Preparation, characterization and photocatalytic activity of the neodymium-doped TiO2 nanotubes

A series of Nd-TiO₂ powders have been prepared by the sol-gel technique with neodymium nitrate and tetra-n-butyl titanium as raw materials, and then Nd-TiO₂ nanotubes were fabricated by the hydrothermal method with a 10 mol l⁻¹ NaOH solution. The as-prepared Nd-TiO₂ nanotubes were characterized by TEM, XRD, DRS, and XPS, and their photocatalytic activity was also tested in the case of the degradation of methyl orange in water. TEM photograph showed that Nd-TiO₂ nanotubes were about 10-20 nm in diameter, with the lengths range from 100 to 300 nm. TiO₂ nanotubes contained anatase and rutile crystallites. However, 0.3% Nd-TiO₂ nanotubes contained anatase crystallites, and only little rutile crystallites, so it is shown that neodymium doping hindered the phase transformation from anatase into rutile. Nd doping increased the visible-light absorption ability of Nd-TiO₂ nanotubes, and a red shift for Nd-TiO₂ nanotubes appeared when compared to TiO₂ nanotubes. XPS analysis showed that two types of oxygen existed on the photocatalyst surface, including metal-O and hydroxyl group, and more hydroxyl group was on the surface of 2% Nd-TiO₂ nanotubes than on the surface of TiO₂ nanotubes. Nd doping enhanced the photocatalytic activities of Nd-TiO₂ nanotubes, and 0.3% Nd-TiO₂ nanotubes exhibited the highest photocatalytic activity.     

Pt/N-codoped TiO2 nanotubes and its photocatalytic activity under visible light

Pt/N-codoped TiO₂ nanotubes were prepared and characterized by various analytical methods, such as transmission electron microscope (TEM), diffuse reflection spectra (DRS), X-ray powder diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS) and fluorescence spectra (FL). The photocatalytic efficiency was evaluated by the photodegradation of Rhodamine B (RB) in an aqueous solution under visible light irradiation. It has been confirmed that Pt/N-codoped TiO₂ nanotubes could be excited by visible light and the recombination rate of electron-hole pairs declined significantly. The higher visible light activity is due to the codoping of nitrogen and platinum.     

Influence of ammonia on the morphologies and enhanced photocatalytic activity of TiO2 micro/nanospheres

TiO₂ micro/nanospheres were synthesized by a combination process contains hydrolysis of titanium tetra-n-butyl in mixed solution of anhydrous ethanol/ammonia and the subsequent calcination under 550 °C for 7 h. The pH values of the mixed solution were tuned to be 10.4, 11.0 and 11.6, respectively, by adding different amounts of ammonia. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the morphologies and the crystallinity. X-ray diffraction (XRD) patterns indicated that pH value of the precursors has an important effect on the crystal phase composition. UV-vis diffuse reflectance spectrum was applied to characterize the optical properties of samples. Degradation of methylene blue under the irradiation of 300 W Hg lamp confirmed the enhanced photocatalytic activity of TiO₂ micro/nanospheres. In addition, the formation mechanism was proposed.     

Enhanced photocatalytic activity and stability of nano-scaled TiO2 co-doped with N and Fe

Titanium dioxide (TiO₂) nanoparticles co-doped with N and Fe were prepared via modified sol-gel process. The products were characterized by transmission electron microscopy (TEM), N₂ adsorption, X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). It is shown that the prepared TiO₂ particles were less than 10 nm with narrow particle size distribution. The addition of MCM-41 caused the formation of Ti-O-Si bond which fixed the TiO₂ on MCM-41 surface, thus restricted the agglomeration and growth of TiO₂ particles. The photocatalytic performance in the degradation of methylene blue showed that N, Fe co-doped TiO₂ exhibited much higher photocatalytic activity than doped sample with nitrogen or Fe³⁺ alone under both UV and visible light. N, Fe co-doping decreased the loss of doping N during the degradation reaction, thus increased the photocatalytic stability. It was also found that the nitridation time had significant influence on the photocatalytic activity of prepared TiO₂ catalysts.     

