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.

Susanta Sinha Roy

Physics

(SoNS) School of Natural Sciences

Bhattacharya G.

Mathur A.

Pal S.

McLaughlin J.

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Shiv Nadar University

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

International Journal of Electrochemical Science

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

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

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.