Method of degrading perfluorinated compound

Abstract

The present disclosure relates to the technical field of degradation of persistent pollutants and discloses a method for efficiently degrading a perfluorinated compound (PFC), through which the problems of harsh reaction conditions and less high defluorination rate existing in prior-art methods for degrading PFCs are solved. In the present disclosure, a 3-indoleacetic acid (IAA) solution is irradiated with 254 nm UV light to generate hydrated electrons, with which the PFC are degraded by reduction under an aerobic condition, where an organo-modified montmorillonite is added to provide a reaction microzone, so the degradation and defluorination effects of the hydrated electrons for the PFC are greatly improved. The method for degrading a PFC according to the present disclosure is not affected by the pH of and the dissolved oxygen in the solution and less affected by the humic substances in a water body, thereby overcoming the defects in existing methods for degrading PFCs with hydrated electrons while the degradation efficiency is ensured. Therefore, the present disclosure is of great application value.

Claims

1. A method for efficiently degrading a perfluorinated compound (PFC), comprising: (a) organically modifying montmorillonite with hexadecyl trimethyl ammonium bromide to obtain an organo-montmorillonite; (b) uniformly mixing a solution of the PFC to be degraded with a 3-indoleacetic acid (IAA) solution, then adding the organo-montmorillonite, and stirring to obtain a mixed solution; and (c) irradiating the mixed solution obtained in Step (b) by using a low-pressure mercury lamp under an aerobic condition, to enable the degradation and defluorination of the PFC.

2. The method of claim 1, wherein the organically modifying montmorillonite in Step (a) comprises: (1) dispersing sodium montmorillonite in water; (2) adding a hexadecyl trimethyl ammonium bromide solution to the dispersed solution in Step (1) and stirring; (3) centrifuging after the stirring in Step (2) is completed and discarding supernatant to obtain a precipitate; and (4) washing the precipitate obtained in Step (3) with water to obtain an HDTMA.sup.+ loaded montmorillonite.

3. The method of claim 1, wherein Step (b) comprises: (i) uniformly mixing the IAA solution and the solution of the PFC to be treated; (ii) dispersing the organo-montmorillonite obtained in Step (a) in the solution in Step (i) and adjusting the pH of the solution, a weight ratio of the organo-montmorillonite to IAA being (7.5-16.6):1; and (iii) stirring the reaction solution in Step (ii) for 30-40 min.

4. The method of claim 1, wherein the degradation in Step (c) is carried out with the low-pressure mercury lamp immersed in the mixed solution.

5. The method of claim 2, wherein a dispersing time in Step (1) is 8 hrs.

6. The method of claim 2, wherein a total amount of hexadecyl trimethyl ammonium bromide added in Step (2) is in accord with cation exchange capacity of the montmorillonite in the solution.

7. The method of claim 2, wherein a stirring time in Step (2) is 24 hrs.

8. The method of claim 3, wherein in Step (ii), the pH of the solution is adjusted to 4.0-10.0.

9. The method of claim 4, wherein a degradation temperature is controlled at 15-35 C., a low-pressure mercury lamp is a 36 W mercury lamp, a reaction time is 1-10 hrs, and a weight ratio of IAA to PFC in the reaction solution is 17:1.

10. The method of claim 9, wherein the reactions are all carried out under an aerobic condition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a route for degrading a PFC by interlamellar hydrated electrons in the organo-montmorillonite in the present disclosure;

(2) FIG. 2 shows an adsorption isotherm for PFOA and IAA of the organo-montmorillonite in the present disclosure;

(3) FIG. 3 shows a kinetic curve for degradation of PFOA by hydrated electrons under various reaction conditions in the present disclosure;

(4) FIG. 4 shows a kinetic curve for degradation of PFOS by hydrated electrons in the present disclosure;

(5) FIG. 5 shows a kinetic curve for production of intermediates in degradation of PFOA by hydrated electrons in the present disclosure;

(6) FIG. 6 shows a kinetic curve for degradation of PFOA by hydrated electrons under various pH conditions in the present disclosure;

(7) FIG. 7 shows a kinetic curve for degradation of PFOA by hydrated electrons in the presence of various concentrations of humic acid in the present disclosure;

(8) FIG. 8 shows production of hydrated electrons under various reaction conditions in the present disclosure; and

(9) FIG. 9 shows defluorination rates of PFOA by hydrated electrons in the presence of various amounts of organo-montmorillonite in the present disclosure.

DETAILED DESCRIPTION

(10) The present disclosure is further described with reference to specific examples.

