Using TiO<Subscript>2</Subscript> supported on Clinoptilolite as a catalyst for photocatalytic degradation of azo dye Disperse yellow 23 in water

In this investigation photocatalytic degradation of azo dye Disperse yellow 23 in water was studied. Titanium (IV) oxide was supported on Clinoptilolite (CP) (Iranian Natural Zeolite) using the solid-state dispersion (SSD) method. The results show that the TiO₂/Clinoptilolite (SSD) is an active photocatalyst. The maximum effect of photo degradation was observed at 10 wt % TiO₂, 90 wt % Clinoptilolite. A first order reaction with k = 0.0119 min^?1 was observed. The effects of some parameters such as pH, amount of photocatalyst, and the initial concentration of dye were examined.     

Photocatalytic degradation of Br-trihalomethanes by nanosized TiO<Subscript>2</Subscript>/diatomite hybrid photocatalyst

Nanosized TiO₂/diatomite catalyst was prepared by sol–gel method at ambient temperature. Diatomite was used as a carrier, tetrabutyl titanate served as a source of titanium. The photocatalytic degradation of Br-THMs was successfully achieved in the presence of TiO₂/diatomite under Xe-light irradiation. It was suggested that Br-THMs were debromized in a stepwise manner. The rate of degradation increases markedly with increasing extent of substitution of Br-THMs by bromine because the C–Br bond is less stable than the C–Cl bond. Furthermore, the degradation of Br-THMs was caused by the action of hydroxyl free radicals, the signals of which were registered by means of electron spin resonance (ESR) spectroscopy.     

Optimized photocatalytic degradation of pefloxacin by TiO<Subscript>2</Subscript>/UV process

The photocatalytic degradation of pefloxacin was studied using modified TiO₂ as a photocatalyst. The effect of various parameters such as the amount of the photocatalyst, the initial concentration of pefloxacin, initial pH value on the process were investigated, and the optimal conditions were determined. The optimal amount of the photocatalyst is 0.3 g/L. The photodegradation rate of pefloxacin decreases with the increase of initial concentration. Alkaline medium is favorable for the photocatalytic degradation process. The primary photo-degradation products were analyzed by HPLC-ESI-MS/MS and thus the process mechanism was discussed.     

Visible-light-driven photocatalytic degradation of microcystin-LR by Bi-doped TiO<Subscript>2</Subscript>

Bi-doped nano-crystalline TiO₂ (Bi–TiO₂) has been synthesized by sonocrystallization at low temperature. The Bi–TiO₂ materials have narrower bandgaps than pristine TiO₂, which endow them with significant visible light absorption. Accordingly, these materials had enhanced photocatalytic activity in the degradation of organic dye pollutants and the cyanotoxin microcystin-LR (MC-LR) under visible irradiation. It was found that degradation of MC-LR is rather efficient. After irradiation with visible light for 12 h the original MC-LR was removed completely, and 78% of the organic carbon was mineralized into CO₂ after irradiation for 20 h. The hydroxyl radical (·OH) is the major active species responsible for the degradation reaction. Identified intermediates primarily originate from attack of ·OH radicals on the double bonds between C4 and C5 (C6 and C7) of Adda and the ethylenic bond of Mdha in MC-LR. Some peptide bonds are also broken with longer irradiation time.     

One-dimensional porous Ag/AgBr/TiO<Subscript>2</Subscript> nanofibres with enhanced visible light photocatalytic activity

