The directional design of constructing surface active centers has been a challenging issue in the development of efficient photocatalysts. In the contribution, the molecular -level surface active centers are created on polymeric carbon nitride (PCN) through 7C -7C interaction with organic conjugated small molecule complex Au-bpy. In the prepared Au-bpy/PCN composite, Au-bpy is decorated on the surface of PCN in the molecular state and molecularly aggregated nanocrystal. Strikingly, the investigations of the optical properties and charge transport behaviors indicate that the modification of Au-bpy effectively extends the light response range, narrows the band gap and improves the separation efficiency of photogenerated carriers. At the same time, the structural evolution of Au-bpy/PCN composite reveals that the Au-bpy in the molecular state can be served as the surface active centers, and Au-bpy nanocrystal is reduced to Au nanoparticles that can induce local surface plasmonic resonance effect, thus significantly boosting the photocatalytic activity with about 100 % selectivity for CO2 reduction to CO. As a consequence, the average CO evolution rate increases from 39.7 mu mol g -1h-1 over primitive PCN up to 113.2 mu mol g -1h-1 over the optimal Au-bpy/PCN-3 in the photocatalytic CO2 reduction reaction. This work opens a new avenue for the design of surface active sites on the photocatalysts on the molecular scale.

The double S-scheme heterojunction of YVO4/TiO2/BiVO4 compoite fibers material was prepared by one-step hydrothermal method using TiO2 electrospun nanofibers as substrate. The structures of the composite catalyst were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet visible diffuse reffectance spectroscopy and photoluminescence. The performance of photocatalytic CO2 reduction over the composite catalyst under simulated sunlight was studied. The results show that photocatalytic activity of YVO4/TiO2/BiVO4 composite fibers was investigated via production of methanogenesis from photocatalytic reduction of CO2. The CO2 reduction capability of composite fibers was better compared to that of monomer materials. The photocatalytic production rate of CH4 and CH3OH of YVO4/TiO2/BiVO4 were 13.88 and 3.46 mu molg-1h-1, respectively. The increased photocatalytic activity of YVO4/TiO2/BiVO4 is attributed to the formation of heterojunctions between YVO4, BiVO4 and TiO2 as well as the S-scheme charge transfer mode of the photogenerated carriers, both of which are conducive to separation efficiency of photo-generated carriers and photocatalytic CO2 reduction activity.

One of the basic challenges of CO2 photoreduction is to develop efficient photocatalysts. As an effective strategy, constructing heterostructure photocatalysts with intimate interfaces can enhance interfacial charge transfer for realizing high photocatalytic activity. Herein, a novel photocatalytic material, Bi4O5Br2/CeO2 composite fiber (B@C-x, x refers to the amount of reactant), was constructed by embeding CeO2 nanofibers on Bi4O5Br2 nanosheets via an electrospinning combined with hydrothermal method. Its composition, morphology and photoelectric properties were characterized. The results show that Bi4O5Br2/CeO2 heterojunction with appropriate Bi4O5Br2 content can significantly improve the photocatalytic performance of CeO2 nanofibers. Compared with pure Bi4O5Br2 and CeO2, B@C-2 exhibited the best photocatalytic activity under simulated sunlight. The Bi4O5Br2/CeO2 exhibited improved photocatalytic CO2 reduction performance with a CO generation rate of 8.26 mu mol center dot h(-1)center dot g(-1) without using any sacrificial agents or noble co-catalysts. This can be attributed to the tight interfacial bonding between Bi4O5Br2 and CeO2 and the formation of S-scheme heterojunction, which enables the efficient spatial separation and transfer of photogenerated carriers. This work provides a simple and efficient method for directional synthesis of Bi-based photocatalytic composites with S-scheme heterojunction and illustrates an applicable tactic to develop potent photocatalysts for clean energy conversion.

