Poly(propylene carbonate)/
Petroleum-derived plastics cause the worldwide environment and earth pollution during their production and disposal. Therefore, the development of biodegradable materials such as starch plastics, cellulose plastics, poly(lactic acid), and soy-based plastics has been receiving considerable research attention [
Meanwhile,
In general, it is very important to find appropriate methods that meet a quality control for determination of metal ions. However, direct detection of metal ions using analytical methods is insufficient due to their low concentrations and the high concentration of interfering matrix components in most real samples. Thus, an effective separation technique is generally necessary for accurate and effective extraction of metal ions. A wide range of treatment techniques are there for separation of metal ions, for example, precipitation [
Similarly, this investigation was devoted to studying and evaluating the effectiveness of newly synthesized PPC-BCD 5 as a specific solid phase extractor for Cd(II) by inductively coupled plasma-optical emission spectrometry. The selectivity of PPC (PPC-BCD 0.5, PPC-BCD 1, PPC-BCD 3, PPC-BCD 5, or PPC-BCD 10) toward Cd(II) was studied. In addition, the influence of pH on the selectivity and effectiveness of PPC-BCD 5 for adsorption of Cd(II) was investigated. Other parameters, like concentration and contact time effects, pursuing the supreme uptake of Cd(II) on the PPC-BCD 5 phase were explored under batch techniques. The thermodynamic behavior of Cd(II) adsorption on the PPC-BCD 5 phase was also investigated.
Poly(propylene carbonate) (PPC) was delivered by SK Innovation Co., Ltd. (Cheonan, Korea).
In this study, five different PPC-BCD extractors were prepared via solution method. Firstly, 30 mL of PPC (2 g) solution was prepared by dissolving in DMF at 50°C. A dispersed solution of BCD was prepared in DMF using 20 min ultrasonication. To explore the influence of BCD on the extraction properties, formulations with several different BCD contents were prepared: 0.5, 1, 3, 5, and 10 wt% with respect to the PPC content. These samples depending on the PPC content were coded as PPC-BCD 0.5, PPC-BCD 1, PPC-BCD 3, PPC-BCD 5, and PPC-BCD 10, respectively. The PPC-BCD solutions were gently put onto a glass plate and kept for 2 hr drying at 120°C. The dried extractor films were approximately 35
A standard solution of Cd(II) was made in 18.2 MΩ·cm distilled water and kept at 4°C. The standard solutions of 1 mg L−1 of Cd(II) were made for selectivity and individually mixed with 20 mg PPC (PPC-BCD 0.5, PPC-BCD 1, PPC-BCD 3, PPC-BCD 5, or PPC-BCD 10). In addition, standard solutions of 1 mg L−1 Cd(II) ion were made in the pH values ranging from 1.0 to 9.0 with appropriate buffer solutions, 0.2 mol L−1 HCl/KCl for pH 1.0 and 2.0, 0.1 mol L−1 CH3COOH/CH3COONa for pH 3.0–6.0, and 0.1 mol L−1 Na2HPO4/HCl for pH 7.0–9.0. Then, all standard solutions were individually mixed with 20 mg PPC-BCD 5 in order to study the effect of pH on the selectivity of PPC-BCD 5 adsorption toward Cd(II). All mixtures were shaken for 1 h using a mechanical shaker at 150 rpm and room temperature. The PPC-BCD 5 phase was then removed by filtration, and the concentration of metal ion of interest in the aqueous solution was checked by inductively coupled plasma-optical emission spectrometer. For investigation of adsorption capacity of Cd(II) under batch conditions, standard solutions of 5, 10, 15, 20, 30, 50, 75, 100, 125, 150, 200, and 250 were made as above, set to the ideal pH value of 6.0, and separately mixed with 20 mg PPC-BCD 5. Additionally, the influence of contact time on Cd(II) uptake capacity was performed at similar batch conditions but at dissimilar equilibrium periods (2.5, 5, 10, 20, 30, 40, 50, and 60 min). For thermodynamic investigation, standard solutions of 5 mg L−1 Cd(II) were made, set to the pH value of 6.0, and separately mixed with 20 mg PPC-BCD 5. Thermodynamic study of the adsorption of PPC-BCD 5 toward Cd(II) was also performed at similar batch circumstances at diverse temperatures (273, 298, 313, 338, and 353 K).
The buffer’s pH was measured by a pH meter (InoLab pH 7200, IL, USA). Inductively coupled plasma-optical emission spectrometer (ICP-OES) model Optima 4100 DV, USA, was utilized for the determination of Cd(II). The ICP-OES instrument was optimized every day before measurement and used with the following parameters: FR power, 1300 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; and wavelength range of monochromator, 165–460 nm. Concentrations of Cd(II) were determined at wavelengths of 228.80 nm for Cd(II).
