CN113262791B - Preparation method of cerium oxide modified biomimetic catalyst - Google Patents

Abstract

The invention discloses a preparation method of a cerium oxide modified biomimetic catalyst, wherein a nickel source is added in the growth process of Eichhornia crassipes, the Eichhornia crassipes absorbs nickel elements, pyrolyzes the nickel elements, and then the nickel elements and a cerium compound are subjected to precipitation reaction under the action of sodium hydroxide, and biochar containing precipitate cerium oxide generated by the reaction is calcined at high temperature to prepare the biomimetic catalyst. The preparation method is simple, the prepared bionic catalyst contains the nickel element and the cerium oxide, and the nickel element and the cerium oxide are uniformly dispersed in the biochar, so that the electron transfer capability in the bionic catalyst is promoted, the removal rate of organic pollutants is improved, the reliability and durability of the bionic catalyst used as an environment repairing material are further improved, and a new development idea is provided for the preparation of the catalyst or the bionic catalyst.

Description

Preparation method of cerium oxide modified biomimetic catalyst

Technical Field

The invention belongs to the technical field of environmental preparation, and particularly relates to a preparation method of a cerium oxide modified biomimetic catalyst.

Background

Nowadays, with the rapid development of science and technology, the global economy has advanced greatly, and the living standard of people is improved to a great extent. Meanwhile, the energy crisis and environmental pollution problems caused by economic development are becoming more serious. These pollutions not only seriously destroy the ecological environment, but also endanger the health of human beings. Among a plurality of pollution problems, the pollution of water containing organic pollutants is one of the most serious problems, and in recent years, the quality of water in the world is reduced year by year, which not only affects the survival of aquatic organisms, but also pollutes soil, causes the yield reduction and even the top-off of agriculture, and causes great loss to human beings. Therefore, the removal of organic contaminants from water pollution is one of the problems that must be addressed by today's society.

Among a plurality of technologies for removing organic pollutants in water pollution, the photocatalytic technology has wide application prospect due to the characteristics of high efficiency, no toxicity and the like, and the synthesis of a photocatalyst with high activity and high stability is always the focus of research.

Particularly, the rare earth metal oxide has good oxidation-reduction property and environmental friendliness, so that the rare earth metal oxide has potential application in the aspect of removing organic pollutants in water. The current research finds that rare earth metal oxides with different morphologies, such as nanorods, nanowires, nanosheets, nanoparticles and the like, show more excellent photocatalytic performance due to the unique nano effect. The pure nano metal oxide is easy to aggregate, so that the catalytic activity surface area of the nano metal oxide is reduced, and the catalytic activity of the nano metal oxide is influenced, so that a carrier with a larger specific surface is required to be introduced, the high dispersion of the nano particles is realized, the using amount of active components of the nano metal oxide can be reduced, and the catalyst cost is saved.

The biochar serving as a catalyst carrier has the advantages of large specific surface area and high reaction activity, and has wide application prospect in the field of environmental remediation, so that the biochar and rare earth metal oxide can be combined to prepare the catalyst under ideal conditions for removing organic pollutants in the environment.

But because the granularity of the rare earth metal oxide is small and the rare earth metal oxide is easy to agglomerate, the specific surface area is reduced and the reaction rate is reduced; and a series of problems that the rare earth metal oxide is easy to fall off in the using process to cause the reduction of the using efficiency and the like when the composite material is compounded with the biochar, most of researches are limited to a laboratory research stage, and a plurality of problems exist in practical application and need to be further explored.

For the above reasons, there is a need to develop a rare earth metal oxide catalyst having high stability and excellent durability.

Disclosure of Invention

In order to overcome the problems, the inventor of the invention carries out keen research on rare earth metal oxide and photocatalyst, and researches a preparation method of a biomimetic catalyst modified by cerium oxide. The preparation method is simple, the prepared biomimetic catalyst contains nickel element and cerium oxide, the nickel element and the cerium oxide are uniformly dispersed in the biochar, the electron transfer capability in the biomimetic catalyst is promoted, the removal rate of organic pollutants is improved, the reliability and durability of the biomimetic catalyst used as an environment repairing material are further improved, and a new development idea is provided for the preparation of the catalyst or the biomimetic catalyst, so that the preparation method is completed.

