UV and visible light photodegradation effect on Fe–CNT/TiO2 composite catalysts

Using multi-walled carbon nanotube (CNT) as an one-dimensional support, we have succeeded in uniformly anchoring of TiO₂ and Fe nanoparticles at its surface. The as-prepared Fe–CNT/TiO₂ composite photocatalysts have been investigated by degrading methylene blue (MB) under UV and differently intensified visible light irradiation. The ability of CNT to store and shuttle electrons, and Fe nanoparticles demonstrate its capability to serve as a yield and transfer electrons on demand to separate h^?+?/e^??? pairs. Moreover, the MB photodegradation increase with an increase of visible light intensity can be ascribed to the enhancement MB cationic radical. In addition, chemical oxygen demand (COD) of piggery waste and reduction efficiency of Cr (IV) was done at regular intervals, which gave a good idea about mineralization of wastewater.     

Effect of deposition of Ag on TiO2 nanoparticles on the photodegradation of Reactive Yellow-17

Nanoparticles of TiO(2) were synthesized by sol-gel technique and the photodeposition of about 1% Ag on TiO(2) particles was carried out. Ag-deposited TiO(2) catalyst was characterised by XRD, TEM and UV-vis spectroscopy. The Ag-TiO(2) catalyst was evaluated for their photocatalytic activity towards the degradation of Reactive Yellow-17 (RY-17) under UV and visible light irradiations. Then the results were compared with synthesized nano-TiO(2) sol and P-25 Degussa and the enhanced degradation was obtained with Ag-deposited TiO(2). This enhanced activity of Ag-TiO(2) may be attributed to the trapping of conduction band electrons. The effect of initial dye concentration, pH and electron acceptors such as H(2)O(2), K(2)S(2)O(8) on the photocatalytic activity were studied and the results obtained were fitted with Langmuir-Hinshelwood model to study the degradation kinetics and discussed in detail.     

Efficient green photocatalyst of Ag/ZnO nanoparticles for methylene blue photodegradation

Journal of Materials Science: Materials in Electronics - Ag/ZnO nanoparticles photocatalysts with various Ag concentrations were synthesized through the hydrothermal treatment. The as-prepared...     

Preparation of doped TiO2 nanofiber membranes through electrospinning and their application for photocatalytic degradation of malachite green

Fe³⁺ doped TiO₂ composite nanofiber membranes and pure TiO₂ nanofiber membranes were prepared through electrospinning, and were applied to the photocatalytic degradation of malachite green (MG) in aqueous solutions under simulated sunlight. The effects of ferric ion content, initial concentration of MG, photocatalyst loading, and recycling behavior were studied. Microscopic characterization showed that the products have fiber morphology with bent property and favorable continuity. The degradation results showed that TiO₂ nanofiber membranes containing 0.8 mol% Fe³⁺ performed the best photocatalytic activity against MG under identical light irradiation. The TiO₂:Fe³⁺ composite nanofiber membranes maintained their photocatalytic efficiency through seven recycling processes.     

Sorption of malachite green on chitosan bead

Chitosan bead was synthesized for the removal of a cationic dye malachite green (MG) from aqueous solution. The effects of temperature (303, 313 and 323 K), pH of the solution (2-11) on MG removal was investigated. Preliminary kinetic experiment was carried out up to 480 min. The sorption equilibrium was reached within 5 h (300 min). In order to determine the adsorption capacity, the sorption data were analyzed using linear form of Langmuir and Freundlich equation. Langmuir equation showed higher conformity than Freundlich equation. Ninety-nine percent removal of MG was reached at the optimum pH value of 8. From kinetic experiments, it was obtained that sorption process followed the pseudo-second-order kinetic model. This study showed that chitosan beads can be excellent adsorbents at high pH values. Activation energy value for sorption process was found to be 85.6 kJ mol(-1). This indicates that sorption process can be assumed as chemical process. Due to negative values of Gibbs free energy, sorption process can be considered as a spontaneous. In order to determine the interactions between MG and chitosan bead, FTIR analysis was also conducted.     

Study on activities of vanadium (IV/V) doped TiO2(R) nanorods induced by UV and visible light

Vanadium (IV/V) doped rutile TiO₂ naonorods had been successfully synthesized through a single step hydrothermal method. The photocatalyst was characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV–vis diffusive reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The results showed that the doping of V ions had significant influence on the band gap energy and the surface state of TiO₂. The photo-activities of the new catalysts were investigated under ultraviolet (UV) and visible light. The UV-photocatalytic activity of the as-prepared catalysts was hardly influenced by doping V ions; while under visible light, the samples with 1 wt% and 0.1 wt% V exhibited enhanced activity to the oxidation of methylene blue (MB) and the reduction of Cr (VI), respectively.     