Selectivity of PPC (PPC-BCD 0.5, PPC-BCD 1, PPC-BCD 3, PPC-BCD 5, or PPC-BCD 10) toward Cd(II) was studied based on calculation of the distribution coefficient. The distribution coefficient (
Selectivity study of different phases (20 mg) of adsorption toward Cd(II) (
Phase |
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PPC | 1.213 | 4.04 × 104 |
PPC-BCD 0.5 | 1.205 | 3.35 × 104 |
PPC-BCD 1 | 1.180 | 2.11 × 104 |
PPC-BCD 3 | 1.158 | 1.56 × 104 |
PPC-BCD 5 | 1.248 | 7.80 × 105 |
PPC-BCD 10 | 1.178 | 2.03 × 104 |
Extraction of metal ions from aqueous media by process of adsorption is usually pH dependent because pH has an effect on the surface charge of adsorbent, the extent of ionization, and species of adsorbate [
It can be clearly observed from Figure
Effect of pH on the adsorption of 1 mg L−1 Cd(II) on 20 mg PPC-BCD 5 phase at 25°C.
The highest percentage of Cd(II) extraction and selectivity at pH 6.0 with PPC-BCD 5 phase can be possibly due to the electrostatic interaction between positively charged Cd(II) ions and negatively charged sites presented on PPC-BCD 5. Seeing the above results, the optimum pH value of 6.0 was chosen to be the optimum regarding examination of other parameters responsible for its maximum uptake on PPC-BCD 5 under static conditions.
Adsorption capacity represents the utmost metal amount taken up by 1 g of solid phase and presented by mg metal g−1. In this study, the uptake capacity of Cd(II) was investigated by varying amounts of Cd(II) and individually mixing them with 20 mg PPC-BCD 5 at pH 6.0 under batch procedure. Adsorption capacity can be expressed using the following:
Adsorption profile of Cd(II) on 20 mg PPC-BCD 5 in relation to the concentration at pH 6.0 and 25°C.
It is very important to study adsorption isotherm models for the development of equation that precisely symbolizes the results. Both Langmuir and Freundlich adsorption isotherm models [
A linear plot was obtained from Langmuir isotherm equation based on the least square fit, verifying the validity of Langmuir adsorption isotherm model (Figure
Langmuir adsorption isotherm model of Cd(II) adsorption on 20 mg PPC-BCD 5 at pH 6.0 and 25°C. Adsorption experiments were obtained at different concentrations (5–250 mg L−1) of Cd(II) under batch conditions.
The effect of shaking time on the % extraction of Cd(II) is a significant factor for calculating the possible prejudice order regarding the behavior of PPC-BCD 5 adsorption toward Cd(II) and finding the approximate time needed to acquire equilibrium. In this study, various contact times varying from 2.5 to 60.0 min were examined at the concentration of 150 mg L−1 Cd(II) (Figure
Effect of contact time on the adsorption of 150 mg L−1 Cd(II) on 20 mg PPC-BCD 5 at pH 6.0 and 25°C.
The effect of concentration on reaction rates is very essential in understanding the reaction mechanism. The adsorption kinetic data of Cd(II) adsorption on PPC-BCD 5 were investigated in terms of pseudo-first- and second-order kinetic equations [
The adsorption kinetic data of Cd(II) adsorbed on PPC-BCD 5 were also studied in terms of a pseudo-second-order adsorption. The pseudo-second-order model explains that the rate limiting step is possibly chemical adsorption relating valence forces through sharing or exchanging of electrons between the adsorbent and adsorbate [
Pseudo-second-order adsorption kinetic model of Cd(II) uptake on 20 mg PPC-BCD 5 at pH 6.0 and 25°C.
The study of thermodynamic parameters offers a good understanding of mechanism for the adsorption of Cd(II) on PPC-BCD 5. Therefore, the influence of temperature regarding the adsorption of 20 mg PPC-BCD 5 for 5 mg L−1 Cd(II) was investigated at varied temperatures (273, 298, 313, 338, and 353 K). The distribution adsorption coefficient (
Calculated thermodynamic parameters of 5 mg L−1 Cd(II) adsorption on 20 mg PPC-BCD 0.5 (
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−9.34 | 46.18 | −22.05 | −23.01 | −23.64 | −25.09 | −25.66 |
To investigate the feasibility of PPC to apply for the selective detection of toxic metal ion in complex matrices, a series of PPC-BCD extractors were newly prepared by solution blending of biodegradable PPC and BCD. The proposed method based on the newly synthesized PPC-BCD 5 phase not only had the efficiency toward a selective adsorption of Cd(II) but also provided high uptake capacity of Cd(II). Results obtained from adsorption isotherm models displayed that Langmuir adsorption isotherm model has best described the Cd(II) adsorption on PPC-BCD 5. Kinetic isotherm results demonstrated that the adsorption of PPC-BCD 5 toward Cd(II) followed a pseudo-second-order kinetic reaction. Thermodynamic study reveals that the adsorption mechanism of Cd(II) adsorption on PPC-BCD 5 was a common spontaneous method and thermodynamically favorable. Additionally, the adsorption procedure is found to be exothermic in nature. This method can be an useful approach in providing a selective separation and calculation of Cd(II) from the complex matrices.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, under Grant no. D-004/431. The authors, therefore, acknowledge technical and financial support of KAU.