CN114588872A

CN114588872A - High-adsorption-capacity iron-silver co-doped biochar and preparation method thereof

Info

Publication number: CN114588872A
Application number: CN202210219672.6A
Authority: CN
Inventors: 吴泽葵; 陈志莉; 周自坚; 方义; 李文斌; 张力钊
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2022-03-08
Filing date: 2022-03-08
Publication date: 2022-06-07
Anticipated expiration: 2042-03-08
Also published as: CN114588872B

Abstract

The invention discloses a preparation method of iron-silver co-doped biochar with high adsorption capacity, which comprises the following steps: (1) preparing a mixed solution containing Fe ions and Ag ions: adding concentrated H to the aqueous solution₃PO₄Iron compound, AgNO₃Dispersing the solution uniformly; the iron compound is selected from ferric nitrate, ferrous nitrate or a mixture of the two; in the mixed solution, the iron compound AgNO₃The mass ratio of (A) to (B) is 10-50: 1; (2) crushing plant waste biomass, and adding the crushed plant waste biomass and the solution obtained in the step (1) into the lining of a reaction kettle; (3) placing the reaction kettle in an oven, heating to 180-230 ℃, and maintaining for 1-2.5 hours; (4) and (4) washing the material until the pH value is close to neutral, and drying to obtain the material. The preparation method has simple steps, only needs to uniformly mix the required raw materials and place the mixture in a reaction kettle for one-step hydrothermal carbonization, has short time consumption and low consumption of chemical reagents, and does not have the problem of waste gas discharge inherent in a pyrolysis method.

Description

High-adsorption-capacity iron-silver co-doped biochar and preparation method thereof

Technical Field

The invention relates to the technical field of biochar preparation, in particular to high-adsorption-capacity iron-silver co-doped biochar and a preparation method thereof.

Background

The application of biochar in the field of water treatment is receiving more and more attention, and abundant surface functional groups (carboxyl, hydroxyl, phenolic hydroxyl and the like) are active sites for removing pollutants. In recent years, many scholars greatly improve the adsorption performance of the biochar by modifying the biochar or loading metal, particularly after the biochar is loaded with iron, the adsorption capacity is improved, the existence of the iron endows the biochar with magnetism, the aim of solid-liquid separation after pollutant treatment is fulfilled, and the application range of the biochar is widened. However, due to certain defects in the preparation technology, the biochar and the loaded metal are easy to leach out, so that secondary pollution to the water body is caused.

At present, reports on simultaneous loading of iron and silver on the biochar are few, and the preparation method mainly comprises a liquid phase reduction method and a gel method, for example, the gel method adopted by Chinese patent application CN108115152A, firstly introducing magnesium lithium silicate and polyglutamic acid to prepare a mixed solution containing iron and silver, heating for a long time to form xerogel, and finally heating at a high temperature again to prepare the magnetic biochar loaded with iron and silver; however, the preparation process of the method is complex, more impurity elements and chemical agents are introduced, a large amount of energy is consumed by heating for a long time for many times, and the economic benefit is low. As disclosed in chinese patent application CN106955667A, the method for preparing activated carbon loaded with nano iron and silver clusters by liquid phase reduction method has the disadvantages that the silver loading makes the material have certain catalytic performance, but the silver metal clusters cause the nonuniformity of the material, the silver ions are easy to form precipitate during the preparation process, so the loading efficiency is low, and the preparation steps are complicated, the consumption of chemical reagents is large, and the economical and practical properties are poor.

At present, the schemes of the biochar loaded metal mainly comprise a coprecipitation method, a coprecipitation method and a liquid phase reduction method, the methods not only consume a large amount of chemical reagents to generate secondary pollution, but also are uneven in load and easy to agglomerate, and on the one hand, the bonding capability of the metal and the carbon is poor, and the metal is easy to leach out to cause secondary pollution; an iron and silver co-doped biochar product with low metal leaching risk and high adsorption capacity and a preparation method thereof are lacked.