One-dimensional (1D) Ag/AgBr/TiO₂ nanofibres (NFs) have been successfully fabricated by the one-pot electrospinning method. In comparison with bare TiO₂ NFs and Ag/AgBr/PVP (polyvinylpyrrolidone) NFs, the 1D Ag/AgBr/TiO₂ NFs photocatalyst exhibits much higher photocatalytic activity in the degradation of a commonly used dye, methylene blue (MB), under visible light. The photocatalytic removal efficiency of MB over Ag/AgBr/TiO₂ NFs achieves almost 100 % in 20 min. The photocatalytic reaction follows the first-order kinetics and the rate constant (k) for the degradation of MB by Ag/AgBr/TiO₂ NFs is 5.2 times and 6.6 times that of Ag/AgBr/PVP NFs and TiO₂ NFs, respectively. The enhanced photocatalytic activity is ascribed to the stronger visible light absorption, more effective separation of photogenerated electron-hole pairs, and faster charge transfer in the long nanofibrous structure. The Ag/AgBr/TiO₂ NFs maintain a highly stable photocatalytic activity due to its good structural stability and the self-stability system of Ag/AgBr. The mechanisms for photocatalysis associated with Ag/AgBr/TiO₂ NFs are proposed. The degradation of MB in the presence of scavengers reveals that h⁺ and ^?O ₂ ^? significantly contribute to the degradation of MB.     

Assessment of operating parameters for photocatalytic degradation of a textile dye by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/clinoptilolite nanocatalyst using Taguchi experimental design

In the current study, a nanophotocatalyst doped with of TiO₂ and Fe₂O₃ nanoparticles supported on Iranian clinoptilolite was synthesized and characterized by XRD, XRF, SEM, and EDX analyses. The results suggested the successful loading of TiO₂ and Fe₂O₃ nanoparticles onto the surface of clinoptilolite. The SEM images confirmed the average size of nanoparticles deposited on zeolite, which was about 20–40 nm. Furthermore, application of the synthesized photocatalyst in photocatalytic degradation of Acid Black 172 dye was studied using the Taguchi method and the chosen parameters were as follows: pH (2–7), dye concentration (50–200 mg/l), irradiation time (30–120 min), and catalyst dosage (0.5–1.5 g/l). The results indicate that dye concentration, pH, and irradiation time are respectively the most effective factors in these experiments while with the minimum dosage of the catalyst (0.5 g/l), up to 90 % removal efficiency could be achieved. The optimum value for each parameter was pH = 2, dye concentration = 50 mg/l, catalyst dosage = 1 g/l and irradiation time = 60 min, and the dye removal efficiency reached up to 100 % at these optimal conditions. Furthermore, after five-times recycling and reusing the catalyst, the efficiency of the photocatalytic degradation was reduced from 91.5 to 65.9 %, which is still an acceptable value.     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.     

Influence of oxygen pressure on the photocatalytic oxidation of the azo dye Chrome Yellow with TiO<Subscript>2</Subscript> as the catalyst

The photocatalytic oxidation of the azo dye Chrome Yellow dissolved in water on TiO₂ at high oxygen pressures was is reported. An increase of the oxygen pressure from 0.1 to 0.7 MPa increases the rate of the reaction by a factor of 1.6.     

Visible-light-driven photocatalysis of heterostructure Ag/Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> nanocomposites and their photocatalytic degradation of dye under visible light irradiation

Ag/Bi₂WO₆ nanocomposites were successfully synthesized by a combination of hydrothermal method and ultrasonic vibration. The phases, vibration modes, constituents and morphologies were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The visible-light-driven photocatalytic activitiy of 0–10 wt% Ag/Bi₂WO₆ samples was studied by determining the photodegradation of rhodamine B under xenon lamp. In this research, 10 wt% Ag/Bi₂WO₆ nanocomposites exhibit the highest efficiency and have the promising photocatalytic properties for waste water treatment.     

Flower-like Au/Ag/TiO<Subscript>2</Subscript> nanocomposites with enhanced photocatalytic efficiency under visible light irradiation

Uniform flower-like TiO₂ coated Au nanostars and core-shell Au@Ag nanostars with different amounts of Ag coating were prepared through a facile method by hydrolysis of TiF₄ under an acidic environment. The photocatalytic capability of these flower-like nanocomposites under visible light irradiation was found to be enhanced by up to 4.7-fold compared to commercial P25 TiO₂ nanoparticles. The enhanced photocatalytic activity was ascribed to improved light absorption and hot electron injection from the photo-excited Au@Ag core to the TiO₂ shell.     

