Characterizations of lanthanum trivalent ions/TiO2 nanopowders catalysis prepared by plasma spray

Lanthanum trivalent ions (La(3+)) doped titanium dioxide (TiO(2)) nanopowders in the range of 20-60 nm were prepared successfully by plasma spray in the self-developed plasma spray equipment. The photocatalytic activity of samples at different doping concentrations in photocatalytic degradation of methyl orange was discussed. The nanopowders prepared were characterized by transmission electron microscopy, X-ray diffraction, ultraviolet-visible spectra, photoluminescence (PL) and X-ray photoelectron spectroscopy. The results show that La(3+) doping increased the photocatalytic activity of TiO(2) greatly, the optimal doping concentration was 0.5 at%. The La(3+) doping decreases the particle size and the distribution of particle sizes becomes more uniform. The doped powders were the mixture of anatase and rutile phase. The contents of anatase phase decreased firstly and then increased with an increase in the contents of La(3+). The intrinsic absorption band of La(3+) doped TiO(2) nanopowders appears red shift from that of pure TiO(2) nanopowders. The intensity of PL spectra increases and then decreases with increasing the content of La(3+). The PL spectral intensity reaches its peak when the ratio of La(3+)/TiO(2) is 0.2 at%. There are O, Ti, C and La elements in the prepared La(3+) doped TiO(2) nanopowders, La element still exists in trivalent and Ti element always exists in tetravalent.     

Phase structure and luminescence properties of Eu3+-doped TiO2 nanocrystals synthesized by Ar/O2 radio frequency thermal plasma oxidation of liquid precursor mists

Eu3+-doped TiO2 luminescent nanocrystals have been synthesized in this work via Ar/O2 thermal plasma oxidizing mists of liquid precursors containing titanium tetra-n-butoxide and europium(III) nitrate, with varied O2 input in the plasma sheath (10-90 L/min) and Eu3+ addition in the precursor solution (Eu/(Ti + Eu) = 0-5 atom%). The resultant nanopowders are mixtures of the anatase (30-36 nm) and rutile (64-83 nm) polymorphs in the studied range, but the rutile fraction increases steadily at a higher Eu3+ addition, as revealed by X-ray diffraction (XRD) and Raman spectroscopy, because of the creation of oxygen vacancies in the TiO2 gas clusters by substitutional Eu3+ doping. The amount of Eu3+ that can be doped into a TiO2 lattice was limited up to 0.5 atom%, above which Eu2Ti2O7 pyrochlore was formed in the final products. High resolution transmission electron microscopy (HRTEM) observation indicates that the particles are dense and have sizes ranging from several nanometers up to 180 nm. Efficient nonradiative energy transfer from the TiO2 host to Eu3+ ions, which was seldom reported in the wet-chemically derived nanoparticles or thin films of the current system, was confirmed by combined studies of excitation, UV-vis (ultraviolet-visible), and PL (photoluminescence) spectroscopy. As a consequence of this, bright red emissions were observed from the plasma-generated nanopowders either by exciting the TiO2 host with UV light shorter than 405 nm or by directly exciting Eu3+ at a wavelength beyond the absorption edge (405 nm) of TiO2.     

Influence of Sn4+ on the structural and electronic properties of Ti1-xSnxO2 nanoparticles used as photocatalysts

Ti(1-x)Sn(x)O(2) nanocrystalline materials employed for photocatalysis have been characterised by means of X-ray diffraction, Raman, X-ray absorption (XANES and EXAFS) and UV-Vis spectroscopy and high resolution transmission electron microscopy. Single-phase samples with anatase or rutile type structures and similar tin contents permitted a separate study of the effect of Sn(4+) ions on these crystalline forms, whereas materials composed of anatase and rutile mixtures were used to investigate the distribution of the dopant cations when both phases coexist. The results obtained from the single-phase doped TiO(2) samples indicate that the presence of tin causes a different effect when doping anatase or rutile in both their structural and electronic properties. While a random substitution of Sn(4+) for Ti(4+) seems plausible for the rutile phase, some kind of gradient in Sn(4+) concentration is possible in anatase. On the other hand, when anatase and rutile coexist, effects of doping are visible in both phases. Regarding chemical composition, a homogeneous distribution of tin was found in both calcined and hydrothermal multiphase samples. Photocatalytic experiments show that both tin-doping and coexistence of different phases have a beneficial effect on the activity of the catalysts.     

