BiWO6-C3N4光催化

BiWO6-C3N4光催化
BiWO6-C3N4光催化

Applied Catalysis B:Environmental 108–109 (2011) 100–107

Contents lists available at ScienceDirect

Applied Catalysis B:

Environmental

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /a p c a t

b

Novel visible light-induced g-C 3N 4/Bi 2WO 6composite photocatalysts for ef?cient degradation of methyl orange

Lei Ge ?,Changcun Han,Jing Liu

Department of Materials Science and Engineering,College of Science,China University of Petroleum Beijing,No.18Fuxue Rd,Beijing 102249,PR China

a r t i c l e

i n f o

Article history:

Received 31May 2011

Received in revised form 12August 2011Accepted 12August 2011

Available online 19 August 2011

Keywords:g-C 3N 4Bi 2WO 6

Photocatalysis Functional

Semiconductors

a b s t r a c t

Novel visible light-induced g-C 3N 4/Bi 2WO 6composite photocatalysts were synthesized by introduc-ing polymeric g-C 3N 4.The obtained g-C 3N 4/Bi 2WO 6products were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,high-resolution transmission electron microscopy,ultraviolet–visible diffuse re?ection spectroscopy (DRS),and photoluminescence spec-troscopy.The DRS results revealed that the g-C 3N 4/Bi 2WO 6samples had a red shift and strong absorption in the visible light region.The photocatalytic oxidation ability of the novel photocatalyst was evalu-ated using methyl orange as a target pollutant.The photocatalysts exhibited a signi?cantly enhanced photocatalytic performance in degrading methyl orange.The optimal g-C 3N 4content for the photocat-alytic activity of the heterojunction structures was determined.The synergic effect between g-C 3N 4and Bi 2WO 6was found to lead to an improved photo-generated carrier separation.Consequently,the photo-catalytic performance of the g-C 3N 4/Bi 2WO 6composites under visible light irradiation ( >420nm)was enhanced.The possible photocatalytic mechanism of the composites was proposed to guide the further improvement of their photocatalytic activity.

? 2011 Elsevier B.V. All rights reserved.

1.Introduction

Photocatalysis using semiconductors has received considerable interest.This process enables pollutant decomposition and hydro-gen evolution via the generation of ?OH radicals and other oxidative species [1–3].The semiconductor TiO 2is considered as one of the best photocatalysts [4].However,the light response range and the photo-ef?ciency of TiO 2are limited because of its wide band gap (3.2eV)[5].Therefore,the creation of simple,ef?cient,and sustainable photocatalysts that work well with visible light is a major challenge in this research ?eld [6].Recently,various multi-component oxide,sul?de,oxynitride,and polymer semiconductor photocatalysts have been developed for degrading organic pol-lutants or splitting water.Such photocatalysts include BiVO 4[7],CdS [8],Bi 2WO 6[9],g-C 3N 4[10],BiFeO 3[11],etc.They all exhibit activity in the photocatalytic decomposition of organics and water splitting under visible light irradiation.However,these materials have several limitations.For example,their small speci?c surface areas limit the improvement of their photocatalytic activities.The rapid recombination rate of their photo-generated charge carriers also seriously in?uences their photocatalytic ef?ciency.

?Corresponding author.Tel.:+8601089733200;fax:+8601089733200.E-mail address:gelei08@https://www.360docs.net/doc/b77009743.html, (L.Ge).

Recently,numerous Aurivillius-based compounds have been reported to exhibit interesting photocatalytic activities.Among these compounds,Bi 2WO 6is one of the most studied.It has attracted a great deal of attention because of its good photocatalytic activity in decomposing organic pollutants under visible light irra-diation [12–16].Several methods have been developed to prepare Bi 2WO 6photocatalysts,such as solid-state [17],sol–gel [18],and hydrothermal [19]reactions,etc.However,pure Bi 2WO 6presents photo-absorption only from ultraviolet (UV)to visible light regions shorter than 450nm [20].The high recombination of its photo-generated electron–hole pairs can limit its photocatalytic activity as well [21].To enhance its photocatalytic performance,a num-ber of modi?cation methods have been exploited.These methods include doping Bi 2WO 6with C60[22]or with the noble metals Ag [9],CdS quantum dots (QDs)[23],and Eu [12],as well as combin-ing Bi 2WO 6with narrow band gap semiconductors.Our group has previously reported novel CdS QD-sensitized Bi 2WO 6heterostruc-tures for degrading methyl orange (MO)dye and phenol [23].The results indicated that the QD CdS/Bi 2WO 6had a remarkable photo-catalytic activity for MO degradation under visible light irradiation.Based on the above mentioned modi?cation methods,we expect that Bi 2WO 6can also be coupled with the polymeric semiconduc-tor g-C 3N 4to expand the research on Bi 2WO 6and further improve its photocatalytic activity.

Polymeric graphitic carbon nitride (g-C 3N 4),which has an opti-cal band gap of 2.7eV,is recognized as the most stable allotrope of

0926-3373/$–see front matter ? 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.apcatb.2011.08.014

L.Ge et al./Applied Catalysis B:Environmental108–109 (2011) 100–107101 carbon nitride[24].Recently,photocatalytic activity of polymeric g-

C3N4for hydrogen or oxygen production from water splitting under

visible light illumination was reported by Wang et al.[25]for the

?rst time,and several studies followed[26–30].Yan et al.[31]syn-

thesized g-C3N4and used it as a photocatalyst to degrade organic

dyes such as MO under visible light irradiation.Very recently,the

novel TaON–g-C3N4and TiO2–g-C3N4composite photocatalysts

were prepared and used for the photodegradation of rhodamine

B as well as water splitting[32,33].However,the photocatalytic

activities of those composites were found to be low.Therefore,

more ef?cient photocatalytic structures need to be developed.

In the present study,considering the synergic effect between

Bi2WO6and polymeric g-C3N4,the novel g-C3N4/Bi2WO6het-

erostructured photocatalysts were prepared for the?rst time via

mixing and heating methods.The aim was to improve further the photocatalytic activity of Bi2WO6.The results demonstrated that compared with pure Bi2WO6and g-C3N4,the g-C3N4/Bi2WO6 heterojunction photocatalyst had a remarkably enhanced MO pho-todegradation activity under visible light irradiation.The related properties of the g-C3N4/Bi2WO6photocatalysts were character-ized and discussed.The possible photodegradation mechanism was also proposed based on energy band positions and photolumines-cence(PL)spectra.The novel g-C3N4/Bi2WO6hetero-structured photocatalyst may have potential applications in environmental puri?cation.

2.Experimental

2.1.Synthesis of the photocatalyst

All chemicals were reagent grade and used without fur-ther puri?cation.Bi2WO6was synthesized by the hydrothermal method.The starting materials,Na2WO4and Bi(NO3)3,were mixed in a1:2molar ratio.After deionized water was added,white pre-cipitates immediately appeared,and the mixture was stirred for1h to promote further the precipitate reaction.The obtained precipi-tate was placed in a100mL Te?on-lined autoclave,to which water was added to ca.80%of the capacity.The autoclave was maintained at170?C for20h.The resulting pure Bi2WO6powders were then calcined at300?C in air for1h.

The metal-free g-C3N4powders were synthesized by heating melamine in a muf?e furnace.In a typical synthesis run,5g of melamine was placed in a semi-closed alumina crucible with a cover.The crucible was heated to520?C and held for2h at a heating rate of10?C min?1.Further deammoniation treatment was per-formed at520?C for2h.After the reaction,the alumina crucible was cooled to room temperature.The products were collected and ground into powders.

The g-C3N4and Bi2WO6powders were then ground together. The resultant samples were collected and calcined at300?C for1h in a muf?e furnace.The mechanical mixed g-C3N4and Bi2WO6 powder(70wt%g-C3N4)without heating treatment was also prepared as a reference.The g-C3N4/TaON and g-C3N4/TiO2com-posite photocatalysts were synthesized according to the literature [32,33]in order to compare photocatalytic performance with the g-C3N4/Bi2WO6samples.

2.2.Characterization

The crystal structure of the samples was investigated using X-ray diffraction(XRD;Rigaka D/max2500v/pc X-ray diffractometer) with Cu K?radiation at a scan rate of0.1?2?s?1.The accelerating voltage and the applied current were40kV and40mA,respectively. The morphology of the samples was examined by?eld emission scanning electron microscopy(SEM;FEI Quanta200F;accelerating

306090

3

N

4

3

N

4

/Bi

2

WO

6

3

N

4

/Bi

2

WO

6

3

N

4

/Bi

2

WO

6

30wt% g-C

3

N

4

/Bi

2

WO

6

10wt% g-C

3

N

4

/Bi

2

WO

6

2(Degree)

pure Bi

2

WO

6

5.0wt% g-C

3

N

4

/Bi

2

WO

6

Fig.1.XRD patterns of pure Bi2WO6and g-C3N4,as well as of the g-C3N4/Bi2WO6 composite photocatalysts.

voltage=10kV)and transmission electron microscopy(TEM;JEOL JEM-2100;accelerating voltage=200kV).High-resolution trans-mission electron microscopy(HR-TEM,FEI Tecnai G2F20)was operated at200kV to observe the crystallinity and arrangement of g-C3N4and Bi2WO6.UV–vis diffuse re?ection spectroscopy(DRS) was performed on a Shimadzu UV-3100spectrophotometer using BaSO4as the reference.The PL spectra of the photocatalysts were detected using a Varian Cary Eclipse spectrometer.

