CN115155508B - FeS/LDH nano adsorbent and synthetic method and application thereof - Google Patents

FeS/LDH nano adsorbent and synthetic method and application thereof Download PDF

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CN115155508B
CN115155508B CN202210796113.1A CN202210796113A CN115155508B CN 115155508 B CN115155508 B CN 115155508B CN 202210796113 A CN202210796113 A CN 202210796113A CN 115155508 B CN115155508 B CN 115155508B
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adsorbent
ldh
salt
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CN115155508A (en
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李良
闫瑞鑫
孔龙
刘敏
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Shanghai Jiaotong University
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    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/0203—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of metals not provided for in B01J20/04
    • B01J20/0225—Compounds of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt
    • B01J20/0229—Compounds of Fe
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    • B01J20/0203—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of metals not provided for in B01J20/04
    • B01J20/0274—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of metals not provided for in B01J20/04 characterised by the type of anion
    • B01J20/0285—Sulfides of compounds other than those provided for in B01J20/045
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
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    • B01J20/04—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of alkali metals, alkaline earth metals or magnesium
    • B01J20/041—Oxides or hydroxides
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
    • B01J20/08—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04 comprising aluminium oxide or hydroxide; comprising bauxite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28002—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their physical properties
    • B01J20/28004—Sorbent size or size distribution, e.g. particle size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J20/28057—Surface area, e.g. B.E.T specific surface area
    • B01J20/28059—Surface area, e.g. B.E.T specific surface area being less than 100 m2/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J20/28057—Surface area, e.g. B.E.T specific surface area
    • B01J20/28061—Surface area, e.g. B.E.T specific surface area being in the range 100-500 m2/g
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/288—Treatment of water, waste water, or sewage by sorption using composite sorbents, e.g. coated, impregnated, multi-layered
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/103—Arsenic compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C02F2101/22—Chromium or chromium compounds, e.g. chromates

Abstract

The invention relates to an adsorbent, in particular to a FeS/LDH nano adsorbent, a synthesis method and application thereof, wherein the nano adsorbent is based on LDH and is loaded with amorphous iron sulfide on the surface; the method comprises the following steps: s1: dissolving ferric salt in deoxidized ultrapure water, fully dissolving the ferric salt by ultrasonic stirring, adding NaOH solution by injection, continuously stirring to adjust the pH value to 8, adding sulfur precursor solution, and fully reacting under the protection of inert gas; s2: centrifuging the solution after the reaction in the step S1, washing and drying the precipitate to obtain precursor powder; s3: calcining the precursor powder obtained in the step S2 in an inert gas atmosphere to obtain the FeS/LDH nano adsorbent. Compared with the prior art, the method realizes the efficient removal of common heavy metal anions in the wastewater, reduces the concentration of heavy metals in the water body, and simultaneously achieves the effect of fixing the heavy metals on the surface of the adsorbent.

Description

FeS/LDH nano adsorbent and synthetic method and application thereof
Technical Field
The invention relates to an adsorbent, in particular to a FeS/LDH nano adsorbent, and a synthesis method and application thereof.
Background
Heavy metals are important mineral raw materials manufactured in the nonferrous industry in China, are mostly distributed in soil matrixes, and are important raw materials in the industrial fields of smelting, alloy printing, mining, coal burning, electroplating, leather tanning, semiconductor manufacturing and the like. Excessive heavy metal exploitation not only causes rapid consumption of non-renewable resources, but also causes serious environmental problems due to industrial waste generated by industrial products, such as industrial chromium slag is buried under untreated conditions, diffusion and migration of chromium element are easy to cause, toxic hexavalent chromium is easy to migrate and diffuse under natural conditions, and soil and underground water can be polluted after vertical migration, so that the safety of drinking water and human health are threatened. In addition, the high-concentration heavy metal anion wastewater generated in the electroplating industry also faces the problems of high treatment difficulty, high treatment cost and the like.
