Journal of Hazardous Materials 168(2009)895–900
Contents lists available at ScienceDirect
Journal of Hazardous
compromi
Materials
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 /j h a z m a
t嗜好的意思
Degradation of remazol golden yellow dye wastewater in microwave enhanced ClO 2catalytic oxidation process
Xiaoyi Bi a ,b ,Peng Wang a ,∗,Chunyan Jiao a ,Hailei Cao a
铁路英语a State Key Laboratory of Urban Water Resource and Environment,Harbin Institute of Technology,Harbin 150090,China b
Institute of Environment and Lakes,Yunnan University,Kunming 650091,China
a r t i c l e i n f o Article history:
Received 2November 2007
Received in revid form 17February 2009Accepted 19February 2009Available online 3March 2009
Keywords:Microwave ClO 2
CuO n –La 2O 3/␥-Al 2O 3Remazol golden yellow
a b s t r a c t
Experiments were conducted to investigate the removal of remazol golden yellow dye in order to asss the effectiveness and feasibility of microwave enhanced chlorine dioxide (ClO 2)catalytic oxidation pro-cess.The catalyst ud in this process was CuO n –La 2O 3/␥-Al 2O 3.The operating parameters such as the ClO 2dosage,catalyst dosage,and pH were evaluated.The results showed that microwave enhanced cat-alytic oxidation process could effectively degrade remazol golden yellow dye with low oxidant dosage in a short reaction time and extensive pH range compared to the conventional wet catalytic oxidation.Under the optimal condition (ClO 2concentration 80mg/L,microwave power 400W,contacting time 1.5min,catalyst dosage 70g/L,and pH 7),color removal efficiency approached 94.03%,corresponding to 67.92%of total organic carbon removal efficiency.It was found that the fluorescence intensity in microwave enhanced ClO 2catalytic oxidation system was about 500a.u.which was verified that there was much hydroxyl radical produced.Compared with different process,microwave enhanced ClO 2catalytic oxi-dation system
could significantly enhance the degradation efficiency.It provides an effective technology for dye wastewater treatment.
©2009Elvier B.V.All rights rerved.
1.Introduction
The color and high COD of effluents from dyehou cau rious environmental contamination problems nowadays.In particular,azo dyes reprent about half of the dyes ud in the textile indus-try and,as a conquence,a relevant problem of pollution related to the relea of the products in the environment is taking place [1,2].Although there were veral other technologies available for the removal of color and COD from azo dye wastewater such as biodegradation [3],sorption [4–6],electrochemical and oxidative degradation [7–11],chlorine dioxide (ClO 2)catalytic oxidation was a very attractive and uful technique for treatment of dyehou effluents [12–14].
However,the traditional ClO 2catalytic oxidation process has not been largely implemented for wastewater treatment becau of the vere experimental conditions such as the limited range of pH,long reaction time resulting in high economical costs.Microwave enhanced catalytic process offers a potential solution to the problems.In recent years,some rearch progress in microwave c
hemistry has prented the feasibility to apply microwave in pol-lution control [15].The u of microwave irradiation in catalytic
∗Corresponding author.Tel.:+8645186283801;fax:+8645186283801.E-mail address:pwang73@hit.edu (P.Wang).reactions,including decomposition of volatile organic compounds (VOC)[16]and non-biodegradable organics in wastewater [17–19],has given some remarkable results.
In this paper,CuO n –La 2O 3/␥-Al 2O 3has been ud as the cata-lyst in the microwave enhanced ClO 2catalytic oxidation process to treat synthetic wastewater containing remazol golden yellow RNL and the reaction conditions in this system have been optimized.Comparative studies on the different ClO 2oxidation process have been carried out.Then,the experiment to detect •OH in the microwave enhanced chlorine dioxide catalytic oxidation process and microwave enhanced chlorine dioxide oxidation process has been conducted.2.Experimental 2.1.Materials
All the reagents ud in our work were analytical-grade.The stock ClO 2solution was prepared by mixing a vitriol solution and a sodium chlorite solution.The stock ClO 2solution was stored in dark at 277K and was standardized before using.The azo dye,remazol golden yellow RNL,was chon as the target compound,and its chemical structure is shown in Fig.1.
