2 ·—To obtain SO in the system4 ·—The concentration of (c). Excitation of the same concentration of S-only using a 266nm laser2O8 2‑To obtain SO4 ·—The characteristic transient absorption spectrum and the absorbance value at 450nm are obtained to obtain SO at 450nm4 ·—Molar extinction coefficient of (c). Excitation of unknown concentrations of SO-produced using a 266nm laser4 ·—To obtain SO in the system to be tested4 ·—The concentration of (c).

Description

Method for quantitatively detecting sulfate radical by using laser flash photolysis technology
Technical Field
The invention relates to a method for detecting the concentration of sulfate radicals, in particular to a method for quantitatively detecting sulfate radicals by using a laser flash photolysis technology.
Background
Sulfate radical (SO)4 ·—) Is a one-electron oxidant with strong oxidizing property, and the oxidation-reduction potential of the one-electron oxidant is 2.6V and is slightly lower than that of a hydroxyl radical (E)0＝2.80V)。SO4 ·—Can react with organic substances by hydrogen abstraction, addition and electron transfer, wherein the electron transfer is mainly usedAnd (5) performing main operation. It reacts more selectively with many organic substances than hydroxyl radicals and is capable of mineralizing organic contaminants, which many hydroxyl radicals are not oxidatively degradable, into carbon dioxide and inorganic acids, among others. SO (SO)4 ·—The pH value range is wide, organic pollutants can be effectively degraded under acidic to alkaline conditions, and SO can be dissolved in weakly alkaline (pH 8.0-10.0) solution4 ·—Can react to generate hydroxyl radicals at SO4 ·—With the combined action of the OH free radical and two strong oxidizers, the pollutants can be degraded more rapidly. Because of its high reactivity, it participates in chemical reactions quickly (10)8-1010M-1s-1) The catalyst has the characteristics of long service life (the survival time in aqueous solution can reach about 4s), high oxidation efficiency, no secondary pollution and the like, and is widely applied to air pollution control and advanced wastewater treatment in recent years.
Currently in relation to SO4 ·—Most of the researches are the researches on the kinetics and the mechanism of the pollutants degraded by the pollutants, and a quantitative detection and analysis method thereof is rarely reported. The methods reported so far focus on the complete capture method and the competitive kinetic method. Wherein the complete capture method employs excess capture agent and generated SO4 ·—Reaction, calculation of SO by determination of the key product of metering4 ·—Is a quantitative establishment of key products and SO4 ·—A method of metering relationships of (1). The competitive kinetic method is to use an SO4 ·—Trapping agent and SO4 ·—Indicator to compete for SO consumption4 ·—In the case of the application of the competitive kinetic method, the indicator and the capture reagent used are judiciously selected and the rate constant for the secondary reaction used is determined to be the SO yield4 ·—The key to the exact amount. Both methods indirectly calculate SO by analyzing the product concentration4 ·—The concentration of (2) is complex and complicated to operate, and the accuracy is not high.
The Laser Flash Photolysis (LFP) technology is used for researching low-concentration short-life transient species (such as free radical species)Radical, ion, excited state, etc.), has extremely high sensitivity, can directly capture transient absorption signals of free radicals, and is widely used for research on various chemical reaction mechanisms in which the free radicals participate in recent years. However, quantitative detection of SO by LFP technique4 ·—It has not been reported.
Disclosure of Invention
The present invention is directed to the current SO4 ·—The problems of the prior method such as lack of quantitative detection method, complicated operation, low accuracy and the like are solved, and the method for quantitatively detecting SO by utilizing the laser flash photolysis technology is provided4 ·—The method of (1). The invention can not only quantitatively detect SO4 ·—Can also examine SO4 ·—Lifetime and decay rate constant.
The technical scheme of the invention is as follows:
a method for quantitatively detecting sulfate radicals by using a laser flash photolysis technology is shown as a formula 1, and in a known system, SO is4 ·—Is prepared from potassium persulfate, sodium persulfate, ammonium persulfate or other persulfate-containing radical (S)2O8 2-) of an inorganic or organic compound, under excitation by a 266nm or 355nm laser, S2O8 2-homolytic crack generation occurs.
Figure BDA0001536853620000021
SO4 ·-+Br-→SO4 2-+Br·(formula 2)
Br·+Br-→Br2 ·-(formula 3)
As shown in formula 2, in the known system, the bromide ion (Br)—) From sodium bromide, potassium bromide, ammonium bromide or other bromine-containing inorganic or organic compounds. Wherein, SO4 ·—Oxidized Br—(both are reacted in a molar ratio of 1: 1) to generate bromine radicals (Br. cndot.) in the same molar ratio.