The common treatment means of heavy metal anions in water at present are a chemical precipitation method and an ion exchange method. Because heavy metal anions per se have physicochemical properties, heavy metals in different valence states generally show differential solubility products, corresponding metal oxide or hydroxide precipitates are often obtained by changing the valence state of the heavy metal anions, so that the heavy metal anions such as Cr (VI) can be conveniently separated from a water body, and a method of adding a reducing salt is generally adopted, namely, hexavalent chromium with strong toxicity is firstly converted into trivalent with low toxicity, and then alkaline substances such as lime, caustic soda and the like are utilized to enable the trivalent chromium to form Cr (OH) 3 And precipitating to achieve the purpose of removing hexavalent chromium. However, this method requires a large amount of alkali and a flocculant to be used together, which causes problems in terms of excessive pH of the discharged water and operational costs. The ion exchange method is to exchange ions with heavy metal anions in water through exchange resin or zeolite, and the like, and has the advantages of high purification depth, simple and convenient operation, and the like, and has the disadvantages of high cost and low efficiency. Compared with the two methods, the nano-adsorbent has the characteristics of high reaction activity, large specific surface area, high adsorption speed and the like, can effectively strengthen the atomic utilization rate in the adsorbent, realizes high-efficiency ion transfer and reaction on a solid-liquid interface, and is a common thinking for treating three heavy metals aiming at high-valence metals Cr (VI), as (V) and Sb (V) with higher oxidation-reduction potential, so that development of the nano-adsorbent commonly applicable to heavy metal anions has important significance.
Disclosure of Invention
The invention aims to solve at least one of the problems, and provides a FeS/LDH nano adsorbent, a synthesis method and application thereof, which realize the efficient removal of three common heavy metal anions Cr (VI), as (V) and Sb (V) in wastewater, reduce the concentration of heavy metals in a water body, and simultaneously fix the heavy metals on the surface of the adsorbent, and the adsorbent can be recycled through elution treatment, so that an economic solution for high-concentration wastewater is provided.
The aim of the invention is achieved by the following technical scheme:
the first aspect of the invention discloses a FeS/LDH nano-adsorbent, which is based on LDH and is loaded with amorphous iron sulfide on the surface.
Preferably, the particle diameter of the nano adsorbent is 20-200 nm, and the specific surface area is 80-150 m 2 /g; at pH value<8, the Zeta potential of the surface of the adsorbent shows positive electricity, and has good electrostatic adsorption effect on heavy metal anions. Meanwhile, the larger specific surface area provides a large number of chemical adsorption sites for the adsorption of the adsorbent, thereby ensuring the pH value>8, the adsorbent has good adsorption effect, so that the adsorbent has a wider pH application range.
The invention discloses a method for synthesizing the FeS/LDH nano adsorbent, which comprises the following steps of pre-synthesizing an iron-containing precursor with a hydrotalcite-like layered structure, and calcining at a low temperature after vulcanization to synthesize amorphous iron sulfide with high reactivity, namely FeS/LDH, and specifically comprises the following steps:
s1: dissolving ferric salt in deoxidized ultrapure water, fully dissolving the ferric salt by ultrasonic stirring, slowly injecting and adding NaOH solution to adjust the pH to be about 8, gradually adding sulfur precursor solution, and fully reacting under the protection of inert gas;
s2: centrifuging the solution after the reaction in the step S1, washing and drying the precipitate to obtain precursor powder;
s3: and (3) calcining the precursor powder obtained in the step (S2) at a low temperature in an inert gas atmosphere to obtain the FeS/LDH nano adsorbent.
Preferably, the iron salt in step S1 includes Fe (II) salt and Fe (III) salt, according to Fe (II): fe (III) =3:1 to 4:1 to form a charge-matched hydrotalcite-like structure; the Fe (II) salt is FeCl 2 ·4H 2 O、(NH 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O and FeSO 4 ·7H 2 One or more of O; the Fe (III) salt is FeCl 3 ·6H 2 O、Fe(NO 3 ) 3 ·9H 2 O and Fe 2 (SO 4 ) 3 ·5H 2 One or more of O; the molar ratio of the Fe (II) salt to the Fe (III) salt is 3:1-4:1. The addition of Fe (III) salts can be used to form hydrotalcite-like structures, which, due to the presence of trivalent metals, can result in a layered structure with some charge remaining, which in turn attracts interlayer anions to neutralize the charge.
Preferably, the deoxidized ultra-pure water in the step S1 is ultra-pure water from which dissolved oxygen is removed, and the removal of dissolved oxygen in the ultra-pure water is achieved by continuously introducing nitrogen gas into the ultra-pure water for at least 30 minutes.
Preferably, the concentration of the NaOH solution is 1-4 mol/L, the injection adding speed is 1-2 mL/min, and the continuous stirring time is at least 30min.
Preferably, the sulfur precursor solution in step S1 is one or more of thioacetamide, thiourea and sodium thiosulfate; the sulfur precursor solution is added according to the mole ratio of Fe (II) to S of 1:2-1:4. Since S cannot completely participate in the reaction, excessive S contributes to forward shift of the reaction equilibrium, and vaporization of S occurs during calcination, it is necessary to increase the dosage of S to resist the loss. The excessive S improves the adsorption effect, but is not obvious, so that the S can be controlled within a certain range, and the addition amount of the S is controlled within a proper range.
