1、内嵌硫化镉与上转换纳米颗粒的二氧化钛复合纳米管用于近红外光驱动光催化（英文） 王婉妮 章富 张传玲 汪洋 陶伟 程盛 钱海生 合肥工业大学生物与医学工程学院 合肥工业大学化学与化工学院 合肥工业大学分析测试中心 摘 要： 由于近红外光在太阳光谱中占 44%, 因此, 近红外光驱动的光催化剂的研制具有十分重要的意义.上转换发光材料可将低能量的近红外光子转换为高能光子, 这种高能光子可以通过构建荧光共振转移系统将能量转移并活化量子效率较高的半导体材料, 对于太阳能的转化利用具有潜在的应用前景.在本文中, 通过胶体化学的过程在电纺丝制备的内嵌 CdS 纳米颗粒以及上转换荧光纳米颗粒 (UCNPs)
2、的二氧化硅复合纳米纤维表面外延生长一层二氧化钛层, 通过高温煅烧得到二氧化钛复合纳米管.我们通过二氧化硅结构将 CdS 纳米颗粒与上转换荧光纳米颗粒紧紧束缚在一起, 实现较高的荧光共振能量转移.而且, 选择 -NaYF4:Yb (30%) , Tm (0.5%) NaYF4:Yb (20%) , Er (2%) 作为纳米能量转换器, 替代以前研究工作中使用的 -NaYF 4:Yb (30%) , Tm (0.5%) 或者 -NaYF4:Yb (30%) , Tm (0.5%) NaYF4纳米颗粒, 来进一步提高近红外光的转换效率.通过透射电子显微镜照片很清楚的观察到制备的 Ti O2 复合纳米
3、管内部内嵌有大量的 CdS 与上转换纳米颗粒.通过 X-射线衍射以及 X-射线光电子能谱能仪器对产物的物相以及表面的化学组成进行了细致的表征.结果显示, 通过本实验方法已经成功获得了 Ti O2 复合纳米管.用稳态与瞬态荧光仪研究了最终样品的荧光性质.研究结果揭示, 与上转换纳米颗粒以及二氧化硅复合纳米纤维相比, 复合二氧化钛纳米管可以将上转换荧光纳米颗粒的 (UV-Vis) 部分荧光完全淬灭了.特别是, 铒离子的荧光 (650 nm) 也被有效淬灭转移, 说明本研究采用-NaYF 4:Yb (30%) , Tm (0.5%) NaYF4:Yb (20%) , Er (2%) 纳米能量转换器,
4、 可以提高近红外光的转换效率, 紫外-可见吸收光谱证实, 这种二氧化钛纳米管在紫外-可见光区中的吸收光谱与 -NaYF 4:Yb (30%) , Tm (0.5%) NaYF4:Yb (20%) , Er (2%) 纳米颗粒的荧光光谱具有较大的重叠, 使得上转换荧光纳米颗粒与 CdS 以及二氧化钛组分之间的荧光共振转移的效率大大提高, 进而会显著提高光催化的效果.以罗丹明染料作为污染物为模型, 我们研究了罗丹明染料在氙灯下或者近红外光光照下的光催化分解实验.研究结果表明, 90%的罗丹明染料分子在 20 min 内就被降解掉, 效率高于其它的近红外光催化剂.上转换荧光纳米颗粒的能量转换效率可以
5、得到大幅度提高, 本研究工作中制备的光催化剂利用太阳能的效率将会得到极大提高, 在未来为能源危机以及环境保护提供一种可供选择的方法与技术.关键词： 二氧化钛纳米管; 上转换纳米颗粒; 能量转移; 光催化; 纳米转换器; 作者简介：陶伟 电话/传真: (0551) 62901285;电子信箱:作者简介：程盛 电话/传真: (0551) 62901285;电子信箱:作者简介：钱海生 电话/传真: (0551) 62901285;电子信箱:收稿日期：5 July 2017基金：supported in part by the National Natural Science Foundation o
6、f China (21471043, 21304028, 51403195, 31501576) TiO2 composite nanotubes embedded with CdS and upconversion nanoparticles for near infrared light driven photocatalysisWanni Wang Fu Zhang Chuanling Zhang Yang Wang Wei Tao Sheng Cheng Haisheng Qian School of Biological and Medical Engineering, Hefei
7、University of Technology; School of Chemistry and Chemical Engineering, Hefei University of Technology; Instrumental Analysis Center, Hefei University of Technology; Abstract： We report a colloidal process to coat a layer of TiO2 onto SiO2 composite nanofibers containing embedded Cd S and upconversi
8、on nanoparticles (UCNPs) . The SiO2 composite nanofibers were fabricated by electrospinning. To improve the energy transfer efficiency, UCNPs and Cd S nanoparticles were bound in close proximity to each other within the SiO2 matrix. -NaYF 4:Yb (30%) , Tm (0.5%) NaYF4:Yb (20%) , Er (2%) coreshell nan
9、oparticles were used as nanotransducers for near infrared light. These nanoparticles exhibited enhanced upconversion fluorescence compared with -NaYF 4:Yb (30%) , Tm (0.5%) or NaYF 4:Yb (30%) , Tm (0.5%) NaYF4 nanoparticles. The morphologies, size and chemical compositions have been extensively inve
10、stigated using field emission scanning electron microscopy (FESEM) , transmission electron microscopy (TEM) , X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) , respectively. The TEM images showed that the TiO2 composite nanotubes were embedded with a large amount of UCNPs and Cd S nano
11、particles. The composite TiO2 nanotubes degraded more than 90% of rhodamine B (Rh B) dye during 20 min of irradiation by simulated solar light. In particular, more than 50% of Rh B was decomposed in 70 min, under irradiation of near infrared light (NIR) . This high degradation was attributed to the
12、full spectrum absorption of solar light, and the enhanced transfer efficiency for near infrared light. The as-prepared nanostructures can harness solar energy, and provide an alternative to overcome energy shortages and environmental protection.Keyword： TiO2 nanotubes; Upconversion nanoparticles; En
