Kapil Pareek

Tandem Catalysis of Amines Using Porous Graphene Oxide

Porous graphene oxide can be used as a metal-free catalyst in the presence of air for oxidative coupling of primary amines. Herein, we explore a GO-catalyzed carbon-carbon or/and carbon-heteroatom bond formation strategy to functionalize primary amines in tandem to produce a series of valuable products, i.e., α-aminophosphonates, α-aminonitriles, and polycyclic heterocompounds. Furthermore, when decorated with nano-Pd, the Pd-coated porous graphene oxide can be used as a bifunctional catalyst for tandem oxidation and hydrogenation reactions in the N-alkylation of primary amines, achieving good to excellent yields under mild conditions.

A high performance polysiloxane-based single ion conducting polymeric electrolyte membrane for application in lithium ion batteries

We report a polysiloxane based single-ion conducting polymer electrolyte (SIPE) synthesized via a hydrosilylation technique. Styrenesulfonyl(phenylsulfonyl)imide groups were grafted on highly flexible polysiloxane chains followed by lithiation. The highly delocalized anionic charges in the grafted moiety give rise to weak association with lithium ions in the polymer matrix, resulting in a lithium ion transference number close to unity (0.89) and remarkably high ionic conductivity (7.2 × 10−4 S cm−1) at room temperature. The high flexibility arising from polysiloxane enables the glass transition temperature (Tg) to be below room temperature. The electrolyte membrane displays high thermal stability and a strong mechanical strength. A coin cell assembled with the membrane comprised of the electrolyte and poly(vinylidene-fluoride-co-hexafluoropropene) (PVDF-HFP) performs remarkably well over a wide range of temperatures with high charge–discharge rates.

Melamine–terephthalaldehyde–lithium complex: a porous organic network based single ion electrolyte for lithium ion batteries

Cationic transference number and ionic conductivity of an electrolyte are among the key parameters that regulate battery performance. In the present work, we introduce a novel concept of using porous organic frameworks as a single ion-conducting electrolyte for lithium ion batteries. The synthesized lithium functionalized melamine–terephthalaldehyde framework (MTF–Li), a three dimensional porous organo–lithium complex, in a medium of organic solvent exhibits ionic conductivity comparable to the values of typical gel polymer electrolytes, and the battery cell assembled with the membrane of the material performs at both room temperature and at 80 °C. The rigid three-dimensional framework, functioning as the anionic part of the electrolyte, reduces the anionic transference number to a minimum. As a consequence, the cationic transference number increases to 0.88, close to unity. In addition, by virtue of its synthesis procedure, the electrolyte displays excellent sustainability at high temperatures, which is important for battery safety as well as for enhancing the performance and longevity of the battery.

Highly selective carbon dioxide adsorption on exposed magnesium metals in a cross-linked organo-magnesium complex

A cross-linked organo-magnesium complex (MTF–Mg) was synthesized and investigated for selective CO2 adsorption over N2 at 298 K. Remarkably high selectivity and reversibility were achieved with an isosteric heat of adsorption of 45.2 kJ mol−1 for CO2, consistent with the predicted DFT value of 37.3 kJ mol−1. The CO2 preferential adsorption arises from its strong interaction with the exposed magnesium atoms.

A pre-lithiated phloroglucinol based 3D porous framework as a single ion conducting electrolyte for lithium ion batteries

We report the design and synthesis of an inherently porous single ion conducting gel electrolyte made from a pre-lithiated phloroglucinol-terephthalaldehyde 3D framework for lithium ion batteries, adopting a “bottom-up” approach. The cationic transference number of the membrane obtained by blending the complex with PVDF–HFP followed by solution casting was found to be 0.86, close to unity. The mobile lithium ions shuttle through the low resistant pathways offered by the 3D network by virtue of its high porosity. The electrolyte offers a high ionic conductivity of 6.3 × 10−4 S cm−1 at room temperature (22 °C), comparable to the values of most gel polymer electrolytes. Furthermore, the electrolyte membrane displays high thermal stability and good mechanical strength. Coin cells assembled with the membrane perform well at both room temperature and 80 °C.

