IR spectrum Figure 1A shows the characteristic peaks of uncoated bagasse particles (A) and dithizone-coated bagasse particles (B). Accordingly, the spectrum belongs to [email protected] Figure 1AB contains obvious peaks at 680 (C - H, phenyl group), 1,218 (-NCS-), 1,320 (N-phenyl), 1,439 (N - H, bending), and 1,590 cm-1 (C = C, aromatic) that are not available in the spectrum of uncoated bagasse particles Figure 1A. Appearance of these peaks is good evidence on adhesion of dithizone onto BPs. Figure 1B shows the variation on the XRD patterns of BPs after treatment with KOH and modification with ADBAC and dithizone. As shown, two special peaks related to cellulose at 20.1° and 22.4° appeared. An increase in crystallinity of [email protected], with respect to BPs, was observed, which indicated that the hydrolysis was effective (29).
Figure 1.
A, FTIR spectrums of PB (A), [email protected] (B) and Dz (C); B, X-ray diffraction pattern of bagasse particles (A) and dithizone-modified bagasse particles (B).
4.2. Effect of pH
The effect of pH on the adsorption of Pb(II) by [email protected] was investigated at pH ranging from 2.0 - 8.0 (50 mL, Pb2+ 10 mg L-1, 50 mg adsorbent, 25°C, contact time 10 minutes, 200 rpm). According to the obtained results Figure 2, the best removal efficiency of Pb2+ was at pH 6.0 - 7.0 (> 99.5%). Variation of pH has a significant effect on the adsorption process. Increasing pH of solution accelerates the precipitation rate of lead ions with OH- due to the formation of Pb(OH)2 (Ksppb(OH)2 = 4.0 × 10-15 In addition, the feasibility of H+ to attract on dithizone molecules competes the adsorption process of Pb2+ on [email protected]
Figure 2.
The effect of pH of the solution for quantitative removal of Pb ions using [email protected] at 25°C
4.3. Effect of Contact Time
The contact time required to adsorb Pb (II) in sample solutions was studied at different contact times in the range of 0.5 - 30.0 minutes (10 mg L-1, 50 mL, 50 mg adsorbent, pH 6.0, 25°C, 200 rpm). After ending the removal process, test solutions were collected and analyzed using FAAS. According to the results, the time required to adsorb Pb (II) was quantitatively 1.0 minute (> 99 %). It is believed that the short time needed to adsorb lead ions is due to the high propensity of dithizone to make complex with Pb (II).
4.4. Effect of the Adsorbent Amount
The amount of [email protected] for removal of Pb ions from 50 mL sample solution (10 mg L-1) was studied in the range of 10 - 100 mg (pH 6.0, 25°C and 200 rpm). Acceptable adsorption efficiency (≥ 99%) was achieved when using 50 mg of [email protected]
4.5. Adsorption Isotherm
To study the adsorption behavior of Pb (II) on [email protected], Langmuir (representative of monolayer adsorption on homogenous surface) and Freundlich (representative of multilayer adsorption on heterogeneous surfaces) adsorption isotherm models were studied.
The capacity of [email protected] for adsorption of Pb (II) was determined by evaluating the difference between initial and final concentration of the solutions at batch mode (50 mL, contact time 60 min, pH 6.0, 25°C and stirring speed 200 rpm). Different concentrations of Pb (II) ranging from 20 to 200 mg L-1 in test solutions were examined with fixed amount of adsorbent (50 mg). The results Figure 3 showed that Freundlich model (R2 = 0.998) fitted well with respect to Langmuir (R2 = 0.985) model. The Freundlich isotherm equation was applied for explaining the correlation between the amount of adsorbed analyte and its equilibrium concentration in solution:
Figure 3.
The plot of qe (mgg-1) versus Ce (mgL-1) for removal of Pb (II) by [email protected] at 25°C and pH 6
Where qe and Ce are the equilibrium adsorption capacity (mg g-1) and equilibrium heterogeneous multilayer concentration (mg L-1), respectively. KF and n are Freundlich constants. The linear relationship between ln qe and ln Ce (ln qe = 0.3099 ln Ce + 2.0341) represents the performance of the Freundlich model for the interpretation of adsorption of Pb ions on [email protected] The experiments eventuated 7.64 and 3.22 for KF and n, respectively. Figure 3 Showed The plot of qe (mg g-1) versus Ce (mg L-1) for removal of Pb(II) by [email protected] at 25 ºC and pH 6.
4.6. Effect of Ionic Strength
According to previous knowledge, ionic strength may have a significant effect on the adsorption properties of an adsorbent. To investigate the effect of ionic strength (adjusted by 0.005 - 0.1 M KNO3) on lead adsorption by 50 mg [email protected], 50 mL of sample solution (Pb2+ 10 mg L-1) at 25°C and pH 6.0 was selected. It was observed that the removal efficiency of lead ions was quantitative (95 %) at the concentrations below than 0.01 M KNO3.
4.7. Loading Capacity of Adsorbent
The loading capacity of [email protected] was determined under defined conditions (adsorbent amount 50 mg, pH 6, 25°C, stirring speed 200 rpm) by batch method. The adsorbent was poured in a 50 mL solution containing 200 mg L-1 of Pb ions and stirred for 60 minutes. Removal percent and adsorbed amount of Pb was determined by FAAS measurement of the initial and final concentrations of sample solution. The loading capacity was determined to be 37.20 mg g-1.
4.8. Reusability
Reusability of an absorbent can be a measure for its competency in the removal of hazardous materials in the environment. This ability for the adsorption of lead ions was experimented on the [email protected] in controlled conditions (Pb2+ 10 mg L-1, 50 mL, pH 6.0, adsorbent amount 50 mg, stirring speed 200 rpm and contact time 30 minutes). Prior to each step, 20 mL of HNO3 1 M and sufficient water were used to elute adsorbent. The results showed that the adsorption process can be iterated for four times without a considerable loss in its efficiency (> 95%).
4.9. Effect of Solution Volume on Removal Efficiency
To achieve an acceptable volume of lead sample solution per adsorbent amount, various sample volumes in the range of 50 - 250 mL were studied (50 mg adsorbent amounts, pH 6.0, contact time 60 min., stirring speed 200 rpm and 25°C). Volume of samples was incresaed while the total wheight of Pb2+ in solutions remained fixed at 0.5 mg. The obtained results showed that the effective adsorption (> 90 %) of Pb2+ was applicable up to150 mL of solutions. At volumes higher than 150 mL, the analyte was not adsorbed effectively due to the decrease in probability of collision between the adsorbent and lead ions.
4.10. Simulated Samples
The proposed SPE method was applied to the removal of lead ions in aqueous sample solutions. To determine the reliability and usability of the method, several 50 mL Pb2+ (spiked 5 and 10 mg L-1) contaminated water samples were prepared. The adsorption process was carried out at optimized conditions and removal percent was evaluated using FAAS technique. For the mentioned spiked levels of Pb (5 and 10 mg L-1), removal efficiencies of 94.4 % and 90.9 % were obtained for Karoon river samples; while the removal efficiencies of waste water of sugar factory samples were 93.6% and 89.5%, respectively.
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