Biocidal effects of photocatalytic semiconductor TiO2

Photocatalytic action of the commercial TiO₂ was the subject of study on the destruction of the microbes within the biofilms. The TiO₂ powder was characterized by X-ray diffraction (XRD) for identifying its type and the particle size was determined. The biofilm was allowed to form over TiO₂ coatings over glass slides irradiated with polychromatic light for different time durations and distances. It indicates that a five-fold decrease in bacterial count due to the formation of H₂O₂ at TiO₂/biofilm interface. The formation of H₂O₂ at the TiO₂/biofilm interface is estimated and it does not destroy the entire bacterial population within the biofilm. Bacterial killing effect is supported by FT-IR analysis.     

Antibacterial metal implant with a TiO2‐conferred photocatalytic bactericidal effect against Staphylococcus aureus

Photocatalysis with anatase Titanium dioxide (TiO₂) under ultraviolet A (UVA) has a well recognized bactericidal effect. There have been a few reports, however, on the effects of photocatalysis on bio‐implant‐related infections. The purpose of present study was to evaluate the photocatalytic bactericidal effects of anatase TiO₂ on Staphylococcus aureus (S. aureus) associated with surgical site infections. TiO₂ films were synthesized on commercially pure titanium substrates and SUS316 stainless steel using a plasma source ion implantation method followed by annealing. The chemical composition of the surface layers was determined using GXRD and XPS. The disks were seeded with cultured S. aureus and exposed to UVA illumination from black light. The bactericidal effect of the TiO₂ films was evaluated by counting the survived colonies statistically. A structural gradient anatase type TiO₂ layer formed on all substrates. The viability of the bacteria on the photocatalytic TiO₂ film coated on titanium was suppressed to 7.0% at 30 minutes and 5.5% at 45 minutes, whereas that on a similarly coated stainless steel was suppressed to 45.8% at 30 minute and 28.6% at 45 minutes (ANOVA: p < 0.05). Complete bacterial inactivation was achieved after 90 minutes on titanium and after 60 minutes on stainless steel. The photocatalytic bactericidal effect of TiO₂ is useful for sterilizing the contaminated surfaces of bioimplants. Copyright © 2008 John Wiley & Sons, Ltd.     

Enhanced remote photocatalytic oxidation on surface-fluorinated TiO2

The mobile nature of active oxygen species generated on the UV-illuminated TiO2 surface is now well-recognized. Surface oxidants not only migrate two-dimensionally but also desorb from the surface to be air-borne oxidants. The remote photocatalytic oxidation (PCO) of stearic acids over the surface-fluorinated TiO2 (F-TiO2) film was carried out in the ambient air to study the effects of fluorination on the desorption of oxidants from the surface. The F-TiO2 film was faced to a stearic acid-coated glass plate separated by a small gap (typically 30 microm), and the photocatalytic degradation of the stearic acid was monitored by Fourier transform infrared measurement or gas-chromatographic CO2 production analysis. Remote photocatalytic degradation of stearic acids was markedly faster with F-TiO2 than with the pure TiO2 film, which indicates that the generation of air-borne oxidants is enhanced over the F-TiO2 surface. The remote PCO activity was higher with a higher surface fluoride concentration, higher UV intensity, and smaller gap. The remote photocatalytic activity of F-TiO2 was maximal at a relative humidity of 50% and did not show any sign of deactivation with repeated reactions. The production of CO2 that evolved as a result of the remote PCO of stearic acids was enhanced when H2O2 vapor was present but was strongly inhibited in the presence of ammonia gas that should scavenge OH radicals. Judging from various evidences, the air-borne oxidants in remote PCO are most likely OH radicals and the surface fluorination of TiO2 seems to facilitate the desorption of OH radicals.     

