Nanotube Titanic Acid Research Articles

Preparation of black titanium monoxide nanoparticles and their potential in electromagnetic wave absorption

In this work, black titanium monoxide (TiO) nanoparticles were synthesized by hydrogen assisted magnesium thermal reduction method from nanotube titanic acid (NTA) and their electromagnetic properties were investigated. The black TiO nanoparticles exhibited the optimal reflection loss of −37.7 dB at a thin absorbance layer of 1.2 mm in thickness, which showing a promising candidate in electromagnetic wave absorbing (EA). To explore the mechanism of EA, TiO nanoparticles prepared from the other two initiators (commercial grade TiO and P25 titanium dioxide) was used as a comparison. The results show that the crystalline structure and microscopic defects, which arouse from the formation of TiO in the hydrogen assisted process, affect the electromagnetic performance of Ti-O binary system significantly in addition to their intrinsic effects. We hope this study help to open a new way for the designing of high-performance EA materials.

Synergistic effect of {101} crystal facet and bulk/surface oxygen vacancy ratio on the photocatalytic hydrogen production of TiO2

Anatase titanium dioxide (TiO2) nanocrystals with different percentages (up to 95%) of exposed {101} facet and different concentration ratios of bulk single-electron-trapped oxygen vacancies (SETOVs) to surface oxygen vacancies (SOVs) were prepared by alcohol-thermal method with nanotube titanic acid as the precursor in combination with solid-state reduction by NaBH4. The as-prepared TiO2 nanocrystals were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and ultraviolet–visible light spectrometry. The effects of the percentage of crystal facets and the concentration ratio of bulk SETOVs/SOVs on the photocatalytic hydrogen production rate of TiO2 nanocrystals were investigated with positron annihilation lifetime spectroscopy as well as photocurrent test. Findings indicate that the percentage of the exposed {101} facets of the as-prepared TiO2 nanocrystals and their concentration ratios of bulk SETOVs/SOVs can be well tuned by properly adjusting the amount of NaBH4 and the reduction reaction time as well. Increasing percentage of the {101} facet of anatase TiO2 nanocrystals contributes to improving their photocatalytic hydrogen production activity, because the {101} facets of the anatase TiO2 nanocrystals possess enriched electrons and can act as the reduction sites to enhance the reduction reaction of H+ affording H2 in the sacrifice system of splitting water. Both the bulk SETOVs and SOVs contribute to the improvement of the light absorption while SOVs can facilitate the separation of photogenerated charges, thereby adding to the photocatalytic activity. However, the bulk SETOVs and excessive SOVs are also the combination centers of photogenerated charges, which means it is essential to maintain a suitable concentration ratio of the bulk SETOVs/SOVs so as to enhance the light absorption and achieve the best separation efficiency of photogenerated charges and achieve the best photocatalytic activity for hydrogen production. Particularly, when anatase TiO2 nanocrystal with a high percentage (95%) of exposed {101} facet is reduced by NaBH4 at a mass ratio of 2: 1 for 20 min, the resultant reduced H-TiO2 nanocrystal (denoted as H-TiO2-R20(2:1)) provides the highest photocatalytic hydrogen productive rate. Furthermore, the combination of 0.5% Pt/H-TiO2-R20(2:1) with 0.5% Pt/WO3 can split water to simultaneously produce H2 and O2, showing promising potential for splitting water affording hydrogen and oxygen.

Construction of self-sufficient Z-scheme Ag3PW12O40/TiO2 photocatalysts for the improved visible-light-driven photo-degradation of rhodamine B

Nanotube titanic acid (denoted as NTA), a tubular mesoporous material, after it undergoes heat-treatment at high temperature, is a novel kind of TiO2 containing a single-electron-trapped oxygen vacancy (V O • ) originating from the intra-layered dehydration of NTA that can be achieved. Unfortunately, the presence of oxygen vacancy arouses the response of the novel TiO2 to visible light, but it is inert under visible-light irradiation because of the absence of the efficient electron acceptors. Just making up for the rapid charge recombination of unitary system photocatalyst, by facilitating the electron fast transfer simultaneously, a series of Ag3PW12O40/TiO2 composite photocatalysts were synthesized via a facile hydrothermal route using Ag3PW12O40 (a kind of saturated Keggin polyoxometallate) and nanotube titanic acid (NTA) as starting material. As-fabricated photocatalysts were characterized by XRD, UV–Vis DRS, XPS, ESR, BET, SEM, TEM, PL and photoelectrochemical measurements. The photocatalytic performance of these composites was appraised by monitoring the photo-degradation of organic pollutant rhodamine B (10 mg/L) under visible-light irradiation (420 nm < λ < 800 nm) a with spectrophotometer. The as-prepared Ag3PW12O40/TiO2 composites displayed enhanced photocatalytic performance towards the decomposition of rhodamine B. The active species trapping experiment revealed that the significantly improved photocatalytic activity was attributed to the constructing of Z-scheme Ag3PW12O40/Ag/TiO2, greatly inducing the efficient separation of the photo-generated carriers by means of Ag nanoparticles serving as the charge transmission channel. Herein, Ag nanoparticles were formed via the reduction of Ag+ by the electrons in the oxygen vacancy state during hydrothermal preparation. At the same time, the present work provides a new way to extend application of other polyoxometalates in the photocatalysis field.

