【作者】 张鹏；

【导师】 邵长路；

【作者基本信息】 东北师范大学 ， 材料物理与化学， 2014， 博士

【摘要】 钛基半导体是光催化领域的重要材料，其在催化降解、制氢等环境和能源领域得到了广泛的研究和应用。但钛基半导体依然存在以下几个主要问题：第一，以TiO2、ZnxTiyOz等为代表的宽禁带半导体材料太阳光利用率低；第二，光催化剂的光生电子空穴对复合过快，量子效率低；第三，光催化剂在液相应用中难于分离回收。本文以钛基半导体为主线，基于光催化的本征问题和实际应用的挑战，利用静电纺丝技术结合水热、溶剂热、原位还原等方法制备一系列从二元到三元的高活性钛基复合纳米纤维光催化剂，研究材料制备过程对其形貌、微观结构及光催化性能的影响，探究异质结界面之间的相互作用和电荷传输机制，揭示材料的能带结构、微观结构与催化性能的关系，获得具有高催化活性和良好使用性能的光催化材料。具体研究成果如下：（1）通过静电纺丝技术和水热方法制备了TiO2@Carbon核壳纳米纤维，期望利用碳层对可见光的吸收实现对TiO2敏化，得到能够对可见光响应的高效光催化剂。形貌和结构研究结果表明2nm左右的石墨化碳层通过C-O-Ti键均匀的构造在TiO2纤维表面，并且可以通过控制实验参数实现碳层厚度从2nm到8nm的调控。光催化性质研究表明TiO2@Carbon核壳纳米纤维能够吸收可见光并呈现了较高的可见光催化活性。通过羟基自由基捕获试验进一步证明了通过可见光激发碳层产生光生电子空穴，通过TiO2纤维实现光生载流子的输运和分离的光催化机理。此外，基于这种一维纳米纤维网毡结构，TiO2@Carbon核壳纳米纤维催化剂在光催化过程中具有优异的可分离及重复使用特性。（2）在TiO2@Carbon核壳纳米纤维的基础上，利用液相原位还原方法引入小尺寸、高分散性的Ag纳米颗粒，期望利用TiO2/Ag异质结所形成的肖特基势垒进一步提高量子效率，获得催化效率增强的三元可见光催化剂。研究表明3-5nm的Ag纳米颗粒均匀的引入到TiO2@Carbon核壳纳米纤维体系中，而且，通过对光催化降解罗丹明B和甲基橙两种有机染料的研究，这种三元光催化剂相对于纯TiO2纤维、TiO2@Carbon纤维和TiO2/Ag纤维表现出了增强的可见光催化性质。这种增强可能来源于两方面：贵金属的电子陷阱作用和附近增强的等离子体场效应。此外，基于这种一维纳米网毡结构和碳层对Ag纳米颗粒的保护，该三元催化剂具有优异的可分离及重复使用特性。（3）利用水热方法获得了富碳的g-C3N4纳米片，并在泡沫镍上实现了原位固载化，该材料表现出优良的光电流响应和光催化性质。在此基础上，我们利用静电纺丝技术和原位催化法相结合构造了TiO2@g-C3N4核壳纳米纤维。在电纺TiO2纳米纤维的模板催化作用下，以尿素为前驱体，将厚度1nm的g-C3N4均匀的构造在TiO2纤维表面。这种能带匹配的异质结保证了光生载流子的有效分离，使TiO2@g-C3N4核壳纳米纤维在紫外和可见光照射下分别呈现出增强光电流响应和光催化性质。此外，基于这种一维纳米网毡结构，TiO2@g-C3N4核壳纳米纤维催化剂在实际使用中具有优异的可分离及重复使用特性。（4）通过静电纺丝法获得TiO2/ZnO纳米纤维，在此基础上，利用液相原位还原方法引入小尺寸、高分散性的Au纳米颗粒，期望利用TiO2/Au和ZnO/Au异质结所形成的肖特基势垒建立电子传递三通道的协同体系，获得催化效率增强的三元光催化剂。研究表明3-5nm的Au纳米颗粒均匀的引入到TiO2/ZnO纳米纤维的表面。通过紫外光催化降解4-硝基酚和甲基橙的研究，这种三元TiO2/ZnO/Au异质结构相对于TiO2/Au和ZnO/Au，表现出了增强的光催化活性和效率。对所得材料光致发光光谱的比较研究证明，这种三元异质结有利于光生电子空穴的分离。此外，这种一维纳米网毡结构，使TiO2/ZnO/Au异质结构具有良好的可分离及重复使用特性。（5）通过静电纺丝技术和水热方法制备了Zn2TiO4@Carbon核壳纳米纤维，期望利用石墨化碳层的导电性实现对Zn2TiO4光生电子的传导，得到较高量子产率的高效光催化剂。形貌和结构研究结果表明，通过控制实验参数实现了碳层厚度的调控。紫外光催化性质研究表明，Zn2TiO4@Carbon核壳纳米纤维相对于Zn2TiO4纤维表现出增强的光催化活性。光致发光光谱试验进一步证明了通过Zn2TiO4和石墨化碳层的协同作用可以有效的实现光生载流子的分离和输运的光催化机理。此外，基于这种一维纳米纤维网毡结构，Zn2TiO4@Carbon核壳纳米纤维催化剂在光催化过程中具有良好的可分离及重复使用特性。（6）利用静电纺丝技术和溶剂热方法制备了三维开放的ZnTiO3/Bi2MoO6异质结材料。在溶剂热反应过程中，通过调控反应浓度，在ZnTiO3纳米纤维上分别构造了超薄纳米片、纳米颗粒等不同形貌的Bi2MoO6次级结构。可见光催化降解研究表明，ZnTiO3/Bi2MoO6异质结材料具有优于单组份Bi2MoO6纳米粉体的光催化活性。通过对光催化机理的研究发现，异质结构是加快光生电子空穴对分离的主要原因。相对于纳米颗粒形貌，超薄纳米片提高了可见光的利用率。此外，基于这种一维纳米网毡结构，ZnTiO3/Bi2MoO6异质结材料具有优异的可分离及重复使用特性。更多还原

【Abstract】 Titanium-based semiconductors have been widely studied and used inphotocatalysis. With the potential application in organic degradation and H2production, there still existed several major issues: Firstly, Titanium-basedsemiconductors with wide bandgap suffer from lower sunlight utilization rate, such asTiO2, ZnxTiyOzetc. Secondly, the rapid recombination of photoinduced electrons andholes greatly lowers the quantum efficiency. Thirdly, in the practice application, thephotocatalysts with nanosize are difficult to separate and recycle. Thus, the paperfocuses on the intrinsic problem and the practical application of titanium-basedsemiconductors photocatalytic, a series of nano-photocatalysts from binary to ternarywere fabricated by combining the electrospinning technique, hydrothermal methodand an in situ reduction approach. Such structure with titanium-based semiconductornanofiber as a template to construct heterojunction, shows the concept