Touma B. Issa

Iron and aluminium based adsorption strategies for removing arsenic from water

Arsenic is a commonly occurring toxic metal in natural systems and is the root cause of many diseases and disorders. Occurrence of arsenic contaminated water is reported from several countries all over the world. A great deal of research over recent decades has been motivated by the requirement to lower the concentration of arsenic in drinking water and the need to develop low cost techniques which can be widely applied for arsenic removal from contaminated water. This review briefly presents iron and aluminium based adsorbents for arsenic removal. Studies carried out on oxidation of arsenic(III) to arsenic(V) employing various oxidising agents to facilitate arsenic removal are briefly mentioned. Effects of competing ions, As:Fe ratios, arsenic(V) vs. arsenic(III) removal using ferrihydrite as the adsorbent have been discussed. Recent efforts made for investigating arsenic adsorption on iron hydroxides/oxyhydroxides/oxides such as granular ferric hydroxide, goethite, akaganeite, magnetite and haematite have been reviewed. The adsorption behaviours of activated alumina, gibbsite, bauxite, activated bauxite, layered double hydroxides are discussed. Point-of-use adsorptive remediation methods indicate that Sono Arsenic filter and Kanchan™ Arsenic filter are in operation at various locations of Bangladesh and Nepal. The relative merits and demerits of such filters have been discussed. Evaluation of kits used for at-site arsenic estimation by various researchers also forms a part of this review.

Defluoridation behavior of nanostructured hydroxyapatite synthesized through an ultrasonic and microwave combined technique

The absorption performance of a nano-structured hydroxyapatite produced from a combined ultrasonic and microwave technique was examined for the removal of fluoride from contaminated water. The effect of physical and chemical parameters such as initial pH, contact time, initial fluoride concentration and temperature were investigated. The results indicated that the equilibrium adsorption data followed both the Langmuir and Freundlich isotherms, with a maximum monolayer adsorption capacity of 5.5mg/g at 298K. In addition, the kinetic studies have shown that the fluoride adsorption data followed a pseudo-second order model and that the intra-particle diffusion process played a significant role in determining the rate. The thermodynamic analysis also established that the adsorption process was endothermic and spontaneous. The initial and final fluoride loaded nano-hydroxyapatite samples were characterized using FESEM, TEM, XRD, FTIR and XPS methods. The analysis revealed that structural changes to the adsorbent had taken place.

Determination of inorganic phosphate by electroanalytical methods: A review

Determination of inorganic phosphate is of very high importance in environmental and health care applications. Hence knowledge of suitable analytical techniques available for phosphate sensing for different applications becomes essential. Electrochemical methods for determining inorganic phosphate have several advantages over other common techniques, including detection selectivity, stability and relative environmental insensitivity of electroactive labels. The different electrochemical sensing strategies adopted for the determination of phosphate using selective ionophores are discussed in this review. The various sensing strategies are classified based on the electrochemical detection techniques used viz., potentiometry, voltammetry, amperometry, unconventional electrochemical methods etc., The enzymatic sensing of phosphate coupled with electrochemical detection is also included. Various electroanalytical methods available in the literature are assessed for their merits in terms of selectivity, simplicity, miniaturisation, adaptability and suitability for field measurements.

Arsenic adsorption on goethite nanoparticles produced through hydrazine sulfate assisted synthesis method

Goethite nanoparticles synthesized using hydrazine sulfate as a modifying agent were evaluated for As(V) adsorption capacity. The nanoparticles were characterized for their morphological and structural features. The precipitated goethite particles were spherical with particle size of less than 10 nm. Batch adsorption study was carried out systematically varying parameters such as pH, contact time, initial As(V) concentration and adsorbent doses. The Langmuir isotherm represented the equilibrium data well and the estimated monolayer adsorption capacity at ambient temperature was 76 mg/g, which is significantly higher than most of the adsorbents reported in the literature. Adsorption kinetic data were better represented by the pseudo-second order kinetic model. Intra-particle diffusion played a significant role in the rate controlling process in the initial hour. Desorption study showed that the loaded adsorbent could be regenerated when treated with dilute sodium hydroxide solution of pH 13.

