Hydrogen evolution reaction is an important process in electrochemical energy technologies. Herein, ruthenium and nitrogen codoped carbon nanowires are prepared as effective hydrogen evolution catalysts. The catalytic performance is markedly better than that of commercial platinum catalyst, with an overpotential of only −12 mV to reach the current density of 10 mV cm-2 in 1 M KOH and −47 mV in 0.1 M KOH. Comparisons with control experiments suggest that the remarkable activity is mainly ascribed to individual ruthenium atoms embedded within the carbon matrix, with minimal contributions from ruthenium nanoparticles. Consistent results are obtained in first-principles calculations, where RuCxNy moieties are found to show a much lower hydrogen binding energy than ruthenium nanoparticles, and a lower kinetic barrier for water dissociation than platinum. Among these, RuC2N2 stands out as the most active catalytic center, where both ruthenium and adjacent carbon atoms are the possible active sites.

Semiconductor photocatalysis as a desirable technology shows great potential in environmental remediation and renewable energy generation, but its efficiency is severely restricted by the rapid recombination of charge carriers in the bulk phase and on the surface of photocatalysts. Polarization has emerged as one of the most effective strategies for addressing the above‐mentioned issues, thus effectively promoting photocatalysis. This review summarizes the recent advances on improvements of photocatalytic activity by polarization‐promoted bulk and surface charge separation. Highlighted is the recent progress in charge separation advanced by different types of polarization, such as macroscopic polarization, piezoelectric polarization, ferroelectric polarization, and surface polarization, and the related mechanisms. Finally, the strategies and challenges for polarization enhancement to further enhance charge separation and photocatalysis are discussed.

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The development of highly stable and efficient catalysts for sluggish cathode oxygen reduction reaction (ORR) is extremely important for the long-term operation and the commercialization of proton exchange membrane fuel cells (PEMFCs) but still challenging. We present herein a facile strategy to efficiently embed Pt nanocrystals into N-doped porous carbon/carbon nanotubes (Pt@CNx/CNT). The N-doped porous carbon shells not only effectively prevented Pt nanocrystals from detachment, dissolution, migration, and aggregation during accelerated durability tests or heat-treatment at 900 °C, but also allowed the access of electrolyte to the Pt surface and preserved the good electron transfer of CNT by avoiding the structural damage of carbon nanotubes (CNTs). The interaction between the embedded Pt nanocrystals and the encapsulating CNx layer was found in Pt@CNx/CNT, which markedly affected the electronic structure of Pt nanocrystals and contributed to the improvement on the catalytic activity and stability of Pt@CNx/CNT. As a result, the Pt@CNx/CNT catalyst exhibited an excellent thermal stability, durability, and sufficient catalytic activity for ORR. The demonstrated strategy could be easily extended to produce a wide range of other electrocatalysts with even better activity and extraordinary stability.

The ultimate success of many nanotechnologies will depend on our ability to understand and manage nanomaterial health risks. Carbon nanotubes are now primarily fabricated by catalytic routes and typically contain significant quantities of transition metal catalyst residues. Iron-catalyzed free-radical generation has been hypothesized to contribute to oxidative stress and toxicity upon exposure to ambient particulate, amphibole asbestos fibers, and single-wall carbon nanotubes. A key issue surrounding nanotube iron is bioavailability, which has not been systematically characterized, but is widely thought to be low on the basis of electron microscope observations of metal encapsulation by carbon shells. Here, we validate and apply simple acellular assays to show that toxicologically significant amounts of iron can be mobilized from a diverse set of commercial nanotube samples in the presence of ascorbate and the chelating agent ferrozine. This mobilized iron is redox active and induces single-strand breaks in plasmid DNA in the presence of ascorbate. Iron bioavailability varies greatly from sample to sample and cannot be predicted from total iron content. Iron bioavailability is not fully suppressed by vendor "purification" and is sensitive to partial oxidation, mechanical stress, sample age, and intentional chelation. The results suggest practical materials chemistry approaches for anticipating and managing bioavailable iron to minimize carbon nanotube toxicity.

Hungry nanotubes: Single‐walled carbon nanotubes (SWNTs) compete with cells by interacting with folate and other essential micronutrients in cell culture medium (see picture). Sequestering of folate can cause apparent toxicity even without direct nanotube–cell contact through a new “starvation” mechanism.

Conjugated polymer nanoparticles (CP NPs) are emerging candidates of "all-in-one" theranostic nanoplatforms with dual photoacoustic imaging (PA) and photothermal therapy (PTT) functions. So far, very limited molecular design guidelines have been developed for achieving CPs with highly efficient PA and PTT performance. Herein, by designing CP1, CP2, and CP3 using different electron acceptors (A) and a planar electron donor (D), we demonstrate how the D-A strength affects their absorption, emission, extinction coefficient, and ultimately PA and PTT performance. The resultant CP NPs have strong PA signals with high photothermal conversion efficiencies and excellent biocompatibility in vitro and in vivo. The CP3 NPs show a high PA signal to background ratio of 47 in U87 tumor-bearing mice, which is superior to other reported PA/PTT theranostic agents. A very small IC value of 0.88 μg/mL (CP3 NPs) was obtained for U87 glioma cell ablation under laser irradiation (808 nm, 0.8 W/cm, 5 min). This study shows that CP NP based theranostic platforms are promising for future personalized nanomedicine.

In this work, chitin microspheres (NCM) having a nanofibrous architecture were constructed using a "bottom-up" fabrication pathway. The chitin chains rapidly self-assembled into nanofibers in NaOH/urea aqueous solution by a thermally induced method and subsequently formed weaved microspheres. The diameter of the chitin nanofibers and the size of the NCM were tunable by controlling the temperature and the processing parameters to be in the range from 26 to 55 nm and 3 to 130 μm, respectively. As a result of the nanofibrous surface and the inherent biocompatibility of chitin, cells could adhere to the chitin microspheres and showed a high attachment efficiency, indicating the great potential of the NCM for 3D cell microcarriers.