光催化CO2 还原技术既能实现节能减排,又能缓解能源短缺,符合当今绿色可持续发展的理念.本工作以静电纺丝技术制备的TiO2 纳米纤维为基质,结合水热还原法制备Bi@Bi4O5Br2/TiO2 复合纤维.利用XRD、SEM、HRTEM、XPS、UV-Vis和碳吸附等方法对其微观结构、形貌和光学性能进行表征.结果表明:TiO2 纳米纤维经Bi4O5Br2 复合后,光谱响应范围拓展到可见光区,光生电子还原能力增强,可以将CO2 还原成CH4 和CO;金属Bi的富集不仅能提高催化剂对酸性CO2 分子的吸附能力,增强CO2 转化效率,而且能改变光催化反应路径,并有醇类物质(CH3OH)的生成.模拟太阳光照射 3 h,Bi@Bi4O5Br2/TiO2 光催化CO2 还原生成CH4、CO和CH3OH的速率分别达到 3.87、1.06和 0.32 µmol·h-1·g-1.本文为探索高效二氧化碳光还原催化剂提供了新的机会.

以静电纺丝技术制备的TiO2纳米纤维为基质,硝酸铋为铋源,KOH为矿化剂,成功制备了多异质结Bi2Ti2O7/TiO2/Bi4Ti3O12复合纳米纤维光催化剂.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、紫外可见漫反射光谱(UV-VisDRS)等一系列表征,对其物相组成、微观形貌和光学性质等进行分析.结果表明:TiO2纳米纤维的介入,将Ⅰ型异质结Bi2Ti2O7/Bi4Ti3O12分离为2个Ⅱ型异质结Bi2Ti2O7/TiO2和Bi4Ti3O12/TiO2.Bi2Ti2C7、Bi4Ti3O12和TiO2三者的协同作用,有效提高了可见光吸收能力,改变了光生载流子的传输路径,降低了光生电子与空穴的复合几率,从而获得高效的光催化降解CH3CHO性能.可见光照8 h,Bi4Ti3O12/TiO2Bi2Ti2O7复合纳米纤维对CH3CHO的降解率达到87.1％.

Specially-designed and manufactured microstructures as constitutional units play vital roles in modulating the characteristics and functions of multifunctional materials. In this study, [CoFe2O4/polyvinylpyrrolidone (PVP)]//[polyaniline (PANI)/PVP] Janus nanofiber@[Tb(acac)3bpy/PVP] fiber typed (denoted as [(M//E)@F]) microfiber and array are designed and synthesized by a modified electrospinning device for the first time. Magnetism, electrical conduction and fluorescence are microscopically assembled into a Janus nanofiber@fiber typed microfiber, thus obtaining excellent magnetic-electrically conductive-fluorescent trifunctionality. In addition, the array displays insulation-fluorescence on its surface and magnetic-electrical conduction in interior. The [(M//E)@F] microfiber contains the core layer (CL) of (CoFe2O4/PVP)//(PANI/PVP) Janus nanofiber with magnetic-electrically conductive bifunctionality and shell layer (SL) of Tb(acac)3bpy/PVP fiber with fluorescent functionality, and all the [(M//E)@F] microfibers are aligned in the same direction to form the array. Compared with the corresponding conventional coaxial microfiber with two independent partitions, the Janus nanofiber replaces the microfiber in the CL to form the special structure [(M//E)@F] microfiber, so that the [(M//E)@F] microfiber achieves three independent partitions on the microscopic level. The obtained microstructure can achieve the complete separation of CoFe2O4 nanoparticles (NPs), PANI and rare earth complexes, and PANI has continuity in the matrix, guaranteeing intense fluorescence and high conduction. Due to the special Janus structure, the CL conducts electricity along the lengthwise direction of the Janus nanofiber and is insulated perpendicular to the lengthwise direction (viz. widthwise direction) of the Janus nanofiber, so the CL has aeolotropic conductivity. In view of this unique performance, we advance a new concept, namely "microcosmic aeolotropic electroconductivity", which indicates that for a single constitutional unit, its interior has a key feature of aeolotropic conductivity. [(M//E)@F] microfibers array (designated as [(M//E)@F]-MFA) is obtained by using [(M//E)@F] microfiber as the constitutional unit to align directionally, and its fluorescence intensity is 11 times higher than that of the counterpart conventional composite microfibers array. In addition, the saturation magnetization of [(M//E)@F]-MFA can be adjusted from 2.16 to 27.41 emu.g(-1) by varying the amount of CoFe2O4 NPs. The microcosmic aeolotropic electroconductivity can be modified by changing the contents of PANI in [(M//E)@F]-MFA. A new technique for constructing Janus nanofiber@fiber typed microfiber and array is established, which provides a pathway to construct other multifunctional micro/nanomaterials.

