CN104857960A - Graphene-oriented multi-level structure composite oxide catalyst and preparation method thereof - Google Patents
Graphene-oriented multi-level structure composite oxide catalyst and preparation method thereof Download PDFInfo
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Abstract
A graphene-oriented multi-level structure composite oxide catalyst and a preparation method thereof belong to the technical field of environmental catalysis. A citric acid dispersant and complexing modified co-precipitation method is employed to prepare a Graphene template- oriented multi-level structure LDHs nanosheet array / Graphene hybrid material; then the hybrid material is moderately roasted; based on the guiding role of the graphene template, a composite oxide formed in the roasting process of the LDHs nanosheet array remains a three-dimensional nanosheet array morphology; and the composite oxide nanosheet is assembled by oxide particles in small size and have developed pore structure. The novel multi-level structure composite oxide catalyst shows significantly improved catalytic activity compared to an oxide obtained from roasting of only LDHs in the removal of nitrogen oxides and soot combustion reaction; and the invention overcomes the shortcoming of easy agglomeration of LDHs nanosheet in a traditional preparation method.
Description
Technical field
The invention belongs to environmental catalysis technical field, in particular, provide a kind of Graphene guiding multilevel hierarchy composite oxide catalysts and preparation method thereof, this composite oxide catalysts can be effective to removing of environmental contaminants (nitrogen oxide NOx and carbon soot particles Soot).
Technical background
In recent decades, because Diesel engine (diesel engines) has high fuel efficiency and stable durability, it is made to be widely used on all kinds of vehicles, as bus, light-duty or heavy truck etc.But comprise the harmful substance such as various nitrogen oxide (NOx) and carbon soot particles (Soot) in diesel motor exhaust, the environment of depend on for existence to us and human health cause serious harm.In the catalyst of current NO_x removal and Soot, Pt is catalyst based due to its high Activity and stabill, receives and studies widely.But because Pt Precious Metals Resources is valuable and non-renewable, therefore Development of Novel, efficient non-Pt base catalyst of transition metal oxide are used for NO_x removal and Soot pollutant is an important research direction.
Hydrotalcite (Layered Double Hydroxides, be called for short LDHs) be the lamellar compound formed by positively charged laminate and interlayer balance anion ordered fabrication, LDHs can obtain uniform composite metal oxide (Layered Double Oxides is called for short LDOs) through appropriate roasting.LDHs and derivative composite metal oxide LDOs thereof because of its chemical composition can modulation, Elemental redistribution is homogeneous and intrinsic is alkaline, demonstrates excellent catalytic activity in environmental catalysis field.But, traditional coprecipitation is as the customary preparation methods of LDHs, because reaction is carried out in homophase, reaction rate is fast, nucleation time is asynchronous, cause that gained LDHs nanometer sheet size is uneven, controllability is poor, the LDHs nanometer sheet particle aggregation effect generated thus is strong, decentralization is poor, high-temperature roasting very easily sinters, and above-mentioned reason obviously constrains the efficiency utilization of composite metal oxide LDOs in catalytic reaction.
For preventing the sintering of oxide particle in catalyst, effective method is by the dispersion of the template contral nano particle of high-specific surface area or ad hoc structure and growth in preparation process, thus obtain high dispersive, small size and there is the metal oxide catalyst of specific morphology, and then improve catalytic activity.As (Kwak G, Hwang J, CheonJ Y such as Kwak, et al.J.Phys.Chem.C, 2013,117,1773-1779) with ordered mesoporous carbon material CMK-3 for sacrifice template, adopt equi-volume impregnating mesoporous carbon template be impregnated in certain density Co (NO
3)
2in solution, after the mixture drying obtained, in moving air, roasting can obtain the small size Co of 6 ~ 10nm
3o
4mealy oxide catalyst, for demonstrating excellent catalytic activity in Fischer-Tropsch synthesis.Zhang etc. (Chinese invention patent: ZL201310106570.4) with Graphene (Graphene) for growth templates, adopt traditional coprecipitation that LDHs nanometer sheet is carried on Graphene surface, demonstrate LDHs nanometer sheet to tile at random and be distributed in the shape characteristic on Graphene surface, will can obtain the Co of high-specific surface area, small particle diameter after this composite roasting
3o
4mealy oxide catalyst (specific area 80 ~ 110m
2/ g, pore-size distribution is mesoporous distribution, pore volume 0.3 ~ 0.4cm
3/ g), thus it is active to significantly improve its NOx storage.Although in the preparation of heterogeneous catalysis material, become by nanomaterial assembly the high-dimensional multilevel structure materials such as the nanometer rods of specific morphology (1D), nanometer sheet (2D) or Nano microsphere (3D) that unique character can be shown in multiple catalytic reaction, but in current research, there is not been reported for multilevel hierarchy three-dimensional (3D) the composite metal oxide nano-chip arrays catalyst derivative by Graphene Template preparation LDHs.
