Electrochemical behaviour of uranium (IV) in DMF at vitreous carbon

The electrochemical behaviour of UCl₄ (0.01 mol L⁻¹ up to 0.05 mol L⁻¹) in 0.1 mol L⁻¹ TBAPF₆/DMF solution at vitreous carbon was studied, at room temperature, by cyclic voltammetry and potentiostatic techniques. The electrolytic solutions were analyzed by UV spectroscopy (UV), and the electrodeposited films were characterized by Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction (XRD). The cyclic voltammetric results, at low UCl₄ concentrations (0.01 mol L⁻¹), point that the reduction of U(IV) to U(0) occurs in two steps involving mainly U(IV) and U(III) species. The first electron transfer reaction is quasi-reversible and the second irreversible. The diffusion coefficient of U(IV) in DMF and the charge rate constant were determined to be 4.78 × 10⁻⁷ cm² s⁻¹ and 1.93 × 10⁻³ cm s⁻¹ (at 0.02 V s⁻¹), respectively.RBS data obtained from samples prepared at constant potential (−3.10 V) during 3 h at room temperature, indicated the presence of uranium particles deposited all over the vitreous carbon surface with aggregates in some places, confirming that the second reduction step corresponds to uranium electrodeposition. No crystallographic ordering could be seen by XRD, pointing to an amorphous character of the uranium films.     

Application of silica gel as an effective modifier for the voltammetric determination of dopamine in the presence of ascorbic acid and uric acid

Amorphous silica gel modified carbon paste electrode (CPE) offers substantial improvements in voltammetric sensitivity and selectivity towards determination of dopamine (DA). Cyclic voltammetry of Fe(CN)₆^3−/4− as a negatively charged probe revealed that the surface of the silica gel modified carbon paste electrode had a high density of negative charge at pH 8.0. Therefore, the modified electrode adsorbed DA (pK_a = 8.9) and enhanced its voltammetric response while repulsed ascorbic acid (AA) (pK_a = 4.2) and uric acid (UA) (pK_a = 5.4) and inhibited their interfering effects. The influence of various experimental parameters including percent of silica gel in the CPE, pH of solution, and accumulation time and potentials, on the voltammetric response of DA was investigated. At the optimum conditions, the analytical curve was linear for dopamine concentrations from 2.0 × 10⁻⁷ to 1.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit (3σ) of 4.8 × 10⁻⁸ mol L⁻¹. The prepared electrode was used for determination of DA spiked into DA injection and human serum samples, and very good recovery results were obtained over a wide concentration range of DA.     

Poly (acridine orange) film modified electrode for the determination 1-naphthol in the presence of 2-naphthol

The voltammetric behavior of 1-naphthol was studied with a poly (acridine orange) (PAO) film modified glass carbon electrode (GCE). The electrooxidation of 1-naphthol was an irreversible process with its oxidation overpotential at the PAO electrode 180 mV lower than that on the GCE. PAO electrode demonstrated electrocatalytic activity to the electrooxidation of 1-naphthol giving a greatly improved detection limit down to 8 × 10⁻⁸ mol L⁻¹(S/N = 3). At the optimal experimental condition, the oxidation peak current from the PAO electrode was linearly proportional to the concentration of 1-naphthol in the range of 2 × 10⁻⁷ to 3.2 × 10⁻⁶ mol L⁻¹ and 5.2 × 10⁻⁶ to 1.2 × 10⁻⁴ mol L⁻¹. The differences of the oxidation peak potentials between 1-naphthol and the coexisted 2-naphthol was 170 mV allowing the selective detection of 1-naphthol in a mixed solution with 2-naphthol. The detection of 1-naphthol in tap water and river water was carried out with satisfactory results.     

Immobilization of horseradish peroxidase on self-assembled (3-mercaptopropyl)trimethoxysilane film: Characterization, direct electrochemistry, redox thermodynamics and biosensing

Highly organized (3-mercaptopropyl)trimethoxysilane (3-MPT) films have been prepared via self-assembled coupled with sol–gel linking technology. Horseradish peroxidase (HRP) is successfully immobilized onto the densely packed three-dimensional (3D) 3-MPT network and the direct electrochemistry of HRP is achieved without any electron mediators or promoters. Redox thermodynamics of HRP on the 3-MPT films, which is obtained from the temperature dependence of the reduction potential, suggests that the positive shift of redox potentials of HRP at the interface of 3-MPT originates from the solvent reorganization effects and conformational change of the polypeptide chain of HRP. Based on the direct electrochemistry and electrocatalytic ability of HRP, a sensitive third-generation amperometric H₂O₂ biosensor is developed with two linear dependence ranges of 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ and 1.0 × 10⁻⁴ to 2.0 × 10⁻² mol L⁻¹.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.     

