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Preparation of unsaturated polyester Ce(IV) phosphate by plastic waste bottles and its application for removal of Malachite green dye from water samples
*Corresponding author. Tel.: +91 9897767450 asifkhan42003@Yahoo.com (Asif Ali Khan)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer-review under responsibility of King Saud University.
Available online 20 October 2010
Abstract
In this paper, recycling of polyethyleneterephthalate (PET), a non-biodegradable plastic, was carried out by preparing unsaturated polyester Ce(IV) phosphate (USPECe(IV)P) composite cation exchanger. Various samples of USPECe(IV)P was prepared by mixing different volume ratios of unsaturated polyester in an inorganic Ce(IV) phosphate gel and characterized by TGA/DTA, XRD, SEM, Fourier transform infra-red spectroscopy (FTIR) instrumental methods. The composite has been employed as adsorbents for the removal of Malachite green dye from waste water. The nature of possible adsorbent and dye interaction was examined by the FTIR technique. The adsorption of MG was found to be maximum (98%) at pH 8. The extent of removal of MG was found to be dependent on adsorbent dose, temperature and time. The equilibrium data for adsorption was best represented by the Friendlich isotherm. Thermodynamic parameters (ΔH0 and ΔG0) suggest an endothermic and spontaneous process. Kinetic studies show better applicability of an intraparticle diffusion kinetic model.
Keywords
Polyethyleneterephthalate
Composite
Characterization
Isotherm
Kinetics
Desorption
1 Introduction
Recent development in composite materials offers several outstanding properties as compared to conventional materials. Synthesis of a polymeric inorganic composite received a great deal of attention because it provided new material with special mechanical, chemical, electrochemical, and optical as well as magnetic properties (Chujo, 1996; Sanchez and Ribot, 1994; Judeinstein and Sanchez, 1996). These type of composite materials prepared with electrical conducting polymers have emerged as fascinating materials. Due to a wide range of other desirable properties such as environmental stabilities, ease of fabrication, light weight mechanical properties and so on. Electrical conducting organic–inorganic cation-exchange composite materials are also an advanced class of materials (Fisher et al., 2005) used in various chromatographic studies as well as in making an ion-selective membrane electrode (Khan et al., 2005; Khan and Inamuddin, 2006; Khan et al., 2007, 2008). Synthesis of organic–inorganic composite materials using post consumer waste plastics also created interest for scientists and engineers, because large amount of disposable plastic waste bottles posing environmental problems since they are not biodegradable (Avila and Duarteb, 2003). Recycled polyethylene terephthalate (PET) from post consumer plastic bottles was used for the synthesis of a polymer mortar composite by Mahdi et al. (2007). Encouraging results received the interest to generate organic–inorganic cation-exchange materials using recycled PET from plastic waste bottles. The prepared composite material was used for the separation of heavy metal from water and making an ion-selective electrode (Khan and Khan, 2008).
Dyes are widely used in textile, plastic, food, dyeing, paper, printing, pharmaceutical and cosmetic industries. Textile processing industries now a days are widespread sectors in developing countries. Among the various processes in the textile industry, the dyeing process uses a large volume of water for dyeing, fixing and washing processes. Thus, the wastewater generated from the textile processing industries contains suspended solids, high amount of dissolved solids, un-reacted dyestuffs (color) and other auxiliary chemicals that are used in the various stages of dyeing and processing. These dyes color the water and make penetration of sunlight to the lower layers impossible and hence are affecting aquatic life. Many of these are toxic or even carcinogenic (McKay et al., 1981). Polluted water not only damages plants and animals, but also harms the environment. Discharge of these into water bodies would pollute the water and, by their toxicity, make it unfit for aquatic life.
Some physical and chemical methods such as filtration, sedimentation, degasification ozonation, coagulation, adsorption, photodegradation and ion exchange are available for the treatment of water. Biological treatment methods like aerobic and anaerobic digestions by microorganisms, mostly bacteria are used in the decomposition of wastewaters to stable end products. There are tones and tones of effluents being released every single day and the most effective removal technique is out to be grabbed. Currently sorption process is also proved to be an effective process for the removal of pollutants from wastewaters.
In the following research paper, unsaturated polyester Ce(IV) phosphate (UPECe(IV)P) was synthesized using recycled PET obtained from waste plastic bottles and used as a adsorbent for the removal of Malachite green from waste water. Further studies on dc electrical conductivity will be carried out by doping process in the next paper.
