Acid-modified boron-doped charcoal and application thereof in treating phenol wastewater by activating persulfate

Abstract

The invention belongs to the field of environmental functional materials and water treatment, and particularly relates to acid-modified boron-doped biochar and application of the acid-modified boron-doped biochar in treating phenol wastewater by activating persulfate. The preparation method of the acid-modified boron-doped biochar comprises the following specific steps: S1, adding biochar into an acid solution, stirring, washing with water until the biochar is neutral, and drying to obtain acid-modified biochar; s2, mixing and dispersing the acid-modified biochar and boric acid into an ethanol solution, stirring, drying, and carrying out high-temperature calcination to obtain acid-modified boron-doped biochar; the acid-modified boron-doped biochar can effectively activate persulfate to degrade phenol in wastewater. The prepared acid-modified boron-doped biochar has the characteristics of cheap and easily available raw materials, simple preparation, high reaction rate and no secondary pollution, and is beneficial to popularization of a persulfate advanced oxidation technology in phenol wastewater industrial application.

Description

Technical Field

[0001] The invention belongs to the field of environmental functional materials and water treatment, and particularly relates to an acid-modified boron-doped biochar and application thereof in treating phenol wastewater with activated persulfate. Background Art

[0002] A large number of studies have been conducted on the control of organic pollution in water bodies. Common methods include adsorption, biodegradation, photocatalytic degradation, and sonication. Effectively controlling organic pollution in water bodies is a major problem facing the current environmental field. As a typical organic wastewater, phenol wastewater is highly toxic and has a wide range of sources. In recent years, a new advanced oxidation technology using persulfate (PDS) as an oxidant and a source of active substances has a high efficiency in the degradation of phenol wastewater. In this technology, the activation of persulfate to form active free radicals and the regulation of free radical properties are the key points for its use in pollutant removal. The activation methods of persulfate mainly include physical methods (light, heat, and microwave treatment, etc.) and chemical methods (phenol base and transition metal ion treatment, etc.). At present, the application of sulfate radical advanced oxidation method in water treatment also has some shortcomings. Among them, some methods have harsh reaction conditions, large energy and chemical consumption, and secondary pollution problems: the method of using sulfate radical to treat organic matter is only applicable to the treatment of high-concentration and low-flow wastewater, and has not yet been applied to large-scale water treatment. Groundwater or wastewater contains a variety of interfering ions (hydroxyl, nitrogen, carbonate, etc.) that consume sulfate radicals, reduce their interaction with organic matter, and affect the treatment effect.

[0003] Therefore, it is very necessary to explore a cost-effective and efficient technology for activating persulfate to treat water bodies polluted by organic matter. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an efficient acid-modified boron-doped biochar for activating persulfate to degrade organic pollutants in water bodies in view of the deficiencies in the prior art. Carbon-based materials are gradually being studied in depth because of their high specific surface area, good chemical stability, mild reaction conditions and excellent catalytic performance. Carbon-based materials can activate PDS to degrade pollutants through two pathways, free radicals and non-free radicals, which not only makes the catalyst system more selective for pollutants, but also makes carbon-based materials less affected by various matrices in the polluted system and the pH value of the environment, so they are more suitable for actual water bodies, and the appropriate amount of boron doping can increase the active sites and defect levels on the surface of biochar. Moreover, compared with the original biochar, the acid-modified boron-doped biochar material has obvious wrinkles, hierarchical structures and abundant oxygen-containing functional groups, and also has a higher specific surface area and disordered degree, as well as more defect sites, so it has a better activation effect on persulfate.

[0005] In order to solve the above technical problems, the present invention discloses a method for preparing acid-modified boron-doped biochar, which comprises the following specific steps:

[0006] S1. adding biochar to an acid solution, stirring, washing with water to neutrality, and drying to obtain acid-modified biochar;

[0007] S2. The acid-modified biochar and boric acid are mixed and dispersed in an ethanol solution, dried after stirring, and calcined at high temperature to obtain acid-modified boron-doped biochar.

[0008] Wherein, the biochar is derived from corn stalk waste or sawdust;

[0009] Preferably, the biochar is derived from corn stalk waste. This technical solution is easy to control and can give the biochar specific morphological structure and surface chemical properties after carbonization and activation.