13、ergy transfer; Photocatalysis; Nanotransducer; Received： 5 July 20171. IntroductionComposite nanostructures with enhanced physical and chemical properties have gained scientific and technological interest due to their applications in photocatalysis14, optoelectronic devices5, 6, solar cells710, and
14、drug delivery1113.In the past two decades, much effort has been made to develop techniques for fabricating nanocomposites with well controlled sizes and morphologies.These have included calcination14, co-precipitation1517, epitaxial growth1820, self-assembly2128, electrospinning2931, sol-gel32and hy
15、drothermal33, 34methods.In particular, electrospinning has been recognized as an efficient, low cost and versatile method for synthesizing composite nanofibers including Au/PVP35, Ti O2/polyvinyl pyrrolidone (PVP) 36, graphene oxide/PVA37, Ag/multi-wall nanotubes/polyacrylonitrile (PAN) 38, upconver
16、sion nanoparticles (UCNPs) Si O232, and Sn O2Ti O239.Lanthanide ion-doped upconversion phosphors have been widely used as efficient nanotransducers.They can transform near infrared (NIR) photons to high energy photons with ultraviolet-visible (UV-Vis) wavelengths.This has led to their application in
17、 solid state lasers, solar cells, flat-panel displays, bioimaging, chemotherapy, and photodynamic therapy4048.Nanocomposites incorporated with UCNPs including UCNPs/Cd Se49, 50, UCNPs/Cd Te51, 52, UCNPs/Cd S53, UCNPs/Ti O25461, and UCNPs/reduced graphene oxide62have been prepared and used for optimi
18、zing solar absorption.We recently demonstrated a facile process to fabricate UCNPs/Cd S/Ti O2 nanofibers, which enabled full solar spectrum absorption for enhanced photocatalysis63.However, the distance between the UCNP and Cd S chromophores was difficult to control, which reduced the energy transfe
19、r efficiency.Cd S can be excited by photons from the excited state levels including 1I63F4, 1D23F4, 1D23H6, and1G43H6 of Tm3+for Na YF4:Yb/Tm nanoparticles53, 63.The excited state levels (H11/2I15/2, S3/2I15/2) of Ercan also excite Cd S, according to the proposed energy transfer process in Fig.1.The
20、 fluorescence energy transfer efficiency will also be enhanced if Na YF4:Yb/Tm or Na YF4:Yb/TmNa YF4 nanoparticles are replaced by Na YF4:Yb/TmNa YF4:Yb/Er nanoparticles.The distance between the UCNP and Cd S or Ti O2 chromophores can significantly affect the fluorescence energy transfer efficiency6
21、4.In the current study, we used an electrospinning process to combine Na YF4:Yb/TmNa YF4:Yb/Er and Cd S nanoparticles in close proximity in a Si O2 matrix.We first prepared UCNPs/ethyl silicate (TEOS) /Cd S/PVP nanofibers and UCNPs/Si O2/Cd S/PVP nanofibers by electrospinning, accord-ing to our modi
22、fied protocol63, 65.A sol-gel process was then used to coat a layer of Ti O2 on the UCNPs/Si O2/Cd S/PVP nanofibers, and subsequent calcination at 500C for 2 h yielded Ti O2composite nanotubes embedded with UCNPs and Cd S nanoparticles.Na YF4:Yb/TmNa YF4:Yb/Er core-shell nanocrystals (i.e.UCNPs) wit
23、h enhanced fluorescence emission were prepared as chromophores and nanotransducers.Their fluorescence properties and photocatalytic performance are discussed.Fig.1.Proposed energy transfer processes between Na YF4:Yb/TmNa YF4:Yb/Er (UCNPs) , Cd S, and Ti O2. 下载原图2. ExperimentalAll chemicals were of
24、analytical grade and used as received without further purification.Cd S nanoparticles with an average diameter of 100 nm were synthesized via a hydrothermal method66.-Na YF 4:Yb (30%) , Tm (0.5%) Na YF4:Yb (20%) , Er (2%) core-shell nanoparticles with an average diameter of40 nm were prepared using
25、a sequential growth process67.2.1. Fabrication of UCNPs/TEOS/Cd S/PVP nanofibersThe UCNPs/TEOS/Cd S/PVP composite nanofibers were fabricated via a modified electrospinning process63.In a typical procedure, 0.284 g of PVP was dissolved in 4 m L of absolute ethanol to form a clear solution with vigoro
