Two kinds of TiO_2 nanometer thin films were prepared on stainless steel bythe reverse micellar and sol-gel methods, respectively. The calcined TiO_ 2 thin films werecharacterized by X-ray diffraction (XRD), atomic fo...Two kinds of TiO_2 nanometer thin films were prepared on stainless steel bythe reverse micellar and sol-gel methods, respectively. The calcined TiO_ 2 thin films werecharacterized by X-ray diffraction (XRD), atomic force microscopy (AFM), BET surface area and X-rayphotoelectron spectroscopy (XPS). Photocatalytic activity was evaluated by photocatalyticdecoloration of methyl orange aqueous solution. The results showed that the TiO_2 thin filmsprepared by reverse micellar method (designated as RM-TiO_2 films) showed higher photocatalyticactivity than those by sol-gel method (designated as SG-TiO_2 films). This is attributed to the factthat the former is composed of smaller monodispersed spherical particles with a size of about 15 nmand possesses higher surface areas.展开更多
The nanometer and ordinary anatase titanium dioxide(TiO_2) powders were adopted as the sonocatalysts for the degradation of methyl orange used as a model compound for the first time. It was found that the sonocatalyti...The nanometer and ordinary anatase titanium dioxide(TiO_2) powders were adopted as the sonocatalysts for the degradation of methyl orange used as a model compound for the first time. It was found that the sonocatalytic degradation effect of methyl orange in the presence of TiO_2 powder were much better than that without TiO_2, but the sonocatalytic activity of the nanometer anatase TiO_2 particle was obviously higher than that of ordinary anatase TiO_2 particle. Although there are many factors influencing sonocatalytic degradation of methyl orange, the experimental results showed that the best degradation ratio of methyl orange could be obtained when the experimental conditions were: initial concentration 15 mg/L, nanometer anatase TiO_2 adding amount 750 mg/L, ultrasonic frequency 40 kHz, output power 50 W, pH = 3.0 and temperature 40℃ within 150 min. In addition, the catalytic activity of reused nanometer anatase TiO_2 catalyst was also studied and found to decline gradually comparing with initial nanometer anatase TiO_2 catalyst. All experiments indicated that the method of the sonocatalytic degradation of organic pollutants in the presence of TiO_2 powder was an advisable choice for non- or low-transparent organic wastewaters.展开更多
Investigating lattice vibrations through Raman spectroscopy is a crucial method for studying crystalline materials.Carriers can interact with lattices and influence lattice vibrations;thus,it is feasible to study the ...Investigating lattice vibrations through Raman spectroscopy is a crucial method for studying crystalline materials.Carriers can interact with lattices and influence lattice vibrations;thus,it is feasible to study the effect of photo-generated carriers on phonons by analyzing changes in the Raman spectra of semiconductors.Rutile is one of the predominant crystalline phases of TiO_(2),which is a widely utilized metal oxide semiconductor.In this work,rutile TiO_(2) is coated on a thinned optical fiber to concentrate ultraviolet light energy within the material,thereby enhancing the generation of carriers and amplifying the changes in the Raman spectra.A Raman detection laser with a wavelength of 532 nm is utilized to collect the Raman spectra of rutile TiO_(2) during irradiation.Using this setup,the impact of photo-generated carriers on the phonons corresponding to Raman vibrational modes is researched.The localization and non-radiative recombination of photo-generated carriers contribute to a reduction in both the frequencies and lifetimes of phonons.This work provides a novel approach to researching the effect of carriers on phonons.展开更多
The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling ...The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling the coverage of molecular O_(2)on the surface via increasing or decreasing O_(2)exposure,two chemisorbed O_(2)species on the surface are confirmed,one at the bridging oxygen vacancy(Ov)site(O_(2)^(2-)/Ov)and the other at the five-fold coordinated titanium(Ti_(5c))site(O^(2-)/Ti_(5c)).At low O_(2)exposure,O^(2-)/Ov is the main species on the surface,which only leads to the O-H bond cleavage of CH_(3)OH,producing methoxy groups(CHgO).However,after the Ov sites are nearly filled by O_(2)at about 0.1 L O_(2)exposure,O_(2)/Tisc species begins to appear on R-TiO_(2)(110)surface,resulting in the formation of formaldehyde(CH_(2)O)via the reaction of O_(2)/Tisc species with CH_(3)OH or CH3O to break the C-H bond at low surface temperature.Moreover,the yield of CH_(2)O increases linearly with that of H_(2)O.In addition,when the 1 L O_(2)covered surface is irradiated with 355 nm UV irradiation to desorb and dissociate O_(2)/Ti_(5c)species,the yield of CH_(2)O decreases linearly with that of H_(2)O.Further analysis suggests that the charge state of O_(2)/Ti_(5c)may not change as the exposure of O_(2)changes on the R-TiO_(2)(110)surface,and O_(2)is most likely to adsorb on the Ti_(5c)sites in the form of O_(2)^(2-),not O_(2)^(-),The result not only advances our understanding on the adsorption state of O_(2)on TiO_(2),but also provides clues for low temperature C-H bond activation with O_(2)on TiO_(2).展开更多
