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物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .2015,31(4),771-782
April Received:November 13,2014;Revid:March 2,2015;Published on Web:March 2,2015.∗
Corresponding author .Email:hulxhhhb@;Tel:+86-21-66137771.
The project was supported by the Program for Innovative Rearch Team in Shanghai University,China (IRT 13078).上海大学创新研究团队计划项目(IRT 13078)资助
©Editorial office of Acta Physico -Chimica Sinica
doi:10.3866/PKU.WHXB 201503023
介孔Fe/SBA-15非均相芬顿氧化水中难降解染料罗丹明B
胡龙兴*
许丹丹
中控室
邹联沛
英语作文大全
袁
航
学生自评50字胡
星
(上海大学环境与化学工程学院，上海200444)
摘要:
以介孔二氧化硅SBA-15为载体，采用等体积浸渍法制备了Fe/SBA-15.通过X 射线衍射(XRD)、N 2吸
附-脱附、扫描电镜(SEM)、透射电镜(TEM)和X 射线光电子能谱(XPS)等技术对其进行了表征，并用于对水溶液中罗丹明B (RhB)的芬顿氧化.表征结果表明了Fe/SBA-15维持了长程有序的介孔结构，孔径和比表面积都有所下降，并呈现棒状体的聚集态，平均直径为0.6μm.Fe 以α-Fe 2O 3的形态同时存在于介孔孔道内外.在Fe/SBA-15和H 2O 2同时存在条件下RhB 的去除是吸附和催化氧化降解的协同
作用所致，并且与Fe/SBA-15投加量密切相关，但与初始溶液pH 几乎无关.当Fe/SBA-15投加量为0.15g ∙L -1,RhB 初始浓度为10.0mg ∙L -1,H 2O 2/Fe 3+摩尔比为2000:1，初始溶液pH 为5.4和反应温度为21°C 时,RhB 去除率达到了93%.Fe/SBA-15的Langmiur 单分子层饱和吸附量为99.11mg ∙g -1.此外，采用H 2O 2浸泡方式对使用过的Fe/SBA-15可进行再生，连续6次循环使用后仍可维持80%的RhB 去除率，且每次使用后Fe 浸出浓度都在0.1mg ∙L -1(或者0.6%(质量分数))以下.基于淬灭实验、UV-Vis 光谱和气相色谱-质谱(GC-MS)联用仪分析的结果，提出了RhB 的去除机理.非均相芬顿催化剂Fe/SBA-15可用于去除像RhB 这样的生物难降解有机物.关键词:
非均相芬顿氧化；吸附;Fe/SBA-15；罗丹明B；羟基自由基
中图分类号:
O643
Heterogeneous Fenton Oxidation of Refractory Dye Rhodamine B in
Aqueous Solution with Mesoporous Fe/SBA-15
HU Long-Xing *
XU Dan-Dan
ZOU Lian-Pei
YUAN Hang
陈国和HU Xing
(School of Environmental and Chemical Engineering,Shanghai University,Shanghai 200444,P .R.China )Abstract:An Fe-loaded mesoporous silica SBA-15,Fe/SBA-15,was prepared by incipient wetness impregnation,characterized by X-ray diffraction (XRD),N 2adsorption-desorption,scanning electron microscopy (SEM),transmission electron microscopy (TEM),and X-ray photoelectron spectroscopy (XPS)techniques and ud for heterogeneous Fenton oxidation of dye Rhodamine B (RhB)in aqueous solution.The characterization showed that the Fe/SBA-15retained a mesoporous structure with a long-range ordered arrangement,reduced pore diameter and surface area,and existed as agglomerates of rod-like crystallites with a mean diameter of 0.6μm.The Fe species occurred both inside and outside the support pores in the form of α-Fe 2O 3crystallites.The removal of RhB in the prence of Fe/SBA-15and H 2O 2was shown to be caud by the synergistic effects of adsorption and catalytic oxidative degradation,and was cloly related to Fe/SBA-15dosage.Removal was almost independent of initial solution pH,with approximately 93%achieved a
t an Fe/SBA-15dosage of 0.15g ∙L -1,initial RhB concentration of 10.0mg ∙L -1,H 2O 2/Fe 3+molar ratio of 2000:1;initial solution pH of 5.4and 21°C.The Langmuir monolayer adsorption capacity of the Fe/SBA-15was 99.11mg ∙g -1.In addition,Fe/SBA-15can be easily regenerated by soaking in H 2O 2then reud for up to six runs,with RhB removal greater than 80%and Fe leaching below 0.1mg ∙L -1(or 0.6%(mass fraction))for each run.A removal mechanism for RhB by Fe/
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Acta Phys.-Chim.Sin.2015V ol.31
1Introduction
Textile dyes and other industrial dyestuffs make up one of the largest groups of non-biodegradable materials that impo rious environmental problems becau of their existence in the efflu-ents.A number of techniques have been applied to remove re-fractory organic pollutants from water,such as adsorption,1,2 electrochemical oxidation,3,4ultrasonic degradation,5,6photocat-alytic degradation,7,8ozonation,9,10etc.Adsorption is easy to op-erate with high removal efficiency,but it only transfers the pol-lutants from liquid pha to solid pha,leading to the condary pollution.The other techniques require special devices and equipment,resulting in the high capital and operational