Crotonaldehyde formation from decomposition of ICH2CH2OH on powdered TiO2

Adsorption and reactions of 2-iodoethanol on TiO(2) have been studied by Fourier transform infrared spectroscopy. ICH(2)CH(2)OH possesses two reactive centers of C-I and C-OH. It is found that its decomposition leads to the formation of crotonaldehyde on TiO(2). A reaction sequence of ICH(2)CH(2)OH --> ICH(2)CH(2)O- --> CH(3)CHO --> CH(3)CH=CH-CHO is proposed. Although the decomposition routes of C(2)H(5)OH and C(2)H(5)I, both forming C(2)H(5)O- on TiO(2), suggest that -OCH(2)CH(2)O- may play a role in the crotonaldehyde formation, reaction of HOCH(2)CH(2)OH on TiO(2) shows that this is not the case. Adsorbed H(2)O is formed in the ICH(2)CH(2)OH decomposition on TiO(2); however, it is found that ICH=CH(2), possibly generated by ICH(2)CH(2)OH dehydration, is not important in the crotonaldehyde formation.     

Investigation of the specific adsorption of sulfate ions on powdered TiO2

The specific adsorption of radiolabeled sulfate ions from perchlorate supporting electrolyte onto TiO2 powder (anatase) has been investigated. The pH and concentration dependence of the adsorption was determined. Langmuir-like adsorption behavior similar to that on other oxides was found. From the pH dependence it follows that the protonation of the surface should precede the specific anion adsorption. The results obtained are compared with those reported for TiO2 bulk electrodes.     

Photocatalytic single electron transfer reactions on TiO2 semiconductor

The use of inorganic semiconductor particles such as titanium dioxide(TiO_2) has received relatively less attention in organic chemistry, although semiconductor particles have been widely used as a single electron transfer photocatalyst in waterpurification, air-cleaning, and self-cleaning. In recent years, the photocatalysis on semiconductor particles has become an active area of research even in organic chemistry, since the heterogeneous semiconductor photocatalysis leads to the unique redox organic reactions. In an early stage, the semiconductor photocatalysis was applied to the oxidation of organic molecules.Semiconductor particles have also the potential to induce the reductive chemical transformations in the absence of oxygen(O_2),by using the suitable sacrificial hole scavenger. In this review, we summarize the representative examples of the reductive and oxidative organic reactions using semiconductor particles and the recent applications to the stereoselective reactions.     

Studies on photocatalytic activity of Ag/TiO2 films

Ag/TiO₂ photocatalytic films were produced by hybrid sol-gel method. The photocatalytic degradation of methyl orange (MO) in aqueous solution under 365 nm irradiation on TiO₂ and Ag/TiO₂ thin films was investigated. The state and amount of Ag species within the film and the enhancement mechanism of photocatalytic activity of Ag/TiO₂ were discussed. With a loading molar ratio of Ag/Ti = 0.135 in TiO₂ film, the maximum catalytic efficiency was observed. __________ Translated from Journal of Beijing Normal University (Natural Sciences), 2005, 41(6) (in Chinese)     

Adsorption and photocatalytic degradation of 1,4-dioxane on TiO2

1,4-Dioxane in hexane as a solvent was adsorbed on TiO₂ due to an electrostatic interaction. The porous TiO₂ pellets (SG) prepared by sol–gel method were superior adsorbent to ST-B21 and Degussa P-25. Effects of firing temperature of the pellets and the initial concentrations of 1,4-dioxane on the adsorption percents were examined. Photocatalytic degradation of aqueous 1,4-dioxane gave 1,2-ethanediol diformate and formic acid as intermediates. Analysis of total organic carbon indicated that 1,4-dioxane was mineralized effectively in the following order: P-25 > ST-B21 > SG. The photocatalytic degradation of 1,4-dioxane adsorbed on the TiO₂ pellets in air showed that ST-B21 had a higher activity than SG. These facts indicate that SG pellet acts as a good adsorbent because of its high specific surface area but the internal region of the pores is not illuminated and acts only as a support.     

