Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors

Zr/N co-doped TiO₂ nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO₂ nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO₂ nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO₂ were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.     

Prevention of photocatalytic deterioration of resins using TiO2 pillared fluoromica

The TiO₂ pillared fluoromica powder was kneaded with polylactic acid resin. The composite showed high photocatalytic activity for degradation of acetaldehyde and toluene gas, especially at the range of 1–3 wt.% pillared mica powder, and this photocatalytic activity was higher than that of resins containing even higher amounts of commercial TiO₂ (P-25, Degussa). The composite test pieces of pillared mica showed smaller photocatalytic deterioration than the samples with P-25 powder in out-door weathering tests. Thus, the TiO₂ pillared clay resin composite shows excellent prevention of photocatalytic deterioration and high photocatalytic activity in comparison with P-25.     

Photocatalytic degradation of imidacloprid pesticide in aqueous solution by TiO2 nanoparticles immobilized on the glass plate

The purpose of this study is to appraise the photocatalytic degradation of imidacloprid pesticide in an aqueous solution. To this end, imidacloprid was degraded using TiO₂ nanoparticles immobilized on a glass plate under UV light illumination. The effects of operational parameters (initial concentration of imidacloprid, pH, and light intensity) on the activity of TiO₂ nanophotocatalyst and the kinetics of the reaction were investigated. The results indicated that TiO₂ had impressive photocatalytic proficiency in the presence of UV-C light irradiation for the removal of imidacloprid from the aqueous solution. The highest efficiency for the removal of imidacloprid (R%?=?90.24) was obtained in the initial concentration of 20?mg?L^?1 imidacloprid, pH?=?5, and light intensity of 17?W?m^?2 after 180?min. The results of the mineralization studies represented a subtractive trend of total organic carbon (TOC) and an increase in the mineralization products during the reaction time.     

Blanket-like Bi2MoO6 coated on TiO2 NTA: Solvothermal construction and the enhanced photocatalytic hydrogen generation performance

Photocatalytic water splitting for hydrogen production was recognized as an effective strategy to obtain renewable energy for solving the environmental pollution and resource shortage crisis. Herein, we explored the solvothermal deposition method to successfully prepare blanket-like Bi₂MoO₆ coated on TiO₂ nanotube arrays (TiO₂ NTA/Bi₂MoO₆), and the TiO₂ NTA/Bi₂MoO₆ photocatalyst showed outstanding visible light-driven photocatalytic water splitting capacity, and the hydrogen evolution rate achieved 129.26 μmol h^-1 cm^-2. Moreover, the sample also exhibited high photocatalytic pollutant decomposition performance. The remarkable photocatalytic performance was attributed to the synergistic effect of Bi₂MoO₆ and TiO₂ NTA in the matched energy band location for solar absorption and carrier transportation. The synthesis and photocatalytic water splitting of Bi₂MoO₆/TiO₂ NTA could afford the reproducible lesson for novel resource utilization of semiconductor photocatalysts.     

Electrochemically assisted photocatalytic degradation of oxalic acid on particulate TiO2 film in a batch mode plate photoreactor

Electrochemically assisted photocatalytic degradation of oxalic acid was studied in a batch mode plate photoreactor composed of particulate TiO₂ film immobilized on Ti metal plate (Ti/TiO₂ electrode) and Pt wires immersed in a flowing film of aqueous solution (Pt counter electrode). The degradation rate of oxalic acid was followed as a function of the potential of the Ti/TiO₂ electrode, the oxygen concentration and the light intensity. The presence of oxalic acid caused an increase in the measured photocurrent by one order of magnitude which is due to its reaction with photogenerated holes. The degradation rate increased with increasing potential up to 0.5 V vs SCE, then the increase was more gradual. Electrochemically assisted photocatalytic degradation of oxalic acid also proceeded in the absence of oxygen. The photogenerated electrons caused hydrogen evolution (low oxygen concentration) or predominantely oxygen reduction (high oxygen concentration) on the Pt counter electrode.     

Enhancement of photocatalytic activity of TiO2 by adsorbed aluminium(III)

The photocatalytic activity of TiO₂ (Degussa P-25) in the mineralization of maleic acid in aqueous solution at pH = 3 is greatly enhanced by the previous adsorption of aluminium(III) on the catalyst surface. The nature of the intermediates detected during maleic acid degradation is also affected by the presence of Al(III). The observed differences can be related to an oxygen reactivity enhancement. The effect of aluminium(III) in the maleic acid adsorption over the TiO₂ surface has also been investigated by using the ATR–FT-IR technique. The UV–vis diffuse reflectance spectra of the catalyst shows a red shift due to aluminium adsorption. At neutral pH, the positive effect of adsorbed Al(III) is not observed.     

