【作者】 顾德恩；

【导师】 杨邦朝；

【作者基本信息】 电子科技大学 ， 微电子学与固体电子学， 2008， 博士

【摘要】 二氧化钛（TiO₂）的光诱导特性使其在环境污染物降解、自清洁涂层、光分解水制氢和太阳能电池等环境保护与能源转换领域具有广泛的用途。但受带隙宽度的限制,TiO₂的光诱导特性需要以紫外光为激发光源,这在一定程度上限制了TiO₂的实际工程应用。将TiO₂的光学响应区红移至可见光区,不但可以利用太阳光的可见光成分,而且可以用室内光源作为激发光源,从而促进TiO₂更广泛的应用。近年来,具有可见光响应TiO₂的制备和相关性能研究正成为氧化物半导体研究领域的一个新热点。通过掺杂改变TiO₂的电子结构是制备具有可见光响应TiO₂的重要技术途径。本论文基于几种新型掺杂方法,制备了V掺杂、V/N共掺、C掺杂、C/N/F共掺TiO₂。借助各种分析表征手段,对掺杂TiO₂的微观结构、成分和掺杂元素的化学态进行了表征,并探讨了其中的掺杂机理。通过测试掺杂TiO₂的光吸收性能和可见光催化活性（亚甲基蓝:MB;λ＞420nm）,评价了掺杂TiO₂的光响应性能。论文的主要研究内容和创新点归纳如下:1.基于液相沉积法（LPD）制备金属氧化物薄膜的原理,首次将LPD法用于制备V掺杂TiO₂薄膜,研究了V离子浓度对V掺杂TiO₂薄膜晶体结构、V离子化学态和光响应性能的影响,并提出了原位掺杂机理。V掺杂TiO₂薄膜主要由晶粒尺度为8～20nm的锐钛矿TiO₂构成。在V离子浓度较低时,薄膜中V离子按照原位掺杂机制以V⁴⁺形式存在于TiO₂晶格。掺V导致TiO₂薄膜的吸收边红移,并具有可见光催化活性。随着V离子浓度提高,薄膜中V⁵⁺成分增加、晶粒尺度增大,使V掺杂TiO₂薄膜的可见光催化活性逐渐降低。2.根据V掺杂TiO₂和N掺杂TiO₂电子结构的特点,提出以V、N共掺技术来增强TiO₂的可见光吸收并提高其可见光催化活性。将控制水解工艺与室温氮化工艺结合,在室温下成功地制备了V/N共掺纳米晶（4～5nm）锐钛矿TiO₂粉体。V以V⁴⁺和V³⁺形式占据部分Ti⁴⁺格点位置,N则以替位N和间隙N的形式存在于TiO₂晶格,V对室温掺N有促进作用。纳米晶TiO₂具有的高度化学活性、以及纳米晶表面和晶粒内大量的缺陷为室温下成功掺N提供了基础。V/N共掺使纳米晶TiO₂的带隙相对于单独掺杂（掺V∶2.91eV;掺N∶2.92eV）进一步窄化至2.76eV。V/N共掺纳米晶TiO₂对可见光更多的吸收和更高的光量子效率导致共掺TiO₂具有比单独掺杂TiO₂更高的可见光催化活性。3.首次采用硝酸控制氧化法在低温一步实现了微—介孔结构形成、孔壁晶化和掺C,这种新型掺杂方法避免了常用高温掺C工艺带来的孔洞结构塌陷问题,且具有工艺简单和易于工程化实现等优点。硝酸控制氧化法制备的C掺杂微一介孔双模结构TiO₂,孔壁由纳米晶（3～5nm）锐钛矿TiO₂构成,BET比表面积最高达246.9 m²/g。晶格C由占据TiO₂点阵中部分O格点的替位C和碳酸盐形式的间隙C两部分组成。高含量的替位C（6.3at%）使粉体的光学吸收边红移至453nm。而且,粉体在整个可见光区都有显著吸收。C掺杂微一介孔双模结构TiO₂具有显著的可见光催化活性。乙醇对C掺杂微—介孔双模结构TiO₂粉体的比表面积、晶格C含量具有重要的控制作用。4.首次提出并实现了基于模板剂双功能作用、用于制备非金属元素掺杂介孔TiO₂的PBFT法。与常见模板法制备介孔TiO₂工艺中模板剂仅具有单一功能（形成介孔结构）不同,PBFT法中模板剂具有形成介孔结构和提供掺杂源的双功能作用:高温烧结形成孔洞结构的同时,模板剂分解产物为掺C提供了C源、为掺N提供了部分N源。另一部分晶格N则来自于氟钛酸铵中的铵根离子。基于PBFT法制备的C/N/F共掺介孔TiO₂粉体中高含量的晶格C和晶格N使其吸收边红移至481nm,并在整个可见光区都有显著吸收。这赋予了粉体高的可见光催化活性。TiO₂的快速沉积也使F原子（约1.0at%）被掺入到TiO₂晶格中。掺F有助于增强TiO₂可见光催化活性。深入讨论了PBFT法的掺杂机理,并详细研究了烧结工艺对C/N/F共掺介孔TiO₂的孔洞结构、比表面积、掺杂元素含量以及光响应性能的影响。5.研究了掺杂纳米晶TiO₂的磁性。纳米晶TiO₂具有室温铁磁性,掺N和掺V并没有改变纳米晶TiO₂的室温铁磁性本质。纳米晶TiO₂晶胞参数的c/a值越大,其饱和磁化强度越大。基于该实验结果,就氧化物稀磁半导体室温铁磁性的物理起源首次提出了晶格畸变假设:晶格畸变是诱导氧化物稀磁半导体室温铁磁性的重要因数之一。更多还原

【Abstract】 Due to photoinduced properties,Titanium dioxide（TiO₂） has extensive uses in environment-protection and energy-conversion fields,such as photocatalytic degradation of pollutants,self-cleaning coating,hydregon-production through photochemical water splitting,and fabrication of solar energy cells.However,more widespread practical applications have been hampered by its wide band gap,which requires ultraviolet radiation as the optical excitation source.Shifting the optical response region of TiO₂ towards visible spectral range means that the visible spectrum of sun’ rays,even the indoor irradiation,can be used as the optical excitation source of TiO₂.This will extend applications of TiO₂.Therefore,many researches are now focused on the preparation and properties of TiO₂ with visible response.The modification of the