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1.
The influence of the modification of the TiO2 surface with F? ions on the physicochemical properties of the catalysts and efficiency in the photooxidation of gaseous molecules under atmospheric conditions and under UV irradiation was studied by IR spectroscopy. The fluorine-containing samples adsorb more water molecules than unmodified TiO2. The amount of adsorbed water increases with increasing content of surface fluoride ions. The fluorination of the TiO2 surface first leads to the substitution of the terminal OH groups by F? ions and to an increase in acidity of the bridging acidic OH groups remained on the surface. The modification also results in the structural rearrangement of the surface involving defective and surface Ti4+ sites. Fluorine modification increases the activity of TiO2 in the photocatalytic oxidation of ethanol, acetaldehyde, acetic acid, and acetone. At the same time, benzene and H2S are oxidized more rapidly on unmodified TiO2. The presence of fluorine on the TiO2 surface exerts almost no effect on the oxidation rate of chlorine-containing substrates C3H7Cl and C2H4Cl2. 相似文献
2.
TiO 2 films with a thickness of 75 ± 5 nm (anatase) were formed on SnO 2-film (580 ± 80 nm) coated soda-lime glass substrates (SnO 2/SL-glass) by a sol-gel method. Although the photocatalytic activity for CH 3CHO oxidation ( ex > 300 nm) significantly exceeded that of a standard TiO 2/quartz sample, it decayed with illumination time ( t) at t > 0.75 h. Stripes of anatase TiO 2 films of 40 nm in thickness and 1 mm in width were prepared on the SnO 2/SL-glass substrate in a 1-mm pitch by photolysis of an organically modified sol-gel film. The TiO 2 patterning further increased the photocatalytic activity by a factor of 4.1 as compared to the non-patterned sample, and it was also maintained at 0 < t < 2 h. The flat band potentials of the TiO 2 and SnO 2 films are determined to be –0.34 and +0.07 V (vs. SHE), respectively, at pH = 7 by the Mott-Schottky plots. On the basis of the results, the outstanding patterning effects could be rationalized in terms of the vectorial charge separation at the interface between TiO 2 and SnO 2. 相似文献
3.
A series of W-modified TiO 2 (W–TiO 2) photocatalysts were synthesized by a simple sol–gel method. The new photocatalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis-diffuse reflectance spectroscopy (DRS), and Brunauer, Emmett and Teller (BET) surface area analyzer. The photoactivity of the W–TiO 2 photocatalysts was evaluated by the photocatalytic oxidation of Congo red (CR) dye. It was found that the average size of the prepared photocatalysts is 10 nm. Moreover, they have high surface areas (∼ 216 m 2 g −1) and their light-absorption extends to the visible region compared to pure TiO 2. The effects of W-loading and of the calcination temperature of the prepared photocatalysts on their photocatalytic activity were also studied. The obtained results show that the W 0.5–TiO 2 photocatalyst calcined at 350 °C is much highly photoactive than non-doped or highly doped TiO 2. The enhanced photocatalytic activity of the weakly doped TiO 2 may be attributed to the increase in the charge separation efficiency and the presence of surface acidity on the W 0.5–TiO 2 photocatalyst. 相似文献
4.
The supported nano-TiO 2 electrode was prepared by sol–gel and hydrothermal method, and the photoelectrocatalytic degradation of 4-chlorophenol (4-CP) under UV irradiation has been investigated to reveal the roles of hydroxyl radicals and dissolved oxygen species for TiO 2-assisted photocatalytic reactions. The degradation kinetics, the formation and decay of intermediates, the isotopic tracer experiments with H 2O 18, the removal yield of total organic carbon and the formation of active radical species in the presence of oxygen or not were examined by HPLC, GC–MS, TOC and spin-trap ESR spectrometry. It was found that most of OH radicals in the primary hydroxylated intermediates derived from the oxidation of adsorbed H 2O or HO − by photo-holes in the electrochemically assisted TiO 2 photocatalytic system. It also indicates that the enhancement in the separation efficiency of photogenerated charges by applying a positive bias (+0.5 V vs SCE) has little role in the following decomposition and mineralization of these hydroxylated intermediates in the absence of oxygen. According to above experimental results, the pathway of 4-CP photocatalytic degradation was deduced initially. Due to the combined effect of OH radicals and dissolved oxygen species, the hydroxylated 4-chlorphenol, via cis, cis-3-chloromuconic acid, was decomposed into low molecular weight acid and CO 2. 相似文献
5.