Disclosure of Invention

The invention aims to solve the problems and provides a preparation method of iron and silver co-doped biochar with high adsorption capacity, which is simple to operate, low in consumption and low in metal leaching risk.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of iron and silver co-doped biochar with high adsorption capacity comprises the following steps:

(1) preparing a mixed solution containing Fe ions and Ag ions: adding concentrated H to the aqueous solution₃PO₄Iron compound, AgNO₃Dispersing the solution uniformly; the iron compound is selected from ferric nitrate, ferrous nitrate or a mixture of the two; in the mixed solution, the iron compound AgNO₃The mass ratio of (A) to (B) is 10-50: 1;

(2) taking plant waste biomass dried to constant weight, crushing, adding the crushed biomass and the solution obtained in the step (1) into the inner liner of a reaction kettle, and uniformly mixing; the plant waste biomass is selected from Leersia hexandra straw, rice straw, corn straw, bagasse or bamboo dust; wherein, the plant waste biomass and the concentrated H added in the step (1)₃PO₄The solid-liquid ratio of the iron compound to the biomass is 1g to 0.1-2.0 ml, and the mass ratio of the iron compound to the biomass is 5-1: 1;

(3) placing the reaction kettle in an oven, heating to 180-230 ℃, maintaining for 1-2.5 hours, and cooling to room temperature after completion;

(4) and (4) washing the material obtained in the step (3) until the pH value is close to neutral, and drying to obtain the material.

In the step (3), the temperature is raised from 50-70 ℃ to 180-230 ℃ at the rate of 2-3 ℃/min and is maintained for 1-2.5 hours.

Preferably, the temperature is raised from 60 ℃ to 200 ℃ at a rate of 2-3 ℃/min and maintained for 1.5 h.

The iron compound is Fe (NO)₃)₃·9H₂O, or the iron compound is Fe (NO)₃)₃、Fe(NO₃)₂Mixing according to the mass ratio of 5-3: 2-1.

The step (1) is as follows: preparing a mixed solution system by taking 50mL of water: while stirring, 3mL of concentrated H were added to the beaker in sequence₃PO₄、3g Fe(NO₃)₃·9H₂O、0.3gAgNO₃And the ultrasonic dispersion is uniform.

Said concentrated H₃PO₄The concentration of (B) was 85 wt%.

And (3 g of plant waste biomass in the step (2) and the mixed solution obtained in the step (1) are added into the inner liner of the reaction kettle together.

In the step (4), the material obtained in the step (3) is washed by pure water and absolute ethyl alcohol respectively until the pH value is close to neutral.

The invention also aims to provide the iron-silver co-doped biochar with high adsorption capacity, which is prepared by mixing plant waste biomass and concentrated H₃PO₄Iron compound, AgNO₃The mixture is uniformly mixed and placed in a reaction kettle for one-step hydrothermal carbonization, and the product is prepared by any one of the methods.

The last purpose of the invention is to provide the application of the iron and silver co-doped biochar in removing Cr, As, tetracycline or norfloxacin in a water body.

The iron compound of the present invention is selected from Fe (NO)₃)₃、Fe(NO₃)₂The iron chloride is selected to cause silver precipitation, which is not beneficial to doping(ii) a The invention finally determines to adopt the concentrated H₃PO₄Instead of using H₃PO₄ZnCl with similar effect₂KOH, etc., mainly due to: 1) the hydrolysis and the cracking of the cellulose of the biomass are facilitated, the aromatization is promoted, so that the aromaticity of the biochar is improved, and an FTIR spectrum is 2833cm^-1And 1590cm^-1The sharp absorption peak is one of the evidences of higher aromaticity of the biochar; 2) promote the formation of C ═ O (and ZnCl)₂KOH has little influence on the aromaticity of the biomass), thereby promoting the generation of quinone radical radicals and further strengthening the effect of the free radicals on removing pollutants; 3) part of the phosphoric acid forms spherical Fe with iron ions₅(PO₄)₄(OH)₃Supported on charcoal (refer to SEM atlas in attached figure), Fe₅(PO₄)₄(OH)₃Has good electrical property and is beneficial to electron transfer.

The method can form a metal-O bond by doping metal in the preparation process of the biochar, not only can ensure that the combination of the metal and the biochar becomes tight, but also can keep the reaction activity of the biochar, and if noble metal is doped at the same time to form potential difference between double metals, coupling effects of electrocatalysis, adsorption and degradation can be generated, the pollutant removal capacity is improved on the premise of reducing the risk of metal leaching, and the practical application potential of the biochar is greatly improved.