Cyclohexane is a high-valued chemical receivingsignificant interest in liquid hydrogen storage technology.TiO_(2)-based catalysts show high performance in the photocatalytic dehydrogenation of cyclohexane under mild c...Cyclohexane is a high-valued chemical receivingsignificant interest in liquid hydrogen storage technology.TiO_(2)-based catalysts show high performance in the photocatalytic dehydrogenation of cyclohexane under mild conditions,but the detailed reaction mechanism is not well understood.With the surface science approaches,we have studied the adsorption and surface chemistry of cyclohexane on rutile TiO_(2)(110).The thermal desorption spectroscopy and X-ray photoelectron spectroscopy results both demonstrate the molecular adsorption of cyclohexane on rutile TiO_(2)(110).Upon the UV Hg light irradiation,photodesorption of cyclohexane occurs from both the chemisorbed monolayer and the multilayer.No decomposition nor dehydrogenation of cyclohexane occurs on rutile TiO_(2)(110).These results deepen the fundamental understanding of the surface chemistry of cyclohexane on the TiO_(2)surface.展开更多
The nanometer particles of TiO_2 and TiO_2/SiO_2 oxides wereprepared by sol-gel supercritical fluid drying method. The propertiesof TiO_2 and TiO_2/SiO_2 were characterized by means of BET(Brunner-Emmett- Teller metho...The nanometer particles of TiO_2 and TiO_2/SiO_2 oxides wereprepared by sol-gel supercritical fluid drying method. The propertiesof TiO_2 and TiO_2/SiO_2 were characterized by means of BET(Brunner-Emmett- Teller method), TEM (transmission electronmicroscopy), SEM (scanning electron microscopy), XRD (X-ray diffrac-tion) and FTIR (Fourier transform-infrared) techniques. The effectsof different preparation route, prehydrolysis and non-prehydrolysis,on the properties of TiO_2/SiO_2 oxide were also examined.展开更多
We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact stru...We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.展开更多
By means of first-principles calculations based on the ab initio pseudopotential andplane wave basis, we present self-consistent molecular dynamic calculations to determine a cleanTiO_2 crystal (001) surface geometry ...By means of first-principles calculations based on the ab initio pseudopotential andplane wave basis, we present self-consistent molecular dynamic calculations to determine a cleanTiO_2 crystal (001) surface geometry and surface electronic states structure. All calculations wereperformed for both rutile and anatase phases. Using a total energy minimization strategy, weacquired the general inward relaxations. The s-like surface states just above the lower valenceband at (001) surfaces both in the rutile and anatase phases are found. The band bending effectoccurs both in rutile and anatase (001) surfaces. It reduces the band gap by ac. 0.4 eV in rutileand ac. 0.8 eV in anatase, elevating the Fermi energy levels. Besides the band bending of thevalence band, surface states also lie near the bottom of the conduction band. The lower surfaceenergy of anatase makes nanocrystalline TiO_2 is often in the anatase phase below a critical size.Our results are in good agreement with the previous work and experimental data.展开更多
基金This project is financially supported by the National Natural Science Foundation of China (No.s 50272049, 50072016) The Excellent Young Teachers Program of MOE, China (No. (2002)350)
文摘Two kinds of TiO_2 nanometer thin films were prepared on stainless steel bythe reverse micellar and sol-gel methods, respectively. The calcined TiO_ 2 thin films werecharacterized by X-ray diffraction (XRD), atomic force microscopy (AFM), BET surface area and X-rayphotoelectron spectroscopy (XPS). Photocatalytic activity was evaluated by photocatalyticdecoloration of methyl orange aqueous solution. The results showed that the TiO_2 thin filmsprepared by reverse micellar method (designated as RM-TiO_2 films) showed higher photocatalyticactivity than those by sol-gel method (designated as SG-TiO_2 films). This is attributed to the factthat the former is composed of smaller monodispersed spherical particles with a size of about 15 nmand possesses higher surface areas.
