Degussa P25 Powders Research Articles

Compact device for in situ ultraviolet–visible spectrophotometric measurement of photocatalytic kinetics

In this work, we have designed a compact device that can be easily integrated with Ultraviolet–Visible spectrophotometers, utilizing Light Emitting Diode technology for in situ spectrophotometric measurements of photocatalytic reactions. Using our device, we present the test results for the breakdown of amaranth dye with Degussa P25 powder and compare them with those obtained from a conventional arc discharge reactor. The results show that the reaction constants obtained using our device are practically equivalent to those acquired with a conventional reactor. However, our device significantly simplifies the experimental task by requiring less test solution volume and fewer user interventions while enabling in situ monitoring of the reaction kinetics. Overall, the proposed approach offers a convenient and efficient means of studying photocatalytic materials for dye degradation.

Investigation of the annealing treatment on the performance of TiO2 photoanode

Developing low-cost semiconductor photoanode toward efficient and stable oxygen evolution reaction (OER) is highly desirable for photoelectrochemical (PEC) water splitting. Herein, nanoparticulate titanium dioxide (TiO2) electrodes were prepared using Degussa P25 powders by spin-coating method. The effects of annealing conditions on the PEC performance of the nanoparticulate TiO2 photoanode was systematically investigated including temperature, annealing time and atmosphere. The results demonstrate that the TiO2/fluorine-doped tin oxide substrates (FTO/TiO2) electrode annealed at argon (Ar) atmosphere under 450 °C shows the highest PEC performance. The photocurrent density of FTO/TiO2 annealed in Ar for only 0.5 h reached to 120 μA/cm2 at 0.3 V vs. Hg/HgO which is about 10 times higher than that of the unannealed one. The X-ray photoelectron spectroscopy (XPS) results show the thermal treatment can produce oxygen vacancies on the surface of TiO2 which reduce the recombination of photogenerated electron-hole pairs and expanding the visible light absorption by introducing defective energy levels. The electrochemical impedance spectroscopy (EIS) approves that appropriate annealing treatment can effectively enhance the electron conductivity resulting in low charge transfer resistance. All these factors contribute to improving the PEC activity of TiO2 photoanode.

Low temperature prepared N doped TiO2 photodegradation of janus green B

N doped titanium dioxide (TiO2) was prepared under low temperature calcination of TiO2 Degussa P25 powder and urea at various mixing ratios. Muffle furnace was used as heating media with the temperature used in the range of 300 to 500 °C. The prepared N doped TiO2 was characterized by using UV-Vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). It was observed that N doped TiO2 prepared at 0.5 g urea under the 400 °C calcination process (named as U2-400) is the optimum photocatalyst sample with the highest rate removal of Janus green B (JG) dye. The U2-400 had goes the photodegradation rate removal at 0.1071 min−1 where it is 3.5 times faster compared to unmodified TiO2 sample. The high photodegradation rate removal for U2-400 was due to the N incorporated with TiO2 in U2-400 photocatalyst which narrowed the bandgap energy from 3.2 to 3.0 eV as observed by UV-Vis DRS spectra. This shows the U2-400 sample has increased its photocatalytic activity since it has become more active under wider an optical response compared to the unmodified TiO2

Electronic properties of photocatalytic improved Degussa P25 titanium dioxide powder

The defect structures of photocatalytic improved Degussa P25 powder were evaluated by X-ray photoelectron spectroscopy (XPS), paramagnetic resonance spectroscopy (EPR) and in situ studies of the electrical resistivity in order to understand the charge carrier transport inside the material. Annealing the titanium dioxide in vacuum at temperatures below the phase transition temperature did not increase the oxygen defect concentration drastically. However, annealing Degussa P25 powder in vacuum resulted in a redistribution of Ti3+-lattice states and lattice oxygen vacancies. The diffusion of these lattice oxygen vacancies from the bulk to the surface of the material forms charge carrier trapping sites. Such transformation of the defect structure of TiO2 leads to switching from an insulating state to a conducting state.

