Surface-Functionalized Boron Nanoparticles with Reduced Oxide Content by Nonthermal Plasma Processing for Nanoenergetic Applications

Simultaneous degradation of multiple micropollutants in flowing water by mild and strong microbubble-enhanced cold plasma activation

Elimination of stubborn organic micropollutants from water is crucial for bioaccumulation prevention and ecosystem protection. Cold plasma activation technology is a clean, sustainable, and highly effective approach to the degradation of micropollutants and pathogens in contaminated water. In this study, we focus on understanding the processes of simultaneous degradation of multiple micropollutants (8 types at maximum) in flowing water by the recently developed microbubble-enhanced cold plasma activation (MB-CPA) technology. The degradation of micropollutants with the treatment time was analyzed by using ultrahigh performance liquid chromatography coupled to a triple quadrupole mass spectrometer (UHPLC-QQQ-MS). We found that the degradation efficiencies of all compounds increase rapidly under strong activation conditions that can lead to above 98% removal of a model compound. After long treatment duration or at a fast flow rate, the removal efficiency was sufficiently high for all compounds that were either easy or hard to degrade. The large variation in degradation efficiencies was present under mild activation conditions. The electron spinning resonance measurements reveal a greater abundance of hydroxyl radicals in treated synthetic river water than pure water, highlighting the effects of water matrix on the degradation efficiency. The understanding from this work may help to design the activation process and minimize the energy consumption for the simultaneous elimination of pollutants in diverse and complex water bodies by cold plasma technology.

Plasma-Driven Conversion of 2D Graphene into 3D Pouch for Improved Electromagnetic Absorption Performance

Graphene-based materials are ideal for electromagnetic wave-absorbing materials (EAMs) due to their strong electrical and dielectric losses with reduced thickness and weight. To enhance the electromagnetic wave absorption performance of these materials, additional components are often incorporated. However, this approach not only increases the complexity of the synthesis process but also complicates and destabilizes the control of the material properties. In this study, we successfully employed a one-step method to reduce graphene oxide and transform 2D graphene into a 3D pocket-like structure through plasma treatment. This unique 3D structure is induced by the formation of uneven defects on the surface due to plasma treatment. The distinctive pouch-like structure of the reduced graphene oxide achieved remarkable electromagnetic wave absorption properties. Specifically, the material demonstrated a minimum reflection loss of -38.65 dB at 7.14 GHz, with an effective absorption bandwidth of 5.13 GHz and a thickness of just 1.9 mm. These results highlight the potential of plasma processing as a rapid, efficient, and environmentally friendly approach for the continuous production of advanced EAMs, paving the way for greener manufacturing practices in the industry.

Twisted Structure Induced Solid-State Fluorescence and Room-Temperature Phosphorescence from Furan-Based Carbon Dots

Boron doping can effectively induce solid-state fluorescence (SSF) in carbon dots (CDs); however, research on the intrinsic mechanism underlying this phenomenon is lacking. Herein, a design strategy for boron-doped furan-based CDs is proposed, CDs with aggregation-induced emission (AIE) properties are synthesized, and the mechanism by which boron atom dopants induces SSF and room-temperature phosphorescence (RTP) is elucidated. The morphology and structural characterization of the CDs indicate that boron doping leads to structural twisting of the CDs. The AIE phenomenon of CDs arises from the inhibition of the twisted structure motions and a reduction in the nonradiative relaxation rate during the aggregation process. In addition, CDs with twisted structures exhibit a smaller overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), effectively reducing the singlet-triplet splitting energy (ΔEST). CDs embedded in microcrystalline cellulose (MCC) exhibit green RTP because the nonradiative transitions are suppressed, and the excited triplet species remain stable. For the first time, this study reveals the structure-activity relationship between the twisted structure and optical properties of CDs, providing a new approach for the preparation of solid-state light-emitting CDs.

Combustion and mechanical properties enhancement strategy based on stearic acid surface activated boron powders

Boric acid and other impurities on the surface of boron (B) particles can interact with hydroxyl-terminated polybutadiene (HTPB), weakening the mechanical properties and energy release efficiency of boron-based solid rocket propellants. SA@B composite particles were created by coating stearic acid (SA) on the surface of B particles through solvent evaporation-induced self-assembly. The study investigated the impact of SA coating on the combustion performance of B particles and the mechanical properties of HTPB matrix composites. The results showed that the SA coating enhanced the oxidation efficiency of B particles in air. The combustion heat of SA@B composite particles is 30.29 MJ/g, about 50% higher than that of B particles. During the combustion of SA@B composite particles, fewer molten solid particles surround the flame, which enhances the stability of the combustion process of the B particles. Furthermore, the SA coating effectively enhanced the dispersion of B particles in HTPB. At a stretching speed of 100 mm/min, the tensile strength of the SA@B/HTPB composite materials is higher than that of the B/HTPB composite materials. Moreover, when the mass loading of the SA@B composite particles reaches 50 wt%, the tensile strength of SA@B/HTPB composite materials is 2.46 MPa. Activating the surface of boron particles with SA can significantly improve their compatibility with HTPB, which is crucial for the stable storage of boron-based solid rocket propellants.

