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Activation of natural coal for selective preconcentration of Pb(II) ions prior to its trace determination in aqueous samples by flame atomic absorption spectrometer
Journal Pre-proof Activation of natural coal for selective Preconcentration of Pb(II) ions prior to its trace determination in aqueous samples by flame atomic absorption spectrometer
Sumita Bhatia, Ali Nawaz Siyal, Adnan Ahmed, Qadeer Khan Panhwar, Abdul Majid Channa, Amanullah Mahar PII:
S2590-1826(20)30006-0
DOI:
https://doi.org/10.1016/j.enceco.2020.02.001
Reference:
ENCECO 14
To appear in:
Environmental Chemistry and Ecotoxicology
Received date:
17 January 2020
Revised date:
31 January 2020
Accepted date:
9 February 2020
Please cite this article as: S. Bhatia, A.N. Siyal, A. Ahmed, et al., Activation of natural coal for selective Preconcentration of Pb(II) ions prior to its trace determination in aqueous samples by flame atomic absorption spectrometer, Environmental Chemistry and Ecotoxicology(2020), https://doi.org/10.1016/j.enceco.2020.02.001
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© 2020 Published by Elsevier.
Journal Pre-proof Activation of Natural Coal for Selective Preconcentration of Pb(II) ions Prior to its Trace Determination in Aqueous Samples by Flame Atomic Absorption Spectrometer Sumita Bhatia1, Ali Nawaz Siyal2*, Adnan Ahmed1, Qadeer Khan Panhwar2, Abdul Majid Channa2, Amanullah Mahar1 1
Centre for Environmental Science, University of Sindh, Jamshoro 76080, Pakistan 2
Institute of Chemistry, University of Sindh, Jamshoro 76080, Pakistan
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Corresponding author’s Email: [email protected], Postal address: Institute of Chemistry,
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University of Sindh, Jamshoro 76080, Pakistan
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Abstract
Natural coal was collected from Thar coal field, block IX in Province Sindh, Pakistan. The Thar
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coal was modified to Activated Thar Coal Adsorbent (ATCA) by reacting with concentrated H2SO4, which enhanced its porosity by dehydration as concentrated H2SO4 is strongly
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dehydration agent. The surface oxidation of coal was carried out by refluxing in concentrated HNO3. The ATCA was subjected to FT-IR spectrometer for characterization, which revealed the
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presence of C=O and COOH moieties onto its surface. The ATCA was packed in column for adsorption of Pb(II) ions and recovered ≥95.6% with relative error ≤4.4% with RSD ≤3.7% at
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pH 7.0, ATCA amount of adsorbent packed in column 400 mg, sample volume 400 mL (flow rate of 2.0 mL min−1) and eluent solution 5.0 mL of 0.5 mol L−1 HCl (flow rate of 1.0 mL min−1).
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LOD (0.03 μg L-1) and LOQ (0.11 μg L-1) of method were calculated followed by blank recording (n = 15) with preconcentration factor (PF) of 80. A linear response was observed with regression equation of y = 0.0934x + 0.0411 and R² = 0.99 for concentration ranging 0.5-5.0 mg L-1 (before preconcentration). Similarly, a linear response was also observed with regression equation of y = 7.4358x + 0.0429 and R² = 0.99 for concentration ranging 0.005-0.050 mg L-1 (after preconcentration). Breakthrough curve was plotted for obtaining to saturation capacity (152.5 mg g-1) of ATCA for adsorption of Pb(II) ions. The method worked well on real water samples with recovery ≥92±4.5%. Key word: Natural coal, Preconcentration, Pb(II) ions, Solid phase Extraction, Flame Atomic Absorption Spectrometer
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Journal Pre-proof 1. Introductions Due to rapid industrialization, the toxic metal ions contaminated industrial effluents have been routinely discharging in environmental aqueous bodies. The heavy metal ions persist in the environment for years because of their non-biodegradable nature unlike the organic pollutant [1]. Pb(II) ions contaminated effluents have been discharging to environmental water bodies by various industrial processes such smelting, plating, printing, tanning, mining, finishing and production of batteries, etc. In developing countries, these heavy metal ions are ingested by the human being through water and food chain [2,3]. Excess intake of heavy metal ions causes
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serious health problems by binding with hetero atoms of proteins, nucleic acid and small metabolites in living organisms resulting malfunctioning or death of cells [4]. The intake of
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Pb(II) ions above its permissible level (0.05 mgL-1) binds with phosphate and mercapto groups
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of enzymes, ligands and biomolecules which restrain the biosynthesis of haeme units and affect the function of liver, kidney and brain cells [5]. Therefore, it has become prime task for the
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analytical chemist for trace metals determination in variety of environmental samples [6]. Flame
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atomic absorption spectrometer (FAAS) has been routinely applied for metals detection. FAAS cannot detect the metal ions at below its detection limit. For the analysis of these samples,
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preconcentration procedure is advised [7,8]. Various preconcentration procedures have been developed based on ion exchange co-precipitation [9], ion exchange [10], solvent extraction [11] and adsorption [12,13]. Adsorption is the most preferred technique due to operational ease, cost
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effective, environmental friendly and high selectivity, capacity, efficiency, and reusability of
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solid phases [8,14,15]. Different materials such as silica gel, activated carbon, C18 cartridges, polyurethane foam, Chelex-100, fullerene, Amberlite XAD series, alumina and others have been reported as solid phases [16,17]. In this study, Thar coal will be modified to efficient adsorbent for adsorptive of Pb(II) ions. Experimental 2.1 Material PerkinElmer FAAS (Analyst 800, USA) and FT-IR Spectrometer (Thermo Scientific, Nicolet iS10, UK) were used for determination of lead and characterization of coal samples, respectively. Pb(NO3)2 salt (analytical reagent-grade) was used for the preparation of solution of Pb(II) ions in double distilled water. The standards and series of working solutions of Pb(II) ions were
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Journal Pre-proof prepared by dilution procedure. NH4OH/NH4Cl, H3PO4/NaH2PO4, CH3COOH/CH3COONa were used for preparation of buffer solutions for maintaining desired pH. 2.2 Activation of natural coal Natural coal was collected from Thar coal field, block IX in Province Sindh, Pakistan. The thar coal was modified to Activated Thar Coal Adsorbent (ATCA) by reacting with concentrated H2SO4, which enhanced its porosity by dehydration as concentrated H2SO4 is strongly dehydration agent [18]. A piece of the coal was washed with water and dried in an oven at 60 oC for 48 hr. Thereafter, the coal was ground and again dried in an oven at 60 oC for 48 hr.