2.3.Photocatalytic activity

The photocatalytic activities of the g-C3N4/Bi2WO6composite samples were evaluated via the photocatalytic degradation of MO in an aqueous solution under visible light irradiation.A500W Xe lamp with a420nm cutoff?lter provided visible light irradi-ation.In each experiment,0.15g of photocatalyst was mixed with a50mL MO solution(10mg L?1).Prior to irradiation,the suspen-sions were magnetically stirred in the dark for30min to achieve a saturated MO absorption onto the catalyst.At irradiation time intervals of0.5h,the suspensions were collected and centrifuged (5000rpm,10min)to remove the photocatalyst particles.The MO concentrations were monitored at505nm during the photodegra-dation process using a UV–vis spectrophotometer(Japan Shimadzu UV–vis1700).

3.Results and discussion

3.1.Characterization of the g-C3N4/Bi2WO6samples

The powder XRD patterns of the as-prepared g-C3N4/Bi2WO6 composite samples are shown in Fig.1.The results showed that the photocatalysts were well crystallized.The XRD peaks of the pure Bi2WO6sample were in good agreement with the orthorhom-bic phase of Bi2WO6(JCPDS73-1126).The pure g-C3N4sample had two distinct peaks at27.4?and13.1?,which can be indexed as(002)and(100)diffraction planes(JCPDS87-1526).For the g-C3N4/Bi2WO6composites,only Bi2WO6diffraction peaks were found when the g-C3N4content was below50wt%.The character-istic peaks of Bi2WO6(28.2?)and g-C3N4(27.4?)were too close to distinguish.Nevertheless,weak diffraction peaks corresponding to g-C3N4(27.4?)appeared when the g-C3N4content increased from 50wt%to90wt%.Therefore,the g-C3N4/Bi2WO6samples had two phases:g-C3N4and Bi2WO6.

The morphology and microstructure of the g-C3N4/Bi2WO6 composite samples were revealed by SEM,TEM and HR-TEM.Fig.2

102L.Ge et al./Applied Catalysis B:Environmental 108–109 (2011) 100–

107

Fig.2.SEM micrographs of the samples.(a)Pure Bi 2WO 6.(b)50wt%g-C 3N 4–Bi 2WO 6.(c)70wt%g-C 3N 4–Bi 2WO 6.(d)Pure g-C 3N 4.

shows the SEM micrographs of the as-prepared samples with differ-ent g-C 3N 4doping amount.The pure Bi 2WO 6samples appeared to have aggregated particles,which contained many smaller Bi 2WO 6crystals.After introducing g-C 3N 4,the g-C 3N 4/Bi 2WO 6composite samples showed agglomeration structures,which were simi-lar with pure Bi 2WO 6.Fig.2d shows the morphologies of the pure g-C 3N 4samples,where even larger particles (diameters of 1000–2000nm)are observed.Fig.3a shows the microstructures of the g-C 3N 4/Bi 2WO 6samples via TEM,where g-C 3N 4/Bi 2WO 6is found to consist of irregular 10–30nm particles.Polycrystalline rings resulting from crystalline particles with the preferred orien-tation were obtained by selected area electron diffraction.Fig.3b shows the arrangement of the g-C 3N 4and Bi 2WO 6particles via HR-TEM,where Bi 2WO 6and g-C 3N 4crystallites are seen as having various orientations and lattice spacings.By carefully measuring the lattice parameters using a DigitalMicrograph and comparing with the data in JCPDS,three different kinds of lattice fringes were clearly observed.One fringe with d =0.336nm matched the (002)crystallographic plane of g-C 3N 4(JCPDS 87-1526).The lat-tice spaces of the Bi 2WO 6crystallites were determined as 0.272and 0.315nm,belonging to the (020)and (113)crystallographic planes of orthorhombic Bi 2WO 6(JCPDS 73-1126).After heating at 300?C,obvious interfaces between g-C 3N 4and Bi 2WO 6nanoparticles were observed.This ?nding suggested that the hetero-junction structure indeed formed from these two materials,and was con?rmed by the HRTEM analysis.

The optical absorption of the as-prepared g-C 3N 4/Bi 2WO 6samples was investigated using a UV–vis spectrometer.Fig.4shows that the pure Bi 2WO 6sample absorbs UV to visible lights,

which signi?es its visible-light-induced photocatalytic https://www.360docs.net/doc/b77009743.html,pared with the pure Bi 2WO 6sample,the absorption of the g-C 3N 4/Bi 2WO 6composite samples within the visible light range apparently increased and a red shift appeared upon the addition of g-C 3N 4powder.These results are attributed to the interac-tion between g-C 3N 4and Bi 2WO 6in the composite samples.The absorption intensity of the as-prepared samples also strengthened with increased g-C 3N 4amount (from 50%to 70%).The wave-length threshold was determined by elongating the baseline and the steepest tangent of the UV–vis spectra (the wavelength of the intersection was g ).The absorption edge of the pure Bi 2WO 6sample was estimated at 460nm corresponding to the band gap of 2.70eV.The UV–vis diffuse re?ectance spectra of pure g-C 3N 4was also investigated,which had wavelength threshold of 461nm,corresponding to the band gap of 2.69eV.The wavelength thresh-olds of the g-C 3N 4/Bi 2WO 6composite samples were 480nm for 50wt%g-C 3N 4/Bi 2WO 6and 530nm for 70wt%g-C 3N 4/Bi 2WO 6.The enhanced light absorption of the composite samples led to the pro-duction of more electron–hole pairs under the same visible light irradiation,which subsequently results in a higher photocatalytic activity.

3.2.Photocatalytic activity of the samples

To study the photocatalytic activity,the MO molecule (major absorption band at 505nm)was used as the representative dye for the photo-oxidation reaction.Fig.5shows the photocatalytic activities of the g-C 3N 4/Bi 2WO 6composite samples with different g-C 3N 4concentrations under visible light irradiation ( >420nm).

L.Ge et al./Applied Catalysis B:Environmental 108–109 (2011) 100–107

103

Fig. 3.TEM and HR-TEM images of the samples.(a)TEM micrographs of g-C 3N 4–Bi 2WO 6.(b)HR-TEM images of g-C 3N 4–Bi 2WO 6showing the arrangement of g-C 3N 4and Bi 2WO 6crystallites.

200

300

400

500

600

700

800

0.00.4

0.8

1.2

1.6

2.0

A b s o r b a n c e (a .u )

Wavelength (nm)

6

Fig.4.UV–vis diffuse re?ectance spectra of the as-prepared samples.(a)Pure Bi 2WO 6.(b)50wt%g-C 3N 4–Bi 2WO 6.(c)70wt%g-C 3N 4–Bi 2WO 6.

0.0

0.5 1.0 1.5 2.0 2.5

3.0

0.0

0.2

0.4

0.6

0.8

1.0

C /C 0

Irradiation time (h)

Fig.5.Degradation rates of methyl orange under visible light irradiation using (a)

pure Bi 2WO 6,(h)pure g-C 3N 4,as well as g-C 3N 4/Bi 2WO 6with different g-C 3N 4con-centrations of (b)5.0wt%,(c)10.0wt%,(d)30wt%,(e)50wt%,(f)70wt%,and (g)90wt%.

MO concentration very gradually decreased in the presence of pure Bi 2WO 6under visible light.Only 14.2%MO was pho-todegraded after irradiation for 3h.However,the photocatalytic performance was signi?cantly enhanced after modi?cation by polymeric g-C 3N 4.When the g-C 3N 4amount was 70wt%of the total catalyst weight,g-C 3N 4/Bi 2WO 6performed best and almost 100%MO was photo-degraded.The inset in Fig.5illustrates the variations in MO absorbance around 505nm using 70wt%g-C 3N 4/Bi 2WO 6.The absorbance obviously decreased with increased irradiation time.No absorbance peak was observed after irradi-ation for 3h,which indicated complete MO decomposition.The photocatalytic results indicated that the doping amount of poly-meric g-C 3N 4had a signi?cant effect on the catalytic performance of the g-C 3N 4/Bi 2WO 6composite photocatalyst.Fig.5shows that the degradation rates were 0.211,0.376,0.452,0.896,0.999and 0.844,respectively,for the g-C 3N 4/Bi 2WO 6ratios of 5.0%,10%,30%,50%,70%and 90%.The rate was 0.814for pure g-C 3N 4.At g-C 3N 4dop-ing amounts below 70wt%,the photocatalytic activities improved with increased g-C 3N 4doping amount.The degradation ratio of MO increased from 21.1%to 99.9%after irradiation for 3h.At g-C 3N 4loading amounts more than 70wt%,the photocatalytic activities decreased with increased g-C 3N 4amount.The optimal g-C 3N 4loading amount on Bi 2WO 6to achieve an improved photocatalytic activity was determined to be 70wt%.Hence,the photocatalytic activity of g-C 3N 4/Bi 2WO 6was effectively enhanced compared with that of pure Bi 2WO 6.This enhancement is attributed to the synergic effect between polymeric g-C 3N 4and Bi 2WO 6,which had an important role in the separation of electron–hole pairs.To con?rm the signi?cance of chemical bond formation for the photocatalytic activity of g-C 3N 4and Bi 2WO 6,the photocatalytic degradation experiment over the mechanical mixed powder of C 3N 4and Bi 2WO 6(70wt%g-C 3N 4content)was also investigated and illustrated in Fig.5.The mechanical mixed g-C 3N 4and Bi 2WO 6showed much lower photocatalytic activity than that of 70wt%g-C 3N 4/Bi 2WO 6composite;the degradation rate was only 0.297after irradiated for 3h.The result implied that heating treatment pro-moted the formation of chemically bonded interfaces between the two materials,and then increased the photocatalytic performance.

To quantitatively investigate the reaction kinetics of the MO degradation,the experimental data were ?tted by applying a ?rst-order model as expressed by Eq.(1).This equation is well

104L.Ge et al./Applied Catalysis B:Environmental 108–109 (2011) 100–107

012345

67l n (C 0/C )

Irradiation time (h )

Fig.6.First-order kinetics plot for the photodegradation of methyl orange by g-C 3N 4/Bi 2WO 6composite photocatalysts with different g-C 3N 4loading amounts.

established for photocatalytic experiments when the pollutant is

within the millimolar concentration range.

