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In this study, selenium microparticles (SeMPs) were green-synthesized by utilizing the Terminalia catappa leaves extract as an effective reducing agent. SeMPs were then decorated onto graphene oxide (GO) with the assistance of ultrasound using the ex-situ technique to obtain the SeMPs-GO composite. SeMPs and SeMPs-GO were thoroughly characterized with modern analytical methods, whereas the antibacterial performance of the composites was evaluated via the optical density method. Particularly, SeMPs-GO held up an inhibition of 99 % against both Gram-positive and Gram-negative bacteria strains as well as restrained 50 % of fungal activity. SeMPs-GO was additionally incorporated onto chitosan (CTS) to collect the SeMPs-GO/CTS membrane which was characterized by similar advanced analysis methods. The antibacterial property of the membrane was determined by the inhibition zone diameter. Furthermore, the membrane exhibited good thermal and mechanical characteristics, showing no sign of degradation at a temperature below 260 °C, and a tensile strength of 38 N/mm

In this study, silver immobilizing onto graphene oxide (Ag/GO) was synthesized by the in-situ method. Subsequently, silver immobilizing reduced graphene oxide cotton fabric (Ag/rGO/cotton) was made by the dip-coating method in Ag/GO suspension followed by the chemical reduction with the presence of vitamin C as an environmentally friendly reducing agent. The characteristics of Ag/GO, Ag/GO/cotton, and Ag/rGO/cotton were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscope, and energy-dispersive X-ray spectroscopy. The results showed that AgNPs were uniformly distributed on the surface of GO sheets with an average size of 10–15 nm. Regarding Ag/rGO/cotton, the fiber surface was evenly covered by Ag/rGO materials. Besides, there was no significant difference between the two samples of Ag/GO/cotton and Ag/rGO/cotton, indicating the reduction reaction possessed no effect on the cotton structure. Moreover, the Ag/rGO/cotton also exhibited effective hydrophobicity with a wetting angle of 103.85 ± 0.75 o. The antibacterial performance of Ag/GO, Ag/GO/cotton, and Ag/rGO/cotton against the Gram-positive (Staphylococcus aureus-S. aureus) and Gram-negative (Pseudomonas aeruginosa-P. aeruginosa) bacteria were determined via the diameter zone of inhibition. The results indicated that the appropriate reducing agent is L-ascorbic acid-vitamin C (VC) with the conditions: the VC:Ag/GO mass ratio of 1:1, the reducing temperature of 140 oC, and the reducing time of 120 min showed the highest antibacterial effect against two types of bacteria. All results of the study confirmed that Ag/rGO/cotton possesses significant potential for several antibacterial applications such as protective equipment.

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.

In this work, a one-pot hydrothermal route was synergistically applied for TiO2 immobilized reduced graphene oxide (TiO2/rGO) facilitation. The material was characterized by modern analysis methods and studied the photocatalytic performance with methylene blue (MB) in the water. The characteristic results expressed that TiO2 in truncated octahedral bipyramidal structure with 4–25 nm was disseminated onto the rGO base. Simultaneous effects of the reaction temperature, pH, adsorption time, photocatalytic time, MB concentration, and catalyst dosage on the MB photodegradation of TiO2/rGO were also conducted by full factorial experimental design according to Placket–Burman and Box–Behnken designs. At room temperature, after 2h–adsorption and photodegradation with MB concentration of 23 mg/L in pH of 10 solution and 20 mg catalyst, nearly 100% of MB was productively decomposed out of the medium with a relatively high reaction rate constant. The photocatalytic performance showed an excellent impact toward other types of organic contaminants with the above condition, indeed affirming an extensive use in wastewater treatment with organic pollutants.

In this study, we reported the synthesis of graphene oxide aerogel (GOA) through ice segregation induced self-assembly of GO sheets. The formation mechanism of GOA was studied via Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Energy-dispersive X-ray spectroscopy, and Brunauer–Emmett–Teller surface area. The GOA with GO concentration of 10 mg/mL was applied as an adsorbent to remove heavy metal ions (Cd2+, Ni2+). The adsorption processes of GOA for Cd2+, Ni2+ fitted well with pseudo-second-order kinetics and Langmuir isotherm models. The maximum adsorption capacities for Cd2+ and Ni2+ were determined to be 108.70 and 91.74 mg/g, respectively. Moreover, the electrostatic attraction was found to be the main interaction between GOA and Cd2+, Ni2+. The adsorption of phenolic compounds (phenol and bisphenol A) was studied to expand the adsorption applications of GOA. In addition, The maximum adsorption capacities for phenol and bisphenol A were determined to be 129.37 and 64.76 mg/g, respectively. Therefore, GOA has the potential to be used as a highly efficient adsorbent for the treatment of heavy metal ions and phenolic compounds from water.

