Treatment of lead-contaminated water using activated carbon adsorbent from locally available papaya peel biowaste

Accepted Manuscript Treatment of lead-contaminated water using activated carbon adsorbent from locally available papaya peel biowaste Sahar Abbaszadeh, Sharifah Rafidah Wan Alwi, Colin Webb, Nahid Ghasemi, Ida Idayu Muhamad PII:

S0959-6526(16)00089-5

DOI:

10.1016/j.jclepro.2016.01.054

Reference:

JCLP 6642

To appear in:

Journal of Cleaner Production

Received Date: 27 October 2015 Revised Date:

31 December 2015

Accepted Date: 21 January 2016

Please cite this article as: Abbaszadeh S, Wan Alwi SR, Webb C, Ghasemi N, Muhamad II, Treatment of lead-contaminated water using activated carbon adsorbent from locally available papaya peel biowaste, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.01.054. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 9021

Treatment of lead-contaminated water using activated carbon adsorbent from locally available papaya peel biowaste

Idayu Muhamad5

2 3

Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia

School of Chemical Engineering and Analytical Science, University of Manchester, Manchester, United Kingdom 4

5

SC

Process Systems Engineering Centre (PROSPECT), Research Institute of Sustainable Environment (RISE), Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia

Department of Chemistry, Sciences Faculty, Islamic Azad University, Arak branch, Arak, Iran

Bioprocess Engineering Dept., Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

M AN U

1

RI PT

Sahar Abbaszadeh1,2, Sharifah Rafidah Wan Alwi1,2*, Colin Webb3, Nahid Ghasemi4, Ida

*Corresponding author: e-mail: [email protected]

TE D

Abstract

The performance of activated carbon (AC) produced from papaya peel (PP) as a locally available bioderived adsorbent in the removal of Pb(II) from metal-contaminated water is

EP

reported. Utilization of natural biowastes, such as papaya peel, in this way could assist with waste minimization at the same time as providing a new source of activated carbon for

AC C

wastewater treatment. Lead pollution in water bodies is critical in countries such as Malaysia, yet removal via this locally sourced waste material has not been considered before. Using papaya peel activated carbon (PP–AC) in batch mode, the effects of initial pH (3–7), adsorbent dosage (10–200 mg), initial Pb(II) concentration (10–200 mg/L), contact time (10–180 min) and temperature (25, 35 and 50 °C) were studied separately. The best result was obtained at pH 5, with an adsorbent dosage of 100 mg, Pb(II) ion concentration of 200 mg/L and a contact time of

1

ACCEPTED MANUSCRIPT 9021 2 h, with over 93% of the Pb(II) being adsorbed. It was observed that the time required to reach equilibrium decreased with increasing initial concentration of Pb(II) in the solution. The experimental data were consistent with both Langmuir and Freundlich adsorption models. The

RI PT

data also fitted very well (R2 = 0.99) to a pseudo-second-order kinetic model, suggesting that the bioadsorption is a chemisorption process. In addition, thermodynamic parameters such as ∆G°, ∆H° and ∆S° were calculated. The adsorption of Pb(II) on PP–AC was found to be spontaneous

SC

and exothermic under standard conditions. Desorption studies confirmed the applicability of hydrochloric acid (HCl) as a desorbing agent with great efficiency (>97%) and a regeneration of

M AN U

approximately 96%. Overall, the efficiency of the Pb(II) uptake process using PP–AC was more than 40% higher than values reported for most crop-based adsorbents, confirming its potential for use in wastewater treatment processes.

Keywords: Wastewater treatment, Pb(II) removal, Papaya peel, Bioadsorbent, Activated

TE D

carbon.

EP

1. Introduction

AC C

Lead(II) contamination has health and environmental significance due to its persistence and toxic properties in addition to a vast range of usages in industry, such as petrochemicals, paints and battery manufacturing. Pb(II) is listed as one of the biomagnified metal elements whose concentration in living organisms increases over time via the food chain, causing chronic detrimental effects on certain organs, e.g. the kidneys, nervous system and immune system (WHO, 1998). As reported by the International Lead Association (2012), the annual production of lead is estimated at approximately 5 million tonnes, and the trend is expected to rise. 2

ACCEPTED MANUSCRIPT 9021 Approximately 60% of its production is utilized in battery manufacturing, while the remaining is used for other industrial products, such as pigments and plastics (Zahra, 2012). In fact, the growing global population continually questing for more of these products creates high risks to

RI PT

both the workforce and neighbouring environment because toxic heavy metal elements cannot break down and degrade biologically. Accordingly, this necessitates that industries treat the contaminated effluents and maintain the concentration of toxic elements below the prescribed

SC

limit before discharging to the environment. Following that, several decontamination methods have been developed and established over recent decades to remove organic and inorganic

M AN U

pollutants from water and wastewater, including flotation, precipitation, membrane separation, biosorption and activated carbon adsorption (Wan Ngah and Hanafiah, 2008). Those conventional methods to minimize the environmental and health impacts of large quantities of industrial effluents containing low concentrations of heavy metals are not promising due to the

TE D

low efficiency and high operational costs (Cechinel et al., 2014). In fact, wastewater treatment for industrial effluents containing lead in hot weather is more challenging than in moderate climates because of the increased lead solubility in aqueous media as the temperature rises.

EP

Nevertheless, lead removal before discharging to the environment is essential in tropical

AC C

countries, such as Malaysia.

One of the most efficient physicochemical methodologies for a broad range of

applications is adsorption, which is suitable for low-concentration metal ion uptake from a variety of aqueous media. Its effectiveness stems from the surface compatibility of the activated carbon adsorbent to bind the metal ions. However, the higher the quality of activated carbon, the higher is its production cost. In addition, the existing activated carbon adsorbents need to undergo a complexing process through a chemical agent to enhance their inorganic removal 3

ACCEPTED MANUSCRIPT 9021 performance, further adding to the cost. In recent decades, metal binding using biomaterials has been a research trend because the surface characterization of such materials shows an excellent capability to remove metal ions from aqueous solutions, they are generally both cheap and

RI PT

environmentally benign (Kaouah et al., 2013). If they are also agricultural by-products, that adds to their attractiveness. In particular, agricultural lignocellulosic low-cost by-products, such as rice husks, fruit peels and nut shells, offer good accessibility, simple application, minimal

SC

processing requirements and the creation of almost no harmful residues; they have been evaluated extensively for metal uptake options from water (Pino et al., 2006). It has also been

M AN U

proved that such lignocellulosic agrowastes are attractive resources for the preparation of carbonaceous materials implemented in adsorption processes (Ghaedi et al., 2014). In addition, the existence of particular functional groups in their surface structure, which consist of cationbinding components, e.g. carboxylic and hydroxyl groups, potentially indicates a good capability

TE D

for the metal uptake process (Hashem et al., 2005). In general, two different processes of physical and chemical activations are used to prepare activated carbon (Li et al., 2010). Physical activation involves carbonization of raw materials at the high temperatures in the presence of

EP

suitable oxidizing gases such as carbon dioxide, steam and air. However, the activated carbons produced by physical activation do not always have satisfactory characteristics to be used as

AC C

adsorbents. Chemical activation involves impregnation of the raw materials with dehydrating agents and oxidants such as sulphuric acid (H2SO4), phosphoric acid (H3PO4), sodium hydroxide (NaOH), potassium hydroxide (KOH) and zinc chloride (ZnCl2) (Zuo et al., 2009). Chemical activation offers several advantages, such as only requiring a single step and performed at lower temperatures. It also combines carbonisation and activation, therefore resulting in the development of a better porous structure (Ioannidou and Zabaniotou, 2007).

4

ACCEPTED MANUSCRIPT 9021 Papaya (Carica papaya) is a tropical fruit cultivated widely in equatorial and subequatorial countries in Central America, Africa and Asian tropical countries. It can be consumed fresh (as food or juice), in processed forms (as a flavouring agent, meat tenderizer or

RI PT

wide range of cosmetic products), and in the form of traditional medicines and drugs. Its high annual production of around 342 million tonnes (FAOStat3, 2011) also generates a large amount of waste. Based on official agricultural reports, Malaysian annual papaya production is

SC

approximately 72,000 tonnes (Hameed, 2009); a massive amount of papaya wastes (peel, seeds, etc.) is produced concurrently due to its high rate of consumption in this country, creating serious

M AN U

waste control problems for the community. Although many research groups have investigated various papaya waste parts, such as the seed or leaves, no attempt has yet been made to use papaya peel waste as a possible alternative for the treatment of lead-contaminated aqueous solutions (Abbaszadeh et al., 2015).

