Structure and Photocatalytic Activity of Iron Oxide Nanotubes Prepared from Ferritin

We report structure and photocatalytic activity of solid nanotubes comprising iron oxide (hematite, α-Fe₂O₃) nanoparticles. The initial precursor cylinders were prepared by alternating layer-by-layer assembly of poly-l-arginine (PLA) and iron-storage protein ferritin in a track-etched polycarbonate membrane (pore diameter: 400 nm) with subsequent dissolution of the template. The obtained (PLA/ferritin)₃ nanotubes (outer diameter: 410 ± 14 nm) were calcinated at 500 or 700 °C under air, yielding iron oxide nanotubes. After the calcination, the cylindrical hollow structure completely remained, but its diameter, wall thickness, and maximum length were significantly diminished. SEM measurements revealed that the nanotubes prepared at 500 °C consist of uniform hematite nanoparticles with ca. 5 nm diameter and the nanotubes calcinated at 700 °C are composed of ca. 20 nm hematite nanoparticles. These nanotubes showed efficient photocatalytic activity for degradation of 4-chlorophenol; higher catalytic activity was observed in the reaction with 5 nm hematite nanoparticle nanotubes.     

Modified Sol–Gel Based Nanostructured Zirconia Thin Film: Preparation,Characterization, Photocatalyst and Corrosion Behavior

In this work, AISI 316L stainless steel was coated by nanostructured zirconia using the sucrose assisted sol–gel dip-coating route. Then, the effect of different calcination temperatures and the thickness of the coating on the corrosion protection of 316L stainless steel was investigated. Here, Zr(acac)₄ and sucrose were used as starting materials and gelation agents, respectively. Thermogravimetry and differential thermal analysis, X-ray powder diffraction (XRD), Fourier transform infrared, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the coatings. XRD revealed that the pure tetragonal phase of zirconia was obtained at the calcination temperature of 300–500 °C. However, the mixture of monoclinic (m) and tetragonal (t) phase found in the zirconia coating calcined at 650 °C. Also, by increasing the calcination temperature from 300 to 650 °C, the mean of the crystallite size of structures was increased from 7 to 27 nm. AFM result show that the average roughness value of the sample calcined at 300 °C is 10.5 nm and the dimensions of the particles on the surface of this sample smaller than 50 nm. The potentiodynamic polarization and electrochemical impedance spectroscopy results revealed that the as-synthesized nanostructured sol–gel zirconia coatings exhibited a barrier property for the protection of the substrate. However, the highest corrosion resistance was obtained by the zirconia coating calcined at 300 °C. This was as a result of the desirable compromise of good adhesion, low defect density, and high barrier behaviour. Furthermore, zirconia nanoparticles were synthesized by calcination of the gel at the different temperature. The photocatalytic activity of samples was tested for degradation of methyl orange solutions. It is found that ZrO₂ nanoparticles calcined at 500 °C have higher photocatalytic activity than the other samples under UV light.     

Temperature Stability and Photocatalytic Activity of Nanocrystalline Cristobalite Powders with Cu Dopant

The SiO₂ nanoparticles doped by 10 % mol Cu were prepared via a sol-gel method under process control. The effects of doping and calcination temperature on the structural and photo-catalytic properties of SiO₂ nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. Cristobalite and tridymite crystalline phases were found at a calcinations temperature range of 900～1200 °C and amorphous phase was formed at a temperature of 800 °C for doped SiO₂. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methyl orange (MO) under visible radiation. The results show that the photocatalytic activity of the 10 % mol Cu doped SiO₂ nanopowders have a larger degradation efficiency than pure SiO₂ under visible light at 900 °C temperature.     

