CN111825123A - Preparation method of iron oxides with different crystal forms - Google Patents
Preparation method of iron oxides with different crystal forms Download PDFInfo
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- CN111825123A CN111825123A CN202010781233.5A CN202010781233A CN111825123A CN 111825123 A CN111825123 A CN 111825123A CN 202010781233 A CN202010781233 A CN 202010781233A CN 111825123 A CN111825123 A CN 111825123A
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- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 title claims abstract description 47
- 239000013078 crystal Substances 0.000 title claims abstract description 33
- 235000013980 iron oxide Nutrition 0.000 title claims abstract description 28
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 title claims abstract description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 36
- 150000001340 alkali metals Chemical class 0.000 claims abstract description 32
- 229910052783 alkali metal Inorganic materials 0.000 claims abstract description 31
- 238000000034 method Methods 0.000 claims abstract description 30
- 238000001354 calcination Methods 0.000 claims abstract description 28
- 239000012692 Fe precursor Substances 0.000 claims abstract description 21
- 229910006297 γ-Fe2O3 Inorganic materials 0.000 claims abstract description 15
- 150000001875 compounds Chemical class 0.000 claims abstract description 13
- 229910003145 α-Fe2O3 Inorganic materials 0.000 claims abstract description 13
- 150000003839 salts Chemical class 0.000 claims abstract description 12
- 239000003513 alkali Substances 0.000 claims abstract description 11
- 239000007864 aqueous solution Substances 0.000 claims abstract description 11
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims abstract description 8
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 21
- 239000002244 precipitate Substances 0.000 claims description 19
- 239000000243 solution Substances 0.000 claims description 19
- 238000003756 stirring Methods 0.000 claims description 19
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 18
- 238000005406 washing Methods 0.000 claims description 14
- 239000008367 deionised water Substances 0.000 claims description 12
- 229910021641 deionized water Inorganic materials 0.000 claims description 12
- 238000001035 drying Methods 0.000 claims description 8
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 6
- 230000001476 alcoholic effect Effects 0.000 claims description 5
- 238000000227 grinding Methods 0.000 claims description 5
- 229910052708 sodium Inorganic materials 0.000 claims description 5
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 4
- 238000000975 co-precipitation Methods 0.000 claims description 4
- 239000002184 metal Substances 0.000 claims description 4
- 239000002904 solvent Substances 0.000 claims description 4
- 238000001308 synthesis method Methods 0.000 claims description 4
- 229910002651 NO3 Inorganic materials 0.000 claims description 3
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 3
- 238000000593 microemulsion method Methods 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 238000004729 solvothermal method Methods 0.000 claims description 3
- 238000005979 thermal decomposition reaction Methods 0.000 claims description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 claims description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 claims description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 2
- 239000002202 Polyethylene glycol Substances 0.000 claims description 2
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 2
- 229910052792 caesium Inorganic materials 0.000 claims description 2
- -1 ester salt Chemical class 0.000 claims description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 claims description 2
- 238000005470 impregnation Methods 0.000 claims description 2
- 229920001223 polyethylene glycol Polymers 0.000 claims description 2
- 229910052700 potassium Inorganic materials 0.000 claims description 2
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 claims description 2
- 229910052701 rubidium Inorganic materials 0.000 claims description 2
- 238000000967 suction filtration Methods 0.000 claims description 2
- 230000008569 process Effects 0.000 abstract description 7
- 239000002994 raw material Substances 0.000 abstract description 4
- 230000007547 defect Effects 0.000 abstract description 2
- 238000003912 environmental pollution Methods 0.000 abstract 1
- 239000011734 sodium Substances 0.000 description 16
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 14
- 229960002089 ferrous chloride Drugs 0.000 description 9
- NMCUIPGRVMDVDB-UHFFFAOYSA-L iron dichloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 description 9
- 229910000029 sodium carbonate Inorganic materials 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 4
- 239000001913 cellulose Substances 0.000 description 4
