In the last few years, high-entropy oxides (HEOs), a new class of single-phase solid solution materials, have attracted growing interest in both academic research and industry for their great potential in a broad range of applications. This work investigates the possibility of producing pure single-phase HEOs with spinel structure (HESOs) under milder conditions (shorter heat treatments at lower temperatures) than standard solid-state techniques, thus reducing the environmental impact. For this purpose, a large set of HESOs was prepared via sol-gel and electrospinning (by using two different polymers). Ten different equimolar combinations of five metals were considered, and the influence of the synthesis method and conditions on the microstructure, morphology and crystalline phase purity of the produced HESOs was investigated by a combination of characterization techniques. On the other hand, the presence of specific metals, such as copper, lead to the formation of minority secondary phase(s). Finally, two representative pure single-phase HESOs were preliminarily evaluated as active anode materials in lithium-ion batteries and possible strategies to enhance their rate capability and cyclability were proposed and successfully implemented. The approaches introduced here can be extensively applied for the optimization of HEO properties targeting different applications.

Pomegranate use is increasing worldwide, as it is considered a tasteful healthy food. It is mainly used as fruit, juice, and jam. The pomegranate peel represents about 40–50% of the total fruit weight and contains numerous and diverse bioactive substances. The aim of this research was to analyze the pomegranate peel chemical composition of Wonderful cultivated in Southern Italy and treated with an innovative physic dry concentration procedure in comparison with the peel composition of freeze-dried Wonderful cultivated in Southern Italy, freeze-dried Wonderful cultivated in South Africa, and freeze-dried pomegranate cultivated in India. The specific aim was to verify how much the growth area, cultivar type, and dry procedure influenced the chemical composition of the peels in terms of valuable bioactive compounds. Spectrophotometric and HPLC identification methods were used to detect antioxidants, antioxidant activities, and phenolic and flavonoid components. Results evidenced that in pomegranate peels of Wonderful cultivated in Calabria and dried with the innovative process, total phenolic substances, total flavonoids, vitamin C, vitamin E, and antioxidant activities were the highest. Great amounts of single phenolic acids and flavonoids were found in Calabrian Wonderful peels dried with the innovative process. Overall, it emerged that a great amount of bioactive and diverse compounds found in Calabrian Wonderful pomegranate peel comes from the niche pedoclimatic conditions, and the physic drying innovative methodology turned out to be an advantageous procedure to concentrate and conserve biocompounds.

High-entropy oxide nanofibers, based on equimolar (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, were prepared by electrospinning followed by calcination. The obtained hollow nanofibers exhibited a porous structure consisting of interconnected nearly strain-free (Cr_1/5Mn_1/5Fe_1/5Co_1/5Ni_1/5)₃O₄, (Cr_1/5Mn_1/5Fe_1/5Co_1/5Zn_1/5)₃O₄ and (Cr_1/5Mn_1/5Fe_1/5Ni_1/5Zn_1/5)₃O₄ single crystals with a pure Fdm spinel structure. Oxidation state of the cations at the nanofiber surface was assessed by X-ray photoelectron spectroscopy and cation distributions were proposed satisfying electroneutrality and optimizing octahedral stabilization. The magnetic data are consistent with a distribution of cations that satisfies the energetic preferences for octahedral vs. tetrahedral sites and is random only within the octahedral and tetrahedral sublattices. The nanofibers are ferrimagnets with relatively low critical temperature more similar to cubic chromites and manganites than to ferrites. Replacing the magnetic cations Co or Ni with non-magnetic Zn lowers the critical temperature from 374 K (Cr,Mn,Fe,Co,Ni) to 233 and 105 K for (Cr,Mn,Fe,Ni,Zn) and (Cr,Mn,Fe,Co,Zn), respectively. The latter nanofibers additionally have a low temperature transition to a reentrant spin-glass-like state.

