Preparation and characterization of L-glutamic acid-functionalized graphene oxide for adsorption of Pb(II)

An efficient adsorbent (L-Glu/GO) was successfully synthesized by the reaction between L-glutamic acid (L-Glu) and graphene oxide (GO). The structure and morphology of this adsorbent were characterized by FTIR, SEM, XRD, and TGA. The SEM result indicated that the adsorbent was a nanomaterial with a size of about 50–400 nm. The adsorption experiments of various heavy ions on L-Glu/GO demonstrated that the adsorption performance of Pb(II) was better than others. Various variables affecting the adsorption of L-Glu/GO for Pb(II) were systematically explored. The experimental results indicated that the maximum adsorption capacity and equilibrium time of Pb(II) on L-Glu/GO were 513.4 mg g^?1 and 40 minute, respectively. The sorption kinetics and isotherm fitted well with the pseudo-second-order model and Langmuir model, respectively. The sorption mainly was a chemical process. Thermodynamic studies revealed that the adsorption was a spontaneous and exothermic process. The adsorbent could be regenerated with HCl solution. Hence, it was suggested that the L-Glu/GO could be applied in the removal of Pb(II) from wastewaters.     

Graft copolymerization of epichlorohydrin and ethylenediamine onto cellulose derived from agricultural by-products for adsorption of Pb(II) in aqueous solution

In order to develop a low-cost and high efficient absorbent, cellulose was extracted from peanut hulls, soybean shells and grapefruit peels using 17.5 % NaOH and then copolymerized with epichlorohydrin and ethylenediamine. Infrared spectra and N contents show that the cellulose was copolymerized successfully with the ethylenediamine. Factors affecting the adsorption behavior of Pb(II), such as pH, temperature, ratio of solid to liquid, competitive sorption of various metal ions, initial metal concentration and adsorption time, were then investigated. The adsorption equilibrium could be obtained within 120 min and the kinetic adsorption processes fitted well with the pseudo-second order kinetic model. The isotherm adsorption data fitted well with Langmuir adsorption model and the maximum absorption capacities of the modified peanut hulls, soybean shells and grapefruit peels were 47.8, 101 and 232 mg g^?1, respectively. The competitive adsorption of mixed metal ions demonstrated that Pb(II) was preferentially removed from solution by the modified peanuts shells, soybean shells and grapefruit peels, then Cu(II) and Cr(III). Desorption of Pb(II) from modified peanut hulls, soybean shells and grapefruit peels was effectively achieved in a 1 mol L^?1 HCl solution. Ethylenediamine-modified grapefruit peels exhibited higher absorption performance than the ethylenediamine-modified soybean shells and peanut hulls and can be used as potential low-cost and high efficient absorbents for the removal of lead ions from wastewater.     

Adsorption of Pb(II) and Ni(II) From Aqueous Solution by a High-Capacity Industrial Sewage Sludge-Based Adsorbent

In the present study, adsorption of Ni(II) and Pb(II) from aqueous solution was investigated using activated carbon synthesized with industrial wastewater sludge. The synthesized adsorbent was analyzed using nitrogen adsorption–desorption and Fourier transfer infrared (FTIR) techniques. Batch adsorption mode was used to evaluate the effect of solution pH, contact time, adsorbent dose, initial metal ion concentration, and temperature on the adsorption capacity of the synthesized adsorbent. The kinetic data were analyzed using different kinetic models. The pseudo-second-order equation gave the best fit to the experimental data for both metal ions. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm models. The results showed that the data obtained for the Ni(II) and Pb(II) adsorption are in good agreement with the Langmuir model. The Langmuir mono-layer maximum adsorption capacities for Ni(II) and Pb(II) ions were estimated to be 74.06 and 88.76 mg g^?1 at 25°C, respectively. In addition, the thermodynamic studies proved that the adsorption process of both metals could be considered endothermic.     

