Commercial Titania Photocatalysts Research Articles

Evaluation of Antifungal Properties of Titania P25.

Commercial titania photocatalyst—P25 was chosen for an antifungal property examination due to it exhibiting one of the highest photocatalytic activities among titania photocatalysts. Titania P25 was homogenized first (HomoP25) and then annealed at different temperatures. Additionally, HomoP25 was modified with 0.5 wt% or 2.0 wt% of platinum by a photodeposition method. The obtained samples were characterized by diffuse-reflectance spectroscopy (DRS), X-ray photoabsorption spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy. Moreover, photocatalytic activity was tested for methanol dehydrogenation under UV/vis irradiation. The spore-destroying effect of photocatalysts was investigated against two mold fungal species, i.e., Aspergillus fumigatus and Aspergillus niger. Both the mycelium growth and API ZYM (estimation of enzymatic activity) tests were applied for the assessment of antifungal effect. It was found that annealing caused a change of surface properties of the titania samples, i.e., an increase in the noncrystalline part, a growth of particles and enhanced oxygen adsorption on its surface, which resulted in an increase in both the hydrogen evolution rate and the antifungal effect. Titania samples annealed at 300−500 °C were highly active during 60-min UV/vis irradiation, inhibiting the germination of both fungal spores, whereas titania modification with platinum (0.5 and 2.0 wt%) had negligible effect, despite being highly active for hydrogen evolution. The control experiments revealed the lack of titania activity in the dark, as well as high resistance of fungi for applied UV/vis irradiation in the absence of photocatalysts. Moreover, the complete inhibition of 19 hydrolases, secreted by both tested fungi, was noted under UV/vis irradiation on the annealed P25 sample. It is proposed that titania photocatalysts of large particle sizes (>150 nm) and enriched surface with oxygen might efficiently destroy fungal structures under mild irradiation conditions and, thus, be highly promising as covering materials for daily products.

The property-governed activity of silver-modified titania photocatalysts: The influence of titania matrix.

Commercial titania photocatalysts were modified with silver nanoparticles (NPs) by the photodeposition method in the presence/absence of methanol. The obtained photocatalysts were characterized by XRD, XPS, diffuse reflectance spectroscopy, STEM, and time-resolved microwave conductivity (TRMC) methods. The photocatalytic activity was tested under UV/vis irradiation for (i) methanol dehydrogenation (during silver deposition), (ii) oxygen evolution with in situ silver deposition, and (iii) oxidative decomposition of acetic acid, as well as under vis irradiation for 2-propanol oxidation. The action spectra of 2-propanol oxidation were also performed. It has been confirmed that modification of titania with silver causes significant improvement of photocatalytic activity under both UV and vis irradiation as silver works as an electron scavenger (TRMC data) and vis activator (possibly by an energy transfer mechanism). The obtained activities differ between titania samples significantly, suggesting that the type of crystalline phase, particle/crystallite sizes, and electron traps' density are crucial for both the properties of formed silver deposits and resultant photocatalytic activity. It might be concluded that, under UV irradiation, (i) high crystallinity and large specific surface area are recommended for rutile- and anatase-rich samples, respectively, during hydrogen evolution, (ii) mixed crystalline phases cause a high rate of oxygen evolution from water, and (iii) anatase phase with fine silver NPs results in efficient decomposition of acetic acid, whereas under vis irradiation the aggregated silver NPs (broad localized surface plasmon resonance peak) on the rutile phase are promising for oxidation reactions.

Development of Monodisperse Mesoporous Microballs Composed of Decahedral Anatase Nanocrystals

Mesoporous monodisperse microballs of amorphous titania were prepared from solution of absolute ethanol, tetrabutyl titanate (TBOT) and potassium chloride via a sub-zero sol–gel route. The as-obtained microballs were used as the precursor in an alcohothermal (ethanol with a small amount of water) process to synthesize monodisperse mesoporous microballs built of decahedral anatase nanocrystals. FE-SEM observation and XRD analysis have confirmed that the formed decahedral anatase-rich powder retained the original spherical morphology of the precursor. Importantly, a hierarchical structure composed of faceted anatase has been achieved under “green” conditions, i.e., fluorine-free. Additionally, the hysteresis loops (BET results) have confirmed the existence of mesopores. Interestingly, faceted microballs show noticeable photocatalytic activity under UV/vis irradiation for hydrogen generation without any co-catalyst use, reaching almost forty times higher activity than that by famous commercial titania photocatalyst—P25. It has been proposed that enhanced photocatalytic performance is caused by mesoporous structure and co-existence of two kinds of facets, i.e., {001} and {101}, and thus hindered charge carriers’ recombination.