基金Foundation item: The National Natural Science Foundation of China(No. 20371023)
文摘The nanometer and ordinary anatase titanium dioxide(TiO_2) powders were adopted as the sonocatalysts for the degradation of methyl orange used as a model compound for the first time. It was found that the sonocatalytic degradation effect of methyl orange in the presence of TiO_2 powder were much better than that without TiO_2, but the sonocatalytic activity of the nanometer anatase TiO_2 particle was obviously higher than that of ordinary anatase TiO_2 particle. Although there are many factors influencing sonocatalytic degradation of methyl orange, the experimental results showed that the best degradation ratio of methyl orange could be obtained when the experimental conditions were: initial concentration 15 mg/L, nanometer anatase TiO_2 adding amount 750 mg/L, ultrasonic frequency 40 kHz, output power 50 W, pH = 3.0 and temperature 40℃ within 150 min. In addition, the catalytic activity of reused nanometer anatase TiO_2 catalyst was also studied and found to decline gradually comparing with initial nanometer anatase TiO_2 catalyst. All experiments indicated that the method of the sonocatalytic degradation of organic pollutants in the presence of TiO_2 powder was an advisable choice for non- or low-transparent organic wastewaters.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52122008,51978024,and 52370003)the Science and Technology and Innovation Commission of Shen Zhen Municipality(Grant No.JCYJ20200109105212568).
文摘Investigating lattice vibrations through Raman spectroscopy is a crucial method for studying crystalline materials.Carriers can interact with lattices and influence lattice vibrations;thus,it is feasible to study the effect of photo-generated carriers on phonons by analyzing changes in the Raman spectra of semiconductors.Rutile is one of the predominant crystalline phases of TiO_(2),which is a widely utilized metal oxide semiconductor.In this work,rutile TiO_(2) is coated on a thinned optical fiber to concentrate ultraviolet light energy within the material,thereby enhancing the generation of carriers and amplifying the changes in the Raman spectra.A Raman detection laser with a wavelength of 532 nm is utilized to collect the Raman spectra of rutile TiO_(2) during irradiation.Using this setup,the impact of photo-generated carriers on the phonons corresponding to Raman vibrational modes is researched.The localization and non-radiative recombination of photo-generated carriers contribute to a reduction in both the frequencies and lifetimes of phonons.This work provides a novel approach to researching the effect of carriers on phonons.
