CN109759116B

CN109759116B - Method for promoting decomposition and purification of perfluorinated compounds by photoelectric coupling

Info

Publication number: CN109759116B
Application number: CN201910131218.3A
Authority: CN
Inventors: 柳丽芬; 石朋; 张旭
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2019-02-22
Filing date: 2019-02-22
Publication date: 2021-06-04
Anticipated expiration: 2039-02-22
Also published as: CN109759116A

Abstract

The invention provides a method for promoting the decomposition and purification of perfluorinated compounds by photoelectric coupling, which belongs to the technical field of perfluorinated compound treatment and energy saving and resource utilization. Carbon nanosheets/g‑C ₃ N ₄ /BiWO ₆ were prepared, and catalytic electrodes were prepared by using silica sol to be fixed and coated on stainless steel meshes. The circuits were connected to construct a system of coupling photocatalysis and electrocatalysis, respectively. The degradation and purification of perfluorooctanoic acid under the action of photocatalysis, electrocatalysis, dark adsorption and photoelectric catalysis, the effect of degrading perfluorooctanoic acid under different pH conditions, and the effect of degrading perfluorooctanoic acid in the system with and without aeration. The synergistic effect of photocatalytic technology and electrocatalytic technology greatly improves the degradation performance of photoelectric catalysis.

Description

Method for promoting decomposition and purification of perfluorinated compounds by photoelectric coupling

Technical Field

The invention belongs to the technical field of perfluorinated compound treatment and energy conservation and recycling, and relates to carbon nanosheet/g-C₃N₄/BiWO₆The preparation of the nano composite catalyst and the photoelectrocatalysis synergistic effect of the nano composite catalyst decompose and purify pollutants and generate electric energy, and the degradation efficiency and the electricity generation capability of perfluorinated compounds are improved.

Background

Perfluorocompounds are widely used in the fields of industrial production and consumer goods. It can be detected in different environmental media worldwide due to direct or indirect emissions during manufacturing, use and disposal. The perfluoro compound has environmental pollutants with strong biological toxicity, and is mainly manifested by neurobehavioral toxicity, organ toxicity, reproductive toxicity, genetic toxicity and carcinogenicity. Especially, the representative compound of perfluorooctanoic acid can seriously pollute the environment and harm human beings and the global ecosystem if the perfluorooctanoic acid is not properly treated. Different purification methods (physical removal, chemical removal and biological removal) have their limitations while being able to perform their purification functions. It is therefore necessary to find an effective and efficient treatment.

The photoelectrocatalysis technology combines two processes of electrolysis and catalysis, can prolong the service life of photoproduction electrons and holes, reduce the recombination rate of the electrons and the holes, and greatly enhance the activity of photocatalysis, thereby thoroughly removing pollutants or decomposing the pollutants into useful substances. Among them, the photocatalyst is the key of the photoelectrocatalysis technology. Bi₂WO₆As an excellent visible light driving photocatalyst, the photocatalyst has a narrow band gap and a proper energy band position (Eg ═ 0.58-3.30 eV). Due to double halogen interlayer [ Bi ]₂O₂]²⁺And WO₆The octahedral nanosheets are overlapped to form an alternate layered structure, so that the octahedral nanosheets have a large internal electric field and an asymmetric polarization effect, and show excellent visible light catalytic activity, thereby facilitating electron-hole separation. Graphitic carbon nitride (g-C)₃N₄) Is a metal-free polymer semiconductor, and has great application in the field of photocatalysis due to good thermochemical stability, electronic and optical properties, low price and no toxicity. Due to g-C₃N₄The potential of the CB of (1.12 eV) is negative enough, and the strong reduction capability of electrons in the surface CB has great potential for the purification of pollutants.

In recent years, carbon nanomaterials have been extensively studied due to their excellent power density, fast charge/discharge rates and excellent cycle stability. The two-dimensional carbon material has a large aspect ratio and a porous structure, so that the ion transmission distance of a nano scale can be shortened, the pore structure and the conductivity of the material can be improved, the transfer process of electrons and electrolyte ions is improved, the electron transmission is facilitated, and the conductivity is improved.

The application uses carbon nano sheet/g-C₃N₄/BiWO₆As experimental catalysts, enhanced photoelectrocatalysisThe degradation performance and the electricity generation performance of the technology effectively treat the perfluorooctanoic acid.

Disclosure of Invention

The invention designs a carbon nano sheet/g-C₃N₄/BiWO₆The photoelectrocatalysis component successfully constructs a photoelectrocatalysis purification system. The system not only can be used as an electrode, but also has the photocatalysis function and the electric conduction, the whole treatment and purification efficiency is greatly improved, the energy consumption is lower, and the concentration of pollutants is greatly reduced. The degradation efficiency and the power generation capability of the photoelectrocatalysis technology are greatly improved under the condition of low energy consumption. The system can theoretically treat perfluorooctanoic acid, expands the application of a photoelectrocatalysis technology, and provides a new idea for photoelectrocatalysis and treatment of perfluorocompounds.