Specifically, the present invention aims to provide the following:

on the one hand, the preparation method of the bionic catalyst is provided, and the bionic catalyst is prepared by carrying out thermal reaction and calcination on biochar and a rare earth metal compound.

In another aspect, there is provided a biomimetic catalyst made by the method of the first aspect.

The invention has the advantages that:

(1) according to the bionic catalyst provided by the invention, the nickel and the cerium oxide are uniformly coated or loaded in the biochar, so that the electron transfer capability in the bionic catalyst is promoted, the removal efficiency of organic pollutants is improved, and the reliability and durability of the bionic catalyst used as an environment repairing material are improved.

(2) According to the preparation method of the biomimetic catalyst provided by the invention, nickel element is uniformly loaded in biomass in the growth process of the Eichhornia crassipes, and the prepared biomimetic catalyst is high in nickel element loading amount.

(3) According to the preparation method of the biomimetic catalyst, the biochar containing the precipitate cerium oxide is calcined by stages to prepare the biomimetic catalyst, so that the stability of the cerium oxide in the biochar is improved, and a new development idea is provided for the preparation of the catalyst or the biomimetic catalyst.

Drawings

FIG. 1 shows TEM characterization photographs of the biomimetic catalyst prepared in example 1 of the present invention;

FIG. 2 shows SEM-Mapping characterization photographs of different elements of the biomimetic catalyst prepared in example 1 of the present invention;

FIG. 3 shows a XRD characterization picture of the biomimetic catalyst prepared in example 1 of the present invention;

FIG. 4 is a graph showing the change of the removal rate curve of 2, 4-dichlorophenol in Experimental example 1 of the present invention;

FIG. 5 shows a graph of the rhodamine-B removal rate curve in Experimental example 2 of the invention;

FIG. 6 is a graph showing the change of sulfamethoxazole removal rate curve in Experimental example 3 of the present invention.

Detailed Description

The invention is explained in more detail below with reference to the figures and examples. The features and advantages of the present invention will become more apparent from the description.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

On the one hand, the invention aims to provide a preparation method of the biomimetic catalyst, which is prepared by carrying out thermal reaction and calcination on biochar and a rare earth metal compound.

According to the invention, the biochar is biochar enriched with metallic nickel.

In the invention, the removal rate of organic pollutants such as 2, 4-dichlorophenol by the biomimetic catalyst prepared from the nickel-rich biochar is higher than that of the biomimetic catalyst prepared from the biochar without the enriched metal nickel, which is probably because the multiple valence states of nickel promote the electron transfer in the biochar material, so that the biomimetic catalyst has better performance.

According to the present invention, in order to uniformly load or enrich the nickel element in the biochar, it is preferable to add a nickel compound during the plant cultivation process, so as to be absorbed by the plant.

Further, the plant is an aquatic plant, preferably a floating plant, such as Eichhornia crassipes, Azalea papyrifera, and Spirodela sophorae, more preferably Eichhornia crassipes.

In the invention, the roots, stems and leaves of the aquatic plants form complete and developed aeration tissues and developed root system tissues, so that the absorption of various nutrient substances is ensured; the floating plants have high propagation and growth speed, particularly the phoenix-eye blue has developed fibrous roots, and a gas chamber consisting of columnar cells is arranged in a petiole, and the most important is that the phoenix-eye blue has excellent nickel enrichment effect.

According to the invention, the plants are cultivated by means of soilless culture, and a nickel compound is added to the nutrient solution for cultivating the plants.

The nutrient solution is Hoagland nutrient solution and can meet the requirement of plants on nutrient substances.

Wherein the nickel compound comprises an ionic nickel compound and/or a complex nickel compound, preferably an ionic nickel compound, such as nickel sulfate, nickel nitrate, nickel halide, more preferably nickel sulfate.

In the invention, the plant has better absorption effect on the ionic nickel compound, and particularly has more prominent absorption effect on nickel ions in the form of nickel sulfate.

