Cellulose-lanthanum hydroxide nanocomposite as a selective marker for detection of toxic copper
© Marwani et al.; licensee Springer. 2014
Received: 13 June 2014
Accepted: 25 August 2014
Published: 3 September 2014
In this current report, a simple, reliable, and rapid method based on modifying the cellulose surface by doping it with different percentages of lanthanum hydroxide (i.e., 1% La(OH)3-cellulose (LC), 5% La(OH)3-cellulose (LC2), and 10% La(OH)3-cellulose (LC3)) was proposed as a selective marker for detection of copper (Cu(II)) in aqueous medium. Surface properties of the newly modified cellulose phases were confirmed by Fourier transform infrared spectroscopy, field emission scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopic analysis. The effect of pH on the adsorption of modified cellulose phases for Cu(II) was evaluated, and LC3 was found to be the most selective for Cu(II) at pH 6.0. Other parameters, influencing the maximum uptake of Cu(II) on LC3, were also investigated for a deeper mechanistic understanding of the adsorption phenomena. Results showed that the adsorption capacity for Cu(II) was improved by 211% on the LC3 phase as compared to diethylaminoethyl cellulose phase after only 2 h contact time. Adsorption isotherm data established that the adsorption process nature was monolayer with a homogeneous adsorbent surface. Results displayed that the adsorption of Cu(II) onto the LC3 phase obeyed a pseudo-second-order kinetic model. Selectivity studies toward eight metal ions, i.e., Cd(II), Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Ni(II), and Zn(II), were further performed at the optimized pH value. Based on the selectivity study, it was found that Cu(II) is highly selective toward the LC3 phase. Moreover, the efficiency of the proposed method was supported by implementing it to real environmental water samples with adequate results.
Over the years, copper (Cu(II)) has gain the attention of chemists due to its prohibitive toxicity and nonbiodegradable nature. The elevated concentration of Cu(II) produces severe ecological and public health issues [1, 2]. Several methodologies have been evaluated for the separation of Cu(II) in aqueous medium. However, the adsorption technique has proved to be one of the promising solutions due to its simple implementation and economical and effective behavior [3, 4]. Currently, some of the available adsorbents have limitations, such as low uptake capacity, long equilibrium, and low selectivity . In order to overcome these weaknesses, some new organic-inorganic hybrid adsorbents, capable of separating heavy metals from the solution, have been established. Several studies have been concentrated on the extraction of Cu(II) by applying amine group functionalized matrices [6–9]. It is well understood that organic functional group modified adsorbents usually exhibit relatively high adsorption capacity and selectivity as compared to unmodified adsorbents [6, 10–12].
Different separation techniques, however, are being successfully utilized, for example, liquid-liquid extraction , ion exchange , coprecipitation , cloud point extraction , and solid phase extraction (SPE) [17, 18]. The conventional methods, such as liquid-liquid extraction and coprecipitation, require excess amount of organic solvents with high purity that could be harmful to living organisms and cause environmental pollution. On the other hand, the SPE method proved to be a more efficient technique when it comes to the exposure and usage of solvents, extraction time, and disposal cost. Presently, this recognition of SPE leads to the appearance of several adsorbents with the goal of succeeding a selective separation of the analytes, for instance, alumina , C18 , molecular imprinted polymers , cellulose , silica gel , and activated carbon [24, 25].
Cellulose is considered to be one of the highly abundant naturally existing polymers in the world. This comprises repeating units of β-d-glucopyranose, covalently linked with OH group of C4 and C1 carbon atoms [26–28]. Naturally occurring cellulose shows less adsorption capacity and physical stability due to the steric hindrance offered by three hydroxyl groups with the same ring. Moreover, these hydroxyl moieties are chemically unreactive as the polymer matrix contains crystalline regions [27, 29]. In order to develop adsorption capacity and structural stability of natural cellulose, modifications were employed in the matrix by means of chemical reactions, such as halogenation, etherification, esterification, and oxidation. Such modified matrices were found to be capable of separating heavy metal ions from aqueous solutions . The cellulose beads when treated mainly with 2-(diethylamino) ethyl chloride hydrochloride along with some other treatments produced diethylaminoethyl cellulose . Recently, we have also developed some surface modified cellulose adsorbents for the selective separation of Ni(II) and Cr(VI) ions [31, 32].