The technical scheme of the invention is as follows:

the method for promoting decomposition and purification of the perfluorinated compounds by photoelectric coupling comprises the following steps:

(1) preparation of carbon Nanosheet/g-C₃N₄/BiWO₆The compound is as follows:

preparing GO according to an improved Hummers method for later use; adding the overdue flour and KOH into deionized water at the temperature of 80 ℃, stirring and mixing for 10 minutes, controlling the mass ratio of the overdue flour to the KOH to be 1: 1-2, and controlling the concentration of the overdue flour in a mixing system to be 10-15 mg/ml; adding GO, continuously stirring for 1.5-3 hours at the same temperature, controlling the mass ratio of KOH to GO to be 65-70: 1, adding urea when the mixed solution is cooled to 20-30 ℃, controlling the mass ratio of KOH to urea to be 1-3: 1, and continuously stirring for 0.5-2 hours; obtaining a mixture by freeze-drying; activating the freeze-dried mixture at 550-700 ℃ for 3-5 hours; treating the obtained product with dilute hydrochloric acid, neutralizing with deionized water, and freeze-drying overnight to obtain carbon nanosheets; heating melamine in a vacuum tube furnace at 500-600 ℃ for 3-5 hours, and heating the heated product at 480-550 ℃ for 1.5-3 hours to obtain g-C₃N₄；

(2) Cetyl trimethyl ammonium bromide and Na₂WO₄·2H₂O and Bi (NO)₃)·5H₂Adding O into deionized water, cetyl trimethyl ammonium bromide and Na₂WO₄·2H₂O and Bi (NO)₃)·5H₂The mass ratio of the oxygen to the sulfur to the oxygen is 1: 6-7: 19-20, the concentration of cetyl trimethyl ammonium bromide in the mixed solution is 0.6-0.7 mg/ml, after the mixture is uniformly stirred, the prepared carbon nanosheet and g-C are added₃N₄Continuously stirring for 0.5-1 hour, reacting for 20-26 hours at the temperature of 100-130 ℃, and cooling to obtain a mixture; washing, centrifuging, drying and grinding to obtain the carbon nano sheet/g-C₃N₄/BiWO₆(ii) a Wherein g-C₃N₄And BiWO₆The mass ratio of (1): 3-5 carbon nanosheet and g-C₃N₄/BiWO₆The mass ratio of (1): 180-220 parts by weight;

(3) preparing a photoelectrocatalysis electrode: firstly, cutting a stainless steel net into proper sizes, washing with deionized water, ultrasonically washing with absolute ethyl alcohol, and drying in a blast furnace for later use; mixing carbon nanosheets with g-C₃N₄/BiWO₆The ratio of the total mass of the silica sol to the silica sol in terms of mass-volume ratio g/mL is 1:1, then uniformly brushing the mixture on a stainless steel net to obtain the carbon nano sheet/g-C₃N₄/BiWO₆An electrode;

(4) constructing a photoelectrocatalysis treatment system: with carbon nanosheet/g-C₃N₄/BiWO₆The electrode is used as a cathode, the iron rod is used as an anode, and the electrodes are connected by a lead to form a circuit and are arranged in the long tubular single-chamber reactor; the light source vertically irradiates on the carbon nano-sheet/g-C₃N₄/BiWO₆On the electrode.

The invention has the beneficial effects that: the system integrates photocatalytic purification, electro-catalytic purification and photoelectric cooperative operation, degrades and removes perfluorinated compounds, especially perfluorooctanoic acid, is favorable for degrading organic pollutants more thoroughly and rapidly, and enhances the power generation capacity and level. The catalytic electrode of the system has good stability, and can continuously degrade pollutants and generate electricity.

Drawings

Fig. 1 is a graph comparing the removal effect of degraded perfluorooctanoic acid by four systems of Photocatalysis (PC), Electrocatalysis (EC), Dark adsorption (Dark) and Photoelectrocatalysis (PEC). In the figure, the abscissa is time (min) and the ordinate is the ratio of the current concentration to the initial concentration.

Figure 2 is a graph comparing the removal of perfluorooctanoic acid by PEC system treatment at

pH

3, 7, 11. In the figure, the abscissa is time (min) and the ordinate is the ratio of the current concentration to the initial concentration.

FIG. 3 is a graph comparing the effect of degrading perfluorooctanoic acid with and without aeration in a photoelectrocatalysis system. In the figure, the abscissa is time (min) and the ordinate is the ratio of the current concentration to the initial concentration.

Detailed Description

The following detailed description of the invention refers to the accompanying drawings.

The first embodiment is as follows: photoelectric coupling system for treating perfluorooctanoic acid

The catalytic electrode is placed in a long tubular quartz reactor, connected above the catalytic electrode by an alligator clip, connected by a lead to form a circuit and connected with a 1000 ohm resistor. Aeration is provided at the bottom of the reactor. The visible light source is a 50W tungsten halogen lamp. Before the reaction, 0.01mol/L sodium hydrogen sulfite was added to and dissolved in a 10mg/L perfluorooctanoic acid solution, and after the reaction, samples were taken every 30min and the concentration was measured by HPLC-MS. The reaction was carried out for a total of 2 hours, and the removal rate of perfluorooctanoic acid was calculated.

