Selectivity Control in the Direct CO Esterification over Pd@UiO-66: The Pd Location Matters.

The selectivity control of Pd nanoparticles (NPs) in the direct CO esterification with methyl nitrite toward dimethyl oxalate (DMO) or dimethyl carbonate (DMC) remains a grand challenge. Herein, Pd NPs are incorporated into isoreticular metal-organic frameworks (MOFs), namely UiO-66-X (X=-H, -NO2 , -NH2 ), affording Pd@UiO-66-X, which unexpectedly exhibit high selectivity (up to 99 %) to DMC and regulated activity in the direct CO esterification. In sharp contrast, the Pd NPs supported on the MOF, yielding Pd/UiO-66, displays high selectivity (89 %) to DMO as always reported with Pd NPs. Both experimental and DFT calculation results prove that the Pd location relative to UiO-66 gives rise to discriminated microenvironment of different amounts of interface between Zr-oxo clusters and Pd NPs in Pd@UiO-66 and Pd/UiO-66, resulting in their distinctly different selectivity. This is an unprecedented finding on the production of DMC by Pd NPs, which was previously achieved by Pd(II) only, in the direct CO esterification.

Endowing Porphyrinic Metal-Organic Frameworks with High Stability by a Linker Desymmetrization Strategy.

The fabricating of metal-organic frameworks (MOFs) that integrate high stability and functionality remains a long-term pursuit yet a great challenge. Herein, we develop a linker desymmetrization strategy to construct highly stable porphyrinic MOFs, namely, USTC-9 (USTC represents the University of Science and Technology of China), presenting the same topological structure as the well-known PCN-600 that readily loses crystallinity in air or upon conventional activation. For USTC-9, the involved porphyrinic linker (TmCPP-M) with carboxylate groups located in the meta-position presents a chair-shaped conformation with lower C2h symmetry than that (D4h) of the common porphyrinic carboxylate (TCPP) linker in PCN-600. As a result, the wrinkled and interlocked linker arrangements collectively contribute to the remarkable stability of USTC-9. Given the high stability and porosity as well as Lewis acidity, USTC-9(Fe) demonstrates its excellent performance toward catalytic CO2 cycloaddition with diverse epoxides at moderate temperature and atmospheric pressure.

Charge Separation by Creating Band Bending in Metal-Organic Frameworks for Improved Photocatalytic Hydrogen Evolution.

Metal-organic frameworks (MOFs) have been intensively studied as a class of semiconductor-like materials in photocatalysis. However, band bending, which plays a crucial role in semiconductor photocatalysis, has not yet been demonstrated in MOF photocatalysts. Herein, a representative MOF, MIL-125-NH2 , is integrated with the metal oxides (MoO3 and V2 O5 ) that feature appropriate work functions and energy levels to afford the corresponding MOF composites. Surface photovoltage results demonstrate band bending in the MOF composites, which gives rise to the built-in electric field of MIL-125-NH2 , boosting the charge separation. As a result, the MOF composites present 56 and 42 times higher activities, respectively, compared to the pristine MOF for photocatalytic H2 production. Upon depositing Pt onto the MOF, ∼6 times higher activity is achieved. This work illustrates band bending of MOFs for the first time, supporting their semiconductor-like nature, which would greatly promote MOF photocatalysis.

Non-Bonding Interaction of Neighboring Fe and Ni Single-Atom Pairs on MOF-Derived N-Doped Carbon for Enhanced CO2 Electroreduction.

Single-atom catalysts (SACs), featuring high atom utilization, have captured widespread interests in diverse applications. However, the single-atom sites in SACs are generally recognized as independent units and the interplay of adjacent sites is largely overlooked. Herein, by the direct pyrolysis of MOFs assembled with Fe and Ni-doped ZnO nanoparticles, a novel Fe1-Ni1-N-C catalyst, with neighboring Fe and Ni single-atom pairs decorated on nitrogen-doped carbon support, has been precisely constructed. Thanks to the synergism of neighboring Fe and Ni single-atom pairs, Fe1-Ni1-N-C presents significantly boosted performances for electrocatalytic reduction of CO2, far surpassing Fe1-N-C and Ni1-N-C with separate Fe or Ni single atoms. Additionally, the Fe1-Ni1-N-C also exhibits superior performance with excellent CO selectivity and durability in Zn-CO2 battery. Theoretical simulations reveal that, in Fe1-Ni1-N-C, single Fe atoms can be highly activated by adjacent single-atom Ni via non-bonding interaction, significantly facilitating the formation of COOH* intermediate and thereby accelerating the overall CO2 reduction. This work supplies a general strategy to construct single-atom catalysts containing multiple metal species and reveals the vital importance of the communitive effect between adjacent single atoms toward improved catalysis.

Piezo-Photocatalysis over Metal-Organic Frameworks: Promoting Photocatalytic Activity by Piezoelectric Effect.

