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Asian Journal of Applied Chemistry Research 1(1): 1-9, 2018; Article no.AJACR.41300

Isotherm Studies of Adsorption of Methylene Blue by Palm Kernel Shell Oladokun Benjamen ‘Niran1*, Salaudeen Abdulwasiu Olawale2 and Utam John Ushie1 1

University of Abuja, Abuja, Nigeria. National Mathematical Centre, Sheda-Kwali Abuja, Nigeria.

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Authors’ contributions This work was carried out in collaboration between all authors. Author SAO designed the study, performed the statistical analysis. Author OBN wrote the protocol and wrote the first draft of the manuscript. Authors SAO, OBN and UJU managed the analyses of the study. Authors SAO and OBN managed the literature searches. All authors read and approved the final manuscript. Article Information DOI: 10.9734/AJACR/2018/41300 Editor(s): (1) Olalekan David Adeniyi, Department of Chemical Engineering, Federal University of Technology, PMB 65, Minna, Nigeria. (2) Endang Tri Wahyuni, Professor, Department of Chemistry, Gadhah Mada University, Indonesia. Reviewers: (1) Atiya Firdous, Jinnah University for Women, Pakistan. (2) Farid I. El-Dossoki, Port Said University, Egypt. (3) Ünal Geçgel, Trakya University, Turkey. (4) Nobuaki Tanaka, Shinshu University, Japan. (5) Muhammad Raziq Rahimi Kooh, Brunei Darussalam. Complete Peer review History: http://www.sciencedomain.org/review-history/24768

Original Research Article

Received 12th March 2018 Accepted 21st May 2018 Published 25th May 2018

ABSTRACT The main aim of this work is determine the feasibility of palm kernel shell (PKS) with phosphoric acid impregnation to biosorb methylene blue (MB) from aqueous solution by carrying out isotherm studies of the process. The influence of various factors such as contact time, initial dye concentration, adsorbent dosage, pH of dye solution and temperature were investigated in a batch adsorption technique. Result showed that adsorption of methylene blue (MB) dye was favourable at acidic pH. The percentage adsorption was found to increase with time of agitation, temperature, and mass of adsorbent but decreased with increase in initial MB concentration. In order to obtain a suitable model for the MB adsorption process, obtained data were fitted into different isotherm models like Langmuir and Freundlich models. Results showed that Freundlich adsorption isotherm model best describe MB adsorption onto palm kernel shell (PKS). _____________________________________________________________________________________________________ *Corresponding author: Email: [email protected];

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

Keywords: Adsorption; methylene blue; palm kernel shell; isotherm. damage or retardation of their catalytic abilities. Organic dyes are an inherent part of many industrial effluents and require an efficient method of disposal. There are numerous conventional techniques of removing dyes including coagulation and flocculation, membrane filteration, oxidation or ozonation and precipitation. Activated carbon has been extensively used as an adsorbent in the removal of dye from waste water due to their micro porous structure, large surface area and high sorption ability [6]. The above techniques are expensive and large part of the cost is associated with high cost of maintaining the techniques and cost of chemicals. Hence, the use of indigenous techniques and locally sourced low-cost materials are imperative and seem to be the brightest solution to the ever increasing challenges of wastewater treatment. Adsorption is a process whereby molecules of gas, liquid, or dissolved solids adhere to a surface. This process creates a thin layer of the adsorbed material (atoms or molecules being adsorbed) onto the surface of the adsorbing material. Just like surface tension, adsorption is as a result of surface energy [7]. In a bulk material, all the bonding requirements (be they ionic, covalent, or metallic) of the component atoms of the material are filled by other atoms in the material. Growing interest in finding new materials for adsorption treatment has developed many researches on materials that have low or no values such as water fern [8], agrowastes [9,10], yeast [11,12], fungus [13], clay [14] and mud [15]. In addition to good removal of pollutants from aqueous solution, these materials are abundant, environmental friendly and low cost, making adsorption treatments to be more attractive than the conventional treatments such as photodegradation [16] and catalytic degradation [17].