?ln

C C 0

=kt,

(1)

where C 0and C are the dye concentrations in solution at times 0and t ,respectively,and k is the apparent ?rst-order rate constant.

Fig.6shows the effect of g-C 3N 4content on the MO photodegra-dation rate using g-C 3N 4/Bi 2WO 6.Upon varying the g-C 3N 4content within 5.0–90%,the plot of the irradiation time (t )against ln (C 0/C )was nearly straight line.Fig.7shows that the g-C 3N 4content greatly in?uenced the photo-degrading rate (k )of the composite samples.The 70wt%g-C 3N 4/Bi 2WO 6exhibited the highest photo-degrading ef?ciency,which was about 47-folds higher than that

of pure Bi 2WO 6.The g-C 3N 4content was pivotal for achieving the high photocatalytic activity of the g-C 3N 4/Bi 2WO 6composite.The suitable g-C 3N 4content caused its well dispersion on the Bi 2WO 6surface,which favored the transfer and separation of the charge carriers.However,at contents higher than 70wt%,the interfaces and heterojunction structures between the g-C 3N 4and Bi 2WO 6particles decreased.As a result,the interfacial charge transfer was suppressed and the photocatalytic activity was lowered.Therefore,the 70wt%g-C 3N 4/Bi 2WO 6was the best performing sample and was selected

the cycling study.

0.0

0.5

1.0

1.5

2.0

K / h

-1

g-C 3N 4 contents

100%90%70%50%30%

10%5%0%mixed sample

Fig.7.Photocatalytic degradation rate constant k as a function of g-C 3N 4content.

06

4210812

0.0

0.20.40.60.81.0C /C 0

Irradiation time (h)

Fig.8.Cycling runs for the photocatalytic degradation of methyl orange in the

presence of 70wt%g-C 3N 4/Bi 2WO 6composite under visible light irradiation.

The stability of a photocatalyst is important for its assessment and application.The cycling runs for the photo-oxidation of MO using the 70wt%g-C 3N 4/Bi 2WO 6photocatalysts were performed to evaluate its photocatalytic stability.After every 3h of photodegra-dation,the separated photocatalysts were washed with deionized water and dried.Fig.8shows the decrease in MO in every run.A high MO photodegradation could be maintained after 4cycling runs and there was no obvious catalyst deactivation.This result con?rmed that g-C 3N 4/Bi 2WO 6was not photo-corroded during the degradation.Variations in the XRD analysis (Fig.9)also illustrated that the crystal structure of the g-C 3N 4/Bi 2WO 6photocatalysts did not change after the photocatalytic reaction.Therefore,the g-C 3N 4/Bi 2WO 6photocatalyst can be concluded as stable given that photo-corrosion did not occur.

For comparison,different composite materials such as g-C 3N 4/TaON and g-C 3N 4/TiO 2were also synthesized and used as photocatalysts in degradation of methyl orange.Fig.10shows the degradation rate of methyl orange over different composite pho-tocatalysts under visible light irradiation.As shown in Fig.10,the degradation rates of methyl orange were 0.999,0.894,and 0.850respectively,for the samples of g-C 3N 4/Bi 2WO 6,g-C 3N 4/TaON and

3060

90

2(Degree)

fresh sample

used sample

Fig.9.XRD patterns of 70wt%g-C 3N 4/Bi 2WO 6before and after the cycling photo-catalytic experiments.

L.Ge et al./Applied Catalysis B:Environmental 108–109 (2011) 100–107

105

0.0

0.5 1.0 1.5 2.0 2.5

3.0

0.0

0.20.40.6

0.8

1.0

C /C 0

Irradiation time (h)

https://www.360docs.net/doc/b77009743.html,parison of methyl orange degradation over different composite pho-tocatalysts under visible light irradiation:(a)70wt%g-C 3N 4/Bi 2WO 6;(b)60wt%g-C 3N 4/TaON;(c)50wt%g-C 3N 4/TiO 2;(d)Pure g-C 3N 4.

g-C 3N 4/TiO 2.The present experiments clearly indicated that the g-C 3N 4/Bi 2WO 6was determined as an ef?cient visible light photo-catalyst for the methyl orange degradation.

3.3.Photocatalytic mechanisms

The photocatalytic results have shown the excellent photoac-tivity of the novel g-C 3N 4/Bi 2WO 6composite photocatalysts on the degradation of MO.Based on the above data,a possible mechanism for the MO photodegradation using the g-C 3N 4/Bi 2WO 6hetero-junction photocatalyst under visible light irradiation is proposed.The purpose is to guide the further improvement of the photocat-alytic performance of the novel composite.

To improve photogenerated carrier separation and enhance the ef?ciency of interfacial charge transfer,two semiconductors in con-tact with different conduction band (CB)and valence band (VB)redox energy levels can be used [6].In the present study,polymeric g-C 3N 4served

as a sensitizer for the visible-light-induced redox process,whereas Bi 2WO 6was the substrate.The metal-free g-C 3N 4is a polymeric compound with graphitic planes constructed from tri-s-triazine units connected by planar amino groups,as shown in Fig.11.The optical band gap of this polymer semiconductor was determined to be 2.7eV [25].Therefore,g-C 3N 4has the pho-tocatalytic ability for water splitting and organic dye degradation under visible light irradiation.On the other hand,the semiconduc-tor Bi 2WO 6has the ability to absorb visible light,which is attributed

Fig.12.Diagrams of the energy position and photogenerated electron–hole pair

transfers between polymeric g-C 3N 4and Bi 2WO 6.

to the transition of its electrons from the VB (the hybrid orbital of O2p and Bi6s)to the CB (the W5d orbital)in the catalyst.The band gap of Bi 2WO 6was determined as 2.7eV from the DRS spec-tra,which fairly conforms to a previously reported experimental result [20].

When the polymeric g-C 3N 4was introduced to Bi 2WO 6,the two types of semiconductor materials closely combined together and the heterojunction structure was formed.Fig.12illustrates the ?at potentials of the CBs at pH 7(versus the normal hydrogen electrode)for g-C 3N 4and Bi 2WO 6with their band gap energies.

Based on the band gap positions,the CB and VB edge poten-tials of polymeric g-C 3N 4were determined at ?1.13and +1.57eV [25,33],respectively.The CB and VB edge potentials of Bi 2WO 6were at +0.24and +2.94eV,respectively.The CB and VB edge potentials of g-C 3N 4were more negative than that of Bi 2WO 6.Obviously,the difference between the CB edge potentials of g-C 3N 4and Bi 2WO 6allowed the electron transfer from the CB of g-C 3N 4to that of Bi 2WO 6.When the system was irradiated with visible light,the polymeric g-C 3N 4(band gap =2.7eV)and Bi 2WO 6(band gap =2.7eV)in the

composite photocatalyst absorbed pho-tons as well as excited electrons and hole pairs.The process can be described as follows:

g-C 3N 4/Bi 2WO 6h

?→h ++e ?

(2)

The electrons were promoted from the VB to the CB of g-C 3N 4and Bi 2WO 6,leaving the holes behind.The excited state electrons produced by g-C 3N 4were then injected into the CB of the coupled Bi 2WO 6.Subsequently,simultaneous holes on the VB of Bi 2WO 6migrated to that of g-C 3N 4because of the enjoined electric ?elds

Fig.11.Schematic diagram of the chemical structure of polymeric g-C 3N 4.

106L.Ge et al./Applied Catalysis B:Environmental 108–109 (2011) 100–

107

Fig.13.Redox process of the g-C 3N 4/Bi 2WO 6composite photocatalysts under visi-ble light irradiation.

of the two materials.The photo-excited electrons were effectively

collected by Bi 2WO 6;and the holes by g-C 3N 4,as shown in Fig.13.Therefore,the recombination process of the electron–hole pairs was hindered,and charge separation as well as stabilization was achieved.

The electrons in Bi 2WO 6crystals are good reductants that could capture the adsorbed O 2onto the composite catalyst surface and reduce it to O 2?.The highly oxidative species ?OH is produced as a consequence of the reduction of oxygen.The photo-generated holes (h +)in g-C 3N 4can also react with H 2O and cause the forma-tion of ?OH groups,leading to a constant stream of the surface ?OH groups.Therefore,the ef?cient photocatalytic degradation of MO can smoothly proceed.The process is described as follows:

g-C 3N 4/Bi 2WO 6h

?→g-C 3N 4(e ?+h +)/Bi 2WO 6(e ?+h +

)

(3)

g-C 3N 4(e ?+h +)/Bi 2WO 6(e ?+h +)→g-C 3N 4(h +)/Bi 2WO 6(e ?)

(4)

e ?+O 2→O 2

??

(5)

2e ?+O 2+2H +→H 2O 2

(6)H 2O 2+O 2??→?OH +OH ?+O 2

(7)h +

+H 2O →

?OH

+H

+

(8)

?OH

+MO →degradation products

(9)

To further investigate the effect of the g-C 3N 4modi?cation and con?rm the above-proposed mechanism,the PL spectra of g-C 3N 4/Bi 2WO 6were obtained.PL spectra reveal the migra-tion,transfer,and recombination processes of photo-generated electron–hole pairs in semiconductors.Fig.14presents the PL spec-tra of the g-C 3N 4/Bi 2WO 6composite photocatalysts at an excitation wavelength of 365nm.At room temperature,the emission band for pure g-C 3N 4was centered at 440nm,which was attributed to the radiative recombination process of self-trapped excitations.The positions of the g-C 3N 4/Bi 2WO 6emission peaks were sim-ilar with pure g-C 3N 4.However,the emission intensity of the g-C 3N 4/Bi 2WO 6composite photocatalysts signi?cantly decreased,with the 70wt%g-C 3N 4/Bi 2WO 6sample having the weakest intensity.This result clearly indicated that the recombination of photo-generated charge carriers was inhibited in the composite semiconductors.The PL results conform to the discussion on the charge carrier separation and photocatalytic experiments.Over-all,the g-C 3N 4/Bi 2WO 6heterojunction photocatalyts have very promising applications in the ?eld of environmental puri?cation.

