CN107670691B

CN107670691B - Metal-free heterogeneous Fenton-like catalyst and preparation method and application thereof

Info

Publication number: CN107670691B
Application number: CN201710861138.4A
Authority: CN
Inventors: 吕来; 胡春
Original assignee: Guangzhou University
Current assignee: Guangzhou University
Priority date: 2017-09-21
Filing date: 2017-09-21
Publication date: 2020-04-14
Anticipated expiration: 2037-09-21
Also published as: CN107670691A

Abstract

The invention discloses a metal-free heterogeneous Fenton-like catalyst and a preparation method and application thereof, wherein the preparation method of the catalyst comprises the following steps: adding graphite powder and NaNO into concentrated sulfuric acid as solvent₃And potassium permanganate, heating to react, adding H₂O₂Until the solution becomes a golden brown suspension, washing, drying and grinding to obtain solid powder; mixing 4-phenoxyphenol and solid powder F, dissolving in ethanol, heating for reaction, evaporating to remove the solvent to obtain a solid precursor, and reacting at 350-380 ℃ to obtain solid powder, namely the metal-free heterogeneous Fenton-like catalyst. The metal-free heterogeneous Fenton-like catalyst is not obviously influenced by the pH value of a reaction system. The pH value of the system does not need to be adjusted to 2-3 in the reaction process, and the good removal effect is achieved on the degradation of the toxic and harmful organic pollutants which are difficult to biodegrade under the neutral room temperature condition.

Description

Metal-free heterogeneous Fenton-like catalyst and preparation method and application thereof

Technical Field

The invention belongs to the technical field of water treatment, and particularly relates to a metal-free heterogeneous Fenton-like catalyst, and a preparation method and application thereof.

Background

The composite micro-pollution of water is one of the key environmental problems facing human beings. This problem has been particularly acute in recent years due to the continual release of large quantities of toxic and harmful organic pollutants into the water. These pollutants include chlorophenols, endocrine interferons, pharmaceuticals and the like, most of which have persistence and difficult biodegradability and are often seriously threatened to the life health of human beings through accumulation and enrichment. Therefore, the development of technologies and methods for removing such pollutants with low cost, high efficiency and no harm is urgent.

Fenton's reaction using reduced metalReduction of hydrogen peroxide (H)₂O₂) Generating hydroxyl radicals (^●OH) becomes an effective technology for removing organic matters which are difficult to degrade in water. In the classical fenton reaction and the heterogeneous fenton catalytic system constructed based on the principle of the classical fenton reaction, metal species are the most core components, and they often play an important role as active components, so that the redox capability of the metal species becomes the guarantee of the catalyst activity. Therefore, even if the catalyst shows poor stability, the water quality after Fenton reaction treatment cannot be guaranteed (the content of the metal ions exceeds the standard). Furthermore the reduction step of the metal species is also the rate limiting step of the classical Fenton reaction and H₂O₂And (5) an invalid decomposition step. In the actual water treatment process, the mass production of a catalyst containing a large amount of metal components also makes the production cost high. Thus, the presence of metal species in fenton's catalytic system is a "double-edged sword", which is both a guarantee of activity and a source of a series of key problems.

Disclosure of Invention

The invention aims to provide a preparation method of a metal-free heterogeneous Fenton-like catalyst, which is characterized in that Graphene Oxide (GO) synthesized by an improved Hummers method is subjected to 4-phenoxyphenol (POP) molecular doping and dehydration condensation annealing reduction treatment.

The invention also aims to provide the metal-free heterogeneous Fenton-like catalyst prepared by the method, the catalyst is a 4-phenoxyphenol molecule doped reductive graphene oxide nano hybrid (POP-rGO Nhs), the preparation method brings about the doping of the POP and the formation of intrinsic C-O-C, so that the electron density around the doped oxygen atom is increased, and further, countless electron-rich oxygen centers and electron-deficient carbon centers are generated, and similarly, countless galvanic cathode anode pairs are constructed on the surface of the catalyst to form a double-reaction center catalytic system. In electron-rich oxygen centers, H₂O₂Is continuously reduced to generate^●OH，^●OH attacks the contaminants to degrade them; in the electron-deficient carbon center, H₂O₂Oxidized to produce superoxide radical (HO)₂ ^●/O₂ ^●-) Furthermore, the contaminants can also be continuously oxidatively degraded in this core.