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Experimentally, 5.0 g of dried coal was taken into round bottom flask containing 100 mL of
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concentrated of H2SO4 and refluxed with magnetically stirring for 96 hr at 40 oC. The acidic mixture was poured slowly into 1000 ml of water, worked-up cautiously and filtered by suction.
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This procedure was repeated several times until free from the acid and oven-dried at 60 oC for 48 hr. Furthermore, acid treated coal was oxidized by refluxing it in 250 mL of concentrated HNO3
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at 40 oC for 48 hr. The acidic mixture was worked-up cautiously by the same procedure and
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oven-dried at 60 oC for 72 hr. The material (ATCA) was characterized and used as efficient adsorbent for adsorptive preconcentration of Pb(II) ions.
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2.3 Preconcentration experiment
For column experiment, the column (packed with 400 mg of ATCA) was saturated with buffer solution of desired pH. Thereafter, the model solution (50 mL) contained 2.5 μg of Pb(II) ions of
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pH 7.0 an subjected to the column. Aadsorbed Pb(II) ions onto ATCA were recovered ≥95.5%
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with 0.5 mol L-1 HCl (5.0 mL). Results and discussion
3.1 Characterization of ATCA Figure 1 shows the FT-IR Spectra of unmodified Thar coal (A) sulphuric acid treated coal (B) and Nitric acid treated coal (C). The characteristic peaks at 2919.08, 1596.35 and 1163.04 cm-1 in Spectrum A & B correspond to stretching vibrations of C-H of sp3C-H bonds, C=O bonds of carbonyl and C-O bonds of ether or ester, respectively [19]. The intensity of peak in spectrum-B at 1596.35 cm-1 of C=O of carbonyl was comparatively deceased. This fact can be explained as coal contains various C=O moieties, some of them were converted to carbon black by reacting with concentrated sulphuric acid. The characteristic additional peaks at 1533.28 cm-1 (sharp) and 2500-3500 cm-1 (broad) in spectrum-C corresponds to stretching vibration of C=O and O-H 3
Journal Pre-proof bonds of carboxylic acid moieties. This spectral information confirmed the oxidation of carbon of coal to -COOH moieties. The elemental analysis of nitric acid treated coal i.e. ATCA was carried out by EDX analysis. Result revealed ATCA contained 61.6, 34.3 and 2.8% of C, O and S, respectively as shown in figure 2. Furthermore, pHPZC (pH at point of zero charge) of ATC was evaluated followed by pH drift method [20]. ATCA possessed zero charge at pH 6.0 and became negatively charged with increase of pH 6-12 due to the deportation of -COOH groups. 3.2 Effect of pH The chemical behavior of adsorbent and adsorbate is pH dependent, which pH is key factor for
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engineering the adsorption extent. Thus, the influence of pH on adsorption of Pb(II) ions was
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studied. Experimentally, 50 mL of model solution containing 2.5 μg of Pb(II) ions of pH 2-9 was passed through the column (packed with 400 mg of ATCA). Pb(II) ions were adsorbed 94.0%
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with RSD ≤4.0% at pH 7 as shown in figure 3. This trend can be explained H+ ions and Pb2+ ions were competition to interact with adsorbent in acidic medium. Thus, with increase of pH 4-7, H+
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ions were decreased and adsorption of Pb(II) ions was dominated. Adsorption was decreased
3.3 Effect of adsorbent dosage
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with further increase in pH 7-10 due to the formation lead hydroxides.
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Experimentally, 200-600 mg of ATCA was tested by column procedure. Adsorption was increased with increasing of ATCA dosage 200-400 mg, it became quantitative (≥95.8%) at ATCA dosage ranging 400-500 mg and declined with further increasing ATCA dosage ranging
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3.4 Effect of eluent
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500-600 mg. Therefore, 400 mg of ATCA can work well in column for SPE of Pb(II) ions.
