Improvement of sonocatalytic activity of TiO2 by using Yb,N and F-doped Er3+:Y3Al5O12 for degradation of organic dyes

In this study, several up-conversion luminescence agents (Er³⁺:Y₃Al₅O₁₂, Er³⁺:Yb_0.2Y_2.79Al₅O₁₂, Er³⁺:Yb_0.2Y_2.79Al₅N_0.01O_11.99, Er³⁺:Yb_0.2Y_2.79Al₅F_0.01O_11.99 and Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98) were synthesized using sol–gel method. And then, the corresponding sonocatalyst (Er³⁺:Y₃Al₅O₁₂/TiO₂, Er³⁺:Yb_0.2Y_2.79Al₅O₁₂/TiO₂, Er³⁺:Yb_0.2Y_2.79Al₅N_0.01O_11.99/TiO₂, Er³⁺:Yb_0.2Y_2.79Al₅F_0.01O_11.99/TiO₂ and Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98/TiO₂ coated composites) were prepared by sol–gel coating process. The synthesized up-conversion luminescence agents and their coated composites were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). And that, the sonocatalytic activities were detected through the degradation of Azo Fuchsine (AF) dye in aqueous solution by UV–vis spectroscopy. Some key influences such as heat-treated temperature and heat-treated time on the sonocatalytic activity of Er³⁺:Yb_aY_2.99−aN_xF_yAl₅O_12−x−y/TiO₂ coated composite, as well as ultrasonic irradiation time and initial dye concentration on the sonocatalytic degradation were studied. The results showed that the doping of Yb, N and F into Er³⁺:Y₃Al₅O₁₂/TiO₂ significantly enhanced the sonocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂ coated composite in the degradation of organic dyes. Particularly, Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98/TiO₂ coated composites with 3:7 M ratio heat-treated at 550 °C for 60 min showed the highest sonocatalytic activity. At last, the experiments also indicated that the Er³⁺:Yb_0.2Y_2.79Al₅N_0.01F_0.01O_11.98/TiO₂ coated composites has a good sonocatalytic activity to degrade other organic dyes under ultrasonic irradiation.     

Synergistic effects of C-Cr codoping in TiO2 and enhanced sonocatalytic activity under ultrasonic irradiation

C and Cr co-doped TiO₂ (C-Cr-TiO₂) sonocatalyst were synthesized by doping TiO₂ with glucose and CrCl₃ in a sol-gel method. The samples were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and X-ray photoelectron emission spectroscopy (XPS). C and Cr were detected by XPS analysis. The influence of dopants on the properties and sonocatalytic activity of TiO₂ was studied. The sonodegradation products of methylene blue were analyzed by UV-vis absorption spectroscopy. The presence of C-Cr-TiO₂ catalysts substantially enhanced the sonocatalytic degradation of MB in aqueous suspensions. The possible sonocatalytic mechanisms were also discussed.     

Sonodegradation and photodegradation of methyl orange by InVO4/TiO2 nanojunction composites under ultrasonic and visible light irradiation

The InVO₄/TiO₂ nanojunction composites with different weight ratio of 1:10, 1:25, 1:50 and 1:100 were successfully constructed using an ion impregnate method, followed by calcining temperature 400 °C for 2 h in Ar. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were evaluated through the degradation of methyl orange (MO) in aqueous solution under ultrasonic and visible light irradiation, respectively. The experimental results determined that the (1:50) InVO₄/TiO₂ nanojunction composite has exhibited the highest sonocatalytic activity. It can be ascribed to vectorial charge transfer at the co-excited InVO₄/TiO₂ interface under ultrasonic irradiation, results in the complete separation of electrons and holes. Interestingly, the (1:25) InVO₄/TiO₂ nanojunction composite displayed superior photocatalytic activity for MO degradation under visible light, indicating that InVO₄ as a narrow band gap sensitizer can expand photocatalytic activity of TiO₂ to visible region, and the charge transfer can be formed from high energy level of InVO₄ conduction band to the low energy level of TiO₂ conduction band in a present of excited InVO₄ alone under visible light irradiation. The sono- and photo-catalytic activities of the InVO₄/TiO₂ nanojunction composites were found to be dependent significantly on different InVO₄ contents, which can be explained by the influence of charge transfer on the basis of the work functions of different catalysis mechanism.     

