CN107398268A - A kind of preparation method of manganese oxide carbon nano-fiber catalytic membrane - Google Patents

Abstract

A method for preparing a manganese oxide/carbon nanofiber composite catalytic membrane, comprising the following steps: A, preparation of casting solution: mixing 8wt% to 15wt% polymer and 85wt% to 92wt% organic solvent, fully stirring at normal temperature, to obtain Uniform polymer casting solution; during continuous stirring, add manganese acetate tetrahydrate of different quality, fully stir to obtain dark red homogeneous casting solution, degassing for later use; B, fiber film spinning: to the electrospinning propeller Inject the casting solution, and the droplets are sprayed into filaments under the action of a high-voltage electric field to form a Mn(oAc) ₂ /polymer nanofiber composite film; C, carbonization of the composite film: the fiber composite film is pre-oxidized in the air, and then enters High-temperature carbonization in an inert gas-protected medium to form a manganese oxide/carbon nanofiber composite catalytic membrane.

Description

A kind of preparation method of manganese oxide carbon nanofiber composite catalytic membrane

technical field

The invention relates to the field of catalytic ozone oxidation, in particular to a method for preparing a manganese oxide carbon nanofiber composite catalytic membrane.

Background technique

With the increasingly prominent environmental problems and water resource problems, the severity of wastewater discharge has become increasingly prominent, and most of the wastewater has complex components, which have caused varying degrees of harm to the environment, human health and ecology. Some refractory organics have the characteristics of poor biodegradability. Traditional biochemical treatment is difficult to completely mineralize and degrade them. Advanced Oxidation Process (AOPs) can directly mineralize them or increase the concentration of pollutants through oxidation. Biodegradability. Experimental studies have shown that the advanced oxidation method can completely mineralize most of the refractory organic matter, and has a good application prospect.

The advanced oxidation method using ozone as the oxidant has the advantages of strong oxidation ability, wide application range, fast reaction rate, etc., and has good application potential in wastewater treatment. But EL-Din et al. (EL-Din M G, Smith D W. Ozonation of kraft pulp mill efluents: process dynamics [J]. J Environ Eng Sci, 2002, 1(1): 45-57.) research shows that the use of ozone alone The economic benefits of mineralizing organic matter are very low, and there are problems such as low utilization rate and high processing cost. Ozone catalytic oxidation is an advanced oxidation technology that has been widely used in recent years. It can realize the mineralization of refractory organic compounds at normal temperature and pressure, and has high ozone utilization rate and good selectivity, which makes up for the single ozone oxidation. shortcomings. Catalytic ozonation technology combines ozone with metal oxides with adsorption and oxidation properties to degrade refractory organic substances into carbon dioxide, water and small molecular substances under normal conditions, without the need for ultraviolet light, high temperature and high pressure reaction conditions .

Due to their unique structural characteristics, nanomaterials have quantum size effects, small size effects, interface or surface effects, and macroscopic quantum tunneling effects, making them play an important role in the fields of optoelectronic devices, sensors, catalysts, and functional composite materials. Metal oxide nanomaterials are widely used in the production of catalysts, semiconductor materials, magnetic materials, fluorescent materials and so on. In practical applications, loading metal oxides on a carrier with a large specific surface area can well solve the shortcomings of nano-powders that are easy to agglomerate and difficult to recycle, and can also increase its stability, catalytic activity and achieve reuse. performance.

Electrospinning technology is a process in which molten polymer or polymer solution is formed into fibers under the action of a high-voltage electrostatic field. In the high-voltage electrostatic field, the charged molten polymer or polymer solution undergoes spraying, stretching, splitting, solvent volatilization or solidification, and finally forms a fibrous substance.

Due to its special physical and chemical properties, manganese oxide is widely used in various fields such as catalysts and electrochemistry, and it is abundant in nature, cheap and non-toxic. The synthesis methods of nano-manganese oxide mainly include hydrothermal method, liquid-phase synthesis method, and precursor conversion method, but the synthesis of nano-materials has problems such as difficult recovery and low recycling rate in actual catalytic applications, which greatly limit its use. application in wastewater treatment.