1. INTRODUCTION In Africa and some other developing countries, availability of safe drinking water is a sustainability issue. Most domestic and industrial activities depend greatly on supply of clean water. Water sources available to most developing countries are rivers, natural ponds, crack rocks and rainfall. In few areas there are underground water supplies through boreholes and water distribution tankers. A common feature about these water bodies is that they are in some ways contaminated (polluted) by heavy metals discharged from industries [1], dyes and textile industry as well as the rocky pathways through which they discharge to the open. Dyes are extensively used either as a minor or major components industries such as textiles, rubber, plastics, printing, leather and cosmetics among several others to impart color to their products. As a result, large amount of colored wastewater are produced. There are more than 10,000 commercially available dyes with over 79105 tonnes of dyestuff produced annually. On average, 2% of dyes produced annually end up being discharged as industrial effluents from related industries [2]. Textile industry tops various industries in usage of dyes for coloration of fiber. Textile industries consume as high as 107 kg/year of dye, with about nine-tenth of this amount ending up on fabrics. As a result, more than 1,000 tonnes/year of dyes are discharged into waste streams by the textile industry worldwide [3]. Discharge of dye-bearing wastewater into water bodies poses serious danger to the aquatic life (flora and fauna), food web and can destroy the aesthetic nature of the environment. Dyes can have intense and/or chronic effects on both exposed organisms and environment depending on the extent of exposure and dye concentration. According to Mishra and Tripathy (1993), dyes can lead to allergic dermatitis, skin irritation, cancer and mutation among several others. Due to the chemical stability and low biodegradability of dyes, conventional biological wastewater treatment systems are inefficient in treating dye wastewater [4].

Wang et al. (2008) described the adsorption capacity and mechanism of malachite green and MB adsorption onto rice bran and wheat bran. Rice bran and wheat bran are low-cost byproducts. The adsorption of both basic dyes was found to be highly dependent on changes in initial pH of aqueous solution. Both dyes are basic in nature, which upon dissociation release colored dye cations into solution. The adsorption of these cationic dye groups onto the adsorbent is mainly influenced by the surface charge on the adsorbent, which is as well influenced by the surface charge on the adsorbent, which in

Most dyes incorporate intricate aromatic molecular configuration which makes them difficult to undergo degradation hence, very stable [5]. In addition, many dyes are toxic to some microorganisms and may cause direct 2

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

depends on solution pH. As the pH of the aqueous solution is raised, higher cation removal is obtained [18].

such as moisture content, ash content and volatile content on it. 2.3.1 Moisture content

In this work, the adsorption isotherm of MB onto PKS impregnated with phosphoric acid was studied. The study of adsorption isotherm is significant as it provides valuable insights into the feasibility of the adsorbent. Langmuir and Freundlich models are used to explain the isotherm of the adsorption process.

This was done by weighing 1 g of PKS into a crucible. This was placed in the oven and heated for 4 hours at constant temperature of 110 °C. The sample was then removed and put rapidly into a desiccator in order to prevent more moisture uptake from atmosphere. The sample was re-weighed. This procedure was repeated several times until a constant weight was obtained. The difference in the mass constitutes the amount of moisture content of the adsorbent.

2. MATERIALS AND METHODS The raw materials used in this study is PKS were collected from a factory producing palm oil in Ogbomoso, Oyo State, Nigeria. The chemicals used for this research are products of BDH Limited which includes phosphoric acid, hydrochloric acid, Sodium Hydroxide, MB.

Moisture Content (%) =

(1)

Where, A = weight of sample used, B = weight of sample after heating 2.3.2 Ash content

2.1 Pre-treatment of Waste PKS

2.0 g of sample was placed into a crucible, and reweighed with its content heated in a furnace at 900°C for 3 hours. The sample was cooled to room temperature and reweighed. Ash content was by difference [20].

The PKS was washed several times to remove sand particles and all other dirt. The washed PKS was then sun dried for about three weeks and was crushed in a nut cracking machine to reduce the size and oven dried at 110°C for 24 hours, the crushed PKS was passed through set of sieves with final particles size ranging from 1 to 2 mm [19].

2.2 Production of Activated (Carbonization/Activation)

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2.3.3 Volatile content The volatile content of PKS was determined by weighing 1 g PKS into a crucible, covered and placed in the muffle furnace at 930 oC for 1 hour. The crucible and its content were cooled in a desiccator and the volatile component determined using the relationship. The volatile content was then weighed and the difference in mass represented the mass of organic material present in the sample.

Carbon

60 g of the PKS from above was weighed into a 1000 ml beaker. 60% phosphoric acid was added to submerge the samples. The sample was left for 96hrs impregnation with the phosphoric acid acting as activating agent. After 96 hours impregnation, the sample was filtered to remove excess acid which was later carbonize in the muffle furnace for three hours at 600°C. The sample was allowed to cooled and washed with distill water. It was later dried and stored in airtight container to be used for the adsorption study and to be analyzed for pore volume, bulk density, ash content, moisture content and for fixed carbon content.

2.3.4 Fixed carbon content The fixed carbon content of PKS was obtained from the relation: Fixed carbon (%) = 100 - (moisture + ash + volatile). (2) 2.3.5 Bulk density 5.0 g of the activated carbon was transferred into 25 ml of distilled water using measuring cylinder. The volume of the water displaced was recorded. The bulk density was calculated by dividing the mass of the activated carbon by the volume of water displaced which was repeated for about

2.3 Characterization of the Adsorbate (Activated Carbon) The suitability of the PKS for the production of AC was ascertained by carrying out analysis 3

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

five samples and the average of the five was now taken as the bulk density.