Polymeric organo–magnesium complex for room temperature hydrogen physisorption

We report a facile synthesis of a polymeric organo–magnesium complex (MTF–Mg) by reacting Mg-modified-melamine with terephthalaldehyde for room temperature hydrogen physisorption. The pre-modification of melamine allows incorporation of exposed magnesium sites into the complex. The synthesized MTF–Mg complex exhibits a moderate BET surface area up to 137 m2 g−1 and a Langmuir surface area up to 222 m2 g−1. In this complex, magnesium metal sites act as the active sites for molecular hydrogen adsorption via an electrostatic interaction. The material shows a high isosteric heat of adsorption up to 12 kJ mol−1 and a maximum excess hydrogen uptake up to 0.8 wt% at 298 K and 100 atm, comparable to the values of high surface area MOFs with exposed metals sites under similar conditions. The role of the exposed metal sites in enhancing hydrogen uptake capacity and isosteric heat of adsorption is demonstrated experimentally.

Hydrogen physisorption in ionic solid compounds with exposed metal cations at room temperature

Phenol- and phloroglucinol-based organo-magnesium ionic solid compounds were synthesized for room temperature hydrogen storage via physisorption. These materials contain magnesium dications balanced with highly charge-delocalized anionic species, making the cations highly exposed with relatively weak electrostatic interactions with the anions, and thus facilitates an interaction with molecular hydrogen. It was found that the driving force for the hydrogen physisorption in these materials is largely electrostatic with the σ electrons of hydrogen partially polarized by the cationic charges. The synthesized amorphous complexes exhibit moderate surface areas up to 165 m2 g−1 and 115 m2 g−1 with maximum excess hydrogen sorption capacities of 0.22 wt% and 0.8 wt%, respectively, at 298 K and 100 atm. The isosteric heat of adsorption was calculated from Clausius-Clapeyron equation using isotherms at 323 K, 298 K and 273 K. The results confirm low coverage isosteric heat of adsorption of 7.2 kJ mol−1 and 12 kJ mol−1, respectively.

Synthesis, Characterization and Properties of New Fluorinated Poly(imide siloxane) Co-polymers from 4,4′-(Hexafluoro-isopropylidene)diphthalic Anhydride

Several new poly(imide siloxane)s co-polymers have been prepared by the reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with commercially available 4,4′-oxydianiline (ODA) and with five different novel trifluoromethyl-substituted diamines, each with 20 wt% aminopropyl-terminated polydimethylsiloxane (APPS). The poly(imide siloxane)s are well characterized by different spectroscopic, thermal, mechanical and electrical techniques. The synthesized polymers exhibit good solubility in different organic solvents. The 1H-NMR indicates that the siloxane incorporation is about 17–19% for polymers 1a–f. These poly(imide siloxane) films show low water absorption rate (0.88–0.09%) and a low dielectric constant (2.43–2.58) at 1 MHz. The polymers show very good thermal stability, even up to 419°C for 5% weight loss in synthetic air and a glass transition temperature of up to 230°C. All poly(imide siloxane)s formed tough transparent films, with a tensile strength of up to 79 MPa, a modulus of elasticity of up to 1.38 GPa and elongation-at-break of up to 30%. Thermal, mechanical and dielectric properties of these polymers have been evaluated and compared with their non-siloxane analogues.

Hydrogen Storage in a Crosslinked Phloroglucinol-TerephthalaldehydeFramework with Exposed Iron Sites

Hydrogen adsorption has been studied in a cross-linked polymeric complex with coordinatively unsaturated iron metals. The complex displays hydrogen storage capacity up to 1.3 wt% at 298 K and 100 atm with an isosteric heat of adsorption up to 11.5 kJ mol-1.