Thermodynamic and kinetic studies for the adsorption of Hg(II) by nano-TiO2 from aqueous solution

Titanium dioxide nanocrystals were employed, for the first time, for the sorption of Hg(II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initial metal concentration, and contact time on the adsorption process were examined. Adsorption equilibrium was established in 420 min and the maximum adsorption of Hg(II) on the TiO₂ was observed to occur at pH 8.0. The adsorption data correlated with Freundlich, Langmuir, Dubinin–Radushkevich (D–R), and Temkin isotherms. The Freundlich isotherm showed the best fit to the equilibrium data. The Pseudo-first order and pseudo-second-order kinetic models were studied to analyze the kinetic data. A second-order kinetic model fit the data with the (k₂ = 2.8126 × 10^?3 g mg^?1min^?1, 303 K). The intraparticle diffusion models were applied to ascertain the rate-controlling step. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were calculated which showed an endothermic adsorption process. The equilibrium parameter (R_L) indicated that TiO₂ nanocrystals are useful for Hg(II) removal from aqueous solutions.     

Preparation of surface modified zinc oxide nanoparticle with high capacity dye removal ability

In this paper, the surface modification of zinc oxide nanoparticle (ZON) by amine functionalization was studied to prepare high capacity adsorbent. Dye removal ability of amine-functionalized zinc oxide nanoparticle (AFZON) and zinc oxide nanoparticle (ZON) was also investigated. The physical characteristics of AFZON were studied using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Acid Blue 25 (AB25), Direct Red 23 (DR23) and Direct Red 31 (DR31) were used as model compounds. The effect of operational parameters such as dye concentration, adsorbent dosage, pH and salt on dye removal was evaluated. The isotherm and kinetic of dye adsorption were studied. The maximum dye adsorption capacity (Q₀) was 20 mg/g AB25, 12 mg/g DR23 and 15 mg/g DR31 for ZON and 1250 mg/g AB25, 1000 mg/g DR23 and 1429 mg/g DR31 for AFZON. It was found that dye adsorption followed Langmuir isotherm. Adsorption kinetic of dyes was found to conform to pseudo-second order kinetics. Dye desorption tests (adsorbent regeneration) showed that the maximum dye release of 90% AB25, 86% for DR23 and 90% for DR31 were achieved in aqueous solution at pH 12. Based on the data of the present investigation, it can be concluded that the AFZON being an adsorbent with high dye adsorption capacity might be a suitable alternative to remove dyes from colored aqueous solutions.     

Tannin-immobilized mesoporous silica bead (BT–SiO2) as an effective adsorbent of Cr(III) in aqueous solutions

This study describes a new approach for the preparation of tannin-immobilized adsorbent by using mesoporous silica bead as the supporting matrix. Bayberry tannin-immobilized mesoporous silica bead (BT–SiO₂) was characterized by powder X-ray diffraction to verify the crystallinity, field-emission scanning electron microscopy to observe the surface morphology, and surface area and porosity analyzer to measure the mesoporous porous structure. Subsequently, the adsorption experiments to Cr(III) were applied to evaluate the adsorption performances of BT–SiO₂. It was found that the adsorption of Cr(III) onto BT–SiO₂ was pH-dependent, and the maximum adsorption capacity was obtained in the pH range of 5.0–5.5. The adsorption capacity was 1.30 mmol g^?1 at 303 K and pH 5.5 when the initial concentration of Cr(III) was 2.0 mmol L^?1. Based on proton nuclear magnetic resonance (HNMR) analyses, the adsorption mechanism of Cr(III) on BT–SiO₂ was proved to be a chelating interaction. The adsorption kinetic data can be well described using pseudo-first-order model and the equilibrium data can be well fitted by the Langmuir isothermal model. Importantly, no bayberry tannin was leached out during the adsorption process and BT–SiO₂ can simultaneously remove coexisting metal ions from aqueous solutions. In conclusion, this study provides a new strategy for the preparation of tannin-immobilized adsorbents that are highly effective in removal of heavy metals from aqueous solutions.     