Synthetic dyes, dispersed in water, have harmful effects on human health and the environment. In this work, Ti and/or Zn oxide nanofibers (NFs) with engineered architecture and surface were produced via electrospinning followed by calcination. Calcination and subsequent cooling were operated at fast rates to generate porous NFs with capture centers to reduce the recombination rate of the photogenerated charges. After morphological and microstructural characterisation, the NFs were comparatively evaluated as photocatalysts for the removal of methylene blue from water under UV irradiation. The higher band gap and lower crystallinity were responsible for the lower photocatalytic activity of the ternary oxides (ZnTiO₃ and Zn₂TiO₄) towards the degradation of the dye. The optimal loads of the highly performing binary oxides were determined. By using 0.66 mg mL⁻¹ wurtzite ZnO for the discoloration of an aqueous solution with a dye concentration of 15 µM, a higher rate constant (7.94 × 10⁻² min⁻¹) than previously reported was obtained. The optimal load for anatase TiO₂ was lower (0.33 mg mL⁻¹). The corresponding rate constant (1.12 × 10⁻¹ min⁻¹) exceeds the values reported for the commonly used P25–TiO₂ benchmark. The catalyst can be reused twice without any regeneration treatment, with 5.2% and 18.7% activity decrease after the second and third use, respectively.

Soil microorganisms are key drivers of soil biochemical processes, but the resilience of microbial communities and their metabolic activity after an extreme environmental change is still largely unknown. We studied structural (bacterial and fungal communities) and functional responses (soil respiration, adenosine triphosphate (ATP) content, hydrolase activities involved in the mineralization of organic C, N, P and S, and microbial community-level physiological profiles (CLPPs)) during the microbial recolonization of three heat-sterilized forest soils followed by cross- or self-reinoculation and incubation for 1, 7 and 30 days. Soil ATP content, biochemical activities and CLPP were annihilated by autoclaving, whereas most of the hydrolase activities were reduced to varying extents depending on the soil and enzyme activity considered. During the incubation period, the combination of self- and cross-reinoculation of different sterilized soils produced rapid dynamic changes in enzymatic activity as well as in microbial structure and catabolic activity. Physicochemical properties of the original soils exerted a major influence in shaping soil functional diversity, while reinoculation of sterilized soils promoted faster and greater changes in bacterial community structure than in fungal communities, varying with incubation period and soil type. Our results also confirmed the importance of microbial richness in determining soil resilience under severe disturbances. In particular, the new microbial communities detected in the treated soils revealed the occurrence of taxa which were not detected in the original soils. This result confirmed that rare microbial taxa rather than the dominant ones may be the major drivers of soil functionality and resilience.

Water pollution and scarcity are serious concerns for the growing world population. To meet the ever-pressing demand of fresh water, a variety of desalting techniques of seawater have been developed. Due to its environmental friendliness, high efficiency, easy regeneration of the electrodes, ambient operating pressure, and low operating potential suitable for the use in remote areas, the capacitive deionization (CDI) method is one of the most sustainable among them. This work focuses on the preparation of high-entropy oxides (HEOs) and carbon/HEO composites and the evaluation of their specific capacitance in view of their possible use as CDI electrode materials. CrMnFeCoNi-HEO, having spinel structure (sHEO), is obtained in the form of nanoparticles (NPs) and nanofibers (NFs) by the sol–gel method and electrospinning, respectively. Composite NFs with embedded sHEO NPs or MgCoNiCuZn-HEO NPs with rock-salt structure (rHEO) are also produced. In the 5–100 mV s⁻¹ scan rate range, the specific capacitance improves in the order C/rHEO NFs (8–32 F g⁻¹) ≅ sHEO NPs (9–32 F g⁻¹) < sHEO NFs (8–43 F g⁻¹) < C/sHEO NFs (12–66 F g⁻¹). The highest capacitance is obtained when the beneficial contributions of the carbon matrix and smaller-sized HEO NPs are synergistically coupled.