掺锌的TiO2纳米粉的结构相变及发光性质

采用溶胶-凝胶法制备了掺锌的TiO₂纳米粉末,并用XRD、TEM、TG和DSC等技术考察了掺入的锌对TiO₂的锐钛矿→金红石结构相变的影响.研究结果表明,锌的掺入可促进TiO₂的结构相变,使相变温度显著降低.纳米态TiO₂存在室温光致发光现象,在TiO₂的纳米粉中掺入适量的锌,可显著增强体系的发光强度.     

Effect of TiO2 crystalline phase composition on the physicochemical and catalytic properties of Pd/TiO(2) in selective acetylene hydrogenation

Pd/TiO(2) catalysts have been prepared using TiO(2) supports consisting of various rutile/anatase crystalline phase compositions. Increasing percentages of rutile phase in the TiO(2) resulted in a decrease in Brunauer-Emmett-Teller surface areas, fewer Ti(3+) sites, and lower Pd dispersion. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti(3+) in the TiO(2) samples. When TiO(2) samples with 0-44% rutile were used, high ethylene selectivities (58-93%) were obtained whereas ethylene losses occurred for those supported on TiO(2) with 85% or 100% rutile phase. X-ray photoelectron spectroscopy and electron spin resonance experiments revealed that a significant amount of Ti(3+) existed in the TiO(2) samples composed of 0-44% rutile. The presence of Ti(3+) in contact with Pd can probably lower the adsorption strength of ethylene resulting in an ethylene gain. Among the five catalysts used in this study, the results for Pd/TiO(2)-R44 suggest an optimum anatase/rutile composition of the TiO(2) used to obtain high selectivity of ethylene in selective acetylene hydrogenation.     

Crystallization kinetics study of In-doped and (In-Cr) co-doped TiO2 nanopowders using in-situ high-temperature synchrotron radiation diffraction

The influence of TiO₂ nanopowder doping with 4 wt% indium and 2 wt% each of indium and chromium on phase transformation was studied. Samples were heated from ambient temperature to 950 °C in sealed quartz capillaries, and in-situ synchrotron radiation diffraction measurements were obtained. Capillary sealing yielded an increase in capillary gas pressure to 0.42 MPa at 950 °C in proportion to absolute temperature by Gay-Lussac’s Law. The initial synthesized samples were amorphous, and crystalline anatase appeared at 200 °C. Crystalline rutile appeared at 850 °C for the nanomaterials that were doped with In and In and Cr. A change in sealed-capillary oxygen partial pressure yielded a decrease and an increase in crystallization temperature, respectively, for the amorphous-to-anatase and anatase-to-rutile transformations. Crystalline titania (anatase and rutile) formed from the amorphous titania by 800 °C and 900 °C, for materials doped with In and In-Cr, respectively. The anatase concentration that was dominant in the In-doped materials up to 950 °C and the higher rutile concentration for the In-Cr doped materials from 900 to 950 °C results from the defect structure that was induced by doping. Cr-ions in the Ti sub-lattice retarded the transformation of anatase to rutile when compared with the retarding effect of mixed In/Cr ions. The transformation results because of the relatively smaller radius of Cr-ions when compared with the In-ions. The differences in phase-transformation kinetics for In, In-Cr and for undoped nanopowders in the literature agree with the calculated transformation activation energies.     

The role of crystal phase in determining photocatalytic activity of nitrogen doped TiO2

Two series of nitrogen doped TiO(2) samples with different ratios of anatase to rutile phases were prepared by milling the mixture of P25 TiO(2) and C(6)H(12)N(4) in air and gaseous NH(3) atmosphere, respectively. Compared to air, NH(3) atmosphere plays an important role in delaying the crystallite transformation from anatase to rutile in the mechanochemical reaction of TiO(2) and C(6)H(12)N(4). In contrast to the previously reported results for pure TiO(2), it is found that nitrogen doped TiO(2) with higher content of rutile phase demonstrates higher photocatalytic activity in photodegrading pollutant Rhodamine B under both UV light and visible light irradiation (lambda>420 nm), and the amount of the surface-adsorbed water and hydroxyl groups on nitrogen doped TiO(2) have little correlations with their crystallite phases (anatase or rutile) and photocatalytic activity. The more abundant surface states characterized by photoluminescence spectroscopy together with the lowered valence band maximum of rutile TiO(2) by nitrogen doping are considered as the key factors for the higher activity of nitrogen doped TiO(2) with higher content of rutile phase.     