Through the method of electrospinning, the nanofibrous membrane prepared by mixing the metal oxide precursor and the polymer casting liquid under the action of a high-voltage electrostatic field can well solve the defects of the above metal oxide nanopowder materials. , and can have a better catalytic effect of ozone oxidation. Moreover, in the existing research, the manganese oxide/carbon nanocomposite fiber membrane is mostly used as the research content of the electrochemical direction, but the preparation of the composite fiber catalytic membrane by this method is rarely reported.

Contents of the invention

In view of this, the present invention aims at the above problems, and the main purpose is to propose a method for preparing a manganese oxide/carbon nanofiber composite catalytic membrane, which has strong operability, simple process, high recycling rate and easy recycling. It shows good catalytic activity and stability in the catalytic ozonation process.

The present invention achieves the above object through the following technical methods: a preparation method of manganese oxide/carbon nanofiber composite catalytic membrane:

Step 1: Preparation of casting solution

Put 85wt%~92wt% dispersed organic solvent, 8wt%~15wt% polymer into the mixing tank and stir well, set the normal temperature to get a uniform transparent polymer casting solution, and then add different quality tetrahydrate during the continuous stirring process Manganese acetate, fully stirred to obtain a dark red homogeneous casting solution, degassing for subsequent use, the dispersed organic solvent is N,N-dimethylformamide (DMF), dimethylacetamide (DMAC), dimethylmethylene Sulfone (DMSO), dichloromethane (DCM);

Step 2: Preparation of Mn(oAc) ₂ /polymer nanofiber composite membrane

Inject the film casting solution prepared in step 1 into the electrospinning propeller, and the droplets are jet-spun to form a film under the action of a high-voltage electric field, and the Mn(oAc) ₂ /polymer nanofiber composite film is obtained after drying;

Step 3: Preparation of manganese oxide/carbon nanofiber composite catalytic membrane

The fiber composite membrane in the above step 2 is thermally stabilized in the air, and then carbonized in an atmosphere furnace protected by an inert gas, and lowered to room temperature to obtain a manganese oxide/carbon nanocomposite fiber catalytic membrane.

Further, the polymer described in step 1 is polyacrylonitrile (PAN), N-vinyl-2-pyrrolidone (PVP), polyvinylidene fluoride (PVDF) or polymethyl methacrylate (PMMA).

Further, the addition amount of manganese acetate tetrahydrate described in step 1 is 10wt%, 20wt%, 30wt%, 40wt%, 50wt% polymer addition.

Further, the electrospinning conditions in step 2 are as follows: spinning voltage 16kv-20kv, distance between the spinneret and the negative electrode receiver 15cm, spinning solution propulsion rate 0.6-2.0ml/min, spinning temperature 30°C, composite membrane The drying conditions were 12 hours at 50°C.

Further, the heat stabilization described in step 3 is also called pre-oxidation treatment. In the air at 200-300°C, anneal at this temperature for 2 hours to convert it into a heat-stable state. During the process, aluminum oxide high-temperature splints are used to make the nanofiber film stereotyped.

Further, the carbonization process described in step 3 is to heat the composite membrane under an inert gas atmosphere including high-purity nitrogen N ₂ , Ar or He, and continue heating at 800°C for 1 hour to carbonize the nanofiber membrane. Aluminum high temperature splints give it shape.

Further, the pre-oxidation heating process described in step 3 is a programmed temperature increase, and the programmed temperature increase rate is 5° C./min. The carbonization temperature increase in step 3 is a programmed temperature increase, and the temperature increase rate is 3°C/min.

The manganese oxide/carbon nanofiber composite catalytic membrane prepared by the above method is used to catalyze the oxidation and degradation of refractory organic matter by ozone.

The beneficial effects of the present invention are:

The invention adopts the electrospinning method to prepare the manganese oxide/carbon nanometer composite fiber catalytic membrane, which is simple in operation and strong in controllability, and can control the loading capacity of the catalyst according to the actual requirement. The microstructure of the composite membrane presents a nano-network structure interwoven by nanofibers, and the sintered nano-manganese oxide particles are distributed on the surface of carbon nanofibers, achieving high specific surface area and uniform pore size distribution. In the actual catalytic ozone oxidation experiment, the composite membrane showed excellent catalytic ozone oxidation effect, improved ozone utilization rate, high repeatability and strong stability.

