Chitosan modified with Reactive Blue 2 dye on adsorption equilibrium of Cu(II) and Ni(II) ions

This study aimed at immobilizing Reactive Blue 2 (RB 2) dye in chitosan microspheres through nucleophilic substitution reaction. The adsorbent chemical modification was confirmed by Raman spectroscopy and thermogravimetric analysis. This adsorption study was carried out with Cu(II) and Ni(II) ions and indicated a pH dependence, while the maximum adsorption occurred around pH 7.0 and 8.5, respectively. The pseudo second-order kinetic model resulted in the best fit with experimental data obtained from Cu(II) (R = 0.997) and Ni(II) (R = 0.995), also providing a rate constant, k₂, of 4.85 × 10⁻⁴ and 3.81 × 10⁻⁴ g (mg min)⁻¹, respectively, thus suggesting that adsorption rate of metal ions by chitosan-RB 2 depends on the concentration of ions on adsorbent surface, as well as on their concentration at equilibrium. The Langmuir and Freundlich isotherm models were employed in the analysis of the experimental data for the adsorption, in the form of linearized equations. Langmuir model resulted in the best fit for both metals and maximum adsorption was 57.0 mg g⁻¹ (0.90 mmol g⁻¹) for Cu(II) and 11.2 mg g⁻¹ (0.19 mmol g⁻¹) for Ni(II). The Cu(II) and Ni(II) ions were desorbed from chitosan-RB 2 with aqueous solutions of EDTA and H₂SO₄, respectively.     

A novel agricultural waste based adsorbent for the removal of Pb(II) from aqueous solution: Kinetics,equilibrium and thermodynamic studies

Fig sawdust was used as a precursor for the production of activated carbon by chemical activation with H₃PO₄. The developed Fig sawdust activated carbon (FSAC) was used as a biosorbent for the removal of Pb(II) from aqueous solution. Highest adsorption of Pb(II) (95.8%) was found at pH 4. Equilibrium data fitted very well with the Langmuir isotherm model. Maximum adsorption capacity was determined 80.645 mg g⁻¹ at pH 4. Kinetic studies demonstrated that the adsorption followed a pseudo second order kinetics model. The negative value of ΔG° confirmed the feasibility and spontaneity of FSAC for Pb(II) adsorption.     

A novel magnetic ion imprinted polymer for selective adsorption of trace amounts of lead(II) ions in environment samples

In this work a novel ion imprinted polymer (IIP) based on 4-(vinylamino)pyridine-2,6-dicarboxylicacid (VPyDC), was coated on Fe₃O₄ nano-particles. The application of this magnetic sorbent was investigated for preconcentration and determination of trace Pb(II) ions by flame atomic absorption spectrometry. Effects of various parameters such as sample pH, adsorption/desorption time and eluent were investigated during this study. The relative standard deviation and limit of detection of the method were found to be 1.8% and 0.9 ng mL⁻¹, respectively. The accuracy of this method was confirmed using various standard reference materials, then it was used for Pb(II) determination in environmental samples.     

Separation of Co(II) and Mn(II) from sulphate media via a HFSLM: Reaction flux model and experimental verification

Separation of Co(II) and Mn(II) from sulphate media through triple HFSLM in series using D2EHPA was explored. Mn(II) was extracted preferentially over Co(II) at the pH value of 5, 100 ppm of Co(II) and Mn(II), 5% (v/v) of D2EHPA, 0.2 M HCl. The highest extraction percentage of Mn(II) was 98.14%, and Co(II) remained at 94.05% in the raffinate stream. The reaction order (n) and the reaction rate constant (k_f) were found to be 1.00 and 0.0180 min⁻¹, respectively. Furthermore, the reaction flux model proved to be in good agreement with the experimental data at an average deviation of 2.24%.     

Adsorption of Pb(II) ions from aqueous solutions by carbon nanotubes oxidized different methods

This study investigated the heavy metal adsorption of the carbon nanotubes (CNTs) oxidized different methods. Besides the conventional ultrasonication method, the UV-light used as an oxidation agent. The two oxidation methods compared with each other by Pb(II) adsorption. The characterizations of oxidized CNTs were analyzed by FTIR, XRD, DTG, SEM and total acidity capacity analysis. The adsorption capacities of carbon nanotubes were compared with using Langmuir and Freundlich isotherms. Two different kinetic theories were applied to experimental data. These theories are pseudo-second order and intra-particle diffusion models. The adsorption results can be compared using non-linear Langmuir isotherm parameters. For single wall carbon nanotubes (SWCNTs), theoretical adsorption capacity value (Q_m) of UV-light method is 511.99 mg/g and ultrasonication method is 342.36 mg/g. The UV-light increased the surface acidity of the carbon nanotubes more than ultrasonication. After the adsorption experiments, it is apparently seen that the UV-light oxidation method is a useful method for heavy metal adsorption.     

