Chemistry - An Asian Journal最新文献

Urea-assisted water electrolysis is a promising and energy-efficient alternative to electrochemical water splitting due to its low thermodynamic potential of 0.37 V, which is 860 mV less than that needed for water splitting (1.23 V). Ni(OH)₂ has proven to be an efficient catalyst for this reaction. However, the non-spontaneous desorption of CO₂ molecules from the catalyst surface leads to active site poisoning, which significantly impacts its long-term stability. Herein, we have demonstrated that Pd incorporated NiOH₂ (Pd/Ni(OH)₂) results in a significant decrease in the overpotential by 40 mV at 10 mA cm⁻² as compared to Ni(OH)₂. The decrease in the Tafel slope and charge transfer resistance of Pd/Ni(OH)₂ indicates an improvement in the kinetics of the reaction, resulting in a maximum current density of 380 mA cm⁻² at 1.5 V, which is higher than that observed for Ni(OH)₂ (180 mA cm⁻²). XAS analysis was utilized to determine the nature of the metal species in the catalyst. It revealed that while Pd predominantly exists in its metallic state within the bulk of the catalyst, the surface is enriched with the oxide phase. The presence of Pd prevents the strong adsorption of CO₂ at the active site in Pd/Ni(OH)₂, resulting in a substantial improvement of stability of up to 300 h as compared to Ni(OH)₂. DFT calculations were performed to explore the detailed reaction mechanism of urea oxidation on Ni(OH)₂ and Pd/Ni(OH)₂. These calculations provided further insight into the experimental observations and evaluated the contribution of Pd in enhancing the catalytic efficiency of Ni(OH)₂. Additionally, the operando Raman and IR spectroscopy were used to understand the formation of the active sites and the intermediates during urea electrooxidation.

The observation of slow relaxation of magnetization in low-spin square planar cobalt complexes is exceedingly rare, likely due to the synthetic challenges of stabilizing such geometries, along with the complexities introduced by hyperfine interactions and spin-orbit coupling. Additionally, accurately characterizing the ground-state electronic configuration of these complexes remains a significant challenge. In this article, we report a unique and rare square planar cobalt complex, [Co(L1⋅^-)₂] (1), where the coordination sites are occupied by the phenanthroiminoquinone (L1). The molecular structure of complex 1 was determined using single-crystal X-ray diffraction studies. A structurally analogous nickel complex, [Ni^II(L1⋅^-)₂] (2), was also synthesized and characterized. Detailed DC magnetic susceptibility measurements of 2 reveal strong antiferromagnetic exchange interactions between the radical centers, rendering it diamagnetic. For cobalt complex 1, this strong antiferromagnetic coupling results in a doublet ground state, as corroborated by X-band EPR measurements (at 5 K) conducted on both polycrystalline and frozen solution samples. To gain deeper insights into the electronic structure of the cobalt ion in 1, a comprehensive suite of experimental and theoretical investigations was conducted, including X-ray diffraction, DC magnetic studies, X-band EPR, UV-Vis-NIR spectroscopy, and ab initio calculations. These studies collectively indicate that the cobalt ion in 1 exists in a divalent low-spin state. Furthermore, the observed slow relaxation of magnetization for the doublet state of 1 highlights its potential as an ideal candidate for designing spin-based molecular qubits.

The research progress of solid solution materials in the field of photocatalysis was introduced. The synthesis methods of solid solution photocatalytic materials are comprehensively expounded, and the modification strategies of solid solution photocatalysts are analyzed and discussed. This paper systematically summarizes the characteristics and development of the main catalytic systems of solid solution materials, and explored the application of first-principles calculations in the photocatalysis of solid solution materials in combination with practical research. Subsequently, the main application progress of photocatalysis of solid solution materials in the fields of environmental remediation and energy conversion was introduced. Finally, the current challenges, development directions and prospects are prospected.