- 229920002678 cellulose Polymers 0.000 description 4
- 238000005303 weighing Methods 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 238000005119 centrifugation Methods 0.000 description 3
- 238000003760 magnetic stirring Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000012716 precipitator Substances 0.000 description 3
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 2
- 229910000640 Fe alloy Inorganic materials 0.000 description 2
- 238000001237 Raman spectrum Methods 0.000 description 2
- JZQOJFLIJNRDHK-CMDGGOBGSA-N alpha-irone Chemical compound CC1CC=C(C)C(\C=C\C(C)=O)C1(C)C JZQOJFLIJNRDHK-CMDGGOBGSA-N 0.000 description 2
- 239000001099 ammonium carbonate Substances 0.000 description 2
- 235000012501 ammonium carbonate Nutrition 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000003980 solgel method Methods 0.000 description 2
- 239000006228 supernatant Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 150000003863 ammonium salts Chemical class 0.000 description 1
- 238000010923 batch production Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005518 electrochemistry Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 238000002354 inductively-coupled plasma atomic emission spectroscopy Methods 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- SZQUEWJRBJDHSM-UHFFFAOYSA-N iron(3+);trinitrate;nonahydrate Chemical compound O.O.O.O.O.O.O.O.O.[Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O SZQUEWJRBJDHSM-UHFFFAOYSA-N 0.000 description 1
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000000696 magnetic material Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000008204 material by function Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000005408 paramagnetism Effects 0.000 description 1
- 235000010333 potassium nitrate Nutrition 0.000 description 1
- 239000004323 potassium nitrate Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 239000010865 sewage Substances 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G49/00—Compounds of iron
- C01G49/02—Oxides; Hydroxides
- C01G49/06—Ferric oxide [Fe2O3]
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
- C01P2002/82—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by IR- or Raman-data
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Nanotechnology (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Composite Materials (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Materials Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Compounds Of Iron (AREA)
Abstract
The invention relates to a preparation method of iron oxides with different crystal forms, wherein an Fe precursor is prepared from Fe salt and an alkali compound aqueous solution containing alkali metal, and the content of the alkali metal remained in the Fe precursor is controlled to modulate the calcined Fe2O3Middle alpha-Fe2O3And gamma-Fe2O3The content of (a). Compared with the prior art, the preparation method is simple and easy to implement, and the preparation method of the nano iron oxide with low raw material cost, simple equipment and controllable crystal form is provided, so that the defect of uncontrollable crystal form in the prior art is overcome; according to Fe on calcination2O3The proportion of alkali metal contained in the nano iron oxide is increased from 0, the crystal form is gradually changed from alpha to gamma, and the crystal form modulation of the nano iron oxide product is realized through the control of process conditions; meanwhile, the preparation raw materials are easy to obtain, the environmental pollution is small, and the possibility of industrialization is provided.
Description
Technical Field
The invention relates to a preparation method of iron oxide, in particular to a preparation method of iron oxide with different crystal forms.
Background
Iron oxide, as a transition metal oxide, is a catalyst widely used in reactions such as sewage treatment, synthesis gas conversion and the like, and is also one of important functional materials in inorganic materials. Iron oxides can be classified into FeO and Fe according to valence states2O3And Fe3O4In which Fe2O3And can be divided into alpha, beta and gamma forms according to crystal forms. The most studied in the literature reports at present is alpha-Fe2O3And gamma-Fe2O3。α-Fe2O3Is the most stable crystal structure, usually reddish brown, and has not only good corrosion resistance, light resistance and weather resistance, but also good dispersibility and remarkable ultraviolet absorption and shielding effects. gamma-Fe2O3Is Fe2O3The metastable crystal form is brown generally, has a spinel structure, has strong paramagnetism, and can be used as an excellent magnetic medium of an adsorbent. Nano alpha-and gamma-Fe2O3Has shown wide application prospect in the fields of catalysis, electrochemistry, adsorption, sensors, magnetic materials, biomedicine and the like.
