Nanotube Photocatalyst Research Articles

Adsorption of CO 2 on heterostructure CdS(Bi 2S 3)/TiO 2 nanotube photocatalysts and their photocatalytic activities in the reduction of CO 2 to methanol under visible light irradiation

TiO 2 nanotubes (TNTs) photocatalyst was synthesized by hydrothermal reaction, while the heterostructure CdS(or Bi 2S 3)/TiO 2 nanotube photocatalysts were prepared by direct precipitation reaction. The photocatalysts were studied by TEM, EDX, XRD and XPS to characterize its structure and chemical compostion. Their photocatalytic activities for reducing CO 2 to CH 3OH under visible light irradiation and the performance for CO 2 adsorption were also investigated. The results indicate that the synthetical TNTs photocatalyst is almost in good and uniform shapes, with the diameter of 17.77 nm and the surface area of 99.57 m 2/g. The amounts adsorbed of CO 2 on TNTs are 0.269 mmol/g at 1 atm pressure and 298 K,which are larger than those on other two heterostructure photocatalysts. The adsorption isotherms of CO 2 on three photocatalysts can be well described by the Freundlich adsorption equation. The modification of Bi 2S 3 or CdS can enhance the visible light absorbance and photocatalytic performance of TNTs photocatalyst. The photocatalytic activity, the amounts adsorbed of CO 2 and visible light absorption capability of Bi 2S 3-modified TNTs photocatalyst are all better than those of CdS-modified TNTs photocatalyst. Especially, the largest yield of methanol on TNTs photocatalyst modified by Bi 2S 3 under visible light irradiation over 5 h is 224.6 μmol/g, which was about 2.2 times as large as that of TNTs.

Design and high efficient photoelectric-synergistic catalytic oxidation activity of 2D macroporous SNO2/1D TiO2 nanotubes

A novel catalyst was constructed by assembling 1D TiO2 nanotubes (TiO2 NTs) photocatalyst and 2D macroporous SnO2 electrocatalyst, which presents simultaneously the outstanding photocatalytic and electrocatalytic properties, and was applied to the photoelectric synergistic catalytic oxidation of biorefractory pollutants. Liquid crystal soft template was prepared by block copolymer self-assembly, and the macroporous SnO2 membrane grew orderly on the TiO2 NTs using the soft template by one-step assembly. The macroporous SnO2 has the pore size distribution between 150 and 400nm, small particle size (14.2nm), and high loading amount (27.3gm−2). The band gap of the 2D macroporous SnO2/TiO2 NTs is 2.93eV. Compared with the general TiO2 NTs and the SnO2/TiO2NTs, the 2D macroporous SnO2/TiO2 NTs possess better optical absorption and photocatalytic properties, with a photoelectric conversion efficiency of 35.2% at 365nm. Moreover, the hybrid anode presents smaller surface impedance and solution interface impedance, larger electrochemical surface absorption volume and lower electrochemical reaction activation energy. In the photoelectrocatalytic process, the 2D macroporous SnO2/TiO2 NTs exhibited higher removal rate for 2,4-dichlorophenoxyacetic acid, the initial instantaneous current efficiency was 100%, and COD removal rate reached 90.1% within 3h. The study showed that the intermediates was generated faster and removed quickly on the prepared catalyst.

High photoactive and visible-light responsive graphene/titanate nanotubes photocatalysts: Preparation and characterization

A series of graphene/titanate nanotubes (TNTs) photocatalysts using graphene and nanoscale TiO 2 or P25 as original materials were fabricated by hydrothermal method. Both low hydrothermal temperature and proper amount of graphene are propitious to better photoactivity. The photocatalytic activities of these nanocomposites far exceed that of P25, pure TNTs and reported TiO 2-based nanocomposites for the degradation of Rhodamine-B under visible-light irradiation. These prepared photocatalysts were characterized by TEM, XRD, XPS, BET, FTIR and UV–vis diffuse reflection spectra, and the results indicate that the outstanding photoactivities in visible-light region result from sensitization effect of graphene rather than impurity level in the band gap of TNTs. Furthermore, large BET surface areas of these photocatalysts (almost 10 times larger than that of previously reported graphene/TiO 2 nanoparticles) evidently enhance their absorption abilities and photocatalytic performances (the rate constants of degrading Rhodamine-B are at least 5 times higher than that of previously reported photocatalysts). These photocatalysts show good stability, and their photoactivities do not obviously decrease after four times of repeated uses. A detailed photocatalytic mechanism is suggested, as well.

