Saurabh S. Soni

Aggregation behavior of pyridinium based ionic liquids in water--surface tension, 1H NMR chemical shifts, SANS and SAXS measurements.

The aggregation behavior of short alkyl chain ionic liquids (ILs), namely 1-butyl, or 1-hexyl or 1-octylpyridinium and 1-octyl-2-, or -3-, or -4-methylpyridinium chlorides, in water has been assessed using surface tension, electrical conductance, (1)H NMR, small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) measurements. Critical aggregation concentrations (CACs), adsorption (at air/water interface) and thermodynamic parameters of aggregation have been reported. The values of CAC and area per adsorbed molecule decrease with the number of carbon atoms in the alkyl chain. The aggregation process is driven by both favorable enthalpy and entropy contributions. An attempt was made to examine the morphological features of the aggregates in water using SANS and SAXS methods. SANS and SAXS curves displayed diffuse structural peaks that could not be model fitted, and therefore, we calculated the mean aggregation numbers from the Q(max) assuming that IL molecules typically order into cubic type clusters.

Improved molecular architecture of D–π–A carbazole dyes: 9% PCE with a cobalt redox shuttle in dye sensitized solar cells

Two new D–π–A dyes (SK2 & SK3) based on carbazole, and vinylene-phenylene (π-bridge) with rhodanine-3-acetic acid and cyanoacrylic acid as electron withdrawing–injecting as well as anchoring groups were designed and synthesised under conditions that were free from precious metal-catalysts and well characterized for dye-sensitized solar cell (DSSC) applications. A high power conversion efficiency (PCE) of 9% (AM 1.5 G, 100 mW cm−2) has been achieved using cyanoacrylic acid as an acceptor in D–π–A carbazole dye (SK3) with a cobalt based redox shuttle, while a PCE of 7.1% was exhibited in triiodide based redox mediators. A short-circuit current density, Jsc of ∼18.2 mA cm−2, an open-circuit voltage, Voc of ∼725 mV, and a fill factor, FF of ∼67% have been afforded by the SK3 based DSSC incorporating the Co2+/Co3+ electrolyte as the one-electron redox mediator. In contrast, SK2 dye based DSSCs with a cobalt based redox mediator have shown a Jsc ≈ 8.4 mA cm−2, a Voc ≈ 587 mV, and a FF ≈ 48%, yielding a PCE of 2.4%. The devices based on SK3 showed outstanding stability performance without significant degradation even after 1000 h of illumination under standard conditions in the Co2+/Co3+ electrolyte.

Symmetrical and unsymmetrical Brønsted acidic ionic liquids for the effective conversion of fructose to 5-hydroxymethyl furfural

Symmetrical and unsymmetrical Bronsted acidic Ionic Liquids (ILs) have been synthesized via a one-pot halogen-free route and characterized by TGA-DTA and DSC to compare their stability and activity. The acidities of the four ILs have also been tested by the Hammett method. These ILs were utilised as catalysts for the dehydration of fructose to 5-hydroxymethylfurfural (HMF) in the presence of dimethylsulphoxide (DMSO) as solvent. The effects of reaction time, temperature and catalyst concentration were studied. The ILs are very efficient for the reaction at relatively lower temperature with very good HMF yield and selectivities. The used ILs could be easily recycled without any significant loss in fructose conversion and HMF yield.

Effect of self-assembly on triiodide diffusion in water based polymer gel electrolytes: An application in dye solar cell

The preparation of ordered polymer gels from the amphiphilic block copolymers, Pluronic® F77, P123 and polyethylene glycol in the presence of ionic liquid, iodine and organic additives is presented. At 35%(w/w) concentration these copolymers (F77 and P123) self-assembled into cubic liquid crystalline phase in aqueous solution and characterized by using SAXS and AFM measurements. The effects of micellar aggregation formed by polymers on the ionic transport and triiodide diffusion have been studied by electrochemistry and SANS experiments. The ionic migration or triiodide diffusion through these polymer gels is found to be affected by the PEO/PPO content in the polymer backbone. These gels were successfully employed as an electrolyte in a dye sensitized solar cell. A remarkable solar to electricity conversion efficiency and good stability was obtained using Pluronic® F77 based gel, which is attributed to its thermoreversible sol to gel transition.

Ionic Conductivity through Thermoresponsive Polymer Gel: Ordering Matters

Thermoreversible polymer gel has been prepared using PEO-PPO-PEO block copolymer (Pluronic F77) which self-assembles into different microcrystalline phases like cubic, 2D-hexagonal, and lamellar. Addition of electrolyte (LiI/I(2)) converts the gel into a polymer gel electrolyte (PGE) which exhibits microphase-dependent ionic conductivity. The crystalline phases have been identified by SAXS as a function of the polymer concentration. It is found that the optimum value for the ionic conductivity (≈1 × 10(-3) S x cm(-1)) is achieved in the Im3m phase due to faster diffusion of ions through the 3D-interconnected micellar nanochannels. This fact is further supported by FTIR study, ionic transference number, and diffusion coefficient measurements.

