Triiodide-in-Iodine Networks Stabilized by Quaternary Ammonium Cations as Accelerants for Electrode Kinetics of Iodide Oxidation in Aqueous Media.

The Zn-polyiodide redox flow battery is considered to be a promising aqueous energy storage system. However, in its charging process, the electrode kinetics of I- oxidation often suffer from an intrinsically generated iodine film (I2-F) on the cathode of the battery. Therefore, it is critical to both understand and enhance the observed slow electrode kinetics of I- oxidation by an electrochemically generated I2-F. In this article, we introduced an electrogenerated N-methyl-N-ethyl pyrrolidinium iodide (MEPI)-iodine (I2) solution, designated as MEPIS, and demonstrated that the electrode kinetics of I- oxidation were dramatically enhanced compared to an I2-F under conventional electrolyte conditions, such as NaI. We showed that this result mainly contributed to the fast electro-oxidation of triiodide (I3-), which exists in the shape of a I3--in-I2 network, [I3-·(I2)n]. Raman spectroscopic and electrochemical analyses showed that the composition of electrogenerated MEPIS changed from I3- to [I3-·(I2)n] via I5- as the anodic overpotential increased. We also confirmed that I- was electrochemically oxidized on a MEPIS-modified Pt electrode with fast electrode kinetics, which is clearly contrary to the nature of an I2-F derived from a NaI solution as a kinetic barrier of I- oxidation. Through stochastic MEPIS-particle impact electrochemistry and electrochemical impedance spectroscopy, we revealed that the enhanced electrode kinetics of I- oxidation in MEPIS can be attributed to the facilitated charge transfer of I3- oxidation in [I3-·(I2)n]. In addition, we found that the degree of freedom of I3- in a quaternary ammonium-based I2-F can also be critical to determine the kinetics of the electro-oxidation of I-, which is that MEPIS showed more enhanced charge-transfer kinetics of I- oxidation compared to tetrabutylammonium I3- due to the higher degree of freedom of I3-.

Biocompatible and functional inorganic magnesium ceramic particles for biomedical applications.

Magnesium ceramics hold promise for numerous biological applications. This review covers the synthesis of magnesium ceramic particles with specific morphologies and potential modification techniques. Magnesium ceramic particles possess multiple characteristics directly applicable to human biology; they are anti-inflammatory, antibacterial, antiviral, and offer anti-cancer effects. Based on these advantages, magnesium hydroxide nanoparticles have been extensively utilized across biomedical fields. In a vascular stent, the incorporation of magnesium ceramic nanoparticles enhances re-endothelialization. Additionally, tissue regeneration for bone, cartilage, and kidney can be promoted by magnesium ceramics. This review enables researchers to identify the optimum synthetic conditions to prepare magnesium ceramics with specific morphologies and sizes and select the appropriate modification protocols. It is also intended to elucidate the desirable physicochemical properties and biological benefits of magnesium ceramics.

Network structure and enzymatic degradation of chitosan hydrogels determined by crosslinking methods.

Polysaccharides can be modified by reactive functional groups to enable chemical crosslinking. We studied how different methods of crosslinking methacrylate-functionalized chitosan affected the network structures and various properties relevant for utilization of the chemically crosslinked hydrogels in biomedical applications, including tissue engineering and delivery of therapeutic agents. Four chitosan hydrogels were made by either the free radical polymerization with varying initiation kinetics and an addition of chain transfer agents or the based-catalyzed Michael-type addition reaction. Four chitosan hydrogels having identical polymer fractions at equilibrium swelling exhibited marked differences in shear moduli, dextran diffusion rate, and especially enzymatic degradation behaviors. Hydrogels made by the free radical polymerization with no chain transfer agent were highly resistant to complete degradation by enzyme for an extended period. We inferred that such resistance originated from chain bundles characterized by densely branched networks of chitosan chains, which was determined by small-angle X-ray scattering analysis.

Preparation of an imogolite/poly(acrylic acid) hybrid gel.

Many efforts in the field of hydrogels have been focused toward increasing the mechanical strength of the gel using inorganic materials. In this study, we synthesized a hydrogel that has excellent mechanical properties using surface-modified inorganic nanofibers composed of imogolite (Al2SiO3(OH)4), which is a hydrated aluminum silicate that has a hollow tube structure. Gamma ray radiation generates peroxide radicals on the nanofibers (imogolite), resulting in an additive free hybrid hydrogel. Structural optimization was carried out by changing the composition of imogolite and poly(acrylic acid). Chemical bonding between the nanofiber and the polymer was simulated by a cluster model and characterized by wide area Raman spectroscopy. The results indicate that imogolite embedded in a polymer matrix can align along the direction of an elongational force, as confirmed by small angle X-ray scattering (SAXS).