Example 1

(11) The adsorption rates of HDTMA.sup.+-montmorillonite and Na.sup.+-montmorillonite for perfluorooctanoic acid (PFOA) and 3-indoleacetic acid (IAA) were determined. The steps were as follows.

(12) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd., cation exchange capacity: 730 mmol/kg) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(13) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with water, to obtain an HDTMA.sup.+ loaded montmorillonite.

(14) (3) Each 10 mL of the aqueous PFOA solutions having an initial concentration ranging from 0.00483 to 2.415 mmol/L was prepared, and 22 mg Na.sup.+-montmorillonite or HDTMA.sup.+-montmorillonite was added respectively, agitated at room temperature for 24 hrs, and centrifuged. The PFOA concentration in the supernatant was determined. The adsorption isotherm of the Na.sup.+-montmorillonite or HDTMA.sup.+ montmorillonite for PFOA was fitted by using the Langmuir model: q.sub.e=(K.sub.LC.sub.maxC.sub.e)/(1+K.sub.LC.sub.e), where q.sub.e denotes the amount of PFOA or IAA adsorbed onto the montmorillonite (in mmol/kg), C.sub.e denotes the concentration of PFOA or IAA in the solution after adsorption equilibrium (in mmol/L), K.sub.L denotes an adsorption constant (in L/mmol), and C.sub.max denotes a maximum adsorption (in mmol/kg). The result shows that the maximum adsorption C.sub.max (mmol/kg) of PFOA on the Na.sup.+-montmorillonite is 8.199, and is 277.312 on the HDTMA.sup.+ montmorillonite. Similarly, each 10 mL of the aqueous IAA solutions having an initial concentration ranging from 0.05 to 2.1 mmol/L was prepared, and 22 mg Na.sup.+ montmorillonite or HDTMA.sup.+-montmorillonite was added respectively, agitated at room temperature for 24 hrs, and centrifuged. The IAA concentration in the supernatant was determined, and an adsorption isotherm was plotted. The result shows that the maximum adsorption C.sub.max (mmol/kg) of IAA on the Na.sup.+-montmorillonite is 4.673, and is 70.005 on the HDTMA.sup.+-montmorillonite.

(15) It can be concluded that the adsorption of montmorillonite for PFOA and IAA is greatly promoted by organo-modification. The specific adsorption isotherms are shown in FIG. 2, wherein FIG. 2A shows the adsorption of montmorillonite for PFOA and FIG. 2B shows the adsorption of montmorillonite for IAA.

Example 2

(16) A method for efficiently degrading a PFC was as follows.

(17) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(18) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(19) (3) Before the degradation by reduction, the formulated IAA solution, and PFOA solution were mixed uniformly. Then, the organo-montmorillonite was dispersed in the solution and adjusted to pH 6.0 with 0.1 mmol/L NaOH and HCl. The formulated reaction solution was magnetically stirred for 30 min and then transferred to a cylindrical glass reactor. Under an aerobic condition, a low-pressure mercury lamp was immersed in the reaction solution and the degradation was initiated. The overall reaction volume was 300 mL, the reaction temperature was controlled at 252 C., the light source was a 36 W Philips low-pressure mercury lamp (having a central radiation wavelength of 253.7 nm), the reaction time was 10 hrs, the concentrations of IAA and PFOA in the reaction solution were 1 mmol/L and 10 mg/L respectively, and the concentration of the organo-montmorillonite was 2.2 g/L. 5 mL of the reaction solution was sampled every hour. The sample was divided into two portions, one portion was extracted with two-fold volume of methanol and then determined for the remaining PFOA content by high-performance liquid chromatography (HPLC), and the other portion was filtered and then determined for the content of generated fluoride ions by ion chromatography (IC), from which the degradation and defluorination rates of PFOA were calculated. The specific degradation and defluorination curves are shown in FIGS. 3A and 3B.

(20) It can be concluded that by adding the organo-montmorillonite, the degradation of PFOA by reduction is greatly promoted. After, PFOA is completely degraded, and the defluorination rate can be up to 90% or higher after the 10-hr reaction. Moreover, the reaction is not affected by dissolved oxygen in the solution.

Example 3

(21) A method for efficiently degrading a PFC was as follows.