costs. Fenton reaction(Fe2+/H2O2)has been widely applied in treating organic pollutants in water becau it is rapid and inexpensive. However,it has veral significant drawbacks such as the acidic pH requirement(pH2-4),a high Fe dosage generating a large amount of iron sludge,and the limited TOC(total organic carbon) removal.11-13Heterogeneous Fenton oxidation using Fe-bad solid materials as catalysts has emerged as a promising alternative to the conventional Fenton process due to the abnce of the usual disadvantages and feasibility of the catalyst recycle.
To date,iron-bad solid catalysts as promising heterogeneous Fenton catalysts for degradation of organic pollutants have been reported,and can be classified as unsupported iron oxides in-cluding Fe2O3,Fe3O4,and zero-valence iron,14-16unsupported iron composites including some non-ferrous metals with variable va-lence,17-19and supported iron catalysts including iron-immobilized resin,20membrane,21clay,22,23carbon,24-26zeolite,27-29mesostructured silica materials,13,30-45and alumina.46,47
Mesoporous silica SBA-15,one of the mesoporous molecular sieves,has highly ordered structure,large pore size,and high surface area,48,49which favors the loading and dispersion of the catalytic active components which posss the nano effect due to the nano-size domain.Accordingly,it is possible for Fe loaded mesoporous molecular sieves to exhibit high activity
and stability in heterogeneous Fenton oxidation of organic pollutants.Melero et al.31investigated a nanocomposite of Fe2O3loaded SBA-15 which acted as an efficient and stable catalyst for wet peroxidation of phenolic aqueous solutions.They also ud the SBA-15loaded Fe2O3and CuO crystallites as the heterogeneous Fenton catalyst, preventing the leaching of Fe species and enhancing the TOC degradation.32Xiang et al.36synthesized a Fe/SBA-15by different impregnation and co-condensation approaches,and ascertained the most active catalysts in the total phenol oxidation by H2O2in aqueous solution.Shukla et al.37prepared Fe/SBA-15by im-pregnation and tested for adsorption and heterogeneous advanced oxidation of2,4-dichlorophenol(DCP)in aqueous solution in the prence of H2O2.Botas et al.13synthesized various Fe/SBA-15 catalysts for the oxidation of phenol aqueous solution with H2O2. Mayani et al.38evaluated the Fe/SBA-15for the oxidation of phe-nols in the prence and abnce of H2O2with satisfactory results. In the previous investigations,phenolic contaminants were usually ud as the target substrates,and Fe loaded mesoporous materials were usually regarded as catalysts.Few investigations were concerned with other refractory organic pollutants and the adsorption performance of the catalysts in heterogeneous Fenton oxidation.23,27,29,34,37,43The dye Rhodamine B(RhB)with four N-ethyl groups at either side of the xanthene ring and chromophore has the complex molecular structure and stable property,which make it resistant to biological degradation or photodegrada-tion.This paper deals with
the dual functions of the prepared Fe/ SBA-15as both an adsorbent and a catalyst in the heterogeneous Fenton oxidation of RhB in aqueous solution.The effects of re-action parameters such as Fe/SBA-15dosage,initial RhB con-centration,molar ratio of H2O2/Fe3+,and initial solution pH on RhB removal,and the regeneration and recycling performance of the Fe/SBA-15are examined,and the removal mechanism of RhB from aqueous solution is propod on the basis of experimental results.
