Irradiated TiO2 Research Articles

Synthesis of TiO2 Nanoparticles with Narrow Size Distribution and Their Evaluation in the Photocatalytic Oxidative Degradation of Bis(4-nitrophenyl) Phosphate

A new synthesis method of anatase titanium dioxide (TiO2) nanoparticles (NPs) of an average size of 2.1 ± 0.3 nm is reported. This is a fast, inexpensive, one-pot, and one-step method. It takes place under normal reaction conditions in dimethyl sulfoxide (DMSO) colloidal dispersions. The electronic absorption spectrum of these TiO2 colloidal particles shows an absorption band edge blue shift with respect to the macrocrystal due to the quantum confinement effect. After TiO2 NPs precipitation, the isolated powder changes its crystalline phase with the annealing process, up to 500 °C anatase is the unique phase, and at 1000 °C the precipitate is totally rutile. UV irradiated aqueous TiO2 NPs suspensions play an active role in the degradation of the bis-4-nitrophenyl phosphate (BNPP), as well as of its primary decomposition products, the 4-nitrophenyl phosphate (4-NPP) and the 4-nitrophenol (4-NP). As far as we now, the complete BNPP and 4-NPP photocatalytic or just catalytic degradation, using inorganic nano...

Effects of UV-irradiated titania nanoparticles on cell proliferation, cancer metastasis and promotion

The antitumor activity of irradiated Degussa P25 TiO 2 nanoparticles (anatase/rutile ratio of about 3:1; average diameters of the anatase and rutile particles estimated at 25 and 85 nm, respectively) was investigated in vitro: sarcoma cells killing, lipooxygenase enzymic action inhibition; and ex vivo: human platelets aggregation, in order to get insight into the possible effects of photoexcited titanium dioxide in cancer treatment. Irradiated and non-irradiated TiO 2 concentrations (varying from 0.8 μM to 1000 μM) did not show any toxicity when cultured with fibroblasts MRC-5. In vitro cultured sarcoma cells, derived and isolated from sarcoma tumors produced on experimental Wistar rats after their treatment with benzo-[a]-pyrene, were completely killed in the presence of TiO 2 (40 μg/ml). The antimetastatic capability of titanium oxide in haematogenous spread of cancer cells was also confirmed in tests involving fresh human platelets with a number of different stimulators, including sarcoma cells, platelet activated factor (PAF), diphosphoric adenosine (ADP) and arachidonic acid. Sarcoma cells-human platelets mixtures irradiated by UV-C in the presence of TiO 2 showed a significant decrease in aggregation, effect that becomes more pronounced by increasing the titania concentration. Platelet aggregation triggered by PAF and arachidonate addition was totally inhibited by photoexcited TiO 2, while partial inhibition of aggregation triggered by ADP was observed. Addition of TiO 2 followed by irradiation with UV-C also resulted in an important decrease of lipooxygenase enzyme's activity.

Homogeneous liquid crystal orientation on ion beam exposure TiO2 surfaces depending on an anisotropic dipole field

We studied homogeneous liquid crystal (LC) alignment properties on ion-beam (IB) irradiated TiO2 films deposited by the electron beam evaporation method. Stable homogeneous LC alignment on a TiO2 surface resulted from IB irradiation energy over 1800 eV. X-ray photoelectron spectroscopy analyses showed that Ti4+ 2p3/2 and Ti4+ 2p1/2 peaks were increased with increasing IB energy. Assuming that the increased peaks produced anisotropy dipole fields in the direction of the IB exposure process, we confirmed that the increasing IB energy induced strengthened the surface energy for entirely clear and stable LC molecule orientation. The voltage-transmittance characteristics of the twisted-nematic cell on the TiO2 surface indicate that the TiO2 film has potential for use as the LC alignment layer.

Nitrogen dioxide removal and nitrous acid formation on titanium oxide surfaces—an air quality remediation process?

