Ag-doped TiO2 Research Articles

Effect of Ag doping concentration on the electronic and optical properties of anatase TiO2: a DFT-based theoretical study

The electronic and optical properties of pure and Ag-doped anatase TiO2 have been calculated by spin-polarized density functional theory. Ag-doped TiO2 with different Ag doping concentrations ranging from 2.08 to 8.33 % was investigated, and the electronic and optical properties evaluated. Substitutional Ag doped at Ti sites introduced Ag 4d states just above the valence-band maximum, which may help in shifting visible-light excited electrons to the conduction band. Our results show that increasing the doping concentration will enhance visible-light absorption up to Ag doping concentration of 6.25 %; however, further increase of the doping concentration leads to a decrease in visible-light absorption. These results indicate the possibility of tailoring the band gap and optical absorption of TiO2 doped with Ag by varying the doping concentration. The enhanced visible-light absorption for Ag-doped TiO2 with doping concentration of 6.25 % may be due to the existence of widely distributed Ag 4d states above the valence-band maximum and the optimal doping concentration. Ag doping shifted the absorption edge of TiO2 towards visible light, consistent with recent experimental results. Our calculation results provide a reasonable explanation for the experimental findings.

Influence of temperature on the photodegradation process using Ag-doped TiO2 nanostructures: Negative impact with the nanofibers

In this study, the influence of the temperature on the photodegradation process using Ag-doped TiO2 nanostructures was investigated. Two morphologies were used; nanoparticles and nanofibers. The nanofibers were synthesized by electrospinning of a sol–gel consisting of titanium isopropoxide, silver nitrate and poly(vinyl acetate). The silver nitrate amount was changed to produce nanofibers having different silver contents. Typically, sol–gels containing 0.5, 1.0, 1.5, 2.0 and 2.5wt% silver nitrate were utilized. Calcination of the electrospun mats at 700°C led to produce well morphology Ag-doped TiO2 nanofibers for all formulations. The nanoparticles were prepared from the same sol–gels, however, instead of spinning the gels were dried, grinded and sintered at 700°C. Photodegradation under UV irradiation for the rhodamine B at 5, 15, 25, 45 and 55°C were performed. For the nanoparticles, increasing the temperature has positive impact as the best degradation was obtained at 55°C. In contrast to the known influence of the temperature on the chemical reactions, in case of the nanofibrous morphology, the temperature has negative impact as the experimental work indicated that the optimum temperature is 25°C. The observed strange effect of the temperature in case of the nanofibrous morphology indicates instant degradation of the dye molecules in the active zones surrounding the nanofibers. Therefore, the increase of temperature results in increase the kinetic energy of the dye molecules so the molecules escape from the active thin film surrounding the photocatalyst. Overall, this study shows that the nanofibrous morphology strongly enhances the surface activity of the photocatalyst which generates negative influence of the temperature.

Correlation of Photodegradation Efficiency with Surface Potential of Silver-TiO2 Nanocomposite Thin Films

The present work focuses on photocatalytic performance of Ag-TiO2 systems. Nanocrystalline thin films of TiO2-and Ag-doped TiO2 are grown by sol–gel method, followed by spin-coating technique on Si ⟨100⟩ surface. The crystallinity and crystal size were measured from X-ray diffraction and transmission electron microscopy studies. Lateral distribution of work function (WF) was examined through contact potential difference measurement done by scanning Kelvin probe microscopy. Local WFs of Ag-TiO2 thin films were found to be smaller than that of TiO2, and the minimum WF expected from the polynomial curve fitting was that of pure Ag. The photocatalytic efficiency of these thin films is estimated from photodegradation of methyl orange analyzed by UV–vis spectrophotometer. The photodegradation efficiency of Ag-TiO2 nanocrystalline thin films increases up to a certain dopant concentration of silver, beyond which it decreases. The changes in the photodegradation efficiency of these films are correlated with variation in contact potential difference.