Summary of the invention
The object of the present invention is to provide a kind of Graphene to lead multilevel hierarchy composite oxide catalysts and preparation method thereof, preparation process is easy and avoid the use of the operating condition of HTHP and a large amount of organic reagent.The composite metal oxide of this multilevel hierarchy pattern demonstrates the feature of small size, high dispersive, substantially increases it and is removing NO
xand the catalytic activity in Soot reaction.
The coprecipitation that the present invention adopts citric acid dispersant and complexing agent to modify first prepares the multilevel hierarchy LDHs nano-chip arrays/Graphene hybrid material of Graphene template direction, then by this hybrid material appropriateness roasting, based on the template direction effect of Graphene, the composite oxides that LDHs nano-chip arrays is formed in roasting still maintain three-dimensional manometer chip arrays pattern, and its composite oxides nanometer sheet is assembled by the oxide particle of small particle diameter and has flourishing pore structure.The multilevel hierarchy composite oxide catalysts of this novelty is removing in nitrogen oxide (NOx) and soot (Soot) combustion reaction the catalytic activity showing more simple LDHs roasting gained oxide and significantly improve.
The multilevel hierarchy composite oxide catalysts of Graphene template direction of the present invention is in Multilevel-structure hydrotalcite (LDHs) nano-chip arrays/Graphene (Graphene) hybrid material, Graphene quality is 8% ~ 25% of LDHs quality, LDHs nanometer sheet size range is 20 ~ 120nm, thickness ~ 5nm, pattern is that LDHs nanometer sheet is orthogonal, interlocking is grown on Graphene basal plane both sides, forms three-dimensional " honeycomb " shape array pattern; By this hybrid material roasting, based on the template direction effect of Graphene, the composite oxides that LDHs nano-chip arrays is formed in roasting still maintain three-dimensional manometer chip arrays pattern, its composite oxides nanometer sheet (thickness is 7 ~ 12nm) is assembled by the oxide particle of small particle diameter (8 ~ 10nm) and has flourishing pore structure, obtains multilevel hierarchy composite oxide catalysts.
Preparation process of the present invention and principle thereof are: in initial preparation, graphene oxide is first with the metal cation in strong electrostatic force absorption salting liquid, citric acid is as dispersant simultaneously, can effectively promote that metal cation is dispersed in surface of graphene oxide; Then, with NaOH/Na
2cO
3mixed alkali liquor be precipitating reagent, the metal cation of surface of graphene oxide absorption can the LDHs crystal seed of in-situ preparation high dispersive, simultaneously citric acid reduces nucleation, the growth rate of LDHs as complexing agent, and control LDHs crystal seed is in surface of graphene oxide original position, slowly grow; After crystallization completes, graphene oxide is reduced to Graphene in strong base solution, obtains multilevel hierarchy LDHs nano-chip arrays/Graphene hybrid material.The shape characteristic of this hybrid material shows as the LDHs nanometer sheet vertical-growth that intermeshes in the both sides of Graphene basal plane, form three-dimensional " honeycomb " shape array pattern, by this hybrid material roasting, based on the template direction effect of Graphene, the composite oxides that LDHs nano-chip arrays is formed in roasting still maintain three-dimensional manometer chip arrays pattern, its composite oxides nanometer sheet is assembled by the oxide particle of small particle diameter and has flourishing pore structure, obtains multilevel hierarchy composite oxide catalysts.Its preparation method comprises the following steps:
(1) with natural flake graphite (325 order) for raw material adopt chemical oxidization method prepare graphite oxide, drying mode adopts freeze drying condition, freezing 1h at prior to-60 DEG C, fluffy graphite oxide is obtained after dry 12h again under vacuum condition, the above-mentioned graphite oxide of set amount is scattered in deionized water, uniform graphene oxide colloidal suspension after ultrasonic disperse, can be obtained.