Br is shown in formula 3·With Br—The reaction (the two are reacted in a molar ratio of 1: 1) generates dibromo radicals (Br) with the same molar ratio2 ·—)。
As shown in formulas 2-3, in known systems, SO4 ·—Concentration and Br2 ·—At a concentration ratio of 1:1, i.e.
Figure BDA0001536853620000031
The method comprises the following steps:
step 1: adding Br—Adding S in excess of known concentration2O8 2-In the system, S is excited at a specific laser wavelength by a laser flash photolysis technology2O8 2-Production of SO4 ·—，Br—Is immediately treated by SO4 ·—Oxidation to Br·，Br·With Br—Further reaction to produce Br2 ·—Excess of Br—The reaction is favorable to move towards the positive direction. Whereby Br can be obtained2 ·—The abscissa of the characteristic transient absorption spectrum is the wavelength, and the ordinate is the absorbance value. Br is reported in the literature2 ·—Has characteristic transient absorption property at 360nm and molar extinction coefficient epsilon of 9 multiplied by 103L mol-1cm-1. According to the Lambert-Beer law: br can be obtained by A ═ ε · b · c2 ·—The concentration of (c).
Step 2: br obtained according to step 12 ·—And the Br, and2 ·—with SO4 ·—The concentration ratio of (1: 1) to obtain SO4 ·—The concentration of (c).
And step 3: SO is obtained by laser flash photolysis technology4 ·—Characteristic transient absorption spectrum of (3), SO4 ·—There is a characteristic transient absorption property at 450 nm. The abscissa of the characteristic transient absorption spectrum is the wavelength and the ordinate is the absorbance value. According to Lambert-Beer law: the SO at 450nm can be determined by4 ·—Has a molar extinction coefficient of 1.393X 103L mol-1cm-1And the value reported in the literature is 1.0X 103L mol-1cm-1And (6) matching.
And 4, step 4: known SO according to step 34 ·—The molar extinction coefficient is actually measured, and the SO in a system to be measured is measured by utilizing a laser flash photolysis technology4 ·—Transient absorption spectrum at 450 nm. According to the Lambert-Beer law: and (A) obtaining SO in the system to be tested, wherein A is epsilon, b and c (wherein A, epsilon and b are known)4 ·—The concentration of (c).
The Lambert-Beer law: a ═ epsilon · b · c, where a is the absorbance value, unitless; epsilon is the molar extinction coefficient and the unit is L mol-1cm-1(ii) a b is the thickness of the liquid layer in cm, usually with a value of 1 cm; c is the concentration in mol L-1；
The specific laser wavelength is 266nm or 355nm, and the laser energy is 10-30 mJ;
the test systems are required to be kept in an anaerobic environment;
br added into the system to be measured—Is SO in a concentration of4 ·—Yielding 2-10 times the concentration.
The pH value range of the system to be detected is 1-7.
The pH value of the system to be detected is adjusted by sodium dihydrogen phosphate or potassium dihydrogen phosphate buffer solution.
The temperature range of the system to be tested is 18-70 ℃.
Quantitative determination of SO in the System to be tested4 ·—The concentration range is 1 × 10-6～95×10-3mol/L，SO4 ·—When the concentration is more than 95mmol/L, SO is generated by diluting the system to be detected4 ·—The concentration is in the range, and then the diluted SO of the system to be measured4 ·—The concentration is multiplied by the dilution times to obtain the SO of the original system to be measured4 ·—And (4) concentration.
The laser used by the laser flash photolysis spectrometer is a Quantel Nd YAG laser. The sensitivity of the instrument is high, and the detection limit Δ OD (RMS noise) of single sampling is 0.002 (fast detection mode) and 0.0005 (slow detection mode) respectively. The detector is an image enhancement type CCD, and the spectral response range is 200-850 nm.
The invention has the beneficial effects that: provides a novel quantitative detection method for SO by utilizing laser flash photolysis technology4 ·—The method of (1). The method is simple, sensitive, accurate and rapid, and can directly detect SO on line4 ·—And (4) concentration.
Drawings
FIG. 1 is SO4 ·—Characteristic transient absorption spectrum of (1).
FIG. 2 is Br2 ·—Characteristic transient absorption spectrum of (1).