Preparation and performance of photocatalytic TiO2 immobilized on palladium-doped carbon fibers

Pd-modified carbon fibers (CFs) are obtained by a facile oxidation-reduction method and then dip-coated in a sol-gel of titanium dioxide (TiO₂) to form supported TiO₂/Pd-CF photocatalysts. The morphology of the Pd-modified CFs and the amount Pd deposited are characterized by field emission scanning electron microscopy and atomic absorption spectrometry, respectively. X-ray diffraction is used to investigate the crystal structures of the TiO₂ photocatalyst. Acid orange II is used as a model contaminant to evaluate the photocatalytic properties of the photocatalyst under UV irradiation. TiO₂/Pd-CF exhibits higher catalytic activity than TiO₂/CF towards the degradation of acid orange II. Optimum photocatalytic performance and support properties are achieved when the Pd particle loading is about 10.8 mg/g.     

Effect of surface roughness of TiO2 films on short-circuit current density of photoelectrochemical cell of ITO/TiO2/PVC-LiClO4/graphite

This paper reports the effect of surface topography of titanium dioxide films on short-circuit current density of photoelectrochemical solar cell of ITO/TiO₂/PVC-LiCLO₄/graphite. The films were deposited onto ITO-covered glass substrate by screen-printing technique. The films were tempered at 300 °C, 350 °C, 400 °C, 450 °C and 500 °C for 30 min to burn out the organic parts and to achieve the films with porous structure. The surface roughness of the films were studied using scanning electron microscope (SEM). Current–voltage relationship of the devices were characterized in dark at room temperature and under illumination of 100 mW cm⁻² light from tungsten halogen lamp at 50 °C. The device utilising the TiO₂ film annealed at 400 °C produces the highest short-circuit current density and open-circuit voltage as it posses the smoothest surface topography with the electrolyte. The short-circuit current density and open-circuit voltage of the devices increase with the decreasing grain size of the TiO₂ films. The short-circuit current density and open-circuit voltage are 0.6 μA/cm² and 109 mV respectively.     

Composite SiO2/TiO2 and amine polymer/TiO2 nanoparticles produced using plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition was used to conformally coat commercial TiO₂ nanoparticles to create nanocomposite materials. Hexamethyldisiloxane (HMDSO)/O₂ plasmas were used to deposit SiO₂ or SiO_xC_yH_z films, depending on the oxidant concentration; and hexylamine (HexAm) plasmas were used to deposit amorphous amine-containing polymeric films on the TiO₂ nanoparticles. The composite materials were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These analyses reveal film composition on the nanoparticles was virtually identical to that deposited on flat substrates and that the films deposit a conformal coating on the nanoparticles. The performance of the nanocomposite materials was evaluated using UV-vis spectroscopy to determine the dispersion characteristics of both SiO_x and HexAm coated TiO₂ materials. Notably, the coated materials stay suspended longer in distilled water than the uncoated materials for all deposited films.     

Visible-light-activated Ce-Si co-doped TiO2 photocatalyst

To enhance the visible photocatalytic activity and thermal stability of TiO₂, Ce-Si co-doped TiO₂ materials were synthesized through a nonaqueous method of which the purpose was to reduce the aggregation between TiO₂ particles. The obtained materials maintained anatase phase and large surface area of 103.3 m² g⁻¹ even after calcined at 800 °C. The XPS results also indicated that Si was weaved into the lattice of TiO₂, and Ce mainly existed as oxides on the surface of TiO₂ particles. The doped Si might enhance surface area and suppress transformation from anatase to rutile, while the doped Ce might cause visible absorption and inhibit crystallite growth during heat treatment. Evaluated by decomposing dye Rhodamine B, visible photocatalytic activity of Ce-Si co-doped TiO₂ was obviously higher than that of pure TiO₂ and reached the maximum at Ce and Si contents of 0.5 mol% and 10 mol%.     