Desorbing efficiency and reusability of adsorbent depend on nature of eluent. A solvent is said to be best eluent if its minimum volume and concentration works well for desorption of retained analyte. Thus, different volume and concentration of HNO3 and HCl were examined as eluent. Results revealed that 5.0 mL of 0.5 mol L-1 HCl worked well for quantitative recovery (96.5±3.0) of Pb(II) ions as shown in table 1. 3.5 Effect of flow rate In column procedure, the contact time between adsorbate and adsorbent can be controlled by controlling the flow rate of sample solution of adsorbate. Thus, flow rates of eluent and sample solutions were optimized on vacuum-manifold. Results revealed that the recovery of Pb(II) ions was achieved ≥95.0 with RSD ≤3.0% at flow rate of 1.0 and 2.0 mL min-1 of sample and eluent 4
Journal Pre-proof solutions, respectively. Thus, 2.0 and 1.0 mL min-1 were chosen as optimum flow rate of eluent and sample solution, respectively. 3.6 Effect of sample volume Sample volume can be used to calculate numerical value of PF and LOD of the method. Experimentally, 50 mL of model solution containing 2.5 μg of Pb(II) ions of pH 7.0 was further diluted and subjected to the subjected to the column. The retained Pb(II) ions were eluted with 5.0 mL of 0.5 mol L-1 HCl. The quantitative recovery (≥95.0%) of Pb(II) ions with RSD ≤4.0% was achieved until 400 mL of sample volume as depicted in figure 4. PF calculated was 80 as
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400 mL (sample volume) was divided by 5.0 mL (effluent volume that was obtained after the
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elution). 3.7 Sorption capacity
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Experimentally, 500-1360 mL of 50 mg L-1 model solution of pH 7 was subjected to column, packed with 400 mg of ATCA. Breakthrough curve was plotted as Cf/Ci versus volume of the
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solution. Where Ci is initial concentration of sample volume and Cf is concentration of effluent.
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Breakthrough point occurred at 1220 mL of the solution. Therefore, total saturation capacity of column for adsorption of Pb(II) ions was found to be 152.5 mg g-1. Furthermore, equilibrium study was carried out at adsorbent dosage 400 mg, pH 7, shaking time 60 min and concentration
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range of 2-10 mg L-1 of Pb(II) ions at 25 °C followed by batch procedure. DubininRadushkevich (D-R) and Langmuir isotherms was plotted and fitted well to adsorption data with
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correlation coefficient (R2) of 0.991 and 0.986, respectively. The monolayer sorption and total
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sorption capacities of ATCA for Pb(II) ions were found 145.5±3.5 and 164.7±4.0 mg g-1, respectively. Separation factor (RL) values calculated were in the range of 0.004-0.08, which indicated feasibility of adsorption. The sorption energy calculated was 14.12±2.5 kJ mol-1, which indicated that adsorption mechanism was chemisorption and/or ion exchange [28,29]. 3.8 Effect of matrix ions The selectivity and sensitivity of proposed method was investigated by examining the effect of common matrix ions. Experimentally, the procedure was applied in presence of different level of studied matrix ions. The quantitative (≥92.6%) recovery of Pb(II) ions with RSD ≤4.1% was achieved in presence of significant amount of matrix ions as mentioned in table 2, which shows high tolerance limits of ATCA for common ions. 3.9 Method’s Performance 5
Journal Pre-proof The precision and accuracy of method as checked by analyzing of spiked water samples as shown in table 3. Limit of detection (LOD) and limit of quantification (LOQ) of method were found to be 0.03 and 0.11 μg L-1, respectively followed by bank recording (n = 15) with PF of 80. A linear response was observed with regression equation of y = 0.0934x + 0.0411 and R² = 0.99 for concentration ranging 0.5-5.0 mg L-1 (before preconcentration). Similarly, a linear response was also observed with regression equation of y = 7.4358x + 0.0429 and R² = 0.99 for concentration ranging 0.005-0.050 mg L-1 (after preconcentration). Experimental PF was 79.6 which is the ratio of slope (7.4358) of plot after preconcentration to the slope (0.0934) of plot
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before the preconcentration procedure. The experimental PF was found good in agreement with
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theoretical PF (80). The ACTA was packed in column and reused for 300 times without significant decline in sorption capacity.
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3.10 Applications of developed method
Proposed method was applied on tap water and waste water samples collection from combined
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effluent treatment plant in Korangi, Karachi, Pakistan. The samples were spiked and subjected to
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the column at optimized conditions. Pb(II) ions were recovered ≥92.0% from the spiked water samples with RSD ≤4.5% as shown in table 4. The result revealed that sample are not Pb(II) ions
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contaminated.
3.11 Comparison with reported methods
Various methods based on SPE of Pb(II) ions have been reported for trace Pb(II) determination
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in water by FAAS. Chemically modified Amberlite XAD series have been widely used as solid
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phases for adsorptive preconcentration of Pb(II) ions. Present method based on the chemical modification of natural coal (thar coal). Comparative parameters (PF, DOL and capacity) of the methods are summarized in table 5. 4. Conclusion Physico-chemical properties of coal depend on its porosity, surface area and surface functionality. Coal contains C, H, N, O and S in different proportion. Coal possesses different functional groups such as OH, COOH, C=O onto its surface. In water, the surface of coal can be negatively charged due to the ionization of –COOH and –OH moieties. The Natural coal (Thar coal) was activated by reacting with concentrated H2SO4, which enhanced its polarity and porosity by dehydration as concentrated H2SO4 is dehydrating agent. The surface oxidation of coal was carried out by refluxing in concentrated HNO3. Acid treated coal possesses COOH 6
Journal Pre-proof moiety onto the surface of thar coal. ATCA possessed zero charge at pH 6.0 and became negatively charged with increase of pH 6-12 due to the deportation of -COOH groups. In water, the surface of ATCA can be negatively charged due to the ionization of –COOH and –OH moieties. The ionization can be enhanced in basic medium due to ease of deprotonating. The ATCA was applied as an efficient adsorbent for adoptive preconcentration of Pb(II) ions. The Pb(II) ions adsorbed quantitatively at pH 7, adsorbent amount packed in column 400 mg and
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flow rate of sample solution 2.0 mL min−1.
