Synthesis and Characterization of rGO/Ag2O Nanocomposite and its Use for Catalytic Reduction of 4-Nitrophenol and Photocatalytic Activity

Green hydrothermal synthesis and characterization of Ag2O-supported MgO/rGO nanocomposites by using Phoenix leaf extract: a promising approach for enhanced photocatalytic and anticancer activities

The present work was designed to synthesize Ag2O-supported MgO/rGO nanocomposites (NCs) via green method using Phoenix leaf extract for improved photocatalytic and anticancer activity. Green synthesized Ag2O-supported MgO/rGO NCs were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman, ultraviolet-visible (UV-vis) spectroscopy, and photoluminescence (PL) spectroscopy, and gas chromatography-mass spectroscopy (GC-MS) was applied to examine the chemical components of the Phoenix leaf extract. Characterization data confirmed the preparation of MgO NPs, Ag2O-MgO NCs, and Ag2O-MgO/rGO NC with particle size of 26-28 nm. UV-vis study exhibited that the band gap energy of MgO NPs, Ag2O-MgO NCs, and Ag2O-MgO/rGO NC were in the range of 3.53-3.43 eV. The photocatalytic results showed that the photodegradation of Rh B dye of Ag2O-supported MgO/rGO NCs (82.81%) was significantly higher than pure MgO NPs. Additionally, the biological response demonstrates that the Ag2O-supported MgO/rGO NCs induced high cytotoxicity against MCF-7 cancer cells for 24 h and 48 h compared with both pure MgO NPs and Ag2O-MgO NCs. This study suggests that the adding of Ag2O and rGO sheets played significant role in the enhanced photocatalytic and anticancer performance of MgO NPs.

Amine-functionalized reduced graphene oxide-supported silver nanoparticles for superior catalytic reduction of organic pollutants

In this work, a simple and environmentally friendly approach has been followed to synthesize amine-functionalized reduced graphene oxide (RGO)-supported silver nanoparticle (AgNPs) having superior catalytic efficiency towards the reduction of organic pollutants. RGO/AgNPs nanohybrid was synthesized by a one-pot hydrothermal reduction of silver nitrate in the presence of amino-propyl trimethoxy silane (APTMS)-functionalized graphene oxide (GO) nanosheets. The structural and morphological characterization of as-synthesized RGO/AgNPs nanohybrid was done by using XRD, SEM, TEM, FT-IR, and Raman spectroscopy techniques. APTMS plays an important role in controlling the size of anchored AgNPs on the nanohybrid in the present study. The -NH2 groups on the surface of APTMS-modified GO function as effective and well-organized nucleation centers facilitating uniform growth of discrete and smaller-sized spherical AgNPs on the surface of RGO nanosheets. In the absence of APTMS, the nanohybrid comprised of bigger-sized AgNPs with few hundred of nanometers in dimension. The catalytic efficiency of RGO/AgNPs nanohybrid was evaluated for the reduction of two model organic pollutants: 4-nitrophenol (4-NP) and methylene blue (MB). Due to the synergistic effects of RGO, APTMS, and Ag components, RGO/AgNPs nanohybrid developed in the present study exhibited superior catalytic activity towards the reduction of 4-NP and MB in comparison with previously reported graphene/graphene oxide/reduced graphene oxide-supported AgNPs catalysts. The catalytic reduction of 4-NP and MB followed pseudo-unimolecular kinetics and the rate constants were found to be 18.83 × 10-3 s-1 and 131.5 ×10-3 s-1 respectively for 4-NP and MB. Furthermore, RGO/AgNPs nanohybrid showed admirable recyclability with negligible loss in its activity until five recycle runs. The superior catalytic activity, favorable kinetic parameters, and sustained catalytic efficiency after recycling make RGO/AgNPs nanohybrid a promising catalyst for the reduction of organic pollutants in environmental remediation.

