Mudasir Ahmad Rather

Determination of cmc of imidazolium based surface active ionic liquids through probe-less UV-vis spectrophotometry.

In the first of its kind we herein report the results of our studies undertaken on the micellization behaviour of imidazolium based surface active ionic liquids (SAILs) to prove that their critical micelle concentration (cmc) can be estimated through ultraviolet-visible (UV-vis) spectroscopy without using any external probe. Tensiometric and spectrophotometric investigations of a series of freshly prepared SAILs viz. 1-octyl-3-methylimidazolium chloride ([OMIM][Cl]), 1-octyl-3-methylimidazolium dodecylsulphate ([OMIM][DS]), 1-octyl-3-methylimidazolium benzoate ([OMIM][Bz]), 1-octyl-3-methylimidazolium salicylate ([OMIM][Sc]), 1-octyl-3-methylimidazolium acetate ([OMIM][Ac]) are presented as a case study in support of the said claim. The cmcs estimated through spectrophotometric method were found to be close to the values estimated through tensiometry for the said SAILs. The cmcs for the investigated SAILS were found to vary in order of [OMIM][Cl]>[OMIM][Ac]>[OMIM][Bz]>[OMIM][Sc]>[OMIM][DS]. To the best of our knowledge the present communication will be the first report about the synthesis, characterization and micellization behaviour of [OMIM][Bz] and [OMIM][Sc].

PdAg Bimetallic Nanoalloy-Decorated Graphene: A Nanohybrid with Unprecedented Electrocatalytic, Catalytic, and Sensing Activities

Recent reports about the promising and tunable electrocatalytic activity and stability of nanoalloys have stimulated an intense research activity toward the design and synthesis of homogeneously alloyed novel bimetallic nanoelectrocatalysts. We herein present a simple one-pot facile wet-chemical approach for the deposition of high-quality bimetallic palladium-silver (PdAg) homogeneous nanoalloy crystals on reduced graphene (Gr) oxide sheets. Morphological, structural, and chemical characterizations of the so-crafted nanohybrids establish a homogeneous distribution of 1:1 PdAg nanoalloy crystals supported over reduced graphene oxide (PdAg-Gr). The PdAg-Gr nanohybrids exhibit outstanding electrocatalytic, catalytic, and electroanalytical performances. The PdAg-Gr samples were found to exhibit exceptional durability when subjected to repeated potential cycles or long-term electrolysis. In the CVs recorded for fuel cell reactions, viz. methanol oxidation reaction and oxygen reduction reaction, and for detoxification of environmental pollutants, viz. electroreduction of methyl iodide and chloroacetonitrile over PdAg-Gr with potential sweep rate of 25 mVs-1, the peak potentials were observed to be just -0.221, -0.297, (vs Ag/AgCl, 3 M KCl) -1.508, and -1.189 V (vs Fc+/Fc), respectively. The potential of PdAg-Gr nanohybrid for simultaneous and sensitive electrochemical sensing and estimation of hydroxybenzene isomers with very low detection limits (0.05 μM for hydroquinone, 0.06 μM for catechol, 6.7 nM for 4-aminophenol, and 13.7 nM for 2-aminophenol) is demonstrated. Additionally, PdAg-Gr was observed to offer excellent solution-phase catalytic performance in bringing about the reduction of notorious environmental pollutant 4-nitrophenol to pharmaceutically important 4-aminophenol with an apparent rate constant ( kapp) of 3.106 × 10-2 s-1 and a normalized rate constant ( knor) of 6.21 × 102 s-1 g-1. The presented synthetic scheme besides being high yielding, low cost, and easy to carry out results in the production of PdAg-Gr nanohybrids with stability and activity significantly better than most of the nanomaterials purposefully designed and testified so far by various groups.

Self-assembled AuNPs on sulphur-doped graphene: a dual and highly efficient electrochemical sensor for nitrite (NO2−) and nitric oxide (NO)

A simple strategy for the synthesis of self-assembled gold nanoparticles (AuNPs) on sulphur-doped graphene (S-Gr) to form AuNPs-S-Gr nanohybrids is presented. Structural, chemical and morphological characterization of AuNPs-S-Gr nanohybrids through UV-Vis spectroscopy, the X-ray diffraction technique (XRD), Raman spectroscopy, force field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and electrochemical techniques establishes the AuNPs-S-Gr nanohybrid as a monolayer of AuNPs assembled on S-Gr. The lead underpotential deposition experiments ascertain that nano Au in AuNPs-S-Gr nanohybrids is better exposed for faradic processes than in citrate-stabilized AuNPs, with the faradic response in the former being dominated by the Au-(111) planes. The AuNPs-S-Gr nanohybrids are demonstrated to be electrochemically stable, reusable and with an excellent prospect for the sensitive and selective electrochemical detection of two biologically and environmentally important oxides of nitrogen viz. nitrite (NO2−) and nitric oxide (NO). The electrocatalytic electron transfer rate constants (kcat) of the AuNPs-S-Gr nanohybrid towards electro-oxidation of NO2− and NO were observed to be 0.98 (±0.03) × 105 M−1 s−1/2 and 0.51 (±0.02) × 104 M−1 s−1/2, respectively. The AuNPs-S-Gr nanohybrid was demonstrated to ensure selective and sensitive electrochemical quantification of NO2− and NO with a very high sensitivity (20766.17 and 21046.72 μA M−1 cm−2), a wide linear range (12.5–680.92 and 24.9–680.93 μM) and very low detection limits (0.003 and 0.009 μM), respectively. Importantly, the AuNPs-S-Gr nanohybrid exhibited appreciable selectivity towards the detection of NO2− and NO even in the presence of a very high concentration of common interfering ions. The stability and reproducibility of faradic signals for NO2− and NO detection at the AuNPs-S-Gr nanohybrid were found to be excellent for standard laboratory and real samples. The electrocatalytic activity and sensing results of the AuNPs-S-Gr nanohybrid for NO2− and NO are much better than those recently reported over surfaces purposefully designed for electrocatalytic oxidation and electrosensing of these analytes.

Ionic Liquids: Additives for Manipulating the Nucleophilicity

Kinetic investigations of the SN2 reaction at the sulfur atom of p-toluenesulfonyl chloride with sodium azide in dried methanol in the presence of varying amounts of room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium acetate ([C4C1im][CH3COO]), 1-butyl-3-methylimidazolium chloride ([C4C1im]Cl) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im][PF6]), were carried out in order to explore and understand the impact of these additives on the rate of such reactions. The observed results indicate that the rate constant of the reaction increase appreciably with increases in the concentration of RTILs in RTIL–methanol binary solvent systems. The results were analyzed in light of a Kamlet–Taft model system, which established that the observed impact of RTILs can be attributed to the cumulative effects of increase in the β value (hydrogen bonding acceptor ability) which is expected to enhance the reactivity of p-toluenesulfonyl chloride as well as the nucleophilicity of the azide ion and decrease in the π* value (solvent dipolarity/polarizability) which is expected to enhance the reactivity of the azide ion. Of the three ionic liquids used in the presented studies, [C4C1im][CH3COO] was observed to be more effective in accelerating the rate constant; this we attribute to its comparatively stronger ability to increase the β value and decrease the π* value in the mixed solvent system.