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1.
A magnetically separable nitrogen-doped photocatalyst TiO 2−xN x/SiO 2/NiFe 2O 4 (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO 2/NiFe 2O 4 (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO 2−xN x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO 2/NiFe 2O 4 (SN) nanoparticles adhere to the surface of TiO 2−xN x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO 2 coating round the surface of NiFe 2O 4 nanoparticles prevents effectively the injection of charges from TiO 2 particles to NiFe 2O 4, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity. 相似文献
2.
An important improvement of the photocatalytic activity of sol–gel prepared TiO 2 has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples. The presence of sulphuric acid clearly stabilised TiO2 surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO2 surface was studied. Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO2. Simultaneously sulphated and platinised TiO2 samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO2 Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples. A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported. 相似文献
3.
采用水热法制备N掺杂TiO2,将其与二氰二胺混合进行高温焙烧合成N-TiO2/g-C3N4复合光催化剂。采用XRD、UV-Vis、N2吸附-脱附和SEM等对催化剂进行微观结构表征,以200W氙灯模拟光源并过滤掉420nm以下的紫外光,对比研究TiO2、g-C3N4、N-TiO2和复合光催化剂对罗丹明B的可见光降解性能。结果表明,N掺杂后TiO2的禁带宽度降低,催化活性提高;而复合光催化剂可见光吸收边距相对N-TiO2进一步红移,禁带宽度为2.75eV,降解罗丹明B的一级动力学常数k可达0.12158min-1,是g-C3N4、N-TiO2的2倍;复合催化剂重复使用4次后,对罗丹明B的降解率仍达92%以上,表明催化剂具有较好的光催化活性和稳定性。 相似文献
4.
Catalytic oxidation of monochlorobenzene (667 ppm) in wet air was investigated over PtHFAU(5) catalysts, differing by their Pt content (from 0 to 1.1 wt.%), their Pt dispersion (for identical Pt content) and the electronic state of Pt. PtHFAU(5) catalysts show a higher activity compared to more conventional PtAl 2O 3 and PtSiO 2 samples. For a given temperature, chlorobenzene oxidation over PtHFAU(5) is independent of the platinum particles size. On the other hand, a plateau in activity is reached from 0.4 to 0.6% Pt. Amount of polychlorinated benzenes (PhCl2+) were produced in the order PtAl2O3 > PtSiO2 > PtHFAU(5). The formation of these compounds, especially PhCl2, over PtHFAU(5) was function on the Pt content (PhCl2 isomers appear only from 0.6% PtHFAU), and of the electronic state of Pt. Thus PhCl2, were mainly found over reduced Pt0 particles certainly through a chlorination of platinum (formation of PtClx species). A reaction scheme for the PhCl2 formation was proposed. 相似文献
5.
The effects of platinum (Pt) and silver (Ag) metallisation in the photocatalytic oxidation of resorcinol at pH 3 ± 0.5 have been investigated. The photocatalytic degradation of resorcinol was significantly improved by Pt/TiO 2, while the presence of Ag/TiO 2 enhanced the initial photocatalytic degradation rate of resorcinol slightly. Likewise, the photocatalytic mineralisation of resorcinol continued to be enhanced by Pt/TiO 2, but it was retarded when Ag/TiO 2 was used. The function of Pt and Ag deposits on the surface of TiO2 has been found to be markedly influenced by the interaction of resorcinol and its degradation products with the metal deposits. The presence of Pt or Ag on the surface of TiO2 altered the distribution of degradation products of resorcinol as well as the production of photoactive species for the photocatalytic oxidation of resorcinol. The X-ray photoelectron spectroscopy (XPS), zeta potential and transmission electron microscopy (TEM) analyses have indicated that the contrasting effect of Pt and Ag deposits were governed by the oxidation states and the catalytic property of metal deposits. In addition to that, it has been found that the roles of metal deposits are specific and should not be generalised. 相似文献
6.