Influence of ThO<Subscript>2</Subscript> on the photocatalytic activity of TiO<Subscript>2</Subscript>

Microcomposites consisting of TiO₂ (or Ce-doped TiO₂) and ThO₂ (0.5–2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of ThO₂. X-ray diffraction study reveals the effects of ThO₂ (compared to the ThO₂-free TiO₂, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant. The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent. The highest photocatalytic activity is observed for TiO₂ obtained at 550°C and containing 1% ThO₂. The composite exhibits activity in dark, also. The presence of Ce⁴⁺ ions is not an obligatory requirement for the realization of the ThO₂ effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors responsible for the increased photocatalytic activity of TiO₂.      

Qualitative investigations of the photocatalytic dye destruction by TiO<Subscript>2</Subscript>-coated polyester fabrics

The preparation of TiO₂-coated polyester fabrics for purposes of photocatalytic water purification requires coating agents with crystalline TiO₂ particles preferably in the anatase modification. The resulting coatings should exhibit a high water resistance and high photocatalytic activity according to reaction with structurally different dyestuffs. For this, the synthesis of anatase sols by hydrolysis of tetraisopropyltitanate in acidic medium under reflux was optimized. By precoating or addition of polymeric epoxysilanes a good adhesion on the polyester support could be realized. The photocatalytic activity was tested with different dyestuffs as: Methylene blue, Rhodamine B and the azo dyes AcidOrange 7 and C.I. Reactive red 158. The rate of photodestruction depends strongly on the type of used dye and its structure. Surprisingly, no differences in photodegradation were found in case of investigations with Rhodamine B, if the photoreaction is performed under exposure with UV or with visible light. A possible explanation of the similar behavior of photoreaction under different light sources could be a photodestruction by electron transfer from Rhodamine B to TiO₂. Therefore, Rhodamine B seems to be generally not suitable for the evaluation of the photoactivity of TiO₂ under irradiation with visible light.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Fabrication and photocatalytic property of TiO<Subscript>2</Subscript> nanofibers

TiO₂ nanofibers were prepared from tetrabutyl titanate sol precursors by using electrospun method. X-ray diffraction (XRD) and atomic force microscope (AFM) were used to characterize their crystal structure and morphology feature. The results demonstrated that TiO₂ nanofibers possessed anatase phase and the average diameter of TiO₂ nanofibers was about 150 nm. The photocatalytic property of TiO₂ nanofibers was evaluated for the photodecomposition of methyl orange solution. And TiO₂ nanofibers exhibited high photocatalytic activities with transfer efficiency about 100% after 20 min.     

Enhancement of photocatalytic H<Subscript>2</Subscript> evolution over TiO<Subscript>2</Subscript> nano-sheet films by surface loading NiS nanoparticles

NiS/TiO₂ nano-sheet films (NiS/TiO₂ NSFs) photocatalysts were prepared by loading NiS nanoparticles as noble metal-free cocatalysts on the surface of TiO₂ films through a solvothermal method. The prepared samples were characterized by XRD, SEM, EDS, UV–Vis absorption spectra and XPS analysis. The photocatalytic H₂ evolution and photoluminescence spectroscopy (PL) experiments indicated that the NiS cocatalysts could efficiently promote the separation of photogenerated charge carriers in TiO₂ and consequently enhance the H₂ evolution activity. The hydrogen yield obtained from the optimal sample reached 4.31 μmol cm^–2 at 3.0 h and the corresponding energy efficiency was about 0.26%, which was 21 times higher than that of pure TiO₂ NSF. A possible photocatalytic mechanism of NiS cocatalyst on the improvement of the photocatalytic performance of TiO₂ NSF was also proposed.     