In fig. 1, the different degradation effects of four systems, Photocatalytic (PC), Electrocatalytic (EC), Dark adsorption (Dark) and Photoelectrocatalytic (PEC), were measured and compared to the electrogenic performance. Wherein, the PFC photoelectrocatalysis degradation rate is the highest, and can reach 90% in 1 hour.

In fig. 2, the removal of perfluorooctanoic acid by PEC at different initial pH conditions was determined. When the pH is not adjusted (pH 7), the degradation rate is the highest, which can reach 90% in 1 hour, while when the pH is 3 and 11, the degradation rate at 1 hour is lower than when the pH is not adjusted (pH 4.6), but the degradation tendency is the same, and finally the perfluorooctanoic acid can be degraded. Demonstrating that the PEC system's degradation of perfluorooctanoic acid can be applied to a wider range of pH.

Example two: treatment of perfluorooctanoic acid with and without aeration system

In fig. 3, the degradation effect and the electricity generation performance of the system aeration (aeration) and the system non-aeration (no aeration) are compared. Wherein, the photoelectrocatalysis degradation rate is the highest in aeration, and can reach 90 percent in 1 hour, which is far higher than that in non-aeration.

Claims

1. a method for photoelectric coupling to promote the decomposition and purification of perfluorinated compounds, is characterized in that, step is as follows:

(1) Preparation of carbon nanosheets and gC ₃ N ₄ :

GO was prepared according to the improved Hummers method, and it was ready for use; the expired flour and KOH were added to deionized water at 80°C, stirred and mixed for 10 minutes, and the mass ratio of expired flour and KOH was controlled to be 1:1-2, and the expired flour was The concentration in the mixed system is 10-15 mg/ml; then GO is added, and stirring is continued for 1.5-3 hours at the same temperature, and the mass ratio of KOH and GO is controlled to be 65-70:1, and the mixed solution is cooled to 20-30 ℃, add urea, control the mass ratio of KOH to urea to be 1～3:1, continue stirring for 0.5～2 hours; obtain the mixture by freeze drying; activate the freeze dried mixture at 550～700 ℃ for 3～5 hours; The obtained product was treated with dilute hydrochloric acid, neutralized with deionized water, and then freeze-dried overnight to obtain carbon nanosheets; the melamine was heated in a vacuum tube furnace at 500-600 °C for 3-5 hours, and the heated product was at 480-550 °C. Heating at ℃ temperature for 1.5-3 hours to obtain gC ₃ N ₄ ;

(2) Cetyltrimethylammonium bromide, Na ₂ WO ₄ ·2H ₂ O and Bi(NO ₃ ) ₃ ·5H ₂ O were added to deionized water, and cetyltrimethylammonium bromide The mass ratio of Na ₂ WO ₄ ·2H ₂ O and Bi(NO ₃ ) ₃ ·5H ₂ O is 1:6～7:19～20, and cetyltrimethylammonium bromide is in the mixed solution The concentration is 0.6～0.7mg/ml, after stirring evenly, add the prepared carbon nanosheets and gC ₃ N ₄ , continue stirring for 0.5～1 hour, react at 100～130℃ for 20～26h, cool, The mixture is obtained; after washing, centrifugation, drying and grinding, it is carbon nanosheets/gC ₃ N ₄ /Bi ₂ WO ₆ ; wherein, the mass ratio of gC ₃ N ₄ to Bi ₂ WO ₆ is 1:3-5, The mass ratio of carbon nanosheets to gC ₃ N ₄ /Bi ₂ WO ₆ is 1:180-220;

(3) Preparation of photoelectric catalytic electrodes: First, cut the stainless steel mesh into suitable size, wash with deionized water and ultrasonically with absolute ethanol, and then dry it in a blast furnace before use; carbon nanosheets/gC ₃ N ₄ /Bi ₂ The total mass of WO ₆ and the silica sol are completely mixed according to the mass-to-volume ratio g/mL of 1:1, and then the mixture is evenly brushed on the stainless steel mesh, which is the carbon nanosheet/gC ₃ N ₄ /Bi ₂ WO ₆ electrode;

(4) Construction of photoelectric catalytic treatment system: carbon nanosheets/gC ₃ N ₄ /Bi ₂ WO ₆ electrodes are used as cathodes, iron rods are used as anodes, and wires are connected to form circuits, which are placed in a long tubular single-chamber reactor; the light source is vertical Irradiated on the carbon nanosheet/gC ₃ N ₄ /Bi ₂ WO ₆ electrode.

2 . The method for promoting the decomposition and purification of perfluorinated compounds by photoelectric coupling according to claim 1 , wherein photocatalytic technology and electrocatalytic technology are coupled, and the perfluorinated compound is perfluorooctanoic acid. 3 .