TE D

In the current study, the activated carbon from agrowaste of the Carica papaya fruit peel (PP) was investigated for its Pb(II) removal capacity from aqueous media following batch experiments. The PP–AC was characterized via different techniques, such as field emission

EP

scanning electron microscopy (FESEM), scanning electron microscopy (SEM), energy-

AC C

dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), elemental analyser and Brunauer–Emmett–Teller (BET) analysis. The effects of pH (3–7), adsorbent dosage (10–200 mg), initial concentration of Pb(II) ions in the solution (10–200 mg/L), contact time (10–180 min) and temperature (25, 35 and 50 °C) were evaluated. The results obtained from the batch experiments were analysed and integrated with the existing equilibrium isotherms, kinetic and thermodynamic models.

5

ACCEPTED MANUSCRIPT 9021

2. Material and methods 2.1. Reagents A 1,000 mg/L Pb(II) synthetic stock solution was prepared by the dissolution of an

RI PT

appropriate amount of lead(II) nitrate, Pb(NO3)2, in distilled water utilizing a 1,000 mL volumetric flask, and the obtained stock solution was used for further solution preparation required for each experiment. All analytical grade chemicals required in this research were

SC

obtained from Merck. The initial pH of the stock solution was adjusted using 0.1 M HCl or 0.1 M NaOH. The batch procedure was conducted at room temperature (25 ± 1 °C) throughout all

M AN U

experimental stages.

2.2. Adsorbent preparation (oxidation of PP carbon)

The ripened papaya fruit (Carica papaya) was collected from the local market, washed exhaustively with distilled water to remove dirt and then peeled. The peeled samples were then

TE D

dried in an oven for 24 h at 105 °C until they became crisp. To prepare the activated carbon, the dried samples were heated to 450 °C for 5 h in a furnace to perform the carbonization process and then ground and sieved using a 45 mesh (355 µm). After that, the charcoal was oxidized

EP

using 1 M phosphoric acid (99%) for 48 h at room temperature followed by filtration. The oxidized char was then continually dried for another 24 h in an oven at 105 °C to ensure

AC C

complete removal of all moisture. The oxidized papaya peel was kept in the furnace at 450 °C for another 5 h, and after cooling, its pH was neutralized using 0.1 M NaOH. The final product of PP activated carbon (PP–AC) was stored in an air-tight glass container for future experiments.

2.3. Characterization of PP–AC The morphological characterizations of the raw papaya peel (PP) powder and papaya activated carbon (PP–AC) were investigated using FESEM (JSM-6701F, JEOL, Ltd.) and SEM 6

ACCEPTED MANUSCRIPT 9021 (TM3000, HITACHI, Japan) coupled with EDX. The samples were also evaluated regarding their surface functional groups, as well as elemental composition, using FTIR (NICOLET 5700, Thermo Electron Corporation, Japan) and an elemental analyser (Elementar-15135057, vario

RI PT

MICRO CUBE, Germany). In addition, the samples of raw PP and PP–AC were analysed using a BET analyser instrument (Surfer Analyser-SRFA11.0010-Thermo Fisher Scientific, Italy) and

determination.

M AN U

2.4. Batch adsorption experiments

SC

X-Ray diffraction (XRD) to measure specific surface area, porosity and crystalline structure

The Pb(II) adsorption capacity of PP–AC from aqueous solution was evaluated following a batch procedure. All adsorption experiments were performed in 100 mL flasks containing 20 mL of Pb(II) aqueous solution with a desired concentration at room temperature. The pH adjustment and measurement were made using 0.1 M NaOH and HCl and a pH meter (ORION 2

TE D

STAR pH benchtop, Thermo Scientific). The samples were agitated for a certain period of time (10–180 min) under specific stirring conditions (speed of 150 rpm) (using an automatic shaker, Systec Laboratory equipment). The Smith filter paper (125 mm) and Millipore Millex (GN nylon

EP

0.20 µm) syringe filter were also used for the filtration of the adsorbent from the aqueous solution. The filtrate was then analysed using an atomic absorption spectrophotometer (AAS)

AC C

(Shimadzu AA-680, Japan) to determine the uptake concentration of Pb(II) after each single test. The Pb(II) uptake study was conducted to consider the effects of various parameters; contact time (10 to 180 min), adsorbent dosage (10 to 200 mg), pH of solution (3 to 7) and initial concentration of Pb(II) ions in the solution (10 to 200 mg/L). The Pb(II) adsorption’s isotherms, kinetics and thermodynamics for PP–AC were measured at different initial Pb(II) concentrations, contact time and temperature intervals under optimized conditions.

7

ACCEPTED MANUSCRIPT 9021 The amount of Pb(II) removed per gram of PP–AC, qe (mg/g PP–AC), was calculated using a mass balance equation (Eq. (1)), and the remaining Pb(II) ion concentration of the filtrate

RI PT

after adsorption was then measured using AAS. q e = (C 0 − C e )V / W ,

(1)

where C0 and Ce (mg/L) are the liquid phase concentrations of lead initially and at equilibrium, V

SC

(L) is the solution volume and W (g) is the dry mass of adsorbent used. The removal efficiency

% Re moval =

(C 0 − Ce ) × 100 C0

2.5. Lead desorption practice

M AN U

of the Pb(II) adsorption process can be calculated using Eq. (2):

(2)

The lead desorption was performed using 100 mg of PP–AC in contact with 20 mL of

TE D

100 mg/L Pb(II) aqueous solution at pH = 5 at a time of 2 h. The filtered adsorbent was washed thoroughly with distilled water and oven dried for 5 h and the filtrate analysed using AAS. As the next step for the desorption process, the saturated PP–AC was agitated (150 rpm) with

EP

different concentrations of 20 mL HCl solution (0.1, 1 and 5 M) as desorbing agent for 2 h at room temperature. After filtration, the liquid phase samples were analysed using AAS and the

AC C

amount of desorbed Pb(II) was calculated using Eq. (3) (Cechinel et al., 2014). The HCl concentration with the highest percentage of desorbed lead was considered as the optimum concentration for the PP–AC reuse process.

Desorption % =

Amount desorbed ions Amount adsorbed ions

× 100

(3)

8

ACCEPTED MANUSCRIPT 9021

2.6. Adsorbent regeneration To determine the PP–AC regeneration possibility, a set of batch experiments was conducted. The regeneration analysis was started with a Pb(II) adsorption followed by the lead

RI PT

desorption process using 25 mg of PP–AC in contact with 100 mL of 100 mg/L Pb(II) solution in a period of 1 h. Five regenerating cycles were performed and after each cycle the adsorbent was washed with distilled water, oven dried at 105 °C and then reused. The filtered liquid phase was

SC

analysed using AAS for each cycle to assure the accuracy of the process.

M AN U

3. Results and discussion 3.1. Characterization of PP–AC

Fig. 1 illustrates the morphological characterization of raw PP, PP–AC and Pb–PP–AC, analysed by FESEM and SEM and Table 1 shows the chemical composition and crystalline status of the adsorbents from PP (see Fig. A.1, A.2, A.3, A.4). The surface properties and

TE D

elemental analyses of both pristine PP and PP–AC shown in Table 2 consist of the specific surface areas and pore volume measured by the N2–BET method. The surface areas of the samples show significant improvement from 9.63 m2/g in raw PP to 15.28 m2/g for PP–AC

EP

(Table 2). However, based on the SEM and FESEM images (Fig. 1), the surface area of raw PP is slightly changed by the phosphoric acid treatment, whereas compared with PP–AC in Table 2,

AC C

the data varied significantly. A heterogeneous surface without pores was observed for raw PP before activation; however, the surface textural property of PP–AC becomes porous with deep holes and no significant crystalline pattern (Fig. A.4) after chemical modification. The increased specific area of PP–AC could be connected to the carbonization process at high temperature (in the furnace) and oxidation of raw PP with phosphoric acid. In addition, acid treatment generally improves the adsorption capacity of the adsorbent and its metal affinity through enhancement of

9

ACCEPTED MANUSCRIPT 9021 its surface characteristics, i.e. better ion exchange properties, formation of new functional groups or more active binding sites (Wan Ngah and Hanafiah, 2008).