2 Materials and methods
2.1 Reagents
Soft drink waste bottles of PET were obtained in the form of beverage bottles from the City of Aligarh; UP; India. After the removing of caps and labels, the bottles were shredded to sizes of approximately 1.5–3.0 cm. The shredded PET was washed by tap water and dried at room temperature. The adhesives on the bottles were not purposely removed, most of them still remained. Cerric sulphate and disodiumhydrogenphosphate, zincacetate, maleic and phthalic anhydride, Malachite green[4-[(4-dimethylaminophenyl)-phenyl-methyl]-N,N-dimethyl-aniline] were obtained from CDH and Qualigens (India Ltd.) and were used as received. All other chemicals used were of analytical reagent grade and supplied by CDH India.
2.2 Instruments
The following instruments were used in the experimental work: a FTIR spectrophotometer (Perkin Elmer, USA, model Spectrum-BX); digital pH-meter (Elico Li-10, India); X-ray diffractometer – Phillips (Holland), model PW 1148/89; UV/Vis spectrophotometer – Elico (India), model EI 301E; a thermal analyzer – V2.2A DuPont 9900; an elemental analyzer – Elementary Vario EL III, Carlo-Erba, model 1108; an electronic balance (digital, Sartorius-21OS, Japan). T70-UV/Vis spectrophotometer (PG Instrument Ltd., UK); scanning electron microscope (LEO 435 VP) and transmission electron microscope (Philips EM-400).
3 Preparation of materials
3.1 Glycolysis experiment
The conversion of polyethylene terephthalate (PET) in the presence of glycol is known as alcoholyses or glycolysis in the presence of a catalyst. One-litre three-necked round bottomed flask (reactor) was used for all glycolysis experiments. In order to ensure that the moisture content in the reactor was as low as possible, the reactor was heated up to 100 °C and held at that temperature for at least 5 min. The reactor was equipped with a thermometer and a reflux condenser. A magnetic stirrer was put in the reactor to ensure proper mixing. The ratio of diethylene glycol to PET used in the glycolysis experiment was 4:1 by weight i.e. the weight of diethylelene glycol and PET flakes were 84 and 21 g, respectively. Glycolysis temperature was set at 190 °C and glycolysis time was 2 h and the amount of the catalyst was fixed 0.25% by weight of PET.
3.2 Synthesis of unsaturated polyester (UPE)
After glycolysis, the maleic and phthalic anhydrides were added into the reactor for non-catalyzed melt polyesterification reaction. The reaction was carried out at 190 °C for 8 h, and 0.5% hydroquinone by weight of PET was added to check the back depolymerization. The slurry was allowed to cool at room temperature.
3.3 Preparation of Ce(IV) phosphate
The method of preparation of the inorganic precipitate of Ce(IV) phosphate ion-exchanger was very similar to that of De and Chowdhury (1974) with a slight modification (Khan et al., 2007). A solution of 0.1 M Ce(SO4)2·4H2O prepared in 1 M H2SO4 was mixed in different molar solutions of H3PO4 and the pH was maintained at 1. Yellowish gel type slurries obtained were kept for 24 h at room temperature.
3.4 Preparation of unsaturated polyester Ce(IV) phosphate composite cation exchanger
The composite cation-exchanger was prepared by the sol–gel mixing of unsaturated polyester (UPA) and Ce(IV) phosphate inorganic material. In this process when the gels of unsaturated polyester were added to the white inorganic precipitate of cerrium(IV) phosphate with a constant stirring at room temperature, the resultant mixture was turned slowly into white colored slurries. The resultant white colored slurries were kept for 24 h at room temperature.
Now the unsaturated polyester based composite cation-exchanger gels were filtered off, washed thoroughly with DMW to remove excess acid and any adhering traces. The washed gels were dried over P4O10 at 30 °C in an oven. The dried products were immersed in DMW to obtain UPECe(IV)P as granules. They were converted to the H+ form by keeping it in 1 M HNO3 solution for 24 h with occasional shaking intermittently replacing the supernatant liquid. The excess acid was removed after several washings with DMW. The material was finally dried at 40 °C and sieving to obtain particles of a particular size range of ∼125 μm. Hence a number of unsaturated polyester Ce(IV) phosphate composite cation-exchanger samples were prepared and on the basis of Na+ exchange capacity (IEC), a percent of the yield sample S-2 (Table 1) was selected for further studies. PET = polyethylenetrephthalate. DEG = diethyleneglycol. MA = maleic anhydride. PthA = phthalic anhydride.
