Removal of Toxic Pb(II) Ions from Aqueous Solution by Nano Sized Flamboyant Pod (Delonix regia)

1 Chemistry Department, Sohag University, 82534 Sohag, Egypt 2 Chemistry Department, King Khalid University, 61321 Abha, Saudi Arabia 3 Department of organic chemistry and inorganic chemistry, relevant Faculty of Chemistry, University of Oviedo, 33006, Oviedo, Spain 4 Medicinal and Aromatic Plants Researches Department, Horticulture Research Institute (HRI), Agriculture Research Center (ARC), Giza, Egypt


Introduction
Toxic Heavy metals can be released into water through metal smelters, effluents from plastics, textiles, There is evidence that present in the environment, even in low concentration of heavy metals cause dermal damage and cancer [1,2]. Lead is considered as the most toxic metal exists in several industrial wastes, such as chemicals, lead acid storage batteries. Lead poisoning in human causes damaging to the kidneys, liver, and brain [2,3]. The removal of heavy metal from contaminated sites is very important to restore ecosystem functions and stability [4]. The search for low-cost techniques to remove heavy metals from wastewater using agricultural materials such as Maize leaves, loquat leaves (Eriobotrya japonica), Psidium guajava leaves, Scolymushis panicus, Azadirachta indica (Neem leaves), Ulmus leaves, Oleaeuropaea (Olive leaves), and Prunusvium leaves [5], rice straw, rice bran, rice husk, hyacinthroots, neem leaves [6]. Delonix regia is a species of flowering plant in the family Fabaceae, subfamily Caesalpinioideae [7]. Delonix regia possesses several

Removal of Toxic Pb(II) Ions from Aqueous
Solution by Nano Sized Flamboyant Pod (Delonix regia)

Effect of dosage
In each biosorption experiment, 50 ml of Pb 2+ ions solution of concentration (20 mg/L) was added to different dosage of the adsorbent in bottle and then the mixture was stirred for 1 hr on a shaker at 300 rpm.

Effect of contact time
In the biosorption kinetics experiment, 0.2 L of Pb 2+ ions solution of different concentrations was added to 1.2 g of the adsorbent in flat bottle and then the mixture was stirred for 1 hr on a shaker at 300 rpm and a contact time (20: 120) minutes with time interval 20 minutes.

Effect of temperature and determination of thermodynamic parameters
A total of 50 ml of different concentrations of Pb 2+ ions solution was added to 0.3 g of the adsorbent in bottle at different temperature and then the mixture was stirred for 1 hr on a shaker at 300 rpm. Then the mixture was centrifuged and the concentration of Pb 2+ ions was determined. Were calculated using the relationships (1) and (2) [2,16,17] can be used to calculate ΔH, ΔS, and ΔG( the thermodynamic parameters for the adsorption process.

Calculation of metal uptake
The Pb 2+ ions uptake at equilibrium was calculated by: where q e is Pb 2+ ions absorption capacity, v is the volume of the Pb 2+ ions solution and w is the amount of the adsorbent, C o and C e are initial Pb 2+ ion concentrations and C e are final (equilibrium) Pb 2+ ion concentrations. The efficiency of the Pb 2+ ions removal was also determined using; Where, RE% is the percentage of the removed Pb 2+ ions.
removal from aqueous solution [2,13]. This study can introduce an economic value biosorbent for removing of toxic heavy metal by using nanosized Delonix regia pod.

Sample collection
The pods of Delonix regia were obtained from Shandawil Research Station, Agriculture Research Center, Sohag, Egypt.

Sample pretreatment
Delonix regia pods were cleaned with water, and then dried. Delonix regia pods were grinded to obtain a fine powder. The fine powder was used as biosorbent in the experiments.

Treatment of Delonix regia (DR) by Citric Acid
Chemical modification of nano sized powder Delonix regia (DR) using NaOH followed by citric acid treatment. The synthesis of CADR was carried out as followed, 200 grams of the powder was placed in 4 L of 0.1 N NaOH, then was stirred at 300 rpm for 1 h at 23 o C to remove base. The powder was rinsed with water and added to 4 L of distilled water. This biomass was mixed with citric acid (CA) in a ratio of 1.0 g powder to 7.0 mL of CA (0.6 M). The acid/powder Slurry was dried over night at 50 o C and then heated to 120 o C for 1.5 h. Citric acid (CA) treated DR powder (CADR) was filtered and washed in a Buchner funnel under vacuum with 150-200 mL of distilled water per gram of the product to remove excess CA. This volume of water was sufficient to remove un reacted CA since no turbidity from lead citrate was observed when the washed powder was suspended in 10 mL of water to which 10 mL of 0.1 M lead nitrate was added. The modified powder was dried at 50 o C overnight [2,14,15].