400425450475500525

2WO 6

I n t e n s i t y (a .u )

Wa velength (nm)

6

Fig.14.Photoluminescence spectra of the g-C 3N 4/Bi 2WO 6composite photocata-lysts.

4.Conclusions

Novel visible-light-induced g-C 3N 4/Bi 2WO 6composite photo-catalysts were synthesized by introducing polymeric g-C 3N 4via a mixing and heating method.The g-C 3N 4/Bi 2WO 6samples had a red shift and strong absorption in the visible light region and had obviously enhanced photocatalytic activities in MO degradation.The highest degradation ef?ciency was observed for the 70wt%g-C 3N 4/Bi 2WO 6sample.The synergic effect was explained and a photocatalytic mechanism was proposed as well as discussed based on energy band positions and PL spectra.The novel heterojunction materials,as highly ef?cient photocatalysts,may have potential applications in pollutant removal.

Acknowledgments

This work was ?nancially supported by the National Science Foundation of China (Grant no.21003157),Beijing Nova Program (Grant no.2008B76),Key Project of Chinese Ministry of Education (Grant no.108024)and Doctor Foundation of Chinese Ministry of Education (Grant no.200804251014).We thank the Microstructure Laboratory for Energy Materials and Prof.Lishan Cui for the support of TEM and SEM testing.

References

[1]M.Shang,W.Z.Wang,S.M.Sun,J.Ren,L.Zhou,L.Zhang,J.Phys.Chem.C 113

(2009)20228–20233.

[2]R.Asahi,T.Morikawa,T.Ohwaki,K.Aoki,Y.Taga,Science 293(2001)269–272.[3]R.Shi,J.Lin,Y.J.Wang,J.Xu,Y.F.Zhu,J.Phys.Chem.C 114(2010)6472–6477.[4]L.Ge,M.X.Xu,H.B.Fang,Mater.Lett.61(2007)63–66.

[5]L.Ge,M.X.Xu,H.B.Fang,Appl.Surf.Sci.253(2006)720–725.

[6]M.C.Long,W.M.Cai,J.Cai,B.X.Zhou,X.Y.Chai,Y.H.Wu,J.Phys.Chem.B 110

(2006)20211–20216.

[7]A.Kudo,K.Omori,H.Kato,J.Am.Chem.Soc.121(1999)11459–11467.[8]Y.L.Lee,C.F.Chi,S.Y.Liau,Chem.Mater.22(2010)922–927.

[9]J.Ren,W.Z.Wang,S.M.Sun,Appl.Catal.B Environ.92(2009)50–55.

[10]X.C.Wang,K.Maeda,X.F.Chen,K.Takanabe,K.Domen,Y.D.Hou,X.Z.Fu,M.

Antonietti,J.Am.Chem.Soc.131(2009)1680–1681.

[11]Y.Huo,Y.Jin,Y.Zhang,J.Mol.Catal.A:Chem.331(2010)15–20.

[12]Z.J.Zhang,W.Z.Wang,W.Z.Yin,M.Shang,L.Wang,S.M.Sun,Appl.Catal.B:

Environ.101(2010)68–73.

[13]J.W.Tang,Z.G.Zou,J.H.Ye,Catal.Lett.92(2004)53–56.[14]C.Zhang,Y.F.Zhu,Chem.Mater.17(2005)3537–3545.

[15]H.B.Fu,C.S.Pan,W.Q.Yao,Y.F.Zhu,J.Phys.Chem.B 109(2005)22432–22439.[16]H.B.Fu,L.W.Zhang,W.Q.Yao,Y.F.Zhu,Appl.Catal.B:Environ.66(2006)

100–110.

[17]S.Mahanty,J.Ghose,Mater.Lett.11(1991)254–256.

[18]G.K.Zhang,F.Lu,M.Li,J.L.Yang,X.Y.Zhang,B.B.Huang,J.Phys.Chem.Solid 71

(2010)579–585.

L.Ge et al./Applied Catalysis B:Environmental108–109 (2011) 100–107107

[19]S.W.Liu,J.G.Yu,J.Solid.State.Chem.181(2008)1048–1055.

[20]Z.J.Zhang,W.Z.Wang,M.Shang,W.Z.Yin,J.Hazard.Mater.177(2010)

1013–1018.

[21]L.Jiang,L.Z.Wang,J.L.Zhang,https://www.360docs.net/doc/b77009743.html,mun.46(2010)8067–8069.

[22]S.B.Zhu,T.G.Xu,H.B.Fu,J.C.Zhao,Y.F.Zhu,Environ.Sci.Technol.41(2007)

6234–6239.

[23]L.Ge,J.Liu,Appl.Catal.B:Environ.105(2011)289–297.

[24]A.Thomas,A.Fischer,F.Goettmann,M.Antonietti,J.O.Muller,R.Schlogl,J.M.

Carlsson,J.Chem.Mater.18(2008)4893–4908.

[25]X.C.Wang,K.Maeda,A.Thomas,K.Takanabe,G.Xin,J.M.Carlsson,K.Domen,

M.Antonietti,Nat.Mater.8(2009)76–80.

[26]X.F.Chen,J.S.Zhang,X.Z.Fu,M.Antonietti,X.C.Wang,J.Am.Chem.Soc.131

(2009)11658–11659.[27]Y.J.Zhang,T.Mori,J.H.Ye,M.Antonietti,J.Am.Chem.Soc.132(2010)

6294–6295.

[28]F.Z.Su,S.C.Mathew,G.Lipner,X.Z.Fu,M.Antonietti,J.Am.Chem.Soc.132

(2010)16299–16301.

[29]K.Maeda,X.C.Wang,Y.Nishihara,D.L.Lu,M.Antonietti,K.Domen,J.Phys.

Chem.C113(2010)4940–4947.

[30]G.Liu,P.Niu,C.H.Sun,S.C.Smith,Z.G.Chen,G.Lu,H.M.Cheng,J.Am.Chem.

Soc.132(2010)11642–11648.

[31]S.C.Yan,Z.S.Li,Z.G.Zou,Langmuir25(2009)10397–10401.

[32]S.C.Yan,S.B.Lv,Z.S.Li,Z.G.Zou,Dalton Trans.39(2010)1488–1491.

[33]H.J.Yan,H.X.Yang,J.Alloys Compd.509(2011)L26–L29.

光电催化氧化

光电催化氧化原理、反应器及其在环境污染控制中的应用 钱丹 福州大学环境与资源学院 030620340 TiO2光电催化水处理是一种电化学辅助的光催化反应技术,通过施加外部偏压减少光生 电子和空穴的复合,从而提高其量子效率使有机污染物彻底矿化。 光激活半导体(通常使用TiO2)价带上的光生空穴,在水中产生氧化能力极强的氢氧自由基,可使水中难于降解的有机污染物完全矿化,且作用物几乎无选择性,降解过程可在常温常压下进行,加之该法毋须添加化学试剂,无二次污染,故成为当前水净化技术在国内外的研究前沿和开发热点[1-10]。 迄今为止,大量研究揭示出该过程的主要问题之一是量子效率太低。近年来有研究者采用电化学辅助的光催化方法(或称光电催化方法)阻止光生电子和空穴发生简单复合以提高量子效率[11-19]。实验证明:使用TiO2光电极可显著提高过程的量子效率,同时具有增加半导体表面·OH的生成效率和取消向系统内鼓入电子俘获剂O2的两大优点[20-23]。 1 光电催化氧化反应研究进展 1.1 光电催化反应发展 光电催化氧化在过去十五年间,主要是在企图开发一种可以利用太阳能以获得清洁能源氢的所谓光电化学电池的鼓舞下面迅速发展起来的。光电化学效应实际上早在1839年已为E.Becquerel所发现。1955年,W.H.Brattain和C.G.B.Garratt根据锗电极得到的试验结果指出,Becquerel效应是由于生成半导体-电解液结的关系,从而产生了利用照射置于电解槽中的半导体电极生产化学品或电能的概念,以后直至1972年,A.Fujishima和K.Honda 利用n型半导体TiO2将水在比H2O/O2队的标准氧化电位负的多的情况下生产氧获得成功之后,才引起人们的广泛注意。这种利用半导体电极的光电化学电池被认为是将光能转变为电能和化学能的一种最有希望的发现。在以后的年代里,为了对半导体在构成这种光电化学电池中的作用有更清楚的了解,进行了大量的理论和试验工作,并使光电催化氧化发展到用于水处理领域。 用TiO2处理水中有机物的早期研究主要是用粉末状TiO2分散水中形成悬浆,该方法有两个明显缺点:即悬浆中TiO2粒子难以分离回收,并且量子化效率低。有学者通过均匀沉积法或溶胶凝胶法将TiO2粒子固定在玻璃、陶瓷或硅砂等载体颗粒表面,制成固定态TiO2催化剂,该方法虽然解决了TiO2难以回收的问题,但大多数研究结果表明,固定态催化剂由于反应和传质的表面积大幅度降低,导致光催化氧化的效率降低,并且量子化效率低的问题仍然没有得到解决。 在光催化反应中,光生电子-空穴的复合一直是限制光催化剂效率的主要因素,光电催化的提出为解决这一难题提供了一个可行的研究方向。光电催化氧化是在用固定态TiO2作阳极,铂作阴极的电化学体系中,用外电路来驱动电荷,使光生电子转移到阴极,利用这种

