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Publicly Available Published by De Gruyter October 25, 2016

Synthesis, characterizations and Pb(II) sorption properties of cobalt phosphonate materials

Bianca Maranescu, Lavinia Lupa and Aurelia Visa

Abstract

Due to the large amount of industrial activity during the last century, heavy metal contamination of the environment has become a serious problem. Therefore, it is important to develop new and efficient methods of heavy metals removal from aqueous solutions. In this respect, three phosphonate metal organic frameworks were obtained in our labs by the reaction of divalent inorganic salt (CoSO4·7H2O), phosphonic acid [phosphonoacetic (CP), N,N-bis(phosphonomethyl)glycine (Gly) and vinylphosphonic (VP)] in hydrothermal conditions. The synthesized compounds were characterized by FTIR, X-Ray crystallography scanning electron microscopy and thermogravimetric analysis. These materials were used in the removal process of lead ions from aqueous solutions in order to determine the possibilities of their use as adsorbent materials. The effect of pH, lead initial concentrations and contact time upon the adsorption properties were investigated. From the experimental data it can be observed that the Co-Gly material developed a higher adsorption capacity for lead metal ions than the Co-VP and Co-CP, increasing following Co-CP<Co-VP<Co-Gly trend.

Introduction

Water pollution is a universal problem, which has been causing a global attention. Pollutant removal adsorption over porous material [zeolites, organic-inorganic hybrids, metal organic frameworks (MOFs)] was extensively studied [1,2].

Generally, MOFs are based on metal organic carboxylic derivatives that form a controlled supramolecular structure with transition metal ions. Phosphonate metal organic frameworks are quickly gaining a central position amongst the various families of MOFs materials. Most of the phosphonates metal organic frameworks have a layered structure in which the metal centers are bridged by the phosphonate group, although a variety of 1D chain, 2D layer, and 3D network with micropores, among which the 2D layer is the most common structural type [3].

The combination of the surface areas and microporosity increase the interest in the area of phosphonate metal organic framework and allows the preparation of composite materials with enhanced properties, exemplified with a variety of applications.

In order to improve the adsorption capacity of MOFs in a relatively large range of pH, it is suggested to choose inherent stable MOFs in water media. These materials are well known due to their ordered supramolecular structure, high surface area and very good water stability. The phosphonates metal organic frameworks with high water stability are promising candidates [4], [5], [6], [7], [8], [9], [10].

The adsorption capacity of the obtained materials was studied. Lead was therefore selected in this study as modelled pollutant because it is used in a lot of industry processes such as: acid metal plating and finishing, electric battery manufacturing, painting, dying, lead smelting, internal combustion engines, ceramic and glass industry [11,12]. From these processes results waste waters which must be treated before discharge, due to the fact that lead is a toxic metal ion to the human even when found in trace concentrations. The assimilation of relatively small amounts of lead over a long period of time in the human body can lead to malfunctioning of the organs and chronic toxicity [13], [14], [15]. In order to avoid the contamination with lead ions or to keep the lead concentration in the permissible level, the researcher focused to find the most efficient method to remove lead ions from aqueous solutions. The adsorption proved to be the most efficient method for heavy metals removal from aqueous solutions due to easy of operation, efficient and economical method [11], [12], [13], [14], [15]. The used adsorbent should have developed a high adsorption capacity in the removal process of lead from aqueous solution, but in the same time must present a high affinity and selectivity for lead to be capable to remove it from waters with trace content.

Using our previous experience for the synthesis of phosphonates metal organic frameworks, in this paper we describe briefly the synthesis and characterization of materials [16], [17], [18], [19]. Various phosphonate metal organic frameworks were used, starting from tree different ligands with one phosphonate moiety – vinyl phosphonic acid, a carboxy-phosphonate ligand – phosphonoacetic acid and a carboxy-diphosphonate ligand – N,N-bis(phosphonomethyl) glycine [20], [21]. The structure, morphology and properties of materials were investigated by FTIR, XRD, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA).