Photochemical production of nitric oxide from a nitrosyl phthalocyanine ruthenium complex by irradiation with light in the phototherapeutic window

The photochemical behavior of [Ru(NO)(NO)₂pc] (pc = phthalocyanine) is reported in this paper. In addition to ligand localized absorption bands (λ < 300 nm), the electronic spectrum of this complex in dichloromethane solution was dominated by an intense absorption at 640 nm characterized as Q-bands. Irradiation of [Ru(NO)(NO)₂pc] at 366 and 660 nm led to the production of nitric oxide (NO) as detected by a NO-sensor. NO production by light irradiation at high energy involved excitation of d_π–π^* transition, while a photoinduced electron transfer occurred at long wavelength irradiation. The NO quantum yields varied from 1.4 × 10⁻³ to 2.3 × 10⁻² mol einstein⁻¹, depending on oxygen concentration.     

Development and applications of quaternary ammonium (QA) membrane electrodes in pharmaceutical preparation and in bioavailability of Prostaglandin E1 and Deoxycholate

The two novel ion-pairs (PB-TPB and NB-TPB) of quaternary ammonium drugs; propantheline bromide (PB), N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]-trimethylazanium have been synthesized, respectively and incorporated in poly (vinyl chloride)-based membrane electrodes for the quantification of propantheline bromide and neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane electrodes have been found to substantially improve the performance characteristics. The best performance was reported with membranes having composition (w/w) of PB-TPB or NB-TPB (6%): PVC (34%): o-NPOE (60%). The proposed electrodes exhibit nernstian response in the concentration ranges of 2.1 × 10⁻⁷ M to 1.0 × 10⁻² M and 4.4 × 10⁻⁷ M to 1.0 × 10⁻² M with detection limit of 1.5 × 10⁻⁷ M and 3.3 × 10⁻⁷ M, respectively. Both the membrane electrodes perform satisfactorily over pH ranges of (3.5–7.5 and 4.0–7.0) with fast response times (11 s and 13 s), respectively. These drugs (PB and NB) were further utilized as different ion-pairs of Prostaglandin E₁ (PGE₁) and Deoxycholate (DOC) in poly (vinyl chloride)-based membrane electrodes for the determination of bioavailability of Prostaglandin E₁ and Deoxycholate in plasma of different patients.     

Synthesis, structural characterization and third-order non-linear optical property of new three-dimensional metal-organic polymer [Fe2(μ10-btc)0.5(μ2-ox)0.5(μ2-O)1.5]n

One new metal-organic polymer formulated as [Fe₂(μ₁₀-btc)_0.5(μ₂-ox)_0.5(μ₂-O)_1.5]_n 1 (btc = 1,2,4,5-benzenetetracarboxylate, pyramellitate; ox = oxalate) has been synthesized by low-temperature solid-state reaction and characterized by single-crystal X-ray diffraction, elemental analyses, TGA, IR spectra and UV–visible spectra. Complex 1 presents the first 3D coordination network structure constructed by bridging btc, ox and O mixed ligands. In 1, carboxyl groups of btc are all deprotonated and they have a new type of μ₁₀-btc coordination mode. The third-order non-linear optical (NLO) properties of the title compound 1 were also investigated and they exhibit the reverse saturable absorption and self-defocusing performance with modulus of the hyperpolarizability (γ) 5.98 × 10⁻³⁰ esu for 1 in a 7.45 × 10⁻⁴ mol dm⁻³ DMF solution.     