Preparation of Iron Sulfide Nanomaterials from Iron(II) Thiosemicarbazone Complexes and Their Application in Photodegradation of Methylene Blue

Iron sulfide nanomaterials were prepared by the solvothermal decomposition of two single source precursors i.e. [FeCl₂(cinnamtscz)₂] (1) (cinnamtscz?=?cinnamaldehyde thiosemicarbazone) and [FeCl₂(benztscz)₂] (2) (benztscz?=?benzaldehyde thiosemicarbazone) at different temperatures of 230 and 300 °C in the presence of oleylamine. Powder X-ray diffractometry shows the formation of the pyrrhotite phase at both reaction temperatures. The solvothermal decomposition of [FeCl₂(cinnamtscz)₂] and [FeCl₂(benztscz)₂] at 230 °C produced iron sulfide nanoparticles in the form of spheres. When the temperature was increased to 300 °C, particles in the form of hexagons and nanorods were obtained. Furthermore, the photocatalytic activities of all the four iron sulfide nanomaterials were tested for the degradation of methylene blue under visible light irradiation. Amongst all the materials, nanospheres of iron sulfide obtained by the solvothermal decomposition of [FeCl₂(benztscz)₂] at 230 °C showed the highest photocatalytic efficiency (88.40%).     

Hydrothermal synthesis of titanium dioxide using acidic peptizing agents and their photocatalytic activity

We have prepared TiO₂ nanoparticles by the hydrolysis of titanium tetraisopropoxide (TTIP) using HNO₃ as a peptizing agent in the hydrothermal method. The physical properties of nanosized TiO₂ have been investigated by TEM, XRD and FT-IR. The photocatalytic degradation of orange II has been studied by using a batch reactor in the presence of UV light. When the molar ratio of HNO₃/TTIP was 1.0, the rutile phase appeared on the titania and the photocatalytic activity decreased with an increase of HNO₃ concentration. The crystallite size of the anatase phase increased from 6.6 to 24.2 nm as the calcination temperature increased from 300 °C to 600 °C. The highest activity on the photocatalytic decomposition of orange II was obtained with titania particles dried at 105 °C without a calcination and the photocatalytic activity decreased with increasing the calcination temperature. In addition, the titania particles prepared at 180 °C showed the highest activity on the photocatalytic decomposition of orange II. This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.     

Effect of synthesis highly ordered TiO<Subscript>2</Subscript> nanotube arrays with enhanced photocatalytic properties by time,electrolytic voltage,heating temperature and Polyvinyl pyrrolidone

Highly ordered TiO₂ nanotube arrays were prepared by anodization method with doped Polyvinyl pyrrolidone (PVP) addition. The as-prepared samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscopy. The results suggested that TiO₂ nanotubes arrays modified by 0.10 wt% PVP were better uniform and more highly ordered than that of pure TiO₂. The average inner diameter and the tube length of TiO₂ nanotubes were extended approximately 77 nm and 5.21 μm, respectively. Meanwhile, the optimum synthesis conditions (40 V, 4 h and 450 °C) were determined by SEM and XRD. In addition, the photocatalytic activity of the as-prepared samples was investigated for the degradation of RhB under UV-lamp irradiation. The results showed that almost 100 % of RhB was degradation within 80 min by the as-prepared nanotubes in the optimum synthesis conditions. It was indicated that the photocatalytic activity of the as-prepared nanotubes was improved greatly due to their well morphology, enhanced UV-light absorption property and electron transmission ability. In general, this study could provide a principle method to synthesize TiO₂ nanotube arrays with enhanced photocatalytic activity and improved microstructure by anodization process with PVP addition.     

Synergy effect in the photocatalytic degradation of methylene blue on a suspended mixture of TiO2 and N-containing carbons

N-containing carbon materials were obtained from waste plum stones submitted to pyrolysis under Ar flow at 700 °C or to activation under steam at 800 °C and enriched with nitrogen by heating in a NH₃/air mixture at 270 °C or in NO at 300 °C. In situ mixtures of TiO₂ and carbons were prepared by the slurry method and methylene blue photodegradation was chosen as a model reaction to verify the influence of N-containing carbons on the photocatalytic activity of TiO₂ under artificial visible light irradiation. From the kinetics of methylene blue degradation an important synergy effect between both solids was detected with a remarkable increase up to a factor of 5.3 higher in the photocatalytic activity on TiO₂–C than that on TiO₂ alone. A mechanism for the photoassisting role of N-containing carbons upon the photoactivity of TiO₂ under visible light is discussed.     