The reactivity of NO(2) on irradiated TiO(2)/SiO(2) films was studied, with different TiO(2) contents, as proxies for NO(x) de-polluting materials. The influence of the photocatalyst concentration, the role of molecular oxygen and the effect of nitrate on the reactivity of TiO(2) films were investigated. NO, HONO and nitrate anions are produced as a consequence of the NO(2) loss on UV-illuminated TiO(2) films. The photoinduced nitrate conversion into NO(x) and HONO at the TiO(2) surface is discussed as being a renoxification process, which involves the NO(3) radical. The presence of O(2) in the carrier gas modifies the NO and HONO production yields in the heterogeneous reaction between NO(2) and TiO(2) as well as the products of the renoxification process. Depending on the nature of the surface, the interaction between NO(2) and nitrate with TiO(2) may generate HONO that may have a negative impact on air quality.

Novel accumulation of photo-induced MV+˙ embedded in a TiO2 shell and discharge of electrons to a Pt electrode

After UV-irradiation of a TiO(2) shell on Pt anode was cut off, anodic current was observed continuously for some time because long-lived MV(+)* produced from MV(2+) embedded inside the shell, as a result of the electron transfer from the conduction band of the irradiated TiO(2) shell, diffused slowly and discharged to the shell thus realizing electron accumulation inside the TiO(2) shell.

Surfactant-assisted removal of swep residues from soil and photocatalytic treatment of the washing wastes

The photocatalytic treatment of soil washing wastes containing the pesticide swep and three different surfactants: sodium dodecylsulfate (SDS), hexadecyltrimethylammonium bromide (HTAB) and polyoxyethylene(8) dodecyl ether (C12E8), has been investigated. Better extraction performances of swep (methyl-N-(3,4-dichlorophenyl)carbamate) from contaminated soil samples have been obtained using aqueous SDS solutions. The pesticide abatement in the wastes, performed by photocatalysis in the presence of irradiated TiO2 dispersions, was faster in the presence of SDS and slower in the presence of HTAB, whereas a marked degradation inhibition was observed when C12E8 solutions were used. The monitoring of end products formation in water, together with a detailed MS examination of the transient intermediates formed during the earlier steps of the pesticide degradation, allowed to give insight into the process mechanism operating in aqueous media.

A spectroscopic study of dyes decomposition by irradiated nanocrystalline TiO2

The photocatalytic activity of the TiO2 films prepared by wet-chemical techniques and deposited on the ITO glass was tested by examining the decomposition of violet gentian (VG), methylen blue (MB) and methyl green (MG) aqueous solutions under UV light illumination. The photodegradation processes of dyes have been studied using UV-VIS spectrophotometry and spectrofluorimetry. The comparative results of the present study demonstrate the capability of UV irradiation of the TiO2/ITO photocatalytic system to degrade studied organic dyes from aqueous solutions.

Visible light activated bactericidal effect of TiO 2/Fe 3O 4 magnetic particles on fish pathogens

The purpose of this research is to develop a bactericidal photocatalytic TiO 2 that can be activated by visible light and can be conveniently recollected for reusing. This research synthesizes the 22 to 33 nm TiO 2/Fe 3O 4 particles with magnetization of 2.9 emu/g using modified sol–gel method followed by 500 °C calcinations. The experiment verifies that both household fluorescent light (HFL, contains minor UV-A) and visible fluorescent light (VFL, contains no UV-A) can activate the photocatalytic activity of TiO 2/Fe 3O 4 particles as did ultraviolet A light (UV-A, 360 nm). Regular magnets can be used to separate TiO 2/Fe 3O 4 particles from solution. There have not been any significant weight and photocatalytic activity lost during 2 reusings. After 60 min and 120 min VFL irradiation, the bactericidal efficiencies of TiO 2/Fe 3O 4 are 35% and 72 % for Streptococcus iniae and 35% and 53% for Edwardsiella tarda, respectively. The results indicate that VFL irradiated TiO 2/Fe 3O 4 particles can disinfect fish pathogens in the absence of UV-A and the issue of TiO 2/Fe 3O 4 recollection from water for reusing is also resolved.