Disinfection of water using Pt- and Ag-doped TiO2 photocatalysts

In this article we have reported heterogeneous photocatalytic disinfection using pristine and Ag- and Pt-doped nano TiO2 under near-UV light and solar light irradiation. Disinfection experiments were conducted in slurry reactors with Escherichia coli, artificial light and sunlight. The influence of various amounts of Pt and Ag loading (0.5% to 5%) on the E. coli inactivation was examined and results indicated that 5% Pt-TiO2 and 0.5% Ag-TiO2 showed the highest photocatalytic E. coli inactivation. The Pt- and Ag-doped photocatalysts were characterized using XPS and TEM analysis. The influence of experimental parameters such as various photocatalysts, photocatalyst concentration, reactor geometry effect, pH and temperature on the photocatalytic disinfection was studied. The experimental results show that sunlight or near-UV light with TiO2 photocatalyst strongly inactivates E.coli. The Ag-TiO2 photocatalyst was the most efficient photocatalyst tested for bactericidal activity. A plausible mechanism of photocatalysed E. coli inactivation is discussed. In conclusion, the doped nano TiO2 photocatalysts is a potential candidate for E. coli inactivation.

Ag-doped TiO2 Nanocomposite Prepared by Sol Gel Method: Photocatalytic Bactericidal Under Visible Light and Characterization

In this reaserch, photocatalyst titanium dioxide was doped with silver and modified by polyethylene glycol by sol gel method and the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The purpose of the present study was to evaluate the photocatalytic bactericidal effects of prepared nanocomposite on human pathogenic bacteria under visible light irradiation whereas; many studies have been published on the use of titanium dioxide as a photocatalyst, which decomposes various organic compounds. We observed that TiO2 reveals the bactericidal property against the Staphylococcus aureus, Shigella dysanteriae, Salmonella enterica subsp. enterica serovar Paratyphi bacteria and pathogenic fungi Candidia albicans which is increased by the essence of silver and visible light.

Preparation of TiO2, Ag-doped TiO2 nanoparticle and TiO2–SBA-15 nanocomposites using simple aqueous solution-based chemical method and study of their photocatalytical activity

Nanocrystalline TiO2, Ag-doped TiO2 and TiO2–SBA-15 nanocomposites have been synthesised using a simple aqueous solution-based chemical method. Nanocrystalline TiO2 was synthesised by calcining the precursor prepared by using ethylenediamine tetraacetic acid and TiCl3 in aqueous medium. Formation of crystalline phase (anatase, rutile or mixed phase) and crystallite size were found to be dependent on calcination temperature. To enhance the photocatalytic activity, Ag-doped TiO2 was synthesised by doping of Ag during the synthesis step of TiO2. TiO2–SBA-15 nanocomposites were synthesised by impregnation method. Pure anatase TiO2 nanoparticle was formed in the amorphous matrix of the silicate SBA-15, even though the loading of the TiO2 in the silicate matrix was as low as 5 wt%. The synthesised materials were characterised using thermal analysis, powder X-ray diffraction method, surface area and porosimetry analysis, diffuse reflectance analysis and transmission electron microscopy. The photocatalytic property of the synthesised materials was investigated towards the degradation of methyl orange under sunlight exposure and monitored by UV–visible spectrophotometer. Ag-doped TiO2 exhibited enhanced photocatalytic activity than undoped TiO2. TiO2–SBA-15 nanocomposites showed impressive photocatalytic activity even with 10 wt% TiO2 loading.

Studies on the Microstructure and Properties of TiO<sub>2</sub>/(Ag) Thin Films

TiO2/(Ag) thin films were prepared by DC magnetron sputtering. The effects of Ag-doping on the microstructure and properties were compared studied by atomic force microscopy (AFM), X-ray diffraction (XRD), UV-Vis spectra and photocatalysis tesing, respectively. The results show that when doped with Ag, the surface of TiO2 thin film was improved and the growth of anatase phase was promoted. The absoption properties of Ag-doped TiO2 thin film was enhanced dramatically compared with that of TiO2 thin film. And the photocatalysis properties of Ag-doped TiO2 thin film was increased twice as well.

Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO2 nanofibers in a TiO2 film as electrode

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO2 nanofiber [TN] and Ag-doped TiO2 nanofiber [ATN] have been extended to be included in TiO2 films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO2 photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO2 films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.

Structural and optical characterization of Ag-doped TiO2 nanoparticles prepared by a sol–gel method

Undoped and silver-doped TiO2 nanoparticles (Ti1−xAgxO2, where x = 0.00–0.10) were synthesized by a sol–gel method. The synthesized products were characterized by X-ray diffraction (XRD), particle size analyzer (PSA), scanning electron microscope (SEM), and UV–Visible spectrophotometer. XRD pattern confirmed the tetragonal structure of synthesized samples. Average crystallite size of synthesized nanoparticles was determined from X-ray line broadening using the Debye–Scherrer formula. The crystallite size was varied from 8 to 33 nm as the calcination temperature was increased from 300 to 800 °C. The incorporation of 3 to 5% Ag+ in place of Ti4+ provoked a decrease in the size of nanocrystals as compared to undoped TiO2. The SEM micrographs revealed the agglomerated spherical-like morphology of particles. SEM, PSA, and XRD measurements show that the particles size of the powder is in nanoscale. Optical absorption measurements indicated a red shift in the absorption band edge upon silver doping. Direct allowed band gap of undoped and Ag-doped TiO2 nanoparticles measured by UV–Vis spectrometer were 3.00 and 2.80 eV, respectively, at 500 °C.

UV and visible photodecomposition of organic pollutants over micro arc oxidized Ag-activated TiO2 nanocrystalline layers

Although titania is one of the most important metal oxide photocatalysts, its practical applications are to some extent limited by its relatively wide band gap. Doping TiO2 by metallic species has been expressed as a promising solution to decrease its band gap energy and enhance its photocatalytic performance. In this research, we employed micro arc oxidation technique to grow Ag-doped TiO2 porous layers where influence of the electrolyte composition and the applied voltage on the surface morphology, topography, phase structure, chemical composition, and optical properties was investigated for the first time. The photocatalytic efficiency of the layers was studied using different model materials namely methylene blue and 4-chlorophenol solutions as well as gaseous benzene. A porous morphology with a rough surface was revealed by the SEM and AFM techniques. The pore size varied depending on the voltage and the electrolyte concentration. Compositional studies, conducted by XRD and XPS methods, showed that the fabricated layers mainly consisted of anatase phases. A small amount of rutile phase was also detected at high voltages, i.e. 500V. Considering the XRD patterns, the anatase average crystalline size was determined as 67.8 and 21.5nm for the pure TiO2 and silver doped TiO2 layers, respectively. A red-shift was observed in the absorbance edge of the layers when Ag was introduced into the titania lattice giving rise to a visible-light response. Comparing photocatalytic reaction rate constants of pure and Ag-doped titania, the doped layers exhibited more favorable potential to decompose the pollutants in aqueous phase under ultraviolet and visible lights. Moreover, the doped layers were useful to decompose the pollutants in gaseous phase under ultraviolet light.

Photocatalytic disinfection of P.aeruginosa bacterial Ag-doped TiO2 film

TiO2 and TiO2-Ag composites films were prepared by sol–gel method and coated on glass fibre roving. The surface morphology and properties of synthesized composites films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and UV-vis diffuse reflectance spectroscopy (DRS). The antibacterial activity studies of TiO2 and TiO2 composite films were evaluated by photocatalytic reaction against P.aeruginosa bacteria. The results shown that pure TiO2 and TiO2 porous (TiO2-PEG) films have disinfection efficiency 57% and 93% within 15min under UV irradiation, respectively. TiO2-1Ag film has highest antibacterial effect under UV irradiation and that disinfectionefficiency is 100% within 10min. It has been found that Ag doped TiO2 films have the higher disinfection efficiency than that of pure TiO2 due to the effect of silver species.

