Sorption of Th(IV) ions onto TiO2: Effects of contact time, ionic strength, thorium concentration and phosphate

Summary The sorption of Th(IV) onto TiO₂ was studied by the batch technique as a function of pH and ionic strength at moderate concentration (10^-4-10^-5 mol/l) and in the presence and absence of phosphate. It was found that the sorption rate of Th(IV) was relatively slow, the sorption percent was abruptly increased from pH 2 to 4, and the sorption was decreased with increasing ionic strength as a whole. In the concentration range of Th(IV) from trace concentration to 1.4 ^. 10^-4 mol/l and in the absence of phosphate, the sorption isotherms were roughly fitted the Freundlich equation at different ionic strengths and approximately constant pH. These sorption characteristics of Th(IV) onto TiO₂ were compared with those of uranyl on the same sorbent. In addition, the positive effect of phosphate on the sorption of Th(IV) onto TiO₂ was demonstrated obviously and can be attributed to strong surface binding of phosphate, and the subsequent formation of ternary surface complexes of Th(IV). The difference between the sorption characteristics of Th(IV) ions and uranyl ions onto TiO₂ is discussed.     

Sorption Studies of Cobalt(II) on Colloidal Hematite Using Potentiometry and Radioactive Tracer Technique

The sorption of Co(II) on colloidal hematite was studied as a function of pH, ionic strength, and Co(II) concentration. Two different techniques were used, yielding two different sets of information: (i) potentiometric titrations that provide information on the number of protons released as a function of pH owing to the sorption of Co(II) and (ii) measurement of the amount of cobalt sorbed on the surface as a function of pH using a radioactive tracer, (60)Co. At low Co(II) concentrations (10(-8) M), the sorption was found to be independent of ionic strength but there seems to be a weak ionic strength dependence at higher Co(II) concentrations (10(-4) M). The adsorption edge moved to higher pH with increasing Co(II) concentration. For the high Co(II) concentration, the number of protons released per cobalt sorbed increased from zero to approximately 1.5. The basic charging properties of hematite were modeled with four different surface complexation models. The 1-pK Basic Stern Model (BSM), with binding of electrolyte ions to the Stern plane, seems to be the most reasonable model if the ambition is to describe experimental data at different ionic strengths. The sorption of cobalt was modeled with the 1-pK BSM. By introducing a low concentration of high affinity surface sites for cobalt sorption it was possible to model the sorption in very wide cobalt concentrations, ranging from 10(-8) M to 10(-4) M. Copyright 2000 Academic Press.     

Sorption of divalent metal ions on CrPO4

The divalent metal ion sorption (Cu(2+), Cd(2+), Ni(2+), and Pb(2+)) on chromium phosphate (CrPO(4)) was studied as a function of pH, temperature, and concentration of metal ions. The sorption of metal ions is observed to increase with the increase in pH, temperature, and concentration of metal ions in solution. The mechanism of sorption is found to be the exchange of the hydrolyzed metal cations with the protons from solid at high temperature. The sorption at low temperature is found to be accompanied by the precipitation of the corresponding metal phosphates such as Pb(3)(PO(4))(2).     

Ion exchange studies of U(VI) from aqueous Arsenazo-III solutions using AG-2X8, Dowex-50WX8 and Chelex-100 resins

The distribution of U(VI) between the anion exchanger AG-2X8, the cation exchanger Dowex-50WX8 and the chelating resin Chelex-100 and aqueous solutions of Arsenazo-III at different pH values was studied. The concentration of Arsenazo-III was in the range of 1.53·10^–4–1.23·10^–3M. Equilibrium pH was varied from 1.0 to 8.78 while U(VI) original concentration was held constant at 3.39·10^–4M. The effect of Arsenazo-III concentration and the variation of hydrogen ion concentration on U(VI) species formed in solution as well as the sorbed species was discussed. Use was made of IR spectroscopy to investigate the sorption behavior. The sorption of some interfering ions such as Th(IV), Zr(IV) and Ce(III) on the resins used at optimum conditions for the sorption of U(VI) was also investigated.     