Sorption of heavy metal ions from aqueous solution by a novel cast PVA/TiO2 nanohybrid adsorbent functionalized with amine groups

Sorption of Cd(II), Ni(II) and U(VI) ions onto a novel cast PVA/TiO₂/APTES nanohybrid adsorbent with variations in adsorbent dose, pH, contact time, initial metal concentration and temperature has been investigated. The adsorbent were characterized by SEM and FTIR analysis. BET surface area, pore diameter and pore volume of adsorbent were 35.98 m² g⁻¹, 3.08 nm and 0.059 cm³ g⁻¹, respectively. The kinetic and equilibrium data were accurately described by the double-exponential and Freundlich models for all metals. The maximum sorption capacities were 49.0, 13.1 and 36.1 mg g⁻¹ for Cd(II), Ni(II) and U(VI) ions with pH of 5.5, 5 and 4.5, respectively. Thermodynamic studies showed that the sorption process was favored at higher temperature. The adsorbent can be easily regenerated after 5 cycles of sorption–desorption.     

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Nano-TiO₂ modified with 2-mercaptobenzothiazole (MBT) was investigated as a new adsorbent for preconcentration of Cd(II), Cu(II) and Pb(II). The metal ions are adsorbed onto nano-TiO₂-MBT, eluted by nitric acid and determined by flame atomic absorption spectrometry. The parameters affecting the adsorption were investigated. Under optimized conditions, the calibration curves were linear in the range of 0.2–25.0, 0.2–20.0, and 3.0–70.0 ng mL⁻¹ for cadmium, copper and lead, respectively. The limits of detection for Cd(II), Cu(II) and Pb(II) were 0.12, 0.15 and 1.38 ng mL⁻¹, respectively. The method was applied to determination of Cd(II), Cu(II) and Pb(II) in water and ore samples.     

Nano-alumina coated with sodium dodecyl sulfate and modified with 4-(2-Pyridylazo) resorcinol for extraction of heavy metals in different matrixes

A green, novel and efficient solid phase extraction method based on the use of nano-alumina (nano-Al₂O₃) coated with sodium dodecyl sulfate (SDS) and modified with 4-(2-Pyridylazo) resorcinol (PAR) as a new adsorbent was developed for separation and preconcentration of trace amounts of Ni, Pb, Cu and Zn ions prior to determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Under the optimum conditions (eluent: HNO₃, 4.0 mL, 3.0 mol L⁻¹; adsorbent: 0.8 g of nano-Al₂O₃, 40 mg of SDS, 8.6 mg of PAR; and sample: pH 6, flow rate 2.0 mL min⁻¹), adsorption capacity of nano-Al₂O₃-SDS-PAR, enrichment factors and limits of detection for the analytes were 8.7–12.9 mg g⁻¹, 125–250, and 0.12–0.71 μg L⁻¹, respectively. The proposed method presented excellent repeatability with relative standard deviations less than 1.6% (n = 10), and calculated calibration curves gave good level of linearity with correlation coefficient values between 0.989 and 0.999. Finally, the feasibility of the method was evaluated by extraction and determination of Ni, Pb, Cu and Zn ions in rice seed, apple juice, coriander, lettuce and tap water samples.     

Cooperative adsorption of bisphenol-A and chromium(III) ions from water on activated carbons prepared from olive-mill waste