Development of efficient and cost-effective catalysts for the dehydrogenation of Ammonia-Borane (AB) has been a challenge which affects the advancement of the hydrogen economy. Over the last decades, pincer-type transition metal complexes have been known to show promising results in catalyzing many chemical reactions ranging from CO₂ reduction to C-H bond activation. In this work we investigate the ability of a high-valent Ni-III-Cl complex (complex 1) for the dehydrogenating AB. Our results show that complex 1 can dehydrogenate two equiv. of AB under reaction conditions slightly higher than room temperature. Although the abstraction of H₂ from AB can occur at room temperature, higher temperature is required due to relatively higher free-energy barriers for the formation of molecular H₂. However, when the Ni-III center is substituted by a Fe-III center (complex 2), AB dehydrogenation can occur at room temperature for one equiv. of AB with a free-energetic span of 21.07 kcal/mol, but this does not remain the same for the second catalytic cycle for complex 2 and the free-energy energetic span increases to 36.1 kcal/mol. Therefore, for the initial cycle of AB dehydrogenation, the Fe-III complex has better functionality and this work exhibits the impact of metal mono-substitution, specifically Fe in activating AB dehydrogenation at room temperature and further paves the way for simple modelling of transition metal-based complexes as catalysts for such reactions.

Graphene/Silicon (Gr/Si) heterojunction shows great potential as high-efficiency, cost-effective solar cells compared to traditional Si solar cells. However, the high optical loss of c-Si, mainly originating from abrupt change of refractive index at air/Si interface, and the unsatisfactory conductivity of practically prepared graphene layer, still hinder their extensive applications. Herein, we report the performance improved Gr/Si solar cells by depositing a polymathic methacrylate (PMMA) anti-reflection coating (ARC) layer through a one-step transferred method. The graphene and PMMA ARC with specific thickness were transferred on n-type Si wafer at the same time, which reduces production steps and obtains high-quality graphene layer. By tuning the thickness of the PMMA layer, the reflection can be reduced obviously. Companying with the HNO₃ vapor doping for graphene, the Gr/Si heterojunction solar cell with a high power conversion efficiency (PCE) of 13.7 % was achieved. In addition, the durability of the device is improved under HNO₃ doping. Considering the easy and cost-effective solution processed capability of the one-step transferred graphene and PMMA ARC layer, we believed that PMMA/Gr/Si is a feasible low-temperature technique for high-efficiency Si solar cells.

Recently, we developed a new aggregation-induced emission (AIE) luminogen (AIEgen), bridged stilbene, by incorporating a propylene group into the C=C bond of the luminescent phenyl stilbene. This bridged structure, featuring a seven-membered ring, induces a significant conformational change, causing the C=C bond to twist in the excited state, thereby enhancing non-radiative decay in solution. In this study, we introduced bridged structures with alkylene groups of varying lengths into (E,E)-1,4-diphenyl-1,3-butadiene (DPB). The variation in the bridged structures of the synthesized DPB derivatives notably influenced the environmental sensitivity of fluorescence. Whereas the compound with two six-membered ring structures exhibited emission in solution and in the polycrystalline state, derivatives with a seven-membered ring exhibited AIE properties. Specifically, BDPB[7,7], featuring two seven-membered ring structures, demonstrated AIE characteristics with solid-state luminescence originating from J-aggregates. However, the fluorescence quantum yield was low in poly(methyl methacrylate) (PMMA) dispersion films, where molecular motion was restricted. These findings open new possibilities for designing unique AIEgens that remain nonluminescent even in highly viscous or confined environments, such as PMMA films.