Strong effect of light scattering by distribution of TiO2 particle aggregates on photocatalytic efficiency in aqueous suspensions

This work examines the important role of light power absorbed by TiO2 on the photocatalytic degradation of dichloroacetic acid (DCA) in a semi-continuous slurry photoreactor with UV–Vis radiation. This system is an excellent model for understanding the light matter interaction, because DCA is transparent and the acid pH of the solution prevents the formation of large TiO2 aggregates. Under these conditions, the light power absorbed by four different commercial Titania photocatalysts, along the whole volume of the reactor, has been quantitatively calculated by assuming a Mie scattering model on a distribution of different particle sizes. Although the different chemical nature of the four considered samples (three of them provided by the Evonik Company, P25, P25/20 and P90, together with Hombikat UV 100), and the different catalytic efficiency based on weight, we have found that all the catalytic responses are fundamentally controlled by the absorbed radiation in the four samples. Therefore, in the studied samples, any difference in the catalytic behavior is only due to the light-matter interaction being of lesser importance other mechanisms, as space-charge blocking.

The Influence of The Light-Activated Titania P25 on Human Breast Cancer Cells

Cosmetics and other daily care products contain titanium(IV) oxide (titania). Since multiple risk factors can increase the chance of developing cancer, an evaluation of titania safety has become a matter of concern in recent times. However, it should be pointed out that titania as an efficient photocatalyst has been also applied for inactivation of various pathogens, environmental purification and energy conversion, which might result in significant improvement of human life. Therefore, it is worth considering titania not only as a possible cancer initiator, but also as an efficient solution against cancer cells. Accordingly, in this study, the effect of commercial titania photocatalyst P25 (Degussa/Evonik) on breast adenocarcinoma MCF7 cells (ATCC® HTB-22™, breast adenocarcinoma cell line from human) has been investigated. The cells were treated with titania at doses of 10, 30, and 50 µg/mL under UVA/vis irradiation and in the dark. The significant morphological alterations in living cells were observed for larger doses of titania, such as changes in the shape and the size of cells, the deviation from the normal structure, and an increase in cells’ mortality. Moreover, the effect was significantly higher under irradiation than in the dark confirming strong photocatalytic activity of titania P25. In contrast, the lowest dose of titania (10 µg/mL) did not exhibit a significant impact on MCF7 cells, similarly to the nontreated cells. Accordingly, it has been proposed that locally applied titania might be considered for a cancer therapy after necessary in vivo tests to estimate any possibilities of side effects.

Mapping the Photocatalytic Activity and Ecotoxicology of Au, Pt/TiO2 Composite Photocatalysts

In the present research gold and platinum nanoparticles were deposited simultaneously on three different commercial titania photocatalysts (Evonik Aeroxide P25, Aldrich rutile, and Aldrich anatase). For the synthesis of the composites two noble metal reduction methods (in situ and impregnation) and three noble metal deposition routes (i.e., by changing their deposition order, Au/Pt, Pt/Au, and Au–Pt simultaneously) were used. The photocatalytic performances of the nanocomposites were evaluated under UV irradiation, through degradation of oxalic acid and photocatalytic hydrogen production. The best performing photocatalyst was obtained by sequential noble metal deposition (first Au followed by Pt) on Evonik Aeroxide P25. The morphological and structural properties were studied/investigated by using DRS, TEM, HRTEM, EDX, and XRD. The gold and platinum nanoparticles formed clusters in most of the cases. Furthermore, the ecotoxicity of the composites was investigated using Lemna minor growth inhibition tests using static “lake” approach completed by DLS and ROS indirect measurements. The toxic effect of the composites which showed the highest photocatalytic activity did not differ from that of their commercial counterparts, showing that these nanoparticles were eco-friendly. This result shows the great capacity of these materials to be used in the next future in photocatalytic applications.

