Method for degrading halogenated phenolic compounds by using nano high-purity ferric oxide to activate low-concentration ferrate

Abstract

The application discloses a method for degrading halogenated phenolic compounds by using nano high-purity iron oxide activated low-concentration ferrate, and the method comprises the following steps: dissolving potassium ferrate powder in borax or dipotassium hydrogen phosphate buffer to prepare a Fe(VI) solution at normal temperature; and adding the Fe(VI) solution into a boric acid buffer containing halogenated phenolic compounds and high-purity iron oxide, and stirring to carry out degradation reaction. The method for degrading halogenated phenolic compounds by using nano high-purity iron oxide activated low-concentration ferrate realizes the activation of Fe(VI) through nano alpha-Fe2O3, realizes the in-situ generation of iron oxide through nano-sized particles with size effect instead of added iron salt in the role of Fe(VI) solution activation, rapidly degrades trace amounts of pentachlorophenol in water, and simultaneously realizes the recycling of the activator.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental pollutant degradation, and particularly relates to a method for degrading halogenated phenolic compounds by using nano high-purity ferric oxide to activate low-concentration ferrate. BACKGROUND

[0002] Ferrate (Fe(VI), HFeO4 - ) is an emerging active oxidant that can effectively degrade micro-pollutants such as phenolic derivatives, organophosphorus compounds, sulfur and nitrogen-containing substances, amines and ionic liquids. However, due to the fast self-decomposition of Fe(VI), 5-25 times or even more Fe(VI) is usually required to completely eliminate organic pollutants, and the high cost limits the promotion of Fe(VI) oxidation method in actual water treatment. So far, various reducing activators (such as S2O3 2- , NH2OH and H2O2) have been used to activate Fe(VI), but most of the homogeneous activators are easy to cause secondary pollution. For heterogeneous catalysts, the current research focuses mainly on reducing graphene, oxidized graphene, fullerene and other carbon materials, but the production cost of carbon materials is high, and the preparation process will produce pollutants such as aromatic hydrocarbons. Recent studies have found that metal ions have good catalytic properties for Fe(VI), especially Fe 3+ , which has the most remarkable activation ability. By adding Fe(III) salts to generate active iron hydroxide in situ, the reaction mechanism of Fe(VI) oxidation of pollutants is changed to rapidly degrade the pollutants. The addition of salts in situ each time increases the cost of Fe(VI) activation, and the activation persistence is limited, lacking reusability.

[0003] Pentachlorophenol (PCP) is an organochlorine pesticide, which is widely used as fungicide, herbicide and wood preservative, and is also one of persistent organic pollutants (POPs), and is listed as a priority pollutant. PCP has genetic and reproductive toxicity to aquatic organisms and even humans, but due to the rich halogen in its chemical structure, it passivates the electron transfer, resulting in low degradability, so the removal of PCP has always been the focus in the field of water remediation, and as a model compound, its degradation process can represent the removal of a series of halogenated phenols, which is typical. In the current research, Fe(VI) is used alone to treat PCP in water, and the degradation rate of 72.7 μmol··L -1 PCP is only 80% with 800 μmol··L -1 Fe(VI), and the dosage of Fe(VI) in this study is 11 times the concentration of PCP. It is proved that the utilization rate of oxidant in the Fe(VI) system alone is low, and the degradation capacity of PCP is limited. How to develop a water treatment process to efficiently treat PCP and other organochlorine pesticides at low Fe(VI) dosage through recyclable activators is a field worth developing. SUMMARY

[0004] The technical problem solved by the present application is to provide a method for degrading halogenated phenolic compounds by activating low-concentration ferrate with nano high-purity iron oxide, which solves the technical problems existing in the prior art.

[0005] To solve the above technical problems, the technical solution provided by the present application is:

[0006] The method for degrading halogenated phenolic compounds by activating low-concentration ferrate with nano high-purity iron oxide comprises the following steps:

[0007] At room temperature, potassium ferrate powder is dissolved in borax or dipotassium hydrogen phosphate buffer solution to prepare Fe(VI) solution; the Fe(VI) solution is added to the boric acid buffer solution containing halogenated phenolic compounds and high-purity iron oxide, and stirring reaction is carried out for degradation.