Magnesium-Induced Strain and Immobilized Radical Generation on the Boron Oxide Surface Enhances the Oxidation Rate of Boron Particles: A DFTB-MD Study

Despite their high gravimetric and volumetric energy densities, boron (B) particles suffer from poor oxidative energy release rates as the boron oxide (B2O3) shell impedes the diffusivity of O2 to the particle interior. Recent experiemental studies have shown that the addition of metals with a lower free energy of oxidation, such as Mg, can reduce the oxide shell of B and enhance the energetic performance of B by ∼30-60%. However, the exact underlying mechanism behind the reactivity enhancement is unknown. Here, we performed DFTB-MD simulations to study the reaction of Mg vapor with a B2O3 surface. We found that the Mg becomes oxidized on the B2O3 surface, forming a MgBxOy phase, which induces a tensile strain in the B-O bond at the MgBxOy-B2O3 interface, simultaneously reducing the interfacial B and thereby developing dangling bonds. The interfacial bond straining creates an overall surface expansion, indicating the presence of a net tensile strain. The B with dangling bonds can act as active centers for gas-phase O2 adsorption, thereby increasing the adsorption rate, and the overall tensile strain on the surface will increase the diffusion flux of adsorbed O through the surface to the particle core. As the overall B particle oxidation rate is dependent on both the O adsorption and diffusion rates, the enhancement in both of these rates increases the overall reactivity of B particles.

From Basics to Frontiers: A Comprehensive Review of Plasma-Modified and Plasma-Synthesized Polymer Films

This comprehensive review begins by tracing the historical development and progress of cold plasma technology as an innovative approach to polymer engineering. The study emphasizes the versatility of cold plasma derived from a variety of sources including low-pressure glow discharges (e.g., radiofrequency capacitively coupled plasmas) and atmospheric pressure plasmas (e.g., dielectric barrier devices, piezoelectric plasmas). It critically examines key operational parameters such as reduced electric field, pressure, discharge type, gas type and flow rate, substrate temperature, gap, and how these variables affect the properties of the synthesized or modified polymers. This review also discusses the application of cold plasma in polymer surface modification, underscoring how changes in surface properties (e.g., wettability, adhesion, biocompatibility) can be achieved by controlling various surface processes (etching, roughening, crosslinking, functionalization, crystallinity). A detailed examination of Plasma-Enhanced Chemical Vapor Deposition (PECVD) reveals its efficacy in producing thin polymeric films from an array of precursors. Yasuda's models, Rapid Step-Growth Polymerization (RSGP) and Competitive Ablation Polymerization (CAP), are explained as fundamental mechanisms underpinning plasma-assisted deposition and polymerization processes. Then, the wide array of applications of cold plasma technology is explored, from the biomedical field, where it is used in creating smart drug delivery systems and biodegradable polymer implants, to its role in enhancing the performance of membrane-based filtration systems crucial for water purification, gas separation, and energy production. It investigates the potential for improving the properties of bioplastics and the exciting prospects for developing self-healing materials using this technology.

Electrochemical Modulation of the Flammability of Ionic Liquid Fuels

Flammability and combustion of high energy density liquid propellants are controlled by their volatility. We demonstrate a new concept through which the volatility of a high energy density ionic liquid propellant can be dynamically manipulated enabling one to (a) store a thermally insensitive oxidation resistant nonflammable fuel, (b) generate flammable vapor phase species electrochemically by applying a direct-current voltage bias, and (c) extinguish its flame by removing the voltage bias, which stops its volatilization. We show that a thermally stable imidazolium-based energy dense ionic liquid can be made flammable or nonflammable simply by application or withdrawal of a direct-current bias. This cycle can be repeated as often as desired. The estimated energy penalty of the electrochemical activation process is only ∼4% of the total energy release. This approach presents a paradigm shift, offering the potential to make a "safe fuel" or alternatively a simple electrochemically driven fuel metering scheme.