RI PT

The FTIR spectra of pristine PP, PP–AC and Pb–PP–AC are illustrated in Fig which exhibits a distinctive broad band showing the existence of surface functional groups and their changes through the biosorption process. The change occurring in those peaks could be linked to

SC

the carboxyl (C=O) and hydroxyl (O–H) groups, which commonly contribute to the ion exchange and metal binding process during biosorption. The peak in the frequency range of 1000

M AN U

to 1200 cm–1 is related to the C=O stretch (COOH) in amides, alcohol, carboxylic acids and esters. The peak at 1139.74 cm–1 in PP–AC may be due to the graphite structure (C=C) of PP– AC. The peaks at 1402.02 cm–1 and 2921.67 cm–1 indicate the involvement of the H–C–H asymmetric and symmetric stretches and C–H alkanes stretch (Abdolahi et al., 2014; Hossain et al., 2012; Yargic et al., 2015). The O–H stretch for carboxylic acids between 3000 and 3375.51

TE D

cm–1 is noticeable in the PP-raw spectrum (Abbaszadeh et al., 2015). The strong peak at 1598.72 cm–1 represents the C=C bond. A weak peak of 2348.91 cm–1 observed on the PP-raw surface may be assigned to the amide group. Therefore, the FTIR spectra clearly show the presence of

EP

the functional groups, i.e. carboxyl and hydroxyl groups, which are increased by the amount of

AC C

oxygenated groups at the surface of PP–AC through the acid oxidation process and potentially could bind the Pb(II) ion through biosorption (Xu et al., 2014). Table 1: Papaya fruit adsorbent contents (Gilbert et al., 2011) Attributes

Content per 100 g of edible fruit

Protein

1.5%

Crude Fat

0.1%

Carbohydrates

2.2–7.1%

Minerals (Ca, Mg, Fe)

34.73, 13.60, 2.52 (mg)

Vitamins (C, Niacin, Thiamine, Riboflavin, β-carotene)

41.07, 0.37, 0.28, 0.04, 6204.18 (mg)

10

ACCEPTED MANUSCRIPT 9021 Ash

0.42 ± 0.03 (g/100 g-fruit waste)

Table 2. Elemental analysis and BET characterization analysis of pristine PP and PP–AC. Nitrogen%

Hydrogen%

Surface area (m2/g)

Cumulative pore volume (cm³/g)

Raw PP

38.57

3.20

5.82

9.63

0.0239

PP–AC

44.48

4.75

2.82

15.26

0.0469

SC

RI PT

Carbon%

Sample name

(d)

TE D

M AN U

(a)

(e)

AC C

EP

(b)

11

ACCEPTED MANUSCRIPT 9021

(c)

SC

RI PT

(f)

M AN U

Fig. 1. FESEM (left) and SEM (right) images of raw-PP (a, d), PP–AC (b, e) and Pb–PP–AC (c, f). Moreover, the elemental analysis (Table 2) and EDX of PP–AC (Fig. A.1) and the raw PP (Fig. A.2) confirm the improvement of carbonaceous and nitrogen proportions from 38.57%

AC C

EP

TE D

and 3.20% to 44.48% and 4.75% for the raw PP and PP–AC, respectively.

12

ACCEPTED MANUSCRIPT

M AN U

SC

RI PT

9021

TE D

Fig. 2. FTIR spectra of PP-charcoal (before acidification), PP-raw, PP–AC and Pb–PP–AC.

3.2. Parameters influencing adsorption

EP

The adsorption capacity of Pb(II) onto a bioadsorbent is affected by different types of process conditions. This study investigates the influence of five affecting parameters: pH,

AC C

adsorbent dosage, contact time, initial concentration of Pb(II) ions and temperature in the solution.

3.2.1. Solution pH

The adsorption of Pb(II) onto PP–AC as a function of pH (range 3–7) is illustrated in Fig. 3. The solution pH has a significant impact on the removal proportion of heavy metal ions as it determines the adsorbent surface charge, degree of ionization and specification of the chosen 13

ACCEPTED MANUSCRIPT 9021 adsorbent. Lead adsorption is a very pH dependent process because it is precipitated in solution at pH levels above 6. In general, the effect of pH in an adsorption process highly depends on the chemical structure of the existing heavy metal ions, i.e. pure ionic or hydroxyl-metal form in a

RI PT

specific pH range. Thus, the interacting functional groups on the bioadsorbent surface (as typical metal binding sites) are capable of showing different removal trends in varied pH conditions of different adsorption processes. Depending on the type of bioadsorbent used, an increase in pH

SC

value may substantially increase or decrease the adsorption removal capability (Lian et al., 2013). Fig. 3 demonstrates an increase of the PP–AC Pb(II) adsorption capacity and removal

M AN U

percentage from 14.9 to 17.0 mg/g and 74 to 83% at equilibrium, respectively, in line with increasing the pH value from 3 to 5 in the presence of an initial Pb(II) concentration of 100 mg/L. From Fig. 3, the maximum removal of Pb(II) occurs at a pH of 5, and then, a downward trend of adsorption is observed with pH levels above 5. The lower pH value slows down the

TE D

removal of Pb(II), as H+ and Pb(II) ions are competing for the active sites on the adsorbent surface. Therefore, at a higher pH, the competition weakens and Pb(II) ions are able to replace the H+ and bond with available functional groups such as –OH and –COOH, on the adsorbent

EP

surface (Rama Raju et al., 2013). From the FTIR spectra illustrated in Fig. 2, it is observed that hydroxyl groups (–OH) are active on the surface of PP–AC. Therefore, it can be concluded that

AC C

the adsorption of Pb(II) on the PP–AC occurs due to a cation exchange reaction between the H+ from the hydroxyl groups and cationic ions of Pb(II). Because the Pb(II) ions tend to precipitate at pH levels above 6, a pH level of 5 is considered the optimum pH condition for further experiments.

14

ACCEPTED MANUSCRIPT 9021 The mechanism of Pb(II) adsorption by activated carbons may be accomplished through Cπ interactions to form the Cπ–Pb(II) complex and through the ion exchange reactions with

ACOH + Pb2+ + 3H2O → ACOPbOH + 2H3O+

(4) (5)

TE D

M AN U

SC

2ACCOOH + Pb2+ + 2H2O → Pb(ACCOO)2 + 2H3O+

RI PT

surface hydroxyl and carboxyl groups, which can be given as follows (Ghasemi et al., 2014a):

Fig. 3. Effect of pH on Pb(II) removal.

EP

3.2.2. Adsorbent dosage

The adsorption behaviour as a function of different amounts (10–200 mg) of adsorbent

AC C

dosage (PP–AC) was evaluated considering the optimum pH and contact time in 20 mL of 100 mg/L aqueous Pb(II) solution in 100 mL flasks (see Fig. 4). It was observed that in the presence of higher dosages of PP–AC with particle size of 355 µm, the Pb(II) uptake amount decreases from 140.96 to 8.77 mg/g although the removal efficiency slightly increases from 70.4 to 87.7%. In fact, increasing the adsorbent amount provides more chance for the Pb ions to adhere to the PP–AC surface due to increase in number of available adsorption sites and the surface area. In spite of increase of removal efficiency, Pb(II) uptake amount was decreased as the PP–AC dose 15

ACCEPTED MANUSCRIPT 9021 increased. This may result from unsaturation of adsorption sites through the adsorption process overlapping or aggregation of adsorption sites (Xu et al., 2013). However, at a dosage above 100 mg of PP–AC, the removal percentage of Pb(II) is marginal. Experimental results, with regard to

RI PT

the 20 mL of aqueous Pb(II) solution, initial Pb(II) concentration of 100 mg/L, adsorbent dosage of 100 mg with particle size of 355 µm and agitating speed of 150 rpm for 2 h, produce the

TE D

M AN U

SC

optimal removal percentage of 82.6%.

Fig. 4. Effect of adsorbent dosage on Pb(II) removal.

