Application of beam irradiation in preparation of visible light responsive TiO2 films

TiO₂ films were prepared by sol-gel method. In order to improve the utilization of light, the technologies of implantation of transition metal ions (V⁺ and Cr⁺) and electron beam irradiation to deposit noble metal particles (Ag and Pt) were used. A red shift was found in the spectrum of modified TiO₂ films. The photocatalytic experiments showed that the photocatalytic ability under visible light irradiation could be improved dramatically by both the implantation of transition metal and the electron beam irradiation. __________ Translated from Chinese Journal of Catalysis, 2007, 28(1): 39–44 [译自: 催化学报]     

Ion engineering techniques for the preparation of the highly effective TiO<Subscript>2</Subscript> photocatalysts operating under visible light irradiation

The successful application of ion engineering techniques for the development of TiO₂ photocatalysts operating under visible and/or solar light irradiations has been summarized in this review article. First, we have physically doped various transition metal ions within a TiO₂ lattice on an atomic level by using an advanced metal ion implantation method. The metal ion implanted TiO₂ could efficiently work as a photocatalyst under visible light irradiation. Some field tests under solar light irradiation clearly revealed that the Cr or V ions implanted TiO₂ samples showed 2–3 times higher photocatalytic reactivity than the un-implanted TiO₂. Second, we have developed the visible light responsive TiO₂ thin film photocatalyst by a single process using an RF-magnetron sputtering (RF-MS) deposition method. The vis-type TiO₂ thin films showed high photocatalytic reactivity for various reactions such as reduction of NOx, degradation of organic compounds, and splitting of H₂O under visible and/or solar light irradiations.     

Preparation of the visible light responsive TiO2 thin film photocatalysts by the RF magnetron sputtering deposition method

TiO₂ thin film photocatalysts which could induce photoreactions under visible light irradiation were successfully developed in a single process by applying an ion engineering technique, i.e., the radio frequency (RF) magnetron sputtering deposition method. The TiO₂ thin films prepared at temperatures greater than 773 K showed the efficient absorption of visible light; on the other hand, the TiO₂ thin films prepared at around 573 K were highly transparent. This clearly means that the optical properties of TiO₂ thin films, which absorb not only UV but also visible light, can be controlled by the preparation temperatures of the RF magnetron sputtering deposition method. These visible light responsive TiO₂ thin films were found to exhibit effective photocatalytic reactivity under visible light irradiation (λ > 450 nm) at 275 K for the reductive decomposition of NO into N₂ and N₂O. From various characterizations, the orderly aligned columnar TiO₂ crystals could be observed only for the visible light responsive TiO₂ thin films. This unique structural factor is expected to modify the electronic properties of a TiO₂ semiconductor, enabling the efficient absorption of visible light.     

Effect of Pt loading on the photocatalytic reactivity of titanium oxide thin films prepared by ion engineering techniques

Platinum-loaded titanium oxide thin-film photocatalysts were prepared by using an ionized cluster beam (ICB) deposition method and a RF magnetron sputtering (RF-MS) deposition method as dry processes. From the results of the photocatalytic oxidation of acetaldehyde with O₂ under UV light irradiation, small amounts of Pt loading (less than 10 nm film thickness) were found to dramatically enhance the photocatalytic reactivity. However, when TiO₂ thin films were loaded with relatively larger amounts of Pt (more than 30 nm as the film thickness), the photocatalytic reactivity became lower than for the pure TiO₂ thin films. Moreover, investigations of the ratio of Pt loaded onto the surface of the thin film catalysts by XPS measurements revealed that the small amounts of Pt loaded exist as very small clusters working to efficiently enhance the charge separation, whereas, large amounts of Pt covers the entire surface of the TiO₂ thin films, resulting in a decrease of the photocatalytic reactivity.     