electronic structures of TiO₂ by doping is one of important routes for preparing TiO₂ with visible response.In this dissertation,several novel doping methods have been successfully developed for preparing V-doped,V/N co-doped,C-doped,and C/N/F co-doped TiO₂ with visible response.By means of various characterization techniques,the microstructures,ingredients,and the chemical states of doping elements of TiO₂ were analysed.The doping mechanisms were in detail discussed.The optical response properties of doped TiO₂ were evaluated thought optical absorption spectra and the photocatalytic degradation of methylene blue under visible light irradiation（λ＞420 nm）.The main results are as follows:1.Based on the mechnsim of the formation of metal oxide thin films by the LPD method,this method was first used for preparing V-doped TiO₂ thin films.The effects of V ions concentration on the microstructures,the chemical states of V,and properties of V-doped TiO₂ thin films were investigated.The in situ doping mechanism was proposed.V-doped TiO₂ thin films consist of anatase nano-crystal TiO₂ with the grain size of 8～20nm.For low concentration of V ions,V is incorporated into the TiO₂ lattice in the form of V⁴⁺ by in situ doping.The red-shift was observed in the UV-Vis absorption spectra of V-doped TiO₂ thin films.V-doped TiO₂ thin films show visible （Vis-） photocatalytic activities.With the increase of V ions concentration,the content of V⁵⁺ increases,and the grain size becomes bigger.The latter two factors result in the decrease of Vis-photocatalytic activities of V-doped TiO₂ thin films.2.Taking the electronic structures of N-doped TiO₂ and V-doped TiO₂ into account,V/N co-doping was put forward as a route for preparing doped TiO₂ with enhanced Vis-response and photoeatalytic activities.V/N co-doped nanocrystal TiO₂ powders were prepared at room temperature by controlled hydrlysis followed by room-temperature nitridation.The powders are composed of anatase TiO₂ with grain size of 4～5nm.V occupies some Ti⁴⁺ sites in the forms of V⁴⁺ and V³⁺,N exists in TiO₂ lattice in the forms of substitutional N and interstitial N.V facilitates room-temperature nitridation.The high reactivity and lots of defects on the surface and in the interiors of nano-erystal TiO₂ contribute to the incorporation of N into TiO₂ lattice at room temperature.V/N co-doped TiO₂（2.76eV）shows more band-gap narrowing compared with mono-doped TiO₂（V-doped:2.91eV;N-doped:2.92eV）.The enhanced Vis-photoeatalytie activities of V/N co-doped TiO₂ can be ascribed to more band-gap narrowing and higher quantum efficiency.3.The formation of miero-mesoporous structures and C-doping were first achieved at low temperature by the controlled-nitric-acid-oxidation method at one step.This novel method avoids the