Ti-MWW钛硅分子筛的后处理改性、表征及催化性能

Ti-MWW钛硅分子筛的后处理改性、表征及催化性能 【摘要】:本论文以新一代钛硅分子筛Ti-MWW的后处理改性及催化性能为主线,研究提高Ti-MWW催化活性的新方法,及其液相催化氧化烯烃化合物的催化性能,尤其探索Ti-MWW应用到生产环氧氯丙烷这类大宗化学品的反应过程的可能性。第一部分基于MWW分子筛层状前驱体晶体结构具有可塑性的特点,采用有机硅试剂与Ti-MWW 分子筛前驱体在高温下作用,有机硅烷进入层间,与层间的自由硅羟基发生反应,经过高温焙烧,MWW分子筛前驱体层间脱水缩合被人为阻止,得到了层间为12元环的大孔道分子筛IEZ-Ti-MWW。详细考察了不同Si/Ti比的Ti-MWW层状前驱体、硅烷化试剂用量、硝酸浓度、硅烷化试剂类型等因素的影响。这种大孔道分子筛既保持了MWW 分子筛的基本结构单元,又兼备了反应物易接近的大反应空间结构特点,因此,不论对环状烯烃还是对直链烯烃,都显示出良好的催化性能,尤其对大分子反应物环己烯的环氧化反应表现出很高的转化数(TON)。第二部分,为了提高Ti-MWW的疏水性和催化活性,用胺溶液对具有三维(3D)结构的MWW分子筛进行了后处理改性。当采用哌啶(PI)或者六亚甲基亚胺(HMI)的胺溶液在一定温度下二次晶化的过程中,3D结构材料转向了二维(2D)层状结构,进一步焙烧又将2D层状结构可逆转化到3D晶体结构,而且这种可逆结构转换仅发生在PI或者HMI存在的情况下,而若换成其他胺溶液即使是结构相似的嘧啶或者哌嗪都无法实现。当PI/SiO_2的摩尔比小于0.1在443K条件下处

理一天时,就能将3D结构转向2D层状结构,并且不受母体Si/Ti比的影响。这种结构转化没有改变活性Ti物种的量以及配位状态,但是骨架内部的硅羟基却消除了大约40%,形成了缺陷位少,结构更加“刚性”以及疏水性能良好的Ti-MWW分子筛。在酮类的肟化以及各类不同分子尺寸大小的烯烃环氧化反应中,结构重排的Ti-MWW分子筛都表现出比3DTi-MWW更优异的催化性能。第三部分,通过一种简单的后处理方法制备出含各种杂原子的类似于MCM-56结构的分子筛。酸处理回流MWW层状前驱体形成传统的3D结构材料,但当控制一定的酸处理条件即酸处理温度低于353K时,就形成了MCM-56,并RMCM-56的形成依赖于层状前驱体的晶粒大小,晶粒小有利于前驱体转换形成MCM-56。且MCM-56的形成与前驱体骨架中金属离子类型(包括B,Al,Ti,Ga或者Fe)及其含量无关。与3DTi-MWW相比,含钛MCM-56具有更大的外表面,因此在各类不同分子大小的烯烃以叔丁基过氧化氢为氧化剂的环氧化反应中以及具有更大分子尺寸的脱除轻油中二苯并噻吩的氧化反应中,Ti-MCM-56都表现出优异的催化活性。最后,我们考察了Ti-MWW分子筛在氯丙烯以双氧水为氧化剂环氧化制备环氧氯丙烷过程中的催化活性,并与典型的钛硅分子筛TS-1、Ti-MOR和Ti-Beta进行了比较。采用Ti-MWW分子筛/H_2O_2/乙腈催化体系,通过对环氧氯丙烷合成工艺条件的考察及优化,氯丙烯、双氧水的转化率以及环氧氯丙烷的选择性都能达到99%以上。Ti-MWW的最好溶剂为乙腈或者丙酮,从而有效的抑制了溶剂化开环反应副产物的形成。而最主要副产物之一的3-氯-1,2-丙二醇对

光催化剂的发展前景与突破

光催化剂的发展前景与突破 一、解决人类生存的重大问题 光催化学科是催化化学、光电化学、半导体物理、材料科学和环境科学等多学科交叉的新兴研究领域。光催化剂的研究应用一旦获得突破,将可以使环境和能源这两个二十一世纪人类面临的重大生存问题得以解决。 利用太阳能光催化分解水制氢H2O →H2 + ?O2 彻底解决能源问题利用环境光催化C6H6 + 7 ? O2 → 6 CO2 + 3H2O 彻底解决污染问题光催化以其室温深度反应和可直接利用太阳光作为光源来驱动反应等独特性能而成为一种理想的环境污染治理技术和洁净能源生产技术。 二、光催化研究领域急需解决的重大科技问题 目前以二氧化钛为基础的半导体光催化存在一些关键科学技术难题,使其广泛的工业应用受到极大制约,而这些问题的解决有赖于深入系统的基础研究。 最突出的问题在于: (1)量子效率低(~4%) 难以处理量大且浓度高的废气和废水,难以实现光催化分解水制氢的产业化。 (2)太阳能利用率低 由于TiO2半导体的能带结构(Eg=3.2eV)决定了其只能吸收利用紫外光或太阳光中的紫外线部分(太阳光中紫外辐射仅占~5 %)。 (3)多相光催化反应机理尚不十分明确

以半导体能带理论为基础的光催化理论难以解释许多实验现象,使得改进和开发新型高效光催化剂的研究工作盲目性大。 (4)光催化应用中的技术难题 如在液相反应体系中光催化剂的负载技术和分离回收技术,在气相反应体系中光催化剂的成膜技术及光催化剂活性稳定性问题。 上述关键问题也是目前国内外光催化领域的研究焦点,围绕这些问题开展进一步的研究不仅可望在光催化基础理论方面获得较大的突破,而且有利于促进光催化技术真正能在上述众多领域得到大规模广泛工业应用。 三、光催化领域的最新研究进展 近年来,光催化的基础与应用研究发展非常迅速,特别是在可见光诱导的新型光催化剂的研究、提高光催化过程效率的研究和光催化功能材料的研究等方面都取得了重要进展。 1、可见光诱导的光催化剂研究方面取得重大突破 采用固相合成、过渡金属离子和非金属离子掺杂、金属-有机络合物、表面敏化、半导体复合等多种方法,制备出了一系列新型非二氧化钛系或二氧化钛基可见光光催化材料,这些材料在可见光的照射下,能将H2O分解为H2和O2,或能有效降解空气、水中的有机和无机污染物。 2、为解决多相光催化过程效率偏低的问题,近年从提高催化剂自身的量子效率和改进反应过来程条件两个方面开展了大量的研究工作,取得了重要进展。 采用离子掺杂、半导体复合、纳米晶粒制备、超强酸化等方法,提高光生载流子的分离效率和抑制电子-空穴的重新复合,在一定程度上改善了光催化剂的量子效率。 3、光催化材料超亲水性的发现,开辟了光催化研究和应用的新领域 利用光催化膜的超亲水性和强氧化性等特性,研制开发出一系列光催化功能材料,如光催化自清洁抗雾玻璃、光催化自清洁抗菌陶瓷和光催化环保涂料等。这些功能材料已开始在建筑材料领域应用。与之相应的光催化膜功能材料的基础研究也有大量的文献报道。 4、超分散性及可见光活性实现突破 河南工业大学李道荣教授开发出了超分散性及可见光活性纳米二氧化钛光

二氧化钛光催化剂

Ti O2纳米颗粒的制备及表征 在关于有关Ti O2纳米颗粒的研究中,制备方法的研究是很多的,同时,采用溶胶-凝胶法合成纳米Ti O2的文献报道比较多,通常采用溶胶-凝胶法合成的前驱物为无定形结构的,经过进一步的热处理后或者水热晶化才能得到晶型产物[49]。烧结过程能促使晶型转变,但是往往引起颗粒之间的团聚和颗粒的生长[50]。一般情况下,在大于300℃温度烧结处理得 到锐钛矿型Ti O2、大于600℃的温度烧结处理得到金红石型Ti O2。Ti O2的很多种性质取决于颗粒尺寸和晶化度。优化制备条件,得到分散性良好,催化性能好的光催化剂是很有研究意义的。 实验原理 溶胶-凝胶法是从材料制备的湿化学法中发展起来的一种新方法,是以金属醇盐或无机 盐为原料,其反应过程是将金属醇盐或无机盐在有机介质中进行水解、缩聚反应,使溶液形成溶胶,继而形成凝胶。凝胶经陈化、干燥、煅烧、研磨得到粉体产品。其中由于较多研究者以醇盐为原料,故也将其称为醇盐水解法。在溶胶-凝胶法中,溶胶通常是指固体分散在 液体中形成胶体溶液,凝胶是在溶胶聚沉过程中的特定条件下,形成的一种介于固态和液态间的冻状物质,是由胶粒组成的三维空间网状结构,网络了全部或部分介质,是一种相当稠厚的物质。 本文中,钛酸四丁酯(Ti(OC4H9)4)在水中水解,并发生缩聚反应,生成含有氢氧化钛(Ti(OH)4)粒子的溶胶溶液,反应继续进行变成凝胶,反应方程式如下: 水解Ti(OC4H9)4+4 H2O →Ti (OH)4+ 4HO C4H9 (2-1) 缩聚2Ti (OH)4→[Ti (OH)3]2O+H2O (2-2) 总反应式表示为: Ti(OC4H9)4+ 2H2O→Ti O2 + 4 C4H10O (2-3) 上式表示反应物全部参加反应的情况,实际上,水解和缩聚的方式随反应条 件的变化而变化。反应过程为: (1) 水解反应:可能包含对金属离子的配位,水分子的氢可能与OR 基的氧通过氢键引起 水解。 (2) 缩聚反应:在溶液中,原钛酸和负一价的原钛酸反应,生成钛酸二聚体,此二聚体进 一步作用生成三聚体、四聚体等多钛酸。在形成多钛酸时Ti-O-Ti 键也可以在链的中部形成,这样可得到支链多钛酸,多钛酸进一步聚合形成胶态Ti O2,这就是通常所说的 Ti O2溶胶的胶凝过程[53]。 本论文选用价格较低、使用较为普遍的钛酸四丁酯(Ti(OC4H9)4)作为钛源,选用乙醇为 溶剂,乙醇在钛酸四丁酯的水解反应过程中并不直接参与水解和缩聚反应,但它作为溶剂对体系起着稀释作用,它在Ti(OC4H9)4分子与水分子周围均形成由乙醇分子组成的包覆层, 阻碍反应物分子的碰撞,并在溶胶粒子周围形成“溶剂笼”,从而阻碍了溶胶粒子的生长以及溶胶团簇间的键合,使得干燥后的干凝胶能保持疏松多孔的状态,经焙烧后所得粒子比表面积较大。此外,在制备溶胶的过程中还要加入适量的冰乙酸,冰乙酸在反应过程中可能有两种作用:一是抑制水解,二是使胶体粒子带有正电荷,阻止胶粒凝聚,从而避免干凝胶粒尺寸过大。根据上述机理分析和本实验室前人研究的基础上,确定制备Ti O2溶胶的各物料组分摩尔比为Ti(OC4H9)4:HAc:H2O:Et OH:(NH4)2CO3 =1:2:15:18:X,其中X值变化的范围是0~4,加入碳酸铵的目的是使反应过程中产生气体和微小的固体载体,但又不会对生成的Ti O2造成掺杂等影响,使颗粒分散更均匀,细小。