Summary G2 theory is shown to be reliable for calculating isodesmic and homodesmotic stabilization energies (ISE and HSE, respectively) of benzene. G2 calculations give HSE and ISE values of 92.5 and 269.1 kJ mol –1 (298 K), respectively. These agree well with the experimental HSE and ISE values of 90.5±7.2 and 268.7±6.3 kJ mol –1, respectively. We conclude that basis set superposition error corrections to the enthalpies of the homodesmotic or isodesmic reactions are not necessary in calculations of the stabilization energies of benzene using G2 theory. The calculated values of the enthalpies of formation of such molecules containing multiple bonds such as benzene and s-trans 1,3-butadiene, which are found from the enthalpies of isodesmic and homodesmotic reactions rather than of atomization reactions, demonstrate good performance of G2 theory. Estimates of the H
f
o
value for benzene from the G2 calculated enthalpies of homodesmotic reaction (2) and isodesmic reaction (3) are 80.9 and 82.5 kJ mol –1 (298 K), respectively. These are very close to the experimental H
f
o
value of 82.9±0.3 kJ mol –1. The H
f
o
value of s-trans 1,3-butadiene calculated using the G2 enthalpy of isodesmic reaction (4) is 110.5 kJ mol –1 and is in excellent agreement with the experimental H
f
o
value of 110.0±1.1 kJ mol –1. 相似文献
6.
Fumed oxide alumina/silica/titania was studied in comparison with fumed alumina, silica, titania, alumina/silica, and titania/silica by means of XRD, 1H NMR, IR, optical, dielectric relaxation, and photon correlation spectroscopies, electrophoresis, and quantum chemical methods. The explored Al 2O 3/SiO 2/TiO 2 consists of amorphous alumina (22 wt%), amorphous silica (28 wt%), and crystalline titania (50 wt%, with a blend of anatase (88%) and rutile (12%)) and has a wide assortment of Brønsted and Lewis acid sites, which provide a greater acidity than that of individual fumed alumina, silica, or titania and an acidity close to that of fumed alumina/silica or titania/silica. The changes in the Gibbs free energy (Δ G) of interfacial water in an aqueous suspension of Al 2O 3/SiO 2/TiO 2 are close to the Δ G values of the dispersions of pure rutile but markedly lower than those of alumina, anatase, or rutile covered by alumina and silica. The zeta potential of Al 2O 3/SiO 2/TiO 2 (pH of the isoelectric point (IEP) equals ≈3.3) is akin to that of fumed titania (pH(IEP TiO2) ≈ 6) at pH > 6, but it significantly differs from the ζ of fumed alumina (pH(IEP Al2O3) ≈ 9.8) at any pH value as well as those of fumed silica, titania/silica, and alumina/silica at pH < 6. The particle size distribution in the diluted aqueous suspensions of Al 2O 3/SiO 2/TiO 2 studied by means of photon correlation spectroscopy depends relatively slightly on pH in contrast to the titania/silica or alumina/silica dispersions. Theoretical calculations of oxide cluster interaction with water show a high probability of hydrolysis of Al–O–Ti and Si–O–Ti bonds strained at the interface of alumina/titania or silica/titania due to structural differences in the lattices of the corresponding individual oxides. Ab initio calculated chemical shift δ H values of H atoms in different hydroxyl groups at the oxide clusters and in bound water molecules are in agreement with the 1H NMR data and show a significant impact of charged particles (H 3O + or OH −) on the average δ H values of water droplets with (H 2O) n at n between 2 and 48. 相似文献
7.
A composite nano-ZnO/TiO 2 film as photocatalyst was fabricated with vacuum vaporized and sol-gel methods. The nano-ZnO/TiO 2 film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO 2 and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO 2 film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO 2 film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO 2 film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1 mg l −1, COD values with the linear range of 0.3-10.0 mg l −1 were achieved. The results were in good agreement with those from the conventional COD methods. 相似文献
8.