The invention further aims to provide the application of the metal-free heterogeneous Fenton-like catalyst in the catalytic degradation of organic pollutants such as endocrine interferon bisphenol A (BPA) and pesticide substance 2-chlorophenol (2-CP), wherein the catalytic degradation is not obviously influenced by the pH value, and a series of problems caused by metal components in the traditional Fenton system are solved.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a metal-free heterogeneous Fenton-like catalyst comprises the following steps:

(1) adding graphite powder into concentrated sulfuric acid, and uniformly stirring to obtain a solution A; mixing sodium nitrate (NaNO)₃) Adding the mixture into the solution A, and uniformly stirring to obtain a solution B; mixing potassium permanganate (KMnO)₄) Adding the mixture into the solution B, and uniformly stirring to obtain a solution C;

in the step (1), graphite powder and NaNO are used₃The mass ratio of the potassium permanganate to the potassium permanganate is 1.0 (4.5-5.5) to (2.5-3.5), preferably 1:5: 3;

in the step (1), adding graphite powder into concentrated sulfuric acid, wherein the graphite powder needs to be added in an ice bath, and the graphite powder is slowly added while stirring (400-500 revolutions per minute);

(2) heating the solution C to 35-45 ℃, maintaining for 0.5-1.0 hour, adding water, continuing to heat to 90-100 ℃, stirring and reacting for 1.0-2.0 hours to obtain a solution D; in the process, water must be added to avoid explosion of a concentrated sulfuric acid potassium permanganate system under high-temperature heating;

(3) addition of H to solution D₂O₂Until the solution becomes a golden brown suspension, cooling, washing until the pH value is 6 to obtain a substance E, and drying and grinding the substance E to obtain solid powder F;

in the step (3), the washing is preferably carried out for a plurality of times by using a 5% HCl solution, and then is carried out for a plurality of times by using deionized water;

(4) mixing 4-phenoxy phenol (POP) and solid powder F, dissolving in ethanol, stirring, and ultrasonically mixing to obtain solution G;

in the step (4), the mass ratio of the 4-phenoxyphenol to the solid powder F is 1.0 (2.5-3.5);

(5) heating the solution G to 60-70 ℃, stirring and reacting for 4-5 hours, then continuously heating to above 95 ℃, and evaporating the solvent to obtain a solid precursor H; reacting the solid H at 350-380 ℃ for 1.0-1.5 hours to obtain solid powder I; washing and drying the solid powder I to obtain a metal-free heterogeneous Fenton-like catalyst;

the washing in the step (5) is preferably carried out for several times by alternately washing with absolute ethyl alcohol and deionized water;

the drying in the steps (3) and (5) is preferably carried out at 50-70 ℃ for 10-24 hours.

The metal-free heterogeneous Fenton-like catalyst (POP-rGO Nhs) prepared by the method is black solid powder; wherein the introduction of POP and the formation of intrinsic C-O-C can cause the increase of the electron density around the doped oxygen atoms and the non-uniform distribution of electrons adjacent to large pi bonds, thereby generating countless electron-rich oxygen centers and electron-deficient carbon centers, and similarly constructing countless galvanic cathode-anode pairs on the surface of the catalyst to form a double-reaction-center catalytic system; POP-rGO Nhs needs to be in a liquid environment with H₂O₂Combined to form a Fenton-like system.

The metal-free heterogeneous Fenton-like catalyst and H₂O₂The combination is used for treating organic pollutants in water;

the organic contaminants may include bisphenol a (bpa), 2-chlorophenol (2-CP), ibuprofen, phenytoin, diphenhydramine, 2, 4-dichlorodichlorobenzoic acid, methyl orange, rhodamine B, and methylene blue;

the metal-free heterogeneous Fenton-like catalyst and H₂O₂When the compound is used in water, hydroxyl free radicals and superoxide free radicals can be generated, and the compound can be finally applied to the fields of medical treatment, polishing, material synthesis and the like.

