20 research outputs found
SURFACE PROPERTIES AND CATALYTIC PERFORMANCE OF ACTIVATED CARBON FIBERS SUPPORTED TiO2 PHOTOCATALYST
Activated carbon fibers supported TiO2 photocatalyst (TiO2/ACF) in felt-form was successfully prepared with a dip-coating process using organic silicon modified acrylate copolymer as a binder followed by calcination at 500°C in a stream of Ar gas. The photocatalyst was characterized by SEM, XRD, XPS, FTIR, and BET surface area. Most of carbon fibers were coated with uniformly distributed TiO2 clusters of nearly 100 nm. The loaded TiO2 layer was particulate for the organic binder in the compact film was carbonized. According to XPS and FTIR analysis, amorphous silica in carbon grains was synthesized after carbonizing organic silicon groups, and the Ti–O–Si bond was formed between the interface of loaded TiO2 and silica. Additionally, the space between adjacent carbon fibers still remained unfilled after TiO2 coating, into which both UV light and polluted solutions could penetrate to form a three-dimensional environment for photocatalytic reactions. While loaded TiO2 amount increased to 456 mg TiO2/1 g ACF, the TiO2/ACF catalyst showed its highest photocatalytic activity, and this activity only dropped about 10% after 12 successive runs, exhibiting its high fixing stability of coated TiO2.Activated carbon fibers, titanium dioxide, adsorption, photocatalytic activity
interpositionfixingstructureoftio2filmdepositedonactivatedcarbonfibers
The immobilized photocatalyst, TiO2 film supported on activated carbon fibers (TiO2/ACFs) prepared with molecular adsorption-deposition (MAD), exhibits high stability in cyclic photodegradation runs. The interposition fixing structure between TiO2 film and carbon fiber was investigated by means of SEM-EDX, XRD, XPS and FTIR, and a model was proposed to explain this structure. With SEM examination of carbon fiber surface after removing the deposited TiO2 film, a residual TiO2 super-thin film was found to exist still. By determining surface groups on ACFs, titanium sulfate (Ti2(SO4)3) in burnt remainders of the TiOE/ACFs was thought to be formed with an interracial reaction between TiO2 film and carbon fibers. These provide some evidence of finn attachment of TiO2 film to carbon fiber surface. In the consideration of characteristics of the MAD, the deposition mechanism of TiO2 film on ACFs was proposed, and the interposition fixing structure was inferred to intercrossedly form between TiO2 film and ACFs' surface. This structure leaded to firm attachment and high stability of the TiO2 film
Surf. Rev. Lett.
In the present work, a combined route involving first doping of iron or neodymium ions via sol-gel method followed by acidification of the metal-doped TiO2 particles for the improvement of the photocatalytic capability of TiO2 was reported. The obtained metal-doped/acidified TiO2 photocatalysts were thoroughly characterized by X-ray diffraction, Fourier transform infrared analysis, and photoluminescence emission spectra. At the same time, their photocatalytic activities were evaluated in simulant photodegradation of methylene blue (MB). The results based on these characterizations showed that not only a rutile layer formed on the surface of original TiO2 particles after surface cladding, but also the doped Fe or Nd ion had a favorable effect on suppression of the electron-hole recombination in the titania under ultraviolet light irradiation. Furthermore, the photocatalytic activity of the material obtained by Fe doping and acidification was substantially improved in comparison to the untreated TiO2. However, the sample prepared from Nd-doping and acidification of TiO2 showed decreased capability relative to the untreated TiO2 in degradation of MB under similar conditions. Finally, the reason why the photocatalytic activities of the obtained catalysts are sensitive to the metal-doping was discussed in details.In the present work, a combined route involving first doping of iron or neodymium ions via sol-gel method followed by acidification of the metal-doped TiO2 particles for the improvement of the photocatalytic capability of TiO2 was reported. The obtained metal-doped/acidified TiO2 photocatalysts were thoroughly characterized by X-ray diffraction, Fourier transform infrared analysis, and photoluminescence emission spectra. At the same time, their photocatalytic activities were evaluated in simulant photodegradation of methylene blue (MB). The results based on these characterizations showed that not only a rutile layer formed on the surface of original TiO2 particles after surface cladding, but also the doped Fe or Nd ion had a favorable effect on suppression of the electron-hole recombination in the titania under ultraviolet light irradiation. Furthermore, the photocatalytic activity of the material obtained by Fe doping and acidification was substantially improved in comparison to the untreated TiO2. However, the sample prepared from Nd-doping and acidification of TiO2 showed decreased capability relative to the untreated TiO2 in degradation of MB under similar conditions. Finally, the reason why the photocatalytic activities of the obtained catalysts are sensitive to the metal-doping was discussed in details