EP

3.2.3. Contact time

From Fig. 5(a), it is seen that the Pb(II) uptake amount and removal efficiency increases

AC C

from 19.54 to 37.2 mg/g and 48.8 to 93.2%, respectively, with increasing time from 10 to 120 min and then becomes constant. Greater amounts of metal ions are adsorbed by PP–AC as the agitating time increases, but after a certain time of 120 min the metal removal efficiency remains constant due to saturated receptors on the surface of the PP–AC adsorbent. However, the minimum contact time of 120 min (2 h) is determined as the optimal contact time for PP–AC through agitating 20 mL of standard Pb(II) aqueous solution containing 200 mg/L of Pb(II) at a

16

ACCEPTED MANUSCRIPT 9021 pH level of 5 in the varied interaction time intervals of 5 to 180 min using 100 mg of PP–AC. It is observed that the removal percentage increased rapidly at the initial stages because more unsaturated surface and active sites are available on the adsorbent surface area. As the adsorption

RI PT

process proceeds, more Pb(II) ions are adsorbed onto the surface of PP–AC and, consequently, the number of available active sites decreases. Usually, the metal ions create a monolayer on the adsorbent surface. As a result, the adsorbent surface area becomes gradually exhausted, and the

SC

sorption capacity decreases. Based on the results, the maximum (93.22%) removal of Pb(II) by

indicating adsorption equilibrium.

M AN U

PP–AC was obtained after 2 h, and the uptake trend became downward and then steady after 2 h

3.2.4. Initial concentration of Pb(II) ions

The initial concentration of Pb(II) ions in the aqueous solution, as one of the affecting parameters for adsorption at equilibrium, was investigated considering a range of 10, 20, 50, 100

TE D

and 200 mg/L of Pb(II) (see Fig. 6(a)). Following 2 h of agitation of 100 mg PP–AC in 20 mL of Pb(II) solution with a speed of 150 rpm, the Pb(II) uptake amount increased from 1.8 to 28.8 mg/g, while the removal efficiency of Pb(II) decreased from 90.8 to 70.7% when the initial

EP

concentration was increased from 10 to 200 mg/L. Such a pattern can be predicted because the

AC C

higher initial concentration of metal ions intensifies the adsorption capacity (qe) initially, but as the process proceeds, the higher amount of adsorbate is confronted with a limited (constant) availability of active sites on the adsorbent surface. Therefore, more Pb(II) ions are left unabsorbed in the solution due to the powerful driving force from initial concentration to overcome the resistance to the mass transfer of ions between the aqueous solution and solid phase and saturation of the binding sites, and consequently, the adsorption efficiency decreases. Correspondingly, at a lower concentration, the ratio of metal ions over the adsorption surface is 17

ACCEPTED MANUSCRIPT 9021 low. Therefore, the metal ions quickly adhere to the available adsorption sites, resulting in the higher adsorption efficiency.

RI PT

3.2.5. Temperature The effect of temperature on sorption of Pb(II) ions in the aqueous solution was investigated considering a range of 25, 35, 50 and 100 mg/L of Pb(II) and following 2 h of

SC

agitation of 100 mg PP–AC in 20 mL of Pb(II) solution at a speed of 150 rpm. The results are presented in Fig. 7(a) at three temperatures. It can be seen that the removal efficiency of Pb(II)

M AN U

increased from 30.8%, 19.8% and 9% to 83.1%, 82.1% and 80.3% by increasing the initial concentration from 10 to 50 and 100 mg/L, respectively, while it decreased from 83.1 to 80.3% with the increase in the temperature from 25 °C to 50 °C. This decrease suggests that the adsorption process is an exothermic one. It has been suggested that the decrease in removal efficiency of Pb(II) with increased temperature was due to the tendency of Pb ions to escape

TE D

from the liquid phase to the bulk phase with an increase in temperature of the solution. In addition, this decrease is due to the major force (i.e. electrostatic interactions) involved in ion binding, which might be weakened because of increasing temperature from the exothermic

EP

electrostatic interactions (Gupta et al., 2011).

AC C

4. Adsorption kinetics

To analyse the kinetic parameters of an adsorption process, several established models

are available. Among them, the pseudo-first-order method of Lagergren and second-order method of Ho and Mackay (1998) for kinetic models are the most commonly used to evaluate metal adsorption from a liquid solution (Wang and Chen, 2009). The linear forms of the pseudofirst-order and second-order equations are represented as Eq. (6) and Eq. (7), respectively:

18

ACCEPTED MANUSCRIPT 9021 ln(qe − qt ) = ln qe − k1t ,

(6)

where qe and qt are the metal uptakes at equilibrium and at time t per unit mass of adsorbent

RI PT

(mg/g), and k1 is the reaction rate constant (min–1). qe can be determined from the intercept and k1 from the slope of the linear curve from a plot of ln(qe – qt) vs. time t. The pseudo-first-order

kinetic model assumption considers the rate of active site occupancy to be proportional to the

SC

number of empty sites.

M AN U

For the second-order model,

t  1  t + , = qt  k 2 qe2  qe

(7)

where qe and qt represent the metal uptakes (mg/g) at equilibrium and time t. The variable k2 is

TE D

the rate constant for the pseudo-second-order model (g/(mg min)). qe can be determined from the slope and k2 from the intercept of the linear curve from a plot of t/qt vs. time t. The adsorption mechanism of a sorbate onto the adsorbent follows three steps: film

EP

diffusion, pore diffusion and intraparticle transport. The slowest of the three steps controls the overall rate of the process. In general, for a batch system, pore diffusion and intraparticle

AC C

diffusion are often the rate-limiting steps, while film diffusion is more likely to be the ratelimiting step for a continuous flow system (Ghasemi et al., 2014b). The kinetic model known as the intraparticle-diffusion model is expressed by Eq. (8): q t = k i t1 / 2 + y ,

(8)

19

ACCEPTED MANUSCRIPT 9021 where qt is the amount of Pb adsorbed at time t (mg/g), ki is the initial rate of intraparticle diffusion (mg/(g min0.5)), and y is the intercept. The values of ki and y are obtained from the slopes (ki) and intercepts (y) of the plots of qt versus t1/2, respectively. The plots of qt vs. t1/2 give

RI PT

straight lines, while if two or more steps influence the sorption process, the data may exhibit multi-linear plots. The value of y gives an idea about the thickness of the boundary layer, as the greater the boundary layer effect, the larger the intercept (Ghasemi et al., 2014a).

SC

In addition, from the coefficient of determination (R2), the validity of the kinetic models

which are defined as:

2

1 N  qtmeas − qtcal  NSD = 100 ∑  , N − 1 i =1  qtmeas 

100 N qemeas − qecal ∑ q meas , N i =1 e i

TE D

ARE =

M AN U

was evaluated with the normalized standard deviation (NSD) and average relative error (ARE),

(9)

(10)

EP

where qtmeas and qtcal (mg/g) are experimental and calculated Pb adsorbed on PP–AC at time t, and N is the number of measurements made (Asgari et al., 2012). Smaller NSD and ARE values

AC C

indicate closer estimations of qt values.

20

ACCEPTED MANUSCRIPT 9021 Table 3. Comparison of kinetic models’ data calculated from the experiments. Model’s constants qe

cal

(mg/g)

38.31

(mg/g)

30.84

k1

0.025

2

Pseudo-first order

R

NSD ARE qecal (mg/g) k2 2

Pseudo-second order

Results

R

NSD

0.975 0.633 2.785 42.55 0.001

M AN U

ARE

RI PT

qe

meas

SC

Kinetic models

Intraparticle diffusion

0.992 0.204 1.581

(ki)1

0.388

y1

3.856

2

R

0.963

(ki)2

3.408

y2

116.2

2

0.908

TE D

R

The three mentioned kinetics models (Fig. 5(b), (c) and (d)) constants, correlation

EP

coefficients and error functions for sorption of Pb ions onto PP–AC are given in Table 3. It is observed that the adsorption kinetics follow the pseudo-second-order kinetic model better than

AC C

the pseudo-first-order and intraparticle-diffusion models from its higher correlation coefficient (R2 = 0.992) and its lower NSD and ARE values (0.20 and 1.58). This also suggests that the adsorption process could be controlled by chemical adsorption. The value of qecal obtained from the pseudo-second-order model is in better agreement with the value of qemeas determined experimentally than those obtained from the pseudo-first-order model. It can be seen from Fig. 5(d) that the plots for the intraparticle-diffusion model are not linear and the curves are divided into two portions: the first portion is boundary-layer diffusion (transference of the external 21

ACCEPTED MANUSCRIPT 9021 volume to the surface of the adsorbent), the second portion is the intraparticle diffusion (diffusion of Pb(II) ion to the adsorbent’s more internal sites) (Coelho et al., 2014).

