Mesoporous RuO2–TiO2 nanocomposites at different RuO2 concentrations (0–10 wt %) are prepared through a simple one‐step sol–gel reaction of tetrabutyl orthotitanate with ruthenium(III) acetylacetonate in the presence of an F127 triblock copolymer as structure‐directing agent. The thus‐formed RuO2–TiO2 network gels are calcined at 450 °C for 4 h leading to mesoporous RuO2–TiO2 nanocomposites. The photocatalytic CH3OH oxidation to HCHO is chosen as the test reaction to examine the photocatalytic activity of the mesoporous RuO2–TiO2 nanocomposites under UV and visible light. The photooxidation of CH3OH is substantially affected by the loading amount and the degree of dispersion of RuO2 particles onto the TiO2, which indicates the exclusive effect of the RuO2 nanoparticles on this photocatalytic reaction under visible light. The measured photonic efficiency ξ=0.53 % of 0.5 wt % RuO2–TiO2 nanocomposite for CH3OH oxidation is maximal and the further increase of RuO2 loading up to 10 wt % gradually decreases this value. The cause of the visible‐light photocatalytic behavior is the incorporation of small amounts of Ru4+ into the anatase lattice. On the other hand, under UV light, undoped TiO2 shows a very good photonic efficiency, which is more than three times that for commercial photocatalyst, P‐25 (Evonik–Degussa); however, addition of RuO2 suppresses the photonic efficiency of TiO2. The proposed reaction mechanism based on the observed behavior of RuO2–TiO2 photocatalysts under UV and visible light is explored. 相似文献
The electronic structure and photoactivation process in N‐doped TiO2 is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO2 catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti3+ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO2, the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (Ns.), oxygen vacancies with one electron (Vo.), and Ti3+ ions are produced with light irradiation and the intensity of Ns. species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO2 corresponding to the main absorption band at 410 nm of N‐doped TiO2, but oxygen vacancies and Ti3+ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO2 is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic Ns. species but they stabilize the active nitrogen species Ns?. 相似文献
Spatial isolation of different functional sites at the nanoscale in multifunctional catalysts for steering reaction sequence and paths remains a major challenge. Herein, we reported the spatial separation of dual-site Au and RuO2 on the nanosurface of TiO2 (Au/TiO2/RuO2) through the strong metal-support interaction (SMSI) and the lattice matching (LM) for robust photocatalytic hydrogen evolution. The SMSI between Au and TiO2 induced the encapsulation of Au nanoparticles by an impermeable TiOx overlayer, which can function as a physical separation barrier to the permeation of the second precursor. The LM between RuO2 and rutile-TiO2 can increase the stability of RuO2/TiO2 interface and thus prevent the aggregation of dual-site Au and RuO2 in the calcination process of removing TiOx overlayer of Au. The photocatalytic hydrogen production is used as a model reaction to evaluate the performance of spatially separated dual-site Au/TiO2/RuO2 catalysts. The rate of hydrogen production of the Au/TiO2/RuO2 is as high as 84 μmol h−1 g−1 under solar light irradiation without sacrificial agents, which is 2.5 times higher than the reference Au/TiO2 and non-separated Au/RuO2/TiO2 samples. Systematic characterizations verify that the spatially separated dual-site Au and RuO2 on the nanosurface of TiO2 can effectively separate the photo-generated carriers and lower the height of the Schottky barrier, respectively, under UV and visible light irradiation. This study provides new inspiration for the precise construction of different sites in multifunctional catalysts. 相似文献
A green low-temperature deposition and crystallization method was developed to uniformly coat RuO2/TiO2 nanocomposite onto cotton fabrics for efficient solar photocatalysis. The sequential growth of anatase TiO2 and rutile RuO2 on the surface of the cotton was confirmed by XRD, Raman and XPS characterizations. After the deposition of RuO2, the optical properties of RuO2/TiO2/Cotton revealed better visible light absorption and higher charge mobility, and XPS spectra showed that the peaks of Ti 2p3/2 and O 1 s shifted towards the lower binding energies due to the interfacial charge transfer at the robust RuO2/TiO2 mediated with Ti–O–Ru bonding. The photocatalytic performances of the RuO2/TiO2/Cotton were evaluated towards the photodegradation of o-toluidine (o-TD), an aromatic amine widely used in the chemical industry. Compared with TiO2/Cotton, RuO2/TiO2/Cotton exhibited a remarkable improvement in the photocatalytic activity. The presence of RuO2 on the surface of TiO2/Cotton narrowed the band gap and improved the absorption of visible light. Moreover, the successful formation of a robust heterogeneous interface between TiO2 and RuO2 suppressed the charge carrier (e–/h+) recombination effectively. With the RuO2/TiO2 coating chemically bound to the cotton fibers, RuO2/TiO2/Cotton delivered long-term stability in photocatalytic activity and high mechanical durability even after 20 washing times. Our facile and scalable synthesis strategy paved a universal route to efficient immobilization of visible-light-responsible TiO2-based photocatalysts on the low-heat-resistant substrates for various applications.