Preconcentration of Pb2+ by iron oxide/amino-functionalized silica core–shell magnetic nanoparticles as a novel solid-phase extraction adsorbent and its determination by flame atomic absorption spectrometry

The use of iron oxide/amino-functionalized silica core–shell magnetic nanoparticles for preconcentration of Pb²⁺ followed by its consecutive atomic absorption spectrometry determination is described. Effects of various operating variables, namely, solution pH, initial Pb²⁺ concentration, contact time, adsorbent dosage, sample volume, concentration and volume of desorbing solution, and co-existing ions on solid-phase extraction (SPE) of Pb²⁺ were studied by batch equilibrium technique. The experimental adsorption data were well fitted to the Langmuir isotherm model. The Langmuir adsorption capacity and equilibrium time were found to be 100 mg g^?1 and 20 min, respectively. The adsorption data were also fitted to kinetic pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed pseudo-second-order model. Under the optimal SPE conditions, the enrichment factor, detection limit and relative standard deviation for determination of Pb²⁺ were found to be 211, 1 μg L^?1, and 3.7 % for 50 μg L^?1, respectively. The proposed method was successfully applied to the determination of lead in a real sample with satisfactory results.     

β-Cyclodextrin-based polyurethane (β-CDPU) polymers as solid media for adsorption and determination of Pb(II) ions in dust and water samples

In this work, β-CD-based polyurethane copolymers (β-CDPU) have been prepared by reacting β-CD with hexamethylene diisocyanate as cross-linked agent in dry DMF. This polymer showed high selectivity for preconcentration of Pb(II) at trace level prior to its flame atomic absorption spectrometric determination. The effect of several parameters such as pH, flow rate of sample, eluent kind and volume was investigated. The adsorption behaviors and mechanisms of Pb(II) on the samples were also studied. The maximum adsorption amount of Pb(II) was 8 mg g^?1 with the preconcentration factor of 250 for Pb(II). The Langmuir isotherm was proved to describe the adsorption data better than the Freundlich isotherm and a pseudo-first-order kinetic model fits the adsorption kinetic processes well. The calibration curve was linear in the range of (3–200 ng mL^?1) with a correlation coefficient of 0.9996. The limit of detection based on three times the standard deviation of the blank was 1.15 ng mL^?1. The relative standard deviations for the determination of 10 and 100 ng mL^?1 of Pb(II) were 3.60 and 0.43 % (n = 10), respectively. The method was successfully applied to the determination of lead in some environmental samples such as Tehran and Bushehr drinking water, river water and dust samples.     

Sol–gel derived ion-imprinted silica-supported organic–inorganic hybrid sorbent for selective removal of lead(II) from aqueous solution

The current paper presents a novel Pb(II) ion-imprinted silica-supported organic–inorganic hybrid sorbent functionalized with Schiff base by coupling a surface imprinting technique with a sol–gel process for the selective removal of Pb(II) ions from aqueous solution. Fourier transmission infrared spectroscopy, scanning electron microscopy, N₂ adsorption–desorption isotherms and thermogravimetric analysis were used to characterize the Pb(II)-imprinted hybrid sorbent. The adsorption equilibrium was finished with 30 min. The experiment value of maximum adsorption capacity was found to be 54.9 mg g^?1. There were not significantly influence on the adsorption capacity of Pb(II) in the range of pH 3.5–6.5. The equilibrium data were fitted very well to the Langmuir isotherm model and pseudo-first-order kinetics model. Under competitive adsorption conditions, the Pb(II)-imprinted hybrid sorbent was 3.09, 4.73, 3.34 and 4.96 times more selective than the corresponding non-imprinted sorbent for the systems of Pb(II)/Cu(II), Pb(II)/Cd(II), Pb(II)/Ni(II) and Pb(II)/Zn(II), respectively. The thermodynamic results demonstrated that the adsorption of Pb(II) onto the Pb(II)-imprinted hybrid sorbent took place by a spontaneous and endothermic process with further increase in the degree of freedom at the solid–solution interface.     