of "junction" inthe micro-nano-composite structure. And, the super long one-dimensionalnanostructures and unique fiber network structure could improve photocatalyst’sperformance of separation and reuse. The main researches are list as follow:(1) The TiO2@carbon core/shell nanofibers were fabricated by combining theelectrospinning technique and hydrothermal method. The results showed that auniform graphite carbon layer (2-8nm) was formed around the electrospun TiO2nanofiber via C-O-Ti bonds. By adjusting the hydrothermal fabrication parameters,the thickness of carbon layer could be easily controlled. The photocatalytic studiesrevealed that the TiO2@C NFs exhibited enhanced photocatalytic efficiency ofphotodegradation of Rhodamine B (RB) compared with the pure TiO2nanofibersunder visible light irradiation, which might be attributed to high separation efficiencyof photogenerated electrons and holes based on the existence of carbon as a sensitizer.Notably, the photocatalytic mechanism was confirmed by the hydroxyl radicalsscavenger experiment.(2) Based on TiO2@carbon core/shell nanofibers, Ag nanoparticles werefabricated by an in situ reduction approach. The results showed that a uniformgraphite carbon layer of approximately8nm in thickness was formed around theelectrospun TiO2nanofiber and small Ag nanoparticles (Ag NPs) were dispersed wellinside the carbon layer. And, the TiO2@C/Ag NFs had remarkable light absorption inthe visible region. The photocatalytic studies revealed that the TiO2@C/Ag NFsexhibited enhanced photocatalytic efficiency of photodegradation of Rhodamine B(RB) and Methyl orange (MO) compared with the pure TiO2nanofibers,TiO2@carbon core/shell nanofibers and TiO2/Ag nanofibers under visible lightirradiation, which might be attributed to the good light absorption capability and high separation efficiency of photogenerated electron-hole pairs based on thephotosynergistic effect among the three components of TiO2, carbon and Ag. And, theTiO2@C/Ag NFs could be easily recycled due to their one-dimensional nanostructuralproperty.(3) We firstly highlight a water-solution synthesis approach at low temperatureto prepare the carbon-rich graphitic carbon nitride nanosheets (CCN). Compared withthe bulk CN prepared by solid-state synthesis at high temperature, the as-obtainedultrathin CCN nanosheets show enhancement of photocurrent and photocatalyticactivity, which could be ascribed to its improved electron transport ability along thein-plane direction, and increased lifetime of photoexcited charge carriers.Three-dimensional (3D) free-standing network composed of TiO2@g-C3N4core/shellnanofibers was fabricated by combining the electrospinning technique and an in situcatalytic approach. The results showed that a uniform g-C3N4layer of approximately1nm in thickness was formed around the electrospun TiO2nanofiber. What’s more,it’s interesting to note that the g-C3N4layer with high quality was formed by an in situcatalytic reaction under a mild condition. And, the as-prepared TiO2@g-C3N4networkexhibited enhancement of photocurrent and photocatalytic activity. The enhancementin performance under UV irradiation was induced by the high separation efficiency ofphotoinduced holes from TiO2to the HOMO of C3N4. Under visible light irradiation,the electron excited from the HOMO to the LUMO of C3N4could inject into the CBof TiO2, making TiO2@g-C3N4present visible light photocatalytic activity. Notably,the free-standing3D nanofibrous network structure could improve photocatalyst’sperformance of separation and reuse.