In order to monitor metal ionic species in the environment, the development of rapid, simple, and proficient approach has gain an interest. Different approaches were employed for the determination of metal ions in aqueous medium, namely atomic absorption spectrometry (AAS) , inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) [34–36], anodic stripping voltammetry , and ion chromatography . Despite immense enhancement in selectivity and sensitivity of state-of-the-art instruments, there is still a vital need for improvement in selective separation of chemical species of interest prior to their determination; in particular, the concentration of such analytes is frequently low in complex matrices. Moreover, a cleanup step is frequently needed because of high level of other constituents accompanying the analyte.
Current study emphasizes the development of new cellulose-based adsorbents by surface modification. Lanthanum hydroxide was doped with cellulose with a proportion of 1%, 5%, and 10% [i.e., 1% La(OH)3-cellulose (LC), 5% La(OH)3-cellulose (LC2), and 10% La(OH)3-cellulose (LC3)]. Additionally, the effectiveness of nanocomposites was investigated as a potential adsorbent for a selective extraction of Cu(II) ion prior to its determination by ICP-OES. Several parameters were evaluated in order to acquire the optimum condition for Cu(II) extraction. The pH effect on Cu(II) adsorption was investigated and optimized for the best modified cellulose phase (LC3). In order to understand the mechanism of Cu(II) adsorption, other parameters controlling the maximum uptake of Cu(II) on LC3 was studied at the optimum pH 6.0. Furthermore, adsorption data was modeled by Freundlich and Langmuir adsorption isotherms. The kinetics of adsorption was evaluated by employing pseudo-first- and second-order kinetic models. At optimized pH, selectivity was also scrutinized for other metal ion, including Cd(II), Co(II), Cr(III), Cr(VI), Fe(III), Ni(II), and Zn(II). This study revealed that LC3 was the most selective toward Cu(II) in comparison to other metal ions. Ultimately, the proposed method was further validated by analysis of real environmental water samples.
Chemicals and reagents
Diethylaminoethyl (DEAE) cellulose, lanthanum chloride, and ethanol were purchased from Sigma-Aldrich (Milwaukee, WI, USA). Stock standard solutions of 1,000 mgL-1 Cd(II), Co(II), Cu(II),Cr(III), Cr(VI), Fe(III), Ni(II), and Zn(II) were obtained from Sigma-Aldrich (Milwaukee, WI, USA). All utilized reagents were of high purity and of analytical reagent grade, whereas double-distilled deionized water was used throughout the experiments.
Preparation of the new solid phase extractor based on DEAE cellulose
Different amounts of DEAE cellulose (99%, 95%, and 90%) were first mixed with distilled deionized water. Various portions of lanthanum chloride (1%, 5%, and 10%) were then dissolved in distilled deionized water and mixed with DEAE cellulose water suspensions. All solutions were adjusted to pH 10.0 by a dropwise addition of 0.1-M NaOH. Mixtures were then allowed to stir at 60°C for 24 h. Mixtures were filtered, washed with ethanol twice and 18.2 MΩ cm distilled deionized water, and dried in oven at 80°C for 5 h to obtain LC, LC2, and LC3 nanocomposites.
Samples preparation and procedure
Stock standard solutions of Cd(II), Co(II), Cu(II),Cr(III), Cr(VI), Fe(III), Ni(II), Pb(II), and Zn(II) ions were prepared in 18.2 MΩ cm distilled deionized water and stored in the refrigerator at 4°C. The environmental samples were collected from seawater, wastewater, tap water, and ground water from Jeddah region at Saudi Arabia.
