Plasma-aided green and controllable synthesis of silver nanoparticles and their compounding with gemini surfactant

State of the Art Synthesis of Ag-ZnO-Based Nanomaterials by Atmospheric Pressure Microplasma Techniques

Atmospheric pressure microplasma is a simple, cost-effective, efficient, and eco-friendly procedure, which is superior to the traditional nanomaterials synthesis techniques. It generates high yields and allows for a controlled growth rate and morphology of nanomaterials. The silver (Ag) nanomaterials, with their unique physical and chemical properties, exhibit outstanding antibacterial and antifungal properties. Similarly, zinc oxide (ZnO) nanomaterials, known for their low toxicity and relatively lower cost, find wide applications in wound repair, bone healing, and antibacterial and anticancer applications. The use of core–shell nanomaterials in certain situations where some nanoparticles can cause serious harm to host tissues or organs is a testament to their potential. A benign material is coated over the core to reduce toxicity in these cases. This review compares the numerous configurations of microplasma systems used for synthesizing nanomaterials and their use in producing Ag, ZnO, and their core–shell (Ag-ZnO) nanomaterials for biomedical applications. The summary also includes the effect of control parameters, including cathode diameter, gas flow rate, precursor concentration, voltage, and current, on the nanomaterial’s characteristics and applications. In addition, it provides a research gap in the synthesis of Ag, ZnO, and core–shell nanomaterials by this technique, as well as the development and limitations of this technique and the use of these nanoparticles for biomedical applications.

Preferential role of distinct phytochemicals in biosynthesis and antibacterial activity of silver nanoparticles

Biosynthesis of silver nanoparticles (AgNPs) by plant extracts and its antibacterial utilization has attracted great attention due to the spontaneous reducing and capping capacities of phytochemicals. However, the preferential role and mechanisms of the functional phytochemicals from different plants on AgNPs synthesis, and its catalytic and antibacterial performance remain largely unknown. This study used three widespread arbor species, including Eriobotrya japonica (EJ), Cupressus funebris (CF) and Populus (PL), as the precursors and their leaf extracts as reducing and stabilizing agents for the biosynthesis of AgNPs. A total of 18 phytochemicals in leaf extracts were identified by ultra-high liquid-phase mass spectrometer. For EJ extracts, most kinds of flavonoids participated in the generation of AgNPs by a reduced content of 5∼10%, while for CF extracts, about 15∼40% of the polyphenols were consumed to reduce Ag+ to Ag0. Notably, the more stable and homogeneous spherical AgNPs with smaller size (≈38 nm) and high catalytic capacity on Methylene blue were obtained from EJ extracts rather than CF extracts, and no AgNPs were synthesized from PL extracts, indicating that flavonoids are superior than polyphenols to act as reducer and stabilizer in AgNPs biosynthesis. The antibacterial activities against Gram-positive (Staphylococcus aureus and Bacillus mycoides) and Gram-negative bacteria (Pseudomonas putida and Escherichia coli) were higher in EJ-AgNPs than that in CF-AgNPs, which confirmed the synergistic antibacterial effects of flavonoids combined with AgNPs in EJ-AgNPs. This study provides a significant reference on the biosynthesis of AgNPs with efficient antibacterial utilization underlying effect of abundant flavonoids in plant extracts.

Synthesis of antibacterial hydroxypropyl methylcellulose and silver nanoparticle biocomposites via solution plasma using silver electrodes

The biocomposites of hydroxypropyl methylcellulose (HPMC)/silver nanoparticles (AgNPs) were synthesized using the solution plasma process (SPP). HPMC/AgNPs were synthesized in 1-5 % HPMC solutions using silver electrodes. UV-Vis spectroscopy showed a peak near 400 nm and the peak increased as the concentration of HPMC and discharge time increased. FTIR analysis indicated no change in the chemical structure of the HPMC based biocomposites. Spherical shaped AgNPs with size ranges about 2-18 nm and well dispersed in the porous HPMC matrices with fringed edges were observed by TEM and SEM/EDS analyses. The synthesized biocomposites were found to be thermo-stable by TGA analysis. The inhibition zones of bacterial growth formed by the HPMC/AgNPs biocomposites were in the range of 8-14.3 mm; minimal inhibition concentrations, in the range of 10-15 μg·mL^-1 for Gram-negative bacteria; 25-30 μg·mL^-1 for Gram-positive bacteria. The biocomposites were non-toxic to the HEK293 cells up to 125 μg·mL^-1. The results indicated that the synthesis of antibacterial agents in the HPMC matrix using silver electrodes via SPP would be an efficient and safe way for the development of biopolymer based antimicrobials and wound healing biomaterials.