Nitrogen doped spherical TiO 2 has been prepared by thermal decomposition of Ti–melamine complex in air atmosphere. A clear shift in the onset light absorption from UV region (<400) to visible region (>520 nm) has been observed for the N-doped samples. It has been deduced from the optical absorption spectra that the higher calcination temperature results in the decrease in the amount of N-doping. The XRD results revealed the phase transition of TiO 2 from anatase to rutile crystalline phase, starting at calcination temperature ≥600 °C. The electron microscopic images reveal the formation of spherical and flakes of TiO 2 nanocrystals (25 nm). The chemical nature of N in the N-TiO 2 has been evolved through X-ray photoelectron spectroscopy. The presence of different types of N species have been observed corresponding to different oxidation states and the presence of Ti–N and O–Ti–N have been confirmed from the observed binding energy values. Photocatalytic decomposition of methylene blue has been carried out both in the visible region and UV + visible region. In the visible region, N-TiO 2 showed higher activity compared to the undoped commercial TiO 2 (Degussa P25). 相似文献
7.
The photocatalytic properties of sulphated MoO x/γ-Al 2O 3 catalysts in cyclohexane oxidative dehydrogenation have been determined in a two-dimensional fluidized bed photoreactor and compared to those of sulphated MoO x/TiO 2 catalysts. Photocatalytic tests on MoO x/γ-Al 2O 3 at 8 wt% MoO 3 and various sulphate contents showed the selective (100%) formation of cyclohexene, without production of benzene, as instead found with MoO x/TiO 2. These results show that the selectivity of photocatalytic cyclohexane oxydehydrogenation is dramatically influenced by the catalyst support. Maximum cyclohexane conversion and cyclohexene yield of 11% were obtained for SO4 content of 2.6 wt% at 120 °C. Physico-chemical characterisation of catalysts indicates the presence of both octahedral polymolybdate and sulphate species on alumina surface, as previously found for titania. Increasing sulphate load, thermogravimetry evidenced the presence of up to three sulphate species at different thermal stability. The lower activity observed at high sulphate content is likely due to polymolybdate decoration by sulphates. 相似文献
8.
The nanometer particles of two Fe xO y/TiO 2’s with high photocatalytic activities were obtained through hydrothermal treatment and impregnation method. The XRD result did not show the peaks assigned to the Fe components (for example Fe 2O 3, Fe 3O 4, FeO 3, and Fe metal) on the external surface of the anatase structure in the Fe xO y/TiO 2 attained through hydrothermal treatment. This meant that Fe components were well incorporated into the TiO 2 anatase structure. In addition, it exhibited uniform anatase structure with particle size of below 50 nm. The FeO 3 component on the external surface of the TiO 2 anatase structure was identified in the Fe-loaded TiO 2 prepared through the impregnation method. In particular, the FT-IR spectroscopy revealed that the Fe xO y/TiO 2 particle attained through hydrothermal treatment had higher hydrophilic property compared to the other catalysts. Together with the Fe component, they absorbed wavelength of above 370 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe xO y/TiO 2 particle attained through hydrothermal method. This meant that Fe components were well inserted into the framework of the TiO 2 anatase structure. Despite the red shift in UV-Vis absorption, however, CHCl 3 decomposition on the Fe xO y/TiO 2 catalyst was not largely enhanced compared to pure TiO 2. 相似文献
9.
Activities of a series of metals (Pt, Pd, Rh, Cu, Mn) supported on TiO 2 were investigated for the catalytic oxidation of formaldehyde. Among them, Pt/TiO 2 was found to be the most promising catalyst. Nitrogen adsorption, hydrogen chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed reduction (TPR) by H 2 were used to characterize the platinum catalysts. Using Ce 0.8Zr 0.2O 2, Ce 0.2Zr 0.8O 2, SiO 2 as supports instead of TiO 2, the activity sequence of 0.6 wt.% platinum with respect to the supports is TiO 2 > SiO 2 > Ce 0.8Zr 0.2O 2 > Ce 0.2Zr 0.8O 2, and this appears to be correlated with the dispersion of platinum on supports rather than the specific surface areas of the catalysts. Platinum loading on TiO 2 has a great effect on the catalytic activity, and 0.6 wt.% Pt/TiO 2 catalyst was observed to be the most active, which could be attributed to the well-dispersed platinum surface phase. The reduction temperature greatly affects the particle size and, consequently, the catalytic activity. The smaller particle size of platinum, due to its high dispersion on support, has a positive effect on catalytic performance. Increasing formaldehyde concentration and space velocity exhibits an inhibiting effect on the catalytic activity. 相似文献
10.