Simultaneous Elimination of Formaldehyde and Ozone Byproduct Using Noble Metal Modified TiO2 Films in the Gaseous VUV Photocatalysis
Simultaneous removal of low concentration formaldehyde (HCHO) and ozone byproduct was investigated in the gaseous VUV (vacuum ultraviolet) photocatalysis by using noble metal modified TiO2 films. Noble metal (Pt, Au, or Pd) nanoparticles were deposited on TiO2 films with ultrafine particle size and uniform distribution. Under 35 h VUV irradiation, the HCHO gas (ca. 420 ppbv) was dynamically degraded to a level of 10~45 ppbv without catalyst deactivation, and over 50% O3 byproduct was in situ decomposed in the reactor. However, under the same conditions, the outlet HCHO concentration remained at 125~178 ppbv in the O3 + UV254 nm photocatalysis process and 190~260 ppbv in the UV254 nm photocatalysis process. And the catalyst deactivation also appeared under UV254 nm irradiation. Metallic Pt or Au could simultaneously increase the elimination of HCHO and ozone, but the PdO oxide seemed to inhibit the HCHO oxidation in the UV254 nm photocatalysis. Deposition of metallic Pt or Au reduces the recombination of h+/e− pairs and thus increases the HCHO oxidation and O3 reduction reactions. In addition, adsorbed O3 may be partly decomposed by photogenerated electrons trapped on metallic Pt or Au nanoparticles under UV irradiation
IMPROVEMENT OF PHOTOCATALYTIC ACTIVITY OF TiO2 VIA COMBINED ROUTE OF METAL DOPING AND SURFACE ACIDIFICATION
In the present work, a combined route involving first doping of iron or neodymium ions via sol–gel method followed by acidification of the metal-doped TiO2 particles for the improvement of the photocatalytic capability of TiO2 was reported. The obtained metal-doped/acidified TiO2 photocatalysts were thoroughly characterized by X-ray diffraction, Fourier transform infrared analysis, and photoluminescence emission spectra. At the same time, their photocatalytic activities were evaluated in simulant photodegradation of methylene blue (MB). The results based on these characterizations showed that not only a rutile layer formed on the surface of original TiO2 particles after surface cladding, but also the doped Fe or Nd ion had a favorable effect on suppression of the electron–hole recombination in the titania under ultraviolet light irradiation. Furthermore, the photocatalytic activity of the material obtained by Fe doping and acidification was substantially improved in comparison to the untreated TiO2. However, the sample prepared from Nd-doping and acidification of TiO2 showed decreased capability relative to the untreated TiO2 in degradation of MB under similar conditions. Finally, the reason why the photocatalytic activities of the obtained catalysts are sensitive to the metal-doping was discussed in details.TiO2, metal, doping, modification, photocatalysis
Photodegradation of Methylene Blue in a Batch Fixed Bed Photoreactor Using Activated Carbon Fibers Supported TiO_2 Photocatalyst
A batch fixed bed photoreactor, using felt-form activated carbon fibers (ACF) supported TiO2 photocatalyst (TiO2/ACF), was developed to carry out photocatalytic degradation of methylene blue (MB) solution. The effects of TiO2 particle size, loaded TiO2 amount, initial MB concentration, airflow rate and successive run on the decomposition rate were investigated. The results showed that photodegradation process followed a pseudo-first-order reaction kinetic law. The apparent fLrst-order reaction constant kapp was larger than 0.047 min^-1 with half reaction time tl/2 shorter than 15 min, which was comparable to reported data using suspended Degussa P-25 TiO2 particles. The high degradation rate was mainly attributed to adsorption of MB molecules onto the surface of TiO2/ACE The photocatalytic efficiency still remained nearly 90% after 12 successive runs, showing that successive usage of the designed photoreactor was possible. The synergic enhancement effect in combination of adsorption with ACF and photodegradation with TiO2 was proved by comparing MB removal rates in the successive degradation and adsorption runs, respectively
Recovery of Gold and Iron from Cyanide Tailings with a Combined Direct Reduction Roasting and Leaching Process
Cyanide tailings are the hazardous waste discharged after gold cyanidation leaching. The recovery of gold and iron from cyanide tailings was investigated with a combined direct reduction roasting and leaching process. The effects of reduction temperature, coal dosage and CaO dosage on gold enrichment into Au-Fe alloy (FexAu1−x) were studied in direct reduction roasting. Gold containing iron powders, i.e., Au-Fe alloy, had the gold grade of 8.23 g/t with a recovery of 97.46%. After separating gold and iron in iron powders with sulfuric acid leaching, ferrous sulfate in the leachate was crystallized to prepare FeSO4·7H2O with a yield of 222.42% to cyanide tailings. Gold enriched in acid-leaching residue with gold grade of 216.58 g/t was extracted into pregnant solution. The total gold recovery of the whole process reached as high as 94.23%. The tailings generated in the magnetic separation of roasted products, with a yield of 51.33% to cyanide tailings, had no toxic cyanide any more. The gold enrichment behaviors indicated that higher reduction temperature and larger dosage of coal and CaO could promote the allocation of more gold in iron phase rather than in slag phase. The mechanism for enriching gold from cyanide tailings into iron phase was proposed. This work provided a novel route to simultaneously recover gold and iron from cyanide tailings