Compared with the prior art, the invention has the following advantages and effects:

(1) the metal-free heterogeneous Fenton-like catalyst is not obviously influenced by the pH value of a reaction system. The pH value (pH value) of the system does not need to be adjusted to 2-3 in the reaction process, and the method has a good removing effect on the degradation of the toxic and harmful organic pollutants which are difficult to biodegrade under the condition of neutral room temperature.

(2) The catalyst of the invention does not produce solid foreign matters such as iron mud and the like in the reaction process, and does not need a foreign matter removing device.

(3) The catalyst has high hydrogen peroxide utilization rate (60-80%) in the process of removing organic pollutants.

(4) The invention has good stability in the process of removing organic pollutants, and no metal ions are released.

(5) The catalyst of the invention belongs to a solid catalyst, is convenient to separate from water and is convenient to recycle.

(6) The base material of the catalyst is cheap, and has no metal doping, low cost and simple operation.

Drawings

FIG. 1 is a Transmission Electron Micrograph (TEM) of POP-rGO Nhs prepared in example.

FIG. 2 is X-ray photoelectron spectroscopy (XPS) of O1s and C1s of the products obtained in examples and comparative examples.

FIG. 3 is Electron Paramagnetic Resonance (EPR) spectra of products obtained in examples and comparative examples.

FIG. 4 is a graph of the degradation curves for 2-CP and BPA degradation for the products obtained in the examples and comparative examples.

FIG. 5 shows the effect of initial pH on degradation of 2-CP in the POP-rGO Nhs Fenton-like system prepared in the example.

FIG. 6 is a continuous cycle degradation activity curve for 2-CP with the POP-rGO Nhs Fenton-like system prepared in the example.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

Examples

The preparation method of the metal-free heterogeneous Fenton-like catalyst (POP-rGO Nhs) comprises the following steps:

(1) under the ice-bath condition below 0 ℃, 5.0g of graphite powder is slowly added into 115mL of concentrated sulfuric acid (98%), and stirred for 30 minutes (the rotating speed is 400 rpm) to obtain a solution A. 25.0g NaNO₃Added into the solution A and stirred for 30 minutes (the rotating speed is 450 rpm) to obtain a solution B. Mixing KMnO₄Slowly adding the mixture into the solution B, and stirring the mixture for 3 hours (the rotating speed is 350 revolutions per minute) to obtain a solution C.

(2) And (3) heating the solution C to 38 ℃ for the first time, stirring for 30 minutes (the rotating speed is 450 revolutions per minute), adding 250mL of deionized water, heating to 95 ℃ again, and stirring for 1 hour (the rotating speed is 450 revolutions per minute) to obtain a solution D.

(3) 50mL of H₂O₂(30%) add solution D until the solution turns golden brown. After cooling, it was washed three times with 5% HCl and then with deionized water until the pH was close to 6 to give an undried solid material E. E was dried at 70 deg.C (18 hours) and ground to give solid powder F.

(4) 0.2G of 4-phenoxyphenol and 0.5G of solid powder F were mixed and dissolved in 25mL of ethanol, stirred for 1.0 hour (rotation speed 450 rpm), and subjected to ultrasonic treatment for 30 minutes (working frequency 40KHz, electric power 300W, temperature 70 ℃ C.) to obtain solution G.

(5) And (3) placing the solution G in a 70 ℃ water bath, stirring for 4 hours (the rotating speed is 500 revolutions per minute), heating to 95 ℃, and continuing stirring for 3 hours (the rotating speed is 500 revolutions per minute) to completely evaporate the liquid to obtain a solid precursor H. And drying the solid H at 90 ℃ (about 3 hours), then placing the solid H in a muffle furnace for copolymerization annealing treatment at 350 ℃ for 1.0 hour at the heating rate of 5 ℃/min, and cooling to obtain solid powder I. The solid powder I was then washed alternately with absolute ethanol and with deionization three times each. And finally, drying at 70 ℃ (about 12 hours), and grinding to obtain the metal-free heterogeneous Fenton-like catalyst POP molecule doped reducing graphene oxide nano hybrid POP-rGO Nhs.