Preferably, the reaction time described in step S1 is 4h.
Preferably, the drying in step S2 is vacuum drying at a temperature of 40 to 60 ℃.
The precursor powder obtained in step S2 is prepared by dissolving Fe (II) salt and Fe (III) salt sufficiently in water, and may be dissolved with the aid of ultrasound. When the pH is regulated by NaOH, stirring is continuously carried out for at least 30min, so that divalent and trivalent ions directly form a hydrotalcite-like sheet structure instead of flocculent precipitate, the concentration of NaOH can be 1-4 mol/L, the injection speed is 1-2 mL/min, the hydrotalcite-like structure can be fully grown, and the formation of high specific surface area is facilitated. As the proportion of the hydrotalcite-like structure in the FeS/LDH nano adsorbent can influence the crystallinity of the generated iron sulfide (FeS), the longer the NaOH participates in the reaction, the more obvious the lamellar structure is, the more uniform dispersion effect of the hydrotalcite-like structure on the FeS can be exerted, meanwhile, the crystal growth of the FeS is inhibited, and the obtained small-size amorphous FeS is beneficial to increasing the selective chemical adsorption of heavy metal anions. Therefore, the addition amount and the speed of NaOH are required to be controlled, namely, the mass ratio of FeS to LDH in the FeS/LDH nano adsorbent is controlled to be 1:1 to 1:4.
preferably, the calcination temperature in step S3 is 150-300 ℃ for 2-4 hours.
Preferably, the inert gas in step S1 and step S3 is nitrogen, argon or other inert gases.
According to the synthesis method, uniformly distributed iron sulfide is loaded on the hydrotalcite-like compound laminate as a reaction site, and the characteristic of high specific surface area of a layered structure is utilized, so that material synthesis can be realized at a lower calcination temperature (150-300 ℃).
The third aspect of the invention discloses an application of the FeS/LDH nano adsorbent in removing heavy metal anions in water.
Preferably, the FeS/LDH nano adsorbent is used for removing heavy metal anions such As Cr (VI), as (V) and Sb (V) in a water body with the pH value of 3-10.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, hydrotalcite-like minerals are used as carriers, so that the extra introduction of toxic and harmful substances is reduced or even eliminated in the actual application process, and the risk of secondary pollution to water is reduced. Furthermore, the synthetic process of the adsorbent is simple and nontoxic, is suitable for one-time mass production, has the adsorption capacities of more than 200mg/g for hexavalent chromium (Cr (VI)), pentavalent antimony (Sb (V)) and pentavalent arsenic (As (V)), can rapidly remove low-concentration wastewater in a short time, realizes deep purification of water within half an hour, and is an efficient and convenient adsorption material.
2. The invention utilizes the layered structure of hydrotalcite-like compound, firstly obtains Fe (II) sites uniformly distributed on the surface of the layered structure, and then synthesizes FeS in situ on the sites, thereby realizing uniform dispersion of adsorption sites; the produced nano adsorbent has larger specific surface area, can provide a large number of chemical adsorption sites and can improve the adsorption effect.
3. The FeS/LDH synthesized by the method can reach the equilibrium of adsorption reaction within 24 hours, and can realize the deep purification of heavy metal anions (< 0.01 mg/L) within 30 minutes, thereby greatly shortening the treatment time and saving the time cost; meanwhile, the larger adsorption capacity reduces the use cost of the adsorbent, and the subsequent post-treatment of the adsorbent can be facilitated.
4. The FeS/LDH synthesized by the method has the advantages that a part of the FeS/LDH is removed from the electrostatic attraction of the surface of the adsorbent to anions, and the other part of the FeS/LDH is derived from the larger specific surface area to provide enough chemical adsorption sites, namely the FeS chemically reacts on the three anions. Specifically, the chemical adsorption of heavy metals can be realized by loading the iron sulfide with high reactivity on the surface of the adsorbent, and the residual high-valence anions can be removed by utilizing the electrostatic attraction effect on the surface of the adsorbent, so that the effect of deep purification can be achieved.
5. The FeS/LDH synthesized by the method has stronger selectivity to heavy metal anions, and is tested by ion competition adsorption experiments to contain NO 3 - 、SO 4 2- 、Cl - And CO 3 2- The adsorbent can still maintain higher removal rates of Cr (VI), as (V) and Sb (V).
