阅读说明：本技术 一种液相中大气压冷等离子体制备氧化石墨烯负载钯的方法 (Method for preparing graphene oxide supported palladium by using liquid-phase atmospheric pressure cold plasma ) 是由 底兰波 张腾达 张秀玲 赵倩 周钰发 于 2021-08-16 设计创作，主要内容包括：本发明属于纳米材料制备技术领域,公开了一种液相中大气压冷等离子体制备氧化石墨烯负载钯的方法。包括配制含有氧化石墨烯粉末和一定浓度的钯前驱体的混合液体；在大气压冷等离子体石英反应器中处理含有氧化石墨烯粉末和钯前驱体的混合液体；对大气压冷等离子体处理后的混合液体进行离心、洗涤、烘干得到氧化石墨烯负载钯催化材料。大气压冷等离子体在液相中只还原钯而不还原氧化石墨烯,简化制备步骤,提升催化性能,节约制备资源。(The invention belongs to the technical field of nano material preparation, and discloses a method for preparing graphene oxide supported palladium by using liquid-phase atmospheric pressure cold plasma. Preparing mixed liquid containing graphene oxide powder and a palladium precursor with a certain concentration; treating mixed liquid containing graphene oxide powder and a palladium precursor in an atmospheric pressure cold plasma quartz reactor; and centrifuging, washing and drying the mixed liquid treated by the atmospheric pressure cold plasma to obtain the graphene oxide supported palladium catalytic material. The atmospheric pressure cold plasma only reduces palladium but not graphene oxide in a liquid phase, so that the preparation steps are simplified, the catalytic performance is improved, and the preparation resources are saved.)

1. A method for preparing graphene oxide supported palladium by using liquid-phase atmospheric pressure cold plasma is characterized by specifically comprising the following steps:

(1) preparing mixed liquid containing graphene oxide powder and a palladium precursor with a certain concentration, wherein the palladium precursor in the mixed liquid is Pd (NO)₃)₂Or PdCl₂In the concentration range of 2.35-7.27 mM;

(2) treating mixed liquid containing graphene oxide powder and a palladium precursor in an atmospheric pressure cold plasma quartz reactor;

(3) and centrifuging, washing and drying the mixed liquid treated by the atmospheric pressure cold plasma to obtain the graphene oxide supported palladium catalytic material, wherein the supported amount of palladium in the catalytic material is 0.1-5.0 wt%.

2. The method for preparing graphene oxide supported palladium by using cold plasma at atmospheric pressure in liquid phase according to claim 1, wherein the step (1) is specifically as follows: weighing 0.1g of graphene oxide powder, putting the graphene oxide powder into a glass bottle, transferring a certain volume of palladium precursor solution into the glass bottle by using a liquid transfer gun, and shaking up.

3. The method for preparing graphene oxide supported palladium by using cold plasma at atmospheric pressure in liquid phase according to claim 1, wherein the step (2) is specifically as follows: pouring mixed liquid containing graphene oxide powder and a palladium precursor into an atmospheric pressure plasma quartz reactor, adjusting the distance between the quartz reactor and an electrode, adjusting the discharge frequency and the discharge voltage of atmospheric pressure cold plasma, introducing gas with certain components, and setting the rotating speed of a magnetic stirrer to treat the mixed liquid.

4. The method for preparing graphene oxide supported palladium by using cold plasma at atmospheric pressure in liquid phase according to claim 1, wherein the step (3) is specifically as follows: pouring the treated mixed liquid into a 50ml centrifuge tube at 7000 r.min^-1Centrifuging for 5min at the rotating speed, pouring out the supernatant, washing and centrifuging for three times by deionized water, and drying for 4h at 100 ℃ in an oven.

5. The method for preparing graphene oxide supported palladium according to claim 3, wherein the atmospheric pressure plasma in the step (2) adopts atmospheric pressure surface dielectric barrier discharge cold plasma, the treated mixed liquid is not in direct contact with the electrode, the liquid surface of the mixed liquid is 2-4mm away from the electrode, and the depth of the mixed liquid is 3-5 mm.

6. The method for preparing graphene oxide supported palladium by using liquid-phase atmospheric pressure cold plasma according to claim 3, wherein the atmospheric pressure cold plasma in the step (2) applies an alternating voltage with the frequency of 8.3-12.3kHz and the sine peak value of 4.0-8.0kV, and the treatment time is 6-12 min.