Comparative example 1

Graphene Oxide (GO) was prepared as follows:

(1) slowly adding 5.0g of graphite powder into 11 under the ice bath condition below 0 DEG C5mL of concentrated sulfuric acid (98%), and stirred for 30 minutes (400 rpm) to obtain solution A. 25.0g NaNO₃Added into the solution A and stirred for 30 minutes (the rotating speed is 450 rpm) to obtain a solution B. Mixing KMnO₄Slowly adding the mixture into the solution B, and stirring the mixture for 3 hours (the rotating speed is 350 revolutions per minute) to obtain a solution C.

(3) 50mL of H₂O₂(30%) add solution D until the solution turns golden brown. After cooling, it was washed three times with 5% HCl and then with deionized water until the pH was close to 6 to give an undried solid material E. E was dried at 70 deg.C (18 hours) and ground to give solid powder F. The solid powder F is the Graphene Oxide (GO).

Comparative example 2

Reduced graphene oxide (rGO) was prepared as follows:

(4) 0.5G of the solid powder F was dissolved in 25mL of ethanol, stirred for 1.0 hour (rotation speed of 450 rpm), sonicated for 30 minutes (working frequency of 40KHz, electric power of 300W, temperature of 70 ℃ C.), to obtain solution G. And (3) putting the solution G into a water bath at 95 ℃ and stirring for 4 hours (the rotating speed is 500 rpm), so that the liquid is completely evaporated to obtain a solid precursor H. And drying the solid H at 90 ℃, then placing the solid H in a muffle furnace for annealing reduction treatment at 350 ℃ for 1.0 hour at the heating rate of 5 ℃/min, cooling to obtain a solid I, and grinding to obtain the reducing graphene oxide (rGO).

Evidence for structural characterization of the products obtained in the examples and comparative examples:

FIG. 1 is a Transmission Electron Micrograph (TEM) of POP-rGO Nhs prepared in example. A and B show low-power TEM images of POP-rGONhs. From the figure, it can be seen that POP-rGO Nhs has a typical nano-layered structure with an overall morphology like a wrinkled silk gauze kerchief. The rolling and waving are essential features of the graphene nanosheets, which are caused by slight bending and twisting in order to maintain the thermodynamic stability of the two-dimensional thin film layer. These nanosheets are soft and transparent and exhibit stable properties under electron beam. C and D show high-power TEM images of POP-rGO Nhs with disordered regions being the main structural feature, but some ordered graphite lattices can still be clearly observed, indicating that POP-rGO Nhs are partially restored to an ordered crystal structure. The diffraction spot rings identified in SAED are represented by the hexagonal structure of the graphite planar honeycomb carbon lattice.

FIG. 2 is O1s and C1s X-ray photoelectron spectroscopy (XPS) for GO, rGO and POP-rGO Nhs. The intense signal at 530-. For GO C1s XPS (fig. 2B), the two strong characteristic peaks at 284.9eV and 286.9eV are assigned to graphitic C-C/C ═ C species and C-O species in C-O-C or C-OH, respectively. The two fitted characteristic peaks at 288.1eV and 289.1eV are respectively assigned to the GO surface C ═ O and O ═ C-OH groups. According to XPS analysis, the O content of GO is 37.4 wt%.

For rGO, the C-O peak with a binding energy of 532.2eV for O1s XPS (fig. 2C), the C ═ O peak with a binding energy of 531.4eV, and the C-O peak with a binding energy of 286.0eV in C1 XPS (fig. 2D) were significantly reduced, and the O content in rGO decreased to 14.6 wt%. These results indicate that their surface oxygen-containing groups are greatly removed, indicating that GO is efficiently reduced to rGO. As can be seen from fig. 2C, of these remaining minor surface groups, C-OH is the most predominant oxygen-containing group present on the rGO surface. Furthermore, the C-O peak binding energy (532.2eV) in rGO O1s was reduced by 0.5eV from that of GO (532.7eV), indicating that the residual C-O groups were different from the previous C-O groups, most likely contributed by their surface ether C-O-C, as evidenced by the C1s XPS of rGO (FIG. 2D), i.e., the C-O peak binding energy (286.0eV) in rGO C1s was significantly reduced by 0.9eV from that of GO C-O peak binding energy (286.9eV) in GO C1 s. Furthermore, the strong increase in the C-C/C ═ C peak in the graphite skeleton in rGO C1s indicates a restoration of the graphite crystal structure and more carbon rings are exposed at the surface.

