The purpose of this work is to investigate the batch removal of Pb2+ from aqueous solutions using marine dried brown seaweed S. baccularia. Seaweed was used as a low-cost adsorbent. The effects of pH, contact time, temperature, shaking speed and the concentration of the Pb2+ solution were examined in the biosorption process with S. baccularia. The results showed that when S. baccularia was used as the bioadsorbent, the optimum pH, Pb2+ concentration, equilibrium time, temperature, and shaking speed were 3, 20 ppm, 120 min, 30°C, and 120rpm. The equilibrium adsorption data are fitted to the Langmuir isotherm model. The separation factor (RL) in the experiment was less than one (<1), indicating that the adsorption of metal ions on Sargassum baccularia adsorbent is favorable. The calculated activation energy (Ea) implies that the adsorption of Pb (II) on brown seaweed is a physical adsorption. Thermodynamic results show that adsorption occurs spontaneously in nature.

Contamination of wastewater by toxic metals is a global environmental concern. In this study, the possibility of using inactive (dead) Sargassum bacilluria powder as a natural adsorbent was investigated in the removal of cadmium from aqueous solutions. The biosorption process was found to be highly dependent on a set of variables such as pH, temperature, contact time, shaking speed and initial metal concentration. The results showed an optimum pH value, (6.0) for cadmium, where was the biosorption capacity (842.15±0.252) for cadmium, and the lowest biosorption value for Cd was found at pH 2.0. The optimum temperature in this study was 30 °C. The time required for equilibrium was investigated over a period of 360 min and found to be 180 min. The capacity of biosorption increased with increasing shaking speed, and the highest uptake value was found at 120 rpm. The maximum removal of Cd+2 was found at 20 mg/l. The models Freundlich and Langmuir were used to study the equilibrium process of these systems. The Langmuir model was found to be more suitable for the interpretation of these systems by the value of the correlation coefficients higher than 0.99. Brown seaweed powder is an effective, low-cost, .and environmentally friendly adsorbent for removing metals from aqueous solutions, according to the results obtained.

We have described the development of electrochemical nano sensor for the detection of total arsenic in groundwater, soil, food and honey samples based on the formation of gold nanoparticles. Screen printed carbon electrodes were modified with gold nanoparticles and linked with 1,6-hexanedithiol self-assembled monolayers. The electrodeposition of Au nanoparticles was applied in 10 mL of the solution that totally cover the screen-printed carbon electrode while applying a constant potential of –0.4 V (vs. Ag within SPCE) for 600 sec. Cyclic voltammetry was used to characterize the gold nanoparticles before and after modified with 1,6-hexanedithiol self-assembled monolayers on screen printed carbon electrode. Square wave anodic stripping voltammetry with multi point standard addition method was examined for the detection of As(III) and As(V) on Au NPs-1,6-hexanedithiol modified screen printed carbon electrode under optimized conditions. As(III) and As(V) was firstly, deposited for 60 seconds by the reduction of arsenic in buffer solution: (citric acid, sodium chloride and ascorbic acid pH 2.0), followed by As stripping between –0.20 and 0.35 V at the following parameters: scan rate: 100 mV s–1, frequency: 60 Hz, amplitude: 0.025 V and increment: 5.0 mV. it was found that Au-NPs with 1,6-hexanedithiol modified screen-printed carbon electrode had a highest anodic stripping peak current at 0.201 V. The limit of detection value for arsenic was identified to be 1.7 ng ml –1. Also, the electrochemical nanosensor showed excellent reproducibility and high stability. The developed method was successfully applied to detect total arsenic in ground water, soil and honey samples.

Abstract

It has been described the development of electrochemical nano sensor for the detection of mercury ions from aqueous solutions based on the formation of polyaniline nanoparticle films. Screen printed carbon electrodes were modified with polyaniline nanoparticles. Electropolymerization of polyaniline nanoparticles was performed by the pulsed potentiostatic method. The sample of polyaniline nanoparticles was prepared by repeating the potential step process three times. Structural and morploigcal characterization of polyaniline nanoparticles modified screen printed carbon electrode was performed using Fourier Transmission infrared (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). PANI nanoparticles were spherical shaped having an apparent dimeter varying from 20 to 45 nm. Square wave anodic stripping voltammetry was used for the detection of Hg(II) on PANI NPs modified screen printed carbon electrode under optimized conditions. Hg(II) was deposited for 60 seconds by the reduction of Hg(II) in buffer solution:(citric acid and sodium chloride pH 2.30), followed by Hg stripping between 0.3 and 0.8 V at the following parameters: Scan rate: 100 mV s-1, frequency: 60 Hz, amplitude: 0.025 V and increment: 4.0 mV. it was found that the PANI NPs modified screen printed carbon electrode had a highest anodic stripping peak current in solution of pH 2.30. The limit of detection value for Hg(II) was found to be 2.50 ± 0.03 ppb. The limits of detections determined are below the corresponding guideline value from the World Health Organization (WHO). In addition, the modified nano electrode exhibited excellent reproducibility and high stability. The developed method was successfully applied to determine Hg(II) in real water samples with satisfactory results.

