CN109019746A - The method of active carbon mediation aqueous electron deoxidization, degradation PFASs - Google Patents

Abstract

The invention discloses a method for reducing and degrading PFASs mediated by activated carbon by hydrating electrons. First, the activated carbon is ground and passed through a 100-mesh sieve; firstly, an indole solution is prepared, and then the PFOA solution to be degraded and the prepared indole solution are evenly mixed And add a certain amount of activated carbon, and then stir for 1 hour; under aerobic conditions, use a low-pressure mercury lamp to illuminate the mixed solution to realize the degradation and defluorination of PFOA. The invention has the beneficial effect of forming a method capable of efficiently degrading PFASs without causing secondary pollution to water bodies. The research results can provide a new method for degrading PFASs, which is of great significance for dealing with the environmental pollution of PFASs.

Description

Activated carbon-mediated reduction and degradation of PFASs by hydration electrons

technical field

The invention belongs to the technical field of environmental treatment and relates to the reduction and degradation of PFASs by hydrated electrons with activated carbon as a carrier.

Background technique

Perfluorinated compounds (Perfluoroalkyl substances, PFASs) are one of the most concerned new pollutants in recent years. After nearly half a century of production and use, PFASs have been detected in almost all environmental media, human and animal tissues. PFASs are very stable, difficult to degrade naturally in the environment, and are not metabolized in animals. They have bioaccumulation and amplification in food webs, and pose serious threats to ecosystems and human health. Due to the strong polarity and high bond energy of the C-F bond of PFASs molecules, it is extremely difficult to break, and the common water treatment technology cannot degrade it. Perfluorinated compounds have strong heat resistance and chemical stability, and are widely used in various industrial and civil fields, among which perfluorooctanoic acid (Perfluorooctanoic acid, PFOA) and perfluorooctane sulfonate (Perfluorooctane sulfonate, PFOS) are two most typical (Wang Yawei et al., 2010; Wang et al., 2017). Due to mass production and use, PFASs are distributed in various parts of the world, including some remote areas and even bipolar areas (Giesy et al., 2002; Heydebreck et al., 2016), and are found in organisms and human serum, breast milk, and urine detected (Jin et al., 2016; Chen et al., 2017). Such substances are very stable, difficult to degrade naturally in the environment, and are not metabolized in animals, so they can be transported over long distances around the world, and have bioaccumulation and amplification in food webs (Kelly et al., 2009 ; Houtz et al., 2013), causing serious threats to ecosystems and human health (Shi Yali et al., 2014; Midgett et al., 2015; Pedersen et al., 2016). The C-F bonds in PFASs molecules have strong polarity and high bond energy, and are extremely difficult to be hydrolyzed, photolyzed, oxidized and reduced. Therefore, commonly used water treatment technologies, such as ozone oxidation, activated sludge, anaerobic digestion, chlorine disinfection, PFASs cannot be degraded by carbon dioxide oxidation, etc. Methods such as activated carbon adsorption, ion exchange and reverse osmosis can remove PFASs in water, but follow-up methods are still needed to completely eliminate them to avoid secondary pollution (Pan et al., 2016; Merino et al .,2016), so it is of great significance to develop methods that can effectively degrade PFASs.

Contents of the invention

The purpose of the present invention is to provide a method for degrading PFASs through reduction of hydrated electrons mediated by activated carbon. The beneficial effect of the present invention is to form a method that can efficiently degrade PFASs without causing secondary pollution to water bodies. The research results can provide a new method for degrading PFASs, which is of great significance for dealing with the environmental pollution of PFASs.

The technical scheme adopted in the present invention is

Follow the steps below:

(a) milling activated carbon and passing through a 100-mesh sieve;

(b) First prepare the indole solution, then uniformly mix the PFOA solution to be degraded and the prepared indole solution and add a certain amount of activated carbon, and then stir for 1 hour;

(c) Under aerobic conditions, use a low-pressure mercury lamp to irradiate the mixed solution obtained in step (b) to realize the degradation and defluorination of PFOA.

Further, the step of milling and sieving activated carbon in step (a) is:

(1) weigh 5g of activated carbon and place it in an agate mortar;

(2) milling;

(3) Pass through a 100-mesh sieve to obtain activated carbon with a particle size less than 150 μm.

Further, the step of preparing reaction solution in step (b) is:

(i) uniformly mix the prepared indole solution and the PFOA solution to be treated;

(ii) the gac obtained in the step (a) is dispersed in the solution prepared in the step (i) and the pH value of the solution is adjusted;

(iii) Stir the reaction solution prepared in step (ii) for 1 hour using magnetic stirring.

