Method for photocatalytic reduction of phenols in cooperation with Cr (VI)
By regulating the substituent structure of phenol molecules and using a secondary calcined g-C3N4 photocatalyst, the problem of synergistic removal of phenols and Cr(VI) composite pollutants was solved, achieving a highly efficient photocatalytic reduction effect.
Patent Information
- Application Number
- CN202511343549.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-19
- Publication Date
- 2025-12-19
AI Technical Summary
The reason why existing technologies have failed to effectively solve the problem of the coexistence of phenols and heavy metals is that existing technologies, especially the complex pollution of phenolic derivatives and Cr(VI), are difficult to remove efficiently and synergistically. Traditional photocatalytic technology is limited in efficiency in the competition between oxidation and reduction pathways.
By regulating the substituent structure of phenolic molecules and utilizing their electron-donating ability, combined with a secondary calcined g-C3N4 photocatalyst, the oxidative degradation of phenolic pollutants and the reduction of Cr(VI) are achieved. The photocatalytic reaction is carried out at room temperature and pressure using a visible LED light source.
It improves the utilization efficiency of electrons and holes, achieves the synergistic removal of phenolic pollutants and Cr(VI), and demonstrates the application prospects of green water purification strategies.
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Figure CN121158883A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of water pollution treatment, in particular to a method for photocatalytic reduction of phenols in cooperation with Cr(VI). BACKGROUND
[0002] Currently, there is a common problem of coexistence of organic matter and heavy metals in industrial wastewater, such as the combined pollution of phenolic derivatives and Cr(VI), which is common in coal chemical industry, pharmaceutical industry, dye industry, and metal surface treatment industry. The difficulty in treating this kind of combined pollution lies in the need to consider both oxidation and reduction reaction paths. Conventional photocatalytic technology is difficult to achieve efficient and cooperative removal due to fast electron-hole recombination and mutual competition between oxidation and reduction reactions.
[0003] In view of the above challenges, photocatalytic technology has great potential in the field of pollutant degradation due to its green and sustainable characteristics, and has significant advantages compared to traditional methods such as adsorption, membrane filtration and biological treatment. However, the conventional photocatalytic system has problems such as mutual competition between oxidation and reduction paths, limited reaction efficiency, and thus affecting the efficiency of photocatalytic degradation. A core limitation is that current research focuses on using the strong oxidizing ability of photo-generated holes to drive pollutant degradation, but often ignores the huge reduction potential of photo-generated electrons, resulting in a large amount of energy being wasted. Moreover, current research still focuses on single pollutant systems, and the molecular mechanism of the synergistic effect between pollutants in the combined pollution system is not thoroughly analyzed.
[0004] In existing research, g-C3N4 has become a typical visible light responsive photocatalyst due to its narrow band gap and chemical stability. Some research uses defect regulation to improve the carrier separation efficiency, but most of them do not pay attention to the specific influence of molecular structure on electron supply ability. Based on this, how to provide a green water treatment method that uses phenolic wastewater itself as an electron donor to regulate the photocatalytic Cr(VI) reduction efficiency through its structural differences has become a technical problem to be solved in the field. SUMMARY
[0005] The purpose of the present application is to provide a method for photocatalytic reduction of phenols in cooperation with Cr(VI), which is based on the structural regulation effect of the electron supply ability of phenolic molecules and guides the selection of pollutants and optimization of reaction conditions.
[0006] In order to achieve the above-mentioned application purpose, the present application provides the following technical solutions:
[0007] The present application provides a method for photocatalytic reduction of phenols in cooperation with Cr(VI) under the regulation of substituents, comprising the following steps:
[0008] The wastewater containing phenolic pollutants, Cr(VI) and the secondary calcined g-C3N4 photocatalyst are mixed to perform a photocatalytic degradation reaction, so as to realize the oxidative degradation of the phenolic pollutants and the reduction of Cr(VI).
[0009] The phenolic pollutants are phenol or phenol derivatives with substituents, and the substituents include electron-donating groups or electron-withdrawing groups.
[0010] Optionally, the preparation method of the secondary calcined g-C3N4 photocatalyst comprises the following steps:
[0011] The dicyandiamide is subjected to primary calcination to obtain a primary calcination material, and the primary calcination material is subjected to secondary calcination to obtain the secondary calcined g-C3N4 photocatalyst.
