CdS光化學(xué)修飾介孔TiO2及其增強(qiáng)的可見光催化活性

袁淑筠，孫豐強(qiáng)，龍培英，劉波雄

(華南師范大學(xué)化學(xué)與環(huán)境學(xué)院，廣東廣州　510006)

CdS光化學(xué)修飾介孔TiO2及其增強(qiáng)的可見光催化活性

袁淑筠，孫豐強(qiáng)，龍培英，劉波雄

(華南師范大學(xué)化學(xué)與環(huán)境學(xué)院，廣東廣州510006)

摘要:【目的】提高介孔TiO2材料的光催化活性?！痉椒ā坎捎谜舭l(fā)誘導(dǎo)自組裝法(EISA)，以四氯化鈦和鈦酸丁酯為鈦源，嵌段共聚物P123(EO20PO70EO20)為模板劑，制備介孔TiO2。用光化學(xué)修飾法將CdS摻進(jìn)介孔TiO2中，合成對(duì)可見光有較好響應(yīng)的復(fù)合材料，并利用X射線衍射(XRD)、透射電鏡(TEM)、原子吸收分光光度法(AAS)和光催化等手段對(duì)樣品進(jìn)行表征?！窘Y(jié)果】XRD和TEM結(jié)果表明成功合成有序的六方介孔材料；AAS確定復(fù)合材料中Cd的含量為0.96 mg/g；光催化于500 W氙燈下以2×10-5mol/L次甲基藍(lán)(MB)為模型污染物，結(jié)果顯示CdS/TiO2復(fù)合材料的可見光催化活性明顯提高。【結(jié)論】光化學(xué)修飾法制備的介孔CdS/TiO2復(fù)合材料可增強(qiáng)其可見光催化活性。

關(guān)鍵詞:介孔CdS/TiO2光化學(xué)光催化可見光EISA

0Introduction

【Research significance】Mesoporous TiO2has better adsorption property and higher catalytic activity than non-mesoporous materials due to its high specific surface area.It is widely used for effective decomposition of organic pollutants in water or air under UV light irradiation.However,limited by titania’s low quantum efficiency and high band gap (3.0～3.2 eV,located at the ultraviolet (UV) wavelength range),very few visible light is available.To depress the recombination of photogenerated electron-hole pairs in photocatalytic processes,ingredient or structure modification have thus become an appealing challenge for developing photocatalytic technologies.【Previous research progress】Accordingly，semiconductor[1-5]，transition metal[6-9],noble metal[10-12]or ion[13-17]doped mesoporous TiO2and photosensitized[18]mesoporous TiO2have been developed.The couple of TiO2with narrow band gap materials such as CdS,CdSe,PbS,etc.,was found to be effective for enhancing its visible light activity due to the fact that the photogenerated electrons from CdS could be injected into the conduction bands of TiO2,resulting in the photocatalytic reaction[19-23].Meanwhile,CdS/TiO2composites have been extensively investigated for their applications in solar energy cells,catalysis,water purification and electrochromic devices[24].CdS/TiO2composite nano-materials were studied frequently in the sol-gel[25-27],photoelectrochemical[24，28-30],coprecipitation[31-35]system.A self-assembly method was also used to prepared macroporous CdS/TiO2films materials[36]or solar cells[35].【Research breakthrough point】To date,the studies of CdS doped mesoporous TiO2compounds synthesized by photochemical modification technology have not yet been established.Nevertheless，compared to the photochemical method[37-40],hereinbefore synthesis methods often require a long time and multiple-step procedures with the problem of high costs.For instance,as the most widely used method of mesoporous TiO2modification,the sol-gel method has to take alkoxide type,water,temperature,gel formation time and catalyst into account[8-9，16，41-42].And the coprecipitation method has to bath with a great deal of organic solvent to control its hydrolysis rate[31-35].【Key issues to be resolved】By changing the light intensity and illumination time at room temperature to control the intensity of reaction，photochemical modification of nano-materials is more feasible.In this present work,using P123 as a template agent,mesoporous TiO2was prepared using the EISA method.Applying a vacuum-aided photochemical reduction technique,CdS was incorporated into its framework.The mesoporous CdS/TiO2composite was obtained with UV-light irradiation.And its physical and photochemical performances were studied.The preparation of mesoporous CdS/TiO2is schematically shown in Fig.1.