Sorption of Cu(II) onto silica gel immobilized calix[4]arene derivative with tripodal structure

This study contains the synthesis of silica gel-immobilized calix[4]arene derivative (TR-CL[4]P) as a new sorbent and its sorption studies towards Cu (II) ion in aqueous solution. The aldehyde pointed calix[4]arene derivative 5 was synthesized and then it was immobilized onto 3-aminopropilsilica gel (APS). In batch sorption experiments, the experimental results showed that TR-CL[4]P is effective sorbent towards Cu (II) ion. Therefore, the effect of solution pH, sorption time, temperature and initial metal ion concentration onto Cu (II) sorption was investigated. Maximum Cu(II) removal was obtained at 30?°C, 30?min and pH 6.0 for TR-CL[4]P and the batch sorption capacity was found as 17.8?mg/g. The characteristics of the sorption process for Cu (II) ion were evaluated by using the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) adsorption isotherms. Also, thermodynamic parameters, i.e., ΔG, ΔS, and ΔH were calculated for the system.     

Effect of humic acid, pH and ionic strength on the sorption of Eu(III) on red earth and its solid component

Sorption and desorption of radioeuropium on red earth and its solid components to remove organic matter was studied at pH 5.3±0.1 and 4.5±0.1, and in 0.01M and 0.001M NaClO₄ solutions, respectively. Eu(III) sorption showed strong pH and humic acid concentration dependency, and NaClO₄ concentration independency. The sorption increased with increasing pH and amount of HA adsorbed on red earth. The sorption of Eu(III) on red earth was mainly dominated by surface complexation. Humic acid and high pH had a great tendency to immobilize the movement of Eu(III) in red earth. Sorption-desorption hysteresis of Eu(III) on red earth indicated that the sorption was irreversible.     

Determination of nicotinamide (NA) using its polarographic catalytic wave in the presence of KIO3

Nicotinamide (NA) yields a polarographic catalytic wave with a peak potential -1.38 V (vs. SCE) in 0.1 mol/L HAc-NaAc (pH 4.7)/4 x 10(-3) mol/L KIO3 buffer solution. The sensitivity of the catalytic wave increased in one order of magnitude as compared to that of the responding reduction wave without KIO3. Based on this observation, a new method for the determination of NA was recommended. The second order derivative peak current was proportional to the NA concentration in the range of 5 x 10(-8)- 6 x 10(-7) mol/L. 0.11-fold vitamin B1, 0.13-fold B2, 0.14-fold B6 and 8-fold nicotinic acid amounts do not interfere the determination of 1 x 10(-6) mol/L NA. The proposed method was used to determine the NA content in multivitamin tablets, with good agreement to the declared amount.     

Divinyl Sulfide-4-Vinylpyridine Copolymer as an Effective Sorbent for Mercury

The sorption power of divinyl sulfide-4-vinylpyridine copolymer toward Hg(II) ions was studied. The influence of the kind and concentration of an acid on the sorption characteristics is examined. Mechanisms of the interaction of the active sorption centers of the copolymer with Hg(II) ions are discussed.     

Sorption of uranium on magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticle was synthesized using a solid state mechanochemical method and used for studying the sorption of uranium(VI) from aqueous solution onto the nanomaterial. The synthesized product is characterized using SEM, XRD and XPS. The particles were found to be largely agglomerated. XPS analysis showed that Fe(II)/Fe(III) ratio of the product is 0.58. Sorption of uranium on the synthesized nanomaterials was studied as a function of various operational parameters such as pH, initial metal ion concentration, ionic strength and contact time. pH studies showed that uranium sorption on magnetite is maximum in neutral solution. Uranium sorption onto magnetite showed two step kinetics, an initial fast sorption completing in 4–6 h followed by a slow uptake extending to several days. XPS analysis of the nanoparticle after sorption of uranium showed presence of the reduced species U(IV) on the nanoparticle surface. Fe(II)/Fe(III) ratio of the nanoparticle after uranium sorption was found to be 0.48, lower than the initial value indicating that some of the ferrous ion might be oxidized in the presence of uranium(VI). Uranium sorption studies were also conducted with effluent from ammonium diuranate precipitation process having a uranium concentration of about 4 ppm. 42% removal was observed during 6 h of equilibration.     

