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- Evolution of atomically dispersed co-catalysts during solar or UV photocatalysis for efficient and sustained H2 productionPublication . Capelo, Anabela; Fattoruso, Domenico; Valencia-Valero, Laura; Esteves, M. Alexandra; Rangel, Carmen M.; Puga, AlbertoABSTRACT: The evolution of metal/titania photocatalysts during photocatalytic H-2 evolution is herein studied. Samples containing atomically dispersed Pt co-catalysts (single atoms, clusters and sub-nanoparticles) formed after calcination were compared to pre-reduced analogues mostly having metallic nanoparticles (diameters >1 nm) during ethanol photoreforming under either UV-rich irradiation or natural sunlight. Aggregation of ultra-dispersed oxidised platinum entities (Pt delta+) with concomitant reduction into Pt-0 nanoparticles (1-2 nm) was observed after UV irradiation by transmission electron microscopy (TEM), and diffuse reflectance UV-visible (DRUV-vis) and X-ray photoelectron (XPS) spectroscopies. A parallel, albeit slower, evolution trend was evidenced during solar photocatalysis. Conversely, atomically dispersed Cu co-catalyst species did not grow and became in-situ reduced into sub-nanometric Cu-0 under irradiation. Hydrogen production rates were remarkably high during initial stages of UV irradiation, and then declined to a sustained regime (approximate to 50 and 8 mmol g(-1) h(-1) for Pt/TiO2 or Cu/TiO2, respectively, for up to 24 h of irradiation). Steadier solar photoreforming was observed in experiments performed in a compound parabolic collector tubular reactor (approximate to 7.6 and 1.7 mmol g(-1) h(-1) for Pt/TiO2 or Cu/TiO2, respectively). Despite the non-negligible effect of co-catalyst rearrangement on activity rationalised herein, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy measurements pre- and post-photocatalysis suggest that accumulation of strongly adsorbed degradation intermediates, chiefly acetate, is a major cause for rate decreases. Notwithstanding, this phenomenon did not result in total deactivation, so that sustained hydrogen production upon long-term irradiation was not compromised.
- Dielectric UV filters for protection of fire-resistant glass based on intumescent layersPublication . Silva, Ricardo Magno Lopes; Hashim, Hurraira; Roy, Deepto; Oliveira Fernandes, Carolina; Oliveira, Kevin; Leitão Pinheiro, Xavier Alexandre; Esteves, M. Alexandra; Capelo, Anabela; Donato, Mariana; Oliveira, Fernando; Ferreira, Cristina; Alves, Isabel N.; Cunha Diamantino, Teresa; Barreiros, Maria Alexandra; Rocha, Jorge; Passos Teixeira, Jennifer; Salomé, PedroABSTRACT: Structures such as OLEDs, perovskite solar cells, intumescent glasses, and other components in modern devices and buildings contain materials suscep-tible to degradation when exposed to UV radiation, requiring protection to with-stand outdoor environmental conditions. In this work, multilayer coating config-ured as a Bragg Reflector on glass is employed as spectral filtering to protect the intumescent component of fire-resistant glass from degradation due to prolonged UV solar radiation exposure. By alternating low-n (SiO2)/high-n (TiO2) dielectric layers through spin-coating, precise control over film thickness could be achieved, allowing the fabrication of thin (<700 nm) UV filters with high trans-mission of visible sunlight – 88% of the 780 to 380 nm wavelength range – while reflecting almost all the incident UV – 90% of the wavelength below 380nm. Using relatively simple techniques, high precision coating was successfully achieved, resulting in an effective UV radiation protective barrier applied to en-hance the durability of the components in fire-resistant glass.