Plasma-Assisted Synthesis of Platinum Nitride Nanoparticles under HPHT: Realized by Carbon-Encapsulated Ultrafine Pt Nanoparticles

Catalytic and anti-cancer properties of platinum, gold, silver, and bimetallic Au-Ag nanoparticles synthesized by Bacillus sp. bacteria

Metallic nanoparticles play a significant role in the catalysis of chemical processes, besides, bimetallic nanoparticles with abundant active sites can reduce metallic nanoparticles toxicity in addition to increasing their catalytic performances. In this work, the platinum, gold, and silver nanoparticles are bio-synthesized using a native bacterium (GFCr-4). Also, the Au-Ag and Au@Ag bimetallic nanoparticles with alloy and core-shell structures, respectively, are biologically synthesized. To improve the synthesis, the effects of various factors like pH, temperature, electron donor, and ionic liquids were investigated. The as-synthesized nanoparticles were characterized with different techniques. The microscope images and dynamic light scattering (DLS) analysis confirm the uniform distribution of as-synthesized nanoparticles with average sizes of 25, 30, 47, 77, and 86 nm obtained for Ag, Au, Pt, Au-Ag alloy, and Au@Ag core-shell, respectively. The catalytic performances of as-synthesized nanoparticles were investigated. The Au-Ag alloy nanoparticles exhibit better catalytic performance than the as-synthesized metallic Au nanoparticles, according to the Gewald reaction. According to the photocatalytic study, the yield can be increased by up to 92% by using PtNPs in the presence of a green LED. Additionally, for the first time, PtNPs were utilized as an effective catalyst in a peroxyoxalate chemiluminescence (POCL) system in the presence of nuclear fast red (NFR) as a novel fluorophore. In addition, the results of the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay revealed that the synthesized eco-friendly nanoparticles have a low effect on the lethality of 3T3 normal cells whereas MCF-7 cancer cells were inhibited up to 77.3% after treatment by PtNPs nanoparticles.

Chemical Vapor Deposition Mechanism of Graphene-Encapsulated Au Nanoparticle Heterostructures and Their Plasmonics

Direct encapsulation of graphene shells on noble metal nanoparticles via chemical vapor deposition (CVD) has been recently reported as a unique way to design and fabricate new plasmonic heterostructures. But currently, the fundamental nature of the growth mechanism of graphene layers on metal nanostructures is still unknown. Herein, we report a systematic investigation on the CVD growth of graphene-encapsulated Au nanoparticles (Au@G) by combining an experimental parameter study and theoretical modeling. We studied the effect of growth temperature, duration, hydrocarbon precursor concentration, and extent of reducing (H₂) environment on the morphology of the products. In addition, the influence of plasma oxidation conditions for the surface oxidation of gold nanoparticles on the graphene shell growth is evaluated in combination with thermodynamic calculations. We find that these parameters critically aid in the evolution of graphene shells around gold nanoparticles and allow for controlling shell thickness, graphene shell quality and morphology, and hybrid nanoparticle diameter. An optimized condition including the growth temperature of ∼675 °C, duration of 30 min, and xylene feed rate of ∼10 mL/h with 10% H₂/Ar carrier gas was finally obtained for the best morphology evolution. We further performed finite-element analysis (FEA) simulations to understand the equivalent von Mises stress distribution and discrete dipolar approximation (DDA) calculation to reveal the optical properties of such new core-shell heterostructures. This study brings new insight to the nature of CVD mechanism of Au@G and might help guiding their controlled growth and future design and application in plasmonic applications.