Photocatalytic Activity of AgBr as an Environmental Catalyst

The photocatalytic activity of AgBr has been investigated. AgBr(N₂) was prepared by solid(AgNO₃)–solid(KBr) reaction at different temperatures in a stream of N₂. AgBr(N₂) prepared at 250 °C showed the highest H₂ generation activity although the larger crystallites of Ag were observed. When the preparation was carried out under air [AgBr(air)] at 250 °C, the photoactivity and the crystallization of Ag were lowered by the formation of silver oxides species in AgBr(air) probably during the natural cooling under air. It is pointed out however that the amount of hydrogen of both AgBr(N₂) and AgBr(air) increased linearly increasing with reaction time regardless of the formation of large Ag crystallites even after UV irradiation for 50 h. This suggests that the behavior of Ag formed might be different from that of the latent image in the photographic process.     

Preparation and visible light photocatalytic activity of carbon quantum dots/TiO2 nanosheet composites

Carbon quantum dots (C QDs)/TiO₂ nanosheet (TNS) composites were prepared by a simple low temperature process in which TNS were dispersed in C QDs solution, and dried at 60 °C. The C QDs/TNS composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM) and high-resolution TEM. The results indicated that C QDs were well combined with TNS through surface carbon–oxygen groups. The photocatalytic activity was investigated by degradation of rhodamine B under visible light irradiation. The photocatalytic activity of C QDs/TNS composites was significantly enhanced compared with that of C QDs/P25 composites and pure TNS, which indicated that the unique up-converted photoluminescence behavior of C QDs and highly reactive {0 0 1} facets of TNS both played important roles in the enhancement of photocatalytic activity of C QDs/TNS composites.     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Photocatalytic degradation of dyestuff wastewater under visible light irradiation using micron‐sized mixed crystal TiO2 powders

A phase transformation of micron‐sized TiO₂ powder from anatase to rutile was attempted by heat‐treatment in order to generate a new mixed crystal TiO₂ with high associated photocatalytic activity. Heat‐treated micron‐sized TiO₂ powders at different transition stages were characterized by X‐ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM) methods. The tests of photocatalytic activity of the heat‐treated micron‐sized TiO₂ powders were conducted by the photocatalytic degradation of Rhodamine B and Acid Red B under visible light irradiation. The results indicate that mixed crystal TiO₂ photocatalyst heat‐treated at 400 °C for 60 min shows the highest photocatalytic activity. It can effectively decompose the Rhodamine B and Acid Red B in aqueous solution after 6 h visible light irradiation. A remarkable improvement in photocatalytic activity of TiO₂ is caused by the formation of combined rutile–anatase phases and separation of photogenerated electron–hole pairs. Copyright © 2007 Society of Chemical Industry     

Advanced visible-light photocatalytic property of biologically structured carbon/ceria hybrid multilayer membranes prepared by bamboo leaves

Biologically structured carbon/cerium dioxide materials are synthesized by biological templates. The microscopic morphology, structure and the effects of different oxidation temperatures on materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) ultraviolet-visible light spectrum (UV–Vis) and X-ray Photoelectron Spectroscopy (XPS). Moreover, by splitting water under visible light irradiation, the hydrogen production is measured to test the photocatalytic property of these materials. The results show that materials made with bamboo biological templates which are immersed in 0.1 mol L^?1 of cerium nitrate solution, then carbonizated in nitrogen (700 °C) and oxidized in air (500–600 °C), can obtain the biological structure of bamboo leaves. The product is in the composition of hybrid multilayer membrane, which one is carbon membrane form plant cell carbonation and another is ceria membrane by nanoparticle self assembly. The best oxidation temperature is 550 °C and the band gap of carbon/cerium dioxide materials synthesized at this optimum oxidation temperature could be reduced to 2.75 eV. After exposure to visible light for 6 h, the optimal hydrogen production is about 302 μmol g^?1, which is much higher than that of pure CeO₂.     

Freestanding hematite nanofiber membrane for visible-light-responsive photocatalyst

Freestanding mesoporous hematite (α-Fe₂O₃) nanofiber membranes were successfully fabricated by sol–gel electrospinning process using ferratrane precursor for use as a high-performance material for visible-light-responsive photocatalyst. Non-porous nanofiber membranes spun on the heated collector at 300 °C were crystalline α-Fe₂O₃ phase. Upon calcination, pure mesoporous nanofiber membranes were obtained even at a low temperature of 400 °C. The photocatalytic membrane calcined at 400 °C showed the highest efficiency for methylene blue (MB) degradation under visible-light irradiation. The synergetic effects of higher surface area, pore volume and pore diameter promoted the photocatalytic efficiency for MB degradation under visible light. The utilization of photocatalyst in the form of membrane could not only solve the problems of catalyst separation and recovery, but also produce high photodegradation efficiency for both systems without and with hydrogen peroxide even at a catalyst loading as low as 0.04 g/L. No appreciable loss in photocatalytic activity was observed and structural integrity was retained, even after five cycles of photodegradation, which predicted the stability and reusability of these nanofiber membranes for practical use in environmental applications.     