Formation of bromoform in irradiated titanium dioxide suspensions with varying photocatalyst, dissolved organic carbon and bromide concentrations

We report the formation of bromoform in TiO 2 suspensions (P25) under simulated solar UV irradiation at different concentrations of photocatalyst (0.5–1.5 g L −1) as well as initial concentrations of bromide ions (1–3 mg L −1) and 2,4-dihydroxybenzoic acid (2–10 mg L −1). The extent of bromoform formation (3–17 μg L −1) was most strongly affected by the amount of photocatalyst present and by the initial bromide concentration, increasing either of which leads to increased bromoform formation. Important interaction effects were observed when simultaneously increasing the concentrations of TiO 2 and bromide as well as of bromide and DHBA. The time it takes for bromoform to appear in measurable concentrations in the irradiated TiO 2 suspensions was between 10 and 90 min and most strongly depended on the initial concentration of dissolved organic carbon present in the suspensions, along with the amount of photocatalyst, also in interaction with the initial bromide concentration.

Liquefied petroleum gas (LPG) sensing performance of electron beam irradiated chemically deposited TiO2 thin films

We report on the liquefied petroleum gas (LPG) sensing performance of high energy (7MeV) electron beam irradiated chemically deposited nanocrystalline TiO2 thin films. The results of X-ray diffraction suggest that the electron beam irradiation leads to improved crystallinity. The occurrence of grain growth after electron beam irradiation was observed due to coalescence. The electron beam irradiated TiO2 thin films were hydrophilic with water contact angle of about 9°. The LPG sensing performance of pristine and electron beam irradiated TiO2 films was investigated at different operating temperatures and LPG concentrations. After irradiation, the LPG response of 27.45% for pristine TiO2 film was increased to 38.70% upon exposure of 5200ppm LPG.

Ferrate(VI) enhanced photocatalytic oxidation of pollutants in aqueous TiO2 suspensions

Photocatalytic oxidation using UV irradiation of TiO(2) has been studied extensively and has many potential industrial applications, including the degradation of recalcitrant contaminants in water and wastewater treatment. A limiting factor in the oxidation process is the recombination of conduction band electrons (e(-)(cb)) with electron holes (h(vb)(+)) on the irradiated TiO(2) surface; thus, in aqueous conditions, the presence of an effective electron scavenger will be beneficial to the efficiency of the oxidation process. Ferrate (FeO(4)(2-)) has received much recent attention as a water treatment chemical since it behaves simultaneously as an oxidant and coagulant. The combination of ferrate [Fe(VI)] with UV/TiO(2) photocatalysis offers an oxidation synergism arising from the Fe(VI) scavenging of e(-)(cb) and the corresponding beneficial formation of Fe(V) from the Fe(VI) reduction. This paper reviews recent studies concerning the photocatalytic oxidation of problematic pollutants with and without ferrate. The paper reviews the published results of laboratory experiments designed to follow the photocatalytic degradation of selected contaminants of environmental significance and the influence of the experimental conditions (e.g. pH, reactant concentrations and dissolved oxygen). The specific compounds are as follows: ammonia, cyanate, formic acid, bisphenol-A, dibutyl- and dimethyl-phthalate and microcystin-LR. The principal focus in these studies has been on the rates of reaction rather than on reaction pathways and products. The presence of UV/TiO(2) accelerates the chemical reduction of ferrate, and the reduction rate decreases with pH owing to deprotonation of ferrate ion. For all the selected contaminant substances, the photocatalytic oxidation rate was greater in the presence of ferrate, and this was believed to be synergistic rather than additive. The presence of dissolved oxygen in solution reduced the degradation rate of dimethyl phthalate in the ferrate/photocatalysis system. In the study of microcystin-LR, it was evident that an optimal ferrate concentration exists, whereby higher Fe(VI) concentrations above the optimum leads to a reduction in microcystin-LR degradation. In addition, the rate of microcystin-LR degradation was found to be strongly dependent on pH and was greatest at pH 6. The initial rate of photocatalytic reduction under different conditions was analysed using a Langmuirian form. Decrease in rates in the presence of dissolved oxygen may be due to competition between oxygen and ferrate as electron scavengers and to non-productive radical species interactions. The reaction between ferrate(VI) and microcystins-LR in the pH range of 6.0-10.0 is most likely controlled by the protonated Fe(VI) species, HFeO(4)(-). The photocatalytic oxidation of selected, recalcitrant contaminants was found to be significantly greater in the presence of ferrate, arising from the role of ferrate in inhibiting the h(vb)(+)-e(-)(cb) pair recombination on TiO(2) surfaces and the corresponding generation of highly oxidative Fe(V) species. The performance of the ferrate/photocatalysis system is strongly influenced by the reaction conditions, particularly the pH and dissolved oxygen concentration, arising from the complex nature of the interactions between the catalyst and the solution. Overall, the treatment performance of the Fe(VI)-TiO(2)-UV system is generally superior to alternative chemical oxidation methods. The formation of intermediate Fe(V) species in the photocatalytic reduction of ferrate(VI) requires confirmation, and a method involving electron paramagnetic resonance spectroscopy could be applied for this. The reactivity of Fe(V) with the selected contaminants is required in order to better understand the role of ferrate in the Fe(VI)-TiO(2)-UV oxidation system. To increase the practical utility of the system, it is recommended that future studies involving the photocatalytic oxidation of pollutants in the presence of ferrate(VI) should focus on developing modified TiO(2) surfaces that are photocatalytic under visible light conditions.