7. The method for preparing graphene oxide supported palladium according to claim 3, wherein the gas introduced in the step (2) is argon-hydrogen mixed gas, the hydrogen content of the mixed gas is 10-100%, and the total flow rate of the gas is 50-150 ml-min^-1。

8. The method for preparing graphene oxide supported palladium according to claim 1, wherein the palladium precursor in the mixed liquid in the step 1 is Pd (NO)₃)₂。

Technical Field

The invention belongs to the technical field of nano material preparation, and particularly relates to a preparation method of graphene oxide supported palladium (Pd/GO) in a solution.

Background

P-nitrophenol (4-NP) is a common degradation-resistant substance in industrial wastewater and is internationally listed as one of environmental priority pollutants. The 4-NP is reduced into p-aminophenol (4-AP), so that the problem of water resource pollution can be effectively solved, and the reduced product 4-AP can be used in the fields of pesticides, dyes, surfactants, medicines, cosmetics and the like, so that resource recycling is realized. Therefore, the preparation of high-efficiency catalytic materials and the conversion of the pollutant 4-NP into valuable 4-AP become a research hotspot.

The carbon material contains abundant oxygen-containing functional groups such as hydroxyl (OH) and alkoxy (O-C) groups on the surface. These oxygen-containing functional groups can improve the distribution of the metal active component and can act synergistically therewith to increase the catalytic activity. Graphene-based palladium-supported catalytic materials have been widely used for catalytic reduction of p-nitrophenol (4-NP).

The preparation methods of the graphene-based palladium-supported catalytic material are various, such as a chemical reduction method, a hydrogen thermal reduction method and the like. The patent "graphene supported palladium-nickel/cerium oxide nanocomposite, preparation method and ammonia borane catalytic decomposition method" (CN106378150A) discloses that graphene oxide and hexadecyl trimethyl ammonium bromide are dissolved in ultrapure water, after ultrasonic treatment, noble metal salt is added into the system, and sodium borohydride as a reducing agent is rapidly added into the mixed solution under stirring. Finally, absolute ethyl alcohol is used for ultrasonic centrifugal washing for three times, and vacuum drying is carried out to obtain the nano composite material. In the patent "preparation method of graphene supported palladium nanoparticle composite catalyst" (CN111589443A), graphene oxide is dipped in palladium chloride solution, then spray-dried to obtain powder, and then put in H₂And (3) carrying out high-temperature reduction under the atmosphere to obtain palladium-containing graphene powder, and carrying out chemical reduction after impregnation to obtain the graphene supported palladium nanoparticle catalyst. Researchers have developed various preparation methods to obtain high-performance carbon material-supported palladium catalytic materials. Chemical reduction methods, however, require the use of excessive amounts of toxic chemicals; the hydrogen thermal reduction method requires high temperature and high energy consumption, and easily causes Pd nanoparticles to agglomerate, thereby reducing the catalytic performance. It is emphasized that these methods support Graphene Oxide (GO) during the reduction of palladium ionsThe body is reduced to reduced graphene oxide (rGO), which is not beneficial to the promotion of catalytic performance. If a simple and green method can be developed, the GO is not reduced while palladium ions are reduced, and more active defects can be generated, so that the method has important significance.

The plasma is a particle aggregation state with a certain charged particle density and a macroscopic charge neutrality. It is referred to as a fourth state of matter other than solid, liquid and gaseous. Plasmas are generally classified according to thermodynamic equilibrium into non-thermodynamic equilibrium plasmas (cold plasmas), local thermodynamic equilibrium plasmas (hot plasmas), and full thermodynamic equilibrium plasmas (high temperature plasmas). Cold plasma is a typical non-thermodynamic equilibrium system, which T of it_eUp to 1-10eV, and T_gAnd T_iCan approach room temperature and is therefore referred to as a non-thermodynamic equilibrium plasma. There are various ways of generating cold plasma, such as dielectric barrier discharge, glow discharge, corona discharge, etc. Cold plasma is composed of electrons, ions, radicals, excited species, etc., and these active species are widely used in many ways. As disclosed in the patent "method for preparing metal nanoparticles by using atmospheric pressure cold plasma" (CN103008684A), the metal nanoparticles are prepared by reduction using atmospheric pressure dc discharge to generate cold plasma.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for preparing graphene oxide supported palladium in a solution by using atmospheric pressure surface dielectric barrier discharge cold plasma, which does not need any other reducing chemical reagent, does not reduce a graphene oxide carrier while reducing palladium ions, and causes more defects on the surface of graphene oxide, so that the prepared graphene oxide supported palladium shows excellent catalytic reduction p-nitrophenol activity.