RI PT

Similar reports have been presented in other studies of either Pb(II) uptake using bioadsorbents, such as periwinkle shell (Badmus et al., 2007), almond shell and apricot stone (Demirbas et al.,

AC C

EP

TE D

M AN U

SC

2004), fig sawdust (Ghasemi et al., 2014) and Rosa canina L leaves (Ghasemi et al., 2014b).

Fig. 5. (a) Effect of contact time on Pb(II) removal, (b) pseudo-first-order, (c) second-order and (d) intraparticle-diffusion model plots.

22

ACCEPTED MANUSCRIPT 9021

5. Adsorption isotherms An equilibrium study is a crucial part of any adsorption process because it explains the adsorption isotherms, interaction between metal ions and active sites on the adsorbent surface

RI PT

and capacity of an adsorbent to demonstrate its surface capability. In the current study, the equilibrium results of Pb(II) uptake on PP–AC were correlated using two established isotherm

SC

models, those of Langmuir and Freundlich.

The Langmuir isotherm is derived based on the assumption that all existing active sites

M AN U

are equivalent without any preference and the optimum uptake occurs due to a saturated monolayer of metal ions on the adsorbent surface. It is assumed that the adsorption energy is constant and there is no movement of adsorbate in the plane of the surface (Aman et al., 2008). In contrast, the Freundlich isotherm (El-Ashtoukhy et al., 2008) is suitable for non-ideal

TE D

adsorption processes onto a heterogeneous surface.

A linear equation of the Langmuir isotherm is expressed below:

(11)

EP

Ce = Ce + 1 , qe qm qm K L

AC C

where qe and Ce (mg/L) are the amount of solute adsorbed per unit weight of adsorbent and equilibrium concentration of solute in bulk solution. qm (mg/g) is the maximum monolayer adsorption capacity and KL (L/mg) is a constant related to the free energy of adsorption. The Langmuir constants qm and KL were calculated from the slope and intercept of the plot, respectively, from the result of isotherm experiments. The separation factor, RL, is a crucial dimensionless characteristic of the Langmuir model that defines the feasibility of the isotherm, as expressed by Eq. (12). 23

ACCEPTED MANUSCRIPT 9021

RL =

1 1 + K L C0

(12)

RI PT

The values of RL represent (RL > 1) an unfavourable isotherm, (RL = 1) linear isotherm, (0 < RL < 1) a favourable and RL = 0 irreversible isotherm (Yargic et al., 2015).

The linearized equation for the Freundlich isotherm is expressed below:

SC

1 log qe = log k F +   log Ce , n

(13)

M AN U

where kF (mg/(g(L/mg)1/n)) is the Freundlich constant representing adsorption capacity (bond strength), 1/n is the empirical factor representing the favourability of adsorption and ‘n’ constant represents the bond energies for the metal ion, where values n > 1 indicate favourable adsorption conditions. kF and 1/n were calculated from the intercept and slope of the graph of log qe vs. log

TE D

Ce, respectively. The Freundlich model was plotted as a straight line together with the coefficient of determination, R2 (Tong et al., 2011).

EP

The conformity between the experimental data and the calculated data was tested by the coefficients of determination (R2). Besides the value of correlation coefficients, the applicability

AC C

of the adsorption isotherm to describe the adsorption process was validated by the root mean square error (RMSE) and the chi-square test (χ2), which can be described as:

RMSE =

1 N meas (qe − qecal ) 2 , ∑ N − 2 i=1

(qemeas − qecal ) 2 , χ =∑ qemeas i =1

(14)

N

2

(15)

24

ACCEPTED MANUSCRIPT 9021 where qemeas is the observation from the batch experiment at pint i, qecal is estimated from the isotherm for the corresponding qemeas and N is the number of observations in the experimental

estimations of qe values.

SC

Table 4. Isotherm constants for adsorption of Pb(II) onto PP–AC.

Freundlich

qm (mg/g)

38.31

KL (L/mg)

0.047

R2

0.989

RL

0.112

RMSE

5.790

χ

2.625

kF (mg/g)

2.108

n

1.464

R2

0.973

RMSE

15.11

χ2

24.22

TE D

M AN U

Langmuir

2

RI PT

isotherm (Ramavandi et al., 2014). The smaller RMSE and χ2 values reveal more accurate

Figs. 6(b) and (c) show the linearized forms of the Langmuir and Freundlich models fitted to the

EP

experimental data, respectively. The parameters derived by fitting the two isotherm models are

AC C

presented in Table 4. The results demonstrate that the experimental data are better fitted by the Langmuir isotherm model than the Freundlich isotherm model. As can be seen, on the basis of R2 values, both the Langmuir and Freundlich isotherm fit the experimental data. The results from the values of the RMSE and χ2 tests in the Langmuir isotherm were lower than in the Freundlich model, showing more compatibility with the Langmuir model. The maximum adsorption capacity (qm) obtained for PP–AC adsorbent is 38.31 mg/g. On the other hand, the Langmuir RL = 0.112 value from the experimental data (0 < RL < 1) demonstrates the favourable adsorption of 25

ACCEPTED MANUSCRIPT 9021 Pb(II) onto PP–AC. The Freundlich model describes more accurately the intraparticle metal uptake onto heterogeneous surfaces like PP–AC as activated carbon adsorbent (Cechinel et al., 2014). Moreover, the value of n > 1 from the correlation of the experimental data with the

RI PT

Freundlich isotherm (n = 1.464) shows favourable Pb(II) biosorption using PP–AC (Hameed, 2008). The value of R2 shows the overall goodness of fit of the experimental results with the

AC C

EP

TE D

M AN U

SC

isotherm models (El-Ashtokhy et al., 2008).

Fig. 6. (a) Effect of initial concentration on Pb(II) removal. (b) Langmuir and (c) Freundlich isotherm model plots.

26

ACCEPTED MANUSCRIPT 9021

6. Adsorption thermodynamics In addition to the adsorption kinetics and equilibrium isotherm studies, the sorption thermodynamics, i.e. enthalpy (∆Ho), entropy (∆So) and Gibbs free energy (∆Go), are very

RI PT

important parameters to predict and identify the adsorption mechanism (Ghasemi et al., 2015). In practice, thermodynamic parameters can be a good indication for the application of a desired

SC

process. The Gibbs free energy can be calculated using Eq. (16). ∆ G o = − RT ln K c ,

(16)

M AN U

where ∆Go is the change in standard free energy, R is the universal gas constant (8.314 J mol–1 K–1), T is the absolute temperature and Kc is the equilibrium constant, which can be determined from the slope of plotting ln(qe/Ce) versus Ce at different temperatures. Eq. (17) expresses the

∆S o ∆H o . − R RT

ln K c =

TE D

relationship between Gibbs free energy, entropy and enthalpy change (Ghaedi et al., 2014):

(17)

EP

The values of activation energy (Ea) and sticking probability (S*) were calculated from the experimental data by using a modified Arrhenius-type equation related to surface coverage

AC C

(θ) as follows (Hajati et al., 2014):

S * = (1 − θ )e−( Ea / RT ) .

(18)

The value of θ can be calculated from the following equation:

θ = (1 −

Ce ). C0

(19)

27

ACCEPTED MANUSCRIPT 9021 The sticking probability, S*, is a function of the adsorbate–adsorbent system under investigation, its value lies in the range 0 < S* < 1 and is dependent on the temperature of the system. The activation energy and sticking probability were estimated from a plot of ln(1 – θ)

RI PT

versus 1/T.