FIG. 3 is SO4 ·—With Br2 ·—Characteristic transient absorption spectrum in coexistence.
Detailed Description
The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
(1) The laser energy was set at 10mJ, ambient temperature 24 ℃ and solution pH 5.5.
(2) The formulation contains 0.08M K2S2O80.01M KBr in water, using a 266nm laser to excite the solution to give Br2 ·—Characteristic transient absorption spectrum at 360nm to obtain Br2 ·—The absorbance value A at 360nm was 0.3974.
(3) According to the Lambert-Beer law: a ═ epsilon · b · c (where b is 1cm), and reported Br2 ·—Molar extinction coefficient of free radical (epsilon-9X 10)3L mol-1cm-1) To obtain Br2 ·—The concentration c of (2) was 44.16. mu. mol/L.
(4) According to Br2 ·—With SO4 ·—The concentration ratio of (1: 1) of (B) to (C) of (D) is known as SO4 ·—The concentration c of (2) was 44.16. mu. mol/L.
(5) The formulation contains 0.08M K2S2O8Aqueous solution, using 266nm laser to excite the solution to obtain SO4 ·—Characteristic transient absorption spectrum at 450nm to obtain SO4 ·—The absorbance value A at 450nm was 0.0615.
(6) According to the steps (3) and (4) and the Lambert-Beer law: since A is ε · b · c, and all of A, b, and c are known, SO at 450nm can be obtained4 ·—Has a molar extinction coefficient epsilon of 1.393X 103And the value reported in the literature is 1.0X 103And (6) matching.
(7) The formulation contains 0.04M K2S2O8Aqueous solution, using 266nm laser to excite the solution to obtain SO4 ·—Characteristic transient absorption spectrum at 450nm to obtain SO4 ·—The absorbance value A at 450nm was 0.0451.
(8) According to the steps (6) and (7) and the Lambert-Beer law: since a is ═ epsilon · b · c, and a, epsilon, b are known, 0.04M K was obtained2S2O8SO at 450nm in aqueous solution4 ·—Has a concentration of 3.24X 10-5M。
Example 2
(1) Same as example 1
(2) Same as example 1
(3) Same as example 1
(4) Same as example 1
(5) Same as example 1
(6) Same as example 1
(7) The preparation contains 0.008M K2S2O8Aqueous solution, using 266nm laser to excite the solution to obtain SO4 ·—Characteristic transient absorption spectrum at 450nm to obtain SO4 ·—The absorbance value A at 450nm was 0.0158.
(8) According to the steps (6) and (7) and the Lambert-Beer law: since a is ═ epsilon · b · c, where a, epsilon, b are known, 0.008M K was obtained2S2O8SO at 450nm in aqueous solution4 ·—Has a concentration of 1.13X 10-5M。

Claims (10)

1. A method for quantitatively detecting sulfate radicals by utilizing a laser flash photolysis technology is characterized in that,
as shown in formula 1, in the known system, the SO4 ·—Is prepared from potassium persulfate, sodium persulfate, ammonium persulfate or other inorganic or organic compounds containing persulfate radical by exciting at 266nm or 355nm laser2O8 2-The occurrence of homolytic fission;
Figure FDA0002302604850000011
SO4 ·-+Br-→SO4 2-+Br·(formula 2)
Br·+Br-→Br2 ·-(formula 3)
As shown in formula 2, in the known system, the bromide ion is derived from sodium bromide, potassium bromide, ammonium bromide or other bromine-containing inorganic compounds or organic compounds; wherein, SO4 ·—Oxidized Br—Formation of bromine radicals, SO4 ·—And Br—Reacting at a molar ratio of 1: 1;
br is shown in formula 3·With Br—Reaction to generate dibromo radical, Br·With Br—Reacting at a molar ratio of 1: 1;
as shown in formulas 2-3, in known systems, SO4 ·—Concentration and Br2 ·—At a concentration ratio of 1:1, i.e.
