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Sunday, 16 October 2016
Using polypyrrole nanocomposites coated on rice husk ash for the removal of anions, heavy metals, COD from textile wastewater
Published Date
doi:10.1016/j.hbrcj.2015.08.002
Open Access, Creative Commons license, Funding information
In Press, Corrected Proof — Note to users
Author
Neama Ahmed Sobhy Ahmed Reyad
Sanitary & Environmental Institute, Housing & Building National Research Center, 87 el Tahrir St., Dokki, Egypt
Received 24 December 2014. Revised 6 July 2015. Accepted 9 August 2015. Available online 16 September 2015.
Abstract
In this study, a new application of polypyrrole (PPy) synthesized chemically in presence of ferric chloride as an oxidant coated on rice husk ash (RHA) by oxidative chemical polymerization method is used, ferric chloride has been found to be the chemical oxidant and water has been reported the best solvent for chemical polymerization of pyrrole. The removal of anions, heavy metals such as copper, iron and zinc and COD (chemical oxygen demand) from textile wastewater using completely mixed batch reactor (CMBR) technique is investigated when polypyrrole and its blend and nanocomposites with rice husk ash were used. Experiments were done using PPy/RHA during 30 min with 5 min intervals. It is observed that by increasing the time (5–20 min) removal efficiency increased but, after 20 min the efficiency did not increase significantly. It can be concluded that RHA in the composites does not play significant role in the anions and COD removal but the role of RHA in the removal of the metals is considerable and it causes an increase in the removal efficiency of the composites. Besides, the morphology was tested by scanning electron microscopy (SEM) to characterize the surface of PPy nanocomposites at very high magnification at an accelerating voltage of 15 kV, and chemical structure was tested by Fourier Transform Infrared spectroscopy (FTIR) in the wavelength range of 400–4000 cm−1, respectively. It was found that PPy/RHA can be used as an effective adsorbent in the removal of anions, heavy metals and COD from textile wastewater.
Keywords
Rice husk ash
Heavy metals
Textile wastewater
Nanocomposites
1. Introduction
Heavy metals are very toxic to both man and animal. They also constitute pollution problems to the environment. When these contaminants are found in effluent, they may decrease fertility of the sediment and consequently lead to eutrophication, which in open waters can progressively lead to oxygen deficiency, algal bloom and death of aquatic life [1]. Although, several separation methods are available, the process of adsorption is the most versatile and plays a significant role in removal of heavy metal contaminants from water bodies [2]. Considerable attention was given in recent years for the removal of heavy metals such as nickel, cadmium, iron, zinc, lead, and copper by polymeric beads [3]. Adsorption of metal ions by several functionalized polymers based on amines derivatives such as polyacrylonitrile fibers, ethylenediamine, polyacrylamides, poly-4-vinylpyridine, polyethyleneimine and aniline formaldehyde condensate has been reported [4] and [5]. Polypyrrole was used in the removal of fluoride ions from aqueous solution by conducting polypyrrole [6]. Conductive polymers such as polyacetylene, polyaniline, polypyrrole, and polythiophene, have attracted so much research interest in wide range applications such as rechargeable batteries [7], electromagnetic interference (EMI) shielding [8], antistatic coatings [9], gas sensors [10], optical devices [11] and removal of heavy metals [12] and [13].
The main purpose of present research is the removal of anions, heavy metals and COD from textile wastewater by using polypyrrole/rice husk ash nanocomposite.
2. Materials and methods
2.1. Instrumentation
A magnetic mixer (Model JLT6, VELP Scientifica, Europe), digital scale (Model AP250D-0, OHAUS, Switzerland), scanning electron microscope (SEM) (Model Inspect S, FEI Ltd., Holland), Fourier Transform Infrared (FTIR) spectrometer (Model FTIR-4100, JASCO, Japan) and oven (Model TK3108, EHRET, Germany) were employed, and atomic absorption spectrometer (AAS) (Model ICE3300, Thermo Scientific Ltd., UK) was used to analyze the concentration of heavy metal ions. Transmission Electron Microscopy (TEM) (Model Tecnai F12, FEI Ltd., Japan) was employed.
2.2. Materials
Pyrrole monomer was purified by simple distillation. Materials used in this work were ferric chloride (FeCl3), sodium hydroxide (NaOH) and sulfuric acid from Merck. Distilled-deionized water was used throughout this work. Rice husk obtained from rice mill was washed and dried.
2.3. Preparation and characterization of rice husk ash
Rice husk is a by-product generally obtained from rice mill. Rice husk ash is a solid obtained after burning of rice husk. A SEM micrograph of rice husk ash is shown in Fig. 1. Characteristics of the adsorbent such as surface area, bulk density and particle size were determined. The results are summarized in Table 1. The rice husks were washed with distilled water, dried in an oven at about 60 °C for 2 h, then washed with acetone and sodium hydroxide (0.3 M) to remove dirt and other contaminants present in them and then dried in an oven at about 60 °C for 4 h. Samples of rice husk were heated at 500 °C for 5 h in a muffle furnace at heating rate of 25–30 °C/min to obtain rice husk ash.