Summary. The thermal and photoassisted catalytic oxidation of CO at metal oxide supported RuO2·xH2O was studied at room temperature. Contrary to neat RuO2·xH2O the supported catalysts suffer from fast deactivation attributed to strong adsorption of the reaction product carbon dioxide.
The latter can be efficiently removed from the catalyst surface at elevated temperatures. In some cases, i.e. for catalysts supported with selected n-type semiconductors (TiO2, SnO2, WO3), efficient CO2 desorption and good, constant catalytic activity was observed upon visible light irradiation. Under such conditions the CO
to CO2 conversion observed for RuO2·xH2O/TiO2 was nearly as good and stable as for the unsupported catalyst. It is suggested that light absorption promotes carbon dioxide
desorption through positive charging of the catalyst surface. 相似文献
Anatase TiO2 nanosheets with exposed {001} facets have been controllably modified under non‐thermal dielectric barrier discharge (DBD) plasma with various working gas, including Ar, H2, and NH3. The obtained TiO2 nanosheets possess a unique crystalline core/amorphous shell structure (TiO2@TiO2?x), which exhibit the improved visible and near‐infrared light absorption. The types of dopants (oxygen vacancy/surface Ti3+/substituted N) in oxygen‐deficient TiO2 can be tuned by controlling the working gases during plasma discharge. Both surface Ti3+ and substituted N were doped into the lattice of TiO2 through NH3 plasma discharge, whereas the oxygen vacancy or Ti3+ (along with the oxygen vacancy) was obtained after Ar or H2 plasma treatment. The TiO2@TiO2?x from NH3 plasma with a green color shows the highest photocatalytic activity under visible‐light irradiation compared with the products from Ar plasma or H2 plasma due to the synergistic effect of reduction and simultaneous nitridation in the NH3 plasma. 相似文献
Nickel, nitrogen-codoped mesoporous TiO2 microspheres (Ni–N–TiO2) with high surface area, and an effective direct band gap energy of ∼2.58 eV. Nickel sulfate used as the Ni source and ammonia gas as the N source here. The efficiency of the as-prepared samples was investigated by monitoring the degradation of Rhodamine B under visible light irradiation. The experimental results indicate that Ni-doped mesoporous TiO2 microspheres show higher photocatalytic activity than mesoporous TiO2 microspheres under visible light irradiation. It mainly due to that the electron trap level (Ni2+/Ni+) promoting the separation of charge carriers and the oxygen vacancies inducing the visible light absorption. In addition, Ni–N–TiO2 shows enhanced activity compared with Ni–TiO2. Codopants and dopants are found to be uniformly distributed in TiO2 matrix. Among the all samples the 0.5% molar quantity of Ni dopant and 500 °C 2 h nitriding condition gives the highest photocatalytic activity. The treatment of ammonia gas on Ni–TiO2 sample induced oxygen vancancies, substitutional and interstitial N. A suitable treatment by ammonia gas also promote separation of charge carriers and the absorption of visible light. The active species generated in the photocatalytic system were also investigated. The strategy presented here gives a promising route towards the development of a metal and non-metal codoped semiconductor materials for applied photocatalysis and related applications. 相似文献
