Basu Saha

Greener and sustainable method for alkene epoxidations by polymer-supported Mo(VI) catalysts

A polybenzimidazole supported Mo(VI) (PBI.Mo) catalyst has been prepared and characterised. The catalytic activities of the PBI.Mo catalyst in epoxidation of alkenes with tert-butyl hydroperoxide (TBHP) as an oxidant have been studied under different reaction conditions in a batch reactor. As alkene representatives we have chosen cyclohexene, limonene, ?-pinene and 1-octene (a less reactive terminal alkene). The order of reactivity of the alkenes was found to be: cyclohexene>limonene>?-pinene>1-octene. The stability of each polymer catalyst was assessed by recycling a sample in batch reaction using conditions that will form the basis of the continuous process. The loss of Mo from each support has been investigated by isolating any residue from the reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions.

Removal of Cr(VI) by solvent impregnated resins (SIR) containing aliquat 336

Abstract Solvent impregnated resins (SIR) have been prepared by a wet-impregnation technique using two different polymer matrices, Diaion HP-20 and HP-2MG. Diaion HP-20 possesses a hydrophobic styrene–divinylbenzene polymeric structure whereas HP-2MG is a hydrophilic methacrylic based polymer. Aliquat 336 was employed as the extractant and acetone as the solvent for impregnation. Batch sorption studies have shown that solvent impregnated resins containing Aliquat 336 can be effectively used for the removal of hexavalent chromium from aqueous solutions. The Langmuir adsorption isotherm gave a satisfactory fit of the equilibrium data. A kinetic study has been performed for SIR at two different concentrations of Cr(VI) (2×10 −4 and 4×10 −4 M). A finite-bath diffusion-control model with changing bulk concentration was used for sorption of Cr(VI) by SIR. Increasing the impregnation ratio from 0.5 to 1.0 (g Aliquat 336/g polymer adsorbent) increased the breakthrough capacity in a column-mode sorption study. The Cr(VI) bound by the SIR has been quantitatively desorbed using 0.1 M NaOH–0.1 M NaCl mixture.

Physicochemical Characterization of Granular Ferric Hydroxide (GFH) for Arsenic(V) Sorption from Water

Abstract Physical and chemical characterization of granular ferric hydroxide (GFH) [e.g., scanning electron micrographs (SEM), X‐ray diffraction (XRD) analysis, Brunauer‐Emmett‐Teller (BET) and Langmuir surface area measurements, pore size distribution, pH titration, and zeta potential measurements] were conducted to determine its performance as an adsorbent for trace arsenic(V) removal. Speciation diagrams for arsenate and phosphate were produced for the present system. The equilibrium adsorption isotherms were measured over initial arsenate concentrations ranging from 100–750 µg/L and the pH range of 4–9. The adsorption of arsenate was found to decrease as the pH of the solution was increased, thus giving the optimal adsorption of arsenate onto GFH at pH 4. Adherence to the Langmuir isotherm was found at all pHs for the arsenate adsorption. The competitive effect of phosphate on the uptake of arsenate at pH 4 by GFH was investigated, outlining the greater affinity of GFH for arsenate adsorption compared to phosphate. The kinetic performance of GFH was assessed and the results were analyzed by applying a particle diffusion model.

Characterisation and sorption performance of a Hypersol-Macronet polymer and an activated carbon

The physical and chemical properties of a hypercrosslinked Macronet polymer, MN-600, have been compared with a charcoal based activated carbon, A1100, to evaluate their performance as sorbents for trace toxic metal removal from water. The characterisation includes scanning electron micrographs (SEM), BET and Langmuir surface area measurements, Fourier transform infra red spectroscopy (FTIR) analysis, sodium capacity measurement, pH titration, direct titration and zeta potential measurements. Pore size distribution data were analysed using the density functional theory (DFT) model. These sorbents were used in mini-column experiments for the removal of copper, zinc and nickel from aqueous solutions. The sorbents were regenerated by eluting with 0.1 M hydrochloric acid solution. These studies were performed to elucidate the relationship between sorptive performance and the physical and chemical structure of these materials.

