查找使用阿拉丁产品的科研文献

Mechanical properties, thermophysical properties, and long-term ablation behaviours of C/C–ZrC– ZrB2– W–Cu composites

Junjie Xu,Wei Sun,Xiang Xiong,Hongbo Zhang,Lingkun Yang

Spacecraft thermal protection materials need to survive long-term exposure to oxygen-containing environments at 2400 °C. In this study, a high-density and low-porosity metal-ceramic-modified composite was prepared at a low temperature (1500 °C) in the presence of W and Cu using combined slurry brushing and reactive melt infiltration methods. An investigation of the composite formation mechanism and the effects of W and Cu indicated that W and ZrB 2 were formed via dissolution-precipitation and the external diffusion of C and B, respectively. The low reaction temperature and the metallic phases significantly improved the mechanical properties, thermophysical properties, and long-term ablation behaviours of C/C–ZrC–ZrB 2 –W–Cu. Compared to traditional C/C–ZrC, the flexural strength and fracture toughness of the composite increased by 71.56 % and 90.05 % to 345.95 MPa and 14.52 MPa m 1/2 , respectively, and the thermal conductivity increased by 174.93 % to 59.11 W/m·K. In addition, W and Cu effectively lowered the surface temperature by nearly 250 °C during 300 s ablation, and the mass and line ablation rates decreased to −0.272 mg/s and −0.247 μm/s, respectively.

Visible-light-driven selective cleavage of lignin C-C bonds on the TiO2@g-C3N4 heterostructured photocatalyst

Gang Xiao,Zishuai Wang,Yu Jin,Fengping Wang

The selective cleavage of lignin C–C bonds is a highly sought-after process with the goal of obtaining low-molecular-weight aromatic chemicals from renewable resources. However, it remains a challenging task to achieve under mild conditions. Photocatalysis is a potentially promising approach to address this issue, but the development of efficient photocatalysts is still in progress. In this study, we introduce the heterostructured TiO2@g-C3N4 photocatalyst for the development of a visible light photocatalytic procedure for the selective cleavage of lignin C–C bonds under mild conditions. The photocatalyst displays favourable visible light absorption, efficient charge separation efficiency, and promising reusability. A typical β–O–4 dimer model, 2-phenoxy-1-phenylethanol, was effectively (96.0% conversion) and selectively (95.0 selectivity) cleaved under visible light at ambient conditions. This photocatalytic procedure was also effective when subjected to solar irradiation or other lignin dimer models with β–O–4 or β-1 linkages. This reaction occurred through a Cβ-centred radical intermediate and a six-membered transition state with photogenerated holes as the primary active species. The Cα–OH oxidative dehydrogenation of the substrate could also take place but was a relatively minor route. This study provides a new photocatalytic procedure for visible-light-driven lignin valorisation and sheds light on the design of high-performance nanocomposite photocatalysts for C–C bond cleavage.

Enhanced oxidation resistance of Yb2O3-HfB2-SiC/SiC coatings for protecting C/C composites at 1973 K

Zhilun Zhang,Wei Xie,Xuanru Ren,Bingqing Zhao,Ziqi Zhao,Qian Wang,Mingliang Li,Hailong Wang

To enhance oxidation resistance of carbon/carbon (C/C) composite materials at 1973 K in static air, a novel bilayer Yb 2 O 3 -HfB 2 -SiC/SiC (denoted YHSS) coatings were engineered via a two-step process combining pack cementation and slurry method. A substantial loading of ceramic phases (∼60 wt %) was incorporated into the SiC ceramic layer to improve thermal stability of the oxide scale at 1973 K. Following pre-oxidation, the YHSS coatings impart effective oxidation protection to C/C composite materials for over 228 h at 1973 K. Coupled experimental and theoretical analyses confirm that Yb and Hf atoms diffuse into the thermally grown SiO 2 layer, thereby reinforcing the SiO 2 network structure. Furthermore, the coating's exceptional performance is attributed to its dense, flaw-free surface morphology and the homogeneous dispersion of high-content ceramic phases throughout the SiC layer, collectively suppressing oxygen permeation.