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Journal Pre-proof Figure 1 Shows the FT-IR Spectra of unmodified Thar coal (A) sulphuric acid treated coal (B) and Nitric acid treated coal (C) Figure 2 EDX of ATCA Figure 4 Effect of pH on the adsorption of Pb(II) ions
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Figure 4 Effect of sample volume on the recovery of Pb(II) ions
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Journal Pre-proof Table 1 Effect of HCl and HNO3 solutions on recovery of Pb(II) ions (V = 50 mL, replicate = 3) Concentration (mol L-1)
Volume (mL)
Recovery (%)±RSD
HCl
2.0
5.0
95.7±3.0
HCl
1.0
5.0
95.0±2.6
HCl
0.5
5.0
96.5±3.0
HCl
0.5
4.0
88.3±2.5
HNO3
2.0
5.0
55.0±2.0
HNO3
2.0
10.0
78.0±2.0
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Eluent
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Table 2
Effect of matrix ions on the recovery of Pb(II) ions (Volume = 50 mL, n = 3) Na+
NaNO3
K+
KCl 2+
Concentration (mg L–1) 7000
94.5±4.0
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Salt added
Recovery (%)±RSD
7000
95.5±3.5
5000
93.5±2.5
5000
96.0±2.5
4000
95.0±2.5
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Ions
MgCl2
Ca2+
CaCl2
Ba2+
BaCO3
Cl−
NaCl
8000
97.0±4.0
NaF
5000
95.0±2.5
NaHCO3
1000
94.0±2.6
Na2CO3
1000
96.5±3.3
SO42−
(NH4)2SO4
1000
92.6±2.7
PO43−
Na3PO4
8000
96.5±4.1
NO3−
KNO3
5000
94.5±3.3
CH3COO−
CH3COONa
9000
95.5±2.9
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HCO3
−
2−
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F−
CO3
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Mg
14
Journal Pre-proof Table 3 Precision and accuracy of the method: Determination of trace Pb(II) ions in spiked samples (sample volume = 400 mL, n = 3) Recovery (%)
Relative error
RSD
2.5
99.6
(0.4)
3.5
5
99.8
(0.1)
3.2
10
99.1
(0.9)
3.0
15
98.9
(1.2)
2.5
20
95.6
(4.4)
2.9
25
97.0
(3.0)
3.7
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Added(µg)
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Table 4
Added (µg)
Found (µg)
Recovery (%)±RSD
S-I
0.0
ND
-
2.3
92.0±4.5
4.7
94.0±4.0
9.5
95.0±3.0
ND
-
2.5
2.4
96.0±4.5
5.0
4.7
94.0±3.0
10
9.2
92.0±3.5
0.0
ND
-
2.5
2.4
96.0±2.5
5.0
4.7
94.0±3.0
10.0
9.7
97.0±3.5
5.0 10
S-III
0.0
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S-II
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2.5
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Sample
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Determinations of Pb(II) ions in spiked samples (sample volume = 400 mL, n = 3)
S-I: Tap water sample collected from research laboratory, IARCSC, University of Sindh Jamshoro, Pakistan. S-II and S-III: Waste water samples collection from combined effluent treatment plant in korangi, Karachi, Pakistan.
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Journal Pre-proof Table 5 Reported methods: Comparative PF, LOD and capacity values Ligand
Capacity (mg g-1)
PF
LOD (µg L-1) Ref.
Amberlite XAD-2
o-Aminophenol
3.3
40
25.0
[18]
Amberlite XAD-2
Quinalizarin
5.3
50
15.0
[19]
Amberlite XAD-2
Pyrocatechol Violet
0.6
23
40.0
[20]
Amberlite XAD-2
SA: Salicylic acid
0.5
140
7.0
[21]
Amberlite XAD-4
Salicylic aspartide
78.1
50
0.2
[7]
Amberlite XAD-4
o-Aminobenzoic acid
12.4
400
2.5
[22]
Amberlite XAD-4
Alizarin Red-S
0.3
40
-
[23]
SP70
α-Benzoin oxime
-
75
16.0
[24]
ATCA
-
152.5
80
0.03
This work
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Absorbents
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Journal Pre-proof Highlights Natural coal was oxidized by reacting with concentrated nitric acid Activated coal worked well for the selective adsorption of Pb(II) ions Saturation capacity of column for adsorption of Pb(II) ions was found to be 152.5 mg g-1. New method was developed for trace determination of Pb(II) ions by FAAS water LOD and LOQ of Pb(II) ions were found to be 0.0321 and 0.108 μg L-1, respectively. Linear response was observed with regression equation of y = 7.4358x + 0.0429 and R² =
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0.9902 for concentration ranging 0.005-0.050 mg L-1
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Figure 1
Figure 2
Figure 3
Figure 4
Sumita Bhatia, Ali Nawaz Siyal, Adnan Ahmed, Qadeer Khan Panhwar, Abdul Majid Channa, Amanullah Mahar PII:
S2590-1826(20)30006-0
DOI:
https://doi.org/10.1016/j.enceco.2020.02.001
Reference:
ENCECO 14
To appear in:
Environmental Chemistry and Ecotoxicology
Received date:
17 January 2020
Revised date:
31 January 2020
Accepted date:
9 February 2020
Please cite this article as: S. Bhatia, A.N. Siyal, A. Ahmed, et al., Activation of natural coal for selective Preconcentration of Pb(II) ions prior to its trace determination in aqueous samples by flame atomic absorption spectrometer, Environmental Chemistry and Ecotoxicology(2020), https://doi.org/10.1016/j.enceco.2020.02.001
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© 2020 Published by Elsevier.
