CN114634235A

CN114634235A - Application of polyaniline embedded Pt/CNT (carbon nanotube) based catalyst in treatment of Cr (VI)

Info

Publication number: CN114634235A
Application number: CN202210273751.5A
Authority: CN
Inventors: 郑寿荣; 余乐; 许昭怡; 龙莉; 郑长龙; 孙玉菡
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2022-03-19
Filing date: 2022-03-19
Publication date: 2022-06-17

Abstract

The invention discloses application of a polyaniline-embedded Pt/CNT (carbon nano tube) based catalyst in treatment of Cr (VI). The application method comprises the following steps: s1, adjusting the pH value of the water body: adjusting the pH value of the water body containing Cr (VI) pollutants to 2.0-3.0; s2, applying polyaniline embedded Pt/CNT based catalyst: adding polyaniline embedded Pt/CNT-based catalyst powder into a water body containing Cr (VI) pollutants, and performing S3 hydrogenation reaction: introducing nitrogen into the water body for 2-3 h, and then introducing hydrogen into the water body to perform a reduction reaction of Cr (VI). The catalyst is combined by adopting an immersion method and an ammonium persulfate oxidation method, firstly, precious metal is deposited on the surface of the carbon nano tube, and then a layer of polyaniline is coated on the surface of the carbon nano tube. The material shows good activity and stability in the reaction of liquid phase catalytic reduction of Cr (VI), can effectively remove or reduce the toxicity of Cr (VI), prolong the service life of the catalyst, and can effectively improve the catalytic activity by regulating the thickness of the aniline embedding layer.

Description

Application of polyaniline embedded Pt/CNT (carbon nanotube) based catalyst in treatment of Cr (VI)

Technical Field

The invention relates to the technical field of liquid phase catalysis and industrial wastewater treatment, in particular to application of a polyaniline-embedded Pt/CNT (carbon nanotube) -based catalyst in Cr (VI) treatment.

Background

With the development of industry, heavy metal pollution is attracting people's attention, wherein the middle chromium pollution from the sewage of chromium-containing ore processing, metal surface treatment, leather tanning and printing and dyeing industry becomes an important environmental pollution problem. Chromium in industrial wastewater is mainly a hexavalent compound, which is a strong mutagenic substance, and skin contact may cause allergic inhalation, may cause carcinogenesis, and is easily absorbed by the human body, and it may invade the human body through the digestive tract, respiratory tract, skin and mucous membrane. Cr (vi) is also characterized as a persistent environmental hazard, with excess (over 10ppm) hexavalent chromium being lethal to aquatic life. Chromium is often present in aqueous environments in the form of hexavalent and trivalent chromium, both of which are harmful to human health, whereas hexavalent chromium is about 100 times more toxic than trivalent chromium.

The currently common method for removing hexavalent chromium in industrial wastewater is a chemical precipitation method, which firstly converts hexavalent chromium into trivalent chromium by chemical reduction and then removes the trivalent chromium precipitate. In order to overcome the defect of higher cost of the traditional method and improve the environmental friendliness of the removal method, reduction of zero-valent iron, photocatalytic reduction and the like provide multiple approaches for treatment of hexavalent chromium. The method utilizes hydrogen as a reducing agent, adopts heterogeneous catalysis in which a solid catalyst is dispersed in a pollutant solution at normal temperature and normal pressure, and has the characteristics of easy operation, high efficiency and cleanness, and no secondary pollution because products are products and water.

The important part in catalytic hydrogenation is catalyst, the embedded catalyst is a composite material of a load type material which adopts an embedding strategy to solve the problem of inactivation, and the active component of the catalyst is coated with a protective layer and then consists of three parts of a carrier, noble metal and an embedding layer. Because of the protection of the coating layer, the direct contact of the core metal with reactants and reaction media is avoided, so that the poisoning of active components and the loss of noble metals can be prevented. The wrapping layer of the embedded catalyst is usually made of polymer, carbon-based and silicon-based materials, wherein the organic high molecular polymer can improve the adsorption and complexation capacity through functional group modification and has good electrochemical performance; the carbon-based material has the characteristics of good conductivity, large specific surface area and unique interaction with metal particles; the silicon-based material has the advantages of easily-regulated structure and pore channel condition. Since the noble metal cannot be in direct contact with the reaction medium, the activation of hydrogen in the catalytic hydrogenation process can be ensured only by electron transfer of the encapsulating layer. Therefore, the polymer and the carbon-based material are preferably used for the embedded layer of the embedded catalyst in the catalytic hydrogenation.