(2) slaine and citric acid are dissolved in deionized water simultaneously obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, gained slurries are ultrasonic while stirring, obtain brown color slurries B.
(3) by NaOH, Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in deionized water simultaneously.The brown color slurries B obtained in step 2 and mixed ammonium/alkali solutions C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, then crystallization under water bath condition, gained black precipitate spends deionized water to pH=7, obtains multilevel hierarchy LDHs nano-chip arrays/Graphene hybrid material after freeze drying.
(4) corresponding multilevel hierarchy O composite metallic oxide catalyst can be obtained by after the hybrid material appropriateness roasting in step 3.
The mass ratio of the graphite oxide described in step (1) and deionized water used is 2:1, and the graphene oxide colloidal suspension concentration obtained is 2mg/mL, and ultrasonic power is 300W, and ultrasonic time controls as 0.5h ~ 1h.
Slaine described in step (2) comprises the slaine of divalence and trivalent, its existence form is one in nitrate or acetate or its mixed form, bivalent metal ion (M2+) in slaine is one or both combinations in Co2+, Ni2+, Mg2+, Mn2+, trivalent metal ion (M3+) is the one in Al3+, Fe3+, and the molar ratio of M2+ and M3+ is fixed as [M2+]/[M3+]=3:1.
The mass ratio of the citric acid described in step (2) and graphite oxide used is 0.5:1 ~ 1.5:1, the total ionizable metal salt [M of every 100mg citric acid correspondence 0.005 ~ 0.02mol
2++ M
3+], the volume ratio of graphene oxide colloidal suspension and mixed solution A controls as 3:1 ~ 5:1, and ultrasonic power is 300W, and ultrasonic time controls as 10min ~ 30min.
In the mixed base of the every 100mL volume described in step (3), [NaOH]/[M
2++ M
3+] molar ratio is 1.6:1, [Na
2cO
3]/[M
3+] molar ratio is 2:1, time for adding remains between 30 ~ 60min, and crystallization temperature is chosen as 60 ~ 90 DEG C, and the time is 4 ~ 24h, and the freezing dry process of the same step of drying condition (1), obtains multilevel hierarchy M
2+ 3m
3+ 1-LDHs nano-chip arrays/Graphene hybrid material.
Roasting condition described in step (4) to be chosen as in still air 400 ~ 600 DEG C, and heating rate 5 DEG C/min, the retention time is 4h, obtains multilevel hierarchy M
2+ 3m
3+ 1(O) composite metal oxide.
It is pointed out that and the synthetic method (bibliography Kovtyukhova N I, Chem.Mater., 1999,11,771-778) that the chemical oxidization method reference that in the present invention, the preparation of graphite oxide adopts is reported before comprise following corrective measure:
(1) pre-oxidation of graphite.Successively by dense for 24mL H
2sO
4(mass fraction 98%), 5g K
2s
2o
8with 5g P
2o
5join in four-hole boiling flask, add 10g graphite powder under stirring, vigorous stirring reaction 6h in 80 DEG C of water-baths, then four-hole boiling flask is naturally cooled to room temperature, spend deionized water to pH=7,60 DEG C of dryings obtain pre-oxidation graphite powder.
(2) preparation of graphite oxide.The dense H of 115mL is measured in four-hole boiling flask
2sO
4, under agitation successively by 5g pre-oxidation graphite powder and 2.5g NaNO
3join dense H
2sO
4in, and slowly add 15g KMnO
4, under ice-water bath condition, control reaction temperature be no more than 4 DEG C, stir 90min; Then four-hole boiling flask is transferred in the water bath with thermostatic control of 35 DEG C, stirs 30min; After shifting out water-bath, add deionized water while stirring, reaction system very exothermic, control reaction temperature between 95 ~ 98 DEG C, stir 15min; When temperature of reaction system no longer raising when continuing to add water, adding about 200mL deionized water fast, then using the H of 30 ~ 50mL
2o
2(mass fraction 5%) processing reaction liquid, to presenting golden yellow, then fully washs to filtrate without SO with 5%HCl
4 2-(with BaCl
2solution detects without precipitation), finally spend deionized water again and be precipitated to pH=7.By above-mentioned sample freezing 1h in advance at-60 DEG C, then obtain fluffy graphite oxide after dry 12h under vacuum condition.