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.

In this study, three-dimensional graphene aerogel materials fabricated by self-assembly of graphene oxide (GO) sheets with ethylenediamine was used as a reducing agent. GO sheets were briefly synthesized from graphite by improved Hummers’ method, then partially reduced to create the 3D structure. The GA materials were characterized by density, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscope, and Brunauer – Emmett – Teller specific surface area. The formation mechanism of aerogel was investigated through the evaluation of reduction and drying by sublimation conditions. The adsorption process followed pseudo-second-order kinetic models. The adsorption data was well-fitted to Langmuir isotherm model. The adsorption abilities of GA for methylene blue (MB) and methyl orange (MO) were elaborated with factors including time, pH, and initial concentration. The maximum adsorption capacities of GA for MB and MO were calculated to be 221.77 and 166.66 mg/g, respectively. MO dye was chosen for estimating the simultaneous impact of different factors (pH, contact times, and initial concentration of dye) on the adsorption ability of GA and determine the ideal values for optimal performance by full factorial experimental design according to Box–Behnken designs. Moreover, the adsorption mechanism of GA for dyes also was investigated. Accordingly, GA could be applied as a potential adsorbent for the removal of dyes from aqueous media.

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.

Herein, silver/graphene oxide (Ag/GO) nanocomposite was fabricated by co-precipitation with green reducing agent and then was characterized with modern analytical techniques. The antibacterial activities were conducted via the effects of Ag/GO concentration, time, and pH. Results show that silver nanoparticles were uniformly distributed on the GO sheets nanosized of 17.65 ± 4.76 nm. The antibacterial performance was optimized at pH 5.6, eradicating P. aeruginosa in 180 min at 50 µg/mL Ag/GO concentration and S. aureus in 480 min at 300 µg/mL Ag/GO. This demonstrates the potential of Ag/GO as an antibacterial nanocomposite material.

Herein, MgFe2O4-doped TiO2/reduced graphene oxide (MFO-TiO2/rGO) was synthesized via the ultrasound-assisted hydrothermal method and directly used for photodegradation p-nitrophenol from water. 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 photodegradation studies via the catalytic recovering property were also investigated with comparing to TiO2/rGO, TiO2, and MFO. The results showed that the MFO and TiO2 nanoparticles were homogeneously distributed on the GO sheet with an average diameter of 5–14 nm. The empirical data indicated a good photocatalytic property under visible light of MFO-TiO2/rGO compared to others with the photodegradation yield 99.53% in 50 min via 40 mg amount of catalysts, 1 mL H2O2 substitution, and a pH of 9. The kinetic studies exhibited that the reaction followed the pseudo-first order with a rate constant of 0.1011 min−1. Besides, it can be easily separated and reused with an insignificant change in photodegradation yield. According to the results, MFO-TiO2/rGO is highly promising for organic contaminant elimination in the effluent for the future wastewater treatment plant.

In this study, silver/graphene oxide (Ag/GO) nanocomposites were synthesized using the in situ method. Glucose was selected as an eco-friendly reducing agent for the reduction of Ag+ into silver nanoparticles (AgNPs). The characterization of GO and Ag/GO with Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopye, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Results showed that Ag/GO was successfully synthesized. Silver nanoparticles (AgNPs) with an average size of 17.68 ± 4.48 nm were uniformly distributed onto GO sheets. The antibacterial activity of GO, AgNPs, and Ag/GO were tested against Staphylococcus aureus ATCC 25,923 (S. aureus) and Salmonella enterica ATCC 35,664 (S. enterica) bacteria by optical density and plate colony–counting methods. Test results showed that Ag/GO had higher antibacterial activity than its precursors (bare AgNPs and GO) with a bactericidal rate of more than 99.90 %. Thus, Ag/GO was selected for further experimentation. Simultaneous effects of the interaction time, Ag/GO concentration, pH, annealing temperature, and S. aureus density on the antibacterial activity of Ag/GO were also investigated with full factorial experimental design according to Placket–Burman and Box–Behnken designs. After 10 min of interaction time at 37 °C, the optimal values of these factors were determined to be: Ag/GO concentration of 48 μg/mL, pH 5, and S. aureus density 5.3 × 106 CFU/mL, corresponding to an antibacterial capacity of 99.95 % towards S. aureus. The presented experiment confirmed Ag/GO to be able of eliminating about 99.99 % of S. aureus. All results of the present study affirmed the potential applications of Ag/GO as an antibacterial agent in the medical field.