6. After adsorbing heavy metal anions, the FeS/LDH synthesized by the method is washed by hydrochloric acid for a short time, can be recycled for at least more than 5 times, can keep the removal rate at the optimal pH value (pH=3) to be more than 90%, and can keep the removal rate in a slightly alkaline water body to be at least 60%. In addition, the adsorbent can also be used for regulating the pH of the water body, the adsorbent is added into the water body containing heavy metal anions with the initial pH of 3-10, and after full adsorption, the pH of the water body can be regulated to 6-9, so that the ecological environment can be regulated.
Drawings
FIG. 1 is the adsorption capacity of FeS/LDH for Cr (VI) at various initial concentrations in example 1;
FIG. 2 is the schematic representation of examples 2-5: a XRD patterns of FeS/LDH obtained at different calcining temperatures; b, removing Cr (VI) by FeS/LDH obtained at different calcining temperatures;
fig. 3 is a diagram of example 6: XRD patterns of a FeS and LDH in different ratios; adsorption kinetics of b FeS and LDH in different ratios;
FIG. 4 is the adsorption capacity of FeS/LDH for Cr (VI) at various initial pH values in example 7;
FIG. 5 is the adsorption capacity after the FeS/LDH acid wash cycle of example 9.
Detailed Description
The invention is described in detail below in connection with specific examples, but in no way limits the invention.
The reagents and measurement methods used in the following examples may be those commercially available and conventional methods which can be conventionally obtained by those skilled in the art unless otherwise specified.
The main steps in the following embodiments include:
(1) Introducing nitrogen into the ultrapure water for at least 30min to fully remove dissolved oxygen contained in the water body, and then adding quantitative Fe (II) salt and Fe (III) salt reagents;
(2) Ultrasonically dispersing the solution in the step (1) for 10min to fully dissolve Fe (II) salt and Fe (III) salt, then adding NaOH solution to adjust the pH to about 8, and continuously stirring for more than 30 min;
(3) Continuously injecting sulfur precursor solution under stirring in nitrogen atmosphere for full reaction, centrifuging the reaction product at 6000rpm, washing and vacuum drying the precipitate for 4h, wherein the obtained yellow powder is a precursor of a final product;
(4) Calcining for 2-4 h at 150-300 ℃ in a tube furnace under the nitrogen environment to obtain the final adsorbent FeS/LDH.
Example 1
Nitrogen was purged with 800mL of ultrapure water for 30 minutes to remove dissolved oxygen, and 1.9881g of FeCl was weighed 2 ·4H 2 O and 1.212gFe (NO) 3 ) 3 ·9H 2 O was dissolved in ultrapure water and sonicated for 10min to disperse it thoroughly and stirring was continued for 30min. Under the condition of introducing nitrogen, continuously injecting 1mol/LNaOH solution into the solution at a speed of 1ml/min until the pH value is stabilized to 8, continuously stirring and reacting for 2 hours, injecting a solution dissolved with 1.5g of thioacetamide into the reaction solution for reacting for 2 hours, centrifugally separating and precipitating the reacted solution at 6000rpm, washing the separated precipitate with ultrapure water and acetone in sequence, and then drying the precipitate in vacuum at 60 ℃ for 4 hours. And transferring the dried powder and the powder into an alumina crucible, and calcining the powder in a tube furnace at 200 ℃ in a nitrogen atmosphere for 3 hours to obtain the final FeS/LDH black powder.
Adsorption test (taking Cr (VI) as an example):
40 mg/L-300 mg/L of Cr (VI) solution is weighed into a 50ml centrifuge tube, 20mg of FeS/LDH is weighed and added into the Cr (VI) solution, the mixture is sealed and vibrated for 3 hours in a shaking table at 25 ℃, the removal rate (adsorption capacity) is shown as figure 1, and the adsorption capacity of the mixture to Cr (VI) can reach more than 200 mg/g.