The inventor finds that the nickel ions are transported in the plant body more rapidly, can be combined with organic acid in the nutrient solution to exist in a complex form, and form a stable chelate so as to be beneficial to the absorption, transportation and transfer of nickel. The nickel ions absorbed by the phoenix-eye blue are mainly accumulated on the overground part because the phoenix-eye blue has good nickel absorption effect and belongs to a nickel accumulation type plant.

According to the invention, the absorption capacity of the plants to the nickel element is increased along with the increase of the content of the nickel element, but the excessive nickel element causes the toxic necrosis of the plants, and when the concentration of the nickel element in the nickel compound in the nutrient solution is 100-400 mg/L, the normal growth of the plants can be promoted, and the high enrichment of the plants to the nickel element can also be realized.

In a further preferred embodiment, the concentration of the nickel element in the nickel compound in the nutrient solution is 200-300 mg/L.

In a further preferable embodiment, the concentration of nickel element in the nickel compound in the nutrient solution is 250-260 mg/L.

According to the invention, in order to further ensure the normal growth of the plants and the high enrichment of nickel, the nutrient solution of the plants is preferably replaced irregularly, and the replacement period is not more than 10 days, preferably 3-7 days, and more preferably 5 days.

According to the invention, the plants are cultivated through the nutrient solution, the nickel element in the nickel compound is absorbed by the plants, and the nickel element is transmitted to tissues such as roots, stems, leaves and the like, and the planting period of the plants is as long as possible in order to ensure the enrichment effect of the nickel element. A planting period of more than 30 days is necessary to ensure the nickel enrichment effect, and a planting period of more than 45 days may be more advantageous, for example a planting period of 60 days.

According to the present invention, since nickel is distributed in each tissue of a plant, the biomass of the whole plant is pyrolyzed to produce biochar.

In the present invention, it is preferable that the plant is dried and pulverized before pyrolysis.

Further, the pyrolysis temperature is 500-800 ℃, preferably 600-700 ℃, and more preferably 620-630 ℃.

In the invention, with the increase of the pyrolysis temperature, the content of carbon element is increased, the evaporation of water and the degradation of organic components cause the reduction of the content of hydrogen element and oxygen element, the specific surface area of the biochar is increased, but the excessive temperature causes the reduction of the content of carbon element and the reduction of the specific surface area; the nickel element in the biochar changes the crystalline phase along with the rise of the temperature, the generated simple substance nickel and nickel oxide cause the specific surface area of the biochar to be increased, and the special nickel and carbon space structure in the pyrolysis process also causes the specific surface area to be increased.

According to the invention, when the pyrolysis temperature is 500-800 ℃, the biochar has good structural characteristics and electrochemical characteristics, the specific surface area is the largest, and especially when the pyrolysis temperature is 620-630 ℃, the electrochemical performance of the biochar is optimal, and nickel elements are uniformly coated in the biochar or enriched on the surface of the biochar.

In the invention, the pyrolysis time is related to the pore size of the biochar, the pore size of the biochar can be effectively increased by prolonging the pyrolysis time, and too long pyrolysis time causes decomposition or volatilization of organic substances to leave more ash.

According to a preferred embodiment, the pyrolysis time is 0.5 to 3 hours, preferably 1 to 2 hours, and more preferably 1.5 hours.

In the present invention, the rate of temperature increase of the pyrolysis has an effect on the mechanical properties of the biochar. With the acceleration of the heating rate, the distance between carbon layers of the biochar is reduced firstly and then increased, so that the mechanical strength of the biochar is increased firstly and then reduced, and when the heating rate is 1-8 ℃/min, the carbon material has the highest mechanical performance and the biochar has the best durability.

Preferably, the heating rate is 3-5 ℃/min, and more preferably, the heating rate is 4 ℃/min. According to the invention, the nickel element of the biochar subjected to pyrolysis treatment is uniformly dispersed and coated or loaded in the biochar, although the nickel element can enhance the treatment capability of the biochar on organic pollutants to a certain extent, the activation performance of the biochar is low and the capability of treating the organic pollutants is not strong due to relatively weak electron transfer capability of the biochar.