(Invited) Multielectron Oxygen Reduction in Photocatalytic Organics Decomposition By Nano/Micrometer-Sized Hierarchical Structured Bismuth Tungstate Particles

It has been reported that hydrothermally prepared flake ball (FB)-shaped bismuth tungstate (Bi2WO6: BWO) particles exhibit photocatalytic activity for oxidative decomposition of organic compounds, which is comparable to that of a commercial titania photocatalyst, while the activity for methanol dehydrogenation is almost negligible even in the presence of loaded with platinum [1]. These facts suggest that two (or four)-electron transfer to the surface-adsorbed oxygen (O2), requiring relatively lower, i.e., more anodic potential of electrons in photocatalyst particles, proceeds on photoirradiated FB-BWO, but there has been reported no evidence for this multielectron-transfer mechanism. In the present study, light-intensity dependence of the rate of acetic-acid decomposition was studied to obtain kinetic evidence for the multielectron transfer. FB-BWO, spherical assembly of BWO flakes, was prepared following the previous report [1]. As-prepared FB, its ball-milled samples (L and H) and their 773 K-calcined samples (500FB, 500L and 500H) were used for decomposition of acetic acid in aerobic aqueous suspensions under monochromatic photoirradiation by (A) a diffraction grating-type illuminator (Jasco CRM-FD; max. 10 mW) or (B) a 365-nm UV-LED (max. 320 mW). It was found that order (n) of light-intensity dependences at four wavelengths (irradiation A) calculated by assuming; R = a × I n (R: rate, a: constant and I: light intensity). Except for the samples L and H at 380 and 410 nm, BWO showed almost first-order light-intensity dependences at wavelengths between 320 and 410 nm. With the higher intensity irradiation (irradiation B), the order (n) was changed (decreased) to ca. 0.5 for FB and L at a folding point (Fig. 1). As has been reported previously, photocatalytic acetic-acid decomposition proceeds through radical-chain mechanism with an alkyl peroxy radical as a chain carrier when titania was used as a photocatalyst, and the observed order of light-intensity dependence was ca. 0.5 [2]. The above-mentioned first-order light-intensity dependence for the most BWO samples can be interpreted by combination of second-order dependence for the accumulation of two electrons to reduce O2 and 0.5th-order dependence owing to the radical-chain mechanism. Difference in folding points of plots between FB and L was observed; a folding point for FB was appreciably lower than that of L. One of the possible reasons for this difference is that the probability of the second-photon absorption by one photon-absorbed FB particle within its lifetime is higher than that of L particle owing to larger volume of FB particles [3]. Fig. 1 Double-logarithmic plots of the reaction rate (R) and light intensity (I) observed in the FB or ML-photocatalyzed acetic-acid decomposition under high-intense 365-nm UV-LED photoirradiation (open circles). Data obtained by the diffraction grating type illuminator were also plotted; closed triangles, circles and squares correspond to irradiation wavelength of 320, 350 and 380 nm.

Noble metal-modified titania with visible-light activity for the decomposition of microorganisms.

Commercial titania photocatalysts were modified with silver and gold by photodeposition, and characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). It was found that silver co-existed in zero valent (core) and oxidized (shell) forms, whereas gold was mainly zero valent. The obtained noble metal-modified samples were examined with regard to antibacterial (Escherichia coli (E. coli)) and antifungal (Aspergillus niger (A. niger), Aspergillus melleus (A. melleus), Penicillium chrysogenum (P. chrysogenum), Candida albicans (C. albicans)) activity under visible-light irradiation and in the dark using disk diffusion, suspension, colony growth (“poisoned food”) and sporulation methods. It was found that silver-modified titania, besides remarkably high antibacterial activity (inhibition of bacterial proliferation), could also decompose bacterial cells under visible-light irradiation, possibly due to an enhanced generation of reactive oxygen species and the intrinsic properties of silver. Gold-modified samples were almost inactive against bacteria in the dark, whereas significant bactericidal effect under visible-light irradiation suggested that the mechanism of bacteria inactivation was initiated by plasmonic excitation of titania by localized surface plasmon resonance of gold. The antifungal activity tests showed efficient suppression of mycelium growth by bare titania, and suppression of mycotoxin generation and sporulation by gold-modified titania. Although, the growth of fungi was hardly inhibited through disc diffusion (inhibition zones around discs), it indicates that gold does not penetrate into the media, and thus, a good stability of plasmonic photocatalysts has been confirmed. In summary, it was found that silver-modified titania showed superior antibacterial activity, whereas gold-modified samples were very active against fungi, suggesting that bimetallic photocatalysts containing both gold and silver should exhibit excellent antimicrobial properties.