系统生物催化的原理及应用(欧阳平凯院士)

系统生物催化的原理 及应用
欧阳平凯
南京工业大学 2005.08.13

生物秀-专心做生物
https://www.360docs.net/doc/b77009743.html,
现代化学工业面临重大的挑战
n
物 以石油等化石资源为源头的化学工业所面 生 做 om 临的挑战在于化石资源日益枯竭 心 .c 专 ioo - b 秀 .b 物 w 化石资源的市场价格上涨迅速,现代化学 生 ww 工业的原料成本猛增
n
生物秀论坛-学术交流、资源共享与互助社区
https://www.360docs.net/doc/b77009743.html,

生物秀-专心做生物
https://www.360docs.net/doc/b77009743.html,
现代化学工业面临的机遇
光合作用产生的 生物质循环
物 生 做 om 心 .c 目前世界 专 ioo 65 亿吨 C/年 - b 化石资源消耗 秀 .b 物 w 生 ww
仅需使用小于 10% 生物质循环, 即可替代化石资源
950亿吨 C/年
随着生物技术的发展,生物质资源的生产不断 提高
生物秀论坛-学术交流、资源共享与互助社区 https://www.360docs.net/doc/b77009743.html,


生物秀-专心做生物
https://www.360docs.net/doc/b77009743.html,
n n n n n
n
The amount of biomass circulation by photosynthesis is 95 billion tons per year. Independence from fossil fuels can be achieved by using less than 10% of this carbon energy. A fundamental sustainable society through natural circulation of Biomass driven by an external energy is realized. This is in principle a sustainable society. Determining the amount of biomass that will not give an negative impact to the environment, namely the sustainable limit of harvest, is an important task of the future. Considering the improvement of harvesting efficiency of biomass or the advance of artificial photosynthesis, it is not a dream that in spite of petroleum, the total amount of energy and organic feed stocks can be obtained from biomass.
物 生 做 om 心 .c 专 ioo - b 秀 .b 物 w 生 ww
生物秀论坛-学术交流、资源共享与互助社区
https://www.360docs.net/doc/b77009743.html,

二氧化钛光催化剂及其在环境中的应用

二氧化钛光催化剂及其在环境中的应用 随着工业化的迅猛发展与人口的不断增长,全球范围内的环境污染问题逐步加剧。光催化技术的核心——光催化剂可以利用清洁的太阳能有效地降解各类有机污染物,从而可以在一定程度上解决环境污染问题。二氧化钛基光催化剂研究包括能源领域的光解水制氢、太阳能电池、水体内污染物的去除以及CO2资源化利用等方面。本文简要分析了二氧化钛光催化剂的特点及在环境中的应用。 标签:二氧化钛;光催化剂;环境;应用分析 二氧化钛本身具有反应条件温和,无毒,无二次污染等优点,且能够降解难降解的有机污染物,在处理水污染等其他环境污染方面比传统的工艺有明显的优势。也可以循环利用,极大降低了成本。所以二氧化钛成为处理环境污染问题中的新兴材料,对环境保护有重要的意义。 一、二氧化钛的特点 在已开发的光催化剂中,二氧化钛由于具有较高活性、优异的稳定性、超亲水性以及低成本、环境友好等优点,成为目前研究最为广泛的光催化剂。虽然对TiO2的研究报道很多,但TiO2在实际应用中的缺点和不足却是无法避免的,主要包括:①TiO2的禁带宽度较大,只能对波长在390nm以下的紫外光产生响应,使其对太阳光的利用率较低;②光生载流子的复合概率比较大,从而降低了TiO2的催化活性;③TiO2在液相反应中容易流失、较难分离。基于这些缺点,目前针对TiO2的研究主要集中于TiO2的负载和改性技术,如图1。 二、纳米二氧化钛光催化剂的应用 光催化剂对环境保护和节约能源具有重大意义,纳米TiO2 在废水处理、大气净化等领域应用也越来越广泛。 (一)二氧化钛光催化剂在气体净化中的应用 近年来,空气中有害物质的去除引起了人们的关注。由于大部分空气污染物(如醛、酮、醇等)较易被氧化,因此用氧化法去除空气中的有害物质具有一定的可行性。去除空气中污染物常用的多相催化氧化法大都需要在较高温度下进行,而光催化能在室温下利用空气中的水蒸气和O2去除空气污染物。利用二氧化钛光催化剂在光照条件下可将空气中的有机物分解为CO2、HO2及相应的有机酸。目前,国内外学者对烯烃、醇、酮、醛、芳香族化合物、有机酸、胺、有机复合物、三氯乙烯等气态有机物的二氧化钛光催化降解进行了大量研究,其量子效率(反应速率,入射光密度)是降解水溶液中同样有机物的10倍以上。另外,在二氧化钛光催化反应中,一些芳香族化合物的光催化降解过程往往伴随着各种中间产物的生成,有些中间产物具有相当大的毒性,从而使芳香族化合物不适于液相光催化反应过程,如水的净化处理。但在气相光催化反应中,生成的中

总结光催化剂的摘要

1、Al 掺杂TiO2介孔材料的合成、表征和光催化性能 摘要:以钛酸四丁酯为钛源、十八水硫酸铝为铝源、三乙醇胺为模板剂, 采用研磨溶胶技术合成了Al 掺杂的TiO2介孔材料, 并利用XRD、EDS、TEM、BET、UV-vis 和IR 等手段表征了材料的结构、形貌、比表面积、孔径分布及光学性能。结果表明:Al 掺杂能够减小TiO2光催化剂的粒径, 提高介孔TiO2的热稳定性;Al 掺杂TiO2介孔材料的平均孔径为4.5 nm, 比表面积达到110.2 m2/g;相比商用P25 和介孔TiO2,Al 掺杂介孔TiO2 的吸收边发生红移,对初始浓度为20 mg/L 的甲基橙进行催化降解1 h 后,其降解率达到92.5%。 2、CuFe2O4/TiO2复合光催化剂在模拟太阳光下对大肠杆菌杀灭作用的研究 摘要:采用溶胶-凝胶法制备了纳米CuFe2O4,然后与TiO2固相烧结成复合光催化剂,并通过TEM,XRD和UV-visDRS对复合光催化剂进行了表征,表明样品由粒径约为80 nm的粒子组成,晶体结构均匀。以大肠杆菌为研究对象,考察了复合光催化剂在模拟太阳光(150W 氙灯,λ= 200~900 nm)照射下的杀菌性能。结果表明:复合光催化剂比单一光催化剂杀菌效果好,在最佳条件下,模拟太阳光照射30 min后,CuFe2O4/TiO2复合光催化剂的杀菌率分别为单纯CuFe2O4和TiO2杀菌率的1.71倍和1.13倍。复合光催化剂杀菌性能受CuFe2O4与TiO2质量比及固相合成时焙烧温度的影响,当TiO2质量分数为80%、焙烧温度为600℃时,所制得的复合光催化剂处理大肠杆菌,在模拟太阳光照射30 min后,细菌的存活率仅为3·2%,而单纯CuFe2O4和TiO2光催化剂在最佳条件下杀菌30 min后细菌存活率分别为43.3%和14.2%。同样条件下在黑暗中使用催化剂或在光照下不用催化剂时细菌存活率分别为97.0%,93.2%。 3、N、C共掺TiO2光催化剂的制备与性能研究 摘要以三聚氰胺为掺杂源,采用溶胶-凝胶法制得了平均粒径为20.1nm的锐钛矿型N、C共掺TiO2光催化剂。当n(N)∶n(C)∶n(Ti)为0.064∶0.055∶1时,TiO2对亚甲基蓝3h 日光降解率可达68%。探讨了三聚氰胺的用量和煅烧温度对TiO2光催化性能的影响,确定了最佳制备工艺。XPS和FTIR分析表明,N主要以替代O的形式生成O-Ti-N,少量N以填隙式生成-Ti-N-O,而C主要以替位式生成O-Ti-C,以填隙式生成-Ti-C-O、-Ti-COOO。UV-Vis分析表明,N、C掺杂TiO2的吸收边从掺杂前的383nm红移到427nm,禁带宽度从掺杂前的3.2eV 降到2.9eV,将TiO2的光响应波长拓展到了可见光区。 4、N、S共掺杂纳米二氧化钛的水热法制备和表征 摘要:采用水热法制备了具有可见光响应的硫掺杂、氮掺杂以及硫氮共掺杂纳米二氧化钛,并测试其光催化活性.产物用X-射线衍射(XRD)、紫外漫反射光谱(UV-visDRS)、N2-吸附脱附曲线(BET)、透射电镜(TEM)等进行分析表征;利用SGY-Ⅰ型多功能光反应仪进行光催化活性测试.实验研究发现,离子掺杂提高了催化剂对紫外光的吸收,而且将光吸收范围拓展到可见光区;掺杂没有改变产物的晶相;掺杂TiO2的光降解效率高于纯TiO2,其中以在550℃下焙烧制得的S,N-TiO2催化效果最好. 而N-TiO2, S,N- TiO2的光降解率都远高于纯TiO2,其中S,N- TiO2的光降解率最高,在20 min时其光降解率已将近100%.这说明加入掺杂元素提高了二氧化钛的光催化活性,也再次证明了S、N元素在催化过程中是起协同作用的,二者共同掺杂的催化效果比单一掺杂要好的多. 5、p-n结型光催化剂Co3O4/In2O3的制备、表征及其光催化性能的研究 摘要:p-n结型Co3O4/In2O3光催化剂是用共沉淀法制备的,并用X射线衍射对其进行表征。用光催化还原Cr6+和光催化氧化甲基橙的效率来评价该催化剂的活性。实验分别研究了Co3O4的掺杂比、焙烧温度和焙烧时间对光催化活性的影响。实验结果表明,Co3O4的最佳掺杂比(质量分数)为5%。催化剂的最佳焙烧温度和最佳焙烧时间分别为300°C和2h。在可见光和紫外光的照射下,p-n结型光催化剂Co3O4/In2O3的光催化氧化活性和光催化还