The synergistic effect of phase heterojunction and surface heterojunction to improve photocatalytic activity of VO•–TiO2: the co-catalytic effect of H3PW12O40

With nanotube titanic acid (abbreviated as NTA) and the 12-tungstophosphoric acid (H3PW12O40•xH2O, denoted as HPW) as start materials, respectively, according to a simple hydrothermal process in acid medium, we successfully prepared HPW modified VO•–TiO2 composite photocatalysts. During heat treatment companied by the transformation of NTA to TiO2, a kind of single-electron-trapped oxygen vacancy (VO•) could be formed contributing to the visible light absorption of catalysts. The morphology, phase and chemical structure, optical and electronic properties, and so on of the produced catalysts with various HPW loadings are characterized. The size range of synthesized photocatalyst nanoparticles are about 10~50 nm. Taking aqueous rhodamine B (RhB) dye as model pollutant, we carried out photocatalytic activity test of the achieved catalysts, revealing that the hybrid photocatalysts display significantly enhanced visible light-driven (λ ≥ 420 nm) photocatalytic activity for degradation of RhB. Among various catalysts, HPWN-0.1-120 composite with nominal loading of 0.1 g HPW and heat treatment temperature of 120 °C possesses the highest photocatalytic performance in visible light, which is closely related to the co-effect of phase heterojunction of rutile/anatase, surface heterojunction of anatase/HPW, and oxygen vacancy (VO•). The two types of heterojunction promote greatly the separation efficiency of photoelectrons and photoholes and oxygen vacancy lures response of catalysts to visible light.

Effect of annealing ambience on the formation of surface/bulk oxygen vacancies in TiO2 for photocatalytic hydrogen evolution

Abstract The surface and bulk oxygen vacancy have a prominent effect on the photocatalytic performance of TiO 2 . In this study, TiO 2 possessing different types and concentration of oxygen vacancies were prepared by annealing nanotube titanic acid (NTA) at various temperatures in air or vacuum atmosphere. TiO 2 with the unitary bulk single-electron-trapped oxygen vacancies (SETOVs) formed when NTA were calcined in air. Whereas, TiO 2 with both bulk and surface oxygen vacancies were obtained when NTA were annealed in vacuum. The series of TiO 2 with different oxygen vacancies were systematically characterized by TEM, XRD, PL, XPS, ESR, and TGA. The PL and ESR analysis verified that surface oxygen vacancies and more bulk oxygen vacancies could form in vacuum atmosphere. Surface oxygen vacancies can trap electron and hinder the recombination of photo-generated charges, while bulk SETOVs act as the recombination center. The surface or bulk oxygen vacancies attributed different roles on the photo-absorbance and activity, leading that the sample of NTA-A400 displayed higher hydrogen evolution rate under UV light, whereas NTA-V400 displayed higher hydrogen evolution rate under visible light because bulk SETOVs can improve visible light absorption because sub-band formed by bulk SETOVs prompted the secondary transition of electron excited.

Effect of the calcination temperature on the visible light photocatalytic activity of direct contact Z-scheme g-C3N4-TiO2 heterojunction

Z-scheme g-C3N4-TiO2 heterojunctions containing g-C3N4 nanosheets with different thickness were prepared by sintering the mixture of g-C3N4 and nanotube titanic acid (denoted as NTA) at different temperatures in air. As-prepared Z-scheme g-C3N4-TiO2 heterojunctions were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible light diffuse reflectance spectrometry, electron spin resonance, and photoluminescence spectrometry. Findings indicate that the annealing temperature has crucial effects on the visible-light photocatalytic activity (λ≥420nm) of the as-prepared Z-scheme g-C3N4-TiO2 heterojunctions. The Ti3+ and porous g-C3N4 nanosheets formed upon the calcination at 600°C as well as the low concentration of bulk single-electron trapped oxygen vacancy are favorable to the transport of the photoexcited charge carriers. This, in association with the Z-scheme system, contributes to improving the photocatalytic activity of g-C3N4-TiO2 photocatalysts. As a result, g-C3N4-TiO2 photocatalyst prepared at 600°C exhibits good photocatalytic activity towards the degradation of propylene and hydrogen generation by water-splitting under visible light irradiation.