Bimodal nanocrystalline mesoporous TiO 2 powders with high photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate (TiO(C 4H 9) 4, TBOT) as precursor. The as-prepared TiO 2 powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N 2 adsorption–desorption measurements. The photocatalytic activity of the as-prepared TiO 2 powders was evaluated by the photocatalytic degradation of acetone (CH 3COCH 3) under UV-light irradiation at room temperature in air. The effects of hydrothermal temperature and time on the microstructures and photocatalytic activity of the TiO 2 powders were investigated and discussed. It was found that hydrothermal treatment enhanced the phase transformation of the TiO 2 powders from amorphous to anatase and crystallization of anatase. All TiO 2 powders after hydrothermal treatment showed bimodal pore-size distributions in the mesoporous region: one was intra-aggregated pores with maximum pore diameters of ca. 4–8 nm and the other with inter-aggregated pores with maximum pore diameters of ca. 45–50 nm. With increasing hydrothermal temperature and time, the average crystallite size and average pore size increased, in contrast, the Brunauer-Emmett-Teller (BET) specific surface areas, pore volumes and porosity steadily decreased. An optimal hydrothermal condition (180 °C for 10 h) was determined. The photocatalytic activity of the prepared TiO 2 powders under optimal hydrothermal conditions was more than three times higher than that of Degussa P25. 相似文献
11.
To realize the utilization of visible light and improve the photocatalytic efficiency of organic pollutant degradation in wastewater, a nitrogen-doped titanium-carbon composite (N-TiO 2/AC) prepared by sol-gel methods was applied in the photodegradation of phenol assisted by persulfate under visible light irradiation (named N-TiO 2/AC/PS/VIS). The results show that a synergistic effect exists between visible-light photocatalysis and persulfate activation. Compared with TiO 2/PS/VIS, the phenol degradation rate was found to be observably improved by 65% in the N-TiO 2/AC/PS/VIS system. This significant increase in degradation rate was mainly attributed to the following two factors: 1) The N and C doping can change the crystal structure of TiO 2, which extends the TiO 2 absorption wavelength range to the visible light region. 2) As an electron acceptor, PS can not only prevent electrons and holes from recombining with each other but can also generate strong oxidizing radicals such as ∙SO 4– and ∙OH to accelerate the reaction dynamics. The process of phenol degradation was found to be consistent with the Langmuir pseudo-first-order kinetic model with an apparent rate constant k of 1.73 min –1. The N-TiO 2/AC/PS/VIS process was proven to be a facile method for pollutant degradation with high pH adaptability, excellent visible-light utilization and good application prospects. 相似文献
12.
The local zirconium and iron arrangements of the iron-doped ZrO 2-TiO 2 system, prepared by sol–gel impregnation method, were studied by EXAFS spectroscopy. Only a tetragonal ZrO 2 structure is located on TiO 2 surface. For the iron-doped ZrO 2-TiO 2 system, the presence of the Fe-O-Fe species as well as and Fe-O-Zr species located on the surface/pre-surface region are shown; it seems that iron is heterogeneously distributed, forming small iron oxide nanoclusters and Fe x/ZrO 2 (tetragonal) spots at the catalyst surface. The photocatalytic activity of the un-doped and iron-doped binary system ZrO 2-TiO 2 was investigated in two kind of photoreactions: the salicylic acid photooxidation and the photocatalytic reduction of Cr(VI). Different photocatalytic behaviour has been found for the un-doped and iron-doped ZrO 2-TiO 2 systems which have been explained in terms of the EXAFS study. This study represents an example of attempt to prepare a new potential photoactive mixed oxide system, containing two ions (Ti4+ and Zr4+) with good photocatalytic activity if it is compared with commercial TiO2 (Degusssa P25) calcined at 600 °C. 相似文献
13.
