Effects of Single Metal-Ion Doping on the Visible-Light Photoreactivity of TiO_2

Titanium dioxide (M-TiO_2), which was doped with 13 different metal ions (i.e., silver (Ag^+), rubidium (Rb^+), nickel (Ni^(2+)), cobalt (Co^(2+)), copper (Cu^(2+)), vanadium (V^(3+)), ruthenium (Ru^(3+)), iron (Fe^(3+)), osmium (Os^(3+)), yttrium (Y^(3+)), lanthanum (La^(3+)), platinum (Pt^(4+), Pt^(2+)), and chromium (Cr3+, Cr6+)) at doping levels ranging from 0.1 to 1.0 at. %, was synthesized by standard sol−gel methods and characterized by X-ray diffraction, BET surface area measurement, SEM, and UV−vis diffuse reflectance spectroscopy. Doping with Pt(IV/II), Cr(III), V(III), and Fe(III) resulted in a lower anatase to rutile phase transformation (A−R phase transformation) temperature for the resultant TiO_2 particles, while doping with Ru(III) inhibited the A−R phase transformation. Metal-ion doping also resulted in a red shift of the photophysical response of TiO_2 that was reflected in an extended absorption in the visible region between 400 and 700 nm. In contrast, doping with Ag(I), Rb(I), Y(III), and La(III) did not result in a red shift of the absorption spectrum of TiO_2. As confirmed by elemental composition analysis by energy dispersive X-ray spectroscopy, the latter group of ions was unable to be substituted for Ti(IV) in the crystalline matrix due to their incompatible ionic radii. The photocatalytic activities of doped TiO_2 samples were quantified in terms of the photobleaching of methylene blue, the oxidation of iodide (I^(−)), and the oxidative degradation of phenol in aqueous solution both under visible-light irradiation (λ > 400 nm) and under broader-band UV−vis irradiation (λ > 320 nm). Pt- and Cr-doped TiO_2, which had relatively high percentages of rutile in the particle phase, showed significantly enhanced visible-light photocatalytic activity for all three reaction classes

Effect of synthesis parameters on the structural characteristics and photo-catalytic activity of ordered mesoporous titania

In this dissertation, pristine ordered, metal- (Fe, Co, and Ni), and nonmetal- (N) doped ordered mesoporous titania were synthesized via co-precipitation using the EISA method combined with the LCT pathway. In addition, for un-doped mesoporous TiO2, various parameters were systematically varied including solvent evaporation temperature, surfactant extraction conditions, molar surfactant/titanium ratio, and titanium source. Moreover, the photocatalytic activity of the synthesized materials was evaluated in the photodegradation of phenol under various irradiation sources

Photocatalytic degradation of organic compounds using carbon based composite catalysts

In recent decades, the applications of advanced oxidation processes (AOPs) for organic pollutants treatment in wastewater have been thoroughly investigated. These techniques base on chemical destruction and give a complete solution to the problem of wastewater containing toxic organics. Among these processes, semiconductor-based photocatalytic process has been employed as a low-cost, environmentally friendly and sustainable technique to purify water/wastewater. Meanwhile, chemical oxidation process is also considered as an effective remediation technique to reduce the concentrations of targeted toxic organics in wastewater to acceptable levels.The aim of this work is emphasizing the role of new synthesized catalysts in advanced oxidation process for wastewater treatment. The key conclusion of this thesis is that novel photocatalysts being capable to degrade organics in aqueous phase at room temperature were successfully synthesized and the investigation of “green cobalt based catalysts” for degradation of organic pollutants via advanced oxidation processes was achieved. Various types of catalysts were synthesized with hydrothermal carbonization method or wet impregnation method, and used for degradation of phenol in aqueous phase with UV-vis and visible light irradiation. Titanates: ZnTiO3, FeTiO3 and Bi4Ti3O12 were modified by coating cobalt (Co) to prepare photocatalysts. Microcarbon spheres were also synthesized by hydrothermal method, and used to support TiO2 (C-TiO2), nanoscaled zerovalent iron (nano-Fe0@CS), cobalt (micro-CS@Co) and graphitic carbon nitride (C-g-CN). All of these catalyst materials were tested for phenol degradation. Some of these synthesized catalysts were also examined for activating peroxymonosulfate (PMS, Oxone) for the decomposition of phenol

A review on plasmonic metal-TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

The titania based nanomaterials are an attractive candidates for energy and environmental applications. TiO2 is one of the most important photocatalyst for its special multiple characteristics like high reactivity, low toxicity, low cost, high flexibility, long term stability especially in aqueous medium, shows relatively high energy conversion efficiency, easy to prepare several modifications with various morphologies, with good recycle ability, favorable band edge positions and superior physicochemical and optoelectronic properties. However, large band gap of titania and massive charge carrier recombination impairs its wide photocatalytic applications. As an alternative to various strategies reported extensively in literature, noble metal deposition on the titania surface seems to be effective and reliable method for increasing the life time of excitonic pairs and to extend the band gap absorption to visible range of the solar spectrum. In this focused review, we discuss the fundamental and critical issues in the photocatalytic activity of metal deposited titania taking into consideration the influence of various parameters like preparation methods, metal dispersion on titania, formation of heterojunctions and optimum metal loadings on the interfacial charge carrier dynamics. The metal deposition onto the varied hierarchical morphology, crystal structure, defective surface of titania along with extended modification like simultaneous doping and heterostructure coupling with other semiconductors is also highlighted. It was revealed that deposited metal is involved in multiple crucial roles like; (i) it serves as passive electron sink with high capacity to store electrons to suppress photogenerated charge carrier recombination; (ii) it facilitates rapid dioxygen reduction to generate reactive free radicals; (iii) visible light response for titania can be achieved through surface plasmon resonance effect; (iv) direct excitation of metal nanoparticles especially under visible light and vectorial electron transfer to the TiO2 CB. This review attempts to provide a comprehensive update of design and fabrication of metallization on the surface of TiO2 semiconductor particles highlighting some of the advancements made in the energy and environment applications. © 2015 Elsevier B.V. All rights reserved