TiO2-yNx纳米光催化剂的制备及其可见光响应机理

利用溶胶-凝胶技术,以尿素为氮源,采用原位掺杂方式制备了TiO2-yNx纳米粉体;以亚甲基蓝(MB)溶液在可见光下的光催化降解评价其可见光催化活性;考察了体系初始pH值、N的掺杂量和焙烧温度对样品可见光催化活性的影响。 结合XRD、XPS、ESR和DRS测试技术,研究了N掺杂纳米TiO2的可见光响应机理。 研究结果表明,TiO2-yNx纳米粉体的优化制备工艺条件为：体系初始pH=0.52,掺杂比n(N)∶n(Ti)=1∶6,焙烧温度为440 ℃。 此条件下制备的样品N含量为0.77%,为单一的锐钛矿相,平均粒径为19.0 nm,具有良好的可见光催化活性。 N掺杂导致TiO2纳米粉体的表面羟基含量增加,形成了大量束缚单电子的氧空位;N取代晶格O形成了N-Ti-O和O-N-Ti键合结构。 N掺杂导致TiO2纳米粒子的吸收带边红移,对可见光的吸收能力明显增强,这表明N掺杂改变TiO2电子结构,使带隙窄化,降低光响应阈值。 N掺杂TiO2纳米粒子的可见光响应归因于N取代掺杂形成的掺杂能级与氧空位形成的缺陷能级共同作用所致。     

Doped titanium dioxide nanocrystalline powders with high photocatalytic activity

Doped titanium dioxide nanopowders (M:TiO₂; M=Fe, Co, Nb, Sb) with anatase structure were successfully synthesized through an hydrothermal route preceded by a precipitation doping step. Structural and morphological characterizations were performed by powder XRD and TEM. Thermodynamic stability studies allowed to conclude that the anatase structure is highly stable for all doped TiO₂ prepared compounds. The photocatalytic efficiency of the synthesized nanopowders was tested and the results showed an appreciable enhancement in the photoactivity of the Sb:TiO₂ and Nb:TiO₂, whereas no photocatalytic activity was detected for the Fe:TiO₂ and Co:TiO₂ nanopowders. These results were correlated to the doping ions oxidation states, determined by Mössbauer spectroscopy and magnetization data.     

碘掺杂对纳米TiO2催化剂光催化活性的影响

用溶胶-凝胶法制得了碘掺杂纳米TiO2催化剂, 考察了诸因素对相结构的影响, 这对深入揭示I-TiO2光催化降解有机物的本质具有重要意义.     

Sol-Gel法制备La~(3+)改性的TiO_2纳米粉体

在常用的半导体光催化材料中,研究较多的有TiO2、ZnO、CdS等[1-3],其中TiO2因性能稳定、催化活性高、无毒、不产生二次污染和成本低廉等优点,在光催化降解污染物领域显示出优越的应用前景[3-6].     

树叶为模版制备网状TiO2和Fex/TiO2及光催化活性研究

以梧桐树叶为模板制备了具有网状结构的TiO2和Fex/TiO2光催化材料.通过扫描电镜(SEM)、X-射线衍射(XRD)、X-射线光电子能谱(XPS)、荧光发射光谱(PL)、紫外-可见吸收光谱(UV-Vis)等对这两类光催化材料的结构和物理性能进行了表征.结果表明,以树叶为模板制得的Fe0.005/TiO2呈网状结构.在600～800℃范围内,随煅烧温度的升高,网状TiO2和Fe0.005/TiO2中锐钛型TiO2的含量减少,Fe3+的掺杂能促进锐钛型向金红石型的转变.与Degussa P25相比,网状TiO2和Fex/TiO2的荧光光谱强度明显减弱,光生电子-空穴对的复合情况得到改善;吸收光谱范围明显红移,禁带宽度有不同程度的缩小.孔雀石绿的光催化降解实验表明,网状TiO2和Fex/TiO2具有比Degussa P25更强的催化活性.光催化活性的稳定性研究表明,网状Fe0.005/TiO2具有良好的稳定性,能多次重复使用.     

