Andrews Nirmala Grace

Adsorption, photodegradation and antibacterial study of graphene–Fe3O4 nanocomposite for multipurpose water purification application

Graphene–Fe3O4 (G–Fe3O4) composite was prepared from graphene oxide (GO) and FeCl3·6H2O by a one-step solvothermal route. The as-prepared composite was characterized by field-emission scanning electron microscopy, transmission electron microscopy, dynamic light scattering and X-ray powder diffraction. SEM analysis shows the presence of Fe3O4 spheres with size ranging between 200 and 250 nm, which are distributed and firmly anchored onto the wrinkled graphene layers with a high density. The resulting G–Fe3O4 composite shows extraordinary adsorption capacity and fast adsorption rates for the removal of Pb metal ions and organic dyes from aqueous solution. The adsorption isotherm and thermodynamics were investigated in detail, and the results show that the adsorption data was best fitted with the Langmuir adsorption isotherm model. From the thermodynamics investigation, it was found that the adsorption process is spontaneous and endothermic in nature. Thus, the as-prepared composite can be effectively utilized for the removal of various heavy metal ions and organic dyes. Simultaneously, the photodegradation of methylene blue was studied, and the recycling degradation capacity of dye by G–Fe3O4 was analyzed up to 5 cycles, which remained consistent up to ∼97% degradation of the methylene blue dye. Although iron oxide has an affinity towards bacterial cells, its composite with graphene still show antibacterial property. Almost 99.56% cells were viable when treated with Fe3O4 nanoparticle, whereas with the composite barely 3% cells survived. Later, the release of ROS was also investigated by membrane and oxidative stress assay. Total protein degradation was analyzed to confirm the effect of the G–Fe3O4 composite on E. coli cells.

Co9S8 nanoflakes on graphene (Co9S8/G) nanocomposites for high performance supercapacitors

Co9S8/graphene nanocomposites (Co9S8/G) at various concentrations of graphene and Co9S8 were prepared by a simple chemical route from cobalt nitrate and graphene as precursors in the presence of PVP as surfactant and thioacetamide (TAA) as sulfur source. To gain knowledge about the structural, morphological and physical properties, the composite material was analyzed by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric Analysis (TGA). SEM measurements showed the presence of well dispersed, ∼300 nm sized Co9S8 nanoflakes. To assess the properties of the nanocomposites for their applicability in supercapacitors, electrochemical analysis was carried out in 6 M KOH electrolyte. A maximum specific capacitance of 808 F g−1 was observed for Co9S8/G-d at 5 mV s−1 scan rate. Galvanostatic charge–discharge curves showed the excellent cyclic stability of Co9S8/G-d composite with higher charge–discharge duration than pure Co9S8. The excellent electrochemical performance of the composite could be due to the better electrical conductivity behavior of graphene on Co9S8 nanoflakes.

Enhanced properties of porous CoFe2O4–reduced graphene oxide composites with alginate binders for Li-ion battery applications

Porous CoFe2O4 nanoclusters with different concentrations of graphene based composites were synthesized by a simple solvothermal process. The electrochemical properties of prepared CoFe2O4–reduced graphene oxide (rGO) composites were evaluated using polyvinylidene fluoride and Na-alginate as binder materials. The CoFe2O4 + 20% rGO composite with alginate exhibited a high stable capacity of 1040 mA h g−1 at 0.1 C (91 mA g−1) rate with excellent rate capability. The observed enhancement in electrochemical properties of the CoFe2O4 + 20% rGO composite with alginate is due to the high stability and good transportation network while charging–discharging.