The present invention compared with prior art has the following advantages and feature:
(1) the present invention is by introducing Graphene template, first the co-precipitation route adopting citric acid dispersant and complexing agent to modify prepares multilevel hierarchy LDHs nano-chip arrays/Graphene hybrid material, then this hybrid material appropriateness roasting is obtained three-dimensional composite metal oxide nano-chip arrays catalyst, in this multilevel hierarchy catalyst, oxide particle demonstrates the feature of small size, high dispersive.The preparation process of this invention is easy, avoids the operating condition of HTHP and the use of a large amount of organic reagent, has good commercial application prospect.
(2) this multilevel hierarchy oxide catalyst shows the catalytic activity that more simple LDHs roasting gained oxide significantly improves in Catalytic Decomposition of Nitric Oxide (NOx) and soot (Soot) combustion reaction, overcome the shortcoming that conventional method prepares LDHs base composite oxidate catalyst high temperature easy-sintering, widen hydrotalcite and the application of grapheme material in catalytic field.
Accompanying drawing explanation
Fig. 1 is the XRD spectra of graphite oxide sample in embodiment 1-5.
Fig. 2 is the SEM figure of graphite oxide sample in embodiment 1-5.
Fig. 3 is embodiment 1 multilevel hierarchy Co
2mg
1al
1the SEM figure of-LDHs nano-chip arrays/Graphene hybrid material.
Fig. 4 is embodiment 1 multilevel hierarchy composite metal oxide Co
2mg
1al
1(O) SEM figure.
Fig. 5 is embodiment 1 multilevel hierarchy composite metal oxide Co
2mg
1al
1(O) TEM figure.
Fig. 6 is embodiment 2 multilevel hierarchy Ni
2mg
1al
1the SEM figure of-LDHs nano-chip arrays/Graphene hybrid material.
Fig. 7 is embodiment 3 multilevel hierarchy Ni
2.5mn
0.5fe
1the SEM figure of-LDHs nano-chip arrays/Graphene hybrid material.
Detailed description of the invention
Following embodiment further illustrates using as the explaination to the technology of the present invention content for content of the present invention; but embodiments of the present invention are not limited to following preparation parameter, those of ordinary skill in the art can and should know any simple change based on connotation of the present invention, replace all should belong to protection domain of the presently claimed invention.
Embodiment 1:
Step 1: be that raw material adopts chemical oxidization method to prepare graphite oxide with natural flake graphite.Specifically comprise two steps: the pre-oxidation of (1) graphite.Successively by dense for 24mL H
2sO
4(mass fraction 98%), 5g K
2s
2o
8with 5g P
2o
5join in four-hole boiling flask, add 10g graphite powder under stirring, vigorous stirring reaction 6h in 80 DEG C of water-baths, then four-hole boiling flask is naturally cooled to room temperature, spend deionized water to pH=7,60 DEG C of dryings obtain pre-oxidation graphite powder.(2) preparation of graphite oxide.The dense H of 115mL is measured in four-hole boiling flask
2sO
4, under agitation successively by 5g pre-oxidation graphite powder and 2.5g NaNO
3join dense H
2sO
4in, and slowly add 15g KMnO
4, under ice-water bath condition, control reaction temperature be no more than 4 DEG C, stir 90min; Then four-hole boiling flask is transferred in the water bath with thermostatic control of 35 DEG C, stirs 30min; After shifting out water-bath, add deionized water while stirring, reaction system very exothermic, control reaction temperature between 95 ~ 98 DEG C, stir 15min; When temperature of reaction system no longer raising when continuing to add water, adding about 200mL deionized water fast, then using the H of 30 ~ 50mL
2o
2(mass fraction 5%) processing reaction liquid, to presenting golden yellow, then fully washs to filtrate without SO with 5%HCl
4 2-(with BaCl
2solution detects without precipitation), finally spend deionized water again and be precipitated to pH=7.By above-mentioned sample freezing 1h in advance at-60 DEG C, then under vacuum condition, obtain fluffy graphite oxide after dry 12h, in 2 θ=10 in its XRD (accompanying drawing 1) spectrogram
othe position display of left and right goes out strong graphite oxide (001) diffraction maximum, and SEM Electronic Speculum (accompanying drawing 2) shows that prepared graphite oxide has obvious fold and bending features, and size can reach micron level.Above-mentioned for 400mg graphite oxide powder to be directly scattered in 200mL deionized water and under 300W power ultrasonic disperse 60min, obtain uniform graphene oxide colloidal suspension (concentration is 2mg/mL).