Effect of pH
The effect of pH on the adsorption of Cu(II) ion onto n% La(OH)3 DEAE cellulose was investigated. Standard solutions of 5.0 mgL-1 Cu(II) were adjusted to pH values ranging from 1.0 to 8.0 with appropriate buffer solutions, i.e., HCl/KCl buffer for pH 1.0 and 2.0, acetate buffer for pH 3.0 to 5.0, and KH2PO4/NaOH buffer for pH 6.0 to 8.0. Each solution was individually mixed with 25.0 mg of modified cellulose phases (LC, LC2, or LC3) and unmodified DEAE cellulose phase and mechanically shaken for 2 h by a mechanical shaker at 150 rpm and 25°C temperature.
Effect of concentration
To estimate the uptake capacity of Cu(II) under batch conditions, standard solutions of 0, 1, 5, 10, 20, 30, 40, 50, 80, 100, 150, 200, 300, 400, and 500 mgL-1 were prepared and adjusted to the optimum pH 6.0 with the buffer solution of KH2PO4/NaOH. Each solution was individually added to 25.0 mg LC3 (or unmodified DEAE cellulose). All mixtures were then allowed to be mechanically shaken for 2 h at 25°C.
Effect of temperature
For the effect of temperature, standard solutions of 5.0 mgL-1 Cu(II) were prepared, adjusted to the pH 6.0 as above, and individually mixed with 25.0 mg LC3. Thermodynamic study of the adsorption of LC3 toward Cu(II) was also performed under the same batch conditions at different temperatures (298, 308, 323, and 338 K).
Effect of shaking time
The effect of shaking time on LC3 adsorption for Cu(II) was performed under the same batch conditions as above by given various equilibrium periods (5, 10, 20, 30, 50, 80, 100, and 120 min) and at a concentration of 400 mgL-1 of Cu(II).
In order to investigate the selectivity of modified cellulose adsorbents toward different metal ions, including Cd(II), Co(II), Cu(II), Cr(III), Cr(VI), Fe(III), Ni(II), Pb(II), and Zn(II), 5 mgL-1 of each metal ion solution was individually added to 25.0 mg of modified phases ( LC, LC2, or LC3) and unmodified DEAE cellulose separately as well. Mixtures were then allowed to be stirred for 2 h at 25°C under the same batch conditions as above.
The surface morphology of the nanocomposites was investigated by operating a field emission scanning electron microscope (FE-SEM) instrument (JSM-7600 F, JEOL Ltd., Akishima-shi, Japan). Elemental analysis was performed using energy dispersive X-ray spectroscopy (EDS) from JEOL, Japan. X-ray diffraction (XRD) patterns were acquired with X-ray diffractometer (Rigaku X-ray diffractometer, MiniFlex 2, Rigaku, Shibuya-ku, Japan) equipped with Cu-Kα1 radiation (λ = 1.5406 nm) using a generator voltage (40.0 kV) and a generator current (35.0 mA). Data of X-ray photoelectron spectroscopy (XPS) were acquired from Thermo Scientific K-α KA1066 spectrometer (Bonn, Germany). The Al Kα X-ray radiation monochromatic sources were utilized as excitation sources, whereas the size of beam spot was set at 300.0 μm. The fixed analyzer transmission mode was used to record the spectra adjusting pass energy at 200 eV. The scan of spectra was performed at a pressure less than 10-8 Torr. Fourier transform infrared (FT-IR) spectroscopic analyses were carried out by using Shimadzu IR 470 spectrophotometer (Shimadzu, Kyoto, Japan) to confirm the formation of newly prepared nanocomposites. The pH measurements were performed on pH meter (inoLab® pH 7200, WTW, Lincolnwood, IL, USA) with absolute accuracy limits at the pH measurement being defined by NIST buffers. A PerkinElmer ICP-OES Optima 4100 DV model (PerkinElmer, Waltham, MA, USA) was applied for the determination of metal ions concentration. The optimization of ICP-OES instrument was performed daily before analysis and operated as recommended by the manufacturers.
