Xinle Li

A three-dimensional microporous metal-metalloporphyrin framework.

A new porphyrin-based microporous MOF, {Mn(II)0.5[Mn(II)4Cl(Mn(III)Cl-ttzpp)2(H2O)4]}·(DEF)20·(CH3OH)18·(H2O)12 (UTSA-57), has been constructed from {5,10,15,20-tetrakis[4-(2,3,4,5-tetrazolyl)phenyl]porphyrinato} manganese(III) chloride as the metalloligand. The MOF adopts the rare scu topology with one-dimensional square nanotube-like channels of about 20 Å. UTSA-57a exhibits permanent porosity and displays moderately high performance for C2H2/CH4 separation at room temperature.

High‐Temperature‐Stable and Regenerable Catalysts: Platinum Nanoparticles in Aligned Mesoporous Silica Wells

We report the synthesis, structural characterization, thermal stability study, and regeneration of nanostructured catalysts made of 2.9 nm Pt nanoparticles sandwiched between a 180 nm SiO2 core and a mesoporous SiO2 shell. The SiO2 shell consists of 2.5 nm channels that are aligned perpendicular to the surface of the SiO2 core. The nanostructure mimics Pt nanoparticles that sit in mesoporous SiO2 wells (Pt@MSWs). By using synchrotron-based small-angle X-ray scattering, we were able to prove the ordered structure of the aligned mesoporous shell. By using high-temperature cyclohexane dehydrogenation as a model reaction, we found that the Pt@MSWs of different well depths showed stable activity at 500 °C after the induction period. Conversely, a control catalyst, SiO2 -sphere-supported Pt nanoparticles without a mesoporous SiO2 shell (Pt/SiO2 ), was deactivated. We deliberately deactivated the Pt@MSWs catalyst with a 50 nm deep well by using carbon deposition induced by a low H2 /cyclohexane ratio. The deactivated Pt@MSWs catalyst was regenerated by calcination at 500 °C with 20 % O2 balanced with He. After the regeneration treatments, the activity of the Pt@MSWs catalyst was fully restored. Our results suggest that the nanostructured catalysts-Pt nanoparticles confined inside mesoporous SiO2 wells-are stable and regenerable for treatments and reactions that require high temperatures.

Metal–Organic‐Framework‐Derived Carbons: Applications as Solid‐Base Catalyst and Support for Pd Nanoparticles in Tandem Catalysis

The facile pyrolysis of a bipyridyl metal-organic framework, MOF-253, produces N-doped porous carbons (Cz-MOF-253), which exhibit excellent catalytic activity in the Knoevenagel condensation reaction and outperform other nitrogen-containing MOF-derived carbons. More importantly, by virtue of their high Lewis basicity and porous nature, Cz-MOF-253-supported Pd nanoparticles (Pd/Cz-MOF-253-800) show excellent performance in a one-pot sequential Knoevenagel condensation-hydrogenation reaction.

Morphology inherence from hollow MOFs to hollow carbon polyhedrons in preparing carbon-based electrocatalysts

Hollow carbon nanostructures are emerging as advanced electrocatalysts for the oxygen reduction reaction (ORR) due to the effective usage of active sites and the reduced dependence on expensive noble metals. Conventional preparation of these hollow structures is achieved through templates (e.g. SiO2, CdS, and Ni3C), which serve to retain the void interiors during carbonization, leading to an essential template-removal procedure using hazardous chemical etchants. Herein, we demonstrate the direct carbonization of unique hollow zeolitic imidazolate frameworks (ZIFs) for the synthesis of hollow carbon polyhedrons (HCPs) with well-defined morphologies. The hollow ZIF particles behave bi-functionally as a carbon source and a morphology directing agent. This method evidences the strong morphology inherence from the hollow ZIFs during the carbonization, advancing the significant simplicity and environmental friendliness of this synthesis strategy. The as-prepared HCPs show a uniform polyhedral morphology and large void interiors, which enable their superior ORR activity. Iron can be doped into the HCPs (Fe/HCPs), providing the Fe/HCPs with enhanced ORR properties (E1/2 = 0.850 V) in comparison with those of HCPs. We highlight the efficient structural engineering to transform ZIFs into advanced carbon nanostructures accomplishing morphological control and high electrocatalytic activity.

MOF-253-Pd(OAc)2: a recyclable MOF for transition-metal catalysis in water

We report palladium(II)-functionalized MOF-253 (MOF-253-Pd(OAc)2) as a recyclable catalyst to form all-carbon quaternary centers via conjugate additions of arylboronic acids to β,β-disubstituted enones in aqueous media. We demonstrate MOF-253-Pd(OAc)2 can be reused 8 times to form ketone products in yields above 75% while maintaining its crystallinity. Additions of a range of stereoelectronically diverse arylboronic acids to a variety of β,β-disubstituted enones catalyzed by MOF-253-Pd(OAc)2 occur in modest-to-high yields (34–95%).