Visible-Light Photocatalyst of Tetramethoxyphenylporphyrin Sensitized TiO<sub>2</sub> Nanotube

This paper investigated the performance of photocatalysts of TiO2 nanotubes sensitized by photosensitizers of tetramethoxyphenylporphyrin(TMPP) for producing H2 from water under visible light. This photocatalyst might have a smaller band gap (2.6 eV). The investigation shows that a photosensitized catalyst combined TiO2 nanotube with TMPP can be used to extend the absorption of solar light region and enhance the efficiency of energy conversion, and the quantity of H2 evolution is 1.427 L m-2h-1g-1. It was a way to apply the dye sensitized TiO2 nanotubes photocatalyst in the visible light for clean energy.

Highly efficient TiO 2 nanotube photocatalyst for simultaneous hydrogen production and copper removal from water

1-D mesoporous TiO 2 nanotube (TNT) with large BET surface area was successfully synthesized by a hydrothermal-calcination process, and employed for simultaneous photocatalytic H 2 production and Cu 2+ removal from water. Cu 2+, across a wide concentration range of 8–800 ppm, was removed rapidly from water under irradiation. The removed Cu 2+ then combined with TNT to produce efficient Cu incorporated TNT (Cu-TNT) photocatalyst for H 2 production. Average H 2 generation rate recorded across a 4 h reaction was between 15.7 and 40.2 mmol h −1 g −1 catalyst, depending on initial Cu 2+/Ti ratio in solution, which was optimized at 10 atom%. In addition, reduction process of Cu 2+ was also a critical factor in governing H 2 evolution. In comparison with P25, its large surface area and 1-D tubular structure endowed TNT with higher photocatalytic activity in both Cu 2+ removal and H 2 production.

Highly efficient CuO incorporated TiO 2 nanotube photocatalyst for hydrogen production from water

Highly dispersed CuO was introduced into TiO 2 nanotube (TNT) made by hydrothermal method via adsorption–calcination process or wet impregnation process, to fabricate CuO incorporated TNT photocatalysts (CuO-TNT) for hydrogen production. It was found that CuO-TNT possessed excellent hydrogen generation activity, which was constantly vigorous throughout 5 h reaction. Depending on the preparation method, hydrogen evolution rates over CuO-TNT were founded in the range of 64.2–71.6 mmol h −1 g −1 catalyst, which was much higher than the benchmark P25 based photocatalysts, and even superior to some Pt/Ni incorporated TNT. This high photocatalytic activity of CuO-TNT was mainly attributed to the unique 1-D tubular structure, large BET surface area and high dispersion of copper component. Compared to wet impregnation, adsorption–calcination process was superior to produce active photocatalyst, since it was prone to produce photocatalyst with more highly dispersed CuO.

Fabrication and photocatalytic activity of TiO2/SiO2 composite nanotubes

TiO2/SiO2 composite nanotube photocatalysts supported on Al substrates were prepared by the anodic aluminum oxide (AAO) liquid-phase deposition method for degradation of 100 mg/L methyl blue (MB). AAO templates were prepared in H3PO4 acidic electrolytes through the two-step anodic oxidation method. The photocatalysts were characterized by field-emission scanning electron microscopy, thermal analysis (TG-DTA), and Fourier-transform infrared, x-ray photoelectron, and UV–Vis diffuse spectroscopies. The results showed that the presence of SiO2 in TiO2 inhibited the crystal phase transformation temperature effectively, with a greater wall thickness of 80–100 nm. It was found that Ti–O–Si bonds were formed on the surface and the surface hydroxyl concentration was increased, resulting in enhanced photocatalytic activity, being about 20% higher than for pure TiO2 films. The calculated band structure for TiO2/SiO2 was investigated using first-principle calculations. The TiO2/SiO2 composite exhibited a wider conduction band which would effectively prohibit recombination of photogenerated electrons and holes.