Application of Solar Photocatalytic Treatment to Industrial Wastewater from a Chrome Plating Unit

The present study is targeted on the feasibility of photocatalytic treatment of industrial wastewater containing metal ions. Photoreductive deposition of metal ions using solar energy irradiated TiO2, has been investigated in presence of citric acid as a hole scavenger. Treatment studies have also been performed at pH values 2, 4, 7, 8, and 10 to determine optimum reaction conditions. Results showed that at the pH value of 2, 100% reduction was achieved for Cr(VI) in a minimum time period. A maximum removal of 95.5% was achieved for Ni(II) at the pH value of 10.

Formation of appropriate sites on nanofiltration membrane surface for binding TiO 2 photo-catalyst: Performance, characterization and fouling-resistant capability

Titanium dioxide (TiO 2) nanoparticles were assembled on the surface of nanofiltration blend membrane. For settling TiO 2 on the membrane surface, two membrane categories were used: (i) unmodified polyethersulfone (PES)/polyimide (PI) blend membrane, and (ii) –OH functionalized PES/PI blend membrane with different concentrations of diethanolamine (DEA). These membranes were radiated by UV light after TiO 2 depositing with different concentrations. 15 min immersion in colloidal suspension and 15 min UV irradiation with 160 W lamps were used for modification. The modification resulted in the formation of a photo-catalytic property with enhanced membrane hydrophilicity. The self-assembly of TiO 2 nanoparticles was established through coordinance bonds with –OH functional groups on the membrane surface. A comparison between the UV irradiated TiO 2 deposited blend membrane and deposited-functionalized blend membranes showed that –OH groups originate excellent adhesion of TiO 2 nanoparticles on the membrane surface, increase reversible deposition, and diminish irreversible fouling. The membranes were characterized using SEM, FTIR, EDX, contact angle, cross flow filtration, and antifouling measurements. SEM images show that the presence of –OH groups on the DEA-modified membrane surface is the main parameter for extra uniformly settlement of TiO 2 nanoparticles on the membrane surface. This procedure is a superior technique for modification of PES/PI nanofiltration membranes to enhance water flux and minimization membrane fouling.