Microplasma synthesized gold nanoparticles for surface enhanced Raman spectroscopic detection of methylene blue

Surface enhanced Raman scattering (SERS) is a powerful and sensitive spectroscopic technique that allows for rapid detection of trace-level chemical species in a non-invasive and non-destructive manner.

Non-thermal atmospheric pressure plasma as a powerful tool for the synthesis of rhenium-based nanostructures for the catalytic hydrogenation of 4-nitrophenol

Here we have presented a new method for the synthesis of Re nanostructures with defined optical, structural, and catalytic properties. The Re-based nanoparticles (NPs) were obtained using a reaction-discharge system that is unique in its class, because of its working in the high-throughput mode. Within this application, direct current atmospheric pressure glow discharge (dc-APGD) was used as a non-thermal atmospheric pressure plasma (NTAP) source, which led to the reduction of Re(vii) ions and the formation of Re nanostructures through the plasma-liquid interactions. The Re-based NPs were synthesized in a flow-mode reaction-discharge system, where their precursor solution was a flowing liquid anode (FLA) or a flowing liquid cathode (FLC). The resultant NPs were analyzed using UV/Vis absorption spectrophotometry and transmission electron microscopy (TEM), which were supported by selected area X-ray diffraction (SAED) and the energy dispersive X-ray spectroscopy (EDX). Additionally, the mechanism for the reduction of Re(vii) ions was explained by the differences in the concentrations of the selected reactive nitrogen species (RNS) and reactive oxygen species (ROS) produced by dc-APGD. It was found that the application of dc-APGD, operating in a FLA configuration (FLA-dc-APGD), resulted in the formation of ReNPs with Re0, while the use of dc-APGD operating in a FLC configuration (FLC-dc-APGD) led to the formation of Re oxide NPs. In the latter case, a much greater oxidizing environment was likely provided, therefore the RNS and ROS contributed to the formation of Re oxide nanostructures. The ReNPs with Re0 were characterized by a size of 6.02 ± 3.01 nm, and the Re oxide NPs were characterized by a size of 4.97 ± 3.82 nm. Both types of nanostructures were then employed in the catalytic hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Based on the results, both of the nanocatalysts effectively reduced 4-NP with an apparent rate constant (k app) of 2.6 × 10-3 s-1. At the same time, the catalytic activity was linked with the average size distribution of the Re nanostructures, as opposed to their morphology.

Statistically Optimized Production of Saccharides Stabilized Silver Nanoparticles Using Liquid-Plasma Reduction Approach for Antibacterial Treatment of Water

Various conventional approaches have been reported for the synthesis of nanomaterials without optimizing the role of synthesis parameters. The unoptimized studies not only raise the process cost but also complicate the physicochemical characteristics of the nanostructures. The liquid-plasma reduction with optimized synthesis parameters is an environmentally friendly and low-cost technique for the synthesis of a range of nanomaterials. This work is focused on the statistically optimized production of silver nanoparticles (AgNPs) by using a liquid-plasma reduction process sustained with an argon plasma jet. A simplex centroid design (SCD) was made in Minitab statistical package to optimize the combined effect of stabilizers on the structural growth and UV absorbance of AgNPs. Different combinations of glucose, fructose, sucrose and lactose stabilizers were tested at five different levels (-2, -1, 0, 1, 2) in SCD. The effect of individual and mixed stabilizers on AgNPs growth parameters was assumed significant when p-value in SCD is less than 0.05. A surface plasmon resonance band was fixed at 302 nm after SCD optimization of UV results. A bond stretching at 1633 cm-1 in FTIR spectra was assigned to C=O, which slightly shifts towards a larger wavelength in the presence of saccharides in the solution. The presence of FCC structured AgNPs with an average size of 15 nm was confirmed from XRD and EDX spectra under optimized conditions. The antibacterial activity of these nanoparticles was checked against Staphylococcus aureus and Escherichia coli strains by adopting the shake flask method. The antibacterial study revealed the slightly better performance of AgNPs against Staph. aureus strain than Escherichia coli.