Effects on the removal of Pb2+ from aqueous solution by crab shell

The effects of temperature, pH, chitin and chitosan on Pb²⁺ removal by crab shell were investigated. Pb²⁺ removal by crab shell was greater than that of chitin and chitosan, indicating that chitin did not contribute to Pb²⁺ removal by crab shell. The quantity and rate of Pb²⁺ removal increased as the pH value increased. The rate of Pb²⁺ removal increased with increased temperature, but the maximum amount of Pb²⁺ removal was constant irrespective of temperature. Metal ions (K⁺, Na⁺, Mg²⁺, Ca²⁺) were released from crab shell concomitant with Pb²⁺ removal by ion exchange. The amount of Ca²⁺ released was greater than any for other metal ions in both Pb²⁺ and Pb²⁺‐free solutions. The amount of Ca²⁺ released in Pb²⁺ solution was greater than that in Pb²⁺‐free solution, whereas CO₃^2? release in Pb²⁺ solution was less than in Pb²⁺‐free solution. Pb²⁺ removal was mainly a consequence of dissolution of CaCO_3(s) with consequence precipitation of Pb₃(CO₃)₂(OH)_2(s) and PbCO_3(s). Pb²⁺ accelerated the dissolution of CaCO_3(s) by ion exchange and the precipitation occurred both at the surface and in the inner part of the crab shell. © 2001 Society of Chemical Industry     

LAMELLAR INORGANIC ION-EXCHANGERS.BEHAVIOUR OF γ-TITANIUM PHOSPHATE IN THE H+/Na+ION-EXCHANGE

H⁺/Na⁺ ion-exchange in Ti(HP0₄) ₂.2H₂0 (γ TiP) was studied. The exchange isotherm, titration and hydrolysis curves at 25°C were obtained. In initially acidic or neutral solutions the 25% of the material exchange capacity was reached. The half-exchanged phase was obtained by additions of stoichiometric amounts of NaOH, with hydrolysis lower than 3% and at acidic equilibrium pH. For additions of NaOH over 4.0 me/g Y-TiP conversions higher than 50% were reached with an increase in the values of the equilibrium pH and the hydrolysis. The evolution of the solid was followed by X-ray diffraction. The substituted phases of samples dried in air at room temperature showed the following hydration degrees: ----H N ----------------------- conversion phase stored over P205 was dehydrated originating H1-5Na0.5 When i t is heated at 80°C-200°C i t transformed i n t o mixtures o f iTFi ( 9. 1 A ) and HNa (10.1 Å ).     

IR spectroscopy investigations of acidic character of carbonaceous films oxidized with HNO3 solution

Sorption of bases on carbonaceous films from liquid (NaHCO₃, Na₂CO₃ and NaOH solutions) and gaseous phases (NH₃) was studied using IR spectroscopy. Parallel to the IR spectroscopy the exchange of H⁺ ions for Na⁺ ions was determined by alkalimetry as well and NH₃ sorption isotherms were measured. The IR spectra indicate that chemisorption of NH₃ leads to the formation of amide structures and ammonium salts of carboxylic acids. The surface acidic centers on the films oxidized with HNO₃ solution are centres of Bronsted type.     

Removal of Chlorophenols from Aqueous Solution by Anion-Exchange Resins

Abstract

The effects of pH value and chloride ion concentration on the removal of chlorophenols from aqueous solutions by Purolite A-510 resin [macroreticular polystyrene-divinylbenzene resin with R(CH₃)₂(C₂H₄OH)N⁺ group] are discussed by the species distributions of chlorophenols. Those chlorophenols include phenol, 2-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. The investigations showed that the chlorophenols could be removed effectively at alkaline conditions where the ion-exchange reaction was dominant. Also, the removal of chlorophenols increased with the number of chlorine atoms on the chlorophenols. The removal of chlorophenols via the ion-exchange reaction was hindered by the presence of chloride ions. The effect of chloride ions, however, was diminished in acidic solutions where the adsorption reaction was dominant. The proposed equilibrium model, which considers both adsorption and ion-exchange reactions, adequately describes the sorption behavior of chlorophenols. The partition constants of the protonated chlorophenols can be estimated from the octanol/water partition coefficients of the phenolic compounds.     

