Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Although humans have been exposed to airborne nanosized particles (NSPs; < 100 nm) throughout their evolutionary stages, such exposure has increased dramatically over the last century due to anthropogenic sources. The rapidly developing field of nanotechnology is likely to become yet another source through inhalation, ingestion, skin uptake, and injection of engineered nanomaterials. Information about safety and potential hazards is urgently needed. Results of older bio-kinetic studies with NSPs and newer epidemiologic and toxicologic studies with airborne ultrafine particles can be viewed as the basis for the expanding field of nanotoxicology, which can be defined as safety evaluation of engineered nanostructures and nanodevices. Collectively, some emerging concepts of nanotoxicology can be identified from the results of these studies. When inhaled, specific sizes of NSPs are efficiently deposited by diffusional mechanisms in all regions of the respiratory tract. The small size facilitates uptake into cells and transcytosis across epithelial and endothelial cells into the blood and lymph circulation to reach potentially sensitive target sites such as bone marrow, lymph nodes, spleen, and heart. Access to the central nervous system and ganglia via translocation along axons and dendrites of neurons has also been observed. NSPs penetrating the skin distribute via uptake into lymphatic channels. Endocytosis and biokinetics are largely dependent on NSP surface chemistry (coating) and in vivo surface modifications. The greater surface area per mass compared with larger-sized particles of the same chemistry renders NSPs more active biologically. This activity includes a potential for inflammatory and pro-oxidant, but also antioxidant, activity, which can explain early findings showing mixed results in terms of toxicity of NSPs to environmentally relevant species. Evidence of mitochondrial distribution and oxidative stress response after NSP endocytosis points to a need for basic research on their interactions with subcellular structures. Additional considerations for assessing safety of engineered NSPs include careful selections of appropriate and relevant doses/concentrations, the likelihood of increased effects in a compromised organism, and also the benefits of possible desirable effects. An interdisciplinary team approach (e.g., toxicology, materials science, medicine, molecular biology, and bioinformatics, to name a few) is mandatory for nanotoxicology research to arrive at an appropriate risk assessment.

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Nanotoxicology: An Emerging Discipline Evolving from Studies of Ultrafine Particles

Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Understanding TiO2 photocatalysis: mechanisms and materials.

http://publicationslist.org/data/meng.chong/ref-18/sdarticle.pdf

Recent Developments in Photocatalytic Water Treatment Technology: A Review

Photoinduced reactivity of titanium dioxide

Catalysis for NOx abatement

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1-xMxO2±δ The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25 The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2

Structure and Photocatalytic Activity of Ti1-xMxO2±δ (M = W, V, Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion Method

Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer−Emmett−Teller surface area, thermogravimetric−differential thermal analysis, FT-IR spectroscopy, NMR, UV−vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving Ti...

Synthesis and structure of nanocrystalline TiO2 with lower band gap showing high photocatalytic activity.

The solar photocatalytic degradation of various dyes such as methylene blue (MB), remazol brill blue R (RBBR) and orange G (OG) has been studied over combustion synthesized nano TiO2 and the activity was compared with that of commercial Degussa P-25 TiO2 under similar conditions. The effect of catalyst loading, initial concentrations of the dyes and the deactivation studies of the catalysts were also investigated. The catalyst was characterized by techniques like X-ray diffraction (XRD), BET, gravimetric-differential thermal analysis (TG-DTA), IR and UV absorption. The initial degradation rates with combustion synthesized nano TiO2 was 20 times higher for RBBR, 4 times higher for MB and 1.6 times higher for OG, compared to Degussa P-25 TiO2. The enhanced photocatalytic activity of combustion synthesized catalyst is attributed to the crystallinity, nano-size, large amount of surface hydroxyl species and reduced band-gap.

Solar photocatalytic degradation of dyes: high activity of combustion synthesized nano TiO2

The 8–10 nm pure anatase phase titania with $156 m^2/g$ BET surface area was prepared by solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and BET surface area. This catalyst was used for the photocatalytic degradation of various dyes such as heteropolyaromatic dye (Methylene blue), anthraquinonic dye (Alizarin S), and azoic dyes (Methyl red, Congo red, and Orange G). The effect of catalyst loading, initial concentrations of the dyes, pH, and transition metal doping on $TiO_2$ was investigated. Substitution of $TiO_2$ with transition metal had a detrimental effect on the photocatalytic activity. However, this inhibition effect was not observed with Pt impregnated $TiO_2$. This was attributed to the metals being in ionic state in metal substituted $TiO_2$ synthesized by combustion method, and zero state of metal in impregnated catalysts as evidenced by XPS study. The degradation of dyes was also investigated in solar exposure. The photoactivity of the combustion synthesized titania was higher than commercial $TiO_2$(Degussa P-25) for both UV and solar exposure. The experimental data followed Langmuir–Hinshelwood (L–H) rate form and the kinetic parameters were obtained.

M. S. Hegde

Papers

Catalysis for NOx abatement

Structure and Photocatalytic Activity of Ti1-xMxO2±δ (M = W, V, Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion Method

Synthesis and structure of nanocrystalline TiO2 with lower band gap showing high photocatalytic activity.

Solar photocatalytic degradation of dyes: high activity of combustion synthesized nano TiO2

Photocatalytic degradation of various dyes by combustion synthesized nano anatase TiO2