Morphology and photocatalytic activity of TiO2 Aerogels

In this paper we describe a methodology to form a data base that will allow us to investigate the correlation between the morphology of Ti?₂ aerogels and their photocatalytic activity with respect to photodecomposition of a water soluble organic compound. We start with a qualitative theoretical argument in which we show that any functionality that involves optimization of different length scale should require some kind of ramified structure. For photocatalytic activity we need to optimize substrate and light absorptions with diffusion of products and reactants. We proceed to describe the techniques that we use to analyze and parametrize the morphology of the aerogels, using nitrogen adsorption and Small Angle Neutron Scattering. The photocatalytic activity is monitored through the photodecomposition of salicylic acid. We compare the adsorption and photodegradation of salicylic acid on the aerogels to many other forms of TiO₂ and report that under our experimental conditions the photocatalytic activity of the aerogels is superior.     

Adsorption and photocatalytic decomposition of amino acids in TiO2 photocatalytic systems

The adsorption and photodecomposition of seven kinds of amino acids on a TiO2 surface were investigated by zeta potential measurements and 1H NMR spectroscopy in TiO2 aqueous suspension systems. The decomposition rates increased in the order of Phe < Ala < Asp < Trp < Asn < His < Ser. For Phe, Trp, Asn, His, and Ser, the isoelectric point (IEP) of TiO2 shifted to a lower pH with increasing decomposition rates upon adsorption on TiO2, suggesting that the effective adsorption and photocatalytic sites for these amino acids should be the basic terminal OH on the solid surface. Since the amino acids that decomposed faster than the others contain -OH (Ser), -NH (Trp, His), or -NH2 (Asn) in their side chain, they are considered to interact with the basic terminal OH groups more preferably by the side chain and are vulnerable to photocatalytic oxidation. On the other hand, Ala interacts with the acidic bridged OH on TiO2 to cause an IEP shift to a higher pH. The correlation of the surface hydroxyl groups with the photocatalysis of amino acids was verified by the use of calcined TiO2 without surface hydroxyl groups.     

TiO2 assisted photocatalytic degradation of macrolide antibiotics

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二氧化钛纳米管的制备与光催化活性

用阳极氧化法,室温条件下在含NH4F和H2O的电解液(丙三醇+NH4F+H2O;乙二醇+NH4F+H2O)中制备了TiO2纳米管阵列。用环境扫描电子显微镜(SEM)、X射线衍射仪(XRD)表征二氧化钛纳米管阵列的微观形貌和物相结构。在丙三醇电解液中,电压为60 V,65 V,70 V,75 V制备的纳米管直径依次为160、170、190、220 nm。对甲基橙(10 mg/L)降解测试TiO2纳米管阵列的光催化性能。研究结果表明:在100 V阳极电压制备经过500℃退火处理后的TiO2纳米管阵列的光催化效果最好,其光催化降解率在光照时间120 min时达到89.2%。     

A theoretical investigation on photocatalytic oxidation on the TiO2 surface

The TiO(2) photocatalytic oxidation mechanism was theoretically investigated by using long-range corrected time-dependent density functional theory (LC-TDDFT) with a cluster model of the anatase TiO(2)(001) surface. We found that LC-TDDFT with the cluster model quantitatively reproduces the photoexcitations of the TiO(2) surface by calculating the electronic spectra of a clean TiO(2) surface and one with oxygen defects. We calculated the electronic spectra of a molecularly adsorbed TiO(2) surface for the adsorptions of phenol, methanol, and methane molecules as typical organic molecules. We obtained the surprising result that the main peak of the phenol-adsorbed TiO(2) surface, which overlaps with the main peak of the clean TiO(2) surface, corresponds to charge transfers from the phenol molecule to the TiO(2) surface. This indicates that the TiO(2) photocatalytic oxidation proceeds through direct charge transfer excitation from the substrate molecules to the TiO(2) surface. In contrast, we found slight and no charge transfer for methanol and methane adsorption, respectively, in agreement with the experimental findings for their reactivities. In light of these results, we propose a new mechanism for heterogeneous TiO(2) photocatalytic oxidations.     