Further, the step of degrading PFOA in step (c) is:

(m) first transfer the reaction solution obtained in step (b) to a cylindrical quartz glass reactor, then immerse a low-pressure mercury lamp in the reaction solution, turn on the lamp to carry out the degradation reaction, the reaction system is an open system, no Do isolation air treatment.

Further, in step (ii), the pH value of the solution is adjusted to 7.0 with 0.1 mol/L HCl and NaOH.

Further, the total reaction volume in step (m) is 260mL, the reaction temperature is controlled at 25±1°C, the reaction time is 15 hours, and the light source is a 36W Philips low-pressure mercury lamp (the wavelength of the emitted light is mainly concentrated at 254nm); the reaction solution The concentrations of indole and PFOA were 1mmol/L and 10mg/L respectively.

Further, the water was ultrapure water, and the reactions were all carried out under open conditions without air isolation.

Description of drawings

Figure 1 is a schematic diagram of the reaction of activated carbon as a carrier for the reduction and degradation of PFASs by hydration electrons;

Fig. 2 is the adsorption thermodynamic curve figure of activated carbon to PFOA among the present invention;

Fig. 3 is the adsorption thermodynamic curve figure of gac in the present invention to indole;

Fig. 4 is the kinetic curve figure of PFOA degradation under different reaction conditions in the present invention;

Fig. 5 is the kinetic curve figure of PFOA defluorination under different reaction conditions in the present invention;

Fig. 6 is the intermediate product kinetics curve figure of PFOA degradation among the present invention;

Figure 7 shows the generation of hydrated electrons under different reaction conditions in the present invention.

Detailed ways

The present invention will be described in detail below in combination with specific embodiments.

The invention uses active carbon as a carrier and indole as a parent material for generating hydration electrons to carry out research on degrading PFASs by hydration electrons. Taking perfluorooctanoic acid (PFOA) as a typical representative substance of PFASs, the adsorption behavior and degradation kinetics were studied through adsorption and photochemical experiments, the products were quantitatively and qualitatively analyzed, and the degradation path was deduced. The influence of the pore structure and surface properties of activated carbon on the degradation of PFOA by hydration electrons, the mechanism of action is clarified, and the efficient degradation of PFOA by hydration electrons in the aerobic range is realized. The schematic diagram of the hydration electron reduction degradation of PFOA with activated carbon as the carrier is shown in Figure 1.

Example 1

Determination of the adsorption capacity of activated carbon to PFOA and indole, the steps are;

(1) Prepare 10 mL of PFOA aqueous solution with an initial concentration ranging from 0.00483 to 2.415 mmol/L, add 5 mg of activated carbon, shake at room temperature for 24 hours, centrifuge to take the supernatant to measure the concentration of PFOA, and use the langmuir model to fit the adsorption isotherm of activated carbon to PFOA line, the model is q _e =(K _L ×C _max ×C _e )/(1+K _L ×C _e ), the maximum adsorption capacity of PFOA on activated carbon is C _e (mmol/g)=0.462, R ² = 0.996. Similarly, prepare 10 mL of indole aqueous solutions with an initial concentration ranging from 0.01 to 1.5 mmol/L, add 5 mg of activated carbon, shake at room temperature for 24 hours, centrifuge to take the supernatant, measure the concentration of indole, and draw an adsorption isotherm. Similarly, indole can be obtained The maximum adsorption amount on activated carbon is C _e (mmol/g) = 2.832, R ² = 0.986.

It can be concluded that activated carbon has good adsorption capacity for PFOA and indole, which can be used as a reaction carrier to adsorb and concentrate PFOA and indole on its surface. See Figures 2 and 3 for specific curves.

Figure 2 Adsorption of PFOA by activated carbon. It can be seen from Figure 2 that activated carbon can effectively adsorb PFOA in water, but the activated carbon after adsorbing PFOA needs further treatment to achieve the complete degradation of PFOA, so as to avoid secondary pollution. Figure 3 Adsorption of indole by activated carbon. It can be seen from Figure 3 that activated carbon also has excellent adsorption capacity for indole, and the adsorption capacity is relatively high.