The very promising part is adsorption performance of phosphonates metal organic frameworks materials, which is extensively described. The effect of pH, lead initial concentrations and contact time upon the adsorption properties.

All cobalt phosphonates analyzed are layered structures being structurally similar with an increase number of coordination groups (carboxylate and phosphonate). These materials were not extensively studied as adsorbants and this is an attractive research also due to their possible further utilization of the exhausted adsorbant as catalyst in various processes.

Experimental

Synthesis of phosphonate metal organic frameworks

A 100 mL round-bottomed flask was charged with CoSO4·7H2O (50.0 mmol), phosphonoacetic, N,N-bis(phosphonomethyl)glycine or vinylphosphonic (50.0 mmol), urea (50.0 mmol), and distilled water (50 mL). The pH was adjusted to 2.8 with an aqueous solution of NaOH (0.1 M). The solution was heated in an oil-bath at 80°C for 75 h. The resulting crystals were collected by filtration, washed with distilled water and dried in air (yield: 50–83%) [16], [22], [23].

Instrumentation

Thermal analysis (TG-DTA) data were recorded on an SDT-Q600 analyzer from TA instruments. A Perkin Elmer Diamond thermogravimetric analyzer was used applying temperatures between 30 and 650°C under a flow of N2 with a heating rate of 10°C/min. FTIR spectra were recorded on a Jasco-FT/IR-4200 instrument in the range 400–4000 cm−1 using the KBr pellet method. The pH was measured using a pH HI 2221 Calibration Check pH/ORP Meter by Hanna Instruments. The X-Ray diffraction patterns were recorded at room temperature with a XRD using a Rigaku Ultima IV diffractometer, using Cu Kα radiation (λ=1.5418 Å). SEM images were recorded using a Quanta FEG 250 microscope, equipped with an EDAX/ZAF quantifier. The specific surface area and the pore volume of the studied materials were measured using a Micrometrics ASAP 2020 BET surface area analyzer, by cold nitrogen adsorption. The lead ions concentrations were measured using a Varian SpectrAA 280 FS atomic adsorption spectrophotometer. The adsorption studies were performed in batch mode using a Julabo SW23 shaker bath.

Adsorption studies

The adsorption studies of lead were carried out in batch mode. In the first step, the effect of pH upon the adsorption capacity of the studied materials was determined. For each experiment 25 mL of synthetic water sample containing 30 mg/L Pb(II) was added to a calculated amount of adsorbent in order to have a solid:liquid (S:L) ratio of 2 g/L. The pH adjustment of the solution was done using 1.0 M NaOH. The samples were stirred for 1 h at constant speed (200 rpm). After the time elapsed, the samples were filtered and the residual concentration of Pb(II) ions and the concentration of Co (if there is a possible leaching of Co ions during the adsorption studies) were was analysed in the filtrate by atomic adsorption spectrophotometer.

The effect of the initial concentration of Pb(II) was studied. Therefore, 0.05 g of studied materials were suspended in 25 mL of Pb(II) solutions having different concentrations (2.5–200 mg/L) and an initial pH of 4. The suspension were stirred for 1 h at 25°C, after the completion of experiment, the suspensions were filtered and analysed for Pb(II) residual concentration. To study the effect of contact time on adsorption, the experiments were carried out using the same S:L ratio, a concentration of 30 mg/L of Pb(II), initial pH of the solutions=4, but the suspension were kept in contact different times (15–120 min) at 25°C. After contact time elapsed, the suspensions were filtered and the filtrate was collected for Pb(II) analysis.

The amount of Pb(II) ions adsorbed during the series of batch investigations was determined using the mass balance equation:

(1)q=(C0Ce)Vm

where: q is the amount of Pb(II) adsorbed on the studied materials (mg/g); Co and Ce represents the initial and equilibrium concentration of Pb(II) ions in the solutions (mg/L), respectively. V is the volume of the solution (L) and m is the mass of the adsorbent (g) used in the experiments.