[0012] Optionally, the temperature of the primary calcination is 550 DEG C, and the time is 4h; and the temperature of the secondary calcination is 500 DEG C, and the time is 2-4h.
[0013] Optionally, the concentration of the phenolic pollutants in the wastewater is 5-20mg / L.
[0014] Optionally, the concentration of Cr(VI) in the wastewater is 5-10mg / L.
[0015] Optionally, the concentration of the secondary calcined g-C3N4 photocatalyst in the wastewater is 0.5-1g / L.
[0016] Optionally, the phenol derivatives with substituents include p-cresol, p-chlorophenol or p-nitrophenol.
[0017] Optionally, the time of the photocatalytic degradation reaction is 60-120min.
[0018] Compared with the prior art, the present application has the following beneficial effects:
[0019] 1. For the first time, the structure of the pollutants is introduced into the design of the photocatalytic reaction as a factor for regulating the electron donor capacity. This rule not only reveals the regulation mechanism of the structure on the reaction behavior, but also can be used as a molecular screening standard to assist in developing a composite pollution treatment strategy for optimizing specific electron supply paths.
[0020] 2. The operation steps of the present application are simple, that is, the visible LED light source, the natural pH range, the normal temperature and pressure can effectively improve the application potential of the electron in the photoreduction system in practice.
[0021] 3. The g-C3N4 prepared by simple secondary calcination is used as a catalyst, without complex modification of the photocatalyst, so as to promote the synergistic oxidation and reduction of the phenolic pollutants and Cr(VI), and realize the synergistic removal of the organic pollutants and the toxic Cr(VI) in water.
[0022] 4. The reaction process does not require additional addition of exogenous organic matter, and the phenol itself can be degraded, which provides a strategy of "waste treatment with waste" for green water purification by utilizing the consumed holes in the pollutant degradation process and improving the utilization efficiency of electrons and holes. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1 Schematic diagram for the reduction of Cr(VI) and degradation of phenols in the composite water body of phenols and Cr(VI);
[0024] Figure 2 Schematic diagram for the influence of phenol concentration on the reduction of Cr(VI);
[0025] Figure 3 Schematic diagram for the reduction of Cr(VI) in single Cr(VI) water body;
[0026] Figure 4 Comparison chart of photocatalytic performance of g-C3N4 and secondary calcined g-C3N4. DETAILED DESCRIPTION
[0027] A number of exemplary embodiments of the present application are now described in detail below. The following description of certain examples of the application should not be taken as limiting the application, but rather providing a detailed description of certain aspects of the application. Descriptions of well-known methods, procedures, components and mining are omitted so as not to obscure the disclosure.
[0028] It should be understood that the terms described in the present application are only for the description of the specific embodiments, and are not used to limit the present application. In addition, for the numerical range in the present application, it is understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value within the stated range and any other stated value or intermediate value within the stated range is also included in the present application. The upper limit and lower limit of these smaller ranges can be independently included or excluded from the range.
[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, only the preferred methods and materials are described. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are concerned. In the event of conflict between the content of this specification and any incorporated document, the content of this specification controls.
[0030] Many modifications and variations to the illustrative embodiments described herein will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. Additional embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the application being indicated by the following claims.
[0031] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to mean including, but not limited to.
[0032] The raw materials used in the present application can be obtained commercially or prepared by prior art.
[0033] The present application provides a method for photocatalytic reduction of phenolic compounds under the regulation of substituents and Cr(VI), comprising the following steps:
[0034] The wastewater containing phenolic pollutants, Cr(VI) and the secondary calcined g-C3N4 photocatalyst are mixed to carry out photocatalytic degradation reaction, so as to realize the synchronous and efficient reduction of phenolic oxidation and Cr(VI);
[0035] The present application uses phenolic wastewater itself as an electron donor to actively regulate and synergistically promote the efficient reduction of Cr(VI) in the photocatalytic system. This strategy not only provides an efficient new path and theoretical basis for the synergistic removal of phenol and Cr(VI) composite pollutants, but also deepens the relationship between the substituent structure of pollutants and the electron supply capacity and Cr(VI) reduction efficiency. The secondary calcined g-C3N4 photocatalyst is added to the wastewater containing phenolic organic matter and Cr(VI), and under visible light irradiation, the electron supply capacity is regulated by the type of substituents (electron-donating group, electron-withdrawing group) of phenolic molecules, revealing a structure-oriented self-driven photocatalytic mechanism, driving the effective separation of photo-generated electron-hole, and simultaneously realizing the oxidation degradation of phenols and the efficient reduction of Cr(VI). Experiments show that the type of substituents of phenolic molecules significantly affects the HOMO energy level, thereby regulating the electron transfer rate and Cr(VI) reduction kinetics, revealing a structure-oriented self-driven photocatalytic mechanism for pollutants, which significantly improves the synergistic purification efficiency of the composite pollution system.
