Evaluating the antimicrobial activity and cytotoxicity of polydopamine capped silver and silver/polydopamine core-shell nanocomposites

Fabrication of bioactive nanomaterials with improved stability and low toxicity towards healthy mammalian cells have recently been a topic of interest. Bioactive metal nanomaterials such as silver nanoparticles (AgNPs) tend to lose their stability with time and become toxic to some extent, limiting their biological applications. AgNPs were separately encapsulated and loaded on the surface of a biocompatible polydopamine (PDA) to produce Ag-PDA and Ag@PDA nanocomposites to unravel the issue of agglomeration. PDA was coated through the self-polymerization of dopamine on the surface of AgNPs to produce Ag-PDA core-shells nanocomposites. For Ag@PDA, PDA spheres were first designed through self-polymerization of dopamine followed by in situ reduction of silver nitrate (AgNO3) without any reductant. AgNPs sizes were controlled by varying the concentration of AgNO3. The TEM micrograms showed monodispersed PDA spheres with an average diameter of 238 nm for Ag-PDA and Ag@PDA nanocomposites. Compared to Ag@PDA, Ag-PDA nanocomposites have shown insignificant toxicity towards human embryonic kidney (HEK-293T) and human dermal fibroblasts (HDF) cells with cell viability of over 95% at concentration of 250 µg/mL. A excellent antimicrobial activity of the nanocomposites was observed; with Ag@PDA possessing bactericidal effect at concentration as low as 12.5 µg/mL. Ag-PDA on the other hand were only found to be bacteriostatic against gram-positive and gram-negative bacteria was also observed.The University of Witwatersrand School of Chemistry, The University of the Witwatersrand Postgraduate Merit Award and the National Research Foundation of South Africa.https://www.journals.elsevier.com/arabian-journal-of-chemistryhj2023Physic

Colloidal synthesis of molybdenum diselenide nanomaterials for supercapacitor applications

ii Abstract Herein we report on the synthesis of MoSe2 nanomaterials using novel colloidal synthetic methods and their application as electrode materials in supercapacitors. Supercapacitors are energy storage devices with high power density and high cycle stability that can be used in applications that require rapid charge/discharge. The drawback in supercapacitors is their low energy density. Nanomaterials with high surface area are being explored as alternatives to activated carbon which has been a commonly used electrode material in supercapacitors. This is done to increase the energy density of supercapacitors. MoSe2 has been identified as an excellent candidate for use as an electrode material in supercapacitors because of its interesting properties. MoSe2 is a layered transition metal dichalcogenide (TMD) that is similar to graphene in structure and possesses interesting structural, optical and electronic properties. MoSe2 also has a high surface to volume ratio. A colloidal synthetic process was used for the synthesis of the MoSe2 nanomaterials, after which the effect of various reaction parameters was investigated. The reaction was run at 300 °C using oleylamine (OAm) as the solvent and surfactant. A time study on the synthesis of the nanomaterials revealed MoSe2 few-layer nanosheets grow from a flocculate formed in the initial stages of the reaction (30 min). At longer reaction times (e.g. 90 min) the flocculate is consumed to form wrinkled few-layer nanosheets. A variation of the metal precursor in the reaction results in changes to the morphology of the MoSe2 nanomaterials. The formation of the flocculate in the initial stages of the reaction when molybdenum hexacarbonyl is used as the metal precursor results in the formation of wrinkled few-layer nanosheets. The use of molybdic acid as the metal precursor results in the formation of nanoparticles with a central core which leads to the formation of MoSe2 nanoflowers. The effect of adding a co-surfactant to the reaction system was also investigated. The effect of adding oleic acid as a co-surfactant in the reaction along with oleylamine resulted in changes to the thickness of the nanosheets synthesized and slight changes in the morphology. The use of 1-octadecene as a co-surfactant resulted in the increased reactivity of the selenium precursor which increased the number of nanosheets growing per nanoflower. The electrochemical properties of the MoSe2 nanomaterials were investigated to determine the suitability of the nanomaterials for use as supercapacitor electrodes. The MoSe2 nanomaterials synthesized using colloidal synthesis exhibited electric double layer capacitance behaviour. The effect of the morphology on the electrochemical performance of the MoSe2 nanomaterials was investigated using MoSe2 nanoflowers and few-layer nanosheets. The MoSe2 nanoflowers were shown to have a higher specific capacitance at 81 Fg-1 than the few-layer nanosheets at 30 Fg-1. The nanoflowers also had better capacitance retention at higher current densities in the charge-discharge analysis compared to the few-layer nanosheets. The nanoflowers had higher capacitance retention of 68% compared to 20% for the few-layer nanosheets. The nanoflowers also had a lower equivalence series resistance (ESR) of 34.0 Ω compared to that of the few-layer nanosheets at 57.1 Ω.EM201

Hierarchical Nanoflowers of Colloidal WS2 and Their Potential Gas Sensing Properties for Room Temperature Detection of Ammonia

A one-step colloidal synthesis of hierarchical nanoflowers of WS2 is reported. The nanoflowers were used to fabricate a chemical sensor for the detection of ammonia vapors at room temperature. The gas sensing performance of the WS2 nanoflowers was measured using an in-house custom-made gas chamber. SEM analysis revealed that the nanoflowers were made up of petals and that the nanoflowers self-assembled to form hierarchical structures. Meanwhile, TEM showed the exposed edges of the petals that make up the nanoflower. A band gap of 1.98 eV confirmed a transition from indirect-to-direct band gap as well as a reduction in the number of layers of the WS2 nanoflowers. The formation of WS2 was confirmed by XPS and XRD with traces of the oxide phase, WO3. XPS analysis also confirmed the successful capping of the nanoflowers. The WS2 nanoflowers exhibited a good response and selectivity for ammonia

Unraveling the effects of surface functionalization on the catalytic activity of ReSe2 nanostructures towards the hydrogen evolution reaction

Herein, the surface functionalization of ReSe2 nanostructures by surfactants was investigated. This was done to understand how the use of various surfactants affects the catalytic activity of ReSe2 nanostructures towards the hydrogen evolution reaction (HER), and to determine which surfactant would result in maximal exposure of the active edge sites without impeding the catalytic processes of the HER. Oleylamine (OLA), oleic acid (OA), and trioctylphosphine oxide (TOPO) were used as the surfactants. Powder X-ray diffraction confirmed the formation of ReSe2 nanostructures that crystallized in a distorted 1 T phase triclinic system with a P-1 space group. The FTIR, XPS, NMR, and computational studies revealed that the surfactants bind to the surface of the ReSe2 nanostructures through their respective head groups. The ReSe2 nanostructures synthesized using TOPO (ReSe2-TOPO) had the lowest on-set potential, Tafel slope, and overpotential at 10 mA/cm2 at 73 mV, 58 mV/dec, and 171 mV, respectively. The catalytic performance of the nanostructures was significantly affected by their interaction with the surfactants. A high degree of passivation by the surfactant resulted in poor catalytic activity, and a lower degree of passivation resulted in excellent catalytic activity towards the HER