Results and discussion

Materials characterization

The structure, morphology, and properties of phosphonates metal organic frameworks were investigated by FTIR, XRD, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA).

FTIR spectra of Co-VP [Co(C2H3PO3)·H2O] were recorded using KBr pellets and formation of metal phosphonic framework is presented in Fig. 1. The absence of the peak at 2400–2800 cm−1 attributed to P–OH vibrations confirms the formation on Co phosphonate network. The presence of a broad band at 3455 cm−1 is due to the stretching vibration of the water molecule OH coordinated to the central cobalt atom. The position and shape of the absorption band suggest strong interaction through hydrogen bonds. The weak band from 1620 cm−1 corresponds to the double C=C bonds from vinyl moiety. Also the spectrum presents two intense bands between 1100 and 900 cm−1, which corresponds to the –PO3 stretching vibration and a weak band at 800–1800 cm−1 belonging to the substituted vinyl moiety, depicted in Fig. 1(a). The Co–CP [Co(O2CH2PO3]2· 2H2O) spectrum shows the asymmetric and symmetric vibrations of the carboxylate group at 1541 and 1429 cm−1, respectively, the vibrations of the phosphonic group in the region 900–1100 cm−1 and the typical broad band of the coordinated water around 3400 cm−1. The absence of a band in the region 1690–1730 cm−1 (the O–H vibration of a COOH group) is in agreement with a deprotonated carboxyl group. The FT-IR spectrum of Co-Gly ([Co(C4H9O8NP2)(H2O)2]·2H2O) shows strong absorptions for the various vibrationally active groups. Antisymmetric and symmetric vibrations for the carboxylate group of the coordinated N,N-bis(phosphonomethyl)glycine ligand dominated the spectrum. Antisymmetric stretching vibrations were present for the deprotonated carboxyl group around 1540 cm−1. Symmetric vibrations for the same group were present in the range 1430–1398 cm−1. The presence of a broad band at 3400 cm−1 is due to the stretching vibration of the water molecule OH coordinated to the central cobalt atom [24].

Fig. 1: FT-IR spectra of the obtained materials: (a) Co-VP; (b) Co-CP; (c) Co-Gly.

Fig. 1:

FT-IR spectra of the obtained materials: (a) Co-VP; (b) Co-CP; (c) Co-Gly.

The Co-VP and Co-CP sample showed a good crystallinity with well defined peaks in the X-Ray powder diffraction, judging from the high intensity of the peaks in the 2θ region. The patterns give a good indication that the Co-VP and Co-CP are layered structures (Fig. 2). The Co-Gly compound is not very crystalline, therefore in the spectrum we could observe only a broad pick in the 2θ region 8°–9°. From this reason the diffractogram was not included. Due to the fact that this compound is amorphous in nature we will expect that it will develop the highest adsorption capacity in the removal process of Pb ions from aqueous solutions. The XRD data of all compounds are comparable with the theoretical one [25], [26], [27].

Fig. 2: X-Ray powder diffractograms of the obtained materials: (a) Co-VP; (b) Co-CP.

Fig. 2:

X-Ray powder diffractograms of the obtained materials: (a) Co-VP; (b) Co-CP.

In case of Co-CP phosphonate and carboxylic groups of symmetry connected molecules are linked to each other by medium strong O–H···O hydrogen bonds, comparative with Co-VP where the hydrogen bonds are present between O atoms of each of the hydroxyl groups phosphonate by weak O–H···O hydrogen bonds.