Theoretical study of the permeation of water through TiO2 nanotubes using molecular dynamics simulation

In this study, the theoretical structures of armchair (6, 6) and zigzag (12, 0) TiO₂ nanotubes (TiNTs) were constructed by rolling the (101) layer of an anatase TiO₂ crystal. The (101) layer was made using Materials Studio (MS) by cutting the cleave plane (101) of the anatase TiO₂ crystal. Based on these structures, the basic properties of TiO₂ nanotubes were investigated using MS. Molecular dynamics simulations were performed using the software NAMD to investigate the status and permeation of water through the TiO₂ nanotubes. Structure analysis shows that both the inner and outer walls of the structures were terminated with oxygen atoms. The thicknesses of single tube walls are smaller than that of a perfect triple layer (2.20?Å) in bulk anatase TiO₂. With regard to the bulk Ti–O bond length, the Ti–O bonds in the outer layer are elongated, and are shortened in the inner layer. Molecular dynamics simulation shows that the water molecules in the nanotubes move back and forth, as in one-dimensional Brownian motion. Moreover, the penetration properties of TiNTs are associated with their radii, with the TiNT with larger radii having better penetration properties. Thus, when used in drug delivery or filtration systems, armchair TiNT has a better effect than zigzag TiNT.     

The enhanced photocatalytic activity of CdS/TiO2 nanocomposites by controlling CdS dispersion on TiO2 nanotubes

CdS/TiO₂ nanocomposites were prepared via a simple wet chemical method, and characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their ability to degrade Acid Rhodamine B was investigated under visible light irradiation. The results indicate that CdS/TiO₂ nanocomposite with a mass ratio of 4:1(TiO₂:CdS) showed high photocatalytic activity and the CdS loaded on TiO₂ nanotube surface exhibited a hexagonal phase. The dispersion of CdS on TiO₂ nanotube surface had an important effect on the degradation efficiency of pollutant, which provides a strategy for practical industry application.     

Fabrication,characterization and biocompatibility of TiO2 nanotubes via anodization of Ti6Al7Nb

Ti6Al7Nb has been used as an implant material because of its good corrosion resistance and high mechanical properties. However, the presence of aluminium (Al), which may lead to ostemalacia, anaemia and nervous system disorders, limited its wide clinical use. In this study, a titanium oxide (TiO₂) nanoporous layer was fabricated on a Ti6Al7Nb alloy using an electrochemical anodic oxidation method. The structure of the TiO₂ nanoporous layer was examined by scanning electron microscopy. The chemical compositions of the samples were analysed by X-ray photoelectron spectroscopy (XPS). Biocompatibility was evaluated by culturing rat osteoblast cells. The result showed that TiO₂ nanoporous layers comprise a mixed oxide containing TiO₂ and a small amount of nobium oxides (Nb₂O₅) and almost no elemental aluminium. The outer layer of the TiO₂ nanoporous layer comprises highly ordered nanotubes and the inner layer forms disordered nanopores. The TiO₂ nanoporous layer could support the adhesion, proliferation, differentiation and gene expression of osteoblast cells. Therefore, a TiO₂ nanoporous layer could enhance the biocompatibility of Ti6Al7Nb alloy and is as a promising candidate for Ti6Al7Nb alloy implants.     

Effect of structure on the photocatalytic activity of Pt-doped TiO2 nanotubes

Highly ordered TiO₂ nanotubes with different tube length were fabricated by anodization using C₂H₂O₄·2H₂O containing 0.5 wt.% NH₄F (electrolyte A) and anhydrous dimethyl sulfoxide containing 1% HF (electrolyte B), respectively. Then cathodic reduction method was used to dope Pt in TiO₂ nanotubes in chloroplatinic acid. The results indicated that cathodic reduction could efficiently platinize TiO₂ nanotubes. Pt-doped TiO₂ nanotubes with the longer length had the higher photocatalytic activity for degrading methyl orange under UV and visible irradiation. The longer tube length has a positive effect on the photocatalytic activity of Pt-doped TiO₂ nanotubes. Besides, as the content of anatase further decreases, the photocatalytic activity drops gradually due to the reduction reaction in the surface area.     