Preparation and characterization of amine-functionalized SiO2/TiO2 films for formaldehyde degradation

This paper investigated the gaseous formaldehyde degradation by the amine-functionalized SiO₂/TiO₂ photocatalytic films for improving indoor air quality. The films were synthesized via the co-condensation reaction of methyltrimethoxysilane (MTMOS) and 3-aminopropyltrimethoxysilane (APTMS). The physicochemical properties of prepared photocatalysts were characterized with N₂ adsorption/desorption isotherms measurement, X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FT/IR). The effect of amine-functional groups and the ratio of MTMOS/APTMS precursors on the formaldehyde adsorption and photocatalytic degradation were investigated. The results showed that the formaldehyde adsorption and photocatalytic degradation of the APTMS-functionalized SiO₂/TiO₂ film was higher than that of SiO₂/TiO₂ film due to the surface adsorption on amine sites and the relatively high of the specific surface area of the APTMS-functionalized SiO₂/TiO₂ film (15 times higher than SiO₂/TiO₂). The enhancement of the formaldehyde degradation of the film can be attributed to the synergetic effect of adsorption and subsequent photocatalytic decomposition. The repeatability of photocatalytic film was also tested and the degradation efficiency was 91.0% of initial efficiency after seven cycles.     

Photocatalytic activity of multielement doped TiO2 in the degradation of congo red

TiO₂ although considered a promising photocatalyst for the degradation of aqueous pollutants, it suffers from poor absorption in the visible region and hence requires ultraviolet (UV) light for activation. To make TiO₂ a visible active photocatalyst, multielement (C, N, B, and F) doping has been done. The synthesised CNBF/TiO₂ catalysts were calcined at different temperatures and characterized by XRD, BET surface area, UV DRS, XPS, HRSEM-EDAX, and TEM techniques. These catalysts found to show less band gap values when compared to bare TiO₂. These catalysts were tested for their catalytic activity towards the degradation of a textile dye - congo red (CR) under different reaction conditions. It was found that the photocatalytic activity was dependent on both doping of multielement and the calcination temperature of CNBF/TiO₂. The co-doped catalysts which were calcined at 400 °C and 600 °C (100% intensity in anatase phase) were found to be the best catalysts (100% decolourisation of CR in 21/2 h and 2 h respectively). TOC analysis carried out for the samples at the reaction time of 5 h showed very high percentage (83%) degradation of CR over CNBF/TiO₂ catalysts calcined at 600 °C when compared to the other catalysts calcined at different temperatures. CNBF/TiO₂ (1000 °C) showed very less photocatalytic activity due to the formation of rutile phase.     

N-doped TiO2 photo-catalyst for the degradation of 1,2-dichloroethane under fluorescent light

The photo-catalytic degradation of 1,2-dichloroethane (1, 2-DCE) using nitrogen-doped TiO₂ photo-catalysts under fluorescent light irradiation was investigated. Highly pure TiO₂ and nitrogen-doped TiO₂ were prepared by a sol-gel method and characterized by thermo-gravimetric/differential-thermal analysis (TG/DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results indicate that the photo-catalysts were mainly nano-size with an anatase-phase structure. The degradation reaction of 1,2-DCE was operated under visible-light irradiation, and the photo-catalytic oxidation was conducted in a batch photo-reactor with various nitrogen doping ratios (N/Ti = 0-25 mol%). The relative humidity (RH) was controlled at 0-20% and the oxygen concentration was controlled at 0-21%. The photo-degradation with nitrogen-doped TiO₂ showed superior photo-catalytic activity compared to that for pure TiO₂. TiO₂ doped with 15 mol% nitrogen exhibited the best photo-catalytic efficiency under the tested conditions. The products from the 1,2-DCE photo-catalytic oxidation were CO₂ and water; the by-products included dichloromethane, methyl chloride, ethyl chloride, carbon monoxide, and hydrogen chloride. The reaction pathway of 1,2-DCE indicates that oxygen molecules are the major factor that causes the degradation of 1,2-DCE in the gas phase.     

