CN109485128B

CN109485128B - Method for degrading organic matters based on platinum nanoparticle homogeneous electrocatalytic system

Info

Publication number: CN109485128B
Application number: CN201811394613.2A
Authority: CN
Inventors: 顾桐旭; 李翔
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2018-11-20
Filing date: 2018-11-20
Publication date: 2020-11-13
Anticipated expiration: 2038-11-20
Also published as: CN109485128A

Abstract

The invention relates to a method for degrading organic matters based on a platinum nanoparticle homogeneous electrocatalysis system, which is realized by catalytic water decomposition reaction of platinum nanoparticles on the surface under a direct-current electric field. Platinum nano-particles are uniformly dispersed in a solution of an organic matter to be degraded to be used as an electrolyte for electrolysis. The platinum nanoparticles are prepared by a sodium borohydride reduction method, polarization on the surface of the platinum nanoparticles under an electric field is utilized to promote decomposition of water molecules around to generate hydroxyl radicals, and organic dye in water is oxidized and decomposed into carbon dioxide, water and inorganic ions. The homogeneous electrocatalysis method can effectively remove organic matters in the aqueous solution, and has the advantages of mild reaction conditions, simple operation and easy control.

Description

Method for degrading organic matters based on platinum nanoparticle homogeneous electrocatalytic system

Technical Field

The invention relates to the technical field of dye wastewater treatment, in particular to a method for degrading organic matters based on a platinum nanoparticle homogeneous electrocatalysis system.

Background

As the traditional industry in China, the dye industry generates wastewater which has the characteristics of high concentration of mail, complex components, high chromaticity, more difficultly-degraded substances and the like, and becomes a great problem in the field of water treatment. With the increasing emission standard of industrial wastewater, enterprises need to improve the original treatment process or perform advanced treatment and upgrading transformation on biochemical effluent.

The current advanced treatment technology for fuel wastewater mainly comprises a physical-chemical method, an oxidation method, an electrochemical method and the like. The electrocatalytic oxidation method in the electrochemical method has the advantages of simple equipment, high reaction speed and high degradation efficiency, can convert substances which are difficult to be biodegraded into substances or deeply oxidize organic matters into carbon dioxide and water, and has no secondary pollution. The electrocatalytic oxidation process is mainly divided into direct oxidation and indirect oxidation, wherein the direct oxidation is that organic matters directly exchange electrons with oxides on the surface layer of an electrode on the surface of the electrode so as to generate redox reaction, change the molecular structure of the organic matters and achieve the aim of harmlessness or mineralization; the indirect oxidation is to utilize a strong oxidation intermediate generated on the surface of the electrode to attack organic molecules, so that the organic molecules are gradually innoxious and even completely mineralized.

The strong oxidation intermediate generated in the indirect oxidation is most typically represented by hydroxyl radical (. OH), and organic substances can react with. OH in series to divide the organic substances intoThe seed is oxidized until it is completely converted to CO₂And H₂And O. And the OH has high activity and short service life, and organic molecules can contact with OH through a mass transfer process to trigger a reaction. Therefore, the contact area of OH with organic molecules tends to be critical for the rate control of the electrocatalytic oxidation process. In the traditional electrocatalytic oxidation means, OH is only generated on the surface of an electrode, and due to the restriction of a mass transfer process, OH in an adsorbed state on the surface of the electrode cannot be fully contacted with organic molecules, a large amount of OH is wasted due to free radical recombination, and finally the apparent catalytic efficiency is low.

From the above analysis, to improve the performance of electrocatalytic oxidation, it is necessary to increase the probability of contact reaction between the adsorbed OH and organic molecules and improve the utilization rate of OH, so as to correspondingly promote and strengthen the degradation process of organic substances.

Disclosure of Invention

The invention aims to provide a method for treating organic dye wastewater by a homogeneous electrocatalysis system, which is based on hydroxyl radicals generated by catalytic water decomposition reaction of platinum nanoparticles under an electric field, utilizes the high specific surface area of a nano material to increase the contact efficiency of dye molecules and the hydroxyl radicals, and effectively solves the problems in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme: a method for degrading organic matters based on a platinum nanoparticle homogeneous electrocatalytic system comprises the following steps:

uniformly dispersing platinum nano particles into a solution of an organic matter to be degraded, and electrolyzing the solution serving as an electrolyte; the solution of the organic matter contains water and ions for conduction; the platinum nanoparticles catalyze the water decomposition reaction under the action of an electric field to generate hydroxyl radicals, and catalyze and oxidize organic matters to decompose into carbon dioxide, water and inorganic ions.

Further, the platinum nanoparticles are synthesized by a room-temperature sodium borohydride reduction method with PVP as a stabilizer, and are stably suspended in an aqueous solution without sedimentation.

