Marta Jiménez-Salcedo

Seven bio-based solvents ((-)-β-pinene, α-phellandrene, α-terpinene, p-cymene, DL-limonene, γ-terpinene and terpinolene) are tested as environmentally friendly alternatives for use in a plastic recycling process based on dissolution–precipitation of post-consumer high-density polyethylene (PC-HDPE). In addition to evaluating cleaning performance, this work aims to develop and validate a new analytical method for the determination of residual bio-based solvents in the treated polymer, a critical aspect for evaluating the safety and quality of recycled materials. The suitability of the solvents for contaminant removal was assessed via challenge test, showing high cleaning efficiencies (>93.3%) for volatile, non-volatile, polar and non-polar compounds in most cases. To monitor residual solvent levels, a pressurized liquid extraction and gas chromatography–mass spectrometry (PLE-GC/MS) method was developed, optimized and validated. The method demonstrated adequate sensitivity (with LODs ranging between 2 and 4 mg kg⁻¹), accuracy and precision (with intra- and inter-day relative standard deviations of less than 11 and 31%, respectively) for the simultaneous determination of the seven bio-based solvents in recycled HDPE. Overall, results demonstrate both the potential of bio-based solvents in polymer recycling and the importance of robust analytical tools to assess residual contamination, supporting the development of safer and more sustainable recycling processes.

Deep eutectic solvents (DES) were selected for the extraction of anthocyanins from red grape skins as an efficient and environmentally friendly solvent alternative to traditional mixtures based on methanol. In silico studies (COSMO-RS) were employed as screening tools to identify the most suitable options, significantly reducing the chemical space of potential DES to be studied. A total of 30,132 DES combinations were assessed. The DESs selected were polyalcohols (ethyleneglycol, glycerol, 1,2-propanediol, and 1,6-hexanediol) and carboxylic acids (citric, oxalic, malic, and lactic acid) as hydrogen bond donors (HBD) and choline chloride, betaine, or salts (potassium carbonate, sodium acetate, and propionate), as hydrogen bond acceptors (HBA). Choline chloride:glycerol and choline chloride:oxaclic acic were selected as solvents to optimize time, temperature, and water content in ultrasound- and microwave-assisted extraction of anthocyanins. In both cases, around 20 wt% of water was found to be the optimum to maximize the extractions, whereas extraction time and temperature depended on the type of anthocyanin. The amount of malvidin-3-O-glucoside extracted by microwave-assisted extraction with choline chloride: oxalic acid was 172 ± 7 mg/kg and 119.5 ± 0.5 mg/kg by ultrasound-assisted extraction with choline chloride: glycerol, which means an increase in performance of, respectively, 64 and a 13% compared to the traditional method.

TiO₂ nanoparticles (NPs) were modified to obtain photocatalysts with different composition sophistication and displaying improved visible light activity. All of them were evaluated in the photodegradation of ciprofloxacin. The band gap of TiO₂ NPs was successfully tailored by the formation of an N-doped porous carbon (NPC)-TiO₂ nanohybrid through the pyrolysis of melamine at 600 °C, leading to a slight red-shift of the absorption band edge for nanohybrid NPC-TiO₂ 1. In addition, the in-situ formation and grafting of plasmonic AuAg NPs at the surface of NPC sheets and in close contact with TiO₂ NPs leads to AuAg-NPC-TiO₂ nanohybrids 2–3. These nanohybrids showed superior photocatalytic performance for the degradation of ciprofloxacin under visible light irradiation, compared to pristine P25 TiO₂ NPs or to AuAg-PVP-TiO₂ nanohybrid 4 in which polyvinylpyrrolidone stabilized AuAg NPs were directly grafted to TiO₂ NPs. The materials were characterized by transmission electron microscope (TEM), High Angle Annular Dark Field—Scanning Transmission Electron Microscopy—Energy Dispersive X-ray Spectroscopy HAADF-STEM-EDS, X-ray photoelectron spectroscopy and solid UV-vis spectroscopy. Moreover, the active species involved in the photodegradation of ciprofloxacin using AuAg-NCS-TiO₂ nanohybrids were evaluated by trapping experiments to propose a mechanism for the degradation.

The photocatalytic degradation of paracetamol (a common analgesic also known as acetaminophen) in ultrapure water with different photocatalytic systems was performed under ultraviolet or visible irradiation. The photocatalysts employed were: commercial Degussa-P25 TiO₂and Au–TiO₂under UVA irradiation (365 nm) and g-C₃N₄and Au-g-C₃N₄under visible light irradiation (low-power (4 × 10 W) white light LEDs), improving the effectiveness of degradation rates when the gold nanoparticles (Au NPs) were combined with the semiconductors. The nanostructured photocatalysts were synthesised and characterised by transmission electron microscope (TEM), UV–vis diffuse reflectance spectroscopy and, in the case of g-C₃N₄photocatalysts by X-ray photoelectron spectroscopy (XPS). The influence of the pH in the depletion of paracetamol with g-C₃N₄and visible light was evaluated. In addition, the stability and lifetime of the photocatalyst g-C₃N₄in the degradation of paracetamol were studied.Graphical abstract

Au-Ag/g-C₃N₄ nanohybrids 2–3 were synthesized by the one-pot self-reduction of the organometallic precursor [Au₂Ag₂(C₆F₅)₄(OEt₂)₂]_n in the presence of graphitic carbon nitride (g-C₃N₄), leading to two populations of alloyed Au-Ag nanoparticles (NPs) of different size and composition on the surface of g-C₃N₄, i.e., Ag-enriched Au-Ag NPs of smaller size and Au-enriched Au-Ag NPs of larger size. The combination of these two types of plasmonic NPs with g-C₃N₄ semiconductor displays enhanced photocatalytic properties towards the degradation of ibuprofen under visible light by the increased charge carrier separation provided by the inclusion of the plasmonic NPs on g-C₃N₄.