A. Naeem

Surface properties of the mixed oxides of iron and silica

Amorphous synthetic mixed oxides of iron and silicon of varying composition (1.5 M SiO2:0.5 M Fe(OH)3, 0.5 M SiO2:0.5 M Fe(OH)3, 0.5 M SiO2:1.5 M Fe(OH)3) were prepared by sequential precipitation and their surface properties were explored. The Fourior transform infrared (FTIR), X-ray differactometry (XRD), Electron scanning microscopy (SEM), Electron probe micro-analysis (EPM) and Surface area measurement were used to characterize the synthetic mixed oxides. The point of zero charge (PZC) was determined by the salt addition and fast titration techniques. In the present investigation, the focus was on the surface charge, surface dissociation constants and PZC determination from the potentiometric titration data in the temperature range 293–323 K. During this study two common intersection points (CIPs) and two PZCs were observed for the mixed oxides, one corresponding to SiO2 and other to Fe(OH)3.

Chromium (III) removal by weak acid exchanger Amberlite IRC-50 (Na)

Chromium (III) sorption on a weakly macroporous cation exchanger Amberlite IRC-50 (Na) is studied as a function of time and temperature. The rate constant values for chromium (III) sorption are calculated both for film and particle diffusion processes. The temperature is found to have a positive effect on both the diffusional processes. The high values of energy of activation confirm the particle diffusional nature of the process. The pH changes in the system show a competition between the Cr(OH)(2+) and H(+) ions for the exchange sites of the adsorbent. Equilibrium data are explained with the help of Langmuir equation. Various thermodynamic parameters (DeltaH degrees , DeltaS degrees and DeltaG degrees) from chromium (III) exchange on the resin are calculated.

Cation exchange removal of Pb from aqueous solution by sorption onto NiO

This paper reports NiO as a novel and an efficient adsorbent for the removal of Pb from aqueous solutions. In the present investigation, Pb adsorption experiments on NiO were conducted on aqueous solution at different initial Pb concentration, pH of the solution and adsorption temperature. The mechanism of adsorption was observed to be an ion exchange between the surface proton and Pb in aqueous solution. Experimental data were best described by the Langmuir isotherms. The surface structure of the NiO before and after adsorption of Pb was analyzed by using FTIR spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analyses (EDX).

The Current Case of Quinolones: Synthetic Approaches and Antibacterial Activity

Quinolones are broad-spectrum synthetic antibacterial drugs first obtained during the synthesis of chloroquine. Nalidixic acid, the prototype of quinolones, first became available for clinical consumption in 1962 and was used mainly for urinary tract infections caused by Escherichia coli and other pathogenic Gram-negative bacteria. Recently, significant work has been carried out to synthesize novel quinolone analogues with enhanced activity and potential usage for the treatment of different bacterial diseases. These novel analogues are made by substitution at different sites—the variation at the C-6 and C-8 positions gives more effective drugs. Substitution of a fluorine atom at the C-6 position produces fluroquinolones, which account for a large proportion of the quinolones in clinical use. Among others, substitution of piperazine or methylpiperazine, pyrrolidinyl and piperidinyl rings also yields effective analogues. A total of twenty six analogues are reported in this review. The targets of quinolones are two bacterial enzymes of the class II topoisomerase family, namely gyrase and topoisomerase IV. Quinolones increase the concentration of drug-enzyme-DNA cleavage complexes and convert them into cellular toxins; as a result they are bactericidal. High bioavailability, relative low toxicity and favorable pharmacokinetics have resulted in the clinical success of fluoroquinolones and quinolones. Due to these superior properties, quinolones have been extensively utilized and this increased usage has resulted in some quinolone-resistant bacterial strains. Bacteria become resistant to quinolones by three mechanisms: (1) mutation in the target site (gyrase and/or topoisomerase IV) of quinolones; (2) plasmid-mediated resistance; and (3) chromosome-mediated quinolone resistance. In plasmid-mediated resistance, the efflux of quinolones is increased along with a decrease in the interaction of the drug with gyrase (topoisomerase IV). In the case of chromosome-mediated quinolone resistance, there is a decrease in the influx of the drug into the cell.

Removal of Co2+ ions from aqueous solution by cation exchange sorption onto NiO

Batch adsorption technique was used to study the adsorption of cobalt on NiO. The aim of this work was to examine the effect of pH, concentration and temperature on the ion exchange removal of Co2+ from aqueous solution by the NiO surface. We used Langmuir model to interpret the adsorption data. The Kurbatov-type plots were tested to determine the adsorption mechanism. The kinetics of Co2+ adsorption on NiO was best described by film diffusion model. A well-known thermodynamic equation was used to assess the enthalpy and entropy of the system. The thermodynamic data were indicative of the spontaneous nature of the endothermic sorption process of Co2+ onto the NiO.