Example 2
The method for synthesizing the FeS/LDH nano adsorbent comprises the steps of mixing Fe (II) ferric salt and Fe (III) ferric salt with NaOH and thioacetamide according to stoichiometric ratio to prepare a precursor, and then calcining at low temperature to obtain the FeS/LDH nano adsorbent, wherein the specific operation steps are as follows:
(1) Weigh 12mmol FeCl 2 ·4H 2 O was dissolved in 800mL of deoxidized ultra pure water, and 4mmol of FeCl was weighed again 3 ·6H 2 O was added to the solution, and the solution was dispersed in the above solution by ultrasonic treatment for 10min, stirring was continued for 30min, nitrogen was continuously introduced into the above mixed solution, and 1mol/L NaOH solution was injected at a rate of 1ml/min to adjust pH to 8, and reacted for 1h under magnetic stirring. Then injecting a solution dissolving 32mmol of thiourea into the reaction solution for reaction for 2 hours;
(2) Centrifuging the reacted solution at 6000rpm to separate precipitate, sequentially cleaning the separated precipitate with ultrapure water and acetone, and vacuum drying at 60deg.C for 4 hr to obtain precursor powder;
(3) Transferring the dried precursor powder into an alumina crucible, and calcining for 2 hours in a tube furnace at 200 ℃ in a nitrogen atmosphere to obtain the final FeS/LDH black powder.
Example 3
Substantially the same as in example 2, except that the ferrous salt solution used was (NH) 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O, the sulfur precursor used is sodium thiosulfate.
Example 4
Substantially the same as in example 2, except that the ferrite solution used was FeSO 4 ·7H 2 O, the calcination temperature used was 300 ℃.
Example 5
Substantially the same as in example 2 was conducted except that thiourea was used as the sulfur precursor solution.
The final samples obtained in examples 2-5 were tested for amorphous FeS (as shown in FIG. 2 a) and when calcined at 400℃, feS crystals grew, inhibiting the removal efficiency of heavy metals (as shown in FIG. 2 b). Because of the different anions of the different ferrous salts, the interlayer anions of the final FeS/LDH formed are different, and thus the ion exchange effect on the different heavy metal anions will be slightly different depending on the ferrous salts selected.
Example 6
A method for synthesizing FeS/LDH nano adsorbent for controlling FeS crystallinity comprises the following specific steps:
(1) Weigh 12mmol FeCl 2 ·4H 2 O and 4mmol FeCl 3 ·6H 2 O is dissolved in 800ml of deoxidized ultrapure water, 20ml,40ml and 80ml of NaOH solution with the concentration of 1mol/L are respectively injected (the dosage of hydrotalcite-like structures formed in a final sample is different and is called 1:1;1:2; 1:4), 24mmol of thioacetamide solution is continuously injected under the condition of nitrogen gas introduction, and the reaction is carried out for 4 hours under the magnetic stirring state;
(2) Centrifuging the reacted solution at 6000rpm to separate precipitate, sequentially cleaning the separated precipitate with ultrapure water and acetone, and vacuum drying at 60deg.C for 4 hr to obtain precursor powder containing LDH at different ratios;
(3) Transferring the dried precursor powder into an alumina crucible, and calcining for 2 hours in a tube furnace at 200 ℃ in a nitrogen atmosphere to obtain FeS/LDH black powder with different crystal forms.
In the final sample obtained, iron sulfide in the 1:1 ratio sample presents FeS 2 While the iron sulfides in the 1:2 and 1:4 samples exhibit an amorphous form, the crystal forms of which correspond to hydrotalcite layered structures (as shown in fig. 3 a).
The prepared sample is added into a solution containing heavy metal anions Cr (VI), the adsorption reaction is carried out for 30min, the deep purification capacity of a 1:4 sample is lower than that of 1:2 and 1:1 samples, and a 1:2 (pH is about 8) sample has a faster adsorption speed (as shown in fig. 3 b), so that the sample is an optimal sample. The secondary pollution of releasing Fe and S to the environment in the application process of the 1:4 sample is less.
Example 7
The application of the FeS/LDH nano adsorbent in solutions containing heavy metal anions at different pH values comprises the following specific steps:
(1) 10 groups of 50mg/L solutions of heavy metal anions (Cr (VI)) were magnetically stirred, of which 5 groups were adjusted to pH 2, 3, 4, 5, 6 with 0.5mol/L hydrochloric acid, respectively, and the other 5 groups were adjusted to pH 7, 8, 9, 10, 11 with 0.5mol/L NaOH solution, respectively. The adsorption test was also performed according to the procedure of the adsorption test in example 1, and it should be noted that the reaction time in this example was prolonged to 24 hours, so that the reaction was sufficient and the pH of the water body after adsorption was stable;
(2) Standing the solution reacted in the step (1) for a period of time, taking supernatant, filtering with a 0.22 mu m filter head, quantitatively analyzing heavy metal elements in the supernatant by using an ICP-OES instrument, and simultaneously detecting the pH of the solution after the reaction is finished;
the experimental results are shown in fig. 4, and the FeS/LDH has the best effect of removing heavy metal anions at an initial ph=3, which is close to 100%.