The aim of this study was to investigate the simultaneous adsorption of bisphenol A (BPA) and chromium ions from aqueous solution on activated carbons (both commercial and prepared from olive-mill waste), analyzing both kinetic and equilibrium adsorption data. The effects of solution pH and ionic strength on the adsorption processes were also studied, as well as the chemical interactions between the carbon surface and the pollutants. The activated carbon prepared from olive-mill waste showed: a large surface area (up to 1641 m² g⁻¹), a highly heterogeneous micropore distribution, and a basic chemical nature. The pore volume diffusion model was used to predict the adsorption kinetics of both pollutants. The effective diffusion coefficients ranged between 1.15 × 10⁻⁶ and 9.18 × 10⁻⁷ cm² s⁻¹ for the BPA–Cr(III) system and between 1.65 × 10⁻⁶ and 2.8 × 10⁻⁶ cm² s⁻¹ for the Cr(III)–BPA system. The presence of both Cr(III) and BPA in the binary systems increases the adsorption effective diffusion coefficients and therefore the overall adsorption rate of each pollutant. The increased adsorption of each adsorbate when both pollutants are present is due to the in situ formation of complex compounds between Cr(III), acting as central metallic cation, and BPA, acting as ligand, during adsorption of both adsorbates on activated carbon.     

Kinetic and equilibrium studies of Pb(II) and Cd(II) removal from aqueous solution onto colemanite ore waste

The adsorption characteristics of Pb(II) and Cd(II) onto colemanite ore waste (CW) from aqueous solution were investigated as a function of pH, adsorbent dosage, contact time, and temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were applied to describe the adsorption isotherms. Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The adsorption capacity of CW was found to be 33.6 mg/g and 29.7 mg/g for Pb(II) and Cd(II) ions, respectively. Analyte ions were desorbed from CW using both 1 M HCl and 1 M HNO₃. The recovery for both metal ions was found to be higher than 95%. The mean adsorption energies evaluated using the D-R model indicated that the adsorption of Pb(II) and Cd(II) onto CW were taken place by chemisorption. The thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) showed that the adsorption of both metal ions was feasible, spontaneous and exothermic at 20-50 °C. Adsorption mechanisms were also investigated using the pseudo-first-order and pseudo-second-order kinetic models. The kinetic results showed that the adsorption of Pb(II) and Cd(II) onto CW followed well pseudo-second order kinetics.     

A new cyclic binuclear Ni(II) complex as a catalyst towards nitroaldol (Henry) reaction

A new cyclic binuclear Ni(II) complex, [Ni₂(H₂L)₂] · 4MeOH (1), has been synthesized using the Schiff base N′¹,N′³-bis(2-hydroxybenzylidene)malonohydrazide (H₄L). The X-ray crystal structure of 1 shows that the ligand coordinates in the dianionic keto form (H₂L^2 −) via mutual sharing of two Ni(II) ions. Complex 1 acts as a heterogeneous catalyst for the Henry reaction in water. A maximum conversion of ca. 93% was obtained under optimized conditions.     

Metal sorption on macroporous poly(GMA-co-EGDMA) modified with ethylene diamine

Two samples of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), poly(GMA-co-EGDMA), with different porosity parameters were synthesized by suspension copolymerization and modified by ring-opening reaction of the pendant epoxy groups with ethylene diamine (EDA). The samples were characterized by mercury porosimetry, FT-IR spectroscopy and elemental analysis. The sorption rate of the modified copolymer, poly(GMA-co-EGDMA)-en for Cu(II) ions determined under non-competitive conditions was relatively rapid, i.e. the maximum capacity was reached within 30 min. Batch sorption capacities for Cu(II), Fe(II), Mn(II), Cd(II), Zn(II), Pb(II), Cr(III) and Pt(IV) ions were determined under non-competitive conditions in the pH range 1.25–5.5 at room temperature. The maximum sorption capacities of poly(GMA-co-EGDMA)-en under non-competitive conditions were 1.30 mmol/g for Pt(IV) at pH 5.5, 1.10 mmol/g for Cu(II) at pH 5.5, 1.06 mmol/g for Pb(II) at pH 1.25 and 0.67 mmol/g for Cd(II) ions at pH 5.5. The selectivity of poly(GMA-co-EGDMA)-en towards Cu(II), Co(II), Ni(II), Pb(II) and Pt(IV) ions was investigated under competitive conditions. Poly(GMA-co-EGDMA)-en showed high selectivity for Pt(IV) over Cu(II), Co(II), Ni(II) and Pb(II) ions at pH 2.1. At pH 5.5, the metal sorption capacities of poly(GMA-co-EGDMA)-en decreased in the order: Cu(II) > Co(II) > Pt(IV) ≈ Ni(II) > Pb(II). Regeneration of the Cu(II), Ni(II) and Pb(II) loaded poly(GMA-co-EGDMA)-en with 2 M H₂SO₄ showed that the polymer can be reused in several sorption/desorption cycles.     