The impact of introducing a redox-active system to the molecular framework of an organic small molecule on the resistive switching memory behaviour is studied using a series of novel quinoxaline-ferrocene systems. The quinoxaline acceptor part has been modified with different substitutions, impacting the overall electronic properties and leading to diverse device performances. The devices exemplified appreciable non-volatile WORM memory behaviour with an ON/OFF ratio exceeding 104 and the lowest recorded threshold voltage of -0.69 V with substantially good endurance (100 cycles) and retention (104 s) characteristics. The photophysical studies revealed good intramolecular charge transfer between the ferrocene and quinoxaline units. The electrochemical investigation demonstrated a weak redox activity of the ferrocene unit when attached to strong electron-withdrawing quinoxaline units, resulting in a decrease in the intensity of the reduction peak. Furthermore, an optimum band gap was found for all the compounds, which ranged between 2.74 to 2.97 eV. The resistive switching mechanism was validated by molecular simulations, and charge transfer and charge trapping processes, along with the redox activity of the ferrocene center, contributed to the observed memory behaviour in these devices.

This study presents a novel and practical strategy for synthesizing cannabinoids using a fluorinated alcohol solvent for the first time. Hexafluoroisopropanol (HFIP) was found to efficiently promote intermolecular Friedel-Crafts alkylation between allylic alcohols and electron-rich aromatics. This approach enabled the successful synthesis of cannabidiol (CBD) derivatives bearing various alkyl substituents, as well as the corresponding unnatural regioisomer (abnCBD), achieving moderate to high yields under mild conditions without the need for additional catalysts or other reagents. Insights in the mechanistic details were obtained through DFT calculations. Furthermore, a streamlined three-step synthesis of 5-alkyl resorcinol derivatives, essential starting materials for CBD synthesis, from the readily available chalcones was developed. Preliminary cytotoxicity assays using MTT revealed that some synthetic CBD derivatives exhibited promising anticancer activities.

A metal free oxidative desulfitative C−N coupling reaction through activation of latent thiol group using hypervalent iodine reagent is being reported in eco-friendly solvent ethanol. Here, the thio-amide group present in 5-alkylidene-rhodanine has been utilized as latent thiol functionality and C−N coupling with amines is realized. The reaction occurs evading the use of metal catalysts, inert atmosphere, high temperature or microwave heating, and strong base which is normally required for metal catalyzed C−N coupling reaction. Pertinently, here poorly nucleophilic aromatic amines react very efficiently. Desulfitative C−N coupling involving free thiol moiety and poorly nucleophilic aromatic amines in metal free condition has never been accomplished in one step, without requiring high temperature microwave heating or strong bases. The reaction occurs at just 50 °C in few hours under ambient atmosphere. Moreover, here no H₂S is released in the environment, since solid sulphur is precipitated out as side product, making this protocol environmentally friendly. Metal free condition, low temperature, use of non-toxic solvent and reagent, prevention of the release of H₂S in the environment make this protocol very much environmentally friendly and highly suitable for C−N coupling in a sustainable way.

Given the high similarity in physical and chemical properties, especially in terms of molecular size and boiling point, of acetylene (C₂H₂), carbon dioxide (CO₂), and ethylene (C₂H₄) molecules, traditional separation techniques encounter great challenges. Fortunately, metal organic framework (MOF) materials have demonstrated significant potential for efficient separation of these gases at the molecular level due to their finely tunable pore structure and surface functional properties. In this paper, we have successfully synthesized a cadmium-based MOF (FJI-W-708), which exhibits negative electrostatic potential pores and exceptional thermal stability. It is worth noting that FJI-W-708 exhibits high C₂H₂ capacity (61 cm³/g), as well as appropriate selectivity towards C₂H₂/CO₂ (3.39) and C₂H₂/C₂H₄ (3.47). The dynamic breakthrough experiments of C₂H₂/CO₂ (50/50) mixture and C₂H₂/C₂H₄ (1/99) mixture clearly demonstrated the actual separation performance. The breakthrough time for C₂H₂/CO₂ (50/50) was observed to be 23 min/g, while for a C₂H₂/C₂H₄ (1/99) mixture it could reach up 46 min/g, demonstrating excellent recyclability and achieving a benchmark productivity of C₂H₄ at 4.12 mmol/g.