Adsorption of As(V) by boehmite and alumina of different morphologies prepared under hydrothermal conditions.

Morphology-controlled materials at the micro- and nanoscale levels are of great significance to the design and application of materials. Stable and well-dispersed boehmite and alumina with different morphologies were fabricated under hydrothermal conditions. The nitrate, chloride, and sulfate aluminum salts yielded nanoplate, microspindle, and microsphere morphologies, respectively. Calcination of the prepared boehmite samples yielded alumina samples with retention of the morphologies. In comparisons of samples with identical morphologies, alumina exhibited better uptake of As(V) than boehmite; the As(V) concentration was analyzed by the standard molybdenum blue method. The adsorption capabilities of the morphologically controlled materials are ranked microspindle > microsphere > nanoplate. The impacts of process parameters, such as reaction time; initial As(V) concentration; solution pH; competing ions (Ca2+, Mg2+, NO3-, PO43-), which are common in most aquatic ecosystems; and co-contaminants (Cr(VI), Pb(II)), on removal efficiencies were examined. A well-defined mesostructure, superior surface area, chemical and electrostatic interaction, and surface charge distribution over the aluminol surface sites could be factors in the uptake of As(V). The design and synthesis of functional hierarchical micro- and nanostructured materials with the desired adsorptive properties, which are suitable for water treatment applications, can be achieved through environmentally benign hydrothermal fabrication.

Distinctive green recovery of silver species from modified cellulose: mechanism and spectroscopic studies.

The present study aimed to recover precious silver in order to identify the adsorption coupled reduction pathways that determine this process. A combination technique of adsorption and nanocrystallization was used to investigate the recovery of silver species from taurine-cellulose (T-DAC) samples. The non-synthetic route of nanocrystallization yielded spherical zero-valent silver sized ∼ 18 nm. Rate-controlling steps were modeled by adsorption parameters by the best fit of Langmuir capacity (55 mg/g), pseudo-second order curves, and exothermic chemical reactions. The T-DAC was an excellent sorbing phase for the treatment of silver-polluted waters over a broad range of pH (2.1-10.1) and varying ionic strengths (8.5-850 mM, as NaCl), which are the conditions often encountered in industrial and mining effluents. A good recovery of silver (40-65%) was also obtained in the presence of Cd(II), Co(II), Cr(VI), Ni(II), and As(V) at lower or equivalent concentrations with Ag(I), either from individually added metals or from all metal ions mixed together. Desorption was compared with a series of five eluents including complexing agents. In these experiments acidified thiourea yielded 86% desorption of Ag(I). Aqueous silver reduced to metallic silver on the surface of the T-DAC samples, which was confirmed by X-ray photo electron spectroscopy.

Protocol for development of various plants leaves extract in single-pot synthesis of metal nanoparticles.

This article is aimed to extend a simple protocol for preparation of various plant leaves extract and their application to green synthesis of the metallic nanoparticles. Five plant leaves extract showed mild reduction and stabilization ability for silver and gold nanoparticles (AgNPs and AuNPs) at room temperature. The particle size range varied from 25 to 42 nm and 21 to 47 nm for AgNPs and AuNPs, respectively. Plant leaves extract-mediated nanoparticles were characterized to confirm the shape, size, crystallinity, and content using different spectroscopic investigations. Differences in stability of nanoparticles at different pH were also measured by zeta potential.

Bioprospective of Sorbus aucuparia leaf extract in development of silver and gold nanocolloids.

At the present time the bioprospective field is a dynamic area of research. The rapid biosynthesis of silver and gold nanoparticles without using toxic chemicals is reported here. Sorbus aucuparia is omnipresent in Europe. The aqueous leaves extract of the plant were used as reducing agent for the synthesis of silver and gold nanoparticles from their salt solutions. The synthesized nanoparticles were spherical, triangular and hexagonal in shape with an average size of 16 and 18nm for silver and gold, respectively. Different extract quantities, metal concentrations, temperatures and contact times were investigated to find their effect on nanoparticles synthesis. The resulting silver and gold nanoparticles were characterized by transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). The concentration of residual silver and gold ions was measured by Inductively Coupled Plasma (ICP) spectroscopy. Silver and gold nanoparticle suspensions gave maximum UV-vis absorbance at 446 and 560nm, respectively. The XRD data illustrated characteristic diffraction patterns of the elemental silver and gold phases and the average size of the crystallites were estimated from the peak profiles by Scherrer method. FTIR spectra of the leaf extract before and after the development of nanoparticles were determined to allow identification of possible functional groups responsible for the conversion of metal ions to metal nanoparticles.

Utility of adsorbents in the purification of drinking water: a review of characterization, efficiency and safety evaluation of various adsorbents.