Photocatalytic properties of P25-doped TiO2 composite film synthesized via sol–gel method on cement substrate

TiO2 films have received increasing attention for the removal of organic pollutants via photocatalysis. To develop a simple and effective method for improving the photodegradation efficiency of pollutants in surface water, we herein examined the preparation of a P25-TiO2 composite film on a cement substrate via a sol–gel method. In this case, Rhodamine B (RhB) was employed as the target organic pollutant. The self-generated TiO2 film and the P25-TiO2 composite film were characterized by X-ray diffraction (XRD), N2 adsorption/desorption measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS). The photodegradation efficiencies of the two films were studied by RhB removal in water under UV (ultraviolet) irradiation. Over 4day exposure, the P25-TiO2 composite film exhibited higher photocatalytic performance than the self-generated TiO2 film. The photodegradation rate indicated that the efficiency of the P25-TiO2 composite film was enhanced by the addition of the rutile phase Degussa P25 powder. As such, cooperation between the anatase TiO2 and rutile P25 nanoparticles was beneficial for separation of the photo-induced electrons and holes. In addition, the influence of P25 doping on the P25-TiO2 composite films was evaluated. We found that up to a certain saturation point, increased doping enhanced the photodegradation ability of the composite film. Thus, we herein demonstrated that the doping of P25 powders is a simple but effective strategy to prepare a P25-TiO2 composite film on a cement substrate, and the resulting film exhibits excellent removal efficiency in the degradation of organic pollutants.

An improvement of photocatalytic activity of TiO2 Degussa P25 powder

The photocatalytic activities of Degussa P25 powders annealed at various temperatures in vacuum and air were studied together with investigations of their compositions by XPS, of their crystal structures by XRD and of their specific surface areas by BET. It is shown that the photocatalytic activity of P25 powders was remarkably enhanced after vacuum annealing; the kinetic coefficient can be raised by 75% during annealing at 400°C. It is obvious that this enhancement is not related to the adhesion ability of the P25 powders.

Rutile TiO2mesocrystallines with aggregated nanorod clusters: extremely rapid self-reaction of the single source and enhanced dye-sensitized solar cell performance

This paper reports a simple and environmentally friendly approach for the synthesis of rutile TiO2 mesocrystals (RTM) composed of single crystal aggregated nanorod clusters. It is a hydrothermal method involving titanium(III) chloride as the only reactant. The resulting one-dimensional rutile nanorods can easily assemble into three-dimensional hierarchical architectures without any surfactants or additives. By selecting appropriate experimental conditions, such as reaction time and ripening temperature, we can easily manipulate the RTM microstructure. Detailed experiments suggest that the growth of the RTM is spontaneous and an extremely rapid self-reaction of titanium(III) chloride, which is controlled by the thermodynamics process. Furthermore, the composites photoanode was fabricated by hybridizing RTM and TiO2 nanoparticles (Degussa-P25 powder) for use in dye-sensitized solar cells (DSSCs). The composite photoanode-based DSSC possesses superior performance to TiO2 nanoparticle cells. A high light-to-electricity conversion yield of 7.3% for composite photoanodes was achieved, significantly higher than that of TiO2 nanoparticle photoanodes with a similar thickness (5.45%). This result can be attributed to their synergistic effect of high crystallinity, light scattering and fast charge transfer capability.

Synthesis of three-dimensional ordered macroporous TiO2, Gd/TiO2 and their photocatalytic activity

In this paper, three-dimensional ordered macroporous (3DOM) TiO2 and Gd/TiO2 materials were synthesized by colloidal crystal templating process. The obtained samples were analyzed by field-emission scanning electron microscope, transmission electron microscopy, X-ray diffraction, diffuse reflectance spectra and Brunauer–Emmett–Teller method. The photocatalytic activity of various samples was evaluated by degradation of methyl orange in aqueous solution under UV and visible light irradiation. At the same time, Degussa P25 (a commercial Titania) powders were used for comparison. The results indicated that 3DOM Gd/TiO2 samples showed a significant shift in the onset absorption towards the longer wavelength compare to pure 3DOM TiO2, and displayed excellent photocatalytic activity under both UV and visible light irradiation.