Kinetic Study on Multielectron-Transfer Mechanism for Flake-Ball-Shaped Bismuth-Tungstate Photocatalyst

It has been reported that flake ball (FB)-shaped particulate bismuth tungstate (Bi2WO6: BTO) particles prepared by hydrothermal method exhibit photocatalytic activity for oxidative decomposition of organic compounds comparable to that of a commercial titania photocatalyst, while the activity for methanol dehydrogenation is relatively low even with platinum-loaded ones [1]. These facts suggest that two (or four)-electron transfer to the surface-adsorbed oxygen (O2), requiring more anodic potential of electrons in photocatalyst particles, happens in FB-BTO, but no report on the evidence for the multielectron-transfer mechanism have been published. In this study, light-intensity dependence of the rate of acetic-acid decomposition was investigated to obtain kinetic evidence for the multielectron transfer. FB-BTO, composed of particles of spherical assembly of BTO flakes, was prepared following the previous report [1]. As-prepared FB, its ball-milled samples (L and H) and their 773 K-calcined samples (500FB, 500L and 500H) were used for decomposition of acetic acid in aerobic aqueous suspensions under monochromatic photoirradiation by (A) a diffraction grating-type illuminator (Jasco CRM-FD; maximum 10 mW) or (B) a 365-nm UV-LED (maximum 320 mW). Figure 1 shows order (n) of light-intensity dependences at four wavelengths (irradiation A) calculated by assuming; r = a × I n (r: rate, a: constant and I: light intensity). Except for the samples L and H at 380 and 410 nm, BTO showed almost first-order light-intensity dependences at wavelengths between 320 and 410 nm. With the higher intensity irradiation (irradiation B), the order was decreased to ca. 0.5 order for FB and L as shown in Fig. 2. As has been reported previously, photocatalytic acetic-acid decomposition proceeds through radical-chain mechanism with an alkyl peroxy radical as a chain carrier when titania was used as a photocatalyst, and the order of light-intensity dependence was ca. 0.5 [2]. The above-mentioned first-order light-intensity dependence for the most BTO samples can be interpreted by combination of second-order dependence for the accumulation of two electrons to reduce O2 and 0.5-order dependence owing to the radical-chain mechanism. Difference in folding points of plots in Fig. 2 between FB and L was observed; a folding point for FB was appreciably lower than that of L. One of the possible reasons for this difference is that the probability of the second-photon absorption by one photon-absorbed FB particle within its lifetime is higher than that of L particle owing to larger volume of FB particles. [1] F. Amano, K. Nogami, R. Abe, B. Ohtani, J. Phys. Chem. C. 112, 9320 (2008). [2] T. Torimoto, Y. Aburakawa, Y. Kawahara, S. Ikeda, and B. Ohtani, Chem. Phys. Lett., 392, 220 (2004). Figure 1

Photodegradation of aniline in water in the presence of chemically activated halloysite

Photocatalytic degradation of aniline was investigated in aqueous solutions containing halloysite (Hal) nanotubes, chemically activated halloysite (AHal), and photocatalysts: TiO2 (anatase) and commercial titania P25, under UV illumination. Powder X-ray diffraction (XRD), UV–Vis/DR spectra and nitrogen adsorption isotherms were carried out to characterize the activated halloysite. The effects of the AHal and titania photocatalyst amount as well as aniline concentration were examined. It is observed that the photodegradation of aniline has a similar course in the presence of AHal and in the presence of P25 and TiO2, both with respect to the decomposition of aniline and in decreasing the amounts of photoproducts being formed during the irradiation of aniline. The photodegradation of aniline is clearly slower in presence of Hal nanotubes than for AHal and P25. The disappearance of aniline follows approximately according to the Langmuir–Hinshelwood kinetics. The values of rate photodegradation constant are decreasing in the following order: P25>TiO2>AHal>Hal nanotubes. These results have indicated that halloysite containing titanium dioxide could be employed during photocatalytic removal of aniline from the aqueous solution, similarly to commercial titania photocatalysts.

