Metal-Support Interaction in Pt Nanodisk-Carbon Nitride Catalyst: Insight from Theory and Experiment.

Metal-support interaction plays a critical role in determining the eventual catalytic activity of metals loaded on supporting substrates. This interaction can sometimes cause a significant drop in the metallic property of the loaded metal and, hence, a drop in catalytic activity in the reactions, especially in those for which low charge carrier transfer resistance is a necessary parameter. Therefore, there should be a case-by-case experimental or theoretical (or both) in-depth investigation to understand the role of support on each metal. Here, onto a layered porous carbon nitride (g-CN), we grew single crystalline Pt nanodisks (Pt@g-CN) with a lateral average size of 21 nm, followed by various characterisations such as electron microscopy techniques, and the measurement of electrocatalytic activity in the O2 reduction reaction (ORR). We found that intercalating Pt nanodisks in the g-CN interlayers causes an increase in electrocatalytic activity. We investigated the bonding mechanism between carbon support and platinum using density functional theory and applied the d-band theory to understand the catalytic performance. Analysis of Pt's density of states and electronic population across layers sheds light on the catalytic behaviour of Pt nanoparticles, particularly in relation to their thickness and proximity to the g-CN support interface. Our simulation reveals an optimum thickness of ~11 Å, under which the catalytic performance deteriorates.

ALD-Engineered CuxO Overlayers Transform ZnO Nanorods for Selective Production of CO in Electrochemical CO2 Reduction.

The electrochemical CO2 reduction reaction (CO2RR) holds tremendous promise as a strategy for lowering atmospheric CO2 levels and creating new clean energy sources. The conversion of CO2RR to CO, in particular, has garnered significant scientific interest due to its industrial feasibility. Within this context, the CuZn-based electrocatalyst presents an attractive alternative to conventional CO-selective electrocatalysts, which are often costly and scarce. Nevertheless, the wide-range utilization of CuZn electrocatalysts requires a more comprehensive understanding of their performance and characteristics. In this study, we synthesized ZnO nanorods through electrodeposition and subsequently coated them with CuxO overlayers prepared by atomic layer deposition (ALD). CuxO significantly enhanced CO selectivity, and 88% CO selectivity at a relatively low potential of -0.8 V was obtained on an optimized CuxO overlayer thickness (CuxO-250/ZnO). The addition of CuxO on ZnO was found to dramatically increase the electrochemical surface area (ESCA), lower the charge-transfer resistance (Rct), and introduce new active sites in the ε-CuZn4 phase. Furthermore, electrochemical Raman spectroscopy results showed that the CuxO-250/ALD electrode developed a ZnO layer on the surface during the CO2RR, while the bare ZnO electrode showed no evidence of ZnO during the reaction. These results suggest that the addition of CuxO by ALD played a crucial role in stabilizing ZnO on the surface. The initial amount of CuxO was shown to further affect the redeposition of the ZnO layer and hence affect the final composition of the surface. We attribute the improvement in CO selectivity to the introduction of both ε-CuZn4 and ZnO that developed during the CO2RR. Overall, our study provides new insights into the dynamic behavior and surface composition of CuZn electrocatalysts during CO2RR.

Templated Synthesis of Exfoliated Porous Carbon with Dominant Graphitic Nitrogen.

We present here a new approach for the synthesis of nitrogen-doped porous graphitic carbon (g-NC) with a stoichiometry of C6.3H3.6N1.0O1.2, using layered silicate as a hard sacrificial template. Autogenous exfoliation is achieved due to the heterostacking of 2D silicate and nitrogen-doped carbon layers. Micro- and meso-porosity is induced by melamine and cetyltrimethylammonium (C16TMA). Our density functional calculations and X-ray photoelectron spectroscopy (XPS) observations confirm that the most dominant nitrogen configuration in g-CN is graphitic, while pyridinic and pyrrolic nitrogens are thermodynamically less favored. Our large-scale lattice dynamics calculations show that surface termination with H and OH groups at pores accounts for the observed H and O in the composition of the synthesized g-NC. We further evaluate the electrocatalytic and the supercapacitance activities of g-NC. Interestingly, this material exhibits a specific capacitance of ca. 202 F g-1 at 1 A g-1, retaining 90% of its initial capacitance after 10,000 cycles.

Voriconazole incorporated nanofiber formulations for topical application: preparation, characterization and antifungal activity studies against Candida species.