26、us stirring.0.22 g of as-prepared hydrophilic UCNPs and 0.58 g of Cd S nanoparticles were added to the previous solution, which was then ultrasonicated for 10 min.1.5 m L of TEOS was added and the resulting mixture was stirred vigorously.The mixture was then poured into a 10 m L plastic syringe for
27、electrospinning under a flow rate of 1.1 m L h1 and a voltage of 7 k V.The nanofibers acquired from the collector were UCNPs/TEOS/Cd S/PVP nanofibers.2.2. Synthesis of UCNPs/Si O2/Cd S/Ti O2 composite nanotubesBefore coating the Ti O2 layer on the surface of the UCNPs/Cd S/PVP/TEOS nanofibers, the a
28、cquired microfibers were calcined in air at 400C for 1 h at a heating rate of 1C min1, to prepare UCNPs/Si O2/Cd S/PVP nanofibers.In a typical procedure, 0.1 g of UCNPs/Si O2/Cd S/PVP nanofibers were dispersed in ethanol (20 m L) under vigorous stirring.200L of TBT and 90L of ammonia solution (2830
29、wt.%) were added to the above solution.The resulting mixture was stirred at room temperature for 4 h.The product was collected by centrifugation, washed with ethanol three times, and then dried at50C for 8 h.Finally, the asprepared product was calcined in air at 400C for 1 h at a heating rate of 1C
30、min1.This improved the crystallization of the formed titania, and removed the PVP matrix, yielding the UCNPs/Si O2/Cd S/Ti O2 composite nanotubes.2.3. CharacterizationThe morphologies of the samples were characterized using field-emission scanning electron microscopy (FESEM) with a SU8020 spectropho
31、tometer (Hitachi, Japan) .and transmission electron microscopy (TEM) with a JEM-2100F microscope (JEOL, Japan) .The crystal phases of the samples were characterized using an XPert PRO MPD X-ray diffractometer (PANalytical B.V., Netherlands) , using graphite monochromatized Cu K radiation at 40 k V a
32、nd 40 m A.X-ray photoelectron spectra (XPS) were recorded on an ESCALab 250Xi X-ray photocatalysts-electron spectrometer (Thermo-VG Scientific, Massachusetts, USA) .Fluorescence spectroscopy (Edinburgh FLS980, UK) was used to obtain steady state and dynamic fluorescence spectra of the samples.Absorp
33、tion spectra were recorded with a CARY 5000 spectrophotometer (Agilent Technologies Inc, California, USA) .Total organic carbon (TOC) analysis was carried out using an elementar Liqui II apparatus (Germany) .3. Results and discussion3.1. Fabrication of UCNPs/TEOS/Cd S/PVP nanofibersFig.2a and b show
34、 FESEM images of the product obtained from electrospinning 0.284 g of PVP, 0.22 g of hydrophilic UCNPs, 0.58 g of Cd S nanoparticles, and 1.5 m L of TEOS.The images show that the product consisted of nanofibers of tens ofm in length and 500 nm in diameter.The nanofibers were decorated or embedded wi
35、th a high population of nanoparticles, as shown by the TEM images in Fig.2c and d.The chemical composition of the UCNPs/TEOS/Cd S/PVP nanofibers was studied using scanning transmission electron microscopy (STEM) and elemental mapping analysis.Fig.2en show that Si, O, Y, Yb, Er, Tm, Si, Cd, S and Na
36、were detected, confirming their co-existence in the as-obtained nanofibers.The chemical composition was also investigated using energy dispersive X-ray (EDX) analysis, as shown in Fig.3.Fig.2. (a, b) FESEM images of the UCNPs/Cd S/PVP/TEOS nanofibers. (c, d) TEM images of the UCNPs/Cd S/PVP/TEOS nan
37、ofibers. (e) STEM image of a single UCNPs/Cd S/PVP/TEOS nanofiber. (fn) Elemental mapping images of elements in the nanofiber shown in (e) .All scale bars are 500 nm. 下载原图Fig.3.EDX spectrum of the UCNPs/Cd S/PVP/TEOS nanofibers. 下载原图3.2. Fabrication of UCNPs/Si O2/Cd S/Ti O2 composite nanotubesFig.4
