Harnessing mechanical forces to activate latent catalysts has emerged as a novel approach to control the catalytic reactions in organic syntheses and polymerization processes. However, using polymer mechanochemistry to activate platinum-based catalysts, a class of important organometallic catalysts in industry, has not been demonstrated so far. Here we show that the platinum–acetylide complex is mechanoresponsive and can be incorporated into a polymer backbone to form a new mechanophore. The mechanically induced chain scission was demonstrated to be able to release catalytically active platinum species which could catalyze the olefin hydrosilylation process. Various control experiments were conducted to confirm that the chain scission and catalytic reaction were originated from the ultrasound-induced dissociation of platinum–acetylide complex. This work further exemplifies the utilization of organometallic complexes in design and synthesis of latent catalysts for mechanocatalysis and development of self-healing materials based on silicone polymers.

It is known that introducing metal nanoparticles (e.g., Fe and Co) into N-doped carbons can enhance the activity of N-doped carbons toward the oxygen reduction reaction (ORR). However, introducing metals into N-doped carbons inevitably causes the formation of multiple active sites. Thus, it is challenging to identify the active sites and unravel mechanisms responsible for enhanced ORR activity. Herein, by developing a new N-heterocyclic carbene (NHC)–Co complex as the nitrogen- and metal-containing precursor, we report the synthesis of N-doped carbon nanosheets embedded with Co nanoparticles as highly active ORR catalysts without direct metal–nitrogen bonding. Electrochemical measurements and X-ray absorption spectroscopy indicate that the carbon–nitrogen sites surrounding Co nanoparticles are responsible for the observed ORR activity and stability. Density functional theory calculations further reveal that Co nanoparticles could facilitate the protonation of O2 and thus promote the ORR activity. These results provide new prospects in the rational design and synthesis of heteroatom-doped carbon materials as non-precious-metal catalysts for various electrochemical reactions.Keywords: carbon nanosheets; cobalt nanoparticles; electrocatalysis; N-doping; oxygen reduction reaction;

Stimuli-responsive coordination polymer particles (CPPs) show great promise for encapsulating and releasing cargos due to their unique and highly tailorable structures and properties. In particular, photoresponsive CPPs have received enormous interest, as noninvasive light can be spatially and temporally controlled, resulting in great safety and efficiency. In this work, we report the design and synthesis of novel photodegradable CPPs by infinite coordination polymerization of Zn2+ and a photocleavable organic linker containing o-nitrobenzyl derivatives. We further demonstrate that these novel photodegradable CPPs are able to efficiently encapsulate cargos and are applicable for on-command drug release upon low-power UV light irradiation (5.78 mW/cm2). Because light is a highly desirable remote-trigger and can be used externally, we expect that these photodegradable CPPs can provide a unique platform for controlled cargo release.Topics: Controlled-release drug delivery systems; Coordination polymers; Dissolution; Electromagnetic wave; Materials processing; Photodegradation; Polyesters;

Creating ordered two-dimensional (2D) metal–organic framework (MOF) nanosheets has attracted extensive interest. However, it still remains a great challenge to synthesize ultrathin 2D MOF nanosheets with controlled thickness in high yields. In this work, we demonstrate a novel intercalation and chemical exfoliation approach to obtain MOF nanosheets from intrinsically layered MOF crystals. This approach involves two steps: first, layered porphyrinic MOF crystals are intercalated with 4,4′-dipyridyl disulfide through coordination bonding with the metal nodes; subsequently, selective cleavage of the disulfide bond induces exfoliation of the intercalated MOF crystals, leading to individual freestanding MOF nanosheets. This chemical exfoliation process can proceed efficiently at room temperature to produce ultrathin (∼1 nm) 2D MOF nanosheets in ∼57% overall yield. The obtained ultrathin nanosheets exhibit efficient and far superior heterogeneous photocatalysis performance compared with the corresponding bulk MOF.

