Pure TiO₂ and Fe- and Co-doped TiO₂ nanoparticles (NPs) as photocatalysts were synthesized using wet chemical methods (sol-gel + precipitation). Their crystalline structure and optical properties were analyzed using X-ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible light (UV-Vis) diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The photocatalytic activity of the synthesized nanoparticles was evaluated through degradation of carbamazepine (CBZ) under UV-A and visible-light irradiations. The XRD and Raman analyses revealed that all synthesized nanomaterials showed only the anatase phase. The DRS results showed that the absorption edge was blue-shifted for Fe-doped TiO₂ NPs. The decrease in charge recombination was evidenced from the PL investigation for both Co-doped and Fe-doped TiO₂ nanomaterials. An enhancement in photocatalytic degradation of carbamazepine in aqueous suspension under both UV-A light and visible-light irradiations was observed for Fe-doped Titania NPs by comparison with pure TiO₂. These results suggest that the doping cations could suppress the electron/hole recombination. Therefore, the photocatalytic activity of TiO₂-based nanomaterials was enhanced.

Spent coffee grounds (SCGs) are known for containing many organic compounds of interest, including carbohydrates, lipids, phenolic compounds and proteins. Therefore, we investigated them as a potential source to obtain carbon dots (CDs) via a nanotechnology approach. Herein, a comparison was performed between CDs produced by SCGs and classic precursors (e.g., citric acid and urea). The SCG-based CDs were obtained via the one-pot and solvent-free carbonization of solid samples, generating nanosized particles (2.1–3.9 nm). These nanoparticles exhibited a blue fluorescence with moderate quantum yields (2.9–5.8%) and an excitation-dependent emission characteristic of carbon dots. SCG-based CDs showed potential as environmentally relevant fluorescent probes for Fe³⁺ in water. More importantly, life cycle assessment studies validated the production of CDs from SCG samples as a more environmentally sustainable route, as compared to those using classic reported precursors, when considering either a weight- or a function-based functional unit.

Doping ZnO with appropriate foreign metal and/or non-metal ions is one of the most promising ways to improve both the extension of ZnO photosensitization to the visible region and the separation of charge carriers. Herein, Mn-doped ZnO nanoparticles were synthesized using a precipitation method. The effect of the Mn amount on the physico-chemical properties of these nanomaterials was investigated using X-ray diffraction, Fourier-transform infrared spectroscopy, UV–visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photocatalytic properties of the synthesized nanomaterials were assessed through methyl orange (MO) under visible light. The obtained results showed that the structural and optical properties of the synthesized Mn-ZnO nanomaterials depended greatly on the Mn amount. It was found that the substitution of Zn²⁺ by Mn²⁺/Mn³⁺ within the lattice of ZnO occurred. The photocatalytic experiments revealed that the sample containing 10 wt% exhibited the best MO conversion. For this sample, the discoloration reached 96%, while the chemical oxygen demand reached 1% after 820 min of visible illumination. The enhanced photocatalytic activity was attributed to the efficient separation of charge carriers. The active species quenching experiments showed that the holes are the main active species in MO degradation under visible light in the presence of 10%Mn-ZnO.