30 Mar 05:25
by Jisu Park,
Seongbin Kim,
Taehoon Hwang,
Hyekyeong Kim,
Hyunseo Jang,
Minseob Lim,
Hoseong Son,
Dashdendev Tsogbayar,
Yumin Kim,
Suhyun Oh,
Siyoung Lee,
Hyungju Ahn,
Yong‐Ho Choa,
Hwa Sung Lee
ABSTRACT
Miniaturization and rising power densities exacerbate localized hot spots on electrically insulating substrates, where heat spreads non-selectively. A boron nitride nanotube (BNNT)/epoxy “thermal guide” is developed for selective, geometry-programmable heat routing. A viscosity-tuned BNNT/epoxy ink is processed by micro-nozzle extrusion; confinement-induced shear aligns BNNTs into an orientation-defined architecture, as confirmed by small-angle X-ray scattering and supported by flow simulations identifying nozzle size as a key alignment control. Aligned bulk composites exhibit pronounced in-plane anisotropy (k
y/k
x ≈ 2.53; 2.96 vs 1.17 W m−
1 K−
1, parallel vs transverse to the fiber direction), and infrared thermography visualizes alignment-guided heat transport: at 5 cm from a 70°C source, the y-axis-oriented specimen reaches 55.8°C after 30 s, compared with 48.1°C for the x-axis-oriented specimen. Dielectric integrity is retained at network-forming loadings, with volume resistivity of ∼1013 Ω·m at 20 wt.% BNNT and low dielectric loss. Dispenser printing enables ∼200 µm-wide guides; contacting a 70°C source at the guide terminus produces >20°C terminal contrast relative to the surrounding region outside the printed pattern. This method therefore enables electrically safe thermal routing to guide heat from a localized source to a target region while suppressing parasitic lateral diffusion into heat-sensitive areas.
29 Jan 01:44
by Youdong Xing,
Xianfeng Yi,
Fengqing Liu,
Yao Xiao,
Wanyi Gan,
Molly Meng‐Jung Li,
Anmin Zheng
Strong Brønsted acidity accelerates zeolite deactivation. We demonstrate that hydroxylating framework aluminum strategically weakens Brønsted acid sites, as quantified by solid-state NMR spectroscopy assisted with 2–13C-acetone probe and DFT calculations. This reduces methanol over-activation and significantly extends catalyst lifetime in the methanol-to-olefins reaction, thus positioning coordination design as a key strategy for catalytic optimization.
ABSTRACT
The strong acidity of Brønsted acid sites in zeolites often leads to uncontrollable reactions and rapid deactivation. Therefore, strategically weakening zeolite acidity is essential for balancing reactivity with stability. The local coordination environment of framework aluminum usually governs its acidity. Hydroxylation of framework aluminum is often inevitable under high-temperature and humid “working” conditions; however, the impact of hydroxyl coordination on the relevant acidity and catalytic behavior remains unclear. Here, we demonstrate how hydroxylation of framework aluminum strategically moderates acidity and enhances catalytic stability. Density functional theory (DFT) calculations predict that an increase in the hydroxyl groups coordinated to framework aluminum leads to a progressive weakening of Brønsted acidity. We experimentally validate this prediction by precisely manipulating hydroxylation in ZSM-5 zeolite via steaming treatment and analyzing the effects using 2D NMR spectroscopy with 2–13C-acetone as a probe molecule. The hydroxylated aluminum sites exhibit reduced adsorption and activation of methanol in the dehydration reaction, consistent with their weaker acidity. Catalytic tests reveal that the hydroxylated samples significantly enhance catalyst lifespan in the MTO process, while preserving stable reactivity. These findings provide key insights into how coordination perturbations influence zeolite acidity and catalytic performance, offering valuable guidance for designing zeolites with targeted catalytic functions.
06 Jan 10:32
by Yuetong Qian,
Zhengchen Wu,
Xiaowei Lv,
Lei Wang,
Longjun Rao,
Min Liu,
Ruixuan Zhang,
Renchao Che
Utilizing curvature and porous structures in the configuration significantly enhances C-band magnetic resonance absorption performance. It achieves an effective absorption bandwidth of 4–8 GHz while maintaining a thickness of just 2.5 mm.
ABSTRACT
The stability of intelligent life and industry primarily relies on the signal interference shielding among different equipment. The key challenge lies in efficient absorption of electromagnetic waves within the C-band, which dominates the satellite internet, high-speed WLAN, and 5/6G communication spectra. Herein, the structural symmetry and surface anisotropy co-dominated magnetic engineering has been proposed to realize the effective electromagnetic wave absorption within 4–8 GHz. The hierarchical structural morphology optimization has been first developed to guide the configuration integration of symmetric anisotropy, streamline surface, and porous for CoNi-based alloys. Such hierarchical architecture allows synergy of diversified magnetic configuration, external domain symmetry, and enhanced dipolar coupling interaction, dramatically enhancing magnetic resonance absorption within C-bands. Our results provide a preparation idea for acquiring precise modulation of magnetic resonance eigenfrequency while realizing high-performance low-frequency microwave absorbers.
14 Apr 13:14
by Chuang Ma,
Shumei Wang,
Lili Gao,
Zhuo Xu,
Xin Song,
Tinghuan Yang,
Haojin Li,
Xinmei Liu,
Shengzhong (Frank) Liu,
Kui Zhao
The crystal structure of low-dimensional perovskite can be modulated by halides. Here, halide modulation enables the transition of (4AP)PbX4 (4AP = 4-amidinopyridine) crystal structures from one-dimensional perovskitoid (Cl) to two-dimensional perovskite (Br or I). The (4AP)PbBr4 X-ray detector reaches the sensitivity of 373.1 µC Gyair
−1 cm−2.
Abstract
Low-dimensional perovskites (LDPs) have attracted significant attention due to their high stability, great chemical flexibility, and fertile “playground” for structural modulation, which are expected to herald the next-generation multifunctional devices. While there is a high diversity of LDPs in the literature, the organic cations in most of the literature are still limited to amines. Here, the preparation of centimeter-sized LDP single crystals with amidino-based spacers is described, which enables systematic investigations on how halides initiate different structural stacking and on their physical properties. The 4-amidinopyridine (4AP) cation in (4AP)PbX4 (X = Br, I) is vertically distributed between the inorganic layers to form a two-dimensional perovskite. While the Cl-based exhibits one-dimensional perovskitoid packing. The change of halogens from Cl to Br and I leads to a lower hydrogen bonding, hardness and activation energy of the crystal. Finally, the potential of these crystals for X-ray detectors is demonstrated. The (4AP)PbBr4 device achieves the highest sensitivity among three devices (373.1 µC Gyair
−1 cm−2, 10 V), benefiting from the balanced charge transport and ionic migration. It is anticipated that this work will lead to further studies on the exploration and physics of novel LDP with properties suitable for radiation detection.