Thermogravimetric analysis of Co-VP compound revealed in black curve, Fig. 3, shown two main weight losses. The first one corresponds to the loss of the cobalt-coordinated water molecule. This process takes place at lower temperature, between 150 and 250°C, with an associated weight loss of 10.48%, closely corresponding to the theoretical 9.85%. The semicrystalline anhydrous phase stays stable until 500°C [16]. Co-CP compound shows a first weight loss in mass before 150°C and a similar loss between 150–300°C that marks the expulsion of water molecules of crystallization. This process was concomitant with P–C bond scission and the decomposition of the compound. In the case of Co-Gly ([Co(C4H9O8NP2)(H2O)2]·2H2O) removal of water starts immediately upon heating: the first, second water molecule until 130C (calcd 10.6%, obsd 9.9%). The remaining two H2O molecules are lost slowly between 130 and 300°C, followed by slow decomposition at ~300°C.

Fig. 3: Thermal behaviour of Co-VP, Co-CP and Co-Gly.

Fig. 3:

Thermal behaviour of Co-VP, Co-CP and Co-Gly.

The morphology of the obtained materials can be observed from the SEM images presented in Fig. 4. It can be observed that the Co-CP material is presented as acicular shape, the Co-Gly morphology is presented like spherical porous flakes, while the Co-VP have an irregular plate-like shape, being crystallized in accordance with the results obtained from the XRD analysis. For this reason it is expected that the Co-Gly sample to obtain the highest adsorption capacity in the removal process of Pb ions from aqueous solutions, Fig. 6.

Fig. 4: SEM images of the obtained materials: (a) Co-CP; (b) Co-VP; (c) Co-Gly.

Fig. 4:

SEM images of the obtained materials: (a) Co-CP; (b) Co-VP; (c) Co-Gly.

Qualitative and quantitative EDX analyses showed a high purity and suitable stoichiometry of the investigated materials (Fig. 5).

Fig. 5: EDX spectrum of the obtained materials: (a) Co-CP; (b) Co-VP; (c) Co-Gly.

Fig. 5:

EDX spectrum of the obtained materials: (a) Co-CP; (b) Co-VP; (c) Co-Gly.

The chemical composition of the studied materials calculated theoretical from the chemical formulas and resulted from energy dispersive X-ray analysis (EDX) is presented in Table 1. It can be observed that even the EDX analysis is a semi-quantitatively one the obtained results are similar with the chemical composition calculated theoretically.

Table 1:

The chemical composition of the studied materials determined theoretically and from the EDX analysis.

SymbolChemical formulaChemical composition,% wt
Co-CPCoC4O12H12P2CoCOHP
Theoretic15.8012.8851.473.1416.61
EDX16.3113.9051.718.09
Co-VPCoC2O4H5PCoCOHP
Theoretic32.2113.1334.982.7516.93
EDX35.216.7533.2414.81
Co-GlyCoC4H12O12NP2CoCOHNP
Theoretic15.2412.449.613.13.6116.02
EDX15.2814.5550.472.4117.29

The porous structure of Co-Gly was evidenced by BET surface analyses obtaining a specific surface area of 32 m2/g and the pore volume of 0.25 cm3/g. The specific surface area decrease in the following Co-Gly>Co-VP>Co-CP trend. The values of specific surface area for Co-VP are 22.2 m2/g and the pore volume of 0.16 cm3/g and 18.4 m2/g and the pore volume of 0.12 cm3/g for Co-CP, respectively. The results are in accordance with conclusion raised from SEM analyses.

Adsorption studies

Solution chemistry (i.e. hydrolysis, complexation, precipitation) of heavy metals is strongly influenced by the pH, and the solution chemistry influences the speciation and the adsorption availability of heavy metals. Therefore, the effect of the initial pH on the adsorption capacity of the studied materials in the removal process of Pb(II) ions, was studied. The results are presented in Fig. 6.

Fig. 6: Effect of initial pH on the adsorption capacity of the studied materials in the removal process of Pb(II) ions from aqueous solutions Ci=30 mg/L, S:L=2 g/L, t=60 min, v=200 rpm.

Fig. 6:

Effect of initial pH on the adsorption capacity of the studied materials in the removal process of Pb(II) ions from aqueous solutions Ci=30 mg/L, S:L=2 g/L, t=60 min, v=200 rpm.