Clean drinking water is one of the implicit requisites fora healthy human population. However the growing industrialization and extensive use of chemicals for various concerns, has increased the burden of unwanted pollutants in the drinking water of developing countries like India. The entry of potentially hazardous substances into the biota has been magnifying day by day. In the absence of a possible stoppage of these, otherwise, useful chemicals, the only way to maintain safer water bodies is to develop efficient purifying technologies. One such immensely beneficial procedure that has been in use is that of purification of water using 'adsorbents'. Indigenous minerals and natural plants products have potential for removing many pollutants viz. fluoride, arsenic, nitrate, heavy metals, pesticides as well as trihalomethanes. Adsorbents which are derived from carbon, alumina, zeolite, clay minerals, iron ores, industrial by products, and natural products viz. parts of the plants, herbs and algal biomass offer promising potential of removal. In the recent years attention has been paid to develop process involving screening/pretreatment/activation/impregnation using alkalies, acids, alum, lime, manganese dioxide, ferric chloride and other chemicals which are found to enhance their adsorbing efficiency. Chemical characterization of these adsorbents recapitulates the mechanism of the process. It is imperative to observe that capacities of the adsorbents may vary depending on the characteristics, chemical modifications and concentration of the individual adsorbent. Removal kinetics is found to be based on the experimental conditions viz. pH, concentration of the adsorbate, quantity of the adsorbent and temperature. It is suggested that isotherm model is suitable tool to assess the adsorption capacities in batch and column modes. Safety evaluation and risk assessment of the process/products may be useful to provide guidelines for its sustainable disposal.

Application of natural adsorbent from silver impregnated Arachis hypogaea based thereon in the processes of hexavalent chromium for the purification of water.

Different industries generate huge amounts of chromium, both in solid and liquid form which leached out and find their way to the aquifers. Here we report the removal of Cr(VI) by the silver impregnated activated carbon developed from agricultural waste material at pH 3 from drinking water. Result revealed that adsorption of chromium(VI) on silver impregnated groundnut husk carbon was endothermic in nature. Thermodynamic parameters such as the entropy change, enthalpy change and Gibbs free energy change were found to be 1.68 kJ mol(-1)K(-1), 0.46 kJ mol(-1) and -4.38 kJ mol(-1), respectively. The measured adsorption kinetics is well described by a pseudo first-order kinetic model. The effect of flow rate, column depth and initial concentration of chromium(VI) on the removal of chromium by the impregnated adsorbent is presented. Scanning Electron Microscope (SEM), Electron Dispersive X-ray Analysis (EDX) and FTIR analysis show that the silver is impregnated on the surface. Shifts in the FTIR spectra suggest that dichromate binding occurs with silver and other functional groups and that silver treated groundnut husk carbon removes chromium. The 96h static acute toxicity test was conducted to ensure the safe disposal of the used adsorbent.

Adsorption of chromium(VI) on low cost adsorbents derived from agricultural waste material: a comparative study.

Two low cost adsorbents were prepared by using groundnut husk and were tested for the removal of chromium. All the experiments were carried out in batch process with chromium spiked samples of drinking water. Silver impregnated groundnut husk carbon and groundnut husk carbon were tested for the removal of chromium(VI). Effects of adsorbent quantity, pH, contact time and agitation rate were investigated on removal of chromium. The adsorption data were fitted well by Freundlich adsorption isotherm. Approximately, 97% of hexavalent chromium was removed at pH 3 within 5h. It was found that adsorbents chemically modified with an oxidizing agent demonstrated better chromium removal capabilities as compared to pure adsorbents in terms of their adsorption rate. On the basis of present studies, it can be concluded that groundnut husk carbon oxidized with silver treatment, has a higher chromium adsorption capacities.

Chlorination byproducts, their toxicodynamics and removal from drinking water.

No doubt that chlorination has been successfully used for the control of water borne infections diseases for more than a century. However identification of chlorination byproducts (CBPs) and incidences of potential health hazards created a major issue on the balancing of the toxicodynamics of the chemical species and risk from pathogenic microbes in the supply of drinking water. There have been epidemiological evidences of close relationship between its exposure and adverse outcomes particularly the cancers of vital organs in human beings. Halogenated trihalomethanes (THMs) and haloacetic acids (HAAs) are two major classes of disinfection byproducts (DBPs) commonly found in waters disinfected with chlorine. The total concentration of trihalomethanes and the formation of individual THM species in chlorinated water strongly depend on the composition of the raw water, on operational parameters and on the occurrence of residual chlorine in the distribution system. Attempts have been made to develop predictive models to establish the production and kinetics of THM formations. These models may be useful for operational purposes during water treatment and water quality management. It is also suggested to explore some biomarkers for determination of DBP production. Various methods have been suggested which include adsorption on activated carbons, coagulation with polymer, alum, lime or iron, sulfates, ion exchange and membrane process for the removal of DBPs. Thus in order to reduce the public health risk from these toxic compounds regulation must be inforced for the implementation of guideline values to lower the allowable concentrations or exposure.