Journal Pre-proof Activation of Natural Coal for Selective Preconcentration of Pb(II) ions Prior to its Trace Determination in Aqueous Samples by Flame Atomic Absorption Spectrometer Sumita Bhatia1, Ali Nawaz Siyal2*, Adnan Ahmed1, Qadeer Khan Panhwar2, Abdul Majid Channa2, Amanullah Mahar1 1
Centre for Environmental Science, University of Sindh, Jamshoro 76080, Pakistan 2
Institute of Chemistry, University of Sindh, Jamshoro 76080, Pakistan
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Corresponding author’s Email: [email protected], Postal address: Institute of Chemistry,
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University of Sindh, Jamshoro 76080, Pakistan
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Abstract
Natural coal was collected from Thar coal field, block IX in Province Sindh, Pakistan. The Thar
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coal was modified to Activated Thar Coal Adsorbent (ATCA) by reacting with concentrated H2SO4, which enhanced its porosity by dehydration as concentrated H2SO4 is strongly
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dehydration agent. The surface oxidation of coal was carried out by refluxing in concentrated HNO3. The ATCA was subjected to FT-IR spectrometer for characterization, which revealed the
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presence of C=O and COOH moieties onto its surface. The ATCA was packed in column for adsorption of Pb(II) ions and recovered ≥95.6% with relative error ≤4.4% with RSD ≤3.7% at
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pH 7.0, ATCA amount of adsorbent packed in column 400 mg, sample volume 400 mL (flow rate of 2.0 mL min−1) and eluent solution 5.0 mL of 0.5 mol L−1 HCl (flow rate of 1.0 mL min−1).
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LOD (0.03 μg L-1) and LOQ (0.11 μg L-1) of method were calculated followed by blank recording (n = 15) with preconcentration factor (PF) of 80. A linear response was observed with regression equation of y = 0.0934x + 0.0411 and R² = 0.99 for concentration ranging 0.5-5.0 mg L-1 (before preconcentration). Similarly, a linear response was also observed with regression equation of y = 7.4358x + 0.0429 and R² = 0.99 for concentration ranging 0.005-0.050 mg L-1 (after preconcentration). Breakthrough curve was plotted for obtaining to saturation capacity (152.5 mg g-1) of ATCA for adsorption of Pb(II) ions. The method worked well on real water samples with recovery ≥92±4.5%. Key word: Natural coal, Preconcentration, Pb(II) ions, Solid phase Extraction, Flame Atomic Absorption Spectrometer
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Journal Pre-proof 1. Introductions Due to rapid industrialization, the toxic metal ions contaminated industrial effluents have been routinely discharging in environmental aqueous bodies. The heavy metal ions persist in the environment for years because of their non-biodegradable nature unlike the organic pollutant [1]. Pb(II) ions contaminated effluents have been discharging to environmental water bodies by various industrial processes such smelting, plating, printing, tanning, mining, finishing and production of batteries, etc. In developing countries, these heavy metal ions are ingested by the human being through water and food chain [2,3]. Excess intake of heavy metal ions causes
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serious health problems by binding with hetero atoms of proteins, nucleic acid and small metabolites in living organisms resulting malfunctioning or death of cells [4]. The intake of
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Pb(II) ions above its permissible level (0.05 mgL-1) binds with phosphate and mercapto groups
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of enzymes, ligands and biomolecules which restrain the biosynthesis of haeme units and affect the function of liver, kidney and brain cells [5]. Therefore, it has become prime task for the
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analytical chemist for trace metals determination in variety of environmental samples [6]. Flame
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atomic absorption spectrometer (FAAS) has been routinely applied for metals detection. FAAS cannot detect the metal ions at below its detection limit. For the analysis of these samples,
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preconcentration procedure is advised [7,8]. Various preconcentration procedures have been developed based on ion exchange co-precipitation [9], ion exchange [10], solvent extraction [11] and adsorption [12,13]. Adsorption is the most preferred technique due to operational ease, cost
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effective, environmental friendly and high selectivity, capacity, efficiency, and reusability of
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solid phases [8,14,15]. Different materials such as silica gel, activated carbon, C18 cartridges, polyurethane foam, Chelex-100, fullerene, Amberlite XAD series, alumina and others have been reported as solid phases [16,17]. In this study, Thar coal will be modified to efficient adsorbent for adsorptive of Pb(II) ions. Experimental 2.1 Material PerkinElmer FAAS (Analyst 800, USA) and FT-IR Spectrometer (Thermo Scientific, Nicolet iS10, UK) were used for determination of lead and characterization of coal samples, respectively. Pb(NO3)2 salt (analytical reagent-grade) was used for the preparation of solution of Pb(II) ions in double distilled water. The standards and series of working solutions of Pb(II) ions were
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Journal Pre-proof prepared by dilution procedure. NH4OH/NH4Cl, H3PO4/NaH2PO4, CH3COOH/CH3COONa were used for preparation of buffer solutions for maintaining desired pH. 2.2 Activation of natural coal Natural coal was collected from Thar coal field, block IX in Province Sindh, Pakistan. The thar coal was modified to Activated Thar Coal Adsorbent (ATCA) by reacting with concentrated H2SO4, which enhanced its porosity by dehydration as concentrated H2SO4 is strongly dehydration agent [18]. A piece of the coal was washed with water and dried in an oven at 60 oC for 48 hr. Thereafter, the coal was ground and again dried in an oven at 60 oC for 48 hr.
