Preparation of high active nanometer TiO2 sonocatalyst by partial transition crystal in hydrogen peroxide solution under ultrasonic irradiation

The transition crystal nanometer TiO₂ sonocatalyst with high sonocatalytic activity was prepared utilizing the method of ultrasonic irradiation in hydrogen peroxide solution. The sonocatalytic activity of transition crystal nanometer TiO₂ powder was validated through the degradation of acid red B and azo fuchsin solutions by ultrasonic irradiation, respectively. The results show that the sonocatalytic activity of the transition crystal nanometer TiO₂ powder is obviously higher than ones of both original nanometer rutile and anatase TiO₂ powders. The degradation ratios of acid red B and azo fuchsin in the presence of the transition crystal nanometer TiO₂ catalyst surpass 96.5% and 85.3% within 40 min ultrasonic irradiation, respectively. At the same conditions, the degradation ratios are 62.5% and 45.0% in the presence of original nanometer anatase TiO₂ powders, 73.5% and 59.5% in the presence of original nanometer rutile TiO₂ powders, respectively, while the corresponding degradation ratios are only 29.8% and 14.2% in the absence of any TiO₂ catalyst, respectively. The degradation processes of both acid red B and azo fuchsin solutions are the pseudo-first-order reaction.     

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     

Preparation, crystal structure, and photocatalytic activity of TiO2 films by chemical vapor deposition

Photocatalytic activities of TiO₂ films were experimentally studied. TiO₂ films with different crystal structures (amorphous, anatase, rutile) were prepared by a Low Pressure Metal Organic Chemical Vapor Deposition (LPMOCVD) at different reaction temperatures and also by a Sol-Gel method using TTIP (Titanium Tetra Iso-Pro-poxyde). The Effect of CVD preparation method, CVD reaction conditions, crystal structure and wave-length of UV light on the photocatalytic decomposition rate of methylene blue in aqueous solution were studied. First, the characteristics of CVD preparation of TiO₂ films, such as the CVD film growth rate, crystal structure and morphology of the grown TiO₂ films, were experimentally studied as a function of CVD reaction temperature. Secondly, photocatalytic activities of TiO₂ films were evaluated by using two types of photo-reactors. The results indicated that TiO₂ films prepared by CVD exhibit higher photocatalytic activity than a catalyst prepared by the Sol-Gel method. Among the CVD grown TiO₂ films, anatase and rutile showed high photocatalytic activities. However, amorphous TiO₂ films showed lower activities. The activity of the photocatalysts of anatase films was excellent under all types of UV-lamps. The activity of CVD-prepared anatase films was four to seven times higher than that of photocatalyst films prepared by the Sol-Gel method.     

Sonocatalytic damage of bovine serum albumin (BSA) under ultrasonic irradiation with TiO2/tooth composite

BACKGROUND: In order to effectively degrade bovine serum albumin (BSA) under ultrasonic irradiation, biological mineral material (tooth powder) was adopted to mix with nano‐sized TiO₂ powder. A TiO₂/tooth composite with high sonocatalytic activity and remarkable selectivity was prepared. RESULTS: TiO₂/tooth composite with tooth content of 30% (w/w) heat‐treated at 500 °C for 40 min was used as sonocatalyst and the catalytic degradation of BSA under ultrasonic irradiation was examined. Some influencing factors, such as ultrasonic irradiation time, TiO₂/tooth catalyst amount, solution acidity and NaCl concentration, were studied by UV‐vis and fluorescence spectroscopic analysis. Furthermore, the BSA attack site for the TiO₂/tooth composite was identifies by synchronous fluorescence spectra. CONCLUSION: The results indicated that, under ultrasonic irradiation, the TiO₂/tooth composite can promote the degradation of BSA more effectively than pure nano‐sized TiO₂ powder. The attack site is identified as tyrosine (Tyr) residue. These results are of great significance for the use of a sonocatalytic method to treat tumours in clinical applications. Copyright © 2011 Society of Chemical Industry     