The above purpose of the invention is realized by the following technical scheme: a method for preparing graphene oxide supported palladium by using liquid-phase atmospheric pressure cold plasma specifically comprises the following steps:

1. preparing mixed liquid containing graphene oxide powder and a palladium precursor with a certain concentration;

2. treating mixed liquid containing graphene oxide powder and a palladium precursor in an atmospheric pressure cold plasma quartz reactor;

3. and centrifuging, washing and drying the mixed liquid to obtain the graphene oxide supported palladium catalytic material.

Wherein, the step 1 specifically comprises the following steps: weighing 0.1g of graphene oxide powder, putting the graphene oxide powder into a glass bottle, transferring a certain volume of palladium precursor solution into the glass bottle by using a liquid transfer gun, and shaking up.

The step 2 specifically comprises the following steps: pouring mixed liquid containing graphene oxide powder and a palladium precursor into an atmospheric pressure plasma quartz reactor, adjusting the distance between the quartz reactor and an electrode, adjusting the discharge frequency and the discharge voltage of atmospheric pressure cold plasma, introducing gas with certain components, and setting the rotating speed of a magnetic stirrer to treat the mixed liquid.

The step 3 specifically comprises the following steps: pouring the treated mixed liquid into a 50ml centrifuge tube at 7000 r.min^-1Centrifuging for 5min at the rotating speed, pouring out the supernatant, washing and centrifuging for three times by deionized water, and drying for 4h at 100 ℃ in an oven.

The palladium precursor in the step 1 is Pd (NO)₃)₂Or PdCl₂And the concentration range of the palladium precursor in the mixed solution is 2.35-7.27 mM.

In the step 3, the loading amount of palladium in the graphene oxide supported palladium ranges from 0.1 to 5.0 wt%.

In the step 2, the atmospheric pressure plasma adopts atmospheric pressure surface dielectric barrier discharge cold plasma, the treated mixed liquid is not directly contacted with the electrode, the distance between the liquid level and the electrode is 2-4mm, and the depth of the mixed liquid is 3-5 mm.

In the step 2, the atmospheric pressure plasma applies alternating voltage with the frequency of 8.3-12.3kHz and the sine peak value of 4.0-8.0kV, and the solution treatment time is 6-12 min.

The gas introduced in the step 2 is argon-hydrogen mixed gas, the hydrogen content in the mixed gas is 10-100%, and the total flow of the gas is 50-150 ml.min^-1。

Compared with the prior art, the invention has the beneficial effects that: adopting an atmospheric pressure surface dielectric barrier discharge cold plasma technology, treating mixed liquid of a palladium precursor and graphene oxide by using mixed gas of argon and hydrogen as working gas, and preparing a graphene oxide palladium-loaded catalytic material (Pd/GO), wherein the graphene oxide palladium-loaded catalytic material has excellent catalytic reduction activity on p-nitrophenol (4-NP); the atmospheric pressure cold plasma only reduces palladium but not graphene oxide in a liquid phase, so that the preparation steps are simplified, the catalytic performance is improved, and the preparation resources are saved.

Drawings

FIG. 1: GO, Pd/GO-H₂XRD patterns of/Ar-G, Pd/GO and Pd/GO-Ar-L catalytic materials;

FIG. 2: raman spectra of GO carrier and Pd/GO catalytic material;

FIG. 3: XPS energy spectra of GO support and Pd/GO catalytic material (a) C1s and (b) O1 s;

FIG. 4: FT-IR spectrograms of a GO carrier and a Pd/GO catalytic material;

FIG. 5: GO, Pd/GO-H₂Reduction of 4-NP at 400nm with/Ar-G, Pd/GO and Pd/GO-Ar-L_t/A₀A time-varying graph;

FIG. 6: Pd/GO-H₂Reaction kinetics diagrams of reduction of 4-NP by using/Ar-G, Pd/GO and Pd/GO-Ar-L catalytic materials.

Detailed Description

The invention is described in more detail below with reference to specific examples, without limiting the scope of the invention. Unless otherwise specified, the experimental methods adopted by the invention are all conventional methods, and experimental equipment, materials, reagents and the like used in the experimental method can be obtained from commercial sources.