(22) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(23) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(24) (3) Before the degradation by reduction, the formulated IAA solution, and perfluorooctane sulfonate (PFOS) solution were mixed uniformly. Then, the organo-montmorillonite was dispersed in the solution and adjusted to pH 6.0 with 0.1 mmol/L NaOH and HCl. The formulated reaction solution was magnetically stirred for 30 min and then transferred to a cylindrical glass reactor. Under an aerobic condition, a low-pressure mercury lamp was immersed in the reaction solution and the degradation was initiated. The overall reaction volume was 300 mL, the reaction temperature was controlled at 252 C., the light source was a 36 W Philips low-pressure mercury lamp, the reaction time was 10 hrs, the concentrations of IAA and PFOS in the reaction solution were 1 mmol/L and 10 mg/L respectively, and the concentration of the organo-montmorillonite was 2.2 g/L. 5 mL of the reaction solution was sampled every hour. The sample was divided into two portions, one portion was extracted with the two-fold volume of methanol and then determined for the remaining PFOS content by HPLC, and the other portion was filtered and then determined for the content of generated fluoride ions by IC, from which the degradation and defluorination rates of PFOS were calculated. The specific degradation and defluorination curves are shown in FIGS. 4A and 4B.

(25) Compared with Example 2, the degradation and defluorination rates of PFOS in this example have no obvious difference from those of PFOA. Therefore, the method is suitable for the degradation of PFCs.

Example 4

(26) A method for efficiently degrading a PFC was as follows.

(27) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(28) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(29) (3) Before the degradation by reduction, the formulated IAA solution, and PFOA solution were mixed uniformly. Then, the organo-montmorillonite was dispersed in the solution and adjusted to pH 6.0 with 0.1 mmol/L NaOH and HCl. The formulated reaction solution was magnetically stirred for 30 min and then transferred to a cylindrical glass reactor. Under an aerobic condition, a low-pressure mercury lamp was immersed in the reaction solution and the degradation was initiated. The overall reaction volume was 300 mL, the reaction temperature was controlled at 252 C., the light source was a 36 W Philips low-pressure mercury lamp, the reaction time was 10 hrs, the concentrations of IAA and PFOA in the reaction solution were 1 mmol/L and 10 mg/L respectively, and the concentration of the organo-montmorillonite was 2.2 g/L. 5 mL of the reaction solution was sampled every hour. The sample was extracted with the two-fold volume of methanol, and then the contents of intermediates produced during the degradation of PFOA were determined by HPLC/MS/MS. Small-molecule perfluorinated compounds were detected, indicating that the degradation is mainly caused by the breakage of carbon-fluorine bonds. The specific degradation curve is shown in FIG. 5.

Example 5

(30) A method for efficiently degrading a PFC was as follows.

(31) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(32) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(33) (3) The degradation efficiency by reduction was investigated under various pH conditions. Before the degradation by reduction, the formulated IAA solution, and PFOA solution were mixed uniformly, to prepare 4 identical mixed solutions of IAA and PFOA. Then, the organo-montmorillonite was dispersed in the 4 mixed solutions and adjusted to pH 4.0, 6.0, 8.0, and 10.0 with 0.1 mmol/L NaOH and HCl respectively. The formulated reaction solution was magnetically stirred for 30 min and then transferred to a cylindrical glass reactor. Under an aerobic condition, a low-pressure mercury lamp was immersed in the reaction solution and the degradation was initiated. The overall reaction volume was 300 mL, the reaction temperature was controlled at 252 C., the light source was a 36 W Philips low-pressure mercury lamp, the reaction time was 10 hrs, the concentrations of IAA and PFOA in the reaction solution were 1 mmol/L and 10 mg/L respectively, and the concentration of the organo-montmorillonite was 2.2 g/L. 5 mL of the reaction solution was sampled every hour. The sample was divided into two portions, one portion was extracted with the two-fold volume of methanol and then determined for the remaining PFOA content by HPLC, and the other portion was filtered and then determined for the content of the generated fluoride ions by IC, from which the degradation and defluorination rates of PFOA were calculated. The specific degradation and defluorination curves are shown in FIGS. 6A and 6B.

(34) It can be concluded that the degradation and defluorination of PFOA are scarcely affected by the pH of the solution.

Example 6

(35) A method for efficiently degrading a PFC was as follows.

(36) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(37) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(38) (3) The effect of humic acid on degradation and defluorination was investigated. Before the degradation by reduction, the formulated IAA solution, and PFOA solution were mixed uniformly, and various concentrations of aqueous humic acid solutions were added according to the reaction conditions. Then, the organo-montmorillonite was dispersed in the solution and adjusted to pH 6.0 with 0.1 mmol/L NaOH and HCl. The formulated reaction solution was magnetically stirred for 30 min and then transferred to a cylindrical glass reactor. Under an aerobic condition, a low-pressure mercury lamp was immersed in the reaction solution and the degradation was initiated. The overall reaction volume was 300 mL, the reaction temperature was controlled at 252 C., the light source was a 36 W Philips low-pressure mercury lamp, the reaction time was 10 hrs, the concentrations of IAA and PFOA in the reaction solution were 1 mmol/L and 10 mg/L respectively, the humic acid contents were 2, 5, and 10 mg/L separately, and the concentration of the organo-montmorillonite was 2.2 g/L. 5 mL of the reaction solution was sampled every hour, The sample was divided into two portions, one portion was extracted with two-fold volume of methanol and then determined for the remaining PFOA content by HPLC, and the other portion was filtered and then determined for the content of the generated fluoride ions by IC, from which the degradation and defluorination rates of PFOA were calculated. The specific degradation and defluorination curves are shown in FIGS. 7A and 7B.