Na0.5Li0.5CoO2 nanopowders: Facile synthesis,characterization and their application for the removal of methylene blue dye from aqueous solution

In this paper, delafossite-type Na_0.5Li_0.5CoO₂ nanoparticles (NPs) with an average particle size of 50 nm were successfully synthesized by sol–gel method. Prepared NPs were characterized by differential thermal analysis, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and scanning tunneling microscopy. The nanoparticles showed the excellent adsorption properties towards methylene blue dye (MBD) as a reactive dye. The kinetics of removal of MBD in aqueous solutions was studied in a series of experiments which were varied in the amount of NPs, contact time, pH, and temperature. The experimental data were fitted very well in the pseudo-second order kinetic model and the Freundlich adsorption isotherm model. 92% of dye was successfully removed in 10 min using 0.02 g Na_0.5Li_0.5CoO₂ NPs in a pH = 11. Thermodynamic study indicates that the adsorption of MBD is feasible, and spontaneous in nature.     

Preparation of chitosan/magnetite composite beads and their application for removal of Pb(II) and Ni(II) from aqueous solution

A simple and effective process has been proposed to prepare chitosan/magnetite nanocomposite beads with saturation magnetization value as high as uncoated Fe₃O₄ nanoparticles (ca. 54 emu/g). The reason was that the coating chitosan layer was so thin that it did not affect magnetic properties of these composite beads. Especially, chitosan on the surface of the magnetic Fe₃O₄ nanoparticles is available for coordinating with heavy metal ions, making those ions removed with the assistance of external magnets. Maximum adsorption capacities for Pb(II) and Ni(II), occurred at pH 6 and under room temperature were as high as 63.33 and 52.55 mg/g respectively, according to Langmuir isotherm model. These results permitted to conclude that chitosan/magnetite nanocomposite beads could serve as a promising adsorbent not only for Pb(II) and Ni(II) (pH = 4–6) but also for other heavy metal ions in wastewater treatment technology.     

Equilibrium and kinetics of cadmium adsorption from aqueous solutions using untreated Pinus halepensis sawdust

Untreated Pinus halepensis sawdust has been investigated as an adsorbent for the removal of cadmium from aqueous solutions. Batch experiments were carried out to investigate the effect of pH, adsorbent dose, contact time, and metal concentration on sorption efficiency. The favorable pH for maximum cadmium adsorption was at 9.0. For the investigated cadmium concentrations (1–50 mg/L), maximum adsorption rates were achieved almost in the 10–20 min of contact. An adsorbent dose of 10 g/L was optimum for almost complete cadmium removal within 30 min from a 5 mg/L cadmium solution. For all contact times, an increase in cadmium concentration resulted in decrease in the percent cadmium removal (100–87%), and an increase in adsorption capacity (0.11–5.36 mg/g). The equilibrium adsorption data were best fitted with the Freundlich isotherm (R² = 0.960). The kinetics of cadmium adsorption was very well described by the pseudo-second-order kinetic model (R² > 0.999).     

Removal and preconcentration of lead (II), copper (II), chromium (III) and iron (III) from wastewaters by surface developed alumina adsorbents with immobilized 1-nitroso-2-naphthol

The potential removal and preconcentration of lead (II), copper (II), chromium (III) and iron (III) from wastewaters were investigated and explored. Three new alumina adsorbents of acidic, neutral and basic nature (I–III) were synthesized via physical adsorption and surface loading of 1-nitroso-2-naphthol as a possible chelating ion-exchanger. The modified alumina adsorbents are characterized by strong thermal stability as well as resistance to acidic medium leaching processes. High metal up-take was found providing this order: Cu(II) > Cr(III) > Pb(II) owing to the strong contribution of surface loaded 1-nitroso-2-naphthol. The outlined results from the distribution coefficient and separation factor evaluations (low metal ion concentration levels) were found to denote to a different selectivity order: Pb(II) > Cu(II) > Cr(III)) due to the strong contribution of alumina matrix in the metal binding processes. The potential applications of alumina adsorbents for removal and preconcentration of Pb(II), Cu(II), Cr(III) from wastewaters as well as drinking tap water samples were successfully accomplished giving recovery values of (89–100 ± 1–3%) and (93–99 ± 3–4%), respectively without any noticeable interference of the wastewater or drinking tap water matrices.     