Step 2: by 0.01mol Co (NO
3)
26H
2o, 0.005mol Mg (NO
3)
26H
2o, 0.005molAl (NO
3)
39H
2o slaine and 400mg citric acid are dissolved in 50mL deionized water simultaneously and obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, by gained slurries ultrasonic 30min in the ultrasonic machine of 300W power, obtain brown color slurries B.
Step 3: by 0.064mol NaOH and 0.02mol Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in 200mL deionized water.The brown color slurries B obtained in step 2 and mixed alkali liquor C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, time for adding is 30min, then crystallization 4h in 65 DEG C of water-baths, gained black precipitate spends deionized water to pH=7, and freeze drying obtains multilevel hierarchy Co
2mg
1al
1-LDHs nano-chip arrays/Graphene hybrid material.The SEM Electronic Speculum (accompanying drawing 3) of material demonstrates Co
2mg
1al
1-LDHs nanometer sheet vertical-growth is in the both sides of graphene film, and form three-dimensional " honeycomb " shape array pattern, wherein LDHs nanometer sheet size ~ 35nm, thickness ~ 5nm, graphene film size still remains on micron level.
Step 4: by multilevel hierarchy Co in step 3
2mg
1al
1-LDHs/Graphene hybrid material (heating rate 5 DEG C/min) roasting 4h in 500 DEG C of still airs obtains multilevel hierarchy O composite metallic oxide catalyst Co
2mg
1al
1(O).The SEM Electronic Speculum result (accompanying drawing 4) of catalyst shows, oxide catalyst demonstrates the feature (lamellar spacing ~ 10nm) of three-dimensional composite metal oxide nano-chip arrays, examine and can see that this three-dimensional composite metal oxide nano-chip arrays is rearranged by the small particle diameter metal oxide particle of high degree of dispersion, and it is staggered the locus of three-dimensional composite metal oxide nanometer sheet to exist to a certain degree, thus preventing the reunion between the nanometer sheet that obtains, the above results shows that catalyst that roasting obtains inherits the multilevel hierarchy pattern of precursor.TEM Electronic Speculum (accompanying drawing 5) shows that this oxide lamella is made up of (~ 8nm) the oxide particle of numerous small particle diameter further, there is numerous hole between oxide particle, grain size, catalyst shape characteristic are consistent with its SEM characterization result.
Embodiment 2:
Step 1: be that raw material adopts chemical oxidization method to prepare graphite oxide with natural flake graphite.300mg graphite oxide to be directly scattered in 150mL deionized water and under 300W power ultrasonic disperse 45min, obtain uniform graphene oxide colloidal suspension (concentration is 2mg/mL).
Step 2: by 0.02mol Ni (NO
3)
26H
2o, 0.01mol Mg (NO
3)
26H
2o and 0.01molAl (NO
3)
39H
2o slaine and 450mg citric acid are dissolved in 50mL deionized water simultaneously and obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, by gained slurries ultrasonic 20min in the ultrasonic machine of 300W power, obtain brown color slurries B.
Step 3: by 0.128mol NaOH and 0.04mol Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in 200mL deionized water.The brown color slurries B obtained in step 2 and mixed alkali liquor C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, time for adding is 45min, then crystallization 12h in 90 DEG C of water-baths, gained black precipitate spends deionized water to pH=7, and freeze drying obtains multilevel hierarchy Ni
2mg
1al
1-LDHs nano-chip arrays/Graphene hybrid material.The SEM Electronic Speculum (accompanying drawing 6) of material demonstrates Ni
2mg
1al
1-LDHs nanometer sheet vertical-growth, in the both sides of graphene film, forms three-dimensional " honeycomb " shape array pattern, wherein LDHs nanometer sheet size ~ 20nm, thickness ~ 5nm.
Step 4: by multilevel hierarchy Ni in step 3
2mg
1al
1-LDHs/Graphene hybrid material (heating rate 5 DEG C/min) roasting 4h in 400 DEG C of still airs obtains multilevel hierarchy O composite metallic oxide catalyst Ni
2mg
1al
1(O).Embodiment 3:
Step 1: be that raw material adopts chemical oxidization method to prepare graphite oxide with natural flake graphite.160mg graphite oxide to be directly scattered in 80mL deionized water and under 300W power ultrasonic disperse 30min, obtain uniform graphene oxide colloidal suspension (concentration is 2mg/mL).