2Experimental
2.1Preparation of SBA-15and Fe/SBA-15
SBA-15as a support was prepared according to the procedure described by Zhao et al.48Pluronic P123triblock copolymer(EO20-PO70-EO20(EO:ethoxy;PO:propoxy),Aldrich)and tetra ethlyl orthosilicate(TEOS,Aldrich)acted as a template agent and a silica source,respectively.The Fe/SBA-15with the Fe loading of 10%(mass ratio of Fe to SBA-15,simplified as Fe/SBA-15in this investigation)was prepared by incipient wetness impregnation.A typical synthesis could be described as follows:the precursor Fe(NO3)3∙9H2O(AR,SCRC)was dissolved in deionized water at a concentration dependent on the desired Fe loading,then a cer-tain amount of the prepared SBA-15w
as disperd into the above solution forming a suspension,and the suspension was stirred to make Fe easy to impregnate,and the yielded mixture was dried in oven at60°C overnight to evaporate the solvent,finally followed by the calcination at750°C for5h in air with a heating rate of 10°C∙min-1.
2.2Characterization of prepared SBA-15and Fe/
SBA-15
SBA-15and H2O2was propod bad on the quenching tests,UV-Vis spectra,and gas chromatography-mass spectrometry(GC-MS)analysis.The heterogeneous Fenton catalyst Fe/SBA-15can be applied to remove non-biodegradable organics such as dye RhB.
Key Words:Heterogeneous Fenton oxidation;Adsorption;Fe/SBA-15;Rhodamine B;
消防安全知识讲座Hydroxyl radical
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HU Long-Xing et al.:Heterogeneous Fenton Oxidation of Refractory Dye Rhodamine B in Aqueous Solution No.4
The crystalline form of the prepared samples were identified by X-ray diffraction(XRD,Model,Rigaku D/Max-2200X)using a diffraction meter with Cu Kαradiation source of wavelength 0.154056nm at40kV and40mA.The small-angle data were collected from0.5°to5.0°(2θ)with a scan speed of0.5(°)∙min-1; the wide-angle data were collected from10°to80°(2θ)with a scan speed of5(°)∙min-1.N2adsorption-desorption isotherms of the samples were acquired using Micromeritics Tristar3000ap-paratus at77K.Pore volumes were determined from the data at a relative pressure(p/p0)of0.99,the specific surface areas were calculated with BET(Brunner-Emmet-Teller)equation,and pore size distributions were determined by BJH(Barrett-Joyner-Halenda)method according to the adsorption branch of the iso-therms.The external morphology of samples was collected on a JSM-6700F scanning electron microscope(SEM).The internal structure of samples was characterized by a JEM-2010F(JEOL) high resolution-transmission electron microscope(HRTEM) with field emission gun at200kV.X-ray photoelectron spec-troscopy(XPS)measurements were recorded on a ESCALAB 250Xi device.
2.3Adsorption(adsorption mode)
The adsorption tests were carried out respectively at∼21°C in 100and1000mL glass vesls with50and500mL of RhB(AR, >99%,SCRC)solutions which were magnetically stirred,re-spectively.T
he initial solution pH was not adjusted.Only a known amount of Fe/SBA-15was added into the aqueous solution to start the contact.The vesl was covered to avoid volatilization.At the end of the contact or at fixed intervals,the suspension samples of 7mL for each were taken with a syringe.The suspensions were parated by centrifugation at3500r∙min-1for10min to obtain the supernatant for analysis.