Removal of Co, Cs, and Zr radioisotopes from aqueous solutions using cellulose iminodiacetic acid chelating cum cation-exchanger

The iminodiacetic acid group containing resin acts as a chelating ion exchanger as well as a weakly acidic cation exchanger, depending upon the species present in the solution. Iminodiacetic acid group has been incorporated onto cellulose by a modified Porath's method of functionalization of polysaccharides. The resin has been used for removal of ⁵⁸Co, ¹³⁴Cs, and ⁹⁵Zr radioisotopes from their separate aqueous solutions. ⁹⁵Zr as [Zr(OH)₂(H₂O)₄]⁸⁺ tetrameric species is adsorbed from the aqueous solution at low pH through cation exchange cum chelate formation. ⁵⁸Co as Co²⁺ is complexed with the resin. ¹³⁴Cs as Cs⁺ is exchanged with equivalent amount of H⁺ ions. Cs⁺ was eluted from resin using 0.3N HCl, Co²⁺ with 4N HCl and Zr(IV) with 5N HCl. Final disposal of the resin can be done by encapsulation in the cement concrete.     

pH-dependent anodic reaction behavior of tungsten in acidic phosphate solutions

Potentiodynamic and potentiostatic polarization experiments, and the electrochemical impedance spectroscopy technique were used to study the pH dependent anodic behavior of tungsten (W) in acidic phosphate solution. At very low pH values (pH < 2.6) the dissolution of tungsten was H⁺-assisted and as the pzc (pH 2.6) was approached H₂O-assisted dissolution became main dissolution pathway. Above pH 2.6, however, tungsten dissolution was OH⁻-assisted. The thickness and dielectric properties of the W-oxide barrier layer were observed almost pH independent at corrosion potential. The oxygen vacancy transport across the oxide film caused a capacitive response at very acidic solutions (pH ≤ 3.5) and as the dissolution rate increased (pH > 4.5) the capacitive response turned into the inductive one due to the accelerating effect of negative surface charge in Tafel region. The inductive response in the tungsten impedance spectra shifted to a very low frequency range as the tungsten dissolution rate decreased in the pseudo-plateau and potential independent regions. Fitting of the tungsten impedance data according to the surface charge approach showed that the resistance to the defect migration increased as the pzc was approached and the film capacitance decreased above pH 3.5 due to the accelerated formation rate of the non-protective loosely bound hydrated layer on the metal oxide surface.     

Evidence for the rate determining step at the solution—oxide film interface in the anodic growth of thin oxide films at platinum and nickel electrodes in aqueous solutions

The rates of growth of anodic oxide films at Pt in acid and alkaline solutions and Ni in alkaline solutions are compared. In acid solutions, the rates are pH independent. In alkaline solutions, they are affected by pH. The exchange current densities, i₀, in alkaline solutions increase one decade as pH increases one unit. The dependence of i₀ on pH is not expected for the model of high field assisted formation of films with either the step at the metal—oxide film interface or a step within the film as rate determining. It is suggested that a process at the oxide film—solution interface is rate determining with OH^? as reaction species. In acid solutions, too, this step is rate determining but with H₂O as reacting species. The possibility that this step can be rate determining is usually overlooked in analyses of growth of anodic films.     

Effect of potassium ion on the stability and release rate of hydrogen peroxide encapsulated in silica hydrogels

Hydrogen peroxide (H₂O₂) is encapsulated in silica hydrogels using sol‐gel method and the effects of the K⁺ : Na⁺ ion ratio on gelation time, hydrogel structure, stability, and release rate of H₂O₂ were investigated. As the amount of K⁺ ions increased relative to the amount of Na⁺ ions at the same pH, the gel structure became less compact and the pore diameter increased. Hydrogen peroxide retention values up to 90 and 80% were observed at the end of 7 and 20 days, respectively, in the presence of K⁺ ions at low pH values when the initial H₂O₂ concentration was 19.9 wt %. Release rate of hydrogen peroxide decreased with decreasing pH for the two K⁺ : Na⁺ ion ratios studied. This work presents an environmentally friendly, low cost, and easy to scale up method to increase the stability of high initial concentrations of H₂O₂ at room temperature and customize the release rate. © 2016 American Institute of Chemical Engineers AIChE J, 63: 409–417, 2017     