Cation exchange removal of Cd from aqueous solution by NiO

Detailed adsorption experiments of Cd from aqueous solution on NiO were conducted under batch process with different concentrations of Cd, time and temperature of the suspension. The solution pH is found to play a decisive role in the metal ions precipitation, surface dissolution and adsorption of metal ions onto the NiO. Preliminary adsorption experiments show that the selectivity of NiO towards different divalent metal ions follows the trend Pb>Zn>Co>Cd, which is related to their first hydrolysis equilibrium constant. The exchange between the proton from the NiO surface and the metal from solution is responsible for the adsorption. The cation/exchange mechanism essentially remains the same for Pb, Zn, Co and Cd ions. The sorption of Cd on NiO particles is described by the modified Langmuir adsorption isotherms. The isosteric heat of adsorption (ΔH) indicates the endothermic nature of the cation exchange process. Spectroscopic analyses provide evidence that Cd is chemisorbed onto the surface of NiO.

Selectivity reversal and dimerization of chromate in the exchanger Amberlite IRA-400

Abstract Chromate sorption on the strong basic anion exchanger, Amberlite IRA-400 is studied as function of pH (2–11), temperature (20–40°C) and different initial concentrations (1.030–15.449 mmol/l). The sorption increases with the decrease in pH and increase in temperature. The ratios of chloride released/chromate sorbed are determined, which are found to decrease with the decrease in pH of the solution, while the effect of temperature on mole ratios is negligible. It is suggested that the chromate sorption takes place initially as CrO 4 2− followed by HCrO 4 − . The differential isosteric heats of adsorption, Δ H , are also computed which show the process to be endothermic in nature. IR spectra of chromate sorption on the chloride form of the resins have been studied as a function of pH at 20°C. These spectra reveal the dimerization of HCrO 4 − to Cr 2 O 7 2− at lower pH inside the exchanger.

Equilibrium and kinetics studies of arsenate adsorption by FePO4

The present work is focusing on removal of arsenate from aqueous solution using FePO4. The equilibrium study regarding the removal of arsenic by FePO4 was carried out at 298, 308, 318 and 328K. Langmuir parameters were found to increase with the increase in temperature indicating that the adsorption is favorable at high temperature. Kinetic study of arsenate adsorption on FePO4 was also carried out at different temperatures and at pH 6 and 8. Different kinetic models were used to the kinetic data amongst which pseudo second order model was best fitted. The mechanism of the adsorption kinetics was investigated by employing intraparticle diffusion and Richenberg models. The energy of activation (Ea) was found to be 30 and 35.52kJmol(-1) at pH 6 and pH 8, respectively, suggesting chemisorption nature of the adsorption process. The negative entropic values of activation signified the existence of entropy barrier while the positive ΔG(#) values indicated the existence of energy barrier to be crossed over for the occurrence of a chemical reaction. Both the spectroscopic studies and increase in equilibrium pH reveal the anion exchange removal of arsenate from aqueous solution to the solid surface.

Heterogeneous Fenton degradation of organic dyes in batch and fixed bed using La-Fe montmorillonite as catalyst

The La-Fe montmorillonite (La-Fe MMT) composite was synthesized by a simple precipitation method and was used for the degradation of dyes in both batch and fixed bed experiments. X-ray diffraction (XRD) and high-resolution transmission electron microscope analysis (HRTEM) confirmed the existence of Fe2O3 and La2O3 in the composite. The presence of La enhanced the degradation efficiency of dyes by the composite at neutral pH and results in little iron leaching consequently increasing the lifetime. More than 97% and 96% removal of the MB and RhB (100mg/L each) by the La-Fe MMT Fenton system could be achieved in less than 1h. The catalyst also exhibited excellent efficiency in fixed bed reactor with 91% MB degradation corresponds to 65% COD removal, even after 200h of use. The factors such as solution pH, catalyst dosage, H2O2 dosage and temperature on the degradation of dyes were investigated. Fluorescence and quenchers experiments indicated that OH was the main reactive species for the degradation of dyes. Due to the low cost, efficient reactivity, high stability and low metal leaching, the La-Fe MMT possesses a great potential to be a green catalyst for the heterogeneous Fenton-like degradation of hazardous dyes.

Selective Removal of Chromates by Macroporous Exchanger Amberlyst A-21

Sorption studies of chromate on weakly basic macroporous anion exchanger Amberlyst A-21 were performed as a function of pH (2 - 9), temperature (20 - 40 °C) and concentration (0.4 - 80 mmol.l−1). Chromate sorption was observed to decrease with the increase in initial pH of the solution, with a sorption maxima at pH 2 and increased with the increase in temperature. The changes in pH and in the ratio of chloride ions released to chromate ions sorbed suggested that the anion exchange process was accompanied by hydrolysis and Donnan invasion. The FTIR spectra and isosteric heat of sorption besides showing the hydrolysis / Donnan invasion of resin under different experimental conditions of concentration, pH and temperature also showed the dimerization of the chromate species inside the resin phase.