Search Results (64)

Ammonia borane (AB), with a theoretical hydrogen content of 19.6 wt%, is constrained by its low crystalline density (0.758 g/cm³) and poor thermal stability (decomposing at 100 °C). In this study, AB/ammonium perchlorate (AP) composites were synthesized via freeze-drying at a 1:1 molar ratio. The integration of AP introduced intermolecular interactions that suppressed AB decomposition, increasing the onset temperature by 80 °C. Subsequent vacuum calcination at 100 °C for 2 h formed oxygen/fuel-integrated ammonium perchlorate borane (APB), which achieved decomposition temperatures exceeding 350 °C. The proposed mechanism involved AB decomposing into borazine and BN polymers at 100 °C, which then NH₃BH₂⁺/ClO₄⁻ combined to form APB. At 350 °C, APB underwent the following redox reactions: 4NH₃BH₂ClO₄ → N₂↑ + 4HCl↑ + 2B₂O₃ + N₂O↑ + O₂↑ + 7H₂O↑ + H₂↑, while residual AP decomposed. The composite exhibited improved density (1.66 g/cm³) and generated H₂, N₂, O_2, and HCl, demonstrating potential for hydrogen storage. Additionally, safety was enhanced by the suppression of AB’s exothermic decomposition (100–200 °C). APB, with its high energy density and thermal stability, was identified as a promising high-energy additive for high-burning-rate propellants. Full article

Ammonia borane (AB) has attracted much attention in the field of solid-state hydrogen storage due to its high hydrogen storage capacity. Nanoconfinement in UiO-66 can reduce the hydrogen release temperature. In particular, terephthalic acid was used as a linker to further improve the dehydrogenation properties through the modification of -NH₂, -OH, -NO₂, -Br, and -F groups. The hydrogen release content of 0.5AB/UiO-66 was 1.98 wt.%, whereas the hydrogen release content of UiO-66-2OH modified by -OH groups increased to 3.85 wt.%. The non-covalent interaction results show that -NH₂ and -OH preferred adsorption with -BH₃, and the H in -NH₂ and -OH were able to interact directly with the H in AB to modify the dehydrogenation process of AB, whereas -NO₂, -Br, and -F indirectly affected the charge density of hydrogen atoms in AB to alter the dehydrogenation property of AB. The modification of functional groups provides a theoretical basis for the design of high-performance MOF nanoconfinement AB composite hydrogen storage materials. Full article

Ammonia borane (NH₃BH₃, AB) is recognized as a promising hydrogen carrier due to its high hydrogen storage density (146 gL⁻¹, mass fraction 19.6%), safety, non-toxicity, and high chemical stability. The hydrolysis of AB has also become a research hotspot in recent years and offers a viable route for hydrogen production. However, the practical application of AB hydrolysis encounters substantial challenges, including undefined catalytic mechanisms, suboptimal catalytic performance, and intricate issues in AB regeneration. Thus, elucidating catalytic mechanisms, developing highly efficient catalysts, and exploring effective regeneration methods for NH₃BH₃ are critical and urgent. This paper delves into the catalytic hydrolysis process of AB, detailing the mechanisms involved, and simplifies the steps that affect AB hydrolysis activity into the adsorption, activation, dissociation of reactants, and the formation and desorption of H₂. It discusses the structural characteristics of metal catalysts used in recent studies, assessing their performance through metrics such as turnover frequency (TOF), activation energy (E_a), and reusability. On this basis, this paper conducts a relatively comprehensive analysis and summary of the strategies for optimizing the performance of AB hydrolysis catalysts, including three aspects, focusing on optimizing the number and dispersion of active centers, enhancing reactant adsorption and activation, and facilitating hydrogen desorption. In addition, it also addresses strategies for controlled hydrogen release during AB hydrolysis and methods for regenerating AB from spent solutions. Finally, corresponding conclusions and prospects are proposed, to provide a certain reference for the subsequent development of safe and efficient catalysts and research on the catalytic mechanism of AB hydrolysis. Full article

