Scholarly article on topic 'Adsorption of Lead on Gel Combustion Derived Nano ZnO'

Adsorption of Lead on Gel Combustion Derived Nano ZnO Academic research paper on "Nano-technology"

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Abstract of research paper on Nano-technology, author of scientific article — V. Venkatesham, G.M. Madhu, S.V. Satyanarayana, H.S. Preetham

Abstract Many naturally available materials were used as adsorbents to remove heavy metal ions from water, which are not effective because of low surface area. Novel nano materials are used as adsorbents to remove metal ions to treat potable water. In the present work nano sized large surface area Zinc Oxide (ZnO) was synthesized by gel combustion method and used as an adsorbent to remove lead (II) (Pb2+) from aqueous solution. The nano ZnO was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive X-Ray analysis (EDAX) and surface area analysis. Effect of lead concentration, adsorbent dosage and pH on adsorption was studied. Increase in the initial concentration of Pb, decreases the percentage of adsorption, whereas increase in the adsorbent dosage and pH of the solution, increases the adsorption of Pb2+ on ZnO. Synthesized nano ZnO shows almost complete Pb adsorption at lower initial concentration. The equilibrium adsorption capacity of Pb on nano ZnO adsorbent were measured and extrapolated using Langmuir and Freundlich adsorption isotherm models and the experimental data perfectly fits both adsorption isotherms.

Academic research paper on topic "Adsorption of Lead on Gel Combustion Derived Nano ZnO"

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SciVerse ScienceDirect Procedia

Engineering

Procedia Engineering 51 (2013) 308 - 313 =

www. el sevi er. com/1 ocate/procedi a

Chemical, Civil and Mechanical Engineering Tracks of 3rdNirma University International Conference on

Engineering (NUiCONE 2012)

Adsorption of lead on gel combustion derived nano ZnO

V Venkateshama, G M Madhua, S V Satyanarayanab, H S Preethama

aDepartment of Chemical Engineering, M.S. Ramaiah Institute of Technology, Bangalore-560054, India. bDepartment of Chemical Engineering, Jawaharlal Nehru Technological University Anantapur, Anantapur-515002, India.. Corresponding E-mail: madhugm_2000@yahoo.com

Abstract

Many naturally available materials were used as adsorbents to remove heavy metal ions from water, which are not effective because of low surface area. Novel nano materials are used as adsorbents to remove metal ions to treat potable water. In the present work nano sized large surface area Zinc Oxide (ZnO) was synthesized by gel combustion method and used as an adsorbent to remove lead (II) (Pb2+) from aqueous solution. The nano ZnO was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive X-Ray analysis (ED AX) and surface area analysis. Effect of lead concentration, adsorbent dosage and pH on adsorption was studied. Increase in the initial concentration of Pb, decreases the percentage of adsorption, whereas increase in the adsorbent dosage and pH of the solution, increases the adsorption of Pb2+ on ZnO. Synthesized nano ZnO shows almost complete Pb adsorption at lower initial concentration. The equilibrium adsorption capacity of Pb on nano ZnO adsorbent were measured and extrapolated using Langmuir and Freundlich adsorption isotherm models and the experimental data perfectly fits both adsorption isotherms.

© 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of Institute of Technology, Nirma University, Ahmedabad.

Keywords: Nano Zinc oxide, Lead, Adsorption, Gel Combustion, Water.

1. Introduction

Living beings require heavy metals in very less concentration for their normal and healthy life, but the excess of heavy metals cause many more hazardous to living beings. Heavy metals are increasing in the environment by the improper disposal of industrial effluents during manufacture of fertilizers, pesticides, dyes, drugs, tannery, battery manufacturing and fossil fuel [1]. Day by day large amount of heavy metals are accumulating in the environment leading to both acute and chronic toxicity. Few heavy metals like cadmium, lead, copper, nickel, mercury, chromium, zinc, etc. are present as contaminants in soil and water. As Lead is nonbiodegradable and it should be removed from water [2]. Lead in water causes gastrointestinal diseases, constipation, abdominal pain, cancer and anemia [3], besides effecting central nervous system [45]. Heavy metal ions can be removed from solutions by immobilization and stabilize metals in soils [6]. Immobilization is transferring of metals from labile to nonlabile phases. Activity of heavy metals present in soil is governed by the sorption desorption reactions with other substituent's of soil [7]. Many researchers used several adsorbents like activated carbon, fly ash, crab shell, coconut shell, zeolite, manganese oxide and rice husk for adsorption of heavy metals [8-11] from solutions. These adsorbents were cheap, but not very effective adsorbents for the adsorption of heavy metals because of less surface area. Hydroxyapatite, minerals like smectite, illite, kaolinite and Fe-Mn oxides, phosphatic clays [6-7, 12-16] were used as binding or chelating agents to remove the heavy metals. Carbon nanotubes such as single-walled carbon nanotubes, multi walled-carbon nanotubes, carbon beads, carbon fibers and nanoporous carbon were used as good sorbents [17-18]. Fe3O4 nanoparticles- DMSA (dimercaptosuccinic acid) was used as a good adsorbent for the removal of heavy metals like Pb, Hg and Cd [19]. y-Al2O3, ferrite-thio^ea composite, ferrite rubber composites and y-Fe2O3 [20-24] were also used as adsorbents for the removal of Pb.