[0010] Wherein, before adding the biochar to the acid solution, the biochar needs to be ground into fine particles, washed and then dried;

[0011] In S1, the acid solution is any one or a combination of hydrochloric acid, sulfuric acid or nitric acid; the concentration of the acid solution is 1M;

[0012] Preferably, in S1, the acid solution is hydrochloric acid;

[0013] More preferably, in S1, the stirring time is 6 to 9 hours.

[0014] In S1, the drying process temperature is 70-90°C and the time is 8-15h;

[0015] Preferably, in S1, the drying process temperature is 80° C. and the time is 12 hours.

[0016] In S2, the molar ratio of the acid-modified biochar to the boric acid is (2-6):3; the concentration of the ethanol solution is 40-60 wt%;

[0017] Preferably, in S2, the molar ratio of the acid-modified biochar to boric acid is 4:3; and the concentration of the ethanol solution is 50 wt%.

[0018] In S2, the stirring process is specifically stirring at room temperature for 6 to 10 hours, then heating to 50 to 60°C and stirring for 3 to 5 hours; the drying process temperature is 70 to 90°C for 8 to 15 hours; the high temperature calcination condition is uniformly heating to 600 to 800°C at a rate of 20°C / min and calcining for 1 to 2 hours;

[0019] Preferably, in S2, the stirring process is specifically stirring at room temperature for 8 hours, then heating to 55°C and stirring for 4 hours; the drying process temperature is 80°C and the time is 12 hours; the high-temperature calcination condition is uniformly heating to 700°C at a rate of 20°C / min and calcining for 1.5 hours.

[0020] Specifically, in some embodiments of the present invention, acid-modified boron-doped biochar was prepared by the above-mentioned preparation method, and its microscopic morphology was characterized. It was observed that the acid-modified boron-doped biochar obviously had a three-dimensional loose flaky structure, with fewer surface particles and impurities, and many wrinkles, which is conducive to increasing the formation of a larger specific surface area group, and ultimately conducive to the adsorption of pollutants and providing channels for their degradation.

[0021] Specifically, in some embodiments of the present invention, by adding persulfate and acid-modified boron-doped biochar to a phenol solution and observing the degradation curve of the phenol standard solution, the application prospect of the above-mentioned acid-modified boron-doped biochar in activating persulfate to degrade phenol in wastewater is demonstrated.

[0022] The present invention also provides a method for using acid-modified boron-doped biochar in activating persulfate to degrade phenol in wastewater. The specific method of the application is to add persulfate and acid-modified boron-doped biochar to the wastewater containing phenol, adjust the temperature and pH, and degrade phenol through an oxidation reaction.

[0023] The phenol concentration in the phenol-containing wastewater is 10-50 mg / L; the molar ratio of the persulfate to the phenol is (30-50):1; the persulfate includes sodium persulfate or sodium peroxydisulfate; the dosage of the acid-modified boron-doped biochar is 50-800 mg / L; the temperature is 10-30° C.; the pH value is 3.1-11.1;

[0024] Preferably, the phenol concentration in the phenol-containing wastewater is 10 to 30 mg / L;

[0025] More preferably, the phenol concentration in the phenol-containing wastewater is 10 mg / L

[0026] Preferably, the molar ratio of the persulfate to phenol is 40:1;

[0027] Preferably, the dosage of the acid-modified boron-doped biochar is 600-800 mg / L;

[0028] More preferably, the dosage of the acid-modified boron-doped biochar is 800 mg / L.

[0029] Preferably, the pH value is 3.1 to 6.9;

[0030] More preferably, the pH value is 6.9.

[0031] Beneficial effects: (1) The present invention increases the specific surface area of ​​biochar and expands the pore volume by acid-modified boron-doped biochar activation. After acid modification and boron atom doping, the adsorption performance of biochar for organic pollutants is effectively improved, and the catalytic activity of biochar for persulfate is also improved;

[0032] (2) The volume percentages of disordered carbon and fixed carbon in the biochar of the present invention are significantly increased by modification and heteroatom doping, which indicates that the defect degree of the biochar is relatively high, which can provide more active sites for persulfate activation and also provide a place for the degradation of pollutants;

[0033] (3) The present invention has the characteristics of cheap and readily available catalyst raw materials, simple preparation, fast reaction rate, and no secondary pollution, which is conducive to the promotion of the industrial application of persulfate advanced oxidation technology in phenol wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0035] Figure 1 The SEM comparison pictures of the acid-modified boron-doped biochar materials prepared in Example 1; wherein (a) is the biochar material before modification, and (b) is the boron-doped biochar material after acid modification;