Solar photocatalytic removal of metal ions from industrial wastewater

AbstractThis article describes the photocatalytic reduction and deposition of four metal ions Cr(VI), Ni(II), Zn(II), and Cu(II) present in the wastewater from a chrome plating industry using solar energy irradiated TiO2. A parabolic trough reactor was used to carry out the reaction. Experiments were carried out to find an optimum dose of hole scavenger used (citric acid). The adsorption and reduction of the metal ions at different pH values was also investigated.It was observed that the solar photocatalytic process was effective in removing most of the metal ions in specific reaction conditions. Alkaline pH was found to be more suitable for removal of nickel and zinc. However, Cr(VI) reduced completely even at catalyst concentrations as low as 0.5 mg/L at pH 2. Maximum reaction was completed in the first 4 h of solar exposure. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Photocatalytic decomposition of acephate in irradiated TiO2 suspensions

In the present study, the photocatalytic degradation of acephate (O,S-dimethyl acetyl phosphoramidothioate ((CH(3)O)(CH(3)S)P(O)NHCOCH(3))) in aqueous TiO2 suspensions is extensively investigated, pertaining to the concentration of photocatalyst and substrate on degradation rate of acephate. It is found that the acephate can be degradated and mineralized. The high-degradation rate is obtained with 4 g/L concentration of TiO2. Moreover, Langmuir-Hinshelowood rate expression is employed for the degradation of acephate with adsorption constant and rate constant, i.e., 2.0 L/mmol and 0.6 mmol/(min L), respectively. The main target is to identify the products by a number of analytical techniques, such as HPLC, IC, ESR and GC-MS. Under acidic condition, the primary products are phosphorothioic acid, O,O',S-trimethyl ester (CH(3)O(CH(3)S)P(O)OCH(3)) and phosphoramidothioic acid, O,S-dimethyl ester (CH(3)O(CH(3)S)P(O)NH(2)), etc. It indicates that the decomposition of acephate begin from the destruction of C-N and P-N bonds. Subsequently, the P-S, P-O, P-C bonds may be oxidized gradually or simultaneously, and the final products such as CO(2), H(3)PO(4), were formed. About 100% sulfur atoms are transformed into SO(4)(2-) in 180 min, however; only 3% nitrogen atoms and 2% phosphorus atoms were transformed into NO(3)(-) and PO(4)(3-).

Photocatalytic degradation of phenol and m-nitrophenol using irradiated TiO 2 in aqueous solutions

Photocatalytic degradation of single and binary phenol and m-nitrophenol ( m-NP) in aqueous solutions by commercial TiO 2 powders (Degussa P-25) under UV irradiation was examined. The influences of various operating parameters including the initial reactant concentration (0.13–0.71 mM), solution pH (4.1–12.7), and the presence of the second reactant on photodegradation were studied. The effect of TiO 2 pre-wetting with aqueous solution on phenol photodegradation was also studied. It was shown that the degradation rates of phenol and m-NP decreased with increasing initial reactant concentrations. The optimal solution pH for the photodegradation of single phenol and m-NP was at around 7.4 and 8.9, respectively. Compared to the single systems, the photodegradation rates of phenol and m-NP in binary systems decreased, particularly when the second reactant was in excess. Moreover, the photodegradation of either single or binary reactants in aqueous solutions satisfactorily followed the pseudo-first-order kinetics.

UV-induced chemical coating of titanium surfaces with eicosapentaenoic acid

Eicosapentaenoic acid (EPA) is an n-3 polyunsaturated fatty acid (PUFA) that has been reported to have beneficial effects on bone remodeling. Coating of titanium (Ti) implant surfaces with EPA could be used to achieve better bone healing. The aim of this study was to compare methods to coat polished Ti surfaces with a thin layer of EPA, either physically adsorbed or chemically bound, the latter being produced by UV irradiation of TiO2 and EPA. Surface characterization of the coatings was achieved by FTIR, profilometry, water contact angle (CA) measurements, and scintillation counting of [14C]-EPA. UV irradiation resulted in peroxidation of EPA molecules, while Ti surfaces became amphiphilic indicating dissociation of hydroxide molecules. The amount of [14C]-EPA that remained on UV irradiated surfaces was significantly higher than on non-irradiated surfaces. Surfaces with chemically bound EPA did not affect the viability of MC3T3-E1 cellsin vitro and were able to enhance cell attachment and differentiation, as indicated by increased gene expression of osteoblast-specific markers. Our results suggest that UV light is a suitable method to bind EPA on the surface of Ti disks, to improve cell attachment and differentiation of osteoblastic cells.