Fig. 1. SEM image of rice husk ash.
Table 1. Characteristics of rice husk ash.
Adsorbent
Rice husk ash
Surface area (m2/g)
52
Bulk density (g/cm)
0.85
Particle size (mm)
0.3–0.5
2.4. Preparation of PPy/RHA nanocomposite
During chemical polymerization of pyrrole, electroneutrality of the polymer matrix is maintained by incorporation of anions of oxidant from the reaction solution. Ferric chloride has been found to be the chemical oxidant and water has been reported the best solvent for chemical polymerization of pyrrole. For preparation of PPy/RHA nanocomposite, 5 g FeCl3 was added to 100 mL of water and then a uniform solution was resulted by using magnetic mixer. Then, 1 g of rice husk ash was added to the solution and 1 mL fresh distilled pyrrole monomer was added to stirred solution. The reaction was carried out for 4 h at room temperature. Consequently, the product was filtered to separate the impurities; product was washed several times with deionized water and dried at temperature about 60 °C in oven for 24 h.
2.5. Removal mechanism
Completely mixed batch reactor (CMBR) technique was used to remove heavy metals, anions and COD from textile wastewater. Adsorption experiments were performed by agitating 0.5 g of sorbents with 50 mL of textile wastewater at room temperature in magnetic mixer with the rotating speed of 600 rpm. At the end of predetermined time intervals, the sorbate was filtered and the concentration of heavy metals, anions and COD was determined. All experiments were carried out twice. Table 2 shows the characteristics of the wastewater (wastewater was collected from the end of process (before treatment) of El Tawfik textile factory).
Table 2. Textile wastewater characterization.
Compound
Concentration in wastewater before removal (mg/l)
Cl−
2625
SO32−
15
Cu
0.91
COD
2300
Fe
1.2
Total nitrogen (NO31−,NO21−)
35
Zn
0.2
Atomic absorption spectrophotometer was used for the analysis of heavy metals and anions in aqueous solution. Concentrations were determined after calibrating the instrument with standards within the concentration range of 0.5–10 mg/L for all components. To measure the unknown ions concentration in aqueous solution, the solution was diluted to bring the concentration within the calibration range.
3. Results and discussion
3.1. Surface morphology
In this study, a scanning electron microscope was used to characterize the surface of PPy nanocomposites at very high magnification at an accelerating voltage of 15 kV. Samples were coated with gold by a sputter coater to improve the quality of micrograph. The thickness of the coating was 35 nm. The morphology of rice husk ash before and after coating with PPy is illustrated in Fig. 1 and Fig. 2. The coating of RHA has always been found to be uniform, while coating defects have been suspected in the case of RHA at low PPy contents. Fig. 3 shows the TEM images of PPy/RHA nanocomposites for 100 nm. It is found that presence of black spots indicates the presence of PPy nanoparticles into rice husk ash matrix without any aggregation. The average particle size of PPy nanoparticles from TEM images is 35–40 nm.
The chemical structures of the obtained products were determined by FTIR analyzer in the wave number range of 400–4000 cm−1, and samples for FTIR spectroscopic characterization were prepared by grinding the dry blends with KBr and compressing the mixtures to form sheet. The FTIR spectra analysis has been done to identify the characteristic peaks of product. Comparison between a and b be introduced at Fig. 4. As can be seen in Fig. 4, one characteristic of the pyrrole unit is at 1542 cm−1. The peaks are at 1307 cm−1 (CAN stretching vibration), 1164 cm−1 (CAH in-plane deformation), 1044 cm−1 (NAH in-plane deformation) and 894 cm−1 (CAH out-of-plane deformation) [14], [15] and [16]. These peaks can also be seen in the spectra of PPy/RHA nanocomposites. As shown in Fig. 4, all bands in nanocomposites are slightly shifted, which indicates that there is some interaction between PPy and RHA.
Fig. 4. FTIR spectra of (a) PPy and (b) PPy/RHA in aqueous media.
3.3. Mechanism of removal
Polypyrrole has a reactive NAH group in a polymer chain flanked on either side by a phenylene ring, imparting a very high chemical flexibility. It is known that the main adsorption sites for anions and heavy metal ions are the nitrogen atoms in the macromolecular chains because the nitrogen atom has a lone pair of electrons that can efficiently bind a metal ions to form a metal complex. Anions and heavy metals adsorption could be responsible for a complexation between anions and heavy metal ions and the nitrogen atoms of the NC groups through sharing their lone pair of electrons could act as adsorption or ion exchange. Processes such as anion exchange, chemical oxidation, and chelation seem to be possible reactions which are occurred during anions and heavy metal ions removal.