Cation exchange and sorption properties of crystalline alpha-titanium(IV) phosphate

The ion-exchange and sorption properties of alpha-titanium bis(monohydrogen orthophosphate) monohydrate of composition Ti(HPO(4))(2).H(2)O was studied in aqueous electrolyte solutions of KCl over the temperature range of 300-320 K, varying the pH and metal ion concentration in the solution. The data were explained on the basis of the law of chemical equilibrium and the metal ion sorption data were fitted to Langmuir parameters. Further, the extent of sorption was found to increase with increasing temperature and metal ion concentration in the selectivity order Fe(3+)>Cu(2+)>Co(2+)>Mn(2+)>Cr(3+)>Ni(2+). The values of Langmuir constants were used to calculate the various thermodynamic parameters, such as DeltaG(0), DeltaH(0), and DeltaS(0), during the sorption process.     

Nitroanilines as Quenchers of Pyrene Fluorescence

The quenching of pyrene and 1‐methylpyrene fluorescence by nitroanilines (NAs), such as 2‐, 3‐, and 4‐nitroaniline (2‐NA, 3‐NA, and 4‐NA, respectively), 4‐methyl‐3‐nitroaniline (4‐M ‐3‐NA), 2‐methyl‐4‐nitroaniline (2‐M‐4‐NA), and 4‐methyl‐3,5‐dinitroaniline (4‐M‐3,5‐DNA), are studied in toluene and 1,4‐dioxane. Steady‐state fluorescence data show the higher efficiency of the 4‐NAs as quenchers and fit with a sphere‐of‐action model. This suggests a 4‐NA tendency of being in close proximity to the fluorophore, which could be connected with their high polarity/hyperpolarizability. In addition, emission and excitation spectra evidence the formation of emissive pyrene—NA ground‐state complexes in the case of the 4‐NAs and, in a minor degree, in the 2‐NA. Moreover, time‐resolved fluorescence experiments show that increasing amounts of NA decrease the pyrene fluorescence lifetime to a degree that depends on the NA nature and is larger in the less viscous solvent (toluene). Although the NA absorption and the pyrene (Py) emission overlap, we found no evidence of dipole–dipole energy transfer from the pyrene singlet excited state (¹Py) to the NAs; this could be due to the low NA concentration used in these experiments. Transient absorption spectra show that the formation of the pyrene triplet excited state (³Py) is barely affected by the presence of the NAs in spite of their efficiency in ¹Py quenching, suggesting the involvement of ¹Py—NA exciplexes which—after intersystem crossing—decay efficiently into ³Py.     

Sorption onto insoluble β-cyclodextrin polymer for 2,4-dinitrophenol

The sorption of β-cyclodextrin polymer (β-CDP) towards 2,4-dinitrophenol (2,4-DNP) in aqueous solutions was investigated. The influence of sorption conditions including initial 2,4-DNP concentration, contact time and pH on sorption capability were discussed. The sorption isotherm can be correlated to Freundlich model. The maximum sorption capacity of 2,4-DNP for β-CDP was measured to be 192?mg/g with the initial concentration at 1,000?mg/L at 303?K. The β-CDP was easily recovered by ethanol as washing solvent and they could be used as a kind of recyclable sorbents.     

Sorption thermosiphon apparatus (STA): A novel and accurate system for gas mixtures sorption measurements

One of the main challenges in membrane gas separation is the plasticizing effect that reduces selectivity. For a better understanding of this phenomenon, the knowledge of the sorption behavior of each component of the mixture is necessary. For this purpose, the sorption thermosyphon apparatus (STA), was successfully designed and tested with gas sorption measurements. One of the main advantages of the STA compared to actual other methods is to ensure concentration uniformity at the headspace using a thermosiphon, as pressure decay is recorded. The equilibrium condition is not disturbed during the sampling and allow the obtention of accurate data at the end of the sorption experiment. To validate the novel system, the sorption, diffusion and permeation coefficients of pure CO2 and CH₄, as well as for a CO₂/CH₄ (50/50) mixture, in polydimethylsiloxane (PDMS) were obtained through STA and other experimental techniques showing good agreement with literature data.     

2,4-Dichlorophenol sorption on cyclodextrin polymers

The sorption of β-cyclodextrin polymer (β-CDP) and γ-cyclodextrin polymer (γ-CDP) toward 2,4-dichlorophenol (2,4-DCP) in aqueous solutions was investigated. The influence of sorption conditions including initial 2,4-DCP concentration, contact time and pH on sorption capability were discussed. Their sorption behaviors for 2,4-DCP were conducted and it was found the sorption kinetics followed the Ho and McKay equation and the film diffusion was the rate-determined step. The sorption isotherm can be correlated to Freundlich model and the sorption capacity on β-CDP was much larger than that on γ-CDP. The maximum sorption capacity of 2,4-DCP for β-CDP was measured to be 0.16 mmol/g with the initial concentration at 0.67 mmol/L at 288 K. The CDPs were easily recovered by ethanol as washing solvent and they could be used as a kind of recyclable sorbents.     