Synthesis and electrochemical characterization of new thioether-and ferrocene-containing copolymers

Random copolymers containing both ferrocene groups and thioether groups were synthesized by free-radical copolymerization of vinylferrocene and 2-(methylthio)ethyl methacrylate, and the random nature of the copolymerization was confirmed by spectroscopic studies. Copolymers with ferrocene-to-thioether ratios of 8 : 1 and 1.2 : 1 were used to modify the surfaces of gold electrodes, and the behaviours of the resulting surface-modified electrodes were investigated by cyclic voltammetry. The SMEs based on the copolymers showed superior stability compared to SMEs based on poly(vinylferrocene), with the most stable SMEs being formed from the copolymer with the higher proportion of thioether groups.

1,1'-Bis(11-mercaptoundecyl)ferrocene for potentiometric sensing of H+ ion in sulfuric acid media simulating lead acid battery electrolyte

The measurement of state of charge of a lead–acid battery by remotely monitoring H+ ion concentration of the battery electrolyte potentiometrically is much more attractive than the labour intensive method of measuring specific gravity of the electrolyte. Unfortunately, the traditional H+ potentiometric sensors such as the glass electrode cannot be used in the concentrated sulfuric acid battery electrolyte. This paper describes our work on the possibility of using 1,1′-bis(11-mercaptoundecyl)ferrocene Fc(C11SH)2 for measuring changes in the hydrogen ion concentration with a view to developing a miniaturized battery state of charge determining device. A cyclic voltammetric study of the electrochemical response and chemical stability of the alkanethiol ferrocene derivative redox couple is discussed. It is found that the oxidation peak potential of the investigated ferrocene is independent of pH in the range 2–10. However, in concentrated sulfuric acid media 1–5 M, which is more relevant to the targeted application, the oxidation peak shifts linearly to less positive potentials as a function of the acid concentration. The promise of this observation for determining state of charge of lead–acid batteries is explored.

Electrochemical Behavior of LiFePO4 in Aqueous Lithium Hydroxide Electrolyte

The electrochemistry of olivine-type iron phosphate (FePO4) as a battery cathode material, in aqueous lithium hydroxide (LiOH), has been investigated. The material forms intercalated LiFePO4 reversibly on electroreduction/oxidation. The formation of Fe3O4 phase, in addition to the regeneration of FePO4 during reverse oxidation of LiFePO4, also occurs. In this regard, the mechanism of FePO4 discharge/charge in aqueous LiOH differs from that in non-aqueous solvents.

Synthesis and Electrochemical Behaviour of Vinylferrocene-Propylene Sulfide-Graft Copolymers

Poly(vinylferrocene)–graft–poly(propylene sulfide) copolymers have been synthesized and were used to form surface-modified gold electrodes (SMEs) by self-assembly and drop-evaporation techniques. The electrochemical behaviours and stabilities of the polymer films in the SMEs in 1 M H2SO4 media were investigated by cyclic voltammetry. The SMEs exhibited the expected electrochemical response and it was confirmed that the electrontransfer reactions occurred on the surface of the electrode. Repeated cycling of new SMEs indicated that films containing sulfur groups were more robust than similar SMEs based on simple poly(vinylferrocene). The stability of the SMEs increased with increasing proportions of propylene sulfide in the graft polymers.

Smart Technology Applications in Business Environments

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Electrochemical lithium insertion into a manganese dioxide electrode in aqueous solutions

Intercalation of lithium into the vacant sites of a host compound can be achieved electrochemically using non-aqueous electrolytes. The use of aqueous electrolyte is less common because of the reactivity of many lithium intercalation compounds with water. Here we propose that lithium could be intercalated using aqueous solutions, lithium hydroxide as the electrolyte. The X-ray photoelectron spectroscopy (SIMS) data on the discharged material indicate that lithium is intercalated into the host structure of EMD without the destruction of its core structure. A significant improvement on cell performance was obtained by adding small amounts (<3 wt%) of titanium disulphide (TiS2) to the cathode.