The adsorption capacity of the studied materials increases with the pH of the solution increasing. At pH around 2–3 the low adsorption of Pb(II) ions can be explained by the presence of high concentration of H+ ions, which compete with the metal ions adsorption on adsorbent surface. With pH increasing the concentration of H+ ions gradually diminish and corresponding the adsorption of Pb(II) ions increases, until it reached a constant value at pH 4–5 for all the studied materials. Additional increase in the pH was not considered because the beginning of the insoluble hydroxide precipitating from solution makes true metal adsorption studies impossible. The further experiments were carried out at an initial pH around 4 in order to avoid the precipitation of Pb(II) ions as hydroxide.

In all the cases the concentrations of Co ions in the resulted solutions following the adsorption of Pb ions were under detection limit, these confirming again the stability of the phosphonate metal organic frameworks (Co-VP, Co-CP and Co-Gly).

In order to evaluate the adsorption as an unit operation, two important physicochemical aspects were discussed: equilibrium and the kinetics of the Pb(II) adsorptions onto the studied materials.

Equilibrium studies give information regarding the maximum capacity and affinity of the studied adsorbent for the studied pollutant. The equilibrium isotherms of Pb(II) adsorption onto the studied materials is presented in Fig. 7. The increasing of the initial concentration of metal ions determines the increasing of the active sites which lead to a higher Pb(II) uptake by the studied adsorbent. It can be observed that Co-Gly developed a higher adsorption capacity than the other two studied materials in the removal process of Pb(II) ions from aqueous solutions.

Fig. 7: Equilibrium isotherm of Pb(II) adsorption onto the studied materials.

Fig. 7:

Equilibrium isotherm of Pb(II) adsorption onto the studied materials.

In order to describe the equilibrium between the studied adsorbent and Pb(II) ions two models: Langmuir and Freundlich isotherms were used [11], [12], [13], [14], [15]. The Langmuir isotherm assumes that the adsorption take place only on a single layer on the adsorbent, and after the formation of this monolayer no further adsorption take place [14].

The linear form of Langmuir isotherm is given by the following equation [11], [12], [13], [14], [15]:

(2)Ceqe=1KLqm+Ceqm,

where: qe is the amount of Pb(II) adsorbed per gram of adsorbent, i.e. metal uptake (mg/g), and Ce is the equilibrium concentration of adsorbate in the bulk solution after adsorption (mg/L). qm is the measure of the monolayer sorption capacity (mg/g) and KL denotes the Langmuir isotherm constant related to the affinity between adsorbent and the adsorbate (L/mg). The values of qm and KL can be determined by plotting Ce/qe vs. Ce (Fig. 8).

Fig. 8: Langmuir isotherm for Pb(II) adsorption onto the studied materials.

Fig. 8:

Langmuir isotherm for Pb(II) adsorption onto the studied materials.

The Freundlich adsorption isotherm supposes that the adsorbent surface is heterogenous. The Freundlich isotherm in its linear form can be expressed by Eq. (3) [11], [12], [13], [14], [15]:

(3)lnqe=lnKF+1nlnCe,

where K and 1/n are characteristic constants that can be related to the relative adsorption capacity of the adsorbent (mg/g) and the intensity of the adsorption, respectively. The values of 1/n and KF were calculated from the intercept and slope of logarithmic plot of qe against Ce (Fig. 9).

Fig. 9: Freundlich isotherm for Pb(II) adsorption onto the studied materials.

Fig. 9:

Freundlich isotherm for Pb(II) adsorption onto the studied materials.

The isotherm parameters together with the correlation coefficients are presented in Table 2.

Table 2:

Parameters of Langmuir and Freundlich isotherms for Pb(II) adsorption onto the studied materials.