Samples
Mixing volume ratios (mL)
Glycolysis of PET
Polyesterification after glycolysis
Ion-exchange capacity (meg−1)
Ce(SO4)2·4H2O in 1 M H2SO4
H3PO4
PET (g)
DEG (mL)
Heating time (h)
Heating temperature (°C)
MA (g)
PthA (g)
S-1
100
100 (2 M)
1
10
4
0.5
0.5
3.62
S-2
50
50 (2 M)
2
15
4
85
1
1
2.7
S-3
250
100 (2 M)
3
15
4
85
1
1
2.3
S-4
100
100 (2 M)
–
–
–
–
–
–
1.14
S-5
75
75 (2 M)
4
20
4
85
1.5
1.5
1.58
S-6
75
125 (1 M)
5
25
4
85
2
2
1.69
S-7
–
–
1
10
4
85
0.5
0.5
0.17
S-8
125
100 (4 M)
6
30
4
85
2.5
2.5
1.06
4 Adsorption studies
Adsorption studies were carried out by batch process. In batch process 0.1 g of the adsorbent (unsaturated polyester Ce(IV) phosphate) was placed in a conical flask in which 100 mL solution of MG of the desired concentration (50, 80 and 100 ppm) was added and the mixture was shaken in a temperature controlled shaker incubator for 30 min at 200 rpm. The mixture was then filtered using Whatman filter paper No. 40 and the final concentration of dye was determined in the filtrate by UV–Vis spectrophotometer (Elico, Sl-164).
5 Results and discussion
5.1 Characterization
Various samples of organic–inorganic composite unsaturated polyester Ce(IV) phosphate cation-exchange material have been developed by the incorporation of unsaturated polyester into the inorganic matrices of Ce(IV) phosphate. Due to high percentage of yield, better ion-exchange capacity, reproducible behaviour, chemical and thermal stability, sample S-1 (Table 1) was chosen for detailed studies. The exchanger possessed a better Na+ ion-exchange capacity (3.62 meg g−1) as compared to an inorganic precipitate of amorphous Ce(IV) phosphate (1.14 meg g−1).
It is clear from the thermogravimetric analysis (TGA) curve (Fig. 1) of the material that up to 85 °C only 5% weight loss was observed, which may be due to the removal of external H2O molecules present at the surface of the composite (Duval, 1963). Further weight loss of mass approximately 6.5% between 100 and 200 °C may be due to the slight conversion of inorganic phosphate into pyrophosphate. Slow weight loss of mass about 7.5% in between 200 and 700 °C may be due to the slight decomposition of the organic part of the material. A broad peak at ∼90 and 550 °C in DTA curve shows that the reaction is exothermic during the change of phase of material.
Simultaneous TGA–DTA curves of unsaturated polyester Ce(IV) phosphate as prepared.
The X-ray diffraction pattern of this material (S-1 as prepared) recorded in powdered sample exhibited some small peaks in the spectrum, which suggest the semi-crystalline nature of the composite material.
The scanning electron microphotograph (SEM) of unsaturated polyester Ce(IV) phosphate composite, unsaturated polyester and Ce(IV) phosphate are represented in Fig. 2. Small and big flakes are seen in the unsaturated polyester Ce(IV) phosphate composite cation exchange material. Thus the morphology of the material has been changed with the formation of organic inorganic composite material unsaturated polyester Ce(IV) phosphate after adhesion of organic polymer (UPE) with inorganic precipitate Ce(IV) phosphate.
SEM photographs of unsaturated polyester Ce(IV) phosphate (a), unsaturated polyester (b) and Ce(IV) phosphate (c).
FTIR spectrum of the composite (Fig. 3) shows the twisting and wagging vibration frequencies of the methylene group in the region of 1300–1200 cm−1 (Rao, 1963). The vibration frequency at 1700 cm−1 shows an aromatic ring. A small peak in the region of 1600 cm−1 may be due to the presence of a carbonyl group of the composite. A peak at ∼3000 cm−1 shows the presence of –CH stretching vibration frequency of a benzene ring in the plane while 600 cm−1 show –CH out of the plane deformation vibration frequency of the benzene ring.