Influence of MnO<Subscript>2</Subscript> on the photocatalytic activity of P-25 TiO<Subscript>2</Subscript> in the degradation of methyl orange

Influences of α-MnO₂, β-MnO₂, and δ-MnO₂ on the photocatalytic activity of Degussa P-25 TiO₂ have been investigated through the photocatalytic degradation of methyl orange. The TiO₂ photocatalyst, before and after being contaminated by MnO₂, was characterized by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). The results showed that photocatalytic activity of TiO₂ could be inhibited significantly or completely deactivated due to the presence of even a small amount of MnO₂ particles. It was found that the poisoning effect varied with the crystal phases of MnO₂ and the effect was in the order δ-MnO₂ >α-MnO₂ >β-MnO₂. The poisoning effect was attributed to the formation of heterojunctions between MnO₂ and TiO₂ particles. The heterojunctions changed the chemical state of Ti⁴⁺ and O²⁻ sites in the crystalline phase of TiO₂. MnO₂ in contact with TiO₂ particles also broadens the band-gap of TiO₂, which decreases UV absorption of TiO₂. It can also create some deep impurity energy levels serving as photoelectron-photohole recombination center, which accelerates the electron-hole recombination. Supported by the National Natural Science Foundation of China (Grant No. 20477009) and the Natural Science Foundation of Hebei Province (Grant No. E2005000183)     

Effects of TiO<Subscript>2</Subscript> surface fluorination on photocatalytic degradation of methylene blue and humic acid

Photocatalytic degradation (PCD) reactions of cationic methylene blue (MB) and anionic humic acid (HA) were studied in naked TiO₂ and fluorinated TiO₂ (F-TiO₂) suspensions in order to investigate how the modification of the TiO₂ surface functional group influenced PCD reactions. Adsorption behaviors of MB and HA in the naked TiO₂ followed a typical pH-dependent electrostatic interaction mechanism. On the other hand, those in the F-TiO₂ were markedly changed and even showed a reversed dependence in specific pH ranges due to surface fluoride interrupting the interaction of substrates and surface titanol groups. PCD rates of MB (k _MB) and its N-demethylation (Δλ _max) were significantly increased by surface fluorination below circum-neutral pH range, in particular, by a factor of 12 and 54 at pH 2, respectively. In the case of HA, the fluorination had an insignificant effect on its degradation rate but appeared to change its degradation behavior. It has been suggested that, although the primary effect of fluorination enhances the photocatalytic production of hydroxyl radicals, the change in electrostatic interaction with substrates could affect PCD as well.     

Enhanced visible light photocatalytic H<Subscript>2</Subscript> evolution over CeO<Subscript>2</Subscript> loaded with Pt and CdS

CdS-Pt@CeO₂ ternary composites are successfully prepared by an in situ redox precipitation followed by a subsequent precipitation. The prepared CdS-Pt@CeO₂ sample exhibits high photocatalytic activity for hydrogen evolution from lactic acid aqueous solution under visible light irradiation, with a H₂-evolation rate of 20.09 mmol h^?1g^?1 and apparent quantum yield (AQY) of 15.32%. With techniques such as XRD, TEM, DRS, XPS, N₂ adsorption/desorption and electrochemistry measurements, the physicochemical properties of the CdS-Pt@CeO₂ ternary composites are discussed, and a possible mechanism for the hydrogen evolution is proposed.     

Photocatalytic degradation of dichloroacetyl chloride adsorbed on TiO<Subscript>2</Subscript>

Dichloroacetyl chloride (DCAC) attracted our attention as an intermediate product of the photocatalytic degradation of trichloroethylene (TCE). The adsorption and photocatalytic reaction of DCAC on TiO₂ have been investigated by FTIR spectroscopy. The influence of the surface structure of several TiO₂s on the reaction mechanism was discussed in order to understand the complete degradation mechanism of TCE as well as DCAC. DCAC was transformed into dichloroacetic acid (DCAA) on the relatively hydrophobic TiO₂ surface by the small amount of the water molecules weakly adsorbed on the surface. This DCAA was degraded to phosgene, CO₂, and CO during UV irradiation. For the hydrophilic TiO₂, DCAC was mainly transformed into the dichloroacetate anion. UV irradiation allowed this species to produce chloroform in addition to phosgene, CO₂, and CO. It is suggested that DCAC easily reacts with the Ti–OH group on the hydrophilic TiO₂ and forms the bidentate titanium chelate of dichloroacetate, which efficiently degrades into chloroform.