• Volume 120, Issue 6

November 2008,   pages  505-662

• Foreword

• Facially amphiphilic thiol capped gold and silver nanoparticles

A series of bile acid-derived facially amphiphilic thiols have been used to cap sliver and gold nanoparticles. The self-assembling properties of these steroid-capped nanoparticles have been investigated and reported in this article.

• Synthesis of silver nanoparticles by sophorolipids: Effect of temperature and sophorolipid structure on the size of particles

We report in situ synthesis of silver nanoparticles using biosurfactants called sophorolipids as reducing and capping agents. We further study the effect of temperature and the structure of sophorolipid on the size of silver nanoparticles obtained. The silver nanoparticles were characterized by UVvisible, transmission electron microscope (TEM) and light scattering (DLS) analysis techniques.

• Role of carboxylate ion and metal oxidation state on the morphology and magnetic properties of nanostructured metal carboxylates and their decomposition products

Sub-micron rods and spheres of cobalt succinate sesquihydrate and iron succinate trihydrate/pentahydrate respectively have been synthesized by the reverse micellar route. These precursors are an excellent source for the synthesis of metal and metal oxide nanoparticles. Cubes of (edge length ∼ 150 nm) Fe3O4 and elongated particles of Fe2O3 (∼ diameter of 200 nm) were obtained. The role of oxidation state of the metal ion in controlling the morphology of the nanostructured dicarboxylates has been investigated. Rods with shorter length were obtained when longer chain dicarboxylate was used as ligand. Heating in nitrogen atmosphere also provided pure Co and 𝛼-Fe nanoparticles. The Fe nanoparticles show nearly 100% superparamagnetism. Temperature-dependent magnetic studies show a Morin-like transition for Fe2O3 nanoparticles at 223 K and the Verwey transition at 115 K for Fe3O4 nanoparticles. Co3O4 nanoparticles showed antiferromagnetic ordering at 20 K.

• Nanostructured phosphomolybdates

Phosphomolybdate nanorods were synthesized using dodecyl pyridinium cations as structure directing agent. Composition and morphology of the nanorods were established by powder X-ray diffraction, energy dispersive X-ray analysis, fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy and scanning electron microscopy. Effect of synthetic variables such as pH and nature of templating agent on structure and morphology of the nanorods under ambient condition is discussed.

• Removal of phase transfer agent leads to restricted dynamics of alkyl chains in monolayer protected clusters

The effect of phase transfer agent in the dynamics of monolayer protected gold nanoparticles has been investigated by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies. The experiments were performed with octadecane thiol and dodecane thiol protected gold nanoparticles. The materials prepared were characterized by UV-Visible spectroscopy, transmission electron microscopy and IR spectroscopy. Repeated purification of the monolayer protected gold clusters made the alkyl chains defect-free. Such effects are reflected in the infrared spectra. Interdigitation of the monolayers that followed the purification leads to alkyl chains with limited mobility. This was reflected in 13C and 1H NMR linewidths. The NMR measurements indicate that the removal of phase transfer agent affects the dynamics of isolated clusters and those with interdigitated monolayers in different ways.

• 𝑝-Aminoacetanilide mediated formation of assembly of Au nanoparticles

In this article, we report the formation of assembly of Au nanoparticles (NPs) of different sizes in the presence of 𝑝-aminoacetanilide. Citrate stabilized spherical Au NPs assembled into a linear array, the extent of which depended on the concentration of 𝑝-aminoacetanilide in the medium. Higher concentrations led not only to the formation of longer assemblies but also branched ones. In addition, substantial fusion of NPs was observed at higher concentrations. UV-Vis spectra showed the appearance of a second peak at higher wavelength - the position of which shifted to the red with increasing concentration of 𝑝-aminoacetanilide. Interestingly, the second peak could not only be influenced by the concentration of 𝑝-aminoacetanilide but also by choosing different sizes of the spherical NPs at the initial stages. For example, when the particles were larger the shift could be observed at higher wavelengths than those starting with smaller particles. The present method allows organization of NPs into linear arrays based on the molecular properties of the assembler’ i.e. 𝑝-aminoacetanilide. Also, the optical properties of the assembled NPs could be tuned with the choice of suitable sizes of the assembling NPs.

• Synthesis and spectroscopic study of high quality alloy Cd$_x$Zn$_{1-x}$S nanocrystals

In the present study, we report the synthesis of high quality Cd$_x$Zn$_{1-x}$S nanocrystals alloy at 150°C with changing the composition. The shifting of absorption and emission peak in shorter wavelength is obtained with increasing the mole fraction of zinc. The quantum yield (QY) value decreases with increasing the Cd mole fraction and the values are 0.08, 0.13 and 0.40 for Cd0.62Zn0.38S, Cd0.52Zn0.48S and Cd0.31Zn0.69S nanocrystals, respectively after 120 min of reaction. However, the full width at halfmaximum (fwhm) values are 45, 34 and 28 nm and the corresponding quantum yield (QY) values are 0.52, 0.17 and 0.13 for 0.5 mM, 1.5 mM and 3 mM of initial S concentrations, respectively. It is interesting to note that the radiative decay time is dominating with increasing the Cd content. Analysis suggests that the decay dynamics depends on the composition of Cd$_x$Zn$_{1-x}$S nanocrystals.