Adsorbent materialqm, exp (mg) Pb(II)/gLangmuir isothermFreundlich isotherm
KL (L/mg)qm, calc (mg/g)R2KF (mg/g)1/nR2
Co-CP23.50.45123.80.9995.920.3400.905
Co-VP380.309400.9977.560.4080.945
Co-Gly490.313500.9969.150.4340.962

It was observed that results fitted better in the Langmuir model in terms of R2 value. Moreover, the maximum adsorption capacity of the studied material obtained from the Langmuir plot is very close to that obtained experimentally. This indicates that the Langmuir isotherm describes better the adsorption process of Pb(II) onto the studied material. The essential feature of the Langmuir equation can be expressed in terms of a dimensionless separation factor, RL defined as: The value of RL indicates the shape of the isotherm: unfavorable, RL>1; linear, RL=1; favorable, 0<RL<1; and irreversible, RL=0. RL values were found to be between 0 and 1 for all the concentration of Pb(II) showing that the adsorption is favorable.

(4)RL=11+KLC0

One important characteristic of the Freundlich isotherm is the 1/n which indicates the tendency of the adsorbate to be adsorbed. In our cases, all the values are below one indicating a favourable adsorption of Pb(II) ions onto the studied adsorbent. It can be observed that Co-Gly presents the highest adsorption capacity for Pb(II) removal from aqueous solutions.

Is significant to note that the dominant interaction which might make important influence on the adsorption process can be different in different conditions and the real mechanism for the adsorption is complex. Therefore, the crystallinity, the porosity, metal clusters and pH will affect not only the adsorption capacity but also its selectivity. Therefore, in the case of Co-Gly which is not well crystallized compound the specific surface is higher and the adsorption process is better. This is in good agreement with SEM images and X-Ray powder diffraction of this compound.

Table 3 presents some reported adsorption capacity for Pb(II) of different materials. The comparison of the maximum capacity of adsorption of the various adsorbents is difficult considering the experimental conditions vary from one study to another. However, it can be concluded that the studied materials present a good efficiency in the removal process of Pb(II) from aqueous solutions.

Table 3:

Comparison of adsorption capacity for Pb(II) with different adsorbents.

Adsorbentqm (mg/g)Reference
Chitosan16.36[28]
Clinoptilolite58.73[28]
Activated carbon from Militia Ferruginea plant leaves3.3[29]
PANI/M.B18.75[30]
PANI/W.B28.93[30]
PANI/R.B30.11[30]
Diatomite26[31]
GAC1.37[32]
Co-CP23.8Present work
Co-VP40
Co-Gly50

Figure 10 shows removal of lead ion from water using different adsorbents as a function of time. The equilibrium between adsorbent and adsorbate is reached in 60 min, obtaining a Pb removal degree more than 98.5%.

Fig. 10: Effect of contact time on the adsorption capacity of the studied materials in the removal process of Pb(II) from aqueous solutions.

Fig. 10:

Effect of contact time on the adsorption capacity of the studied materials in the removal process of Pb(II) from aqueous solutions.

The Pb(II) adsorption is initial faster due to the availability of the uncovered surface area of the adsorbents. At higher stirring times the adsorption capacity becomes linearly constant. At higher stirring time the active sites become progressively filled and the sorption becomes more difficult, concluding that the adsorption kinetic depend by the surface area of the adsorbent [14].

In order to quantify the changes in adsorption function of stirring time, for designing an appropriated adsorption system, two kinetic models were used to fit the experimental data: pseudo-first-order equation and pseudo-second-order reaction model.

The pseudo-first-order kinetic model based on the solid capacity is defined by the equation [11], [12], [13], [14], [15]:

(5)ln(qeqt)=lnqtk1t,

where qe and qt are the amount of the Pb(II) adsorbed onto the studied adsorbents (mg/g) at equilibrium and after time t, respectively; t is the contact time (min), k1 is the specific adsorption rate constant (min−1). The values of the adsorption rate constant (k1) were determined from the plot of ln(qeqt) in terms of t (Fig. 11). The linear form of the pseudo-second order model based on the solid phase adsorption and implying that the chemisorption is the rate controlling step is defined by [11], [12], [13], [14], [15]:

Fig. 11: Pseudo-first order kinetic model for Pb(II) adsorption onto the studied materials.