新型N-TiO2的固相法制备及其光催化性能

以纳米管钛酸为前驱体,以NH4HCO3为N源,先机械研磨使二者混合均匀,再在Ar保护下,于不同温度焙烧4h制得N掺杂TiO2 (N-TiO2),并采用X射线粉末衍射、X射线光电子能谱、紫外-可见吸收光谱、透射电镜及N2吸附-脱附对样品进行了表征.结果显示,N以间隙掺杂方式进入TiO2晶格内.在热处理过程中,生成中间体(...     

Y掺杂纳米TiO2的合成及晶型转变过程

溶胶-凝胶;锐钛型;金红石型;Y掺杂纳米TiO2的合成及晶型转变过程     

Synthesis, surface morphology, and photoluminescence properties of anatase iron-doped titanium dioxide nano-crystalline films

Iron (Fe)-doped (0 to 4%) TiO(2) nano-crystalline (nc) films with the grain size of about 25 nm have been deposited on n-type Si (100) substrates by a facile nonhydrolytic sol-gel processing. X-ray diffraction measurements prove that the films are polycrystalline and present the pure anatase phase. X-ray photoelectron spectroscopy spectra indicate that the chemical valent state of Fe element is +3 and the Fe(3+) ions replace the Ti(4+) sites. The Fe dopant effects on the surface morphology, microstructure, and dielectric functions of the nc-Fe/TiO(2) films have been studied by atomic force microscope, ultraviolet Raman scattering and spectroscopic ellipsometry. With increasing Fe composition, the intensity of Raman-active mode B(1g) increases, while that of the A(1g) phonon mode decreases. The dielectric functions have been uniquely extracted by fitting ellipsometric spectra with the Adachi's dielectric function model and a four-phase layered model. It is found that the real part of dielectric functions in the transparent region and the optical band gap slightly decrease with the Fe composition due to the introduction of acceptor level Fe t(2g). Finally, the composition and temperature dependence of the surface and lattice defects in the Fe/TiO(2) films have been investigated by photoluminescence spectra in detail. At room temperature, the emission intensities decrease with increasing Fe compositions since the Fe incorporation could prolong the radiative lifetime and/or shorten the non-radiative lifetime. By analyzing the low temperature photoluminescence spectra, the intensities and positions of five emission peaks and shoulder structure can be unambiguously assigned. The phenomena could be reasonably explained by the physical mechanisms such as oxygen vacancies, localized excitons, self-trapped excitons, and indirect transitions, which are strongly related to the electronic band structure perturbed by the Fe doping.     

N doping of TiO2(110): photoemission and density-functional studies

The electronic properties of N-doped rutile TiO2(110) have been investigated using synchrotron-based photoemission and density-functional calculations. The doping via N2+ ion bombardment leads to the implantation of N atoms (approximately 5% saturation concentration) that coexist with O vacancies. Ti 2p core level spectra show the formation of Ti3+ and a second partially reduced Ti species with oxidation states between +4 and +3. The valence region of the TiO(2-x)N(y)(110) systems exhibits a broad peak for Ti3+ near the Fermi level and N-induced features above the O 2p valence band that shift the edge up by approximately 0.5 eV. The magnitude of this shift is consistent with the "redshift" observed in the ultraviolet spectrum of N-doped TiO2. The experimental and theoretical results show the existence of attractive interactions between the dopant and O vacancies. First, the presence of N embedded in the surface layer reduces the formation energy of O vacancies. Second, the existence of O vacancies stabilizes the N impurities with respect to N2(g) formation. When oxygen vacancies and N impurities are together there is an electron transfer from the higher energy 3d band of Ti3+ to the lower energy 2p band of the N(2-) impurities.     

