Adsorption of Rhodamine B dye from aqueous solution on Irvingia gabonensis biomass: Kinetics and thermodynamics studies

RESEARCH ARTICLE A.A. Inyinbor, F.A. Adekola and G.A. Olatunji, S. Afr. J. Chem., 2015, 68, 115–125, <http://journals.sabinet.co.za/sajchem/>. 115 Adsorption of Rhodamine B Dye from Aqueous Solution on Irvingia gabonensis Biomass: Kinetics and Thermodynamics Studies a,b, b b Adejumoke A. Inyinbor *, Folahan A. Adekola and Gabriel A. Olatunji a Department of Physical Sciences, Landmark University, P.M.B. 1001, Omu Aran, Nigeria. b Department of Industrial Chemistry, University of Ilorin, P.M.B. 1515, Ilorin, Nigeria. Recieved 23 September 2014, revised 13 March 2015, accepted 17 April 2015. ABSTRACT Raw Irvingia gabonenses (dika nut) (DN) and its acid-treated form (ADN) were used for the uptake of rhodamine B (RhB) dye from aqueous solution. The adsorbents were characterized by Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett– Teller (BET) surface area analysis and scanning electron microscopy (SEM). The adsorbents were found to have characteristic functional groups such as –OH, C-N and C=O. SEM revealed that acid treatment resulted in the development of several pore sizes. Sorption data fitted the Freundlich adsorption isotherm better than the Langmuir isotherm. The maximum sorption capacities, qmax, obtained from the Langmuir adsorption isotherm were 212.77 and 232 mg g–1 for DN and ADN, respectively. The pseudosecond-order kinetics model was observed to fit the adsorption data. Solution pH and temperature significantly influenced the adsorption process and negative values of DG° suggest that the sorption process was spontaneous and feasible. Intraparticle diffusion mainly controlled the uptake of RhB onto DN and ADN; however, boundary layer diffusion also occurred in the RhB-ADN system. The desorption efficiency of RhB from the adsorbents was tested with a number of eluents. The eluents were found to follow the order: H2O>CH3COOH>HCl and CH3COOH>HCl>H2O for DN and ADN, respectively. KEYWORDS Irvingia gabonenses, adsorption, rhodamine B, thermodynamics, kinetics, biomass. 1. Introduction Textile industries use large volumes of water in their operations and thus release large amounts of waste water. Waste waters from textile industries are unique in their composition;they are usually released containing various dyes and heavy metals.1 In particular, the dyes tend to be reactive dyes since these have such qualities that make them a preferred option in textile industries. However, they have been reported to be the most problematic of all dyes used in these industries.2,3 Their high solubility makes their treatment by conventional methods difficult.2,3 The effects of dyes in the water body are not limited to toxicity, but also include reduction in dissolved oxygen and interruption of photosynthetic processes. Most of the reactive dyes, including rhodamine B, used in the textile and allied industries are known to be carcinogenic.4,5 Among the various conventional methods of waste water treatment, adsorption has been found to combine economic advantage, design and operational simplicity, and with the uptake of very low concentration of toxicants.6 Activated carbons have been employed in effluent treatment over the years and have been found to exhibit great affinity for organic compounds.7 However, due to the precursors used for the preparation of commercial activated carbons, it has been found to be economically unviable and therefore other precursors are being sought.1,8,9 Agricultural wastes and other waste materials, such as coconut husk and bunch waste,8,10 date stone,11 jujuba seed,12 peanut * Authors for correspondence. E-mail: / hulls and its immobilized form,13 cocoa pod husk,14 cashew nut shell,15 periwinkle shell,16 garlic peel,17 sugar cane bagasse,18 calcined egg shell,19 bagasse pith,20 olive waste cake,21 apple wastes,22 Bengal gram seed husk,23 oil palm fruit waste,24 castor bean cake,25 maize stem tissue26 and lignite27 have been utilized as cheap alternatives for activated carbon preparation as well as low cost adsorbents in the uptake of dyes. Irvingia gabonensis (sweet bush mango, also known as Dika nut) is common in the southwestern part of Nigeria. It is a drupe with a thin epicarp, a soft fleshy thick mesocarp and a hard endocarp encasing a soft dicotyledonous kernel.28,29 Sweet bush mango in all its part serves as food for humans with the exception of its endocarp; the mesocarp and the epicarp can be eaten fresh while the cotyledon encased in the endocarp serves as an ingredient for soup. The endocarp, however, is a waste and its use as an adsorbent will result in waste reduction and economic advantages. The characteristics of adsorbents generally depend on the type of treatment employed in theirpreparation;chemical treatments such as acid treatment usually result in large pores which are suitable for the removal of large molecules such as dyes.30 Hence, the focus of this work was to investigate the potential of raw Irvingia gabonensis waste and its acid-treated form for the uptake of a cationic dye (rhodamine B). To the best of our knowledge, this biomass has not been given much attention in relation to its application in environmental remediation operations. Operational parameters, kinetics, isothermal and thermodynamic studies governing the adsorption process were investigated. ISSN 0379-4350 Online / ©2015 South African Chemical Institute / http://saci.co.za/journal DOI: http://dx.doi.org/10.17159/0379-4350/2015/v68a17 RESEARCH ARTICLE A.A. Inyinbor, F.A. Adekola and G.A. Olatunji, S. Afr. J. Chem., 2015, 68, 115–125, <http://journals.sabinet.co.za/sajchem/>. 2. Materials and Methods 2.1. Preparation of Adsorbents 2.1.1. Preparation of Raw Dika Nut (DN) Endocarps of Irvingia gabonensis were collected from farmers in Omu Aran, Kwara State of Nigeria. The biomass was thoroughly washed to remove dirt and dried in an oven operated at 105 °C overnight. It was then pulverized and screened into a particle size of 150–250 µm before it was stored in an airtight container for subsequent use. 2.1.2. Preparation of Acid-treated Dika Nut (ADN) An equal volume to mass ratio of concentrated sulphuric acid and the biomaterials was thoroughly mixed in a clean beaker and was subjected to thermal treatment (200 °C) for 2 h with continuous agitation for one hour. About 10 cm3 of deionized water was injected into the carbon material, the carbon material obtained was allowed to cool to room temperature, washed to neutrality, soaked in 8 M KOH and heated at 200 °C for another one hour. It was then washed thoroughly with deionized water to neutrality, dried in the oven at 105 °C and stored in a tightly sealed container for subsequent use. 116 2.3. Adsorbate Preparation Rhodamine B (RhB) supplied by BDH was used to investigate the adsorptive properties of the adsorbents prepared. Table 1 shows the properties of rhodamine B and Fig. 1 shows the structures of rhodamine B in its cationic and zwitterionic forms. A parent solution of 1000 mg (...truncated)