Search Results (14)

In this work, Etna ash-derived photocatalysts were investigated for the first time for solar H₂ production. Volcanic ash, commonly treated as a special waste in eastern Sicily (Italy), was modified through chemical treatment followed by microwave-assisted crystallization, avoiding the conventional high-temperature thermal route. The obtained material was tested both as a bare photocatalyst and as a support for a Nb₂O₅/graphitic carbon nitride composite prepared by a hydrothermal method. The Etna-derived photocatalyst exhibited a solar H₂ production rate (by TEOA photoreforming) of 920 μmol/g_cat∙h. Upon incorporation of the Nb-based composite, the H₂ evolution rate increased by about 2.5 times, reaching 2370.5 μmol/gcat∙h, demonstrating a strong synergistic effect. Notably, the developed materials largely outperformed commercial TiO₂ P25 (25 μmol/g_cat∙h). The enhanced photocatalytic activity was attributed to the tailored modifications of Etna ash, which increased porosity and promoted aluminosilicate framework reorganization, favoring an optimal distribution of the photocatalytically active TiO₂ and iron oxide phases. The obtained Nb oxide/carbon nitride supported on modified Etna ash also showed a remarkable stability after six consecutive runs of solar photocatalytic H₂ production. This work demonstrates a sustainable strategy for converting volcanic waste into efficient multifunctional photocatalysts while minimizing the use of critical raw materials. Full article

Polyimide, a class of high-performance polymers, is renowned for its exceptional thermal stability, mechanical strength, and chemical resistance. However, in the context of high-integration and high-frequency electronic packaging, polyimides face critical challenges including relatively high dielectric constants, inadequate thermal conductivity, and mechanical brittleness. Recent advances have focused on molecular design and composite engineering strategies to address these limitations. This review first summarizes the intrinsic properties of polyimides, followed by a systematic discussion of chemical synthesis, surface modification approaches, molecular design principles, and composite fabrication methods. We comprehensively examine both conventional polymerization synthetic routes and emerging techniques such as microwave-assisted thermal imidization and chemical vapor deposition. Special emphasis is placed on porous structure engineering via solid-template and liquid-template methods. Three key modification strategies are highlighted: (1) surface modifications for enhanced hydrophobicity, chemical stability, and tribological properties; (2) molecular design for optimized dielectric performance and thermal stability; and (3) composite engineering for developing high-thermal-conductivity materials with improved mechanical strength and electromagnetic interference (EMI) shielding capabilities. The dielectric constant of polyimide is reduced while chemical stability and wear resistance can be enhanced through the introduction of fluorine groups. Ultra-low dielectric constant and high-temperature resistance can be achieved by employing rigid monomers and porous structures. Furthermore, the incorporation of fillers such as graphene and boron nitride can endow the composite materials with high thermal conductivity, excellent EMI shielding efficiency, and improved mechanical properties. Finally, we discuss representative applications of polyimide and composites in electronic device packaging, EMI shielding, and thermal management systems, providing insights into future development directions. Full article

In the present investigation, aluminum metal matrix composites (AMMs) reinforced with aluminum nitride (AlN) nanoparticulates at different volumetric ratios of (0, 0.5, 1, 1.5, and 2 vol.%) were manufactured via a microwave-assisted powder metallurgy technique. The morphological, physical, mechanical, and electrochemical properties of the produced billets were examined to reflect the impact of the successive addition of AlN into the aluminum (Al) matrix. The morphological analysis revealed the high crystalline patterns of the formation of the Al-AlN composites. The microstructural analysis confirmed the presence of the elemental constituents of Al and AlN particles in the fabricated composites, showing an enhanced degree of agglomeration in conjunction with the additional amount of AlN. Positive behavior exhibited by the micro- and nanohardness was noticeable in the Al-AlN composites, especially at the ultimate concentration of AlN in the Al matrix of a 2 vol.%, where it reached 669.4 ± 28.1 MPa and 659.1 ± 11 MPa compared to the pure Al metal at 441.2 ± 20 MPa and 437.5 ± 11 MPa, respectively. A declining trend in the compressive strength was recorded in the reinforced Al samples. The corrosion resistance of the AlN-reinforced Al metal matrix was estimated at 3.5 wt.% NaCl using electrochemical impedance spectroscopy and potentiodynamic polarization. The results reveal that the inclusion of 2.0 vol.%AlN led to the lowest corrosion rate. Full article

