A MnO 2 -Plasma synergistic catalytic degradation of organic pollutants by atmospheric pressure mass spectrometry online monitoring system

Abstract

The present invention belongs to the field of analytical chemistry, and specifically relates to an atmospheric pressure mass spectrometry online monitoring system for MnO2-plasma synergistic catalytic degradation of organic pollutants. The atmospheric pressure mass spectrometry online monitoring system is composed of a plasma synergistic catalytic part, a liquid extraction part and a mass spectrometry online detection part: the present invention provides a new method for MnO2-plasma synergistic catalytic degradation of pollutants in view of the vacancy in the direction of single plasma degradation of pollutants. This method can not only achieve efficient degradation of pollutants, but also controllably monitor the reaction process through atmospheric pressure mass spectrometry. By characterizing the materials in the degradation process and capturing important intermediates and products online, it was found that •OH plays the main role, and its reaction mechanism was deduced.

Description

Technical Field

[0001] The invention belongs to the field of analytical chemistry, and in particular relates to a normal pressure mass spectrometry online monitoring system for MnO2-plasma synergistic catalytic degradation of organic pollutants. Background Art

[0002] In recent years, with the rapid development of social science and technology, the degradation of pollutants has become one of the key prerequisites for human health development. Faced with numerous pollutants with different toxicities and different degradation difficulties, the establishment and research of efficient, green and versatile degradation methods has become one of the research hotspots in the current environmental field. Compared with traditional degradation technologies, low-temperature plasma has attracted attention and research because it has high-energy electrons and active species such as free radicals and ions that can decompose and oxidize pollutants. However, due to the low energy efficiency and uncontrollable reaction of single plasma degradation technology, it is difficult to achieve industrial application. In view of the problems existing in the degradation of organic pollutants by single low-temperature plasma technology, the high reactivity of plasma is combined with the high catalytic performance of catalysts to solve the defects of low energy utilization, low yield and high application conditions when plasma is used alone, showing great application prospects in the green and efficient degradation of pollutants. However, the process has high energy and fast reaction speed, and it is difficult to observe short-lived intermediates, which is not conducive to the derivation of the mechanism. Therefore, it is a necessary prerequisite for the application and development of such degradation methods to monitor its degradation process online, observe the dynamic changes of the structures of reactants, intermediates and products, and then explore its degradation mechanism.

[0003] Atmospheric pressure mass spectrometry can directly sample at atmospheric pressure, and has the characteristics of high resolution, high sensitivity, high throughput, and easy operation. It can realize real-time, continuous, and online analysis of samples without sample pretreatment, and plays an important role in material structure analysis and mechanism exploration. At present, there are few studies that use atmospheric pressure mass spectrometry to monitor the progress of heterogeneous catalytic reactions and the changes of important intermediates online. Therefore, using it for plasma-coordinated catalytic degradation can better explore the reaction mechanism and promote its practical application. Summary of the invention

[0004] In view of the low efficiency, uncontrollable reaction and unclear reaction pathway of the current pollutant degradation process, the present invention creates a MnO2-plasma synergistic catalytic degradation system. The catalyst MnO2 is combined with plasma degradation to fill the existing technical gap. Air plasma is directly introduced into a solution containing MnO2 and pollutants to make them evenly mixed with MnO2 nanoparticles and fully act to improve the degradation efficiency of pollutants. At the same time, atmospheric pressure mass spectrometry is used to perform online real-time monitoring of important intermediates in the degradation process. In order to prevent the catalytic MnO2 from interfering with the detection signal after entering the mass spectrometer, an inclined sampling method is developed to use gravity to remove MnO2 particles in the solution during the formation of the spray, thereby reducing the interference of the material with the mass spectrometry signal, accurately obtaining the important intermediate structure information in the degradation process, and further exploring the reaction mechanism.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0006] The present invention provides a normal pressure mass spectrometry online monitoring system for MnO2-plasma synergistic catalytic degradation of organic pollutants. The system is composed of a plasma synergistic catalytic part, a liquid extraction part and a mass spectrometry online detection part:

[0007] The plasma synergistic catalytic part: synthesizes MnO2 nanomaterials, disperses them uniformly in the pollutant solution after ultrasonic treatment, generates plasma between two copper electrodes (2) on the surface of the quartz tube (1) under the action of an AC power supply, and introduces dissociated gas air through the quartz tube and directly passes it into the pollutant solution (3) containing MnO2 to perform oxidative cracking;

[0008] The liquid extraction part is composed of two layers of quartz capillaries, the inner layer is a capillary (4), one end of which is inserted into the solution (3) containing pollutants, and the other end is transported at an angle to 1 cm away from the mass spectrometer injection port. The external high voltage (5) from the mass spectrometer is simultaneously inserted into the solution (3). The outer layer is a quartz tube (6) through which N2 flows. Under the action of high-flow nitrogen, the liquid is automatically extracted to the mass spectrometer detector (7);

[0009] The mass spectrometry online detection part utilizes the micro-droplets formed by electrospray to realize continuous sampling of the pollutant degradation process, and is combined with a mass spectrometry detector (7) to ionize important species in the reaction system and simultaneously enter the mass spectrometry for detection, thereby obtaining intermediates through detection.

[0010] The MnO2 nanomaterial used in the present invention is a nanorod structure, and the specific preparation method is: MnSO4·H2O and Na2S2O8 are mixed in distilled water and stirred evenly; the solution is transferred to a high-pressure reactor, heated for reaction, washed, filtered, dried, and calcined in an air atmosphere to obtain the product MnO2 nanomaterial.

[0011] The molar ratio of the MnSO4·H2O and Na2S2O8 is 1:1; the concentration of the MnSO4·H2O in distilled water is 9.5 mmol / 70 mL; the reaction is carried out at 90°C for 24 h; and the calcination is carried out at 350°C for 3 h.

[0012] Furthermore, the inner diameter of the quartz tube (1) is 3.0 mm, and the outer diameter is 6.0 mm; and the AC power source is 8 W.

[0013] Furthermore, the concentration of MnO2 in the pollutant solution is 10 mg / mL; the pollutant is HCQ; the concentration of the pollutant solution is 50 μM, and the air flow rate is 20 L / h.

[0014] Furthermore, the size of the capillary (4) is 0.52-0.69*200 mm, the inclination angle is between 40º and 60º, the high voltage is 5 kV; the gap between the quartz tube (6) and the inner capillary (4) is 0.5-1 mm; and the flow rate of the nitrogen is 10 L / min.

[0015] Furthermore, the mass spectrometry detection conditions are: full scan test in the positive ion mode in the range of m / z 50-500; the mass spectrometry injection capillary temperature (Capilary Temp) is 275 °C; the capillary voltage (Capilary Voltage) is 35 V, and the tube lens compensation voltage (Tube lens) is 80 V.

[0016] Furthermore, the intermediates are IM 2, IM 3 and KP, and the specific structural formula is:

[0017] ;

[0018] Under the action of high pressure and nitrogen gas, the sample solution of the present invention can easily form an electrospray, thereby quickly entering the mass spectrometer detection, and realizing online monitoring of the degradation process. Since small MnO2 particles tend to enter the injection tube of the mass spectrometer through the internal capillary, this will affect the mass spectrometer signal. In combination with the atmospheric pressure mass spectrometer, a new tilted sampling method is developed, in which the capillary is tilted downward so that MnO2 is separated from the electrospray under the action of gravity, so that the solution can stably detect the degradation reaction intermediates through the mass spectrometer. In this way, the plasma is directly introduced into the heterogeneous solution of MnO2 without any loss. Therefore, the device can effectively and controllably monitor the degradation process in the plasma MnO2 catalytic system.

