TiO2 photocatalyst loaded on hydrophobic Si3N4 support for efficient degradation of organics diluted in water

TiO₂ photocatalyst loaded on Si₃N₄ (TiO₂/Si₃N₄) was prepared by a conventional impregnation method and its photocatalytic performance for the degradation of organics (2-propanol) diluted in water was compared with that of TiO₂ photocatalysts (TiO₂/SiO₂, TiO₂/Al₂O₃, and TiO₂/SiC) loaded on various types of supports (SiO₂, Al₂O₃, and SiC). The formation of the well-crystallized anatase phase of TiO₂ was observed on the calcined TiO₂/Si₃N₄ photocatalyst, while a small anatase phase of TiO₂ was observed on the TiO₂/SiC photocatalyst and amorphous TiO₂ species was the main component on the TiO₂/SiO₂ and TiO₂/Al₂O₃ photocatalysts. The measurements of the water adsorption ability of photocatalysts indicated that the TiO₂/Si₃N₄ photocatalyst exhibited more hydrophobic surface properties in comparison to other support photocatalysts. Under UV-light irradiation, the TiO₂/Si₃N₄ photocatalyst decomposed 2-propanol diluted in water into acetone, CO₂, and H₂O, and finally, acetone was also decomposed into CO₂ and H₂O. The TiO₂/Si₃N₄ photocatalyst showed higher photocatalytic activity than TiO₂ photocatalyst loaded on other supports. The well-crystallized TiO₂ phase deposited on Si₃N₄ and the hydrophobic surface of Si₃N₄ support are important factors for the enhancement of photocatalytic activity for the degradation of organic compounds in liquid-phase reactions.     

Photocatalytic decomposition of 2-propanol and acetone in air by nanocomposites of pre-formed TiO2 particles and mesoporous silica

The photocatalytic efficiency in the degradations of gaseous 2-propanol and acetone has been studied on nanocomposite materials prepared by embedding well-crystallized titanium dioxide (TiO₂) particles (Degussa P25) into surfactant-templated mesoporous silica. The composite materials adsorbed the organic substances considerably in dark conditions and decomposed them completely to CO₂ under photoirradiation. The efficiency was influenced remarkably by the surface modification of TiO₂ particles. According to the transmission electron microscope observations, using carbon-coated TiO₂ particles gave a composite MCT-C with well-ordered channels of the mesoporous silica, but not all the TiO₂ particles were embedded in silica. MCT-C showed a high CO₂ production rate comparable to that of pristine TiO₂ (P25) when the concentrations of gaseous 2-propanol and acetone were as low as several ppm. On the other hand, using n-octadecyl-grafted TiO₂ particles resulted in a composite MCT-S in which most of the TiO₂ particles were well embedded in mesoporous silica, but the degree of channel-ordering was comparatively lower than that in MCT-C. The CO₂ production rate for MCT-S was lower than that for P25. This is probably due to the deactivation of TiO₂ surface by the silane-coupling reagent and/or the disorder of the mesopore channels. These composite photocatalysts could suppress the emission of unhealthy degradation products by adsorptive capacity of mesoporous silica.     

In situ DRIFTS study of photocatalytic CO2 reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

In situ DRIFTS study of photocatalytic CO<Subscript>2</Subscript> reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

Highly visible light responsive metal loaded N/TiO2 nanoparticles for photocatalytic conversion of CO2 into methane

Photocatalytic reduction of carbon dioxide (CO₂) into valuable hydrocarbon such as methane (CH₄) using water as reducing agent is a good strategy for environment and energy applications. In this study, a facile and simple sol-gel method was employed for the synthesis of metal (Cu and Ag) loaded nanosized N/TiO₂ photocatalyst. The prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, BET Surface area analyzer, X-ray photoelectron spectroscopy and UV–vis diffuses reflectance spectroscopy. The photocatalytic conversion of CO₂ into methane was carried out under visible light irradiation (λ≥420 nm) by prepared photocatalysts in order to evaluate the photocatalytic efficiency. The results demonstrate that Ag loaded N/TiO₂ showed enhanced photocatalytic performance for methane production from CO₂ compared to other Cu–N/TiO₂, N/TiO₂ and TiO₂ photocatalysts. The improvement in the photocatalytic activity could be attributed to high specific surface area, extended visible light absorption and suppressed recombination of electron – hole pair due to synergistic effects of silver and nitrogen in the Ag–N/TiO₂ photocatalyst. This study demonstrates that Ag–N/TiO₂ is a promising photocatalytic material for photocatalytic reduction of CO₂ into hydrocarbons under visible light irradiation.     