• Tuning of Ag-SPR band position in refractive index controlled inorganic-organic hybrid SiO2-PEO-TiO2 films

Inorganic (silica-titania)-organic (polyethylene oxide) hybrid films with variable refractive index (RI) values were synthesized and Ag nanoparticles were generated in situ inside such hybrid films to develop coloured coatings specially on plastic substrates. The hybrid films and the corresponding Agincorporated films were prepared from sols derived from a mixture of silicon tetraethoxide (STE), 3-(glycidoxypropyl)trimethoxysilane (GPTMS), titanium tetraisopropoxide (TTIP) and silver nitrate following a sol-gel dip-coating method and cured at low temperature (90°C), followed by UV treatment with an energy equivalent to $5.3 \pm 0.1$ J cm-2. The equivalent SiO2: SiO1.5(CH2)3OCH2CH(CH2)O : TiO2: Ag molar ratios (nominal) of the final cured films are varied in the ranges (67.9-0) : 29.1 : (0-67.9) : 3. The refractive index values of the cured hybrid films were found to be increased systematically from 1.475 to 1.710 with increasing Ti-component. The Ag-SPR peak, in case of silica-polyethylene oxide host (RI = 1.475), observed at 419 nm, gradually red-shifted to 497 nm upon increasing the Ticomponent (equivalent TiO2 content 67.9 mol%; RI = 1.710) of the film. As a consequence, a systematic change of Ag-SPR position yielded yellow, yellowish-orange, orange, brownish-orange and orangish-brown coloured coatings.

• Two approaches for enhancing the hydrogenation properties of palladium: Metal nanoparticle and thin film over layers

In the present study, two approaches have been used for enhancing the hydrogenation properties of Pd. In the first approach, metal thin film (Cu, Ag) has been deposited over Pd and hydrogenation properties of bimetal layer Cu (thin film)/Pd(thin film) and Ag(thin film)/Pd(thin film) have been studied. In the second approach, Ag metal nanoparticles have been deposited over Pd and hydrogenation properties of Ag (nanoparticle)/Pd (thin film) have been studied and compared with Ag(thin film)/Pd(thin film) bimetal layer system. The observed hydrogen sensing response is stable and reversible over a number of hydrogen loading and deloading cycles in both bimetallic systems. Alloying between Ag and Pd is suppressed in case of Ag(nanoparticle)/Pd(thin film) bimetallic layer on annealing as compared to Ag (thin film)/Pd(thin film).

• Synthesis of agarose-metal/semiconductor nanoparticles having superior bacteriocidal activity and their simple conversion to metal-carbon composites

Agarose, a naturally occurring biopolymer is used for the stabilization of metal, semiconductor nanoparticles. Ag and Cu nanoparticles stabilized in agarose matrix show excellent antibacterial activity against E. coli bacteria. The well dispersed metal nanoparticles within the agarose composite films can be readily converted to carbon-metal composites of catalytic importance.

• Investigation of hybrid molecular material prepared by ionic liquid and polyoxometalate anion

A solid hybrid molecular material containing 1-butyl 3-methyl imidazolium cations and Keggin anions of phosphotungstic acid has been synthesized. It is fully characterized by CHN analysis, FTIR, XRD, UV-Vis-NIR DRS, 31P MAS NMR, TGA and SEM. The FTIR spectrum of the compound shows the fingerprint vibrational bands of both Keggin molecular anions and imidazolium cations. The aromatic C-H stretch region (2700-3250 cm-1) of imidazolium cation is split due to the interaction between the ring C-H and bulky Keggin anion. The red-shift in the UV-Vis spectra and the downfield 31P MAS NMR chemical shift also confirm the electrostatic interaction between the ions in the compound. Near IR spectral region (1000-2500 nm) shows the elimination of water in the compound which is hydrophobic.

• Magnetocaloric effect across the coupled structural and ferromagnetic transition in Pr0.1Ce0.4Sr0.5MnO3

We have investigated the magnetocaloric effect across a first order structural transition coupled to the ferromagnetic transition ($T_C \sim 270$ K) in Pr0.1Ce0.4Sr0.5MnO3 using magnetization and heat capacity measurements. The adiabatic magnetic entropy change |$\Delta S$| obtained from magnetization measurements for a magnetic field change of 2 T is around 1.3 J/kg K. A similar value of |$\Delta S$| was obtained from the analysis of heat capacity data.