Visible photocurrent response of TiO2 anode

The photoelectrochemical response to the electromagnetic radiation over the visible range is particularly sought for from the point of view of the efficiency of hydrogen generation by water photolysis in a photoelectrochemical solar cell, PEC. The PEC used in this work comprises thin film TiO₂ - based photoanode, Pt foil covered with Pt black as a cathode and SCE as a reference electrode, immersed in an electrolyte solution. Titanium dioxide thin films are deposited by means of rf reactive sputtering and modified, when necessary, by Au or Ag ultra-thin overcoatings. Here we show that even unmodified TiO₂ photoanode, shows a photocurrent peak over the visible range of the light spectrum (λ = 500-650 nm). The effect of the surface modification by noble metals and properties of the aqueous electrolyte on the visible photocurrent are studied. The optical spectra indicate an increased absorption due to noble metal deposits at 410 nm for Ag and at 600 nm for Au. In contrast, the photocurrent peak over the visible range (500 nm < λ < 650 nm) changes its symmetry and decreases in intensity with the increasing thickness of noble metals layers. The visible photoresponse is explained in terms of OH formation at the interface between TiO₂ electrode and aqueous electrolyte.     

STM imaging of a model surface of Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 dye-sensitized TiO2 photoelectrodes

A TiO₂(1 1 0)-(1 × 1) surface was prepared in an ultra-high vacuum, transported in laboratory air, and observed with a scanning tunneling microscope (STM) operated in a vacuum of 10⁻⁴ Pa. Empty state images showed atomically flat terraces separated by single-height steps, on which 5-fold-coordinated surface Ti atoms were observed as spots arranged in a rectangular lattice. The Ru(4,4′-dicarboxy-2,2′-bipyridine)₂(NCS)₂ (N3) dye was adsorbed on the TiO₂ surface by immersing the TiO₂ wafer into an acetonitrile solution of the dye. In the empty state images, individual N3 molecules were observed as oval particles protruding by 0.6 nm from the TiO₂ surface. The oval shape elongated to the [1  0] directions was attributed to electron tunneling from tip to unoccupied states localized at the two carboxyl groups bound to the TiO₂ surface.     

Dynamics of water adsorption on TiO2 monitored by work function spectroscopy

Water adsorption dynamics on two TiO₂ (1 1 0) rutile surfaces at room temperature has been investigated using the work function (WF) change as a function of time. The first surface was prepared in a standard way using sputtering/annealing cycles, whereas the second one was long term annealed at 620 K in moderate vacuum conditions (the residual gas pressure of about 1 × 10⁻⁷ mbar) and cleaned afterwards. The WF change show striking difference as compared to those obtained for highly reduced TiO₂ (1 1 0) rutile or the (2 × 1) reconstructed surfaces. For the first kind of surface we show that the observed adsorption dynamics can be qualitatively explained by the present understanding of the water adsorption on non-reconstructed TiO₂ (1 1 0) rutile surface according to which the bridging oxygen vacancies and Ti rows are the main adsorption sites. Although generally similar to the former results, water adsorption dynamics on the second kind of the surface has an additional feature that can be only explained by a new adsorption site, which we suggest to be due to (2 × 1) reconstructed regions coexisting with the non-reconstructed TiO₂ (1 1 0) surface.     

Visible-light photocatalytic behavior of two different N-doped TiO2

The visible-light photocatalytic behavior of two different N-doped TiO₂ correlated with their physicochemical properties was investigated. The results show that N-TiO₂-1, prepared by a novel TiO₂ with unique defect structure, is more active in visible-light photocatalytic oxidation of C₃H₆ than N-TiO₂-2, prepared by standard P25-TiO₂ (Degussa). The specific rate constant of the former is ca. 5 times that of the latter. One model of photoactive center (V_o-NO-Ti) in anatase phase responsible for the visible-light photocatalytic activity is proposed. The higher the V_o-NO-Ti concentration is, the better the visible-light photocatalytic activity is.     

Preparation and photocatalytic properties of silver nanoparticles loaded on CNTs/TiO2 composite

In this study, new nanoscale photocatalyst based on silver and CNTs/TiO₂ was successfully prepared by photoreduction method. The prepared Ag-CNTs/TiO₂ was characterized by TEM, XRD and XPS. The photocatalytic activity was also evaluated by photocatalytic degradation of Reactive Brilliant Red X-3B dye. The results indicated that the photocatalytic efficiency of CNTs/TiO₂ increased in the presence of Ag nanoparticles and the photocatalysis reaction followed a first order kinetics. The kinetic constant of Ag-CNTs/TiO₂ for dye degradation was nearly 1.2 times than that of CNTs/TiO₂, which indicated decorating Ag nanoparticles on CNTs/TiO₂ could enhance the photocatalytic ability.     