CO2 Photoreduction in the Liquid Phase over Pd-Supported on TiO2 Nanotube and Bismuth Titanate Photocatalysts

CO2 Photoreduction in the Liquid Phase over Pd-Supported on TiO2 Nanotube and Bismuth Titanate Photocatalysts

Nanoparticles enwrapped with nanotubes: A unique architecture of CdS/titanate nanotubes for efficient photocatalytic hydrogen production from water

CdS/titanate nanotubes (CdS/TNTs) photocatalysts with a unique morphology were successfully synthesized via a simple one-step hydrothermal method. Compared with traditional CdS@TNTs composite photocatalysts prepared by the common two-step method, CdS/TNTs exhibited much higher activity for photocatalytic hydrogen evolution under visible light irradiation. Transmission electron microscopy (TEM) revealed that the CdS nanoparticle was intimately enwrapped by the surrounding TNTs. This unique architecture resulted in the appropriate dispersion of CdS nanoparticles and the intimate multipoint contacts between the CdS nanoparticle and TNTs, which led to significant enhancement of charge separation in CdS/TNTs. Accordingly, the photoactivity was improved. Meanwhile, X-ray powder diffraction (XRD) demonstrated that the highly crystalline hexagonal CdS was obtained in CdS/TNTs, which was also essential for the enhanced photocatalytic performance. The unique morphology and photocatalytic activity of CdS/TNTs were influenced by the Cd/Ti molar ratio with an optimal value of 0.05. Under this condition, the CdS amount was only 6 wt% of the total photocatalyst, which was important from an environmental point of view. The influence of loaded Pt on the activity of CdS/TNTs had also been investigated. The hydrogen production rate of 2.0 wt% Pt-loaded CdS/TNTs reached 353.4 μmol h−1, with the apparent quantum yield of 25.5% at 420 nm. This study provides a potential way to synthesize highly efficient composite photocatalysts with a novel architecture.

Heterogeneous photocatalysis of methylene blue over titanate nanotubes: Effect of adsorption

Titanate nanotubes were synthesized with hydrothermal reaction using TiO 2 and NaOH as the precursors and subsequent calcination at 400 °C for 2 h. The products were characterized with SEM and XRD. Adsorption and photocatalysis of methylene blue over titanate nanotubes and TiO 2 were investigated. The results indicated that titanate nanotubes exhibited a better photocatalytic degradation of methylene blue in a simultaneous adsorption and photodegradation system than that in equilibrium adsorption followed by a photodegradation system, whereas TiO 2 showed no significant differences in photocatalytic activity in the two systems. The methylene blue overall removal efficiency over TNTs in the first system even exceeded that over TiO 2. The different catalytic performances of titanate nanotubes in the two systems were tentatively attributed to different effects of adsorption of methylene blue, i.e., the promoting effect in the former and the inhibition effect in the latter. Decantation experiments showed that the titanate nanotube photocatalyst could be easily separated from the reaction medium by sedimentation. Thus titanate nanotubes with high sedimentation rates and concurrent adsorption represent a new catalyst system with a strong potential for commercial applications.

Photocatalytic reduction of CO 2 with H 2O on Pt-loaded TiO 2 catalyst

A gas–solid heterogeneous system for solar–chemical energy conversion of CO 2-SCR (Selective Catalytic Reduction) with H 2O on different nanostructure photocatalysts and the photocatalysis pathway were discussed. Different crystal phases and sizes of low-dimensional nano-TiO 2 and Pt-metal supported photocatalysts are synthesized and characterized with X-ray diffraction, high-resolution transmission electron microscopy, photoluminescence, CO pulse chemisorptions, N 2 adsorption–desorption analysis at 77 K and X-ray fluorescence spectrometry. The catalytic activity was tested in a fixed-bed photocatalysis reactor and the CH 4 yield on the Pt/TiO 2 nanotube photocatalysts is more remarkable. It increased with the increase of the UV irradiation time and accumulated to about 4.8 μmol h −1 g Ti −1, enhanced as the increase of the reaction temperature and H 2O/CO 2 molar ratio as well.

