Dipalee D. Malkhede

Supercritical Carbon Dioxide Extraction of Uranium from Acidic Medium Employing Calixarenes

Various calixarenes were evaluated for the supercritical fluid extraction of uranium from nitric acid medium. The extraction efficiency was found to be affected by various parameters, namely pressure, temperature, CO2 flowrate, extraction time, and molarity of nitric acid. The addition of HPFOA (pentadecafluoro-n-octanoic acid) for the production of CO2-phillic fluorinated counter ion enhanced the extraction efficiency. Under optimized conditions (pressure of 200 atm, temperature of 323 K, 30 minutes of static time followed by 30 minutes of dynamic time, CO2 flowrate of 2 mL min−1, nitric acid molarity of 0.1 M) for uranium: calixarene: HPFOA mole ratio of 1:5:10, highest extraction efficiency could be obtained with p-tert.-butyl calix[6]arene (79.9%). Solvent extraction study with hexane as the organic phase indicated the formation of [UO2 (calixarene)]2+. In order to assess the suitability of the developed method to extract uranium in the presence of a host of other ions, extraction efficiency for other metal ions was estimated.

Molecular-recognition-assisted pKa shifts and metal-ion-induced fluorescence regeneration in p-sulfonatocalix[6]arene-encapsulated acridine.

The host-guest interactions of cationic (AcH(+) ) and neutral (Ac) forms of the dye acridine with the macrocyclic host p-sulfonatocalix[6]arene (SCX6) were investigated by using ground-state absorption, steady-state and time-resolved fluorescence, and NMR measurements. The cationic form undergoes significant complexation with SCX6 (Keq =2.5×10(4)  M(-1) ), causing a sharp decrease in the fluorescence intensity and severe quenching in the excited-state lifetime of the dye. The strong binding of the AcH(+) form of the dye with SCX6 is attributed to ion-ion interactions involving the sulfonato groups (SO3 (-) ) of SCX6 and the positively charged AcH(+) at pH of approximately 4.3. Whereas, the neutral Ac form of the dye undergoes weak complexation with SCX6 (Keq =0.9×10(3)  M(-1) ) and the binding constant is lowered by one order of magnitude compared with that of the SCX6-AcH(+) system. The strong affinity of SCX6 to the protonated form leads to a large upward pKa shift (≈2 units) in the dye. In contrast, strong emission quenching upon SCX6 interaction and the regeneration of fluorescence intensity of the dye in the presence of Gd(3+) through competitive binding have also been demonstrated.

Encapsulation of rhodamine-6G within p-sulfonatocalix[n]arenes: NMR, photophysical behaviour and biological activities

The inclusion complexes of rhodamine-6G (Rh6G) dye within p-sulfonatocalix[4]arene (SCX4), p-sulfonatothiacalix[4]arene (TSCX4), p-sulfonatocalix[6]arene (SCX6) hosts has been characterized using the 1H NMR, 2D NMR NOESY, infrared, fluorescence experiments and scanning electron microscopy analysis. The inclusion complexes show encapsulation of the phenyl ring of the Rh6G guest within the SCXn (n = 4 and 6) or TSCX4, with its ester functionality protruding outside the cavity along the direction bisecting two adjacent sulfonato groups of the macrocyclic host; the inference that has been corroborated through the density functional theory. The aromatic protons of Rh6G confined within the host cavity of the complex reveal shielded signals in the measured NMR spectra. The formation of inclusion complexes has been confirmed through 2D NMR NOESY experiments. Fluorescence experiments demonstrated that the quenching constant of the SCX6 complex was ∼104 times larger than those for the SCX4 and TSCX4 complexes. Biological activity measurements further revealed that the Rh6G⊂SCX4 complex possesses remarkable antiproliferative and antimicrobial activities.

