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Insights into different photocatalytic oxidation activities of anatase, brookite, and rutile single crystal facets
摘要： For the understanding of the activity of TiO2 photocatalysts knowledge of the activities of different crystal facets is necessary. This information can be achieved by the investigation of well-defined single crystalline TiO2 surfaces. In this study, the photocatalytic activity of different anatase, brookite, and rutile single crystal wafers with only one exposed surface has been investigated via the oxidation of methanol and the hydroxylation of terephthalic acid, respectively. XRD and SEM measurements have shown that all surfaces are clearly defined and possess a smooth surface, which allows a reliable comparison of the photocatalytic activities. The investigated anatase surfaces show a higher activity than the rutile surfaces, while the brookite surface is interestingly the least active one. To the best of our knowledge, there are no other reports based on the investigation and comparison of well-defined TiO2 anatase (100), anatase (001), and brookite (100) single crystalline surfaces concerning their photocatalytic activity. Furthermore, the influence of the coordination of the titanium and the oxygen ions on the photocatalytic activity is discussed.
关键词： rutile,terephthalic acid hydroxylation,anatase,TiO2 modifications,photocatalytic methanol oxidation,TiO2 surfaces,brookite,single crystalline surfaces
更新于2025-09-09 09:28:46
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Influence of the Heat Treatment on the Particles Size and on the Crystalline Phase of TiO2 Synthesized by the Sol-Gel Method
摘要： Titanium biomaterials’ response has been recognized to be affected by particles size, crystal structure, and surface properties. Chemical and structural properties of these nanoparticle materials are important, but their size is the key aspect. The aim of this study is the synthesis of TiO2 nanoparticles by the sol-gel method, which is an ideal technique to prepare nanomaterials at low temperature. The heat treatment can affect the structure of the ?nal product and consequently its biological properties. For this reason, the chemical structure of the TiO2 nanoparticles synthesized was investigated after each heat treatment, in order to evaluate the presence of different phases formed among the nanoparticles. FTIR spectroscopy and XRD have been used to evaluate the different structures. The results of these analyses suggest that an increase of the calcination temperature induces the formation of mixed-crystalline-phases with different content of anatase and rutile phases. The results obtained by SEM measurements suggest that an increase in the particles size accompanied by a noticeable aggregation of TiO2 nanoparticles is due to high temperatures achieved during the thermal treatments and con?rmed the presence of different content of the two crystalline phases of titanium dioxide.
关键词： titania,sol-gel method,rutile,FTIR,nanoparticles size,anatase
更新于2025-09-09 09:28:46
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Photocatalytic reduction of uranyl: Effects of organic ligands and UV light wavelengths
摘要： Although previous studies demonstrate the photochemical reduction of uranyl (UO2) in the presence of various organic compounds, the actual roles of organic molecules as ligands and electron donors during the photoreaction are poorly understood. In this study, photochemical reduction of uranyl is examined with respect to organic ligands as electron donors and complexing agents, the role of titanium oxide (TiO2) nanoparticles as a photocatalyst, and the influence of UV light irradiation with emission peaks in the UV-A, UV-B, and UV-C ranges. Organic compounds with different binding affinities to uranyl such as acetate, ethylenediaminetetracetate (EDTA), oxalate, and hydroquinone were selected. Uranyl solutions prepared with one organic compound in a 1:8 molar ratio were irradiated under anoxic and acidic conditions (O2 < 1 ppm, pH 2.5). Uranyl removal by UV irradiation was better than 70 percent in the presence of oxalate and acetate, followed by hydroquinone (≈ 45 %) and EDTA (≈ 10 %). Uranyl removal was nearly constant at the UV-A, UV-B, and UV-C regions in the presence of acetate and oxalate whereas greater removal was observed in the EDTA and hydroquinone solutions exposed to UV-C and UV-A, respectively. These results reveal that uranyl reduction is mediated primarily by TiO2 nanoparticles and is highly dependent on the electron-donor compound. Addition of acetate enhances the uranyl photoreaction in hydroquinone solution. Dissolved EDTA species act as good electron donors at limited EDTA concentrations (1:2 to 1:4 uranyl to EDTA ratios) but at higher concentrations (for example, 1:8), uranyl-EDTA complexes such as [(UO2)HEDTA] compete for the surface sites on the TiO2 nanoparticles, hindering the photoreduction of uranyl. X-ray photoelectron spectroscopy (XPS) of the dried TiO2 powder shows that more than 70 percent of uranium partitioned into the solid phase is present as reduced forms with oxidation states (V) and (IV). The U4f spectra of U partitioned to the solid phase from the photoreaction with acetate reveal the predominance of U(IV) over U(V), whereas U(V) is the dominant oxidation state as a result of the photoreduction with EDTA. Our results suggest that formation of uranium-ligand complexes plays a critical role in controlling the reactivity of uranyl species and the stability of reduced uranium species in the course of the photoreaction.