According to a preferred embodiment, the pyrolysis is carried out under an inert atmosphere, such as argon.

The biomimetic catalyst is prepared by further taking the biochar as a catalyst load carrier and modifying through a rare earth metal compound, so that the electron transfer capability in the biochar can be enhanced by utilizing the rare earth metal, organic pollutants can be removed by utilizing the adsorption effect of the biochar, and the activation performance of the biomimetic catalyst is obviously improved.

According to the present invention, the rare earth metal compound is a cerium-containing compound, such as cerium nitrate, cerium sulfate, etc., preferably cerium nitrate.

In the invention, cerium is used as a rare earth metal with high abundance and low price in nature and has excellent performance, cerium oxide is prepared from cerium nitrate by a precipitation method, the pH value of a reaction system is easily controlled by the content of strong base reacting with the cerium nitrate, the generated precipitate is not decomposed, and impurity ions generated by the reaction are easily removed.

According to the present invention, the strong base is preferably an inorganic strong base such as sodium hydroxide, potassium hydroxide, calcium hydroxide, etc., more preferably sodium hydroxide, which is strong in alkalinity, not too violent in reaction, and easy to control in reaction rate.

In the invention, the weight ratio of the biochar to the cerium compound to the strong base is 1: (1-6): (10-20), preferably 1: (2-5): (15-17), more preferably 1: (3.9-4): (16-16.2).

According to the invention, when the weight ratio of the biochar, the cerium compound and the strong base is 1: (1-6): (10-20), the content of cerium oxide in the biomimetic catalyst is high, and the removal effect on organic pollutants is best.

In the invention, because the biochar is in a porous structure and contains a nano channel, in order to load more cerium oxide on the pore channel or the surface of the biochar, a cerium compound and strong base are preferably mixed and stirred in a solution, and then the mixture is subjected to thermal reaction at the temperature of 80-260 ℃ for 24-48 h, and the precipitate is calcined.

According to the invention, because the biochar contains nickel elements, the stirring time is short, the cerium compound cannot be fully mixed with the biochar, the nickel elements in the biochar fall off and the content of the nickel elements is reduced to a certain extent due to the overlong stirring time, and the stirring time is 0.5-8 h, preferably 2-4 h, and more preferably 3 h.

According to the invention, the reaction rate is improved by raising the temperature of the reaction system, but the excessive thermal reaction temperature causes the precipitation generated by the reaction to be too fast and the contact time with the biochar to be too short, so that the content of cerium oxide loaded on the biochar is low. The thermal reaction temperature is preferably 100-200 ℃, more preferably 150-180 ℃, for example 160 ℃.

In the invention, as the thermal reaction time is prolonged, the generated precipitate is increased, the time is too long, the weight of the generated precipitate is not obviously increased any more, and in order to shorten the reaction time, the thermal reaction time is preferably 30-40 h, and more preferably 36-38 h.

The inventor finds that the calcination of the precipitate generated by the reaction is beneficial to improving the stability of the biomimetic catalyst, and because the precipitate contains a large amount of free water and partial oxidation state metal such as nickel oxide, the calcination is preferably carried out in a reducing gas or a mixed gas of an inert gas and a reducing gas, and the oxidation state metal in the precipitate is reduced into a metal simple substance, and the calcination comprises two stages:

the first stage is as follows: the calcination temperature is 100-300 ℃, the heating rate is 4-8 ℃/min, and the heat preservation time is 0.1-3 h;

and a second stage: the calcination temperature is 500-900 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 0.5-2 h.

According to the invention, the first stage of calcination is aimed at removing free water from the precipitate and the second stage of calcination is aimed at coating or enriching the cerium oxide in the biochar. In the second stage of calcination, the enrichment amount of cerium oxide on the surface or in the pore channels of the biochar is increased along with the increase of the reaction temperature, and the structure of the biochar is collapsed due to the excessively high reaction temperature, so that the specific surface area is reduced. In the calcining process, the finally prepared biomimetic catalyst has high content of loaded cerium oxide and nickel elements and excellent stability and mechanical property.