In this study, voriconazole (VCZ) incorporated polyvinyl alcohol/sodium alginate electrospun nanofibers were produced and, then crosslinked with glutaraldehyde for topical antifungal treatment. The nanofibers were characterized in terms of fiber size, surface morphology, and compatibility between drug-polymer and polymer-polymer using scanning electron microscopy, atomic force microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, and high pressure liquid chromatography. After optimization studies, in vitro drug release, skin penetration, and deposition studies were performed using Franz diffusion cells. Antifungal activities of the nanofiber formulations against Candida albicans, Candida tropicalis, and Candida parapysilosis strains were evaluated using susceptibility test and subsequently time-kill study was performed against C. albicans. The cytotoxicity study was performed using 4-succinate dehydrogenase viability assay on mouse fibroblast cell line. The release rate of VCZ from crosslinked nanofibers was slower than that of non-crosslinked nanofibers and Higuchi kinetic model best fitted to the in vitro release data of both of formulations. VCZ deposited in deeper skin layers from nanofiber formulations was higher than that of the control formulation (VCZ solution in propylene glycol (1% (w/v)). According to the susceptibility and time-kill studies, all of the nanofiber formulations showed antifungal activity against C. albicans with confirming no cytotoxicity on mouse fibroblast cells.

Preparation and characterization of naftifine-loaded poly(vinyl alcohol)/sodium alginate electrospun nanofibers

In this study, naftifine (a topical antifungal drug) loaded poly(vinyl) alcohol (PVA)/sodium alginate (SA) nanofibrous mats were prepared using the single-needle electrospinning technique. The produced nanofibers were crosslinked with glutaraldehyde (GTA) vapor. The morphology and diameter of the electrospun nanofibers were studied by scanning electron microscopy (SEM). SEM images showed the smoothness of the nanofibers and indicated that the fiber diameter increased with crosslinking and drug loading. Atomic force microscopy (AFM) images confirmed the uniform production of the scaffolds, and elemental mapping via energy dispersive X-ray spectroscopy (EDS) showed the uniform distribution of the drug within the nanofibers. An attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy study demonstrated that naftifine has sufficient secondary interactions with the polymer blend. The crosslinking treatment decreased the burst drug release effectively and the release mechanism followed Korsmeyer-Peppas Super Case-II transport. Overall, these findings suggest the potential use of naftifine-loaded PVA/SA nanofibers as a topical antifungal drug delivery system.

One-Pot Synthesis of Hybrid Conjugated Oligomer-Ag Nanoparticles.

Here we report one-pot, straightforward synthesis of hybrid conjugated oligomer-silver nanoparticles (AgNPs) by utilizing tertiary alkyl amine and fluorene-benzothiodiazole-containing conjugated oligomer that both acts as a reducing agent in the reduction of silver ions into metallic silver and as a matrix to accommodate the newly formed AgNPs. By tuning the reaction conditions, it is possible to control the sizes and the structural features of hybrid nanoparticles as either raspberry or core-shell type hybrid structures.

Incorporation of growth factor loaded microspheres into polymeric electrospun nanofibers for tissue engineering applications.

Nanofibrous double-layer matrices were prepared by electrospinning technique with the bottom layer formed from PCL (poly-ε-caprolactone)/PLLA (poly-l-lactic acid) nanofibers and the upper layer from PCL/Gelatin nanofibers. Bottom layer was designed to give mechanical strength to the system, whereas upper layer containing gelatin was optimized to improve the cell adhesion. Gelatin microspheres were incorporated in the middle of two layers for controlled growth factor delivery. Successful fabrication of the blend nanofibers were shown by spectroscopy. Scanning electron microscopy results demonstrated that bead-free nanofibers with uniform morphology could be obtained by 10% w/v concentrations of PCL/PLLA and PCL/Gelatin solutions. Microspheres prepared by 15% gelatin concentration and cross-linked with 7.5% glutaraldehyde solution were chosen after in vitro release studies for the incorporation to the double-layer matrices. The optimized conditions were used to prepare fibroblast growth factor-2 (FGF-2) loaded microspheres. Preliminary cell culture studies showed that the FGF-2 could be actively loaded into the microspheres and enhanced the cell attachment and proliferation. The complete system had a slow degradation rate in saline (18% weight loss in 2 months) and it could meanwhile preserve its integrity. This sandwich system prevented microsphere leakage from the scaffold, and the hydrophilic and bioactive nature of the fibers at the upper layer promoted cell attachment to the surface. PLLA/PCL layer, on the other hand, improved the mechanical properties of the system and enabled better handling.

The growth of Co:ZnO/ZnO core/shell colloidal quantum dots: changes in nanocrystal size, concentration and dopant coordination.

We report a synthesis route for the growth of Co:ZnO/ZnO core/shell quantum dots. This procedure consists of successive steps, comprising the addition of diluted precursor salt solutions, and heat treatment at 50 degrees C. By deriving a relation between the extinction coefficient at 250 nm and the nanocrystal diameter, we are able to monitor changes in quantum dot concentration during shell growth. We found that a mechanism based on the nucleation of new particles after salt addition and subsequent Ostwald ripening during the heat treatment is responsible for the shell growth. Based on ligand-field absorption spectroscopy, we demonstrate that the Co(2+) ions adsorbed at the surface of Co:ZnO quantum dots are incorporated inside the ZnO shells. Finally, EPR spectroscopy indicates that the surface-adsorbed Co(2+) ions can be incorporated as substitutional as well as interstitial Co(2+) ions.