Extraction and separation of Pt(IV)/Rh(III) from acidic chloride solutions using Aliquat 336

Extraction and separation of Pt(IV)/Rh(III) from chloride solutions using Aliquat 336 (Quaternary ammonium salt made by the methylation of mixed tri octyl/decyl amine) diluted in kerosene as an extractant/synergist alone and mixed with organophosphorous extractants as synergists/extractants were carried out from an aqueous feed containing 0.0005 mol L⁻¹ Pt(IV)/Rh(III).Variation of hydrochloric acid concentration of aqueous phase from 0.005 to 10.0 mol L⁻¹ increased the percentage extraction of platinum up to 5.0 mol L⁻¹ there after it decreases. Whereas in the case of rhodium, from 0.005 to 1.0 mol L⁻¹ acid range the percentage extraction was decreased from 1.0 to 10.0 mol L⁻¹ acid range is favorable for extraction. Platinum(IV)/rhodium(III) separation factor of 279.2 was obtained at 1.0 mol L⁻¹ HCl concentration with 0.005 mol L⁻¹ Aliquat 336 and separation factor of 612.3 was obtained at 3.0 mol L⁻¹ HCl concentration with 0.01 mol L⁻¹ Aliquat 336. The present study optimized the various experimental parameters like phase contact time, effect of extractant, salts, temperature, loading capacity of extractant, stripping studies with various mineral acids/bases, recycling and reusing capacity of extractant up to ten cycles.     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Electrodeposited amorphous iron(III) oxides as anodes for photoelectrolysis of water

Deposition of amorphous iron(III)-oxide films on a conducting glass substrate was achieved via a cathodic bias in a 0.1 M hydrated ammonium iron(II) sulfate ((NH₄)₂Fe(SO₄)₂·6H₂O) solution at −1.6 V versus Ag/AgCl. Analysis by X-ray absorption near edge structure confirmed the iron(III) feature of the amorphous films. The deposited films exhibited n-type semiconducting characteristics by showing photoresponses under an anodic bias. The Mott–Schottky method and cyclic voltammetry were employed to characterize the semiconducting properties of the deposited films, which included the band gap (2.2 eV), the potentials of the conduction and valence band edges and flat band (−0.6, +1.6 and −0.58 V versus Ag/AgCl at pH 7, respectively), and the donor density (1 × 10²²/cm³). The deposited iron(III)-oxide films were suitable to serve as an anode for water splitting under illumination.     

Preparation and electrochemical properties of functionalized ionic liquid self-assembled modified graphite electrode

A modified graphite electrode with functionalized ionic liquid (IL) pyridinium derivative of β-cyclodextrin ([CDbPy]BF₄) was prepared by layer-by-layer self-assembly technique. With ferrocene as probe, the characterization of the (CDIL/PDDA)_n/GE SAMs in the solution of phosphate (PBS, pH 7.0) was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry. The electrochemical behavior of p-chloronitrobenzene (p-CNB) at the modified electrode was studied. It was found that the modified electrode could catalyze the reduction of p-CNB and made the cathode peak move about 100 mV in positive direction in the solution of 0.1 mol/L PBS (pH 7.0). Differential pulse voltammetry (DPV) was applied to the determination of p-CNB in waste water with satisfactory results. The detection limit and the linear range of the concentration of p-CNB to the reduction peak current were 8.0 × 10⁻⁸ mol/L and 3.0 × 10⁻⁷–1.0 × 10⁻⁵ mol/L, respectively.     

Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

Spontaneous adsorption of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4α-Co^IITAPc) on glassy carbon (GC) electrode leads to the formation of a stable self-assembled monolayer (SAM). Since the SAM of 4α-Co^IITAPc is redox active, its adsorption on GC electrode was followed by cyclic voltammetry. SAM of 4α-Co^IITAPc on GC electrode shows two pairs of well-defined redox peaks corresponding to Co^III/Co^II and Co^IIIPc⁻¹/Co^IIIPc⁻². The surface coverage (Γ) value, calculated by integrating the charge under Co^II oxidation, was used to study the adsorption thermodynamics and kinetics of 4α-Co^IITAPc on GC surface. Cyclic voltammetric studies show that the adsorption of 4α-Co^IITAPc on GC electrode has reached the saturation coverage (Γ_s) within 3 h. The Γ_s value for the SAM of 4α-Co^IITAPc on GC electrode was found to be 2.37 × 10⁻¹⁰ mol cm⁻². Gibbs free energy (ΔG_ads) and adsorption rate constant (k_ad) for the adsorption of 4α-Co^IITAPc on GC surface were found to be −16.76 kJ mol⁻¹ and 7.1 M⁻¹ s⁻¹, respectively. The possible mechanism for the self-assembly of 4α-Co^IITAPc on GC surface is through the addition of nucleophilic amines to the olefinic bond on the GC surface in addition to a meager contribution from π stacking. The contribution of π stacking was confirmed from the adsorption of unsubstituted phthalocyanatocobalt(II) (CoPc) on GC electrode. Raman spectra for the SAM of 4α-Co^IITAPc on carbon surface shows strong stretching and breathing bands of Pc macrocycle, pyrrole ring and isoindole ring. Raman and CV studies suggest that 4α-Co^IITAPc is adopting nearly a flat orientation or little bit tilted orientation.     

