Visible Light Photocatalysis of Ni-Deposited TiO_2 Nanotubes for Methyl Orange Degradation in Alkaline Medium

The photocatalysis of Ti O2nanotubes(Ti/TNT) and Ni-deposited Ti O2nanotubes(Ti/TNT–Ni) for methyl orange degradation was investigated.Methyl orange was selected as the model pollutant,and its photocatalytic degradation was determined in 1 mol/L KOH solution.Ti/TNT was produced by anodizing method,and the electrodeposition of nickel on TNT was performed galvanostatically.The characterization of electrodes was performed by scanning electron microscopy,energy-dispersive X-ray spectroscopy and X-ray diffraction analysis.The electrochemical behavior of the electrodes was determined by cyclic voltammetry and electrochemical impedance spectroscopy.The irradiation was applied by visible light source(k = 635 nm) for 48 h.UV/vis spectroscopy was used for determination of the concentration of methyl orange.Furthermore,after 48-h irradiation,the solutions were analyzed by Fourier transform infrared spectroscopy.Results showed that the concentration of methyl orange decreased from 100 ppm(10-6) to 16 ppm,after48-h irradiation with the photocatalysis of Ti/TNT–Ni.     

The effects of thermal spray technique and post-deposition treatment on the photocatalytic activity of TiO2 coatings

Titanium dioxide coatings were deposited by two thermal spray methods: high velocity oxygen fuel and atmospheric plasma spray. The coatings were characterized by XRD, SEM, Raman and UV-vis spectroscopy. The photocatalytic activities of the samples towards decomposition of methylene blue were also determined. As-prepared samples showed a very limited photocatalytic activity. In contrast, post-deposition oxidation of the samples in air resulted in significantly improved catalytic performance of the coatings. It appears that the oxidation state of titania played a critical role in photocatalytic activity given that partially reduced coatings resulted a very low activity. This conclusion was consistent with the observation of the Ti₈O₁₅ phase in the as-prepared samples. However, when oxidized, parameters such as the anatase content became a dominant factor in catalytic performance of the samples. The coating sprayed by high velocity oxygen fuel resulted in much higher activity than the atmospheric plasma sprayed coating, which can be attributed to higher anatase content of the former.     

Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

Amphiphilic TiO₂ nanotube arrays (TiO₂ NTs) were fabricated through electrochemical oxidation of Ti in solution containing H₃PO₄ and NaF. Scanning electron microscopic analysis shows that the as-prepared TiO₂ NTs have an average pore diameter of 100 nm and a wall thickness of 15 nm. The electrochemical oxidation of Ti can be divided into four stages. In the first stage, when the potential is very low, oxygen formation and Ti dissolution are the major reactions. The second stage corresponds to a slightly higher potential, but less than 2.5 V. In this stage, the formation of TiO₂ film occurs. When the potential is increased to the even higher range from 2.5 V to 6 V, the TiO₂ film dissolves and nanoporous surface structure is generated. This is the third stage. Further increase of the potential enters stage four. The high potentials cause the self-organization of the nanostructure and allow the formation of well-aligned TiO₂ NTs. We also found that the change in surface condition of Ti by annealing heat treatment affects the film dissolution kinetics. As compared with TiO₂ thin film, the TiO2 NTs show higher photocatalytic activity on decomposing Rhodamine B. The surface of the TiO₂ NTs can be wetted by both water and oil. Such an amphiphilic property comes from the capillary effect of the nanochannel structure of the TiO₂ NTs. Because of the amphiphilic property and the photocatalytic activity, we conclude that the TiO₂ NTs have the capability of self-cleaning.     

TiO_2/EP复合光催化材料的制备及其催化性能研究

以膨胀珍珠岩(EP)为载体,用微波合成了TiO2/EP光催化材料。研究结果表明:微波功率240W,加热时间5m in,焙烧温度550℃,焙烧时间2h为制备TiO2/EP复合光催化材料的最佳条件。将制得的催化剂进行光催化降解实验,可使浓度为15mg/L的罗丹明B的去除率达90%以上。     

TiO2光催化技术在饮用水深度处理中的研究进展

TiO2光催化技术能有效降解饮用水中微量有机污染物使之彻底矿化,并且具有很好的杀菌和抑制病毒活性的作用,是一种极具应用前景的饮用水处理技术.就光催化技术对饮用水中消毒副产物、腐殖质和内分泌干扰物的降解,微生物的灭活等诸方面的研究现状进行了系统总结与评述,并指出对其进一步研究的重要性和今后主要的研究方向.     

