Roberta Licheri

The development of multicomponent diborides is driven by the expectation that combining different transition metals within the AlB ₂ ‐type structure may yield properties superior to those of the individual constituents. In this framework, the fabrication and oxidation resistance of Zr–Hf–Ta equiatomic diborides are systematically investigated in this work to demonstrate synergistic effects and possible benefits arising when moving from unary to ternary systems. All materials are synthesized through a combined self‐propagating high‐temperature synthesis (SHS) and spark plasma sintering (SPS) approach, producing dense single‐phase diborides except for (Hf _0.5 Ta _0.5 )B ₂ , which retained ∼6.3 wt.% of a Ta‐rich secondary phase. Oxidation tests show that the behavior of such ceramics strongly depends on the specific oxide phases formed during their exposure. Higher protection is obtained when the scale is dominated by stable, single‐phase, oxides such as HfO ₂ and A ₆ Ta ₂ O ₁₇ (A = Zr, Hf), while the formation of detrimental oxides (ZrO ₂ , Ta ₂ O ₅ , TaO ₂ ) is minimized. In particular, when the complex A ₆ Ta ₂ O ₁₇ phase becomes the predominant oxidation product, as observed for the (Zr _1/3 Hf _1/3 Ta _1/3 )B ₂ composition, the resulting oxide scale is compact, stable, and significantly more resistant to oxygen transport. The critical role of compositional design in enabling synergistic oxidation behavior is discussed.

In situ resource utilization (ISRU) and in situ fabrication and repair (ISFR) are critical research and technological paradigms for future space exploration. They aim to reduce reliance on Earth-supplied materials by utilizing resources available on celestial bodies, while enabling on-site fabrication and repair through the use and processing of local resources. ISRU and ISFR are strongly interconnected, with the shared objective of enabling more sustainable and autonomous long-duration missions to the Moon, Mars, and beyond. This work presents a comprehensive and critical review of scientific and patent literature published primarily between 2010 and 2025, complemented by selected earlier seminal contributions for context. The analysis provides an integrated perspective on major technological developments, key challenges, and emerging research directions in low-gravity and microgravity environments.

Controlling the selectivity of CO₂ hydrogenation to produce value-added fuels and chemicals is an actual challenge in catalysis research. The exact mechanisms underlying selectivity control often remain poorly understood, slowing the design of more efficient catalysts. In this study, we investigated RuO₂ nanoparticles supported on MXene or TiO₂ for CO₂ hydrogenation at atmospheric pressure. Microalgal extracts were incorporated in the synthesis to explore their influence on catalyst properties, such as surface area, morphology, and elemental distribution. Although lower surface area and less uniform RuO₂ dispersion were observed on MXenes than on TiO₂, after reductive pretreatment Ru/MXene exhibited superior catalytic activity, demonstrating that its unique textural properties and active site availability compensated for the lower surface area. A reducibility study revealed that MXene-supported catalysts undergo a more complex reduction process than those with TiO₂ as the support. Additionally, bridge adsorption sites on MXene likely contributed to the enhanced CO₂ hydrogenation activity, whereas TiO₂ seemed to present a twin CO binding environment. Higher Ru loading on MXene increased the methane selectivity and conversion, whereas lower loading favored CO formation, highlighting the importance of optimizing catalyst loading. Operando diffuse reflectance infrared Fourier transform spectroscopy analysis revealed the critical role of methoxy intermediates in affecting the catalytic pathway, suggesting the potential for tuning synthesis conditions to improve yields. A partial encapsulation of Ru on MXene enhances the catalytic performance, while the stronger SMSI effect on TiO₂ leads to complete encapsulation, reducing the catalytic efficiency. The findings underscore the promise of MXene as a support material for metal catalysts in CO₂ hydrogenation toward environmentally friendly fuel production.

The development of efficient photocatalysts is crucial in addressing water pollution concerns, specifically in the removal of organic dyes from wastewater. In this context, the use of silver nanoparticles (Ag NPs) might represent a method to achieve high dye degradation efficiencies. On the other hand, the classical Ag NP production process involves several reactants and operating conditions, which make it poorly sustainable. In the present work, Ag NPs were synthesized according to a new sustainable process involving the use of natural extracts of Spirulina platensis and milder operating conditions. The material was also calcined to determine the influence of organic content on the properties of Ag NPs. The X-ray diffraction (XRD) analysis displayed the AgCl and Ag phases with a crystalline size of 11.79 nm before calcination. After calcination, only the Ag phase was present with an increased crystalline size of 24.60 nm. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the capping role of the metabolites from the extract. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) revealed the spherical or quasi-spherical morphologies with agglomeration due to the calcination. Energy-dispersive X-ray spectroscopy (EDX) and Thermogravimetric (TGA) analyses further confirmed the involvement of metabolites in the synthesis of Ag NPs. The optical changes in the products were observed in a UV-Vis analysis. The Ag NPs were tested for their photocatalytic activity against the laboratory dye brilliant blue r in visible light in various conditions. The highest degradation efficiency of 81.9%, with a k_app value of 0.00595 min⁻¹, was observed in alkaline medium after 90 min of light irradiation.

Synthesis of silver nanoparticles (Ag NPs) using microalgae is gaining recognition for its environmentally friendly and cost-effective nature while maintaining high activity of NPs. In the present study, Ag NPs were synthesized using a methanolic extract of Chlorella vulgaris and subjected to calcination. The X-ray diffraction (XRD) analysis showed a crystalline nature of the products with Ag₂O and Ag phases with an average crystalline size of 16.07 nm before calcination and an Ag phase with 24.61 nm crystalline size after calcination. Fourier transform infrared spectroscopy (FTIR) revealed the capping functional groups on Ag NPs, while scanning electron microscopy (SEM) displayed their irregular morphology and agglomeration after calcination. The organic coating was examined by energy-dispersive X-ray spectroscopy (EDX) and thermogravimetric (TGA) analyses, confirming the involvement of the metabolites. The UV–Vis analysis showed a difference in optical properties due to calcination. Synthesized Ag NPs were applied for the photodegradation of hazardous dye Brilliant Blue R in visible light. Different values of light intensity, catalyst dose, initial dye concentration, and pH were tested to identify the optimal set of operating conditions. The highest degradation efficiency of 90.6% with an apparent rate constant of 0.04402 min⁻¹ was achieved after 90 min of irradiation in the highest tested catalyst dosage.