Extensive investigation on extraction and leaching kinetics study of Cu and Cr from spent catalyst using acetic acid.

The application of organic acids towards the extraction of both Cu and Cr from the Cu-Cr spent catalyst was investigated. A series of organic acid such as acetic acid, citric acid, formic acid, ascorbic acid and tartaric acid were adopted, and after screening, acetic acid showed a profound effect on dissolution of either of the metals over other green reagents. The spent catalyst was characterized by XRD and SEM-EDAX to confirm the existence of the oxide phase due to both Cu and Cr metals. For efficient dissolution of metals, the critical parameters such as agitation speed, acetic acid concentration, temperature, particle size, as well as S/L ratio affecting on it was systematically investigated. It was observed that at approximately 99.99% of Cu along with 62% of Cr was extracted at the optimised conditions (agitation speed: 800 rpm, 1.0 M CH3COOH, 353 K temperature, particle size of (75-105) µm and S/L: 2% (W/V). The leach residue obtained after the first stage of leaching was analysed by SEM-EDAX and XRD, indicating no peaks due to the presence of Cu ensures complete dissolution of Cu at the optimum conditions. Further, to attain the quantitative leaching yield of Cr, the leach residue obtained after the first stage was sequentially investigated using varied acetic acid concentration and temperature. Leaching kinetics was established based on obtained results at the varied operating parameters, and it revealed support for fitting a model of the leaching data to the shrinking core chemical control model (R2 = 0.99) for both metals (Cu and Cr). The activation energy determined to be 34.05 kJ mol-1 and 43.31 kJ mol-1 for Cu and Cr, respectively, validates the proposed leaching kinetics mechanism.

Green Synthesis of Metallic Nanoparticles via Biological Entities.

Nanotechnology is the creation, manipulation and use of materials at the nanometre size scale (1 to 100 nm). At this size scale there are significant differences in many material properties that are normally not seen in the same materials at larger scales. Although nanoscale materials can be produced using a variety of traditional physical and chemical processes, it is now possible to biologically synthesize materials via environment-friendly green chemistry based techniques. In recent years, the convergence between nanotechnology and biology has created the new field of nanobiotechnology that incorporates the use of biological entities such as actinomycetes algae, bacteria, fungi, viruses, yeasts, and plants in a number of biochemical and biophysical processes. The biological synthesis via nanobiotechnology processes have a significant potential to boost nanoparticles production without the use of harsh, toxic, and expensive chemicals commonly used in conventional physical and chemical processes. The aim of this review is to provide an overview of recent trends in synthesizing nanoparticles via biological entities and their potential applications.

Surface-plasmon-based colorimetric detection of Cu(II) ions using label-free gold nanoparticles in aqueous thiosulfate systems.

We report colorimetric, label-free and non-aggregation-based gold nanoparticle (AuNP) probes for the highly selective detection of Cu(II) ions in aqueous environments. This detection scheme relies on the ability of Cu(II) ions to catalyze the leaching of gold at room temperature in the presence of thiosulfate species and ammonia. This simple and cost-effective probe provides rapid detection of Cu(II) ions at concentrations as low as 10 ppm. A similar detection method using AuNPs in ammonia-free thiosulfate solution is also viable at moderate reaction temperature (50 °C). The ammonia-free method also leads to marked damping and red-shifting of the surface plasmon resonance signal of the AuNP dispersion. The two methods clearly differ in the nature of the surface plasmon damping phenomenon, and their working mechanisms are plausibly explained based on the experimental investigations.

Highly selective colorimetric detection of hydrochloric acid using unlabeled gold nanoparticles and an oxidizing agent.

We report a colorimetric system for the detection of HCl in aqueous environments using unlabeled gold nanoparticle (AuNP) probes. This nonaggregation-based detection system relies on the ability of chloro species to cause rapid leaching of AuNPs in an aqueous dispersion containing a strong oxidizing agent, such as HNO(3) or H(2)O(2). The leaching process leads to remarkable damping of the surface plasmon resonance peak of the AuNP dispersion. This method works only with AuNPs of a particular size (∼30 nm diameter). It is highly selective for HCl over several common mineral acids, salts, and anions. This simple and cost-effective sensing system provides rapid and simple detection of HCl at concentrations as low as 500 ppm (far below the hazard limit) in natural water systems.

Microbial synthesis of gold nanoparticles using the fungus Penicillium brevicompactum and their cytotoxic effects against mouse mayo blast cancer C 2 C 12 cells.

