In the present work, the suitability of Aloe vera (AV) as a 'green reducing agent' has been investigated for the reduction of graphene oxide (GO). The extent of reduction was studied by varying the amount of AV. The physical and chemical properties of the GO and reduced graphene oxide (rGO) were investigated using UV-Vis spectrophotometry, FT-IR spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED). Partially reduced graphene oxide sheets obtained with 7.5 g of AV (rGO-7.5) demonstrated a maximum reduction efficiency of about 73\% as evident from FT-IR data. Cyclic voltammetry and electrochemical impedance spectroscopy studies revealed a significant enhancement in current density and a decrease in charge transfer resistance for the rGO-7.5 sample. Moreover, the as prepared rGO-7.5 sample showed a remarkable dye removal ability with a maximum efficiency of ∼98\%. The enhanced surface area, π-π interaction and strong electrostatic attraction were correlated with the dye removal capability. The adsorption kinetics were also studied and pseudo second order adsorption phenomena were confirmed. The recyclability of the rGO-7.5 sample was further investigated and an excellent desorption capability was established. © 2017 The Royal Society of Chemistry.

Susanta Sinha Roy

Physics

(SoNS) School of Natural Sciences

Bhattacharya G.

Sas S.

Wadhwa S.

Mathur A.

McLaughlin J.

Fulltext

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

RSC Advances

Flexible micro-supercapacitors, with high energy and power density, and using materials with a low environmental impact are attractive for next-generation energy storage devices. Carbon-based materials are widely used for supercapacitors but can be increased in energy density via combination with metal oxides. Red mud is an iron-oxide-rich by-product of aluminum production, which needs to be more widely utilized to reduce its environmental damage. To achieve a flexible micro-supercapacitor device with increased energy density, a laser-induced graphene (LIG) supercapacitor is realized from a polyimide substrate, decorated with red-mud nanoparticles (LIG-RM), employing a solid-state ionic liquid electrolyte with a mixture of poly(vinylidene fluoride) (PVDF), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]). The fabricated two-electrode flexible device, in an interdigitated planar design, with inkjet-printed silver current collectors, has a high energy of 0.018 mWh cm−2 at a power of 0.66 mW cm−2, with 81\% of capacitance retained after 4000 cycles and good resistance to bending and flexing. The high energy storage performance, brought about through the combination of graphene and red-mud nanoparticles, which would—if not utilized—be an environmental liability, shows a promise as a material for future energy storage with low environmental impact. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Advanced Sustainable Systems

Recycled Red Mud–Decorated Porous 3D Graphene for High-Energy Flexible Micro-Supercapacitor

Titania–zeolite Y composites were synthesized by a facile solid-state dispersion method. The synergistic effects of porous zeolite structure and novel photocatalysis properties of titania nanoparticles were exploited. The physical properties of the composites were characterized by scanning electron microscopy, energy-dispersive X-ray, X-ray diffraction, diffuse reflectance spectroscopy, fourier transform infra-red spectroscopy and photoluminescence spectroscopy. Porosity and surface area of the composites were determined from Brunauer–Emmett–Teller studies. The antibacterial effect and the photocatalysis properties of these composites were studied. Composites exhibited higher growth reduction of Escherichia coli and Staphylococcus aureus as compared with the pure forms (P25 titania and zeolite Y). Maximum growth reduction of both types of bacterial cells (gram-positive as well as gram-negative) was observed with 20\% titania–zeolite composite. The composite demonstrated 40 and 30\% enhancement in the growth reduction of E. coli and S. aureus, respectively, as compared with the pure forms; 10\% composite exhibited 50\% enhancement in the photocatalysis efficiency of methylene blue dye degradation as compared with P25 titania nanoparticles and led to a complete removal of the dye in the first 60 min of photocatalysis process. Mechanisms for both applications have been proposed in light of the observed results. © 2020, Indian Academy of Sciences.

Bulletin of Materials Science

Titania-based porous nanocomposites for potential environmental applications

The aluminum industrial waste red mud was successfully utilized as a novel adsorbent for the removal of arsenic (As) ions from water. The arsenate (As (V)) adsorption efficacy of red mud nanoparticles was also investigated. Red mud nanoparticles were prepared by ball milling raw red mud for 10 h, yielding particles’ size of 20 nm on average. The As (V) adsorption on these nanoparticles strongly depended on the size of the nanoparticles. As (V) removal increased from 58 to 83\% by reducing the size of red mud particles from 200 to 20 nm. Detail kinetics and transport study confirmed the pseudo-second-order kinetic process which was governed by external mass transport. The Freundlich (and Langmuir) isotherms confirm that the arsenate adsorption capacity changes from 2.28 mg/g (1.84 mg/g) to 2.54 mg/g (1.96 mg/g) for reduction of particles from size 200 nm to 20 nm. Water filter columns made with red mud nanoparticles prepared by ball milling for 10 h showed better filtration performance than the filter packed with raw red mud. Both the hydraulic conductivity and the As (V) removal (8 mm/h and 61\% respectively) of influent 1 mg/L As (V) by red mud nanoparticles were greater than the raw red mud (3.2 mm/h and 54\%). The modified red mud column filters also exhibited a higher efficiency than the raw red mud filters to remove Escherichia coli and Staphylococcus aureus from the water. Overall, this research shows that nanomaterials derived from aluminum processing waste can be a promising material for water filtration. © 2020, Springer Nature Switzerland AG.