Green synthesis of amphiphilic carbon dots from organic solvents: application in fluorescent polymer composites and bio-imaging

Carbon dots (CDs) have sparked tremendous attention due to their unique properties and vast potential in diverse fields. Herein, we report a green and cost-effective hydrothermal route for the synthesis of a series of CDs from readily available organics solvents. Since the organics were completely recyclable after the separation of CDs, this method holds immense potential for the large-scale synthesis of CDs. We found the DMF-CDs and DMAc-CDs possessed amphiphilicity and the diameter of amphiphilic DMF-CDs was ca. 3.5 nm with a narrow distribution. Moreover, these amphiphilic CDs emitted blue light under UV irradiation (365 nm) and the quantum yield could reach more than 30%. Due to their good solubility in organic solvent, DMF-CDs were successfully imbedded into polymers (i.e., PS and PMMA), which revealed their potential in painting, coating, and optical devices. In addition, benefiting from high quantum yield and low cytotoxicity, the DMF-CDs in aqueous media were used as fluorescent probes in living cells, which demonstrated their great potential in bio-imaging.

Water-dispersible PEG-curcumin/amine-functionalized covalent organic framework nanocomposites as smart carriers for in vivo drug delivery

Covalent organic frameworks (COFs) as drug-delivery carriers have been mostly evaluated in vitro due to the lack of COFs nanocarriers that are suitable for in vivo studies. Here we develop a series of water-dispersible polymer-COF nanocomposites through the assembly of polyethylene-glycol-modified monofunctional curcumin derivatives (PEG-CCM) and amine-functionalized COFs (APTES-COF-1) for in vitro and in vivo drug delivery. The real-time fluorescence response shows efficient tracking of the COF-based materials upon cellular uptake and anticancer drug (doxorubicin (DOX)) release. Notably, in vitro and in vivo studies demonstrate that PEG-CCM@APTES-COF-1 is a smart carrier for drug delivery with superior stability, intrinsic biodegradability, high DOX loading capacity, strong and stable fluorescence, prolonged circulation time and improved drug accumulation in tumors. More intriguingly, PEG350-CCM@APTES-COF-1 presents an effective targeting strategy for brain research. We envisage that PEG-CCM@APTES-COF-1 nanocomposites represent a great promise toward the development of a multifunctional platform for cancer-targeted in vivo drug delivery.Despite their potential application as drug-delivery carriers, covalent organic frameworks (COF) have been only evaluated in vitro. Here the authors show by real time tracking in vivo the cell uptake of anticancer-drug loaded and water dispersible COFs.

Conversion of confined metal@ZIF-8 structures to intermetallic nanoparticles supported on nitrogen-doped carbon for electrocatalysis

We report a facile strategy to synthesize intermetallic nanoparticle (iNP) electrocatalysts via one-pot pyrolysis of a zeolitic imidazolate framework, ZIF-8, encapsulating precious metal nanoparticles (NPs). ZIF-8 serves not only as precursor for N-doped carbon (NC), but also as Zn source for the formation of intermetallic or alloy NPs with the encapsulated metals. The resulting sub-4 nm PtZn iNPs embedded in NC exhibit high sintering resistance up to 1,000 °C. Importantly, the present methodology allows fine-tuning of both composition (e.g., PdZn and RhZn iNPs, as well as AuZn and RuZn alloy NPs) and size (2.4, 3.7, and 5.4 nm PtZn) of the as-formed bimetallic NPs. To the best of our knowledge, this is the first report of a metal-organic framework (MOF) with multiple functionalities, such as secondary metal source, carbon precursor, and size-regulating reagent, which promote the formation of iNPs. This work opens a new avenue for the synthesis of highly uniform and stable iNPs.

Unveiling the Effects of Linker Substitution in Suzuki Coupling with Palladium Nanoparticles in Metal–Organic Frameworks

AbstractThe establishment of structure–property relationships in heterogeneous catalysis is of prime importance but remains a formidable challenge. Metal–organic frameworks (MOFs) featuring excellent chemical tunability are emerging as an auspicious platform for the atomic-level control of heterogeneous catalysis. Herein, we encapsulate palladium nanoparticles (Pd NPs) in a series of isoreticular mixed-linker MOFs, and the obtained MOF-Pd NPs catalysts were used to unveil the electronic and steric effects of linker substitution on the activity of these catalysts in the Suzuki–Miyaura cross-coupling reactions. Significantly, m-6,6′-Me2bpy-MOF-Pd exhibits a remarkable enhancement in the activity compared to non-functionalized m-bpy-MOF-Pd and m-4,4′-Me2bpy-MOF-Pd. This study unambiguously demonstrates that the stereoelectronic properties of linker units are crucial to the catalytic activity of nanoparticles encapsulated in MOFs. More interestingly, the trend of activity change is consistent with our previous work on catalytic sites generated in situ from Pd(II) coordinated in MOFs bearing the same functional groups, which suggests that both MOF-Pd NPs and MOF-Pd(II) catalysts generate similar active centers during Suzuki–Miyaura coupling reactions. This work paves a new avenue to the fabrication of advanced and tunable MOF-based catalysts through rational linker engineering.Graphical AbstractWe encapsulate palladium nanoparticles in a series of isoreticular mixed-linker MOFs, and the obtained Pd-doped MOFs catalysts were used to unveil the electronic and steric effects of linker substitution on the activity of these catalysts in the context of Suzuki–Miyaura cross-coupling reactions. Impressively, m-6,6′-Me2bpy-MOF-Pd exhibits a remarkable enhancement in the activity compared to non-functionalized m-bpy-MOF-Pd and m-4,4′-Me2bpy-MOF-Pd, thus implementing atomic-level controls of heterogeneous catalysis.