The invention has the beneficial effects that:

(1) compared with the complex preparation process in the prior art, the preparation method disclosed by the invention has simple steps, can obtain the iron and silver co-doped biochar only by uniformly mixing the required raw materials and placing the mixture in a reaction kettle to finish one-step hydrothermal carbonization, and has the advantages of short time consumption, low consumption of chemical reagents and no waste gas discharge problem inherent in a pyrolysis method.

(2) The loading effect on iron and silver is good, the loaded metal is uniformly dispersed, the loaded metal is tightly combined with the carbon matrix, the iron leaching amount is small, and the drinking water standard is met.

(3) The prepared composite material couples the functions of adsorption, catalysis and degradation, has a certain antibacterial effect, can realize separation by using an external magnetic field, can release active oxygen, and can effectively treat refractory organic matters because the bimetal and the carbon base form a catalytic system; the method also has the advantages of rich active oxygen and uniform metal load of the biological carbon prepared by a hydrothermal carbonization method, and a microcell structure of iron and silver on the carbon substrate, and the two outstanding characteristics are simultaneously coupled with rich functional groups and pore adsorption capacity of the carbon, so that adsorption removal and degradation of various pollutants can be realized.

(4) The novel composite adsorbing material with high adsorption performance is prepared by taking iron, silver and Leersia hexandra Swartz as raw materials, a new way is provided for the resource utilization of the Leersia hexandra Swartz, the resource utilization of wastes is realized, and the prepared material has a good effect of removing heavy metals, for example, the adsorption capacity to Cr (VI) can reach above 85.41 mg/g.

Drawings

Fig. 1 is an SEM image of FSHC prepared.

Fig. 2 is an SEM image of FHC prepared.

Figure 3 is the XRD scan of FSHC.

Fig. 4 is an FTIR spectrum of FSHC.

FIG. 5 is an EPR profile of FSHC.

Figure 6 is the effect of solution initial pH on FSHC removal performance.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to be limiting.

The experimental methods in the following examples are all conventional methods unless otherwise specified; the chemical reagents used, unless otherwise specified, are conventional in the art and are commercially available.

Example 1 preparation of iron and silver codoped biochar (FSHC) and iron doped biochar (FHC)

First, FSHC preparation method

Drying the Leersia hexandra Swartz plant body to constant weight to obtain Leersia hexandra Swartz biomass, then co-doping iron and silver, and operating according to the following steps:

(1) taking 50mL of ultrapure water to prepare a mixed solution system: while stirring, 3mL of concentrated H were added to the beaker in sequence₃PO₄(concentration 85 wt.%), 3gFe (NO)₃)₃·9H₂O、0.3gAgNO₃Placing in an ultrasonic cleaning instrument, and ultrasonically treating for 10min to uniformly disperse the solution;

(2) taking 3g of dried Leersia hexandra plant biomass (a sample obtained after drying a Leersia hexandra plant body) to constant weight, crushing to the size of below 1cm, adding the crushed Leersia hexandra plant biomass and the solution obtained in the step (1) into a 100ml polytetrafluoroethylene reaction kettle lining together, and performing ultrasonic treatment for 10min to uniformly mix the materials;

(3) placing the reaction kettle in an oven, heating from 60 ℃ to 200 ℃ at the heating rate of 2-3 ℃/min, maintaining for 1.5h, and naturally cooling to room temperature;

(4) washing with pure water and absolute ethyl alcohol respectively until pH is close to neutral, and drying in oven at 60 deg.C for 12 hr to obtain FSHC.

Second, FHC preparation method

Taking Leersia hexandra Swartz biomass, doping iron, and operating according to the following steps:

(1) taking 50mL of ultrapure water to prepare a mixed solution system: while stirring, 3mL of concentrated H were added to the beaker in sequence₃PO₄(concentration 85 wt.%), 3g Fe (NO)₃)₃·9H₂Placing the solution in an ultrasonic cleaner for ultrasonic treatment for 10min to uniformly disperse the solution;

(2) taking 3g of dried Leersia hexandra Swartz biomass to constant weight, crushing to the size of below 1cm, adding the crushed Leersia hexandra Swartz biomass and the solution obtained in the step (1) into a 100ml polytetrafluoroethylene reaction kettle lining together, and carrying out ultrasonic treatment for 10min to uniformly mix;

(4) washing with pure water and absolute ethyl alcohol respectively until pH is close to neutral, and drying in an oven at 60 deg.C for 12h to obtain FHC.