SN Applied Sciences

Potential use of smartly engineered red mud nanoparticles for removal of arsenate and pathogens from drinking water

One-dimensional diamond nanorods (DNRs) were fabricated from nanocrystalline diamond films using a facile combination of microwave plasma enhanced chemical vapor deposition and reactive ion etching (RIE) techniques. Structural and electrochemical properties of undoped and nitrogen doped DNRs were thoroughly investigated. A cyclic voltammetry study revealed the increase in density of charge carriers when doped with nitrogen. Mott Schottky analysis was implemented for the quantitative determination of the flat band potential, effective density of charge carriers and energy band diagram, which revealed that the undoped sample exhibit p-type behavior, whereas the nitrogen doped sample showed n-type behavior. Defect related damage due to graphitization and hydrogen termination in the undoped DNRs (during RIE) was correlated with the p-type conductivity. Nitrogen doping induces n-type conductivity and enhances effective density of charge carriers. © 2017 Elsevier Ltd

Electrochimica Acta

Probing the flat band potential and effective electronic carrier density in vertically aligned nitrogen doped diamond nanorods via electrochemical method

A novel nanocomposite consisting of π-conjugated 2-aminoterephthalic acid (ATA) coated iron oxide (Fe3O4) nanoparticles and reduced graphene oxide (RGO) has been synthesized using a facile combination of wet-chemistry and low-power sonication. The ATA-Fe3O4/RGO nanocomposites exhibited a high specific capacitance of the order of 576 F g−1; significantly higher than that of pristine Fe3O4 (132 F g−1) and RGO (60 F g−1) counterparts, indicative of a synergistic effect between the ATA-Fe3O4 and RGO components. Furthermore, the maximum energy storage density was calculated to be 75 W h kg−1 (at a current density of 6 A g−1). The charging-discharging analysis showed promising long-term stability with nearly 86\% retention of the capacitance after 5000 cycles. The superior capacitive behaviour of these ATA-Fe3O4/RGO nanocomposites is attributed to the synergistic effect of the π-conjugated ATA coating on Fe3O4 which enhances the pseudo-capacitive charge transfer process of Fe3O4 and works in conjunction with the surface functional groups (such as carboxylic, amino and amide) present on the RGO surface, providing enhanced double layer capacitance. Thus, the current system exploits the advantages of both the double layer capacitors and pseudocapacitors in a hybrid structure. © The Royal Society of Chemistry.

Novel π-conjugated iron oxide/reduced graphene oxide nanocomposites for high performance electrochemical supercapacitors

In this study, a non-faradaic electrochemical impedance spectroscopy has been employed for estimation of caffeine concentration in beverages. Impedance spectra were recorded by using a two electrode system without adding any redox reagents in the measured solutions. Electrochemical impedance data of caffeine solutions in pure water and beverages were measured and an appropriate equivalent electrical circuit model is developed to help in this investigative analysis. The interaction of caffeine molecules with the electrodes was primarily correlated to the formation of electrical double-layer at modified interface. Overall system impedance (|Z|), inverse of solution resistance (1/RS) and constant phase element of the system were further investigated from the equivalent electrical circuit and plotted as a function of pure caffeine concentration. Finally, the results obtained from spiked diluted cola beverages were compared with the pure caffeine sample. © 2016 The Authors.

International Journal of Electrochemical Science

Equivalent circuit models and analysis of electrochemical impedance spectra of caffeine solutions and beverages

Journal of Water Process Engineering

One-step facile synthesis of mesoporous graphene/Fe 3 O 4 /chitosan nanocomposite and its adsorption capacity for a textile dye

An adsorbent, SnO2 quantum dots (QDs) decorated reduced graphene oxide (RGO) nanocomposite, is used for removal of different organic dyes (methylene blue (MB), methyl orange (MO) and rhodamine B (RhB)), toxic metal ions (Co2+, Ni2+, Cu2+, Cd2+, Cr3+, Pb2+, Hg2+ and As3+), and pathogenic bacteria (Escherichia coli) from wastewater. It exhibits good removal capacity and fast adsorption rate for cationic dye MB. In binary solution the nanocomposite registered an excellent separation efficiency of 94% for MB/MO mixtures, whereas the same is 76% for MB/RhB mixture. The effect on removal process by different influencing parameters such as dosage of adsorbent (0.1-0.6 g/L), initial solution pH (3-11), initial dye concentration (10-50 ppm), contact time (0-60 min) and temperature (303-333 K) is investigated in order to find the optimum adsorption conditions. Adsorption isotherm data are extensively investigated using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms; it is found to fit well in Freundlich model. Adsorption kinetics is described by pseudo-second order kinetics. Thermodynamic study suggested that the MB adsorption on QDs-RGO is a spontaneous and exothermic process. QDs-RGO also shows good removal efficiency for lead (II) from individual as well as mixed solution. Adsorption kinetics and isotherm data are extensively investigated for adsorption of lead (II) and found to be better described by pseudo-second order kinetics and Freundlich model. Furthermore, QDs-RGO showed higher antibacterial activity towards E. coli than the individual constitute materials. It is essentially established from the results that QDs-RGO is an ideal aspirant for removal of positively charged organic dyes, toxic heavy metal ions and bacteria pathogen from wastewater. © 2016 Elsevier B.V.