2.4Catalytic oxidative degradation(catalytic
degradation mode)
The catalytic activity of Fe/SBA-15was evaluated by the deg-radation of RhB instead of the adsorption.The catalytic oxidative degradation tests of RhB were carried out respectively at a given temperature in1000mL glass vesls with500mL of RhB so-lution for each which was magnetically stirred.The Fe/SBA-15 was first added into the RhB solutions and the suspensions were stirred overnight to achieve the adsorption-desorption equilibrium of RhB.The RhB concentrations at the equilibrium were taken as the initial concentrations(c0)for the RhB catalytic degradation. Then a given amount of H2O2solution(AR,30%(w,mass frac-tion),SCRC)was added into the vesl to initiate the reaction. The vesl was also covered to avoid volatilization.At fixed in-tervals,the suspen
sion samples of7mL for each were taken with a syringe and quenched with excess methanol to stop the reaction. The following procedures were the same as above.
2.5Combined adsorption and catalytic oxidative
degradation(combined mode)
The tests with the combined mode were carried out respectively at∼21°C in100and1000mL glass vesls with50and500mL of RhB solutions which were magnetically stirred for14h,re-spectively.The initial solution pH was adjusted by1.0mol∙L-1NaOH and1.0mol∙L-1H2SO4solutions using a pH meter(pHS-3C,Shanghai,China).A known amount of Fe/SBA-15was added into the aqueous solution,immediately followed by the addition of a given amount of H2O2solution to start the reaction.The subquent procedures were the same as above.
2.6Analytical methods
The RhB concentrations were quantified with a UV-Vis spec-trophotometer(UV-5300PC,Shanghai)at552nm.The Fe con-centration in solution was measured by an inductively coupled plasma(ICP)emission spectrometer(Prodigy).The concentration of H2O2in aqueous solution
was determined by the titanium complexing method described by Vassilakis et al.50The UV-Vis spectra were obtained using a UV-Vis spectrophotometer(UV-5300PC,Shanghai)at different reaction time,with the spectrum scanned from350to650nm.The principal degradation products of RhB were detected by GC-MS,with an Agilent7890A gas chromatograph equipped with a DB-5capillary column(30mm´0.25mm´0.18mm)combined with an Agilent5975C mass spectroscopy equipment employed.
Generally,the tests were conducted in duplicate and the errors of the experimental results were below3%.
3Results and discussion
3.1Characterization of SBA-15and Fe/SBA-15
3.1.1XRD
The small and wide angle XRD patterns of different samples are shown in Fig.1(a,b),respectively.As en from the
small
Fig.1Small(a)and wide(b)angle XRD patterns of
SBA-15and Fe/SBA-15
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Acta Phys.-Chim.Sin.2015V ol.31
angle XRD patterns(Fig.1(a)),SBA-15and Fe/SBA-15exhibit a strong diffraction peak and two obvious sub-peaks,corresponding to the diffraction planes(100),(110),and(200),respectively, indicating that the SBA-15posss the typical highly ordered hexagonally mesoporous structure and the Fe/SBA-15maintains the structure of SBA-15.However,the obvious decrea in in-tensity of the diffraction peaks in Fe/SBA-15compared with SBA-15could be obrved,which was attributed to the decrea in average electron density contrast and the formation of iron oxides inside the channels of SBA-15.51,52As en from Fig.1(b),besides one major peak at24°for SBA-15and Fe/SBA-15,there also exist other peaks for Fe/SBA-15which can be ascribed to the existence ofα-Fe2O3.Fe2O3is very stable under ambient conditions and is usually the end product of the transform
ation of other iron ox-ides.53Fe2O3,Fe3O4,and FeO are the principal Fe species available, and the specific species loaded into the supports tend to be de-pendent on the preparation methods and conditions.54-56
3.1.2N2adsorption-desorption
N2adsorption-desorption isotherms and pore size distribution at77K of SBA-15and Fe/SBA-15are shown in Fig.2.It is evi-dent in Fig.2(a)that Fe/SBA-15has similar isotherm to SBA-15, exhibiting type IV isotherms with a H1-type hysteresis loop, which was the characteristic of mesoporous materials having cylindrical type mesostructures.For the isotherm of the pure SBA-15,with incread relative pressure,a sharp jump resulting from capillary condensation of N2was obrved at p/p0of0.6-0.8, while the relative pressure with the emergence of the sharp step for Fe/SBA-15decread to0.45-0.75,indicating the reduced pore size due to Fe species introduction into the channel of SBA-15.The lower sharp jump of Fe/SBA-15than that of SBA-15 could also be explained by the reduced order degree of mesopo-rous structure due to Fe loading.The profiles of pore size distri-bution(Fig.2(b))show that the pore sizes of SBA-15and Fe/SBA-15are relatively uniform and center at6-10nm.The BET spe-cific surface areas and pore parameters of prepared SBA-15and Fe/SBA-15are listed in Table1.The results indicated that loading Fe into SBA-15reduced the specific surface
area,total pore volume,and pore diameter of the support,implying that a fraction of Fe loaded after calcination occupied part of the pore channel of SBA-15.