The peaks for O1s XPS (fig. 2E) for the POP-rGO Nhs sample, with binding energies of 530.9eV O ═ C-OH, 531.5eV C ═ O and 533.6eV C — OH, were further attenuated, while the peak for the 532.1eV C — O-C, increased, indicating that oxygen species introduced by doping of POP molecules recombine by copolymerization into the planar honeycomb framework of POP-rGO Nhs, an increase in O content (16.3 wt%) relative to the O content (14.6 wt%) in rGO confirms this. Furthermore, the binding energy of C-O (285.7eV) in C1s of POP-rGO Nhs (FIG. 2F) was reduced by 0.3eV from the C-O binding energy of rGO (286.0eV), indicating that the newly formed C-O-C in POP-rGO Nhs is different from the surface ether C-O-C in rGO. The C-O-C is formed by bonding (dehydration condensation) the exposed oxygen atom after deprotonation of the hydroxyl group in the POP molecular structure with the C atom on the surface of the graphene. In addition, the strong weakening of the peak of the graphite framework C-C/C ═ C with the binding energy of 284.6eV in the POP-rGO Nhs C1s suggests that the perfection of the planar hexagonal carbon lattice is weakened to some extent by doping POP molecules to the surface of the POP-rGO Nhs planar honeycomb framework.

FIG. 3 is Electron Paramagnetic Resonance (EPR) spectra of GO, rGO and POP-rGO Nhs. The GO sample showed a very sharp and symmetric EPR signal at g 1.994 compared to the rGO and POP-rgynhs samples. The signal is due to a single electron induced by the presence of a large number of oxygen-containing groups on the GO surface. For rGO, this sharp symmetrical peak disappears, indicating a sharp decrease in the number of single electrons as the surface oxygen-containing groups disappear. A broad, low EPR signal remains at g-1.996, which may be represented by the remaining-OH groups of the rGO surface or unpaired electrons of the surface ether C-O-C. Compared with rGO, the wide EPR signal intensity of POP-rGO Nhs at the g-1.996 position is obviously enhanced. POP molecules are doped, dehydrated, condensed and recombined with GO, and then O enters a POP-rGO Nhs structure to form a large amount of C-O-C. The enhancement of the EPR signal intensity here indicates that the formation of C-O-C results in the accumulation of a large number of free electrons around the introduced O atoms, forming countless electron-rich oxygen centers in the POP-rGO Nhs molecular structure.

Application experiments:

0.02g of the above synthesized catalyst was charged into 50mL of 10mg L^-1Maintaining the natural pH value (about 6.5), keeping the temperature at 35 ℃, continuously stirring for 30 minutes until the adsorption equilibrium between the pollutant and the catalyst is reached, and adding 10mM H₂O₂The Fenton reaction was started and samples were taken at different time points to determine the concentration of contaminants, TOC concentration and H₂O₂And (4) concentration.

FIG. 4 is a degradation curve for GO, rGO and POP-rGO Nhs Fenton like systems for 2-CP and BPA degradation. FIG. 4A shows the degradation of 2-CP by each Fenton system. In the graphite suspension fenton system, no significant removal of 2-CP was observed. At 120min, the degradation rate of 2-CP in the GO Fenton system is only 8.1%. In the rGO Fenton system, the degradation rate of the 2-CP is improved to 41.9 percent. In the POP-rGO Nhs Fenton system, the degradation rate of the 2-CP is remarkably improved to 88.7 percent. According to the first order kinetic fit, the degradation rates of POP-rGO Nhs for 2-CP were 35.8 times, 25.6 times and 3.5 times that of graphite, GO and rGO, respectively.

Similarly, for the degradation of another contaminant BPA (fig. 4B), at 120min, the degradation sequence of each fenton catalytic system is: graphite (1.1%) < GO (4.0%) < rGO (19.0%) < < POP-rGO Nhs (75.7%).

