Xiaofei Zhang

Flexible coordination networks (CNs) offer the potential for exceptional selectivity to enable hydrocarbon separations. The key to performance in such sorbents is guest-induced structural transformations that result in induced-fit binding. Unfortunately, the underlying mechanisms of such transformations remain largely unexplored. Herein, we report an investigation of the phase switching behavior of the square lattice (sql) CN [Cu(4,4'-bipyridine)₂(CF₃CO₂)₂]_n (sql-1-Cu-CF₃CO₂) induced by xylene adsorption. Competitive adsorption studies in binary and ternary xylene mixtures revealed high p-xylene (PX) selectivity of 10.83 over o-xylene (OX) and of 14.18 over m-xylene (MX), with an overall PX selectivity of 10.01, surpassing most commercial sorbents such as zeolites. Crystallographic studies revealed three distinct xylene-loaded phases with varying pore/channel dimensions and porosity: 1D (void: 33.9%) for PX, 2D (void: 45.8%) for OX, and 3D (void: 48.4%) for MX. The PX-loaded structure exhibited the smallest void but the strongest host-guest interactions, making it the preferred phase for PX separation from xylene mixtures.

Nature’s redox enzymes achieve remarkable selectivity by organizing active sites with precise spatial control, an ability difficult to replicate in synthetic systems. Inspired by this, we report a class of stable, metal-free bicarbenium-based molecular catalysts that undergo electrochemical two-electron reduction to form biradical intermediates. These radicals are confined within a rigid xanthene bridge (~4.3 Å), creating a spatially defined pocket that engages paramagnetic substrates like O₂ and NO. This biradical-mediated synergistic catalysis enables highly selective two-electron oxygen reduction (99.3% H2O2 selectivity, 96.8% Faradaic efficiency, 2.21 mol g⁻¹cat h⁻¹ productivity) and three-electron nitric oxide reduction (NH₂OH as major product, 87.2% Faradaic efficiency, 1.68 mol g-¹cat h-¹ productivity). Experimental and computational studies confirm sustained redox cycling supported by favorable spin-pairing and substrate binding geometries, which enhance catalytic selectivity and efficiency. This work demonstrates a blueprint for pathway-specific, radical-mediated catalysis and offers new design principles for metal-free electrocatalytic platforms exploiting open-shell reactivity.

The preactivation of reactants within the cavities of carbon nanotubular materials has remained largely unexplored due to the scarcity of materials with well-defined sizes and precisely engineered doping sites. Herein, we demonstrate that the catalytic activity toward the oxygen reduction reaction (ORR) is primarily governed by the cavity sizes of well-defined nanobelt materials with precisely doped sp²-nitrogen atoms. Our results show that the confinement effect induced by cavity size and the electron-rich chemical environment within the cavity are crucial for O₂ adsorption and preactivation, leading to enhanced catalytic activity. Belt2, with its medium-sized cavity (6.3 Å), exhibits superior ORR catalytic performance compared to Belt1 with its narrower cavity and Belt3/Belt4 with its larger cavities. Notably, Belt2 achieves high half-wave and onset potentials of 0.84 and 0.97 V, respectively, along with an open-circuit voltage of 1.32 V and a peak power density of 181 mW cm^-2 in a zinc-air battery. This work not only provides a deeper understanding of the geometric factors influencing the ORR electrocatalysis of nanocarbon materials but also offers insights into the future design of nanocarbon electrocatalysts for enhancing catalytic efficiency. These findings may also be beneficial for other energy conversion and catalytic materials.

Water sorption isotherms of [Zn(tmz) ₂ ] _n (MAF-7) were measured across a broad temperature range to evaluate its water sorption performance based on water uptake, sorption kinetics, recyclability, and regeneration temperature.

The electrocatalytic production of hydrogen peroxide (H ₂ O ₂ ) through the two‐electron oxygen reduction reaction (2e ⁻ ORR) has garnered significant research attention in recent years due to its numerous appealing advantages, such as being eco‐friendly and exhibiting high energy conversion efficiency. Metal‐free carbon materials with specific catalytic sites have been recognized as potential electrocatalysts for 2e ⁻ ORR; however, the design of highly efficient catalysts with well‐defined structures and long‐term stability for large‐scale H ₂ O ₂ production remains unsatisfactory. In this study, three covalent organic frameworks (COFs) – imine‐linked LZU‐1, oxazole‐linked LZU‐190, and thiazole‐linked LZU‐190(S), are successfully synthesized to explore their catalytic activity in electrocatalytic H ₂ O ₂ production. Among these, the carbon sites LZU‐190(S) are predominantly activated by the introduced adjacent heteroatoms via electronic effects, resulting in much higher H ₂ O ₂ selectivity compared to the oxazole and imine linkages. This work provides new insights into developing COFs‐based electrocatalysts for efficient H ₂ O ₂ generation.

A well-known Werner complex, [Ni(4-methylpyridine)₄(NCS)₂], has been revisited to investigate its phase switching and shape-memory effect induced by p-xylene vapor.

Monomers with low symmetries can form different topological structures in the preparation of organic two-dimensional (2D) materials. However, it remains challenging to modulate the topologies in practical synthesis. Leveraging theoretical insights into the formation energy of potential structural configurations, we report the topology modulation of a graphdiyne (GDY) derivative constructed from two-fold symmetric tetrakis(4-ethynylphenyl)ethene precursor by changing solvent combinations in a liquid-liquid interfacial system. An aqueous-organic (water-dichloromethane) interface afforded GDY with a kagome topology while a rhombic topology was formed at an organic-organic (hexane-acetonitrile) interface. A comprehensive evaluation of their structures and optoelectronic properties was conducted through various characterization techniques and theoretical computations. Our study provided new insights to modulate the topology of not only GDY but also other framework structures and obtain topologically pure materials in situations where different topologies are possible during practical synthesis.

Numerous efforts are being made toward constructing artificial nanopockets inside heterogeneous catalysts to implement challenging reactions that are difficult to occur on traditional heterogeneous catalysts. Here, the enzyme-mimetic nanopockets are fabricated inside the typical UiO-66 by coordinating zirconium nodes with terephthalate (BDC) ligands and monocarboxylate modulators including formic acid (FC), acetic acid (AC), or trifluoroacetic acid (TFA). When used in transfer hydrogenation of alkyl levulinates with isopropanol toward γ-valerolactone (GVL), these modulators endow zirconium sites with enhanced activity and selectivity and good stability. The catalytic activity of UiO-66FC is ~30 times that of UiO-66, also outperforming the state-of-the-art heterogeneous catalysts. Distinct from general consensus on electron-withdrawing or electron-donating effect on the altered activity of metal centers, this improvement mainly originates from the conformational change of modulators in the nanopocket to assist forming the rate-determining six-membered ring intermediate at zirconium sites, which are stabilized by van der Waals force interactions.