On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen‐isotope‐labeled Ti 18O 2 as the photocatalyst, we demonstrate that 18O s atoms behave as real catalytic species in the photo‐oxidation of acetonitrile‐dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO 2. The experimental evidence allows a terminal‐oxygen indirect electron‐transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence‐band holes at O s species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO 2 surface and their subsequent healing with oxygen atoms from either O 2 or H 2O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO 2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO 2 photocatalytic phenomena. 相似文献
9.
The reactions of iron(III) with -hydroxyethylimino- N, N-diethanoic acid (H 2Heida) and dicarboxy-lic acids (oxalic (H 2Ox), malonic (H 2Mal), and succinic (H 2Suc)) are studied using the spectrophotometric method. The equilibrium pattern in the binary and ternary systems is investigated. The complexation processes were shown to be complicated by hydrolysis and to depend strongly on the acidity of the medium. The following complexes were detected: FeHeida +, Fe(OH)Heida, Fe(OH) 2Heida –, Fe(Heida)Ox –, Fe(OH)(Heida)Ox 2–, Fe(OH) 2(Heida)Ox 3–, Fe(Heida)Mal –, Fe(OH)(Heida)Mal 2–. Logarithms of the stability constants of these complexes calculated at = 0.1 (NaClO 4) and T = 20 ± 2°C are equal to 11.64 ± 0.05, 22.97 ± 0.05, 31.17 ± 0.05, 18.83 ± 0.03, 28.27 ± 0.02, 36.14 ± 0.02, 17.64 ± 0.03, and 26.39 ± 0.03, respectively. 相似文献
10.
Summary The kinetics and mechanisms of the oxidation of Nb(CN)
inf8
sup5–
by the oxyanions S 2O
inf8
sup2–
, BrO
inf3
sup–
, and IO
inf4
sup–
have been investigated in alkaline aqueous media (pH 12). The second-order rate constant for the electron transfer reaction between Nb(CN)
inf8
sup5–
and S 2O
inf8
sup2–
at 25.0 °C, I = 0.36 m (K +), is 11.1± 0.3 m
–1
s
–1 with H
= 30 ± 2kJmol –1 and S
= - 125 + 7JK –1 mol –1. The rate constant for the oxidation of Nb(CN)
inf8
sup5–
by BrO
inf3
sup–
at 25.0 °C, I = 0.20 m (Na +), is 2.39 ± 0.08 m
–1
s
–1 with H = 28 ± 2kJmol –1 and S
= -139 ± 7JK –1mol –1. The oxidation of Nb(CN)
inf8
sup5–
by IO
inf4
sup–
proceeds by two parallel pathways involving the monomeric IO
inf4
sup–
ion and the hydrated dimer H 2I 2O
inf10
sup4–
. The second-order rate constant for the oxidation of Nb(CN)
inf8
sup5–
by monomeric IO
inf4
sup–
at 5.0 °C, I = 0.050 m (Na +), is (3.3 ± 0.6) × 10 3
m
–1
s
–1 with H
= 75 ± 6 kJ mol –1 and S
= 94 ± 15 J K –1 mol –1, while the rate constant for the oxidation by H 2I 2O
inf10
sup4–
is (1.8 ± 0.1) × 10 3
m
–1
s
–1 with H
= 97 ± 5 kJ mol –1 and S
= 166 ± 16 J K –1 mol –1 under the same reaction conditions. The rate constants for each of the oxidants employed display specific cation catalysis with the order of increasing rate constants: Li + < Na+ < NH
inf4
sup+
< K + < Rb + < Cs +, in the same direction as the electronic polarizability of the cations. The results are discussed in terms of the outer-sphere electron-transfer processes and compared with the corresponding data and mechanisms reported for other metal-cyano reductants. 相似文献
11.