Annealing-free synthesis of C[sbnd]N co-doped TiO2 hierarchical spheres by using amine agents via microwave-assisted solvothermal method and their photocatalytic activities

The annealing-free synthesis of CN co-doped TiO2 hierarchical spheres is proposed in this study. C and N were doped into the TiO2 structure via a direct chelating process to the Ti-precursor by using different amine agents, including hexadecylamine (HDA), diethylamine (DEA), trimethylamine (TMA), and diethylenetriamine (DETA). CN co-doped TiO2 spheres (300nm to 500nm) composed of nanoparticles approximately 11nm to 13nm in size were obtained via an efficient microwave-assisted solvothermal reaction at 190°C for 60min. The effects of C and N doping by using different amine compounds on the bandgap energy and photocatalytic performance of TiO2 were investigated. Among the amine compounds, DETA provided the highest chelating efficiency because it provides two primary amine groups, which resulted in the highest C and N doping concentrations and the largest degree of bandgap narrowing (2.77eV); nevertheless, the high chelating ratio of C and N restrained the crystallization of TiO2 and considerably decreased its photocatalytic activity. The use of TMA produced optimal C and N doping concentrations, which effectively reduced the bandgap of TiO2 to 2.85eV without affecting its crystallization. Its photodecomposition activity to rhodamine B was eightfold of that of commercial Degussa P25 powders under visible light irradiation.

Highly crystalline and silica-embedded titania rhombic shaped nanoparticles with mesoporous structure and its application in photocatalytic degradation of organic compound

Highly crystalline and silica-embedded titania rhombic shaped nanoparticles with mesoporous structure are successfully obtained via a facile solvothermal method using Ti(OC4H9)4 as precursor, acetic acid as solvent and Si(OC2H5)4 (TEOS) as stabilizer. Various characterization techniques, including Transmission electron microscopy(TEM), X-ray diffraction(XRD), UV–vis diffuse reflection spectroscopy, Raman spectroscopy, N2 adsorption–desorption isotherms and X-ray photoelectron spectra (XPS), have been applied to investigate the physical–chemical properties and the formation process of silica-embedded titania. The photocatalytic performances of all the silica-embedded titania samples are also studied by the degradation of methylene blue (MB) dye under UV irradiation. The results indicate that the mesoporous silica-embedded titania nanocrystals exhibit rhombic or truncated rhombic shapes and have extremely high special surface area of 260.7 m2 g−1. All the highly crystalline and mesoporous silica-embedded titania samples show better photocatalytic activity than that of the pure titania. The maximum photocatalytic activity is obtained on the silica-embedded titania nanoparticles with 0.6 ml TEOS, which is 6.7 times that achieved on the pure titania sample and 1.5 times that performed on the Degussa P25 powders. This is attributed to high crystallinity, increased surface area by embedding amorphous silica and proper assembly of TiO2 nanoparticles.

Polymorphic phase transformation of Degussa P25 TiO2 by the chelation of diaminopyridine on TiO62− octahedron: Correlation of anatase to rutile phase ratio on the photocatalytic activity

A series of nitrogen-doped Degussa P25 photocatalysts were synthesized successfully by grinding and calcination method using 2,6-diaminopyridine (DAP) as a nitrogen precursor. The prepared samples were characterized by various analytical methods. The phase contents of anatase and rutile in the Degussa P25 powders have been altered by simply changing the proportion of DAP. A mechanism involving chelated DAP molecule on TiO62− octahedron is discussed. The enhanced activity is attributed to synergistic effect in the two phase solid material. Due to the low activation barrier, the effective inter particle electron transfer between the two polymorphs is quite efficient only when they are in close proximity with similar crystallite sizes. The transfer of electrons from the rutile phase to lattice/electron trapping sites of anatase and also to the Ti3+-Vo defect level created by the dopant favors effective charge separation and enhance the photocatalytic activity under solar illumination.

Preparation and photocatalyic properties of TiO2-P25 film prepared by spray pyrolysis method

TiO2 films were synthesized by immobilization of Degussa P25 powders on stainless steel support by spray pyrolysis technique. After preparation, the films were annealed at different temperatures in order to obtain materials with different morphological, structural, and textural properties. The photocatalytic activity of obtained films was investigated by monitoring the degradation of arylazo pyridone dye. The results showed that with increasing annealing temperature the photoactivity of films decreased. A comparative photocatalytic activity of the synthesized films and corresponding commercial powders was evaluated under the same experimental conditions. Films generally showed lower photoactivity than powders, due to mass transfer limitations inside film layer, smaller surface exposure to light, and possible presence of metal ions in film layer.