Disclosure of Invention

In view of the problems pointed out by the background technology, the invention provides an application of a polyaniline embedded Pt/CNT-based catalyst in treatment of Cr (VI).

In order to solve the technical problems, the technical scheme of the invention is as follows:

the application of the polyaniline-embedded Pt/CNT-based catalyst in Cr (VI) treatment comprises the following steps:

s1, adjusting the pH value of the water body:

adjusting the pH value of the water body containing Cr (VI) pollutants to 2.0-3.0;

s2, applying polyaniline embedded Pt/CNT based catalyst (Pt/CNT @ PANI):

adding polyaniline embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) powder into a water body containing Cr (VI) pollutants,

s3, hydrogenation:

introducing nitrogen into the water body for 2-3 h, and then introducing hydrogen into the water body to perform a reduction reaction of Cr (VI).

Description of the drawings: according to the invention, polyaniline-embedded Pt/CNT is used as a catalyst, the catalyst is prepared by embedding supported carbon-based noble metal Pt in an organic high polymer polyaniline layer, activating hydrogen by using noble metal to assist the self redox cycle of polyaniline to promote the oxidation reduction of hexavalent chromium with high oxidation potential, protecting the noble metal by the embedded layer to prevent the loss of the noble metal and ensure high stability, and the technical problems of the falling of active components of the catalyst, the inactivation of poison and the like are solved. The catalyst has remarkable activity and stability in Cr (VI) liquid phase catalytic reduction reaction through tests.

Further, in the above scheme, in step S2, the dosage of the polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) is 0.05 to 0.20 g/L.

Further, in the scheme, the temperature of the hydrogenation reaction is 273-328K, the flow rate of nitrogen and hydrogen is 100-200 mL/min, and the time of the reduction reaction is 4-5 h.

Further, in the above scheme, the preparation method of the polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) is as follows:

s2-1, preparing a precursor Pt/CNT:

taking 0.88-2.65 mL of chloroplatinic acid with the concentration of 10.0g/L and purified 1.0g of CNT into 30-50 mL of water, stirring for 4-5 h, evaporating in a water bath at 80-90 ℃, introducing nitrogen, roasting for 4-6 h at 250-350 ℃, introducing hydrogen, and reducing for 2-3 h at 200-300 ℃ to obtain a precursor Pt/CNT;

s2-2, coating polyaniline:

dispersing the precursor Pt/CNT in an aqueous solution containing hydrochloric acid and aniline, stirring at a low temperature, slowly dropwise adding ammonium persulfate until the solution turns green, keeping the low temperature for 10-12 h, washing with water and drying to obtain the Pt-based catalyst (Pt/CNT @ PANI) with the polyaniline-coated layer.

Description of the drawings: according to the catalyst, carbon nano tubes are used as carriers to load noble metals, polyaniline is used as an embedding layer, and the polyaniline is formed by chemical self-polymerization of aniline and is coated on the surfaces of the noble metals and the carbon nano tubes, so that the polyaniline-embedded packaged noble metal catalyst, namely the polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI), can be obtained. The polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) is used for liquid-phase catalytic reduction of Cr (VI) in a water body, the polyaniline-embedded layer can adsorb and complex heavy metal ions and reduce the heavy metal ions with high oxidation potential, and compared with other embedded layers, due to the modification of functional groups of polymers, the material surface has better hydrophilicity, can promote the adsorption of anionic pollutant hexavalent chromium in an aqueous solution and reduce partial hexavalent chromium, and in addition, an embedded structure effectively inhibits the inactivation phenomenon of noble metals and shows higher stability.

According to the polyaniline embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) prepared according to the proportion, the weight of the noble metal accounts for about 0.3-1.0 wt.% of the total weight of the precursor Pt/CNT.

Further, in the scheme, in the step S2-2, the ratio of aniline to the precursor Pt/CNT is 1.0-10 mL: 1 g. Can ensure that the carbon nano tube can be uniformly coated with a polyaniline embedded layer with the thickness of about 8-20 nm.