[0008] Further improvement of the above technical solution is:

[0009] Preferably, the specific steps of the method are:

[0010] Step 1: At room temperature, a borax / dipotassium hydrogen phosphate buffer solution stock solution is prepared in deionized water, and the pH of the mixed borax / dipotassium hydrogen phosphate buffer solution should be in the range of 9-11; K2FeO4 powder is dissolved in the borax / dipotassium hydrogen phosphate buffer solution to prepare Fe(VI) mother liquor.

[0011] Step 2: The pH range is stabilized at 6-9 by mixing boric acid solution and sodium tetraborate solution, and the boric acid buffer solution is prepared; the boric acid buffer solution concentration range is generally 10-20 mol·L -1 ; the low Fe(VI) solution concentration can be 2-10 times the pollutant concentration; the Fe(VI) solution prepared in step 1 is added to the boric acid buffer solution containing PCP and α-Fe2O3, and continuous magnetic stirring is carried out to obtain the degraded solution;

[0012] Step 3: After centrifugation to remove solid particles, the degraded solution in step 2 is transferred to a container bottle for high-performance liquid chromatography analysis to detect the residual concentration of the target pollutant.

[0013] Preferably, the pH of the borax or dipotassium hydrogen phosphate buffer solution is 9.0.

[0014] Preferably, the borax concentration is 0.1-2.0 mol·L-1 , the concentration of the dipotassium hydrogen phosphate buffer is 0.5-10.0 mol / L -1 .

[0015] Preferably, the pH value in the stirring reaction process is 7.0.

[0016] Preferably, in the step 2, the concentration of the boric acid buffer is 10-20 mol / L in terms of boron element -1 .

[0017] Preferably, after the degradation is completed, the solution is subjected to centrifugation or natural sedimentation to obtain α-Fe2O3 particle precipitate, and the precipitate is dried and recycled.

[0018] The method for degrading halogenated phenolic compounds by using nano high-purity iron oxide activated low-concentration ferrate provided by the application has the following advantages compared with the prior art:

[0019] (1) The method for degrading halogenated phenolic compounds by using nano high-purity iron oxide activated low-concentration ferrate provided by the application has the following advantages compared with the prior art:

[0020] (2) The method for degrading halogenated phenolic compounds by using nano high-purity iron oxide activated low-concentration ferrate provided by the application has the following advantages compared with the prior art:

[0021] (3) The method for degrading halogenated phenolic compounds by using nano high-purity iron oxide activated low-concentration ferrate provided by the application has the following advantages compared with the prior art: BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a column chart of the activation capacity of nano α-Fe2O3 under different Fe(VI) concentrations in the embodiments of the application.

[0023] Figure 2 is a kinetic curve graph of the catalytic degradation of PCP with different α-Fe2O3 dosages in embodiment 4 of the application.

[0024] Figure 3Figure 5 is the PCP degradation over time curve of the Fe(VI) / nano-α-Fe2O3 system in the present application with nano-α-Fe2O3 particles cycled 5 times.

[0025] Figure 4 (a) is a high-resolution electron microscope picture of α-Fe2O3 nanoparticles.

[0026] Figure 4 (b) is a high-resolution electron microscope picture of α-Fe2O3 nanoparticles after being cycled 5 times.

[0027] Figure 5 (a) is an X-ray photoelectron spectrogram of the surface Os of α-Fe2O3 nanoparticles before and after being cycled.

[0028] Figure 5 (b) is an X-ray photoelectron spectrogram of the surface Fe of α-Fe2O3 nanoparticles before and after being cycled.

[0029] Figure 6 Figure 6 is an X-ray y diffraction spectrogram of α-Fe2O3 nanoparticles before and after being cycled. DETAILED DESCRIPTION

[0030] The detailed description of the present application is described below. It should be understood that the detailed description described herein is only used to illustrate and explain the present application, and is not used to limit the present application.