In this work, we prepared double heterojunction Bi2Ti2O7/TiO2/Bi4Ti3O12 composite nanofibers by employing electrospun TiO2 nanofibers as the substrate, bismuth nitrate as the bismuth source, and potassium hydroxide as the mineralizing agent. Through a series of tests such as X-ray diffraction (XRD), scanning electron microscope (SEM), UV-visible diffuse reflectance spectrum (UV-Vis DRS), the phase composition, micromorphology, and optical properties of the Bi2Ti2O7/TiO2/Bi(4)Ti(3)O(12)catalyst were analyzed. The results showed that the TiO2 changed type. heterojunction into multi-heterojunction integrating two type. heterojunctions. Photocatalytic tests demonstrated the activity of as-constructed multi-heterojunction was higher than that of single type. or. heterojunctions, respectively, where photogenerated electrons were accumulated on the surface of TiO2 and photogenerated holes were accumulated on Bi2Ti2O7 and Bi4Ti3O12, respectively. The synergistic effect of Bi2Ti2O7, Bi4Ti3O12, and TiO2 effectively improves the visible light absorption capacity, changes the transmission path of photo-generated carriers, and reduces the recombination probability of photogenerated electron-hole pairs, thereby obtaining the efficient photocatalytic degradation of CH3CHO. The acetaldehyde degradation rate of Bi2Ti2O7/TiO2/Bi4Ti3O12 reached 87.1% under visible light illumination for 8 h.

Multifunctional materials have more extensive applications than their counterpart single-functional materials due to their superior polyfunctions, among which fluorescent-conductive-magnetic (FCM) multifunctional materials have been extensively investigated for their unique performance and application value. However, the material properties may be degraded due to the adverse interactions among the fluorescent, conductive and magnetic materials with three different functions when they are directly blended. Hence, such adverse interactions brought by the direct contact of different functional materials should be avoided by designing and preparing unique structures. In this study, a one-dimensional (1D) tri-coaxial microbelt is innovatively designed, which can effectively separate and integrate different materials at the micro-level to obtain excellent macroscopic polyfunction. Generally, the preparation of tri-coaxial structure requires multistep procedures. To facilely construct the designed tri-coaxial microbelt, as a case study, a novel [CoFe2O4/polymethyl methacrylate (PMMA)]@[polyaniline (PANI)/PMMA]@[Tb(acac)3bpy/PMMA] (defined as [M@C@F]) tri-coaxial microbelts and arrays are synthesized through the one-pot direct electrospinning (ES) process. The tri-coaxial microbelts are assembled by the CoFe2O4/PMMA magnetic core layer, the PANI/PMMA conductive intermediate layer, and the Tb(acac)3bpy/PMMA insulated-fluorescent shell layer. It is the first time to integrate three different functions into the tri-coaxial microbelts and restrict three functions into three independent zones in the microbelt to shun adverse mutual interferences. The function of each layer can be regulated by adjusting the position and content of the three functional materials. Comparison with the control samples indicates that the property of the tri-coaxial microbelts array is directly impacted by structure and the arrangement modes of the building units. Hence, excellent macroscopic polyfunctions are obtained via designing and preparing microscopic partitioned building units and arranged modes. Array displays superior green fluorescence at 549 nm, tunable electrical conduction and magnetism. The new technique of one-pot direct construction of the tri-coaxial microbelts is significant and can be extended to for assemble other multifunctional materials. Moreover, the constructed [M@C@F] tri-coaxial microbelts and arrays have applications in various fields, such as micro-integrated circuits, microchips, and micro/nanodevices.