This study focuses on fabricating cobalt particles deposited on graphitic carbon nitride (Co/gCN) using annealing, microwave-assisted and hydrothermal syntheses, and their employment in hydrogen and oxygen evolution (HER and OER) reactions. Composition, surface morphology, and structure were examined using inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The performance of Co-modified gCN composites for the HER and OER were investigated in an alkaline media (1 M KOH). Compared to the metal-free gCN, the modification of gCN with Co enhances the electrocatalytic activity towards the HER and OER. Additionally, thermal annealing of both Co(NO₃)₂ and melamine at 520 °C for 4 h results in the preparation of an effective bifunctional Co₃O₄/gCN catalyst for the HER with the lower E_onset of −0.24 V, a small overpotential of −294.1 mV at 10 mA cm⁻², and a low Tafel slope of −29.6 mV dec⁻¹ in a 1.0 M KOH solution and for the OER with the onset overpotential of 286.2 mV and overpotential of 422.3 mV to achieve a current density of 10 mA cm⁻² with the Tafel slope of 72.8 mV dec⁻¹. Full article

The preparation of visible-light-driven photocatalysts has become highly appealing for environmental remediation through simple, fast and green chemical methods. The current study reports the synthesis and characterization of graphitic carbon nitride/titanium dioxide (g-C₃N₄/TiO₂) heterostructures through a fast (1 h) and simple microwave-assisted approach. Different g-C₃N₄ amounts mixed with TiO₂ (15, 30 and 45 wt. %) were investigated for the photocatalytic degradation of a recalcitrant azo dye (methyl orange (MO)) under solar simulating light. X-ray diffraction (XRD) revealed the anatase TiO₂ phase for the pure material and all heterostructures produced. Scanning electron microscopy (SEM) showed that by increasing the amount of g-C₃N₄ in the synthesis, large TiO₂ aggregates composed of irregularly shaped particles were disintegrated and resulted in smaller ones, composing a film that covered the g-C₃N₄ nanosheets. Scanning transmission electron microscopy (STEM) analyses confirmed the existence of an effective interface between a g-C₃N₄ nanosheet and a TiO₂ nanocrystal. X-ray photoelectron spectroscopy (XPS) evidenced no chemical alterations to both g-C₃N₄ and TiO₂ at the heterostructure. The visible-light absorption shift was indicated by the red shift in the absorption onset through the ultraviolet-visible (UV-VIS) absorption spectra. The 30 wt. % of g-C₃N₄/TiO₂ heterostructure showed the best photocatalytic performance, with a MO dye degradation of 85% in 4 h, corresponding to an enhanced efficiency of almost 2 and 10 times greater than that of pure TiO₂ and g-C₃N₄ nanosheets, respectively. Superoxide radical species were found to be the most active radical species in the MO photodegradation process. The creation of a type-II heterostructure is highly suggested due to the negligible participation of hydroxyl radical species in the photodegradation process. The superior photocatalytic activity was attributed to the synergy of g-C₃N₄ and TiO₂ materials. Full article

Visible-light-active, organic, heterogeneous photocatalysts offer an ecologically friendly and sustainable alternative to traditional metal-based catalysts. In this work, we report the microwave synthesis of nanocarbon dots (CDs), loaded with graphitic carbon nitride (g-C₃N₄). The fabricated nanocomposite was shown to exhibit various properties, such as the Schottky heterojunction. The optical properties, functional group analysis, surface morphology, crystallinity, chemical stability, electronic properties, and pore size distribution of the synthesized nanocomposite were analyzed by Ultraviolet-Diffuse Reflectance Spectroscopy (UV-DRS), Photoluminescence (PL), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Zeta potential, X-Ray Photoelectron Spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). Until now, to the best of our knowledge, there have been no reports published on the light-assisted synthesis of O-arylation of 2-chloroquinoline-3-carbaldehyde. Therefore, we explored the photocatalytic activity of the fabricated nanocomposite in the production of the O-arylated 2-chloroquinoline-3-carbaldehyde. This facile technique uses a blue LED light source as a non-conventional source and operates under moderate conditions, resulting in useful O-arylated products. The experimental data shows the good recyclability of the catalyst for up to five cycles without a loss in catalytic activity, a simple operational protocol, easy recoverability of the catalyst, and good product yields (65–90%) within 12–24 h. Additionally, the preliminary mechanistic investigations are discussed. The results show that the phenoxy and quinoline-3-carbaldehyde radicals generated upon blue LED irradiation during the course of the reaction are responsible for C-O bond formation, which results in O-arylation. The present study clearly indicates that 0D/2D nanocomposites have a bright future as metal-free, heterogeneous photocatalysts suitable for organic reactions. Full article

