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To effectively address environmental pollution, we synthesized Au-loaded ZnO nanocomposites and applied for the photocatalytic degradation of 2-chlorophenol (2-CP) under visible light irradiation. The as-prepared nanophotocatalysts delivered much improved photocatalytic degradation activities as compared to the bare ZnO nanoparticles and 32% of the pollutant was degraded with 2AuZnO in 1 hr. These improved photoactivities are attributed to the extended visible light absorption due to the surface plasmon resonance property of the loaded Au nanoparticles. Moreover, Au nanoparticles played important role in charge separation by inducting excited electrons to the conduction band of ZnO photocatalyst and surface catalysis as confirmed from photoluminescence spectra and amount of the generated hydroxyl radicals. The trapping experiments confirmed that positive holes were the major degrading species during the photocatalytic degradation of 2-CP. This work provides a feasible way to improve the photocatalysis by introducing a proper amount of noble metals over the surface of semiconductor photocatalysts.

Desirable cost and removal effectiveness of the adsorbents can be obtained by the use and modification of agricultural waste products. Therefore, in this study rice husk (RH), rice husk char (RHC) and chemically modified rice husk char (CMRHC) were prepared and used as adsorbents for the removal of Congo Red dye from aqueous media under different experimental conditions. It was observed that the adsorption of Congo Red dye was not only affected with the types of adsorbents used but also with other experimental variables such as time, adsorbent dose, dye concentration, pH and temperature. Thermodynamics study indicated that the adsorption of Congo Red dye on the three adsorbents is spontaneous and exothermic process. Kinetics data showed that the adsorption of Congo Red dye on these adsorbents follow pseudo-second order model better than the pseudo-first order model. Equilibrium adsorption data were tested with Langmuir, Freundlich, and Temkin adsorption isotherm models. It was observed that the equilibrium data of RH and RHC were found best fit to the Langmuir adsorption isotherm model whereas that of CMRHC was best fit to the Freundlich and Temkin models. CMRHC showed better efficiency compared to both RH and RHC.   Bull. Chem. Soc. Ethiop. 2020, 34(1), 41-54. DOI: https://dx.doi.org/10.4314/bcse.v34i1.4

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The green synthesis of nanoparticles using plants and their extracts is considered as a representative approach in material synthesis for environmental benignity. Numerous metal nanoparticles with potential bioactivities have been prepared based on plant extracts. In this paper, we report an eco-friendly technique for the preparation of silver nanoparticles using plant extract of Justicia diffusa Willd. and the evaluation of their antioxidant, antidiabetic, and cytotoxicity activities. UV-visible spectroscopy, transmission electron microscopy, scanning electron microscopy and atomic force microscopy analysis were used to characterize the morphology and size of silver nanoparticles. The stability of silver nanoparticles toward acidity, alkalinity, salinity and temperature showed that they remained stable at room temperature for more than two months. UV-vis spectrum of the aqueous medium containing silver nanoparticles showed an absorption peak at around 420 nm. The scanning electron microscopy analysis of the silver nanoparticles showed that they have a uniform spherical shape with an average size in the range of 40-78 nm. This was confirmed by transmission electron microscopy analysis which showed an average size of about 50 nm. Thus green system showed better capping and stabilizing agent for the fine particles. Further 1-diphenyl-2picrylhydrazl radical in Justicia diffusa mediated silver nanoparticles showed a maximum activity of 67% at concentration of 200 μg/mL. Hydrogen peroxide scavenging assay in Justicia diffusa mediated silver nanoparticles showed a maximum activity of 89% at concentration of 200 μg/mL. Reducing power of Justicia diffusa silver nanoparticles exhibited a higher activity of 246 μg/mL at concentration of 200 μg/mL. These NPs showed the cytotoxic effects against brine shrimp (Artemia salina) Nauplii with a value of 35% and LD value of 271 μg/mL. The AgNPs synthesized using Justicia diffusa Willd. extract also show remarkable antidiabetic activities.

The current study sought to synthesize silver nanoparticles (AgNPs) from Amaryllis vittata (L.) leaf and bulb extracts in order to determine their biological significance and use the toxic plants for human health benefits. The formation of silver nanoparticles was detected by a change in color from whitish to brown for bulb-AgNPs and from light green to dark brown for leaf-AgNPs. For the optimization of silver nanoparticles, various experimental physicochemical parameters such as pH, temperature, and salt were determined. UV-vis spectroscopy, Fourier transform infrared spectroscopy, X-ray dispersion spectroscopy, scanning electron microscopy, and energy dispersion spectroscopy analysis were used to characterize nanoparticles. Despite the fact that flavonoids in plant extracts were implicated in the reduction and capping procedure, the prepared nanoparticles demonstrated maximum absorbency between 400 and 500 nm. SEM analysis confirmed the preparation of monodispersed spherical crystalline particles with fcc structure. The bioinspired nanoparticles were found to show effective insecticidal activity against Tribolium castaneum and phytotoxic activity against Lemna aequincotialis. In comparison to plant extracts alone, the tested fabricated nanoparticles showed significant potential to scavenge free radicals and relieve pain. Antibacterial testing against human pathogenic strains, i.e., Escherichia coli and Pseudomonas aureginosa, and antifungal testing against Aspergillus niger revealed the significant potential for microbe resistance using AgNPs. As a result of the findings, the tested silver nanoparticles demonstrated promising potential for developing new and effective pharmacological and agricultural medications. Furthermore, the effects of biogenic AgNPs on an in vitro culture of Solanum tuberosum L. plants were investigated, and the findings indicated that bulb-AgNPs and leaf-AgNPs produced biomass and induced antioxidants via their active constituents. As a result, bulb-AgNPs and leaf-AgNPs may be recommended for use in Solanum tuberosum L. tissue culture for biomass fabrication and metabolic induction.

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