As(V) removal from aqueous media using α-MnO2 nanorods-impregnated laterite composite adsorbents

We present a novel way of enhancing the utility of low cost readily available laterite by impregnating it with the α-MnO₂ nanorods, thus making a composite material suitable for the removal of As(V) from aqueous media. The composites were synthesized by two methods: (i) ball-milling of a physical blend of laterite with pre-synthesized MnO₂; and (ii) in situ formation of MnO₂ in the presence of laterite. The BET surface area of composites prepared by both methods was markedly higher compared to un-modified laterite, and the presence of MnO₂ in the composite was also confirmed by XRD analysis and TEM microscopy. The adsorption capacity for As(V) was found to be highly pH dependent and the adsorption kinetics followed a pseudo second-order kinetic model. The Langmuir adsorption isotherm was found to be the best model to describe the adsorption equilibrium of As(V) onto un-modified laterite as well both ball-milled and in situ formed composite. The adsorption capacities at room temperature and pH 7.0 were found to be 1.50 mg g^?1, 8.93 mg g^?1 and 9.70 mg g^?1, for un-modified laterite, ball-milled and in situ formed composite, respectively.     

Adsorption of Cr(VI) from aqueous solution by hydrous zirconium oxide

A type of ZrO₂·nH₂O was synthesized and its Cr(VI) removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The Cr(VI) adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model. The adsorption capacity increased from 61 to 66 mg g^?1 when the temperature was increased from 298 to 338 K. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. The effective desorption of Cr(VI) on ZrO₂·nH₂O could be achieved using distilled water at pH 12.     

Synthesis,characterisation, and adsorption evaluation of carbon-natural-zeolite composites

Natural zeolite is well known for the removal of heavy metals and has wide spread applications, however it has a negligible adsorption capacity for organic contaminants from aqueous solution. Several composites of carbon and natural zeolite with varying amounts of carbon were synthesised as prospective adsorbents to adsorb organic contaminants from waste water. The composites were prepared by saturating a natural zeolite with carbon precursor (furfural alcohol) and then carbonised at 800 °C in inert atmosphere. The structure and properties of the composites were characterised using various techniques such as XRD, FT-IR, FT-Raman, SEM and TEM. In phenol adsorption tests, adsorption isotherm indicated an enhanced adsorption of phenol on the composites as compared with the natural zeolite. It was also showed that the adsorption increased with increase in carbon content of the composite. The equilibrium data were modelled with the Langmuir, Freundlich, Temkin and Smith models.     

Adsorption of lead(II) ions onto 8-hydroxy quinoline-immobilized bentonite

In this study, the immobilization of 8-hydroxy quinoline onto bentonite was carried out and it was then used to investigate the adsorption behavior of lead(II) ions from aqueous solutions. The changes of the parameters of pH, contact time, initial lead(II) ions concentration and temperature were tested in the adsorption experiments. The XRD, FTIR, elemental and thermal analyses were done to observe the immobilization of 8-hydroxy quinoline onto natural bentonite. The adsorption was well described by the Langmuir adsorption isotherm model at all studied temperatures. The maximum adsorption capacity was 142.94mgg(-1) from the Langmuir isotherm model at 50 degrees C. The thermodynamic parameters implied that the adsorption process is spontaneous and endothermic. The kinetic data indicate that the adsorption fits well with the pseudo-second-order kinetic model. 8-Hydroxy quinoline-immobilized bentonite can be used as well respective adsorbent for the removal of the heavy metal pollutants according to the results.     

Isotherm studies of lead(II), manganese(II), and cadmium(II) adsorption by Nigerian bentonite clay in single and multimetal solutions

This study was aimed at evaluating the isotherm of lead(II), manganese(II), and cadmium(II) adsorption in single and multimetal solutions using Nigerian bentonite. The natural and calcined clays were characterized for specific surface area, surface morphology, elemental composition, and cation exchange capacity (CEC). The adsorption data were analyzed and interpreted using isotherm models. The natural bentonite exhibits a specific surface area of 23.5?m²/g and a CEC value of 47.7 mEq/100?g and displays a higher adsorption capacity of all heavy metals in both single and multimetal solutions than the calcined bentonite. The removal of lead(II) by natural bentonite in single-component system is 0.0448?mmol/g. The order of selectivity is lead(II)?>?cadmium(II)?>?manganese(II). Result also shows that both clays demonstrate a preferable adsorption toward lead(II). Lead(II) adsorption is less affected by the presence of counter cations in multimetal solution. The adsorption of heavy metals onto Dijah-Monkin bentonite is site selective and site specific, and the adsorption data are well presented by the Langmuir model. The CEC could be the primary mechanism for the uptake of heavy metals, and the removal capacity was shown to depend on the ionic radius of metal ions.     

