Rare-earth high-entropy oxides are a new promising class of multifunctional materials characterized by their ability to stabilize complex, multi-cationic compositions into single-phase structures through configurational entropy. This feature enables fine-tuning structural properties such as oxygen vacancies, lattice distortions, and defect chemistry, making them promising for advanced technological applications. While initial research primarily focused on their catalytic performance in energy and environmental applications, recent research demonstrated their potential in optoelectronics, photoluminescent materials, and aerospace technologies. Progress in synthesis techniques has provided control over particle morphology, composition, and defect engineering, enhancing their electronic, thermal, and mechanical properties. Rare-earth high-entropy oxides exhibit tunable bandgaps, exceptional thermal stability, and superior resistance to phase degradation, which positions them as next-generation materials. Despite these advances, challenges remain in scaling up production, optimizing compositions for specific applications, and understanding the fundamental mechanisms governing their multifunctionality. This review provides a comprehensive analysis of the recent developments in rare-earth high-entropy oxides as relatively new and still underrated material of the future.

High-entropy fluorite oxides offer exceptional tunability of structure and functionality through controlled multi-cation substitution. In this work, Ce-Zr-Pr-Sm-Eu-based high-entropy oxides, with systematically varied Pr content, were synthesized using a modified sol–gel citrate method to investigate the influence of Pr incorporation on lattice structure, defect formation, and photocatalytic performance. All compositions crystallized in a single-phase cubic fluorite structure, where increasing Pr concentration induced gradual lattice expansion and microstrain due to the substitution of larger Pr³⁺ ions. Morphological and surface analyses revealed porous nanostructures at moderate Pr levels, while excessive Pr promoted densification and reduced surface accessibility. Spectroscopic studies confirmed the coexistence of Pr³⁺/Pr⁴⁺ and Ce³⁺/Ce⁴⁺ redox couples, strong 4f–2p orbital hybridization, and enhanced defect-related electronic states that narrowed the optical bandgap. The optimized Pr-doped composition exhibited almost 100% degradation of methylene blue under UV light over 30 min, untypical for semiconductors with a narrower bandgap, and is enabled by efficient charge separation and redox cycling between Ce and Pr centers.

A new copper(II) complex was synthesized using chromone-2-carboxylic acid as the main ligand, and coordinated pyridine molecules. The complex was successfully crystallized and structurally characterized by single crystal X-ray diffraction. This revealed a mononuclear structure with a distorted square pyramidal geometry around the central Cu(II) ion. The coordination sphere comprises oxygen atoms from the chromone moiety and nitrogen atoms from pyridine, resulting in a five-coordinate complex. A comprehensive physicochemical characterization was performed using Fourier transform infrared spectroscopy (FT-IR), UV–Vis spectroscopy, elemental (C, H, N), electrochemical (CV) and thermal analysis (TGA/DSC) to confirm the coordination environment and thermal stability of the compound. The complex exhibits distinct spectroscopic features indicative of ligand–metal charge transfer and d–d transitions typical of Cu(II) species. In addition, the synthesized complex was subjected to antimicrobial screening against Gram-positive and Gram-negative bacteria. The compound showed promising antibacterial activity, particularly against Escherichia coli, indicating its potential as a bioactive coordination compound. These results contribute to the growing body of research on metal-based chromone derivatives and emphasize the importance of copper complexes for the development of new antibacterial agents with defined crystal structures.

Rare-earth high-entropy oxides are a new promising class of multifunctional materials characterized by their ability to stabilize complex, multi-cationic compositions into single-phase structures through configurational entropy. This feature enables fine-tuning structural properties such as oxygen vacancies, lattice distortions, and defect chemistry, making them promising for advanced technological applications. While initial research primarily focused on their catalytic performance in energy and environmental applications, recent research demonstrated their potential in optoelectronics, photoluminescent materials, and aerospace technologies. Progress in synthesis techniques has provided control over particle morphology, composition, and defect engineering, enhancing electronic, thermal, and mechanical properties. Rare-earth high-entropy oxides exhibit tunable bandgaps, exceptional thermal stability, and superior resistance to phase degradation, positioning them as next-generation materials. Despite these advances, challenges remain in scaling up production, optimizing compositions for specific applications, and understanding the fundamental mechanisms governing their multifunctionality. This review provides a comprehensive analysis of the recent developments in rare-earth high-entropy oxides as relatively new and still underrated material of the future.

In line with the circular economy approach and the pursuit of sustainable solutions for spent coffee grounds, this study investigates the valorization of spent coffee grounds as a source of cellulose-based enzyme immobilization carriers. Considering that global coffee consumption generates approximately 6.9 million tonnes of spent coffee grounds annually, their disposal represents both an environmental challenge and an opportunity for value-added applications. A multistep extraction process, including Soxhlet extraction followed by sequential subcritical extraction with ethanol and water, and alkaline treatment, led to the production of cellulose-enriched carriers. The carriers obtained were characterized by their morphology, porosity and surface properties and subsequently used for the two lipases immobilization, Burkholderia cepacia (BCL) and Pseudomonas fluorescens (PFL), using three techniques: adsorption and covalent binding via direct and indirect methods. The immobilized lipases were analyzed for key biochemical and operational properties and compared with each other and with their free enzymes. Based on their stability, catalytic activity, and reusability, the lipases immobilized by adsorption were identified as the most efficient biocatalysts. These immobilized enzymes were then used in two selected reactions to demonstrate their practical utility: cocoa butter substitute synthesis using PFL and the enzymatic pretreatment of wastewater from the oil processing industry using BCL. Both immobilized lipases showed excellent catalytic performance and maintained their high activity over four consecutive reuse cycles.

Up to date, the development of highly efficient, visible light-active catalysts remains a formidable challenge due to the enhanced rising of atmospheric CO2 concentration. This study discusses a class of ceria-based high-entropy oxides designed to optimize charge carrier dynamics, surface reactivity, and CO2 activation efficiency. Due to the advantages of high configurational entropy and multi-element synergy, these materials achieved improved photocatalytic performance, surpassing conventional ceria-based systems. Structural and spectroscopic analyses reveal that Pr3+/Pr4+ redox pairs and abundant oxygen vacancies create an electronically disordered yet thermodynamically stable environment, which enhances charge separation and suppresses electron-hole recombination. Photocatalytic experiments demonstrated that Ce0.2Zr0.2La0.2Pr0.2Sm0.2O2−δ (CZLPS) achieves the highest CO2 conversion rate, reaching a conversion of 20.3% under visible light irradiation, significantly surpassing pure ceria (1.4%), with a calculated space-time yield (STY) of 10.15 molCOkg–1h–1 under the same conditions. First-principles density functional theory (DFT) simulations were employed to investigate the CO2 reduction mechanism on CZLPS catalysts. The study elucidates the Gibbs free energy changes (ΔG) for each step of the reaction pathways leading to CO and HCOOH formation, highlighting the Zr site of CZLPS as the most active for the CO2RR, which is responsible for the outstanding catalytic activity.