钛硅分子筛的合成研究 1

钛硅分子筛TS-1合成及应用研究 ****学院***0902 *** 摘要:本文重点综述了近年来钛硅分子筛催化材料的合成、改性及其催化应用的研究进展,包括钛硅分子筛( T S-1) 的水热合成方法和同晶取代合成法、钛硅分子筛双氧水体系的应用研究及近年中孔钛硅分子筛的进展. 关键词:钛硅分子筛TS-1;催化氧化;双氧水;合成 The Syntheses and Applications of Titanium Silicalite TS Molecular Sieves Abstract:Recent developments in the synthesis,modification andcatalytic properties of titanium silicalite molecular sieve are reviewed,including the developments in the synthesis of TS-1 with hydrothermal,applicat ions of t itanium silicalite cataly tic ox idation system using hydr ogen pero xide, and research of mesopo rous titanium silicalite mo lecular sieves. 自1983年有专利报道了以TS-1类钛硅分子筛为催化剂、稀双氧水(H 2O 2 质量分 数为30%)为氧化剂催化氧化苯酚同时生产邻、对苯二酚以来,有关分子筛类催化剂的羟基化反应报道甚多,研究得也最为充分。TS-1分子筛的诞生掀起了有机物非均相选择性催化氧化的一场革命,特别是对于在温和条件下,用稀双氧水溶液为氧化剂的选择性氧化具有独特的性能。TS-1分子筛催化剂使反应具有如下显著优点:①反应条件温和,可在常压、低温(20~100℃)下进行;②氧化目的产物收率高,选择性好;③工艺过程简单;④由于使用低浓度过氧化氢作为氧化剂,氧化源安全易得;⑤还原产物为H 2 O,反应体系没有引入杂质,不会造成环境污染。它的成功开发被认为是20世纪80年代沸石催化的里程碑,为研究高选择性的烃类氧化反应、开发绿色工艺奠定了基础。 1. 钛硅分子筛TS-1 水热合成方法 钛硅沸石分子筛是指在沸石分子筛骨架中含有钛原子的一类杂原子分子筛, 现有TS-1、TS-2、TiB、TS-48、ETS-10 等,。T S-1 的合成是由Taramasso等人[1]于1983 年首先报道的, 合成使用硅酸四乙酯( TEOS) 为硅源, 钛酸四乙酯

二氧化钛光催化剂研究进展

二氧化钛光催化剂研究进展 工业催化张春明 摘要:催化是工业生产中追求高效率、高纯度、低耗能的有效手段。纳米TIO2以光催化凭着可以利用可见光进行催化反应而受到催化领域的亲昧,就纳米TIO2光催化剂目前的研究状况展开论述,并列举了TIO2光催化剂应用领域和目前的制备方法。讨论了光催化剂的发展前景,揭示了目前光催化技术对当代化工事业的影响,并对未来的发展发表了预期的倡想。 关键词:二氧化钛光催化剂纳米材料研究进展 前言 通俗意义上讲触媒就是催化剂的意思,光触媒顾名思义就是光催化剂。催化剂是加速化学反应的化学物质,其本身并不参与反应。光催化剂就是在光子的激发下能够起到催化作用的化学物质的统称。 光催化技术是在20世纪70年代诞生的基础纳米技术,在中国大陆我们会用光触媒这个通俗词来称呼光催化剂。典型的天然光催化剂就是我们常见的叶绿素,在植物的光合作用中促进空气中的二氧化碳和水合成为氧气和碳水化合物。总的来说纳米光触媒技术是一种纳米仿生技术,用于环境净化,自清洁材料,先进新能源,癌症医疗,高效率抗菌等多个前沿领域。 目前光催化反应已经在废水处理这一领域逐渐成效。光催化氧化具有很强的氧化能力,在环境污染治理等方面显示出了巨大的应用潜力,是近年来国内外的一个热点研究领域。由于TiO2半导体光催化具有生物降解所无可比拟的速度快、无选择性、降解完全等优点,又在价廉、无毒、可以长期使用等方面明显优于传统的化学氧化方法,在环境污染治理方面具有广阔的应用前景。另外最新研究成果显示将TIO2 光催化分子负于磁性,可有效的进行分离回收和再生循环使用。因此,可磁分离的技术的研究成果更为TIO2 光催剂的应用进展画上了光辉的一笔。 作为高新技术纳米材料。纳米TiO2的制备方法主要分为气相法和液相法,前者包括氢氧火焰水解法、气相氧化法、钛酸盐气相水解法和气相分解法等,后者则包括溶胶一凝胶法、微乳法、水解法、水热合成法和一步合成法等。尽管气相法制备的TiO2粉体粒度小、纯度高、分散性好,但工艺复杂、成本高且对设备和原料的要求较高。相比而言,液相法制备TiO2的工艺简单、成本低廉、设备投资小,已成为国内研究纳米TiO2常用的方法。现主要列举有关制备TiO2 光催化剂的研究进展。 1.光催化剂 光催化是在光的辐照下使催化剂周围的氧和水转化成极具活性的氧自由基,氧化能力极强,几乎可分解所有对人体或环境有害的有机物质。可用作光催化剂化合物,大多是具有半导体性质的,如Ti02、ZnO、WO3以及CdS、ZnS等。TiO2是最常用的光催化剂,因为他的光化学稳定性好,无毒且与人体相容性好[1]。 1.1.光催化反应的发现 1972年Fujishima等[7]报道了在可持续发生水的氧化还原反应,并产生氢气,这个特性引起了环保领域科研工作者的极大兴趣,从此开创了半导体光催化技术的新纪元。TiOz因光催化活性高、氧化能力强、无毒、化学稳定性好、价廉等优点而最受重视。在提高半导体催化活性方面,金属或金属氧化物与半导体复合组成的光催化剂发展得非常迅速,制备和开发纳米二氧化钛成为国内外科技界研究的热点。 1.2.Ti02光催化剂作用原理 当Ti02吸收光子能量后,其价带上的一个电子跃迁到导带;原价带保留一个空缺,称为空穴,带正电荷。跃迁电子和电空穴都及不稳定,可供给周围介质,使其还原或氧化。因为Ti02的带隙宽约为

tio2光催化技术

纳米TiO2光催化剂安全环保性能研究 作者:北京化工大学徐瑞芬教授 纳米科技的发展为人类治理环境开辟了 一条行之有效的途径,我们可以合理利用 自然光资源,通过纳米TiO2半导体的光催化效应,在材料内部由吸收光激发电子,产生电子-空穴对,即光生载流子,迅速迁移到材料表面,激活材料表面吸附氧和水分,产生活性氢氧自由基(oOH)和超氧阴离子自由基(O2·-),从而转化为一种具有安全化学能的活性物质,起到矿化降解环境污染物和抑菌杀菌的作用。 纳米TiO2光催化应用技术工艺简单、成本低廉,利用自然光即可催化分解细菌和污染物,具有高催化活性、良好的化学稳定性和热稳定性、无二次污染、无刺激性、安全无毒等特点,且能长期有益于生态自然环境,是最具有开发前景的绿色环保催化剂之一。 本研究在用亚稳态氯化法合成纳米二氧化钛的技术基础上,根据光催化功能高效性的需要,进行掺杂和表面处理,制成特有的在室内自然光和黑暗区微光也能显著发挥光催化作用的纳米二氧化钛,将其作为功能粉体材料,复合到塑料、皮革、纤维、涂料等材料中,研制成无污染、无毒害的纳米TiO2光催化绿色复合材料,充分发挥抗菌、降解有机污染物、除臭、自净化的功能,这类环保型功能材料实施方便、应用性强,能实用到生活空间的多种场合,发挥其多功能效应,成为我们生活环境中起长期净化作用的环保材料。 2 纳米TiO2光催化剂对环境的净化功能研究 2.1室内环境的净化 随着建筑材料中各种添加物的使用,室内装饰材料和各种家用化学物质的使用,室内空气污染的程度越来越严重。调查表明,室内空气污染物浓度高于室外,甚至高于工业区。据有关部门测试,现代居室内空气中挥发性有机化合物高达300多种,其中对人体容易造成伤害、甚至致癌的就有20多种,极大地威胁着人类的健康生活。随着人们健康和环保意识的增强,人们对具有光催化净化室内外空气、抗菌杀毒等功能性绿色环保材料的需求日益迫切,纳米TiO2光催化剂的出现为环境净化材料的发展开辟了一片新天地,也为人们对健康环境需求的解决提供了有效的途径。