Engineered Surface Chemistry and Enhanced Energetic Performance of Aluminum Nanoparticles by Nonthermal Hydrogen Plasma Treatment

Extracting the maximum chemical energy from aluminum nanoparticles (Al NPs) during oxidation is essential for their use in energetic applications. However, the shell of native Al₂O₃ limits the release of chemical energy by acting as a diffusion barrier and dead weight. Engineering the surface properties of Al NPs by modifying their shell chemistry can reduce the inhibiting effects of the oxide shell on the rate and heat release of oxidation. Here, we employ nonthermal hydrogen plasma at high power and a short time to alter the shell chemistry by doping it with Al-H, as examined and confirmed by HRTEM, FTIR, and XPS. Thermal analysis (TGA/DSC) shows that Al NPs with modified surfaces exhibit augmented oxidation and heat release (33% higher than those of untreated Al NPs). The results demonstrate the promising effect of nonthermal hydrogen plasma in engineering the shell chemistry of Al NPs to improve their overall energetic performance during oxidation.

Metal-Doped Boron Quantum Dots for Versatile Detection of Lactate and Fluorescence Bioimaging

To improve the stability and fluorescence (FL) of monoelemental boron nanomaterials, this work put forward a metal-coordination strategy to explore emerging metal-doped boron quantum dots, Co@BQDs. Through theoretical calculations, B-Co bonding as predicted can suppress the B-O reaction and protect the electronic structures of exfoliated two-dimensional (2D) boron from oxidation and decomposition upon exposure to oxygen. In experimental studies, Co²⁺ was added into a dispersion liquid of bulk boron and subjected to probe sonication to promote Co²⁺ adsorption on the surface of exfoliated 2D boron, followed by Co²⁺ coordination with exposed boron atoms. Solvothermal treatment of exfoliated 2D boron resulted in the generation of Co²⁺-doped 0D boron Co@BQDs. Experimental results confirm that Co@BQDs have higher colloidal and FL stability than BQDs as a reference. B-Co bonding formation to suppress the B-O reaction ensures the high stability of exfoliated boron structures. A dispersion liquid of Co@BQDs with stable and bright FL was used for visual FL imaging of solutions and solid substrates. Based on enzymatic and cascade oxidation-induced FL quenching of Co@BQDs, a novel FL bio-probe of lactate was explored. This bio-probe, with a broad detection range of 0.01-10 mM and a low detection limit of 3.1 μM, enables FL sensing of lactate in biosamples and shows high detection recoveries of 98.0-102.8%. Moreover, this bio-probe realized versatile FL imaging and visual detection of lactate in liquid/solid-phase systems. These results demonstrate great prospects of Co@BQDs as emerging and efficient imaging reagents for long-term tracking and bioimaging applications.

Enhanced Energetic Performance of Aluminum Nanoparticles by Plasma Deposition of Perfluorinated Nanofilms

The performance of Al as nanoenergetic material in solid fuel propulsion or additive in liquid fuels is limited by the presence of the native oxide layer at the surface, which represents a significant weight fraction, does not contribute to heat release during oxidation, and acts as a diffusion barrier to Al oxidation. We develop an efficient technique in which the oxide layer is effectively turned into an energetic component via a reaction with fluorine that is coated in the form of a fluorocarbon nanofilm on the Al surface by plasma-enhanced chemical vapor deposition. Perfluorodecalin vapors are introduced in a low-pressure plasma reactor to produce nanofilms on the surface of Al nanoparticles, whose thickness is controlled with nanolevel precision as demonstrated by high-resolution transmission electron microscopy images. Coated particles show superior heat release, with a maximum enhancement of 50% at a thickness of 10 nm. This significant improvement is attributed to the chemical interaction between Al₂O₃ and F to form AlF₃, which removes the oxide barrier via an exothermic reaction and contributes to the amount of heat released during thermal oxidation. The chemistry and mechanism of the enhancement effect of the plasma nanofilms are explained with the help of X-ray photoelectron spectroscopy, X-ray diffraction, high-angle annular dark-field scanning transmission electron microscopy-energy dispersive spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.

Nanoenergetic Materials: Enhanced Energy Release from Boron by Aluminum Nanoparticle Addition

Boron has the highest enthalpy of oxidation per unit mass (and volume) among metals and metalloids and is an excellent candidate as a solid fuel. However, the native oxide present on the surface limits the available energy and rate of its release during oxidation. Here, we report a simple and effective method that removes the oxide in situ during oxidation via an exothermic thermite reaction with aluminum that enriches the particle in B at the expense of Al. B/Al blends with different compositions are optimized using thermogravimetry and differential scanning calorimetry, and the best sample in terms of energy release is characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive spectroscopy, and X-ray diffraction. All compositions release more energy than the individual components, and the blend containing 10% Al by weight outperforms pure B by 40%. The high energy release is due to the synergistic effect of B oxidation and thermite reaction between Al and B2O3. We demonstrate the formation of ternary oxide by the oxidation of the B/Al blend that provides porous channels for the oxidation of B, thereby maximizing the contact of the metal and oxidizer. Overall, the results demonstrate the potential of using B/Al blends to improve the energetic performance of B.