This study highlights the mechanism of formation for Bentonite clay surface properties. It investigates specific gravity and the influence of physicochemical characteristics on clay stability of structural forces on adsorbed water molecules. In particular, it describes the chemical composition, as well as cation exchange capacity (CEC). Bentonite clay is collected from the Murzuq city located 1150 km south of Tripoli i.e. southernmost town of Libya. The CEC value is leached by 500ppm Ca+2 at pH=8 equaled 84.5 mmoles/kg. While at pH=2, the value is (20.5 mmoles/kg). The leaching process is carried out by 500ppm K+ using flame emission photometer. The CEC value at pH =8 for sample is 91.5 mmoles/kg. Also the specific gravity is found to be 2.597. This value is in agreement with the obtained standard values for Wyoming (USA). The % MxOy of the clay is calculated by gravimetric method as follows: SiO2, 53.75; Al2O3, 21.46; Fe2O3, 1.4;CaO, 0.97; MgO, 2.13, and agreed with the XRF analysis as follows: SiO2, 54.93; Al2O3, 21.46; Fe2O3, 1.71; MgO, 3.18 ; CaO, 0.81; Na2O, 5.48; K2O, 0.54; TiO2,0.32. The results are adequately approximate and reasonable for both methods. The percent is very limited for trace elements Pb, Cr, Cd, Cu, Fe, and Zn. In the sample, it is about 0.21%. The result of XRD analysis (intensities) for sample is presented as follows: 50% quartz, 50% kaolinite, 5% Analcine, 7.5% Illite, 5% Natrolite, 10% Nontronite, 7% Montmorillonite. The formula calculation depends on the purity of clay and consequently the structural formula for Libyan Bentonite is: K0.094Na1.45Ca0.118 (Al2.92Fe0.175Ti0.033Mg0.646)VI( Al0.52Si7.48 …

Abstract: Monitoring the concentrations of heavy metals in natural and waste water at and below the level of their maximum permissible concentrations is an urgent environmental problem. Hence, new procedures for the preconcentration of heavy metals with their subsequent determination by different methods are required. Along with other sorbents, significant attention is attracted to polymer chelating sorbents, which provide individual or group extraction of trace elements, eliminate matrix effects, and provide high concentration factors. The effect of the various parameters such as electrochemically and chemically synthesis methods, physical oxidation state of the polymer, polymer thickness, solution pH and metal ion concentration on the adsorption, kinetics and efficiency were investigated. The results showed a vary broad concentration range of the heavy metals from (0.05 to 10 mg/L) can be adsorbed on different kinds of polymers at different pH values and different efficiently. The adsorption capacity of the polymer to different concentrations of heavy metals was evaluated as the milligram of metal ions by one gram of various forms of the polymer. The DC conductivity measurements were also employed on the solid polymer before and after adsorption of metal ions. The experimental adsorption date was fitted to different mathematical isotherms to estimate the binding constant of heavy metals with the polymer in both single and mixed ion solutions. The method provides the extraction of analytes from natural water of complex composition containing high concentrations of alkali, alkaline-earth and other elements and is characterized by rapidly, selectivity, low detection limits, and a high reproducibility of the results. The relative standard deviation is 2-4%. The technique was test with real waste water samples.  

 carbon materials2 through their unique combination of excellent processability and high carbon yield. The enediyne functionality of the monomers undergo a thermal Bergman cycloaromatization reaction that yields reactive naphthalene diradicals which polymerize to form polynapthalene.(Figure 1) The tetrafunctionality of the monomers allows for both a higher processing window due to extensive branching and ultimately the formation of network polymers. The high carbon yield results in less shrinkage of the polymer upon pyrolysis to the glassy carbon state. This allows for the faithful templating of carbon structures from a polymeric precursor.