[0019] The beneficial effects of the present invention are as follows: the present invention provides a new method for MnO2-plasma synergistic catalytic degradation of pollutants in view of the lack of single plasma degradation of pollutants. The method can not only achieve efficient degradation of pollutants, but also controllably monitor the reaction process through atmospheric pressure mass spectrometry. By characterizing the materials in the degradation process and capturing important intermediates and products online, it is found that •OH plays the main role, and its reaction mechanism is deduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 These are the XRD and SEM morphology images of MnO2 in Example 1.

[0021] Figure 2 Schematic diagram of the atmospheric pressure mass spectrometry system consisting of the MnO2-plasma synergistic catalytic degradation part, the sample solution extraction part and the mass spectrometry online monitoring part.

[0022] Figure 3 The CID diagram of MnO2-plasma synergistic catalytic degradation performance and important intermediates.

[0023] Figure 4 This is the kinetic curve of important intermediates in the MnO2-plasma synergistic catalytic degradation process.

[0024] Figure 5 This is the UV spectrum of ·OH detection.

[0025] Figure 6 Energy diagram of the degradation process. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further explained and illustrated by means of specific embodiments below.

[0027] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0028] 1. Materials and reagents

[0029] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0030] The water used in the experiment was ultrapure water, which was processed by the Milli-Q ultrapure water purification system. The high-purity argon gas used was purchased from Beijing Qianxi Capital Gas Sales Center.

[0031] The instrument used in the following examples is a LTQ linear ion trap mass spectrometer (Thermo Fisher Scientific, USA).

[0032] Capillaries with a size of 0.52-0.69*150 mm were purchased from Shanghai Great Wall Scientific Instruments, and quartz capillaries were purchased from Yongnian Ruifeng Chromatographic Devices Co., Ltd.

[0033] Example 1

[0034] The pollutant hydroxychloroquine (HCQ) was used as the detection object for method validation.

[0035] (1) Synthesis and characterization of MnO2 nanoparticles

[0036] MnSO4·H2O (0.1123 g, 9.5 mmol) and Na2S2O8 (0.0838 g, 9.5 mmol) were mixed in 70 mL of distilled water and stirred evenly. The solution was transferred to a stainless steel autoclave and heated at 90 °C for 24 h. After washing, filtering, and drying, the product MnO2 nanomaterial was obtained by calcining at 350 °C in air atmosphere for 3 h. Figure 1 As shown in the figure, the morphology of MnO2 nanoparticles was determined by XRD and SEM characterization. The morphology is the shape of nanorods with a length of 1 to 2 μm. These nanorods are combined together to form a shape similar to micro-nano flowers.

[0037] (2) Solution preparation

[0038] 10 mg / mL MnO2 was added to 50 mL of 50 μM pollutant HCQ solution and dispersed evenly by ultrasound (HZ, 10 min).

[0039] The MnO2-plasma synergistic catalytic degradation part is to introduce air plasma into the MnO2 heterogeneous solution containing pollutants to fully react with MnO2. The hydroxyl groups on the surface of MnO2 can catalyze the plasma to produce a large amount of active oxygen species •OH, thereby achieving the purpose of degrading pollutants. Wherein, plasma is generated between two copper electrodes (2) on the surface of a quartz tube (1) under the action of an AC power supply (8 W), and dissociated gas air is introduced through the quartz tube to generate air plasma at a flow rate of 20 L / h.

[0040] The liquid extraction part is composed of two layers of quartz capillaries, the inner layer is a capillary (4), one end of which is inserted into the solution containing pollutants (3), and the other end is transported to the vicinity of the mass spectrometer injection port at an angle, so that the insoluble MnO2 particles are separated from the solution under the action of gravity, and a high voltage of 5 kV is applied to the solution. The outer layer is a quartz tube (6) through which N2 flows. Under the action of high-flow nitrogen, the liquid can be automatically extracted to the mass spectrometer detector to complete the extraction of the sample, so that the sample solution can be detected by the mass spectrometer detection part (7). Figure 2Schematic diagram of the detection system consisting of MnO2-plasma synergistic catalytic degradation part, sample solution extraction part and mass spectrometry online monitoring part.