ZSM-5/TiO<Subscript>2</Subscript> Hybrid Photocatalysts: Influence of the Preparation Method and Synergistic Effect

In this work, the influence of the preparation method of ZSM-5/TiO₂ hybrids on the photocatalytic performance for removal of formaldehyde (HCHO) or trichloroethylene (C₂HCl₃) in gas phase was analyzed. For this purpose, two methods for the synthesis of the hybrids, the incipient wetness impregnation (I) and the mechanical mixing method (M), were selected. The photocatalysts were characterized by N₂ adsorption–desorption, TEM, UV–Vis spectroscopy, XRD and electrophoretic migration. Also, the adsorption ability of the individual materials and hybrids was analyzed. ZSM-5/TiO₂ hybrids showed higher photocatalytic activity than bare TiO₂, independently of the preparation method selected. Mechanical mixing is a simple and easily scalable method to prepare highly active photocatalyst with high amounts of titania. The internal diffusion processes of the reactants to the active sites could be improved due to the micro–mesoporous structure developed on these hybrids. Incipient wetness impregnation method leads to photocatalysts with higher photodegradation rates per active site. The hybrids synthetized by this method show TiO₂ nanoparticles homogeneously dispersed on the ZSM-5 phase. The fraction of TiO₂ exposed on the surface ca. 75 mol% was similar for materials prepared by both methods, explaining the similar adsorption and photocatalytic properties, independently of the TiO₂ content. The nature of the pollutant has an important role in the adsorption and photocatalytic properties of the composites. Finally, the effect of the incorporation of the zeolite in the photocatalytic system was analyzed. For this purpose, the influence of the zeolite and titania arrangement in the sample holder on the photodegradation rate was analyzed. Although the incorporation of the zeolite induces a positive effect on the photocatalytic performance, independently of the position on the sample holder, a clear synergistic effect when both phases were in intimate contact such as in the ZSM-5/TiO₂ hybrid was observed.     

Preparation of Unique TiO2 Nano-particle Photocatalysts by a Multi-gelation Method for Control of the Physicochemical Parameters and Reactivity

A novel multi-gelation method to prepare TiO₂ nano-particle photocatalysts showed good performance in controlling the important parameters determining the photocatalytic reactivity, i.e., the particle size, surface area, crystallinity, pore-volume, pore-diameter as well as the anatase and rutile phase composition of the catalysts. In particular, this method at higher pH swing times could prevent the phase transition from anatase to rutile, leading to higher photocatalytic activity. By adopting variations in the pH swing, the TiO₂ nano-particle photocatalysts showed significantly higher photocatalytic reactivity for the complete oxidation of 2-propanol diluted with water into CO₂ and H₂O. It can be considered a viable alternative method for the preparation of high performance TiO₂ nano-particle photocatalysts for widespread commercial applications.     

Photocatalytic degradation of omethoate using NaY zeolite-supported TiO2

The degradation of omethoate was conducted using H₂O₂ as oxidant, TiO₂ supported on NaY zeolite as photocatalyst and a 300W lamp as light source. The effect of the calcination temperature of the photocatalyst, the amount of TiO₂ loaded on NaY zeolite, the photocatalyst amount, the pH value and the radiation time on the degradation ratio of omethoate were investigated. The results show that TiO₂/NaY zeolite photocatalyst prepared by sol-gel method had good photocatalysis. The photocatalytic optimum oxidation conditions of omethoate are as follows: the calcination temperature of the photocatalyst is 550°C,the amount of TiO₂ loaded on NaY zeolite is 35.2 wt-%, the amount of photocatalyst is 5 g/L, pH = 8 and the radiation time is 180 min. Under these conditions, the removal ratio of omethoate is up to 93%.     