Further, in the scheme, in the step S2-2, the concentration of the ammonium persulfate solution is 150-200 g/L, the dosage is 50-60 mL, and the ammonium persulfate is used as an oxidizing agent to promote the polymerization of aniline.

Further, in the above scheme, in the step S2-2, the concentration of the hydrochloric acid solution is 0.5-1.0M, and the amount is 10-20 mL; the total volume of the aqueous solution was 200 mL. Aniline is capable of undergoing chemical auto-polymerization under acidic conditions.

Further, in the above scheme, in step S2-2, the low-temperature maintaining temperature is-10 ℃ to 0 ℃, and the low-temperature condition ensures that the polyaniline can uniformly embed the carrier and the noble metal.

Further, in the above scheme, in the step S2-2, the concentration of the hydrochloric acid solution is 0.5-1.0M, and the amount is 10-20 mL; the total volume of the aqueous solution was 200 mL.

Compared with the prior art, the beneficial effects of the invention are embodied in the following points:

firstly, the polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) synthesized by the method has certain mechanical strength and shows obvious stability in a liquid-phase catalytic hydrogenation reaction.

Secondly, compared with the supported noble metal material, the polyaniline embedding material can adsorb and oxidize hexavalent chromium under the condition of no hydrogen, and does not remove hexavalent chromium under the condition of no hydrogen of the supported noble metal catalyst, and the conductivity of polyaniline ensures the activation of hydrogen by the noble metal, thereby effectively combining self oxidation reduction and catalytic reduction of hexavalent chromium and improving the catalytic activity.

Thirdly, compared with the polyaniline embedded material without precious metals, the polyaniline embedded type Pt/CNT based catalyst (Pt/CNT @ PANI) can be subjected to catalytic hydrogenation reduction, through the electron transfer of polyaniline, the precious metals can effectively activate hydrogen to reduce oxidized polyaniline, and assist in catalytic reduction of hexavalent chromium, and for the polyaniline embedded material without precious metals, the removal effect cannot be improved by introducing hydrogen.

Fourthly, compared with the supported catalyst, the polyaniline embedded structure can fix the noble metal, isolate the direct contact with the reaction environment, and effectively prevent the deactivation caused by the shedding and poisoning of the noble metal component, so the embedding strategy has obvious effect on improving the stability of the catalyst.

Fifthly, the polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) synthesized by the method is used for reducing Cr (VI) in a water body, can effectively remove or reduce the toxicity of the Cr (VI), and is high in removal efficiency and high in speed. And no special equipment condition is needed, the wastewater does not need to be pretreated, and the pretreatment can be carried out at normal temperature and normal pressure.

Sixth, the polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) of the present invention improves the cycle utilization rate and saves the amount of noble metals, and has good economic and environmental benefits.

Drawings

FIG. 1 is a transmission electron micrograph of Pt/CNT @ PANI and Pt/CNT series;

wherein (a) is Pt/CNT, (b) is Pt/CNT @ PANI-1.0, (c) is Pt/CNT @ PANI-2.0, (d) is Pt/CNT @ PANI, (e) is Pt/CNT @ PANI-10.0, and (f) is CNT @ PANI;

FIG. 2 is an XRD pattern of Pt/CNT @ PANI and Pt/CNT series;

FIG. 3 is an XPS spectrum of Pt/CNT @ PANI series:

FIG. 4 is a Raman spectrum of the Pt/CNT @ PANI series;

FIG. 5 is a plot of the adsorption and desorption isotherms of N2 for the Pt/CNT @ PANI series;

FIG. 6 is a graph of pore size distribution for the Pt/CNT @ PANI series;

FIG. 7 is a graph showing PZC measurements of Pt/CNT @ PANI and Pt/CNT,

FIG. 8 is a graph of the reaction of different catalysts for Cr (VI) catalytic hydrogenation reduction;

FIG. 9 is a graph of the reaction of Pt/CNT @ PANI with Cr (VI) catalytic hydrogenation reduction at various catalyst loadings;

FIG. 10 is a graph of the initial activity of Pt/CNT @ PANI for Cr (VI) catalytic hydrogenation reduction at various catalyst loadings;