Step 2: by 0.010mol Ni (NO
3)
26H
2o, 0.002mol Mn (CH
3oO)
24H
2o and 0.004molFe (NO
3)
39H
2o slaine and 80mg citric acid are dissolved in 16mL deionized water simultaneously and obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, by gained slurries ultrasonic 10min in the ultrasonic machine of 300W power, obtain brown color slurries B.
Step 3: by 0.0512mol NaOH and 0.016mol Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in 200mL deionized water.The brown color slurries B obtained in step 2 and mixed alkali liquor C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, time for adding is 60min, then crystallization 24h in 60 DEG C of water-baths, gained black precipitate spends deionized water to pH=7, and freeze drying obtains multilevel hierarchy Ni
2.5mn
0.5fe
1-LDHs nano-chip arrays/Graphene hybrid material.The SEM Electronic Speculum (accompanying drawing 7) of material demonstrates Ni
2.5mn
0.5fe
1-LDHs nanometer sheet vertical-growth, in the both sides of graphene film, forms three-dimensional " honeycomb " shape array pattern, wherein LDHs nanometer sheet size ~ 120nm, thickness ~ 5nm.
Step 4: by multilevel hierarchy Ni in step 3
2.5mn
0.5fe
1-LDHs/Graphene hybrid material (heating rate 5 DEG C/min) roasting 4h in 600 DEG C of still airs obtains multilevel hierarchy O composite metallic oxide catalyst Ni
2.5mn
0.5fe
1(O).
Embodiment 4:
Step 1: be that raw material adopts chemical oxidization method to prepare graphite oxide with natural flake graphite.400mg graphite oxide to be directly scattered in 200mL deionized water and under 300W power ultrasonic disperse 60min, obtain uniform graphene oxide colloidal suspension (concentration is 2mg/mL).
Step 2: by 0.03mol Co (NO
3)
26H
2o and 0.01mol Al (NO
3)
39H
2o slaine and 400mg citric acid are dissolved in 50mL deionized water simultaneously and obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, by gained slurries ultrasonic 30min in the ultrasonic machine of 300W power, obtain brown color slurries B.
Step 3: by 0.128mol NaOH and 0.04mol Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in 200mL deionized water.The brown color slurries B obtained in step 2 and mixed alkali liquor C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, time for adding is 40min, then crystallization 12h in 65 DEG C of water-baths, gained black precipitate spends deionized water to pH=7, and freeze drying obtains multilevel hierarchy Co
3al
1-LDHs nano-chip arrays/Graphene hybrid material.
Step 4: by multilevel hierarchy Co in step 3
3al
1-LDHs/Graphene hybrid material (heating rate 5 DEG C/min) roasting 4h in 600 DEG C of still airs obtains multilevel hierarchy O composite metallic oxide catalyst Co
3al
1(O).
Embodiment 5:
Step 1: be that raw material adopts chemical oxidization method to prepare graphite oxide with natural flake graphite.300mg graphite oxide to be directly scattered in 150mL deionized water and under 300W power ultrasonic disperse 45min, obtain uniform graphene oxide colloidal suspension (concentration is 2mg/mL).
Step 2: by 0.03mol Ni (NO
3)
26H
2o and 0.01mol Fe (NO
3)
39H
2o slaine and 450mg citric acid are dissolved in 50mL deionized water simultaneously and obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, by gained slurries ultrasonic 30min in the ultrasonic machine of 300W power, obtain brown color slurries B.
Step 3: by 0.128mol NaOH and 0.04mol Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in 200mL deionized water.The brown color slurries B obtained in step 2 and mixed alkali liquor C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, time for adding is 60min, then crystallization 6h in 80 DEG C of water-baths, gained black precipitate spends deionized water to pH=7, and freeze drying obtains multilevel hierarchy Ni
3fe
1-LDHs nano-chip arrays/Graphene hybrid material.
Step 4: by multilevel hierarchy Ni in step 3
3fe
1-LDHs/Graphene hybrid material (heating rate 5 DEG C/min) roasting 4h in 400 DEG C of still airs obtains multilevel hierarchy O composite metallic oxide catalyst Ni
3fe
1(O).
The above is the preferred embodiment of the present invention, it should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention, can also make some improvement, and these improvement also should be considered as protection scope of the present invention.