Silver-modified titania with enhanced photocatalytic and antimicrobial properties under UV and visible light irradiation

Commercial titania photocatalysts were modified with 2wt% of silver by photodeposition. The properties of the samples were characterized by DRS, XPS, XRD, FE-SEM and STEM. The modified samples exhibited activity under visible light and enhanced activity under UV irradiation for 2-propanol and acetic acid oxidation, respectively. The time-resolved microwave conductivity (TRMC) analysis indicated that enhanced activity (2.5–8-fold enhancement depending on titania) under UV irradiation was caused by an electron storage in metallic nanoparticles (NPs), and therefore decreasing the recombination between charge carriers. The action spectrum (AS) analysis proved that localized surface plasmon resonance (LSPR) of silver NPs induced the photocatalytic activity under visible light irradiation. The increase of antimicrobial properties under visible light irradiation indicated that not only intrinsic properties of silver in the dark, but also plasmonic properties of Ag@TiO2 were responsible for overall bacteria killing. The evolution of carbon dioxide under both irradiation ranges indicated mineralization of bacteria cells, and therefore possible application of silver-modified titania for decomposition of chemical and biological pollutants.

Biogenic C-doped titania templated by cyanobacteria for visible-light photocatalytic degradation of Rhodamine B

Cyanobacteria, which occurred in eutrophic water harvest solar light to carry out photosynthesis with high efficiency. In this work, cyanobacteria (Microcystis sp.) were used as biotemplate to synthesize titania structure. The synthesized titania sample had similar morphology to that of the original template in spite of the fragile unicellular structures and extremely high water content of cyanobacterial cells. Incorporation of biogenic C, as well as the morphology inherited from biotemplate improved visible-light absorbance of the titania structure. The sample exhibited higher visible-light photocatalytic activity than commercial titania photocatalyst Degussa P25 for Rhodamine B (RhB) degradation. Compared with those C-doped titania photocatalysts prepared by other methods, cyanobacteria templated titania photocatalyst offer some potential for competitive advantages. The reported strategy opened up a new use for the cyanobacteria. It could also be used for titania in applications such as treatment of polluted water, dye-sensitized solar cells, or other regions.

Effect of ball-milling and Fe-/Al-doping on the structural aspect and visible light photocatalytic activity of TiO2 towards Escherichia coli bacteria abatement

Escherichia coli abatement was studied in liquid phase under visible light in the presence of two commercial titania photocatalysts, and of Fe- and Al-doped titania samples prepared by high energy ball-milling. The two commercial titania photocatalysts, Aeroxide P25 (Evonik industries) exhibiting both rutile and anatase structures and MPT625 (Ishihara Sangyo Kaisha), a Fe-, Al-, P- and S-doped titania exhibiting only the rutile phase, are active suggesting that neither the structure nor the doping is the driving parameter. Although the MPT625 UV–visible spectrum is shifted towards the visible domain with respect to the P25 one, the effect on bacteria is not increased. On the other hand, the ball milled iron-doped P25 samples exhibit low activities in bacteria abatement under visible light due to charge recombinations unfavorable to catalysis as shown by photoluminescence measurements. While doping elements are in interstitial positions within the rutile structure in MPT625 sample, they are located at the surface in ball milled samples and in isolated octahedral units according to 57Fe Mössbauer spectrometry. The location of doping elements at the surface is suggested to be responsible for the sample cytotoxicity observed in the dark.