Electrocatalytic activity of Cu2O nanocubes based electrode for glucose oxidation

Abstract.A direct electrocatalytic activity of glucose oxidation on cuprous oxide modified glassy carbon electrode is reported. Cu2O nanocubes were synthesized by a simple wet chemical route in the absence of surfactants. Purity, shape and morphology of Cu2O are characterized by XRD, SEM, XPS and DRS-UV. The Cu2O nanocubes-modified glassy carbon electrode (GCE) exhibited high electrocatalytic activity towards glucose oxidation compared with bare GCE electrode. At an applied potential of +0.60 V, the Cu2O electrode presented a high sensitivity of 121.7 μA/mM. A linear response was obtained from 0 to 500 μM, a response time less than 5 s and a detection limit of 38 μM (signal/noise=3). The Cu2O nanocubes modified electrode was stable towards interfering molecules like uric acid (UA), ascorbic acid (AA) and dopamine (DA). In short, a facile chemical preparation process of cuprous oxide nanocubes, and the fabricated modified electrode allow highly sensitive, selective, and fast amperometric sensing of glucose, which is promising for the future development of non-enzymatic glucose sensors. The direct electrocatalytic oxidation of glucose at GCE modified with Cu2O nanocubes is studied. The fabricated electrode showed a good activity, an excellent linear range (0-500 µM), high sensitivity of 121.7 µA/mM, response time less than 5 s and a detection limit of 38 µM (signal/noise=3).

A template-free facile approach for the synthesis of CuS–rGO nanocomposites towards enhanced photocatalytic reduction of organic contaminants and textile effluents

Copper sulfide–reduced graphene oxide nanocomposites were synthesized hydrothermally from copper nitrate and thiourea as precursor materials. In the hydrothermal route, rGO is formed by the reduction of GO with simultaneous formation of CuS–rGO nanocomposites. The CuS–rGO nanocomposites was investigated using powder XRD, FE-SEM, HR-TEM, DRS UV-vis spectroscopy, photoluminescence (PL) measurements, infra-red spectroscopy and photoelectron spectroscopy (XPS). DRS UV-vis measurements of CuS–rGO nanocomposites feature a strong absorption in the range 400–800 nm, which suggests that they have photocatalysis applications. Three different composites were prepared with different loadings of rGO to study the effect of loading on methylene blue (MB) dye degradation. The photocatalytic properties of the composites were tested in a visible light photoreactor chamber. The CuS–rGO nanocomposites were found to exhibit high photocatalytic activities with a maximum efficiency of 99.27% after 60 min in a visible source. These interesting and enhanced catalytic properties of CuS–rGO-x nanocomposite was further tested for organic contaminant and textile effluents collected from two different sites situated in the Thirupur textile industries, India. Results showed the CuS–rGO-x nanocomposite is an efficient photocatalyst.

CO2 Absorption and Sequestration as Various Polymorphs of CaCO3 Using Sterically Hindered Amine

One aspect of the attempt to restrain global warming is the reduction of the levels of atmospheric CO2 produced by fossil fuel power systems. This study attempted to develop a method that reduces CO2 emissions by investigating the absorption of CO2 into sterically hindered amine 2-amino-2-methyl-1-propanol (AMP), the acceleration of the absorption rate by using the enzyme carbonic anhydrase (CA), and the conversion of the absorption product to stable carbonates. CO2 absorbed by AMP is converted via a zwitterion mechanism to bicarbonate species; the presence of these anions was confirmed with (1)H and (13)C NMR spectral analysis. The catalytic efficiency (kcat/Km), CO2 absorption capacities, and enthalpy changes (ΔHabs) of aqueous AMP in the presence or absence of CA were found to be 2.61 × 10(6) or 1.35 × 10(2) M(-1) s(-1), 0.97 or 0.96 mol/mol, and -69 or -67 kJ/mol, respectively. The carbonation of AMP-absorbed CO2 was performed by using various Ca(2+) sources, viz., CaCl2 (CAC), Ca(OOCCH3)2 (CAA), and Ca(OOCCH2CH3)2 (CAP), to obtain various polymorphs of CaCO3. The yields of CaCO3 from the Ca(2+) sources were found in the order CAP > CAA > CAC as a result of the effects of the corresponding anions. CAC produces pure rhombohedral calcite, and CAA and CAP produce the unusual phase transformation of calcite to spherical vaterite crystals. Thus, AMP in combination with CAA and CAP can be used as a CO2 absorbent and buffering agent for the sequestration of CO2 in porous CaCO3.