TiO2体系对酸性红B的催化超声降解过程的影响

采用处理过的市售的锐钛型和金红石型纳米TiO2作为声催化剂,低功率的超声波作为激发源,研究了纳米TiO2对酸性红B催化超声降解过程的影响.结果表明:锐钛矿纳米TiO2和金红石型纳米TiO2对酸性红B有着不同的超声降解过程.锐钛型纳米TiO2以空穴氧化为主,使酸性红B脱色和降解过程同时进行,而金红石型纳米TiO2则以自由基氧化为主,是先脱色后降解.锐钛型纳米TiO2降解效果明显优于金红石型纳米TiO2.单纯超声照射下酸性红B没有明显的脱色和降解过程发生.因此,锐钛型纳米TiO2催化超声降解有机污染物的方法具有很好的应用前景.     

Different Effects of Fluoride Surface Modification on the Photocatalytic Oxidation of Phenol in Anatase and Rutile TiO2 Suspensions

The effect of calcination temperature on the photocatalytic degradation of phenol with aqueous suspensions of synthetic anatase and rutile TiO₂ under UV light irradiation (λ > 320 nm), was studied in the absence and presence of NaF. The presence of fluoride accelerates the degradation of phenol in anatase TiO₂, with this positive effect increasing at first, before declining with increasing calcined temperature. A negative effect of fluoride was observed for all the rutile TiO₂ suspensions. The selectivity of catechol increased in the presence of fluoride in both anatase and rutile TiO₂ suspensions.     

One-step preparation of size-defined aggregates of TiO2 nanocrystals with tuning of their phase and composition

One-step route based on the thermal decomposition of the double salt (NH₄)₂TiO(SO₄)₂ (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO₂, nitrogen-doped TiO₂, TiN_xO_1−x, to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO₂ in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO₂, TiN_xO_1−x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH₃ gas by varying the temperatures. The network of anatase TiO₂ with a specific surface area up to 64 m² g⁻¹ contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO₂ and nitrogen-doped TiO₂ under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO₂ nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO₂ powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.     

Preparation and characterisation of silver‐ or copper‐doped TiO2 catalysts and their catalytic activity in dye degradation

In this study, silver‐ or copper‐doped TiO₂–Ce‐, TiO₂–La‐, and commercial TiO₂ (P25)‐supported catalysts were prepared. The catalysts and supports were characterised by powder X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and nitrogen adsorption studies. UV‐light‐assisted heterogeneous Fenton‐like oxidation of two different‐structure dyes (anionic azo dye Orange II, CI Acid Orange 7 and cationic triphenylmethane dye Crystal Violet, CI Basic Violet 3) was investigated over the catalysts. Higher catalytic activity was observed in the oxidation of Orange II than in the oxidation of Crystal Violet. For both dyes, the TiO₂–Ce and TiO₂–La‐supported catalysts, which were in the form of anatase only, gave higher photocatalytic activity than the P25‐supported catalysts, which were in the form of anatase and rutile. Complete colour removal was observed during oxidation of Orange II over Cu/TiO₂–Ce and Cu/TiO₂–La catalysts, whereas the highest degree of decolorisation, 89.3%, was achieved by oxidation of Crystal Violet over Ag/TiO₂–Ce. The pH of the solution affected the surface state of the TiO₂, thus affecting the photocatalytic degradation of the dyes. The surface area of the catalysts is also a key parameter that influences their photocatalytic activity. It was observed that catalysts having higher surface areas brought about greater dye degradation.     

Formation of the Ti4O7 phase through interaction between coated carbon and TiO2

Fine particles ofphotocatalytic anatase TiO₂ prepared through hydrolysis of titanium tetraisopropoxide were coated by carbon. A reduced phase, Ti₄O₇, was formed through interaction between TiO₂ and the coating carbon. EXAFS analysis on this Ti₄O₇ phase showed an intermediate Ti-Ti distance between those in anatase and rutile, which agreed with the structure composed of two-dimensional slabs of Ti-O octahedra separated by a shear plane. This carbon-coated Ti₄O₇ was confirmed to have photocatalytic activity, even though a little lower than anatase, examining the decomposition of methylene blue in water under LTV irradiation.     