The ICP-OES spectrometer was operated with the following parameters: FR power, 1,300 kW; frequency, 27.12 MHz; demountable quartz torch, Ar/Ar/Ar; plasma gas (Ar) flow, 15.0 L min-1; auxiliary gas (Ar) flow, 0.2 L min-1; nebulizer gas (Ar) flow, 0.8 L min-1; nebulizer pressure, 2.4 bar; glass spray chamber according to Scott (Ryton), sample pump flow rate, 1.5 mL min-1; integration time, 3 s; replicates, 3; wavelength range of monochromator, 165 to 460 nm. The concentrations of the metal ions were determined at wavelengths of 226.50 nm for Cd(II), 230.80 nm for Co(II), 267.72 nm for Cr(III and VI), 327.40 nm for Cu(II), 259.94 nm for Fe(III), 231.60 nm for Ni(II), and 202.55 nm for Zn(II).
Results and discussion
Effect of pH
Effect of shaking time
Effect of temperature
where Kd is distribution adsorption coefficient, Co and Ce denote initial and final concentrations of the metal before and after adsorption, respectively, V corresponds to the volume (mL), m represents the weight of the phase (g), R is the universal gas constant (8.314 Jmol-1 K-1), and T corresponds to the temperature in Kelvin.
Thermodynamic parameters associated with the adsorption of Cu(II) on LC3 phase
T = 298 K
T = 303 K
T = 323 K
T = 338 K
Adsorption isotherm models
where b is the Langmuir constant, indicating the nature of adsorption and the shape of the isotherm and Co is the initial concentration of the analyte of interest. The RL values specify the type of isotherm, and RL values within 0 to 1 suggest a favorable adsorption .
where Kf and n are the Freundlich isotherm constants related to adsorption capacity and intensity of adsorption, respectively. Freundlich constants (Kf and n) can be calculated from the intercept and slope, respectively, of the linear plot of logqe versus logCe.
Langmuir and Freundlich adsorption isotherm parameters for the adsorption of Cu(II) on LC3 phase
where υo = k2 is the initial adsorption rate (mgg-1 min-1) where k2 (gmg-1 min-1) corresponds to the rate constant of the pseudo-second-order adsorption, qe (mgg-1) is the amount of metal ion adsorbed at equilibrium, and qt (mgg-1) refers to the amount of metal ion on the adsorbent surface at any time t (min). The plot of t/qt versus t was developed in order to deduce kinetic parameters of υo and qe from the intercept and slope, respectively.
Pseudo-first- and second-order kinetic model parameters for extraction of Cu(II) by LC3 phase
Pseudo-first-order kinetic model
Pseudo-second-order kinetic model
Performance of proposed method
Selectivity studies of modified and unmodified DEAE cellulose adsorbents toward different metal ions, including Cd(II), Co(II), Cu(II),Cr(III), Cr(VI), Fe(III), Ni(II), and Zn(II), were investigated by determining the distribution coefficient of all the phases at optimum pH value (pH 6.0). Distribution coefficient (Kd) values were determined from Equation 1.
Uptake capacities and distribution coefficient values of different metal ions against unmodified DEAE cellulose and modified cellulose phases at pH 6.0 and 25°C
Unmodified DEAE cellulose
1.42 × 102
1.76 × 102
2.24 × 102
1.71 × 102
1.70 × 102
6.15 × 102
5.93 × 102
8.70 × 102
7.53 × 102
4.07 × 103
5.88 × 103
9.67 × 102
1.61 × 104
4.83 × 103
1.51 × 104
3.78 × 101
5.01 × 103
7.68 × 103
4.54 × 105
8.98 × 102
6.85 × 102
3.02 × 103
6.02 × 103
5.46 × 101
5.69 × 101
1.05 × 102
1.92 × 102
2.03 × 102
7.79 × 102
2.79 × 102
Application in real environmental samples
Determination of Cu(II) at different concentrations in real water samples utilizing LC3 phase
This paper was funded by King Abdulaziz University, under grant No. (T-001/431). The authors, therefore, acknowledge technical and financial support of KAU.
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