Catalysis by Metals on Perovskite-Type Oxides

The acceptance and preference of the sensory properties of foods are among the most important criteria determining food choice. Sensory perception and our response to food products, and finally food choice itself, are affected by a myriad of intrinsic and extrinsic factors. The pressing question is, how do these factors specifically affect our acceptance and preference for foods, both in and of themselves, and in combination in various contexts, both fundamental and applied? In addition, which factors overall play the largest role in how we perceive and behave towards food in daily life? Finally, how can these factors be utilized to affect our preferences and final acceptance of real food and food products from industrial production and beyond for healthier eating? A closer look at trends in research showcasing the influence that these factors and our senses have on our perception and affective response to food products and our food choices is timely. Thus, in this Special Issue collection “Consumer Preferences and Acceptance of Food Products”, we bring together articles which encompass the wide scope of multidisciplinary research in the space related to the determination of key factors involved linked to fundamental interactions, cross-modal effects in different contexts and eating scenarios, as well as studies that utilize unique study design approaches and methodologies

Visible light responsive titania photocatalysts codoped by nitrogen and metal (Fe, Ni, Ag, or Pt) for remediation of aqueous pollutants

Various cation and nitrogen doped and codoped TiO2 photocatalysts, such as N–TiO2, Pt–TiO2, N–Fe–TiO2, N–Ni–TiO2, N–Ag–TiO2 and N–Pt–TiO2, were prepared by an acid-catalysed sol–gel process. The photocatalysts were characterised by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, UV–visible diffuse reflectance absorption spectroscopy (UV–vis DRS), and X-ray photoelectron spectroscopy (XPS). The activities of the photocatalysts were evaluated in photodegradation of phenol solutions under simulated sunlight irradiations. A negative effect of some transition metals (iron and nickel) onphotocatalysis was observed on N-metal codoped TiO2, while enhancements in photocatalysis from noble metals (silver and platinum) were obtained. N–Pt codoped TiO2 showed a higher activity under UV–vis irradiations than Degussa P25, with an enhancement of 5.9 times higher. The synergistic effect of N–Pt-codoping was ascribed to the multivalent states of platinum. In addition, photocatalytic activity of N-, Pt-doped and N–Pt-codoped materials were further investigated under visible light irradiations with lambda > 430 nm and lambda > 490 nm. This study therefore demonstrated a promising strategy for design of highly efficient photocatalysts for remediation of aqueous pollutants

Combinatorial doping of TiO_2 with platinum (Pt), chromium (Cr), vanadium (V), and nickel (Ni) to achieve enhanced photocatalytic activity with visible light irradiation

Titanium dioxide (TiO_2) was doped with the combination of several metal ions including platinum (Pt), chromium (Cr), vanadium (V), and nickel (Ni). The doped TiO_2 materials were synthesized by standard sol-gel methods with doping levels of 0.1 to 0.5 at.%. The resulting materials were characterized by x-ray diffraction (XRD), BET surface-area measurement, scanning electron microscopy (SEM), and UV-vis diffuse reflectance spectroscopy (DRS). The visible light photocatalytic activity of the codoped samples was quantified by measuring the rate of the oxidation of iodide, the rate of degradation of methylene blue (MB), and the rate of oxidation of phenol in aqueous solutions at λ > 400 nm. 0.3 at.% Pt-Cr-TiO_2 and 0.3 at.% Cr-V-TiO_2 showed the highest visible light photocatalytic activity with respect to MB degradation and iodide oxidation, respectively. However, none of the codoped TiO_2 samples were found to have enhanced photocatalytic activity for phenol degradation when compared to their single-doped TiO_2 counterparts

Highly dispersed FeOOH to enhance photocatalytic activity of TiO2 for complete mineralisation of herbicides

Although there were many new photocatalysts reported recently, TiO2 has still been considered as one of the best candidates for real application of environmental decontamination. Fe-based oxides were synthesised as efficient and equally important non-toxic active species to improve the efficiency of TiO2 photocatalysts. Such nano-architectured FeOx/TiO2 was tested for herbicides mineralisation e.g. 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4-dichlorophenoxyacetic acid (2,4-D) under full arc light irradiation. The consistent results were achieved by HPLC, TOC and UV–vis spectra measurements, which show among three Fe species, Fe4NO3(OH)11, FeOOH and Fe2O3, FeOOH is the best to improve TiO2 activity. This active specie of FeOOH was readily controlled by synthesis temperature and precursor concentration, leading to 250 °C being the optimum temperature for the synthesis of very stable FeOOH/TiO2 nanocomposite with excellent photocatalytic activity, representing nearly two times activity of the benchmark PC50 TiO2 photocatalyst for all herbicides tested. Such high activity was attributed to the enhanced photo-generated electron-hole separation and improved generation of hydroxyl radicals by FeOOH. The multifunction of FeOOH is very crucial for organic pollutants mineralisation. The mechanistic studies also show that degradation of 2,4,6-TCP was mostly dominated by hydroxyl radicals and superoxide radicals. The possible degradation pathway of 2,4,6-TCP was also proposed