3.1 Influence of Contact Time on Dye Removal

2.4 Isotherm Studies

The effect of contact time on adsorption percentage of MB is shown in the Fig. 1.

100 ml of MB solution of concentrations 20 ppm, 40 ppm, 60 ppm, 80 ppm and 100 pm were prepared. 0.6 g of the adsorbent was added to the conical flasks containing the solutions. The flasks were shaken at pH 5, 250 rpm and at room temperature for 50 minutes. At the end of 50 minutes, samples were collected from each flasks and residual dye concentrations were determined using a UV spectrophotometer at 664 nm (Debi Prasad Samal, 2014). Percentage adsorption was calculated using: % adsorption

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The dependence of adsorption on contact time was studied using fixed amount of 0.2 g of adsorbent on 20 ppm MB solution in a fixed volume of 100 ml. It was observed that percentage adsorption increases as the time of agitation increased. The percentage adsorption of MB is drawn against agitation time as shown in Fig. 1. It was found from the plots that the percentage adsorption increased withinin the first 20 min of agitation. Beyond the agitation time of 20 min, the % adsorption is more or less constant. So the equilibrium was reached at agitation time of 50 min. The most favourable contact time for the removal of MB into palmkernel shell activated carbon is 50 min. The rate of percentage adsorption is higher in the initial stages because adequate surface area of the adsorbent is available for the adsorption of MB. As time increases, more amount of MB is adsorbed onto the surface of PKS adsorbent and surface area available decreases.

(3)

Where, Ci = initial concentration in ppm Cf = final concentration in ppm

3. RESULTS AND DISCUSSION The proximate analysis of the activated PKS is shown in the Table 1.

3.2 Influence of Initial pH on Dye Removal

Table 1. Proximate analysis of the samples

% removal of Methylene Blue

Moisture Content (%) Ash Content (%) Volatile Matter Content (%) Fixed Carbon (%) Bulk Density(kg/m3 ) pH

The effect of pH on percentage adsorption of MB is given in Fig. 2.

2.85 1.88 11.23 84.04 451.2 2.84

Effect of pH on the removal of MB was evaluated at a pH range of 2-10. The percentage adsorption was found to increase significantly between the pH of 2 to 4. Further increase in pH does not lead to corresponding increase in

100 90 80 70 60 50 40 30 20 10 0

0

20

40

60

80

100

Contact time in minutes

Fig. 1. Effect of contact time on percentage adsorption of MB at pH 5 and 20 ppm solution 4

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

% removal of methylene blue

96 95 94 93 92 91 90 0

2

4

6

8

10

12

pH

Fig. 2. Effect of pH on the percentage adsorption of MB of 20 ppm. It was observed from the plot that increasing the dosage increases the % removal of MB. This can be ascribed to high carbon surface area and availability of more adsorption sites. As there was no drastic increase in the percentage adsorption on increasing the dosage of adsorbent beyond 0.6 g of activated carbon, hence, 0.6 g was taken as optimum dosage for removal of MB.

3.3 Influence of Adsorbent Dosage on Dye Removal

The variation of percentage adsorption of the MB with temperature is shown in the Fig. 4.

The adsorbent dose was varied in the given range of 0.2 - 1 g at pH of 4 in aqueous solution

Adsorption of MB at five different temperatures (293 K, 313 K, 333 K, 353 K and 373 K) at pH 4

% removal of methylene blue

percentage adsorption. The solution pH influences the surface charge of PKS adsorbent, the level of ionization and speciation of the surface functional groups. There is a strong relation between the adsorption and the number of negative charges at the biomass surface which is itself related to the functional groups. Therefore, Fig. 2 above shows that the adsorption behavior of MB is sensitive to pH changes. Lower percentage removal of MB at acidic pH was probably due to hydrogen ions competing with the cationic charge of dye solution for adsorption on activation sites of activated carbon. The optimum pH was found to be at 4.

The variation of adsorbent dosage on % adsorption of MB is shown in the Fig. 3.