The present investigation aimed at adsorption of Pb2+ or lead (II) on nano zinc oxide. Nano ZnO was prepared from zinc nitrate by gel combustion method. Sugar was used as a fuel for combustion. Synthesized ZnO was calcinated and used as adsorbent for the removal of Pb2+ from the aqueous solution. ZnO was characterized by using XRD, SEM and EDAX. Surface area was estimated using nitrogen desorption technique. The effect of lead concentration, pH, and adsorbent dosage on adsorption was studied.

ELSEVIER

1877-7058 © 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of Institute of Technology, Nirma University, Ahmedabad. doi:10.1016/j.proeng.2013.01.041

2. Experimental

2.1. Materials and Methods

Zinc nitrate hexahydrate (Merck; >96.0%, AR grade) was used as a precursor. Commercial sugar purchased from the local market was used as a fuel for combustion. Standard lead solution was used for adsorption, which was prepared by dissolving lead nitrate (Merck; >99%, LR grade).

2.2. Synthesis of ZnO

Synthesis of ZnO was carried out by the gel combustion process. Zinc nitrate hexahydrate was used as the zinc precursor. 14.9 g of zinc nitrate and 5.4 g of sugar were dissolved in 125 mL distilled water. Fuel to nitrate ratio (mole ratio) was maintained at 0.156 in the reaction mixture. The reaction mixture was placed on a hot plate. Water vapour and nitric gases were released while heating and the formation of gel takes place. The powder was then calcinated at 600°C and characterized as explained below.

2.3. Instrumentation

Surface area of the zinc oxide was estimated using Multi point BET analyzer (Nova, Quantachrome Instruments, USA). X-ray diffraction (XRD) study of the metal oxide was carried out (Bruker D2 Phaser, USA) at 20, 5-60° with a step size of 0.02° per 0.5 sec. Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray analysis (EDAX) were carried out (JEOL, JSM 6380-LA, USA) to study the surface morphology, size and composition. Lead concentration was analyzed using Atomic Absorption Spectroscopy (GBC 932 plus). The readings were taken in triplicate at a wavelength of 283 nm.

2.4. Adsorption Studies ofPb on ZnO Surface for SEM and EDAX Analysis

One gram of synthesized ZnO was added to the 100 mL of 1N lead nitrate solution taken in a 250 mL conical flask and the solution was subjected for shaking in mechanical shaker for three hours. ZnO adsorbent was filtered and filtrate was dried at 250°C. The dried powder was characterized by SEM and EDAX.

3. Results and Discussions

3.1. Surface area and X-ray diffraction (XRD) analysis

The calcined ZnO density was found to be 0.0960 g cc 1 by surface area analyzer. The specific surface area of the sample was 80.425 m2 g 1, which is very high compared to the values reported earlier (Shen et al [25] reported 47.3 m2 g 1, Park et al [26] reported 56 m2g 1 and Du et al [27] reported 28.7 m2 g 1). The total pore volume was 0.1102 cc g 1. All pores are smaller than 2634.131A° and average pore diameter was 54.721 A°. The plot of cumulative pore volume versus pore diameter is shown in the Figure 1. XRD of calcinated ZnO is represented in Figure 2. The peaks in Figure 2 match with the ZnO standard in the Wurtzite phase [28] having crystalline morphology with broad peaks, which was in close agreement with JCPDS data [29]. A crystal size of the sample was calculated by Scherrer equation. The average particle size of the zinc oxide was found to be 40 nm.