X-ray photoelectron spectroscopy characterization of composite TiO2–poly(vinylidenefluoride) films synthesised for applications in pesticide photocatalytic degradation

X-ray photoelectron spectroscopy (XPS) was adopted for the analytical characterization of composite titanium dioxide–poly(vinylidenefluoride) (TiO₂–PVDF) films developed for applications in the photocatalytic degradation of pollutants.

The composites were deposited on glass substrates by casting or spin coating from TiO₂–PVDF suspensions in dimethylformamide (DMF). XPS data on the TiO₂–PVDF surface composition were used to optimize preparation conditions (composition of the TiO₂/PVDF suspension, deposition technique) in terms of titanium dioxide surface amount and film stability.

The use of spin-coating deposition and the increase of TiO₂ amount in the DMF suspensions were found to improve the titanium surface content, although high TiO₂/PVDF ratios led to film instability. PVDF–TiO₂ films were also used in preliminary photocatalytic degradation tests on isoproturon, a phenylurea herbicide, under solar UV irradiation; the results were compared to direct photolysis to evaluate the catalytic efficiency of immobilized TiO₂ and the role played by the PVDF film during the degradation process.     

Enhanced photocatalytic activity of silver metallized TiO2 particles in the degradation of an azo dye methyl orange: Characterization and activity at different pH values

The photocatalytic activity of silver deposited Degussa P25 titanium dioxide (Ag-DP25) in the photodegradation of methyl orange (MO) was investigated. The photocatalysts were characterized using PXRD, SEM, EDX, FTIR and UV-vis spectrophotometer. The obtained results show that the silver (Ag⁰) deposited TiO₂ exhibited visible light plasmon absorption band. The degradation experiment reveals that the catalytic property of Ag-DP25 in the degradation of MO is more efficient than that of commercially available Degussa P25 TiO₂ (DP25) samples. The improvement of Ag-DP25 catalyst efficiency strongly depends on the content of silver (Ag) deposits. The present study shows that the degradation process is dominated by Ag-TiO₂ photocatalytic system, complying with pseudo-first order rate law. The higher rate of photodegradation observed on Ag-DP25 at pH 6.6 can be correlated to the ratios of the concentrations of the ionized to the neutral dye molecules and also to the higher concentration of hydroxylated surface, which are able to effectively scavenge photogenerated valence band holes. Accumulation of the holes in the semiconductor particles increases the probability of formation of excited oxygen atom which is a reactive species readily oxidizing the organic dye molecule. The reduction of pH during the course of the reaction is attributed to the complete mineralization of the dye.     

滤纸模板法二氧化钛纸的制备及其光催化活性

以滤纸为模板成功制备了由微带组成的二氧化钛纸光催化材料,利用红外光谱、热重量分析、X射线衍射、扫描电子显微镜对其进行了表征. 通过对甲基橙溶液在紫外光下的降解,考察了制得样品的光催化性能. 结果表明：锐钛矿/金红石比为10:1的二氧化钛纸具有最高的催化活性,且滤纸纤维提高样品的结晶度和锐钛矿的相转化温度. 并讨论了对二氧化钛纸的形成机理.     

Low temperature deposition and characterization of TiO2 photocatalytic film through cold spray

Cold spray was employed as a novel low temperature approach to deposit titanium dioxide (TiO₂) photocatalytic film. The film microstructure was characterized using X-ray diffraction and scanning electron microscopy. The photocatalytic performance was examined through acetaldehyde degradation under ultraviolet illumination. Results showed that TiO₂ film was successfully deposited on substrate surface through cold spray. The film thickness reached up to 15 μm. The film presented a rough surface and porous structure. Owing to the low temperature of spray powder, no phase and particle size changes occurred to TiO₂ during deposition. It was found that the cold-sprayed TiO₂ film was active for photodegradation of acetaldehyde.