Single‐atom catalysts (SACs) are witnessing rapid development due to their high activity and selectivity toward diverse reactions. However, it remains a grand challenge in the general synthesis of SACs, particularly featuring an identical chemical microenvironment and on the same support. Herein, a universal synthetic protocol is developed to immobilize SACs in metal–organic frameworks (MOFs). Significantly, by means of SnO2 as a mediator or adaptor, not only different single‐atom metal sites, such as Pt, Cu, and Ni, etc., can be installed, but also the MOF supports can be changed (for example, UiO‐66‐NH2, PCN‐222, and DUT‐67) to afford M1/SnO2/MOF architecture. Taking UiO‐66‐NH2 as a representative, the Pt1/SnO2/MOF exhibits approximately five times higher activity toward photocatalytic H2 production than the corresponding Pt nanoparticles (≈2.5 nm) stabilized by SnO2/UiO‐66‐NH2. Remarkably, despite featuring identical parameters in the chemical microenvironment and support in M1/SnO2/UiO‐66‐NH2, the Pt1 catalyst possesses a hydrogen evolution rate of 2167 µmol g–1 h–1, superior to the Cu1 and Ni1 counterparts, which is attributed to the differentiated hydrogen binding free energies, as supported by density‐functional theory (DFT) calculations. This is thought to be the first report on a universal approach toward the stabilization of SACs with identical chemical microenvironment on an identical support.
Covalent organic framework (COF) chemistry is experiencing
unprecedented
development in recent decades. The current studies on COF chemistry
are mainly focused on the discovery of novel covalent linkages, new
topological structures, synthetic methodologies, and potential applications.
However, despite the fact that noncovalent interactions are ubiquitous
in COF chemistry, relatively little attention has been given to the
role of noncovalent bonds on COF structures and their properties.
In this work, a series of hydrazone-linked COFs involving noncovalent
hydrogen bonds have been constructed, where the hydrogen-bonding interaction
plays critical roles in the COF crystallinity and structures. The
regulation of structural flexibility, the reversible transition between
order and disorder, and the variety of host–guest interactions
have been demonstrated in succession for the first time in COFs. The
results obtained by the hydrogen-bonding-regulated strategy may also
be extendable to other noncovalent interactions, such as π–π
interactions, metal coordination interactions, Lewis acid–base
interactions, etc. These findings will inspire future developments
in the design, synthesis, structural regulation, and applications
of COFs by manipulating noncovalent interactions.
Metal-organic gels (MOGs) of three-dimensional (3D) networks comprising nanosheets of ∼30 nm thickness and square-micrometer in size were easily produced via coordination interactions of iron (Fe(3+)) and 1,4-naphthalenedicarboxylic acid (NDC). Such MOGs exhibit ultrahigh removal of arsenic(v) in water, with the adsorption capacity of 144 mg g(-1), dramatically superior to those of the recently reported Fe-based inorganic and organic adsorbents.
The gelation and crystallization behavior of a biological surfactant, sodium deoxycholate (NaDC), mixed with l-taric acid (L-TA) in water is described in detail. With the variation of molar ratio of L-TA to NaDC (r = n(L-TA)/n(NaDC)) and total concentration of the mixtures, the transition from sol to gel was observed. SEM images showed that the density of nanofibers gradually increases over the sol-gel transition. The microstructures of the hydrogels are three-dimensional networks of densely packed nanofibers with lengths extending to several micrometers. One week after preparation, regular crystallized nanospheres formed along the length of the nanofibers, and it was typical among the transparent hydrogels induced by organic acids with pKa1 value <3.4. Small-angle X-ray diffraction demonstrated differences in the molecular packing between transparent and turbid gels, indicating a variable hydrogen bond mode between NaDC molecules.
Direct and selective oxidation of methane (CH4) into methanol (CH3OH) under ambient conditions remains a grand challenge because of the high energy barrier of CH4 activation and the complicated processes...
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