The catalyst was prepared by impregnation–deposition method,and the ␥-Al 2O 3(ϕ=2–3mm)was ud as the carrier.The
0304-3894/$–e front matter ©2009Elvier B.V.All rights rerved.doi:10.1016/j.jhazmat.2009.02.108
896X.Bi et al./Journal of Hazardous Materials 168(2009)
marker是什么意思
895–900
Fig.1.Chemical structure of remazol golden yellow RNL.
CuO n –La 2O 3/␥-Al 2O 3,was prepared in such a quence that La was first loaded on the ␥-Al 2O 3by dipping 10g of ␥-Al 2O 3in 100mL aqueous solution containing 0.03mol/L of La 3+for 12h under room condition,and the samples were dried at 353K for 12h and then dried at 383K for 2h.The dried samples were calcined at 823K in an oven for 4h,so that the intermediate La 2O 3/␥-Al 2O 3was obtained,and Cu was then loaded on La 2O 3/␥-Al 2O 3by impreg-nation of La 2O 3/␥-Al 2O 3with 100mL aqueous solution containing 0.3mol/L CuCl 2for 24h under room condition.After that,the Cu 2+was deposited with the help of precipitator [20]for 24h,and the samples were dried at 353K for 12h and then dried at 383K for 2h.The dried samples were calcined at 723K in an oven for 4h to get the CuO n –La 2O 3/␥-Al 2O 3catalyst.
The formation of CuO,Cu 2O and La 2O 3loaded on the surface of ␥-Al 2O 3is characterized by X-ra
y diffraction (XRD)and X-ray photoelectron spectroscopy (XPS).The component amounts of Cu and La in CuO n –La 2O 3/␥-Al 2O 3catalyst determined by using XRF are 8.12%and 1.14%respectively.2.2.Experimental method
At the beginning of each test run,100mL of synthetic wastew-ater containing 200mg/L remazol golden yellow dye was placed in a aled reactor.Certain amount of the catalysts and stock ClO 2solution were added.The reactor was shaken sufficiently to mix the stock ClO 2solution and the wastewater,and subquently loaded in a reconstructive commercial microwave oven which was operating at 2450MHz with the continuous power (50–750W).The time was recorded by the stopwatch.After been irradiated in the microwave oven for sometime,the aled reactor was taken out and the reagent of sodium thiosulfate (Na 2SO 3)was added to dechlorinate ClO 2residuals.
The temperature of the wastewater was measured using a thermocouple inrted into the wastewater.The pH value was determined by a pH-3C pH meter.The concentrations of ClO 2,ClO 2−,
ClO 3−and Cl −in the ‘stabilized chlorine dioxide’solution were measured by the method of continuous iodimetry and pre-cipitation titration,respectively.The absorbance and total organic carbon (TOC)of the suspensions were analyzed to investigate the efficiency of the system.The visible light absorbance at 430nm was measured using a 721-type UV–vis spectrophotometer.TOC mea-surement was carried out with a TOC-VCPN Shimadzu TOC analyzer.
For evaluating the catalytic activity of catalysts,both color removal and TOC removal were calculated as shown below:X (%)=
C 0V wastewater −C t (V wastewater +V ClO 2+V Na 2S 2O 3)
C 0V wastewater
×100%
(1)
实习医生格蕾 第六季where C 0and C t are the initial and final absorbances of rema-zol golden yellow dye,or the initial and final TOC,respectively;V wastewater ,V ClO 2and V Na 2S 2O 3are the volumes of wastewater,ClO 2,and Na 2S 2O 3solutions,respectively.
It was known that hydroxyl radicals (•OH)reacted with tereph-thalic acid and generated 2-hydroxyterephthalic acid which could emit fluorescence,as shown in Fig.2.So the terephthalic acid was employed as the hydroxyl radical capturer to detect the formation of •OH in the microwave enhanced catalytic oxidation system.The process was conducted under the following conditions:20g/L
of
Fig.2.Reaction between hydroxyl radical and terephthalic acid.
the catalysts and 40mg/L of ClO 2solution were added into 100mL of 0.3mmol/L terephthalic acid aqueous solution in the reactor,then irradiated the reactor in the microwave oven with the con-tinuous power of 50W.The time was recorded by a stopwatch.The water samples were taken from the reactor to determine the fluorescence spectrum.The fluorescence spectrum of generated 2-hydroxyterephthalic acid was measured on a Jasco FP-6500flu-orescence spectrophotometer.The slit widths were t at 5.0nm.Sequential scans of the emission spectra were carried out between 400nm and 600nm at different excitation wavelengths ranging from 240nm to 400nm.The spectra were recorded at every 5nm intervals.