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.     

Effect of peptisation on nanosized TiO2 particles prepared by hydrolysis from metatitanic acid

Abstract

Nanocrystalline TiO₂ particles were prepared by three methods: direct hydrolysis from metatitanic acid dissolved in the presence of concentrated sulphuric acid; hydrolysis of titanium sulphate (TiSO₄); and from powders obtained by peptising precipitates with hydrochloric acid and tetraethylammonium hydroxide to form crystal phases at lower temperatures. Samples were characterised by transmission electron microscopy, X-ray diffractometry, and Brunauer–Emmitt–Teller surface area analysis. In the photodegradation of anionic sodium dodecylbenzenesulphonate surfactant, nanosized TiO₂ with mixed anatase and rutile phases was found to show improved photocatalytic properties over commercial P-25 titania powder.     

Effect of humidity on the photocatalytic degradation of trichloroethylene in gas Phase over TiO2 thin films treated by different conditions

The effect of humidity on the photocatalytic degradation reaction of trichloroethylene (TCE) in gas phase was investigated by using pretreated TiO₂ sol-gel films. It was observed that the photocatalytic activity of the TiO₂ films depended more greatly on the pretreatment conditions, for example, UV pre-illumination, than on the moisture content. When the relative humidity was over 50%, the reaction rates decreased regardless of treatment conditions of the photocatalyst. The photocatalytic decomposition rate of TCE increased with the increase of light intensity. However, the influence of humidity on the reaction rate was less significant under the increased light intensity. The intermediates and byproducts of the reaction were not changed in different humidity conditions.     

SYNTHESIS FACTORS THAT IMPACT TiO2 NANOTUBE ACTIVITY DURING GAS-PHASE PHOTOCATALYTIC OXIDATION OF METHANOL

Statistically designed experiments determined which steps in the hydrothermal synthesis of TiO₂ nanotubes significantly impacted the rate of photocatalytic oxidation of gas-phase methanol. This study investigated the following synthesis steps: sodium hydroxide treatment time, conductivity of the first and second washings, acid treatment time and pH, calcination temperature, and H₂O₂ post-treatment. The synthesis procedure produced a highly active photocatalyst; the maximum catalyst activity of the TiO₂ nanotubes was approximately seven times that of the starting material, Degussa P-25. Characterization with transmission electron microscopy, X-ray diffraction, and temperature-programmed oxidation revealed that the nanotubes were 10–12 nm in diameter with an average length of approximately 100 nm.     

Photocatalytic mineralisation of organic compounds: a comparison of flame-made TiO2 catalysts

A comparative photocatalytic analysis was carried out on TiO₂ made in a Flame Spray Pyrolysis (FSP) process and flame-made Degussa P25. Both have similar crystallinity, phase composition, phase segregation and a non-porous surface. Hence comparison was made based on their difference in specific surface area, organic adsorption and the amount of OH• generated upon illumination. The photocatalytic activity tests were carried out using the following series of organic compounds: sucrose, glucose, fructose, maleic acid, glyoxylic acid, oxalic acid, isobutyric acid, phenol and methanol. FSP-made TiO₂ outperformed P25 for saccharides mineralisation, while for phenol and methanol mineralisation P25 was better than FSP-made TiO₂. Similar mineralisation rates were observed for both FSP-made and P25 TiO₂ for the mineralisation of carboxylic acids. This shows that the relative performance of the photocatalysts depends on the type of organic compounds to be degraded. The high surface area and possibly a more efficient interfacial charge transfer of FSP-made TiO₂ provided an efficient pathway for saccharides mineralisation. As for phenol and methanol, the mineralisation rates were higher when using P25 due to the greater amount of OH• radicals generated by this photocatalyst. The fast mineralisation rates of carboxylic acids made degradation of these organic compounds to be less affected by the TiO₂ photocatalyst properties and conditions tested in this work.     