The results in fig. 4 fully illustrate that the metal-free fenton catalyst POP-rGO Nhs with a large number of electron rich and electron deficient centers shows the highest catalytic activity for the degradation of pollutants compared to graphite powder, GO and rGO alone.

FIG. 5 shows the effect of the initial pH value of the POP-rGO Nhs Fenton-like system prepared in the example on the degradation of 2-CP. The degradation rate of 2-CP can reach 100% at an initial pH of 3.3, and then the degradation rate of 2-CP is slightly decreased as the initial pH of the solution is increased. However, the degradation rate of 2-CP in 120min is more than 76% in the whole range of the initial pH value of 3.3-9.5, which shows that the change of the initial pH value does not obviously affect the activity of the catalyst, and also shows that POP-rGO Nhs has a wider pH value adaptation range. Dissociative chemisorption of water molecules often causes catalysts containing metal species to form surface hydroxyl groups in aqueous solutions, eventually resulting in catalysts whose activity is readily affected by the pH of the solution. The POP-rGO Nhs belongs to a metal-free Fenton catalyst, so that the pH value is no longer a sensitive influence factor on the catalytic activity of the POP-rGO Nhs.

FIG. 6 is a continuous cycle degradation activity curve of the POP-rGO Nhs Fenton-like system prepared in the example for 2-CP. It can be seen from the figure that the catalyst is continuously and circularly operated for a plurality of times, the degradation activity of the catalyst on the 2-CP is not obviously reduced, the 2-CP degradation rate is still maintained to be more than 86.7 percent after the catalyst is circularly used for 8 times.

The above results fully reflect the stability advantage of the metal-free Fenton catalyst POP-rGO Nhs compared with other metal species-containing catalysts, and can be applied to the treatment of actual micro-polluted water bodies.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a metal-free heterogeneous Fenton-like catalyst is characterized by comprising the following steps of:

(1) adding graphite powder into concentrated sulfuric acid, and uniformly stirring to obtain a solution A; adding sodium nitrate into the solution A, and uniformly stirring to obtain a solution B; adding potassium permanganate into the solution B, and uniformly stirring to obtain a solution C;

in the step (1), graphite powder and NaNO are used₃The mass ratio of the potassium permanganate to the potassium permanganate is 1.0 (4.5-5.5) to (2.5-3.5);

(2) heating the solution C to 35-45 ℃, maintaining for 0.5-1.0 hour, adding water, continuing to heat to 90-100 ℃, and stirring for reaction for 1.0-2.0 hours to obtain a solution D;

(4) mixing 4-phenoxy phenol and solid powder F, dissolving in ethanol, stirring, and ultrasonically mixing to obtain solution G;

(5) heating the solution G to 60-70 ℃, stirring and reacting for 4-5 hours, then continuously heating to above 95 ℃, and evaporating the solvent to obtain a solid precursor H; reacting the solid H at 350-380 ℃ for 1.0-1.5 hours to obtain solid powder I; and washing and drying the solid powder I to obtain the metal-free heterogeneous Fenton-like catalyst.

2. The method of claim 1, wherein: in the step (3), the washing is carried out for a plurality of times by using a 5% HCl solution, and then is carried out for a plurality of times by using deionized water.

3. The method of claim 1, wherein: and (5) washing is alternately washing for a plurality of times by using absolute ethyl alcohol and deionized water.

4. The method of claim 1, wherein: and (5) drying for 10-24 hours at 50-70 ℃.

5. A metal-free heterogeneous fenton-like catalyst, characterized in that: is prepared by the method of any one of claims 1 to 4.

6. An application method for treating organic pollutants in water is characterized by comprising the following steps: the use of the metal-free heterogeneous Fenton-like catalyst of claim 5 in combination with H₂O₂And (5) carrying out combined treatment.

7. The method of application according to claim 6, characterized in that: the organic pollutants comprise bisphenol A, 2-chlorophenol, ibuprofen, phenytoin, diphenhydramine, 2, 4-dichlorodichlorochloroacetic acid, methyl orange, rhodamine B and methylene blue.