FTIR spectra of unsaturated polyester Ce(IV) phosphate before (a) and after (b) adsorption of MG dye.
Carbon, hydrogen, oxygen, phosphorus and cerium contents of the material were determined by different methods of analysis. The percent composition of C, H, O, P and Ce was found to be 14.58%, 1.30%, 46.36%, 11.58%, 26.16% and a tentative molecular formula of the composite is: C12H10O5·Ce(IV)(PO4)(HPO4)0.5(H2O)0.5.
5.2 Nature of the adsorption by FTIR technique
Change in the FTIR spectra after the adsorption of MG on the surface of UPECe(IV)P can be seen in Fig. 3. The vibration frequencies of the methylene group in the region of 1300–1200 cm−1 are not clear due to adsorption of MG in the matrices of composite material. However a sharp band at 1086 cm−1 represents C–OH stretching vibrations which also signify the involvement of dye on the surface of UPECe(IV)P.
5.3 Effect of contact time with different concentration
Adsorption studies were carried out to determine the uptake rates of MG on the adsorbent and to get access to the equilibrium times. The evolution of MG removal with time by UPECe(IV)P for different initial MG concentrations was first studied (Fig. 4), indicating that the equilibrium time is in the 30–35 min range for all MG initial concentrations. More then 90% adsorption of Malachite green (MG) was observed on the surface of unsaturated polyester Ce(IV) phosphate[UPECe(IV)P] composite cation exchange material. It may be due to the interaction between the anionic group present in the matrices of the composite cation exchanger and hydrochloric acid in MG.
Effect of contact time with different concentration.
5.4 Effect of pH
The effect of pH for the adsorption of MG on the UPECe(IV)P from aqueous solution. It was observed that the MG adsorption was highly dependent on the pH of the solution which affected the surface charge of the UPECe(IV)P and the degree of ionization of the adsorbate. It was found that an increase in the solution pH led to an increase in the MG adsorption efficiency. The percent adsorption of MG increased from 71% to 98% by varying the solution pH from 2 to 10. At lower pH, more protons were available (excess H+ ions), thereby decreasing the electrostatic attractions between positively charged dye anions and positively charged adsorption sites of the cation exchanger and therefore ionic repulsion between the positively charged surface and the cationic dye molecules caused a decrease in MG adsorption. The adsorption of MG was found to be maximum (98%) at pH 8, thus all the experiments were performed at pH 8.
5.5 Effect of temperature and thermodynamic parameters
The effect of temperature on adsorption of MG on the UPECe(IV)P was investigated by varying the adsorption temperature at 20–40 °C. The thermodynamic parameters such as standard enthalpy (ΔH0), standard entropy (ΔS0) and standard free energy (ΔG0) were calculated by using the following equations (Wang and Zhu, 2007):
The values of ΔH0 and ΔS0 were calculated from the slope and intercept of van’t Hoff plots of ln Kd versus 1/T and ΔG0 can be calculated using the relation below:
The calculated values of ΔH0, ΔS0 and ΔG0 are listed in Table 2. The positive value of ΔH0 indicates the endothermic nature of the adsorption interaction. The positive value of ΔS0 showed the increased disorder at the solid/solution interface during the adsorption of MG on the UPECe(IV)P. The positive values of ΔS0 show the randomness at the solid–solution interface. The negative value of ΔG0 indicated the feasibility of the process and the spontaneous nature of the adsorption with a high preference of MG onto the UPECe(IV)P.
Temperature (°C)
ΔG0 (kJ mol−1)
ΔH0 (kJ mol−1)
ΔS0 (kJ mol−1)
20
−2.66
48.195
0.165
30
−1.13
48.195
0.165
40
−0.86
48.195
0.165
5.6 Adsorption isotherms
Langmuir isotherm (Langmuir, 1918) is based on an assumption that the adsorption occurs at specific homogeneous sites within the adsorbent and the monolayer adsorption onto a surface containing a finite number of adsorption sites of uniform strategies of adsorption with no transmigration of adsorbate in the plane of the surface. The linear form of Langmuir isotherm equation is given as:
The essential feature of the Langmuir isotherm can be expressed in terms of dimensionless constant separation or equilibrium parameter (RL), which is defined as:
Dye
Langmuir constant
Freundlich constant
qm (mg/g)
b (L/mg)
R2
RL
Kf (mg/g)
n
R2
MG
1.01
0.022
0.97
0.476
44.85
1.006
0.99
Freundlich isotherm on the other hand assumes heterogeneous surface energies, in which the energy term in Langmuir equation varies as a function of the surface coverage. The well-known linear form of Freundlich isotherm (Freundlich, 1906) is given by the following equation:
Freundlich plot for the adsorption of MG on unsaturated polyester Ce(IV) phosphate.