Complexation with calixarenes and efficient supercritical CO2 extraction of Pb(II) from acidic medium

The present study describes the extraction of lead(II) from acidic medium with supercritical carbon dioxide using various calixarenes. It involves the investigation of the effect of temperature, acid molarity, and the metal to complexing agent molar ratio on supercritical fluid extraction efficiency. Efficient extraction of Pb(II) was observed for p-t-butylcalix(4)arene with (92 ± 3)% extraction at 323 K, 20.27 MPa, 30 minute static time followed by 30 minute dynamic time and a metal to complexing agent molar ratio of 1:5. The complexing ability of Pb(II) with calixarene was established by absorption and energy dispersive spectroscopy. The scanning electron micrograph of calixarene and the lead–calixarene complex was studied. The structure of the Pb(II)–calixarene complex has been proposed based on solvent extraction in hexane and IR spectroscopic analysis of the extract. Thermodynamic aspects of extraction were also studied and the extraction reaction was found to be entropy driven. Interference from other metal ions, on Pb(II) extraction behaviour, has been investigated. The developed method has been utilized for extraction of Pb(II) from real samples viz. paints, batteries, tobacco and wastewater.

Studies on morphology of polyaniline films formed at liquid–liquid and solid–liquid interfaces at 25 and 5 °C, respectively, and effect of doping

AbstractIt is well accepted that the morphology of the nanomaterials has great effect on the properties and hence their applications. Therefore, morphology of materials has become a focus of research in the scientific world. The present study shows that interfacial polymerization and subsequent self-assembly provides a control over the morphology, nanorod/nanosheet, of polyaniline (PANI) films synthesized by liquid–liquid interface reaction technique and solid–liquid interface reaction technique. The synthesized PANI films and its particulate structure are characterized by using various spectroscopic techniques such as UV–visible, ATR-IR, Raman and XPS. The study confirmed the formation, the structure, the size and shape of particles and morphology of PANI by using analytical techniques namely, SAED, SEM and TEM. An important observation is that doping with HCl significantly improves the nanorod formation at the interface. The doped PANI electrode exhibits a higher area with rectangular shape in CV cycle and better cycle stability when compared with the performance of undoped PANI films. We believe that the results of these studies can give valuable leads to manoeuvre formation of PANI films with desired morphology for various applications. FigureTime and temperature-dependent morphology of PANI layer leading to the formation of one/two-dimensional structures namely, PANI rods/sheets, is achieved by monitoring of self-assembly of nano particulate film formed at liquid–liquid/solid–liquid interfaces

Calixarene based nanocomposite materials for high-performance supercapacitor electrode

A functionalised calixarene {4-sulphatocalix[6]arene hydrate (SC6)} stabilises MoS2/partially reduced graphene oxide (rGO) nanosheet. Such stabilised SC6–rGO/SC6–MoS2 and SC6 doped polyaniline (PANI) together form a nanocomposite hybrid material for supercapacitor electrodes. The nanocomposite is fabricated by an in situ polymerization method. Transmission electron microscopy (TEM) results suggest that PANI nanostructures grow homogeneously on the surfaces of SC6 functionalised MoS2. Calixarene acts as a dopant for PANI as well as a stabiliser for the 2D nanosheets of rGO/MoS2. The characterisation of composites and the basic components is done using various techniques, namely, solid-state FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical performance is analysed by cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectrometry (EIS). It is found that the SC6 functionalised MoS2 and SC6 doped PANI form a uniform nanocomposite. The synthesised composites show high specific capacitance (691 F g−1) and good cycling stability during charge–discharge process when used as supercapacitor electrodes. The improvement in electrochemical performance of composites is assigned to synergistic effect of SC6 stabilised MoS2 and doped PANI. Our investigation highlights the importance of use of calixarene in composites for improved supercapacitor performance. The role of calixarene in the present study paves the way for the application of alike materials in composite supercapacitors for energy storage applications.

Synthesis and study of calixarene-doped polypyrrole-TiO2/ZnO composites: Antimicrobial activity and electrochemical sensors

The present communication describes the synthesis of an electroactive nanocomposite of calixarene-doped polypyrrole (PPY) containing an oxide of Ti/Zn. The additive TiO2/ZnO serves as an oxidizing agent for the polymerization, thus avoiding the use of hazardous organic solvents while calixarene doping stabilizes the polymer. The materials synthesized herein were characterized by UV-visible spectroscopy, FT-IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) of synthesized nanocomposites. It was revealed that the resulting calixarene-doped polypyrrole-TiO2/ZnO nanocomposite has (1) long-time stability, (2) significant electrochemical activity for sensing formaldehyde, and (3) good antimicrobial activity.