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation of H₂O₂ electrogeneration in a flow electrochemical reactor with RVC cathode, and the optimization of the O₂ reduction rate relative to cell potential. A study of the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H₂O₂ is also reported. Experiments were performed in 0.3 M K₂SO₄ at pH 10 and 2.5. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus Pt for both acidic and alkaline solutions. Then, 100 mg L⁻¹ of 2,4-D was added to the solution. 2,4-D, its aromatic intermediates such as chlorophenols, chlororesorcinol and chlorinated quinone, as well as TOC were removed at different rates depending on pH, the use of UV radiation and addition of Fe(II). The acidic medium favored the hydroxylation reaction, and first order apparent rate constants for TOC removal ranged from 10⁻⁵ to 10⁻⁴ s⁻¹. In the presence of UV and iron, more than 90% of TOC was removed. This value indicates that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as more biodegradable light aliphatic compounds.     

Diffraction Studies on Concentrated Aqueous Hydrochloric Acid Solutions

X-ray diffraction and neutron diffraction experiments with H/D isotopically substituted aqueous 21 mol% hydrochloric acid solutions were carried out in order to obtain detailed features concerning the intermolecular hydrogen-bonded structure in highly concentrated aqueous acidic solutions. Structure parameters, namely, intermolecular distance, root-mean-square amplitude, and coordination number, for the nearest neighbor H₃O⁺···H₂O interaction were determined from the least-squares-fitting analysis of the observed X-ray interference term. These were, respectively, r(H₃O⁺···H₂O) = 2.45(1) Å; l(H₃O⁺···H₂O) = 0.11(1) Å; and n(H₃O⁺···H₂O) = 1.8(1). The intermolecular nearest neighbor distances, r(H···H) = 2.02(5) Å and r(O···H) = 1.69(2) Å, were determined from the least-squares fit to partial structure factors, a_ij (Q), derived from the observed neutron intermolecular interference terms for sample solutions with different H/D isotopic ratios. The present values of intermolecular distances are significantly shorter than those for pure liquid water, implying that extremely strong hydrogen bonds exist in concentrated aqueous acidic solutions.     

Removal of toxic aqueous ions using amorphous AlPO4

Aluminium phosphate (AlPO₄) was characterized using X-ray diffractometry (XRD), Fourier Transform infrared (FTIR), point of zero charge (PZC) and dissolution studies. XRD showed the sample to be amorphous, FTIR confirmed the presence of OH groups on the surface and PZC was determined at pH 3.45. The dissolution study illustrated a decrease in dissolution with an increase in the pH. Potentiometric titration data were fit to the Gaines–Thomas equation, which showed that AlPO₄ is a weakly acidic ion exchanger. Sorption studies were carried out at pH 4–6 and temperatures 293–323 K. The uptake of metal ions was observed to increase with an increase in the pH and temperature. The surface selectivity towards metal ions was found in the order Pb²⁺> Cu²⁺> Cd²⁺. Sorption data were fit to the new equation derived from the proposed mechanism for metal ion uptake. Various parameters such as stoichiometry of the surface H⁺ ion release, equilibrium constant, standard enthalpy, entropy and free energy changes were evaluated from the plots. The values of all these parameters were found to be closely related to the values reported in the literature.     

Electrochemical behavior of AZ91D magnesium alloy in phosphate medium—part I. Effect of pH

The influence of pH on the corrosion behavior of Mg-based AZ91D alloy was investigated in a constant composition phosphate medium using various electrochemical techniques, complemented with surface analysis data. The studied solutions were 0.1 M H₃PO₄, NaH₂PO₄, Na₂HPO₄ and Na₃PO₄ having pH values of 1.8, 4.5, 9.1 and 11.8, respectively. Spontaneous passivation was substantiated from monitoring the continuous positive shift of the open circuit corrosion potential with both immersion time and solution pH. The impedance data indicated more improvement in the insulating properties of the corrosion products formed on the alloy surface with increase in pH. The electrolyte pH plays a determinant influence on surface film properties, as films formed in phosphate solutions with higher pH values are thicker, thus affording better protection for the alloy than those formed in acidic solutions. Good agreement was observed between the results obtained from electrochemical techniques and those from EDX and XRD examinations. The alloy is more susceptible to corrosion in acidic phosphate solutions than in the alkaline ones. Crystalline magnesium (Mg), magnesium hydride (MgH₂) and magnesium oxide (MgO) were found to be the main constituents of the surface film after holding for 2 h in the acidic phosphate medium.     