FIG. 11 is a graph of the reaction of Pt/CNT @ PANI at different initial concentrations of Cr (VI) with Cr (VI) catalytic hydrogenation reduction;

FIG. 12 is a L-H model fit plot of Pt/CNT @ PANI at different initial Cr (VI) concentrations for Cr (VI) catalytic hydrogenation reduction;

FIG. 13 is a graph of the cycling reaction of Pt/CNT @ PANI with Cr (VI) catalytic hydrogenation reduction;

FIG. 14 is a graph of a cycling reaction of Pt/CNTs subjected to Cr (VI) catalytic hydrogenation reduction;

FIG. 15 is a graph of the reaction of Pt/CNT @ PANI of example 1 with Cr (VI) catalytic hydrogenation reduction;

FIG. 16 is a graph of the reaction of Pt/CNT @ PANI for Cr (VI) catalytic hydrogenation reduction for catalysts prepared with different amounts of aniline;

FIG. 17 is a bar graph of the initial activity of Pt/CNT @ PANI catalyst reduction reactions for Cr (VI) catalytic hydrogenation for different amounts of aniline used to prepare the catalyst.

Detailed Description

Example 1

Preparation of polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI):

s2-1, preparing a precursor Pt/CNT:

taking 0.88mL of chloroplatinic acid with the concentration of 10.0g/L and purified 1.0g of CNT in 30mL of water, stirring for 4h, evaporating to dryness in a water bath at 80 ℃, introducing nitrogen, roasting for 4h at 250 ℃, and introducing hydrogen to reduce for 2h at 200 ℃ to obtain a precursor Pt/CNT;

s2-2, coating polyaniline:

dispersing a precursor Pt/CNT in an aqueous solution containing hydrochloric acid and aniline, and stirring at a low temperature, wherein the ratio of the aniline to the precursor Pt/CNT is 1.0 mL: 1g, the concentration of the hydrochloric acid solution is 0.5M, and the dosage is 10 mL; the total volume of the aqueous solution is 200 mL; and slowly dropwise adding ammonium persulfate, wherein the concentration of the ammonium persulfate solution is 150g/L, the using amount is 50mL, till the solution turns green, keeping the solution at-10 ℃ for 10 hours, washing with water and drying to obtain the Pt-based catalyst (Pt/CNT @ PANI) with the polyaniline coating layer.

Example 2

Preparation of polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI):

s2-1, preparing a precursor Pt/CNT:

taking 1.85mL of chloroplatinic acid with the concentration of 10.0g/L and purified 1.0g of CNT in 40mL of water, stirring for 4h, evaporating to dryness in a water bath at 85 ℃, introducing nitrogen, roasting for 5h at 300 ℃, introducing hydrogen, and reducing for 2h at 280 ℃ to obtain a precursor Pt/CNT;

the transmission electron micrograph of Pt/CNT is shown in FIG. 1a, and it can be seen that the noble metal particles are uniformly dispersed on the carbon material, and statistically, the average particle size of the noble metal is about 8.72 nm.

S2-2, coating polyaniline:

dispersing a precursor Pt/CNT in an aqueous solution containing hydrochloric acid and aniline, and stirring at a low temperature, wherein the ratio of the aniline to the precursor Pt/CNT is 6 mL: 1g, the concentration of the hydrochloric acid solution is 0.8M, and the dosage is 15 mL; the total volume of the aqueous solution is 200 mL; and slowly dropwise adding ammonium persulfate, wherein the concentration of the ammonium persulfate solution is 180 g/L, the using amount is 50mL, keeping the solution at the temperature of minus 6 ℃ for 10 hours, washing with water and drying to obtain the Pt-based catalyst (Pt/CNT @ PANI) with the polyaniline coating layer.