Influence of anion induced proton abstraction on Cu(II) adsorption by alginic acid

Alginic acid (AA) synthesized by acidification of commercial sodium alginate was investigated for its Cu(II) adsorption efficiency in the presence of different counter ions. The results of batch adsorption studies indicated an adsorption of 169.86 mg/g of Cu(II) by AA in the presence of acetate ions, however, it significantly decreased in the presence of chloride (126.36 mg/g), sulphate (115.24 mg/g) and nitrate (113.28 mg/g) as counter ions. This can be accounted to the tendency of conjugate base (anion) to abstract proton from AA, which determines the extent of deprotonation of carboxylic acid. The FTIR and TGA/DTA studies support the difference in the coordination of carboxylate to Cu(II) in the presence of various counter anions. Acetate showed strong chelate coordination between Cu(II) and AA, whereas in the presence of Cl⁻, NO₃⁻ and SO₄^2 −, Cu(II) was complexed by weak bridging coordination with AA.     

Multiwalled carbon nanotube impregnated with bis(5-bromosalicylidene)-1,3-propandiamine for enrichment of Pb2+ ion

Multiwalled carbon nanotube impregnated by bis(5-bromosalicylidene)-1,3-propandiamine (BBSPN) was synthesized and applied as adsorbent for the enrichment of trace amount of Pb²⁺ ion subsequent their determination by flame atomic absorption spectroscopy (FAAS). The influences of the analytical parameters including pH, amount of ligand and adsorbent, type and condition of eluent and sample volume on the Pb²⁺ ion recoveries were investigated. The optimum pH value for the separation of Pb²⁺ ion on the new sorbent was 6 and the adsorbed Pb²⁺ ion could be completely eluted by using 5.0 mL of 2.0 mol L⁻¹ HNO₃ solutions with 0.015 g of ligand and 0.100 g of adsorbent. Common coexisting ions did not interfere with the separation and determination of target metal ions. The method has high sorption–preconcentration efficiency with relative standard deviation less than 4.0%, especially for lead determination in radish, vegetable, potato, tomato and cheeps.     

Effect of core-shell reversal on the structural,magnetic and adsorptive properties of Fe2O3-GO nanocomposites

Effect of core-shell reversal on the nanocomposites of graphene oxide (GO) and ferric oxide (Fe₂O₃) was studied. Fe₂O₃@GO core-shell nanosheets were synthesized by sonication method, while the GO@Fe₂O₃ core-shell nanospheres by employing N,N′-dicyclohexylcarbodimide as the binding agent for the wrapping of GO sheets on pre-formed Fe₂O₃ nanoparticles (NPs). The phase composition, crystallinity and morphology of the nanocomposites were characterized by FT-IR, TEM, SEM-EDS, VSM, BET surface area study and XRD techniques. The saturation magnetization (M_s) was 1.25 and 0.51 emu g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO respectively owing to the dependence of magnetic properties on the reversal of core-shell. BET analysis revealed the surface area of 100.32 m² g⁻¹ and 45.69 m² g⁻¹ for GO@Fe₂O₃ and Fe₂O₃@GO nanocomposites respectively. The fabricated nanocomposites were analyzed as adsorbents for the uptake of Pb (II) ions. The impact of various factors affecting adsorption process such as pH, adsorbent dose, contact time, temperature and metal ion concentration was also investigated. GO@Fe₂O₃ core-shell nanospheres showed a higher adsorption capacity for Pb (II) ions as compared to Fe₂O₃@GO core-shell nanosheet with the maximum adsorption capacities (q_m) of 303.0 and 125.0 mg g⁻¹ respectively. The equilibrium data was estimated by Freundlich, Langmuir, D-R and Temkin isotherm models. Thermodynamic analysis confirmed the spontaneous and exothermic nature of the adsorption process. The adsorption kinetics was significantly fitted to pseudo-second order model. The results confirmed that core-shell reversal can significantly alter the adsorptive properties of Fe₂O₃-GO nanocomposite     

Adsorption of Cu(II) ions from aqueous solutions on modified chrysotile: Thermodynamic and kinetic studies

The adsorption of Cu(II) ions by modified chrysotile from aqueous solution was investigated under different experimental conditions. The Langmuir and Freundlich equations were introduced to describe the linear forms about the adsorption of Cu(II) ions on the surface of modified chrysotile, and it was found that the adsorption equilibrium process was well described by the Langmuir isotherm model with the maximum adsorption capacity of 1.574 mmol/g at 333 K. The thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) for adsorption on modified chrysotile were also determined from the temperature dependence. The influences of specific parameters such as temperature, pH value and initial concentration for the kinetic studies were also examined. The adsorption follows a pseudo-second order rate law.     

