Owing to the difficulty in controlling the dopant or defect types and their homogeneity in carbon materials, it is still a controversial issue to identify the active sites of carbon-based metal-free catalysts. Herein, we report a proof of concept study on the active-site evaluation for a highly oriented pyrolytic graphite catalyst with specific pentagon carbon defective patterns (D-HOPG).It is demonstrated that specific carbon defect types (edged pentagon in this work) could be selectively created via controllable N-doping. Work function analyses coupled with macro/microelectrochemical performance measurements suggest that the pentagon defects in D-HOPG served as major active sites for acidic oxygen reduction reaction (ORR), even much superior to the pyridinic nitrogen sites in N-doped highly oriented pyrolytic graphite (N-HOPG). This work enables us to elucidate the relative importance of the specific carbon defects vs N-dopant species and their respective contributions to the observed overall acidic ORR activity.

Drug delivery systems (DDS) are defined as methods by which drugs are delivered to desired tissues, organs, cells and subcellular organs for drug release and absorption through a variety of drug carriers. Its usual purpose to improve the pharmacological activities of therapeutic drugs and to overcome problems such as limited solubility, drug aggregation, low bioavailability, poor biodistribution, lack of selectivity, or to reduce the side effects of therapeutic drugs. During 2015–2018, significant progress in the research on drug delivery systems has been achieved along with advances in related fields, such as pharmaceutical sciences, material sciences and biomedical sciences. This review provides a concise overview of current progress in this research area through its focus on the delivery strategies, construction techniques and specific examples. It is a valuable reference for pharmaceutical scientists who want to learn more about the design of drug delivery systems.

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Newly N-S-C coordination-structured active sites, originating from the integrity of edged thiophene S, graphitic N, and pentagon defects, were reconstructed by N-modified S defects in carbon aerogel with a 3D hierarchical macro-mesomicroporous structure. This metal-free material exhibited outstanding oxygen reduction reaction (ORR) activity (e.g., half-wave potentials of 0.76 V in 0.5 M H 2 SO 4 and 0.1 M HClO 4 ; 0.85 V in 0.1 M KOH) with good stability and high current density in both acidic and alkaline electrolytes. The experimental and computational results reveal that the pentagon S defect is essential for the ORR in acidic electrolytes because it provides a remarkable increase in reactivity. One graphitic-type N in the meta-position of the pentagon defect further significantly improves the reactivity as a result of locally precise control of the electronic structure, thus forming highly active sites for ORR in acid.

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