Effect of Fluoroalkylsilane Surface Functionalization on Boron Combustion

Boron has been regarded as a promising high-energy fuel due to its high volumetric and gravimetric heating values. However, it remains challenging for boron to attain its theoretical heat of combustion because of the existence of its native boron oxide layer and its high melting and boiling temperatures that delay ignition and inhibit complete combustion. Boron combustion is known to be enhanced by physically adding fluorine-containing chemicals, such as fluoropolymer or metal fluorides, to remove surface boron oxides. Herein, we chemically functionalize the surface of boron particles with three different fluoroalkylsilanes: FPTS-B (F3-B), FOTS-B (F13-B), and FDTS-B (F17-B). We evaluated the ignition and combustion properties of those three functionalized boron particles as well as pristine ones. The boron particles functionalized with the longest fluorocarbon chain (F17) exhibit the most powerful energetic performance, the highest heat of combustion, and the strongest BO₂ emission among all samples. These results suggest that the surface functionalization with fluoroalkylsilanes is an efficient strategy to enhance boron ignition and combustion.

Simultaneously Altering the Energy Release and Promoting the Adhesive Force of an Electrophoretic Energetic Film with a Fluoropolymer

Energetic coatings have attracted a great deal of interest with respect to their compatibility and high energy and power density. However, their preparation by effective and inexpensive methods remains a challenge. In this work, electrophoretic deposition was investigated for the deposition of an Al/CuO thermite coating as a typical facile effective and controllable method. Given the poor adhesion of the deposited film and the native inert Al₂O₃ shell on Al limiting energy output, further treatment was conducted by soaking in a Nafion solution, which not only acted as a fluoropolymer binder but also introduced a strong F oxidizer. It is interesting to note that the adhesion level of Al/CuO films was improved greatly from 1B to 4B, which was attributed to Nafion organic network film formation, like a fishing net covering the loose particles in the film. Combustion and energy release were analyzed using a high-speed camera and a differential scanning calorimeter. A combustion rate of ≤3.3 m/s and a heat release of 2429 J/g for Al/NFs/CuO are far superior to those of pristine Al/CuO (1.3 m/s and 841 J/g, respectively). The results show that the excellent combustion and heat release properties of the energetic film system are facilitated by the good combustion-supporting properties of organic molecules and the increase in the film density after organic treatment. The prepared Al/NFs/CuO film was also employed as ignition material to fire B-KNO₃ explosive successfully. This study provides a new way to prepare organic-inorganic hybrid energetic films, simultaneously altering the energy release and enhancing the adhesive force. In addition, the Al/NFs/CuO coating also showed considerable potential as an ignition material in microignitors.

Functionalized Boron Nanoparticles as Potential Promising Antimalarial Agents

Boron nanoparticles (BNPs), functionalized with hydroxyl groups, were synthesized in situ by a cascade process, followed by bromination and hydrolyzation reactions. These functionalized BNPs, (B _m (OH) _n ), were characterized using ¹H and ¹¹B NMR spectra, Fourier-transform infrared (FT-IR) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray photoelectron spectroscopy (XPS) methods. These nanoparticles were also evaluated in vitro for their antimalarial activity against Plasmodium falciparum (3D7 strain) with an IC₅₀ value of 0.0021 μM and showed low toxicity to Uppsala 87 malignant glioma (U87MG) cell lines, malignant melanoma A375 cell lines, KB human oral cancer cell lines, rat cortical neuron cell lines, and rat fibroblast-like synoviocyte (FLS) cell lines.

Enhancing Mechanical and Combustion Performance of Boron/Polymer Composites via Boron Particle Functionalization

High-speed air-breathing propulsion systems, such as solid fuel ramjets (SFRJ), are important for space exploration and national security. The development of SFRJ requires high-performance solid fuels with excellent mechanical and combustion properties. One of the current solid fuel candidates is composed of high-energy particles (e.g., boron (B)) and polymeric binder (e.g., hydroxyl-terminated polybutadiene (HTPB)). However, the opposite polarities of the boron surface and HTPB lead to poor B particle dispersion and distribution within HTPB. Herein, we demonstrate that the surface functionalization of B particles with nonpolar oleoyl chloride greatly improves the dispersion and distribution of B particles within HTPB. The improved particle dispersion is quantitatively visualized through X-ray computed tomography imaging, and the particle/matrix interaction is evaluated by dynamic mechanical analysis. The surface-functionalized B particles can be uniformly dispersed up to 40 wt % in HTPB, the highest mass loading reported to date. The surface-functionalized B (40 wt %)/HTPB composite exhibits a 63.3% higher Young's modulus, 87.5% higher tensile strength, 16.2% higher toughness, and 16.8% higher heat of combustion than pristine B (40 wt %)/HTPB. The surface functionalization of B particles provides an effective strategy for improving the efficacy and safety of B/HTPB solid fuels for future high-speed air-breathing vehicles.