Solar photocatalytic detoxification of cyanide by different forms of TiO<Subscript>2</Subscript>

The photocatalytic efficiencies of TiO₂ nanocrystals of different modifications (anatase, rutile, P25 Degussa, Hombikat), to oxidize cyanide ion and subsequently the cyanate also, under natural sunlight at 950±25W m⁻² in alkaline solution have been compared. The oxides have been characterized by powder XRD, UV-visible diffuse reflectance and impedance spectroscopies. Under identical solar irradiance, the reaction follows Langmuir-Hinshelwood kinetics on cyanide, and depends on the apparent area of the catalyst bed and dissolved oxygen. However, the adsorption of cyanide on TiO₂ in dark is too small to be measured analytically. The photocatalytic activity of TiO₂ is not solely governed by the band gap or charge-transfer resistance or capacitance or phase composition but is in accordance with the specific surface area or the average crystallite size; rutile is an exception.     

Optical properties of Pt-TiO<Subscript>2</Subscript> catalyst and photocatalytic activities for benzene decomposition

In order to improve the photocatalytic decomposition activity of benzene, which has been regarded as a typical volatile organic compound in air, TiO₂ catalysts modified with metals (Pt, Cu, and Fe) were prepared and tested. Certain correlations between the photocatalytic activities and the optical properties of those catalysts were also found and discussed by using UV-visible spectroscopy and a photoluminescence spectroscopy. Among the metal impregnated TiO₂, the Pt impregnated TiO₂ showed the best activity and it was even better than that of P-25 which is widely used in commercial applications. For the various metal impregnated TiO₂ samples, certain proportional relationships were found between the observed photoluminescence values and photocatalytic activities. On the other hand, in UV-visible spectra for metal impregnated TiO₂ samples, the transmittance value was reduced depending upon the loading of metals. It was thought that photocatalytic activity increases from initial reaction state because the number of photoexcited electrons, which exist at Pt surface augment due to the band gap energy change of Pt and TiO₂ by sintering and light energy-absorbed electrons excited easily to conduction. In conclusion, it was confirmed that the enhanced photocatalytic activity for high metal loading on TiO₂ is related with the high concentration of excited electrons, which could be monitored through UV-visible spectra.     

Photocatalytic decolorization of Basic Blue 41 using TiO2-Fe3O4-bentonite coating applied to ceramic in continuous system

Abstract

Photocatalytic degradation/decolorization of Basic Blue 41 dye assisted by UV radiation has been studied over TiO₂-Fe₃O₄ supported by bentonite. In this experiment, photocatalytic decolorization process was performed continuously; where dye feed solution was supplied to a coated-ceramic vessel. The influence of the initial concentration, pH, and flow rate of the dye feed solution on the degradation efficiency process was examined in this study. The results showed that the increase in the dye concentration and flow rate reduces decolorization efficiency. The highest decolorization efficiency was at pH of 5.5. The kinetic study of this photo-decolorization indicated that under the experimental condition, the photocatalytic kinetic process followed first-order kinetics on the basis of Langmuir–Hinshelwood heterogeneous reaction mechanism, where the reaction rate constant, namely k_r, is 0.7707 and the adsorption rate constant, namely K, is 0.01298.     

Characterization of TiO2-coated ceramic foam prepared by modified sol-gel method and optimization of synthesis parameters in photodegradation of Acid Red 73

TiO₂ nanoparticles were synthesized by the P-25 powder modified sol-gel method under different TTIP (Titanium tetraisopropoxide) concentrations, P-25 loading and the gelation pHs. Structural properties of nanoparticles were characterized by XRD, FESEM and BET analysis. Results show that crystallinity level, particle size and the surface area are a function of P-25 loading and gelation pH, whereas TTIP concentration affects only the crystalline composition. Response surface methodology based on central composite design was used to optimize these synthesis parameters in photodegradation of Acid Red 73. The degradation efficiency was significantly affected by P-25 loading, pH value of gelation and the interaction effect between TTIP concentration and P-25 loading. The optimal values of parameters were found to be a pH of 1.34, a TTIP concentration of 0.25M and a P-25 loading of 39.76 g/L. At optimal synthesis conditions, TiO₂ film was coated on alumina foam and its structural properties were characterized by XRD, SEM and BET technique. The photocatalytic activity of the as-prepared films was found to be higher than that of the films prepared by the sol-gel method and those made from the slurries of P-25. The reasonable photocatalytic performance and good stability offered by the optimized film make it as an effective alternative for large application of water treatment.     