3.Results and discussion
3.1.Effect of the ClO 2concentration on color removal
The cost of ClO 2was the primary factor contributing to the chemical costs of microwave enhanced ClO 2catalytic oxidation treatment,so it was important to minimize the required amount of ClO 2.Therefore,investigation of the initial ClO 2concentration on the degradation of remazol golden yellow dye was conducted with varying ClO 2concentration from 0mg/L to 110mg/L.The other experimental conditions were conducted as below:microwave power,50W;contact time,15min;catalyst dosage,50g/L.The results were prented in Fig.3
.
Fig. 3.Effect of ClO 2concentration on removal efficiency ([Dye]=200mg/L;microwave power =50W;time =15min;catalyst dosage =50g/L).
X.Bi et al./Journal of Hazardous Materials168(2009)895–900
897四六级英语成绩
Fig. 4.Effect of microwave power and irradiation time on removal efficiency ([Dye]=200mg/L;[ClO2]=80mg/L;catalyst dosage=50g/L;pH5.6).
As shown in Fig.3,the dosage of ClO2had an important influ-ence on the degradation of remazol golden yellow dye.However,the color removal incread non-linearly with the increasing chlorine dioxide dosage.In the prence of ClO2,firstly,the color removal incread with the ClO2concentration rapidly.This proved that the effect of increasing ClO2concentration wasfirst positive to the degradation of remazol golden yellow dye.However,with the con-tinuous increa in the initial ClO2concentration,the color removal incread slightly.In addition,the color removal in the catalytic oxi-dation system was much higher than that in the oxidation system.In the microwave enhanced catalytic oxidation process,when the con-centration of the ClO2solution was80mg/L,the color removal was 89.5%while the color removal was only44.47%without catalyst. This indicated that the catalysts of CuO n–La2O3/␥-Al2O3had obvi-ous catalytic ability in microwave enhanced ClO2catalytic oxidation process.
3.2.Effect of microwave power and irradiation time on color removal
The degradation of remazol golden yellow RNL at different reac-tion times under different microwave
powers was shown in Fig.4. The other experimental parameters were conducted as below:ClO2 concentration,80mg/L;catalyst dosage,50g/L;pH,5.6.
In our study,it could be obrved from Fig.4that microwave irra-diation could obviously shorten the reaction time.Reaction time could be shortened from90min in the catalytic wet oxidation to 1.5min and the azo dye could be effectively eliminated,and would greatly reduce the economical costs of the catalytic oxidation pro-cess.
As expected,the color removal of the remazol golden yellow RNL regularly enhanced with the microwave power increasing.Under the same power,the color removal incread obviously with the running time at the initial stage,and then the increa slowed down by prolonging the run time.This could be attributed to the relative high concentrations of remazol golden yellow RNL and oxidants resulted in rapid reaction rate in the reactor at the beginning.Bad on the result,the reaction time for the microwave enhanced ClO2 catalytic oxidation of remazol golden yellow RNL was determined to be1.5min under400W microwave irradiation.
3.3.Effect of the dosage of catalyst on color removal
The catalyst played an important role in the microwave enhanced ClO2catalytic oxidation process.Th
e effect of catalyst dosage on dye removal was investigated by the addition of
英语基础知识
differ-Fig. 5.Effect of the catalyst dosage on removal efficiency([Dye]=200mg/L; [ClO2]=80mg/L;microwave power=400W;time=1.5min).
ent amounts of catalyst into100mL of synthetic wastewater,and the results were shown in Fig.5.The other experimental conditions were conducted as below:ClO2concentration,80mg/L;microwave power,400W;contact time,1.5min.
As the catalyst dosage incread,an increa in the color removal was obrved.When the addition of catalyst reached70g/L,the removal efficiency could come up to over90%.Nevertheless,the final removal did not change,showing that the excess amount of the catalyst could not improve the efficiency in the microwave enhanced ClO2catalyst oxidation.