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Experimentally, 5.0 g of dried coal was taken into round bottom flask containing 100 mL of
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concentrated of H2SO4 and refluxed with magnetically stirring for 96 hr at 40 oC. The acidic mixture was poured slowly into 1000 ml of water, worked-up cautiously and filtered by suction.
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This procedure was repeated several times until free from the acid and oven-dried at 60 oC for 48 hr. Furthermore, acid treated coal was oxidized by refluxing it in 250 mL of concentrated HNO3
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at 40 oC for 48 hr. The acidic mixture was worked-up cautiously by the same procedure and
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oven-dried at 60 oC for 72 hr. The material (ATCA) was characterized and used as efficient adsorbent for adsorptive preconcentration of Pb(II) ions.
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2.3 Preconcentration experiment
For column experiment, the column (packed with 400 mg of ATCA) was saturated with buffer solution of desired pH. Thereafter, the model solution (50 mL) contained 2.5 μg of Pb(II) ions of
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pH 7.0 an subjected to the column. Aadsorbed Pb(II) ions onto ATCA were recovered ≥95.5%
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with 0.5 mol L-1 HCl (5.0 mL). Results and discussion
3.1 Characterization of ATCA Figure 1 shows the FT-IR Spectra of unmodified Thar coal (A) sulphuric acid treated coal (B) and Nitric acid treated coal (C). The characteristic peaks at 2919.08, 1596.35 and 1163.04 cm-1 in Spectrum A & B correspond to stretching vibrations of C-H of sp3C-H bonds, C=O bonds of carbonyl and C-O bonds of ether or ester, respectively [19]. The intensity of peak in spectrum-B at 1596.35 cm-1 of C=O of carbonyl was comparatively deceased. This fact can be explained as coal contains various C=O moieties, some of them were converted to carbon black by reacting with concentrated sulphuric acid. The characteristic additional peaks at 1533.28 cm-1 (sharp) and 2500-3500 cm-1 (broad) in spectrum-C corresponds to stretching vibration of C=O and O-H 3
Journal Pre-proof bonds of carboxylic acid moieties. This spectral information confirmed the oxidation of carbon of coal to -COOH moieties. The elemental analysis of nitric acid treated coal i.e. ATCA was carried out by EDX analysis. Result revealed ATCA contained 61.6, 34.3 and 2.8% of C, O and S, respectively as shown in figure 2. Furthermore, pHPZC (pH at point of zero charge) of ATC was evaluated followed by pH drift method [20]. ATCA possessed zero charge at pH 6.0 and became negatively charged with increase of pH 6-12 due to the deportation of -COOH groups. 3.2 Effect of pH The chemical behavior of adsorbent and adsorbate is pH dependent, which pH is key factor for
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engineering the adsorption extent. Thus, the influence of pH on adsorption of Pb(II) ions was
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studied. Experimentally, 50 mL of model solution containing 2.5 μg of Pb(II) ions of pH 2-9 was passed through the column (packed with 400 mg of ATCA). Pb(II) ions were adsorbed 94.0%
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with RSD ≤4.0% at pH 7 as shown in figure 3. This trend can be explained H+ ions and Pb2+ ions were competition to interact with adsorbent in acidic medium. Thus, with increase of pH 4-7, H+
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ions were decreased and adsorption of Pb(II) ions was dominated. Adsorption was decreased
3.3 Effect of adsorbent dosage
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with further increase in pH 7-10 due to the formation lead hydroxides.
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Experimentally, 200-600 mg of ATCA was tested by column procedure. Adsorption was increased with increasing of ATCA dosage 200-400 mg, it became quantitative (≥95.8%) at ATCA dosage ranging 400-500 mg and declined with further increasing ATCA dosage ranging
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3.4 Effect of eluent
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500-600 mg. Therefore, 400 mg of ATCA can work well in column for SPE of Pb(II) ions.
Desorbing efficiency and reusability of adsorbent depend on nature of eluent. A solvent is said to be best eluent if its minimum volume and concentration works well for desorption of retained analyte. Thus, different volume and concentration of HNO3 and HCl were examined as eluent. Results revealed that 5.0 mL of 0.5 mol L-1 HCl worked well for quantitative recovery (96.5±3.0) of Pb(II) ions as shown in table 1. 3.5 Effect of flow rate In column procedure, the contact time between adsorbate and adsorbent can be controlled by controlling the flow rate of sample solution of adsorbate. Thus, flow rates of eluent and sample solutions were optimized on vacuum-manifold. Results revealed that the recovery of Pb(II) ions was achieved ≥95.0 with RSD ≤3.0% at flow rate of 1.0 and 2.0 mL min-1 of sample and eluent 4
Journal Pre-proof solutions, respectively. Thus, 2.0 and 1.0 mL min-1 were chosen as optimum flow rate of eluent and sample solution, respectively. 3.6 Effect of sample volume Sample volume can be used to calculate numerical value of PF and LOD of the method. Experimentally, 50 mL of model solution containing 2.5 μg of Pb(II) ions of pH 7.0 was further diluted and subjected to the subjected to the column. The retained Pb(II) ions were eluted with 5.0 mL of 0.5 mol L-1 HCl. The quantitative recovery (≥95.0%) of Pb(II) ions with RSD ≤4.0% was achieved until 400 mL of sample volume as depicted in figure 4. PF calculated was 80 as
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400 mL (sample volume) was divided by 5.0 mL (effluent volume that was obtained after the
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elution). 3.7 Sorption capacity
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Experimentally, 500-1360 mL of 50 mg L-1 model solution of pH 7 was subjected to column, packed with 400 mg of ATCA. Breakthrough curve was plotted as Cf/Ci versus volume of the
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solution. Where Ci is initial concentration of sample volume and Cf is concentration of effluent.