The water-gas shift (WGS) activity of platinum catalysts dispersed on a variety of single metal oxides as well as on composite MO x/Al 2O 3 and MO x/TiO 2 supports (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, La, Ce, Nd, Sm, Eu, Gd, Ho, Er, Tm) has been investigated in the temperature range of 150–500 °C, using a feed composition consisting of 3% CO an 10% H 2O. For Pt catalysts supported on single metal oxides, it has been found that both the apparent activation energy of the reaction and the intrinsic rate depend strongly on the nature of the support. In particular, specific activity of Pt at 250 °C is 1–2 orders of magnitude higher when supported on “reducible” compared to “irreducible” metal oxides. For composite Pt/MO x/Al 2O 3 and Pt/MO x/TiO 2 catalysts, it is shown that the presence of MO x results in a shift of the CO conversion curve toward lower reaction temperatures, compared to that obtained for Pt/Al 2O 3 or Pt/TiO 2, respectively. The specific reaction rate is in most cases higher for composite catalysts and varies in a manner which depends on the nature, loading, and primary crystallite size of dispersed MO x. Results are explained by considering that reducibility of small oxide particles increases with decreasing crystallite size, thereby resulting in enhanced WGS activity. Therefore, evidence is provided that the metal oxide support is directly involved in the WGS reaction mechanism and determines to a significant extent the catalytic performance of supported noble metal catalysts. Results of catalytic performance tests obtained under realistic feed composition, consisting of 3% CO, 10% H 2O, 20% H 2 and 6% CO 2, showed that certain composite Pt/MO x/Al 2O 3 and Pt/MO x/TiO 2 catalysts are promising candidates for the development of active WGS catalysts suitable for fuel cell applications. 相似文献
14.
采用溶胶-凝胶法制备硼氮共掺杂TiO 2光催化剂,利用X射线衍射、X射线光电子能谱及紫外-可见光漫反射光谱手段对制备的催化剂进行表征。结果表明,硼和氮均以间隙方式进入TiO 2晶格中,形成Ti-O-B、Ti-O-N和Ti-O-B-N结构,提高了催化剂活性;B-N-TiO 2吸收带边明显红移,表明催化剂对可见光吸收增强。可见光降解甲基橙结果表明,B-N-TiO 2的活性明显高于B-TiO 2和N-TiO 2,说明硼氮共掺杂改性对提高TiO 2可见光活性具有协同作用。 相似文献
15.
Chromium oxide catalysts supported on TiO 2 and Al 2O 3 were examined in a fixed-bed flow reactor system for the removal of PCE (perchloroethylene), a simulant of 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo- p-dioxin), and in a pilot plant employing actual flue gas from a sintering plant for the removal of PCDDs/PCDFs (poly-chlorinated dibenzo-dioxin/poly-chlorinated dibenzo-furan). The 12.5 wt.% chromium oxides supported on TiO 2 and Al 2O 3 revealed excellent stability and performance of PCE removal in the feed gas stream containing water vapor. In a pilot plant study, the catalysts washcoated on the honeycomb reactor revealed 93–95% of PCDDs/PCDFs removal activity over CrO x/Al 2O 3-HC20 (CrO x/Al 2O 3 catalyst washcoated on 20 cell-honeycomb), and more than 99% of the decomposition activity over CrO x/TiO 2-HC20 (CrO x/TiO 2 catalyst washcoated on 20 cell-honeycomb) at 325 °C and 5000 h −1 of reactor space velocity without the de novo synthesis of PCDDs/PCDFs. In particular, CrO x/TiO 2-HC20 showed 94% of PCDDs/PCDFs decomposition activity even at 280 °C reaction temperature. The catalyst also exhibited significant NO removal activity. The chromium oxide seems to be a promising catalyst for the removal of PCDDs/PCDFs and NO x contained in the flue gas. 相似文献
16.
