Debaprasad Mandal

Combined effect of ether and siloxane substituents on imidazolium ionic liquids

Ionic liquids (ILs) in combination with ether and siloxane substituents on the imidazolium cation, comprising of bis(trifluoromethylsulfonyl)imide (NTf2) anions, have been synthesized due to their low viscosities, high thermal stabilities and low melting or glass transition temperatures(Tg). The structural flexibility of the ether and siloxane substituents on the imidazolium center overcomes the effect of van der Waals forces and gives them desirable and unique physical properties. These novel ILs show low viscosities (∼72 mPa s at 25 °C), high thermal stabilities up to 430 °C, and a wide liquid range over 500 °C. In addition, these ILs exhibit only an amorphous glassy state on cooling at Tg below −74 °C and cannot order properly to afford crystallization. The detailed thermal stability, phase transitions and heat capacity were studied by TGA, DSC and temperature-modulated DSC analysis. More importantly, we have also reported the large-scale (one kilogram) microwave-assisted synthesis of ILs [BMIM]Br and [1O2O2-Im-2O1]I as efficient and greener processes.

Self-assembly of fluorous amphiphilic copolymers with ionogels and surface switchable wettability

Fluorous amphiphilic copolymers were synthesised by the microwave assisted copolymerization of 1H,1H,2H-perfluoro-1-octene and vinyl imidazole and characterized using size exclusion chromatography, FT-IR and 1H, 13C, 19F, and DOSY NMR. The fluorous amphiphilic copolymer, when coated on a glass surface, exhibited a water contact angle (WCA) of 112°, compared to that of 67° obtained for ionic homopolymers (poly(vinylimidazolium bromide)). Switchable wettability was controlled by tuning both ionic groups and the hydrophobic fluorous segments in the amphiphilic copolymer. The fluorous ionic copolymer offered a variable WCA of 112°, 107° or 97° depending on the surface hydrophobicity of the substrate, such as glass, a compressed carbon sheet or a Teflon surface, respectively. These amphiphilic copolymers self-assembled in different solvents and swelled. The swelling was up to 966% in water and methanol and up to 2036% in DMF with fluorous anions. The micelles formed from the self-assembly of amphiphilic copolymers in different solvents were characterized by dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM). Furthermore, Ag nanoparticles were coated on the amphiphilic ionomer and characterized using scanning electron microscopy and atomic force and electrostatic force microscopy.

Two azo-functionalized luminescent 3D Cd(II) MOFs for highly selective detection of Fe3+ and Al3+

Two cadmium-based 3D luminescent MOFs {[Cd2(SA)2(L)2]·H2O}n (Cd-MOF-1) and [Cd(CDC)(L)]n (Cd-MOF-2) (H2SA = succinic acid, H2CDC = 1,4-cyclohexanedicarboxylic acid, L = [3,3′-azobis(pyridine)]) have been assembled by employing organic dicarboxylic acid linkers with an unexploited azo-functionalized N,N′ spacer via a room temperature slow evaporation process, and they are characterized by single crystal X-ray analysis, TGA, FT-IR, PXRD and elemental analysis. The topological analysis reveals that Cd-MOF-1 features a 6c-uninodal rare ‘rob’ topology with the point symbol {48·66·8}, whereas Cd-MOF-2 shows a ‘pcu’ alpha-Po primitive cubic topology with the point symbol {412·63}. These MOFs are highly emissive at 382 nm and 398 nm when excited at 305 nm and 312 nm, respectively. The exposed azo groups are presumed to act as functional sites for the recognition of metal ions through quenching of fluorescence intensity. The fluorescence measurements show that these MOFs can selectively and sensitively detect Fe3+ as well as Al3+ and thus, they demonstrate potential as dual-responsive luminescent probes for metal-ion sensing. EDS elemental mapping, PXRD of loaded MOF materials, and a plausible quenching mechanism have been discussed. More importantly, both the MOFs exhibit rapid response times toward sensing of Fe3+ and Al3+.