Characterization and activity of visible-light-driven TiO2 photocatalyst codoped with nitrogen and cerium

Nitrogen and cerium codoped TiO₂ photocatalysts were prepared by a modified sol-gel process with doping precursors of cerium nitrate and urea, and characterized by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray photoelectron spectra (XPS) and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Results indicate that anatase TiO₂ is the dominant crystalline type in as-prepared samples, and CeO₂ crystallites appear as the doping ratio of Ce/Ti reaches to 3.0 at%. The TiO₂ starts to transform from amorphous phase to anatase at 987.1 K during calcination, according to the TG-DSC curves. The XPS show that three major metal ions of Ce³⁺, Ce⁴⁺, Ti⁴⁺ and one minor metal ion of Ti³⁺ coexist on the surface. The codoped TiO₂ exhibits significant absorption within the range of 400-500 nm compared to the non-doped and only nitrogen-doped TiO₂. The enhanced photocatalytic activity of the codoped TiO₂ is demonstrated through degradation of methyl orange under visible light irradiation.     

Effect of HF treatment on the activity of TiO2 thin films for photocatalytic water splitting

The effects of HF treatment on the activity of TiO₂ thin films for the photocatalytic water splitting reaction have been investigated. TiO₂ thin films treated with HF solution (HF-TiO₂) were found to exhibit a remarkable enhancement of the photocatalytic activity for H₂ evolution from a methanol aqueous solution, as well as efficient photoelectrochemical performance under UV light irradiation as compared with the untreated TiO₂. Moreover, Pt-loaded HF-TiO₂ thin films were found to act as efficient and stable photocatalysts for the decomposition of water under UV light irradiation. The mechanistic insights obtained in the present study will be useful in the design of highly efficient photocatalysts for the decomposition of water.     

Preparation and characterization of silver and indium vanadate co-doped TiO2 thin films as visible-light-activated photocatalyst

Novel visible-light-activated photocatalytic Ag/InVO₄-TiO₂ thin films were developed in this paper through a sol-gel method from the TiO₂ sol containing Ag and InVO₄. The photocatalytic activities of Ag/InVO₄-TiO₂ thin films were investigated based on the oxidation decomposition of methyl orange in aqueous solution. The Ag/InVO₄-TiO₂ thin films were characterized by X-Ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy (UV-vis). The results revealed that the Ag/InVO₄-TiO₂ thin films extended the light absorption spectrum toward the visible region; the Ag and InVO₄ co-doped thin films significantly enhanced the methyl orange photodegradation under visible light irradiation. It has been confirmed that the Ag/InVO₄-TiO₂ thin films could be excited by visible light (E < 3.2 eV). The significant enhancement in the Ag/InVO₄-TiO₂ photo activity under visible light irradiation can be ascribed to the simultaneous effects of doped noble metal Ag by acting as electron traps and InVO₄ as narrow band gap sensitizer.     

Enhancement of Photocatalytic Activity of Sodium Bismuth Titanate by Doping with Copper,Silver, and Tin Ions

Perovskite type oxides, sodium bismuth titanate (Na_0.5Bi_0.5TiO₃), and Ag⁺, Cu²⁺, and Sn²⁺ doped Na_0.5Bi_0.5TiO₃ were prepared by pechini and ion exchange methods, respectively. Photocatalytic activities of these catalysts were tested by decomposition of methylene blue (MB) under visible light irradiation. Results showed that the photocatalytic activity of metal ion doped Na_0.5Bi_0.5TiO₃ was higher than undoped Na_0.5Bi_0.5TiO₃. Relatively high photocatalytic performance of Ag⁺‐doped Na_0.5Bi_0.5TiO₃ is mainly ascribed to the efficient separation of electron‐hole (e^–, h⁺) pairs, lower bandgap energy and the creation of active hydroxyl radicals ( ^? OH). Further, the Ag⁺‐doped Na_0.5Bi_0.5TiO₃ catalyst showed good reusability up to four cycles. A possible mechanism for the enhanced photocatalytic performance was proposed. The synthesized photocatalysts were characterized by XRD, SEM, EDS, XPS, FT‐IR, and UV/Vis DRS techniques.     