Structural transformation study of TiO2 nanoparticles annealing at different temperatures and the photodegradation process of eosin-Y

Hydrothermal method was used to prepare TiO₂ nanoparticles with annealing temperature at 500 °C–700 °C. The mixture of anatase-rutile phase was investigated by powerful tool of X-ray diffraction (XRD). The structural parameters of anatase and rutile mixture phaseTiO₂ nanoparticles were calculated from the Rietveld refinement. The transformation rate of rutile was increased linearly with an annealing temperature of 500 °C–700 °C. The spherical morphology of the anatase and rutile mixed phase were obtained by scanning electron microscope and transmission electron microscope. The spherical particle of the anatase and rutile TiO₂ shows with great aggregation with different size and within the range of few tens nm. The EDAX study revealed the presence of titanium and oxygen. The best photocatalytic activity was identified as the 87.04% of anatase and 12.96% of rutile mixer phase of TiO₂. Various factors could be involved for a better photocatalytic activity.     

Sonocatalytic degradation of Rhodamine B in the presence of C60 and CdS coupled TiO2 particles

CdS-TiO₂ and CdS-C₆₀/TiO₂ were prepared using C₆₀, cadmium acetate dehydrate [(CH₃COO)₂Cd·2H₂O], sodium sulfide (Na₂S·5H₂O) and titanium (IV) n-butoxide by a sol-gel method. The prepared sonocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and transmission electron microscopy (TEM). A rhodamine B (RhB) solution under ultrasonic irradiation was used to determine the catalytic activity. Excellent catalytic degradation of an RhB solution was observed using the CdS-C₆₀/TiO₂ composites under ultrasonic irradiation. C₆₀ coupled CdS-TiO₂ can enhance the Brunauer-Emmett-Teller (BET) surface area and increase the decolorization rate for rhodamine B solution. The results also shows that increase the content of CdS can enhance the catalytic activity.     

Mechanically induced changes in amylose structure and effect on thermal behavior in the presence of TiO2 nanoparticles

Thermal behavior of amylose/TiO₂ films under ultrasonic irradiation was investigated, and the final product of each process was applied to prepare amylose/TiO₂ nanocomposite films. The effects of different degradation techniques on thermal behavior, crystallinity, and molecular weight distribution of amylose were surveyed. The evaluations of structural changes and thermal behaviors were performed by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetry analysis, FT-IR spectroscopy, and scanning electron microscopy. The XRD results clarified that the crystalline shape of amylose molecules formed is an A-type crystal due to the sonophotocatalytic processing, while the FT-IR spectra does not approve any chemical change in amylose structure. The DSC data submitted a broad endothermic peak for amylose. In the case of high loading of nanoparticles, the endothermic analysis results and diffraction peaks for the sonophotocatalytic process were not significant. This indicates that the length of amylose chains through the sonophotocatalytic degradation became smaller. An increase at the loading of TiO₂ improved the hydrophilic properties of amylose/TiO₂ films, which leads to the modification of water absorption behavior. Mechanical properties of amylose/TiO₂ films were affected by the uniform dispersion of TiO₂ in the polymer matrix.     

Synthesis and photocatalytic oxidation of different organic dyes by using Mn2O3/TiO2 solid solution and visible light

Mn₂O₃/TiO₂ solid solution was prepared from two different oxides, manganese oxide (from KMnO₄ and ethanol) and TiO₂, these samples were characterized by BET, XRD, EDAX, SEM, FT-IR, ESR, XPS and UV–vis absorption spectroscopy. Photocatalytic activities of Mn₂O₃/TiO₂ powder was investigated by photooxidation of different dyes like Rhodamine B, thymol blue, methyl orange and Bromocresol green under visible light (300-W Xe lamp; λ > 420 nm). The results show that the alloy of TiO₂ with 1 mol% of Mn₂O₃ (MNT1) exhibit photocatalytic activity 3–5 times higher than that of P25 TiO₂ for oxidation of various dyes (RB, TB, MO and BG). The average particle size and crystallite size of MNT1 were found to be 100 nm and 12 nm measured from SEM and XRD, respectively. The EPR spectra of the Mn₂O₃/TiO₂ samples is a sharp five-line Mn(III) component centered on g_eff = 1.99.     