Further, the concentration of the platinum nano-particles in the solution of the organic matter to be degraded is more than or equal to 100 mu g/ml.

Further, the platinum nanoparticles may be replaced with other noble metal catalysts with properties similar to platinum, such as palladium, iridium nanoparticles.

Further, the electrodes used in the electrolysis process are inert electrodes including graphite electrodes and platinum electrodes.

Further, the organic matter is the organic matter in the wastewater, and the platinum nano-particles are uniformly dispersed in the wastewater for electrolysis, so that the wastewater treatment can be completed.

The method for treating organic dye wastewater by the platinum nanoparticle-based homogeneous electrocatalysis system has the following advantages:

1. the hydroxyl radical is produced in situ through the catalytic water decomposition reaction of the platinum nanoparticles dispersed in the reaction system under an electric field, and the contact efficiency of organic molecules and the hydroxyl radical in the solution is effectively increased.

2. Due to the brownian motion of the nano particles, the mass transfer process of the system can be strengthened without stirring;

3. the degradation of organic dye molecules can be realized without depending on electrode reaction, and the service life of the electrode can be prolonged.

Drawings

FIG. 1 shows transmission electron micrographs of platinum nanoparticles (a) and high resolution transmission electron micrographs, (b) XRD patterns, and (c) dynamic light scattering particle size analysis in aqueous solutions and salt solutions.

FIG. 2 is a diagram of an experimental setup for isolating platinum electrode reactions and verifying the effect of catalytic oxidation of organic compounds.

FIG. 3 is a graph showing the relationship between an applied output voltage and a current in a closed loop and a voltage across a reaction vessel.

FIG. 4(a) is a graph of methylene blue degradation rate comparing four cases of no treatment, no electric field with platinum particles, no platinum particles with electric field, and platinum particles with electric field; (b) changing the degradation efficiency of the methylene blue under the applied voltage; (c) the relationship between the methylene blue degradation effect and the voltage across the reaction vessel.

FIG. 5 shows the change of APF intensity of the fluorescent probe with hydroxyl radical as the reaction time increases.

FIG. 6(a) is a schematic diagram of the same method for synthesizing Pt, Pd, Ir and Au nanoparticles with the same size and concentration; (b) ultraviolet-visible absorption spectra of the four nanoparticles; (c) dynamic light scattering particle size distribution of the four types of nanoparticles; (d) the effect of four kinds of nanoparticles on degrading methylene blue; (e-h) ultraviolet-visible absorption spectra of four nanoparticles that change with time during the degradation of methylene blue.

Detailed Description

The invention is further described with reference to the following figures and specific examples.

Example 1

The platinum nano-particles are prepared by a sodium borohydride reduction method, PVP is used as a stabilizer, the particle size of a final product is 10-15 nm, and the platinum nano-particles can be stably dispersed in water and a salt solution.

Weighing 64mg of PVP and 1ml of chloroplatinic acid hexahydrate, mixing the PVP and the chloroplatinic acid hexahydrate, dissolving 22mg of sodium borohydride in 36ml of ice water for later use, dropwise adding the aqueous solution of the sodium borohydride into the round-bottom flask, stirring the mixture at room temperature for 4 hours, and concentrating the obtained platinum nanoparticle product through a 100kDa ultrafiltration tube.

Fig. 1(a) is a TEM image of platinum nanoparticles. It can be seen that the platinum nanoparticles have a relatively uniform size distribution. The lattice fringes in the inset high-resolution transmission electron microscope image were measured to obtain interplanar spacings of 0.19nm and 0.23nm, respectively, corresponding to face-centered cubic platinum (PDF #04-0802) of JCPDS cards. The XRD pattern of fig. 1(b) further demonstrates this result. The platinum particles synthesized by this method have good dispersibility in both water and salt solutions, and as can be seen from FIG. 1(c) for dynamic light scattering, the particle size of the platinum nanoparticles is about 15 nm.

The platinum nanoparticles synthesized by the method have the advantages of uniform size, small particle size and high specific surface area, and are convenient for subsequent surface catalytic reaction. Good stability in aqueous solution and salt solution, and lays a foundation for uniform and stable dispersion in organic dye wastewater.

Example 2

In order to shield the influence of the reaction on the electrode and prove that the degradation of the organic matter can be realized only through the platinum nanoparticles, the double-salt-bridge reaction device shown in fig. 2 is designed, and the catalytic oxidation capability of the platinum nanoparticles under an electric field is proved by using methylene blue as a simulation target organic matter.

Because the voltage at the two ends of the reaction vessel containing the organic dye molecules is smaller than the output voltage, fig. 3 determines that the output voltage in the system is in a linear relationship with the actual voltage and current of the reaction vessel, and further defines the actual parameters of the applied voltage and current required by the platinum nanoparticles to play a catalytic oxidation effect.

