A Review on the Visible Light Active Titanium Dioxide Photocatalysts for Environmental Applications

Development of visible light active (VLA) titania photocatalysts Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO 2) semiconductor mate-rials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applica-tions. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 struc-ture, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photo-electrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bac-terial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted

Role of polymeric surfactants on the growth of manganese ferrite nanoparticles

The growth kinetics of manganese ferrite (MnFe2O4) nanoparticles was studied by solvothermal reaction of iron and manganese salts in ethylene glycol as a solvent. To explore the mechanism of the nanoparticle formation and development, polyethylene glycol (PEG) with different molecular weights and polyvinyl pyrrolidone (PVP) were used as polymeric surfactants to investigate their effects on the formation of MnFe2O4 nanoparticles. The size evolution and the size distribution not only dependent on the kind of surfactant but also on the time and temperature of reaction process. In the presence of low molecular weight PEG (PEG300), nanoparticles with diameter of 180 nm and narrow size distribution could be produced at 160°C during 12 h of reaction while the nanoparticles with average size of 330 nm were formed by using PEG300 at 200°C and 48 h. Therefore, by increasing the temperature and the time of reaction, the size of nanoparticles was increased and finally reached a critical size and then collapsed. When a large molecular weight surfactant PEG10000 was used, the nanoparticles with average size of 230 nm were formed at 180°C and 60 h. In the case of PEG300 and PEG10000 as lower and higher molecular weights, the separation between building blocks occurred after 60 h and 48 h for 180°C and 200°C, respectively. However, more collapses between primary building blocks were observed by using PEG10000. The nanoparticles were composed of small building blocks and exhibited a spherical mesocrystal structure which was demonstrated from the TEM and scanning electron microscope (SEM) results. The investigation on the growth mechanism of the nanoparticles indicated that the formation of manganese ferrite was followed by the attachment and growth of primary building blocks and their Ostwald ripening process

On-line preconcentration of ultra-trace thallium(I) in water samples with titanium dioxide nanoparticles and determination by graphite furnace atomic absorption spectrometry

A new method has been developed for the determination of Tl(I) based on simultaneous sorption and preconcentration with a microcolumn packed with TiO2 nanoparticle with a high specific surface area prepared by Sonochemical synthesis prior to its determination by graphite furnace atomic absorption spectrometry (GFAAS). The optimum experimental parameters for preconcentration of thallium, such as elution condition, pH, and sample volume and flow rate have been investigated. Tl(I) can be quantitatively retained by TiO2 nanoparticles at pH 9.0, then eluted completely with 1.0 mol L−1 HCl. The adsorption capacity of TiO2 nanoparticles for Tl(I) was found to be 25 mg g−1. Also detection limit, precision (RSD, n = 8) and enrichment factor for Tl(I) were 87 ng L−1, 6.4% and 100, respectively. The method has been applied for the determination of trace amounts of Tl(I) in some environmental water samples with satisfactory results

Reducing the Carbon Footprint of Air-Blown Bitumen Using Physisorption

This research uses experiments and molecular modeling calculations to study the efficacy of using polyphosphoric acid (PPA) grafted to silica to produce air-blown bitumen with the desired stiffness at a lower air-blowing time and temperature. Lowering the air-blowing time and temperature leads to reductions in the emitted volatile organic compounds (VOCs), the environmental carbon footprint, and the use of energy and resources. Our experiment showed that using PPA-grafted silica reduced the air-blowing time required to achieve the desired penetration [90 (0.1 mm)] and softening point (45 °C) by up to 29 and 50%, respectively, compared to neat vacuum bottom residue (VBR). Molecular modeling calculations showed that the adsorption of PPA to silica changed the intramolecular hydrogen-bond network in the backbone of PPA and promoted the interaction of PPA-grafted silica with VBR molecules, especially with VOCs. Increased intermolecular interactions facilitate the stiffening of VBR, leading to a lower duration of air blowing. Furthermore, these interactions can directly trap the VOCs and reduce their emission to the environment. The study outcomes show the merits of using PPA-grafted silica to produce the desired bitumen grades while reducing the duration of air blowing, to improve the energy efficiency and reduce the environmental impact of the process

Role of polymeric surfactants on the growth of manganese ferrite nanoparticles

The growth kinetics of manganese ferrite (MnFe2O4) nanoparticles was studied by solvothermal reaction of iron and manganese salts in ethylene glycol as a solvent. To explore the mechanism of the nanoparticle formation and development, polyethylene glycol (PEG) with different molecular weights and polyvinyl pyrrolidone (PVP) were used as polymeric surfactants to investigate their effects on the formation of MnFe2O4 nanoparticles. The size evolution and the size distribution not only dependent on the kind of surfactant but also on the time and temperature of reaction process. In the presence of low molecular weight PEG (PEG(300)), nanoparticles with diameter of 180 nm and narrow size distribution could be produced at 160 degrees C during 12 h of reaction while the nanoparticles with average size of 330 nm were formed by using PEG(300) at 200 degrees C and 48 h. Therefore, by increasing the temperature and the time of reaction, the size of nanoparticles was increased and finally reached a critical size and then collapsed. When a large molecular weight surfactant PEG(10000) was used, the nanoparticles with average size of 230 nm were formed at 180 degrees C and 60 h. In the case of PEG(300) and PEG(10000) as lower and higher molecular weights, the separation between building blocks occurred after 60 h and 48 h for 180 degrees C and 200 degrees C, respectively. However, more collapses between primary building blocks were observed by using PEG(10000). The nanoparticles were composed of small building blocks and exhibited a spherical mesocrystal structure which was demonstrated from the TEM and scanning electron microscope (SEM) results. The investigation on the growth mechanism of the nanoparticles indicated that the formation of manganese ferrite was followed by the attachment and growth of primary building blocks and their Ostwald ripening process. (C) 2012 Elsevier B.V. All rights reserved