Table 3 summarizes all the constants, correlation coefficients, R2 values obtained for the two isotherm model for adsorption of MG on the UPECe(IV)P. The Freundlich model yielded the best fit at, as the R2 values were relatively high close to unity.
5.7 Adsorption kinetics
Kinetics of adsorption are quite significant as it decides the residence time of adsorbate at solid–solution interface and helps in determining the rate of adsorption process. The adsorption of dyes from the liquid to solid phase can be considered as a reversible reaction with equilibrium established between the two phases. The kinetics of adsorption of MG on the UPECe(IV)P was studied by applying three different kinetic models. The linear form of pseudo first-order equation given by Langergren and Svenska (1998) is shown by the following equation:
On the other hand, the linear form of pseudo-second-order equation (Ho and McKay, 2000) based on equilibrium adsorption is expressed as:
The kinetic parameter for intraparticle diffusion was determined using the following equation (Weber and Morris, 1963):
Representation of the kinetic data by intraparticle diffusion.
Table 4 summarizes the rate constants and correlation coefficients, R2 of the three kinetic models for this adsorption process. The correlation coefficients, R2 values were obtained from the three kinetic models. The intraparticle diffusion model yielded the best fit at, as the R2 values were relatively high (0.98) close to unity.
Malachite green
Pseudo-first-order equation
qe (mg/g)
72.27
k1 (×102 min−1)
0.0539
R2
0.8576
Pseudo-second-order equation
qe (mg/g)
136.986
k2 (g/mg min)
0.0005
R2
0.931
Intraparticle diffusion equation
kint (mg/g min1/2)
17.077
C
0.1364
R2
0.9804
5.8 Desorption studies
Desorption studies help to elucidate the nature of adsorption recycling of the spent adsorbent and the dye. If the adsorbed dye can be desorbed using neutral pH water, then the attachment of the dye on the adsorbent is weakly bonded. Sodium hydroxide and sulphuric acid (1 M) did not show any desorption but a weak acid, like acetic acid (5 M) solubilized about 65.23% of pure MG from the spent adsorbent (Fig. 7). Desorption of dye in acetic acid indicates that Malachite green dye is adsorbed onto UPECE(IV) through chemisorptions mechanism and very little desorption of the dye in acid or base confirms the strong affinity of dye on the UPECe(IV)P.
Desorption studies of MG adsorbed unsaturated polyester Ce(IV) phosphate by using 5 M acetic acid as an eluent.
6 Conclusion
In the present study recycling of non-biodegradable post consumer waste plastic bottles of polyethylene terephthalate (PET) is carried out by preparing organic–inorganic composite cation exchanger, unsaturated polyester Ce(IV) phosphate, having excellent cation exchange capacity (3.62 meg g−1) as compared to inorganic precipitate of amorphous Ce(IV) phosphate (1.14 meg g−1) having double environmental pollution remediation. The present investigation showed that the adsorption process was very fast, and it reached equilibrium in 30 min of contact, which is much faster than that of the other adsorbents for the removal of dye from waste water. The adsorption studies indicate that Freundlich model is better obeyed. Thermodynamic parameters (ΔH0 and ΔG0) suggest that adsorption process is endothermic and spontaneous. The kinetics data are best fitted in intraparticle diffusion rate equation as is evident from the value of regression coefficients (R2). The maximum efficiency of UPECe(IV)P has been demonstrated by eluting MG from UPECe(IV)P and it has been found that 65% MG could be recovered when 5 M acetic acid was used as eluent. It is concluded that UPECe(IV)P is an effective cation exchanger and can be utilized for the removal and recovery of MG from wastewater.
Acknowledgements
The authors are thankful to the Chairman, Department of Applied Chemistry, Z.H. College of Engineering and Technology, A.M.U. (Aligarh) India for providing research facilities, and also to the Council of Scientific and Industrial Research of India (CSIR) for financial supports.
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