3.4. Removal experiments
The analyzed result of textile wastewater and the effects of PPy/RHA in the removal of heavy metals, anions and COD are shown in Table 3. As can be seen in Table 3, the removal of anions, heavy metals and COD from the wastewater is dependent on the ability of surface absorption. The results indicate that PPy/RHA nanocomposites are able to remove anions and heavy metals from textile wastewater. Experiments were done using PPy/RHA during 30 min with 5 min intervals. As can be seen (Table 4) increasing the time (5–20 min) removal efficiency increased but, after 20 min the efficiency did not increase significantly. In Table 5, the removal efficiency of wastewater is shown using PPy and RHA. As can be seen in Table 5, RHA has low efficiency in the removal of anions and COD, but its performance to remove metals is considerable. PPy has noticeable efficiency in the removal of metals, anions and COD. However, in all experiments, the removal efficiency of PPy is lower than composites. Therefore it can be concluded that RHA in the composites does not play significant role in the anions and COD removal but the role of RHA in the removal of the metals is considerable, and it causes an increase in the removal efficiency of the composites. The results of application of RHA and PPy, RHA blends (not in the composite form) are shown in Table 6. As can be seen, removal efficiency of composites is higher than PPy, RHA blends (not in the composite form). Removal efficiency of anions, COD and heavy metals using regenerated adsorbents is shown in Table 7. The adsorbents were washed by H2SO4, NaOH and deionized water respectively. As shown in Table 7, there is a little difference between regenerated and fresh composites in the removal efficiency.
Table 3. The analysis of textile wastewater before and after removal.
Compound
Concentration in waste water before removal (mg/l)
Removal efficiency of PPy/RHA (%)
Cl−
2621
82.1
SO32−
17
84.8
Cu
0.9
94.2
COD
2400
95.6
Fe
1.2
93.1
Total nitrogen (NO31−, NO21−)
36
86.6
Zn
0.25
90.4
Table 4. Analysis of textile wastewater after removal using PPy/RHA in various reaction times.
Compound
Removal efficiency after 5 min of reaction (%)
Removal efficiency after 10 min of reaction (%)
Removal efficiency after 15 min of reaction (%)
Removal efficiency after 20 min of reaction (%)
Removal efficiency after 25 min of reaction (%)
Cl−
45.2
59.4
70.2
83.6
84.1
SO32−
45.12
59.1
70.3
84.2
84.5
Cu
52.6
67.21
79.7
93.9
94.4
COD
31.8
42.9
56.3
68.5
95.1
Fe
51.47
68.3
80.2
92.7
93.3
Total nitrogen (NO31−, NO21−)
46.1
61.3
72.9
86.2
86.8
Zn
47.8
63.4
75.2
89.7
90.3
Table 5. The analysis of wastewater after treatment using PPy and RHA.
Compound
Removal efficiency by using PPy (%)
Removal efficiency by using RHA (%)
Cl−
79.7
17.7
SO32−
83.2
11.5
Cu
70.4
79.2
COD
62.5
4.1
Fe
74.2
70.3
Total nitrogen (NO31−, NO21−)
82.1
8.8
Zn
76.6
75.2
Table 6. Removal efficiency of PPy/RHA blends.
Compound
Removal efficiency by using PPy and RHA blends (%)
Cl−
80.4
SO32−
77.2
Cu
79.3
COD
64.8
Fe
88.2
Total nitrogen (NO31−, NO21−)
80.6
Zn
80.3
Table 7. Analysis of cotton textile wastewater after removal by regenerated PPy/RHA.
Compound
Removal efficiency by using PPy and RHA blends (%)
Cl−
79.2
SO32−
76.1
Cu
77.3
COD
62.3
Fe
80.2
Total nitrogen (NO31−, NO2−1)
65.8
Zn
78.2
4. Conclusions
In this study, chemical oxidative polymerization method was used to prepare polypyrrole/rice husk ash nanocomposites by coating the rice husk ash substrate with pyrrole and their ability in the removal of heavy metals, COD and anions from textile wastewater was investigated. The nanocomposite of polymer showed considerable potential in the removal of heavy metals and anions from textile wastewater. RHA has low efficiency in the removal of anions and COD, but its performance to remove metals is considerable, and PPy has noticeable efficiency in the removal of metals, anions and COD. Nanocomposites regeneration is performed using NaOH, deionized water and H2SO4. After regeneration, nanocomposites were used for wastewater treatment as there is a little difference between regenerated and fresh composites in the removal efficiency.
Conflict of interest
The author declares that there are no conflicts of interest.
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Peer review under responsibility of Housing and Building National Research Center.
Open access funded by Housing and Building National Research Center
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