Study of Activated Carbon After Oxidation and Subsequent Treatment: Characterization

Modified samples of a coal based activated carbon, Chemviron F400, were oxidized by nitric acid and air. Nitric acid oxidized samples were treated to remove humic type by-products of the oxidation process either by washing with sodium hydroxide solution or heating under vacuum. All samples were characterized to investigate the effect of the treatment and the chemical as well as the physical characteristics of these materials. The characterization included scanning electron micrographs (SEM), Brunauer-Emmett-Teller (BET) and Langmuir surface area measurements, Fourier Transform Infra Red spectroscopy (FTIR) analysis, sodium capacity measurement, pH titration and zeta potential measurements. The results indicated that there was a significant change in the structure of the precursor by oxidation and subsequent treatments. The ion exchange capacity of the carbon was markedly enhanced by the addition of oxygen containing weakly acidic surface groups.

Metal Sorption Performance of an Activated Carbon After Oxidation and Subsequent Treatment

Samples of a coal-based activated carbon, Chemviron F400, were oxidized by nitric acid and air to enhance their metal sorption capacity. Acid oxidized samples were either alkali washed or heated under vacuum to remove organic by-products formed during oxidation. Mini-column breakthrough experiments were conducted to determine the sorption performance of the samples for Cu, Ni, Zn and Cd uptake. The kinetic performance of these samples was assessed. Ion exchange performance of activated carbon samples was significantly enhanced on oxidation. Copper uptake capacity of a 24 h acid oxidized sample was increased by a factor of 60 compared to the unoxidized as-received material. Subsequent treatments reduced the metal uptake capacity of the oxidized carbons indicating that by-products produced during oxidation had metal binding ability. The metal sorbed samples were regenerated using 0.1M HCl solution.

Adsorption of Transition Metals from Aqueous Solutions by Modified Activated Carbons

Samples of a wood-based activated carbon, Ceca BGP, have been modified by acid and air oxidation. The physical and chemical characterizations of these samples in the form of scanning electron micrographs (SEM), Brunauer-Emmett-Teller (BET) and Lang-muir surface area measurements, Fourier transform infra red spectroscopy (FTIR) analysis, sodium capacity determination, pH titration and zeta potential measurements have been conducted to determine their performance as sorbents for trace transition metal removal. Density functional theory (DFT) has been used to analyse the pore size distribution data. The adsorption of transition metal ions (Cu, Zn, Ni and Cd) from aqueous solution onto these sorbents has been studied in batch equilibrium experiments. The influence of pH on metal sorption capacity has been examined. The kinetic performance of acid oxidized samples has been assessed and the results have been analysed by a particle diffusion model. The breakthrough experiments have been conducted in mini-columns to study the selectivity towards the desired metal ion. Results indicated that sorption capacity has been markedly enhanced by modification due to addition of weakly acidic functional groups to the surface of the carbons. The BGP OxII sample showed about 100 times higher copper capacity than conventional Ceca BGP. The metal sorbed carbons have been regenerated using 0.1M hydrochloric acid solution. Both modified samples demonstrated good regeneration efficiencies with 100% of the copper recovered with 0.1M HC1 solution during elution cycles compared to the amount of metal removed during the sorption experiments.

Electrochemically modified viscose-rayon-based activated carbon cloth for competitive and noncompetitive sorption of trace cobalt and lead ions from aqueous solution

Abstract A viscose-rayon-based activated carbon cloth (ACC) was electrochemically oxidized. As-received and electrochemically modified ACCs were characterized by sodium capacity, pH titration, elemental analysis, and Fourier transform infra red (FTIR) spectroscopy analysis. Cobalt and lead noncompetitive sorption capacities for electrochemically oxidized ACC (EO) are 4.3 and 3.9 times, respectively higher than those for unoxidized ACC (UO). Cobalt and lead competitive sorption capacities for EO are 4.1 and 5.1 times, respectively higher than those for UO. Sorption of cobalt and lead onto EO was by ion exchange, while that onto UO was by surface complex formation. Affinity order of metals sorbed by EO and UO is Pb2+ > Co2+. Metal uptake onto EO increased with an increase in solution pH.

N-Acyliminium Cyclization as an Approach for an Asymmetric Synthesis of the Pyrrolo[2,1-a]benzazepine Ring System

Abstract In this article, we report a facile asymmetric synthesis of the pyrrolo[2,1-a]benzazepine ring system based around a stereoselective N-acyliminium cyclization of a novel chiral lactam template. GRAPHICAL ABSTRACT