3.1.3SEM
The external morphologies of the SBA-15and Fe/SBA-15 characterized by SEM can be obrved from Fig.3.It can be found from Fig.3(a)that the SBA-15prents the aggregates with the diameter greater than0.7μm,consisting of rod-like crystallites with the diameter greater than0.2μm and axial length greater than 1.3μm.It can also be found from Fig.3(b)that the Fe/SBA-15 also displays the aggregates with the diameter more than0.6μm, consisting of rod-like crystallites,demonstrating that the Fe loading on SBA-15does not change the original morphology.There are many small particles attached to the surface of the Fe/SBA-15 (Fig.3(b)),which can be ascribed to the sintering of iron
oxides
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Fig.2N2adsorption-desorption isotherms(a)and pore size
卢荣友>吃蜂巢
distributions(b)for SBA-15and
Fe/SBA-15
Table1Pore parameters of SBA-15and Fe/SBA-15
Sample
SBA-15
Fe/SBA-15
BET specific surface area
(m2∙g-1)
858
460
Pore volume
(cm3∙g-1)
1.083
0.570
Pore diameter a
nm
8.260
7.438
a calculated from the desorption branch of the isotherm
Fig.3SEM images of SBA-15(a)and Fe/SBA-15(b)
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HU Long-Xing et al.:Heterogeneous Fenton Oxidation of Refractory Dye Rhodamine B in Aqueous Solution No.4
during high-temperature calcination.56The sintering makes a fraction of Fe2O3supported on the surface forming Fe2O3aggre-gates with the diameter more than0.4μm.
3.1.4TEM
The TEM images of the prepared SBA-15and Fe/SBA-15are prented in Fig.4.Fig.4(a,b)shows the bright-field images of SBA-15and Fe/SBA-15,respectively.Fig.(c,d)shows the bright-and dark-field images of Fe/SBA-15,respectively.The highly ordered hexagonal array of SBA-15with the pore diameter of approximately7nm and uniform channel wall thickness of ap-proximately4nm is obrved from Fig.4(a).Fig.4(b,c,d)dis-plays the reprentative internal morphology of Fe/SBA-15,the distribution of the supported iron oxides,and a better dispersion of Fe2O3crystallites over the SBA-15framework.There exist many small black dots(Fig.4(b))and bright white dots(Fig.4(c, d))in the images,both dots reprenting the Fe2O3crystallites located in the SBA-15channels.From TEM image inrted in Fig.4(b),the measured lattice spacings of0.25nm correspond to (110)interplanar distance ofα-Fe2O3.The growth of the crystal-lites embedded into the SBA-15channels was limited by the channel walls,thus leading to the rod-like shape of the crystallites. From Fig.4(c),it can be en that the crystallites have the diameter of approximately6nm,consistent with the pore diameter of SBA-15,and the average length more than25nm,attributable to the uncontrolled growth of Fe2O3c
rystallites along the channels.The shaded parts circled in Fig.4(b,c,d)reprent a fraction of the aggregates of Fe2O3crystallites loaded outside the channels of SBA-15.
3.1.5XPS
In the XPS spectra of Fe/SBA-15composites shown in Fig.5
(a),strong peaks of Fe2p,Si2p,and O1s are obrved.In Fig.5
(b),peaks at711.58and724.58eV are assigned to Fe2p3/2and
Fe Fig.5XPS analys of Fe/SBA-15
Fig.4TEM images of SBA-15(a)and Fe/SBA-15(b,c,d)
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