Asymmetric C─C Coupling Induced by a Potential Field Boosts Electrocatalytic CO2 Reduction to Multi-Carbon Products

Sihang Hu,Haiquan Liu,Mingyu Yang,Huan Dai,Chongyang Tang,Dong He,Xiangheng Xiao

The complex reaction interface and the high reaction barrier for C─C coupling hinder the conversion of CO 2 toward high-value C 2+ products. In this work, thiol is employed to modify facet-controlled Cu nanoparticles, systematically elucidating the tripartite interaction between organic modifiers, active sites, and key intermediates. Theoretical calculations, Kelvin Probe Force Microscope (KPFM), and in situ investigations reveal that the thiol-derived spatial potential field facilitates CO 2 activation and the formation of hydrocarbon intermediates ( * COH). More importantly, the results demonstrate that the C 2+ products of the thiol-modified catalyst are strongly dependent on the crystal planes: the potential field preferentially drives suitable adsorbed * COH to asymmetric * CO- * COH coupling on Cu (100)/(111) interface. Consequently, the C 2+ selectivity of the thiol-modified Cu (100)/(111) interface-rich Cu nanoparticle is intrinsically enhanced, exhibiting high selectivity to C 2+ products with a faradaic efficiency (FE) of 85.44%. Remarkably, the structure achieves a C 2 H 4 FE of 73.79% ± 2.69% with a peak partial current density of 345.75 mA cm − 2 (total current: 1.38 A). Beyond establishing a high-efficiency CO 2 to C 2+ conversion protocol, this study provides mechanistic insights into the selective steering of C─C coupling through tailored surface modifications.

A Simple Method to Prepare the High Performance Pd(OH)2/C for C–N Bond Cleavage

Bin Zhang,Xiaodong Guo,Xin Feng,Xiaoxia Duan,Guilong Wang,Chao Yang

The debenzylation reaction of hexabenzylhexaazaisowurtzitane (HBIW) and 2,6,8,12-tetraacetyl-4,10-dibenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (TADBIW) to synthesize 2,6,8,12-tetraacetyl-2,4,6,8,10,12-hexaazaisowurtzitane (TAIW) is the major challenge in the production of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW). This is primarily attributed to the reaction needing a lot of palladium catalysts, which tend to deactivate rapidly during the process. In this work, a series of Pd(OH)2/C catalysts were successfully prepared through a convenient deposition-precipitation method by controlling the flow rate of the PdCl2 solution. Employing the 10% Pd(OH)2/C–F0.5 sample, the debenzylation reaction was successfully completed with a lower usage of Pd and shorter time of reaction. For the HBIW debenzylation reaction, the yield of TADBIW was 87.4% at low temperature (25 °C) when 1‰ Pd/HBIW was used, and the higher yield was 89.8% at high temperature (45 °C) when 3‰ Pd/HBIW was used. The TADBIW/Pd/h values of them were 42.5 and 95.7, respectively. For the TADBIW debenzylation reaction, the complete conversion of the reactant was realized when Pd/TADBIW was 2‰. The value of TAIW/Pd/h was 154.6 when Pd/TADBIW was 4‰, which was higher than the reports. Compared to the reported catalysts, the dosage of Pd used in the debenzylation reactions of HBIW and TADBIW was significantly decreased. Furthermore, the 10% Pd(OH)2/C–F0.5 sample was recycled six times with similar performance, demonstrating excellent stability. Based on the analysis of characterization results, it is effortless to find that the flow rate of the PdCl2 solution plays a key role in controlling the adsorption behavior of palladium species on activated carbon. The lower flow rate is beneficial to obtaining Pd nanoparticles with a smaller size, a higher proportion of Pd2+, and a higher metal distribution. This study may provide a simple way to develop palladium catalysts with high performance for related applications.