[0036] The phenolic pollutants are phenol or phenol derivatives with substituents, and the substituents include electron-donating groups or electron-withdrawing groups.
[0037] The electron-donating group includes -CH3, and the electron-withdrawing group includes -NO2.
[0038] It can be understood that the different substituents have a significant influence on the photocatalytic reduction efficiency of Cr(VI), which is specifically manifested as follows: the stronger the electron-donating ability of the substituent is, the higher the HOMO energy level is, the easier the hole capture is, the electron release is promoted, and the reduction rate of Cr(VI) is improved; when the substituent is a strong electron-withdrawing group (such as -NO2), the HOMO energy level is reduced, and the electron supply ability is weakened, thereby inhibiting the reduction of Cr(VI).
[0039] In the embodiment of the present application, the simulated composite pollution wastewater containing phenol and Cr(VI) is placed in a photoreactor, the g-C3N4 photocatalyst prepared by secondary calcination is added to the reactor, and the system is subjected to 500 rpm magnetic stirring for 30 min in the dark to achieve adsorption-desorption equilibrium, and then the photocatalytic degradation reaction is carried out.
[0040] In the present application, the light is visible light, that is, the wavelength range is about 380 nm to 780 nm, and in the embodiment of the present application, the visible light is a 21 W LED lamp (the maximum emission peak is 416 nm).
[0041] In the present application, the preparation method of the g-C3N4 photocatalyst by secondary calcination comprises the following steps:
[0042] The dicyandiamide is subjected to primary calcination to obtain a primary calcination material; and the primary calcination material is subjected to secondary calcination to obtain the g-C3N4 photocatalyst by secondary calcination.
[0043] In the embodiment of the present application, the dicyandiamide is placed in a semi-closed quartz boat in a static air environment, and then subjected to primary calcination in a muffle furnace; next, the calcined material is ground into powder, washed with anhydrous ethanol and deionized water, collected by centrifugation, and dried in an oven to obtain the primary calcination material; then the primary calcination material is dispersed in an open quartz boat, and subjected to secondary calcination in a muffle furnace to obtain the g-C3N4 photocatalyst by secondary calcination.
[0044] In the present application, the temperature of the primary calcination is 550 DEG C, and the time is 4 h; the temperature of the secondary calcination is 500 DEG C, and the time is 2-4 h, for example, which can be 2 h, 3 h or 4 h.
[0045] In the present application, the concentration of the phenolic pollutants in the wastewater is 5-20 mg / L, for example, which can be 5 mg / L, 10 mg / L, 15 mg / L or 20 mg / L, etc.
[0046] In the present application, the concentration of Cr(VI) in the wastewater is 5-10 mg / L, for example, which can be 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L or 10 mg / L, etc.
[0047] In the present application, the concentration of the twice calcined g-C3N4 photocatalyst in the wastewater is 0.5-1 g / L, for example, it can be 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L or 1 g / L, etc.
[0048] In the present application, the phenol derivative with a substituent group includes p-cresol, p-chlorophenol or p-nitrophenol.
[0049] In the present application, the time of the photocatalytic degradation reaction is 60-120 min, for example, it can be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc.
[0050] The technical solutions provided by the present application will be described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.
[0051] In the following examples, the power of the LED lamp is 21 W, and the maximum emission peak is 416 nm.
[0052] Preparation Example
[0053] The dicyandiamide was placed in a semi-closed quartz boat in a static air environment, and then calcined in a muffle furnace at 550℃ for 4 h; next, the calcined material was ground into powder, washed with anhydrous ethanol and deionized water, collected by centrifugation, and dried in an oven at 60℃ for 12 h to obtain a first calcined g-C3N4; then the first calcined material was dispersed in an open quartz boat, and calcined in a muffle furnace at 500℃ for 4 h to obtain a twice calcined g-C3N4 photocatalyst.