Local pH-controlled reactivity investigations by thin-layer scanning tunnelling microscopy

A newly designed thin-layer STM (TLSTM) technique is presented based on a microfabricated probe combining an electrolytic STM probe with an annular iridium oxide microelectrode operating as a potential-controlled generator or scavenger of H⁺. This TLSTM configuration can be used to combine in situ STM studies of electrode processes with the simultaneous investigation of H⁺ flux integrals associated with the electrode reaction. In this paper, the technique is applied to investigate the H⁺ exchange behaviour of electropolymerised polyaniline films and associated STM-relevant properties in 0.5 M NaClO₄+10⁻² M HClO₄. For a polyaniline film kept in the intermediate (emeraldine) oxidation state at 0 mV versus MSE it is shown that its thickness increases due to H⁺ insertion if the pH is lowered from pH 2 to ca. 1.6, and that its conductivity decreases significantly if the pH is increased from 2 to ca. 12. In a second experiment, where the exchange of H⁺ at pH 2 is monitored during film oxidation and reduction within the potential range of both redox transfer steps, it is shown that significant exchange of H⁺ occurs only in the interval of the second (emeraldine/pernigraniline) redox transfer.     

Removal of Malachite Green (MG) From Aqueous Solutions by Adsorption,Precipitation, and Alkaline Fading Using Talc

Malachite green (MG), which is primarily used as a dye, is a chemical that is listed as a class II health hazard because of its toxicity to humans and the environment. Adsorption is frequently used to remove this cationic dye from aqueous solutions. Structural changes of the molecule should be considered during removal, because MG (or chromatic MG⁺ at neutral pH) turns into protonated MG (MGH⁺) at acidic pHs and a carbinol base at basic pHs. In this study, batch sorption experiments were conducted to remove MG from aqueous solutions using talc. We studied specific removal behaviors and mechanisms of the MG for different pH solutions, including adsorption, precipitation, and alkaline fading.     

Determination of analgesics in pharmaceutical formulations and urine samples using nano polypyrrole modified glassy carbon electrode

Three analgesics (acetaminophen, acetylsalicylic acid, and dipyrone) were determined electrochemically using nano polypyrrole modified glassy carbon electrode. The cyclic voltammetric behavior of the three analgesics was studied in aqueous acid, neutral, and alkaline conditions. One well-defined oxidation peak each for acetaminophen and acetylsalicylic acid and three oxidation peaks for dipyrone were observed in the cyclic voltammograms. The influence of pH, scan rate, and concentration reveal the irreversible diffusion controlled loss of 4e⁻ in acid and neutral media and 2e⁻/1H⁺ in basic medium for acetaminophen. In the case of acetylsalicylic acid, 2e⁻ and 1H⁺ loss in acidic and neutral pH and 2e⁻ and 2H⁺ loss in basic pH were observed and the oxidation was irreversible and controlled by adsorption. Irreversible removal of 2e⁻ and 1H⁺ in all pH media was observed for dipyrone and the oxidation was controlled by diffusion. A systematic study of the experimental parameters that affect the differential pulse stripping voltammetric response was carried out and optimized conditions which yield maximum peak current were arrived at. Scanning electron microscopy (SEM) analysis confirms good accumulation of the drugs on the electrode surface. The calibration was made under optimum conditions. The range of study for acetaminophen, acetylsalicylic acid, and dipyrone was 50–250, 40–300, and 100–400 ng/mL and the lower limit of determination was 45, 25, and 70 ng/mL respectively. The suitability of the method for the determination of the three analgesics in pharmaceutical preparations and urine samples was also ascertained.     

pH-controlled morphological structure of polyaniline during electrochemical deposition

