International Materials Reviews

Mixed matrix membranes (MMMs) have emerged as an attractive category of nanofiltration (NF) membranes, offering a promising solution to address the intrinsic trade-off that exist between permeability and selectivity in conventional polymeric membranes. This review article aims to comprehensively discuss advances reported over the past 5–10 years achieved in the field of MMMs and critically analyzes the mechanisms through which a diversity of additives affects nanofiltration behavior. The discussed researches primarily address the separation of target solutes including salts, dyes, pharmaceuticals, and heavy metals, with primary applications in water treatment and wastewater reuse. Particular emphasis is placed not only on material design but also on interfacial compatibility, performance limitations, and the permeability-selectivity trade-off. Advanced inorganic fillers, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and MXenes, have attracted many attentions because of providing special architecture, great specific surface area, and ability to give selective transport pathways. Traditional inorganic fillers (TiO₂, ZnO, SiO₂, halloysite nanotubes, Fe₃O₄, and ZrO₂), carbon-based materials (including graphene derivatives, carbon nanotubes, and graphitic carbon nitride), and organic fillers (such as porous organic cages (POCs), and β-cyclodextrin) are comparatively discussed in terms of their merits and practical restrictions. This review indicates the relationships existing between structure, properties, and performance in various MMM designs, and provides some suggestions for future research directions. Beyond performance enhancement, this review discusses trade-offs between permeability and selectivity, filler dispersion challenges, interfacial defects, long-term stability concerns, and scalability constraints that may hinder practical implementation. The eventual aim is to develop the next generation of nanofiltration mixed matrix membranes possessing high efficiency, improved selectivity, and long-term stability.

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Lithium metal is a critical material in advancing energy storage technologies, particularly for next-generation lithium metal batteries (LMBs). However, industrial lithium metal production relies predominantly on LiCl–KCl electrolysis. This process faces several challenges and limitations, such as the need for high-purity LiCl, low current efficiency, and the generation of chlorine (Cl₂) gas as a by-product. To ensure a sustainable and affordable lithium supply, recent studies have focused on improving process efficiency and developing alternative production routes. Despite this accelerating research activity, the lack of a unified and critical assessment of lithium metal production technologies hinders informed technology selection and scale-up. This review addresses this gap by examining recent advances in lithium metal production technologies, with a focus on improvements to conventional molten salt electrolysis, including feedstock optimisations, electrolyte modifications, and cell design innovations aimed at enhancing yield, purity, and energy efficiency. In addition, alternative low-temperature electrolysis enabled by aqueous-based lithium compounds, innovative electrochemical extraction methods, and thermochemical approaches using carbon and metallic reductants are summarised. The review also considers process–structure–performance relationships, highlighting how production conditions influence lithium metal microstructure and electrochemical properties. Finally, the review discusses the challenges associated with each method and highlights potential improvements to achieve more sustainable large-scale lithium metal production.

Sealing glasses are advantageous materials for joining of metals, ceramics or other glasses. For many applications, the sealed composite has to withstand high temperatures. Above the softening temperature of the glass, simple sealing glasses can usually not be used and crystallizing sealing glasses are required.

The most important properties of the crystallized sealing glass are good adherence to the material to be sealed and a good match of their coefficients of thermal expansion (CTE). The chemical composition of a glass seal can be varied in a wide range and hence also its physical properties. For the joining process, glass powder is given in between the materials to be joined. During subsequent heating, sintering of the glass by viscous flow and finally nucleation and crystal growth takes place. The supplied temperature/time schedule should be designed in such a manner that densification occurs before a notable quantity of crystal phase is formed. The formed crystalline phases and their CTEs are decisive for the CTE of the crystallized seal, because a mismatch in the CTEs results in stresses during cooling. For non-cubic crystalline phases, also the anisotropy of the CTEs is of high importance, because it leads to internal stresses within the crystallized seal. A high degree of anisotropy should hence be avoided.

The chemical composition of the crystallizing glass seal has to be tailored in such a manner that the type and quantity of the respective crystallized phases as well as the composition of the residual glass phase result in the aimed CTE as well as in good adherence to the materials to be joined. During application, both CTE and adherence should not change notably with time. Hence, during application at high temperature, further crystallization should not take place and type and volume concentration of the crystalline phase should remain constant.

Osteochondral tissue exhibits a complex multilayered structure with distinct structural and physiological properties. Recent advancements in extrusion bioprinting have enabled the layer-by-layer assembly of multilayered osteochondral constructs. Alginate, a natural polysaccharide widely used in bioinks, offers tunable properties for supporting cellular functions and engineering tissues. Alginate derived from different sources differ in β-D-mannuronate and α-L-guluronate contents, as well as the length of each block, possesses carboxylate groups that facilitate cross-linking with divalent cations and further functionalization. Several chemical and processing routes can be envisioned to achieve desired processability, mechanical, and biological versatility. Despite its potential, challenges remain in meeting the mechanical and biological requirements for osteochondral grafts. Herein, we examine the technical challenges associated with osteochondral tissue repair and discuss extrusion bioprinters’ requirements and advances in bioprinting methods to address these challenges. We highlight the last decade's key findings dealing with the chemistry and functionalization of alginate-based (bio)inks for osteochondral tissue engineering. Engineering strategies for modulating alginate-based (bio)inks with optimized rheological features, printability, and shape fidelity are overviewed. Finally, obstacles, opportunities, and emerging solutions for better developing alginate (bio)inks for osteochondral tissue engineering are explored, considering advances in artificial intelligence and machine learning.