TiO2:(Fe, S) Thin Films Prepared from Complex Precursors by CVD, Physical Chemical Properties, and Photocatalysis

The TiO2thin films were prepared using Ti(dpm)2(OPri)2and Ti(OPri)4(dpm = 2,2,6,6-tetramethylheptane-3,5-dione,Pri= isopropyl) as the precursors. The volatile compounds Fe[(C2H5)2NCS2]3and [(CH3)C]2S2were used to prepare doped TiO2films. The synthesis was done in vacuum or in the presence of Ar and O2. The pressure in the CVD chamber was varied between1.2×10−4 mbar and 0.1 mbar, with the system working either in the molecular beam or gas flow regime. Physical, chemical, and photocatalytic properties of the (Fe, S)-doped TiO2films were studied. Those TiO2:(Fe, S) films prepared from the Ti(OPri)4precursor show increased photocatalytic activities, very close to those of Degussa P25 powder in UV region.

Bioinspired Au/TiO2 photocatalyst derived from butterfly wing (Papilio Paris)

The reticular hierarchical structure of butterfly wings (Papilio Paris) is introduced as template for Au/TiO2 photocatalyst by depositing the Au nanoparticles on TiO2 matrix, which is carried out by a water–ethanol sol–gel procedure combined with subsequent calcination. The obtained Au/TiO2 nanocomposites present the reticular hierarchical structure of butterfly wings, and Au nanoparticles with an average size of 7nm are homogeneously dispersed in TiO2 substrate. Benefiting from such unique reticular hierarchical structure and composition, the biomorphic Au/TiO2 exhibits high-harvesting capability and presents superior photocatalytic activity. Especially, the biomorphic Au/TiO2 at the nominal content of gold to titanium of 8wt% shows the highest photocatalytic activity and can completely decompose methyl orange within 80min, which is obviously higher than that of commercial Degussa P25 powders.

Enhanced DSSC performance with high surface area thin anatase TiO2 nanoleaves

Thin anatase TiO2 nanoleaves (NLs) with high surface area (∼93 m2/g) are synthesized by hydrothermal route and dye-sensitized solar cells (DSSC) made using such NLs are compared with those made with hydro-thermally synthesized TiO2 nanoparticles and the Degussa P25 powder. The NLs-based DSSCs show increment of 16% and 24% in the total conversion efficiency over the cells made with NPs and P25 respectively. Interestingly, the highest increment in the conversion efficiency (∼35%) is achieved for cells made using a 50:50 (wt/wt) mixture of NLs and NPs. In this case the dye loading is found to be >50% higher than the case of NP films. Moreover the DC resistance of diffusion of I3- in electrolyte (as revealed by the electrochemical impedance spectroscopy) is substantially lower than the NP film case, other cell parameters being nominally comparable.

Photocatalytic Activity of Degussa P25 TiO2/Au Obtained Using Argon (Ar) and Nitrogen (N2) Plasma

Titania Degussa P25 powder was treated with Argon (Ar) and Nitrogen (N2) gas plasma inside of a closed homemade chamber system at 50 Pa of pressure. The electric discharge was generated applying an AC voltage (0–15,000 V) to a pair of aluminum electrodes. Two sets of samples were analyzed. In the first one, the plasma is applied directly on a layer of titania P25 that is spread out on top of one of the electrodes and, in the second one, a gold foil substrate is positioned between the titania powder and the electrode, named TiO2/Au. In the last sample, gold coated titania nanoparticles or clusters of gold are formed, changing the optical properties of the material. The evolution of the optical properties of the obtained samples was analized using UV–Vis diffuse reflectance. The spectra show a shift in the band gap and a broad band in P25/Au associated with the gold plasmonic band. Additionally, the photocatalytic activity was evaluated by monitoring the photodegradation of methylene blue solution (0.01 g/L), using UV–Vis absorption analysis in the range 250–850 nm. After the plasma is applied, the gold impregnation over the titania surface increases the photocatalytic activity.