Example 1

Preparing a Pd/GO catalytic material by argon-hydrogen plasma in a liquid phase:

the method for preparing the Pd/GO catalytic material by argon-hydrogen plasma in a liquid phase comprises the following specific steps: first, 1.28 g.L of a mixture was prepared^-1Pd (NO)₃)₂A solution; 0.1g of GO powder is weighed into a glass bottle, and 4ml of prepared Pd (NO) is transferred by using a pipette₃)₂The solution was put into a glass bottle and shaken well for use. The prepared mixed liquid was poured into a quartz reactor (diameter 3cm, depth 4 mm). The height of the quartz reactor was adjusted to make the liquid level 2mm from the electrode, the device was sealed and connected to a circuit, and the discharge frequency was adjusted to 10.3kHz and the discharge voltage was adjusted to 6.0kV using an oscilloscope. Introduction of H₂Mixed gas of/Ar (V)_H2:V_Ar1:1) for 10min, with a gas flow of 100 ml/min^-1. The discharge time is 9min, and the magnetic stirrer is set at 500 r.min^-1. And after the discharging is finished, the power supply is turned off, and the gas circuit is turned off. Pouring the treatment mixed solution into a 50ml centrifuge tube for 7000r min^-1Centrifuge for 5 min. And (4) pouring out the supernatant, washing with deionized water for three times, centrifuging, putting into an oven for drying at 100 ℃ for 4 hours, and recording the prepared sample as Pd/GO. The mass fraction of Pd was 2.0 wt%.

Example 2

Preparing a Pd/GO-Ar-L catalytic material by using argon plasma in a liquid phase:

the liquid phase argon plasma Pd/GO-Ar-L preparation method is similar to the embodiment 1, only the discharge atmosphere is changed into pure argon, and the gas flow is 100 ml/min^-1The prepared sample was designated as Pd/GO-Ar-L. The mass fraction of Pd was 2.0 wt%.

Example 3

Pd/GO-H preparation by argon-hydrogen plasma in gas phase₂the/Ar-G catalytic material:

Pd/GO-H preparation by argon-hydrogen plasma in gas phase₂the/Ar-G catalytic material comprises the following specific steps: weighing 0.1g of GO powder into a sample bottle, and transferring a proper amount of H by using a liquid transfer gun₂PdCl₄The solution was allowed to soak overnight in a glass vial. The impregnated sample was dried in an oven at 120 ℃ for 2 hours and then ready for use. Putting the dried sample into a plate-plate type dielectric barrier discharge device, and introducing H₂Mixed gas of/Ar (V)_H2:V_Ar1:1) for 10min, with a gas flow of 100 ml/min^-1The discharge frequency was 11.8kHz, and the discharge voltage was 11.0 kV. The discharge time is 6min, and the treated sample is recorded as Pd/GO-H₂Ar-G. The mass fraction of Pd was 2.0 wt%.

XRD pattern analysis:

as can be seen in fig. 1, the GO sample shows a sharp diffraction peak at 2 θ ═ 11 °, which is a characteristic diffraction peak of the GO (001) crystal plane. The Pd/GO sample was prepared by argon-hydrogen plasma in the liquid phase, and the characteristic diffraction peak shifted to 12.4 ° to the right at 2 θ ═ 11 °, which is due to the enhancement of surface defects by plasma treatment (as can be confirmed by Raman results in fig. 2), and the characteristic diffraction peak of reduced graphene oxide (rGO) was not detected, as in the Pd/GO-Ar-L sample prepared by argon plasma in the liquid phase. While argon-hydrogen plasma in gas phase is used for preparing Pd/GO-H₂For the/Ar-G sample, a characteristic diffraction peak of rGO was observed at 24.8 ° 2 θ. It can also be seen from the figure that the argon-hydrogen plasma in the liquid phase prepares Pd/GO sample and the argon-hydrogen plasma in the gas phase prepares Pd/GO-H₂and/Ar-G, wherein a more obvious diffraction peak can be observed at the 2 theta of 40.2 degrees, and corresponds to a face-centered cubic crystal structure Pd (111) crystal face (PDF # 01-075-6724). And the Pd/GO-Ar-L sample is prepared by argon plasma in the liquid phase, namely the characteristic diffraction peak of rGO does not appear, and the characteristic diffraction peak of metal Pd does not appear.

Raman spectrum analysis:

the surface structures and defects of GO and Pd/GO are studied by Raman spectroscopy, and the results are shown in FIG. 2. Both samples were at approximately 1348 and 1573cm^-1Two distinct spectral peaks appear, corresponding to the D and G bands of GO, respectively. The G band peak is due to sp in the 2D hexagonal lattice of graphene²Tangential vibration of carbon atoms, while the D band is due to graphene sp³The existence of defects. Is usually represented by_D：I_GTo reflect the defect density of the carbon material, the higher the value, the higher the defect density. Compared with GO, the intensity of the G band of Pd/GO is reduced, and the intensity of the D band is increased, which shows that the liquid-phase argon-hydrogen plasma can cause GO to generate more defects, and the defects are consistent with the shift result of the characteristic diffraction peak of GO in XRD.