The chemical methods for preparing the nano iron oxide at present mainly comprise a sol-gel method, a hydrothermal method or a solvothermal method, a precipitation method, a microemulsion method, a thermal decomposition method and the like. Different methods have great differences in reaction principles, reaction equipment and reaction conditions, which results in different product shapes and properties, so that in the prior art, the controllable regulation of the content of the nanoscale alpha-iron oxide and the nanoscale gamma-iron oxide in the product is difficult to realize through the regulation and control of specific links in the preparation process, and therefore, the technical problem to be solved at present is how to produce nanoscale Fe in batches2O3In the process, the crystal form modulation of the nano iron oxide product is realized by controlling the process conditions.
Disclosure of Invention
The present invention is directed to overcoming the above-mentioned drawbacks of the prior art and providing a simple and controllable method for preparing nano-scale alpha-iron oxide and gamma-iron oxide, in which an alkali metal is used to induce the calcination of an Fe precursor to form Fe with different crystal phases2O3The preparation method of the nano iron oxide with low raw material cost, simple equipment and controllable crystal form is provided, and the defects in the prior art are overcome; according to Fe on calcination2O3The proportion of alkali metal contained in the nano iron oxide is increased from 0, the crystal form is gradually changed from alpha to gamma, and the crystal form modulation of the nano iron oxide product is realized by controlling the process conditions.
The purpose of the invention can be realized by the following technical scheme:
the preparation method of the iron oxide with different crystal forms, which is disclosed by the invention, prepares the Fe precursor by using the iron salt and the alkali compound aqueous solution containing alkali metal, and modulates the calcined Fe by controlling the content of the alkali metal remained in the Fe precursor2O3Middle alpha-Fe2O3And gamma-Fe2O3The content of (a).
Further, the synthesis method of the Fe precursor is one of a coprecipitation method, an impregnation method, a hydrothermal method, a solvothermal method, a sol-gel method and a microemulsion method or a thermal decomposition method.
Further, the synthesis method of the Fe precursor is a coprecipitation method, and comprises the following steps:
s1: dissolving Fe salt in an alcohol solvent, and then stirring at the temperature of-20 ℃ to obtain 0.02mol/LFe salt alcohol solution;
s2: preparing an alkali compound aqueous solution of alkali metal or ammonium, dripping the alkali compound aqueous solution into the Fe salt alcoholic solution at a constant speed, and keeping stirring;
s3: and (4) taking out the precipitate obtained in the step (S2), washing, controlling the content of alkali metal in the precipitate according to the washing times, and controlling the content of alkali metal to obtain Fe precursors with different crystal forms.
Further, in S3, the residual amount of alkali metal in the precipitate is controlled to 0-15 wt% by the number of washing times.
Further, the alkaline compound is any one of hydroxide, carbonate or bicarbonate containing Na, K, Rb or Cs.
Further, the alkali metal is preferably Na, and when the residual amount r of the alkali metal in the Fe precursor is 0, Fe obtained after calcination is obtained2O3Are all alpha-Fe2O3；
When the residual amount of alkali metal in the Fe precursor satisfies 0<r<2.8 wt.% of Fe obtained after calcination2O3Is alpha-Fe2O3And gamma-Fe2O3Mixing phases;
when the residual amount r of alkali metal in the Fe precursor is more than or equal to 2.8 wt%, obtaining Fe after calcination2O3Are all gamma-Fe2O3。
Further, the Fe salt is any one of nitrate, chloride, sulfate or ester salt.
Further, the concentration of the alkaline compound aqueous solution is 0.1-2.0 mol/L, and the adding volume of the alkaline compound aqueous solution is 1-5 times of the volume of the Fe salt alcoholic solution.
Further, the alcohol solvent in S1 is any one of ethanol, ethylene glycol, polyethylene glycol, propanol, isopropanol, and glycerol.
Furthermore, the rotation speed of stirring in S1 is 500-1000 r/min, and the stirring time is 1-24 h.
Furthermore, the stirring time in S2 is 1-24 h.
Further, washing in S3 is performed in the form of centrifugation or suction filtration.
Further, before calcination, the Fe precursor is dried at 120 ℃ for 6-24 hours, and then ground.
Further, the grinding time is 0.5-5 h.
Further, the temperature rise rate is controlled to be 1-4 ℃/min during calcination, the calcination temperature is 400-900 ℃, and the calcination temperature is kept for 4-24 hours.