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Breakthrough point occurred at 1220 mL of the solution. Therefore, total saturation capacity of column for adsorption of Pb(II) ions was found to be 152.5 mg g-1. Furthermore, equilibrium study was carried out at adsorbent dosage 400 mg, pH 7, shaking time 60 min and concentration
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range of 2-10 mg L-1 of Pb(II) ions at 25 °C followed by batch procedure. DubininRadushkevich (D-R) and Langmuir isotherms was plotted and fitted well to adsorption data with
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correlation coefficient (R2) of 0.991 and 0.986, respectively. The monolayer sorption and total
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sorption capacities of ATCA for Pb(II) ions were found 145.5±3.5 and 164.7±4.0 mg g-1, respectively. Separation factor (RL) values calculated were in the range of 0.004-0.08, which indicated feasibility of adsorption. The sorption energy calculated was 14.12±2.5 kJ mol-1, which indicated that adsorption mechanism was chemisorption and/or ion exchange [28,29]. 3.8 Effect of matrix ions The selectivity and sensitivity of proposed method was investigated by examining the effect of common matrix ions. Experimentally, the procedure was applied in presence of different level of studied matrix ions. The quantitative (≥92.6%) recovery of Pb(II) ions with RSD ≤4.1% was achieved in presence of significant amount of matrix ions as mentioned in table 2, which shows high tolerance limits of ATCA for common ions. 3.9 Method’s Performance 5
Journal Pre-proof The precision and accuracy of method as checked by analyzing of spiked water samples as shown in table 3. Limit of detection (LOD) and limit of quantification (LOQ) of method were found to be 0.03 and 0.11 μg L-1, respectively followed by bank recording (n = 15) with PF of 80. A linear response was observed with regression equation of y = 0.0934x + 0.0411 and R² = 0.99 for concentration ranging 0.5-5.0 mg L-1 (before preconcentration). Similarly, a linear response was also observed with regression equation of y = 7.4358x + 0.0429 and R² = 0.99 for concentration ranging 0.005-0.050 mg L-1 (after preconcentration). Experimental PF was 79.6 which is the ratio of slope (7.4358) of plot after preconcentration to the slope (0.0934) of plot
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before the preconcentration procedure. The experimental PF was found good in agreement with
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theoretical PF (80). The ACTA was packed in column and reused for 300 times without significant decline in sorption capacity.
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3.10 Applications of developed method
Proposed method was applied on tap water and waste water samples collection from combined
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effluent treatment plant in Korangi, Karachi, Pakistan. The samples were spiked and subjected to
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the column at optimized conditions. Pb(II) ions were recovered ≥92.0% from the spiked water samples with RSD ≤4.5% as shown in table 4. The result revealed that sample are not Pb(II) ions
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contaminated.
3.11 Comparison with reported methods
Various methods based on SPE of Pb(II) ions have been reported for trace Pb(II) determination
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in water by FAAS. Chemically modified Amberlite XAD series have been widely used as solid
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phases for adsorptive preconcentration of Pb(II) ions. Present method based on the chemical modification of natural coal (thar coal). Comparative parameters (PF, DOL and capacity) of the methods are summarized in table 5. 4. Conclusion Physico-chemical properties of coal depend on its porosity, surface area and surface functionality. Coal contains C, H, N, O and S in different proportion. Coal possesses different functional groups such as OH, COOH, C=O onto its surface. In water, the surface of coal can be negatively charged due to the ionization of –COOH and –OH moieties. The Natural coal (Thar coal) was activated by reacting with concentrated H2SO4, which enhanced its polarity and porosity by dehydration as concentrated H2SO4 is dehydrating agent. The surface oxidation of coal was carried out by refluxing in concentrated HNO3. Acid treated coal possesses COOH 6
Journal Pre-proof moiety onto the surface of thar coal. ATCA possessed zero charge at pH 6.0 and became negatively charged with increase of pH 6-12 due to the deportation of -COOH groups. In water, the surface of ATCA can be negatively charged due to the ionization of –COOH and –OH moieties. The ionization can be enhanced in basic medium due to ease of deprotonating. The ATCA was applied as an efficient adsorbent for adoptive preconcentration of Pb(II) ions. The Pb(II) ions adsorbed quantitatively at pH 7, adsorbent amount packed in column 400 mg and
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flow rate of sample solution 2.0 mL min−1.
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[27] I. Narin, Y. Surme, E. Bercin, M. Soylak, SP70-α-benzoin oxime chelating resin for preconcentration–separation of Pb(II), Cd(II), Co(II) and Cr(III) in environmental samples, J. Hazard. Mater. 145(1-2) (2007) 113-119. DOI: 10.1016/j.jhazmat.2006.11.001.