The built-in electric field can be generated in the piezoelectric materials under mechanical stress. The resulting piezoelectric effect is beneficial to charge separation in photocatalysis. Meanwhile, the mechanical stress usually gives rise to accelerated mass transfer and enhanced catalytic activity. Unfortunately, it remains a challenge to differentiate the contribution of these two factors to catalytic performance. Herein, for the first time, isostructural metal-organic frameworks (MOFs), i.e., UiO-66-NH2 (Zr) and UiO-66-NH2 (Hf), are adopted for piezo-photocatalysis. Both MOFs, featuring the same structures except for diverse Zr/Hf-oxo clusters, possess distinctly different piezoelectric properties. Strikingly, UiO-66-NH2 (Hf) exhibits ≈2.2 times of activity compared with that of UiO-66-NH2 (Zr) under simultaneous light and ultrasonic irradiation, though both MOFs display similar activity in the photocatalytic H2 production without ultrasonic irradiation. Given their similar pore features and mass transfer behaviors, the activity difference is unambiguously assignable to the piezoelectric effect. As a result, the contributions of the piezoelectric effect to the piezo-photocatalysis can be clearly distinguished owing to the stronger piezoelectric property of UiO-66-NH2 (Hf).

Interfacial Microenvironment Modulation Boosting Electron Transfer between Metal Nanoparticles and MOFs for Enhanced Photocatalysis.

Interfacial electron transfer between cocatalyst and photosensitizer is key in heterogeneous photocatalysis, yet the underlying mechanism remains subtle and unclear. Surfactant coated on the metal cocatalysts, greatly modulating the microenvironment of catalytic sites, is largely ignored. Herein, a series of Pt co-catalysts with modulated microenvironments, including polyvinylpyrrolidone (PVP) capped Pt nanoparticles (denoted as PtPVP ), Pt with partially removed PVP (PtrPVP ), and clean Pt without PVP (Pt), were encapsulated into a metal-organic framework (MOF), UiO-66-NH2 , to afford PtPVP @UiO-66-NH2 , PtrPVP @UiO-66-NH2 , and Pt@UiO-66-NH2 , respectively, for photocatalytic hydrogen production. The PVP appears to have a negative influence on the interfacial electron transfer between Pt and the MOF. Compared with PtPVP @UiO-66-NH2 , the removal of interfacial PVP improves the sluggish kinetics of electron transfer, boosting photocatalytic hydrogen production.

Rational Fabrication of Low-Coordinate Single-Atom Ni Electrocatalysts by MOFs for Highly Selective CO2 Reduction.

Single-atom catalysts (SACs) have attracted tremendous interests due to their ultrahigh activity and selectivity. However, the rational control over coordination microenvironment of SACs remains a grand challenge. Herein, a post-synthetic metal substitution (PSMS) strategy has been developed to fabricate single-atom Ni catalysts with different N coordination numbers (denoted Ni-Nx -C) on pre-designed N-doped carbon derived from metal-organic frameworks. When served for CO2 electroreduction, the obtained Ni-N3 -C catalyst achieves CO Faradaic efficiency (FE) up to 95.6 %, much superior to that of Ni-N4 -C. Theoretical calculations reveal that the lower Ni coordination number in Ni-N3 -C can significantly enhance COOH* formation, thereby accelerating CO2 reduction. In addition, Ni-N3 -C shows excellent performance in Zn-CO2 battery with ultrahigh CO FE and excellent stability. This work opens up a new and general avenue to coordination microenvironment modulation (MEM) of SACs for CO2 utilization.

Adult moyamoya-atherosclerosis syndrome: Clinical and vessel wall imaging features.

INTRODUCTION: We sought to incorporate high-resolution magnetic resonance imaging (HRMRI) into the diagnostic process of intracranial atherosclerosis associated moyamoya syndrome in adult patients. METHODS: From March 2013 to March 2014, HRMRI was consecutively performed on adult patients with angiographic moyamoya. The patients were classified as moyamoya - plaques (MMD-P) if a plaque could be identified or as moyamoya - no plaques (MMD-NP) if a plaque could not be identified. The angiography, HRMRI findings and atherogenic risk factors of these patients were analyzed. RESULTS: Fifty-one patients (mean age 39±9, 20 males) were enrolled. On traditional angiography, probable intracranial atherosclerosis was identified in 5 patients, no definite diagnosis in 12 patients, and moyamoya disease in 34 patients. On HRMRI, 15 out of 32 patients with risk factors and 4 out of 19 patients without risk factors were found to have plaques and were diagnosed as MMD-P, while the other 32 patients were diagnosed as MMD-NP. The MMD-P patients were more likely to be older (P=0.033) and male (P=0.0353) and were less likely to have cerebral hemorrhage (P=0.0066) and a history of disease progression (P=0.0012). CONCLUSIONS: Our study suggests that HRMRI can help diagnose intracranial atherosclerosis more accurately in moyamoya disease patients with atherogenic risk factors. The distinct clinical features between MMD-P and MMD-NP patients suggest different underlying pathophysiology and therefore potentially different treatment strategies.