In this study, the influence of bulk and surface doping sites on chemical compositions, photoactivity, electronic- and micro- structure of V-doped TiO2 were discussed. V2O5 was formed on the surface because the low Tammann temperature induced the diffusion of vanadium ions from bulk lattice toward surface lattice. In addition, some incorporated V5+
ions were reduced to V4+ ions when the bulk V/Ti ratios higher than 1 mol%. The lattice V5+/V4+ not only decreased the anatase-rutile transformation at 300 ºC but also inhibited growth of crystal size of anatase TiO2 at high vanadium concentration. In bulk doped TiO2, lattice-V5+ ions trapped electrons thus increased the number of trapped holes. However, the trapped holes decreased when V/Ti ratios were higher than 1 mol% because lattice-V4+ ions acted as recombination centers. Prompt charge recombination led to the decrease in photoactivities of bulk doped TiO2with increasing contents of vanadium ions. In contrast to bulk doped TiO2, V2O5shell was coated on the surface of TiO2 when vanadium ions were doped in the surface lattice of TiO2. The surface-V5+ ions had no obvious effect on the micro- and electronic- structure of TiO2. However, they promoted electrons diffusion to surface and further facilities charges transfer to reactants because the d-orbital energy of V5+
was lower than that of conduction band of titanium. Therefore, the surface defects contributed to high photoactivity, while bulk ones had detrimental effects on photodegradation of RhB under irradiation of UV light.
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Appendix A Experimental parameters
Appendix A-1 Operational parameter of XPS.
Mode Binding
energy
Pass energy Anode Step size Time/steps
Survey 1200-0 eV 23.5 eV Al 1.0 eV 50 ms
Multiplex Depending on element
23.5 eV Al 0.1 eV 50 ms
Appendix A-2 Detail operational of XPS in multiplex.
Element Pass Energy Step size Scan times BE range ASF
O 1s 23.5 eV 0.1 eV 20 529.3-531.2 0.711
Ti 2p 23.5 eV 0.1 eV 20 458.2 2.001
V 2p 23.5 eV 0.1 eV 80 517.6 2.116
Appendix A-3 Relative sensitivity factor of SIMS.
Sample name
VT 7×10-1 1.74E+18 93785 107849 1.51×1018
VT 1×10-4 2.49E+14 276246 93 7.40×1017
Appendix A-4 Raw data of SIMS.
VT 4.4E-5 50.68 41 47.97 399106 1.55×1014
VT 1.3E-4 50.83 305 47.97 320761 1.44×1015
VT 5.1E-4 50.86 368 47.93 587123 9.48×1014
VT 1.3E-3 50.99 1979 47.94 759273 3.94×1015
VT 1.2E-2 50.90 16152 47.93 683923 3.57×1016
SVT 1.7E-3 50.96 9009 47.97 414003 3.29E×1016
SVT 3.5E-3 51.04 1616 47.87 8317 2.94E×1017
SVT 6.4E-3 50.73 3582 47.87 12480 4.34×1017
SVT 1.1E-2 50.89 8022 47.81 19117 6.35×1017
Appendix A-5 Operational parameter of XRPD.
Scan range Sampling
10-80 degree 0.02 4.0 Ordinary
(without background)
30.0 20.0
Appendix A-6 Operational parameter of UV-vis.
Measurement Data
Appendix B Instrument principle
Appendix B-1 Time-of-Flight Secondary Ion Mass Spectrometer
SIMS is an analytical technique that can be used to characterize the surface and near surface(~30 μm)region ofsolid. Thetechniqueusesa beam ofenergetic(0.5-20 keV) primary ions to sputter the sample surface, producing ionized secondary particles that are detected using a mass spectrometer. Besides, the detection limit for element is ppb ~ ppm, where is more sensitive than AES (0.1 %) or ESCA (0.01 %). And for chemical analysis, SIMS can detect bulk, miro and trace of sample which is shown in Appendix B-1.62, 90
Appendix B-1 Chemical analysis for three different types of sample.90
SIMS measurements were performed with a TOF-SIMS Ⅳ (ION-TOF) spectrometer which use a Ga+or Au+to be analytic source and use an O2+or Cs+to be sputter source. The thickness of sample is around 1 cm and area of sample is around 1 cm2. The detection area is 100×100 μm2. The sputter time is 120 seconds. The surface atomic ratio was calculated from the intensity of secondary ions which are normalized to relative sensitivity factor. A relative sensitivity factor (RSF) is a conversion factor from secondary ion intensity to atom density. The RSF is defined by sub-equation:62
I RSF I
m
i
i (B-1)has unit of atoms/cm3.
The surface atomic ratio can be calculated by sub-equation
2
Where n denotes the atomic numbers, I is the intensity of secondary ions on SIMS spectra, RSF stands for the atomic relative sensitive factor of element.