Effects of Cocatalyst and Calcination Temperature on Photocatalytic Hydrogen Evolution Over BaTi4O9 Powder Synthesized by the Polymerized Complex Method

BaTi₄O₉ powders with improved crystal perfection and relatively large surface area were synthesized by the polymerized complex (PC) method calcined at reduced temperatures (700–1,000 °C) relative to the solid-state reaction (SSR) method. BaTi₄O₉ with a unique pentagonal-prism tunnel structure, combined with different cocatalysts (Pt, Ru, Ni, Cu, Co) as promoters, was investigated towards photocatalytic reactions for H₂ evolution from pure water and aqueous ethanol solution. Pt/BaTi₄O₉ achieved the highest activity from ethanol solution, and subsequently it was focused to study the effect of calcination temperature on photocatalytic activities. The maximum quantum yield for H₂ evolution from pure water and ethanol solution was obtained at 700 and 800 °C separately, with the value of 0.9% and 11.7% over Pt/BaTi₄O₉ photocatalysts.     

Visible light photocatalytic activity of TiO2/heat‐treated PVC film

BACKGROUND: Semiconductor TiO₂ has been investigated extensively due to its chemical stability, nontoxicity and inexpensiveness. However, the wide band gap of anatase TiO₂ (about 3.2 eV) only allows it to absorb UV light. TiO₂ nanoparticles modified by conditional conjugated polymers show excellent photocatalytic activity under visible light. However, these conjugated polymers are not only expensive, but also difficult to process. Polyvinyl chloride (PVC) was heat‐treated at high temperature to remove HCl and a C?C conjugated chain structure was obtained. When TiO₂ nanoparticles were dispersed into the conjugated polymer film derived from PVC, this composites film exhibited high visible light photocatalytic activity. RESULTS: The photocatalytic activity of TiO₂/heat‐treated PVC (HTPVC) film was investigated by degrading Rhodamine B (RhB) under visible light irradiation. The photodegradation of RhB follows apparent first‐order kinetics. The rate constants of RhB photodegradation in the presence of the TiO₂/HTPVC films with different mass content of TiO₂ are 16–56 and 4–14 times that obtained in the presence of the pure HTPVC and TiO₂/polymethyl methacrylate (PMMA) composite film, respectively. The TiO₂/HTPVC film showed excellent photocatalytic activity and stability after 10 cycles under visible light irradiation. CONCLUSION: TiO₂/HTPVC film exhibits high visible light photocatalytic activity and stability. Copyright © 2012 Society of Chemical Industry     

Visible light-irradiated degradation of alachlor on Fe-TiO<Subscript>2</Subscript> with assistance of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

0.1 Fe/Ti mole ratio of Fe-TiO₂ catalysts were synthesized via solvothermal method and calcined at various temperatures: 300, 400, and 500 °C. The calcined catalysts were characterized by XRD, N₂-adsorption-desorption, UV-DRS, XRF, and Zeta potential and tested for photocatalytic degradation of alachlor under visible light. The calcined catalysts consisted only of anatase phase. The BET specific surface area decreased with the calcination temperatures. The doping Fe ion induced a red shift of absorption capacity from UV to the visible region. The Fe-TiO₂ calcined at 400 °C showed the highest photocatalytic activity on degradation of alachlor with assistance of 30 mM H₂O₂ at pH 3 under visible light irradiation. The degradation fitted well with Langmuir-Hinshelwood model that gave adsorption coefficient and the reaction rate constant of 0.683 L mg⁻¹ and 0.136 mg/L·min, respectively.     

