Solvent effects on microstructures and properties of three-dimensional hierarchical TiO2 microsphere structures synthesized via solvothermal approach

In Situ One-Pot Synthesis of C-Decorated and Cl-Doped Sea-Urchin-like Rutile Titanium Dioxide with Highly Efficient Visible-Light Photocatalytic Activity

Titanium dioxide (TiO₂) that offers high light-harvesting capacity and efficient charge separation holds great promise in photocatalysis. In this work, an in situ one-pot hydrothermal synthesis was explored to prepare a C-decorated and Cl-doped sea-urchin-like rutile TiO₂ (Cl-TiO₂/C). The growth of sea-urchin-like 3D hierarchical nanostructures was governed by a mechanism of nucleation and nuclei growth-dissolution-recrystallization growth from time-dependent morphology evolution. The crystal morphology and the content of Cl and C could be controlled by the volume ratio of HCl to TBOT. Systematic studies indicated that the 0.4Cl-TiO₂/C sample (the volume ratio of HCl to TBOT was 0.4) exhibited the highest visible-light photocatalytic activity for the degradation of rhodamine B, with kinetic rate constant (k) of 0.0221 min^-1, being 6.5 and 3.75 times higher than that of TiO₂ and Cl-TiO₂. The enhanced photocatalytic performance could be attributed to the high charge separation and transfer efficiency induced by Cl-doping and C decoration and the excellent light-harvesting capacity caused by its sea-urchin-like nanostructure. Moreover, the 0.4Cl-TiO₂/C sample exhibited good reusability and excellent structural stability for five cycles. This facile one-pot approach provides new insight for the preparation of a TiO₂-based photocatalyst with excellent photocatalytic performance for potential application in practical wastewater treatment.

"Tailoring the TiO2 phases through microwave-assisted hydrothermal synthesis: Comparative assessment of bactericidal activity"

Nanocrystalline titania (TiO₂) is one of the most investigated crystalline nanostructured systems in the field of materials science. The technological applications of this material are related to its optoelectronic and photocatalytic properties, which in turn are strongly dependent on the crystal phase (i.e., anatase, brookite, and rutile), particle size, and surface structure. However, systematic comparative studies of all its crystal phases are scarce in literature due to difficulties in providing a controlled synthesis, which is primarily important in obtaining the brookite phase. In this report, the synthesis of TiO₂ nanoparticles in the anatase, brookite, and rutile structures was explored, using amorphous TiO₂ as a common precursor under microwave-assisted hydrothermal conditions. The influence of parameters such as temperature, acidity, and precursor concentration on phase crystallization were investigated. The TiO₂ materials (amorphous and crystalline phases as well as commercial Degussa P25) were systematically characterized using Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible reflectance spectroscopy, and dynamic and electrophoretic light scattering. The bactericidal activity and photocatalytic antibacterial effectiveness of each material were evaluated through the determination of the minimum inhibitory and bactericidal concentrations, and via the mortality kinetic method under ultraviolet (UV) illumination under similar conditions with two bacterial groups of unique cellular structures: Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). The results are discussed with particular emphasis on the relationship between the synthesis parameters (acidity, precursor concentration, temperature and reaction time) and the bactericidal properties.

Molecularly imprinted carbon nanosheets supported TiO2: Strong selectivity and synergic adsorption-photocatalysis for antibiotics removal

In order to achieve strong specific recognition and remarkable synergy between adsorption and photocatalysis, carbon nanosheets supported TiO₂ (CT) was designed and embellished by molecular imprinting technology with ciprofloxacin (CIP) as template. The molecular imprinted CT (CT-MI) product exhibited remarkable synergy of adsorption-photocatalysis and high selectivity in both aspects, benefitted from specific recognition of imprinted layer, strong carbon adsorption and electroconductivity, and enhanced photocatalysis. Compared to the competitive pollutant, sulfamethoxazole (SMZ) in this study, selectivity coefficient was 7.2 for adsorption and 3.2 for photocatalysis, respectively. This is superior to most of the imprinted photocatalysts reported in the literature. In addition, effect of mass ratio between TiO₂ matrix to imprinted polymers, as well as water quality and composition, to the performance of final product was studied and favorable conditions were proposed. Electron transfer mode, selective recognition mode, and antibiotics degradation mechanism and pathways were also illustrated based on trapping experiments and HPLC-MS technology etc. This study confirmed that alliance between molecular imprinting, carbon nanosheets and well dispersed photocatalyst possessed broad prospect of applications in specific recognition and selective degradation of a highly toxic pollutant in a variety of mixed systems.

Au and AuCu Nanoparticles Supported on SBA-15 Ordered Mesoporous Titania-Silica as Catalysts for Methylene Blue Photodegradation

The photocatalytic degradation of methylene blue (MB) dye has been performed under UV irradiation in aqueous suspension, employing photocatalysts based on Au (1.5 wt %) and AuCu (Au/Cu = 1, 2.0 wt %), and supported on SBA-15-ordered mesoporous silica, with and without titania (Si/Ti = 3), in order to evaluate the versatility of this mesoporous support in this type of reaction of great impact from the environmental point of view. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption at -196 °C, and X-ray photoelectron spectroscopy (XPS), so as to study their structural, optical, and chemical properties. All the prepared catalysts were found to be active in the test reaction. The bimetallic AuCu-based catalysts attained very high MB degradation values, in particular AuCu/SBA-15 titania-silica sample reached 100% of dye oxidation after the monitored reaction period (120 min).