Low-temperature processing of thin films based on rutile TiO2 nanoparticles for UV photocatalysis and bacteria inactivation

Using a low-temperature, simple, and economic processing technique, TiO₂ nanoparticles (rutile phase) are immobilized in an inorganic matrix and then deposited on glass for bacteria inactivation in water. Using this low thermal budget method (maximum processing temperature of 220 °C), thin films of immobilized TiO₂ nanoparticles are obtained so that practical water decontamination after UV radiation is possible by avoiding the additional step of catalyst separation from treated water. In order to validate the photocatalytic activities of these TiO₂ nanoparticles (prepared as thin films), they were tested for bacteria inactivation in water under UV–A radiation (λ > 365 nm), while extensive characterizations by dynamic light scattering, X-ray diffraction, ultra violet–visible absorption spectroscopy, fourier-transform infra red spectroscopy, and profilometry were also carried out. Despite previous reports on the low or lack of photocatalytic activity of rutile-phase TiO₂, inactivation of Escherichia coli in water was observed when thin films of this material were used when compared with the application of UV radiation alone. Physical characterization of the films suggests that size and concentration-related effects may allow the existence of photocatalytic activity for rutile-TiO₂ as long as they are exposed under UV–A radiation, whereas no effect on bacteria inactivation was observed for thin films in the absence of TiO₂ or radiation. In brief, a low thermal budget process applied to thin films based on TiO₂ nanoparticles has shown to be useful for bacteria inactivation, while possible application of these films on widely available substrates like polyethylene terephthalate materials is expected.     

Photocatalytic degradation of polycyclic aromatic hydrocarbons on soil surfaces using TiO(2) under UV light

The photocatalytic degradation of phenanthrene (PHE), pyrene (PYRE) and benzo[a]pyrene (BaP) on soil surfaces in the presence of TiO(2) using ultraviolet (UV) light source was investigated in a photo chamber, in which the temperature was maintained 30 degrees C. The effects of various factors, namely TiO(2), soil pH, humic acid, and UV wavelength, on the degradation performance of polycyclic aromatic hydrocarbons (PAHs) were studied. The results show that photocatalytic degradation of PAHs follows the pseudo-first-order kinetics. Catalyst TiO(2) accelerated the photodegradation of PHE, PYRE and BaP significantly, with their half-lives being reduced from 533.15 to 130.77h, 630.09 to 192.53h and 363.22 to 103.26h, respectively, when the TiO(2) content was 0.5%. In acidic or alkaline conditions, the photocatalytic degradation rates of the PAHs were greater than those in neutral conditions. Humic acid significantly enhanced the PAH photocatalytic degradation by sensitizing radicals capable of oxidizing PAHs. Photocatalytic degradation rates of PYRE and BaP on soil surfaces with 2% TiO(2) were different at UV irradiation wavelengths of 254, 310 and 365nm, respectively. The synergistic effect of UV irradiation and TiO(2) catalysis was efficient for degradation of PAHs in contaminated soil.     

Different methods in TiO2 photodegradation mechanism studies: gaseous and TiO2-adsorbed phases

The development of photocatalysis processes offers a significant number of perspectives especially in gaseous phase depollution. It is proved that the photo-oxidizing properties of photocatalyst (TiO(2)) activated by UV plays an important role in the degradation of volatile organic compounds (VOC). Heterogeneous photocatalysis is based on the absorption of UV radiations by TiO(2). This phenomenon leads to the degradation and the oxidation of the compounds, according to a mechanism that associates the pollutant's adsorption on the photocatalyst and radical degradation reactions. The main objective of the study is the understanding of the TiO(2)-photocatalysis phenomenon including gaseous and adsorbed phase mechanisms. Results obtained with three different apparatus are compared; gaseous phases are analysed and mechanisms at the gaseous phase/photocatalyst interface are identified. This study leads to improve understanding of various mechanisms during pollutant photodegradation: adsorption of pollutants on TiO(2) first takes place, then desorption and/or photodegradation, and finally, desorption of degradation products on TiO(2). The association of analytical methods and different processes makes the determination of all parameters that affect the photocatalytic process possible. Mastering these parameters is fundamental for the design and construction of industrial size reactors that aim to purify the atmosphere.     