Application of ultrasonic wave to clean the surface of the TiO2 nanotubes prepared by the electrochemical anodization

In this study, the TiO₂ nanotubes were fabricated by electrochemical anodization in a NH₄F/Na₂SO₄/PEG400/H₂O electrolyte system. Ultrasonic wave (80 W, 40 kHz) was used to clean the surface of TiO₂ nanotube arrays in the medium of water after the completion of the anodization. Surface morphology (FESEM) and X-ray diffraction spectrum of the nanotubes treated by sonication at 0 min, 9 min, 40 min and 60 min were compared. The experimental results showed that the precipitate on the surface of the nanotube arrays could be removed by the ultrasonic wave. The treating time had an influence on the precipitate removal and 9 min (corresponding to 12 Wh) is the suitable time for surface cleaning of the TiO₂ nanotubes on this experimental condition.     

First-principles study of ferromagnetism in N doped TiO2 and TiO

N doped TiO is nonmagnetic, in which spin-split impurity states are not induced near the Fermi energy (E_F) by N dopant. N doped TiO₂ along with transition-metal (TM) doped TiO is magnetic, in which spin-split impurity states are induced across E_F. The magnetic moment is determined by the 3d4s electron configurations and the valence states of TM-dopant ions when they substitute Ti. Hence, the origin of ferromagnetism of N doped TiO₂ and TiO is not closely related to the width of the band gaps of host oxides, but would be crucially related to that if the dopant can induce spin-split impurity states near E_F.     

Fabrication and characterization of ZnO-coated TiO2 nanotube arrays

In this study, we prepared highly ordered TiO₂ nanotube arrays on Ti through an anodizing process. Then, utilizing its proven antibacterial properties, we coated our TiO₂ nanotubes (TiO₂-NTs) with ZnO using the sol–gel method. We characterized the morphology, structure, and composition of the ZnO-coated TiO₂ nanotubes (ZnO-TNTs) using field-emission scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, respectively. We investigated surface topography and roughness of the coatings by atomic force microscopy operated in the tapping mode. Our results revealed impurity-free, anatase-phase TiO₂ nanotubes that are uniformly coated with a ZnO layer. Finally, we tested the antibacterial activity of ZnO-TNTs against Staphylococcus aureus, and found ZnO-TNTs significantly improved the antibacterial properties of Ti implants. We conclude that ZnO-TNTs provide Ti with antibacterial activity, which highlights its potential in orthopedic and dental implants.     

Quantum chemical calculations of the structural influence on electronic properties in TiO2 nanocrystals

ABSTRACT

Quantum chemical calculations for two TiO₂ nanoparticle cluster models (rutile–(TiO₂)_n with n = 20, and anatase–(TiO₂)_n with n = 92), selected to represent different nanoparticle size regimes, are used to elucidate structural influences on the electronic properties. Structural and electronic properties were obtained using a variety of computational methods and structure optimisation schemes, including a comparison of results for several different density functional theory functionals, as well as complementary Hartree–Fock and semi-empirical calculations. The results demonstrate a strong dependence of electronic properties, such as the optical band gap of importance for photoelectrochemical and photocatalytic applications, on the structure of the nanocrystal. From a methodological point of view, the calculations also provide useful information of broader significance about the viability of different computational schemes to efficiently obtain reliable computational results for intrinsically nanostructured materials.     

