Anjali Pal

Photochemical green synthesis of calcium-alginate-stabilized Ag and Au nanoparticles and their catalytic application to 4-nitrophenol reduction.

Silver and gold nanoparticles have been grown on calcium alginate gel beads using a green photochemical approach. The gel served as both a reductant and a stabilizer. The nanoparticles were characterized using UV-visible spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), energy dispersive X-ray (EDS), and selected area electron diffraction (SAED) analyses. The particles are spherical, crystalline, and the size ranges for both Ag and Au nanoparticles are <10 nm. It is noticed from the sorption experiment that the loading of gold on calcium alginate beads is much more compared to that of Ag. The effectiveness of the as-prepared dried alginate-stabilized Ag and Au nanoparticles as a solid phase heterogeneous catalyst has been evaluated, for the first time, on the well-known 4-nitrophenol (4-NP) reduction to 4-aminophenol (4-AP) in the presence of excess borohydride. The reduction was very efficient and followed zero-order kinetics for both Ag and Au nanocomposites. The effects of borohydride, initial 4-NP concentration, and catalyst dose were evaluated. The catalyst efficiency was examined on the basis of turnover frequency (TOF) and recyclability. The catalytic efficiency of alginate-based Ag catalyst was much more compared to that of the Au catalyst. The as-prepared new solid-phase biopolymer-based catalysts are very efficient, stable, easy to prepare, eco-friendly, and cost-effective, and they have the potential for industrial applications.

Silver nanoparticle catalyzed reduction of aromatic nitro compounds

The combination of catalytic quantities of silver metal nanoparticles with NaBH4 smoothly reduces aromatic nitro compounds to amines in aqueous medium. Silver nanoparticles formed in situ are the active catalyst. The kinetic parameters of the reaction with still growing microelectrode (GME) and full grown microelectrode (FGME) silver metal particles in aqueous solution have been compared taking the plasmon band of the silver metal nanoparticles into consideration. In aqueous solution the reaction follows a first order kinetics with the full-grown (FGME) particles and zero order kinetics with the still growing particles (GME). The metal surface remains active and the activity remains unaltered throughout the course of the reduction. Catalysis was due to the efficient nanoparticle mediated electron transfer from BH4− ion to the nitro compounds. Nitro compounds like 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and 4-nitroaniline (4-NA) were tested with NaBH4 using both GME and FGME as catalyst and their rate of reduction has been observed to follow the sequence, 4-NP>2-NP>4-NA.

Size controlled synthesis of gold nanoparticles using photochemically prepared seed particles

Gold nanoparticles having prechosen size ranging from 5 to 110 nm have been prepared in two steps. Firstly, small spherical particles (seed) of average diameters between 5 and 20 nm were prepared by varying the ratio of gold ion concentration to stabilizer/reductant, TX-100 concentration and using UV irradiation. Secondly, 20–110 nm particles were formed by a non-iterative seed-mediated growth where small particles produced by the above irradiation technique were exploited as seeds and fresh Au(III) ions were reduced onto the surface on the seed particles by ascorbic acid. The kinetics of particle formation has also been reported. These methods were fast and showed improved monodispersity sphericity and excellent reproducibility.

Photoinitiated gold sol generation in aqueous Triton X-100 and its analytical application for spectrophotometric determination of gold

Gold complex, HAuCl(4) has been transformed into pink-coloured stable gold sol having lambda(max) at 523 nm (in=3.06x10(3)1.mol(-1)cm(-1)) at room temperature in aqueous Triton X-100 (TX-100) upon photoirradiation. It is a very rapid and simple process and the absorbance at 523 nm is a direct measure of gold concentration. Beers law is obeyed in the range of 0-150 ppm of gold. The relative standard deviation for 22.7 and 90.9 ppm of gold are 2.8 and 2.5% respectively. The 95% confidence limit (ten determinations) for 22.7 ppm of gold is 23.6+/-0.5 ppm. Sandell sensitivity is 6.44x10(-2) mug cm(-2). TX-100 acts both as a reducing agent and a stabilizer here. Statistical parameters, effects of TX-100 concentration, irradiation time and interferents are studied. The method is applicable for ore and synthetic mixture analysis.

Performance of Waste Activated Carbon as a Low-Cost Adsorbent for the Removal of Anionic Surfactant from Aquatic Environment

Abstract In the present study, different low cost adsorbents were screened for their sodium dodecyl sulfate (SDS, an anionic surfactant) removal capacity. Waste activated carbon (WAC) from the aqua purifier has shown high efficiency for SDS removal. The performance evaluation in the presence of various ions (Ca2+, , and Cl−) and at various pH was studied. Desorption studies were conducted using simple sonication and pH variation technique. Column adsorption studies were performed. SEM and EDS studies were done on the adsorbing material before adsorption, after adsorption and after desorption of SDS.