关键词： organic ligand,rutile,P25,UV wavelength,electron donor,photocatalytic reduction of uranyl,anatase
更新于2025-09-09 09:28:46
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Effect of Physical Properties upon Hydrothermal Treatments on Titanium Dioxide Films
摘要： Titanium dioxide is used extensively as semiconductor since more than five decades. Hydrothermal method is one the method which widely used for the synthesis of TiO2 have been widely developed. The effect of hydrothermal temperatures on the titanium dioxide films is investigated. The TiO2 films were prepared by hydrothermally layering a mixture of aquadest, HCl and titanium(IV) isopropoxide over indium tin oxide glass, at 110, 150, 180 and 200 oC for 10 h. The film on the surface of indium tin oxide glass was calcined at 500 oC and characterized by X-ray diffraction, UV-visible spectroscopy and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) methods. The study shows that the TiO2 has a spherical morphology with the size between 0.5 to 2 μm. The TiO2 consits of rutile and anatase with the particle size ranging from 16.97 to 24.10 nm and from 18.09 to 26.75 nm, respectively. The band gap energy of TiO2 is between 3.17 to 3.48 eV.
关键词： Anatase,Hydrothermal,TiO2,Solar cell
更新于2025-09-04 15:30:14
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Osteoblast Response to Different UVA-Activated Anatase Implant Coatings
摘要： The “activation” of titanium implants by UV-irradiation is reported to enhance osseointegration in vitro as well as in vivo. Anatase-enriched titanium oxide surfaces enable, via photocatalysis, a chairside “activation” of implants by short-term UVA (382 nm) irradiation. The potentially improved clinical performance of these modified surfaces depends not only on the achieved photocatalytic activity, but also on the effects caused by the micro- and nano-structure of the respective surface modification. In this study, three differently manufactured anatase-coated titanium surfaces are characterized regarding surface characteristics, photocatalytic efficiency, and their ability to promote proliferation and differentiation of osteoblasts in comparison to conventional sandblasted (S) and blasted/etched (S/A) titanium implant surfaces. Anatase surfaces are manufactured by suspension plasma spraying (SPS), precursor-based liquid film coating (PLC), and physical vapor deposition (PVD). The tested surfaces exhibit significantly different surface morphologies and anatase/rutile ratios. UVA-irradiation of samples prior to cell seeding leads to significantly improved cell proliferation and surface coverage. UVA-treatment also leads to a generally enhanced osteoblastic differentiation of cells on all anatase-coated surfaces. The anatase-enriched titanium surface modifications promote different aspects of osteoblast reactions, suggesting that the “activation” of anatase-coated titanium implants by UVA treatment is a promising chairside procedure for dental implant optimization.
关键词： anatase,osteoblasts,titanium implant activation,hydrophilization,photocatalysis
更新于2025-09-04 15:30:14
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Synthesis and Characterization of Tio2/C Composite for Photocatalytic Degradation of Dyes.