Polyacrylamide thorium (IV) phosphate as an important lead selective fibrous ion exchanger: synthesis, characterization and removal study

The objective of the present research was to synthesize, characterize and to investigate the removal efficiency of lead (II) ion from synthetic lead solution by a hybrid fibrous ion exchanger. In the present study polyacrylamide thorium (IV) phosphate was synthesized by co-precipitation method and was characterized using SEM, XRD, FTIR and TGA-DSC. To know the practical applicability, a detailed removal study of lead ion was carried out. The removal of lead was 52.9% under neutral condition, and using 0.4 g of adsorbent in 100 mL of lead solution having initial concentration of 100 mg/L. Adsorption kinetic study revealed that the adsorption process followed first order kinetics. Adsorption data were fitted to linearly transformed Langmuir isotherm with R(2) (correlation coefficient)>0.99. Thermodynamic parameters were also calculated to study the effect of temperature on the removal process. In order to understand the adsorption type, equilibrium data were tested with Dubinin-Radushkevich isotherm. The percentage removal was found to increase gradually with increase in pH and 99% removal was achieved at pH 10. The process was rapid and equilibrium was established within first 30 min.     

Removal of Pb(II) ions from aqueous solution by adsorption using bael leaves (Aegle marmelos)

Biosorption of Pb(II) on bael leaves (Aegle marmelos) was investigated for the removal of Pb(II) from aqueous solution using different doses of adsorbent, initial pH, and contact time. The maximum Pb loading capacity of the bael leaves was 104 mg g^?1 at 50 mg L^?1 initial Pb(II) concentration at pH 5.1. SEM and FT-IR studies indicated that the adsorption of Pb(II) occurs inside the wall of the hollow tubes present in the bael leaves and carboxylic acid, thioester and sulphonamide groups are involved in the process. The sorption process was best described by pseudo second order kinetics. Among Freundlich and Langmuir isotherms, the latter had a better fit with the experimental data. The activation energy E_a confirmed that the nature of adsorption was physisorption. Bael leaves can selectively remove Pb(II) in the presence of other metal ions. This was demonstrated by removing Pb from the effluent of exhausted batteries.     

Characterizations of strontium(II) and barium(II) adsorption from aqueous solutions using dolomite powder

In this research, adsorption technique was applied for strontium and barium removal from aqueous solution using dolomite powder. The process has been investigated as a function of pH, contact time, temperature and adsorbate concentration. The experimental data was analyzed using equilibrium isotherm, kinetic and thermodynamic models. The isotherm data was well described by Langmuir isotherm model. The maximum adsorption capacity was found to be 1.172 and 3.958 mg/g for Sr(II) and Ba(II) from the Langmuir isotherm model at 293 K, respectively. The kinetic data was tested using first and pseudo-second order models. The results indicated that adsorption fitted well with the pseudo-second order kinetic model. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were also determined using the equilibrium constant value obtained at different temperatures. The results showed that the adsorption for both ions was feasible and exothermic.     

Removal of heavy metal lead(II) using nanoscale zero-valent iron with different preservation methods

In this study, different nanoscale zero-valent irons (nZVI) were prepared in order to improve their stability and reactivity to heavy metal lead (Pb (II)). The composition, particle size and morphology of obtained nZVI were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscope (SEM). The effects of nZVI dosage, pH, initial Pb (II) concentration and reaction time on the removal efficacy of Pb (II) were investigated. The results show that undried nZVI has more active sites due to its weaker oxidation, and thus the removal efficiency of Pb(II) by undried nZVI was higher than that by dried nZVI. As a result, the same removal efficiency could be achieved with the use of less undried nZVI for the identical concentration of Pb(II). Furthermore, the experimental procedure could be apparently simplified, which eliminates the steps of washing, separation and dehydration compared with the traditional preparation method. The experimental data could be well fitted by the Langmuir adsorption isotherm model, and the maximum adsorption capacity of dried and undried nZVI is 671.14 and 807.23?mg·g^?1 at pH 6, respectively. The experimental data followed the pseudo second-order kinetic model with a kinetic constant of 7.65?×?10^?4 and 1.39?×?10^?3 for undried and dried nZVI, respectively. In conclusion, undried nZVI had high adsorption capacity and adsorption rate for Pb(II) in the solution.     