3.4.Effect of pH on color removal
The initial pH is an important parameter influencing the perfor-mance of ClO2catalytic oxidation process[12].To examine its effect, the initial pH of the samples was adjusted to2–11with the addi-tion of HCl or NaOH.The color removal of dye solutions in various initial pH under the same reaction conditions was shown in Fig.6. The other experimental parameters were conducted as below:ClO2 concentration,80mg/L;microwave power,400W;contact time, 1.5min;catalyst dosage,70g/L.
南非世界杯主题曲中文版
The results prented in Fig.6showed that the color removal in the microwave enhanced ClO2oxidation was lower than50%
and
Fig. 6.Effect of the initial pH value on removal efficiency([Dye]=200mg/L; [ClO2]=80mg/L;microwave power=400W;time=1.5min;catalyst dosage= 70g/L).
898X.Bi et al./Journal of Hazardous Materials168(2009)
在线日语学习
895–900
Fig.7.Effect of wastewater temperature on removal efficiency([Dye]=200mg/L; [ClO2]=80mg/L;catalyst dosage=70g/L).
changed slightly with the initial pH.But in microwave enhanced ClO2catalytic oxidation process,the color removal varied obviously from initial pH2to pH3.It could be concluded that the optimum initial pH value in catalytic system ranges from3to11.The color removal of catalytic system in this pH range was much higher than that in the oxidation system,which indicated that the catalyst asso-ciated with microwave could improve the color removal of system and adapt to extensive pH range,suggesting this process had advan-tages for the engineering application.
3.5.Effect of the wastewater temperature on color removal
The effect of wastewater temperature on dye removal was inves-tigated under different microwave powers.The other experimental parameters were conducted as below:ClO2concentration,80mg/L; catalyst dosage,70g/L.
孽子孤臣Fig.7demonstrates the effect of the wastewater temperature on the color removal.As expected,the te
mperature of wastewater was one of the effect factors.The color removal changed with the varia-tion of temperatures and microwave powers.At the beginning,the removal efficiency incread obviously by increasing the tempera-tures.However,thefinal removal even decread by increasing the system temperatures.As a result,changes in the color removal were not linearly related with temperatures in the microwave enhanced ClO2catalytic oxidation process.Under the same temperature,the different microwave powers got the different color removal effi-ciencies,which showed that the microwave in the process acted as an induced factor.
3.6.Effect of initial dye concentration on color removal
The effect of initial concentration of synthetic dye wastewater on its degradation was illustrated in Fig.8with varying remazol golden yellow RNL concentration from100mg/L to400mg/L.The other experimental conditions were conducted as below:ClO2concen-tration,80mg/L;microwave power,400W;contact time,1.5min; catalyst dosage,70g/L.
The results showed that the color removal of remazol golden yellow RNL decread with increasing the initial remazol golden yellow RNL concentration.This could be attributed to the relative reduction of ClO2/dye molar ratio as remazol golden yellow RNL concentration incread.Thus,the effect of re
mazol golden yellow RNL initial concentration on its degradation was similar to that of ClO2dosage,which was stated
above.Fig.8.Effect of initial concentration of synthetic dye wastewater on removal efficiency([ClO2]=80mg/L;microwave power=400W;time=1.5min;catalyst dosage=70g/L).
3.7.Comparative study on the different treatment process
In order to check the microwave enhanced effect,the color removal in different treatment process was compared.The tem-perature of thermostatic system was350K.The other operation conditions of thermostatic system were the same as the microwave enhanced system,such as ClO2concentration80mg/L;contact time 1.5min;catalyst dosage70g/L.Experimental results were shown in Fig.9.
The reaction between the ClO2and remazol golden yellow RNL was an endothermic reaction,but as shown in Fig.9,the color removal in the microwave ClO2oxidation was higher than tradi-tional ClO2oxidation even at the same temperature.It was indicated that the microwave could improve the efficiency of traditional process not only becau of its calefaction but also becau of its induced function.The catalyst can also enhance the efficiency becau of its function of sorption and catalysis.However,when the microwave and catalyst were ud together,the removal incread obviously and the increa in the removal was more than that of summation of the respective increa
,which confirmed the hypoth-esis mentioned above that there would be microwave induced functions.