Halloysite–TiO2 nanocomposites: Synthesis, characterization and photocatalytic activity

Two halloysite–TiO2 nanocomposites were prepared with two different tubular halloysite clays by depositing anatase-TiO2 on the halloysite surfaces using titanium isopropoxide under hydrothermal treatment at 180°C. The nanocomposites were characterized by X-Ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR), absorption properties by UV–vis spectroscopy and N2 specific surface area (SSA) analysis by BET method. Good dispersion of 3–10nm TiO2 particles on halloysite external surfaces was achieved in both the halloysite–TiO2 nanocomposites and ATR-FTIR results showed the formation of hydrogen bonding between TiO2 and the outer surfaces of halloysite tubes. After treating with TiO2, both halloysite samples largely showed interparticle mesopores of about 5.7nm. However, the macropores of halloysite (lumen or central hole in halloysite tubes) were not detected probably as a result of plugging of the lumens in halloysite tubes by TiO2 nanoparticles. These nanocomposites were tested for their photocatalytic activities in decomposing NOx gas and toluene. The halloysite–titania samples showed significantly higher activity in decomposing NOx gas under visible-light irradiation (λ>510nm) and UV–visible light irradiation (λ>290nm) compared to that of the standard commercial titania photocatalyst, P25. In addition, composite photocatalyst showed larger catalytic activity either under sunlight or pure UV irradiation in decomposing toluene compared to the commercial titania, P25. Our experimental data suggest that the enhanced photocatalytic activity is related with the good dispersion of the TiO2 nanocrystals on the surface of the clay minerals.

Low-Temperature Reverse Microemulsion Synthesis, Characterization, and Photocatalytic Performance of Nanocrystalline Titanium Dioxide

Nanocrystalline titanium dioxide (<svg style="vertical-align:-3.13504pt;width:31.25px;" id="M1" height="14.7125" version="1.1" viewBox="0 0 31.25 14.7125" width="31.25" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.7125)"> <g transform="translate(72,-60.23)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">T</tspan> <tspan style="font-size: 12.50px; " x="7.5268059" y="0">i</tspan> <tspan style="font-size: 12.50px; " x="11.00264" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-51.92,60.28)"> <tspan style="font-size: 8.75px; " x="0" y="0">2</tspan> </text> </g> </g> </svg>) was synthesized in microemulsions by using cetyltrimethylammonium bromide (CTAB) as surfactant. In order to investigate the crystal transformation and photoactivity at low temperature, the as-prepared precipitates were aged at 65&#xb0;C or calcined at various temperatures. Analyses using powder X-ray diffraction (XRD) and Fourier transform infrared microscopy (FT-IR) showed that precursors without aging or calcination were noncrystal and adsorbed by surfactant. After aging for 6&#x2009;h, the amorphous <svg style="vertical-align:-3.13504pt;width:31.25px;" id="M2" height="14.7125" version="1.1" viewBox="0 0 31.25 14.7125" width="31.25" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.7125)"> <g transform="translate(72,-60.23)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">T</tspan> <tspan style="font-size: 12.50px; " x="7.5268059" y="0">i</tspan> <tspan style="font-size: 12.50px; " x="11.00264" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-51.92,60.28)"> <tspan style="font-size: 8.75px; " x="0" y="0">2</tspan> </text> </g> </g> </svg> began to change into anatase. The obtained catalysts, which were synthesized in microemulsions with weight ratios of n-hexanol/CTAB/water as 6&#x2009;:&#x2009;3&#x2009;:&#x2009;1 and calcined at 500&#xb0;C, presented the highest photocatalytic degradation rate on methyl orange (MO), while the catalysts, which were aged at 65&#xb0;C for 90&#x2009;h, also exhibited an outstanding photocatalytic performance and a little higher than that of the commercial titania photocatalyst Degussa P25.

Photocatalytic and immobilization characteristics of immobilized ZnO and TiO2 nanopowders

A kind of photocatalytic ZnO nanopowder and two kinds of photocatalytic TiO2 nanopowders were prepared. The ZnO nanopowder was synthesized by the solution combustion method, which was invented by the present authors. One of the TiO2 nanopowders was synthesized by HPPLT (homogeneous precipitation process at low temperature) method in this work. The other TiO2 nanopowder (P-25 TiO2, a popular commercial titania photocatalyst) was purchased. These photocatalytic nanopowders were immobilized by several kinds of binders. The immobilization characteristics were examined by XRD, ultrasonication, and SEM. The photocatalytic characteristics were measured by photocatalytic Ag ion extraction rate. The Ag ions were extracted from real (not artificial) photographic waste fixing solution. The Ag ion extraction rate with the immobilized ZnO nanopowder was more than twice that reported for other immobilized photocatalysts.