应用射线束制备可见光响应的TiO2薄膜

 由溶胶-凝胶法制备了TiO2薄膜. 为了改善TiO2对光的利用效率,采用过渡金属离子(V+和Cr+)注入和电子束辐照沉积贵金属纳米颗粒(Ag和Pt)两种射线束技术对TiO2薄膜进行改性. 紫外-可见光谱表明,两种射线束技术改性的TiO2薄膜的吸收光谱都发生了红移,说明这两种方法都是拓展TiO2吸收光谱的有效手段. 通过光催化降解甲基橙实验,比较了两种方法对TiO2可见光光催化能力的拓展情况,结果表明,两种方法均可显著提高TiO2在可见光作用下的光催化活性.     

Design of unique titanium oxide photocatalysts by an advanced metal ion-implantation method and photocatalytic reactions under visible light irradiation

The metal ion-implantation of titanium oxide with various transition metal ions was carried out by applying by high voltage acceleration. The subsequent calcination of the implanted TiO₂ in oxygen at around 723 K resulted in a large shift in the absorption spectra of the TiO₂ toward visible light regions, its extent being dependent on the amount and the kind of metal ions implanted. Such metal ion-implanted titanium oxide catalysts were active in carrying out various photocatalytic reactions such as the decomposition of NO into N₂, O₂ and N₂O at 275 K under irradiation with visible light longer than 450 nm. The application of this advanced, high energy metal ion-implantation method enables the novel design of titanium oxide photocatalysts which can absorb and initiate vital reactions under visible light and will contribute to the development of catalytic systems utilizing solar energy.     

Preparation of N-doped and oxygen-deficient TiO2 microspheres via a novel electron beam-assisted method

Nitrogen-doped and oxygen-deficient TiO₂ microspheres (NT) with large specific surface were prepared by a solvothermal method and following with electron beam (EB) irradiation under various doses (140–500 kGy). XPS results show that under the EB irradiation, nitrogen ions have been doped into the TiO₂ lattice successfully, as well as part of Ti⁴⁺ on the surface of the samples changed to Ti³⁺. Photocatalytic performance was tested by decomposing Rhodamine B in the aqueous phase under visible light irradiation. The prepared materials under the EB irradiation at dose of 140 kGy (NT-140) exhibit the best visible light photocatalytic activity. It is attributed to the large specific surface (138.4 m²/g) and a synergistic effect between substitutional nitrogen dopants and oxygen defects in NT-140. The results obtained may provide a new sight for the application of EB-assisted preparation of nanomaterials.     

Synthesis and characterization of novel InVO<Subscript>4</Subscript>–TiO<Subscript>2</Subscript> thin films using the low temperature sol

The InVO₄ sol was obtained by a mild hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). Novel visible-light activated photocatalytic InVO₄–TiO₂ thin films were synthesized through a sol–gel dipping method from the composite sol, which was obtained by mixing the low temperature InVO₄ sol and TiO₂ sol. The photocatalytic activities of the new InVO₄–TiO₂ thin films under visible light irradiation were investigated by the photocatalytic discoloration of methyl orange aqueous solution. The thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–Vis absorption spectroscopy (UV–Vis). The results revealed that the InVO₄ doped thin films enhanced the methyl orange degradation rate under visible light irradiation, 3.0 wt% InVO₄–TiO₂ thin films reaching 80.1% after irradiated for 15 h.     

Molten Ag2SO4‐based Ion‐Exchange Preparation of Ag0.5La0.5TiO3 for Photocatalytic O2 Evolution

Ag_0.5La_0.5TiO₃ with an ABO₃ perovskite structure was synthesized by a newly developed ion‐exchange method. Molten Ag₂SO₄ instead of traditional molten AgNO₃ was used as Ag⁺ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag⁺ for Na⁺ in Na_0.5La_0.5TiO₃ with a stable ABO₃ perovskite structure at a high ion‐exchange temperature (700 °C). Under full‐arc irradiation, the O₂‐evolution activity of Ag_0.5La_0.5TiO₃ was about 1.6 times that of Na_0.5La_0.5TiO₃ due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag⁺ for Na⁺ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light‐response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag⁺ for Na⁺ induced a lattice distortion of the ABO₃ perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible‐light irradiation, Ag_0.5La_0.5TiO₃ displayed notable O₂ evolution whereas Na_0.5La_0.5TiO₃ showed little O₂ evolution, thus demonstrating that the substitution of Ag⁺ for Na⁺ enabled the use of visible light to evolve O₂ photocatalytically. This work presents an effective route to explore novel Ag‐based photocatalysts.     