Example 2 FSHC and FHC product testing

FSHC and FHC from example 1 were examined.

Fig. 1 and 2 are SEM spectra of FSHC and FHC, respectively, in which Fe particles were successfully loaded on hydrothermal charcoal but were large in particle size and easily agglomerated. Compared with FHC, due to the introduction of Ag, the FSHC has the advantages that the load of Fe is uniformly distributed on the hydrothermal carbon, the particle size is about 100nm, and the aggregation is not easy to occur.

The XRD scanning result of FSHC is shown in figure 3, 38.1 degrees, 44.3 degrees, 64.4 degrees and 77.4 degrees respectively correspond to crystal faces (JCPDS No.04-783) of Ag (111), Ag (200), Ag (220) and Ag (311), which indicates that silver particles are successfully doped with biochar in the process of preparing the biochar; 34.3 degrees and 57.8 degrees corresponding to Fe₃O₄The (220) and (511) crystal planes (JCPDS No.19-0629), the broad peak appearing at about 26.6 degrees is due to Fe and SiO in the hydrothermal carbonization process₂The resulting Fe-Si compound. Therefore, the prepared FSHC realizes iron-silver co-doping, the Ag particles have FSHC with certain antibacterial property, and the Fe₃O₄The presence of (b) makes the FSHC magnetic and solid-liquid separation by an applied magnetic field is possible.

The FTIR spectrum of FSHC is shown in FIG. 4, and 3435cm on the FTIR spectrum^-1A nearby broad and intense peak was assigned to the characteristic peak of-OH in FSHC, of which 1590cm^-12833cm-1 and 2956cm-1 correspond to C ═ C of the phenyl ring, C-H of the phenyl ring and R-COOH, respectively. 1364cm^-1The sharp absorption peak may be a large amount of NO adsorbed during FSHC preparation₃ ^-So as to form; 1068-1084cm^-1Is the stretching vibration of the lipid-C-O or O-Si-O in the hydrothermal charcoal, and according to the previous research results, 483cm^-1The absorption peak appeared here may be formed by Fe-O or Fe-OH, 778cm^-1The sharp absorption peak is related to the bending vibration of Si-O or Si-O-Si in FSHC, and Si is derived from the biomass. The results show that the prepared FSHC has high aromaticity and abundant surface functional groups, and can provide sufficient active sites for removing pollutants.

According to the previous study, g₁<0.20030 is a carbon-centered radical, 2.0030<g₂<0.20040 is a carbon-centered radical with an ortho-oxygen atom, g₃>0.20040 is an oxygen-centered radical. The EPR spectrum of FSHC is shown in FIG. 5, from which it can be seen that the g factor in FSHC is less than 0.20030, which is primarily inferred to be carbon-centered free radical, while the FTIR spectrum analysis in FIG. 4 and the hydrothermal carbon preparation process can improve the aromaticity of the carbon matrix, so that the free radical type should be benzene ring-containingThe semiquinone radical also further shows that FSHC not only has adsorption and oxidation-reduction properties, but also contains rich radicals which can catalyze and degrade refractory organic matters.

Example 3 Cr (VI) removal experiment

The FSHC and FHC prepared in example 1 were used for the treatment of wastewater containing Cr (VI):

0.04g of the prepared FSHC and FHC materials are respectively added into a polyvinyl chloride centrifuge tube, 40mL of simulated wastewater containing 100mg/L of Cr (VI) and with the pH value of 2 is added, the mixture is quickly transferred into a gas bath constant temperature oscillator, and the mixture is adsorbed for 24 hours at the rotating speed of 160rpm and the temperature of 25 ℃. The results show that: the adsorption capacity of the FSHC and FHC materials to 100mg/L Cr (VI) wastewater is 85.41mg/g and 65.64mg/g respectively, the Fe leaching capacity in the solution after 24 hours of reaction is 0.25mg/L and 0.05mg/L respectively, and the Fe leaching capacity of the FSHC meets 0.3mg/L of the drinking water standard (GB 5749-one 2006).

