Synergistic effect of nitrate-doped TiO2 aerosols on the fast photochemical oxidation of formaldehyde

Enhanced H-abstraction contribution for oxidation of xylenes via mineral particles: Implications for particulate matter formation and human health

Xylenes are important aromatic hydrocarbons having broad industrial emissions and profound implication to air quality and human health. Generally, homogeneous atmospheric oxidation of xylenes is initiated by hydroxyl radical (OH) resulting in minor H-abstraction and major OH-addition pathways. However, the effect of mineral particles on the homogeneous atmospheric oxidation mechanism of xylenes is still not well understood. In the present study, the heterogeneous atmospheric oxidation of xylenes on mineral particles (TiO₂) is examined in detail. Both the experimental data and theoretical calculations are combined to achieve the feast. The experimental results detected a major H-abstraction (≥87.18%) and minor OH-addition (≤12.82%) pathways for the OH-initiated heterogeneous oxidation of three xylenes on TiO₂ under ultraviolet (UV) irradiation. Theoretical calculations demonstrated favorable H-abstraction on methyl group of xylenes by surface OH with large exothermic energies, because of the reason that their methyl group rather than the phenyl ring is more occupied by TiO₂ via hydrogen bonding. Furthermore, the particle monitor and acute risk assessment results indicated that the H-abstraction products significantly enhance the formation of particulate matter and health risk to human beings. Taken together, these results indicate that the atmospheric oxidation mechanism of xylenes is altered in the presence of mineral particles, highlighting the necessity to re-evaluate its implication in the environment and human health.

Study of the surface species during thermal and plasma-enhanced atomic layer deposition of titanium oxide films using in situ IR-spectroscopy and in vacuo X-ray photoelectron spectroscopy

By the powerful combination of in situ FTIR and in vacuo XPS, the surface species during ALD of TDMAT with different reactants could be identified.

Enhanced photocatalytic activity of rGO/TiO2 for the decomposition of formaldehyde under visible light irradiation

Due to the low concentration of indoor air contaminants, photocatalytic technology shows low efficiency for indoor air purification. The application of TiO₂ for photocatalytic removal of formaldehyde is limited, because TiO₂ can only absorb ultraviolet (UV) light. Immobilization of TiO₂ nanoparticles on the surface of graphene can improve the visible light photocatalytic activity and the adsorption capacity. In this study, rGO (reduced graphene oxide)/TiO₂ was synthesized through a hydrothermal method using titanium tetrabutoxide and graphene oxide as precursors, and was used for the degradation of low concentration formaldehyde in indoor air under visible light illumination. Characterization of the crystalline structure and morphology of rGO/TiO₂ revealed that most GO was reduced to rGO during the hydrothermal treatment, and anatase TiO₂ nanoparticles (with particle size of 15-30nm) were dispersed well on the surface of the rGO sheets. rGO/TiO₂ exhibited excellent photocatalytic activity for degradation of formaldehyde in indoor air and this can be attributed to the role of rGO, which can act as the electron sink and transporter for separating photo-generated electron-hole pairs through interfacial charge transfer. Furthermore, rGO could adsorb formaldehyde molecules from air to produce a high concentration of formaldehyde on the surface of rGO/TiO₂. Under visible light irradiation for 240min, the concentration of formaldehyde could be reduced to 58.5ppbV. rGO/TiO₂ showed excellent moisture-resistance behavior, and after five cycles, rGO/TiO₂ maintained high photocatalytic activity for the removal of formaldehyde (84.6%). This work suggests that the synthesized rGO/TiO₂ is a promising photocatalyst for indoor formaldehyde removal.

Preparation and characterization of Sn/La co-doped TiO2 nanomaterials and their phase transformation and photocatalytic activity

The pure, tin (Sn)-doped, lanthanum (La)-doped and Sn/La co-doped titanium dioxide (TiO2) nanomaterials were synthesized using sol-gel method followed by calcination at the temperature of 360 °C, 450 °C and 600 °C, respectively. The structures of the nanomaterials were characterized by X-ray diffraction (XRD), Thermogravimetric (TG), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrum (EDS), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectrum (XPS), Diffuse Reflectance Spectrum (DRS), Photoluminescence Spectrum (PL), Brunauer-Emmett-Teller Measurements (BET), respectively. The photocatalytic property of the photocatalysts under UV light was evaluated through the degradation of Rhodamine B (RhB). The results show that the anatase-rutile phase transition is promoted by Sn-doping while La-doping retards the phase transition. However, La doping plays a major role in the process of phase transformation. The photocatalytic activity of pure TiO2 is affected by annealing temperature remarkably and the optimal annealing temperature is 450 °C. The photocatalytic activity of TiO2 is enhanced significantly by Sn and La doping at three different temperatures. Sn/La-TiO2 exhibits the highest degradation rates and the fastest reaction rates probably owing to the synergistic effect of Sn4+ and La3+ ions in inhibiting the recombination of photogenerated electron-hole pairs. The formation of extra surface hydroxyl groups and additional surface area are also beneficial for the photocatalytic activity.

Photochemical Vapor Generation of Tellurium: Synergistic Effect from Ferric Ion and Nano-TiO2

Photochemical vapor generation (PVG) is emerging as a promising analytical tool for Te determination, thanks to its efficient matrix separation, and simple and green procedure. However, the low PVG generation efficiency of Te is the bottleneck for its wide application in environmental samples containing trace Te. Herein, we reported a high efficient PVG for Te determination by synergistic effect of ferric ion and nano-TiO₂. The analytical sensitivity was enhanced approximately 15-fold for Te(IV) in the presence of both ferric ions and nano-TiO₂, comparing to conventional PVG. Besides, the use of nano-TiO₂ can provide Te(VI) and Te(IV) an equal and high PVG efficiency in the presence of ferric ions, owned to the high photocatalytic performance of TiO₂ under short-wavelength UV irradiation (254 and 185 nm). Under the optimized experimental conditions, a detection limit of 1.0 ng L^-1 was obtained. The precision of replicate measurements was 2.3% (RSD, n = 7) at 0.5 μg L^-1 for Te(IV). The methodology was validated by successful determination of Te in surface waters and two standard reference sediment samples. To our best knowledge, this is the first report of the synergistic enhancement of transitional metal ions and nano-TiO₂ in PVG, which possesses potential for highly sensitive determination of vapor-forming elements.