Facile synthesis of a conjugation-grafted-TiO2 nanohybrid with enhanced visible-light photocatalytic properties from nanotube titanic acid precursors

A conjugation-grafted-TiO2 nanohybrid was synthesized by chemically grafting conjugated structures on the surface of nanotube titanic acid (NTA) precursor-based TiO2 through the controlled thermal degradation of a coacervated polymer layer of polyvinyl alcohol (PVA). The interfacial interactions between the NTA precursor-based TiO2 and conjugated structures were characterized using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Moreover, the effects of the NTA’s pretreatment temperature and the weight ratio of NTA to PVA on the photocatalytic degradation of methyl orange were also investigated. A higher NTA pretreatment temperature and a lower NTA to PVA weight ratio were found to enhance photogenerated electron–hole separation efficiency and photocatalytic activity. Moreover, the conjugation-grafted-TiO2 nanohybrid synthesized from the NTA precursor displayed a much higher visible-light photocatalytic activity than that of the sample obtained from the P25 precursor. The origin of the enhanced photocatalytic activity under visible-light irradiation is also discussed in detail.

Enhanced visible light activity on direct contact Z-scheme g-C3N4-TiO2 photocatalyst

Direct contact Z-scheme g-C3N4-TiO2 nanocomposites without an electron mediator are prepared via simple annealing the mixture of bulk g-C3N4 and nanotube titanic acid (NTA) in air at 600°C for 2h. In the process of annealing, the bulk g-C3N4 transformed to ultra-thin g-C3N4 nanosheets, and NTA converted to a novel anatase TiO2, then the two components formed a close interaction. The XPS result reveals that some amount of nitrogen is doped into this novel-TiO2, and g-C3N4 nanosheets exist in the composites. The results of XRD, TEM and TG indicate that the thickness of g-C3N4 nanosheets is very thin. The ESR spectrum shows the existence of Ti3+ and single-electron-trapped oxygen vacancy in the 30%g-C3N4-TiO2 composites. In photocatalytic activity test, the 30%g-C3N4-TiO2 nanocomposites showed an excellent photo-oxidation activity of propylene under visible light irradiation (λ≥420nm), and the removal efficiency of propylene reached as high as 56.6%, and the activity kept nearly 82% after four consecutive recycles. Photoluminescence (PL) result using terephthalic acid (TA) as a probe molecule indicated that the g-C3N4-TiO2 nanocomposites displayed a Z-sheme photocatalytic reaction system and this should be the main reason for the high photocatalytic activity. A possible photocatalytic mechanism was proposed on the basis of PL result and transient photocurrent-time curves.

Surface heterojunction between (001) and (101) facets of ultrafine anatase TiO2 nanocrystals for highly efficient photoreduction CO2 to CH4

Shape-dependent ultrafine anatase TiO2 nanocrystals coexposed with (001) and (101) facets are synthesized in isopropanol by the simple solvothermal strategy. Nanotube titanic acid (NTA) was used as the Ti precursor, and hydrofluoric acid was the shape-control reagent. The nanotubular structure of NTA facilitated HF to adsorb on/into NTA, and made the shape-controlled process to be more economical and easier. The ratio of (001) facets of the obtained decahedral TiO2 nanocrystals can be adjusted from 5 to 51%, and the mean diameter of nanoparticles is about 10–30nm. The samples are characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscope, ultraviolet-visible diffuse reflectance spectrum, N2 adsorption-desorption isotherms, fluorescence and Raman spectroscopy. The truncated octahedral bipyramid TiO2 nanocrystals with 51% (001) and 49% (101) facets exposing showed the highest photoactivity for CO2 reduction to CH4. This remarkable photocatalytic efficiency is attributed to the surface heterojunction between (001) and (101) crystal facets, the small size and large surface area of the truncated octahedral bipyramid TiO2 nanocrystals.

Photoreduction of CO2 on TiO 2/SrTiO 3 Heterojunction Network Film.