摘要： Titanium dioxide TiO2 nanoparticles have moderate catalytic activity due to its wide band-gap and high rate of electron-hole recombination [1]. The TiO2 electrical conductivity poor is improved by mixing with other materials. Therefore, TiO2 based nanocomposites have been synthesized to increase the photocatalytic activity, as well as their structural characteristics and electrochemical performance, using dopants like carbon, nitrogen, sulfur and others. TiO2/C composite has been proven to be a promising photocatalyst for pollutants, due to C-doping, morphology, structure and mixed phases [1]. Carbon precursors are reported to synthesize TiO2/C, such as: glucose, oleic acid, carbon nanofiber, graphene oxide, activated carbon, carbon nanotubes, graphite, resorcinol and formaldehyde. Dyes used for industries, are significant sources of environmental pollution, because they are non-biodegradable [2]. Methyl orange (MO) and methyl blue (MB) have been used to help determine the activity of the photocatalyst [3]. The reagents used were: anatase powder 99.8% (metals basis), sucrose (99.5%), H2SO4 (65% wt), distilled water, MO (MW=327.33g/mol) and MB (MW=319.85g/mol). TiO2/C composites were synthesized via infiltrating sucrose into anatase. In a typical synthesis, anatase (A) and sucrose (S) with molar ratio of A/S=6, sulfuric acid and distilled water were mixed completely. The mixture was then put in a drying oven, treated at 100°C for 6h and subsequently at 160°C for 6h. The resulting brown precursor powder was carbonized in a tubular furnace at 800°C for 1h in argon atmosphere. Rigaku D-Max 2200 difractometer was used to obtain XRD patterns using Cu Kα radiation. The surface morphology and the crystalline phases were examined with Field Emission Transmission Electron Microscope, JEM 2010F JEOL. The photocatalytic activity was tested for degradation of MB and MO with an initial concentration of 20 ppm, using 0 and 0.34 g/L of TiO2/C, under radiant flux provided by 175 W UV. The MB and MO concentrations were measured by UV–vis spectroscopy (Aiglet-Vis spectrophotometer). The XRD patterns of TiO2/C composite is shown in Fig. 2, in which all the characteristic diffraction peaks of the TiO2/C composite can be respectively indexed with planes of anatase phase of TiO2 (JCPDS No. 21-1272). Moreover, a small peak at 11.5° is observed, characteristic of weakly ordered graphitic microstructure, indicating the trace amount of graphite in the composite [4]. No significant peaks of carbon or rutile are observed after the precursor powders are heat treated under argon atmosphere, which suggesting its amorphous nature and confirmed the high purity of the TiO2/C composite [5], because impurities have been reported due to the transformation from anatase to rutile phase [1]. The broad diffraction peaks indicate the sample’s nanocrystalline nature. Fig. 3a shows the micrographs of TEM bright field of powders; it is clearly seen that the TiO2/C composite powders have mostly spherical morphology. Further, it can be estimated that the particle size of samples is of the microscale order with grain size of the range of 20-30nm. Fig. 3b shows the atomic structure and the crystallinity of TiO2/C composite through HRTEM. The insert image shown in Figure 3b give the corresponding Fast Fourier Transform (FFT) pattern of the anatase; this pattern displays (101) and (200) planes from the interplanar spacing of 0.352 and 0.189 nm respectively (JCPDS No. 21-1272). The results of XRD concurred with the electron diffraction pattern created by FFT from HRTEM. The degradation percentage for MO and MB were 99.95 and 99.99 % at 15 min on TiO2/C whereas 86 and 81 % at 90 min for MB and MO in the absence of catalyst is illustrated in Fig. 5. TiO2/C composite was synthetized using anatase and sucrose by obtaining a precursor powder at low temperature (160°C), which is carbonized at 800°C in argon atmosphere. The XRD analysis reveals that the TiO2/C composite is a phase anatase unique structure with high crystallization, which had no impurities, but it showed a trace amount of graphite in the composite. The TiO2/C composite were found to be efficient catalyst for the photodegradation of MB and MO dyes under UV irradiation. The reaction was found to follow pseudo-first order kinetics described it well. This method could be extended to synthesize a variety of other composites for photocatalytic degradation of dyes.
关键词： anatase,TiO2/C composite,dyes,photocatalytic degradation,sucrose
更新于2025-09-04 15:30:14