[0041] (3) Degradation performance of MnO2-plasma system synergistic catalytic degradation and mass spectrometry online monitoring

[0042] In order to compare the high efficiency of the MnO2-plasma system synergistic catalytic degradation, a series of comparative experiments were conducted, such as Figure 3 As shown in the figure, compared with the MnO2 system without plasma and the single plasma system, the pollutant HCQ in the MnO2-plasma system was rapidly decomposed within 2 min. After 5 min of reaction, the reactant [HCQ+H] + The mass spectrometry signal (m / z=336) of 100% ion (m / z=336) basically disappeared, and intermediate ions were observed at m / z 320 and m / z 292. The mass spectrometry signal of m / z 159 was observed after 30 min of reaction, which shows that the reaction is efficient and fast, and the intermediates at every moment can be monitored by online mass spectrometry to achieve controllable degradation. In order to further confirm the structural information of these intermediate ions, collision induced dissociation (CID) experiments were carried out on the intermediates of m / z 32, m / z 292 and m / z 159 ( Figure 3 ), the structure of the reaction intermediates in the MnO2-plasma system was successfully obtained. The important intermediates in the degradation process were monitored online. Figure 4 As shown, [HCQ+H] at m / z 336 + The ion intensity decreased rapidly within 5 minutes, indicating that the system has good catalytic activity. At m / z=320, the ion intensity increased rapidly at 2 min and then decreased with time. Similarly, the ion intensity of m / z=292 increased at 3 min, weakened at 10 min, and finally the ion of m / z=159 gradually formed at 30 min.

[0043] (5) Detection of OH radicals

[0044] In order to explore the main role of the substance in the degradation process, UV test experiments were carried out. The single plasma system and the MnO2-plasma synergistic system were studied. 100 μL of 20 mM TMB colorimetric agent was added to the single plasma system and the MnO2-plasma system. Figure 5 As shown, the UV spectrum shows that compared with the single plasma system, the MnO2-plasma system generates a large amount of •OH, indicating that the MnO2-plasma synergistic catalysis accelerates the degradation of pollutants.

[0045] (6) Degradation mechanism research

[0046] Based on previous experiments, we have proved that •OH plays a major role in the degradation process. In order to further explore the mechanism of the degradation process initiated by •OH, theoretical calculations were performed on the reactant HCQ and important intermediates. Figure 6 The step diagram of the reaction and the HOMO orbitals of the reactant HCQ molecule and the intermediates IM 2 (m / z=320) and IM 3 (m / z=292) are shown. From the HOMO orbital of the N1 atom in the HCQ molecule, it can be seen that the N1 atom is rich in electrons and is easy to become a reactive active site. Figure 6 As shown in the figure, the reactant HCQ loses an electron through •OH attack and becomes IM 1 (HCQ •+ ) and OH - IM 1 causes the methyl group to break and generate IM 2 (m / z=320). The HOMO orbital of IM 2 (m / z 320) indicates that the N2 atom is rich in electrons. •OH attacks the N2 atom on IM 2 and becomes IM3. This process releases 3.54 eV of energy and overcomes the energy barrier of 1.63 eV. Subsequently, •OH continues to attack the C1 atom on IM 3 to form IM 4. Hydrogen chloride gas (HCl) is quickly removed from IM 4, and IM 5 is generated through an exothermic process. IM 5 finally breaks into an intermediate ion with an m / z of 159. The reaction intermediates can be observed in the mass spectrometer and are consistent with the theoretical calculation results, which reflects the advantage of atmospheric pressure mass spectrometry in monitoring plasma-coordinated catalytic degradation reactions and thus inferring the reaction mechanism. The energy of the entire reaction has been decreasing, indicating that the degradation process is more likely to occur under the action of •OH generated by the plasma.