Fig.1A schematic procedure for preparation of mesoporous CdS/TiO2

1Materials and methods

1.1Synthesis of mesoporous TiO2

A typical synthesis went as follows:First,1 g block copolymer P123(EO20PO70EO20,Aldrich) was dissolved into 20 mL ethanol,and then 1 mL TiCl4and 3 mL Ti(OC4H9)4were dissolved into this solution,respectively.Here,Ti precursor particles were fully adsorbed on the surface of P123 micelle[43].Second,the resulting mixed solution was aged in an dish(with a lip made of paper )with a low humidity at 40℃ for 12 h,to evaporate the solvent and form a mesostructured copolymer/Ti hybrid transparent gel.Third,the gel was baked at 100℃ for 30 min.In this process,the micelle which adhesion metal ions inside the sol-film self-assembly arranged in the network structure[44].Last,sol-film was calcined in air with a ramp of 5℃/min to 350℃ and remained there for 70 min in non-air atmosphere,to remove the template and obtain crystallined mesoporous TiO2(sample S1).

1.2Photochemical modification of Mesoporous TiO2

An aqueous solution of 80 mL containing 0.15 mol/L CdSO4and 0.0168 mol Na2S2O3was prepared using deionized water,then vacuumed 5 min in order to eliminate the air from mesoporous and made the solution into the pores.Then,the sample was positioned so that radiation intensity received was 0.84 mW/cm2at λ=254 nm,and the diameter of the illumination region was approximately 15 mm.After 24 h,the excess CdSO4and Na2S2O3were washed away with 2% HNO3,and various methods were used to determine the properties of mesoporous CdS/TiO2(sample S2).

1.3Photocatalysis

A 500 W Xenon lamp was positioned inside a cylindrical quartzose vessel and surrounded by a circulating water jacket to cool the lamp.0.05 g of photocatalyst was suspended in a 200 mL aqueous solution of 2×10-5mol/L methylene blue(MB).Prior to irradiation,the suspensions were magnetically stirred for 30 min to ensure establishment of an adsorption/desorption equilibrium among the photocatalyst,MB and atmospheric oxygen.At room temperature and under normal pressure,5 mL of the suspensions were collected every 20 min,and then centrifuged to separate the photocatalyst particles.The degradations of MB were analyzed by a UV-vis spectrophotometer(752，Shanghai Jinghua Technology Instrument Co.,Itd)and the absorption peak at 665 nm was monitored.

1.4Characterization

Low-angle XRD measurement (0.6～3°,40 kV/20 mA,0.25°/min) was made on a Rigaku D/MAX-2200 X-ray diffractometer with Cu Kαradiation,while wide-angle XRD measurement (20～80°,30 kV/20 mA,3.6°/min) was made on a XRD-2000 X-ray diffractometer.Crystal size was measured from XRD peak broadening using the Scherrer equation.Direct TEM (JEM-2010HR,operated at 200 kV) photograph was also used to determine the structure of sample S1.

Sample S2 solution was prepared by melt in 10 mL concentrated H2SO4(150℃,1.5 h),then a TSA-986 flame atomic spectrophotometer(λ=228.9 nm) was used to determin its cadmium content.

2Results and discussion

2.1Characterized by XRD and TEM

Low-angle X-ray diffraction (LXRD,Fig.2b) shown that sample S1 obtained a peak at 1.18°,from Scherrer equation,its crystallite size is near by 9 nm,belonging to mesoporous materials; and the height and narrow diffraction peak sufficiently prove that the mesoporous TiO2sample’s pore structure with good short-range order.The size measured by XRD was found to correspond closely with that measured by direct TEM imaging(Fig.2a) for these powder.Observing reveats that the mesoporous TiO2is prepared with mesoporous ordered distribution,continuous pore,and hexagonal arrays.Wide-angle X-ray diffraction (WXRD) patterns of the prepared sample were shown in Fig.2c.The five Bragg diffraction peaks are found at 20～60°,corresponding to the anatase (101),(004),(200),(105) and (211) crystal planes,respectively.WXRD result of mesoporous sample S2 is similarity to sample S1,but there are some miscellaneous weaker peaks at the range of 20～30°,which may be CdS diffraction peaks because of the small amount CdS doping.However,CdS diffraction peaks and TiO2strong diffraction peaks are adjacent or overlapping.Therefore,it is difficult to tell them apart.

2.2Characterized by AAS

Measurement of cadmium content of sample S2,which has a dosage of 0.012 mol Cd， determines that the incorporation amount of Cd is 0.96 mg/g,that is，n(Ti)∶n(Cd)=1.4×10-4(R=0.99696).

2.3Formed mechanism

(a)TEM photography of sample S1；(b)low-angle XRD of sample S1；(c)Wide-angle XRD figure of the samples S1 and S2

Fig.2Characterizations of mesoporous TiO2(S1) and mesoporous CdS/TiO2(S2)

(1)

(2)

(3)

And then,CdS particles are formed in the pores.