Enhanced photoinduced super-hydrophilicity in sol–gel TiO2 thin films with co-doped Sn/Nb

In this work, Sn and Nb co-doped TiO₂ were coated on glazed porcelain substrates via sol–gel dip coating method. Field emission-scanning electron microscopy, transmission electron microscopy, and UV–vis spectrophotometer were used to evaluate thickness and optical properties of the thin films. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy. Water contact angle on the film surfaces was measured by a contact angle analyzer under solar light irradiation. The optical results indicated that Sn/Nb dopant in TiO₂ thin film changed the absorption edge from ultraviolet to visible light and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under solar irradiation. Wettability results indicated that Sn and Nb dopant ions had significant effect on the hydrophilicity property of thin films.     

Zr离子掺杂TiO2可见光催化剂光催化活性的研究

本文采用溶胶-凝胶法制备了Zr离子掺杂TiO₂光催化剂。光催化降解对氯苯酚实验表明,Zr离子掺杂浓度为10%时活性最高,其紫外光、可见光催化活性分别是纯TiO₂的1.5倍和4倍。利用XRD、Raman、XPS、UV-Vis DRS、PL等技术对样品进行了表征,结果表明：Zr离子以取代式掺杂方式进入TiO₂晶格,在TiO₂导带下方形成掺杂能级,增强了可见光响应,促进了光生载流子的分离,此外Zr离子掺杂在催化剂表面引入大量表面缺陷,增加了表面羟基物种,从而使得Zr离子掺杂TiO₂光催化剂的紫外、可见光催化活性显著提高。     

Characterization and photocatalytic activity of Fe- and N-co-deposited TiO2 and first-principles study for electronic structure

Titanium dioxide (TiO₂), co-deposited with Fe and N, is first implanted with Fe by a metal plasma ion implantation (MPII) process and then annealed in N₂ atmosphere at a temperature regime of 400-600 °C. First-principle calculations show that the (Fe, N) co-deposited TiO₂ films produced additional band gap levels at the bottom of the conduction band (CB) and on the top of the valence band (VB). The (Fe, N) co-deposited TiO₂ films were effective in both prohibiting electron-hole recombination and generating additional Fe-O and N-Ti-O impurity levels for the TiO₂ band gap. The (Fe, N) co-deposited TiO₂ has a narrower band gap of 1.97 eV than Fe-implanted TiO₂ (3.14 eV) and N-doped TiO₂ (2.16 eV). A significant reduction of TiO₂ band gap energy from 3.22 to 1.97 eV was achieved, which resulted in the extension of photocatalytic activity of TiO₂ from UV to Vis regime. The photocatalytic activity and removal rate were approximately two-fold higher than that of the Fe-implanted TiO₂ under visible light irradiation.     

100 keV H+ ion irradiation of as‐deposited Al‐doped ZnO thin films: An interest in tailoring surface morphology for sensor applications

We report the influence of 100 keV H⁺ ion beam irradiation on the surface morphology, crystalline structure, and transport properties of as‐deposited Al‐doped ZnO (Al:ZnO) thin films. The films were deposited on silicon (Si) substrate by using DC sputtering technique. The ion irradiation was carried out at various fluences ranging from 1.0 × 10¹² to 3.0 × 10¹⁴ ions/cm². The virgin and ion‐irradiated films were characterized by X‐ray diffraction, Raman spectroscopy, atomic force microscopy, and Hall probe measurements. Using X‐ray diffraction spectra, 5 points Williamson‐Hall plots were drawn to deduce the crystallite site and strain in Al:ZnO films. The analysis of the measurements shows that the films are almost radiation resistant in the structural deformation under chosen irradiation conditions. With beam irradiation, the transport properties of the films are also preserved (do not vary orders of magnitude). However, the surface roughness and the crystallite size, which are crucial parameters of the ZnO film as a gas sensor, are at variation with the ion fluence. As ion fluence increases, the root‐mean‐square surface roughness oscillates and the surface undergoes for smoothening with irradiation at chosen highest fluence. The crystallite size decreases initially, increases for intermediate fluences, and drops almost to the value of the pristine film at highest fluence. In the paper, these interesting experimental results are discussed in correlations with ion‐matter interactions especially energy losses by the ion beam in the material.     