Nanotube titanic acid (NTA) network film has a porous structure and large BET surface area, which lead them to possessing high utilization of the incident light and strong adsorption ability. We used NTA as the precursor to fabricate a TiO2/ SrTiO3 heterojunction film by the hydrothermal method. In the process of the reaction, part of NTA reacted with SrCl2 to form SrTiO3 nanocubes, and the remainder dehydrated to transform to the rutile TiO2. The ratio of TiO2 and SrTiO3 varied with the hydrothermal reaction time. SEM and TEM images indicated that SrTiO3 nanocubes dispersed uniformly on TiO2 film, and the particle size and crystallinity of SrTiO3 nanocubes increased with the reaction time prolonging. The TiO2/SrTiO3 heterojunction obtained by 1 h showed the best activity for CO2 photoreduction, where the mole ratio of TiO2 and SrTiO3 was 4:1. And the photo-conversion efficiency of CO2 to CH4 improved remarkably after the foreign electron traps of Pt and Pd nanoparticles were loaded. The highest photocatalytic production rate of CH4 reached 20.83 ppm/h cm2. In addition, the selectivity of photoreduction product of CO2 was also increased apparently when Pd acted as the cocatalyst on TiO2/SrTiO3 heterojunction film.

Effect of surface/bulk oxygen vacancies on the structure and electrochemical performance of TiO2 nanoparticles

TiO2 nanoparticles containing oxygen vacancies mostly existed in the bulk phase, and the counterpart with oxygen vacancies both on the surface and in the bulk phase, were successfully prepared via calcination of nanotube titanic acid under air and H2 atmosphere respectively. The effect of surface and/or bulk oxygen vacancies on the structure and electrochemical properties of electrode materials were studied. The materials characterization results demonstrate that under air atmosphere, the obtained TiO2 nanoparticles containing oxygen vacancies mainly in the bulk phase, while its surface still remains the stoichiometric structure. While hydrogenation process leads to a crystalline-disordered core–shell structure, oxygen vacancies existed both on the surface and in the bulk of TiO2 nanoparticles. As-fabricated TiO2 samples containing oxygen vacancies exhibit markedly improved electrochemical properties comparison with TiO2 nanoparticles without defects. Oxygen vacancies can act as physical space for Li-ion storage thus improve the specific capacity of electrode, the enhanced rate performance mainly origin from the bulk oxygen vacancies.

Preparation of Bi-doped TiO2 nanoparticles and their visible light photocatalytic performance

Bi-doped TiO2 photocatalysts were prepared by a hydrothermal method using nanotube titanic acid as the Ti precursor. The samples were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Methyl orange (MO) was used as a model contaminant to evaluate the visible light photocatalytic activity of the Bi-doped TiO2 samples. We found that the Bi ions did not incorporate into the TiO2 lattice but instead existed in the form of BiOCl. The obtained BiOCl-composited TiO2 samples exhibited remarkable photocatalytic activity under visible light irradiation for the photodegradation of MO. The sample obtained when the Bi/Ti molar ratio was 1% and the hydrothermal treatment temperature was 130 °C (BTO-130-1) showed the highest photocatalytic activity. Moreover, a possible mechanism was proposed and the enhanced photocatalytic activity was discussed. The as-prepared catalyst also showed high photocatalytic activity for the photodegradation of 4-chlorophenol.

Hydrothermal Synthesis of Nitrogen-Doped Titanium Dioxide and Evaluation of Its Visible Light Photocatalytic Activity

Nitrogen-doped titanium dioxide (N-dopedTiO2) photocatalyst was synthesized from nanotube titanic acid (denoted as NTA; molecular formulaH2Ti2O5·H2O) precursorviaa hydrothermal route in ammonia solution. As-synthesized N-dopedTiO2catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, diffuse reflectance spectrometry, X-ray photoelectron spectroscopy, electron spin resonance spectrometry and Fourier transform infrared spectrometry. It was found that nanotube ammonium titanate (NAT) was produced as an intermediate during the preparation of N-dopedTiO2from NTA, as evidenced by the N1sX-ray photoelectron spectroscopic peak ofNH4 +at 401.7 eV. The catalyst showed much higher activities to the degradation of methylene blue and p-chlorophenol under visible light irradiation than Degussa P25. This could be attributed to the enhanced absorption of N-dopedTiO2in visible light region associated with the formation of single-electron-trapped oxygen vacancies and the inhibition of recombination of photo-generated electron-hole pair by doped nitrogen.