Photoassisted mineralization of remazole red F3B over NiO/TiO2 and CdO/TiO2 nanoparticles under simulated sunlight

In this work, a series of titania-supported NiO and CdO materials were synthesized by a modified sol-gel process. The prepared photocatalysts were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). The activities of titania-supported NiO and CdO photocatalysts for photocatalytic degradation of Remazole Red F3B (RR) dye, under simulated sunlight, were investigated. The photocatalytic mineralization of an RR dye solution over various NiO-x/TiO₂ and CdO-x/TiO₂ photocatalysts under simulated sunlight was investigated. It was worthy noticing that the photocatalytic activity of titania improved using the prepared catalysts. The prepared TiO₂, NiO-5/TiO₂, and CdO-2/TiO₂ photocatalysts exhibited higher photocatalytic activity under simulated sunlight than did commercial TiO₂. The prepared photocatalysts were stable after photocatalytic degradation of the dye. The observed photocatalytic mineralization of the dye was 51 and 71% over NiO-10/TiO₂ and CdO-2/TiO₂ after 180 min of irradiation, respectively. Juxtaposing a p-NiO-5/TiO₂ semiconductor provided a potential approach for decreasing charge recombination. The prepared photocatalystsNiO-5/TiO₂ and CdO-2/TiO₂ are promising composites for the solar detoxification of textile wastewater.     

Photocatalytic reduction of Pb(II) over TiO2: New insights on the effect of different electron donors

Experiments of Pb(II) photocatalytic removal under nitrogen over TiO₂ (Degussa P-25) were performed in the presence of electron donors such as methanol, ethanol, 2-propanol, citric acid (Cit) and formic acid (FA) in order to study their effects on the removal efficiencies. Formic acid and 2-propanol showed the highest effect, but the first one was considered a better additive because it can be used at a concentration five-fold lower and it does not introduce toxic degradation products in the system. In the case of formic acid addition at low concentration, redissolution of Pb was observed when the electron donor was completely consumed. Product formation was dependent on the reaction conditions and on the nature of electron donor, but the main identified product in all cases was zerovalent Pb, in the form of colloidal particles, as demonstrated by XRD and XPS analysis. Mechanisms involving reducing radicals were proposed to explain Pb(II) removal and the comparative efficiency of the donors.     

Synthesis of TiO2-entrapped EFAL-removed Y-zeolites: Novel photocatalyst for decomposition of 2-methylisoborneol

As a new photocatalyst, TiO₂-entrapped EFAL (extra-framework-aluminium)-removed Y-zeolites (TiO₂–EFAL-removed Y-zeolites) were synthesized, and they were applied to photocatalytic decomposition of 2-methylisoborneol (2-MIB) dissolved in water. UV-absorption spectroscopic and GC-mass spectrometric studies released that the photocatalytic decomposition of 2-MIB is achieved through formation of a cyclopentene-type intermediate. It was found by kinetic studies that TiO₂–EFAL-removed Y-zeolites are highly adsorptive and their photocatalytic quantum efficiency was about 0.04, much larger than that of Degussa P-25 TiO₂. These results suggest that TiO₂–EFAL-removed Y-zeolites would be promising photocatalysts for efficient and rapid removal of taint compounds in natural water resources.     

Photocatalytic Degradation of Polyethylene Plastic with Polypyrrole/TiO2 Nanocomposite as Photocatalyst

The photocatalytic degradation of polyethylene (PE) plastic was carried out directly under the sunlight irradiation with polypyrrole/TiO₂ (PPy/TiO₂) nanocomposite as photocatalyst, which prepared by sol-gel and emulsion polymerization methods. The photocatalytic degradation efficiency was determined by weight loss monitoring, gel permeation chromatography (GPC), atomic force microscopic (AFM) and FT-IR analysis. The photocatalytic degradations of PE plastic with pure TiO₂ and PPy were also investigated and compared with that of PPy/TiO₂. It was noticed that irradiating the PE plastic for 240 h by sunlight reduced its weight up to 35.4% and 54.4% of M _w, respectively. The AFM images showed the formation of cavities on PE plastic surface. FT–IR spectroscopic studies indicated that a strong interaction existed between the interface of PE and PPy/TiO₂ and caused the degradation of PE. The photocatalytic degradation mechanism was also discussed briefly.     

High activity TiO2 Photocatalysts Prepared by a Modified Sol–gel Method: Characterization and their Photocatalytic Activity for the Degradation of XRG and X-GL

A simple method for preparing high photocatalytic activity TiO₂ has been developed by controlled the hydrolysis of titanium butoxide with water generated “in situ” using an esterification reaction between the acetic acid and ethanol. The photocatalytic activity of the samples prepared was higher than that of the reference Degussa P25 TiO₂ for the liquid phase photocatatlytic degradation of active yellow XRG dye and cationic golden X-GL dye.