The photocatalytic oxidation (PCO) of pollutants using TiO₂-based materials can significantly improve indoor air quality (IAQ), which in turn, has a significant impact on human health and life expectancy. TiO₂-based nanoparticles (NPs) are widely used as part of building materials to function as photocatalysts in PCO. In this work, a series of sulfur-doped TiO₂ NPs immobilized on a silica matrix were synthesized by combining a sol-gel process with ball milling. The samples were structurally characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FT-IR) and N₂ adsorption-desorption isotherms. Furthermore, the morphological characteristics were determined by dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activity of the as prepared S-doped TiO₂/SiO₂ NPs in the degradation of liquid and air pollutants under visible-light irradiation was investigated. Our results show that sulfur is an effective dopant for activating TiO₂/SiO₂ photocatalysts under visible-light irradiation. Silica constitutes a “safe-by-design” approach and inhibits the aggregation of NPs during synthesis. The most efficient photocatalyst afforded 79% removal of methyl orange (5 h), 26% removal of acetaldehyde (1 h) and 12% oxidation of NO (1 h).

The chiral N1-Cbz, N2-H derivative of the piperazic acid monomer is a valuable building block in the total synthesis of natural products, comprising this nonproteinogenic amino acid. In that context, we wish to report an improved synthetic protocol for the synthesis of both (3R)- and (3S)-piperazic acids bearing the carboxybenzyl protecting group (Cbz) selectively at the N1 position. Our method builds on previously reported protocols, circumventing their potential shortcomings, and optimizing the ultimate selective deprotection at the N2 position, thus, offering an efficient and reproducible pathway to suitably modified piperazates in high optical purity.