Enhanced sorption and photodegradation of chlorophenol over fluoride-loaded TiO2

The presence of NaF in the aqueous suspension of TiO₂ can accelerate the photocatalytic degradation of organic pollutants. However, disposal of such a fluoride-containing wastewater is not allowed by environmental regulation. In the present work, we report on surface modification of TiO₂ with a hardly water soluble salt, fluorite and fluorapatite. The modified catalysts at low loading displayed a higher activity than bare TiO₂ for the sorption and photocatalytic degradation of phenol and 2,4-dichlorophenol in water. A kinetic study using butanol as hydroxyl radical scavenger revealed that the fluoride-modified catalysts produced more hydroxyl radicals than bare TiO₂. Five repeated experiments showed that the fluorapatite-modified TiO₂ was very stable, and could be re-used without significant loss in activity.     

Photobleaching of metal phthalocyanine sulfonates under UV and visible light irradiation over TiO2 semiconductor

The stability of eleven metal phthalocyanine sulfonates against UV (λ > 320 nm) or visible light (λ > 450 nm) in the presence of TiO₂ semiconductor was studied in an aqueous medium. Although all the dyes were quite photostable in a homogeneous solution, they underwent notably photobleaching in the presence of TiO₂. The degree of dye bleaching was strongly dependent on the central metal in the complex, whereas for each complex the bleaching rate under UV irradiation was much faster than that under visible light irradiation. The spectral analysis showed that the dye photobleaching led to complete destruction of the phthalocyanine ring. In addition, the visible light stability of the dye was greatly affected by physical properties of TiO₂ semiconductor, and the dye photostability could be improved by addition of electron sacrifice such as 4-chlorophenol.     

锐钛矿型银掺杂二氧化钛紫外光及模拟太阳光光催化性能

以钛酸丁酯、硝酸银为原料,采用溶胶-凝胶法制备不同浓度Ag掺杂TiO2光催化剂。分别采用X射线衍射(XRD)、扫描电子显微镜(SEM)、光电子能谱(XPS)、紫外可见漫反射(DRS)及荧光光谱(PL)等测试方法对样品晶体结构、表面形貌、化学成分和光学性质进行表征。以罗丹明B溶液(RhB)为目标降解物,分别采用汞灯与氙灯为光源,研究xAg-TiO2(x=1%,2%,4%,6%,原子分数)光催化剂在紫外光和模拟太阳光照射下的光催化活性。结果表明:Ag的加入降低了光生电子空穴的复合率,增加了对模拟太阳光的吸收,紫外光以及模拟太阳光的光催化活性均得到提升。1%Ag-TiO2表现出最好的光催化活性,在紫外光及模拟太阳光下对RhB的降解率分别为91%与89%,是纯TiO2的1.18倍和1.24倍,反应速率常数k分别为0.01257 min^-1和0.01150 min^-1,是纯TiO2的1.49倍和1.74倍。     

Studies on interfacial interactions of TiO2 nanoparticles with bacterial cells under light and dark conditions

The probable underlying mechanism(s) of bacterial cell–TiO₂ nanoparticles (TiO₂ NPs) interaction in the absence of photo-irradiation has been less studied since most of the prior cytotoxicity studies focused on irradiated TiO₂. The present study draws attention to the possible role of cell surface–TiO₂ NP interactions under dark conditions, through an array of spectroscopic and microscopic investigations. A dominant freshwater bacterial isolate, Bacillus licheniformis, which interacted with environmentally relevant concentrations of TiO₂ NPs (1 μg/mL), was analysed and compared under both light and dark conditions. Aggregation of cells upon NP interaction and adsorption of NPs onto the cell membrane was evident from the scanning electron micrographs under both light and dark conditions. The FT–IR and FT–Raman spectra suggested stress response of bacterial cells by elevated protein and polysaccharide content in the cell–NP interaction. The Xray photoelectron spectroscopic data substantiated the reduction of titanium from Ti(IV) to Ti(III) species which might have contributed to the redox interactions on the cell surface under light as well as dark conditions. The internalization of NPs in the cytoplasm were obvious from the transmission electron micrographs. The consequent cell death/damage was confirmed through fluorescence spectroscopy and microscopy. To conclude, the current study established the substantial role of interfacial interactions in cytotoxicity of the TiO₂ NPs irrespective of the irradiation conditions.     