Example 3

Preparation of polyaniline-embedded Pt/CNT-based catalyst (Pt/CNT @ PANI):

s2-1, preparing a precursor Pt/CNT:

taking 2.65mL of chloroplatinic acid with the concentration of 10.0g/L and purified 1.0g of CNT in 50mL of water, stirring for 5h, evaporating to dryness in a water bath at 90 ℃, introducing nitrogen, roasting at 350 ℃ for 6h, and introducing hydrogen, and reducing at 300 ℃ for 3h to obtain a precursor Pt/CNT;

s2-2, coating polyaniline:

dispersing a precursor Pt/CNT in an aqueous solution containing hydrochloric acid and aniline, and stirring at a low temperature, wherein the ratio of the aniline to the precursor Pt/CNT is 10 mL: 1g, the concentration of the hydrochloric acid solution is 1.0M, and the dosage is 20 mL; the total volume of the aqueous solution is 200 mL; and slowly dropwise adding ammonium persulfate, wherein the concentration of the ammonium persulfate solution is 200g/L, the using amount is 60mL, keeping the solution at 0 ℃ for 12 hours until the solution becomes green, washing with water and drying to obtain the Pt-based catalyst (Pt/CNT @ PANI) with the polyaniline coating layer.

Example 4

The polyaniline-embedded Pt/CNT-based catalyst prepared in example 2 is used for treating Cr (VI) by the following method:

s1, adjusting the pH value of the water body:

adjusting the pH value of the water body containing Cr (VI) pollutants to 2.0;

s2, applying polyaniline embedded Pt/CNT based catalyst (Pt/CNT @ PANI):

adding 0.05g/L polyaniline embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) powder into a water body containing Cr (VI) pollutants,

s3, hydrogenation:

introducing nitrogen into the water body for 2 hours, then introducing hydrogen into the water body, and carrying out reduction reaction on Cr (VI), wherein the reaction temperature is 273K, the flow rates of the nitrogen and the hydrogen are 100mL/min, and the reduction reaction time is 4 hours.

Example 5

s1, adjusting the pH value of the water body:

adjusting the pH value of the water body containing Cr (VI) pollutants to 3.0;

s2, applying polyaniline embedded Pt/CNT based catalyst (Pt/CNT @ PANI):

adding 0.20g/L polyaniline embedded Pt/CNT-based catalyst (Pt/CNT @ PANI) powder into a water body containing Cr (VI) pollutants,

s3, hydrogenation:

introducing nitrogen into the water body for 3 hours, then introducing hydrogen into the water body, and carrying out reduction reaction on Cr (VI), wherein the reaction temperature is 328K, the flow rate of the nitrogen and the hydrogen is 200mL/min, and the reduction reaction time is 5 hours.

Example 6

Preparation of polyaniline-embedded carbon nanotube material CNT @ PANI:

the difference from the example 2 is that: CNT is used instead of Pt/CNT.

Example 7

Preparation of a hetero-nitrogen-carbon-embedded platinum-based carbon nanotube material Pt/CNT @ CN:

the difference from the example 2 is that: in step S2-2, after washing with water and drying, the obtained solid is calcined for 6h at 850 ℃ by introducing nitrogen gas to form the hetero-nitrogen-carbon embedded platinum-based catalyst Pt/CNT @ CN.

FIG. 1 is a transmission electron micrograph of Pt/CNT @ PANI and Pt/CNT series: (a) Pt/CNT, (b) Pt/CNT @ PANI-1.0, (c) Pt/CNT @ PANI-2.0, (d) Pt/CNT @ PANI, (e) Pt/CNT @ PANI-10.0, (f) CNT @ PANI;

from fig. 1d, it can be seen that the pore structure is obvious, the particles are uniformly dispersed, and the outer surface of the carbon material is uniformly coated, and the average particle size of the noble metal is about 7.38nm and the thickness of the coating is 13.32nm according to the particle size statistical calculation.

Hollow structures and coatings can be seen on a transmission electron micrograph of CNT @ PANI (FIG. 1f), and the average thickness of the resulting coating is counted to be 10.69 nm.