[0031] The present application can be used to treat halogenated phenol-containing wastewater, such as PCP and 2,4-dichlorophenol. Halogenated phenol is a very common chemical raw material, which is widely used in fine chemical, dye, pharmaceutical and pesticide production; it is also a chemical product, which is widely used in construction, national defense, agriculture and hospital, and is a common wood preservative, disinfectant and bactericide. Such contaminated wastewater can be treated by the Fe(VI) / nano-α-Fe2O3 system in the present application. The enhanced active iron species Fe(IV) and Fe(V) of nano-α-Fe2O3 have reactivity on the N site of amide and the site on the benzene ring, so it may have catalytic degradation specificity for aromatic and amide-containing pollutants.

[0032] Figures 1 to 6 Figure 5 is the PCP degradation over time curve of the Fe(VI) / nano-α-Fe2O3 system in the present application with nano-α-Fe2O3 particles cycled 5 times.

[0033] Example 1

[0034] Step 1, at room temperature, 0.1059 g of K2FeO4 powder was dissolved in 8 ml of 1.0 mol·L-1 Na2B4O7 / 5.0 mol·L-1 NaOH solution. -1 borax / 5.0 mol·L-1 NaOH solution. -1Fe(VI) stock solution was prepared in potassium phosphate buffer (pH = 9.0) to inhibit the self-decomposition of K2Fe04 and prevent the decay of oxidant activity.

[0035] Step 2, 100 μL of prepared Fe(VI) solution was quickly added into 5 μmol·L -1 of PCP and 0.5 g·L -1 of α-Fe2O3 in 120 mL 10 mol·L -1 of BBS under continuous magnetic stirring to keep the pH value at 7.0.

[0036] Step 3, 1.0 mL of sample solution in step 2 was pipetted into a centrifuge tube pre- added with 0.1 mL of Na2S2O3 (0.2 mol·L -1 ) and 0.3 mL of methanol at reaction time of 0, 15, 30, 60, 180, 300 s respectively to quench the reaction and desorb the organic pollutants captured on the solid particles.

[0037] Na2S2O3 was used to quench the high ferrate, and methanol was used to desorb the PCP pollutants adsorbed on the catalyst, which was used to measure the pollutant concentration in the reaction process.

[0038] Step 4, after removing the solid particles by centrifugation, the sample was transferred to a brown HPLC vial for analysis. The α-Fe2O3 could be recycled after centrifugation and drying.

[0039] All experiments were performed in triplicate. The K2Fe04 powder and α-Fe2O3 nanoparticles used were purchased commercially.

[0040] The reaction equation of the activation process of Fe(VI) by nano α-Fe2O3 is as follows: Fe(VI) + Fe(III) (s) → Fe(V) + Fe(IV), where Fe(V) / Fe(IV) is the active substance that enhances the degradation of PCP, and Fe(III) (s) represents the α-Fe2O3 nanoparticles dispersed in the reaction system. The active iron species will eventually be converted into iron oxide attached to the surface of nano α-Fe2O3.

[0041] In this example, the activation capacity is 3.8, and the final PCP degradation efficiency is 83.4%, which is represented by the promotion multiple of PCP degradation efficiency by the catalyst in the high ferric oxidation system.

[0042] Example 2

[0043] Step 1, 0.1059 g of K2Fe04 powder was dissolved in 8 mL of 1.0 mol·L -1Borax / 5.0 mol·L-1 -1 Fe(VI) solution was prepared in a potassium phosphate buffer (pH = 9.0) to inhibit the self-decomposition of K2Fe04 and prevent the activity of oxidant from decaying.

[0044] Step 2, quickly add 25 μL of prepared Fe(VI) solution into 5 μmol·L-1 -1 PCP and 0.5 g·L-1 -1 α-Fe2O3 in 120 mL 10 mol·L-1 -1 Borax buffer (BBS) with continuous magnetic stirring, and maintain the pH value at 7.0.

[0045] The remaining steps are the same as Example 1.