This study explores the tribological performance of microwave-assisted synthesized g-C₃N₄/MoS₂ coatings. The two-dimensional transition metal dichalcogenide (TMD) nanosheet is getting prominence in the study of tribology due to its layered structure. The graphitic carbon nitride (g-C₃N₄) nanosheet was made using the calcination method and its nanocomposite with molybdenum disulfide (MoS₂) was produced using a microwave-assisted method. The structure and morphology of the samples were characterized by some well-known methods, and tribological properties were studied by a pin-on-disc (POD) apparatus. Morphological analysis revealed that graphitic carbon nitride and molybdenum disulfide coexisted, and the layer structured MoS₂ was well dispersed on graphitic carbon nitride nanosheets. BET analysis was used to determine the pore volume and specific surface area of the synthesized materials. The inclusion of MoS₂ nanoparticles caused the composite’s pore volume and specific surface area to decrease. The reduction in g-C₃N₄ pore volume and specific surface area confirmed that the pores of calcinated graphitic carbon nitride were filled with MoS₂ nanoparticles. The tribological property of g-C₃N₄/MoS₂ nanocomposite was systematically investigated under different factors such as applied loads (5N to 15N), sliding speed (500 to 1000 mm/s) and material composition (uncoated, MoS₂-coated, 9 wt.% of g-C₃N₄ and 20 wt.% of g-C₃N₄ in the composite). The optimal composite material ratio was taken 9%, by weight of g-C₃N₄ in the g-C₃N₄/MoS₂ composite for a variety of levels of loads and sliding speeds. The results indicates that the incorporation of g-C₃N₄ in nanocomposites could reduce friction and improve wear life, which were better than the results with single MoS₂. This study demonstrates a solution to broaden the possible uses of g-C₃N₄ and MoS₂-based materials in the field of tribology. Full article

The aim of the present study was to systematically review studies investigating antibacterial implant abutment surfaces or coatings, which may suppress bacterial growth to prevent plaque-induced peri-implant inflammatory disease. Data were collected after identification of case, assay/laboratory procedure, predicate/reference standard and outcome (CAPO). Seven hundred and twenty (720) records were identified through data base searching. After screening nine publications fulfilled inclusion criteria and were included. The following surfaces/coatings showed antibacterial properties: Electrochemical surface modification of titanium by the anodic spark deposition technique; doxycycline coating by cathodic polarization; silver coating by DC plasma sputter; titanium nitride; zirconium nitride and microwave assistant nano silver coating. Since the current state of the literature is rather descriptive, a meta-analysis was not performed. While several abutment coatings showed to have antibacterial capacity, some of them also influenced the behavior of investigated human cells. None of the studies investigated the long-term effect of surface modifications. Since surface changes are the main contributing factor in the development of antibacterial effects, the biodegradation behavior must be characterized to understand its durability. To date there is no effective structure, material or strategy to avoid peri-implant inflammation used as clinical routine. Furthermore, clinical studies are scarce. Full article

In this study, we implemented a high-performance two-terminal memristor device with a metal/insulator/metal (MIM) structure using a solution-derived In-Ga-Zn-Oxide (IGZO)-based nanocomposite as a resistive switching (RS) layer. In order to secure stable memristive switching characteristics, IGZO:N nanocomposites were synthesized through the microwave-assisted nitridation of solution-derived IGZO thin films, and the resulting improvement in synaptic characteristics was systematically evaluated. The microwave-assisted nitridation of solution-derived IGZO films was clearly demonstrated by chemical etching, optical absorption coefficient analysis, and X-ray photoelectron spectroscopy. Two types of memristor devices were prepared using an IGZO or an IGZO:N nanocomposite film as an RS layer. As a result, the IGZO:N memristors showed excellent endurance and resistance distribution in the 10³ repeated cycling tests, while the IGZO memristors showed poor characteristics. Furthermore, in terms of electrical synaptic operation, the IGZO:N memristors possessed a highly stable nonvolatile multi-level resistance controllability and yielded better electric pulse-induced conductance modulation in 5 × 10² stimulation pulses. These findings demonstrate that the microwave annealing process is an effective synthesis strategy for the incorporation of chemical species into the nanocomposite framework, and that the microwave-assisted nitridation improves the memristive switching characteristics in the oxide-based RS layer. Full article

In the course of this study, the dielectric and physicochemical properties of poly(2-oxazoline) (POx) networks from renewable resources were compared with those of fossil-based polyamide 12 (PA 12) networks. POx was synthesized by the energy-efficient, microwave-assisted copolymerization of 2-oxazoline monomers, which were derived from fatty acids of coconut and castor oil. For the preparation of composites, aluminum nitride nanoparticles n-AlN and microparticles μ-AlN as well as hexagonal boron nitride BN submicroparticles were used. Additionally, 0, 15, or 30 wt.% of a spiroorthoester (SOE) were added as an expanding monomer aiming to reduce the formation of shrinkage-related defects. For the crosslinking of the polymers and the SOE as well as the double ring-opening reaction of the SOE, a thermally triggered dual-cure system was developed. The fully-cured blends and composites containing SOEs exhibited lower densities than their fully-cured SOE-free analogues, which was indicative of a lower extent of shrinkage (or even volumetric expansion) during the curing reaction, which is referred to as relative expansion RE. The RE amounted to values in the range of 0.46 to 2.48 for PA 12-based samples and 1.39 to 7.50 vol.% for POx-based samples. At 40 Hz, the “green” POx networks show low loss factors, which are competitive to those of the fossil-based PA 12. Full article