Photodegradation of Methylene Blue with Ag2O/TiO2 under Visible Light: Operational Parameters

Ag₂O modified TiO₂ nanoparticles were synthesized by precipitation and wet impregnation method. They were characterized by X-ray diffraction technique, UV-vis diffuse reflectance spectrophotometry and Fourier transform infrared spectroscopy. Inductively coupled plasma mass spectrometry was performed to quantify Ag amount in the photocatalysts. The photocatalysts occurred in the concentration range of 0.05%–2% in the Ag/Ti molar ratio. The photocatalytic activity was investigated for the degradation of methylene blue as a model organic dye. Optimum reaction conditions were determined to provide maximum dye degradation efficiencies under visible light. Under visible light illumination, C2-Ag₂O/TiO₂ (Ag/Ti = 0.1/100) showed the highest activity. Reaction rate constants were calculated and compared for various reaction conditions.     

Hydrothermal preparation of Zn2SnO4 nanocrystals and photocatalytic degradation of a leather dye

Zinc stannate (Zn₂SnO₄) powder was prepared by a hydrothermal process at 200 °C for 12 h. The material was characterized by X-ray-diffraction (XRD) and N₂ adsorption–desorption isotherms. The synthesized sample presented a pure phase, an average nanocrystal size of about 19 nm, a surface area (BET) of about 41.8 m² g^?1 and total pore volume of about 0.19 cm³ g^?1. Its photocatalytic activity was tested by the degradation of the leather azo-dye, Direct Black 38, in aqueous solution under UV irradiation. Adsorption kinetic data showed that the pseudo-second-order model was the most appropriate for the dye studied. Adsorption onto the Zn₂SnO₄ surface followed the Langmuir isotherm. The catalyst showed highly photocatalytic activity towards degradation of the dye, almost equal to that of the TiO₂-P25 Degussa photocatalyst. The results indicate that Zn₂SnO₄ could be employed for the removal of dyes from wastewaters.     

Fabrication of high-efficiency anatase TiO2 photocatalysts using electrospinning with ultra-violet treatment

In metal oxide nanofiber fabrication using the electrospinning method, heat treatment is performed at temperatures of 500°C or higher for crystallization and polymer desorption. Therefore, it is difficult to fabricate low-temperature phase metal oxides that crystallize at low temperatures. TiO₂, a representative metal oxide often used as photocatalysts, is known to have higher photocatalytic activity in the low-temperature phase (anatase structure) than in the high-temperature phase (rutile structure). Studies on the fabrication of TiO₂ anatase nanofibers using conventional electrospinning have reported disadvantages such as the partial expression of rutile structures and low crystallinity. This study developed an anatase TiO₂ nanofiber as a high-efficiency catalyst based on the electrospinning method and a residual organic matter cleaning method that employs ultra-violet (UV) light. We fabricated nanofibers using the electrospinning method and implemented TiO₂ nanofibers with the anatase structure through heat treatment at 260°C. Residual organics remaining after heat treatment of the fabricated crystalized TiO₂ nanofibers were removed by exposing them to UV light, thereby improving photocatalytic efficiency. The photocatalytic efficiency of the fabricated TiO₂ nanofibers was confirmed through a methylene blue (MB) decomposition experiment under visible light irradiation. The photocatalytic efficiency (time taken for the concentration of the MB solution to reach 50%) of the UV-treated TiO₂ nanofibers was approximately six times higher than of P25 and the heat-treated nanofibers.     

Gold-Nano Particles Supported on Na-Y and H-Y Types Zeolites: Activity and Thermal Stability for CO Oxidation Reaction

Gold nano particles (GNP) were deposited on Na-Y and H-Y zeolite substrates using chloroauric acid (HAuCl₄) solution. The synthesized catalysts were then characterized and the catalytic activity toward CO oxidation reaction was investigated using a tubular fix bed micro reactor under atmospheric pressure. It was found that CO conversion of 100% and 5% can be achieved at 20 °C on Au/Na-Y and Au/H-Y fresh catalysts, respectively. Thermal stability of catalysts was also investigated by treating the catalysts at 400 °C for 4 h. After thermal stability test, activity tests of the catalysts at 20 °C were shown that CO conversion of Au/Na-Y catalyst was decreased to 65% whereas the activity of the Au/H-Y at 20 °C was increased up to 15%. Characterization tests were revealed that the structures of the zeolitic supports were remained unchanged after thermal pretreatment.