Further, calcining the mixture and then adding Fe2O3Washing alternately with ethanol and deionized water, after which the Fe is washed2O3At 120 deg.CDrying for 6-24 h to obtain Fe without alkali metal2O3。
Further, the temperature is preferably controlled to-20 to 0 ℃ during stirring in S1 and S2.
The main characteristics and advantages of the invention are as follows:
1) the technical scheme is used for precipitation in a low-temperature environment, and the grain size of crystals is not easy to increase; more importantly, the alcoholic solution has good anti-freezing performance and large viscosity at low temperature, prevents the solution from being solidified, and can further inhibit the aggregation of Fe nano-particles.
2) The invention controls Fe before calcination by selecting a precipitator and washing water quantity and times2O3The content of alkali metal in the calcined Fe is further controlled2O3A crystalline form of (a). Through optimization, when ammonium salt is used as a precipitator or alkali metal is used as a precipitator and the washing times are enough, ICP-OES detects that the residual amount of the alkali metal is close to 0, and alpha-Fe is obtained after calcination2O3(ii) a When the mass fraction of alkali metal (taking Na as an example) exceeds 2.8 percent, all the alkali metal obtained after calcination are gamma-Fe2O3(ii) a When the mass fraction of the alkali metal is between 0 and 2.8 percent, alpha-Fe is obtained after calcination2O3And gamma-Fe2O3Mixing phases of (1). gamma-Fe containing alkali metal2O3After water and ethanol are washed alternately for proper times, alkali metal residue can be completely washed away, and the crystal phase is kept unchanged after drying at 120 ℃.
3) The method has the advantages of easily obtained raw materials, easily controlled and not harsh conditions, low equipment requirement, short production period, almost no pollution to the environment and capability of realizing batch production.
Drawings
FIG. 1 shows Fe with different Na mass fractions in the present technical solution2O3XRD spectrogram after calcination;
FIG. 2 shows different Na mass fractions of Fe2O3Raman spectrum after calcination.
Detailed Description
The invention will now be further described with reference to specific embodiments, without limiting the scope of the invention to the following examples.
Example 1
Preparation of alpha-Fe2O3The process is as follows:
firstly, weighing 2.54g of anhydrous ferrous chloride, dissolving the anhydrous ferrous chloride in a beaker containing 60ml of ethylene glycol, and ultrasonically stirring for 10 minutes; then transferring the solution into a three-neck flask, and maintaining the temperature of the three-neck flask at-20 ℃ for 1h by using an oil bath under magnetic stirring;
dissolving 7.52g of ammonium carbonate in prepared 100ml of deionized water, ultrasonically stirring for 5min until the sodium carbonate is completely dissolved, and continuously standing for 30 min; then dropwise adding the ammonium carbonate solution into the ethylene glycol solution of ferrous chloride at the speed of 1.2ml/min, and continuing to age the precipitate for 2 hours after dropwise adding;
filtering the liquid precipitation mixture on a suction filter by using 1000mL of deionized water, transferring the precipitate into an oven after separating to obtain precipitates, and drying for 10h at the temperature of 120 ℃ until the water is evaporated to dryness to obtain the alpha-Fe2O3。
Example 2
Preparation of alkali-free gamma-Fe2O3The process is as follows:
firstly, respectively weighing 2.54g of anhydrous ferrous chloride, dissolving the anhydrous ferrous chloride in a beaker filled with 60ml of ethylene glycol, and ultrasonically stirring for 10 minutes;
then transferring the solution into a three-neck flask, and maintaining the temperature of the three-neck flask at-20 ℃ for 1h by using an oil bath under magnetic stirring; dissolving 8.48g of sodium carbonate in prepared 100ml of deionized water, ultrasonically stirring for 5min until the sodium carbonate is completely dissolved, and continuously standing for 30 min; then dropwise adding the sodium carbonate solution into the ethylene glycol solution of ferrous chloride at the speed of 1.2ml/min, and continuing to age the precipitate for 2 hours after dropwise adding;