Cd2++S+2e-=CdS.

(4)

2.4Enhanced visible-light photocatalytic activity

Fig.3Photocatalytic perforence of mesoporous TiO2before and after doping CdS to its framework

2.5Photocatalysis mechanism

As shown in Fig.4,mesoporous TiO2can be coupled by interparticle electron transfer from irradiated CdS nanocrystals to its conduction band.Upon UV excitation,an electron of anatase TiO2(3.2 eV band gap) may be promoted from the valence band to the conduction band (ECB) leaving behind a beneficial hole in the valence band (EVB)[30].When coupling CdS with TiO2,photogenerated electrons (ECB)flowed toward CdS and accumulated at CdS and formed Schottky barrier between CdS and TiO2(References[45-46]).

Fig.4Schematic diagram illustrating charge injection from excited CdS into TiO2

CdS/TiO2+hυ→CdS(h+)/TiO2(e-).

(5)

The electrons are then scavenged by molecular oxygen O2to yield the superoxide radical anion O2·-in oxygen-equilibrated media.

e-+ O2→O2·-.

(6)

These new formed intermediates can interreact to produce hydroxyl radical OH·.

(7)

H2O+h+→OH·+H+.

(8)

The OH· radical is a powerful oxidizing agent capable of degrading most pollutants.

OH·+MB→degradation products.

(9)

3Conclusion

The mesoporous CdS/TiO2composite material with enhanced visible-light photocatalytic activity can be prepared by photochemical modification technique.Due to its good chemical stability and non-toxic,we can foresee that it will not trigger unnecessary responses,in other words,it may be generate to low foreign objects.The reaction region and its strength can be controlled by light.It is obviously,with moderate price,the material is readily available with the best operability,strong coverage,and high refractive index[40].Therefore,the materials have good prospects in water or soil pollution,dust-proof paints and coatings,and life sciences field.

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(責(zé)任編輯：陸雁)

Photochemical Modification with CdS and Enhanced Visible-light Photocatalytic Activity of Mesoporous TiO2*

YUAN Shujun，SUN Fengqiang**，LONG Peiying，LIU Boxiong

(School of Chemistry and Environment，South China Normal University，Guangzhou，Guangdong，510006，China)

Abstract:【Objective】To improve the photocatalytic activity of mesoporous TiO2.【Methods】Mesoporous TiO2 was prepared by the method of evaporation-induced self-assembly (EISA)，while TiCl4 and Ti(OC4H9)4 as titanium sources,and block copolymer P123(EO20PO70EO20)as the template.Using the photochemical modification technology,composite material was prepared with good response of visible light by doping CdS to its framework.The obtained samples were characterized by X-ray diffraction (XRD),transmission electronic micrograph (TEM),atomic absorption spectrophotometer(AAS)and photocatalytic.【Results】The results of XRD and TEM proved the synthesis of ordered hexagonal mesoporous materials.AAS determined the composite material content of 0.96 mg/g Cd.In 500 W xenon lamp，2×10-5mol/L methylene blue(MB) as model pollutant,the photocatalytic results showed that the photocatalytic activity of the mesoporous CdS/TiO2 composite was further improved.【Conclusion】The mesoporous CdS/TiO2 composite material with enhanced visible-light photocatalytic activity can be prepared by photochemical modification technique.

Key words:mesoporous CdS/TiO2，photochemical，photocatalytic，visible light，EISA

收稿日期：2016-01-08

作者簡(jiǎn)介：袁淑筠(1988-)，女，化學(xué)分析工程師，主要從事高純特種氣體研究。

中圖分類號(hào)：O643.3

文獻(xiàn)標(biāo)識(shí)碼：A

文章編號(hào)：1005-9164(2016)02-0167-07

修回日期：2016-02-03

*國(guó)家自然科學(xué)基金項(xiàng)目(批準(zhǔn)號(hào)：21571068)資助。

**通訊作者：孫豐強(qiáng)(1974-)，男，教授，主要從事多孔材料、光催化等方面的研究，E-mail：fqsun@scnu.edu.cn。

廣西科學(xué)Guangxi Sciences 2016,23(2):167～173

網(wǎng)絡(luò)優(yōu)先數(shù)字出版時(shí)間：2015-05-12

網(wǎng)絡(luò)優(yōu)先數(shù)字出版地址：http://www.cnki.net/kcms/detail/45.1206.G3.20160512.0944.008.html