A NEW METHOD TO PREPARE THE NOVEL ANATASE TiO2

In this paper, a kind of novel anatase TiO 2 nanoparticle with single-electron-trapped oxygen vacancies was prepared by hydrothermal treated nanotube titanic acid. The morphology, structure, and properties of the products were characterized by transmission electron microscope, X-ray diffraction, electron spin resonance, and photoluminescence. Photocatalytic decolorization of the Methylene Blue solution was carried out in the visible light region and showed a high photocatalytic activity.

Photoactive centers responsible for visible-light photoactivity of N-doped TiO2

N-doped TiO2 (anatase) with high visible light photoactivity was obtained by the thermal treatment of nanotube titanic acid (denoted as NTA) in an NH3 flow and investigated by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and photoluminescence (PL). With increasing NH3 treatment temperature at T = 400 to 600 °C, the anatase crystallinity of the N-NTA(400–600) samples was gradually enhanced, while at 700 °C a new phase, TiN, appeared in the N-NTA(700) sample. XPS results show that the doped N atoms incorporated into anatase TiO2 exist in the form of NO. A revised explanation for the triplet ESR signals obtained from the N-NTA(500–700) samples was put forward, i.e. the g = 2.004 main peak is contributed by single-electron-trapped oxygen vacancies (denoted as Vo˙), while two weak peaks (g = 2.023, 1.987) are contributed by chemisorbed NO in well-crystallized anatase TiO2. The visible light photoactivity is proportional to the height of the g = 2.004 main peak, which suggests that the photoactive centers are Vo˙-NO–Ti. The adsorbed NO molecule can effectively suppress the photoluminescence of Vo˙ defects, which facilitates photogenerated charge transfer to the surface reactive centers to conduct redox reactions. The higher the Vo˙-NO–Ti concentration, the better the visible light photoactivity. The highest photoactivity was obtained for the catalyst, NH3-treated at 600 °C. But the formation of TiN at T = 700 °C can readily destruct Vo˙-NO–Ti photoactive centers, and thus readily decreases photoactivity efficiency.

Visible light photocatalytic decoloration of methylene blue on novel N-doped TiO2

Novel N-doped TiO2 (denoted as N-NTA600) was prepared by treating nanotube titanic acid (NTA) in NH3 flow. Its visible light photocatalytic activity, evaluated by decoloration reaction of methylene blue, is higher than that of N-P25(600) prepared by treatment of P25-TiO2 in the same condition. It is suggested that the origin of visible-light photocatalytic activity is single-electron-trapped oxygen vacancy (Vo·) modified by chemisorbed NO.

A novel N-doped TiO 2 with high visible light photocatalytic activity

A novel N-doped TiO 2 with high visible light photocatalytic activity was obtained by treating nanotube titanic acid (NTA) in NH 3 flow and investigated by means of XRD, TEM, ESR and XPS. The ESR results revealed that the visible light photocatalytic activity is originated from N-doping into TiO 2 with the forming of triplet paramagnetic species, the higher triplet paramagnetic species concentration, the better visible light photocatalytic behavior.

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

N/p-Type changeable semiconductor TiO2 prepared from NTA

A novel kind of nano-sized TiO2 (anatase) was obtained by high-temperature (400–700°C) dehydration of nanotube titanic acid (H2Ti2O4(OH)2, NTA). The high-temperature (400–700°C) dehydrated nanotube titanic acids (HD-NTAs) with a unique defect structure exhibited a p-type semiconductor behavior under visible-light irradiation ( $$\uplambda\ge420$$ nm, E photon=2.95 eV), whereas exhibited an n-type semiconductor behavior irradiated with UV light ( $$\uplambda=365$$ nm, E photon=3.40 eV).

Photo and photoelectrochemical properties of p-type low-temperature dehydrated nanotube titanic acid

Nanotube titanic acid (H 2Ti 2O 5 · H 2O, NTA) is thermally unstable. Its low-temperature (100–300 °C) dehydrated product (LD-NTA) possesses a symmetrical ESR signal with a g = 2.003, which is the characteristic of a single-electron-trapped oxygen vacancy (SETOV). High concentration SETOV defects can form a sub-band within the bandgap ( E g ) of LD-NTA and exhibit a response to visible light. Each SETOV possesses one effective positive charge. Under visible light irradiation, the working electrode prepared from LD-NTA shows a p-type I photo– V bias behavior ( I photo = photocurrent, V bias = bias potential), which suggests that SETOV in LD-NTA plays the role of major positive carriers, like h +.