钛硅分子筛催化剂的研究进展

Research progress of titanium silicalite catalys t Zhangxiaoming Zhangzhaorong Soujiquan Lishuben (Lanzhou Institute of Chemical Physics fine petrochemical intermediates National Engineering Research Center, Lanzhou 730000) The role of titanium catalyst in the oxidation reaction of organic compounds is well known [1, 2]. Introduced in the molecular sieve framework due to the molecular sieve having a regular pore structure and large specific surface area characteristics, hetero atom, having an oxidation-reduction ability to preparenovel catalytic oxidation catalyst, has been more interesting subject in 1983 ENI [3] the T ar amasso its collaborators first successful synthesis of the titanium-containing zeolite catalyst of TS-1, a subsequent study found, Tammonia oxidation [7] S-1 with H2O2 aqueous solution as oxidant and the oxidation reaction of a series of organic compounds, such as olefin epoxidation [4], the aromatic hydrocarbon ring hydroxylation [5, 6], ketone, alkane oxidation[8, 9] and the alcohol oxidation [10] and so the process has a unique shape-selective catalytic function as compared with other types of catalytic systems, the system (1) the mild reaction conditions (atmospheric pressure, 0 - 100 ° C); (2) the unique function of the shape-selective catalytic oxidation; (3) environmental friendliness. TS-1 has been very limited because the aperture is only about 0. 55 nm, and its range of applications where the aerodynamic diameter is greater than 0. 60 nm substrate molecules can not enter within its pores without reactivity. Orderovercome this limitation, the type of catalyst to get a wider range of applications, the majority of scientists have successfully synthesized T S-2 [11], Ti-Beta [12] and a series of large aperture zeolite catalysts. In recent years, with the development of the petroleum refining and fine petrochemical technology requires the use of some reorganization of the oil to be effective. M41S [13, 14], HMS [15] and MSU [16] series of mesoporous molecular sieves Tiheteroatom derivatives T i-MCM-41 [17], Ti-MCM-48 [18], Ti-HMS [19, 20] and of Ti-the MSU [16] emerged, the latter in the selective oxidation of organic compoundsshowed higher catalytic activity. This paper reviews the recent years, the progress made in terms of microporous and mesoporous titanium silicalite catalyst preparation, characterization, and catalytic reaction. T S-1 is first synthesized, and also so far been studied most, and more thoroughly of a class of titanium silicalite catalyst. T S-1 is a Silicalite-1 isomorphously substituted derivatives thereof, having the MFI structure. TS- work and the results achieved many comments have been reported [10, 21 - 24] here only a brief overview of the TS-1 preparation, characterization, and their corresponding catalytic reaction. The classical method of preparing a zeolite catalyst is a hydrothermal synthesis method in the the earliest patent literature, Tar amasso [3] reported two preparation T S-1 The method of one is tetraethyl orthosilicate (T EOS) and tetraethylammonium n-titanate (TEOT) as silica source and a titanium source, and tetrapropyl ammonium hydroxide (TPA OH) as templating agent;

生物催化技术

化学化工学工业催化结课论文 生物催化技术 姓名: 指导教师: 院系:化学化工学院 专业: 10化工 提交日期: 2013-1-18

目录 摘要 (3) 英文摘要 (4) 前言 (5) 1.生物催化原理 (5) 1.1生物催化原理 (5) 2.生物催化反应的特征 (6) 3.常见的生物催化剂——酶 (6) 3.1酶的分类 (6) 3. 2 酶的功能和应用 (6) 3.2.1 酶的功能简介 (6) 3.2.2 一些酶的应用 (8) 4.生物催化剂快速定向改造新技术....................................8 4.1定向进化技术的优势 (8) 4.2定向进化目前主要研究方向 (9) 5.生物催化技术的趋势与前景.......................................9 5.1生物催化技术的趋势与前景 (9) 5.1.1国外的发展形势 (9) 5.1.2我国生物催化产业的现状 (10) 5.2前景小结 (10) 结束语 (10) 参考文献 (11) 致谢 (12) 生物催化技术 郭蒙蒙 指导老师:吴斌 (黄山学院化学化工学院,黄山,安徽)

摘要 近几年,全球催化剂市场将以 4.6%的速率增长,环境用催化剂将占有最大的市场份额,约27%,以下依次为聚合用催化剂(22%)、炼油用催化剂(21%)、石油化工用催化剂(20%)、精细化工用催化剂(10%),其中,精细化工用催化剂和环境用催化剂增长速率最快,均接近8%.由于生物催化剂能够减少环境污染,反应速度较快等众多特点,生物催化剂俨然已经成为化工催化的宠儿。生物催化技术在化工生产中应用十分的广泛,它的出现一定程度上提高了生产效率,也降低了生产的成本。同时生物催化也涉及了三个学科的不同部分:化学中的生物化学和有机化学;微生物学、酶学;化工工程雪中的催化、传递过程和反应工程学。人类在很早的时候就知道利用酶,利用酶或微生物细胞作为生物催化剂进行生物催化已有几千年的历史,如麦芽制曲酿酒工艺等。近代认识酶是与发酵和消化现象联系在一起的。后来创造了“酶”这一术语以表达催化活性。本文主要说明生物催化剂催化的原理类别,生物催化反应的特征及生物催化的发展和趋势等关键词生物催化技术酶生物催化技术前景 In recent years, the market of global catalyst will grow at the rate of 4.6%, environmental catalysts will occupy the largest market share, about 27%, followed by polymerization catalysts (22% ), ( 21% ) refining

Ti-MWW钛硅分子筛合成新方法及其催化性能的研究

Ti-MWW钛硅分子筛合成新方法及其催化性能的研究 【摘要】:本论文以提高新一代钛硅分子筛Ti-MWW的催化活性,改善Ti-MWW分子筛的工艺流程为目的,开发了两种新合成方法;以扩大Ti-MWW分子筛在有机反应中的应用范围为目的,开展了含有介孔的Ti-MWW分子筛的合成研究,并将其应用于催化大尺寸底物分子的氧化反应;最后探索Ti-MWW分子筛应用到生产吡啶类氮氧化物这类大宗化学品的反应过程的可能性。第一部分采用廉价的无机钛源六氟钛酸(H2TiF6)在水热条件下合成了Ti-MWW分子筛,考察了各种合成条件包括助晶化剂硼酸的用量、模板剂的用量、凝胶组成等因素对产物的影响。与经典有机钛源法相比,无机钛源法节约了60%以上的硼酸,并且得到的Ti-MWW分子筛的物化性质发生了很大的变化。X-射线粉末衍射表明此方法制备的样品在高温焙烧后保留部分层状结构;红外光谱表明分子筛骨架内部的硅羟基减少,即疏水性能增强,并且与杂原子相关的吸收峰位置发生改变。因此,与经典有机钛源法相比,无机钛源法合成的Ti-MWW分子筛对直链烯烃环氧化、环己酮氨肟化等反应都显示出更优异的催化性能;尤其在大分子反应物环己烯的环氧化、甲基吡啶的氧化反应中,反应物的转化率以及目的产物的收率都提高2倍以上。第二部分采用分子筛二次合成法-杂原子液固相置换法,首次合成出无非骨架钛的Ti-MWW分子筛。利用MWW型分子筛骨架构成以及结构可逆转化的特点,以六氟钛酸为钛源进行杂原子置换;在常温常压下向MWW型分子筛骨架引入活性中心Ti物

种,并且利用无机钛源的阴离子最先占据分子筛表面一些空穴位,有效地阻止非骨架Ti物种(260nm处紫外吸收峰)的形成。本部分详细考察了各种合成条件包括置换反应时间、温度、前驱体的种类、前驱体预处理的酸量、钛源的种类、投料配比(Si/Ti)等因素的影响。类似地,以这种简单的方法合成出高钛含量的且拥有12元环大孔道的IEZ-Ti-MWW分子筛。反应评价表明,此方法制备的Ti-MWW分子筛的催化性能远远高于文献所报道的各种方法合成的Ti-MWW。与现有工业化生产工艺不同的是,以此方法合成的Ti-MWW分子筛将无需酸处理过程,就可以直接用于催化反应,从源头上避免产生大量的有害性废水,为合成工艺的简化以及新技术开发打下了坚实的基础。第三部分采用碱性硅溶胶或正硅酸乙酯作为硅源,钛酸四丁酯作为钛源,以蔗糖炭化得到的碳小颗粒为硬模板,在微孔模板剂六氢吡啶的共同作用下,水热合成了含有介孔的Ti-MWW分子筛;并且对具有介孔的Ti-MWW分子筛的催化性能进行了考察。由于介孔孔道的存在,增加了大分子反应物和催化剂活性中心的接触机会,并且改善了扩散性能,含有介孔的Ti-MWW在3-甲基吡啶氧化反应中表现出更高的单位反应活性(TON)。第四部分,我们考察了以过氧化氢为氧化剂,Ti-MWW 分子筛催化氧化吡啶及其衍生物制备吡啶类氮氧化物的过程中的表现,并与典型的钛硅分子筛TS-1、Ti-Beta和Ti-MOR进行了比较。采用Ti-MWW分子筛/H2O2催化体系,在无溶剂条件下,通过对吡啶氮氧化物合成工艺条件的考察与优化,吡啶的转化率以及吡啶氮氧化物的选择性都能达到97%以上。对于催化大尺寸的甲基吡啶分子氧化反应,

相关文档
最新文档