evenly distributing the suspension to 6 centrifuge tubes with the measuring range of 50mL, adding deionized water to 35mL scale positions, centrifuging for 5min at the rotating speed of 8000r/min, separating supernatant, continuously adding deionized water to 35mL scale positions, repeatedly centrifuging once, separating to obtain precipitates, transferring into an oven, and drying at 120 ℃ for 10h until the water is evaporated to dryness;
grinding the dried precipitate and putting the ground precipitate into a muffle furnaceCalcining, raising the temperature to 450 ℃ at the temperature rise rate of 2 ℃/min, and keeping for 4 h; taking out the calcined product, alternately and repeatedly centrifuging and washing with ethanol and water for 10 times, transferring into a 120 ℃ oven for drying for 10h to obtain the gamma-Fe without alkali metal2O3。
Example 3
Preparation of gamma-Fe by cellulose template dipping method2O3The process is as follows:
firstly, shearing a cellulose template into a size of 0.5cm multiplied by 0.5cm, weighing 1g, and dropwise adding deionized water to measure the saturated water absorption capacity;
then, 1.875g of ferric nitrate nonahydrate and 0.256g of potassium nitrate were dissolved in deionized water equivalent to the saturated water absorption capacity thereof;
then, dropwise adding the prepared nitrate solution onto a 1g cellulose template while stirring, and continuously stirring for 10min after dropwise adding;
transferring the impregnated cellulose template into a 120 ℃ oven for drying for 10h until the water is evaporated to dryness;
grinding the dried precipitate, calcining in a muffle furnace with air, heating to 900 deg.C at a temperature rise rate of 10 deg.C/min, and maintaining for 4 hr to obtain gamma-Fe2O3。
Example 4
Fe of different Na mass fractions2O3Preparation and characterization of
Firstly, weighing 2.54g of anhydrous ferrous chloride, dissolving the anhydrous ferrous chloride in a beaker filled with 60ml of ethylene glycol, and ultrasonically stirring for 10 minutes;
then transferring the solution into a three-neck flask, and maintaining the temperature of the three-neck flask at-20 ℃ for 1h by using an oil bath under magnetic stirring;
dissolving 8.48g of sodium carbonate in prepared 100ml of deionized water, ultrasonically stirring for 5min until the sodium carbonate is completely dissolved, and continuously standing for 30 min; then dropwise adding the sodium carbonate solution into the ethylene glycol solution of ferrous chloride at the speed of 1.2ml/min, and continuing to age the precipitate for 2 hours after dropwise adding;
evenly distributing the suspension to 6 centrifuge tubes with the measuring range of 50mL, adding deionized water to 35mL scale positions, centrifuging for 5min at the rotating speed of 8000r/min, separating supernatant, and continuously adding deionized water to 35mL scale positions for repeated centrifugation once;
repeating the preparation steps, changing the total centrifugation times into three times, four times, six times and ten times respectively, and controlling the degree of washing away residual sodium to obtain iron oxide precursors with different sodium contents;
and separating to obtain a precipitate, transferring the precipitate into an oven, drying for 10h at 120 ℃ until the water is evaporated to dryness, grinding the dried precipitate, putting the ground precipitate into a muffle furnace for calcining, raising the temperature to 450 ℃ at the heating rate of 2 ℃/min, and keeping for 4h to obtain the iron oxide with different sodium contents.
FIG. 1 shows that the mass fraction of Na in the Fe alloy is different from 0-4.4%2O3XRD pattern after calcination. According to standard PDF cards, 2 θ is 30.0 °,35.3 °,42.9 °,56.7 ° and 62.2 ° corresponding to α -Fe2O3Are iron phases present on the three low Na catalysts, Fe-0.2Na and Fe-0.7 Na. On the other hand, the positions of XRD diffraction peaks on Fe-2.8Na and Fe-4.4Na with high Na content are changed, and peaks with 2 theta of 35.1 degrees and 44.2 degrees appear, and are classified as gamma-Fe according to PDF card2O3. It can be seen that Fe increases with the Na mass fraction2O3The crystal form is transformed from alpha to gamma.