38、 shows SEM and TEM images of the final sample, obtainedaftercalcinationoftheas-prepared UCNPs/Cd S/PVP/Si O2/Ti O2derivedfrom0.1gof UCNPs/Si O2/Cd S/PVP nanofibers (Fig.5) and 200L of TBT in90L of ammonia solution.Fig.5 shows that the UCNPs and Cd S nanoparticles were combined in close contact by th
39、e Si O2nanoparticles derived from the UCNPs/TEOS/Cd S/PVP nanofibers.Fig.4a and b show that the as-prepared Ti O2 composites were of several hundred nanometers in diameter and tens ofm in length.This was in accordance with the diameter of the electrospun UCNPs/TEOS/Cd S/PVP nanofibers.The TEM image
40、in Fig.4c demonstrated that the obtained product was tube-like and had a shell thickness of 20 nm.The high resolution TEM image in Fig.4d showed that the shell layer consisted of octahedrite phase of Ti O2 nanoparticles.X-ray diffraction (XRD) was used to study the crystalline phases and chemical co
41、mpositions.Fig.6 shows the XRD pattern of the as-prepared tube-like composite nanofibers of Ti O2.The diffraction peaks at 25.44, 38.02 and 48.122could be indexed to the anatase phase of Ti O2 (JCPDS No.21-1272) , confirming the crystalline Ti O2 shell.Diffraction peaks of the hexagonal phases of Cd
42、 S (JCPDS No.41-1049) 68, 69and Na YF4 (JCPDS No.28-1192) 47, 67were also clearly observed.These results showed that the as-prepared sample consisted of Ti O2, Cd S and UCNPs.STEM spectroscopy and XPS were used to characterize the chemical composition and elemental distribution of the as-prepared UC
43、NPs/Si O2/Cd S/Ti O2 composite nanotubes.Fig.7 shows elemental mapping images for Yb, Y, O, Si, Ti, Tm, S, Na, F, Er and Cd in the composite nanotubes.The images indicated the co-existence of these elements in the UCNPs/Si O2/Cd S/Ti O2 nanotubes.The elemental composition was also investigated by XP
44、S, as shown in Fig.8.These results collectively indicated that the UCNPs/Si O2/Cd S/Ti O2 nanotubes had been prepared.Fig.4. (a, b) SEM images of as-prepared Ti O2 nanotubes embedded with UCNPs and Cd S nanoparticles. (c) TEM image of a Ti O2 composite nanotube. (d) High resolution TEM image of the
45、marked region in (c) . 下载原图Fig.5. (a) SEM and (b) TEM images of UCNPs/Si O2/Cd S/PVP nanofibers. (c) STEM image of a single UCNPs/Si O2/Cd S/PVP composite nanofiber. (dm) Elemental mapping of Y, Yb, Na, Er, Tm, Si, F, Cd, S and O in com-posite nanotubes of Ti O2, respectively.All scale bars are 500
46、nm. 下载原图3.3. Optical and photocatalytic properties of theUCNPs/Si O2/Cd S/Ti O2 composite nanotubesFig.6.XRD patterns of the as-prepared UCNPs/Si O2/Cd S/Ti O2 nanotubes, and standard patterns for its various components. 下载原图Fig.7. (a) STEM image of a single nanotube of the UCNPs/Si O2/Cd S/Ti O2 na
47、nocomposite. (bl) Elemental mapping of Yb, Y, O, Si, Ti, Tm, S, Na, F, Er and Cd in the composite nanotubes of Ti O2, respectively.All scale bars are 500 nm. 下载原图Thefluorescencespectrumoftheasobtained UCNPs/Si O2/Cd S/Ti O2 composite nanotubes is shown in Fig.9a.Compared with the spectrum of the UCN
48、Ps, the fluorescence emissions of the 1I63F4, 1D23F4, D23H6, and 1G43H6 transitions of Tmand the H11/2I15/2 and S3/2I15/2 transitions of Er3+for the as-prepared Ti O2 composite nanotubes were greatly quenched under excitation by a 980 nm continuous wave (CW) laser.This indicated the enhanced fluores
49、cence energy transfer efficiency of the tube-like UCNPs/Si O2/Cd S/Ti O2 nanostructures.Most of the transitions for Tm3+or Er3+were greatly quenched, which was ascribed to the close proximity of the UCNPs and Cd S nanoparticles in the Si O2 matrix.The near infrared (NIR) photon energy could be efficiently transferred to the nearby Cd S nanoparticles via irradiative energy transfer (IET) and non-