The thermodynamic parameters and influence of temperature on the uptake capacity on PP–AC for the adsorption of Pb(II) are illustrated in Table 5 and Fig. 7. The negative values of

SC

∆Go (–13.18, –13.44 and –13.77 kJ/mol) confirmed that the adsorption of Pb ion onto PP–AC

M AN U

adsorbent was spontaneous and thermodynamically favourable. The ∆Go was found to become more negative with an increase of temperature, which demonstrates the chance of any chemical reaction happening during the adsorption of Pb(II) onto PP–AC and the more negative value expresses the more energy favourable adsorption process (Gilbert et al., 2011). The negative value of ∆Ho (–6.233 kJ/mol) indicates that the adsorption process is exothermic and the positive

TE D

value of ∆So (0.022 kJ/(mol K)) indicates the increase in randomness at the solid–solution interface (Kumar and Barakat, 2013). The activation energy, Ea, calculated from the slope of the plot was found to be 4.269 kJ/mol for the adsorption of Pb ions onto PP–AC. The value of S*

AC C

the system.

EP

was found to be 0.944, which lies in the range 0 < S* < 1 and is dependent on the temperature of

Table 5. Thermodynamic constants from the adsorption of Pb(II) onto PP–AC. T (K) 298

∆Go (kJ/mol)

∆Ho (kJ/mol)

∆So (kJ/(mol K))

Ea (kJ/mol)

S*

0.022

4.269

0.944

–13.18

308

–13.44

328

–13.77

–6.233

28

ACCEPTED MANUSCRIPT

SC

RI PT

9021

M AN U

Fig. 7. (a) Effect of temperature on Pb(II) removal. (b) ln KL versus 1/T for evaluation of enthalpy and entropy change of the sorption process.

7. Comparison of sorption capacity of Pb(II) onto different bioadsorbents The adsorption capacities of Pb(II) using different types of bioadsorbents are shown in Table 6. A comparison of the reported results clearly shows that the capability of PP peel waste

TE D

to remove Pb(II) from contaminated water is generally more efficient than the other crop-based bioadsorbents reported. Moreover, using an industrial wastewater sample from an electroplating industry in Johor Bahru (Malaysia), PP–AC was able to remove more than 90% of Pb(II) content

EP

from the effluent, clearly confirming the capability of synthesised PP–AC for metal removal in

AC C

practical applications.

29

ACCEPTED MANUSCRIPT 9021 Table 6. Adsorption capacity of Pb(II) by different agrowastes. Pb(II) removal (mg/g)

Reference

Bagasse fly ash

2.50

Gupta and Ali, 2004.

Sugar cane bagasse

7.30

Lara et al., 2010.

Oriza sativa husk

8.60

Carica papaya leaf powder

11.3

Cereal chaff

12.5

Lalang leaf powder

13.50

Olive tree pruning waste

22.79

Pine cone

27.53

Papaya peel

38.31

Walnut wood activated carbon

41.66

RI PT

Adsorbent

Zulkali et al., 2006. Raju et al., 2012. Han et al., 2005.

Hanafiah et al., 2006.

SC

Blazqez et al., 2011.

Momcilovic et al., 2011. This study.

M AN U

Ghaedi et al., 2015.

8. Pb(II) desorption process and adsorbent regeneration Hydrochloric acid (HCl) was chosen as the desorbing agent due to its low cost and high

TE D

removal efficiency reported in the literature. HCl affects the adsorption process in a way that releases protons into the solution, allowing the replacement of Pb(II) ions by H+ on the PP–AC surface. Therefore, the PP–AC adsorption sites turn out to be fully protonated and ready for the

EP

further uptake process. In the first desorption cycle, the recovered concentration was observed ≥97% using 100 mg of PP–AC and the final concentration of Pb(II) remaining in the solution

AC C

(200 mg/L) after the third cycle was found to be 25.72 mg/g. Considering the Pb(II) solution concentration of 200 mg/L at pH of 5 using 100 mg of

PP–AC, the regenerating capacity of the adsorbent was observed as 97% and 95.3% for the first and second cycles. The reusing capability then decreased dramatically (≥65%) for the third cycle, where the desorption process might be influenced by saturation of the desorbent solution.

30

ACCEPTED MANUSCRIPT 9021 To overcome the problem, one possibility could be to increase the volume or concentration of the desorbent agent.

RI PT

Technically, the recovered Pb(II) ions from the PP–AC can be recycled and employed again by industry to comply significantly with the sustainable development notion. To do so, one of the existing techniques such as electrolysis can be utilized to convert the Pb(II) ions into

SC

elemental lead.

9. Conclusions

M AN U

The adsorption efficiency of Pb(II) using PP–AC bioadsorbent was investigated. There was no record in the literature for the biosorption of Pb(II) using the activated carbon of papaya peel agricultural waste. The results and methodology from the Pb(II) uptake onto modified PP was found to be in good agreement (in most of the cases even with better results) in comparison

TE D

with application of other crop-based adsorbents reported in the literature. The surface characteristic of pristine PP was improved after treatment with phosphoric acid due to higher numbers of surface functional groups on the PP–AC surface enhancing the adsorption and

EP

desorption processes. At pH = 5, 100 mg of PP–AC removed 93.22% of Pb(II) from 20 mL of 200 mg/L Pb(II) solution. It is observed that the minimum time to reach equilibrium decreased in

AC C

line with increasing the initial concentration of Pb(II) using constant adsorbent dosage. However, the optimal contact time of 2 h in this study was determined by altering other adsorption parameters such as pH or adsorbent dosage. The pseudo-second-order model well fitted the experimental results and the equilibrium kinetic studies accurately proved the high initial rate of the biosorption process.

31

ACCEPTED MANUSCRIPT 9021 The sorption equilibrium of Pb(II) onto PP–AC has shown high correlation and good fit with the Langmuir isotherm and the maximum adsorption capacity for PP–AC was 38.31 mg/g at

favourable and spontaneous with an exothermic nature.

RI PT

298 K. The thermodynamic studies found the sorption of Pb(II) onto PP–AC feasible, energy

Using 1 M HCl has shown efficient Pb(II) desorption from the exhausted PP–AC with the

SC

desorption percentage of >97% requiring a minimum time of 1 h to reach desorption equilibrium. However, the Pb(II) desorption capacity reduced for the further cycles, probably due to saturated

M AN U

desorption solution, but a recovery percentage of less than 65% was not observed in all cycles. Furthermore, the PP–AC adsorbent can be reused for three cycles with a regeneration efficiency of >65%.

To conclude, this research proves that, in suitable conditions, PP is an environmentally

TE D

friendly, economical and efficient bioadsorbent for Pb(II) removal from wastewater. In upcoming work, the authors are studying the impact of other types of chemical modification of PP to enhance further the uptake capacity through improvement of the adsorbent surface

EP

characteristics.

AC C

Acknowledgements

The authors wish to acknowledge financial supports of this research received from the Fundamental Research Grant Scheme from the Malaysia Ministry of Higher Education through the research program number R.J130000.7809.45488 and the UNESCO/PhosAgro/IUPAC grant in Green Chemistry by contract number 4500254540. The authors also greatly appreciate the Universiti Teknologi Malaysia (UTM) for the infrastructures and facilities provided for this research. 32

ACCEPTED MANUSCRIPT 9021

Reference

RI PT

Abbaszadeh, S. and Hassim, M.H. 2014. Comparison of methods assessing environmental friendliness of petrochemical process design. J. Clean. Prod.17, 110-117. Abbaszadeh S., Wan Alwi S.R., Ghasemi N., Nodeh H.R., Webb C., Muhamad I.I., 2015, Use of pristine papaya peel to remove pb(ii) from aqueous solution, Chemical Engineering Transactions, 45, 961-966.

SC

Abdolahi, A., Ngo, H.H., Guo, W.S., Lee, D.J., Tung, K.L., Wang, X.C., 2014. Development and evaluation of a new multi-metal binding bioadsorbent. Bioresour. Technol. 160, 98-106.

M AN U

Aman, T., Kazi, A.A., Sabri, M.U., Banoa, Q., 2008. Potato peels as solid waste for the removal of heavy metal copper(II) from wastewater/ industrial effluent. Collides surfaces B; Biointerface. 63, 116-121. Asgari, Gh., Roshani, B., Ghanizadeh. Gh., 2012. The investigation of kinetic and isotherm of fluoride adsorption onto functionalize pumice stone. Journal of Hazardous Materials. 217– 218, 123– 132.