等离子体改性聚氯乙烯的TiO2光催化降解研究

聚氯乙烯(PVC)是一种通用型塑料,无论采用挤出、注射或浸渍等方法均有优异的成型性能,至今仍是大量使用的弹性体.……     

Enhanced photocatalytic degradation of C.I. Basic Violet 2 using TiO2-SiO2 composite nanoparticles

In this report, TiO(2) -SiO(2) composite nanoparticles were prepared by the thermal hydrolysis method using titanium tetrachloride and tetraethylorthosilicate as TiO(2) and SiO(2) precursors, respectively. The prepared nanoparticles were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), nitrogen adsorption/desorption and UV-Vis diffuse reflectance spectroscopy (DRS). The results indicated that, in comparison with pure TiO(2), TiO(2)-SiO(2) composite nanoparticles had a higher thermal stability, which prevents phase transformation from anatase to rutile. In addition, the TiO(2)-SiO(2) nanoparticles had a higher specific surface area, larger pore volume, greater band gap energy and smaller crystallite size. Thus, the surface area of TiO(2)-40% SiO(2) composite nanoparticles was about 17 times higher than that of pure TiO(2) nanoparticles. The photocatalytic activity of TiO(2)-SiO(2) composite nanoparticles in the photodegradation of C.I. Basic Violet 2 was investigated. The photodegradation rate of Basic Violet 2 using TiO(2)-40% SiO(2) nanoparticles calcined at 600°C was much faster than that using pure TiO(2) and Degussa P25 TiO(2) by 10.9 and 4.3 times, respectively. The higher photoactivity of the TiO(2)-SiO(2) composite nanoparticles was attributed to their higher surface area, larger pore volume, greater band-gap energy and smaller crystallite size compared with pure TiO(2).     

Preparation and solar-light photocatalytic activity of TiO2 composites: TiO2/kaolin,TiO2/diatomite,and TiO2/zeolite

Three TiO₂ loaded composites, TiO₂/kaolin, TiO₂/diatomite, and TiO₂/zeolite, were prepared in order to improve the solar-light photocatalytic activity of TiO₂. The results showed that the photocatalytic activity could obviously be enhanced by loading appropriate amount of inorganic mineral materials. Meanwhile, TiO₂ content, heat-treatment temperature and heat-treatment time on the photocatalytic activity were reviewed. Otherwise, the effect of solar light irradiation time and dye concentration on the photocatalytic degradation of Acid Red B was investigated. Furthermore, the degradation mechanism and adsorption process were also discussed.     

4-氯酚在TiO2纳米膜上光催化降解及反应动力学特征

氯酚(ＣＰ)化合物被广泛应用于木材防腐、金属防锈及杀虫剂等,因其毒性大、难降解,对环境造成严重污染[1,2]。目前用于ＣＰ的光催化降解的ＴｉＯ2粉体悬浮体系,催化剂不易回收利用。本文采用Ｓｏｌ Ｇｅｌ法制备的负载型ＴｉＯ2纳米粒子膜作为光催化剂,对4 ＣＰ进行了降解实验研究。同时应用ＸＲＤ法表征了不同实验条件下薄膜中ＴｉＯ2的晶相结构和粒度,考察了不同层数ＴｉＯ2膜的光催化活性,并对4 ＣＰ的降解条件及反应动力学特征进行了探讨。1　实验部分1.1　玻璃负载ＴｉＯ2膜的制备与表征[3-5]按照钛酸四丁酯∶无水乙醇∶水=3∶12∶…     

Electrospun ZnO/TiO2 composite nanofibers as a bactericidal agent

Novel ZnO/TiO(2) composite nanofibers were fabricated by an electrospinning method and showed excellent antimicrobial activity against gram-negative Escherichia coli and gram-positive Staphylococcus aureus under UV irradiation and in the absence of light.