[0036] Figure 2 This is a graph showing the degradation of phenol in water by persulfate activated by acid-modified boron-doped biochar at different dosages in Example 2;

[0037] Figure 3 This is a graph showing the degradation of phenol in water by persulfate activated by acid-modified boron-doped biochar at different system temperatures in Example 3;

[0038] Figure 4 This is a graph showing the degradation of phenol in water by persulfate activated by boron-doped biochar modified with butyric acid at different phenol concentrations in Example 4;

[0039] Figure 5 This is a graph showing the degradation of phenol in water using acid-modified boron-doped biochar to activate persulfate under different pH conditions in Example 5. DETAILED DESCRIPTION

[0040] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0041] In the following embodiments, the biochar raw material is selected from commercially available corn stalks, the corn stalks are crushed or broken, and pretreated with 1M phosphoric acid to increase the yield and stability of the biochar during pyrolysis, and then pyrolyzed in a fixed bed reactor for 2 to 3 hours at a pyrolysis temperature of 500 to 700°C. After the pyrolysis is completed, the prepared biochar is obtained by cooling in a sealed environment for 6 hours.

[0042] Embodiment 1:

[0043] A method for preparing acid-modified boron-doped biochar comprises the following steps:

[0044] Step S1, grinding the biochar into fine particles, repeatedly washing with deionized water until the filtrate is clear, and drying at 105°C;

[0045] Step S2, adding the washed and dried biochar to a hydrochloric acid solution (with a concentration of 1 M), stirring continuously for 8 h with a magnetic stirrer, repeatedly rinsing with deionized water until the filtrate is neutral, and drying in an oven at 80° C. for 12 h to obtain acid-modified biochar;

[0046] Step S3, the dried acid-modified biochar and boric acid are mixed and dispersed in a 50% ethanol solution in a molar ratio of 4:3, wherein the total mass of the acid-modified biochar and boric acid and the volume ratio of the ethanol solution is 2:1, and the mixture is continuously stirred at room temperature for 8 hours, then heated to 55°C and stirred for 4 hours to volatilize excess ethanol solvent, dried in an oven at 80°C for 12 hours, and then calcined at high temperature. During the high-temperature calcination process, the mixture is uniformly heated to 700°C at a rate of 20°C / min in a box furnace and calcined for 1.5 hours. The obtained carbonization product is the acid-modified boron-doped biochar material.

[0047] Microscopic morphology characterization of acid-modified boron-doped biochar:

[0048] Acid-modified boron-doped biochar with specific structure and function was prepared by acidification, grinding and blending, high-temperature calcination and other processes. The microscopic morphology of the biochar material before modification and the prepared acid-modified boron-doped biochar material was characterized by scanning electron microscopy (SEM). Figure 1 As shown in Figure (a), the biochar before modification has a rough surface and is accompanied by many granular substances of different sizes. No obvious pores and thin wrinkled surface were observed. The biochar after acid modification has an obvious three-dimensional loose flaky structure, with fewer surface particles and impurities and more wrinkles, which is conducive to increasing the formation of a larger specific surface area group, which is ultimately beneficial to the adsorption of pollutants and providing channels for their degradation, so that the biochar has an activation ability comparable to that of nanomaterials and transition metals.

[0049] Embodiment 2:

[0050] The acid-modified boron-doped biochar of the present invention activates persulfate to treat phenol wastewater, and the working principle is as follows:

[0051] The method utilizes the acid-modified boron-doped biochar obtained in Example 1 to activate persulfate to generate sulfate radicals (SO4-·) to catalyze the degradation of difficult-to-degrade organic compounds in water, such as phenol, utilizes the adsorption catalytic effect of biochar to adsorb organic matter and persulfate to the surface of biochar, and utilizes the electron transfer between the organic matter and persulfate to degrade them.

[0052] In order to study the effect of the dosage of acid-modified boron-doped biochar on the treatment effect, 150 mL of 20 mg / L phenol solution was added to the reaction container, and the molar ratio of sodium persulfate to phenol was 40:1. The pH was adjusted to 6.45, and the system temperature was maintained at 20 °C. The dosages of acid-modified boron-doped biochar were 50 mg / L, 100 mg / L, 300 mg / L, 600 mg / L and 800 mg / L, respectively. The reaction container was placed on a shaker and oscillated at a uniform speed to achieve adsorption and desorption equilibrium. During the reaction, the shaker speed was controlled at 200 r / min, and samples were taken for detection at different time intervals.