Appendix B-2 X-ray powder diffractometry (XRPD)
The bulk crystal structure of bulk materials weredetected by Bragg’slaw. The device of XRPD is shown in Appendix B-2. And the principle of XRD is Bragg's law, which calculated the d-spacing of the crystal structure, as shown in Appendix B-3. But the thickness of X-ray detectivelimitispositivewith sin α /μ (α isincidenceangleand μ is adsorption constant of materials). Therefore, the thickness of XRPD detection is around 10~100 μm (1/μ). Butthethicknessofthin film isquitelower than limit of XRPD, even several hundred Å. Moreover, while the thin film is detected by XRPD, the signal of sample would be cover by matrix. So, grazing incident diffraction, GID, method could vary the thickness of detection by change the incidence angle. Appendix B-4 shows the relationship between incidence angle and detective thickness. And Appendix B-5 shows the concept of GI-XRD.
Appendix B-2 The concept of x-ray powder diffractometry device.90
Appendix B-3 TheconceptofgeometricfigureforBragg’slaw.91
Appendix B-4 The relationship between incidence angle and detective thickness for GI-XRD.90
Appendix B-5 The concept of grazing incident x-ray powder diffractometry device.90
Appendix B-3 UV-vis diffuse reflectance spectroscopy (DRS)
UV-vis diffuse reflectance spectroscopy (DRS) was applied to study the bonding information for inorganic compounds. And the local structures of the vanadium ions in TiO2
are often associated with the band positions of the ligand1-to-metal charge transfer (LMCT) transition from an O2-ion t1uorbital to a Mn+metal egorbital.76, 92-94 In order to elucidate the optical properties for photocatalysts, UV-visible spectroscopy was used to examine the optical reflectance of the bulk and surface doping materials at different vanadium ions concentration.
Thus, Appendix B-6 is shown the ligand-to-metal charge transfer (LMCT) transition for TiO2.
Appendix B-6 A simplified molecular orbital diagram illustrating the potential ligand to metal charge transfer transitions.5, 67.
1 In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal to produce a coordination complex. The bonding between the metal and ligand generally involving formal donation of one or more of the ligand's electrons. The metal-ligand bonding ranges from covalent to more ionic. Furthermore, the metal-ligand bond order can range from one to three. http://en.wikipedia.org/wiki/Ligand
Appendix B-4 Electron paramagnetic resonance (EPR)
An unpaired electron which is rotating around the rest of the molecule is equivalent to a current flowing in a complete turn of wire without resistance, and thus it produces a magnetic filed which passes through its centre as shown in Appendix B-7. In the other word, the electron is circling around the molecule it acts rather like a gyroscope, with the dame reluctance to change the direction of its axis of spin. If a quantity of these free radicals is placed in strong unidirectional and constant value magnetic field, H, some of the bar magnets will take up a position relative to the d.c. field as shown in Appendix B-8.35
Appendix B-7 How a free radical acts a bar magnet with mass.35
Such EPR spectra (Appendix B-8) are obtained by measuring the attenuation versus frequency (or wavelength) of a beam of electromagnetic radiation as it passes through a sample of matter. Transition can be induced between there levels by applying an oscillating magnetic field of frequency at right angles to the d.c. field. The relation between field and frequency for resonance of the free electron is
H h g / ) (
(B-3)Appendix B-8 Energy-level scheme for the sample (e.g. free electron) as a function of applied magnetic field.83
However, the transition elements are present for which shells inside the valence shell are not filled, so that unpaired electrons are always present. For example, the first transition group is the iron group in which the electrons start filling the 3d shell after the 4s valence electrons have filled. For free electron g factor has the value 2.0023. In most free radicals g lies very close to this value, where in the range 2.002 to 2.004.35
EPR spectra of V-doped anatase are as expected for V4+(S=1/2, I=7/2) being composed of essentially two or three groups of octets due to the coupling of a single electron with the vanadium nucleus. However, the Ti3+ and •OH would not appear after UV irradiation, because the Ti3+ ions would easily oxidization to Ti4+ and the electron would transfer to O2 which is adsorption on the surface of TiO2 (equation B-4). Moreover, oxygen was chemical adsorbed by O2
2-ion in room to low temperature process. Besides, O2
2-simultaneously have hole-reduction agent and electron consumed agent function, and O2
-be the product by hole/electron consumed reaction. That is why O2
-signal can be detected in EPR system after UV irradiation with low vanadium concentration.83
The reaction between Ti3+and oxygen:
)
The reaction between excited electron or hole and oxygen gas or ion :
The reaction between excited electron or hole and water :
The EPR spectra recorded at 77 K of all samples. Each sample contains 0.01 g powder which is filled in quartz tube in the dark or under UV light. Furthermore, the wavelength of UV light system (Moritex, MUV-250U-L) is 365 nm mainly and 150W. And the photograph
The EPR spectra recorded at 77 K of all samples. Each sample contains 0.01 g powder which is filled in quartz tube in the dark or under UV light. Furthermore, the wavelength of UV light system (Moritex, MUV-250U-L) is 365 nm mainly and 150W. And the photograph