Influence of N-Alkylpyridinium Halide Based Ionic Liquids on Micellization of P123 in Aqueous Solutions: A SANS, DLS, and NMR Study

The isotropic micellar state of Pluronic P123 in the presence and absence of N-alkylpyridinium halide ionic liquids (ILs) is investigated using SANS, DLS, and (1)H NMR studies. The micellar structural parameters are obtained as a function of variation in alkyl chain length, anions, and concentrations of ILs by fitting the SANS scattering data with a model composed of core-shell form factor and a hard sphere structure factor of interaction. Addition of ILs decreases the micellar core, aggregation number, and hard sphere radius of P123 micelles. From quantitative analysis, we determined the amount of solvent (D2O + IL) present inside the core and the core-shell interface along with cationic head groups. This is further supported by monitoring interaction between ILs and polymer micelle using (1)H NMR spectroscopy. The results are discussed and explained as a function of concentration of C8PyCl, alkyl chain length, and anions of N-alkylpyridinium halides.

Time-dependent stereoselective Heck reaction using mesoporous Pd/TiO2 nanoparticles catalyst under sunlight

Pd(0)-doped mesoporous TiO2 nanoparticles (Pd/TiO2) have been synthesized using an EISA method. The catalytic activity of Pd/TiO2 nanoparticles (NPs) is significantly enhanced under solar light irradiation for the Heck reaction. The Heck coupling product gives a considerable amount of Z-isomer, due to photochemical isomerization of the initially formed E-isomer, providing a facility for the time-dependent selectivity of E/Z-isomers under sunlight at ambient conditions.

Ionic liquid induced sphere-to-ribbon transition in the block copolymer mediated synthesis of silver nanoparticles

Spherical silver nanoparticles (AgNPs) with size ∼20 nm have been synthesized from an aqueous AgNO3 solution using the amphiphilic block copolymer, Pluronic P123 (EO20–PO70–EO20), under ambient conditions without the use of any other reducing agents. The size of the AgNPs was highly dependent on the size and geometry of the micelles of the block copolymer. The AgNPs synthesized from the block copolymer mediated synthesis were characterized by UV-Vis spectroscopy, Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS). The addition of an ionic liquid (IL), N-alkyl pyridinium dodecyl sulphate, CnPyDs, where n = 4, 6, 8, prepared by modifying N-alkyl pyridinium chloride with an anionic surfactant, sodium dodecyl sulphate (SDS), induced a sphere-to-ribbon (cylindrical) transition of the AgNPs. We observed that the presence of ILs reduces the equilibrium time as well as acting as a shape directing agent. The micelles of P123 and ILs in aqueous solution were characterized by Small Angle Neutron Scattering (SANS) and DLS methods. The size and shape of the AgNPs correlate with the geometry of micelles of the amphiphilic block copolymer and ILs in aqueous solution.

Enhanced photovoltaic performance of meso-porous SnO2 based solar cells utilizing 2D MgO nanosheets sensitized by a metal-free carbazole derivative

Herein, we report the power conversion efficiency (PCE) of ∼3.71%, achieved in a mesoporous SnO2 based solar cell by introducing 15 wt% of 3D porous hierarchical MgO composed of 2D nanosheets by a simple sonochemical route followed by a mixing process, sensitized with a metal-free carbazole dye, namely, 2-cyano-3-(4-(2-(9-p-tolyl-9H-fluoren-6-yl)vinyl)phenyl)acrylic acid (i.e. SK1 dye). We have optimized the performance of solar cell devices with the addition of MgO and performed a comparative study on photovoltaic performances of the fabricated devices, such as SnO2–MgO with pristine SnO2, by employing two different redox mediators, namely, (I−/I3−) and [Co(bpy)3]2+/3+. We observed a significant improvement in the open circuit voltage (Voc) and fill factor (FF) for the SnO2–MgO based dye sensitized solar cell (DSSC) over the pristine SnO2 device, i.e. from 357 mV to 550 mV and from ∼38% to ∼50% respectively, wherein an ∼60% enhancement in PCE for the SnO2–MgO device as compared to bare SnO2 device using the redox mediator (I−/I3−) is achieved. Interestingly, in the case of cobalt tris(2,2′-bipyridyl) redox shuttle, we observed further improvement in the PCE value of the photovoltaic device by 74%, i.e. from ∼1% (pristine SnO2 device, redox mediator I−/I3−) to ∼3.71% (SnO2–MgO device). From electrochemical impedance spectroscopy (EIS) of the devices, we conclude that the charge transfer resistance at the SnO2–MgO/SK1/electrolyte interfaces is lower as compared to SnO2/SK1/electrolyte interfaces, which demonstrates faster charge migration across the interfaces and a slower electron–hole (e−–h+) recombination rate. It was observed that in the presence of MgO, the life time of photoinduced electrons in the conduction band (CB) of SnO2 microspheres increases to τe = 15.9 ms from 7.1 ms (for pristine SnO2 device), by employing [Co(bpy)3]2+/3+ as a redox shuttle, and thus resulting in higher values of open circuit voltage (Voc) and short circuit current density (Jsc). Therefore, hierarchical MgO not only improves the PCE of the photovoltaic devices by minimizing the leakage of trapped electrons in the conduction band level of SnO2/electrolyte interface but also provides more surface area for the adsorption of dye molecules.

Pd doped SiO2 nanoparticles: an efficient recyclable catalyst for Suzuki, Heck and Sonogashira reactions

Palladium doped silica (Pd/SiO2) mesoporous material was synthesized via the sol–gel route using the P123 triblock copolymer as a structure directing agent. Pd/SiO2 was efficiently used as a catalyst for Suzuki, Heck and Sonogashira reactions under microwave irradiation. The catalyst exhibited high activity for all the coupling reactions and can be recycled nine times without a significant loss in its catalytic activity.