Three-dimensional fourfold interpenetrated (10, 3)-b nickel(II) framework with 5-(isonicotinamido)isophthalate

A new three-dimensional nickel(II) metal-organic framework [Ni(INAIP)(H₂O)₂]_n · nH₂O (1) [H₂INAIP = 5-(isonicotinamido)isophthalic acid] was synthesized under hydrothermal conditions, and characterized by single-crystal X-ray structure determination, thermogravimetric analysis, X-ray powder diffraction, IR and magnetic studies. The compound 1 has (10, 3)-b topology with not well known fourfold interpenetration, in which both Ni(II) atoms and INAIP^2? ligands act as three-connected nodes.     

Multiwalled carbon nanotube impregnated with tartrazine: Solid phase extractant for Cd(II) and Pb(II)

A solid phase extraction procedure has been presented by using multiwalled carbon nanotube impregnated with tartrazine for cadmium (Cd(II)) and lead (Pb(II)) ions. The influences of pH, flow rate, eluent and sample volume were investigated. No interference effects were observed from the alkaline, alkaline earth and some transition metals. The detection limits (LOD) were 0.8 and 6.6 μg L⁻¹ for Cd(II) and Pb(II), respectively. The preconcentration factor was 40. The validation of the procedure was controlled by the analysis of certified references materials. The procedure was applied to the determination of cadmium and lead in natural water and food samples.     

Pb(II) sorption on molecular sieve analogues of MCM-41 synthesized from kaolinite and montmorillonite

Mesoporous molecular sieves were prepared with montmorillonite and kaolinite as silica sources, respectively, (denoted as P-M and P-K) by a hydrothermal method. The two prepared materials were characterized by XRD, FTIR and N₂ adsorption–desorption. The results indicated that both P-M and P-K are typical mesoporous molecular sieves with high specific surface areas. Sorption of Pb(II) from aqueous solution to P-M and P-K was studied by using a batch technique. The effect of contact time, pH and temperature on the sorption of Pb(II) to P-M and P-K was investigated. A simplified surface complexation model was used to simulate the complexation of Pb(II) ions onto molecular sieves. The results suggested that sorption of Pb(II) was strongly dependent on pH values. Kinetics of sorption showed that the pseudo-second-order kinetic model held for the sorption process. Equilibrium modeling showed that the sorption of Pb(II) was fitted well by the Langmuir isotherm model. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were calculated from the sorption of Pb(II) at three different temperatures of 283 K, 303 K and 333 K. The sorption reaction was endothermic and the process was favored at high temperature. The results indicated that both P-M and P-K are suitable materials for removal of Pb(II) from large volumes of aqueous solutions.     

Polymer-derived mesoporous Ni/SiOC(H) ceramic nanocomposites for efficient removal of acid fuchsin

In this paper, magnetic porous Ni-modified SiOC(H) ceramic nanocomposites (Ni/SiOC(H)) were successfully prepared via a template-free polymer-derived ceramic route, which involves pyrolysis at 600 °C of nickel-modified allylhydridopolycarbosilane (AHPCS-Ni) precursors synthesized by the reaction of allylhydridopolycarbosilane (AHPCS) with nickel(II)acetylacetonate (Ni(acac)₂). The resultant Ni/SiOC(H) nanocomposites are comprised of in-situ formed nanoscaled Ni socialized with small amounts of NiO and nickel silicides embedded in the amorphous SiOC(H) matrix. The materials show ferromagnetic behavior and excellent magnetic properties with the saturation magnetization in the range of 1.71–7.08 emu g⁻¹. Besides, the Ni/SiOC(H) nanocomposites are predominantly mesoporous with a high BET surface area and pore volume in the range of 253–344 and 0.134–0.185 cm³ g⁻¹, respectively. The measured porosity features cause an excellent adsorption capacity towards a template dye acid fuchsin with the adsorption capacity Q_t at 10 min of 80.7–85.8 mg g⁻¹ and the Q_e at equilibrium of 123.8–129.8 mg g⁻¹.