The Preparation of Composite TiO2 Electrodes for Dye‐Sensitized Solar Cells

AbstractIn this work, the 1D titania nanorods (Tnr) were successfully prepared from commercial Degussa P25 powders (DP25) by alkaline hydrothermal method and applied to fabricate the composite TiO2 photoanodes for DSSCs. The morphology of the obtained 1D titania nanomaterials is controllable and is dependent on the post heat treatment. Anatase Tnr (a‐Tnr) with diameters of 50‐200 nm and lengths of several hundreds nanomaters was obtained after calcination at 600 °C. The BET surface area was 20 m2/g. For DSSCs study, the composite TiO2 pastes with a range of DP25/Tnr weight ratio were used for photoanodes. It was found that by adding the Tnr, the photoconversion efficiency (η) increases, yet, due to the lower surface area of a‐Tnr, the DSSC efficiency is deteriorated for higher Tnr content. The DSSC performance also largely depends on the thickness of composite TiO2 films. The best efficiency of ∼7.56% (Voc = 0.81V, Jsc = 14.9 mA/cm2, FF = 0.63) was achieved for the D80a20 sample (80% DP25, 20% Tnr) with film thickness of 20 μm. To realize the electron transport properties of composite film, the DSSCs were investigated by electrochemical impedance spectroscopy. The results indicated that the electron transport efficiency is affected by the morphology and composition of the composite TiO2 electrodes.

Microwave‐Hydrothermal Preparation and Visible‐Light Photoactivity of Plasmonic Photocatalyst Ag‐TiO2 Nanocomposite Hollow Spheres

Visible-light-driven plasmonic photocatalyst Ag-TiO(2) nanocomposite hollow spheres are prepared by a template-free chemically-induced self-transformation strategy under microwave-hydrothermal conditions, followed by a photochemical reduction process under xenon lamp irradiation. The prepared samples are characterized by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N(2) adsorption-desorption isotherms, X-ray photoelectron spectroscopy, UV/Vis and Raman spectroscopy. Production of .OH radicals on the surface of visible-light illuminated TiO(2) was detected by using a photoluminescence method with terephthalic acid as the probe molecule. The photocatalytic activity of as-prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature under visible-light irradiation. The results show that the surface plasmon absorption band of the silver nanoparticles supported on the TiO(2) hollow spheres was red shifted, and a strong surface enhanced Raman scattering effect for the Ag-TiO(2) nanocomposite sample was observed. The prepared nanocomposite hollow spheres exhibits a highly visible-light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of pure TiO(2) and commercial Degussa P25 (P25) powders. Especially, the as-prepared Ag-TiO(2) nanocomposite hollow spheres at the nominal atomic ratio of silver to titanium (R) of 2 showed the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2.

Photocatalytic Degradation of Mecoprop and Clopyralid in Aqueous Suspensions of Nanostructured N-doped TiO2

The work describes a study of the oxidation power of N-doped and undoped anatase TiO2, as well as TiO2 Degussa P25 suspensions for photocatalytic degradation of the herbicides RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop) and 3,6-dichloro-pyridine-2-carboxylic acid (clopyralid) using visible and UV light. Undoped nanostructured TiO2 powder in the form of anatase was prepared by a sol-gel route. The synthesized TiO2, as well as TiO2 Degussa P25 powder, were modified with urea to introduce nitrogen into the structure. N-doped TiO2 appeared to be somewhat more efficient than the starting TiO2 (anatase) powder when visible light was used for mecoprop degradation. N-doped TiO2 Degussa P25 was also slightly more efficient than TiO2 Degussa P25. However, under the same experimental conditions, no degradation of clopyralid was observed in the presence of any of the mentioned catalysts. When the kinetics of mecoprop degradation was studied using UV light, more efficient were the undoped powders, while in the case of clopyralid, N-doped TiO2 Degussa P25 powder was most efficient, which is probably a consequence of the difference in the molecular structure of the two herbicides.

Intercalated Structure and Photocatalytic Properties of TiO<sub>2</sub>-Graphite Oxide Composite

TiO2-graphite oxide (TiO2-GO) composites were successfully prepared at low temperature (80 ℃) using graphite oxide (GO) and titanium sulfate (Ti(SO4)2) as initial reactants.The photocatalytic properties of TiO2-GO under UV light irradiation were also studied.Results show that the degradation rate of methyl orange is 1.17 mg·min-1·g-1 (referring to the efficiency of the initial 15 min).Compared with Degussa P25 powders,this intercalation composite is far more efficiently.In addition,the crystalline structure,interface status and microscopic structure of TiO2-GO were characterized by X-ray diffraction (XRD),Fourier-transform infrared (FT-IR) spectroscopy,X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM).Result showed that the TiO2 crystallites in the intercalated structure were composed of anatase and rutile phase with the former phase being enriched.The functional groups present in GO such as carboxyl (C=O) were mostly reduced in the intercalation composite.On the other hand,the synthesis mechanism and the main reasons responsible for the superior photocatalytic properties of TiO2-GO are also discussed.