Effect of Isopropanol on Microstructure and Activity of TiO2 Films with Dominant {001} Facets for Photocatalytic Degradation of Bezafibrate
Titanium dioxide (TiO2) films with dominant {001} facets coated on a titanium sheet (Ti) were synthesized with the simple hydrothermal method by using Ti as the precursor and substrate. The effect of addition of isopropanol into the hydrothermal solution on the structure, photocatalytic activity, and stability of as-synthesized TiO2 films was investigated. The presence of isopropanol obviously influenced the microstructure of as-synthesized TiO2 films, which was converted from microspheres into irregular close stack of truncated tetrahedrons. And the percentage of exposed {001} facets calculated from the Raman spectra increased from 48.2% to 57%. Accordingly, the TiO2 films prepared with addition of isopropanol showed high and stable photocatalytic activity, which is nearly 2.6 times as that of the conventional P25 TiO2 coated on Ti-substrate. In addition, the photocatalytic activity of as-synthesized TiO2 films was greatly enhanced after calcination treatment at 600°C, which can be attributed to removal of fluoride ions and organic residuals adsorbed on the surface of the catalyst. Photoluminescence (PL) technique was used for the detection of produced hydroxyl radicals (•OH) on the surface of UV-illuminated TiO2 using terephthalic acid as probe molecule. The photocatalytic degradation intermediates of bezafibrate were analyzed by an ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and accordingly the degradation pathways were proposed
Degradation of Thiol Collectors Using Ozone at a Low Dosage: Kinetics, Mineralization, Ozone Utilization, and Changes of Biodegradability and Water Quality Parameters
Ozonation at a high O3 dosage can achieve high efficiencies in removing flotation reagents but it has a low ozone-utilization rate. The ozonation of potentially toxic thiol collectors (potassium ethyl xanthate (EX), sodium diethyl dithiocarbamate (SN-9), O-isopropyl-N-ethyl thionocarbamate (Z-200) and dianilino dithiophoshoric acid (DDA)) was investigated in an ozone-bubbled reactor at a low O3 dosage of 1.125 mg/(min·L). The degradation kinetics, mineralization, ozone utilization, changes of biodegradability, and water quality parameters were studied, and the degradation behaviors of four collectors were compared. Thiol collectors could be effectively degraded with a removal ratio of >90% and a mineralization ratio of 10‒27%, at a low O3 dosage. The ozonation of thiol collectors followed the pseudo first-order kinetics, and rate constants had the order of kSN-9 > kEX > kZ-200 > kDDA. The Z-200 and DDA were the refractory flotation reagents treated in the ozonation process. After ozonation, the biodegradability of EX, SN-9, and DDA solutions was remarkably raised, but the biodegradability of Z-200 only increased from 0.088 to 0.15, indicating that the Z-200 and its intermediates were biologically persistent organics. After ozonation, the solution pH decreased from 10.0 to 8.0‒9.0, and both the conductivity and oxidation-reduction potential increased. The ozone utilization ratio in decomposing thiol collectors was above 98.41%, revealing almost complete usage of input O3. The results revealed that thiol collectors could be effectively degraded by O3, even at a low dosage, but their degradation behaviors were quite different, due to intrinsic molecular properties
Preparation and Characterization of Three-dimensional Photocatalyst-TiO2 Particulate Film Immobilized on Activated Carbon Fibers
A novel three-dimensional photocatalyst,TiO2 particulate film immobilized on activated carbon fibers (TiO2/ACFs),was prepared by liquid phase deposition. The photocatalyst was characterized by SEM,XRD,BET surface area and photodegradation of methylene blue solution. TiO2 particulate film,with a thickness of nearly 200 nm and grain sizes of 30~50 nm,was deposited on almost each carbon fiber. The inner space between adjacent fibers remained as unmodified ACFs,therefore,both UV illumination and polluted solutions were allowed to pass through the felt-form photocatalyst to form a three-dimensional environment for photocatalytic reactions. With BET surface areas of 400~600 m2/g,the TiO2/ACFs exhibited an enhanced adsorption of pollutants for photocatalysis. Comparative degradations indicated that photocatalytic activity of the TiO2/ACFs was slightly higher than that of Degussa P-25 TiO2. Two special properties,the three-dimensional structure and combined effects of ACFs’ adsorption and titania’s photodegradation,made contribution to high photocatalytic activity. Additionally,the TiO2/ACFs exhibited high stability and potentially application for practical usage