[0054] Example 1: Phenol without substituent group synergistically enhances Cr(VI) photocatalytic reduction
[0055] 100 mL of simulated composite pollution wastewater containing phenol and Cr(VI) was placed in a photoreactor, the concentration of phenol in the wastewater was 20 mg / L, and the concentration of Cr(VI) was 5 mg / L, 50 mg of twice calcined g-C3N4 photocatalyst was added to the reactor. Under dark conditions, 500 rpm magnetic stirring was carried out for 30 min to make the system reach adsorption-desorption equilibrium. The LED lamp was turned on for light reaction, and every 10 min, 4 mL of reaction solution was removed, filtered with a 0.22 μm filter membrane, and the catalyst was separated. The residual concentration of phenol in the filtrate was analyzed by high performance liquid chromatography, and the degradation rate was calculated. The residual concentration of Cr(VI) in the filtrate was determined by ultraviolet-visible spectrophotometry using diphenyl carbazide colorimetry, and the reduction removal rate was calculated.
[0056] As Figure 1As shown, under visible light irradiation, both phenol and Cr(VI) were effectively removed from the reaction system. Phenol, acting as an electron donor, was oxidatively degraded, while significantly promoting the photocatalytic reduction of Cr(VI). After 60 min of reaction, the degradation rate of phenol reached 69.2%, and the reduction rate of Cr(VI) reached 83.8%. This result clearly demonstrates the feasibility of utilizing the target organic pollutant (phenol) itself as an electron donor to synergistically promote the reduction of heavy metal Cr(VI) and achieve simultaneous and efficient removal of complex pollutants.
[0057] Example 2: Synergistic enhancement of Cr(VI) photocatalytic reduction by p-cresol containing electron-donating substituents
[0058] 100 mL of simulated combined polluted wastewater containing p-cresol and Cr(VI) was placed in a photoreactor. The concentration of p-cresol in the wastewater was 20 mg / L, and the concentration of Cr(VI) was 5 mg / L. 50 mg of calcined g-C3N4 photocatalyst was added to the reactor. The system was magnetically stirred at 500 rpm for 30 min in the dark to allow the system to reach adsorption-desorption equilibrium. The reaction was then irradiated with an LED light. Every 10 min, 4 mL of the reaction solution was transferred and filtered through a 0.22 μm filter membrane to separate the catalyst. The residual concentration of p-cresol in the filtrate was analyzed using high-performance liquid chromatography (HPLC), and its degradation rate was calculated. The residual concentration of Cr(VI) in the filtrate was determined using UV-Vis spectrophotometry with a diphenylcarbazide colorimetric method, and its reduction and removal rate was calculated.
[0059] like Figure 1 As shown, under visible light irradiation, both p-cresol and Cr(VI) were effectively removed from the reaction system. p-cresol was oxidized and degraded as an electron donor, while significantly promoting the photocatalytic reduction of Cr(VI). After 60 min of reaction, the degradation rate of p-cresol reached 98.9%, and the reduction rate of Cr(VI) reached 94%.
[0060] Example 3: Synergistic enhancement of Cr(VI) photocatalytic reduction by p-nitrophenol containing electron-withdrawing substituents
[0061] Take 100 mL of simulated composite pollution wastewater containing p-nitrophenol and Cr(VI) in the light reactor, the concentration of p-nitrophenol in the wastewater is 20 mg / L, the concentration of Cr(VI) is 5 mg / L, and 50 mg of secondary calcined g-C3N4 photocatalyst is added to the reactor. Stir at 500 rpm in the dark for 30 min to achieve adsorption-desorption equilibrium. Turn on the LED light for light reaction, remove 4 mL of reaction solution every 10 min, filter with 0.22 μm filter membrane, and separate the catalyst. Use high performance liquid chromatography to analyze the residual concentration of p-nitrophenol in the filtrate, and calculate its degradation rate. Use UV-visible spectrophotometry to determine the residual concentration of Cr(VI) in the filtrate by using diphenyl carbonyl dihydrazine coloration method, and calculate its reduction removal rate.
[0062] As shown in Figure 1 , under visible light irradiation, p-nitrophenol and Cr(VI) in the reaction system are effectively removed. Phenol as an electron donor is oxidized and degraded, and at the same time significantly promotes the photocatalytic reduction of Cr(VI). After 60 min of reaction, the degradation rate of p-nitrophenol reaches 85%, and the reduction rate of Cr(VI) reaches 65.4%. The reduction rate of the electron-withdrawing substituent system Cr(VI) is significantly higher than that of the single Cr(VI) system (24.2%), which confirms that it still has a synergistic enhancement effect.