This research work aims at investigating the influence of a fixed content of silicon nitride (Si₃N₄) and varied contents of graphene nanoplatelets (GNPs) on the physical (density, structural, morphological) and mechanical properties (microhardness, nanoindentation) of Al-Si₃N₄-GNPs composites. The composites were fabricated by a microwave-assisted powder metallurgy route. The Si₃N₄ concentration was fixed at (5 wt.%) in Al-Si₃N₄-GNPs composites while the GNPs concentration was varied between (0 wt.%) to (1.5 wt.%) with an increment of (0.5 wt.%). The structural analysis indicates the formation of phase pure materials with high crystallinity. The microstructural analysis confirmed the presence of the Si₃N₄ and GNPs showing enhanced agglomeration with the increasing amount of GNPs. Moreover, the surface roughness of the synthesized composites increases with an increasing amount of GNPs reaching its maximum value (RMS = 65.32 nm) at 1.5 wt.% of GNPs. The Al-Si₃N₄-GNPs composites exhibit improved microhardness and promising load-indentation behavior during nanoindentation when compared to pure aluminum (Al). Moreover, Al-Si₃N₄-GNPs composites demonstrate higher values of compressive yield strength (CYS) and ultimate compressive strength (UCS) when compared to pure Al despite showing a declining trend with an increasing amount of GNPs in the matrix. Finally, a shear mode of fracture is prevalent in Al-Si₃N₄-GNPs composites under compression loading. Full article

Gallium nitride (GaN) has attracted increased attention because of superior material properties, such as high electron saturation velocity and high electrical field strength, which are promising for high-power microwave applications. We report on a high-performance vertical GaN-based Schottky barrier diode (SBD) and its demonstration in a microwave power limiter for the first time. The fabricated SBD achieved a very low differential specific on-resistance (R_ON,sp) of 0.21 mΩ·cm², attributed to the steep-mesa technology, which assists in reducing the spacing between the edge of the anode and cathode to 2 μm. Meanwhile, a low leakage current of ~10⁻⁹ A/cm²@−10 V, a high forward current density of 9.4 kA/cm² at 3 V in DC, and an ideality factor of 1.04 were achieved. Scattering parameter measurements showed that the insertion loss (S₂₁) was lower than −3 dB until 3 GHz. In addition, a microwave power limiter circuit with two anti-parallel diodes was built and measured on an alumina substrate. The input power level reached 40 dBm (10 watts) in continuous-wave mode at 2 GHz, with a corresponding leakage power of 27.2 dBm (0.5 watts) at the output port of the limiter, exhibiting the great potential of GaN SBD in microwave power limiters. Full article

The integration of block copolymer (BCP) self-assembled nanopattern formation as an alternative lithographic tool for nanoelectronic device fabrication faces a number of challenges such as defect densities, feature size, pattern transfer, etc. Key barriers are the nanopattern process times and pattern formation on current substrate stack layers such as hard masks (e.g., silicon nitride, Si₃N₄). We report a rapid microwave assisted solvothermal (in toluene environments) self-assembly and directed self-assembly of a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) BCP thin films on planar and topographically patterned Si₃N₄ substrates. Hexagonally arranged, cylindrical structures were obtained and good pattern ordering was achieved. Factors affecting BCP self-assembly, notably anneal time and temperature, were studied and seen to have significant effects. Graphoepitaxy within the topographical structures provided long range, translational alignment of the patterns. The effect of surface topography feature size and spacing was investigated. The solvothermal microwave based technique used to provide periodic order in the BCP patterns showed significant promise and ordering was achieved in much shorter periods than more conventional thermal and solvent annealing methods. The implications of the work in terms of manufacturing technologies are discussed. Full article

In this study, magnesium composites with nano-size boron nitride (BN) particulates of varying contents were synthesized using the powder metallurgy (PM) technique incorporating microwave-assisted two-directional sintering followed by hot extrusion. The effect of nano-BN addition on the microstructural and the mechanical behavior of the developed Mg/BN composites were studied in comparison with pure Mg using the structure-property correlation. Microstructural characterization revealed uniform distribution of nano-BN particulates and marginal grain refinement. The coefficient of thermal expansion (CTE) value of the magnesium matrix was improved with the addition of nano-sized BN particulates. The results of XRD studies indicate basal texture weakening with an increase in nano-BN addition. The composites showed improved mechanical properties measured under micro-indentation, tension and compression loading. While the tensile yield strength improvement was marginal, a significant increase in compressive yield strength was observed. This resulted in the reduction of tension-compression yield asymmetry and can be attributed to the weakening of the strong basal texture. Full article