Fig. 11:

Pseudo-first order kinetic model for Pb(II) adsorption onto the studied materials.

(6)tqt=1k2qe2+tqe,

where qe and qt are the amount of the Pb(II) adsorbed onto the studied material (mg/g) at equilibrium and at time t, respectively; t is the contact time (min), k2 is the pseudo-second-order adsorption rate constant [g/(mg·min)]. The value qe and k2 are determined from the slope and intercept of (t/qt) vs. t (Fig. 12). The calculated parameters together with the correlation coefficients are presented in Table 4.

Fig. 12: Pseudo-second order kinetic model for Pb(II) adsorption onto the studied materials.

Fig. 12:

Pseudo-second order kinetic model for Pb(II) adsorption onto the studied materials.

Table 4:

Kinetic parameters for Pb(II) sorption onto the studied materials.

Adsorbent materialPseudo-first-order modelPseudo-second-order model
qe,calc (mg/g)k1 (min−1)R2qe,calc (mg/g)k2 [min/(mg/g)]R2
Co-CP3.450.0230.85713.90.01360.999
Co-VP8.710.0570.97814.90.01160.998
Co-Gly3.580.0160.68715.20.01250.998

From Table 4 it can be observed that the pseudo-second order kinetic model provides the best correlation of data (R2>0.99) for all the studied adsorbent. Also, the qe calculated values fitted the experimental data. This suggests that the pseudo-second-order adsorption mechanism is predominant assuming that the rate limiting step may be a chemical adsorption involving valance forces through sharing or exchange of electrons between adsorbent and adsorbate.

It is assumed that the Pb ions uptake is present as an occluded salt or anion/cation pair. The EDX of the exhausted adsorbent confirm its present in the solid material (Fig. 13).

Fig. 13: EDX spectrum of the materials after adsorption of Pb ions: (a) Co-CP; (b) Co-VP; (c) Co-Gly.

Fig. 13:

EDX spectrum of the materials after adsorption of Pb ions: (a) Co-CP; (b) Co-VP; (c) Co-Gly.

In order to improve the selective adsorption performance more studies of the possible interactions should be taken into considerations.

Conclusions

The obtained materials were used in order to remove Pb(II) ions from aqueous solutions. From the experimental data was observed that the Co-Gly developed the highest efficiency in the removal process of lead ions from aqueous solution then the other two studied materials. The experimental data showed good fit to the Langmuir isotherm, and comparing the maximum adsorption capacity developed by the studied adsorbent was observed that the studied material presents better or comparable adsorption performance in the removal process of lead ions from aqueous solutions than other adsorbent reported in literature. The adsorption kinetics was better described by pseudo-second-order kinetic model compare to pseudo-first-order model. Our results show that these new obtained materials are efficient adsorbents and have potential applications in technologies for Pb(II) recovery and for wastewater treatment.

In order to improve the selective adsorption performance more studies of the possible interactions should be taken into consideration.


Dedicated to: 150th anniversary of the Romanian Academy.

Article note:

A collection of invited papers based on presentations at the 16th International Conference on Polymers and Organic Chemistry (POC-16), Hersonissos (near Heraklion), Crete, Greece, 13–16 June 2016.


Acknowledgments

This work was partially supported by a grant of the Romanian National Authority for Scientific Research, CNCS – UEFISCDI, project number PN-II-RU-TE-2014-4-1398 and by Program no 2, Project no. 2.3 from the Institute of Chemistry Timisoara of Romanian Academy.

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Published Online: 2016-10-25
Published in Print: 2016-11-1

©2016 IUPAC & De Gruyter. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/

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