(4) The TiO2/ZnO nanofibers embedded by Au nanoparticles were fabricated bycombining the electrospinning technique (for TiO2/ZnO nanofibers) and an in situreduction approach (for Au nanoparticles). The results showed that small Aunanoparticles (Au NPs) were dispersed well on the TiO2/ZnO nanofibers (TiO2/ZnONFs). And, the TiO2/ZnO/Au nanofibers showed high charge separation efficiencyunder ultraviolet excitation, as evidenced by photoluminescence spectra. Thephotocatalytic studies revealed that the TiO2/ZnO/Au NFs exhibited enhancedphotocatalytic efficiency of photodegradation of Methyl orange (MO) and4-nitrophenol (4-NP) compared with the pure TiO2nanofibers, ZnO nanofibers andTiO2/ZnO NFs under ultraviolet excitation, which might be attributed to the highseparation efficiency of photogenerated electron-hole pairs based on thephotosynergistic effect among the three components of TiO2, ZnO and Au. And, theTiO2/ZnO NFs could be easily separated and recycled due to their one-dimensionalnanostructural property.(5) Zn2TiO4@carbon core/shell nanofibers (Zn2TiO4@C NFs) with differentthinkness of carbon layers (from2to8nm) were fabricated by combining theelectrospinning technique and hydrothermal method. The results showed that a uniform carbon layer was formed around the electrospun Zn2TiO4nanofiber (Zn2TiO4NFs). By adjusting the hydrothermal fabrication parameters, the thickness of carbonlayer varied linearly with the concentration of glucose and was, thus, able to becontrolled with a resolution in the nanometer range. Furthermore, the core/shellformed between Zn2TiO4and carbon enhanced the charge separation of pure Zn2TiO4under ultraviolet excitation, as evidenced by photoluminescence spectra. Thephotocatalytic studies revealed that the Zn2TiO4@C NFs exhibited enhancedphotocatalytic efficiency of photodegradation of Rhodamine B (RB) compared withthe pure Zn2TiO4NFs under ultraviolet excitation, which might be attributed to highseparation efficiency of photogenerated electrons and holes based on the synergisticeffect between carbon and Zn2TiO4. Notably, the Zn2TiO4@C NFs could be easilyrecycled due to their one-dimensional nanostructural property.(6) The3D open Bi2MoO6/ZnTiO3hierarchical heterostructures with Bi2MoO6ultrathin nanosheets grown on hexagonal-phase ZnTiO3nanofibers were fabricated bycombining the electrospinning technique and solvothermal method. The hierarchicalheterostructures synergistic system exhibited exceptional visible-light photocatalyticactivity, which might be attributed to the synergistic system with excellent chargeseparation characteristics and the unique morphology of Bi2MoO6nanosheets. What’smore, the3D open structure supported on nanofibrous candidates could be easilyrecycled easily by sedimentation without a decrease of the photocatalytic activity.更多还原