Phase control and photocatalytic properties of nano-sized titania particles by gas-phase pyrolysis of TiCl4

Study of paramagnetic defect centers in as-grown and annealed TiO2 anatase and rutile nanoparticles by a variable-temperature X-band and high-frequency (236 GHz) EPR

Detailed EPR investigations on as-grown and annealed TiO₂ nanoparticles in the anatase and rutile phases were carried out at X-band (9.6 GHz) at 77, 120-300 K and at 236 GHz at 292 K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti³⁺, O^-, adsorbed oxygen (O₂^-) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O₂^-) and the Fe³⁺ ions in both Ti⁴⁺ substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000° C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236 GHz) EPR data on anatase and rutile samples, recorded in the region about g = 2.0 exhibit resolved EPR lines, due to O^- and O₂^- ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn²⁺ and Mn⁴⁺ ions in anatase.

4-Nitroaniline Degradation by TiO2Catalyst Doping with Manganese

Stainless steel anode covered with layer film of TiO2doped with manganese was utilized to decompose 4-nitroaniline in rectangular borosilicate glass reactor, while stainless steel mesh was chosen as cathode; the anode and cathode were connected to the direct-current power; meantime two 60 W (λmax= 365 nm) UV lamps were used as light source. The microstructures on TiO2before and after being doped with manganese were analyzed by energy disperse X-ray (EDX) and X-ray diffraction (XRD). The performance of degradation of 4-nitroaniline was evaluated by analyzing cracking ratio of 4-nitroaniline ring, the chemical oxygen demand (COD), and total organic carbon (TOC) in remaining solution. Monitored parameters during all the photocatalytic reaction including dissolved oxygen, direct voltage, and radiation dosage of ultraviolet rays were investigated. When dissolved oxygen concentration, direct voltage, and radiation dosage of ultraviolet rays were, respectively, equivalent to 9 mg/L, 24 V, and 1200 μW/cm2, the degradation ratio of 4-nitroaniline reached maximum. The experimental results indicated that cracking ratio of 4-nitroaniline ring and the removal ratio of COD and TOC were, respectively, more than 99%, 85%, and 80% when reaction was run for 10 hours. The values of COD and TOC were, respectively, less than 16 mg/L and 8 mg/L while the experiment was finished.

Effect of titanium dioxide nanomaterials and ultraviolet light coexposure on African clawed frogs (Xenopus laevis)

Titanium dioxide nanomaterials (nano-TiO(2) ) exhibit stronger photochemical oxidation/reduction capacity compared with their bulk counterparts, but the effectiveness of nano-TiO(2) interaction with ultraviolet (UV) light strongly depends on particle size. In this study, the dependence of nano-TiO(2) toxicity on particle size and interaction with UV light were investigated. Toxicity tests with Xenopus laevis included eight concentrations of nano-TiO(2) in the presence of either white light or UVA (315-400 nm). We quantified viability and growth of Xenopus laevis. Results showed that, regardless of UV light exposure, increasing TiO(2) concentration decreased X. laevis survival (p < 0.05). Coexposure to 5-nm TiO(2) and UVA caused near-significant decreases in X. laevis survival (p = 0.08). Coexposure to 10-nm TiO(2) and UVA significantly decreased X. laevis survival (p = 0.005). However, coexposure to 32-nm TiO(2) and UVA had no statistical effect on X. laevis survival (p = 0.8). For all three particle sizes, whether alone or with UV light, the nano-TiO(2) concentrations significantly affected growth of tadpoles as determined by total body length, snout-vent length, and developmental stage. High-concentration TiO(2) solutions suppressed tadpole body length and delayed developmental stages. Further research to explore reasons for the growth and mortality in tadpoles is still underway in our laboratory. Given the widespread application of nano-TiO(2) , our results may be useful in the management of nano-TiO(2) released from industrial, municipal, and nonpoint sources.