Three catalytic oxidation reactions have been studied: The ultraviolet (UV) light induced photocatalytic decomposition of the synthetic dye sulforhodamine B (SRB) in the presence of TiO 2 nanostructures in water, together with two reactions employing Au/TiO 2 nanostructure catalysts, namely, CO oxidation in air and the decomposition of formaldehyde under visible light irradiation. Four kinds of TiO 2 nanotubes and nanorods with different phases and compositions were prepared for this study, and gold nanoparticle (Au‐NP) catalysts were supported on some of these TiO 2 nanostructures (to form Au/TiO 2 catalysts). FTIR emission spectroscopy (IES) measurements provided evidence that the order of the surface OH regeneration ability of the four types of TiO 2 nanostructures studied gave the same trend as the catalytic activities of the TiO 2 nanostructures or their respective Au/TiO 2 catalysts for the three oxidation reactions. Both IES and X‐ray photoelectron spectroscopy (XPS) proved that anatase TiO 2 had the strongest OH regeneration ability among the four types of TiO 2 phases or compositions. Based on these results, a model for the surface OH group generation, absorption, and activation of molecular oxygen has been proposed: The oxygen vacancies at the bridging O 2? sites on TiO 2 surfaces dissociatively absorb water molecules to form OH groups that facilitate adsorption and activation of O 2 molecules in nearby oxygen vacancies by lowering the absorption energy of molecular O 2. A new mechanism for the photocatalytic formaldehyde decomposition with the Au/TiO 2 catalysts is also proposed, based on the photocatalytic activity of the Au‐NPs under visible light. The Au‐NPs absorb the light owing to the surface plasmon resonance effect and mediate the electron transfers that the reaction needs. 相似文献
12.
本工作采用改进的溶胶-凝胶法和浸渍法制备了TiO 2掺杂稀土离子La 3+的La/TiO 2光催化剂,运用XRD、N 2吸附脱附、紫外可见漫反射光谱(DRS)、表面光电压谱(SPS)等手段进行表征,同时利用原位红外技术考察了La/TiO 2样品光催化降解乙烯、丙酮、苯的气-固相光催化氧化反应,对其光催化降解有机污染物的过程进行了研究。结果表明,TiO 2经适量La 3+掺杂后,锐钛矿晶型的含量增加,晶粒度减小,比表面积增大,禁带宽度增加,表面光电压信号增强,光生电子-空穴对有效分离;La/TiO 2样品对乙烯、丙酮、苯的光催化性能与纯TiO 2相比均有不同程度的改善,乙烯可以被光催化氧化完全矿化生成CO 2,而丙酮被光催化氧化可能生成中间产物丙酸,苯被光催化氧化可能生成中间产物苯酚和苯醌。 相似文献
13.
Nanoparticles of nitrogen-modified TiO 2 (N-doped TiO 2) calcined at 300°C and 350°C, have been prepared with and without water rinsing. Samples were characterized by x-ray diffractrometry (XRD) and optical spectroscopy. The electron paramagnetic resonance (EPR) spectra from centers involving oxygen vacancies were recorded for all samples. These could be attributed to paramagnetic surface centers of the hole type, for example to paramagnetic oxygen radicals O ?, O 2 ? etc. The concentration of these centers increased after water rising and it further increased for samples annealed at higher temperature. Additionally, for samples calcined at 300°C, and calcined at 350°C and rinsed, the EPR spectra evidenced the presence of magnetic clusters of Ti 3+ ions. The photocatalytic activity of samples was studied towards phenol decomposition under unltraviolet-visible (UV-Vis) irradiation. It was found that, in comparison to the starting materials, the rinsed materials showed increased photocatalytic activity towards phenol oxidation. The light absorption (UV-Vis/DRS) as well as surface Fourier transform infrared/diffuse reflectance spectroscopy (FTIR/DR) studies confirmed a significantly enhanced light absorption and the presence of nitrogen groups on the photocatalysts surfaces, respectively. A significant increase of concentration of paramagnetic centers connected with oxygen vacancies after water rising has had an essential influence on increasing their photocatalytic activity. 相似文献
14.
Summary The oxidation of Mn II by S 2O 8
2– to Mn VII in phosphoric acid medium proceeds via a stable Mn III and Mn IV species. The reaction is catalysed by Ag + and exhibits first order dependence on [S 2O 8
2–], [Ag +] and, is independent of [Mn II]. The [H +] has no significant effect on the reaction. It is observed that the PO 4
3– ion stabilises the transient manganese(III) and manganese(IV) species by forming a stable and soluble phosphato-complexes. The activation parameters for the two stages of oxidation, namely Mn II Mn IV and Mn IVMn VII at 25° C are E a=52 ±4 kJ mole –1, S *=–57±2 JK –1 mole –1 and E a =56±4 kJ mole –1, S *=–44±2 JK –1 mole –1, respectively. A mechanism consistent with the experimental observations is proposed.Presented at the National Symposium on Reaction Kinetics and Mechanism, Department of Chemistry, University of Jodhpur, Jodhpur, India, Nov. 15–18, 1986. 相似文献
15.