FIG. 2 shows that the mass fraction of Na in the Fe alloy is different from 0-4.4%2O3Raman spectrum after calcination at 225cm-1,295cm-1,406cm-1And 1320cm-1The peak at (A) is alpha-Fe2O3Characteristic vibration peak of (2). The peak position shifts with increasing N content and at the same time at 660cm-1And 729cm-1Has a new correspondence of gamma-Fe2O3The peak of vibration of (1). It can be seen that Fe increases with the Na mass fraction2O3The crystal form is transformed from alpha to gamma.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, 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 embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (10)
1. The preparation method of the iron oxides with different crystal forms is characterized in that an Fe precursor is prepared from Fe salt and an alkali compound aqueous solution containing alkali metal, and the content of the alkali metal remained in the Fe precursor is controlled to modulate the calcined Fe2O3Middle alpha-Fe2O3And gamma-Fe2O3The content of (a).
2. The method for preparing iron oxides with different crystal forms according to claim 1, wherein the synthesis method of the Fe precursor is one of a coprecipitation method, an impregnation method, a hydrothermal method, a solvothermal method, a sol-gel microemulsion method or a thermal decomposition method.
3. The method for preparing iron oxides with different crystal forms according to claim 2, wherein the synthesis method of the Fe precursor is a coprecipitation method, and comprises the following steps:
s1: dissolving Fe salt in an alcohol solvent, and then stirring at the temperature of-20 ℃ to obtain 0.02mol/L Fe salt alcohol solution;
s2: preparing an alkali compound aqueous solution of alkali metal or ammonium, dripping the alkali compound aqueous solution into the Fe salt alcoholic solution at a constant speed, and keeping stirring;
s3: and (4) taking out the precipitate obtained in the step (S2), washing, controlling the content of alkali metal in the precipitate according to the washing times, and controlling the content of alkali metal to obtain Fe precursors with different crystal forms.
4. The method for preparing iron oxides with different crystal forms according to claim 3, wherein the amount of residual alkali metal in the precipitate is controlled to 0-15 wt% by the number of washing times in S3.
5. The method for preparing iron oxide with different crystal forms according to claim 1, wherein the alkaline compound is any one of hydroxide, carbonate or bicarbonate containing Na, K, Rb or Cs.
6. The method for preparing iron oxides in different crystal forms according to claim 5, wherein the alkali metal is Na, and when the residual amount r of the alkali metal in the Fe precursor is 0, Fe obtained after calcination is obtained2O3Are all alpha-Fe2O3；
When the residual amount of alkali metal in the Fe precursor satisfies 0<r<2.8 wt.% of Fe obtained after calcination2O3Is alpha-Fe2O3And gamma-Fe2O3Mixing phases;
when the residual amount r of alkali metal in the Fe precursor is more than or equal to 2.8 wt%, obtaining Fe after calcination2O3Are all gamma-Fe2O3。
7. The method for preparing iron oxides with different crystal forms according to claim 1, wherein the Fe salt is any one of nitrate, chloride, sulfate or ester salt.
8. The method for preparing iron oxides with different crystal forms according to claim 3, wherein the concentration of the aqueous solution of the alkaline compound is 0.1-2.0 mol/L, and the volume of the aqueous solution of the alkaline compound is 1-5 times of the volume of the alcoholic solution of the Fe salt.
9. The method for preparing iron oxides in different crystal forms according to claim 3, wherein the alcohol solvent in S1 is any one of ethanol, ethylene glycol, polyethylene glycol, propanol, isopropanol and glycerol.
10. The method for preparing the iron oxides with different crystal forms according to claim 3, wherein the stirring speed in S1 is 500-1000 r/min, and the stirring time is 1-24 h;
stirring in the S2 for 1-24 h;
washing in a centrifugal or suction filtration mode in S3;
before calcination, drying the Fe precursor at 120 ℃ for 6-24 h, and then grinding;
controlling the heating rate to be 1-4 ℃/min during calcination, controlling the calcination temperature to be 400-900 ℃, and keeping for 4-24 h;
calcining the mixture to obtain Fe2O3Washing alternately with ethanol and deionized water, after which the Fe is washed2O3Drying at 120 ℃ for 6-24 h to obtain Fe without alkali metal2O3。
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