N-doped carbon materials is of particular attraction for anodes of lithium-ion batteries (LIBs) because of their high surface areas, superior electrical conductivity, and excellent mechanical strength, which can store energy by adsorption/desorption of Li+ at the interfaces between the electrolyte and electrode. By directly carbonization of zeolitic imidazolate framework-8 nanospheres synthesized by an emulsion-based interfacial reaction, we obtained N-doped hollow carbon nanospheres with tunable shell thickness (20 nm to solid sphere) and different N dopant concentrations (3.9 to 21.7 at %). The optimized anode material possessed a shell thickness of 20 nm and contained 16.6 at % N dopants that were predominately pyridinic and pyrrolic. The anode delivered a specific capacity of 2053 mA h g–1 at 100 mA g–1 and 879 mA h g–1 at 5 A g–1 for 1000 cycles, implying a superior cycling stability. The improved electrochemical performance can be ascribed to (1) the Li+ adsorption dominated energy storage mechanism prevents the volume change of the electrode materials, (2) the hollow nanostructure assembled by the nanometer-sized primary particles prevents the agglomeration of the nanoparticles and favors for Li+ diffusion, (3) the optimized N dopant concentration and configuration facilitate the adsorption of Li+; and (4) the graphitic carbon nanostructure ensures a good electrical conductivity.Keywords: carbon nanospheres; hollow structures; lithium-ion batteries; nitrogen-doping; porous materials;

Nanostructured semiconducting polymers have emerged as a very promising class of metal-free photocatalytic materials for solar water splitting. However, they generally exhibit low efficiency and lack the ability to utilize long-wavelength photons in a photocatalytic oxygen evolution reaction (OER). Here, based on first-principles calculations, we reveal that the two-dimensional (2D) aza-fused conjugated microporous polymer (aza-CMP) with a honeycomb network is a semiconductor with novel layer-dependent electronic properties. The bandgap of the as-synthesized aza-CMP nanosheets is measured to be 1.22 eV, suggesting that they can effectively boost light absorption in the visible and near infrared (NIR) region. More importantly, aza-CMP also possesses a valence band margin suitable for a photocatalytic OER. Taking advantage of the 2D layered nanostructure, we further show that the exfoliated ultrathin aza-CMP nanosheets can exhibit a three-fold enhancement in the photocatalytic OER. After deposition of a Co(OH)2 cocatalyst, the hybrid Co(OH)2/aza-CMP photocatalyst exhibits a markedly improved performance for photocatalytic O2 evolution. Furthermore, first-principles calculations reveal that the photocatalytic O2 evolution reaction is energetically feasible for aza-CMP nanosheets under visible light irradiation. Our findings reveal that nanostructured polymers hold great potential for photocatalytic applications with efficient solar energy utilization.

Development of efficient, low-cost, and durable electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is of significant importance for many electrochemical devices, such as rechargeable metal–air batteries, fuel cells, and water electrolyzers. Here, a novel approach for the synthesis of a trifunctional electrocatalyst derived from iron/cobalt-containing polypyrrole (PPy) hydrogel is reported. This strategy relies on the formation of a supramolecularly cross-linked PPy hydrogel that allows for efficient and homogeneous incorporation of highly active Fe/Co–N–C species. Meanwhile, Co nanoparticles are also formed and embedded into the carbon scaffold during the pyrolysis process, further promoting electrochemical activities. The resultant electrocatalyst exhibits prominent catalytic activities for ORR, OER, and HER, surpassing previously reported trifunctional electrocatalysts. Finally, it is demonstrated that the as-obtained trifunctional electrocatalyst can be used for electrocatalytic overall water splitting in a self-powered manner under ambient conditions. This work offers new prospects in developing highly active, nonprecious-metal-based electrocatalysts in electrochemical energy devices.

Metal–organic frameworks (MOFs) represent an emerging class of crystalline materials with well-defined pore structures and hold great potentials in a wide range of important applications. The functionality of MOFs can be further extended by integration with other functional materials, e.g., encapsulating metal nanoparticles, to form hybrid materials with novel properties. In spite of various synthetic approaches that have been developed recently, a facile method to prepare hierarchical hollow MOF nanostructures still remains a challenge. Here we describe a facile emulsion-based interfacial reaction method for the large-scale synthesis of hollow zeolitic imidazolate framework 8 (ZIF-8) nanospheres with controllable shell thickness. We further demonstrate that functional metal nanoparticles such as Pd nanocubes can be encapsulated during the emulsification process and used for heterogeneous catalysis. The inherently porous structure of ZIF-8 shells enables encapsulated catalysts to show size-selective hydrogenation reactions.Keywords: catalysis; emulsion; hollow nanostructures; interfacial reactions; metal−organic frameworks

We present a convenient sonochemical approach for the synthesis of highly photoluminescent carbon nanodots (CDs). CDs were synthesized via pyrolysis of carbon precursors inside implosively collapsing bubbles. We further demonstrate that these CDs can be used for in vitro bioimaging.