Adsorption of Malachite Green by Diatomite: Equilibrium Isotherms and Kinetic Studies

The utilization of diatomite as potential adsorbent to remove malachite green (MG) from aqueous solution was developed. The characterization of the diatomite was evaluated by scanning electron microscope (SEM) and Brurauer Emmerr Teller (BET). The operating variables of pH, diatomite mass, initial MG concentration, and adsorption reaction time were studied. The equilibrium, kinetics, and thermodynamic parameters were investigated as well. It was found that the diatomite was composed of integral and almost circle sieve tray with lots of small pores on it, which afforded the diatomite high specific surface area of 46.09 m² g^?1. The optimum pH and reaction time were 7 and 90 minutes, respectively. The MG removal increased accordingly as the diatomite mass increased. The isotherm results showed that the equilibrium data were fitted to Langmuir model better, indicating the MG adsorption was better characterized by mono-layer. The maximum mono-layer capacity obtained from Langmuir was 23.64 mg g^?1 at 25°C. The kinetic studies indicated that experiment data followed pseudo-second-order model better. It also revealed that intraparticle diffusion was not the only rate-controlling step. The thermodynamic results concluded that the adsorption process was endothermic and more favorable at high temperature. Researches confirmed the applicability of diatomite as an efficient adsorbent and low-cost process to remove hazardous materials.     

Adsorption of cadmium and lead from palm oil mill effluent using bone-composite: optimisation and isotherm studies

The adsorption of Cd and Pb ions from palm oil mill effluent on a mesoporous-activated cow bone composite powder has been investigated. Adsorbent was developed from cow bones, coconut shells and zeolite. The composite examined in the present work has a BET surface area of 248.398 m²/g. The optimisation of the removal efficiency of the heavy metals was investigated using central composite design and analysed using response surface methodology. The analysis of variance of the quadratic model signified that the model suitably predicted the uptake of the heavy metal ions at a 95% confidence level. The optimal operating condition was recorded at pH 4, 50 rpm, within 24 h and 1 mm of particle size and 12.5 gL^?1 of adsorbent dosage. The characteristics of the composite were investigated using the Fourier transform irradiation. The morphology and chemical composition of composite was examined using the scanning electron microscopy equipped with energy dispersive x-ray. Characterisation study was conducted before and after the adsorption process. The results obtained illustrated that the removal of cadmium and lead from POME was influenced by the functional groups available on the surface of the composite. The carboxyl and hydroxyl groups are mainly responsible for the removal of cadmium and lead through chelating process. The point of zero charge (pH_pzc) revealed that the adsorbent contained acidic sites with negatively charge surface which influenced the adsorption process. The experimental data of the heavy metals of Cd and Pb investigated were fitted to the Langmuir and Freundlich models. The result revealed that the adsorption equilibrium data fitted better to the Langmuir model for the adsorption Cd and to the Freundlich model for the adsorption of Pb.     

A chelating polymer resin: synthesis,characterization, adsorption and desorption performance for removal of Hg(II) from aqueous solution

A chloromethylated polystyrene-N-methyl thiourea chelating resin (DMTUR) was successfully prepared by the reaction of chloromethylated polystyrene beads (PS-Cl) with N-methyl thiourea (DMTU). The DMTUR exhibited a high selective adsorption toward Hg(II) in the mixture of different metal ions containing Cu(II), Hg(II), Cd(II), Pb(II), Cr(III) and Ni(II), and the adsorption capacity of Hg(II) approached a maximum with a value of 347 mg/g at pH = 4.0. Moreover, the batch kinetic study showed that the adsorption behavior of Hg(II) presented as a pseudo-second-order manner. And the adsorption isotherms fitted well with Langmuir model, and the maximum uptake of Hg(II) could reach to be 476 mg g^?1 at 35 °C. The thermodynamics study ensured the adsorption process essentially as favorable and endothermic. Finally, an eluent of 4 M HNO₃ solution could completely remove the adsorbed Hg(II) and the adsorption capacity allowed a high level at least five cycles. As aforementioned appealing properties, the DMTUR with simple technology, high adsorption capacity, significant selectivity and good regenerability may have a potential application in industrial scale as a treatment of enriched Hg(II) in wastewater.     

Efficient Adsorption and Recovery of Pb(II) from Aqueous Solution by a Granular pH-Sensitive Chitosan-based Semi-IPN Hydrogel

