Silica Sol-gel Coatings with Improved Light Transmittance and Stability

Silica sol-gel coatings on different substrate materials and their use as model systems have been studied. Mesoporous silica coatings with thicknesses of 85 - 135 nm and porosity of 18 ˗ 37% were prepared by dip-coating on polycarbonate and glass substrates. In order to eliminate the shrinkage of the porous structure acid or base vapour treatment was applied. Thickness and refractive index of the coatings were determined by analysing the transmittance spectra of the samples. Ellipsometric porosimetry measurements were carried out to determine the porosity, pore radius distribution, thickness and refractive index. The thickness of the samples was further confirmed by scanning electron microscopy. The adsorption capacity of the porous coatings was also studied by dye impregnation tests. The temporal stability of the samples was investigated by UV-Vis spectrometry and it was found that the advantageous optical properties (Tmax = 98 – 99%) of the samples remained constant even after a 1 year storage period

Effect of heat treatment temperature on the morphology and upconversion properties of LaF3:Yb,Er nanoparticles

LaF 3 :5%Yb 3+ ,0.5%Er 3+ upconverting nanoparticles were synthesized with co-precipitation method and heat treated at temperatures 300–600 °C. The morphology of the particles was characterized by high-resolution transmission electron microscopy coupled with energy-dispersive spectrometry and dynamic light scattering. Crystal structure was studied by X-ray diffraction (XRD), and thermal behaviour was investigated by simultaneous thermogravimetry and differential thermal analysis (TG/DTA). Upconversion behaviour was studied in detail by fluorescence spectroscopy, with 980 nm excitation. Particle sizes increased with increasing heat treatment temperature, and samples showed significant aggregation above 500 °C. Hexagonal LaF 3 crystal structure was identified for all samples, with increased crystallinity after heat treatment at 400 °C, which was corroborated with TG/DTA results. XRD and energy-dispersive spectrometry results revealed that at higher temperatures new crystal phases formed, as some Yb 3+ and Er 3+ dopant ions segregated into new nanocrystals, made of, for example, YbOF and YbOOH, which caused a significant decrease in the upconversion emission of the samples. The highest upconversion emission was achieved after heat treatment at 400 °C

Effect of Silver Modification on the Photoactivity of Titania Coatings with Different Pore Structures

Nanostructured photoactive systems are promising for applications such as air and water purification, including self-cleaning coatings. In this study, mesoporous TiO2 sol-gel coatings with different pore structures were prepared and modified with silver by two methods: the “mixing” method by adding AgNO3 to the precursor sol, and the “impregnation” method by immersing the samples in AgNO3 solution (0.03 and 1 M) followed by heat treatment. Our aim was to investigate the effects that silver modification has on the functional properties (e.g., those that are important for self-cleaning coatings). Transmittance, band gap energy, refractive index, porosity and thickness values were determined from UV-Vis spectroscopy measurements. Silver content and structure of the silver modified samples were characterized by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, High-resolution transmission electron microscopy and Energy Dispersive X-ray Spectrometry elemental mapping measurements. Wettability properties, including photoinduced wettability conversion behavior were investigated by water contact angle measurements. Photoactivity was studied under both UV and visible light with rhodamine 6G and methylene blue dye molecules, at the liquid–solid and air–solid interfaces modeling the operating conditions of self-cleaning coatings. Samples made with “impregnation” method showed better functional properties, in spite of their significantly lower silver content. The pore structure influenced the Ag content achieved by the “impregnation” method, and consequently affected their photoactivity

Self-division of giant vesicles driven by an internal enzymatic reaction

Giant unilamellar vesicles having pH-sensitive bilayers can undergo self-division triggered by an internal enzymatic (urea–urease) reaction coupled to a cross-membrane transport of the chemical species