Disinfection of spring water and secondary treated municipal wastewater by TiO2 photocatalysis

The photocatalytic disinfection of spring water and secondary treated municipal wastewater by means of UV-A irradiation over TiO₂ suspensions was investigated. Water samples were taken from a spring supplying water to the city of Chania, Western Crete, Greece, while wastewater samples were collected from the outlet of the secondary treatment of Chania municipal wastewater treatment plant. The effect of various operating parameters such as photocatalyst type (rutile, anatase, mixture of anatase and rutile) and concentration (0.5-1 g/L), contact time (up to 60 min) and sample pH (6-8) on the disinfection as assessed in terms of faecal indicator microorganisms (total coliforms and enterococci) inactivation was examined. A commercially available Degussa P25 TiO₂ powder, consisting of 75% anatase and 25% rutile, was found substantially more active than pure anatase or rutile for both groups of bacteria inactivation which increased with increasing contact time and catalyst concentration, whereas small pH changes had little effect on destruction. For both groups of bacteria tested, inactivation followed a first order kinetic expression with the gram positive Enterococcus sp. being considerably more resistant to photocatalytic disinfection than total coliforms.     

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.     

Sonocatalytic damage of bovine serum albumin (BSA) under ultrasonic irradiation by mixed TiO2/SiO2 powder

BACKGROUND: In order to effectively damage some biomolecules under ultrasonic irradiation, a mixed TiO₂/SiO₂ powder with high catalytic activity and selectivity was used as a sonocatalyst. RESULTS: The mixed TiO₂/SiO₂ powder heat treated at 450 °C for 30 min was adopted as a sonocatalyst and the damage to BSA molecules under ultrasonic irradiation was assessed. In addition, the effects of such variables as molar ratio of TiO₂ and SiO₂, treatment temperature and time, ultrasonic irradiation time, catalyst amount, solution acidity, ionic nature and strength, ultrasonic irradiation power and D₂O concentration on the damage to BSA molecules were studied by means of UV‐visible and fluorescence spectra. The results showed that the degree of damage was aggravated by an increase in ultrasonic irradiation time, catalyst amount, solution acidity, ultrasonic irradiation power and D₂O concentration, but was reduced by an increase in ionic strength. CONCLUSION: The results indicated that the mixed TiO₂/SiO₂ powder displayed higher activity and selectivity compared with nano‐sized TiO₂ and SiO₂ powders during the sonocatalytic damage of BSA. The extent of the damage decreased in the order TiO₂/SiO₂ > nano‐sized TiO₂ > nano‐sized SiO₂. These results are of great significance for applying sonocatalytic methods to treat tumours. Copyright © 2008 Society of Chemical Industry     

The Assembly of TiO2 Nanoparticles into Micrometer‐Sized Structures,Photocatalytically Active Under UV and Vis Light

Micrometer‐sized structures consisting of TiO₂ nanoparticles were prepared using the sol–gel technique in combination with the structure‐directing agent triethanolamine (TEA). The interaction of the TEA with the hydrolyzed sol–gel products led to the formation of TEA titanate complexes, which then enabled the assembly of sol–gel‐precipitated nanosized powders. A subsequent thermal treatment of these powders resulted in the formation of micrometer‐sized structures consisting of TiO₂ anatase and rutile nanoparticles. To characterize the prepared powders, FTIR spectroscopy, XRD analysis, the Brunauer‐Emmett‐Teller method (s_BET), UV–Vis spectrometry and electron microscopy (FE‐SEM, and TEM) were employed. The photocatalytic degradation of the azo dye known as methylene blue was monitored under UV and Vis irradiation and showed that the micrometer‐sized structures consisting of TiO₂ nanoparticles exhibited a similar photocatalytic activity to submicrometer‐sized structures consisting of TiO₂ nanoparticles prepared without TEA.     

Bandgap Modulation of TiO2 and its Effect on the Activity in Photocatalytic Oxidation of 2-isopropyl-6-methyl-4-pyrimidinol

Nano-size TiO₂ particles were obtained using various mesoporous materials and the particle sizes were determined by the pore sizes of mesoporous materials. The bandgap increments due to quantum size effect were observed in both anatase TiO₂ and rutile TiO₂. The bandgap increment in anatase TiO₂ did not affect the efficiency of photocatalytic oxidation of 2-isopropyl-6-methyl-4-pyrimidinol. However, the bandgap increment in rutile TiO₂ enhanced the photocatalytic activity by virtue of the increase in redox potential of TiO₂.     

