Effects of Structural Factors of Hydrated TiO2 on Rutile TiO2 Pigment Preparation via Short Sulfate Process

The selection of a nitrogen precursor for the construction of N-doped titanium dioxide with enhanced photocatalytic activity for the removal of gaseous toluene

The preparation of nitrogen-doped TiO2 (i.e., N-TiO2) catalysts is a highly effective option to improve the photocatalytic activity of TiO2. Nonetheless, relatively little is known about the effects of dopant precursors selected for their preparation with regard to the photocatalytic efficacy. In this study, three types of dopants are selected and used as N sources (urea (U), melamine (M), and aqueous ammonia (A)) for N-TiO2 samples with the name codes of NTU, NTM, and NTA, respectively. The photocatalytic efficacy of these N-TiO2 samples is examined against toluene in a packed bed flow reactor. Under optimal conditions (e.g., relative humidity (RH) = 20% and gas hourly space velocity (GHSV) = 1698 h-1), the superiority of NTA is evident over others with a quantum efficiency (QE) of 7.03 × 10-4 molecules photon-1, a space time yield (STY) of 1.38 × 10-4 molecules photon-1 mg-1, and a specific clean air delivery rate (SCADR) of 1148.8 L g-1 h-1. The analysis based on in-situ diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography-mass spectrometry confirms the formation of several intermediates such as benzyl alcohol, benzaldehyde, benzoic acid, and alkane species through ring opening reactions. In addition, the prepared NTA photocatalyst exhibits the highest toluene photocatalytic degradation efficiency among all TiO2-based catalysts surveyed to date. Overall, this study offers as a valuable guideline for the development of advanced TiO2 catalytic systems (such as N-TiO2) for the treatment of aromatic hydrocarbons in indoor air.

Low-temperature Ruby Crystal Growth Via a Supersaturation Process Based on Flux Decomposition

Crystal growth methods that do not require high temperatures are highly needed for the facile growth of oxide single crystals with melting points of several thousand degrees Celsius. This paper represents the first report of a method for the low-temperature growth of ruby crystals (chromium-doped Al2O3) at 750 °C, which is one-third of the conventionally required temperature (2050 °C). In solution-based crystal growth, the target crystal is grown at a temperature considerably lower than its melting point. However, conventional crystal growth processes involving solvent evaporation and cooling require high temperatures to completely liquefy the material, with previously reported solution growth temperatures of ≈1100 °C. Supersaturation based on the decomposition of crystal-solvent intermediates eliminates the need to completely liquefy the material, enabling low-temperature crystal growth. The combination of computational and experimental investigations helps determine the optimum conditions for low-temperature crystal growth. The proposed method is a novel green process that breaks the conventional frontiers of crystal growth while ensuring eco-friendliness and low energy consumption. In addition, its scope can potentially be expanded to the synthesis of various crystals and direct growth on substrates with low melting points.

8-Bromo-cAMP attenuates human airway epithelial barrier disruption caused by titanium dioxide fine and nanoparticles

Titanium dioxide fine particles (TiO2-FPs) and nanoparticles (TiO2-NPs) are the most widely used whitening pigments worldwide. Inhalation of TiO2-FPs and TiO2-NPs can be harmful as it triggers toxicity in the airway epithelial cells. The airway epithelium serves as the respiratory system's first line of defense in which airway epithelial cells are significant targets of inhaled pathogens and environmental particles. Our group previously found that TiO2-NPs lead to a disrupted barrier in the polarized airway epithelial cells. However, the effect of TiO2-FPs on the respiratory epithelial barrier has not been examined closely. In this study, we aimed to compare the effects of TiO2-FPs and TiO2-NPs on the structure and function of the airway epithelial barrier. Additionally, we hypothesized that 8-Bromo-cAMP, a cyclic adenosine monophosphate (cAMP) derivative, would alleviate the disruptive effects of both TiO2-FPs and TiO2-NPs. We observed increased epithelial membrane permeability in both TiO2-FPs and TiO2-NPs after exposure to 16HBE cells. Immunofluorescent labeling showed that both particle sizes disrupted the structural integrity of airway epithelial tight junctions and adherens junctions. TiO2-FPs had a slightly more, but insignificant impact on the epithelial barrier disruption than TiO2-NPs. Treatment with 8-Bromo-cAMP significantly attenuated the barrier-disrupting impact of both TiO2-FPs and TiO2-NPs on cell monolayers. Our study demonstrates that both TiO2-FPs and TiO2-NPs cause comparable barrier disruption and suggests a protective role for cAMP signaling. The observed effects of TiO2-FPs and TiO2-NPs provide a necessary understanding for characterizing the pathways involved in the defensive role of the cAMP pathway on TiO2-induced airway barrier disruption.

Preparation of Hydrated TiO2 Particles by Hydrothermal Hydrolysis of Mg/Al-Bearing TiOSO4 Solution

As the byproduct in the smelting process of vanadium titano-magnetite, titanium-bearing blast furnace slag (TBFS) can be converted to a titanyl sulfate (TiOSO₄) solution containing MgSO₄ and Al₂(SO₄)₃ impurities via dissociation by concentrated H₂SO₄ (80-95%) at 80-200 °C, followed by leaching with H₂O at 60-85 °C. In this study, hydrated TiO₂ was prepared by hydrothermal hydrolysis of a Mg/Al-bearing TiOSO₄ solution at 120 °C and the hydrolysis law was investigated. The experimental results indicate that MgSO₄ and Al₂(SO₄)₃ accelerated the hydrolysis and significantly affected the particle size (increasing the primary agglomerate size from 40 to 140 nm) and dispersion (reducing the aggregate size from 12.4 to 1.5 μm) of hydrated TiO₂. A thermodynamic equilibrium calculation showed TiOSO₄ existed as TiO²⁺ and SO₄^2- in the solution, and MgSO₄ and Al₂(SO₄)₃ led to little change of [TiO²⁺], but an obvious decrease of [H⁺], which favored the hydrolysis process. At the same time, the coordination-dissociation mechanism of SO₄^2- and Al(SO₄)₂^- facilitated the lap bonding of Ti-O-Ti, promoting the growth of hydrated TiO₂ synergistically.

The light aging behavior of daylight fluorescent paints: a colorimetric, photographic, Raman spectroscopic and fluorescence spectroscopic study

Daylight fluorescent pigments with their intense color effects have attracted great interest among artists since their market launch in the mid-twentieth century. Since then they have been widely used in the visual arts. The pigments are mainly compositions of organic fluorescent dyes and optical brighteners diluted in an insoluble resin. Due to the susceptibility of the dyes to visible and UV radiation, their lightfastness is comparatively low. This paper presents a comprehensive study of the color and fluorescence changes of daylight fluorescent paints upon exposure in visible light and ultraviolet radiation conducted on mock-ups of commercial daylight fluorescent pigments. The different aging characteristics of the pigments depend on the color tone. They were recorded by means of photographic and colorimetric documentation. In addition, Raman spectroscopy was used to identify the main dyes of the various pigments, even in the complex system of paints, consisting of primer, binder, resin and dyes, and to determine their degradation during aging. Fluorescence spectroscopy revealed that the change in fluorescent color may not only be due to the decrease in dye concentration, but also to the transformation of the original dyes into other fluorescent compounds during light aging. Finally, this paper provides recommendations for the presentation of artworks containing daylight fluorescent pigments.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s40494-022-00812-4.