A series of granular pH-sensitive semi-interpenetrating polymer network (semi-IPN) hydrogels based on chitosan (CTS), acrylic acid (AA) and gelatine (GE) were utilized for the adsorption and recycle of Pb(II) from aqueous solutions. The composite hydrogels have been characterized by FT-IR and TGA. The effects of contact time, pH value and initial Pb(II) concentration on the adsorption were investigated. Results indicated that the adsorption capacity of the hydrogel increased with increasing pH value and initial Pb(II) concentration, and a pH-sensitive adsorption characteristic was presented. The adsorption rate of the semi-IPN hydrogels on Pb(II) is fast with an adsorption rate constant of 14.9790 mg/(g·s), and adsorption equilibrium could be reached within 10 min. The adsorption isotherms of the hydrogels for Pb(II) could be described well by the Langmuir equation, rather than the Freundlich equation. The as-prepared hydrogels showed good reusability with 0.05 mol/l HNO₃ solutions as the desorbing agent and 0.1 mol/l NaOH solutions as the regeneration agent, respectively. After five consecutive adsorption-desorption processes, the semi-IPN hydrogel with 20 wt% GE may reach 85.26% of its initial adsorption capacity. In addition, the adsorbed Pb(II) can be quantitatively recovered by simply eluting the hydrogel with dilute HNO₃ solution, and a recovery ratio of 89.27% was reached for the semi-IPN hydrogel. The satisfactory adsorption amount is mainly derived from the chelating of functional groups (i.e. –COO^? and –NH₂) with Pb(II) ions. The hydrogel adsorbents exhibited excellent affinity for Pb(II), and can be applied to treat wastewater containing heavy metal ion and simultaneously recover the valuable metal sources.     

Adsorption of Cu(II) and Zn(II) ions from aqueous solutions onto fine powder of Typha latifolia L. root: kinetics and isotherm studies

Fine powder of Typha latifolia L. root was used for adsorption of copper and zinc ions from buffered and nonbuffered aqueous solutions. The adsorption reached equilibrium in 60 min. During this time, more than 90 % of the adsorption process was completed. The effect of initial pH, initial concentration of metal ion, and contact time was investigated in a batch system at room temperature. The optimum adsorption performance was observed at pH 5.00 and 4.25 for nonbuffered solutions of Cu(II) and Zn(II), respectively, while for buffered solutions it occurred at pH 6.00. The total metal uptake decreased on application of ammonium acetate buffer, from 37.35 to 17.00 mg g^?1 and 28.80 to 9.90 mg g^?1 for Cu(II) and Zn(II) solutions, respectively, with 100 mg L^?1 initial concentration. The pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models were used to describe the adsorption kinetics. The experimental data followed the pseudo-second-order kinetic model. The biosorption equilibrium was well described by Langmuir and Freundlich isotherm models.     

Chemical modification of rose leaf with polypyrrole for the removal of Pb (II) and Cd (II) from aqueous solution

The rose leaf was successfully modified through coating with polypyrrole (PPy) in chemical oxidative route in order to remove Pb(II) and Cd(II) from aqueous media. The rose leaf/polypyrrole (RL/PPy) composites were characterized in terms of morphology, chemical structure, and conductivity properties. The spectrum were obtained from FTIR results which support the formation of RL/PPy composites. FTIR and SEM results indicate that the polypyrrole is completely covered on rose leaf. The conductivity of composite (1.8215 S/cm) was higher than polypyrrole (2.06 × 10^?3 S/cm). The metal removal studies were monitored by Ultraviolet Visible Absorption Spectrometer (UV-Vis). The optimum conditions were detected for adsorption by changing some experimental conditions (such as adsorbent dosage, contact time and stirring speed, initial concentration of the metal solutions and pH). Following the determination of the optimum conditions, the results of the metal removal from wastewater studies were performed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Under the optimum conditions, the ICP-OES results obtained for waste water showed the useability of composite for the removal of Pb(II) and Cd(II). The Langmuir and Freundlich models are subjected to adsorption datas. The datas fitted better when by using Freundlich model.     

Multi‐responses optimization of simultaneous adsorption of methylene blue and malachite green dyes in binary aqueous system onto Ni:FeO(OH)‐NWs‐AC using experimental design: derivative spectrophotometry method

In this research, response surface methodology (RSM) approach using Central Composite Design (CCD) coupled by derivative spectrophotometry method was applied to develop mathematical model and optimize process parameters for simultaneous adsorption of methylene blue (MB) and malachite green (MG) from aqueous solution using Ni:FeO(OH) ‐ NWs‐AC. The optimal conditions to adsorption of MB and MG in binary mixture solution from aqueous solution were found at pH 8.0, MB concentration 20 mg L^‐1, MG concentration 20 mg L^‐1, adsorbent dosage 0.033 g and contact time 40 min. At these conditions, high adsorption efficiency (99.39% and 100.0% for MB and MG, respectively) was achieved. Among experimental equilibrium, Langmuir isotherm model fitted well with maximum monolayer adsorption capacity of 28.6 and 29.8 mg g^‐1 for MB and MG, respectively. The adsorption kinetic data followed pseudo second‐order kinetics for MB and MG dyes.     