Cumulative pore volume (cc/g) x10'3 „„

*JO moo 3»«U 3MU9 «12 XI230 «113 78» UK} K>

Pore diameter (A ) Fig. 1. Plot of cumulative pore versus pore diameter for ZnO.

Angle of Incidence (29) Fig. 2. XRD pattern of Calcinated ZnO

3.2. Scanning Electron Microscopy (SEM) Analysis

SEM was used to study the surface morphology of the synthesized zinc oxide nano-particles at low and high magnifications. Figure 3 shows the SEM pictures (magnification of 10000X) of nano ZnO crystalline particles produced by the gel combustion technique. All the particles are regular and are flake like in nature. Figure 4 shows SEM image (10000X) of lead adsorbed zinc oxide nano-particles. Intense flake shaped particles with lead lumps on the surface of zinc oxide nano-particles are seen which indicates the nucleating growth of lead on surface of the adsorbent. These images help to confirm the adsorption of lead (II) on the surface of zinc oxide nano-particles.

Fig. 3. SEM image of as synthesized ZnO nano-particles (10000X). Fig. 4. SEM image of Pb adsorbed ZnO nano-particles (10000X)

3.3. Energy Dispersive X-Ray analysis (EDAX) Analysis

The EDAX spectrum of synthesized ZnO and lead adsorbed ZnO EDAX were shown in Figure 5 and 6 respectively. EDAX spectrum shows the presence of zinc, lead and oxygen element indicating the purity of the adsorbent. By comparing Figure 5 and Figure 6, the first peak between 0 to 1ev corresponds to oxygen and the peaks between 8 to 9 ev and the peak exactly at 1 ev corresponds to zinc. The peaks found in between 1.5 to 3 Kev in Figure 5 indicates lead. EDAX strongly confirmed the adsorption of lead on the surface of ZnO adsorbent. Mass percentages of different elements were: lead 69.6%, oxygen 16.23%, zinc 10.71% and the rest are impurities.

Fig. 5

J S £

Jj H - Z

(J jg U S 3

% i £ 2 1 4 1 a s 4 jz «S3

!,P 1 H 1 II 1 II

: :: ■ : ' > ' 700 E 00 0 00 10 00

Energy (KeV) . EDAX pattern of standard ZnO.

£ u - •3

■si qj 1 1 a 2 s

& s ( ^ ? U I 1 i ss - z: 11 S

iflj 1 1 II II i I II 1 i 1

Energy (KeV) Fig. 6. EDAX pattern of Pb adsorbed ZnO

3.4. Effect of Lead Concentration

To study the effect of lead concentration on adsorption, experiments were carried out by adding 0.5 g of ZnO in 50 mL of various concentrations (20 to 100 mg L-1) of lead solution at pH 2. These samples were well mixed in mechanical shaker for three hours. The solutions were then filtered, centrifuged and analyzed for lead concentration using AAS. The results of these experiments were shown in Figure 7. It is seen from the figure that the adsorption capacity (% adsorption) reduces with increase in lead concentration, at lower concentrations of lead (20 mg L-1) the adsorption capacity was 100% and further increase in the lead concentration the capacity reduces gradually to 79.5% at 100 mg L-1. This shows that the adsorption capacity is highly dependent on the adsorbate concentration. Therefore, ZnO is a very good adsorbent of Pb compared to other adsorbents studied by the earlier researchers [20-24].

3.5. Effect of Adsorbent Dosage

The effect of adsorbent dosage on adsorption capacity was carried out by varying ZnO loading (0.2 to 1.0 g) in 50 mL of 200 mg L-1 Pb solution at pH 2.The adsorbent solutions were well mixed in mechanical shaker for three hours. Then the solution was filtered, centrifuged and analysed using AAS. The percentage adsorption data reported in Figure 8, reveals that the adsorption of Pb2+ increases with the increase in the dosage of ZnO adsorbent.