The initial pH is one of the main factors for removing Cr (VI) in water, and influences the protonation degree of the functional groups on the surface of the adsorbent and the existence form of Cr (VI), therefore, the influence of different initial pH values of the solution on the removal of Cr (VI) in FSHC water is detected, and the result is shown in figure 6, and the FSHC influences Cr (VI) and Cr (VI) at the pH of 2_{General assembly}The maximum adsorption amounts were 87.00mg/g and 60.67mg/g, respectively, and the adsorption amounts exhibited a tendency to decrease significantly and then to plateau as the pH was increased gradually to 8, indicating that acidic conditions favor Cr (VI). This is because the lower pH enhances the protonation of the surface carboxyl, phenolic hydroxyl, etc. of FSHC, on the one hand, and also enhances the corrosion of the surface Fe to produce atomic hydrogen, in which case HCrO in water₄ ^-、Cr₂O₇ ^2-、H₂CrO₄Adsorbed on the FSHC surface under the action of electrostatic force and subjected to electron transfer reduction to Cr (III). With increasing pH to neutrality, the concentration of OH in water increases gradually^-And Cr₂O₇ ^2-Competing for limited binding sites of FSHC, an increase in pH inhibits the generation of atomic hydrogen on the one hand and H on the other hand⁺The reduction in concentration hinders the formation of free radicals in FSHC, resulting in a reduction in the amount of cr (vi) removal during the pH increase.

Claims

1. A preparation method of iron and silver co-doped biochar with high adsorption capacity is characterized by comprising the following steps:

(2) taking plant waste biomass dried to constant weight, crushing, adding the crushed biomass and the solution obtained in the step (1) into the inner liner of a reaction kettle, and uniformly mixing; the plant waste biomass is selected from lees straw, rice straw, corn straw, bagasse or bamboo dust; wherein, the plant waste biomass and the concentrated H added in the step (1)₃PO₄The solid-liquid ratio of the iron compound to the biomass is 1g to 0.1-2.0 ml, and the mass ratio of the iron compound to the biomass is 5-1: 1;

(4) and (4) washing the material obtained in the step (3) until the pH value is close to neutrality, and drying to obtain the material.

2. The method of claim 1, wherein:

in the step (3), the temperature is raised from 50-70 ℃ to 180-230 ℃ at a rate of 2-3 ℃/min and is maintained for 1-2.5 hours.

3. The method of claim 2, wherein: heating from 60 deg.C to 200 deg.C at a heating rate of 2-3 deg.C/min for 1.5 h.

4. The method of claim 1, wherein: the iron compound is Fe (NO)₃)₃·9H₂O, or the iron compound is Fe (NO)₃)₃、Fe(NO₃)₂Mixing according to the mass ratio of 5-3: 2-1.

5. The method of claim 1, wherein: the step (1) is as follows: preparing a mixed solution system by taking 50mL of water: while stirring, 3mL of concentrated H were added to the beaker in sequence₃PO₄、3g Fe(NO₃)₃·9H₂O、0.3gAgNO₃And the ultrasonic dispersion is uniform.

6. The method of claim 5, wherein: said concentrated H₃PO₄The concentration of (B) was 85 wt%.

7. The method of claim 5, wherein: and (3 g of plant waste biomass in the step (2) and the mixed solution obtained in the step (1) are added into the inner liner of the reaction kettle together.

8. The method of claim 1, wherein: in the step (4), the material obtained in the step (3) is washed by pure water and absolute ethyl alcohol respectively until the pH value is close to neutral.

9. The utility model provides a high adsorption capacity's indisputable silver codope biochar which characterized in that: is prepared from plant waste (biomass) and concentrated H₃PO₄Iron compound, AgNO₃The mixture is uniformly mixed and placed in a reaction kettle for one-step hydrothermal carbonization, and is prepared by the method of any one of claims 1 to 8.

10. The use of the iron and silver co-doped biochar of claim 9 in removing Cr, As, tetracycline or norfloxacin from a water body.