[0046] In this example, the activation capacity of Fe(VI) is 2.5 μmol·L-1 -1 , and the final PCP degradation efficiency is 48.0%. Compared with Example 1, the activation capacity of nano α-Fe2O3 for low concentration of Fe(VI) is more significant. In addition, the concentration of Fe(VI) is set to 5, 15 μmol·L-1 -1 , and the final PCP degradation efficiency is 48.0%, 70.6%, 83.4%, and 89.9%, respectively. With the removal rate of target pollutants increasing, the amount of Fe(VI) required is multiplied. The specific activation and degradation performance comparison data are shown in Table 1, and the corresponding degradation rate constant (k obs ) is given. The column chart of the activation capacity of nano α-Fe2O3 under different Fe(VI) concentrations is shown in Figure 1 .

[0047] Table 1 Activation and degradation performance comparison table

[0048] Fe(VI) dose / pmol L -1 ]] 2.5 5.0 10.0 15.0 Degradation efficiency / % 48.0 70.6 83.4 89.9 Apparent rate constant / min -1 ]] 0.40±0.02 0.62±0.03 0.72±0.02 1.23±0.10 Activation capacity 12.0 4.8 3.7 2

[0049] Conditions: [PCP]0= 5.0 μmol·L-1 -1 , α-Fe2O3= 0.5 g·L-1 -1 , pH = 7.0, temperature = 20℃.

[0050] Example 3

[0051] Step 1, at room temperature, dissolve 0.1059 g of K2Fe04 powder in 4 ml of 1.0 mol·L-1 -1 Borax / 5.0 mol·L-1 -1 Potassium phosphate buffer (pH = 9.0) to prepare Fe(VI) solution.

[0052] Step 2, quickly add 250 μL of prepared Fe(VI) solution to 5 μmol·L -1 PCP and 0.5 g·L -1 120 mL 10 mol·L -1 borate buffer (BBS) with continuous magnetic stirring, reaction, pH value maintained at 7.0.

[0053] The remaining steps are the same as Example 1.

[0054] In this example, the concentration of Fe(VI) is 50 μmol·L -1 , and the degradation rate of PCP is 100%. In order to achieve the same degradation rate, the dosage of Fe(VI) in the pure oxidation system needs to be increased to 75 μmol·L -1 . By using the catalyst, the dosage of Fe(VI) can be reduced to 50 μmol·L -1 . At this time, according to Figure 1 the promotion trend line, the catalytic benefit of nano α-Fe2O3 is the lowest, but this process still saves 33.3% of the oxidant consumption.

[0055] Example 4

[0056] Step 1, at room temperature, dissolve 0.1059 g of K2FeO4 powder in 8 ml of 1.0 mol·L -1 borax / 5.0 mol·L -1 potassium phosphate buffer (pH = 9.0) to prepare the Fe(VI) solution.

[0057] Step 2, quickly add 100 μL of prepared Fe(VI) solution to 5 μmol·L -1 PCP and 1 g·L -1 120 mL 10 mol·L -1 borate buffer (BBS) with continuous magnetic stirring, reaction, pH value maintained at 8.0.

[0058] The remaining steps are the same as Example 1.

[0059] In this example, the concentration of α-Fe2O3 nanoparticles is 1 g·L -1 , the concentration of Fe(VI) is 10 μmol·L -1 , and the degradation efficiency of PCP is 84.3%. Thereafter, the concentration of α-Fe2O3 nanoparticles is set to 0, 0.25, 0.5, 2.5, and 5 g·L -1 , and the influence of catalyst concentration on catalytic performance is compared. The specific kinetic curves of different α-Fe2O3 dosages for catalytic degradation of PCP are as follows:Figure 2 As shown in Fig. 1, with the increase of the dosage of a-Fe2O3 from 0 g·L -1 to 1 g·L -1 , the degradation efficiency of PCP increased from 32.1% to 84.3%, and the increase of the concentration of a-Fe2O3 enhanced the oxidation of PCP by Fe(VI). When the concentration of the catalyst was further increased to 5 g·L -1 , the final removal rate did not increase, and the dependence of the degradation on the concentration of the catalyst was limited. Since the dosage of Fe(VI) was low, the highest removal rate of PCP was only 90%, which could not be further improved by increasing the concentration of a-Fe2O3. Considering the reaction efficiency and economic cost, the initial dosage of a-Fe2O3 was 0.5 g·L -1 , which achieved a removal rate of 90% within 10 minutes. If the oxidation process was to be accelerated, the concentration of a-Fe2O3 could be further increased to 1 g·L -1 , and the degradation time could be shortened by half.