Effect of the sonication and coating time on the photocatalytic degradation of TiO2, TiO2-Ag,and TiO2-ZnO thin film photocatalysts

Abstract

Today, the ultrasound utilizing for material synthesis has been extensively investigated. The unusual acoustic cavitation phenomenon caused by ultrasonic waves has created a new world for the production of high efficiency photocatalysts with new structures. In this study, TiO₂, TiO₂-Ag, and TiO₂-ZnO thin film photocatalysts were prepared using titanium isopropoxide Ti[OCH(CH₃)₂]₄, zinc acetate dehydrates (CH₃COO)₂Zn·2H₂O, and silver nitrate AgNO₃ by a sol–gel method under the ultrasonic irradiation. The prepared photocatalysts were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive spectroscopy. The SEM images showed that the Ag and ZnO particles were evenly dispersed in the photocatalysts due to the ultrasonic irradiation, and Ag particles were approximately 90?nm, which is relatively small compared to the photocatalysts which is not treated with ultrasonic irradiation. The catalytic activity of the photocatalysts was determined using Acid Red 27 dye. The most excellent catalytic degradation was obtained with TiO₂-ZnO thin film photocatalyst. In comparison to the conventional photocatalyst, the efficiency of photocatalytic activity of the photocatalyst produced under ultrasonication has been increased due to the reduced size of Ag and ZnO and its uniform dispersion.     

NO and SO2 removal in non-thermal plasma reactor packed with glass beads-TiO2 thin film coated by PCVD process

We analyzed the NO and SO₂ removal in the non-thermal plasma discharge process combined with TiO₂ photocatalyst. The non-thermal plasmas were generated by dielectric barrier discharge with glass beads as dielectric materials. The TiO₂ thin films were coated on the glass beads uniformly without crack by a rotating cylindrical plasma chemical vapor deposition reactor. The NO and SO₂ removal efficiencies obtained in non-thermal plasma–TiO₂ photocatalysts hybrid system were higher than those in plasma process only, because of the additional removal of NO and SO₂ by photocatalysts. The NO and SO₂ removal efficiencies become higher, as applied peak voltage, pulse frequency and gas residence time increase, or as the initial NO and SO₂ concentrations decrease. The hybrid system of non-thermal plasma and photocatalyst thin film on glass beads prepared by PCVD process is quite efficient method to remove NO and SO₂.     

Photodegradation of benzene,toluene, ethylbenzene and xylene by fluidized bed gaseous reactor with TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> photocatalysts

The photodegradation of BTEX (benzene, toluene, ethylbenzene and xylene) in a photocatalytic fluidized bed reactor with TiO₂/SiO₂ was investigated. The TiO₂ film was prepared using the sol-gel method and coated onto silica-gel powder. The effects of the superficial gas velocity and SiO₂ size on the photodegradation of BTEX were examined in a fluidized bed reactor. At steady-state operation, above 79, 79, 99, 98, and 98% removal efficiencies were achieved for benzene, toluene, ethylbenzene, m, p-xylene and o-xylene, respectively, under optimal conditions (2.0 U _mf of superficial gas velocity and 1.43 of height/diameter ratio). The reaction product such as CO₂ was detected and intermediate products such as benzaldehyde, malonic acid, acetaldehyde, and formic acid were identified from the photocatalytic reaction. Also, small amounts of benzoic acid and benzyl alcohol were found through analyzing the intermediate species adsorbed on the photocatalysts. The experimental results can lead to the development of an efficient photocatalytic treatment system that utilizes solar energy and TiO₂/SiO₂ photocatalysts.     

Enhancement of the photocatalytic reactivity of TiO2 nano-particles by a simple mechanical blending with hydrophobic mordenite (MOR) zeolite

The photocatalytic oxidation of gaseous acetaldehyde with O₂ on commercial TiO₂ nano-particles could be successfully enhanced by a simple mechanical blending with a high-silica mordenite (MOR) zeolite, the surface of which showed high hydrophobic properties. When the TiO₂ nano-particles of ca. 5–20 wt% were mixed with the MOR zeolite powders in an agate mortar for only 5 min, the blended TiO₂/MOR samples showed higher photocatalytic reactivity as compared to the pure TiO₂ nano-particles. Since the high-silica zeolite powders are highly transparent in UV light regions, the incident UV light is effectively irradiated onto the whole part of the TiO₂ nano-particles without any loss of light intensity. Furthermore, the siliceous MOR zeolite powders effectively adsorb the gaseous acetaldehyde molecules and supply them onto the surfaces of the blended TiO₂ nano-particles, resulting in an enhancement of the photocatalytic reactivity.     