[0063] Example 4: Effect of initial concentration of phenol on Cr(VI) reduction and its own degradation
[0064] Take 100 mL of simulated composite pollution wastewater containing different initial concentrations of phenol and 5 mg / L Cr(VI) in the light reactor. Add 50 mg of secondary calcined g-C3N4 photocatalyst to the reactor. Stir at 500 rpm in the dark for 30 min to achieve adsorption-desorption equilibrium. Turn on the LED light for light reaction, remove 4 mL of reaction solution every 10 min, filter with 0.22 μm filter membrane, and separate the catalyst. Use high performance liquid chromatography to analyze the residual concentration of p-nitrophenol in the filtrate, and calculate its degradation rate. Use UV-visible spectrophotometry to determine the residual concentration of Cr(VI) in the filtrate by using diphenyl carbonyl dihydrazine coloration method, and calculate its reduction removal rate. Among them, 5 mg / L, 10 mg / L, 15 mg / L and 20 mg / L of phenol initial concentration are selected for study.
[0065] As shown in Figure 2As shown in Figure 2a, with the increase of phenol concentration from 5 mg / L to 20 mg / L, the 60 min degradation rate of phenol decreased significantly from 99.86% to 67.2%. This might be because phenol and Cr(VI) are not only target pollutants, but also necessary factors for inducing reaction. However, in the system, the initial concentration of Cr(VI) is fixed and limited, resulting in an electron transfer bottleneck for high concentration of phenol. On the contrary, with the increase of initial concentration of phenol, the removal efficiency of Cr(VI) in the system increased significantly at the same time. Figure 2 b) When the concentration of phenol increased from 5 mg / L to 20 mg / L, the 60 min removal rate of Cr(VI) increased from 51.1% to 83.7%. This phenomenon is due to the fact that a higher initial concentration of phenol promotes the reaction equilibrium to favor the removal of Cr(VI), further accelerating the reduction of Cr(VI). Phenol as an electron donor promotes the separation of electrons and holes in the process of promoting electron transfer and phenol degradation.
[0066] Supplementary analysis:
[0067] By comparing the Cr(VI) reduction rates of different substituted phenols, the following trend can be observed: p-cresol > phenol > p-nitrophenol. This trend is highly consistent with the HOMO energy level. Electron-donating groups (-CH3) improve the efficiency of hole capture, accelerate the transfer of electrons to Cr(VI), and enhance the reduction reaction kinetics. However, electron-withdrawing groups (-NO2) have a lower energy level, making it difficult for electrons to jump from the molecular orbital to the valence band, resulting in a decrease in reduction efficiency.
[0068] Table 1 Influence of substituent type on HOMO energy level of phenols and Cr(VI) reduction rate
[0069]
[0070] Comparative Example 1: Photocatalytic reduction of single Cr(VI)
[0071] Take 100 mL of simulated wastewater containing 5 mg / L Cr(VI) without phenol solution and place it in a photoreactor. Add 50 mg of g-C3N4 photocatalyst prepared by secondary calcination to the reactor, with the same dosage as in Example 1. Stir the system at 500 rpm in the dark for 30 min to achieve adsorption-desorption equilibrium. Turn on the LED light for light reaction, and every 10 min, remove 4 mL of reaction solution, filter it with a 0.22 μm filter membrane, and separate the catalyst. Use ultraviolet-visible spectrophotometry and diphenyl carbazide colorimetry to determine the residual concentration of Cr(VI) in the filtrate, and calculate the reduction removal rate.
[0072] As shown in Figure 2a, with the increase of phenol concentration from 5 mg / L to 20 mg / L, the 60 min degradation rate of phenol decreased significantly from 99.86% to 67.2%. This might be because phenol and Cr(VI) are not only target pollutants, but also necessary factors for inducing reaction. However, in the system, the initial concentration of Cr(VI) is fixed and limited, resulting in an electron transfer bottleneck for high concentration of phenol. On the contrary, with the increase of initial concentration of phenol, the removal efficiency of Cr(VI) in the system increased significantly at the same time. Figure 3As shown, under the same 60-minute illumination time and experimental conditions, the reduction removal rate of Cr(VI) in the single Cr(VI) system was significantly lower than that in the composite pollution system of Example 1. The reduction rate of the single Cr(VI) system was only 24.2%, significantly lower than that of the composite system (83.8%). This result clearly indicates that in the absence of organic pollutants such as phenol as electron donors, the separation efficiency of photogenerated electron-hole pairs is low, leading to a decrease in the utilization rate of photogenerated electrons, thereby significantly weakening the photocatalytic reduction efficiency of Cr(VI). This further demonstrates the effectiveness and necessity of the strategy of using phenolic pollutants as electron donors to synergistically promote the reduction of Cr(VI) in this invention.