Electrodeposition of polyaniline (PAni) was performed across a broad pH range from pH 0.0 to 14.0. PAni films were found to grow from strong acidic environments at much faster rate and appeared to adopt different growth patterns from those grown from higher pH media, thus producing PAni films with very different morphologies ranging from nanofibres to microsized tubules to flakes like structures. The various morphologies of the PAni films were results of homogeneous and heterogeneous nucleation during electrochemical polymerization. These phenomena occurred under specific conditions which could be induced by varying the pH of the reaction media. Characteristic IR absorptions of the films deposited from increasing pH environment indicated little differences in chemical structure of the polymers except for the film grown from pH 14.0. Cyclic voltammetry data also indicated different electron transfer efficiency as a result of different morphology adopted. All except for PAni films obtained from pH 2.0 to 4.0 gave high specific capacitance at around 450 F g⁻¹ in 0.5 M H₂SO₄ and in 1.0 M NaNO₃ (pH 1.0) solution using 1.0 mA cm⁻² charging and discharging current density.     

The optimization of the photo-oxidation parameters to remediate wastewater from the textile dyeing industry in a continuous stirred tank reactor

The remediation of textile dying wastewater was carried out at ambient temperatures in a pilot-scale continuous stirred tank reactor by using the photo-Fenton oxidation process. The preliminary results suggest that the treatment system reached a steady state condition within 5–10 min after it was started up. By using a 2 ^k factorial design, the effects of various parameters on the removal efficiency of color, BOD and COD were identified under steady state conditions. The removal efficiencies of color and BOD were affected by the feed rate of H₂O₂ and Fe²⁺, whereas none of the parameters in the investigated ranges affected the removal efficiency of COD. Consequently, using univariate analysis to investigate higher parameter range values, the optimum conditions for treating textile wastewater were found to be 25 ml H₂O₂/min, 5 ml Fe²⁺/min and 90 W UV-A power for 20 min. In addition, the removal of all pollutants was enhanced within the acidic pH range. Approximately 69.2, 99.4 and 48.5% of color, BOD and COD were removed, respectively. However, the concentration of TDS increased slightly during the treatment period due to the formation of new species or intermediate oxidation products. Nevertheless, all values of pollutants in the treated wastewater except COD were in the range of the standard values permitted for discharge into the environment.     

聚丁二酸丁二醇酯(PBS)在不同pH条件下的降解

对聚丁二酸丁二醇酯(PBS)薄膜在不同pH值水溶液中的降解进行对比研究.用失重率及薄膜表面形貌观察等时降解结果进行表征,结果表明:PBS薄膜在不同pH值水溶液中的降解速度为:碱性溶液>酸性溶液>中性溶液.降解过程中不同降解溶液的pH值均有一定程度的下降.     

The electrochemical reduction of oxygen on zinc corrosion films in alkaline solutions

Kinetics of the O₂ reduction has been characterized on Zn corrosion films by Pt/Zn rotating ring-disc electrode (RRDE) and EIS methods. On zinc-oxide films a two-step reduction was identified in various buffer solutions of pH 10.5, while a small quantity of H₂O₂ intermediate could be detected. On the basis of results obtained from Pt/Zn and Pt/Pt RRDE experiments in solutions containing H₂O₂, it was further confirmed that the HO₂⁻ was reduced to OH⁻ through the zinc-oxide corrosion layer. Capacitance data of the zinc-oxide/electrolyte interface calculated from steady-state impedance diagrams measured at various cathodic potentials indicate the presence of a space charge layer of the semi-metallic ZnO. The solid-state reaction mechanism of HO₂⁻ disproportion with participation of Zn_i⁺ interstitials, oxygen ion vacancies of the non-stoichiometric Zn-oxide, and chemisorbed HO₂⁻ is discussed.     

The Influence of Counter-Ions on the Properties of a Polyethylene Phosphonic Acid Membrane

Permselective polyethylene-phosphonate membranes have been prepared from polyethylene, both by topochemical reaction and by casting from solution. At capacities around 1–2 meq/g these membranes change their electric resistance by more than four orders of magnitude and deswell in acid solutions. The jump in resistance values takes place at different pH according to capacity and cross-linking of the membrane. The influence of different alkali ions and some tetraalkyl-ammonium ions on conductivity, swelling and hysteresis of these membranes has been determined. The Li⁺ ion deswells the membrane and increases its resistance nearly as much as the H⁺ ion while swelling and conductivity increase in hydroxide solutions with increasing atomic weight of the alkali metals. In non-alkaline solutions the K⁺ form has lower conductivity than the Na⁺ form. Physiological implications of the findings are discussed.