Adsorptive removal of thorium from aqueous solution using diglycolamide functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with diglycolamide (DGA) through chemical covalent route. The adsorption behavior of the DGA-functionalized-MWCNTs (DGA-MWCNTs) towards thorium from aqueous solution was studied under varying operating conditions of pH, concentration of thorium, DGA-MWCNTs dosages, contact time, and temperature. The effective range of pH for the removal of Th(IV) is 3.0–4.0. Kinetic data followed a pseudo-second-order model. The equilibrium data were correlated with the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The equilibrium data are best fitted with Langmuir model. The equilibrium Th(IV) sorption capacity was estimated to be 10.58 mg g^?1 at 298 K. The standard enthalpy, entropy, and free energy of adsorption of the thorium with DGA-MWCNTs were calculated to be 8.952 kJ mol^?1, 0.093 kJ mol^?1 K^?1 and -18.521 kJ mol^?1 respectively at 298 K. The determined value of sticking probability (0.072) and observed kinetic and isotherm models reveal the chemical adsorption of thorium on DGA-MWCNTs.     

Design and evaluation of functionalized multi-walled carbon nanotubes by 3-aminopyrazole for the removal of Hg(II) and As(III) ions from aqueous solution

Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were chemically modified with 3-aminopyrazole (MWCNTs-f) and applied as an efficient adsorbent to mercury and arsenic adsorption from aqueous solutions. The adsorbents were characterized by FT-IR, EDX, FE-SEM, TGA, and BET. The effects of pH, adsorbent dose, and initial ions concentration on the adsorption efficiency and the optimum conditions were investigated by central composite design. The optimum conditions were obtained at pH 7.6–7.9, adsorbent dose 20 mg, and initial ions concentration 20 ppm. So the maximum adsorption efficiencies in these conditions were 80.5 and 72.4% for the removal of Hg(II) and As(III) by MWCNTs-f, respectively. The quadratic model was used for the analysis of variance and indicated that adsorption of metal ions strongly depends on pH. Also, the pseudo-second-order model has been achieved from the adsorption kinetic studies. Furthermore, the experimental data were well fitted to the Langmuir isotherm and the maximum adsorption capacities obtained were 112 and 133 mg g^?1 for the adsorption of Hg(II) and As(III) by MWCNTs-f, respectively. Moreover, a thermodynamic study revealed that the adsorption reactions were spontaneous and endothermic with the increase in randomness. In addition, a desorption study showed the favorable regeneration ability of MWCNTs-f even after three adsorption–desorption cycles. Therefore, the MWCNTs-f adsorbent has good potential for the removal of Hg(II) and As(III) pollutants from aqueous solutions.     

一个与吸附剂浓度有关的Langmuir等温式

实验测定了不同吸附剂浓度下, 高岭土对Pb(II)和Cu(II)的吸附作用, 结果表明存在明显的吸附剂浓度效应, 即吸附等温线随吸附剂浓度升高而降低. 采用传统的Langmuir 吸附等温式对实验数据进行拟合表明, 此等温式可准确地描述给定吸附剂浓度下的吸附结果, 但不能预测其吸附剂浓度效应. 根据表面组分活度(SCA)模型, 假设吸附剂颗粒间存在相互作用, 吸附剂表面吸附位的活度系数不等于1, 而应为吸附剂浓度的函数, 推导出了一个与吸附剂浓度有关的Langmuir (Langmuir-SCA)方程. 运用高岭土吸附Pb(II)和Cu(II)以及文献中蛭石吸附Zn(II)和Cd(II)、咖啡吸附Pb(II)的实验数据检验方程的适用性, 结果表明Langmuir-SCA方程可准确地描述所观察到的吸附剂浓度效应. 方程的两个内禀参数, 热力学平衡常数(K_eq)和特征饱和吸附量(Γ_m⁰), 与吸附剂浓度无关, 并可由吸附实验数据拟合求得.     