TE D

Badmus, M.A.O., Audu, T.O.K. and Anyata, B.U., 2007. Removal of lead ion from industrial wastewaters by activated carbon prepared from periwinkle shells. Turkish J. Eng. and Environ. Sci. 31, 251-263. Blazqez, G., Martin-Lara, M.A., Tenorio, G., Calero, M., 2011. Batch biosorption of lead from aqueous solutions by olive trees pruning waste: equilibrium, kinetics and thermodynamic study. Chem. Eng. J. 44, 1925-1936.

EP

Cechinel, M.A.P., Ulson de Souza, S.M.A.G.U., Ulson de Souza, A.A., 2014.Study of lead(II) adsorption onto activated carbon originated from cow bone. J. Clean. Prod. 65, 342-349.

AC C

Coelho, G.F., Gonçalves Jr. A.C., Tarley, C.R.T., Casarin, J., Nacke, H., Francziskowski. M.A. 2014. Removal of metal ions Cd (II), Pb (II), and Cr (III) from water by the cashew nut shell Anacardium occidentale L. Ecological Engineering. 73, 514–525. Demirbas, E., Kobya, M., Senturk, E. and Ozkan, T., 2004. Adsorption kinetics for the removal of Cr(IV) from aqueous solutions on the activated carbons prepared from agricultural wastes. Water Resources. 30(4), 533-539. El-Ashtoukhy, E.S.Z., Amin, N.K., Abdelwahab, O., 2008. Removal of lead (II) and copper (II) from aqueous solution using pomegranate peel as a new adsorbent. Desalination. 223, 167-173. FAOStat3 database, World Production Report, 2011. , Assessed on: 5 October 2015. 33

ACCEPTED MANUSCRIPT 9021 Ghaedi, M., Golestani Nasab, A., Khodadoust, S., Rajabi, M., Azizian, S. 2014. Application of activated carbon as adsorbents for efficient removal of methylene blue: Kinetics and equilibrium study. Journal of Industrial and Engineering Chemistry. 20, 2317–2324.

RI PT

Ghaedi, M., Danaei Ghazanfarkhani, M., Khodadoust, S., Sohrabi, N., Oftade, M. 2014. Acceleration of methylene blue adsorption onto activated carbon prepared from dross licorice by ultrasonic: Equilibrium, kinetic and thermodynamic studies. Journal of Industrial and Engineering Chemistry. 20, 2548–2560.

SC

Ghaedi, M., Mazaheri, H., Khodadoust, S., Hajati, S., Purkait. M.K. 2015. Application of central composite design for simultaneous removal of methylene blue and Pb2+ ions by walnut wood activated carbon. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. 135, 479–490.

M AN U

Ghasemi, M., Mashhadi, S., Asif, M., Tyagi, I., Agarwal, S., Gupta, V.K. 2015. Microwaveassisted synthesis of tetraethylenepentamine functionalized activated carbon with high adsorption capacity for Malachite green dye. J. Mol. Liq. http://dx.doi.org/10.1016/j.molliq.2015.09.048 Ghasemi, M., Naushad, M., Ghasemi, N., Khosravi-fard, Y. 2014. A novel agricultural waste based adsorbent for the removal of Pb(II) from aqueous solution: Kinetics, equilibrium and thermodynamic studies. Journal of Industrial and Engineering Chemistry. 20, 454– 461.

TE D

Ghasemi, M., Naushad, M., Ghasemi, N., Khosravi-fard, Y. 2014. Adsorption of Pb(II) from aqueous solution using new adsorbents prepared from agricultural waste: Adsorption isotherm and kinetic studies. Journal of Industrial and Engineering Chemistry. 20, 2193– 2199.

EP

Ghasemi, M., Ghasemi, N., Zahedi, G., Alwi, S.R.W., Goodarzi, M., Javadian, H. 2014. Kinetic and equilibrium study of Ni(II) sorption from aqueous solutions onto Peganum harmalaL, Int. J. Environ. Sci. Technol. 11, 1835–1844.

AC C

Gilbert, U.A., Emmanuel, I.U., Adebanjo, A.A., Olalere, G.A., 2011. Biosoptive removal of Pb(II) and Cd(II) onto novel biosorbent: defatted carica papaya seeds. Biomass and Bioenergy. 35, 2517-2525. Gupta, V.K., Ali, I., 2004. Removal of lead and chromium from wastewater using bagasse fly ash- a sugar industry waste. J. Colloid Interface Sci. 271, 321-328. Gupta, V.K., Gupta, B., Rastogi, A., Agarwal, S., Nayak. A. 2011. A comparative investigation on adsorption performances of mesoporous activated carbon prepared from waste rubber tire and activated carbon for a hazardous azo dye—Acid Blue 113. Journal of Hazardous Materials. 186, 891–901. Hajati, S., Ghaedi, M., Karimi, F., Barazesh, B., Sahraei, R., Daneshfar. A. 2014. Competitive adsorption of Direct Yellow 12 and Reactive Orange 12 on ZnS:Mn nanoparticles loaded 34

ACCEPTED MANUSCRIPT 9021 on activated carbon as novel adsorbent. Journal of Industrial and Engineering Chemistry. 20, 564–571. Han, R., Zhang, J., Zou, W., Shi, J., Liu, H., 2005. Equilibrium biosorption isotherm for lead ion on chaff. J. Hazard. Mater. B125, 266-271.

RI PT

Hameed, B.H., 2008. Equilibrium and kinetic studies of methyl violet sorption by agricultural waste. J. Hazard. Mater. 154 (1), 204-212. Hameed, B.H., 2009. Evaluation of papaya seeds as a novel non-conventional low cost adsorbent for removal of methylene blue. J. Hazard. Mater. 162, 939-944.

SC

Hanafiah, M.A.K., Ibrahim, S.C., Yahya, M.Z.A., 2006. Equilibrium adsorption study of lead ions onto sodium hydroxide modified Lalang (Imperata Cylindrica) leaf powder. J. Appl. Sci. Res. 2, 1169-1174.

M AN U

Hashem, A., Abdel-Halim, E.S., El-Tahlawy, K.F., Hebeish, A., 2005. Enhancement of adsorption of Co(II) and Ni(II) ions onto peanut hulls though esterification using citric acid. Adsorp. Sci. Technol. 23, 367-380. Hashemian, S. and Salimi, M., 2012. Nano composite a potential low cost adsorbent for removal of cyanine acid. Chem. Eng. J. 188, 57-63. Ho, Y.S. and Mckay, G., 1998. Psuedo-second order model for sorption process. Chem. Eng. J. 70, 115-124.

TE D

Hossain, M.A., Ngo, H.H., Guo, W.S., Ngheim, L.D., Hai, F.I., Vigneswaran, S., Nguyen, T.V. 2014. Competitive adsorption of metals on cabbage waste from multi-metal solutions. Bioresour. Technol. 160, 79-88.

EP

Ila (international lead association) database, World Lead Production and Statistics, 2012. < http://www.ila-lead.org >. Assessed on. 5 August 2015.

AC C

Ioannidou, O., Zabaniotou, A. 2007. Agricultural residues as precursors for activated carbon production—A review. Renewable and Sustainable Energy Reviews. 11, 1966–2005 Kaouah, F., Boumaza, S., Berrama, T., Trari, M., Bendjama, Z., 2013. Preparation and characterization of activated carbonfrom wild olive cores (oleaster) by H3PO4 for the removalof basic Red 46. J. Clean. Prod. 54, 296-306. Kumar, R., Barakat, M.A. 2013. Decolourization of hazardous brilliant green from aqueous solution using binary oxidized cactus fruit peel. Chemical Engineering Journal. 226, 377– 383 Lara, M.A.M., Rico, I.L.R., Vicete, G.B., Garcia, G.B., Hoces, M.C., 2010. Modification of sportive characteristics of Sugarcane bagasse for removing lead from aqueous solutions. Desalination. 256, 58-63.

