Hydrogels play a crucial role due to their high-water content and 3D structure, which make them ideal for various applications in biomedicine, sensing, and beyond. They can be prepared from a variety of biomaterials, polymers, and their combinations, allowing for versatility in properties and applications. Hydrogels include natural types derived from collagen, gelatin, alginate, and hyaluronic acid, as well as synthetic types based on polyethylene glycol (PEG), polyvinyl alcohol (PVA), and polyacrylamide (PAAm). Each type possesses distinct properties, such as mechanical strength, biodegradability, and biocompatibility, which can be tailored for applications such as wound healing, contact lenses, 3D bioprinting, and tissue engineering. The high-water content of hydrogels mimics natural tissue environments, promoting cell growth and allowing nutrient and waste exchange, which supports the development of functional tissues. They serve as scaffolds in tissue engineering applications, including wound healing, cartilage and bone regeneration, vascular tissue engineering, and organ-on-a-chip systems. Additionally, hydrogels can encapsulate and deliver therapeutic agents, such as growth factors or drugs, to specific target sites in the body. Hydrogels can be prepared through three primary methods: physical crosslinking, which relies on non-covalent interactions such as physical entanglements or hydrogen bonding; chemical crosslinking, which forms covalent bonds between polymer chains to create a stable structure; and irradiation-based crosslinking, where UV irradiation induces rapid hydrogel formation. The choice of crosslinking method depends on the desired properties and applications of the hydrogel. By providing a biomimetic environment, hydrogels facilitate cell growth and differentiation, support tissue formation, and aid in the regeneration of damaged or diseased tissues while delivering therapeutic agents. This review focuses on the critical advancements in processing routes for hydrogel development, summarizing the characterization and application of hydrogels. It also details key applications, including wound healing and cartilage and bone regeneration, as well as the challenges and future perspectives in the field.

This review explores the recent advancements in catalyst technology for hydrogen production, emphasizing the role of catalysts in efficient and sustainable hydrogen generation. This involves a comprehensive analysis of various catalyst materials, including noble metals, transition metals, carbon-based nanomaterials, and metal–organic frameworks, along with their mechanisms and performance outcomes. Major findings reveal that while noble metal catalysts, such as platinum and iridium, exhibit exceptional activity, their high cost and scarcity necessitate the exploration of alternative materials. Transition metal catalysts and single-atom catalysts have emerged as promising substitutes, demonstrating their potential for enhancing catalytic efficiency and stability. These findings underscore the importance of interdisciplinary approaches to catalyst design, which can lead to scalable and economically viable hydrogen production systems. The review concludes that ongoing research should focus on addressing challenges related to catalyst stability, scalability, and the integration of renewable energy sources, paving the way for a sustainable hydrogen economy. By fostering innovation in catalyst development, this work aims to contribute to the transition towards cleaner energy solutions and a more resilient energy future.

Composite of Fe ₃ O ₄ nanofillers in single-layer graphene-assembled porous carbon and PVA matrix explored for its dielectric properties and EMI response.

Currently, there is a considerable demand for materials with inter-balanced dielectric properties to replace the existing traditional insulators in variegated electronic appliances over the range of audio and radio frequency. In the current work, a one-step facile electrospun (E-spun) technique is adopted to fabricate a non woven mat consisting of nano-scale conducting fibers of polyaniline (PANI) and gold nanoparticles (AuNPs) using polyvinyl alcohol (PVA) as a binder. The influence of different amounts of the AuNP solution on the size and distribution of fibers was investigated using high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The dielectric constant, losses, AC conductivity and modulus of nanofibers were investigated over a wide frequency and temperature range of 0.1 Hz to 10 MHz and −40 °C to 60 °C respectively by means of Broadband Dielectric Spectroscopy (BDS). AC conductivity varies as a function of frequency, according to Jonscher's power law (JPL), and the behavior of the temperature dependent frequency exponent using JPL suggests that the Correlated Barrier Hopping (CBH) is the dominant charge transport mechanism for conducting nanofibrous nonwoven mats. By using the CBH model the maximum barrier height, hopping distance and density of state (DOS) were calculated for the whole temperature range. The incremental increase from 1.6 × 10⁻⁶ S cm⁻¹ to 2.5 × 10⁻⁶ S cm⁻¹ with increasing amounts of AuNP solution was noticed and is ascribed to the corresponding increased conducting network and reduced trapping centers in the mat. Dielectric constant increases with both increased loading of nanoparticle solution in the mat and the increased temperature, which may be attributed to enhanced interfacial polarization. Shifting and broadening of well-defined peaks were observed in the imaginary part of the dielectric modulus spectrum, indicating Maxwell–Wargner–Sillars (MWS) interfacial polarization. Effective electro-magnetic (EM) shielding was also evaluated for all compositions and a sharp peak of 22.99 dB (>99%) at 11.18 GHz was noticed for a 0.5 mm thick mat of the composite. This was observed to be dependent on the concentration of AuNPs and the thickness of the mat.

In-situ homogeneous dispersion of noble metals in three-dimensional graphene sheets is a key tactic for producing macroscopic architecture, which is desirable for practical applications, such as electromagnetic interference shielding and catalyst. We report a one-step greener approach for developing porous architecture of 3D-graphene/noble metal (Pt and Ag) nanocomposite monoliths. The resulting graphene/noble metal nanocomposites exhibit a combination of ultralow density, excellent elasticity and good electrical conductivity. Moreover, in order to illuminate the advantages of the 3D-graphene/noble metal nanocomposites, their electromagnetic interference (EMI) shielding and electrocatalytic performance are further investigated. The as-synthesized 3D-graphene/noble metal nanocomposites exhibit excellent EMI shielding effectiveness when compared to bare graphene; the effectiveness has an average of 28 dB in the 8.2–12.4 GHz X-band range. In the electro-oxidation of methanol, the 3D-graphene/Pt nanocomposite also exhibits significantly enhanced electrocatalytic performance and stability than compared to reduced graphene oxide/Pt and commercial Pt/C.