Synthesis of Cobalt Sulfide–Graphene (CoS/G) Nanocomposites for Supercapacitor Applications

Cobalt sulfide (CoS) and graphene nanocomposites were prepared from cobalt nitrate, thioacetamide, and graphene as starting materials in the presence of poly(vinylpyrrolidone) as surfactant. Furthermore, its morphology and properties were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope, diffusive reflectance ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and electrochemical measurements. The XRD reveals the amorphous nature of the nanocomposites. The as-prepared nanocomposites were tested for its supercapacitance property by cyclic voltammetric (CV) experiment in 6M KOH electrolyte. CV was performed at a potential range of 0 to -0.8 V at different scan rates, and results show an excellent capacitive behavior of the nanocomposites. A maximum specific capacitance of 2423.3 F/g was obtained at a scan rate of 5 mV/s.

CoFe2O4 and NiFe2O4@graphene adsorbents for heavy metal ions – kinetic and thermodynamic analysis

Magnetic cobalt and nickel ferrites (CoFe2O4 & NiFe2O4) with graphene nanocomposites (CoFe2O4–G & NiFe2O4–G) were synthesized via a solvothermal process and used as an adsorbent for the removal of lead (Pb(II)) and cadmium (Cd(II)) ions from aqueous solution. The as-prepared materials were characterized by field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), a Brunauer–Emmett–Teller (BET) surface area analyzer, transmission electron microscopy (TEM) and VSM analysis. To probe the nature of the adsorbent, various experiments were investigated like contact time, adsorbent dose, solution pH and temperature were optimized. The isotherm model fitting studies demonstrated that the data fitted the Langmuir isotherm model well. The highest adsorption equilibrium for Pb(II) is 142.8 and 111.1 mg g−1 at pH of 5 and 310 K for CoFe2O4–G & NiFe2O4–G; while for Cd(II) it was 105.26 and 74.62 mg g−1 at pH of 7 and 310 K. The results show that such type of materials could be used for the removal of heavy metal ions from water for environmental applications.

A high capacity MnFe2O4/rGO nanocomposite for Li and Na-ion battery applications

A porous MnFe2O4/reduced graphene oxide (rGO) nanocomposite with high storage capacity was prepared by a hydrothermal method. The MnFe2O4/rGO nanocomposite sample was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and high resolution transmission electron microscopy. The electrochemical characteristics with lithium as well as sodium were studied using cyclic voltammetry and a battery cycle tester. In this work, apart from the lithium storage, the sodium storage ability of the spinel type MnFe2O4 as an anode is demonstrated for the first time. The prepared MnFe2O4/rGO composite with sodium alginate binder shows a highly stable capacity of 905 mA h g−1 versus Li/Li+ and 258 mA h g−1 versus Na/Na+ at 0.1C rate. The enhancement in capacity and excellent cycleability of the MnFe2O4/reduce graphene oxide nanocomposite is due to constrained volume expansion during conversion reactions and enhancement of electrical conductivity.

MnS nanocomposites based on doped graphene: simple synthesis by a wet chemical route and improved electrochemical properties as an electrode material for supercapacitors

Nanocomposites of MnS anchored on graphene, nitrogen-doped graphene and boron-doped graphene have been prepared by a simple wet chemical process. The effect of graphene concentration in MnS and the effect of doping type in the composites are studied through the use of various characterization techniques. An electrochemical performance better than that of pure MnS has been observed in the graphene based composites. The doping of N and B atoms in graphene can further enhance the electrochemical activities of the nanocomposites. The present study demonstrates that MnS with doped graphene has large electrode/electrolyte interfaces, which offers more active sites and ensures a high charge storage capacity of the composite. A maximum specific capacitance of 696.6 and 353.8 F g−1 are measured for MnS/BG-9 and MnS/NG-9 composite, respectively, at a 5 mV s−1 scan rate, whereas the pure graphene composite (MnS/G-9) exhibits only a maximum specific capacitance of 156 F g−1.