Description of drawings

Figure 1 shows the flow chart of the catalytic ozone oxidation experiment.

Among them, 1 oxygen tank; 2 ozone generator; 3 ozone concentration detector; 4 magnetic stirring system; 5 reaction glass bottle; 6 tail gas absorption device; 7 catalyst; 8 sampling port

detailed description

The present invention will be described in further detail below.

The technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and examples, and the given examples are only used to explain the present invention, and are not intended to limit the scope of the present invention.

Experimental Materials

Example 1

A preparation method of MnO ₂ /CNF composite catalytic membrane:

Step 1: Configuration of casting solution

Weigh 4.8g of polyacrylonitrile (PAN) and disperse in 55.2g of DMF, and stir evenly at room temperature. Then add 10wt%, 20wt%, 30wt% PAN manganese acetate tetrahydrate respectively in the process of continuous stirring, fully stir until the dark red homogeneous casting solution is left standing for defoaming.

Step 2: Preparation of Mn(oAc) ₂ /PAN nanofiber composite membrane

Inject the casting solution prepared in step 1 into the electrospinning equipment, the spinning voltage is 16kv, the distance between the spinneret and the negative electrode receiver is 15cm, the spinning solution pushing rate is 1.0ml/min, and the spinning temperature is 30 ℃, through the action of high-voltage electric field, jet spinning to form a film, after drying at 50 ℃ for 12 hours, Mn(oAc) ₂ /PAN-1, Mn(oAc) ₂ /PAN-2, Mn(oAc) ₂ /PAN-3 nano fiber composite membrane.

Step 3: Preparation of MnO ₂ /CNF composite catalytic membrane

The fiber composite membrane obtained in the above step 2 was pre-oxidized in an air atmosphere, the temperature was raised to 250°C at a rate of 5°C/min, and annealed at this temperature for 2 hours. During the treatment, the nanofiber membrane was shaped by using an alumina high-temperature splint.

Further, in the protective medium of high-purity nitrogen N ₂ , Ar or He, the temperature was raised to 800°C at a rate of 3°C/min, and the temperature was maintained for 1 hour to carbonize the nanofibrous membrane. During the treatment, an alumina high-temperature splint was used to shape it. After cooling down to room temperature, take out the prepared MnO ₂ /CNF-1, MnO ₂ /CNF-2, MnO ₂ /CNF-3 composite catalytic membranes.

The diameter of the MnO ₂ /CNF composite catalytic membrane fiber prepared in this example is 100nm-200nm, and the catalytic oxidation degradation rates of MnO ₂ /CNF-1, MnO ₂ /CNF-2, and MnO ₂ /CNF-3 to oxalic acid are 49% respectively . Catalyst dosage is 0.5g/L).

Example 2

The casting solution was prepared by adding 4.8g of polyacrylonitrile (PAN) and 55.2g of DMF into a stirring tank, mixing and stirring thoroughly, setting the temperature at 20°C, and stirring for 6 hours to obtain a uniform polymer casting solution. Add 30wt% PAN manganese acetate tetrahydrate to the continuously stirred polymer casting solution, set the temperature at 20° C., stir for 4 hours to obtain a homogeneous dark red transparent casting solution, and let stand for defoaming.

Spinning to form a film, inject the casting solution prepared in step 1 into the electrospinning spinning propeller, set the spinning propulsion rate to 0.6ml/min, the spinning voltage to 16kv, and the distance between the spinneret and the negative electrode receiver to be 15cm, the spinning temperature is 30°C, through the action of high-voltage electric field, jet spinning to form a film, set the oven temperature to 50°C, and dry for 12h to obtain Mn(oAc) ₂ /PAN nanofiber composite film.

The membrane is carbonized, and the Mn(oAc) ₂ /PAN fiber composite membrane obtained in the above steps is pre-oxidized in an air atmosphere, and the temperature is programmed to rise at 5°C/min to 250°C, and annealed at 250°C for 2 hours. The annealing process uses oxidation The aluminum high temperature resistant splint makes the nanofiber membrane shape.

Further, in the protective medium of high-purity nitrogen N2, Ar or He, set the temperature program to rise at 3°C/min to 800°C, and keep at 800°C for 1h to carbonize, and use alumina high-temperature splints to shape it during the treatment. After cooling down to room temperature, the MnO ₂ /CNF composite catalytic membrane was obtained.