基金This work was supported by the National Natural Science Foundation of China(No.21973010)Liaoning Revitalization Talents Program(No.XLYC1907032)The authors thank Qing Guo at Southern University of Science and Technolog for many insightful discussions。
文摘The activity and adsorption behavior of oxygen on rutile TiO_(2)(110)(RTiO_(2)(110))were investigated using the temperature programmed desorption(TPD)method with methanol(CH_(3)OH)as the probe molecule.By controlling the coverage of molecular O_(2)on the surface via increasing or decreasing O_(2)exposure,two chemisorbed O_(2)species on the surface are confirmed,one at the bridging oxygen vacancy(Ov)site(O_(2)^(2-)/Ov)and the other at the five-fold coordinated titanium(Ti_(5c))site(O^(2-)/Ti_(5c)).At low O_(2)exposure,O^(2-)/Ov is the main species on the surface,which only leads to the O-H bond cleavage of CH_(3)OH,producing methoxy groups(CHgO).However,after the Ov sites are nearly filled by O_(2)at about 0.1 L O_(2)exposure,O_(2)/Tisc species begins to appear on R-TiO_(2)(110)surface,resulting in the formation of formaldehyde(CH_(2)O)via the reaction of O_(2)/Tisc species with CH_(3)OH or CH3O to break the C-H bond at low surface temperature.Moreover,the yield of CH_(2)O increases linearly with that of H_(2)O.In addition,when the 1 L O_(2)covered surface is irradiated with 355 nm UV irradiation to desorb and dissociate O_(2)/Ti_(5c)species,the yield of CH_(2)O decreases linearly with that of H_(2)O.Further analysis suggests that the charge state of O_(2)/Ti_(5c)may not change as the exposure of O_(2)changes on the R-TiO_(2)(110)surface,and O_(2)is most likely to adsorb on the Ti_(5c)sites in the form of O_(2)^(2-),not O_(2)^(-),The result not only advances our understanding on the adsorption state of O_(2)on TiO_(2),but also provides clues for low temperature C-H bond activation with O_(2)on TiO_(2).
基金This work is supported by the National Natural Science Foundation of China(No.22202191).
文摘Cyclohexane is a high-valued chemical receivingsignificant interest in liquid hydrogen storage technology.TiO_(2)-based catalysts show high performance in the photocatalytic dehydrogenation of cyclohexane under mild conditions,but the detailed reaction mechanism is not well understood.With the surface science approaches,we have studied the adsorption and surface chemistry of cyclohexane on rutile TiO_(2)(110).The thermal desorption spectroscopy and X-ray photoelectron spectroscopy results both demonstrate the molecular adsorption of cyclohexane on rutile TiO_(2)(110).Upon the UV Hg light irradiation,photodesorption of cyclohexane occurs from both the chemisorbed monolayer and the multilayer.No decomposition nor dehydrogenation of cyclohexane occurs on rutile TiO_(2)(110).These results deepen the fundamental understanding of the surface chemistry of cyclohexane on the TiO_(2)surface.
基金Supported by PetroChina Company Limited (990801-21-2).
文摘The nanometer particles of TiO_2 and TiO_2/SiO_2 oxides wereprepared by sol-gel supercritical fluid drying method. The propertiesof TiO_2 and TiO_2/SiO_2 were characterized by means of BET(Brunner-Emmett- Teller method), TEM (transmission electronmicroscopy), SEM (scanning electron microscopy), XRD (X-ray diffrac-tion) and FTIR (Fourier transform-infrared) techniques. The effectsof different preparation route, prehydrolysis and non-prehydrolysis,on the properties of TiO_2/SiO_2 oxide were also examined.
文摘We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.
基金The project supported by National Key Project of China for Basic Research on Photovoltaic Cell (No. G2000028200)
文摘By means of first-principles calculations based on the ab initio pseudopotential andplane wave basis, we present self-consistent molecular dynamic calculations to determine a cleanTiO_2 crystal (001) surface geometry and surface electronic states structure. All calculations wereperformed for both rutile and anatase phases. Using a total energy minimization strategy, weacquired the general inward relaxations. The s-like surface states just above the lower valenceband at (001) surfaces both in the rutile and anatase phases are found. The band bending effectoccurs both in rutile and anatase (001) surfaces. It reduces the band gap by ac. 0.4 eV in rutileand ac. 0.8 eV in anatase, elevating the Fermi energy levels. Besides the band bending of thevalence band, surface states also lie near the bottom of the conduction band. The lower surfaceenergy of anatase makes nanocrystalline TiO_2 is often in the anatase phase below a critical size.Our results are in good agreement with the previous work and experimental data.