Figure FDA0002302604850000012
The method comprises the following steps:
step 1: adding Br—Adding S in excess of known concentration2O8 2-In the system, S is excited at a laser wavelength of 266nm by a laser flash photolysis method2O8 2-Production of SO4 ·—，Br—Is immediately treated by SO4 ·—Oxidation to Br·，Br·With Br—Further reaction to produce Br2 ·—Excess of Br—The reaction is favorable to move towards the positive direction; thereby obtaining Br2 ·—The abscissa of the characteristic transient absorption spectrum is the wavelength, and the ordinate is the absorbance value; br2 ·—Has characteristic transient absorption property at 360nm and molar extinction coefficient epsilon of 9 multiplied by 103L mol-1cm-1According to the Lambert-Beer law: obtaining Br when A is equal to epsilon, b, c2 ·—The concentration of (c); wherein A is an absorbance value without unit; epsilon is the molar extinction coefficient and the unit is L mol-1cm-1(ii) a b is the thickness of the liquid layer, the unit is cm, and b is 1 cm; c is the concentration in mol L-1；
Step 2: br obtained according to step 12 ·—Of (b) and Br2 ·—With SO4 ·—To obtain SO according to the concentration ratio of 1:14 ·—The concentration of (c);
and step 3: SO is obtained by laser flash photolysis4 ·—Characteristic transient absorption spectrum of (3), SO4 ·—The characteristic transient absorption property is provided at 450 nm; the abscissa of the characteristic transient absorption spectrum is wavelength, and the ordinate is an absorbance value; according to the Lambert-Beer law: a. epsilon. b. c, and SO at 450nm was obtained4 ·—Has a molar extinction coefficient of 1.393X 103L mol-1cm-1；
And 4, step 4: known SO according to step 34 ·—The molar extinction coefficient is actually measured, and the SO in a system to be measured is measured by using a laser flash photolysis method4 ·—A characteristic transient absorption spectrum at 450 nm; according to the Lambert-Beer law: obtaining SO in the system to be measured4 ·—The concentration of (c).
2. The method of claim 1, wherein the laser wavelength is 266nm or 355nm and the laser energy is 10-30 mJ.
3. The method according to claim 1 or 2, wherein the system to be tested is kept in an oxygen-free environment; the pH value of the system to be measured is 1-7, the temperature of the system to be measured is 18-70 ℃, and the pH value of the system to be measured is adjusted by sodium dihydrogen phosphate or potassium dihydrogen phosphate buffer solution.
4. The method according to claim 1 or 2, characterized in that Br is added to the system to be tested—Is SO in a concentration of4 ·—Yielding 2-10 times the concentration.
5. The method of claim 3, wherein the Br added to the system under test—Is SO in a concentration of4 ·—Yielding 2-10 times the concentration.
6. The method of claim 1, 2 or 5, wherein SO is quantitatively detected in the system under test4 ·—The concentration range is 0.1 × 10-6～95×10-3mol/L，SO4 ·—When the concentration is more than 95mmol/L, SO is generated by diluting the system to be detected4 ·—The concentration is 0.1 × 10-3～95×10-3Within mol/L, diluting the SO of the system to be measured4 ·—The concentration is multiplied by the dilution times to obtain the SO of the original system to be measured4 ·—And (4) concentration.
7. The method of claim 3, wherein the SO is quantitatively determined in the test system4 ·—The concentration range is 0.1 × 10-3～95×10-3mol/L，SO4 ·—When the concentration is more than 95mmol/L, SO is generated by diluting the system to be detected4 ·—The concentration is 0.1 × 10-3～95×10-3Within mol/L, diluting the SO of the system to be measured4 ·—The concentration is multiplied by the dilution times to obtain the SO of the original system to be measured4 ·—And (4) concentration.
8. The method of claim 4, wherein the SO is quantitatively determined in the system under test4 ·—The concentration range is 0.1 × 10-3～95×10-3mol/L，SO4 ·—When the concentration is more than 95mmol/L, SO is generated by diluting the system to be detected4 ·—The concentration is 0.1 × 10-3～95×10-3Within mol/L, diluting the SO of the system to be measured4 ·—The concentration is multiplied by the dilution times to obtain the SO of the original system to be measured4 ·—And (4) concentration.
9. The method of claim 1, 2, 5, 7 or 8, wherein the laser used by the laser flash photolysis spectrometer is a Quantel Nd YAG laser, and the detection limit Δ OD of a single sample is 0.002 for fast detection mode and 0.0005 for slow detection mode; the detector is an image enhancement type CCD, and the spectral response range is 200-850 nm.
10. The method of claim 6, wherein the laser used in the laser flash photolysis spectrometer is a Quantel Nd YAG laser, and the detection limit Δ OD of a single sampling is 0.002 for fast detection mode and 0.0005 for slow detection mode; the detector is an image enhancement type CCD, and the spectral response range is 200-850 nm.
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