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Effect of Various Factors on the Adsorption of Methylene Blue on Silt Fractionated from Bijoypur Soil, Bangladesh

Zaker Y
Department of Chemistry, University of Dhaka, Dhaka-1000, BANGLADESH

Hossain M.A.*
Department of Chemistry, University of Dhaka, Dhaka-1000, BANGLADESH

Islam T.S.A
Department of Chemistry, University of Dhaka, Dhaka-1000, BANGLADESH

Abstract/ Executive Summary:

Silt obtained from the fractionation of Bijoypur (Netrokona, Bangladesh) soil having the particle size (53 – 140 µm) was used as an adsorbent for the removal of Methylene Blue (MB) from aqueous solution. The effect of various factors (pH, temperature and adsorbent dose) on adsorption of MB on silt fraction was investigated. The effect of pH shows that the amount adsorbed increased with the increase of pH of solution. The equilibrium adsorption isotherms were analyzed by Langmuir and Freundlich equations. Both Langmuir and Freundlich models can describe the adsorption equilibrium but the Langmuir model shows better agreement. The amount adsorbed increased with the increase of temperature suggests the formation of dimer in the contact region. SEM micrographs and differential molar isosteric heat of adsorption (?H) calculated at different surface coverage, indicate that the surface is heterogeneous having energetically different adsorption sites. Values of n calculated from Freundlich plots indicate that adsorption of MB on silt is spontaneous. At high surface coverage, the differential heat of adsorption versus surface coverage plot shows maximum value indicating the occurrence of structural rearrangement in the adsorbate. With the increase of adsorbent dose, amount adsorbed increased due to the increased surface area of adsorbent.

Keywords: Methylene blue, Silt, pH, Temperature, Langmuir and Freundlich isotherms, ∆H, Adsorbent dose, Structural rearrangement

Location: Bijoypur (Netrokona, Bangladesh)

Start Date:

End Date:

Program Area: Knowledge Management

Non-commodity: Performance

Objectives:

The present study was carried out to investigate the effect of different factors e.g. pH, temperature and adsorbent dose on the adsorption of MB on silt. The objective was to study whether the adsorption process can be described by Langmuir and Freundlich models, to determine thermodynamic parameters and the change of surface morphology by SEM.

Methodology:

Silt was fractionated from Bijoypur (Netrokona) soil. In our present investigation, titrometric method 23 was used for fractionation of Bijoypur soil into sand, silt and clay on the basis of particle size. Fractionated silt was characterized by LIBS, FT-IR, SEM, XRD and pHzpc 24 . The adsorption experiment was carried out at pH 7.0 with MB of concentration 5.0×10-5 M at 30°C. 0.1 g of silt was taken in each of 6 bottles containing 40 mL MB solution. The bottles were shaken in a thermostatic mechanical shaker (SWB-20, HAAKE, Fisons Ltd, Germany). After a definite interval of time each bottle was withdrawn from the shaker. The supernatant of the bottle was transferred and centrifuged repeatedly until a clear liquid was obtained. The absorbance of the clear solution was measured spectrophotometrically at λmax 663.0 nm. The adsorption experiments were carried out to investigate the effect of pH on adsorption at solution pH 3.0, 7.0 and 11.0 keeping other parameters constant. In all cases, the pH of the solution was adjusted by using acid or alkali without affecting the volume of the solution. To investigate the effect of temperature on adsorption, adsorption experiments were carried out with different initial concentrations of MB from 3.0 to 30.0 mg/L at pH 7.0. The experiments and the analysis were performed as described earlier. The equilibrium concentration and amount adsorbed for different initial concentrations were calculated at different temperatures and adsorption isotherms were constructed. To determine the effect of adsorbent dose on adsorption isotherms, adsorption experiments were performed at pH 7.0 and temperature 30ºC using 0.1, 0.2 and 0.3 g of silt following the same procedure as mentioned earlier. A small portion of fractionated silt were separately taken in a SEM sample holder and made it platinum coated using a Ptcoated auto system (JFC-1600, JEOL, Japan). Platinum coated silt was placed in the SEM sample chamber and SEM picture was taken at 20 kV with 2,000 and 30,000 magnification. Again this procedure was carried out for the sample collected after adsorption of MB on silt with 30,000 and 60,000 magnifications. Results and Discussion Characterization of Adsorbent: Silt was characterized by LIBS, FT-IR, SEM, XRD and pHzpc and results have been discussed in the earlier study 24 . Estimation of Equilibrium: Equilibrium time for adsorption of MB on silt water interface was estimated as 90 minutes beyond which no change of amount adsorbed was found. Effect of pH on Adsorption: Adsorption of MB on silt increases with the increase of pH indicating favorable adsorption at alkaline medium which can be explained from the pHzpc value of silt. The pHzpc value of silt is 6.39±0.0224. When the pH of solution is higher than the pHzpc, the surface becomes negatively charged. MB is a cationic dye. Due to electrostatic force of attraction molecules of MB are adsorbed on the surface of silt. Similar trends were observed in the literature25 .

Source of Information: International Research Journal of Environment Sciences ISSN 2319–1414 Vol. 2(6), 1-7, June (2013)

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Funding Source:

Budget:

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Achievement/Findings:

The present study shows that about 1.3 mg of MB adsorbed per g of silt in 90 minutes at 30ºC and pH 7. The adsorption isotherms follow Langmuir models of 30 to 50ºC. Increase in temperature increased adsorption suggesting the possible formation of dimer of MB molecules. SEM micrographs show the energetically different active sites on the surface like pores and cavities, and formation of aggregates after adsorption. At high surface coverage the differential molar isosteric heat of adsorption shows a maximum value which may be due to the structural rearrangement in the adsorbate molecules.

Knowledge Management: Journal