Nanosized cerium and nitrogen co-doped TiO2 (Ce–TiO2?xNx) was synthesized by sol gel method and characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), FESEM, Fourier transform infrared, N2 adsorption and desorption methods, photoluminescence and ultraviolet–visible (UV–vis) DRS techniques. PXRD analysis shows the dopant decreases the crystallite sizes and slows the crystallization of the titania matrix. XPS confirm the existence of cerium ion in +3 or +4 state, and nitrogen in ?3 state in Ce–TiO2?xNx. The modified surface of TiO2 provides highly active sites for the dyes at the periphery of the Ce–O–Ti interface and also inhibits Ce particles from sintering. UV–visible DRS studies show that the metal–metal charge transfer (MMCT) of Ti/Ce assembly (Ti4+/Ce3+ → Ti3+/Ce4+) is responsible for the visible light photocatalytic activity. Photoluminescence was used to determine the effect of cerium ion on the electron–hole pair separation between the two interfaces Ce–TiO2?xNx and Ce2O3. This separation increases with the increase of cerium and nitrogen ion concentrations of doped samples. The degradation kinetics of methylene blue and methyl violet dyes in the presence of sol gel TiO2, Ce–TiO2?xNx and commercial Degussa P25 was determined. The higher visible light activity of Ce–TiO2?xNx was due to the participation of MMCT and interfacial charge transfer mechanism. 相似文献
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. 相似文献
In the present work, bismuth vanadate composited photocatalysts were synthesized and characterized. X‐ray diffractometry and Raman results showed that the particles were well crystallized, and formed by the complex of monoclinic BiVO4 and TiO2. On electron microscopy, the photocatalyst exhibited high crystallization, agglutination and irregular shape, and was surrounded by numerous TiO2 particles. The study of surface areas showed that the specific surface area of 30‐BiVO4/TiO2 composited was 112 m2·g?1, which was nearly 10 times that of pure BiVO4. The ultraviolet–visible diffuse reflectance spectra indicated the composited photocatalyst were activated in visible light. The activity of photocatalytic water splitting was studied. The results showed that monomer BiVO4 photocatalyst was not able to produce hydrogen under any light source. BiVO4/TiO2 composited photocatalysts, however, were capable of generating hydrogen. Under UV light irradiation for 120 min, 1 g catalyst dispersed in 50 mL deionized water produced almost 1 mL hydrogen, such that the productivity of hydrogen was higher than that of P25‐TiO2. Photocatalytic decomposition of water under visible light also confirmed that the BiVO4/TiO2 composited photocatalyst had the ability of water splitting. 相似文献
Although Cr-doped (0.85 at%) TiO2 absorbs in the visible region, it becomes a photoconductor only through band-gap illumination and the doping causes a considerable decrease in photoconductance. Its activity for oxidations (oxalic acid, propene, 2-propanol) and for oxygen isotope exchange is nil under visible illumination and is 25–1000 times diminished under UV light. This is attributed to an increase in electron—hole recombination at the Cr3+ ion sites. Conversely, similar doping might be envisaged to enhance the light stability of TiO2-containing materials if the colorimetric properties were maintained. 相似文献
The development of visible‐light‐active photocatalysts is being investigated through various approaches. In this study, C60‐based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water‐soluble fullerol (C60(OH)x) instead of C60, we demonstrate that the adsorbed fullerol activates TiO2 under visible‐light irradiation through the “surface–complex CT” mechanism, which is largely absent in the C60/TiO2 system. Although fullerene and its derivatives have often been utilized in TiO2‐based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible‐light sensitizer of TiO2 is not well established. Fullerol/TiO2 exhibits marked visible photocatalytic activity not only for the redox conversion of 4‐chlorophenol, I?, and CrVI, but also for H2 production. The photoelectrode of fullerol/TiO2 also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO2 and C60/TiO2, which confirms that the visible‐light‐induced electron transfer from fullerol to TiO2 is particularly enhanced. The surface complexation of fullerol/TiO2 induced a visible absorption band around 400–500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO2. The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol.+) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO2 cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO2 cluster) as the origin of the visible‐light absorption. 相似文献