Hydrogen fuel cell electrodes require several properties for optimum performance. An ideal electrode would have as high a surface area as possible with an uniform dispersion of nano-scale catalyst particles attached to the surface. The electrode must be electrically conductive and have good mass transport for products and reactants. Carbon supported platinum is the best known catalyst for the oxidation of hydrogen at the anode and the reduction of oxygen at the cathode of a proton exchange membrane fuel cell (PEMFC) 3. The material also must have good compatibility with the material used for the proton exchange membrane in the membrane electrode assembly (MEA), usually a sulfonated fluoropolymer such as Nafion. We have undertaken a study to prepare a high surface area carbon material through a BODA templating method which can then be functionalized with both well dispersed platinum nanoparticles …

The effect of Aldrich humic acid (HA) on the mobility of {sup 137}Cs, {sup 85}Sr, {sup 152}Eu and {sup 239}Pu radionuclides was studied in Ca-montmorillonite suspensions. Verified 2-sites-2-species (2s2s) models correspond to an intensive interaction of all elements with humificated surface, what is in a remarkable contrast with the weak complexation of cesium and even strontium in solutions - the neutral ligand interaction constants {beta} (l/mol) are log {beta} < -9.9 and 7.56 {+-} 0.21 for Cs and Sr, respectively. The result for europium complexation in solution, log {beta} = 12.49 {+-} 0.18 is in a good agreement with literature data. For plutonium(IV) not only high proton competitive constant in solution was obtained, log {beta} = (-0.67 {+-} 0.32)+3pH, but also a strong chemisorption, which at high concentrations of humic acid (above 0.05 g/l) indicates the formation of bridge humate complexes of plutonium on the humificated surface. Logarithms of heterogeneous interaction constants ({beta}{sub 10}, l/g) of the elements with surface humic acid are 4.47 {+-} 0.23, 4.39 {+-} 0.08, and 6.40 {+-} 0.33 for Cs, Sr, and Eu(III), respectively, and the logarithm of the proton competitive constant ({beta}{sub 24}, l/g) for Pu(IV) -3.80 {+-}0.72. Distribution coefficients of humic acid and metal humates between 0.01 g HA/l solution and montmorillonite were derived as log K{sub d}(AH) = -1.04 {+-} 0.11, log K{sub d}(EuA) = 1.56 {+-} 0.11 and log K{sub d}(PuA) = 2.25 {+-} 0.04, while the values for Cs and Sr were obtained with very high uncertainty. Speciation of the elements on montmorillonite surface is illustrated as a function of equilibrium concentration of humic acid in solution and of pH.

Abstract

The high-performance size-exclusion chromatography (HPSEC) and radiochromatography (HPSERC) was used for the identification of radiocesium and radiostrontium interaction with humic acid. It was found that the behavior of humic acid on size-exclusion chromatography is sensitive to the salt concentration and pH of the mobile phase. At lower ionic strength and in acidic region of pH, the Aldrich humic acid exhibited three main fraction within the ranges > 760 kDa, 25-100 kDa and < 5 kDa. Radiocesium was found in the low-molecular fractions (< 1 kDa) of humic acids but radiostrontium interacts preferably with the fractions of humic acid of molecular weight within the range 2-5 kDa. (author) 27 refs.

The effect of humic acid addition on the capacity of inorganic sorbents to sorb radioactive cesium and strontium was studied on montmorillonites in a calcium and potassium form. The Sips isotherm for humic acid sorption and multisite distribution model of ion sorption was found to suit well for the description of mobility of ions as a function of equilibrium humic acid concentration as a single variable at given pH and type of silicate. Complexation of the ions was of minor importance at the conditions investigated. Influence of humic acid on the specific radiocesium interception potential (SRIP) was also evaluated

الوصف

A standard analytical technique for determination of the partial ion exchange capacity of mineral or soil for selective uptake of cesium, the specific radiocesium interception potential (SRIP) is formulated and theoretically discussed. The method is based on the determination of a retained, leached or sorbed fraction of carrier-free cesium-137 in soil contacted with 0.01M KNO ₃ -0.01M Ag thiourea complex solution at the phase ratio solution:sorbent 10 ml:0.1 g. Reliability of the method is discussed in connection of radiocesium carrier and humic substances presence.

In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm⁻³ NaCl was in order zeolite > NiFeCN−SiO₂ > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN−SiO₂ was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN−SiO₂ and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN−SiO₂ > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.