11
Journal Pre-proof [28] S.Q. Memon, S.M. Hasany, M.I. Bhanger, M.Y. Khuhawar, Enrichment of Pb(II) ions using phthalic acid functionalized XAD-16 resin as a sorbent, J. Colloid Interface Sci. 291 (2005) 8491. DOI:10.1016/j.jcis.2005.04.112.
[29] P.S. Kumar, S. Ramalingam, S.D. Kirupha, A. Murugesan, T. Vidhyadevi, S. Sivanesan, Adsorption behavior of nickel(II) onto cashew nut shell: equilibrium, thermodynamics, kinetics, mechanism
and
process
design,
Chem.
Eng.
J.
167
(2011)
122-131.
DOI:
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10.1016/j.cej.2010.12.010.
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Journal Pre-proof Figure 1 Shows the FT-IR Spectra of unmodified Thar coal (A) sulphuric acid treated coal (B) and Nitric acid treated coal (C) Figure 2 EDX of ATCA Figure 4 Effect of pH on the adsorption of Pb(II) ions
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Figure 4 Effect of sample volume on the recovery of Pb(II) ions
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Journal Pre-proof Table 1 Effect of HCl and HNO3 solutions on recovery of Pb(II) ions (V = 50 mL, replicate = 3) Concentration (mol L-1)
Volume (mL)
Recovery (%)±RSD
HCl
2.0
5.0
95.7±3.0
HCl
1.0
5.0
95.0±2.6
HCl
0.5
5.0
96.5±3.0
HCl
0.5
4.0
88.3±2.5
HNO3
2.0
5.0
55.0±2.0
HNO3
2.0
10.0
78.0±2.0
ro
of
Eluent
-p
Table 2
Effect of matrix ions on the recovery of Pb(II) ions (Volume = 50 mL, n = 3) Na+
NaNO3
K+
KCl 2+
Concentration (mg L–1) 7000
94.5±4.0
re
Salt added
Recovery (%)±RSD
7000
95.5±3.5
5000
93.5±2.5
5000
96.0±2.5
4000
95.0±2.5
lP
Ions
MgCl2
Ca2+
CaCl2
Ba2+
BaCO3
Cl−
NaCl
8000
97.0±4.0
NaF
5000
95.0±2.5
NaHCO3
1000
94.0±2.6
Na2CO3
1000
96.5±3.3
SO42−
(NH4)2SO4
1000
92.6±2.7
PO43−
Na3PO4
8000
96.5±4.1
NO3−
KNO3
5000
94.5±3.3
CH3COO−
CH3COONa
9000
95.5±2.9
ur
HCO3
−
2−
Jo
F−
CO3
na
Mg
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Journal Pre-proof Table 3 Precision and accuracy of the method: Determination of trace Pb(II) ions in spiked samples (sample volume = 400 mL, n = 3) Recovery (%)
Relative error
RSD
2.5
99.6
(0.4)
3.5
5
99.8
(0.1)
3.2
10
99.1
(0.9)
3.0
15
98.9
(1.2)
2.5
20
95.6
(4.4)
2.9
25
97.0
(3.0)
3.7
-p
ro
of
Added(µg)
re
Table 4
Added (µg)
Found (µg)
Recovery (%)±RSD
S-I
0.0
ND
-
2.3
92.0±4.5
4.7
94.0±4.0
9.5
95.0±3.0
ND
-
2.5
2.4
96.0±4.5
5.0
4.7
94.0±3.0
10
9.2
92.0±3.5
0.0
ND
-
2.5
2.4
96.0±2.5
5.0
4.7
94.0±3.0
10.0
9.7
97.0±3.5
5.0 10
S-III
0.0
Jo
S-II
ur
2.5
na
Sample
lP
Determinations of Pb(II) ions in spiked samples (sample volume = 400 mL, n = 3)
S-I: Tap water sample collected from research laboratory, IARCSC, University of Sindh Jamshoro, Pakistan. S-II and S-III: Waste water samples collection from combined effluent treatment plant in korangi, Karachi, Pakistan.
15
Journal Pre-proof Table 5 Reported methods: Comparative PF, LOD and capacity values Ligand
Capacity (mg g-1)
PF
LOD (µg L-1) Ref.
Amberlite XAD-2
o-Aminophenol
3.3
40
25.0
[18]
Amberlite XAD-2
Quinalizarin
5.3
50
15.0
[19]
Amberlite XAD-2
Pyrocatechol Violet
0.6
23
40.0
[20]
Amberlite XAD-2
SA: Salicylic acid
0.5
140
7.0
[21]
Amberlite XAD-4
Salicylic aspartide
78.1
50
0.2
[7]
Amberlite XAD-4
o-Aminobenzoic acid
12.4
400
2.5
[22]
Amberlite XAD-4
Alizarin Red-S
0.3
40
-
[23]
SP70
α-Benzoin oxime
-
75
16.0
[24]
ATCA
-
152.5
80
0.03
This work
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Absorbents
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Journal Pre-proof Highlights Natural coal was oxidized by reacting with concentrated nitric acid Activated coal worked well for the selective adsorption of Pb(II) ions Saturation capacity of column for adsorption of Pb(II) ions was found to be 152.5 mg g-1. New method was developed for trace determination of Pb(II) ions by FAAS water LOD and LOQ of Pb(II) ions were found to be 0.0321 and 0.108 μg L-1, respectively. Linear response was observed with regression equation of y = 7.4358x + 0.0429 and R² =
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0.9902 for concentration ranging 0.005-0.050 mg L-1
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Figure 1
Figure 2
Figure 3
Figure 4