A continuous photocatalysis system in the degradation of herbicide

The performance of both batch and continuous photo-catalytic reactors was studied to evaluate their capabilities in removing the sulfonyl urea herbicide of metsulfuron methyl (MM). It was found in a batch reactor that the addition of a small amount of powder activated carbon (PAC) significantly increased the rate of degradation of MM. The continuous photo-catalytic system resulted in 57% of MM removal. When a small dose of activated carbon was added in the photo-catalytic system, MM removal increased to 78–86% MM removal for retention times between of 5.25–21 min (corresponding to withdrawal rates of 10–40 mLmin⁻¹). In this study, the pseudo first order rate constants of a continuous photo-catalytic system revealed that shorter retention times were associated with lower rate constants. Solid phase micro extraction/gas chromatography (SPME/GC) results showed that high concentrations of MM were broken down to small volatile organic compounds (VOCs) by photo-catalytic oxidation. PAC adsorbed the photo-products and increased the degradation of MM.     

Effect of Pt/TiO2 characteristics on temporal behavior of o-cresol decomposition by visible light-induced photocatalysis

Platinum deposited TiO(2) films were prepared on quartz substrates by dip-coating process for the photodecomposition of o-cresol. The characteristics of Pt/TiO(2) and the temporal behavior of o-cresol decomposition by Pt/TiO(2) photocatalysis under visible light irradiation were investigated. Platinum deposited on TiO(2) photocatalysts was characterized by Brunauer-Emmett-Teller (BET) surface area measurement, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), diffuse reflectance UV-Vis spectra (DRS) and photoluminescence (PL) emission spectra. The results indicated that the deposition of platinum on TiO(2) promoted the optical absorption in the visible region and made it possible to be excited by visible light. The decomposition rate of o-cresol under visible light irradiation from a fluorescent lamp was enhanced to noticeably extents for experiments conducted with Pt/TiO(2) containing platinum up to 0.50wt% platinum because of the presence of Ti(3+) resulted from the platinum deposited on the TiO(2) surface; and the formation of Schottky Barrier between platinum and TiO(2) preventing the recombination of electric holes and electrons. Specifically, the reaction rate of o-cresol photodegradation at pH 9 using the 0.50wt% Pt/TiO(2) was 4.8 times than that of using pure TiO(2). The intermediates identified by GC/MS spectroscopy during the photocatalytic oxidation of o-cresol. The proposed kinetic model could be adequately applied to describe the temporal behavior of the o-cresol decomposition with and without the dosage of Pt on TiO(2) in aqueous solution by UV/TiO(2) process.     

The photocatalytic activity and kinetics of the degradation of an anionic azo-dye in a UV irradiated porous titania foam

A porous organic–inorganic hybrid titania foam, prepared from a long chain organic surfactant, hexadecylamine (HDA) and a semiconductor powder was characterized by microscopic and spectroscopic techniques and photocatalytically evaluated for the solution phase decomposition of methyl orange under alkaline conditions. Kinetic data obtained indicate conformity with Langmuir–Hinshelwood kinetic model at the initial stages of the degradation reaction. An attempt was made to study the effect of experimental parameters including catalyst loading and dye concentration on photocatalytic degradation of MO. Results indicate that the rate of reaction is governed by adsorption of azo-dye into the surface of the photocatalyst materials and suggests an optimum catalyst load and dye concentration for the degradation reaction. Light absorption and scattering within the substrate reaction zone and arising from differences in optical properties of catalyst material, made it impossible to interpret entire kinetic data on the basis of a simple Langmuir–Hinshelwood kinetics. However, kinetic data obtained at the initial stages of the reaction suggest conformity with first-order kinetics. The foam promises to be a versatile material in that it can be used for the treatment of low concentrations of pollutants of biological, organic and inorganic origins in water and air.     

Study of the synergic effect of sulphate pre-treatment and platinisation on the highly improved photocatalytic activity of TiO2

An important improvement of the photocatalytic activity of sol–gel prepared TiO₂ has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.

The presence of sulphuric acid clearly stabilised TiO₂ surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO₂ surface was studied.

Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO₂. Simultaneously sulphated and platinised TiO₂ samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO₂ Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.

A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.     

Fabrication, characterization and photocatalytic activity of Gd-doped titania nanoparticles with mesostructure

Gd³⁺-doped mesoporous TiO₂ (m-TiO₂) nanoparticles were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as surfactant-directing agent and pore-forming agent. The resulting products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflection spectra (DRS), and linear sweep voltammetry (LSV) etc. Experimental results indicate that different Gd³⁺-doping levels make great impact on the photocatalytic activity of the obtained m-TiO₂ nanoparticles and the 3.5 at.% Gd³⁺-doped m-TiO₂ nanoparticles calcined at 300 °C exhibit the optimal photoactivity on the degradation of Rhodamine B (RB), which is as nearly two times as that of the commercial photocatalyst P25. The mesoporosity, anatase wall as well as the cooperativity of ‘lattice Gd³⁺’ and ‘free Gd³⁺’ in the m-TiO₂ nanoparticles can be used to explain the observed high photoactivity of the doped m-TiO₂ nanoparticles.