Example 2

Degradation reaction, its steps are:

Before the degradation reaction, the prepared indole solution and the PFOA solution were uniformly mixed first, then the activated carbon was dispersed in the solution and the pH of the solution was adjusted to 7.0 using 0.1mmol/L NaOH and HCl, and the prepared solution was mixed using magnetic stirring. The reaction solution was stirred for 1 hour, and the prepared reaction solution was transferred to a cylindrical quartz glass reactor. In an open environment, a low-pressure mercury lamp was immersed in the reaction solution, and the lamp was turned on to carry out the degradation reaction. The reaction volume is 260mL, the reaction temperature is controlled at 25±1°C, and the reaction time is 15 hours. The light source is a 36W Philips low-pressure mercury lamp (the wavelength of the emitted light is mainly concentrated at 254nm). The concentrations of PFOA and indole in the reaction solution are respectively 10mg/L and 1mmol/L, and the concentration of activated carbon is 1.0g/L. Sampling 2mL every 1 hour, the sample is divided into two parts, one part is extracted with 2 times the volume of methanol, and the remaining content of PFOA is detected by high performance liquid chromatography mass spectrometry (HPLC-MS/MS), and the other part is added with 2 times the volume of pure water , after vortex shaking for 1 minute, filter with a 0.22 μm water phase filter membrane, and then use ion chromatography (IC) to measure the content of F ions generated, so as to calculate the degradation rate and defluorination rate of PFOA. For specific degradation and defluorination curves, see Figures 4 and 5.

It can be concluded that after activated carbon adsorbs PFOA from water, it is difficult to completely degrade the adsorbed PFOA by simply using ultraviolet irradiation. After adding indole, the degradation of PFOA is greatly promoted. It can be completely degraded, and the defluorination rate reaches more than 40% after 15 hours of reaction, and the reaction system is an open system without air isolation treatment, which greatly reduces the difficulty of engineering application. This shows that activated carbon adsorbs PFOA and indole to its surface through adsorption and concentration, and under ultraviolet irradiation, indole generates a large number of hydrated electrons and rapidly degrades the surrounding PFOA.

Figure 4 is the degradation kinetics curve of PFOA under different reaction conditions; Figure 5 is the defluorination kinetics curve of PFOA under different reaction conditions.

Example 3

Determination of intermediate products, the specific steps are:

Before the degradation reaction, the prepared indole solution and the PFOA solution were uniformly mixed first, then the activated carbon was dispersed in the solution and the pH of the solution was adjusted to 7.0 using 0.1mmol/L NaOH and HCl, and the prepared solution was mixed using magnetic stirring. The reaction solution was stirred for 1 hour, and the prepared reaction solution was transferred to a cylindrical quartz glass reactor. In an open environment, a low-pressure mercury lamp was immersed in the reaction solution, and the lamp was turned on to carry out the degradation reaction. The reaction volume is 260mL, the reaction temperature is controlled at 25±1°C, and the reaction time is 15 hours. The light source is a 36W Philips low-pressure mercury lamp (the wavelength of the emitted light is mainly concentrated at 254nm). The concentrations of PFOA and indole in the reaction solution are respectively 10mg/L and 1mmol/L, and the concentration of activated carbon is 1.0g/L. Sampling 2mL every 1 hour, the sample was extracted with 2 times the volume of methanol and then measured by high performance liquid chromatography mass spectrometry (HPLC/MS/MS) The content of intermediate products generated during the degradation of PFOA, the specific degradation curve is shown in Figure 6. Fig. 6 is a kinetic curve diagram of intermediate products of PFOA degradation.

Example 4

The determination of hydrated electrons, the specific steps are:

First, mix the prepared indole solution with activated carbon and transfer it to a 15mL cylindrical quartz reaction tube, use 0.1mmol/L NaOH and HCl to adjust the pH of the solution to 7.0, add the hydrated electron trapping agent lutidine N-oxidation substance (DMPO). The total reaction volume was 10 mL, the concentrations of indole and DMPO were 1 mmol/L and 100 mmol/L, respectively, and the dosage of activated carbon was 1.0 g/L. After irradiating the prepared sample with a mercury lamp for 1.5 minutes, 25 μL of the sample was taken with a quartz capillary and placed in the resonant cavity of an electron paramagnetic resonance (EPR) instrument to detect free radical signals, as shown in Figure 7.