• Near-complete phase transfer of single-wall carbon nanotubes by covalent functionalization

We describe here an efficient phase transfer of single wall carbon nanotubes (SWNTs) from aqueous to non-aqueous media using a unique amide functionalization route, where water soluble SWNTs (2.6 mg/mL) are effectively transferred to solvents like chloroform, toluene and CS2. A maximum of 30 wt% of oxygenated groups have been generated on the side walls by rapid microwave treatment, leading to a solubility of more than 2.6 mg/mL in water. Approximate surface amine coverage of 50% has been accomplished after oxalyl chloride treatment as inferred from thermogravimetry and X-ray photoelectron spectroscopy by controlling several key parameters associated with the extent of functionalization including purity of the sample, temperature and time.

• Covalent and non-covalent functionalization and solubilization of double-walled carbon nanotubes in nonpolar and aqueous media

Double-walled carbon nanotubes (DWNTs) have been functionalized by both covalent and non-covalent means. Covalent functionalization has been carried out by attaching an aliphatic amide function to DWNTs which enable solubilization in non-polar solvents. Solubilization in non-polar solvents has also been accomplished by non-covalent functionalization by using 1-pyrenebutanoicacid succinimidyl ester (PYBS). Non-covalent functionalization of DWNTs has been carried out by using polyethylene glycol (PEG) and polyoxyethylene(40)nonylphenyl ether (IGPAL), both of which enable solubilization in aqueous media. These functionalized DWNTs have been characterized by transmission electron microscopy, IR and Raman spectroscopy.

• Charge density analysis of two proton transfer complexes: Understanding hydrogen bonding and determination of in-crystal dipole moments

An experimental charge density study has been carried out on proton-transfer complexes exhibiting nonlinear optical (NLO) properties-melaminium tartrate monohydrate and L-asparaginium picrate employing high-resolution X-ray diffraction at 100 K. Both the complexes crystallize in non-centric space group P21 and the structures exhibit interesting patterns of N-H…O and O-H…O hydrogen bonding. Experimental determination of the dipole moment (𝜇) for the asymmetric unit reveals that for both the crystals, there is a large cooperative enhancement in the crystalline 𝜇 arising essentially due to hydrogen bond mediated charge transfer between the melaminium ion and the L-tartrate in one case, between the Lasparaginium ion and the picrate in the other complex. We have additionally performed theoretical calculations at the density functional theory (DFT) level to understand the origin of enhancement of the dipole moments in the two systems.

• Competition between elastic and chemical effects in the intermixing of Co and Ag on Rh(111)

We have performed ab initio density functional theory calculations to investigate the formation energy and the effects of low dimensionality and reduced coordination on the magnetic properties of pseudomorphically grown monolayers of Co-Ag surface alloys on a Rh(111) substrate. We find that if such an alloy could form, its magnetic moment would be considerably enhanced relative to that of bulk Co. However, we also find that its formation is energetically disfavoured against phase-segregated forms; this can be mainly attributed to the high chemical’ cost of forming Ag-Co bonds. Trends in the variation of magnetic moment with alloy composition are largely consistent with the Stoner argument.

• Molecular modelling of a chemodosimeter for the selective detection of As(III) ion in water

We have modelled for the first time a chemodosimeter for As(III) detection in water. The chemodosimeter modelled is a 1,3-dithiole-2-thione derivative with an anthracene unit which has been previously described as a chemodosimeter for Hg(II) detection. Quantum chemical calculations at the DFT level have been used to describe the binding energies and selectivity of the chemodosimeter. We find that the dosimeter action is intrinsically dependent on the thiophillic affinity and the coordination sphere of the metal ion. Binding studies for a series of metal ions: Pb(II), Cd(II), Hg(II), Ni(II) and As(III) followed by an analysis of the complete reaction pathway explains the high selectivity of the dosimeter towards As(III). The dosimeter efficiency is calculated as 66% for As(III)-ion.

• Surfactant controlled switching of water-in-oil wetting behaviour of porous silica films grown at oil-water interfaces

Selective permeation of oil and water across a porous medium, as in oil recovery operations, depends on the preferential wetting properties of the porous medium. We show a profound influence of surfactants in wetting of porous media and thus demonstrate a new route for the control of water-in-oil wetting of porous substrates by changing the concentration of surfactants in an aqueous sub-phase below the substrate. This strategy is employed to engineer partial reversible wetting transitions on a porous silica film. The film itself is grown and stabilized on a flat, macroscopic interface between an oil phase and an aqueous sub-phase. On increasing the surfactant (CTAB) concentration in the sub-phase, contact angle of a water drop (placed on the oil side of the film) changes from 140° to 16° in 25 min by diffusion of the surfactant across the porous film. On further replacement of the sub-phase with pure water, diffusion of the surfactant from the water drop back to the sub-phase was slower, increasing the contact angle in the process from 16° to 90° in 2 h. Wettability control by a cationic surfactant (CTAB) was found to be much faster (6 deg/min) than that offered by an anionic surfactant, SDS (0.05 deg/min). Switching of the surface wettability due to the surfactant diffusion may have implications in oil-water separation, chemical bed reactors and microfluidic devices.

• Subject Index

• Author Index

• # Journal of Chemical Sciences

Volume 132, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019