以静电纺丝制备的TiO 2 纳米纤维为基质,葡萄糖为还原剂,在不同的酸碱环境中,采用一步水热法可控合成了异质结型Bi-TiO 2 、（BiO） 2 CO 3 -TiO 2 和（BiO） 2 CO 3 -Bi-TiO 2 复合纳米纤维光催化剂。通过X射线粉末衍射（XRD）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、紫外-可见漫反射光谱（UV-Vis DRS）和光致发光光谱（PL）等对样品进行表征。以洛美沙星、环丙沙星和诺氟沙星为目标污染物,研究了TiO 2 及其复合纳米纤维的光催化降解性能,并探究其降解反应机理。结果表明,（BiO） 2 CO 3 -Bi-TiO 2 光催化活性最高,模拟太阳光照60 min,对诺氟沙星、洛美沙星和环丙沙星的降解率分别达到93.2%、97.5%和100%。

Among tremendous efforts for enhanced photocatalysis, construction of heterojunction has been deemed as an effective means. In comparison with type II heterojunction, type I heterojunction receives less attention due to accumulation and increased recombination of charge carriers in one side of heterojunction. Herein, we take NaBi(MoO4)2/Bi2MoO6 as an example of type I heterojunction and explore means to improve the photocatalytic performance of NaBi(MoO4)2/Bi2MoO6 heterojunction. We employ TiO2 electrospun nanofibers as substrates and separately grow NaBi(MoO4)2 and Bi2MoO6 nanostructures on the skeleton of TiO2. The characterization results show that TiO2 changes type I heterojunction into multiheterojunction integrating two type II heterojunctions. Photocatalytic tests demonstrate that as-constructed multi-heterojunction is of higher activity than that of single type I or II heterojunction, respectively, where photogenerated electrons are accumulated on the surface of TiO2 and photogenerated holes are accumulated on NaBi(MoO4)2 and Bi2MoO6, respectively. This study highlights the potential application of TiO2 electrospun nanofibers in the construction of multiheterojunction for enhanced visible light photocatalysis.

In this study, silver nanoparticles/carbon nanotubes (Ag NPs/CNTs) was successfully synthesized on the surface of glassy carbon (GC) electrode using a facile chemical technique to evaluate determination of cyanide as a toxic substance in food products. The structural properties of synthesized CNTs and Ag NPs/CNTs were studied by scanning electron microscope, energy dispersive X-Ray and X-Ray diffraction analyses. The voltammetric and amperometric techniques were used for electrochemical studies of modified electrodes. The structural studies showed high density, porosity and aspect ratio of the Ag NPs/CNTs electrodes. The cycle voltammetric studies of Ag NPs/CNTs/GC electrode showed sharp and stable oxidation peak at 0.75 V in pH 7 for cyanide. Amperometry results exhibited that Ag NPs/CNTs/GC electrode was sensitive, selective and stable to determinate cyanide. The linear range, sensitivity, and detection limit of modified sensor were 0.1 to 210 mu M, 0.7192 mu A/ mu M and 4 nM, respectively which were better values than those obtained in previous researches. Study on the interfere effect of Br-, SO32-, CH3COO-, I-, C2O42-, Cl-, SO42-, CO32-, Ni+2, Co2+, HPO42-, F- and Zn+2 analytes showed that there was not any interfere in determination of cyanide on Ag NPs/CNTs/GC electrode surface. The recorded amperometrogram results of real sample showed the modified electrode was successfully applied for cyanide detection in apricot juice.

以静电纺丝技术制备的稀土Nd3+掺杂TiO2纳米纤维为基质,结合水热法制备了Bi/Nd3+:TiO2复合纳米纤维光催化剂.利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis DRS)和瞬时光电流(IP)等分析测试手段对样品的物相、形貌和光电性能等进行表征.以三乙醇胺为牺牲剂,研究了Bi/Nd3+:TiO2可见光催化产氢过程.结果表明:Bi作为一种新兴的非贵金属具有独特的等离子体光催化或辅助光催化性能,将其与稀土元素丰富的能级结构和4f电子跃迁特性相结合,对TiO2进行双重修饰改性,有效提高了TiO2的光催化活性和稳定性,可见光照射下产氢速率达到49.2μmol?g-1?h-1.