Photocatalyzed N-de-ethylation and degradation of Brilliant Green in TiO 2 dispersions under UV irradiation

The photocatalytic degradation of Brilliant Green (BG, Bis(4-diethylaminophenyl)phenylmethylium chloride), a cationic dye, was investigated in an irradiated TiO 2 aqueous dispersion. In this study, in order to obtain a better understanding on the mechanistic details of this TiO 2-assisted photodegradation of the BG dye with UV irradiation, four intermediates of the process were separated, identified, and characterized by HPLC-PDA-ESI-MS technique. The results indicated that the N-de-ethylation degradation of BG dye took place in a stepwise manner to yield mono-, di-, tri-, and tetra- N-de-ethylated BG species generated during the processes. The photodegradation of the BG dye featured competitive reactions between N-de-ethylation and cleavage of the BG chromophore ring structure at different pH values. However, most of all, the higher degradation rate at acid pH was observed for the cationic dyes of triphenylmethane of TiO 2-mediated experiments for the first time. These results should be useful for future applications of the treatment technology to dye pollution.

Rate Enhancement and Rate Inhibition of Phenol Degradation over Irradiated Anatase and Rutile TiO2 on the Addition of NaF: New Insight into the Mechanism

Several studies have shown that addition of NaF into the aqueous dispersion of TiO2 (Degussa P25) can result in significant enhancement in the photocatalytic degradation (PCD) of organic pollutants, ascribed to the enhanced production of free OH radicals in solution as a result of fluoride displacement of surface hydroxyl groups. In this work, we have observed different results of NaF addition for the PCD of phenol over synthetic TiO2 in aqueous suspension under UV light irradiation (λ ≥ 320 nm). Upon the addition of NaF, the rate of phenol PCD was only increased with anatase, but it was decreased with rutile under similar conditions. In the presence of AgNO3, however, the fluoride-induced rate enhancement of phenol PCD could be observed with both anatase and rutile, ascribed to the increased rate of scavenging the conduction band electrons. As the catalyst sintering temperature was increased, the amount of fluoride adsorption on TiO2 was decreased, but the degree of PCD rate enhancement due to NaF addition as observed with anatase was first increased and then decreased, the trend of which was similar to that in the absence of NaF. The result reveals that the excess fluoride ions present in the suspension play some positive role to the phenol PCD, which is hardly interpreted by previous mechanism of surface fluorination. Moreover, as initial concentration of fluoride and initial pH of suspension were increased, the degree of rate enhancement was increased and decreased, respectively, which also could not be ascribed solely to the change in fluoride adsorption. Possible interference from catechol and hydroquinone intermediates and the fluoride-induced enhancement in the production of OH radicals in solution are analyzed. A new mechanistic model is proposed, involving enhanced desorption of surface bound OH radicals from irradiated TiO2, by fluoride ions present in the Helmholtz layers, through a fluorine hydrogen bond.

Solar photocatalytic removal of Cu(II), Ni(II), Zn(II) and Pb(II): Speciation modeling of metal–citric acid complexes

The present study is targeted on solar photocatalytic removal of metal ions from wastewater. Photoreductive deposition and dark adsorption of metal ions Cu(II), Ni(II), Pb(II) and Zn(II), using solar energy irradiated TiO 2, has been investigated. Citric acid has been used as a hole scavenger. Modeling of metal species has been performed and speciation is used as a tool for discussing the photodeposition trends. Ninety-seven percent reductive deposition was obtained for copper. The deposition values of other metals were significantly low [nickel (36.4%), zinc (22.2%) and lead (41.4%)], indicating that the photocatalytic treatment process, using solar energy, was more suitable for wastewater containing Cu(II) ions. In absence of citric acid, the decreasing order deposition was Cu(II) > Ni(II) > Pb(II) > Zn(II), which proves the theoretical thermodynamic predictions about the metals.