(39) It can be concluded that the humic acid present in a water body can inhibit the degradation and defluorination of PFOA to some extent; however, the effect is relatively weak.

Example 7

(40) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(41) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(42) (3) The formulated IAA solution was mixed with the organo-montmorillonite, transferred to a 15 mL cylindrical quartz reaction tube, and adjusted to pH 4.0 with 0.1 mmol/L NaOH and HCl. A hydrated electron scavenging agent dimethylpyridine N-oxide (DMPO) was added. The total reaction volume was 10 mL, the concentration of IAA and DMPO was 1 mmol/L and 20 mmol/L respectively, and the concentration of the organo-montmorillonite was 2.2 g/L. After the formulated sample was irradiated for 1 min using a mercury lamp, 20 L was sampled and detected from the free radical signal by electron paramagnetic resonance (EPR). The detection results are specifically shown in FIG. 8.

(43) It can be concluded that in case that no organo-montmorillonite is added, the generated hydrated electrons in solution are reacted immediately with oxygen and hydrogen ions to produce hydroxyl radicals, and thus no signals of hydrated electrons are detected in the sample. After the organo-montmorillonite is added, besides hydroxyl radicals, the signals of hydrated electrons are also detected in the sample, indicating that the presence of organo-montmorillonite protects the hydrated electron from being quenched through reaction with oxygen and hydrogen ions. This confirms that hydrated electrons are generated from IAA under UV irradiation; and the presence of organo-montmorillonite protects the hydrated electrons from being quenched by oxygen and hydrogen ions, thereby promoting the degradation of PFCs by hydrated electrons.

Example 8

(44) A method for efficiently degrading a PFC was as follows.

(45) (1) The commercial sodium montmorillonite (purchased from Zhejiang FengHong Clay Chemicals Co. Ltd.) was placed in a 0.1 mol/L NaCl solution and stirred for 8 hrs, to allow the sodium ions to saturate the montmorillonite fully, and obtain a montmorillonite adsorbed with interlamellar sodium ions. After centrifugation, the supernatant was discarded, and the precipitate was placed in a 0.1 mol/L NaCl solution again. The above process was repeated 6 times. The precipitate was washed with ultrapure water until the washing was found to have no precipitate produced, as detected by an AgNO.sub.3 solution, and then freeze-dried, to obtain a Na.sup.+ loaded sodium montmorillonite.

(46) (2) The prepared Na.sup.+-montmorillonite was stirred for 8 hrs in water, to disperse the montmorillonite uniformly. To the dispersed montmorillonite solution, an aqueous solution of hexadecyl trimethyl ammonium bromide in an amount equivalent to the cation exchange capacity (CEC) of the montmorillonite in the solution was added, stirred for 24 hrs, and then centrifuged. The supernatant was discarded, and the resulting precipitate was washed with ultrapure water, to obtain an HDTMA.sup.+ loaded organo-montmorillonite.

(47) (3) The effect of the amount of organo-montmorillonite added on defluorination rate was investigated. Before the degradation, the formulated IAA solution and PFOA solution were mixed uniformly, and then various amounts of the organo-montmorillonite were dispersed in the mixed solution, wherein the weight ratio of the organo-montmorillonite to IAA is (7.5-16.6):1. The mixed solution was adjusted to pH 6.0 with 0.1 mmol/L NaOH and HCl. The formulated reaction solution was magnetically stirred for 30 min and then transferred to a cylindrical glass reactor. Under an aerobic condition, a low-pressure mercury lamp was immersed in the reaction solution and the degradation was initiated. The overall reaction volume was 300 mL, the reaction temperature was controlled at 252 C., the light source was a 36 W Philips low-pressure mercury lamp, the reaction time was 150 min, and the concentrations of IAA and PFOA in the reaction solution were 1 mmol/L and 10 mg/L respectively. After the reaction had been completed, 5 mL of the reaction solution was sampled. The sample was filtered and then determined for the content of the generated fluoride ions by IC, from which the defluorination rate of PFOA was calculated. The specific defluorination curve is shown in FIG. 9, in which the arrow indicates the most preferred point for defluorination in the experimental range.