Photocatalytic oxidation of ethylene to CO2 and H2O on ultrafine powdered TiO2 photocatalysts: Effect of the presence of O2 and H2O and the addition of Pt

The complete photocatalytic oxidation of C₂H₄ with O₂ into CO₂ and H₂O has been achieved on ultrafine powdered TiO₂ photocatalysts and the addition of H₂O was found to enhance the reaction. The photocatalytic reaction has been studied by IR, ESR, and analysis of the reaction products. UV irradiation of the photocatalysts at 275 K led to the photocatalytic oxidation of C₂H₄ with O₂ into CO₂, CO, and H₂O. The large surface area of the photocatalyst is one of the most important factors in achieving a high efficiency in the photocatalytic oxidation of C₂H₄. The photoformed OH species as well as O ₂ ⁻ and O ₃ ⁻ anion radicals play a significant role as a key active species in the complete photocatalytic oxidation of C₂H₄ with O₂ into CO₂ and H₂O. Interestingly, small amount of Pt addition to the TiO₂ photocatalyst increased the amount of selective formation of CO₂ which was the oxidation product of C₂H₄ and O₂.     

Increasing of Photocatalytic Performance of TiO2 Nanotubes by Doping AgS and CdS

Highly ordered titanium nanotubes (TiO₂ NTs) photocatalyst was prepared by the anodic oxidation method, and AgS, CdS, and AgS/CdS nanoparticles were doped on the surface of TiO₂ NTs by the successive ion adsorption and reaction (SILAR) method. The photocatalysts were characterized by SEM, EDS, XRD, and potentiostat system. The SEM and EDS analyses respectively show that the average outer diameter of prepared photocatalysts is in the range of 50–120?nm, and the presence of Ti, O, Ag, and Cd is successfully proved. The photocatalytic properties of TiO₂ NTs and doped TiO₂ NTs were studied by measuring the degradation of Methylene Blue (MB) solution. The experimental results show that AgS/CdS/TiO₂ photocatalyst exhibited most efficient photocatalytic activity with 340?µA/cm² photocurrent value. AgS/CdS/TiO₂ NTs photocatalyst shows up to 22.20% higher than TiO₂ NTs, 16.42% higher than CdS/TiO₂ NTs, and 4.3% higher than AgS/TiO₂ NTs.     

Photocatalytic degradation of gaseous toluene in an ultrasonic mist containing TiO2 particles

Photocatalytic degradation of toluene gas in a mist formed by ultrasonic atomization of slurried TiO₂ was studied under various conditions. Upon irradiation at 365 nm, toluene was decomposed and mineralized by photocatalytic reaction on the mist surface or inside it. The toluene removal ratio increased as the amount of TiO₂ in the slurry was increased. Under UV_254+185 irradiation, the mineralization ratio was higher than at 365 nm. We propose that under UV_254+185 irradiation, toluene was immediately converted to water-soluble intermediates by direct photolysis and O₃ oxidation in the gas phase and that these intermediates were captured in the mist and photocatalytically mineralized to CO and CO₂. This paper indicates a new effective utilization of ultrasonic mist and TiO₂ photocatalyst.     

Preparation of Highly Active TiO2 Nano-particle Photocatalysts by a Flame Aerosol Method for the Complete Oxidation of 2-Propanol

A flame aerosol method has been employed to prepare spherical TiO₂ nano-particle photocatalysts with controlled anatase/rutile phase ratios without calcination at higher temperatures. This method was found to have important advantages since the main factors in achieving high photocatalytic activity such as the particle size, crystallinity and the anatase/rutile phase ratios could be easily controlled. In particular, the incorporation of small amounts of bimetals, such as Fe and Zn, were found to initiate the formation of well-crystalline, small and uniform spherical nano-size particles with a well-defined anatase/rutile phase ratio of around 60/40, similar to P-25 TiO₂. This suppressed the recombination of the photoformed charge carriers leading to a significant increase in the photocatalytic reactivity of the TiO₂ nano-particles. The incorporation of very small amounts of mono-metals, such as Fe, Cr and Zn (around 1 at.%), within the TiO₂ nano-particles led to a slight increase in the photocatalytic activity of the TiO₂ nano-particle photocatalysts for the complete oxidation of 2-propanol dissolved in water into CO₂ and H₂O as compared with the unincorporated pure TiO₂. The incorporation of bimetals of Fe and Zn within TiO₂ (Fe/Zn–TiO₂) nano-particles, on the other hand, led to a remarkable enhancement in the photocatalytic activity as compared with the unincorporated and mono-metal incorporated TiO₂.     