[0047] result:

[0048] Based on the atmospheric pressure mass spectrometry online monitoring technology, the rapid degradation of pollutants was studied using plasma technology. MnO2 metal oxide materials were introduced into the plasma degradation system, and a plasma synergistic catalytic degradation device was built. At the same time, atmospheric pressure mass spectrometry was used to monitor important intermediates in the degradation process online to study the mechanism of the degradation process. At the same time, the important reaction intermediates in the reaction process were observed using the atmospheric pressure mass spectrometry online monitoring device, and the degradation mechanism of the plasma catalytic reaction was proposed. This method simply and directly monitors the degradation system, overcomes the difficulty of capturing degradation intermediates, and provides new research ideas for the application and mechanism exploration of plasma catalytic degradation.

Claims

1. A atmospheric pressure mass spectrometry online monitoring system for MnO2-plasma synergistic catalytic degradation of organic pollutants, characterized in that: The system is composed of a plasma synergistic catalysis part, a liquid extraction part and a mass spectrometry online detection part: The plasma synergistic catalytic part: synthesizes MnO2 nanomaterials, disperses them uniformly in the pollutant solution after ultrasonic treatment, generates plasma between two copper electrodes (2) on the surface of the first quartz tube (1) under the action of an AC power supply, and introduces dissociated gas air through the quartz tube and directly passes into the pollutant solution (3) containing MnO2 to perform oxidative cracking; The liquid extraction part is composed of two layers of quartz capillaries, the inner layer is a capillary (4), one end of which is inserted into the solution (3) containing pollutants, and the other end is transported at an angle to a position 1 cm away from the mass spectrometer injection port. The external high voltage (5) from the mass spectrometer is simultaneously inserted into the solution (3). The outer layer is a second quartz tube (6) through which N2 flows. Under the action of high-flow nitrogen, the liquid is automatically extracted to the mass spectrometer detector (7); The mass spectrometry online detection part utilizes the micro-droplets formed by electrospray to realize continuous sampling of the pollutant degradation process, and is combined with a mass spectrometry detector (7) to ionize important species in the reaction system and simultaneously enter the mass spectrometry for detection, thereby obtaining intermediates.

2. The atmospheric pressure mass spectrometry online monitoring system according to claim 1, characterized in that: The MnO2 nanomaterial is a nanorod structure, and the specific preparation method is: MnSO4·H2O and Na2S2O8 are mixed in distilled water and stirred evenly; the solution is transferred to a high-pressure reactor, heated for reaction, washed, filtered, dried, and calcined in an air atmosphere to obtain the product MnO2 nanomaterial.

3. The atmospheric pressure mass spectrometry online monitoring system according to claim 2, characterized in that: The molar ratio of the MnSO4·H2O to Na2S2O8 is 1:1; the concentration of the MnSO4·H2O in distilled water is 9.5 mmol / 70 mL; the reaction is carried out at 90° C. for 24 h; and the calcination is carried out at 350° C. for 3 h.

4. The atmospheric pressure mass spectrometry online monitoring system according to any one of claims 1 to 3, characterized in that: The inner diameter of the first quartz tube (1) is 3.0 mm, and the outer diameter is 6.0 mm; the AC power source is 8 W.

5. The atmospheric pressure mass spectrometry online monitoring system according to claim 1, characterized in that: The concentration of MnO2 in the pollutant solution is 10 mg / mL; the pollutant is HCQ; the concentration of the pollutant solution is 50 μM, and the air flow rate is 20 L / h.

6. The atmospheric pressure mass spectrometry online monitoring system according to claim 1 or 4, characterized in that: The size of the capillary (4) is 0.52-0.69×200 mm, the inclination angle is between 40° and 60°, the high voltage is 5 kV; the gap between the second quartz tube (6) and the inner capillary (4) is 0.5-1 mm; the flow rate of the nitrogen is 10 L / min.

7. The atmospheric pressure mass spectrometry online monitoring system according to claim 6, characterized in that: The mass spectrometer detection conditions are: full scan test in the range of m / z 50-500 in positive ion mode; mass spectrometer injection capillary temperature is 275°C; capillary voltage is 35V, and sleeve lens compensation voltage is 80V.

8. The atmospheric pressure mass spectrometry online monitoring system according to claim 7, characterized in that: The intermediates are IM2, IM3 and KP, and the specific structural formula is: 。

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