Solvent Extraction and Separation of Gallium(III) using Hexaacetato Calix(6)Arene

Gallium(III) was extracted at pH 3.5 by equilibrating eight min with 10 mL of 0.0001 M acetyl derivative of calix(6)arene in xylene. Gallium(III) was stripped quantitatively with 0.1 N hydrochloric acid and determined spectrophotometrically with 0.01% PAR at 510 nm. The nature of the extracted species was determined from the log-log plots and its stoichiometry was confirmed by numerical treatment to experimental data. The IR analysis of Ga(III) loaded organic phase was also studied. The conformational change of reagent during complex formation was studied from the 1H NMR treatment. The temperature dependence of the extraction equilibrium and metal loading capacity of the reagent was also evaluated. The proposed method was successfully applied for the extraction and separation of multicomponent mixtures, synthetic mixtures, and binary and ternary separation of gallium from the associated elements. The results obtained were reproducible and accurate.

In situ grown nickel nanoparticles in a calixarene nanoreactor on a graphene–MoS2 support for efficient water electrolysis

Electrochemical production of hydrogen, facilitated in electrolysers, holds great promise for energy storage and solar fuel production. Catalysis of the oxygen evolution reaction (OER) is a bottleneck of this process. However, the sluggish OER kinetics and the utilization of precious metal catalysts are key obstacles in the broad deployment of this energy technology. We report the preparation and use of an inexpensive GrMoS2SC8Ni nanocomposite material as a highly effective OER catalyst in an alkaline electrolyte. Experimental investigations have shown that improvements can be realized in the catalytic performance of Ni metal if it is a component of the composite material. We propose an explanation for these enhancements based on a hydrogen acceptor concept. This concept comprises the stabilization of an *–OOH intermediate, which effectively lowers the potential needed for breaking bonds on the surface. Herein, an inexpensive immobilized SC8 layer was used as the nanoreactor to synthesize metallic Ni nanoparticles (NPs) through an in situ redox process. The process was applied to form immobilized NPs on flat and curved 2D surfaces. The outstanding OER performance of Ni NPs could be attributed to their large surface area, efficient mass and charge transport, and high structural stability arising from the unique SC8 cage structure, built on the GrMoS2 substrate. The GrMoS2SC8Ni nanocomposite shows the highest activity, exhibiting a 214 mV overpotential at 10 mA cm−2 (equivalent to 10% efficiency of solar-to-fuel conversion) and a Tafel slope of 31 mV dec−1 in 1 M KOH solution. It further demonstrates high stability as there is no apparent OER activity loss (based on a chronoamperometry test) or particle aggregation (based on SEM image observation) after a 10 h anodization test. The facile preparation method and high efficiency and durability enable this electrocatalyst to be a promising candidate for future large-scale applications in water splitting. Thus, this work opens a new avenue toward the development of highly efficient, inexpensive OER catalysts.

p-Sulfonatocalix[8]arene and vitamin C complexation: assessment of photophysical, pKa and antioxidant property

Mode of inclusion complexation of p-sulfonatocalix[8]arene and ascorbic acid in aqueous solution has been investigated in acidic pH based by UV–visible, fluorescence, FT-IR, 1H-NMR and HR-MS spectroscopic studies. Addition of ascorbic acid solution to p-sulfonatocalix[8]arene enhances the fluorescence intensity of p-Sulfonatocalix[8]arene with blue shift in absorption spectra. Hypsochromic shift in absorbance maxima and hyperchromic shift in emission maxima indicates that ascorbic acid experiences less polar microenvironment when bind with SCX8. Binding site and stoichiometry are examined by 1H-NMR and HR-MS techniques. Binding constant (K = 0.42 × 102 M−1) for the inclusion complex is calculated. For complexation, forces like electrostatic attraction, hydrogen bonding and hydrophobic environment of p-sulfonatocalix[8]arene cavity play important role. p-sulfonatocalix[8]arene shows upward pKa shift after binding with Ascorbic acid. The antioxidant property of ascorbic acid has been investigated which shows enhancement by 57% upon complexation with p-sulfonatocalix[8]arene.Graphical Abstract