[0060] Example 5

[0061] Step 1, at room temperature, 0.1059 g of K2FeO4 powder was dissolved in 8 ml of 1.0 mol·L -1 borax / 5.0 mol·L -1 dipotassium hydrogen phosphate buffer (pH = 9.0) to prepare a Fe(VI) solution.

[0062] Step 2, 100 μL of the prepared Fe(VI) solution was quickly added to 120 mL of 10 mol·L -1 boric acid buffer (BBS) containing 5 μmol·L -1 PCP and 0.5 g·L -1 a-Fe2O3, and continuously magnetic stirring was performed, the reaction was carried out, and the pH value was maintained at 8.0.

[0063] The remaining steps were the same as those in Example 1.

[0064] In this example, the pH was 6.0, and the degradation efficiency was 77.7%, and the corresponding k obs value was 0.66 min -1 . In Example 1, the pH was 7.0, and the remaining conditions were the same as those in this example, the degradation efficiency was 83.4%, and the corresponding k obs value was 0.72 min -1 . It was shown that the degradation effect had pH dependence. The degradation effects of pH = 6.0, 7.0, 8.0, and 9.0 were compared, and the catalytic degradation effect was best under the condition of pH = 7. The specific activation and degradation performance comparison data are shown in Table 2, and the corresponding degradation rate constant (k obs). It is worth noting that the oxidation ability of Fe(VI) is almost lost under alkaline conditions with pH 9.0, and the oxidation ability of Fe(VI) can be significantly improved by using a-Fe2O3.

[0065] Table 2 Activation and degradation performance control table

[0066] pH 6.0 7.0 8.0 9.0 Degradation efficiency / % 77.7 83.4 79.8 46.9 Apparent rate constant / min -1 ]] 0.66±0.01 0.72±0.02 0.38±0.01 0.06±0.01 Activation capacity 2.0 3.7 5.0 78.2

[0067] Conditions: [PCP]0= 5.0 pmol L -1 , [Fe(VI)]0= 10.0 pmol L -1 , a-Fe2O3= 0.5 g L -1 , temperature = 20 °C.

[0068] Example 6

[0069] The same as Example 1, the pollutant PCP is replaced by 2,4-dichlorophenol at the same concentration, and the rest of the conditions remain unchanged. The removal rate can be achieved within 10 minutes, which is 82%, and the degradation effect can be improved by 71% compared with the degradation rate without the catalytic system.

[0070] Example 7

[0071] Recycle the a-Fe2O3 nanomaterial and compare the degradation effect:

[0072] Step 1, at room temperature, 0.1059 g of K2FeO4 powder is dissolved in 8 ml of 1.0 mol L -1 borax / 5.0 mol L -1 potassium phosphate buffer (pH = 9.0) to prepare a Fe(VI) solution.

[0073] Step 2, quickly take 100 pL of the prepared Fe(VI) solution and add it to 120 mL of 10 mol L -1 boric acid buffer (BBS) containing 5 pmol L -1 PCP and 1 g L -1 a-Fe2O3, continuously magnetic stirring, reaction, and pH value maintained at 7.0.

[0074] Step 3, at reaction times 0, 15, 30, 60, 180, and 300 s, respectively, 1.0 mL of the solution in Step 2 is pipetted into a centrifuge tube pre-added with 0.1 mL of Na2S2O3 (0.2 mol L -1 ) and 0.3 mL of methanol to quench the reaction and simultaneously desorb the organic matter captured on the solid particles.