In a further preferred embodiment, the calcination comprises two stages:

the first stage is as follows: the calcination temperature is 150-230 ℃, the heating rate is 5-7 ℃/min, and the heat preservation time is 3-5 h;

and a second stage: the calcination temperature is 600-800 ℃, the heating rate is 7-9 ℃/min, and the heat preservation time is 0.5-2 h.

In a still further preferred embodiment, the calcination comprises two stages:

the first stage is as follows: the calcination temperature is 210 ℃, the heating rate is 6 ℃/min, and the heat preservation time is 4 h;

and a second stage: the calcining temperature is 700 ℃, the heating rate is 8 ℃/min, and the heat preservation time is 1 h.

In a preferred embodiment, the precipitate obtained by the thermal reaction is washed with water, dried, ground and calcined, so that cerium oxide can be uniformly loaded in the biochar during the calcination process.

According to the invention, the preferable drying time is 24-72 h, and the drying temperature is 30-90 ℃; preferably, the drying time is 36-60 h, and the drying temperature is 50-80 ℃; more preferably, the drying time is 48h and the drying temperature is 70 ℃.

In another aspect, the present invention is directed to a biomimetic catalyst prepared by the method of the first aspect.

Examples

The present invention is further described below by way of specific examples, which are merely exemplary and do not limit the scope of the present invention in any way.

Example 1

Planting the ailanthus altissima blue in an incubator with Hoagland nutrient solution, after one week, dissolving nickel sulfate in distilled water, adding the nickel sulfate into the nutrient solution, finally, enabling the concentration of nickel elements in the obtained nutrient solution to be 260mg/L, culturing for 60 days, replacing the nutrient solution in the incubator in a period of 5 days during the culture period, keeping the pH value of an aqueous solution in the incubator in a range of 5.8-6.0 during the experiment period, and crushing the ailanthus altissima blue to be 12-13 mm after the experiment is finished to obtain biomass.

And (2) putting the biomass into a crucible, putting the crucible into a tubular muffle furnace, heating to 620 ℃ at a heating rate of 4 ℃/min for pyrolysis, introducing argon into the tubular muffle furnace in the pyrolysis process, and preserving heat for 1.5 hours to obtain the biochar.

Mixing the biochar, cerium nitrate hexahydrate and sodium hydroxide according to a weight ratio of 1: 4: 16 the following operations are carried out:

adding biochar and cerium nitrate hexahydrate into distilled water, stirring for 20min, slowly adding sodium hydroxide into a mixed solution of the biochar and the cerium nitrate hexahydrate, continuously stirring for 3h, reacting for 36h at 160 ℃, filtering and collecting precipitates, washing the precipitates for 3 times, drying the precipitates for 48h at 70 ℃, grinding the precipitates to powder with the particle size of 0.6mm, calcining the powder in a tubular muffle furnace according to the following procedures to prepare the biomimetic catalyst, and introducing a mixed gas of 80% (v%) argon and 20% (v%) hydrogen into the tubular muffle furnace in the calcining process:

the first stage is as follows: the calcination temperature is 210 ℃, the heating rate is 6 ℃/min, and the heat preservation time is 4 h;

and a second stage: the calcining temperature is 700 ℃, the heating rate is 8 ℃/min, and the heat preservation time is 1 h.

The TEM photograph of the prepared biomimetic catalyst is shown in fig. 1, the SEM-Mapping containing different elements in the prepared biomimetic catalyst is shown in fig. 2, the SEM-Mapping representation of carbon (C), cerium (Ce), nickel (Ni) and oxygen (O) elements in the biomimetic catalyst is shown in the figure, and the content analysis of C, Ce, Ni and O4 elements is selected in an energy dispersive X-ray spectrometer (EDX), and the obtained results are as follows:

the obtained biomimetic catalyst has XRD characteristics shown in figure 3, wherein the characteristic peaks of cerium oxide correspond to 28.4 degrees, 47.5 degrees and 56.1 degrees, and the characteristic peaks of nickel correspond to 43.1 degrees and 50.1 degrees.