XPS spectroscopy analysis:

carbon and oxygen species on the GO and Pd/GO surfaces were studied using X-ray photoelectron spectroscopy (XPS) and the results are shown in fig. 3. FIG. 3a is the XPS energy spectrum of C1s in GO and Pd/GO. For two samplesThe peak of C1s is subjected to peak-splitting fitting to obtain four peaks, and deconvolution peaks centered on binding energies of 284.65, 286.82, 288.30 and 289.70eV respectively correspond to C-C, C-O (C-O-C), C ═ O and O-C ═ O functional groups. In addition, the peaks of the C1s energy spectrum of the plasma prepared Pd/GO samples were not significantly changed compared to the GO support, indicating that the oxygen-containing functional groups on the GO surface were not destroyed by the plasma treatment. These results are consistent with XRD results. FIG. 3b is XPS energy spectrum of O1s in GO and Pd/GO. As can be seen, the deconvolution peaks centered at the binding energies of 530.97, 531.77, 532.60, and 533.33eV for the two samples correspond to the O-C ═ O, C-OH, and C-O-C functional groups, respectively. In addition, as can be seen from FIG. 3b, the Pd/GO sample retains more oxygen-containing functional groups such as alkoxy (C-O) and hydroxyl (O-H) compared with the peak of the O1s spectrum of GO, which also represents the Ar/H in liquid phase₂The characteristic of the GO support that is not reduced by the plasma.

FT-IR spectral analysis:

FIG. 4 is FT-IR spectra of GO and Pd/GO. As can be seen, GO samples were at 3405 and 1617cm^-1There is a distinct absorption peak, which corresponds to the stretching vibration of O-H. At 1720cm^-1The absorption peak at (b) corresponds to C ═ O carbonyl stretching vibration in COOH. In addition, other functional groups of GO can be observed, such as C-O (1051 cm)^-1)，C-O-C(1220cm^-1) And O ═ C-O (1402 cm)^-1). The peak absorption intensity of the oxygen-containing functional groups in the Pd/GO samples is reduced little compared to the GO support, with more alkoxy (C-O) and hydroxyl (O-H) groups. This is due to the liquid phase Ar/H₂The plasma preparation did not destroy the oxygen-containing functional groups, consistent with the XPS results.

And (3) analysis of catalytic activity:

FIG. 5 is a graph of the absorbance at 400nm as a function of time for catalytic reduction of 4-NP. As can be seen from the figure, under the condition of only adding GO, the absorption peak at 400nm after 200s of reaction is not obviously reduced, and the GO is proved to have almost no reaction activity. Pd/GO-H₂the/Ar-G and Pd/GO-Ar-L samples show certain activity in the reaction process. Pd/GO prepared by argon-hydrogen plasma in the liquid phase shows excellent catalytic activity, and almost completely reacts after 150 seconds.

In order to more intuitively embody the activities of the three samples,the kinetics of the catalytic reduction of 4-NP was studied. The absorbance data at 400nm of FIG. 5 was taken as-ln (A)_t/A₀) The time t is plotted and a linear fit is made. As shown in fig. 6, the slope is calculated from the fit line and the apparent rate constant k of the reaction is obtained. Pd/GO-Ar-L and Pd/GO-H₂The k values of the 4-NP catalyzed and reduced by/Ar-G are 0.579 and 0.517min respectively^-1K of Pd/GO is 1.394min^-1. The k of Pd/GO is about Pd/GO-Ar-L and Pd/GO-H₂2.4 and 2.7 times of/Ar-G.

And (4) conclusion:

in conclusion, in the liquid phase, the argon plasma cannot reduce palladium ions and graphene oxide, and the activity is poor. The preparation method of argon-hydrogen plasma in gas phase has stronger reducing capability, reduces the GO carrier while reducing palladium ions, reduces oxygen-containing functional groups on the carrier, reduces the capability of the carrier for adsorbing 4-NP, and has poorer activity. According to the preparation method of the argon-hydrogen plasma in the liquid phase, the GO carrier is not reduced while palladium ions in the solution are reduced, more active defect sites are generated on the surface of the carrier, and the activity of catalytic reduction of 4-NP is improved.

The embodiments described above are merely preferred embodiments of the invention, rather than all possible embodiments of the invention. Any obvious modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the spirit and scope of the present invention.