Hariom Gupta

Preparation of graphene oxide nano-composite ion-exchange membranes for desalination application

Nano-composite ion-exchange membranes (IEMs) consisting of graphene oxide (GO) (0.5, 1, 2, 5 and 10%) (w/w) and sulfonated polyethersulfone (SPES) of thickness 180 μm are prepared with enhanced electrochemical properties. In particular, the transport properties of SPES are favourably manipulated by the incorporation of GO. Intermolecular interactions between the components in composite membranes are established by FTIR. Membranes are characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) which showed the uniform distribution of GO sheets in SPES matrix. The maximum ionic conductivity has been found in 10% GO composite with higher methanol crossover resistance and selectivity. Water desalination performance of the nano-composite membranes have been evaluated by ionic flux, power consumption and current efficiency during salt removal. 10% GO nano-composite membrane shows 3.51 mol m−2 h−1 ionic flux, 4.3 kW h kg−1 power consumption and 97.4% current efficiency for salt removal. The values of ionic flux and current efficiency are 19% and 12% higher respectively while 20% lower power consumption is observed as compared to SPES membrane. The strong interfacial interactions due to the insertion of GO nanofillers into the SPES matrix improve the thermal and mechanical properties of the nanocomposite membranes. Nano-composite membrane shows the better performance and higher stability which may be used for the practical application such as DMFC and electrodialysis.

An environmentally friendly process for the synthesis of an fGO modified anion exchange membrane for electro-membrane applications

We report the synthesis of an anion exchange membrane (AEM) based on chemically covalently modified graphene oxide (GO) for electrodialysis and fuel cell applications. GO was modified with silica (fGO) using APTEOS which involves an epoxide ring opening reaction. The incorporation of silica particles within the GO flakes is characterized by TEM, EDX, XRD and FTIR while thermal stability is measured by TGA. Furthermore the successful development of the membrane is done by incorporating fGO within quaternized polyethyleneimine (PEI) and poly(vinyl alcohol) by a solution casting method followed by cross linking. The dispersibility of the silica modified graphene oxide is found to be very good within the polymer matrix. Membranes of various fGO content i.e. 1, 2, and 5 wt% within the PEI matrix have been synthesized. The surface morphology and structural analysis of the membranes were done using AFM, FTIR, XRD and 1H NMR. Thermo mechanical analysis of the membranes was done using TGA, DSC and UTM. Physicochemical and electrochemical analysis of the AEM were performed to quantify the ability for electro-membrane processes. The fGO-PEI-2 membrane shows excellent electrochemical properties with comparable stability among the membranes. Furthermore the applicability of AEMs has been analyzed towards electrodialysis and fuel cell application. fGO-PEI-2 membrane show great potential for electrodialysis and fuel cell application.

Sodium Bromide Induced Micelle to Vesicle Transitions of Newly Synthesized Anionic Surface Active Ionic Liquids Based on Dodecylbenzenesulfonate

Dodecylbenezenesulfonate-based anionic surface active ionic liquids (DBS-ILs) paired with onium cations, n-butyltrimethylammonium ([N1114]), 1-butyl-3-methylimidazolium ([C4mim]), and N-butylpyridinium ([C4Py]) have been synthesized. DBS-ILs were found to be highly surface active having critical micelle concentration (CMC) lower than that of their conventional analogue sodium dodecylbenezenesulfonate ([Na][DBS]). The CMC values of DBS-ILs were determined from surface tension (ST) and isothermal titration calorimetry (ITC). DBS-ILs formed micelles predominantly in the aqueous medium, and unlike [Na]DBS, the micelles of DBS-ILs could be transformed into vesicles with the addition of sodium bromide (NaBr). Micelle to vesicle transitions (MVTs) were evidenced from dynamic light scattering (DLS), turbidity, proton nuclear magnetic resonance ((1)H NMR), and cryo-TEM techniques. Thermodynamics of aggregation was investigated from ITC which indicated that the aggregation process is primarily driven by the entropy factor. The formation of a vesicle upon addition of NaBr has been accounted to the increased electrostatic interactions between the less hydrated sulfonate headgroup and the more populated bigger sized counterions along with the favored cation-π or π-π interactions between them as evidenced from 2D-NOESY NMR experiments. The stimuli-responsive morphological transitions in the self-assembly of the reported anionic surface active ionic liquids (SAILs) will be useful for encapsulation and delivery of active (bio)molecules in the targeted biomedical applications.

One-Pot Fabrication of RGO–Ag3VO4 Nanocomposites by in situ Photoreduction using Different Sacrificial Agents: High Selectivity Toward Catechol Synthesis and Photodegradation Ability

Weak photon absorption and fast carrier kinetics in graphene restrict its applications in photosensitive reactions. Such restrictions/limitations can be overcome by covalent coupling of another photosensitive nanostructure to graphene, forming graphene‐semiconductor nanocomposites. Herein, we report one‐pot synthesis of RGO–Ag3VO4 nanocomposites using various sacrificial agents like ethanol, methanol, propanol and ethylene glycol (EG) under visible light illumination. The Raman spectral analysis and 13C MAS NMR suggest ethanol to be the best sacrificial agent among those studied. Thermal analysis studies, further, confirm the stability of the synthesized nanocomposite with ethanol as sacrificial agent. In view of this, the activity toward dye degradation was focused over the composites prepared via ethanol as sacrificial agent. It was observed and proved that cationic dyes could be degraded quantitatively and swiftly compared to anionic dyes (37.79%) in 1.5 h. This suggests that the surface of the nanocomposites is anionic as partial reduction takes place during synthesis process. In case of mixed dye degradation process, it was noticed that the presence of cationic dye doubles the degradation of anionic dye. The activity of these synthesized nanocomposites is more than five‐fold toward the phototransformation of phenol and photodegradation of textile dyes under visible light illumination.