Experimental data

1. And (3) comparing the material properties:

FIG. 2 is an XRD pattern of Pt/CNT @ PANI series. The diffraction peak of 26 degrees is assigned as the (002) crystal face of the graphite structure of the porous carbon material, and two broad diffraction peaks distributed at 40o1 and 46o1 are characteristic peaks of Pt particles with a face-centered cubic (FCC) structure. Only the Pt/CNT spectrum shows an obvious Pt diffraction peak, and the polyaniline embedded catalyst Pt/CNT @ PANI series spectrum does not have an obvious metal platinum diffraction peak and only has a stronger carbon diffraction peak, which indicates that the particle Pt is wrapped. A clearer diffraction peak appears at 25.2 ° 2 θ, which may be attributed to the polyaniline polymer backbone, while the characteristic peaks of PANI gradually overlap those of CNTs near 25o and 26 o. By contrast, after the polyaniline functionalized carbon nanotube, the XRD spectrogram of the obtained embedded material is basically the same as that of the load material. It can be seen that the polyaniline coating has no effect on the structure of the internal metal-supported catalyst.

FIG. 3 is a XPS peak profile of N for the Pt/CNT @ PANI series. The N1s nuclear spectrum shows that most of the nitrogen atoms exist in the form of amine (-NH-) centered at 399.3eV, i.e., in the amide or benzenoid amine group. While the other two weak peaks reveal that some nitrogen atoms are present as positively charged nitrogen (N +) centered at 400.7eV and as imine (═ N-) centered at 398.1 eV. In addition, the peak separation results of C1s show that the binding energies of 287.5eV and 285.6 eV correspond to C ═ N and C-N in PANI respectively, and the peak separation of carbon and nitrogen shows the formation of polyaniline on the surface of the carbon material.

FIG. 4 is a Raman spectrum of the Pt/CNT @ PANI series. Both materials show two peaks at 1336 and 1608cm-1, assigned to the D-band and G-band of the CNT support, respectively, one associated with the vibration of carbon atoms, disordered graphite (D-band), and the other due to the vibrating two-dimensional hexagonal lattice of sp2 bonded carbon atoms (G-band). Distinct characteristic peaks for PANI, corresponding to the C-N-C non-planar deformation mode of PANI and the deformation mode of the protonated amine groups, were observed at 420 and 510-600cm-1 for the cladding materials Pt/CNT @ PANI and CNT @ PANI. Further 810cm-1 are units belonging to the carbon-carbon and carbon-hydrogen bond benzenoid type, 1160 and 1400cm-1 are ascribed to the planar bending mode and carbon-hydrogen bond vibrational mode of the quinoid unit doped polyaniline, while 1480cm-1 may be derived from a quinoid benzenoid unit in the C ═ C tensile mode. The band at 1600cm-1 is associated with the C-N stretch mode of the quinone and benzene units. Particularly, the introduction of Pt shows that the PANI peak in Pt/CNT @ PANI is shifted to a higher wave number, which indicates that a certain strong interaction exists between Pt/CNT and-NH-group of PANI, and the strong interaction is favorable for electron transfer, thereby improving the catalytic activity.

FIG. 5 is a graph showing the adsorption and desorption isotherms of N2 of Pt @ N-CMK-3 and Pt/CNT @ PANI series, and it can be seen that the catalyst has an H1 hysteresis loop in a relative pressure (P/P0) range of 0.40-0.85, which conforms to a typical IV adsorption-desorption isotherm and shows that all the catalysts synthesized by the present invention have a mesoporous structure. After the polyaniline polymer is coated in the carbon nano tube, the surface area of the carbon nano tube @ polyaniline is remarkably reduced to 19.15m2 g < -1 >. After Pt nanoparticle-loaded PANI-CNT support, the BET specific surface area of the resulting Pt/CNT @ PANI sample was further reduced compared to the carbon nanotube support. In addition, as can be seen from the pore size distribution diagram of the catalyst in FIG. 6, the pore size of the catalyst ranges from 2 to 12nm, which also illustrates the mesoporous nature of the catalyst.

FIG. 7 is a zero-potential titration curve of Pt/CNT @ PANI and Pt/CNT, after the material is coated with polyaniline coating, the isoelectric point PZC is increased from 2.15 to 5.20, which shows that the amino functional group of polyaniline can improve the surface chemical property of the material and is beneficial to electrostatic adsorption of anions.

Comprehensive series of characteristics can show that the synthesized catalyst has a polyaniline coating and does not have exposed noble metal particles, and the adsorption reduction effect of polyaniline and hexavalent chromium increases the advantage of high-efficiency removal for reducing hexavalent chromium by catalytic hydrogenation.