Example 8
The application of the FeS/LDH nano adsorbent in solutions containing heavy metal anions at different pH values comprises the following specific steps: treating the solution containing heavy metal anion arsenic, taking 40ml of pentavalent arsenic solution with initial concentration of 50mg/L in a 50ml centrifuge tube, weighing 20mg of FeS/LDH, adding into the arsenic solution, and carrying out oscillation reaction for 30min at room temperature.
Example 9
The application of FeS/LDH nano adsorbent for circularly treating heavy metal anion-containing solution comprises the following specific steps:
(1) FeS/LDH black powder was prepared according to the synthesis method in example 1 and used for adsorption experiments of 50mg/L of a solution containing heavy metal anions (Cr (VI)), and after 3 hours of reaction, the solution was allowed to stand for precipitation;
(2) Separating the supernatant and the black precipitate in the step (1), adding 10ml of 0.05mol/L hydrochloric acid into the precipitate, vibrating for about 30min to desorb the heavy metal complex adsorbed on the surface of FeS/LDH into a hydrochloric acid solution, standing for precipitation, and filtering to obtain the recycled FeS/LDH adsorbent;
(3) After the repeated adsorption test is carried out on the adsorbent obtained in the step (2), 0.05mol/L hydrochloric acid is used again for desorption treatment so as to achieve the effect of recycling the FeS/LDH adsorbent;
after 5 times of circulation tests, the adsorbent can still achieve the removal effect (shown in figure 5) of more than 90% on the heavy metal anion-containing solution with the initial concentration of 20mg/L, has good adsorption effect after a plurality of times of circulation, and can greatly reduce the use cost of the adsorbent.
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.

Claims (9)

1. A method for synthesizing FeS/LDH nano-adsorbent, which is characterized in that the nano-adsorbent is based on LDH and has amorphous iron sulfide loaded on the surface;
the synthesis method comprises the following steps:
s1: dissolving ferric salt in deoxidized ultrapure water, fully dissolving the ferric salt by ultrasonic stirring, adding NaOH solution by injection, continuously stirring to adjust the pH value to 8, adding sulfur precursor solution, and fully reacting under the protection of inert gas;
s2: centrifuging the solution after the reaction in the step S1, washing and drying the precipitate to obtain precursor powder;
s3: calcining the precursor powder obtained in the step S2 in an inert gas atmosphere to obtain the FeS/LDH nano adsorbent;
the ferric salt in the step S1 comprises Fe (II) salt and Fe (III) salt, and the molar ratio of the Fe (II) salt to the Fe (III) salt is 3:1-4:1.
2. The method for synthesizing FeS/LDH nano-adsorbent according to claim 1, wherein the nano-adsorbent has a particle size of 20-200 nm and a specific surface area of 80-150 m 2 /g; at pH value<8, the Zeta potential of the surface of the adsorbent shows positive electricity.
3. The method for synthesizing FeS/LDH nano-adsorbent according to claim 1, wherein the Fe (II) salt is FeCl 2 ·4H 2 O、(NH 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O and FeSO 4 ·7H 2 One or more of O; the Fe (III) salt is FeCl 3 ·6H 2 O、Fe(NO 3 ) 3 ·9H 2 O and Fe 2 (SO 4 ) 3 ·5H 2 One or more of O.
4. The method for synthesizing the FeS/LDH nano adsorbent according to claim 1, wherein the concentration of the NaOH solution is 1-4 mol/L, the injection adding speed is 1-2 mL/min, and the continuous stirring time is at least 30min.
5. The method for synthesizing a FeS/LDH nano-adsorbent according to claim 1, wherein the sulfur precursor solution in step S1 is one or more of thioacetamide, thiourea and sodium thiosulfate; the sulfur precursor solution is added according to the mole ratio of Fe (II) to S of 1:2-1:4.
6. The method for synthesizing the FeS/LDH nano adsorbent according to claim 1, wherein the reaction time in the step S1 is 2-4 hours.
7. The method for synthesizing the FeS/LDH nano adsorbent according to claim 1, wherein the drying in the step S2 is vacuum drying, and the temperature is 40-60 ℃.
8. The method for synthesizing the FeS/LDH nano adsorbent according to claim 1, wherein the calcining temperature in the step S3 is 150-300 ℃ and the calcining time is 2-4 hours.
9. Use of a FeS/LDH nanosorbent as described in any of claims 1-8 in the removal of heavy metal anions from water.
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