The MnO ₂ /CNF composite catalytic membrane fiber diameter that this example makes is 100nm～200nm, and the catalytic membrane that makes is used for catalytic ozone to oxidize oxalic acid, phenol, nitrobenzene, chlorophenol four kinds of refractory organic matter respectively (wherein pollutant The initial concentration is 100ppm, the dosage of ozone is 50mg/L, 50ml/min, the reaction time is 60min, and the dosage of catalyst is 0.5g/L). The results of the removal rates of various pollutants are shown in the following table:

Claims (7)

1. A kind of 1. preparation method of manganese oxide/carbon nano-fiber catalytic membrane, it is characterised in that：

   Step 1：The preparation of casting solution

   85wt%~92wt% is disperseed into organic solvent, 8wt%~15wt% polymer, adds in agitator tank and is sufficiently stirred, if Permanent temperature, obtain homogeneous transparent polymeric casting film liquid, after during continuously stirring add different quality four hydration manganese acetates, It is sufficiently stirred to obtain kermesinus homogeneous casting solution, deaeration is standby, and the scattered organic solvent is DMF (DMF), dimethyl acetamide (DMAC), dimethyl sulfoxide (DMSO) (DMSO), dichloromethane (DCM)；

   Step 2：Mn(oAc)₂The preparation of/polymer nanofiber composite membrane

   By made from step 1 casting solution injection electrostatic spinning propeller in, drop in the presence of high voltage electric field, jet spinning into Film, Mn (oAc) is obtained after drying₂/ polymer nanofiber composite membrane；

   Step 3：The preparation of manganese oxide/carbon nano-fiber catalytic membrane

   Composite fiber membrane in above-mentioned steps 2 is subjected to heat stabilisation process in atmosphere, after it is being had into the gas of inert gas shielding Carbonized in atmosphere stove, be down to room temperature and obtain manganese oxide/carbon nano-composite fiber catalytic membrane.
2. 2. the preparation method of manganese oxide according to claim 1/carbon nano-fiber catalytic membrane, it is characterised in that：Step Rapid 1 polymer is polyacrylonitrile (PAN), NVP (PVP), Kynoar (PVDF) or poly- first Base methyl acrylate (PMMA).
3. 3. the preparation method of manganese oxide according to claim 1/carbon nano-fiber catalytic membrane, it is characterised in that：Step The rapid 1 four hydrations manganese acetate addition is 10wt%, 20wt%, 30wt%, 40wt%, 50wt% polymer addition.
4. 4. the preparation method of manganese oxide according to claim 1/carbon nano-fiber catalytic membrane, it is characterised in that：Step Rapid 2 electrospinning conditions are：The front distance 15cm of spinning voltage 16kv~20kv, spinning head and negative pole receiver, spinning Liquid promotes 0.6~2.0ml/min of speed, 30 DEG C of spinning temperature, 12h is dried under the conditions of 50 DEG C of the drying condition of composite membrane.
5. 5. the preparation method of manganese oxide according to claim 1/carbon nano-fiber catalytic membrane, it is characterised in that：Step Rapid 3 thermostabilization is also known as pre-oxidation treatment, in 200~300 DEG C of air, keeps the 2h that anneals at this temperature, makes its conversion For thermostabilization state, nano fibrous membrane is set to shape using alumina high temperature clamping plate in processing procedure.
6. 6. the preparation method of manganese oxide according to claim 1/carbon nano-fiber catalytic membrane, it is characterised in that：Step Rapid 3 carbonization process is composite membrane in high pure nitrogen N₂, heat under the conditions of inert gas atmosphere including Ar or He, in 800 Continuous heating 1h carbonizes nano fibrous membrane at a temperature of DEG C, makes its sizing using alumina high temperature clamping plate in processing procedure.
7. 7. the preparation method of manganese oxide according to claim 1/carbon nano-fiber catalytic membrane, it is characterised in that：Step The rapid 3 pre-oxidation temperature-rise period is temperature programming, and programmed rate is 5 DEG C/min.Charing heating is journey described in step 3 Sequence heats up, 3 DEG C/min of heating rate.