2. And (5) treatment effect comparison:

(1) in the same manner as the treatment method of example 5, the best effect of Pt/CNT and Pt/CNT @ PANI can be seen in FIG. 8 by comparing the treatment results of Cr (VI) with the Pt/CNT @ PANI treatment results of example 2 using the CNT @ PANI and Pt/CNT @ CN prepared in examples 6 and 7.

(2) Liquid phase catalytic reduction of cr (vi) was carried out using the catalyst prepared in example 1. The catalyst used Pt/CNT @ PANI with concentrations of 0.05g/L, 0.10g/L, 0.15g/L, 0.20g/L, and an initial concentration of Cr (VI) of 0.8mM, and the same treatment method as in example 4 was used. As shown in FIG. 9, after nitrogen gas is introduced for two hours, the surface layer of polyaniline adsorbs and reduces hexavalent chromium to reach equilibrium, and when the concentration of the catalyst is 0.15g/L, the hydrogen gas is introduced to react for 90min, and then Cr (VI) is basically and completely removed. The initial activity histogram is shown in FIG. 10, and the initial activity of the catalyst is basically maintained at 35mMgCat-1h-1, which indicates that no mass transfer resistance exists in the reaction system.

(3) Liquid phase catalytic reduction of cr (vi) was carried out using the catalyst prepared in example 1. The catalyst was Pt/CNT @ PANI at a concentration of 0.10g/L and the initial concentrations of Cr (VI) were 0.6mM, 0.8mM, 1.0mM, and 1.2mM, respectively, according to the same treatment method as in example 4. The reaction curve is shown in FIG. 11. The model fit of fig. 12 shows that catalyst activity and concentration are found to be linear, indicating that this reaction is consistent with adsorption-controlled reactions.

(4) The embedded catalyst Pt/CNT @ PAN-10.0 and the supported catalyst Pt/CNT with substantially the same noble metal content were prepared according to the catalyst preparation method in example 1 and applied to the cyclic reaction of liquid phase catalytic reduction of Cr (VI). The catalyst concentration was 0.10g/L, and the initial concentration of Cr (VI) was 0.8mM, and the same treatment as in example 4 was carried out by washing the product Cr (III) reduced by Cr (VI) with hydrochloric acid, and carrying out the regeneration cycle reaction 5 times. The results of the cycling reaction of the polyaniline-embedded catalyst Pt/CNT @ PAN-10.0 are shown in FIG. 13, and show that stable catalytic activity is maintained during repeated use. Although the initial activity is reduced during secondary use, this may be due to strong elution of the polyaniline coating by hydrochloric acid during elution and regeneration of hexavalent chromium, or to repeated redox of polyaniline and hexavalent chromium leading to polymer chain breakage, and then the inner polyaniline coating is stabilized due to interaction with the inner precious metal carrier Pt/CNT, so that the initial activity remains relatively stable after three and four cycles. The results of the cyclic reaction of the supported catalyst Pt/N-CMK-3 are shown in FIG. 14, the material was greatly deactivated in each cycle, and the deactivation rate of the initial activity at 10min was 92.60% in the 5 th reaction. Thus, the polyaniline-embedded noble metal catalyst Pt/CNT @ PANI shows high stability in the liquid phase catalytic reduction Cr (VI) reaction due to its embedded structure.

Comparative example 1

The polyaniline-embedded Pt metal catalyst Pt/CNT @ PANI is prepared according to the catalyst preparation method in the embodiment 1 and applied to liquid phase catalytic reduction of Cr (VI), and the reaction condition of introducing hydrogen is that nitrogen is introduced for 2 hours and then hydrogen is switched. The reaction curve is shown in FIG. 15. When no hydrogen is introduced, the material reaches adsorption reduction balance within about two hours, and at the moment, the catalytic reduction of hexavalent chromium can be accelerated by introducing the hydrogen.

Comparative example 2

The polyaniline-embedded Pt metal catalysts Pt/CNT @ PANI and CNT @ PANI are prepared according to the preparation method of the catalyst in the embodiment 1, the polyaniline-embedded Pt metal catalysts Pt/CNT @ PANI and the CNT @ PANI are applied to liquid phase catalytic reduction of Cr (VI), the reaction condition of introducing hydrogen is that nitrogen is introduced for 2-2.5 hours and then is switched to hydrogen, and the reaction curve is shown in a figure 8. The results show that only the presence of noble metal hydrogen will play a role in reduction, and the catalytic effect of CNT @ PANI is unchanged after the hydrogen is introduced.