3.4 Influence of Temperature on Dye Removal

120 100 80 60 40 20 0

0

0.2 0.4 0.6 0.8 1 different amount of activated carbon in grams

1.2

Fig. 3. Effect of adsorbent dosage on the adsorption of MB at pH 4 in 20 ppm solution 5

% removal of methylene blue

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

120 100 80 60 40 20 0 285

305

325

345

365

temperature(kelvin)

Fig. 4. Effect of temperature on adsorption at pH 4 in 20 ppm solution 40 ppm, 60 ppm, 80 ppm and 100 ppm of MB solution. The experiment was conducted at using 0.6 g adsorbent dosage room temperature, pH of 5 and contact time of 50 min. For the initial concentration of 20ppm more than 85% adsorption has been observed, whereas for 100 ppm the percentage removal of dye is 72.5%. From the above observation, it is evident that for lower initial concentration of dye, percentage adsorption is high. The percentage adsorption of MB decreases as it concentration is increased due to the fact that with increase in MB concentration, there will be increase competition for the active adsorption sites and the adsorption process will reduce.

in 20 ppm solution onto PKS activated carbon was studied for 20 ppm initial MB concentrations. As the temperature increased from 293 K to 373 K, the percentage removal of dye also increased. The adsorption capacity increases with temperature as a result of increase of the rate of diffusion of the MB molecules across the external boundary layer and the internal pores of the adsorbent particle. Furthermore, change in temperature will have a corresponding effect on the equilibrium capacity of the adsorbent for a particular adsorbate.

3.5 Influence of Different Concentration on Dye Removal

Dye

3.6 Isotherm Model

The effect of initial concentration of MB on it % adsorption is shown in Fig. 5.

Equilibrium relationships between adsorbent and adsorbate are described by adsorption isotherms, generally the ratio between the

% removal of methylene blue

The adsorption of MB onto the activated carbon was studied for different concentrations 20 ppm, 100 90 80 70 60 50 40 30 20 10 0 0

20

40

60

80

100

120

diiferent amount of Methylene Blue in ppm Fig. 5. Effect of change in concentration on adsorption of MB at pH 4 6

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

2.5 R² = 0.9801

Ce/Qe (g/l)

2 1.5 1 0.5 0 0

5

10

15

20

25

30

Ce(mg/l) Fig. 6. Plot for Langmuir isotherm model 1.2 R² = 0.9914

1

LogQe

0.8 0.6 0.4 0.2 0 0

0.5

1 LogCe

1.5

2

Fig. 7. Plot for Freundlich isotherm model Table 2. Langmuir and Freundlich constants obtained from plots

Qmax(mg/g) 16.20

Langmuir isotherm b(L/mg) RL 0.0928 0.186

R2 0.980

Freundlich isotherm n KF(mg/g) 1.855 2.058

1/n 0.539

R2 0.991

solution (mg/L), Qmax the maximum monolayer adsorption capacity (mg/g) and b is the Langmuir isotherm constant which reflects the binding strength between metal ions and adsorbent surface (L/mg). b is the reciprocal of the concentration at which half saturation of the adsorbent is reached.

adsorbate concentration in adsorbent particles and adsorbate concentration in liquid phase at a fixed temperature at equilibrium. To find the model with the best fit for MB adsorption, data were fitted to Langmuir and Freundlich isotherm models. The Langmuir isotherm model is expressed as: [21]

The Freundlich model: [22]

(4) Where qe is the metal uptake (mg/g), Ce the equilibrium concentration of solute in the bulk

.

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(5)

Niran et al.; AJACR, 1(1): 1-9, 2018; Article no.AJACR.41300

linearized to

REFERENCES 1.

(6) where KF is adsorption capacity constant (mg/g) and 1/n is an empirical parameter related to the adsorption intensity.

2.

Comparing the correlation coefficients values of Freundlich adsorption isotherm with that of Langmuir adsorption isotherm it is clear that Freundlich adsorption isotherm gives a better fit for MB adsorption onto PKS with correlation coefficient of 0.9914.

3.

The Freundlich model gives an emperical relationship for the sorption of sorbate to heterogenous sorbent surface with the assumption that different sites with several energies are involved.

4.

5.

The Table 2 shows the Langmuir and Freundlich isotherm constants and the correlation coefficients.

6.

The Langmuir isotherm model was used for the determination of maximum sorption capacity corresponding to complete monolayer coverage. The sorption capacity, Qmax, which indicates what the maximum sorption capacity corresponding to complete monolayer coverage, showed that the PKS had a mass capacity of 16.20 mg/g for MB. An important feature of Langmuir isotherm constant is dimensionless parameter known as separation factor (RL). The separation factor for the MB adsorption onto PKS is less than unity indicating that PKS is an appropriate adsorbent for MB.

7.

8.

9.

4. CONCLUSION This study reveals that activated carbon prepared from PKS with 96 hours impregnation in phosphoric acid is an effective adsorbent for the removal of MB from aqueous solution. The maximum adsorption capacity for MB removal was obtained at pH 5, at contact time of 50 min and an initial dye concentration of 20 ppm. The adsorption of MB followed the Freundlich isotherm model with R2 value of 0.991.

10.

11.

COMPETING INTERESTS Authors have interests exist.

declared that

no competing

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© 2018 Niran et al.; This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Peer-review history: The peer review history for this paper can be accessed here: http://www.sciencedomain.org/review-history/24768

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