Carbon-doped or carbon-covered titania can enhance photocatalytic performance under visible light. Here we report the first instance of synergistic effect of the carbon incorporation in anatase titania (TiO 2−xC x:C) films with both substitutional doping and surface covered characteristics, by reactively co-sputtering Ti metal and graphite targets. The nature of incorporated carbon is characterized by Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The absorption edge of the carbon incorporated titania thin films shifted from ultraviolet to visible region and directly depended on the carbon content. The photocatalytic performance, e.g., photodegradation of methylene blue (MB), photo-reduction of silver-ions and super hydrophilicity, was greatly enhanced with increasing carbon content. The best photocatalytic activity is obtained in the TiO 2−xC x:C film of the most carbon concentration about 9.3 at.% with a degradation rate-constant of 0.108 h −1 for MB under visible-light illumination. 相似文献
17.
Functionalized mesoporous TiO 2 molecular sieves were prepared by treating ordered mesoporous TiO 2 with phosphoric acid or ammonium sulfate at high temperature. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption–desorption measurement, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectrometer (FT-IR). The photocatalytic activity of the samples was evaluated by photocatalytic decomposition of bromomethane (CH 3Br) in air. Results revealed that the functionalized TiO 2 samples preserved ordered mesostructure and exhibited enhanced physicochemical properties. The photocatalytic activity of the functionalized mesoporous TiO 2 sample was about three times higher than that of the pure mesoporous TiO 2. The concentrations of phosphoric acid and ammonium sulfate solutions used for the functionalization of TiO 2 greatly influenced the photocatalytic activity of the resultants materials. The optimal concentrations of phosphoric acid and ammonium sulfate solutions were 0.05 and 0.10 M, respectively. The enhanced photocatalytic performance of the functionalized mesoporous TiO 2 could be attributed to large specific surface area, high hydroxyl density, and enhanced surface chemical state. 相似文献
18.
The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO 2, SiO 2–Al 2O 3, activated carbon, mordenite type zeolites, MgO, TiO 2 and Al 2O 3. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO 2 and Al 2O 3 containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO x catalysts supported on TiO 2 and Al 2O 3 also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO x/TiO 2 revealed stronger water tolerance than CrO x/Al 2O 3 due to the surface hydrophobicity. 相似文献
19.
NO and NO 2 (NO x) sorption, desorption and reduction by hydrogen, carbon monoxide and/or propene were investigated on a TiO 2-supported heteropolyacid, 12-tungstophosphoric acid hexahydrate (HPW), promoted by platinum. A model taking into account NO x sorption, desorption and reduction was established. Kinetic constants for NO x sorption, desorption and reduction were extracted by modelling for the investigated range of temperature (170–300 °C). 相似文献
20.
Kinetics of oxidative photodegradation of Monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in different photocatalytic systems (iron, TiO 2 and combined system iron + TiO 2) were investigated and compared. The influence of iron addition on TiO 2 photocatalyst and of TiO 2 on the photocatalytic cycle Fe(III)/Fe(II) were carefully studied. A very positive effect of iron addition was observed. This phenomenon was more and more pronounced when TiO 2 concentration was lower. In a suspension of TiO 2 (24 mg L −1) with addition of Fe(III) (3 × 10 −4 mol L −1) the measured rate constant was similar to that obtained in a suspension of TiO 2 with a concentration more than 20 times higher (500 mg L −1). The mechanistic approach carried out in this study allows us to identify the main reactions governing the combined system and a photochemical cycle was proposed. The optimisation of the photocatalytic systems was obtained when each photocatalyst plays a specific role: Fe(III) as a main OH radicals source and TiO 2 as an oxidizing agent of Fe(II). 相似文献
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