Irradiation of acidic (pH 2) solutions of RuL32+ 2Cl? (L = diisopropyl 2,2′-bipyridine-4,4′ -dicarboxylate) in the presence of TiO2 at 100°C leads to the loss of one bipyridyl ligand and the chemical fixation of RuL2 at the surface of teh TiO2 particles through formation of Ru-O-Ti bonds. These surface complexes are very stable and shift the absorption onset of TiO2 beyond 600 mm. Efficient sensitization H2-generation is achieved with this system beginning in the wave length domain between 590 and 665 nm. Preliminary water cleavage experiments with bifunctional TiO2/Pt/RuO2 redox catalyst are reported. 相似文献
In situ reduction of previously adsorbed Pt4+ species on TiO2 (anatase) was employed to obtain highly active catalysts for hydrogen photoevolution from a methanol-water solution. A quantum yield as high as 22% was observed. Optimum platinum coverage and the most favourable reaction conditions were established. The influence of surface Cr2O3 admixtures on photoactivity of TiO2 was investigated. It was found that although the dopant shifts the anatase spectrum into the visible, it was not possible to obtain hydrogen with light of energy smaller than the bandgap of TiO2. However, a small amount of Cr2O3 on the TiO2 surface acts as a poor catalyst for hydrogen evolution. 相似文献
Fe3+-doped TiO2 composite nanoparticles with different doping amounts were successfully synthesized using sol-gel method and characterized
by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultravioletvisible spectroscopy (UV-Vis) diffuse reflectance
spectra (DRS). The photocatalytic degradation of methylene blue was used as a model reaction to evaluate the photocatalytic
activity of Fe3+/TiO2 nanoparticles under visible light irradiation. The influence of doping amount of Fe3+ (ω: 0.00%–3.00%) on photocatalytic activities of TiO2 was investigated. Results show that the size of Fe3+/TiO2 particles decreases with the increase of the amount of Fe3+ and their absorption spectra are broaden and absorption intensities are also increased. Doping Fe3+ can control the conversion of TiO2 from anatase to rutile. The doping amount of Fe3+ remarkably affects the activity of the catalyst, and the optimum efficiency occurs at about the doping amount of 0.3%. The
appropriate doping of Fe3+ can markedly increase the catalytic activity of TiO2 under visible light irradiation.
__________
Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(6): 55–56 [译自: 西北师范大学学报(自然科学版)] 相似文献
Phosphotungstic acid (HPW) supported on Ce-doped three-dimensional ordered macroporous (3DOM) TiO2 catalysts are studied in catalytic oxidation desulfurization (ODS) of model oil. The structural and textural of as-synthesized catalysts are characterized by N2 adsorption, XRD, Raman spectroscopy, SEM-EDS, TEM, FT-IR, XPS, UV–Vis and ICP. These results upheld the existence of periodically arranged macroporous structure of catalyst, with Keggin-type of HPW dispersed homogeneously on TiO2 matrix. Among these 3DOM Ce-doped HPW/TiO2 materials, catalyst with 15 wt.% cerium dosage exhibits best ODS performance, which oxidized 99.8% of dibenzothiophene (DBT) into corresponding sulfone within 40 min. The excellent ODS performance of 3DOM Ce-doped HPW/TiO2 catalyst is related to the common influence of more oxygen vacancies produced by electron transformation between Ce3+ and Ce4+. The chemisorbed oxygen on the surface catalyst will facilitate the selective oxidation of sulfides to sulfones. Moreover, the 3DOM structure of catalyst will further promote the mass transfer of reactants and products on the pore channel. The as-prepared catalyst shows excellent reusability in the ODS system, no obviously decrease in catalytic activity even after 6 runs. 相似文献