Atroposelective remote meta-C–H activation

Jian-Jun Li,Jia-Hui Zhao,Hua-Chen Shen,Kevin Wu,Xin Kuang,Peng Wang,Jin-Quan Yu

Enhanced oxidation resistance of CrSi2-SiC ceramic coatings on SiC coated C/C composites via SiC nanowires reinforcement

Xinfa Qiang,Xiangyu Chen,Maoheng Dong,Zi Yang,Wensu Meng,Hai Kan,Keqing Wang,Lijin Wang,Ling Wang,Chao Wu

A unique bead-chain-like SiC nanowires (SiCnws) morphology was successfully synthesized via an aerogel carbothermal reduction method. Microstructural analysis revealed that the SiC chain display diameters ranging from 100 to 200 nm, while the SiO2 bead exceed 1 μm in diameter. A SiCnws reinforced CrSi2-SiC/SiC coating was prepared on C/C composites by a two-step pack cementation. Comparative analysis revealed that SiCnws-reinforced coating exhibited better densification with lesser cracks and pores. Isothermal oxidation tests at 1773 K in static air demonstrated exceptional performance: the SiCnws-reinforced coating showed only 14.98% mass loss after 30 h, while the unreinforced coating suffered 36.53% mass loss after 14 h. XRD/SEM characterization confirmed that SiCnws enhanced structural integrity by promoting the formation of a continuous SiO2-Cr2O3 glassy layer during oxidation, while mitigating crack propagation through pinning and bridging effects.

Engineering Oxygen Vacancies on Ceria via Vanadium Oxide Dispersion for Selective Photocatalytic Cleavage of Lignin C-C Bonds

Zupeng Chen,Yongqi Zhuang,Yuguo Dong,Yanmei Zheng,Wenjun Zhang,Lin Dong

Lignin, the most abundant natural aromatic polymer on Earth, offers a promising feedstock for the production of value-added aromatic products through selective C-C bond cleavage. However, achieving both high product yield and selectivity under mild conditions, such as under visible-light irradiation, remains a significant challenge. In this study, we address this issue by employing ceria (CeO2) as a support to precisely engineer the dispersion of vanadium oxide through two distinct catalyst pretreatment methods: impregnation–calcination (Im-V/CeO2) and physical mixing–calcination (Pm-V/CeO2). The results demonstrate that the Im-V/CeO2 catalyst exhibits superior performance, converting 1,2-diphenylethanol to benzaldehyde with an impressive 89% yield and 98% selectivity, while CeO2 alone yields 52% and Pm-V/CeO2 yields 45%. This enhanced performance of Im-V/CeO2 is attributed to the introduction of low-polymerized vanadium oxide (VOx) species. Unlike highly polymeric V2O5 crystals, these species facilitate the separation of photogenerated electron-hole pairs and reduce charge transfer resistance, thereby improving photocatalytic efficiency. Additionally, the polar nature of VOx species enhances the activation of lattice oxygen, creating more sites for oxygen adsorption and activation. In-depth mechanistic studies reveal that superoxide radicals play a dominant role in the C-C bond cleavage process. This innovative strategy for achieving high-efficiency photocatalytic C-C bond cleavage through the controlled dispersion of vanadium oxide on a cerium oxide support offers valuable insights for the sustainable valorization of lignin.

Renoprotective Effects of Stemona sessilifolia via Suppression of the c-Myc/c-Fos/MAPK Pathway in Hyperuricemic Nephropathy

Xin-Yao Li,Bang-Yin Tan,Yue Zhang,Yan-Lin Lv,Yun-Li Zhao,Xiao-Dong Luo

Ethnopharmacological relevance Stemona sessilifolia (Miq.) Miq. has been employed in traditional medicine for its potential renal benefits, including anti-edema, diuretic, and anti-jaundice properties. However, the renoprotective effects related to these traditional uses remain to be fully elucidated. Aim of the study : To investigate the therapeutic efficacy of S . sessilifolia against hyperuricemic nephropathy and elucidate its underlying signaling pathway. Materials and methods A hyperuricemic nephropathy mouse model, induced by potassium oxonate and hypoxanthine, was employed to evaluate the renal protection of the extract of S. sessilifolia through biochemical tests and histopathological observation. Transcriptomic analysis was applied to explore potential signaling pathways. Subsequently, bioassay-guided isolation was conducted during phytochemical investigation. Uric acid-induced HK-2 cells were then employed to validate the renal cytoprotective effects of the isolated compounds. Results Treatment with S. sessilifolia extract significantly reduced serum uric acid, creatinine, and urea nitrogen levels by 65.15%, 47.95%, and 49.1%, respectively. Additionally, it decreased urinary protein excretion, and ameliorated renal injury and fibrosis in mice. The protective effects might be exerted by inhibiting the c-Myc/c-Fos/MAPK signaling pathway to maintain the homeostasis of renal tissue. Moreover, the bioactive compound stemoninine protected HK-2 cells against uric acid-induced oxidative stress, inflammatory response, proliferation, migration, and apoptosis. Conclusion The S. sessilifolia extract and its major bioactive compound, stemoninine, protected against hyperuricemic nephropathy by suppressing the c-Myc/c-Fos/MAPK signaling pathway.