collapse of porous structures due to the the high-temperature C-doping,a general route for preparing C-doped TiO₂.Moreover,it is simple and easy to sealing up.C-doped micro-mesoporous bimodal TiO₂ prepared by this novel mothod has the pore walls consisting of nanocrystal anatase TiO₂ with the grain size of 3～5nm.The powders has high BET specific surface area up to 246.9 m²/g.C is incorporated into the TiO₂ lattice in the forms of substitutional C and carboneous species（interstitial C）.High content（6.3 at%） of substitutional C causes the optical absorbption edge of 453nm and strong absorption within the whole visible region. C-doped micro-mesoporous bimodal TiO₂ shows high Vis-photocatalytic activities. The content of ethanol influences the specific surface area and the lattice-carbon concentration of C-doped micro-mesoporous bimodal TiO₂ powders.4.A novel method,named PBFT method,based on the bi-function of templates was put forward and successfully used for preparing the nonmetal-doped mesoporous TiO₂.For the methods previously reported for preparing C-doped mesoporous TiO₂, templates work with one function as the supports for the formation of porous structures. Differently,for PBFT method,templates function as both the supports for porous structures and the source for the dopants.The high-temperature calcination simultaneously results in the formation of pores,and C-doping and N-doping from the pyrolysis products of templates.Another N source for N-doping comes from the ammonium ions of（NH₄）₂TiF₆.The optical absorption edge of C/N/F co-doped mesoporous TiO₂ prepared by PBFT method is 481nm,along with strong absorption within the whole vigible region,due to high contents of lattice-carbon and lattice-nitrogen.This provides the powders with high Vis-photoeatalytic activities. About 1.0at%F is incorporated into the TiO₂ lattice due to the fast deposition of TiO₂. F-doping further enhances the Vis-photocatalytic activities of TiO₂.The doping mechanism for PBFT method was discussed.The effects of calcinatin on the porous structures,specicific surface areas,content of dopants,and optical response properties of C/N/F co-doped mesoporous TiO₂ were thoroughly investigated.5.The magnetism of doped nano-crystal TiO₂ was investigated.The nano-crystal TiO₂ powders are room-temperature ferromagnetic.The ferromagnetic essence is not changed after V-doping and N-doping.The correlation between the lattice parameters （c/a） and the saturated magnetization（Ms） was observed as:the bigger c/a,the bigger Ms.The lattice-distortion theory was proposed for understanding the origin of room-temperature ferromagnetism:the lattice distortion is one of the important factors resulting in the room-temperature ferromagnetism of diluted magnetic semiconductor oxide.更多还原