水热法制备TiO2片晶及光催化性能

以稳定的金红石相TiO₂为原料,水热法制备出微米级TiO₂片晶。采用扫描电镜（SEM）、X射线粉末衍射（XRD）、N₂吸附-脱附等分析手段对样品进行了分析。将不同温度下煅烧后样品进行甲基橙降解实验。实验结果表明,反应48 h可获得长60～80μm、宽30～60μm、厚4～9 μm的介孔片晶。经450℃煅烧可得到锐钛矿相占83.6%的混晶,比表面和孔径分别为68 m²·g^-1、21.6 nm,对甲基橙降解率最高,在30 min内降解了92.4%,60 min几乎全部降解,其催化活性优于商用P25,且微米级的颗粒更容易回收再利用。     

Effect of M-doping (M = Fe,V) on the photocatalytic activity of nanorod rutile TiO2 for Congo red degradation under the sunlight

Nanorods TiO₂, Fe-TiO₂ (3 and 2 at.% Fe), V-TiO₂ (5 at.% V) were prepared by a low temperature method and characterized by powder X-ray diffraction, thermal analysis, transmission electron microscope and BTE surface area analysis. The as-prepared samples were evaluated as catalysts for photodegradation of Congo red aqueous solution under the sunlight. Nanorods Fe-doped TiO₂ shows higher adsorption and also higher photocatalytic degradation of Congo red solution compared to pure nanorods TiO₂ rutile. A higher activity is obtained when the amount of doped Fe is 2 at.%, compared to 3 at.%. However, nanorods V-TiO₂ does not show neither adsorption nor photodegradation activity of Congo red solution.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

Photocatalytic partial oxidation of methylpyridine isomers on TiO2 particles under an anaerobic condition

Photocatalytic oxidation of methylpyridine isomers (2-methylpyridine, 3-methylpyridine, and 4-methylpyridine) was investigated in a mixed solution of acetonitrile and water or acetonitrile using various kinds of TiO₂ powders as photocatalysts. The main products from methylpyridine isomers were pyridinecarboxaldehyde isomers (2-pyridinecarboxaldehyde, 3-pyridinecarboxaldehyde, and 4-pyridinecarboxaldehyde). Rutile large TiO₂ particles showed the highest level of activity for oxidation of 2-methylpyridine probably because band bending was necessary for the oxidation of 2-methylpyridine. On the other hand, a fine particle having an anatase or rutile phase showed a higher level of activity than large TiO₂ particles for oxidation of 3-methylpyridine. A rutile fine particle showed the highest level of activity for the reaction. It was found that pure rutile or pure anatase particles were inactive for oxidation of 4-mathylpyridine. If the particles are not extremely small, pure rutile and pure anatase powders show fairly high levels of activity, and those containing both anatase and rutile phases show the highest level of activity. The activity of pure rutile particles was also enhanced by physically mixing them with a small amount of small anatase particles, which were inactive for this reaction. These results can be explained by the synergism between rutile and anatase particles. All of these reactions effectively proceeded even under anaerobic conditions. Photocatalytic reduction of methylpyridine isomers concomitantly proceeded on TiO₂ particles under the conditions used. These results suggest that the activities of TiO₂ photocatalysts for oxidation of methylpyridine isomers are dominated by the oxidation potential of alkylpiridine and band bending of TiO₂ particles.     

Hydrothermal synthesis of S-doped TiO2 nanoparticles and their photocatalytic ability for degradation of methyl orange

A simple synthesis route to nanocrystalline S-doped TiO₂ photocatalysts by a hydrothermal method at 180 °C was developed and the photocatalytic activity of the obtained powders for the degradation of methyl orange was studied. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phase composition (anatase/rutile ratio) and the photocatalytic activity of the final materials were found to be markedly influenced by the amount of the incorporated sulphur. On increasing the S-dopant amount, the anatase/rutile ratio and the photocatalytic activity of the as-prepared powders increased.     

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.