Grafting of silica with a hydrophilic triol acrylamide polymer via surface-initiated "grafting from" method for hydrophilic-interaction chromatography

A novel hydrophilic polymer-coated silica sorbent has been prepared using the radical "grafting from" polymerization method through surface-bound azo initiators for hydrophilic-interaction chromatography (HILIC). The azo groups were introduced to the surface of silica gel through the reaction with amino groups on the surface of silica gel with 4,4'-azobis(4-cyanopentanoic acid chloride) (ACVC). The resultant azo-immobilized silica gel served as surface initiator to polymerize hydrophilic triol acrylamide monomer N-acryloyltris(hydroxymethyl) aminomethane (NA) in methanol to get hydrophilic polymer-coated silica sorbent. The obtained poly(NA)-coated silica (pNA-sil) was characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), and nitrogen sorption porosimetry (NSP). Then the pNA-sil was packed into the stainless-steel column and evaluated in high-performance liquid chromatography (HPLC). Good chromatographic performance for the separation of peptides and nucleosides was obtained under HILIC mode. The results indicated that the pNA-sil stationary phase behaved as mixed-mode retention mechanisms of hydrophilic and ionic interactions. Furthermore, the pNA-sil phase was used to separate tryptic digest of β-casein and our results showed that more than 12 peptides peaks were resolved and well distributed within the elution window. Finally, the pNA-sil stationary phase was demonstrated to possess remarkable reproducibility and stability. Taken together, the pNA-sil stationary phase prepared in the current study offers a potential application in proteomics study.     

Porous glycidyl methacrylate-bentonite composite

Crosslinked macroporous copolymer of glycidyl methacrylate and ethylene glycol dimethacrylate (CP) and copolymer composite with acid modified clay (CP-S_A) were prepared by radical suspension copolymerization and functionalized by ring-opening reaction of the pendant epoxy groups with diethylene triamine (CP-deta and CP-S_A-deta). Both S_Amples were characterized by mercury porosimetry. The influence of pH, sorption time and initial 4-nitrophenol (4-NP) concentration on sorption efficiency of CP-deta and CP-S_A-deta was studied in order to evaluate this material as wastewater sorbent. The isotherm data were best fitted with Langmuir model, while the sorption dynamics obeyed the pseudo-second-order kinetic model.     

Sorption of selenite ions on hematite

The sorption of selenite from aqueous solutions onto hematite was investigated as a function of pH (2-12), ionic strength (0.01-0.1 M), and concentration of selenium (10(-7)-10(-2) M). The sorption may proceed according to two processes: surface complexation, followed by the precipitation of ferric selenite starting at approximate [Se] = 4 x 10(-4) M (surface coverage>ca. 2 at nm(-2)). The sorption isotherms have been fitted by a Tempkin equation. A surface complexation model (2-pK/Constant Capacitance Model) was used to fit the sorption data. The nature of the surface species of selenite cannot be determined by modeling since monodentate >FeOSe(O)O- or >FeOSe(O)OH and bidentate (>FeO)2SeO surface complexes are both able to fit the experimental data. The reversibility and kinetics of sorption were also studied. The affinity of selenite ions toward hematite, expressed as the distribution coefficient with respect to the surface area (K(D) in L m(-2)), was compared with results published for other ferric oxides (goethite and amorphous ferric oxide). It was found that the reactivity toward selenite is similar, contrary to acid-base properties which depend on the nature of the oxide and its level of purity.     

Determination of gold using clay modified carbon paste electrode

Sorption of gold(III) chlorocomplexes was studied by means of a carbon paste electrode modified with montmorillonite. Anionic exchange behavior was found in chloride media with low ionic strength. Anionic sorption of [AuCl4]- can be used as a preconcentration step to the determination of Au(III). Linear calibration dependences were found in the concentration range 4.06 x 10(-6) - 1.22 x 10(-5) mol/L Au(III) after 5 min of sorption and in the range 8.12 x 10(-7) - 6. 1 x 10(-6) mol/L after 10 min of sorption. Interferences of several anions and cations were studied. Model samples of table water were analyzed.