Enhanced Electrochemical Performance of Stable SPES/SPANI Composite Polymer Electrolyte Membranes by Enriched Ionic Nanochannels

Herein, we present the results of sulfonated polyaniline (SPANI) and sulfonated poly(ether sulfone) (SPES) composite polymer electrolyte membranes. The membranes are established for high-temperature proton conductivity and methanol permeability to render their applicability. Composite membranes have been prepared by modifying the SPES matrix with different concentrations of SPANI (e.g., 1, 2, 5, 10, and 20 wt %). Structural and thermomechanical characterizations have been performed using the transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analyzer techniques. Physicochemical and electrochemical properties have been evaluated by water uptake, ion-exchange capacity, dimensional stability, and proton conductivity. Methanol permeability experiment was carried out to analyze the compatibility of prepared membranes toward direct methanol fuel cell application and found the lowest methanol permeability for PAS-5. Also, the membranes reveal excellent thermal, mechanical, and physicochemical properties for their application toward high-temperature electromembrane processes.

Spontaneous Formation of Multiarchitecture Vesicles of [C8mim]Br + [Na]DBS in Aqueous Medium: Synergic Interplay of Electrostatic, Hydrophobic, and π–π Stacking Interactions

A mixture of a cationic surface active ionic liquid, [C8mim]Br and anionic surfactant, [Na]DBS has been shown to form unilamellar vesicles in water over an exceptionally wide mole fraction range of [C8mim]Br (x1 = 0.2 to 0.8). Formation of vesicles has been evidenced from transmission electron microscopy (TEM), cryo-TEM and atomic force microscopy (AFM) imaging. Cryo-TEM imaging of an equimolar mixture showed multiarchitectural unilamellar vesicles (spherical, tubular, and ribbon). Such complex architectures were earlier reported for Janus dendrimers of different structures (Science, 2010, 328, 1014). The synergism between oppositely charged single chain surfactants to form bilayer structures has been explained based on the evidence of π-π stacking interaction from 2D NOESY measurements, Coulombic interactions from zeta potential measurements and magnitude of interaction parameter from the critical aggregation concentration. The aggregation concentrations were measured from tensiometry and fluorescence using pyrene as a polarity probe. The phase behavior at different mixture compositions has been revealed from turbidity measurements and visual inspection. Hydrodynamic radii of self-assembled structures in the bulk solution phase were measured from dynamic light scattering. Vesicles formed have been explored as delivery vehicles for proteins using bovine serum albumin (BSA) as model.

Temperature-Dependent Solubility Transition of Na2SO4 in Water and the Effect of NaCl Therein: Solution Structures and Salt Water Dynamics

Dual, aqueous solubility behavior of Na2SO4 as a function of temperatures is still a natural enigma lying unresolved in the literature. The solubility of Na2SO4 increases up to 32.38 °C and decreases slightly thereafter at higher temperatures. We have thrown light on this phenomenon by analyzing the Na2SO4-water clusters (growth and stability) detected from temperature-dependent dynamic light scattering experiments, solution compressibility changes derived from the density and speed of sound measurements, and water structural changes/Na2SO4 (ion pair)-water interactions observed from the FT-IR and 2D DOSY (1)H NMR spectroscopic investigations. It has been observed that Na2SO4-water clusters grow with an increase in Na2SO4 concentration (until the solubility transition temperature) and then start decreasing afterward. An unusual decrease in cluster size and solution compressibility has been observed with the rise in temperature for the Na2SO4 saturated solutions below the solubility transition temperature, whereas an inverse pattern is followed thereafter. DOSY experiments have indicated different types of water cluster species in saturated solutions at different temperatures with varying self-diffusion coefficients. The effect of NaCl (5-15 wt %) on the solubility behavior of Na2SO4 at different temperatures has also been examined. The studies are important from both fundamental and industrial application points of view, for example, toward the clean separation of NaCl and Na2SO4 from the effluent streams of textile and tannery industries.

Synthesis and characterization of different metal oxide and GO composites for removal of toxic metal ions

ABSTRACT This manuscript deals with graphene oxide (GO) and GO–metal oxide composite for heavy metal adsorption. Metal oxide–GO composites e.g. Fe3O4–GO and Mn3O4–GO have been prepared and explored for heavy metals e.g. lead, chromium, nickel, cadmium etc. adsorption from the water. Metal oxide–GO composites have been prepared through respective techniques. The various characterizations of the nanocomposites viz. structural and thermal have been analysed by transmission electron microscopy, thermogravimetric analyser etc. Different concentration of heavy metal has been taken to examine the efficiency of composites towards adsorption. Furthermore, effect of time on adsorption has also been evaluated. Metal oxide–GO composites illustrate better results as compared to GO showing the usability of composites for heavy metal adsorption for the production of clean water.

Synthesis and characterization of aluminium modified graphene oxide: an approach towards defluoridation of potable water

Abstract An approach towards the synthesis of aluminum modified graphene oxide (GO) has been studied in the present manuscript. Graphene oxide has been modified by the aluminum sulfate followed by alkalization to synthesized Al-GO composite. GO and Al-GO composite has been characterization by the means of different techniques i.e. XRD, FT-IR, FT-Raman, TEM, SEM, TGA and elemental mapping. Analysis confirmed the formation of GO and Al-GO composite. The prepared GO composite has been checked for the removal of fluoride from the potable water with different initial concentration of fluoride ions. Composite shows it’s effectiveness for the removal of fluoride throughout the pH range. The maximum adsorption capacity and Langmuir constant determined for the adsorbent dose of 1 g L−1 are found to be 38.31 mg g−1 and 0.5252 L mg−1 respectively.GRAPHICAL ABSTRACT Graphical Abstract