FIG. 4(a) shows the effect of platinum nanoparticles on the degradation of methylene blue organic dye molecules at a concentration of 10mg/L under an applied DC electric field with an output voltage of 20V and an actual voltage of 7V. Comparing three conditions of no treatment, no platinum nano-particles only by applying an electric field and no external electric field only by applying platinum nano-particles, the platinum nano-particles and the external electric field can be proved to be necessary conditions for catalyzing the degradation of the methylene blue oxide. Fig. 4 (b) shows that by changing the voltage of the applied electric field from 3V to 20V, the degradation effect of the platinum nanoparticles on methylene blue gradually increases with the increase of the voltage, and the degradation degree of the methylene blue is in a proportional linear relationship with the voltage, as shown in fig. 4 (c), it is proved that the applied electric field is the key for influencing the degradation of the catalytic oxidation methylene blue in the present invention.

The hydroxyl radical fluorescent probe APF is used for detecting the condition that the platinum nanoparticles generate hydroxyl radicals under an electric field, and as can be seen from figure 5, the fluorescence intensity of the fluorescent probe APF is almost unchanged in the two conditions of no platinum nanoparticles and no external electric field, and when the platinum nanoparticles and the external electric field are applied together, the fluorescence intensity of the APF is obviously increased along with time, which indicates that the hydroxyl radicals are generated in a reaction container.

Example 3

In order to further explore the effect of the platinum nanoparticles in degrading organic dye molecule methylene blue, the invention synthesizes other three noble metal nanoparticles by the same method: pd, Ir and Au, and the effect thereof on the degradation of methylene blue was investigated.

Four noble metal nanoparticles with the same concentration (100 mu m/ml, see fig. 6(a) and similar size (about 16nm, see fig. 6 (c)) are selected, the ultraviolet-visible spectrum absorption of the noble metal nanoparticles is shown in fig. 6(b), fig. 6(d) shows that when the applied output voltage is 20V, the degradation concentration is 10mg/L of methylene blue organic dye molecule effect, and the detailed change of the methylene blue ultraviolet-visible absorption spectrum along with time is shown in fig. 6 (e-h).

Example 4

In order to prove that the method of the invention also has catalytic oxidation degradation effect on other organic matters, phenol is selected as another analog target organic matter, and a double-salt bridge device shown in figure 2 is adopted to verify the catalytic oxidation capability of the platinum nanoparticles under an electric field.

Adding 100 mu g/ml platinum nano particles into 10mg/L phenol aqueous solution, uniformly stirring, applying a direct current electric field with the output voltage of 20V and the actual voltage of 7V for electrolysis, and determining the concentration of the residual phenol according to the absorbance of the ultraviolet-visible absorption spectrum at 269 nm. After 2.5h of electrolysis, phenol in the electrolyte was completely degraded.

Example 5

To further determine the effect of platinum nanoparticles on the degradation effect of organic matter, the concentration of platinum nanoparticles in the electrolyte was varied based on the procedure for degrading methylene blue in example 2. Platinum nanoparticles with concentrations of 10, 50, 100, 200. mu.g/ml were added to 10mg/L methylene blue aqueous solution, respectively, and a DC electric field of an actual voltage of 7V was applied. After 30 minutes, the degradation rates of methylene blue were 5%, 35%, 60% and 90%, respectively. The higher the concentration of the platinum nanoparticles is, the better the effect of catalytic oxidation degradation of organic matters is proved, wherein the concentration of the platinum nanoparticles of 100 mug/ml can degrade the organic matters by more than half of the total amount, and the concentration of the platinum nanoparticles in the method of the invention is more than or equal to 100 mug/ml when the solution containing the organic matters is degraded.

Claims

1. A method for degrading organic matters based on a platinum nanoparticle homogeneous electrocatalytic system is characterized by comprising the following steps:

2. The method of claim 1, wherein the platinum nanoparticles are synthesized by a room temperature sodium borohydride reduction method using PVP as a stabilizer, and are stably suspended in an aqueous solution without sedimentation.

3. The method according to claim 1, characterized in that the concentration of the platinum nanoparticles in the solution of the organic substance to be degraded is equal to or greater than 100 μ g/ml.

4. The method of claim 1, wherein platinum nanoparticles are replaced with palladium or iridium nanoparticles.

5. The method of claim 1, wherein the electrodes used in the electrolysis process are inert electrodes.

6. The method according to claim 1, wherein the organic matter is organic matter in wastewater, and the wastewater treatment is completed by uniformly dispersing the platinum nanoparticles in the wastewater and performing electrolysis.