[0053] Figure 2 The degradation diagram of phenol in water by persulfate activated by acid-modified boron-doped biochar at different dosages is shown in Figure 2. Figure 2 It can be seen that the degradation efficiency of each component on phenol in the first 30 minutes is 13.3%, 23.1%, 35.5%, 42.2% and 57.8% respectively. The degradation rate of phenol increases with the increase of biochar dosage. The best test result is the component with 800 mg / L biochar dosage. It is speculated that the reaction between biochar and sodium peroxydisulfate in this system is more active than that of the other four groups, and more free radicals and other active components are produced. The degradation efficiency of this group of systems is as high as 97.0% within 180 minutes of the test. The removal rate of phenol by the 600 mg / L component within 180 minutes reaches 93.0%, which also reaches the expected goal. Therefore, acid-modified boron-doped biochar activated sodium peroxydisulfate is a method for degrading phenol.

[0054] Embodiment 3:

[0055] In order to study the influence of system temperature on the treatment effect, 150 mL of 20 mg / L phenol solution was added to the reaction container, and 800 mg / L of acid-modified boron-doped biochar was added to the container at a molar ratio of sodium persulfate to phenol of 40:1. The pH was adjusted to 6.45, and the system temperatures were set to 10°C, 20°C and 30°C, respectively. The reaction container was placed on a shaker and oscillated at a constant speed to achieve adsorption and desorption equilibrium. During the reaction, the shaker speed was controlled at 200 r / min, and samples were taken for detection at different time intervals.

[0056] Figure 3 The degradation diagram of phenol in water activated by persulfate by acid-modified boron-doped biochar at different system temperatures is shown in Figure 2. Figure 3 It can be seen that at 10°C, the degradation rate of phenol in the reaction system within 180 min was 89.2%. When the temperature rose to 20°C, the efficiency of biochar activation of PDS to degrade phenol was 93.0%. When the temperature continued to rise to 30°C, the degradation efficiency of phenol increased to 95.1%. It can be found that the degradation efficiency of phenol by the biochar system under low temperature environment is still very high, indicating that the reaction can still proceed normally under low temperature environment. When the system temperature rises, the degradation rate increases, indicating that the heat generated by the temperature increase will promote the forward reaction and provide energy for the oxidation reaction and electron transfer. The degradation efficiency of phenol at three different temperatures is not much different. It can be inferred that temperature is not the decisive factor affecting the activation of persulfate and the degradation of phenol by biochar. As long as the system temperature meets the conditions within this range, the influence of temperature factors on the reaction can be roughly ignored.

[0057] Embodiment 4:

[0058] In order to study the influence of pollutant concentration on the treatment effect, 800 mg / L of acid-modified boron-doped biochar was added to the reaction container. The molar ratio of sodium persulfate to phenol was 40:1, and the pH was adjusted to 6.45. The system temperature was maintained at 20°C, and 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L and 50 mg / L of phenol solution were added. The reaction container was placed on a shaker and oscillated at a uniform speed to achieve adsorption and desorption equilibrium. During the reaction, the shaker speed was controlled at 200 r / min, and samples were taken for detection at different time intervals.

[0059] Figure 4 The degradation diagram of phenol in water body activated by persulfate with boron-doped biochar modified by acid at different phenol concentrations is shown in Figure 2. Figure 4It can be seen that when the concentration of the pollutant phenol is 10 mg / L, the efficiency can reach more than 90% within the first 60 minutes, and the entire degradation process can be completed within 120 minutes. When the phenol concentration is increased to 20 mg / L, the degradation efficiency of the reaction system in the first 60 minutes also decreases to 80.6%, and the degradation efficiency of phenol is 93.0% within the test time of 180 minutes. The initial concentration of phenol is increased to 30 mg / L, 40 mg / L and 50 mg / L again. It is found that the degradation efficiency of each system within 1 hour is 71.8%, 61.1%, and 47.4%, respectively. It is not difficult to find that when the concentration of phenol is gradually increased, its degradation rate also decreases. This is because the initial base number of phenol is too large. In the same time, the higher the initial concentration, the lower the degradation rate, and the degradation rate also decreases. It can be seen from the figure that the degradation efficiency of the high-concentration phenol system tends to be flat as the reaction process proceeds, the reaction system reaches saturation, and active substances such as free radicals are consumed.