Claims (7)
1. a Graphene guiding multilevel hierarchy composite oxide catalysts, it is characterized in that: in Multilevel-structure hydrotalcite LDHs nano-chip arrays/graphene hybrid material, Graphene quality is 8% ~ 25% of LDHs quality, LDHs nanometer sheet size range is 20 ~ 120nm, thickness ~ 5nm, pattern is that LDHs nanometer sheet is orthogonal, interlocking is grown on Graphene basal plane both sides, forms three-dimensional " honeycomb " shape array pattern; By this hybrid material roasting, based on the template direction effect of Graphene, the composite oxides that LDHs nano-chip arrays is formed in roasting still maintain three-dimensional manometer chip arrays pattern, its composite oxides nanometer sheet (thickness is 7 ~ 12nm) is assembled by the oxide particle 8 ~ 10nm of small particle diameter and has flourishing pore structure, obtains multilevel hierarchy composite oxide catalysts.
2. a preparation method for the multilevel hierarchy composite oxide catalysts of Graphene template direction according to claim 1, is characterized in that, comprise the following steps:
(1) with 325 order natural flake graphites for raw material adopt chemical oxidization method prepare graphite oxide, drying mode adopts freeze drying condition, freezing 1h at prior to-60 DEG C, fluffy graphite oxide is obtained after dry 12h again under vacuum condition, gained graphite oxide is scattered in deionized water, after ultrasonic disperse, namely obtains uniform graphene oxide colloidal suspension;
(2) slaine and citric acid are dissolved in deionized water simultaneously obtain mixed solution A.Then under Keep agitation condition, the graphene oxide colloidal suspension in step 1 is slowly poured in mixed solution A, gained slurries are ultrasonic while stirring, obtain brown color slurries B;
(3) by NaOH, Na
2cO
3be dissolved in obtained mixed ammonium/alkali solutions C in deionized water simultaneously, the brown color slurries B obtained in step (2) and mixed ammonium/alkali solutions C is slowly added dropwise in the four-hole boiling flask filling 100mL deionized water simultaneously, control pH=10 ± 0.1, then crystallization under water bath condition, gained black precipitate spends deionized water to pH=7, obtains multilevel hierarchy LDHs nano-chip arrays/graphene hybrid material after freeze drying;
(4) corresponding multilevel hierarchy O composite metallic oxide catalyst is namely obtained by after the hybrid material appropriateness roasting in step (3).
3. preparation method according to claim 2, it is characterized in that: the graphite oxide described in step (1) and the mass ratio of deionized water are 2:1, the graphene oxide colloidal suspension concentration obtained is 2mg/mL, and ultrasonic power is 300W, and ultrasonic time controls as 0.5h ~ 1h.
4. preparation method according to claim 2, it is characterized in that: the slaine described in step (2) comprises the slaine of divalence and trivalent, its existence form is one in nitrate or acetate or its mixed form, the bivalent metal ion M in slaine
2+for Co
2+, Ni
2+, Mg
2+, Mn
2+in one or both combination, trivalent metal ion M
3+for Al
3+, Fe
3+in one, M
2+and M
3+molar ratio be fixed as [M
2+]/[M
3+]=3:1.
5. preparation method according to claim 4, is characterized in that: the mass ratio of citric acid and graphite oxide used is 0.5:1 ~ 1.5:1, the total ionizable metal salt [M of every 100mg citric acid correspondence 0.005 ~ 0.02mol
2++ M
3+], the volume ratio of graphene oxide soliquid and mixed solution A controls as 3:1 ~ 5:1, and ultrasonic power is 300W, and ultrasonic time controls as 10min ~ 30min.
6. preparation method according to claim 2, is characterized in that: in the mixed base of the every 100mL volume described in step (3), [NaOH]/[M
2++ M
3+] molar ratio is 1.6:1, [Na
2cO
3]/[M
3+] molar ratio is 2:1, time for adding remains between 30 ~ 60min, and crystallization temperature is chosen as 60 ~ 90 DEG C, and the time is 4 ~ 24h, and the freezing dry process of the same step of drying condition (1), obtains M
2+ 3m
3+ 1-LDHs nano-chip arrays/graphene hybrid material.
7. preparation method according to claim 2, is characterized in that: the roasting condition described in step (4) to be chosen as in still air 400 ~ 600 DEG C, and heating rate 5 DEG C/min, the retention time is 4h, obtains multilevel hierarchy M
2+ 3m
3+ 1(O) composite metal oxide.
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