Preparation of Solution
Aqueous solution of Pb 2+ ions was prepared by weighing out 1.60 g of Pb(NO 3 ) 2 and dissolved in a 1000 ml volumetric flask with

Kinetics study
The mechanism of the adsorption of Pb 2+ ions was studied using pseudo first order kinetic models , the intraparticle diffusion and pseudo second order kinetic models [2,[18][19][20] and they are giving in a linear form by Equations 5, 6 and 7, respectively ln(q e -q t ) = lnq e -k 1 t (5) q t = k int t 0.5 (7) kinetic models are tested for suitability using correlation coefficient (R 2 ) [2,20,21].

Effect of chemical treatment
A total of 50 ml of Pb 2+ ions solution of (20 mg/L) concentration was added to 0.3 g of the chemically treatment adsorbent (CADR) in bottle, then the mixture was stirred on a shaker for 1 hr at 300 rpm and the concentration of Pb 2+ ions was determined .

Results and Discussion
Characteristics of the biosorbent FTIR spectral analysis: FTIR spectral analysis of Delonix regia pod (DR) (Figure 1a) and Pb 2+ ions loaded Delonix regia pod (Pb-DR) (Figure 1a) were carried out. FTIR data of Delonix regia (DR) indicates the functional groups. The main characteristic cellulose peak appears in the region of 1000-1200 cm −1 [22]. The strong and broad peak at 3298 cm −1 , indicated the N-H bond of amino groups and hydroxyl group. The shift in the peak to 3330 cm −1 in the spectra of the metal loaded Delonix regia pod powder shows the binding of Lead ions with hydroxyl and amino groups [23][24][25] peak at 2916 cm −1 in the spectra of the Delonix regia pod powder indicated CH 3 and CH 2 groups. The peak at 1594 cm −1 indicates CO, OH and C-O groups, the Shift to 1612 cm −1 indicated the metal binding. Band at 1036 cm −1 indicated the C-O of alcohols, the shift to 1028 cm −1 indicated binding of Pb 2+ ions with C-O group [2,[24][25][26]. Peak at 1738 cm −1 , which is indicative of carbonyl group, shifted to wave number of 1732 cm −1 after Pb 2+ adsorption [2,27,28]. Band at 1243 cm −1 indicates carboxylic acids which shifted to 1233 cm −1 after adsorption of Pb 2+ [29]. The shifts in the absorption peaks indicate the binding of metal ions on the surface of the Delonix regia powder.
Also FT-IR for detection the groups on the modified biosorbents [Citric Acid (CA) treated DR powder (CADR) before and after the biosorption of Pb 2+ ions (Pb-CADR) was shown in Figure 1b.
Comparison of the IR spectra of samples of DR and CA modified DR (CADR) revealed that a characteristic stretching vibration absorption band of carboxyl group at 1733 cm −1 is present in the IR spectrum of CADR samples. This indicates the esterification between alcohol groups of cellulose in DR and citric acid The broad absorptions around 2500-3500 cm −1 centered at 3343 confirm the existence of carboxylic OH groups and free COOH groups after CA modification. It appears from Figure 1b that the different functional groups on CADR are responsible for biosorption of Pb 2+ . A change in peaks position at 3328 cm −1 in the spectrum of Pb 2+ loaded CADR indicates the binding with hydroxyl groups. The peak at 1733 cm −1 shifted to 1728 cm −1 in the spectrum of Pb 2+ loaded CAMO indicating the binding of metal ions to carboxylic groups also [2,30,31].   change due to the appearance of amorphous peak at 2θ=44.7 after adsorption process confirming adsorption of Pb 2+ ions.

Transmission electron microscopy (TEM):
The sample was subjected to TEM analysis (Figure 5a) to indicate the particle size and the major size of the particles was found to be 18 nm (Figure 5b).
Effect of initial concentration: Figure 6 and Table 1  Effect of pH: Figure 7 and Table 2 illustrated the effect of pH of a solution in the adsorption process. R.E. and q e increase as the pH increase. The amount of Pb 2+ ions removed by the Delonix regia at low pH 2 was low (1.91 mg/g) and R.E. 57.3% compared to the amounts removed at pH 4 to 10 were ranged from (2.7 mg/g and R.E. 81% at pH 4) to 3.12 mg/g and R.E. 93.5% at pH 5. Because at low pH the concentration of H + is high [19], as H + ions were being removed by the biosorbent, instead of the Pb 2+ ions, [21,35] at higher concentration of H + ions, the biosorbent becomes more positive charge on the surface and the attraction between biosorbent and Pb 2+ ions is reduced [36]. At higher pH the capacity of the adsorbent reduced, the reduction in adsorption may be due to the increasing of OHions, or Pb 2+ ions were precipitated as lead hydroxide [2,37].