Catalytic activities of NiO–SiO 2 for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maxima in activities. The variations in catalytic activities are closely correlated to the acidity of NiO–SiO 2 catalysts. Catalytic activities of NiO–TiO 2 catalysts modified with H 2SO 4, H 3PO 4, H 3BO 3, and H 2SeO 4 for ethylene dimerization and butene isomerization were examined. The order of catalytic activities for both reactions was found to be NiO–TiO 2/SO 42- >> NiO–TiO 2/PO 43-NiO–TiO 2/BO 33- > NiO–TiO 2/SeO 42-> NiO–TiO 2, showing clear dependence of catalytic activity upon acid strength. The high catalytic activity of supported nickel sulfate for ethylene dimerization was related to the increase of acidity and acid strength due to the addition of NiSO 4. The asymmetric stretching frequency of the S=O bonds for supported NiSO 4 catalysts was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. For NiSO 4/Al 2O 3–ZrO 2 catalyst, the addition of Al 2O 3 up to 5 mol% enhanced catalytic activity for ethylene dimerzation and strong acidity gradually due to the formation of Al–O–Zr bond. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni +, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO 4/ -Al 2O 3 and Ni 2p XPS. 相似文献
16.
The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol –1 dm 3 cm –1. The second order decay rate parameter in water is (2.3±0.5)×10 9 mol –1 dm 3 s –1. The peroxy radicals have the characteristics: max=265–270 nm, max=700–900 mol –1 dm 3 and 2k=(7±2)·10 8 mol –1 dm 3 s –1. 相似文献
17.
Na + complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m 2/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO 2 samples prepared were found to have photocatalytic activity in Cu II, Ni II and Ag I reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO 2 Degussa P25.The effects of the thermal treatment of mesoporous TiO 2 upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO 2/Ag 0 to TiO 2/Ni 0 to TiO 2/Cu 0 was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites. 相似文献
18.
The article studies on the effects of six inorganic ions (Ca 2+, Mg 2+, Cl ?, SO 4 2? , H 2PO 4 ? , and HCO 3 ? ) on titanium dioxide (TiO 2)-based photocatalytic degradation of humic acid (HA). We focus on the effects of the inorganic ions on HA characters, adsorption of HA on TiO 2 and photocatalytic degradation of HA. The results indicate that Ca 2+ and Mg 2+ with HA can form complexes which can decrease the solubility of HA, and then increase the HA adsorbed on TiO 2. However, the complex is more difficult to be degraded than HA. The effects of Cl ? and SO 4 2? are closely related to their influences on HA solubility. The solubility changes of HA to some extent can enhance the adsorption of HA on TiO 2, and promote the photocatalytic degradation. Nevertheless, great solubility decreasing of HA can weaken the photocatalytic degradation. HCO 3 ? and H 2PO 4 ? can inhibit the photocatalytic degradation process seriously, because HCO 3 ? and H 2PO 4 ? are the strong scavengers of hydroxyl radicals, and can weaken the adsorption of HA on TiO 2 due to adsorption competition. 相似文献
19.
TiO 2 was immobilized on to the surface of a pyrex glass tube through a dip coating process, and a pyrex glass tube with TiO 2 thin film was used as a batch reactor and continuous flow reactor for the photocatalytic destruction of PCE in water. TiO 2 could be successfully immobilized with a thickness of 0.3 μm in the pyrex glass tube. The TiO 2-immobilized pyrex glass tube itself showed high photocatalytic activity for the destruction of PCE in water. 相似文献
20.
1. |
During shaping of titanium dioxide there are formed both paramagnetic (NO
3
2–
, NO2, and NO) and nonparamagnetic (NO3–) forms of nitrogen oxides, stabilized in the TiO2 lattice.
| 2. |
In CO the radicals (NO
3
2–
and NO2 are reduced to NO.
| 3. |
It is postulated that during shaping of TiO2 the NO2 molecules formed during oxidation of NH3 may be stabilized both on the lattice O2– and on Ti4+.
| 相似文献
|