Background: Wound healing is a complex and intricate biological process that involves multiple systems within the body and initiates a series of highly coordinated responses to repair damage and restore integrity and functionality. We previously identified that breathing hydrogen can significantly inhibit early inflammation, activate autologous stem cells, and promote the accumulation of extracellular matrix (ECM). However, the broader functions and downstream targets of hydrogen-induced ECM accumulation and tissue remodeling are unknown in the wound-healing process. Methods: Consequently, this thesis developed a hydrogen sustained-release dressing based on a micro storage material and reveals the mechanism of hydrogen in treating wound healing. Upon encapsulating the hydrogen storage materials, magnesium (Mg), and ammonia borane (AB), we found that SiO₂@Mg exhibits superior sustained-release performance, while SiO₂@AB demonstrates a higher hydrogen storage capacity. We used a C57/BL6 mouse full-thickness skin defect wound model to analyze and compare different hydrogen dressings. Results: It was identified that hydrogen dressings can significantly improve the healing rate of wounds by promoting epithelialization, angiogenesis, and collagen accumulation in wound tissue, and that the effect of slow-release dressings is better than of non-slow-release dressings. We also found that hydrogen dressing can promote transcriptome-level expression related to cell proliferation and differentiation and ECM accumulation, mainly through the Wnt1/β-catenin pathway and TGF-β1/Smad2 pathway. Conclusions: Overall, these results provide a novel insight into the field of hydrogen treatment and wound healing. Full article

The urgent global demand for sustainable green energy solutions has recognized hydrogen (H₂) as a viable green energy carrier. This study explores the efficient production of H₂ as a potential source of sustainable, environmentally friendly, high-energy-density fuel characterized by eco-friendly burning by-products. The research focuses on the photohydrolysis reaction of ammonia borane (AB), utilizing CdO-doped ZnO nanoparticles (NPs) embedded in polyurethane (PU) nanofibers (CdO/ZnO NPs@PU NFs) as a novel photocatalyst. Three different amounts of CdO/ZnO NPs were loaded onto PU NFs. The synthesized CdO/ZnO NPs@PU NFs exhibited good photocatalytic performance under visible light, producing approximately 67 mL of H₂ from 1 mmol of AB in 15 min with the sample containing the highest loading of CdO/ZnO NPs@PU NFs. This impressive photocatalytic performance is attributed to the synergistic effects of CdO and ZnO, which enhance charge carrier separation and broaden bandgap absorption in the visible spectrum. Kinetic studies demonstrated that the reaction exhibited first-order kinetics regarding catalyst dosing and zero-order kinetics concerning AB concentration, with an activation energy (E_a) of 32.28 kJ/mol. The results position CdO/ZnO NPs@PU NFs as effective photocatalysts for H₂ photogeneration under visible light irradiation. Full article

Porous carbon particles (PCPs) prepared from sucrose via the hydrothermal method and its modified forms with polyethyleneimine (PEI) as PCP-PEI were used as templates as in situ metal nanoparticles as M@PCP and M@PCP-PEI (M:Co, Ni, or Cu), respectively. The prepared M@PCP and M@PCP-PEI composites were used as catalysts in the hydrolysis of NaBH₄ and NH₃BH₃ to produce hydrogen (H₂). The amount of Co nanoparticles within the Co@PCP-PEI structure was steadily increased via multiple loading/reducing cycles, e.g., from 29.8 ± 1.1 mg/g at the first loading/reducing cycles to 44.3 ± 4.9 mg/g after the third loading/reducing cycles. The Co@PCP-PEI catalyzed the hydrolysis of NaBH₄ within 120 min with 251 ± 1 mL H₂ production and a 100% conversion ratio with a 3.8 ± 0.3 mol H₂/(mmol cat·min) turn-over frequency (TOF) and a lower activation energy (Ea), 29.3 kJ/mol. In addition, the Co@PCP-PEI-catalyzed hydrolysis of NH₃BH₃ was completed in 28 min with 181 ± 1 mL H₂ production at 100% conversion with a 4.8 ± 0.3 mol H₂/(mmol cat·min) TOF value and an Ea value of 32.5 kJ/mol. Moreover, Co@PCP-PEI composite catalysts were afforded 100% activity up to 7 and 5 consecutive uses in NaBH₄ and NH₃B₃ hydrolysis reactions, respectively, with all displaying 100% conversions for both hydrolysis reactions in the 10 successive uses of the catalyst. Full article