Effect of biosorbent dosage:
It is an effective factor to study the capacity of a biosorbent. R.E. increases with least value of 64.65% obtained with 25 mg and highest value of 95.04% with 500 mg of the biosorbent, this because at high dosage, there is an increase in surface area and availability of biosorption sites, but q e decreases as a decrease in the amount of Pb 2+ ions adsorbed per unit weight of biosorbent [2,[38][39][40]. These results are illustrated in Figure 8 and Table 3. Table 4 and Figure 9 illustrated the effect of contact time for the adsorption of Pb 2+ ions by Delonix regia. The amount of Pb 2+ ions absorbed increased with an increase in the contact time and reach equilibrium in 60 minutes. This because long contact time and availability of active sites, it was followed by a reduction in the metal uptake. There was a slightly increasing or remain constant in the Pb 2+ ions removal, as the sites are less available [2,41,42].

Effect of contact time:
Effect of temperature: Table 5 and Figure 10 illustrated the effect of the temperature on adsorption, the Pb 2+ R.E. and q e by Delonix regia increases while the temperature is increasing, as the active sites have increased and encourages the process of biosorption, due to increase in the movement of the Pb 2+ ions and pore size indicating an endothermic process [2,[43][44][45].
Adsorption isotherm: Pb 2+ ions distribution between the solid and liquid phases can be described by the Freundlich and Langmuir      isotherms [46] q e increased with the initial concentration of Pb 2+ , as expected [47,48]. q m is 15.26 mg/g of Delonix regia. Langmuir model suggests that the adsorption take places on homogeneous sites. Langmuir isotherm equation is represented by equation 8 in a linear form [2,49].
Plot of C e /q e against C e give a line with intercept 1/q m b and slope 1/q m is obtained (Figure 11), which shows Lead biosorption isotherms of Langmuir. From the intercept and slope the Langmuir parameters (b and q m ) are calculated. These values may be used for compared and correlate the biosorptive properties of Delonix regia of the Freundlich has the linear form [2,50].
Log q e = log K f +1/n log C e From a plot, a line with slope and intercept 1/n and log K f respectively is obtained (Figure 12).  [51] parameters of Pb 2+ ions adsorption was given in Table 6a dimensionless constant separator factor (R L ) can classify the Isotherms [52] stated as:      Table 5 Effect of temperature on Pb 2+ ions removal efficiency and q e at different initial concentrations (10,20,50) mg/L by Delonix regia pod.

Kinetic studies on the biosorption of Pb 2+ ions
Pseudo first order, pseudo second order kinetic and the intra particle diffusion models can be used to test the mechanism of the adsorption of metal ions [2,[19][20][21]. The adsorption kinetic of the adsorbed Pb 2+ ions was studied (Figures 13 and 14). Correlation coefficient, R 2 can be used to test the suitability of these models [2,21] The variable and constant of each kinetic model were calculated and were presented in Table 9, the calculated q e determined from the plot of the pseudo first order model differs from the experimental q e . This indicates that pseudo first order model is not good in studying the kinetics of the biosorption of Pb 2+ ions compared to pseudo second order models (R 2 =0.999) for Pb 2+ ions, Table 9. So the second order kinetics is good in studying     the kinetics of the biosorption of Pb 2+ ions, as the calculated q e (7.54 mg/g are very close to the experimental q e (7.6 mg/g), suggesting that the biosorption of the Pb 2+ ions solutions involves the Pb 2+ ion and the Delonix regia biosorbent particles [2,58,59].

Effect of chemical treatment of the biosorbents on biosorption efficiency
The effect of chemical treatment of the biosorbents by esterifying with NaOH followed by citric acid treatment (CADR) on the R. E compared with (DR) was studied and shown in Table 10. It was observed that the R.E.% of metal ions by (CADR) was higher than the R.E.% of metal ions by (DR) and this was due to the Chemical treatment of biomass with NaOH and citric acid increases its cation uptake ability as the carboxyl groups of the biomass increases [2,31,32].

Conclusion
1. Nano size of Flamboyant Pod (Delonix regia) was used for biosorption of toxic Pb 2+ ions from solution and is consider a very effective biosorbent in the removal of heavy metals. This study indicated that: The Adsorption process depends on temperature, pH, Contact time, dosage and metal ion concentration.
2. Adsorption of Pb 2+ ions from solutions obeyed Freundlich isotherm models. q m of Pb 2+ ions on Delonix regia is 43.62 mg g −1 .
3. The biosorption process was endothermic an ion-exchange mechanism applies in the biosorption of (Pb 2+ ions). This confirmed by thermodynamic studies.
4. Second order kinetics models is a better than the pseudo first order in studying the kinetics of the biosorption of Pb 2+ ions.