Comparative example 3

The polyaniline-embedded Pt metal catalyst Pt/CNT @ PANI and the supported Pt metal catalyst Pt/CNT @ CN with the nitrogen-carbon coated structure are prepared according to the preparation method of the catalyst in the example 1 and applied to liquid phase catalytic reduction of Cr (VI). The reaction condition of introducing hydrogen is that nitrogen is introduced for 2-2.5 hours and then is switched to hydrogen, and the result is shown in fig. 8, the initial activity of Pt/CNT @ PANI is obviously higher than that of Pt/CNT @ CN, so that the surface hydrophilicity of the polymer material is better than that of a carbon layer, and the polymer material is beneficial to adsorption removal of anionic pollutants.

Comparative example 4

The polyaniline-embedded Pt metal catalyst Pt/CNT @ PANI was prepared according to the catalyst preparation method of example 1, except that aniline was added to form embedded Pt metal catalysts Pt/CNT @ PANI-1.0, Pt/CNT @ PANI-2.0, Pt/CNT @ PANI-7.5, and Pt/CNT @ PANI-10.0 for liquid phase catalytic reduction of Cr (VI). As a result, as shown in fig. 16, the thickness of the embedded layer increased with the increase of the amount of aniline, and although the two-hour adsorption removal rate increased without the introduction of hydrogen, the electron transfer rate decreased and the catalytic reduction efficiency decreased after the introduction of hydrogen. It is apparent from the initial activity bar chart shown in fig. 17 that the initial activity of the catalytic hydrogenation reaction curve decreases with increasing aniline usage.

Claims

1. The application of the polyaniline embedded Pt/CNT-based catalyst in the treatment of Cr (VI) is characterized by comprising the following steps:

s1, adjusting the pH value of the water body:

s2, applying polyaniline embedded Pt/CNT-based catalyst:

adding polyaniline embedded Pt/CNT-based catalyst powder into a water body containing Cr (VI) pollutants,

s3, hydrogenation:

2. The use according to claim 1, wherein in step S2, the polyaniline-embedded Pt/CNT-based catalyst is used in an amount of 0.05-0.20 g/L.

3. The application of the catalyst according to claim 1, wherein the temperature of the hydrogenation reaction is 273-328K, the flow rate of nitrogen and hydrogen is 100-200 mL/min, and the time of the reduction reaction is 4-5 h.

4. The use according to claim 1, wherein the polyaniline-embedded Pt/CNT-based catalyst is prepared by a method comprising:

s2-1, preparing a precursor Pt/CNT:

taking 0.88-2.65 mL of chloroplatinic acid with the concentration of 10.0g/L and 1.0g of purified CNT (carbon nano tubes) into 30-50 mL of water, stirring for 4-5 h, evaporating in a water bath at 80-90 ℃, introducing nitrogen, roasting for 4-6 h at 250-350 ℃, introducing hydrogen, and reducing for 2-3 h at 200-300 ℃ to obtain a precursor Pt/CNT;

s2-2, coating polyaniline:

dispersing the precursor Pt/CNT in an aqueous solution containing hydrochloric acid and aniline, stirring at a low temperature, slowly dropwise adding ammonium persulfate until the solution turns green, keeping the low temperature for 10-12 h, washing and drying to obtain the Pt-based catalyst Pt/CNT @ PANI with the polyaniline-coated layer.

5. The use according to claim 4, wherein in step S2-2, the ratio between aniline and precursor Pt/CNT is 1.0-10 mL: 1g of the total weight of the composition.

6. The use according to claim 5, wherein in the step S2-2, the ammonium persulfate solution has a concentration of 150-200 g/L and is used in an amount of 50-60 mL.

7. The use according to claim 6, wherein in step S2-2, the concentration of the hydrochloric acid solution is 0.5-1.0M, and the amount is 10-20 mL; the total volume of the aqueous solution was 200 mL.

8. The use according to claim 4, wherein in step S2-2, the low temperature is maintained at a temperature of-10 ℃ to 0 ℃.