锐钛矿相纳米TiO2晶体生长动力学及生长过程控制

研究了采用溶胶-凝胶法经由前驱物钛酸四异丙酯水解制备纳米TiO₂结构相变及锐钛矿晶体生长动力学过程. 研究结果表明,在酸性条件下水解,由于高压热处理温度的变化导致锐钛矿向金红石相的结构相变,锐钛矿相纳米TiO₂生长活化能在250℃以下和以上分别为(15.8±4.5)kJ/mol和(80.2±1.0)kJ/mol;而在碱性条件下水解的活化能值为(3.5±0.4)kJ/mol. 在不发生结构相变的条件下,酸性水解条件下锐钛矿相纳米TiO₂生长速 关键词： 2')" href="#">纳米TiO₂ 锐钛矿 生长动力学 溶胶-凝胶法     

Theoretical study on the oxidation of zigzag silicon carbide nanotubes (SiCNTs) by singlet O2

Singlet O₂ produced upon photoexcitation is a very important oxidative reagent. The study on its reaction with nanotube might be useful not only to evaluate the stability of the nanotube upon air exposure and sunlight, but also to modify the properties of the nanotube. Considering the unique properties and wide applications of silicon carbide nanotube (SiCNT), in this paper, we performed extensive density functional theory (DFT) calculations to study the oxidation of a series of zigzag (n,0) SiCNTs (n=6 to 12) by singlet O₂. It is found that the reaction process contains two steps, namely, (i) [2+2] cycloaddition of a singlet O₂ to the Si–C bond, followed by (ii) the dissociation of the O–O bond, leading to the formation of an epoxide configuration with a highly exothermicity (>4.00 eV). Compared with pure SiCNT, the cycloaddition of singlet O₂ on tube leads to the decrease of the band gap, while the formation of the stable epoxy structure render band gap increase. Our results indicate that the SiCNT is more prone to be degraded after exposure to air and sunlight.     

TEM study on the formation mechanism of sodium titanate nanotubes

The formation mechanism of sodium titanate nanotubes via the morphological variation in particle-nanotube transition was investigated by means of TEM. The results show that the formation of sodium titanate nanotubes is carried out by self-assembling of dissolved fragments, the intermediate of TiO₂ reacted with NaOH. The formation process occurs spontaneously in concentrated NaOH solution. After reacting for 20 h, the inside diameters of nanotubes range from 3.9 to 6.8 nm and some straight nanotubes form bundles with hundreds of nanometers long.     

A theoretical study on the kinetics of multichannel Multiwell reaction of H2S(1A1) with HO2(2A′′)

The mechanism and kinetics of the reaction of hydrogen sulphide (H₂S(¹A₁)) with hydroperoxyl radical (HO₂(²A″)) on the lowest doublet potential energy surface have been theoretically studied. The potential energy surface for possible pathways has been investigated by employing Complete Basis Set (CBS), DFT, and CCSD(T) methods. Three possible pathways are suggested for the title reaction. The most probable entrance channel consists of formation of a hydrogen-bonded pre-reaction complex (vdw1) and two energised intermediates. Multichannel RRKM-Steady State Approximation and CVT calculations have been carried out to compute the rate constants over a broad range of temperature from 200?K to 3000?K to cover the atmospheric and combustion conditions and pressure from 0.1 to 2000?Torr. No sign of pressure dependence was observed for the title reaction over the stated range of pressure. We have shown that the major products of the title reaction are H₂O₂ and SH while at higher temperatures, formation of the other products such as H₂O, HOS, HSOH and OH are feasible, too. Our calculated overall rate constant is in agreement with the reported experimental data in the literature.     

Adsorption kinetics of alkanes on TiO2 nanotubesarray - structure-activity relationship

Presented are thermal desorption spectroscopy (TDS) measurements of iso-/n-butane adsorption on a variety of TiO₂ nanotubes (TiNTs) samples which are characterized by different crystal structures. The results are compared with a prior study on anatase(0 0 1) thin films grown on SrTiO₃(0 0 1). A distinct kinetic structure-activity relationship was present, i.e., the binding energies of the alkanes depend on the polymorph (anatase vs. mixed anatase/rutile) of TiO₂. A direct-fitting procedure of the TDS data has been applied to extract the kinetics parameters. The binding energies in the limit of zero coverage decrease as anatase thin film > amorphous-TiNTs ∼ polycrystalline anatase TiNTs > polycrystalline mixed anatase/rutile TiNTs.