The oxygen reduction reaction (ORR) is the core reaction of numerous sustainable energy‐conversion technologies such as fuel cells and metal–air batteries. It is crucial to develop a cost‐effective, highly active, and durable electrocatalysts for ORR to overcome the sluggish kinetics of four electrons pathway. In recent years, the carbon‐based electrocatalysts derived from metal–organic frameworks (MOFs) have attracted tremendous attention and have been shown to exhibit superior catalytic activity and excellent intrinsic properties such as large surface area, large pore volume, uniform pore distribution, and tunable chemical structure. Here in this review, the development of MOF‐derived heteroatom‐doped carbon‐based electrocatalysts, including non‐metal (such as N, S, B, and P) and metal (such as Fe and Co) doped carbon materials, is summarized. It furthermore, it is demonstrated that the enhancement of ORR performance is associated with favorably well‐designed porous structure, large surface area, and high‐tensity active sites. Finally, the future perspectives of carbon‐based electrocatalysts for ORR are provided with an emphasis on the development of a clear mechanism of MOF‐derived non‐metal‐doped electrocatalysts and certain metal‐doped electrocatalysts.

During the solid state foaming, the CO 2 saturated poly(lactic acid) (PLA) sample at 5 MPa and 20 °C has a high crystallinity of 23.2%, and the prepared PLA foams exhibits low foam expansion and nonuniform cell structure. This study presents an interesting effect of nanosilica addition on the cell morphology and expansion ratio of PLA foams. It was found that the presence of nanosilica increased the induced crystallinity of PLA up to 29.7% at 5 MPa. The resultant PLA/silica foams exhibited significant and concurrent increase in cell structure uniformity and cell density: the cell density increased about 5−10 times, the expansion ratio increased 1.4−2.1 times, and the crystallinity of foams increased 1.3 times, compared to pure PLA foams. Further investigation suggested that the formation of the tiny crystallite size and the well dispersed nanosilica aggregates were thought as the main reasons to explain the interesting effect of nanosilica addition on the foaming behavior of PLA.

Metal-organic frameworks (MOFs) with carboxylate ligands as co-catalysts are very e cient for oxygen evolution reaction (OER). However, the role of local adsorbed carboxylate ligands around the in situ transformed metal (oxy)hydroxides during OER is often overlooked. Here we reveal the extraordinary role and mechanism of surface adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER catalytic activity enhancement. The results of X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy and theoretical calculations show that the carboxylic groups around metal (oxy)hydroxides can e ciently induce the interfacial electron redistribution, facilitate abundant high-valence state of nickel species with partial distorted octahedral structure, and optimize the d-band center together with the bene cial Gibbs free energy of intermediate. Furthermore, the results of in-situ Raman and FI-IR spectra rstly reveal that the surface adsorbed carboxylate ligands as Lewis base can promote the sluggish OER kinetics by accelerating proton transfer and facilitating adsorption/ activation/dissociation of hydroxyl ions (OH − ). Our ndings will offer unique insights into the reason for disclosing the origin of excellent electrocatalytic activity for MOF/NiFe-LDHs catalysts.

Electrocatalytic water splitting is considered as a promising route to use renewable energy for hydrogen production; however, its industrial application is limited by the anodic reaction, oxygen evolution reaction (OER). The key solution to unleash this constrain is to find an electrocatalyst that reduces the overpotential (η) of OER. Among the various electrocatalysts, perovskites have attracted intense attention recently for their high OER performance and low cost. To realize the commercial potential of perovskites, understanding its surface chemistry, including leaching, reconstruction, and lattice oxygen participated OER, is crucial to develop the nextgeneration perovskite catalysts,. In this Review, the perovskite surface stability is emphasized to be closely related to the chemical component of perovskite surface, which can be well controlled by surface engineering and further improves its OER performance. A new descriptor (stability level) is proposed to highlight the relationship between OER performance and surface stability of perovskite. This descriptor will provide potential strategies to optimize OER catalytic performance by tuning surface structure of perovskite.

High expansion ratio, well-defined cell structure, and an excellent flame retardant characteristic are essential properties for broadening the applications of polymeric foam. In this study, by applying microcellular foaming technology using compressed CO 2 as the blowing agent, we are challenged to synthesize the desirable poly(lactic acid) (PLA) foams with phosphorus-containing flame retardant (FR) and starch as the natural charring agent. It was interesting to find that the introduction of 15−25 wt % FR increased the limiting oxygen index (LOI) of PLA foams from 18.2% to 24.8−28.4% and simultaneously increased the foam expansion of PLA foams from 4.4 to 7.5−16.0. The addition of starch with content of 1−5 wt % further increased the LOI up to 30.6% and also endowed PLA/FR/St foams with improved antidripping properties. All these wonderful characteristics make the prepared PLA foams very promising for application in green packaging.

No abstract

In this study, poly(lactic acid) (PLA) resins with linear (L-PLA) and branched structure (B-PLA) were selected, and the solid state foaming technology was applied to prepare PLA foams. B-PLA foams exhibited a high expansion ratio of about 40 and cell density of 10 5−6 cells/cm 3 , whereas L-PLA foams only had the highest expansion ratio of 29.8 and cell density of 10 3−6 cells/cm 3 . When PLA resins were induced crystallization during CO 2 saturation, however, the prepared L-PLA foams presented the highest expansion ratio of 37.4 and cell density of 10 6−7 cells/cm 3 . The cell structure evolution of PLA foams with the foaming time suggested that the in situ formed crystal domains supplied nucleating sites to enhance cell nucleation and acted as physical cross-linking points to stabilize cell structure. These interesting results demonstrated that the induced crystallization might be more attractive than the chain modification to improve the foaming behavior using solid state foaming technology.

The fluorescence labeling of viruses is a useful technology for virus detection and imaging. By combining the excellent fluorescence properties of quantum dots (QDs) with the high affinity and specificity of aptamers, we constructed a QD-aptamer probe. The aptamer A22, against the hemagglutinin of influenza A virus, was linked to QDs, producing the QD-A22 probe. Fluorescence imaging and transmission electron microscopy showed that the QD-A22 probe could specifically recognize and label influenza A virus particles. This QD labeling technique provides a new strategy for labeling virus particles for virus detection and imaging.