Microorganisms, their cell filtrates, and live biomass have been utilized for synthesizing various gold nanoparticles. The shape, size, stability as well as the purity of the bio synthesized nanoparticles become very essential for application purpose. In the present study, gold nanoparticles have been synthesized from the supernatant, live cell filtrate, and biomass of the fungus Penicillium brevicompactum. The fungus has been grown in potato dextrose broth which is also found to synthesize gold nanoparticles. The size of the particles has been investigated by Bio-TEM before purification, following purification and after storing the particles for 3 months under refrigerated condition. Different characterization techniques like X-ray diffraction, Fourier transform infrared spectroscopy, and UV-visible spectroscopy have been used for analysis of the particles. The effect of reaction parameters such as pH and concentration of gold salt have also been monitored to optimize the morphology and dispersity of the synthesized gold nanoparticles. A pH range of 5 to 8 has favored the synthesis process whereas increasing concentration of gold salt (beyond 2 mM) has resulted in the formation of bigger sized and aggregated nanoparticles. Additionally, the cytotoxic nature of prepared nanoparticles has been analyzed using mouse mayo blast cancer C(2)C(12) cells at different time intervals (24, 48, and 72 h) of incubation period. The cells are cultivated in Dulbecco's modified Eagle's medium supplemented with fetal bovine serum with antibiotics (streptopenicillin) at 37°C in a 5% humidified environment of CO(2). The medium has been replenished every other day, and the cells are subcultured after reaching the confluence. The viability of the cells is analyzed with 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method.

Bio-synthesis of gold and silver nanoparticles from Candida guilliermondii and their antimicrobial effect against pathogenic bacteria.

In the present study we investigated the extra cellular synthesis of gold and silver nanoparticles by using the yeast Candida guilliermondii. The formation of noble metal nanoparticles was monitored by the UV-Visible spectroscopy. As prepared gold and silver nanoparticles showed distinct surface plasmon peaks at 530 nm and 425 nm respectively. Phase and morphology of the as synthesized materials were investigated by X-ray diffraction and electron microscopy techniques respectively. XRD patterns confirmed the formation of gold and silver nanoparticles with face centered cubic structures. Bio-TEM images showed the formation of near spherical, well dispersed gold and silver nanoparticles in the size range of 50-70 nm and 10-20 nm respectively. The biosynthesized nanoparticles were tested for their antimicrobial activity against five pathogenic bacterial strains. The highest efficiency for both gold and silver nanoparticles was observed against Staphylococcus aureus. A comparative study was also done to find the effect of chemically synthesized noble metal nanoparticles against the above test strains. Chemically synthesized particles had no antimicrobial activity against any of the pathogenic strains. The results obtained suggest that biosynthesized gold and silver nanoparticles can be used as effective antimicrobial agents against some of the potential harmful pathogenic microorganisms.

Synthesis and photocatalytic property of metal@SnO2 core-shell structure nanocomposites.

A simple soft-chemical technique for processing of metal@SnO2 nanocomposites with core-shell morphology is reported. In the present technique metal nanoparticles are prepared by chemical reduction technique followed by deposition of tin dioxide. Thus a core-shell type structure is produced. The phase and morphology has been investigated by X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). As prepared Au@SnO2 and Ag@SnO2 core-shell nanocomposites have shown distinct surface Plasmon band in the UV-visible spectrum at 540 nm and 400 nm respectively. The core-shell morphology is confirmed from the TEM images. XRD patterns have suggested the presence of noble metal and tin dioxide in the Cassiterite form. These metal@SnO2 nanocomposites have been successfully used for the photocatalytic oxidation of acetaldehyde. Our investigations suggest that presence of noble metal core in contact with tin dioxide shell enhances the photocatalytic activity of the material.

Spectroscopic investigation of S-Ag interaction in omega-mercaptoundecanoic acid capped silver nanoparticles.

This paper deals with the synthesis of omega-mercaptoundecanoic acid (MUA) capped silver nanoparticles (NPs) with an average size of 15nm by citrate reduction technique and spectroscopic investigation of S-Ag interaction. We have studied the interaction of thiol with silver NPs in aqueous medium by employing UV-vis, Raman, FT-IR, and photoluminescence spectroscopy. The shifting of silver surface plasmon band in the UV-vis spectra shows the stabilization of the silver nanoparticles by MUA. The disappearance of S-H stretching in both the FT-IR and Raman spectra and the shifting of the NMR signals of the protons in close proximity to the metal center supported the existence of the S-Ag interaction in MUA capped silver NPs. The morphology of the thiol protected silver NPs was investigated by transmission electron microscopy (TEM) and was found to be distinct and spherical entities.