Comparative example

Comparative example 1

A catalyst was prepared in a similar manner to example 1, except that: when the ailanthus altissima is cultivated, nickel sulfate is not added.

Examples of the experiments

Experimental example 1

100mL of 2, 4-dichlorophenol solution with a concentration of 50mg/L was respectively filled in two 250mL beakers, 6mL of sodium persulfate solution with a concentration of 3g/L was added, the mixture was shaken for 90min, the biomimetic catalyst prepared in example 1 and the catalyst prepared in comparative example 1 were respectively added for 120min, and the change of the concentration of 2, 4-dichlorophenol was recorded, and the change curve of the removal rate of 2, 4-dichlorophenol with time is shown in FIG. 4.

Experimental example 2

100mL of 50mg/L rhodamine-B solution is respectively filled in two 250mL beakers, 6mL of 3g/L sodium persulfate solution is added, the mixture is oscillated for 90min, the biomimetic catalyst prepared in the example 1 and the catalyst prepared in the comparative example 1 are respectively added, the reaction is carried out for 120min, the concentration change of the rhodamine-B is recorded, and the change curve of the rhodamine-B removal rate along with the change of time is shown in figure 5.

Experimental example 3

100mL of sulfamethoxazole solution with the concentration of 50mg/L are respectively filled in two 250mL beakers, 6mL of sodium persulfate solution with the concentration of 3g/L is added, the mixture is shaken for 90min, the biomimetic catalyst prepared in the example 1 and the catalyst prepared in the comparative example 1 are respectively added, the reaction is carried out for 120min, the concentration change of sulfamethoxazole is recorded, and the change curve of the sulfamethoxazole removal rate along with the change of time is shown in FIG. 6.

Experimental examples 1-3 the results of removing organic contaminants with respect to the biomimetic catalyst prepared in example 1 and the catalyst prepared in comparative example 1 are summarized as follows:

the invention has been described in detail with reference to the preferred embodiments and illustrative examples. It should be noted, however, that these specific embodiments are only illustrative of the present invention and do not limit the scope of the present invention in any way. Various modifications, equivalent substitutions and alterations can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of the present invention, and these are within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (13)

1. The preparation method of the bionic catalyst is characterized in that the bionic catalyst is prepared by carrying out thermal reaction and calcination on biochar and a rare earth metal compound;

the biochar is rich in metallic nickel, and is prepared by adding a nickel compound in the process of plant cultivation and pyrolyzing the plants absorbing nickel elements.

2. The method of claim 1, wherein the nickel compound comprises an ionic nickel compound and/or a complexed nickel compound.

3. The method according to claim 2, wherein the concentration of nickel element in the nickel compound in the plant cultivation nutrient solution is 100-400 mg/L, and the pyrolysis temperature is 500-800 ℃.

4. The method of claim 1, wherein the rare earth metal compound is a cerium compound.

5. The method according to claim 4, wherein the rare earth metal compound is cerium nitrate or cerium sulfate.

6. The method of claim 4, wherein the rare earth metal compound is cerium nitrate.

7. The method as claimed in claim 4, wherein the bio-carbon, the cerium compound and the strong base are mixed in the solution, and then the mixture is thermally reacted for 24-48 hours at the temperature of 80-260 ℃, and the precipitate is calcined to prepare the biomimetic catalyst.

8. The method of claim 7, wherein the strong base is an inorganic strong base.

9. The method of claim 8, wherein the strong base is sodium hydroxide, potassium hydroxide, calcium hydroxide.

10. The method of claim 8, wherein the strong base is sodium hydroxide.

11. The method according to claim 7, wherein the weight ratio of the biochar, the cerium compound and the strong base is 1: (1-6): (10-20).

12. The method according to claim 1, characterized in that said calcination comprises two phases:

the first stage is as follows: the calcination temperature is 100-300 ℃, the heating rate is 4-8 ℃/min, and the heat preservation time is 0.1-3 h;

and a second stage: the calcination temperature is 500-900 ℃, the heating rate is 5-10 ℃/min, and the heat preservation time is 0.5-2 h.

13. A biomimetic catalyst prepared by the method of any one of claims 1 to 12.

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