Characterization of sodium dodecyl sulfate modified iron pillared montmorillonite and its application for the removal of aqueous Cu(II) and Co(II)

Anionic surfactant modified Fe-pillared montmorillonites were prepared by Fe-hydrate solution and sodium dodecyl sulfate (SDS) solution. These organo–inorgano complex montmorillonites were divided into three types (CM1, CM2 and CM3) depending on different intercalation processes. X-ray diffraction spectra, the Fourier transform infrared (FTIR) spectra were used to analyze the structure of the raw and modified montmorillonites. X-ray photoelectron spectra of the simples have been studied to determine spectral characteristics to allow the identification of Fe(III) hydroxide. The specific surface area of the host montmorillonite (M0) is 73.2 m²/g, while for the modified montmorillonites it is 114.0 m²/g, 117.2 m²/g, and 115.8 m²/g, respectively. The mesopore volumes of the montmorillonites decrease after modification. Ions of copper and cobalt were selected as adsorbates to evaluate the adsorption performance of each montmorillonite. The adsorption data was analyzed by both Freundlich and Langmuir isotherm models and the data was well fit by the Langmuir isotherm model. The adsorption was efficient and significantly influenced by metal speciation, metal concentration, contact time, and pH. Higher adsorption capacity of the modified montmorillonites were obtained at pH 5–6. The results of desorption indicated that the metal ions were covalently bound to the modified montmorillonites.     

Poly(N,N-dimethylaminoethyl methacrylate) modification of activated carbon for copper ions removal

Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) functionalization of rice husk-based activated carbon was prepared and its application in the removal of copper ions was investigated. The structural properties of the resulting composite material were characterized by means of N₂ adsorption/desorption, Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA). The obtained composite is observed to hold a relatively large pore diameter of 3.8 nm and high surface area of 789 m² g^?1 with 12 wt% of PDMAEMA coated, which is significant for its use as adsorbent. The ability of the composite material for removing Cu²⁺ from aqueous solution was studied by batch experiments. The adsorption data obeyed the Langmuir isotherms, which revealed that 1 g of the prepared material could adsorb 31.46 mg of Cu²⁺ from its aqueous solution. The PDMAEMA functionalized activated carbon is expected to be used as an efficient adsorbent for removing other heavy metal ions and dyes in water.     

Synthesis and characterization of amino acid containing Cu(II) chelated nanoparticles for lysozyme adsorption

Immobilized metal ion affinity chromatography (IMAC) is a useful method for adsorption of proteins that have an affinity for transition metal ions. In this study, poly(hydroxyethyl methacrylate-methacryloyl-l-tryptophan) (PHEMATrp) nanoparticles were prepared by surfactant free emulsion polymerization. Then, Cu(II) ions were chelated on the PHEMATrp nanoparticles to be used in lysozyme adsorption studies in batch system. The maximum lysozyme adsorption capacity of the PHEMATrp nanoparticles was found to be 326.9 mg/g polymer at pH 7.0. The nonspecific lysozyme adsorption onto the PHEMA nanoparticles was negligible. In terms of protein desorption, it was observed that adsorbed lysozyme was readily desorbed in medium containing 1.0 M NaCl. The results showed that the metal-chelated PHEMATrp nanoparticles can be considered as a good adsorbent for lysozyme purification.     

Preparation of biomorphic porous calcium titanate and its application for preconcentration of nickel in water and food samples

Biomorphic porous nanocrystalline-calcium titanate (SPCTO) was successfully prepared using the sol–gel method and with sorghum straw as the template. Characterization was conducted through XRD, SEM and FTIR. The ability of SPCTO to adsorb nickel ion in water was assessed. Elution and regeneration conditions, as well as the thermodynamics and kinetics of nickel adsorption, were also investigated. The result showed that the sorbent by the sol–gel template method was porous and has a perovskite structure with an average particle diameter of 26 nm. The nickel ion could be quantitatively retained at a pH value range of 4–8, but the adsorbed nickel ion could be completely eluted using 2 mol L^? 1 HNO₃. The adsorption capacity of SPCTO for nickel was found to be 51.814 mg g^? 1 and the adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 33.520 kJ mol^? 1. At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (E_a) was 25.291 kJ mol^? 1 for the adsorption. These results demonstrate that the adsorption was an endothermic and spontaneous physical process. This same method has been successfully applied in the preconcentration and determination of nickel in water and food samples with good results.