[0075] Step 4: After centrifuging to remove solid particles, the sample is transferred to a brown HPLC vial for analysis. α-Fe₂O₃ is separated by centrifugation, dried, and then recycled.

[0076] Step 5: Using the nano-α-Fe2O3 recovered in Step 4 as a catalyst, repeat Steps 1-4, and recycle the α-Fe2O3 nanomaterial five times in total.

[0077] Figure 3 The figure shows the PCP degradation curves over time for nano-α-Fe2O3 particles in the Fe(VI) / nano-α-Fe2O3 system after five cycles. After five cycles, the PCP degradation efficiency remained essentially constant at 83.4%, 85.4%, 87.9%, 85.4%, and 88.1%, respectively, indicating that α-Fe2O3 has good reusability. Simultaneously, other techniques such as high-resolution electron microscopy were employed. Figure 4 X-ray photoelectron spectroscopy (XPS) Figure 5 X-ray diffraction pattern Figure 6 Characterization of α-Fe₂O₃ nanoparticles revealed that their morphology, surface Fe valence state, and lattice stability remained good before and after pollutant treatment. Reaction conditions: [PCP]₀ = 5.0 μmol·L⁻¹ -1 [Fe(VI)]0 = 10.0 μmol·L -1 α-Fe₂O₃ = 0.5 g L -1 pH = 7.0, temperature = 20℃.

[0078] The above embodiments are merely preferred examples of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for degrading halogenated phenolic compounds by activating low-concentration ferrates with nano-high-purity iron oxide, characterized in that, The method is as follows: at room temperature, potassium ferrate powder is dissolved in borax / dipotassium hydrogen phosphate buffer to prepare Fe(VI) solution; the Fe(VI) solution is added to borate buffer containing halogenated phenolic compounds and high-purity iron oxide, and the reaction is stirred to carry out degradation; The method for activating low-concentration ferrates to degrade halogenated phenolic compounds using nano-high-purity iron oxide comprises the following steps: Step 1: At room temperature, prepare a stock solution of borax / dipotassium hydrogen phosphate buffer in deionized water. The pH range of borax and dipotassium hydrogen phosphate buffer is 9-11 after mixing. Dissolve K2FeO4 powder in borax / dipotassium hydrogen phosphate buffer to prepare Fe(VI) stock solution. Step 2: Mix boric acid solution and sodium tetraborate solution to stabilize the pH range at 6-9, prepare borate buffer solution, add the Fe(VI) solution obtained in step 1 to the borate buffer solution containing PCP and α-Fe2O3, and continuously stir magnetically to obtain the degraded solution; Step 3: After centrifuging the degraded solution from Step 2 to remove solid particles, perform high performance liquid chromatography analysis to detect the remaining concentration of the target pollutant.

2. The method for degrading halogenated phenolic compounds by activating low-concentration ferrates with nano-high-purity iron oxide according to claim 1, characterized in that, In step 1, the pH of the borax or dipotassium hydrogen phosphate buffer solution is 9.

0.

3. The method for degrading halogenated phenolic compounds by activating low-concentration ferrates with nano-high-purity iron oxide according to claim 2, characterized in that, The concentration of borax is 0.1–2.0 mol•L. -1 The concentration of dipotassium hydrogen phosphate buffer is 0.5–10.0 mol / L. -1 .

4. The method for degrading halogenated phenolic compounds by activating low-concentration ferrates with nano-high-purity iron oxide according to claim 1, characterized in that, In step 2, the pH value is 7.0 during the stirring reaction.

5. The method for degrading halogenated phenolic compounds by activating low-concentration ferrates with nano-high-purity iron oxide according to claim 1, characterized in that, In step 2, the concentration of the borate buffer solution, measured in boron element, is 10–20 mol·L⁻¹. -1 .

6. The method for degrading halogenated phenolic compounds by activating low-concentration ferrates with nano-high-purity iron oxide according to claim 1, characterized in that, After degradation is complete, the solution is centrifuged or allowed to settle naturally to obtain α-Fe2O3 particulate precipitate, which is then dried and recycled.

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