Lorena Barrientos

Photocatalytic nitrogen conversion over iron oxide-based materials remains challenging, particularly under gas-phase conditions, where reaction pathways and product distributions are poorly understood. Herein, nanostructured Fe2O3 and metal-modified Fe2O3 photocatalysts (M = Ni, Cu, Mo, Ru, and Pt) were investigated for gas-phase photocatalytic nitrogen conversion under visible-light irradiation in N2/H2 mixtures. The materials were characterized by BET, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and UV−vis DRS to examine relationships between phase composition, surface chemistry, electronic structure, and photocatalytic response. Although samples retained hematite as the crystalline phase and displayed similar optical band gaps, metal incorporation produced distinct secondary phases, surface chemical environments, and band-edge positions. Among the catalysts, Mo/Fe2O3 showed the highest NH3 formation after prolonged irradiation, whereas Ni/Fe2O3 displayed a quasi-steady-state behavior. Pt/Fe2O3 exhibited a distinct response, with the detection of N2H4 suggesting hydrogenation-favored pathways, consistent with the presence of surface-accessible Pt0 species. In contrast, Cu/Fe2O3 showed limited NH3 formation, in agreement with its lower H2 consumption and less favorable hydrogenation behavior under the applied conditions. Overall, the results indicate that gas-phase photocatalytic nitrogen conversion over nanostructured metal-modified Fe2O3 cannot be explained by a single unified band-alignment framework but rather by the combined influence of phase composition, surface oxygen chemistry, electronic structure, and the balance between N2 and H2 activation.

Greywater reuse has emerged as a promising strategy to reduce pressure on freshwater resources, but little is known about the impact that emerging contaminants may have on its safe application. This study evaluated the performance of hollow fiber membrane bioreactors (HFMBs) for synthetic greywater treatment under control conditions and exposure to two widely used pharmaceutical compounds: ibuprofen and diclofenac. Nine HFMBs were operated for 11 days using synthetic greywater without pharmaceuticals (control), ibuprofen-amended greywater, or diclofenac-amended greywater. Reactor performance was assessed through physicochemical parameters and microbial community analysis. Turbidity and soluble chemical oxygen demand (sCOD) decreased in all reactors and were adequately described by an empirical temporal stabilization model. Turbidity removal was comparable among treatments, whereas final sCOD removal differed among reactor conditions. Anionic surfactants were markedly reduced, with removal efficiencies above 98% in all systems. In contrast, ibuprofen and diclofenac showed small and variable decrease in measured concentrations, but no statistically significant differences were detected between initial and final concentrations. Microbial community analysis revealed that Pseudomonadota was the dominant phylum in the HFMB reactors. Functional prediction further indicated an enrichment of pathways associated with aromatic compound degradation and biofilm-related processes across the reactor configuration and operating conditions. Moreover, the diclofenac treatment exhibited an additional enrichment of functions related to environmental stress resistance and an enhanced potential for aromatic compound degradation compared with the control treatment.

BACKGROUND: High water consumption and the toxic pollutants found in industrial wastewater are key challenges in achieving a more sustainable development. In this sense, it is crucial to develop sustainable ways to reduce the organic pollutants found in wastewater and to promote its reuse.RESULTS: In this study, a simple, low‐cost, and environmentally friendly path for dairy wastewater decontamination through photocatalysis using rod‐shaped α‐Fe₂O₃/TiO₂ type II heterojunctions is reported. The photoreaction of the model solution was evaluated under UVA‐visible irradiation with different amounts of α‐Fe₂O₃ over TiO₂, lactose as pollutant concentrations, Cl⁻ and SO₄²⁻ anions effects, and oxidant ambient showing up to 42% lactose degradation without the addition of oxidant ambient. Optimized parameters (1.0%wt α‐Fe₂O₃/TiO₂, [catalyst] = 0.5 g L⁻¹, [lactose] = 0.7 g L⁻¹, [H₂O₂] = 10 mM, [O₂] = constant) were used on dairy wastewater, which showed a 63% total organic carbon reduction and a 56% chemical oxygen demand reduction. The composite was easily recovered by decantation with a turbidity reduction of ~ 99%. The photocatalyst reusability was assessed over three successive uses and it maintained its activity with a loss of only 10%.CONCLUSION: This study offers a promising approach for the development of innovative sustainable nanotechnology to efficiently degrade organic pollutants commonly found in dairy wastewater and improve its quality within a shorter timeframe. Our approach could contribute to the development of efficient and cost‐effective complementary technologies for the Sequencing Batch Reactor in the treatment of dairy wastewater, thus contributing to the sustainability of the dairy industry. © 2024 Society of Chemical Industry (SCI).

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb₂O₅ with different crystal phases was studied. Nb₂O₅ particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb₂O₅ was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb₂O₅ spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb₂O₅ favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed.

We studied the oxidation reactions of thiocyanate and L-cysteine on iron phthalocyanine (FePc) coupled via a bridging ligand of the 4-mercatopyridine (4MP) type to a gold cluster (Au₂₆), aiming to simulate a modified gold electrode. Theoretical models have been used based on the framework of density functional theory. Several mechanistic pathways are explored for the study of these reactions, finding that the most favorable mechanism involves an electron transfer process as the rate-determining step. Along the process, the ability of the gold cluster to act as an electron acceptor facilitating the reactions was detected. In addition, the proposed models presented a correlation between the energy obtained for the rate-determining step of the reaction and the experimental oxidation potentials of the thiocyanate and L-cysteine.