The utilization of hydrogen in safety conditions is crucial for the development of a hydrogen-based economy. Among all methodologies, solid-state hydrogen release from ammonia borane through thermal stimuli is very promising due to the high theoretical hydrogen release. Generally, carbonaceous or inorganic matrices have been used to tune the reactivity of ammonia borane. Nevertheless, these solutions lack chemical tunability, and they do not allow one to properly tune the complex chemical pathway of hydrogen release from ammonia borane. In this study, we investigated the effect of a bioderived multifunctional polymeric matrix on hydrogen release from ammonia borane, reaching pure hydrogen release of 1.2 wt.% at 94 °C. We also describe new chemical pathways involving the formation of anchored intermediates, namely BxNy species. Full article

We have investigated the thermodynamic property modification of ammonia borane via nanoconfinement. Two different mesoporous silica scaffolds, SBA-15 and MCM-41, were used to confine ammonia borane. Using in situ Raman spectroscopy, we examined how pore size influences the phase transition temperature from tetragonal (I4mm) to orthorhombic (Pmn21) for ammonia borane. In bulk ammonia borane, the phase transition occurs at around 217 K; however, confinement in SBA-15 (with ~8 nm pore sizes) reduces this temperature to approximately 195 K, while confinement in MCM-41 (with pore sizes of 2.1–2.7 nm) further lowers it to below 90 K. This suppression of the phase transition as a function of pore size has not been previously studied using Raman spectroscopy. The stability of the I4mm phase at a much lower temperature can be interpreted by incorporating the surface energy terms to the overall free energy of the system in a simple thermodynamic model, which leads to a significant increase in the surface energy when transitioning from the tetragonal phase to the orthorhombic phase. Full article

In this study, bimetallic NiCo nanoparticles (NPs) were encapsulated within the mesopores of carboxylic acid functionalized mesoporous silica (CMS) through the chemical reduction approach. Both NaBH₄ and NH₃BH₃ were used as reducing agents to reduce the metal ions simultaneously. The resulting composite was used as a catalyst for hydrolysis of ammonia borane (NH₃BH₃, AB) to produce H₂. The bimetallic NiCo NPs supported on carboxylic group functionalized mesoporous silica, referred to as Ni_xCo_100−x@CMS, exhibited significantly higher catalytic activity for AB hydrolysis compared to their monometallic counterparts. The remarkable activity of Ni_xCo_100−x@CMS could be ascribed to the synergistic contributions of Ni and Co, redox reaction during the hydrolysis, and the fine-tuned electronic structure. The catalytic performance of the Ni_xCo_100−x@CMS nanocatalyst was observed to be dependent on the composition of Ni and Co. Among all the compositions investigated, Ni₄₀Co₆₀@CMS demonstrated the highest catalytic activity, with a turn over frequency (TOF) of 18.95 mol_H2min⁻¹mol_catalyst⁻¹ and H₂ production rate of 8.0 L min⁻¹g⁻¹. The activity of Ni₄₀Co₆₀@CMS was approximately three times greater than that of Ni@CMS and about two times that of Co@CMS. The superior activity of Ni₄₀Co₆₀@CMS was attributed to its finely-tuned electronic structure, resulting from the electron transfer of Ni to Co. Furthermore, the nanocatalyst exhibited excellent durability, as the carboxylate group in the support provided a strong metal–support interaction, securely anchoring the NPs within the mesopores, preventing both agglomeration and leakage. Full article

A series of bench-stable Co(II) complexes containing hydrazone Schiff base ligands were evaluated in terms of their activity and selectivity in carbon-carbon multiple bond transfer hydrogenation. These cobalt complexes, especially a Co(II) precatalyst bearing pyridine-2-yl-N(Me)N=C-(1-methyl)imidazole-2-yl ligand, activated by LiHBEt₃, were successfully used in the transfer hydrogenation of substituted styrenes and phenylacetylenes with ammonia borane as a hydrogen source. Key advantages of the reported catalytic system include mild reaction conditions, high selectivity and tolerance to functional groups of substrates. Full article

This work focuses on the comparison of H₂ evolution in the hydrolysis of boron-containing hydrides (NaBH₄, NH₃BH₃, and (CH₂NH₂BH₃)₂) over the Co metal catalyst and the Co₃O₄-based catalysts. The Co₃O₄ catalysts were activated in the reaction medium, and a small amount of CuO was added to activate Co₃O₄ under the action of weaker reducers (NH₃BH₃, (CH₂NH₂BH₃)₂). The high activity of Co₃O₄ has been previously associated with its reduced states (nanosized CoB_n). The performed DFT modeling shows that activating water on the metal-like surface requires overcoming a higher energy barrier compared to hydride activation. The novelty of this study lies in its focus on understanding the impact of the remaining cobalt oxide phase. The XRD, TPR H₂, TEM, Raman, and ATR FTIR confirm the formation of oxygen vacancies in the Co₃O₄ structure in the reaction medium, which increases the amount of adsorbed water. The kinetic isotopic effect measurements in D₂O, as well as DFT modeling, reveal differences in water activation between Co and Co₃O₄-based catalysts. It can be assumed that the oxide phase serves not only as a precursor and support for the reduced nanosized cobalt active component but also as a key catalyst component that improves water activation. Full article