Development of a visible-light-responsive titania nanotube photocatalyst by site-selective modification with hetero metal ions

A titania nanotube (TNT), which was obtained by calcinations of a titanate nanotube, was modified with two kinds of transition metal ions, iron(III) (Fe3+) and zinc(II) (Zn2+) ions. TNT with site-selective modification with metal ions showed higher photocatalytic activity than that of bare TNT, presumably due to separation of redox sites, and oxidation on the outside surface and reduction on the inside surface were the preferable separated redox sites on the tubular structure for decomposition of acetaldehyde. Modification of TNT with Fe3+ ions induced improvement of photocatalytic activity under visible-light irradiation as well as ultraviolet (UV) irradiation. On the other hand, TNT modified with Zn2+ ions showed the largest enhancement of photocatalytic activity under UV irradiation, though increase in visible-light activity was hardly observed. Double-beam photoacoustic spectroscopic analyses indicated that Zn2+ ion works efficiently as an electron acceptor, while Fe3+ ion is an effective sensitizer for visible light.

Preparation of PW 12O 403−/Cr–TiO 2 nanotubes photocatalysts with the high visible light activity

The development of photocatalysts with high visible light photocatalytic activity is of significance. In this study, PW 12O 40 3− and Cr 3+ modified TiO 2 nanotubes, a new type photocatalysts, were prepared with anodization and impregnation methods to increase the visible light catalytic activity of TiO 2. The Cr 3+ doping narrowed the band gap of TiO 2 to enhance the visible light response. Moreover, the Cr 3+ doping increased the standard reduction potential of the conduction band electrons of TiO 2 enhancing the electron transfer between conduction band electrons from TiO 2 (electron donor) and PW 12O 40 3− (electron acceptor), so electrons and holes were efficiently separated. The reaction rate constant of PW 12O 40 3−/Cr–TiO 2 was significantly higher than that of Cr–TiO 2 or PW 12O 40 3−/TiO 2, which was attributed to the synergetic effect between Cr 3+ and PW 12O 40 3− modification. The synergetic fact of PW 12O 40 3− and Cr 3+ in PW 12O 40 3−/Cr–TiO 2(2.36 at%) reached 1.42.

Constructing Stake Structured TiO2-NTs/Sb-Doped SnO2 Electrode Simultaneously with High Electrocatalytic and Photocatalytic Performance for Complete Mineralization of Refractory Aromatic Acid

This Article puts forward a new idea to construct an electrode combining the advantages of a TiO2 nanotube photocatalyst and an excellent Sb-doped SnO2 electrocatalyst, which realized high electrocatalytic (EC) and photocatalytic (PC) oxidation efficiency at the same time. Under vacuum conditions, in virtue of the titanium oxide nanotubes (TiO2-NTs) as a template, well dispersed Sb-doped SnO2 (particle size 20 nm) was embedded into TiO2-NTs (diameter 60−90 nm and wall thickness 10−20 nm), resulting in the stake structured TiO2-NTs/Sb-doped SnO2 electrode (TiO2-NTs/SnO2). The loading amount of Sb-doped SnO2 on a TiO2-NTs/SnO 2 electrode is 21.4 g m−2, which is increased by 2 times compared with the situation of direct loading Sb-doped SnO2 on the Ti substrate (Ti/SnO2). The crystal lattice parameter of SnO2 becomes smaller, and crystal lattice parameter of TiO2 is larger, so the combination between TiO2-NTs and Sb-doped SnO2 becomes more tight. Compared with the electrochemical properties of Ti/SnO2, the a...

A novel CdS/S-TiO 2 nanotubes photocatalyst with high visible light activity

CdS and S 6+-modified TiO 2 nanotubes were prepared to enhance the visible light activity of TiO 2. The S 6+ doping narrowed the band gap of TiO 2 and increased the visible light response. Moreover, the S 6+ doping decreased the standard reduction potential of the conduction band electrons to enhance the electron transfer of conduction band electrons from CdS to TiO 2. CdS/S-TiO 2 showed the higher activity as compared with CdS/TiO 2 or S-TiO 2, which was attributed to the synergetic effect between CdS and S 6+ modification .