Fig. 7. Plot of concentration of Pb versus percentage of Pb adsorbed. Fig. 8. Plot of percentage of Pb adsorbed versus adsorbent dosage

3.6. Effect of pH

Keeping initial concentration of adsorbate (50 mL of 50 mg L-1 Pb solution), adsorbent (0.2 g ZnO) and mixing time (3 h) constant, the experiment were conducted by varying pH from 2.0 to 10.0. The results of these experiments are shown in the Figure 9. It was found that the adsorption capacity (% adsorption) of zinc oxide increases with increase in pH. The optimal adsorption of lead on nano zinc oxide was at pH 4 and the adsorption becomes constant above the pH 4. At lower pH, H+ ions are strongly competes with Pb2+ to adsorb on nano ZnO. With increase in pH of a solution, the competition between H+ and Pb2+ decreases by the minimization of repulsive force [30-31] and results optimum adsorption at pH 4. In basic solution the adsorbent surface was negatively charged and adsorption of Pb2+ results. So, that the adsorption of Pb2+ on nano ZnO remains constant in basic condition up to pH 10. Above the pH 10, there was a possibility of precipitation of OH-and Pb2+. The percentage of Pb adsorption with different pH was as shown in Figure 9.

Fig. 9. Plot of percentage of Pb adsorbed versus pH range

3.7. Adsorption Isotherms

The equilibrium distribution of metal ions (Pb2+) among sorbent (ZnO) and the solution can be determined using Langmuir and Freundlich adsorption isotherm models.

3.7.1. Langmuir adsorption isotherm

Langmuir adsorption was used to explain the adsorption capacity of the substance by the sorbent. According to Langmuir adsorption isotherm, adsorption takes place at specific homogeneous sites of adsorbent surface and no transmigration of adsorbate in the surface plane [32]. The Langmuir adsorption is represented by the Equation 1.

- = T-7r + — (1)

Re bqmCe qm

Where qe (mg g-1) is the adsorbed amount of cadmium, Ce (mg L-1) is the equilibrium concentration of the cadmium in solution, qm is the monolayer adsorption capacity, and b is the constant related to the free energy of adsorption. The plot of l l

— versus — is shown in the Figure 10. The experimental data perfectly fits to the Langmuir adsorption isotherm model. The qe Ce '

b, R2 and was found to be 0.004117 L g-1, 0.9987 and 26.109 mg g-1 respectively. Monolayer concentration of lead on ZnO (qm= 26.109 mg g-1) is very high compared with literature for the adsorption of lead on different adsorbents [33-34].

3.7.2. Freundlich adsorption isotherm

The adsorption data of lead is also analyzed by Freundlich adsorption isotherm model in logarithmic form and is given by the Equation (2).

lnqe = InKt + — lnCe (2)

Where qe is the amount of cadmium adsorbed (mg g-1), Ceis the equilibrium concentration of the adsorbate (mg L-1), Kf (mg g-1) and n are Freundlich constants related to adsorption capacity and adsorption intensity, respectively [35]. The plot of lnqeversus lnCe for the adsorption data of lead are given in Figure 11, which clearly shows that theexperimental data fits very well to the Freundlich model also. The Freundlich constants Kf and n were calculated from the best-fit line (Kf = 0.1524 mg g-1; n =1.1655; R2 = 0.9999). The n value is greater than one which shows that the adsorbent is beneficial to Pb adsorption [36].

Fig. 10. Langmuir adsorption isotherm for lead adsorption on ZnO, Fig. 11. Freundlich adsorption isotherm for lead adsorption on ZnO

4. Conclusions

The present paper was aimed at studying the synthesis of nano ZnO by gel combustion technique and their applications towards adsorption studies. Synthesized material was calcinated at 600°C and characterized using XRD, SEM and EDAX.

Surface area was measured using multiple BET adsorption technique. The surface area of the powder was 80.425 m2 g-1, which has large surface area compared to normal zinc oxide, was used as adsorbent for the adsorption of Pb from aqueous solution. Adsorption of Pb on ZnO was confirmed by SEM and EDAX. The factors such as initial concentration, adsorbent dosage and pH of solution govern the adsorption of Pb on ZnO. Adsorption of Pb is maximum for the lower concentration of Pb solution, acidic solution and becomes constant in basic solution and also adsorption increases with increase in the adsorbent dosage. The correlation coefficient (R2) obtained from Langmuir and Freundlich adsorption isotherm was almost same. Therefore, both the adsorption isotherm perfectly fits to lead adsorption on nano ZnO.

Acknowledgment

The authors are thankful to Dr A B Halgeri and Dr Nalini G Sundaram, Poornaprajna Institute of Scientific Research, Bangalore for their guidance and help during material characterization. We also thankful to Dr Bhatt, Bangalore Institute of Technology, Bangalore for providing surface area analyzer.

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