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The nanocomposite of graphene oxide and silver nanoparticles with uniform particle distribution was successfully green synthesized for bioactive assessment and hydrogen peroxoide electro-sensing application.

In this study, the utilization of Vietnamese Ganoderma lucidum (G. lucidum) extract was scrutinized under different operational conditions including reaction time, AgNO3:extract mass ratio, and reaction temperature to establish a rapid, cost–effective, and eco–friendly method with a high yield rate and nanoparticle stabilization. The characterization showed that the as–synthesized silver nanoparticles (AgNPs) were well–crystalline with an average size of 11.38 ± 5.51 nm. Meanwhile, the Fourier–transform infrared spectrometry of AgNPs and extract samples showed the absorption bands including –OH stretching, symmetric aliphatic bending, and C–OH stretching vibrations belonging to the presence of polyphenols, triterpenoids, and polysaccharides, respectively. These bands reveal an astounding decline in the polyphenol, triterpenoid, and flavonoid content of the crude G. lucidum extracts, which is consistent with the results obtained from colorimetric methods. In liquid chromatography–mass spectrometry of AgNPs and extract samples, various peaks were detected and they shared significant differences in intensity after the reaction. As a result, the phytochemicals from G. lucidum extracts were confirmed to play the role of reducing silver ions to AgNPs and act as a capping agent to stabilize the colloid mixture. In the biological tests, the colloidal AgNPs demonstrated an extraordinary antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, and Candida albicans, with IC50 values of 17.97, 17.06, 1.32, 54.69, and 27.78 µg/mL, respectively. The antioxidant capacity of AgNPs was evaluated using 2,2–diphenyl–1–picrylhydrazyl free radical reagent (IC50 = 447.120 ± 0.084 µg/mL). In addition, the colloidal AgNPs possessed better anticancer activity against the human epidermic carcinoma cancer cell line (KB) with IC50 values of 190.06 ± 3.62 µg/mL when compared to the crude extract. The results of the bioactivity evaluations exhibited the potential utilization of G. lucidum extract as a natural source for the colloidal AgNPs biosynthesis and their application in various areas, particularly as an antimicrobial agent in food, pharmaceutical, and cosmetic product preservation to combat bacterial infection.

Herein, the surface modification of graphene oxide with silver nanoparticles was examined with the type of reducing agents, the reducing agent:AgNO3 mass ratio, reduction temperature, reduction time, and AgNO3:GO mass ratio. The optimal fabrication condition was determined based on the AgNPs density on GO, AgNPs size, and the antibacterial activity of the Ag/GO by plate colony–counting and optical density methods. The as-prepared materials were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV–vis spectroscopy. Results revealed that the appropriate reducing agent is ascorbic acid (AA) with the conditions: the ratio AA:AgNO3 = 1:1; reaction at 40 °C in 10 min with AgNO3:GO ratio of 1.25:1. More than 99.99 % of bacteria was inhibited, with a minimum bactericidal concentration of 50 and 100 µg/mL for P. aeruginosa, and S. aureus, respectively. Furthermore, the materials were surveyed in terms of their interface sorption and sensing applications. The maximum adsorption capacity of the nanocomposite reached 98.04 mg/L at 40–100 mg/L methylene blue, while the limit of detection for detecting Hg(II) in water was indicated to be 223 nM. Therefore, Ag/GO has shown sustainably promising usage for multiple purposes.

Zinc oxide - doped titanium dioxide/reduced graphene oxide (ZnO-TiO2/rGO) nanocomposite was fabricated by the two-step hydrothermal method and used for adsorption and photodegradation of methylene blue in aqueous solution under UV irradiation. The characteristics of the catalyst material were confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscope, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller specific surface area, thermal gravimetric analysis, and UV-vis spectroscopy. The results showed that the presence and uniform distribution of TiO2 and ZnO nanoparticles on the rGO surface with an average diameter of 20 – 30 nm and high specific surface area (182.52 m2/g). The photodegradation was investigated via the pH media. The equilibrium adsorption at pH of 9 achieved the highest adsorption efficiency after 60 min (43.68 %) and 60 min photodegradation (99.84 %). According to the results, the photodegradation using ZnO-TiO2/rGO nanocomposite was stated to be a promising pathway for removing the organic dye from water.