Solar Photocatalytic Degradation of MCRR by Ag-Doped TiO<sub>2</sub> Films

The photocatalytic degradation of MCRR has been investigated using Ag-doped TiO2 films as photocatalyst and sunlight as irradiation source. Ag-doped TiO2 films can significantly accelerate the degradation of MCRR both in distilled water and in lake water, although the efficiency in lake water was not good as in distilled water. The photocatalytic activity was affected by the number of coating cycles and the best performance was found in films prepared with five coatings. Solution pH can also significantly influence the photocatalytic degradation of MCRR, and acidic pH was more efficient for the degradation of MCRR.

Preparation of Silver-Doped TiO<sub>2 </sub>Photoatalyst via a Simple Sol-Hydrothermal and their Visible Light Photocatalytic Activity

Silver-doped nano-TiO2 photocatalyst were synthesized via a simple hydrothermal route. The samples were characterized by XRD, XPS, FE-SEM and UV-Vis absorption spectrum techniques. Rhodamine B was selected as the model-pollutant to evaluate the photocatalytic activity of the samples. The XRD results indicated that the Ag-doped TiO2 were pure anatase phase. The UV-Vis spectroscopy revealed that the Ag doping can increase the absorption intensity of TiO2 in the visible region, which results in the improving the photocatalytic activity of TiO2 photocatalyst. Photocatalytic experimental results revealed that Ag-doping TiO2 catalyst shows the enhancement photocatalytic activity.

Photocatalytic Activities of Transition Metal-Doped TiO<sub>2</sub> Nano-Powders by Sonochemical Method and their Physicochemical Properties

With respect to metal doping into TiO2, the doping limits for V, Cr, Zr, Nb, Mo, and W are predicted to be higher than other transition metals according to the binding energy calculations in a unit cell model of anatase TiO2, which suggests that Cr and W can be doped into anatase structure more easily than Ag or Pt, for example. Our investigation has twofold research objectives. One is to prepare metal-doped TiO2 nano-powders from these transition metals, and the other is to test photocatalytic activity of each resulting powder. For the former, sonochemical process has been used to produce Cr-doped, W-doped, Ag-doped, and Pt-doped TiO2 nanoparticles. For the latter, we have performed photocatalytic oxidation of methylene blue. The combined results of the morphology and photocatalytic activites have enabled characterization of the physicochemical properties of these transition metal-doped nanoparticles.

Preparation of nano and microcrystals of silver using titania xerogel matrix as template

Ag-doped TiO2 wet gels were prepared by sol–gel process using a mixture of titanium isopropoxide and silver nitrate as precursor solution, with Ag:Ti molar ratio of 1:6. After drying, the titanium oxide xerogels were used as template in the preparation of nano and microcrystals of metallic silver. The porous network and the structure of the titania matrix influenced the type and distribution of silver crystal produced on the composite surface. Silver nanoparticles segregated to the surface of titania xerogel during the heating step, giving rise to nanocrystals that coalesced forming microcrystals with different shapes and faceting. The microcrystals grew on the composite surface, reaching sizes between 5 and 20 microns and self-organized of different ways. The xerogel heated at 600 °C formed by anatase, rutile and silver nanoparticles exhibited considerable photocatalytic activity to degrade methylene blue.

Low Ag-Doped Titanium Dioxide Nanosheet Films with Outstanding Antimicrobial Property

Novel Ag-doped TiO(2) perpendicular nanosheet films were synthesized by a mild solvothermal method. The width of TiO(2) nanosheets was facilely tuned by controlling reaction time, and furthermore the pattern of TiO(2) nanosheets was easily obtained via predesigned seed layer. The antibacterial effects of Ag-TiO(2) thin films against Escherichia coli and Staphylococcus aureus were examined by film attachment method. The coating films showed excellent performance in killing bacteria under UV light. Moreover, the potent antimicrobial ability of the film was well-sustained even in the dark environment.