Studies on the adsorption behaviors of Pb(II) onto an acyl-thiourea resin

In this paper, an acyl-thiourea resin (PIDTR) was synthesized and its adsorption performances to Pb(II) were investigated by adsorption tests, scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. A pH of 6.0 was found to be the optimum pH to obtain the maximum adsorption capacity in 12 hours of equilibration time. The Langmuir model was well fitted to the adsorption data with adsorption capacity of 0.756?mmol?·?g^?1. The adsorption kinetics showed that the adsorption process experienced liquid film diffusion and chemical reaction. The thermodynamic studies indicated that the adsorption for Pb(II) was spontaneous and endothermic. The results of SEM suggested that Pb(II) adsorbed on the surface of PIDTR. The FTIR and XPS analyses further confirmed Pb(II) might chemisorb onto PIDTR surfaces and N–Pb, O–Pb, and S–Pb were formed with the breakage of C?O, C?S, and N-H bonds in the PIDTR molecule.     

Amorphous titanium dioxide as an adsorbent for dye polluted water and its recyclability

Amorphous TiO₂, synthesized from TiCl₄ and diluted NH₃ solution, was characterized by X-ray diffraction spectrometry, UV–Vis diffused reflectance spectroscopy, Fourier-transformed infrared spectroscopy, and scanning electron microscopy. The powder exhibited high specific surface area at 508 m²/g as measured by the Brunauer-Emmett-Teller method. The pH at point of zero charge of the as-prepared amorphous TiO₂ was determined by the pH drift method to be 6.8. The product was studied for its sorption efficiency using two dyes—crystal violet (CV) and malachite green (MG). Studies on the effects of various sorption parameters (contact time, TiO₂ dosage, pH of solution, and initial concentration of dye) were carried out in order to find the optimum adsorption conditions for which the results were: contact time ~30 min, TiO₂ dosage ~0.05–0.1 g, pH 7–9, and initial concentration <1 × 10^?4 M. The adsorption data were analyzed and fitted better with the Langmuir model than the Freundlich model. The maximum adsorption capacities obtained from the Langmuir model were 0.4979 and 0.4075 mmol dye/g TiO₂ for CV and MG dye, respectively. In addition, the regeneration and the recyclability of the prepared amorphous TiO₂ were also studied. The used adsorbent should be regenerated 10–12 h before reuse in the next cycle for the best result.     

Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Poly-L-Histidine Attached Poly(glycidyl methacrylate) Cryogels for Heavy Metal Removal

Poly-L-histidine immobilized poly(glycidyl methacrylate) (PGMA) cryogel discs were used for the removal of heavy metal ions [Pb(II), Cd(II), Zn(II) and Cu(II)] from aqueous solutions. In the first step, PGMA cryogel discs were synthesized using glycidyl methacrylate (GMA) as a basic monomer and methylene bisacrylamide (MBAAm) as a cross linker in order to introduce active epoxy groups through the polymeric backbone. Then, the metal chelating groups are incorporated to cryogel discs by immobilizing poly-L-histidine (mol wt ≥ 5000) having poly-imidazole ring. The swelling test, fourier transform infrared spectroscopy and scanning electron microscopy were performed to characterize both the PGMA and poly-L-histidine immobilized PGMA [P-His@PGMA] cryogel discs. The effects of the metal ion concentration and pH on the adsorption capacity were studied. These parameters were varied between 3.0–6.0 and 10–800 mg/L for pH and metal ion concentration, respectively. The maximum adsorption capacity of heavy metal ions of P-His@PGMA cryogel discs were 6.9 mg/g for Pb(II), 6.4 mg/g for Cd(II), 5.6 mg/g for Cu(II) and 4.3 mg/g for > Zn(II). Desorption of heavy metal ions was studied with 0.1 M HNO₃ solution. It was observed that cryogel discs could be recurrently used without important loss in the adsorption amount after five repetitive adsorption/desorption processes. Adsorption isotherms were fitted to Langmuir model and adsorption kinetics were suited to pseudo-second order model. Thermodynamic parameters (i.e. ΔH° ΔS°, ΔG°) were also calculated at different temperatures.