Construction of ternary Ag@ZnO/TiO2 fibrous membranes with hierarchical nanostructures and mechanical flexibility for water purification

Rational design of semiconductor membrane photocatalyst with good mechanical flexibility and excellent photocatalytic activity is of significance for environmental remediation. Herein, flexible Ag@ZnO/TiO₂ fibrous membranes with hierarchical nanostructures were fabricated through combining a simple electrospinning method and subsequent hydrothermal reaction and photodeposition process. In the ternary nanocomposite, ZnO nanorods were firmly anchored onto TiO₂ nanofibers, while Ag nanoparticles were evenly decorated on the surface of both ZnO and TiO₂. Benefiting from the improved light absorption, large surface area, and effective charge separation, the resultant Ag@ZnO/TiO₂ membranes displayed superior photocatalytic degradation efficiency of 91.6% toward tetracycline hydrochloride within 1 h, and also exhibited prominent antibacterial activity with a 6.5 log inactivation of E. coli after 1 h simulated solar light exposure. Significantly, the membrane photocatalyst still preserved structural integrity and mechanical flexibility after utilization. This study provides an alternative approach for designing and synthesizing flexible TiO₂-based membrane photocatalysts toward high-efficiency water purification.     

Efficient decomposition of organic compounds with FeTiO3/TiO2 heterojunction under visible light irradiation

FeTiO₃/TiO₂, a new heterojunction-type photocatalyst working at visible light, was prepared by a simple sol–gel method. Not only did FeTiO₃/TiO₂ exhibit greatly enhanced photocatalytic activity in decomposing 2-propanol in gas phase and 4-chlorophenol in aqueous solution, but also it induced efficient mineralization of 2-propanol under visible light irradiation (λ ≥ 420 nm). Furthermore, it showed a good photochemical stability in repeated photocatalytic applications. FeTiO₃ showed a profound absorption over the entire visible range, and its valence band (VB) position is close to that of TiO₂. The unusually high photocatalytic efficiency of the FeTiO₃/TiO₂ composite was therefore deduced to be caused by hole transfer between the VB of FeTiO₃ and TiO₂.     

Photocatalytic reduction of N2O on metal-supported TiO2 powder at room temperature in the presence of H2O and CH3OH vapor

Ag- and Cu-supported TiO₂ photocatalysts showed high activity for the reduction of N₂O to N₂ at room temperature in the presence of CH₃OH and H₂O vapor. The suppression by H₂O on the activity was not observed in the present photocatalyst system. The remarkable behavior of the Ag and Cu co-catalysts for TiO₂ photocatalysts agreed well with that of electro- and thermal catalyses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterizations of TiO2/SiO2/Ni–Cu–Zn Ferrite Composite for Magnetic Photocatalysts

The TiO₂/SiO₂/Ni–Cu–Zn ferrite composite for magnetic photocatalysts with high photocatalytic activity is successfully prepared in this study. The composite are composed of spherical or elliptical Ni–Cu–Zn ferrite nanoparticles about 20–60 nm as magnetic cores, silica as barrier layers with thickness of 15 nm between the magnetic cores and titania shells with thickness approximately 1.5 nm. Photodegradation examination of TiO₂/SiO₂/ Ni–Cu–Zn ferrite composite was carried out in methylene blue (MB) solutions illuminated under a Xe arc lamp with 35 W and color temperature of 6000 K. The results indicated that about 47.1% of MB molecules adsorbed on the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite within 30 min mixing due to it higher pore volume of 0.034 cm³/g, and after 6 h Xe lamp irradiation, 83.9% of MB 16.1% was photodegraded. Compared with the TiO₂ /Ni–Cu–Zn ferrite composite, the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite with silica barrier layer prohibited the photodissolution and enhanced the photocatalytic ability. The magnetic photocatalyst shows high photocatalytic efficiency that the apparent first‐order rate constant k_obs is 0.18427 h^?1, and good magnetic property that the saturation magnetization (M_s) of is 37.45 emu/g, suggesting the magnetic photocatalyst can be easily recovered by the application of an external magnetic field.