[0073] Comparative Example 2: Enhanced Removal Effect of G-C3N4 by Secondary Calcination on Complex Pollutants
[0074] Dicyandiamide was placed in a semi-enclosed quartz boat in a static air environment and then calcined in a muffle furnace at 550°C for 4 hours. Next, the calcined material was ground into powder, washed with anhydrous ethanol and deionized water, collected by centrifugation, and dried in an oven at 60°C for 12 hours to obtain a single-calcined g-C3N4.
[0075] 100 mL of simulated combined polluted wastewater containing phenol and Cr(VI) was placed in a photoreactor. The concentration of phenol in the wastewater was 10 mg / L, and the concentration of Cr(VI) was 5 mg / L. 50 mg of a second-calcined g-C3N4 photocatalyst was added to the reactor. Another reactor was prepared with 50 mg of a first-calcined g-C3N4 photocatalyst added. The system was magnetically stirred at 500 rpm for 30 min in the dark to allow the system to reach adsorption-desorption equilibrium. The reaction was then irradiated with an LED light. Every 10 min, 4 mL of the reaction solution was transferred and filtered through a 0.22 μm filter membrane to separate the catalyst. The residual concentration of Cr(VI) in the filtrate was determined using UV-Vis spectrophotometry with a diphenylcarbazide colorimetric method, and the reduction removal rate was calculated.
[0076] like Figure 4 As shown, under the same 60 min illumination time and experimental conditions, in the coexisting system, the reduction rate constant of Cr(VI) by secondary calcination of g-C3N4 is k = 0.0203 min. -1 Compared to g-C3N4 (k=0.0038min) -1 The rate of change was increased by 5.3 times. When phenol was degraded using g-C3N4 after secondary calcination, the reaction rate constant (k) increased from 0.0096 min⁻¹. -1 Significantly increased to 0.0464 min -1The second calcination is 4.8 times of the first calcination of g-C3N4. The second calcination can further optimize the energy band structure and surface active sites of g-C3N4, thereby improving the separation efficiency of photo-generated electron-hole pairs. Therefore, the photocatalytic redox activity of the second calcination g-C3N4 is better than that of g-C3N4 for the removal of the two pollutants.
[0077] The above merely describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.
Claims
1. A method for the photocatalytic reduction of Cr(VI) by phenols in synergistic effect, characterized in that, Includes the following steps: Wastewater containing phenolic pollutants and Cr(VI) is mixed with a secondary calcined g-C3N4 photocatalyst to carry out a photocatalytic degradation reaction, thereby achieving the oxidative degradation of phenols and the reduction of Cr(VI). The phenolic contaminants are phenol or phenol derivatives with substituents, including electron-donating or electron-withdrawing groups.
2. The method according to claim 1, characterized in that, The preparation method of the g-C3N4 photocatalyst after secondary calcination includes the following steps: Dicyandiamide is calcined once to obtain a first-calcined material; the first-calcined material is then calcined a second time to obtain a second-calcined g-C3N4 photocatalyst.
3. The method according to claim 2, characterized in that, The first calcination is carried out at a temperature of 550°C for 4 hours; the second calcination is carried out at a temperature of 500°C for 2 to 4 hours.
4. The method according to claim 1, characterized in that, The concentration of phenolic pollutants in the wastewater is 5–20 mg / L.
5. The method according to claim 1, characterized in that, The concentration of Cr(VI) in the wastewater is 5–10 mg / L.
6. The method according to claim 1, characterized in that, The concentration of the secondary calcined g-C3N4 photocatalyst in the wastewater is 0.5–1 g / L.
7. The method according to claim 1, characterized in that, The phenol derivatives with substituents include p-cresol, p-chlorophenol, or p-nitrophenol.
8. The method according to claim 1, characterized in that, The photocatalytic degradation reaction takes 60–120 min.