Recovery properties of hydrogen gas sensor with Pd/titanate and Pt/titanate nanotubes photo-catalyst by UV radiation from catalytic poisoning of H2S

Abstract Recovery properties after H2S catalytic poisoning of catalytic-type gas sensor with photo-catalysts and UV radiation have been examined. Each sensing material of the sensor consists of Pd, Pt supported on γ-Al2O3 and Pd/titanate, Pt/titanate nanotubes or TiO2 particles. Pd/titanate and Pt/titanate nanotubes photo-catalyst were synthesized by hydrothermal synthesis method. All the sensors were deactivated after 500 ppm H2S exposure for 20 h. The sensors with Pd/titanate or Pt/titanate nanotubes showed regenerated voltage response under UV radiation. However the sensor with TiO2 particles showed negligible regenerated voltage response. Regenerated voltage response with Pd/titanate or Pt/titanate nanotubes may stem from location of Pd or Pt catalyst on the titanate nanotube photo-catalyst.

Preparation and Characterization of Anodized Pt-TiO2 Nanotube Arrays for Water Splitting

Self-organized TiO2 nanotube-layers were formed by the electrochemical anodization of Ti in an HF electrolyte. The nanotube layers were then treated at different temperatures (300–600°C) in the air. Platinum was doped on the TiO2 nanotube layer by e-beam sputtering. The samples were characterized by EDX, BET, XPS, SEM, XRD and photoelectrochemistry. The results clearly showed the successful Pt-doping of the TiO2 nanotubes. The photocatalytic evolution of H2 due to the decomposition of water in the alkaline solution was investigated using the Pt–TiO2 nanotubes as a photocatalyst and iodide ions in the form of KI as a redox mediator. The results showed that the Pt–TiO2 nanotube photocatalyst generated H2 successfully.

Microwave assisted rapid and complete degradation of atrazine using TiO 2 nanotube photocatalyst suspensions

A technology, microwave-assisted photocatalysis on TiO 2 nanotubes, which can be applied to degrade atrazine rapidly and completely, was investigated. TiO 2 nanotubes were prepared, and confirmed by XRD, TEM and ESR. Microwave-assisted photocatalytic degradation of atrazine in aqueous solution was investigated. The result indicates that atrazine is completely degraded in 5 min and the mineralization efficiency is 98.5% in 20 min, which is obviously more efficient than that by the traditional photocatalytic degradation methods. It may be attributed to the intense UV radiation generated by electrodeless discharge lamps under microwave irradiation, the increased number of OH, additional defect sites on TiO 2 under the irradiation of microwave and larger specific surface area of TiO 2 nanotubes which could adsorb more organic substances to degrade than TiO 2 nanoparticles. Along with the degradation of atrazine, the concentrations of Cl − and NO 3 − increase gradually. In 20 min [Cl −] and [NO 3 −] are 3, 27.8 mg/L, respectively, which are close to their stoichiometric values. The major intermediates of atrazine were identified by HPLC/MS and possible degradation pathways of atrazine in microwave-assisted photocatalysis on TiO 2 nanotubes were proposed.

Preparation of a Novel TiO2-Based p−n Junction Nanotube Photocatalyst

TiO2 nanotube semiconductors contain free spaces in their interior that can be filled with active materials such as chemical compounds, enzymes, and noble metals, giving them a fundamental advantage over colloids. Although the unique shape of semiconductor nanotubes makes them promising for a range of potential applications, significant developmental research is required. In this research, a novel TiO2 nanotube photocatalyst was prepared that has a p-n junction. The photocatalyst particle surface is physically divided into reduction and oxidation surfaces, which poses a potential driving force for the transport of photogenerated charge carriers. The structure of this nanotube catalyst was characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The catalyst activity was evaluated by coating the catalyst on HEPA filters and determining the destruction rate of toluene in air. The p-n junction nanotube catalyst was shown to have a much higher photocatalytic destruction rate than that of commercially available, nonnanotube structured material, and a higher destruction rate for nanotube catalysts that did not contain a p-n junction.