Selective precipitation of cadmium from nickel cadmium sulphate solutions using sodium decanoate

Each year in France, about 1300 tons of spent Ni–Cd batteries are collected. Their treatment consists of crushing, physical separation, acidic leaching of electrode materials, separation and recovery of metals leached with different processes. In this work, the selective precipitation of cadmium in synthetic Ni–Cd mixtures was investigated using sodium decanoate as precipitant. A factorial design of experiments was used to improve the separation using variables such as cadmium concentration, pH, molar ratio between decanoate and cadmium, time of addition of precipitant and rest time of the solution. In the best conditions defined by a 2⁵⁻² fractional factorial design, starting with concentrations of 0.1 mol L⁻¹ of nickel (5.9 g L⁻¹) and 0.05–0.15 mol L⁻¹ of cadmium (5.6–16.8 g L⁻¹) it is possible to recover in only one stage about 99% of cadmium without precipitating more than 5% of nickel. The results of the separation are on one side a pure solution of nickel at 2.39 × 10⁻² mol L⁻¹ (1.4 g L⁻¹) containing 3.44 × 10⁻⁴ mol L⁻¹ of cadmium (about 40 mg L⁻¹) and on the other side a precipitate of cadmium decanoate with a cadmium content equal to 23.6 wt% and nickel content lower than 0.8 wt%. These results demonstrated the viability of this separation.     

Gasification of charcoal using supercritical CO2 at high pressures

A novel one-shell high temperature and high pressure semi-continuous reactor has been developed for the study of the Boudouard reaction at temperatures up to 820 °C and pressures up to 32.5 MPa. Semicontinuous gasification of charcoal using supercritical CO₂ has been achieved at conversions up to 90.8% (w/w) at LSHV between 20 and 30 h⁻¹ after 5–9 h. A gasification model is proposed and validated. Effective rates of gasification (1.32 ± 0.12) × 10⁻⁶ to (6.10 ± 2.03) × 10⁻⁵ s⁻¹ were obtained. The results indicated that this method is technically feasible for the on-line production of high pressures streams of CO/CO₂ in the lab for carrying out further chemistries, avoiding the use of CO high pressure bottles.     

Electrochemical behaviour of N-acetyl-l-cysteine on gold electrode—A tentative reaction mechanism

The electrochemical behaviour of N-acetyl-l-cysteine (NAC) has been investigated by linear and cyclic voltammetry on gold electrode at room temperature. The results showed two oxidation peaks under acid and neutral conditions and only one in basic medium. For each oxidation, as many electron was exchanged as proton. The influence of both the concentration and the potential scan rate on the peak currents highlighted a diffusion-controlled phenomenon for the first peak and an adsorption-limited reaction rate for the second one. The diffusion coefficient of NAC in solution and the surface concentration of the adsorbed species at pH 3 and 7 were close to 2 × 10⁻⁴ to 2 × 10⁻⁵ cm² s⁻¹ and 6 × 10⁻⁹ to 6 × 10⁻¹⁰ mol cm⁻², respectively. Film transfer experiments resulted in an irreversible adsorption of NAC on gold electrode, and the formation of a self-assembled monolayer (SAM).     