Ultrasensitive and Highly Selective Electrochemical Detection of Dopamine Using Poly(ionic liquids)–Cobalt Polyoxometalate/CNT Composite

A novel sandwich polyoxometalate (POM) Na12[WCo3(H2O)2(CoW9O34)2] and poly(vinylimidazolium) cation [PVIM+] in combination with nitrogen-doped carbon nanotubes (NCNTs) was developed for a highly selective and ultrasensitive detection of dopamine. Conductively efficient heterogenization of Co5POM catalyst by PVIM over NCNTs provides the synergy between PVIM–POM catalyst and NCNTs as a conductive support which enhances the electron transport at the electrode/electrolyte interface and eliminates the interference of ascorbic acid (AA) at physiological pH (7.4). The novel PVIM–Co5POM/NCNT composite demonstrates a superior selectivity and sensitivity with a lowest detection limit of 500 pM (0.0005 μM) and a wide linear detection range of 0.0005–600 μM even in the presence of higher concentration of AA (500 μM).

Nitrogen containing carbon spheres as an efficient electrocatalyst for oxygen reduction: Microelectrochemical investigation and visualization

The oxygen reduction reaction (ORR) in low temperature fuel cells limits the obtainable output triggering the necessity of screening the employable catalysts precisely. A nitrogen-containing carbon sphere (NCS) catalyst was synthesized using a soft template and was studied for the oxygen reduction reaction. The NCS catalyst was shown to have superior activity with an onset potential of 0.985 V (vs. RHE) and a diffusion-limited current density of 6.16 mA cm−2. The kinetic insight from the rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) revealed an overall 4e− reduction by a (2 + 2) electron pathway with a rate constant of 4.6 × 10−4 cm s−1 at the onset potential. A fast screening of the localized electrochemical activity using sample generation-tip collection (SG-TC) in combination with a chronoamperometric multiple pulse technique was applied in the present study to trace the formation, evolution and conversion of intermediate species using a Pt ultramicroelectrode. The local catalytic activity of the NCS catalyst was successfully visualized by scanning electrochemical microscopy (SECM) in highly alkaline medium.

Perfluoroalkylated Calix[4]pyrroles: Fluoride Ion Extraction from an Aqueous Medium

Octaalkenyl calix[4]pyrrole ((CH2 =CH(CH2 )2 )8 C4P) is highly useful for the postfunctionalization of different calix[4]pyrroles with desired functionalities. Functionalization with perfluoroalkyl chains [CF3 (CF2 )n ; Rfn ] gave perfluoroalkyl calix[4]pyrroles (Rfn (CH2 )4 )8 C4P; n=6, 8), having >60 % fluorine content, which created a hydrophobic environment inside the calix[4]pyrrole cavity and recognized fluoride and chloride ions in solution as well as in the solid state. The fluoride ion is extracted efficiently from aqueous CsF and TBAF solutions by using (Rf6 (CH2 )4 )8 C4P, as droplets. The fluorinated chain generated a hydrophobic environment which broke the hydration shell associated with the anion and separated out fluoride ions as droplets from aqueous medium. Furthermore, the fluoride ions competitively replaced chloride ions from the (Rf6 (CH2 )4 )8 C4P cavity.

Thermo-reversible self-healing in a fluorous crosslinked copolymer

Thermo-reversible self-healing of a partially fluorinated crosslinked polymer was achieved by utilizing reversible Diels–Alder (DA) chemistry. Copolymers (PHFBA-co-PFMA) of perfluorobutyl acrylate (HFBA) and furfurylmethacrylate (FMA) with controlled stoichiometric ratios were synthesized by microwave-assisted radical polymerization by controlling the individual components. The microstructures and stoichiometries of these copolymers of PHFBA and PFMA were analyzed by 1H, 19F, 13C, and DOSY NMR spectroscopy and their molecular weights were analyzed by GPC. The glass transitions (Tg) of the different stoichiometric copolymers correlate well with the estimated Tg values from the Fox equation. A thermo-reversible crosslinked polymer network was achieved via Diels–Alder (DA) and retro-DA reactions between the furan moiety of the copolymer (PHFBA-co-PFMA) and bismaleimide; the self-healing ability of this network was investigated using 1H NMR, DSC and solution experiments. The self-healing process and recovery of the crosslinked polymers was screened by microscopic visualization and stress–strain tensile studies. The surface properties of the fluorous copolymers and crosslinked polymers were studied by water contact angle measurements, and their mechanical properties were investigated by nanoindentation and DMA.