[0060] Embodiment 5:

[0061] In order to study the effect of pH on the treatment effect, 150 mL of 20 mg / L phenol solution was added to the reaction container, and 800 mg / L of acid-modified boron-doped biochar was added. The sodium persulfate and phenol molar ratio was 40:1. The system temperature was maintained at 20 °C, and the pH was adjusted to 3.10, 5.20, 6.90, 9.40 and 11.10 respectively. The reaction container was placed on a shaker and oscillated at a uniform speed to achieve adsorption and desorption equilibrium. The shaker speed was controlled at 200 r / min during the reaction, and samples were taken for detection at different time intervals.

[0062] Figure 5 Figure 2 shows the degradation of phenol in water by acid-modified boron-doped biochar activated with persulfate under different pH conditions. Figure 5 It can be seen that the phenol removal effect is best when the pH value of the pollutant is not changed, that is, when the system pH value is 6.90, the degradation rate reaches 92.3% within 180 minutes of the test, and the removal rate is fastest in the first 30 minutes of the test, which is consistent with the previous test. Figure 5As shown in the figure, when the pH value of the system is in the acidic condition, the removal efficiency of pollutants is relatively high. When the pH value is 3.10, the degradation rate reaches 83.3% within 3 hours. It is speculated that the main role of the system is sulfate radicals, which are acid-resistant. When the pH value of the system increases to 5.40, the degradation efficiency drops to 77.5%, and the concentration of sulfate radicals is low. When the system is neutral, the degradation effect is the best. We believe that sulfate radicals and hydroxyl radicals work together at this time. When the pH value is raised to 9.20 again, the degradation efficiency of phenol is 69.8%. It is speculated that the main radical at this node is hydroxyl radicals, and sulfate radicals play a synergistic role. When the pH value rises to 11.20, the degradation effect is the worst, only 50.4%, which may be because the sulfate ion radicals react with OH- at this stage and cannot play a role in decomposing phenol. Therefore, under the premise that other influencing factors remain unchanged, the optimal pH of the system is 6.45.

[0063] The present invention provides an acid-modified boron-doped biochar and its application idea and method in the treatment of phenol wastewater by activated persulfate. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for preparing acid-modified boron-doped biochar, characterized in that: The specific steps are: S1. adding biochar to an acid solution, stirring, washing with water to neutrality, and drying to obtain acid-modified biochar; S2. The acid-modified biochar and boric acid are mixed and dispersed in an ethanol solution, dried after stirring, and calcined at high temperature to obtain acid-modified boron-doped biochar.

2. The preparation method according to claim 1, characterized in that: In S1, the biochar is derived from corn stalk waste or wood chips.

3. The preparation method according to claim 1, characterized in that: In S1, the acid solution is any one of hydrochloric acid, sulfuric acid or nitric acid or a combination of them; the concentration of the acid solution is 1M.

4. The preparation method according to claim 1, characterized in that: In S1, the drying process temperature is 70-90°C and the time is 8-15 hours.

5. The preparation method according to claim 1, characterized in that: In S2, the molar ratio of the acid-modified biochar to boric acid is (2-6):3; and the concentration of the ethanol solution is 40-60 wt%.

6. The preparation method according to claim 1, characterized in that: In S2, the stirring process is specifically stirring at room temperature for 6 to 10 hours, then heating to 50 to 60°C and stirring for 3 to 5 hours; the drying process temperature is 70 to 90°C and the time is 8 to 15 hours; the high-temperature calcination condition is uniformly heating to 600 to 800°C at a rate of 20°C / min and calcining for 1 to 2 hours.

7. Acid-modified boron-doped biochar prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the acid-modified boron-doped biochar according to claim 7 in activating persulfate to degrade phenol in wastewater.

9. The use according to claim 8, characterized in that: The specific application method is: adding persulfate and acid-modified boron-doped biochar to wastewater containing phenol, adjusting the temperature and pH value, and degrading phenol through oxidation reaction.

10. The use according to claim 9, characterized in that: The phenol concentration in the phenol-containing wastewater is 10-50 mg / L; the molar ratio of the persulfate to phenol is (30-50):1; the persulfate is sodium persulfate or sodium peroxydisulfate; the dosage of the acid-modified boron-doped biochar is 50-800 mg / L; the temperature is 10-30° C.; and the pH value is 3.1-11.1.

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