以电纺TiO 2 纳米纤维为基质和反应物、乙二醇为还原剂,采用溶剂热法原位合成了新型Bi@Bi 4 Ti 3 O 12 /TiO 2 等离子体复合纤维。利用XRD、 SEM、高倍透射电子显微镜（HRTEM）、 XPS、紫外-可见漫反射光谱（UV-Vis DRS）和光致发光图谱（PL）等分析测试手段研究了Bi@Bi 4 Ti 3 O 12 /TiO 2 复合纤维的结构和性能。结果表明:当反应温度低于210℃时, Bi@Bi 4 Ti 3 O 12 /TiO 2 复合纤维的Bi 4 Ti 3 O 12 纳米片随反应温度升高逐渐缩小、增厚,且有金属Bi纳米粒子生成;当反应温度高于210℃时, Bi@Bi 4 Ti 3 O 12 /TiO 2 复合纤维的纳米片发生堆积、变形、表面金属Bi被氧化成Bi 2 O 3 。反应温度对Bi@Bi 4 Ti 3 O 12 /TiO 2 等离子体复合纤维的形貌和物相组成有重要影响; Bi@Bi 4 Ti 3 O 12 /TiO 2 复合纤维对罗丹明B表现出优异的光催化活性,可见光照5 h其降解率达97.8%。Bi@Bi 4 Ti 3 O 12 /TiO 2 复合纤维光催化性能提高归结于Bi 4 Ti 3 O 12 与TiO 2 间形成异质结、金属Bi等离子体共振效应及等离子体共振效应与异质结的协同作用。

The double heterojunction of Pr2Sn2O7@Bi2Sn2O7/TiO2 composite was prepared by one-step hydrothermal method using TiO2 electrospun nanofibers as substrate. The structures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet (UV)-visible diffuse reflectance spectroscopy and photoluminescence. The performance of photocatalytic hydrogen production over the composite catalyst was studied under UV-visible light. The Pr2Sn2O7@Bi2Sn2O7/TiO2 composite nanofibers showed high photocatalytic activity for hydrogen production. The hydrogen production rate reached 587.1 mu mol h(-1) g(-1), which was 2.7 and 7.1 times that of Bi2Sn2O7/TiO2 and TiO2, respectively. The main reasons for the high photocatalytic activity included broadened spectral range, 4f-4f transition from Pr3+ of Pr2Sn2O7 and increased separation of the photogenerated carriers by double hetemjunction via direct Z-scheme transfer.

Bi deposited Yb3+, Er3+ codped TiO2 nanofiber photocatalysts were synthesized from Yb3+ and Er3+ Co - doped TiO2 substrate by combining electrospinning technique and hydrothermal method. Using triethanolamine as a sacrificial agent, we studied the ultraviolet, visible, near infrared and full spectrum photocatalytic hydrogen production over Bi/Yb3+, Er3+:TiO2. The results showed that the full-spectrum illumination for 5 h resulted in a hydrogen production rate of 1 650.3 mu mol.g(-l).h(-1). As an emerging non-noble metal, Bi displays unique plasma photocatalytic or assisted photocatalytic properties. The advantages of Bi metal can be further combined with a rich energy level structure of rare earth elements and unique up-conversion luminescence properties. The double synergistic modification of TiO2 can effectively improve the photocatalytic activity of TiO2 nanofibers.

Bi deposited Yb3+ , Er3+ codped TiO2 nanofiber photocatalysts were synthesized from Yb3+ and Er3+ co ‐ doped TiO2 substrate by combining electrospinning technique and hydrothermal method. Using triethanolamine as a sacrificial agent, we studied the ultraviolet, visible, near infrared and full spectrum photocatalytic hydrogen produc‐ tion over Bi/Yb3+, Er3+∶TiO2. The results showed that the full‐spectrum illumination for 5 h resulted in a hydrogen production rate of 1 650.3 μmol·g-1·h-1. As an emerging non‐noble metal, Bi displays unique plasma photocatalytic or assisted photocatalytic properties. The advantages of Bi metal can be further combined with a rich energy level structure of rare earth elements and unique up‐conversion luminescence properties. The double synergistic modifi‐ cation of TiO2 can effectively improve the photocatalytic activity of TiO2 nanofibers.