Robust Core–Shell C@C/SiO2 Nanofibers for Superior Electromagnetic Shielding Withstanding Repeated Joule Heating and Multiple Bending

Fujian Liu,Min Li,Mengnan Liu,Yujie You,Su Liu,Qiangyu Xue,Azim Abdullaev,Yinsong Si

Flexible electromagnetic interference (EMI) shielding inorganic materials integrated with thermal management remain highly desirable for next-generation wearable electronics in protective applications. Here, a core–shell carbon@carbon/silica (C@C/SiO 2 ) composite nanofiber is fabricated via a coaxial electrospinning and subsequent carbonization. By tailoring the carbon content in the core and the carbonization temperature, the resulting C@C/SiO 2 nanofiber achieves a gradient interfacial architecture. Benefiting from the continuous C core and the groove-like C/SiO 2 shell, the C@C/SiO 2 nanofiber exhibits high flexibility, superior EMI shielding, and reliable thermal control performance. The optimized conductivity and impedance matching endow the composite membrane with an outstanding EMI shielding effectiveness of 30.8 dB and a high shielding effectiveness/thickness value of 133.7 dB mm −1 at only 0.23 mm thickness, corresponding to a shielding efficiency exceeding 99.92%. Moreover, it delivers ultrafast and stable Joule heating behavior, reaching ≈220 °C within 10 s at a low voltage of 10 V and a maximum temperature of 250 °C. Meanwhile, the membrane also maintains structural and functional stability even after 8000 bending cycles and 100 thermal shock cycles. This work provides a tunable route toward lightweight, durable, and highly efficient EMI shielding membranes for applications in flexible electronics and harsh-environment protection systems.

Ablation behavior of (ZrC/SiC)3 alternate coating prepared on sharp leading edge C/C composites by CVD

B. Li,H.J. Li,X.Y. Yao,X.F. Tian,Y.J. Jia,G.H. Feng

A (ZrC/SiC) 3 alternate coating was deposited on sharp leading edge (SLE) C/C composites by chemical vapor deposition (CVD). The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m 2 . The results indicated that the alternate coating exhibited great ablation resistance, providing an effective protection for C/C composites. In initial rapid heating stage, the (ZrC/SiC) 3 alternate coating can relieve thermal stress, avoiding the peeling of coating and keeping an intact coating structure. In subsequent ablation, the SiC layers in central region were consumed rapidly, leaving layered interspaces. Three stacked ZrO 2 layers were reserved with the assistance of the release of thermal stress by interspaces, offering a great anti-scouring effect. In transition and border regions, the alternate SiC layers can delay oxygen erosion of inner coating and C/C substrate by the formation of SiO 2 . It is believed that the results would be helpful for the design and application of anti-ablation coatings on SLE C/C composites.

Nitrogen doped mesoporous carbon supporting Pd–Ni nanoparticle as a highly efficient catalyst for C–C coupling reactions

Zhou Lin,Wang Ruo-Bing

Nitrogen doped mesoporous carbon (N-MPC)-supported monometallic and bimetallic catalysts were synthesized by using hydrothermal and impregnation method, and the catalytic activity of the catalyst to carbon–carbon bond-forming reactions (Suzuki, Heck and Sonogashira reactions) was studied. The bimetallic catalyst Pd-Ni@N-MPC with high Ni to Pd atomic ratios showed highly activity in the C–C coupling reactions of aryl halide under optimized condition. In contrast to their monometallic counterparts, such Pd-Ni@N-MPC catalyst not only show higher catalytic activity but also show more economic and stable. The catalysts were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope and transmission electron microscopy, which demonstrated that the Pd–Ni NPs highly dispersed and possessed uniform size. Graphical abstract