To investigate the oxidation degree of remazol golden yellow RNL,the TOC of treated wastewater was tested.The result showed that the color removal was94.03%while the TOC removal was only 67.92%.It suggested that the remazol golden yellow RNL in
this
Fig.9.Color removal efficiency in different treatment process([Dye]=200mg/L; [ClO2]=80mg/L;catalyst dosage=70g/L;time=1.5min;T w=350K).
X.Bi et al./Journal of Hazardous Materials 168(2009)895–900899
process was not entirely oxidized into carbon dioxide.So,much effort should be given to the detection of the new products which remazol golden yellow RNL is oxidized into and improve the TOC removal in further study.
3.8.Evaluation of •OH in microwave enhanced ClO 2catalytic oxidation system
The mechanism of the ClO 2catalytic oxidation was not very clear.It was generally reported that the oxygenous group over the catalyst can initiate the ClO 2to be changed into radicals,such as •OH.Microwave irradiation could be cooperative with catalyst to initiate the more formation of free radicals in the prence of ClO 2.To verify the above mentioned theory,the fluorescence technol-ogy was applied to detect the hydroxyl radicals (•OH)produced in microwave enhanced ClO 2catalytic oxidation system with the cat-alyst dosage of 20g/L.(If the optimal catalyst dosage of 70g/L was lected,the fluorescence intensity exceeded the detection range.)First,quential scans were conducted to verify the product in the microwave enhanced ClO 2catalytic oxidation system.The result was shown in Fig.10.
Fig.10shows that the fluorescence peak of product of reaction between ClO 2and terephthalic acid in
microwave enhanced ClO 2catalytic oxidation system was located in the vicinity of excita-tion/emission wavelength pair 315nm/425nm (±2nm).It was the same with the fluorescence characteristic of 2-hydroxyterephthalic acid reported in the article [21].Therefore,perhaps,the fluores-cent product formed during microwave enhanced ClO 2catalytic oxidation was due to the reaction between •OH with terephthalic acid.It was indicated that the •OH was produced in the microwave enhanced ClO 2catalytic oxidation system.
Influence of irradiation time on fluorescence spectrum in microwave enhanced ClO 2catalytic oxidation process was shown in Fig.11.It could be obrved that the fluorescence intensity of microwave enhanced ClO 2catalytic oxidation system was increas-ing with the time and the increa was fast at the beginning.It probably could be attributed to the fact that the relative high con-centrations of terephthalic acid and ClO 2would result in rapid reaction rate in the reactor at the initial stage.As the oxidation reac-tions proceeded,on the other hand,it gave ri to the appearance of 2-hydroxyterephthalic acid which would inhibit the reaction.
The fluorescence intensity of different systems was shown in Fig.12.It was found obviously that the fluorescence intensity
of
Fig.10.Contour plot of three-dimensional fluorescence spectra of degradation prod-uct ([ClO 2]=40mg/L;[terephthalic acid]=0.3mmol/L;microwave power =50W;time =15min;catalyst dosage =20
g/L).
Fig.11.Influence of irradiation time on fluorescence spectrum in microwave enhanced ClO 2catalytic oxidation process ([ClO 2]=40mg/L;[terephthalic acid]=0.3mmol/L;microwave power =50W;catalyst dosage =20
g/L).
Fig.12.Fluorescence spectrum of degradation product in different pro-cess ([ClO 2]=40mg/L;[terephthalic acid]=0.3mmol/L;microwave power =50W;time =10min;catalyst dosage =20g/L).
catalytic oxidation system was about two times that of the oxida-tion system.It was indicated that the quantity of •OH generated in the microwave enhanced system incread by the addition of catalyst.Perhaps,in the above microwave enhanced ClO 2catalytic oxidation process,•OH could be generated by a free radical chain auto-oxidation process.4.Conclusions
The microwave enhanced chlorine dioxide catalytic oxidation process was a novel technique for the t
reatment of wastewater.When the remazol golden yellow RNL initial concentration was 200mg/L,the color removal efficiency could reach 94.03%,corre-sponding to 67.92%of TOC.The optimum experimental conditions were as follows:volume of synthetic wastewater was 100mL,ClO 2concentration was 80mg/L,contact time was 1.5min,microwave power was 400W and the solution pH was 7.The fluorescence technology verified that there was •OH produced in microwave enhanced ClO 2catalytic oxidation system and the formation quan-tity of •OH incread with irradiation time.The formation rate of •OH in catalytic oxidation process was about two times of that in oxidation process.