以电纺Ho3+-TiO2纳米纤维为基质,葡萄糖酸钠为还原剂,采用水热法制备Ho3+-TiO2/Bi等离子体复合纤维光催化剂.利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis DRS)和瞬时光电流(IP)等分析测试手段对样品的物相、形貌和光电性能等进行表征.以三乙醇胺为电子给体,研究了Ho3+-TiO2/Bi光催化分解水产氢的反应过程.结果表明:在水热过程中,Bi3+被葡萄糖酸钠还原成单质Bi纳米颗粒,复合在Ho3+-TiO2纳米纤维表面形成肖特基结.金属Bi通过局域表面等离子体共振效应结合稀土元素丰富的能级结构和4f电子跃迁特性,对TiO2进行双重修饰改性,有效提高了TiO2的光催化活性和稳定性,可见光下产氢速率最大为43.6μmol/(g·h).

以电纺TiO2纳米纤维为基质,利用水热法制备了异质结型Eu3+掺杂NaBi(MoO4)2/TiO2复合纤维.利用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、高分辨透射电镜(TEM)、紫外-可见漫反射(UV-Vis DRS)光谱以及荧光(PL)光谱等分析测试手段对样品的物相、形貌和光学性能等进行表征.以三乙醇胺为电子给体,研究了Eu3+掺杂NaBi(MoO4)2/TiO2复合纤维光催化裂解水制氢的反应过程.结果表明:NaBi(MoO4)2与TiO2复合形成异质结,使光生电子-空穴对得到较好分离,而Eu3+掺杂进入NaBi(MoO4)2晶格,部分取代Bi3+离子,导致晶胞膨胀,在拓宽光谱响应范围的同时,形成光生载流子的浅势捕获阱,进一步促进了光生电荷的产生、转移,有效提高材料的光催化制氢活性.最佳产氢速率达到7.86 mmol·h-1·g-1.

By employing electrospun TiO2 nanofiber as substrate, Bi@Bi2Sn2O7/TiO2 plasmonic composite fibers were prepared via one-step hydrothermal method. The composition, morphology and optical properties were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-visible diffuse reflection spectra (UV-Vis DRS) and photoluminescence spectroscopy (PL) analysis. The photocatalytic water splitting for hydrogen evolution was investigated over Bi@Bi2Sn2O7/TiO2 plasmonic composite fibers with triethanolamine as the donor residue. The results showed that the Bi nanoparticles were generated onto Bi2Sn2O7 nanoparticle via the in situ reduction of Bi3+ by glucose, meanwhile grew on the TiO2 nanofibers surface. The enhanced photocatalytic activity of the Bi@Bi2Sn2O7/TiO2 plasmonic composites fibers can be further improved mainly attributed to the formation of high-quality p-n heterojunctions between Bi2Sn2O7 and titanium dioxide, the plasma resonance effect of metal bismuth, and the synergistic effect of plasma resonance effect and p-n heterojunction. The corresponding H-2 production rate was 7.26 mmol.h(-1).g(-1).

Gd and N co-doped SrTiO3/TiO2 composite nanofibers were prepared via one step hydrothermal synthesis growth of SrTiO3 nanostructures using electrospun anatase TiO2 nanofibers as both substance and reactant. The phase composition, microstructure, morphology and optical properties of the sample were characterized by X-ray diffraction (XRD), scanning electron mictoscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and photoluminescence spectroscopy (PL). The results indicated that the heterostructure formed by SrTiO3 and Tio(2), plays an important role in the suppression of electron-hole recombination and improves the photocatalytic performance of TiO2 nanofibers. The excellent visible light photocatalytic activity of this substance may be due to the generation of a new band gap that enables the catalyst to absorb visible light and results in the lattice defects which acts as a recombination center of photoinduced electrons and holes. The synergistic effect of Gd-N co-doping and heterojunction could effectively improve the visible-light photocatalytic activity of SrTiO3/TiO2 composite nanofibers.