Silver nanoparticle aggregate formation by a photochemical method and its application to SERS analysis

Photochemical reduction of silver(I) to silver nanoparticles was achieved, for the first time, in aqueous Triton X-100 medium using ascorbic acid. The particles show the usual plasmon absorption band of silver at 410 nm and a new band at 650 nm. Transmission electron microscope studies show that the size of the individual particles varies from 15 to 60 nm and the particles are in a string-like assembly. The particles are extremely stable and SERS active. Copyright

Anisotropic growth of gold clusters to gold nanocubes under UV irradiation

A chiral reagent, 2-naphthol, has been introduced under alkaline solution as a reductant for HAuCl(4) in CTAB micelle to produce exclusively cubic gold nanoparticles under UV photoactivation. Prolonged irradiation helped the digestion of the primarily evolved spherical particles into smaller gold nanocubes, which then act as tiny cubic seeds, leading to the formation of larger nanocubes. The smaller cubes take the assistance of CTAB under alkaline condition to serve as the seed in directing the transformation of all the spherical colloids into cubic shapes under continuous irradiation via Ostwald ripening. The shape transformation of the nanoparticles has been monitored by repetitive TEM imaging and absorption spectral analysis. The FTIR analysis proves that the gold nanocubes are capped by CTAB. The XRD pattern authenticates the formation of the fcc gold nanocubes. GCMS studies in turn confirmed the presence of hydroxylation of 2-naphthol in the course of the reaction, leaving exclusively cubic gold nanoparticles at the final stage of the photoactivation reaction.

Synthesis of Highly Fluorescent Silver Clusters on Gold(I) Surface

Evolution of fluorescence from a giant core-shell particle is new and synergistic, which requires both gold and silver ions in an appropriate ratio in glutathione (GSH) solution. The formation of highly fluorescent Ag(2)/Ag(3) clusters on the surface of Au(I) assembly results in giant Au(I)(core)-Ag(0)(shell) water-soluble microparticles (~500 nm). Here, Au(I) acts as the template for the generation of fluorescent Ag clusters. The presence of gold under the synthetic strategy is selective, and no other metal supports such synergistic evolution. The core-shell particle exhibits stable and static emission (emission maximum, 565 nm; quantum yield, 4.6%; and stroke shift, 179 nm) with an average lifetime of ~25 ns. The drift of electron density by the Au(I) core presumably enhances the fluorescence. The positively charged core offers unprecedented long-term stability to the microparticles in aqueous GSH solution.

Resin-Immobilized CuO and Cu Nanocomposites for Alcohol Oxidation

Resin immobilized stable, spherical CuO nanoparticles prepared in the presence of cyclodextrin (CD) act as catalysts for liquid phase alcohol oxidation in air. The catalytic activity of the CuO nanocomposites and its green chemistry approach make it superior to the related resin-bound Cu(0) nanocomposite. The effect of alcohol chain length and electron-donating or -withdrawing groups influence product yield. The nanocomposites exhibit good reusability, simple workup procedure, and a straightforward approach to aldehyde formation.

Adsorption of anionic surfactant on alumina and reuse of the surfactant-modified alumina for the removal of crystal violet from aquatic environment

Abstract The adsorption characteristics of sodium dodecyl sulfate (SDS), an anionic surfactant on neutral alumina were studied in detail. Alumina was found to be an efficient adsorbent for SDS and could be used for the removal of SDS from its highly concentrated (several thousand ppm) solution. The equilibrium time found was 2 h. Though the removal efficiency was low (∼65%) at neutral pH, but in slightly acidic condition and in the presence of NaCl the efficiency could be increased dramatically (up to >98%). The adsorption isotherm study showed distinct four regions. The effects of various other parameters such as adsorbent dose, time, and the presence of different ions (Cl- NO- 3, SO2- 4, and Fe3+), and nonionic surfactant on the SDS adsorption were also studied. It was observed that the adsorption capacity was increased due to the presence of these ions in general. After the adsorption of SDS on alumina, the surfactant-modified alumina (SMA) was used for the removal of crystal violet (CV), a well-known cationic dye from aquatic environment. The kinetic studies showed that 1 h shaking time was sufficient to achieve the equilibrium. The removal of CV followed the second order kinetics. Studies were conducted to see the effects of adsorbent dose and initial CV concentration on the removal of CV using SMA. The pH was maintained at 6.7 ± 0.1. SMA was found to be very efficient, and ∼99% efficiency could be achieved under optimised conditions for the removal of CV when present even at a high concentration (200 ppm). To test whether the removal of CV was possible from real water using SMA, the adsorption study was conducted using CV spiked samples using distilled water, tap water, and synthetically prepared wastewater. It was interesting to note that the removal efficiency was even better for tap water and much better for wastewater when compared to that using distilled water. Desorption of both SDS and CV from the SMA surface was possible using 1 M sodium hydroxide solutions.