35

ACCEPTED MANUSCRIPT 9021 Li, Y., Du, Q., Wang, X., Zhang, P., Wang, D., Wang, Z., Xia. Y. 2010. Removal of lead from aqueous solution by activated carbon prepared from Enteromorpha prolifera by zinc chloride activation. Journal of Hazardous Materials. 183, 583–589

RI PT

Li, Y.H., Xu, C.L., Wei, B.Q., Zhang, X.F., Zhen, M.X., Wu, D.H. and Ajayan, P.M., 2002. Selforgnized ribbons of aligned carbon nano-tubes. J. Chem. Mater. 148, 483-485. Lian, L., Cao, X., Wua, Y., Lou, D., Han, D., 2013. Synthesis of organo-functionalized magnetic microspheres and application for anionic dye removal, J. Taiwan Institute of Chem. Eng. 44, 67–73.

SC

Momcilovic, M.,Purenovic, M., Bojic, A., Zarubica, A., Randelovic, M., 2011. Removal oflead(II) ions from aqueous solutions by adsorption onto pine cone activated carbone. Desalination 276 (1-3), 53-59.

M AN U

Nwofla, G., Ojimelukwe, P., Eji, C., 2012. Chemical composition of leaves, fruit pulp and seeds in some Carica papaya (L) morphotypes. Int. J. Arom. Plants. 2(1), 200-206. Ramavandi, B., Asgari, Gh., Faradmal, J., Sahebi, S., Roshani, B., 2014. Abatement of Cr (VI) from wastewater using a new adsorbent, cantaloupe peel: Taguchi L16 orthogonal array optimization. Korean J. Chem. Eng. 31(12), 2207-2214. Rama Raju, D.S.S., Rao, V.N., Prasad, P.R., and Babu, N.C., 2012. Sorption of lead (II) ions from wastewater using carica papaya leaf powder. Int. J. Eng. Advance. Technol. 2(6), 1577-1581.

TE D

Rama Raju, D.S.S., Ravi, Kiran G.A., Rao, V.N., 2013. Comparison studies on biosorption of lead (II) from an aqueous solution using anacardium occidentale and carica papaya leaves powder. Int. J. emerging trends in engineering and development. 3, 273-283.

EP

Regalbuto, J.R., Robles, J.O., 2004. The Engineering of Pt/ Carbon Catalyst Preparation for Application on Proton Exchange Fuel Cell Membrane (PEFCM). University of Illinois at Chicago, USA. REU 2004 summer program. Final report.

AC C

Pino, G.H., Mesquita, L.M.S., Torem, M.L., Pinto, G.A.S., 2006. Biosorption of cadmium by green coconut shell powder. Miner. Eng. 19(5), 380-387. Shao, D.D., Jiang, Z.Q., Wang, X.K., Li, J.X., Meng, Y.D., 2009. Plasma induced grafiting carboxymethyl cellulose on multiwalled carbon nanotubes for the removal of UO22+ from aueous solution. J. Phys. Chem. B 113, 860-864. Shao, D.D., Jiang, Z.Q. and Wang, X.K., 2010. SDBS modified XC-72 carbon for removal of Pb(II) from aqueous solutions. Plasma Process and Polymer. 7, 552-556. Tong, K.S., Jain, Kassim, M., Azraa, A., 2011. Adsorption of copper ion from its aqueous solution by novel bioadsorbent Uncaria gambir: Equilibrium, kinetics, and thermodynamic studies. Chem. Eng. J. 170, 145-153.

36

ACCEPTED MANUSCRIPT 9021 Wan Ngah, W.S. and Hanafiah, M.A.K.M., 2008. Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: A review. Bioresour. Technol. 99, 3935-3948.

RI PT

Wang, J. and Chen, C., 2009. Bioadsorbents for heavy metals removal and their future. Biotechnol. Advanc. 27, 195-226. WHO, 1998. Environmental health criteria, No.200, Lead exposure. Ch-1211, Geneva27, Switzerland.

SC

Xu, P., Zeng, G., Huang, D., Hua, S., Feng, C., Lai, C., Zhao, M., Huang C., Li, N., Wei, Z., Xie, G. 2013. Synthesis of iron oxide nanoparticles and their application in Phanerochaete chrysosporium immobilization for Pb(II) removal. Colloids and Surfaces A: Physicochem. Eng. Aspects. 419, 147– 155.

M AN U

Xu, L., Pang, M., Kano, N. and Imaizumi, H., 2014. Removal of U(VI) from aqueous solution using carbon modified with nitric acid. J. Chem. Eng. Japan. 47(4), 319-323. Yargic, A.S., Yarbay Sahin, R.Z., Ozbay, N., Onal, E., 2015. Assessment of toxic copper(II) biosorption from aqueous solution by chemically- treated tomato waste. J. Clean. Prod. 88, 152-159. Zahra, N., 2012. Lead removal from water by low cost adsorbents: A review. Pak. J. Anal. Environ. Chem. 13(1), 1-8.

TE D

Zulkali, M.M.D., Ahmed, A.C., Norulakmal, N.H., 2006. Oriza Sativa husk as heavy metal adsorbent: optimization with lead as model solution. Bioresour. Technol. 97, 21-25.

AC C

EP

Zuo, S., Liu, J., Yang, J., Cai, X., 2009. Effects of the crystallinity of lignocellulosic material on the porosity of phosphoric acid-activated carbon. Carbon. 47, 3574–3584.

37

ACCEPTED MANUSCRIPT 9021

Appendices Appendix 1. EDX analysis of PP–AC before adsorption.

EP

TE D

M AN U

SC

RI PT

(a)

AC C

Fig. A.1. EDX mapping of PP–AC before adsorption.

38

ACCEPTED MANUSCRIPT 9021

TE D

M AN U

SC

RI PT

Appendix 2. EDX analysis of raw PP.

AC C

EP

Fig. A.2. EDX mapping analysis of raw PP.

39

ACCEPTED MANUSCRIPT 9021

TE D

M AN U

SC

RI PT

Appendix 3. EDX analysis of PP–AC after adsorption.

AC C

EP

Fig. A.3. EDX mapping analysis of Pb–PP–AC.

40

ACCEPTED MANUSCRIPT 9021 Appendix 4. XRD analysis of PP–AC.

RI PT

__ PP-AC

M AN U

SC

__ Carbon C

AC C

EP

TE D

Fig. A.4. XRD analysis of PP–AC.

41

ACCEPTED MANUSCRIPT 9021

List of Tables Table 1. Papaya fruit adsorbent contents.

RI PT

Table 2. Elemental analysis and BET characterization analysis of the pristine PP and PP-AC. Table 3. Comparison of kinetic models data calculated from the experiments.

SC

Table 4. Isotherm constants for the adsorption of Pb(II) onto PP-AC.

M AN U

Table 5. Thermodynamic constants from the adsorption of Pb(II) onto PP-AC. Table 6. Adsorption capacity of Pb(II) by different agro-wastes.

List of Figures

TE D

Figure 1. FESEM (left) and SEM (right) images of raw-PP (a, d), PP-AC (b, e) a and Pb - PP-AC (c, f).

EP

Figure 2. FTIR spectra PP-raw, PP-AC and Pb - PP-AC.

AC C

Figure 3. Effect of pH on Pb(II) removal. Figure 4. Effect of adsorbent dosage on Pb(II) removal (a) Figure 5. (a) Effect of contact time on Pb(II) removal (b), Pseudo-first-order (c), second-order (d) and; intra particle diffusion model plots. Figure 6 (a) Effect of initial concentration on Pb(II) removal. (b) Langmuir and; (c) Freundlich isotherm models plots. 42

ACCEPTED MANUSCRIPT 9021

Figure 7. (a) Effect of temperature on Pb(II) removal (b) ln KL versus 1/T for evaluation of

SC

RI PT

enthalpy and entropy change of the sorption process.

M AN U

List of Appendices Fig. A.1. EDX mapping of PP-AC before adsorption. Fig. A.2. EDX mapping analysis of raw PP.

TE D

Fig. A.3. EDX mapping analysis PP-AC Pb(II) loaded (Pb-PP-AC).

AC C

EP

Fig. A.4. XRD analysis of PP–AC.

43

ACCEPTED MANUSCRIPT

Research Highlights Activated carbon papaya peel (PP-AC) has high Pb(II) adsorption capacity (38.31 mg/g).

•

Optimum pH, adsorbent dosage, agitating time, initial concentration and contact time are presented.

•

Best equilibrium isotherms and kinetic models are evaluated.

•

The Pb (II) biosorption from PP-AC is feasible, spontaneous with exothermic nature.

AC C

EP

TE D

M AN U

SC

RI PT

•