Fe2BiTaO7纳米催化剂的组织结构及光催化性能

用固相反应合成法合成了光催化剂Fe₂BiTaO₇,通过XRD、SEM、TEM、紫外-可见漫反射等表征方法对其组织结构及光催化性能进行了研究.结果表明Fe₂BiTaO₇为立方晶系烧绿石结构,空间群为Fd₃m,禁带宽度为1.72eV.通过比较Fe₂BiTaO₇、P₂₅TiO₂、掺氮TiO₂和Bi₂InTaO₇的可见光光催化降解罗丹明B,发现Fe₂BiTaO₇降解效果及催化活性均高于其它催化剂,并且Fe₂BiTaO₇降解罗丹明B效率是掺氮二氧化钛的1.5倍.Fe₂BiTaO₇降解罗丹明B的曲线符合一级动力学,一级动力学常数为0.02293 min^-1.研究了罗丹明B可能的降解路径和Fe₂BiTaO₇在可见光下降解苯酚的效果.Fe₂BiTaO₇(可见光)光催化剂系统适用于纺织工业废水处理.     

Medium energy,heavy and inert ion irradiation of metallic thin films: studies of surface nano‐structuring and metal burrowing

In context to the ion induced surface nanostructuring of metals and their burrowing in the substrates, we report the influence of Xe and Kr ion‐irradiation on Pt:Si and Ag:Si thin films of ~5‐nm thickness. For the irradiation of thin films, several ion energies (275 and 350 keV of Kr; 450 and 700 keV of Xe) were chosen to maintain a constant ratio of the nuclear energy loss to the electronic energy loss (S_n/S_e) in Pt and Ag films (five in present studies). The ion‐fluence was varied from 1.0 × 10¹⁵ to 1.0 × 10¹⁷ ions/cm². The irradiated films were characterized using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images show ion beam induced systematic surface nano‐structuring of thin films. The surface nano‐structures evolve with the ion fluence. The RBS spectra show fluence dependent burrowing of Pt and Ag in Si upon the irradiation of both ion beams. At highest fluence, the depth of metal burrowing in Si for all irradiation conditions remains almost constant confirming the synergistic effect of energy losses by the ion beams. The RBS analysis also shows quite large sputtering of thin films bombarded with ion beams. The sputtering yield varied from 54% to 62% by irradiating the thin films with Xe and Kr ions of chosen energies at highest ion fluence. In the paper, we present the experimental results and discuss the ion induced surface nano‐structuring of Pt and Ag and their burrowing in Si. Copyright © 2016 John Wiley & Sons, Ltd.     

Fe2BiTaO7纳米催化剂的组织结构及光催化性能

用固相反应合成法合成了光催化剂Fe2BiTaO7,通过XRD、SEM、TEM、紫外-可见漫反射等表征方法对其组织结构及光催化性能进行了研究。结果表明Fe2BiTaO7为立方晶系烧绿石结构,空间群为Fd3m,禁带宽度为1.72 e V。通过比较Fe2BiTaO7、P25TiO2、掺氮Ti O2和Bi2In Ta O7的可见光光催化降解罗丹明B,发现Fe2BiTaO7降解效果及催化活性均高于其它催化剂,并且Fe2BiTaO7降解罗丹明B效率是掺氮二氧化钛的1.5倍。Fe2BiTaO7降解罗丹明B的曲线符合一级动力学,一级动力学常数为0.022 93 min-1。研究了罗丹明B可能的降解路径和Fe2BiTaO7在可见光下降解苯酚的效果。Fe2BiTaO7(可见光)光催化剂系统适用于纺织工业废水处理。