It can be concluded that without the addition of activated carbon, most of the hydrated electrons generated in the system react with oxygen to form hydroxyl radicals, so only a very small amount of hydrated electrons can be detected in the sample. Finally, in addition to the signal of hydroxyl radicals detected in the sample, a strong signal of hydrated electrons was also detected, indicating that the presence of activated carbon can protect hydrated electrons from being quenched by oxygen, which proves two conclusions: first, indium Indole can produce hydrated electrons under ultraviolet irradiation; second, when indole is adsorbed on the inner surface of activated carbon pores, the pores of the microporous structure can limit the diffusion of oxygen in the water body into its pores, thereby protecting the indole produced by indole in the pores. Hydrated electrons are not quenched by oxygen. When PFOA is also adsorbed on the inner surface of activated carbon pores, these hydrated electrons can quickly attack PFOA, thereby achieving rapid degradation and defluorination of PFOA. Fig. 7 Generation of hydrated electrons under different reaction conditions. The circles in the figure are the electron paramagnetic resonance signals of hydroxyl radicals, and the asterisks are the electron paramagnetic resonance signals of hydrated electrons.

The present invention has the advantages of:

(1) The present invention utilizes the special properties of activated carbon, and by putting the reaction between activated carbon channels, the utilization rate of hydrated electrons is improved;

(2) The surface of activated carbon in the present invention is naturally hydrophobic, so PFOA and indole can be adsorbed and concentrated to its surface, and the pore structure is not conducive to the rapid expansion of oxygen in the water to the inside of the pore, effectively weakening the effect of oxygen on hydration electrons. Quenching can achieve the degradation of PFOA in an open environment, and always maintain a high degradation and defluorination efficiency;

(3) The present invention makes full use of the characteristics of activated carbon, and adding activated carbon to pollutant treatment will not cause secondary pollution. After the reaction, the activated carbon settles rapidly in the water body, and can be recycled and reused after regeneration, which provides convenience for the design of the reaction process.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Any simple modifications made to the above embodiments according to the technical essence of the present invention, equivalent changes and modifications, all belong to this invention. within the scope of the technical solution of the invention.

Claims (7)

1. the method for active carbon mediation aqueous electron deoxidization, degradation PFASs, it is characterised in that follow the steps below:

(a) it mills, and sieves with 100 mesh sieve to active carbon；

(b) indoles solution is first prepared, is then uniformly mixed and added into PFOA solution to be degraded and prepared indoles solution Then a certain amount of active carbon stirs 1 hour；

(c) under aerobic condition, illumination is carried out to mixed solution obtained in step (b) using low pressure mercury lamp, realizes PFOA's Degradation and defluorinate.

2. the method for mediating aqueous electron deoxidization, degradation PFASs according to active carbon described in claim 1, it is characterised in that: described The step of being sieved of milling is carried out to active carbon in step (a) are as follows:

(1) it weighs in the placement of 5g active carbon and agate mortar；

(2) it mills；

(3) it sieves with 100 mesh sieve, obtains active carbon of the partial size less than 150 μm.

3. the method for mediating aqueous electron deoxidization, degradation PFASs according to active carbon described in claim 1, it is characterised in that: described The step of reaction solution is prepared in step (b) are as follows:

(i) prepared indoles solution and PFOA solution to be processed are uniformly mixed；

(ii) active carbon obtained in step (a) is dispersed in the solution of step (i) preparation and is adjusted the pH value of solution；

(iii) reaction solution prepared in step (ii) is stirred 1 hour using magnetic agitation.

4. the method for mediating aqueous electron deoxidization, degradation PFASs according to active carbon described in claim 1, it is characterised in that: described In step (c) the step of degradation PFOA are as follows:

(m) reaction solution obtained in step (b) is transferred in cylindrical quartz glass reactor first, it is then low by one Pressure mercury lamp is immersed into reaction solution, is turned on light and is carried out degradation reaction, and reaction system is open system, does not do air insulating treatment.

5. the method for mediating aqueous electron deoxidization, degradation PFASs according to active carbon described in claim 1, it is characterised in that: described In step (ii), the pH value of solution is adjusted to 7.0 with the HCl and NaOH of 0.1mol/L.

6. the method for mediating aqueous electron deoxidization, degradation PFASs according to active carbon described in claim 1, it is characterised in that: described Total reaction volume is 260mL in step (m), and at 25 ± 1 DEG C, the reaction time is 15 hours for reaction temperature control, and light source is one The Philip low pressure mercury lamp of 36W (outgoing light wavelength is concentrated mainly on 254nm)；The concentration of indoles and PFOA are respectively in reaction solution 1mmol/L and 10mg/L.

7. the method for mediating aqueous electron deoxidization, degradation PFASs according to active carbon described in claim 1, it is characterised in that: described Water is ultrapure water, and reaction carries out under open condition, does not do air insulating treatment.