Functionalized sepiolite for heavy metal ions adsorption

Surface modification of clays has become increasingly important due to the practical applications of clays such as fillers and adsorbents. The surface modification of sepiolite with [3-(2-aminoethylamino)propyl]trimethoxysilane has been employed. The modified sepiolite surface was investigated by FTIR, XRD and DTA/TG analysis. It was found that the chemical bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and methoxy groups of [3-(2-aminoethylamino)propyl]trimethoxysilane. The changes on electrokinetic properties of modified sepiolite particles were studied by measuring the zeta potential of particle as a function of metal concentration and equilibrium pH of solution. It was found that the zeta potential of the clay particles was always negative independent of the metal concentration in solution. This study also provides some evidence for the adsorption of metal ions on modified sepiolite. The adsorption of metal ions onto modified sepiolite has varied with the type of metal cations. The available basic nitrogen centers covalently bonded to the sepiolite skeleton were studied for Co(II), Cu(II), Mn(II), Zn(II), Fe(III) and Cd(II) adsorption from aqueous solutions. It was found that the amount of metal ion adsorbed onto modified sepiolite increases with increase in solution equilibrium pH and temperature, whereas it generally decreases with the ionic strength. The experimental data were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (q_m and K) were calculated. The ability to adsorb the cations gave a capacity order of Zn(II) > Cu(II) ~ Co(II) > Fe(III) > Mn(II) > Cd(II) with affinities of 2.167×10⁻⁴, 1.870×10⁻⁴, 1.865×10⁻⁴, 1.193×10⁻⁴, 0.979×10⁻⁴ and 0.445×10⁻⁴ mol g⁻¹, respectively.     

Zinc(II) complex of terpyridine-crown macrocycle: A new motif in fluorescence sensing of zwitterionic amino acids

A new fluorescence macrocyclic receptor based on the Zn(II) complex of a C₂-terpyridine and a crown ether has been developed for molecular recognition of zwitterionic amino acids in water/DMF solution with remarkable selectivity towards l-aspartate (K = 4.5 × 10⁴ M⁻¹) and l-cysteine (K = 2.5 × 10⁴ M⁻¹).     

Photodegradation of tetrahalobisphenol-A (X = Cl, Br) flame retardants and delineation of factors affecting the process

The photoassisted degradation (HPLC-UV absorption), dehalogenation (HPLC-IC) and mineralization (TOC decay) of the flame retardants tetrabromobisphenol-A (TBBPA) and tetrachlorobisphenol-A (TCBPA) were examined in UV-irradiated alkaline aqueous TiO₂ dispersions (pH 12), and for comparison the parent bisphenol-A (BPA, an endocrine disruptor) in pH 4–12 aqueous media to assess which factor impact most on the photodegradative process. Complete degradation (2.7–2.8 × 10⁻² min⁻¹) and dehalogenation (1.8 × 10⁻² min⁻¹) of TBBPA and TCBPA occurred within 2 h of UV irradiation, whereas only 45–60% mineralization (2.3–2.7 × 10⁻³ min⁻¹) was complete within 5 h for the flame retardants at pH 12 and ca. 80% for the parent BPA. Factors examined in the pH range 4–12 that impact the degradation of BPA were the point of zero charge of TiO₂ particles (pH_pzc; electrophoretic method), particle or aggregate sizes of TiO₂ (light scattering), and the relative number of OH radicals (as DMPO–OH adducts; ESR spectroscopy) produced in the UV-irradiated dispersion. Dynamics of BPA degradation (2.0–2.4 × 10⁻² min⁻¹) were pH-independent and independent of particle/aggregate size, but did correlate with the number of OH radicals, at least at pHs 4 to 8–9, after which the rates decreased somewhat at pH > 9 with decreasing adsorption owing to Coulombic repulsive forces between the very negative TiO₂ surface and the anionic forms of BPA (pK_as ca. 9.6–11.3), even though the number of OH radicals continued to increase at the higher pHs.     

Sawdust: A green and economical sorbent for thallium removal

Removal/preconcentration of thallium(I) ions from aqueous solution by sawdust; a waste material derived from the commercial processing of Cedrus Deodar wood for furniture production was investigated. A simple and low-cost modification results in increasing the sorption capacity of raw sawdust from 2.71 to 13.18 mg g⁻¹. Sorption was found to be rapid (98% within 8 min). The binding of metal ions was found to be pH dependent, optimal sorption accruing at around pH 6–9. Potentiometeric titrations of sawdust revealed two distinct pK_a values, the first having the value similar to carboxylic groups (3.3–4.8) and second comparable with that of amines (8.53–10.2) with the surface site densities of 1.99 × 10⁻⁴ and 7.94 × 10⁻⁵ mol g⁻¹, respectively. Retained Tl(I) ions were eluted with 5 ml 0.1 mol l⁻¹ HCl. Detection limit of 0.0125 μg ml⁻¹ was achieved with an enrichment factor of 160. Recovery was quantitative using sample volume of 800 ml. The Langmuir, Freundlich and D–R isotherm equations were used to describe partitioning behavior for the system at different temperatures. Kinetic and thermodynamic behavior of sawdust for Tl(I) ions removal was also studied.