Kinetics of Ag/TiO2-photocatalyzed iodide ion oxidation

Ag-doped TiO2 (anatase) samples (mass fraction w Ag = 0.01 and w Ag = 0.02) of 15.9 and 14.5 nm mean particle size and 11.46 and 10.14 m2 g−1 BET surface area were prepared by photodeposition. Doping results in surface plasmon resonance of the metallic silver nanoclusters at around 500 nm, but the absorption edge remains unaltered at 365 nm. Ag-doping remarkably enhances the photooxidation of iodide ion under UV light; iodine formation with Ag/TiO2 with w Ag = 0.01 is 16 times greater than with bare TiO2. The reaction conforms to Langmuir–Hinshelwood kinetics with regard to both I− and O2. Increase of pH slows down iodine formation and sacrificial electron donors arrest the reaction. Pre-sonication of the catalyst slurry hinders the photocatalysis. Generation of iodine is much greater in acetonitrile than in water. Under the experimental conditions, Ag/TiO2 with w Ag = 0.01 is more efficient than Ag/TiO2 with w Ag = 0.02, and the enhanced photocatalysis is likely to be because of suppression of electron–hole pair recombination. Kinetic analysis reveals that increasing the Ag mass fraction from 0.01 to 0.02 enhances the surface pseudo-first-order rate constant but inhibits the adsorption of iodide ion and the oxygen molecule on the illuminated oxide surface.

Photocatalytic degradation of methylene blue using undoped and Ag-doped TiO2 thin films deposited by a sol–gel process: Effect of the ageing time of the starting solution and the film thickness

Abstract Undoped and Ag-doped TiO 2 thin films were deposited on glass substrates by the sol–gel method. A novel propose to prepare the solution is the use of titanium monohydrate oxyacetyl acetonate as the starting reagent. The effect of the ageing time of the starting solution as well as the number of coatings on the photocatalytic degradation of methylene blue (MB) was studied. The variation of the absorption spectra shows the degradation of MB dissolved in water, as a result of the reaction produced on the surface of the films, and promoted by ultraviolet irradiation during 5 h. The results show an optimum photocatalytic activity, in the order of 35%, presented in the 5-immersion Ag-doped TiO 2 thin films, deposited from 7- and 14-day aged solutions. On the other hand, the Ag-doped TiO 2 films deposited at different coatings show small changes in the photocatalytic activity. Morphological studies show the presence of silver particles on the film surface, due to the different number of coatings, affecting the photocatalytic performance.

Photocatalytic and Self-Cleaning Properties of Ag-Doped TiO2~!2009-10-16~!2009-10-30~!2010-01-27~!

Photocatalytic and Self-Cleaning Properties of Ag-Doped TiO2~!2009-10-16~!2009-10-30~!2010-01-27~!

Comparison of the substrate dependent performance of Pt-, Au- and Ag-doped TiO2 photocatalysts in H2-production and in decomposition of various organics

Pt-, Au- and Ag-deposited Degussa P25 photocatalysts [at 1% (m/m) noble metal loading] were prepared in which the noble metals are most likely to be very finely dispersed on the surface of the TiO2 nanocrystals. Deposition of noble metals increased the photocatalytic efficiency (relative to the bare photocatalyst) in the decomposition of oxalic- and formic acid, while decreased it in phenol containing systems. In H2-production, a very high quantum yield has been found for the Pt–TiO2 photocatalyst in the presence of oxalic and formic acids as sacrificial reagents, which opens the possibility for the economic use of industrial side products (e.g., oxalic- and formic acid) for photocatalytic H2-production.