Photo/Electrocatalytic Hydrogen Peroxide Production by Manganese and Iron Porphyrin/Molybdenum Disulfide Nanoensembles.

The oxygen reduction reaction (ORR) 2e- pathway provides an alternative and green route for industrial hydrogen peroxide (H2 O2 ) production. Herein, the ORR photo/electrocatalytic activity in the alkaline electrolyte of manganese and iron porphyrin (MnP and FeP, respectively) electrostatically associated with modified 1T/2H MoS2 nanosheets is reported. The best performing catalyst, MnP/MoS2 , exhibits excellent electrocatalytic performance towards selective H2 O2 formation, with a low overpotential of 20 mV for the 2e- ORR pathway (Eons  = 680 mV vs RHE) and an H2 O2 yield up to 99%. Upon visible light irradiation, MnP/MoS2 catalyst shows significant activity enhancement along with good stability. Electrochemical impedance spectroscopy assays suggest a reduced charge transfer resistance value at the interface with the electrolyte, indicating an efficient intra-ensemble transfer process of the photo-excited electrons through the formation of a type II heterojunction or Schottky contact, and therefore justifies the boosted electrochemical activities in the presence of light. Overall, this work is expected to inspire the design of novel advanced photo/electrocatalysts, paving the way for sustainable industrial H2 O2 production.

Core-Shell Pd@M (M=Ni, Cu, Co) Nanoparticles/Graphene Ensembles with High Mass Electrocatalytic Activity Toward the Oxygen Reduction Reaction.

Herein, it is demonstrated that pyrene butyric acid (PBA)-stabilized metal nanoparticles with core-shell morphology, Pd@MNPs (M=Ni, Cu, Co), non-covalently supported on graphene (G) sheets, are more active towards oxygen electroreduction in alkaline environments than the benchmark Pd/C catalyst, albeit with a 70 % lower precious metal loading. The PBA-stabilized Pd@MNPs (M=Ni, Cu, Co)/G ensembles were prepared by employing a simple modified polyol method and galvanic replacement and thoroughly characterized with advanced microscopy imaging and complementary spectroscopic techniques. Electrochemical studies revealed that Pd@NiNPs /G presents the optimum performance, exhibiting a 30 mV more positive onset potential and 3.2 times greater mass activity over Pd/C. Moreover, chronoamperometric assays showed the minimum activity loss for Pd@NiNPs /G, not only among its core-shell counterparts but importantly when compared with the benchmark catalyst. The excellent performance of Pd@NiNPs /G was attributed to the (a) presence of PBA as stabilizer, (b) uniform Pd@NiNPs dispersion onto the graphene sheets, (c) efficient intra-ensemble interactions between the two species, (d) existence of the core-shell structure for Pd@NiNPs , and (e) stability of the Ni core metal under the reaction conditions. Last, the oxygen reduction on Pd@NiNPs /graphene occurs by the direct four-electron reduction pathway, showing great potential for use in energy related applications.

Covalently functionalized layered MoS2 supported Pd nanoparticles as highly active oxygen reduction electrocatalysts.

Molybdenum disulfide nanosheets covalently modified with a 1,2-dithiolane derivative were used as a novel substrate for the immobilization of Pd nanoparticles (PdNPs) towards the development of a highly efficient hybrid electrocatalyst, namely PdNPs/f-MoS2, for the oxygen reduction in an alkaline medium. The newly prepared hybrid material was thoroughly characterized through complementary techniques such as Raman and IR spectroscopy, TGA, HRTEM, STEM/EELS, and EDS. The PdNPs/f-MoS2 nanohybrid exhibited excellent performance towards oxygen electroreduction with a positive onset potential of +0.066 V and a half-wave potential of -0.116 V vs. Hg/HgO, along with a high current response, which are superior to those of its graphene counterpart and comparable to those of the benchmark Pd/C product. Moreover, PdNPs/f-MoS2 was proved to be remarkably stable as chronoamperometric assays showed minimum activity loss among the tested materials, clearly outperforming the commercial catalyst. The excellent performance of PdNPs/f-MoS2 is attributable to (i) the high affinity of the catalytic PdNPs with the f-MoS2 substrate, (ii) the absence of any capping agent for the stabilization of PdNPs onto f-MoS2, and more importantly (iii) the preservation of the integrity of the MoS2 basal plane during the functionalization process. Lastly, the oxygen reduction on PdNPs/f-MoS2 proceeded through the energy efficient four-electron pathway, showing great potential for the use of layered transition metal dichalcogenides in energy conversion applications, comprising fuel cells.

Toxicity determinants of multi-walled carbon nanotubes: The relationship between functionalization and agglomeration.

The elucidation of toxicity determinants of multi-walled carbon nanotubes (MWCNT) is still incomplete. Functionalization with carboxyl groups is, however, commonly used to mitigate MWCNT toxicity, although the rationale for the mitigating effect has not been fully clarified yet. In this work, two optimized chemical vapor deposition methods were employed to obtain MWCNT of comparable length but different diameter, which were subsequently functionalized. For MWCNT of diameter larger than 40 nm, no detrimental effects on cell viability of macrophages were observed, while mild cytotoxicity was recorded for diameters between 15 and 40 nm, with a mitigating effect of functionalization. To investigate the factors responsible for the mitigation, we used the thinnest MWCNT preparation on different cell models, evaluating several endpoints, such as viability, production of nitric oxide (NO), expression of pro-inflammatory markers, the Trans-Epithelial Electrical Resistance (TEER), and clonogenic activity. Substantial mitigation of the changes caused by pristine MWCNT was observed not only with carboxyl- but also with amino-functionalized MWCNT, suggesting that negative or positive surface charge was not the main factor responsible for the effect. Instead, either functionalized preparation exhibited a stronger tendency to agglomerate that was strictly dependent on the presence of proteins. Moreover, we found that either carboxyl- or amino-functionalized MWCNT adsorbed a larger amount of serum proteins than pristine counterparts, with a distinctive pattern for each type of MWCNT. We propose, therefore, that the formation of larger agglomerates, dependent upon different protein coronae, contributes to mitigate the biological effects of functionalized MWCNT in protein-rich biological media.