Theoretical study of the structure and optical properties of carbon-doped rutile and anatase titanium oxides

The structure and optical properties of carbon-doped titanium oxides, TiO2, in the rutile and anatase forms have been investigated theoretically from first principles. Two possible doping sites were studied, carbon at an oxygen site (anion doping) and carbon at a titanium site (cation doping). The calculated structures suggest that cation-doped carbon atoms form a carbonate-type structure, whereas anion-doped carbon atoms do not invoke any significant structural change. A density-of-states analysis revealed three in-gap impurity states for anion doping. The optical properties of anion-doped cells qualitatively agree with the experimentally reported visible-light absorbance values. We ascribe part of the absorption to transitions from the valence band to one of the impurity states. These transitions should be able to promote photocatalytic reactions, because electron holes in the valence band are considered to be crucial for this process. Neither in-gap impurity states nor visible-light absorbance were observed in the case of cation doping. The effect of oxygen vacancies was also investigated. Introduction of oxygen vacancies into anion-doped TiO2 populates the impurity states and thus suppresses photocatalysis. The interaction of a doped carbon atom with an oxygen vacancy at a finite spatial separation was also carried out. The possibility of either a carbon-oxygen vacancy pair or higher carbon-oxygen vacancy complex existing is discussed.     

氧缺位型TiO2的制备、表征及其光催化析氧活性

采用69 ℃饱和水蒸气和H2混合气, 于927 ℃下处理金红石型TiO2, 得到不同氧缺位的光催化剂, 并用X射线衍射(XRD)、比表面(BET)、电子顺磁共振(EPR)、紫外-可见漫反射(DRS)、光电子能谱(XPS)对其进行了表征. 考察了热处理时间对氧缺位型TiO2光催化分解水析氧活性的影响. 结果表明, 适量的氧缺位能显著提高金红石型TiO2光催化分解水的析氧活性, 其最大析氧速率达222 μmol·L-1·h-1.     

Electronic and Structural Properties of Highly Aluminum Ion Doped TiO2 Nanoparticles: A Combined Experimental and Theoretical Study

This study presents the experimental and theoretical study of highly internally Al‐doped TiO₂ nanoparticles. Two synthesis methods were used and detailed characterization was performed. There were differences in the doping and the crystallinity, but the nanoparticles synthesized with the different methods share common features. Anatase to rutile transformation occurred at higher temperatures with Al doping. X‐ray photoelectron spectroscopy showed the generation of oxygen vacancies, which is an interesting feature in photocatalysis. In turn, the band‐gap energy and the valence band did not change appreciably. Periodic density functional calculations were performed to model the experimentally doped structures, the formation of the oxygen vacancies, and the band gap. Calculation of the density of states confirmed the experimental band‐gap energies. The theoretical results confirmed the presence of Ti⁴⁺ and Al³⁺. The charge density study and electron localization function analysis indicated that the inclusion of Al in the anatase structure resulted in a strengthening of the Ti?O bonds around the vacancy.     

Effects of surface oxygen vacancies on photophysical and photochemical processes of Zn-doped TiO2 nanoparticles and their relationships

In this paper, TiO(2) nanoparticles doped with different amounts of Zn were prepared by a sol-gel method and were mainly characterized by means of X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and surface photovoltage spectrum (SPS). The effects of surface oxygen vacancies (SOVs) of Zn-doped TiO(2) nanoparticles on photophysical and photocatalytic processes were investigated along with their inherent relationships. The results show that the SOVs easily bind photoinduced electrons to further give rise to PL signals. The SOVs can result in an interesting sub-band SPS response near the band edge in the TiO(2) sample consisting of much anatase and little rutile, except for an obvious band-to-band SPS response. Moreover, the intensities of PL and SPS signals of TiO(2), as well as the photocatalytic activity for degrading phenol solution, can be enhanced by doping an appropriate amount of Zn. These improvements are mainly attributed to the increase in the SOV amount. It can be suggested that the SOVs should play an important role during the processes of PL, surface photovoltage, and photocatalytic reactions, and, for the as-prepared TiO(2) samples doped with different amounts of Zn by thermal treatment at 550 degrees C, the larger the SOV amount, the stronger the PL and SPS signal, and the higher the photocatalytic activity.