TiO2 nanoparticles catalysed synthesis of 2-arylbenzimidazoles and 2-arylbenzothiazoles using hydrogen peroxide under ambient light

A H₂O₂/TiO₂ P25 nanoparticle system has been examined and applied towards synthesis of a wide range of 2-substituted benzimidazole and benzothiazole derivatives from oxidative coupling of aromatic 1,2-phenylendiamine and 2-aminothiophenol with aromatic aldehydes bearing different types of substituents.     

Synthesis, characterization and photocatalytic evaluation of visible light activated C-doped TiO2 nanoparticles

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO(2) (C-TiO(2)) nanoparticles, synthesized by a modified sol-gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C-TiO(2) nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO(2). Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti-C and C-O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C-TiO(2), whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C-TiO(2) nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO(2), behavior that is attributed to the incorporation of carbon into the titania lattice.     

Sonochemical preparation of TiO2 nanoparticles

TiO₂ nanoparticles with mean diameter of about 20 nm, average crystallite size of 15 nm and BET specific surface area of 78.88 m²/g, were prepared through a simple sonochemical method and initial treatment in 10 M NaOH aqueous solution. XRD results exhibited that the obtained nanoparticles composed of pure rutile phase. During the initial treatment with NaOH aqueous solution, the Ti–O–Ti bonds in the TiO₆ octahedra structure of the raw material were broken, and new octahedras formed after ultrasonic irradiation. It is supposed that edge sharing was favored during ultrasonic treatment, leading to formation of the rutile nanoparticles.     

Visible light response and superior dispersed S-doped TiO2 nanoparticles synthesized via ionic liquid

Visible light response and superior dispersed S⁶⁺-doped TiO₂ nanoparticle catalysts (S-TiO₂) were prepared via ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate. The phenol was used for the evaluation of the S-TiO₂ photocatalytic activity. S-TiO₂ was characterized by XPS, UV–vis DRS, FE-SEM, TEM, XRD, TG/DSC, FTIR, and BET. The results showed that S-TiO₂ with appropriate S doping prepared via ionic liquid had smaller particle size, better dispersion, higher activity, and higher surface area (S_BET) than that prepared in water. Cationic S⁶⁺ incorporation into TiO₂ lattice substitutes for Ti⁴⁺ lattice site, generates Ti–O–S bonds in TiO₂, and leads to the formation of donor defect levels in band gap, so that the photocatalytic sensitization of TiO₂ has been extended to visible light region. The optimal content in S doping for the better photocatalytic performance can optimize electrical properties of the intrinsic n-type TiO₂ by adding the adequate amount of donor defect of S_Ti²⁺ for considering the lifetime of the photo-induced charge pairs.     

用于紫外光电导探测器的TiO2薄膜研究

采用直流反应磁控溅射的方法,制备了TiO2薄膜。用X射线衍射,原子力显微镜(AFM)和紫外-可见光分光光度计分别测试了TiO2薄膜的晶体结构、表面形貌及其紫外-可见光吸收谱,采用C／TiO2／ITO三层结构制备了TiO2光电导型紫外探测器,研究了它的光响应。初步实验结果表明：TiO2薄膜在4W的紫光灯辐射下,光电流可达2．1mA,10min的辐射时间内,光电流基本保持稳定,可见TiO2薄膜对紫外光有较高的灵敏度和稳定性,可作为一种良好的紫外光探测材料。     

Photocatalytic performance of Sn-doped TiO2 nanostructured thin films for photocatalytic degradation of malachite green dye under UV and VIS-lights

Sn-doped and undoped nano-TiO₂ particles have been synthesized by hydrotermal process without acid catalyst at 225 °C in 1 h. Nanostructure-TiO₂ based thin films, contain at different solid ratio of TiO₂ in coating, have been prepared on glass surfaces by spin-coating technique. The structure, surface morphology and optical properties of the thin films and the particles have been investigated by element analysis and XRD, BET and UV/VIS/NIR techniques. The photocatalytic performance of the films was tested for degradation of malachite green dye in solution under UV and VIS-lights. The results showed that the hydrothermally synthesized nano-TiO₂ particles are fully anatase crystalline form and are easily dispersed in water, the coated surfaces have nearly super-hydrophilic properties and, the doping of transition metal ion efficiently improved the photocatalytic performance of the TiO₂ thin film. The results also proved that malachite green is decomposed catalytically due to the pseudo first-order reaction kinetics.