Graphene is a good support for immobilizing catalysts, due to its large theoretical specific surface area and high electric conductivity. Solid chemical converted graphene, in a form with multiple layers, decreases the practical specific surface area. Building pores in graphene can increase specific surface area and provide anchor sites for catalysts. In this study, we have prepared porous graphene (PG) via the process of equilibrium precipitation followed by carbothermal reduction of ZnO. During the equilibrium precipitation process, hydrolyzed N,N-dimethylformamide sluggishly generates hydroxyl groups which transform Zn²⁺ into amorphous ZnO nanodots anchored on reduced graphene oxide. After carbothermal reduction of zinc oxide, micropores are formed in PG. When the Zn²⁺ feeding amount is 0.12 mmol, the average size of the Pt nanoparticles on PG in the catalyst is 7.25 nm. The resulting Pt/PG exhibited the highest turnover frequency of 511.6 min⁻¹ for ammonia borane hydrolysis, which is 2.43 times that for Pt on graphene without the addition of Zn²⁺. Therefore, PG treated via equilibrium precipitation and subsequent carbothermal reduction can serve as an effective support for the catalytic hydrolysis of ammonia borane. Full article

Carbon-doped boron nitride (denoted by BN/C) was prepared through the pyrolysis at 1100 °C of a nanostructured mixture of an alkyl amine borane adduct and ammonia borane. The alkyl amine borane adduct acts as a soft template to obtain nanospheres. This bottom-up approach for the synthesis of nanostructured BN/C is relatively simple and compelling. It allows the structure obtained during the emulsion process to be kept. The final BN/C materials are microporous, with interconnected pores in the nanometer range (0.8 nm), a large specific surface area of up to 767 m²·g⁻¹ and a pore volume of 0.32 cm³·g⁻¹. The gas sorption studied with CO₂ demonstrated an appealing uptake of 3.43 mmol·g⁻¹ at 0 °C, a high CO₂/N₂ selectivity (21) and 99% recyclability after up to five adsorption–desorption cycles. Full article

The present study involves the synthesis of photocatalytic composite nanofibers (NFs) comprising ilmenite nickel titanite-supported carbon nanofibers (NiTiO₃/TiO₂@CNFs) using an electrospinning process. The photocatalytic composite NFs obtained were utilized in hydrogen (H₂) production from the photohydrolysis of ammonia borane (AB). The experimental findings show that the photocatalytic composite NFs with a loading of 25 mg had a good catalytic performance for H₂ generation, producing the stoichiometric H₂ in 11 min using 1 mmol AB under visible light at 25 °C and 1000 rpm. The increase in catalyst load to 50, 75, and 100 mg leads to a corresponding reduction in the reaction time to 7, 5, and 4 min. The findings from the kinetics investigations suggest that the rate of the photohydrolysis reaction is directly proportional to the amount of catalyst in the reaction system, adhering to a first-order reaction rate. Furthermore, it was observed that the reaction rate remains unaffected by the concentration of AB, thereby suggesting a reaction of zero order. Increasing the reaction temperature results in a decrease in the duration of the photohydrolysis reaction. Furthermore, an estimated activation energy value of 35.19 kJ mol⁻¹ was obtained. The composite nanofibers demonstrated remarkable and consistent effectiveness throughout five consecutive cycles. The results suggest that composite NFs possess the capacity to function as a feasible substitute for costly catalysts in the process of H₂ generation from AB. Full article

In this study, the successful titanium tetrachloride-catalyzed reduction of aldehydes, ketones, carboxylic acids, and nitriles with borane–ammonia was extended to the reduction (deoxygenation) of a variety of aromatic and aliphatic pri-, sec- and tert-carboxamides, by changing the stoichiometry of the catalyst and reductant. The corresponding amines were isolated in good to excellent yields, following a simple acid–base workup. Full article