Synthesis and characterization of Ag2O, CoFe2O4, GO, and their ternary composite for antibacterial activity

Currently, nanomaterials with exceptional antibacterial activity have become an emerging domain in research. The optimization of nanomaterials against infection causing agents is the next step in dealing with the present-day problem of antibiotics. In this research work, Ag₂O, CoFe₂O₄, and Ag₂O/CoFe₂O₄/rGO are prepared by chemical methods. Ag₂O was prepared by co-precipitation method, while solvothermal technique was utilized for the synthesis of CoFe₂O₄. The ternary nanocomposite was synthesized by a simple in situ reduction using a two-step approach. The structural and morphological properties were studied by UV-Vis spectroscopy, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (SEM), dynamic light scattering (DLS), and Fourier-transform infrared spectroscopy (FTIR). From the X-ray diffraction analysis, the crystallite size is found to be 14 nm, 5 nm, and 6 nm for Ag₂O, CoFe₂O₄, and Ag₂O/CoFe₂O₄/rGO respectively. The synthesized nanomaterials were investigated for antibacterial activities against gram-positive strain Staphylococcus aureus (S. aureus) and gram-negative strain Escherichia coli (E. coli) using Agar well diffusion method. Ag₂O and CoFe₂O₄ showed zones of inhibition (ZOI) of 13 mm and 11 mm against gram positive bacteria while 12 mm against gram negative bacteria respectively, while ternary nanocomposite showed 14 mm and 13 mm of ZOI. The antibacterial activity of nanomaterials showed a gradual increment with an increase in the concentration of the materials. Ag₂O, CoFe₂O₄, and Ag₂O/CoFe₂O₄/rGO showed minimum inhibitory concentration (MIC) values of 4.5, 6.5, and 4.5 μg/mL for S. aureus and 6.5, 7.2, and 4.8 μg/mL for E. coli respectively. Minimum bactericidal concentrations were found to be same as the MIC values. Additionally, a time-kill curve analysis was performed and for ternary nanocomposite; the killing response was most effective as the complete killing was achieved at 3 h of incubation at 3-MIC (9.75 μg/mL). These results demonstrate that all the nanomaterials, as a kind of antibacterial material, have a great potential for a wide range of biomedical applications.

Adsorption and Kinetics Studies of Cr (VI) by Graphene Oxide and Reduced Graphene Oxide-Zinc Oxide Nanocomposite

In this work, graphene oxide (GO) and its reduced graphene oxide-zinc oxide nanocomposite (rGO-ZnO) was used for the removal of Cr (VI) from aqueous medium. By employing a variety of characterization techniques, morphological and structural properties of the adsorbents were determined. The adsorption study was done by varying concentration, temperature, pH, time, and amount of adsorbent. The results obtained confirmed that rGO-ZnO is a more economical and promising adsorbent for removing Cr (VI) as compared to GO. Kinetic study was also performed, which suggested that sorption of Cr (VI) follows the pseudo-first-order model. For equilibrium study, non-linear Langmuir was found a better fitted model than its linearized form. The maximum adsorption capacity calculated for GO and rGO-ZnO nanocomposite were 19.49 mg/g and 25.45 mg/g, respectively. Endothermic and spontaneous nature of adsorption was detected with positive values of ΔS (change in entropy), which reflects the structural changes happening at the liquid/solid interface.

Cosmetic wastewater treatment technologies: a review

Over the past three decades, environmental concerns about the water pollution have been raised on societal and industrial levels. The presence of pollutants stemming from cosmetic products has been documented in wastewater streams outflowing from industrial as well as wastewater treatment plants. To this end, a series of consistent measures should be taken to prevent emerging contaminants of water resources. This need has driven the development of technologies, in an attempt to mitigate their impact on the environment. This work offers a thorough review of existing knowledge on cosmetic wastewater treatment approaches, including, coagulation, dissolved air flotation, adsorption, activated sludge, biodegradation, constructed wetlands, and advanced oxidation processes. Various studies have already documented the appearance of cosmetics in samples retrieved from wastewater treatment plants (WWTPs), which have definitely promoted our comprehension of the path of cosmetics within the treatment cycle; however, there are still multiple blanks to our knowledge. All treatments have, without exception, their own limitations, not only cost-wise, but also in terms of being feasible, effective, practical, reliable, and environmentally friendly.