Photocatalytic evolution of hydrogen and oxygen from ceramic wafers of commercial titanias

Several commercial titania photocatalyst powders were formed into thin (ca. 350 μm), 25 mm diameter ceramic wafers, sputter deposited with Pt on one side. The activities of each of the ceramic wafers were tested for hydrogen and oxygen evolution from aqueous sacrificial systems. The commercial sample PC50 (Millennium Chemicals, UK) yielded reproducible ceramic wafers with high activity for water photoreduction. Many of the ceramic wafers displayed low water photo-oxidation activities; however, these were greatly increased with addition of a NiO co-catalyst. In a selected case, hydrogen evolution activity was compared between a PC50 wafer and an identical weight of platinised PC50 powder suspension.

Synthesis of Au–ZnO and Pt–ZnO nanocomposites by one-step flame spray pyrolysis and its application for photocatalytic degradation of dyes

Abstract Au–ZnO and Pt–ZnO nanocomposites have been synthesized by one-step flame spray pyrolysis (FSP) and characterized by X-ray diffraction (XRD), nitrogen adsorption, UV–vis spectroscopy, photoluminescence (PL), and transmission electron microscopy (TEM). The XRD and TEM results revealed that Au and Pt metallic phase were formed late during flame synthesis after ZnO was formed. Their average particle/cluster sizes were ranged between 3 and 7 nm depending on the amount loading (1 and 3 wt%). Although both of the FSP-derived Au–ZnO and Pt–ZnO possessed similar physical properties (i.e., crystallite size and specific surface area), an improvement in photocatalytic degradation of methylene blue in comparison to pure ZnO and commercial titania photocatalysts (JRC-TiO 2 and P-25) was observed only for the Au–ZnO and not for the Pt–ZnO due probably to the different type of Fermi-level equilibration between Au and Pt.

Photocatalytic Degradation of Polynitrophenols on Various Commercial Suspended or Deposited Titania Catalysts Using Artificial and Solar Light

Phenol (PH) and three polynitrophenols (4-nitrophenol (PNP), 2,4-dinitrophenol (DNP), 2,4,6-trinitrophenol (TNP)) were photocatalytically degraded by using titania under either artificial or solar light. These four reactions were chosen as test reactions to compare the efficiencies of two suspended commercial titania photocatalysts (Degussa P-25 and Millennium PC-500). It appears that P-25 has a higher initial efficiency in all nitrophenol disappearance reactions. However, for the overall degradation rate, measured by the chemical oxygen demand (COD) disappearance, the performance of PC-500 was similar to that of P25. This was attributed to a favorable textural effect since PC-500 has a much higher surface area which facilitates the readsorption of intermediates. PC-500 was subsequently supported on a special photoinert paper provided by Ahlstrom Company (38-Pont Evèque, France). The influence of the silica binder used for sticking titania particles on the paper fibers was put in evidence as an inhibitor of the coulombic adsorption of anionic species, especially 2,4,6-trinitrophenol, because of the low pzc of silica. Once validated, this supported photocatalyst was introduced in an autonomous solar pilot photoreactor identical to the several prototypes built in the European AQUACAT program. It was demonstrated that the purification of water could be efficiently obtained in a larger scale without any final tedious filtration.

Immobilization and photocatalytic efficiency of titania nanoparticles on silica carrier spheres

Immobilization of titania nanoparticles on submicron-sized silica carrier spheres was achieved, and the relevant photocatalytic efficiency was studied. In contrast to the commonly adopted practice of either free suspending nano-sized catalyst particles or immobilized catalyst particles on large supports for photocatalytic applications, the present approach offers a third option, avoiding the disadvantages of the above-mentioned two practices. In the model system of photo-degradation of methylene blue, the photocatalytic efficiency of the present catalyst form was found comparable to that of free-suspending P25 nanoparticles, a popular commercial titania photocatalyst, of the same total catalyst surface area. The present photocatalytic process was found to be diffusion dominant, and its impressive catalytic performance was attributed to the well-separated, smaller than usual titania particles immobilized on the surfaces of submicron-sized silica spheres.