Malaysian Journal of Analytical Sciences Vol 20 No 2 (2016): 358 - 364

 

 

 

Equilibrium and Themodynamic Studies of Anionic Dyes Removal by an Anionic Clay-Layered double hydroxide

 

(Kajian Keseimbangan dan Termodinamik dalam Penyingkiran Pewarna Anionik daripadaTanah Liat Anionik-Dwi Hidroksida Berlapis)

 

Nesamalar Kantasamy* and Siti Mariam Sumari

 

School of Chemistry and Environment,

Faculty of Applied Sciences,

Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia.

 

*Corresponding author: nesam337@salam.uitm.edu.my

 

 

Received: 24 February 2015; Accepted: 27 October 2015

 

 

Abstract

Adsorption isotherm describes the interaction of adsorbates with adsorbent in equilibrium. Equilibrium data was examined using Langmuir and Freundlich isotherm models. Thermodynamic studies were used to evaluate the thermodynamic parameters; heat of enthalpy change (ΔH°), Gibbs free energy change (ΔG°) and heat of entropy change (ΔS°) in order to gain information regarding the nature of adsorption (exothermic or endothermic). Four reactive dyes of anionic type, Acid Blue 29 (AB29), Reactive Black 5 (RB5), Reactive Orange 16 (RO16) and Reactive Red 120 (RR120) were used to obtain equilibrium isotherms at 25 °C, 35 °C, 45 °C and 55 °C. Based on Giles' classification, the isotherm produced were of L2-type, indicating strong dye affinity towards the adsorbent, and with weak competition with the solvent molecules for active adsorption sites. Equilibrium data fitted both Langmuir and Freundlich isotherm models with high correlation coefficient (R² > 0.91) indicating the possibility of both homogeneity and heterogeneous nature of adsorption. The negative values of ΔG° indicate the adsorption processes were spontaneous and feasible. The negative values of ΔH° lie between -20 to -75 kJ/mol, suggesting these processes were exothermic and physical in nature. The negative values of ΔS° are indication of decreased disorder and randomness of spontaneous adsorption of reactive dyes on layered double hydroxide as adsorbent.

 

Keywords: anionic dyes, layered double hydroxides, equilibrium isotherm, thermodynamic parameters

 

Abstrak

Isoterma penjerapan menerangkan interaksi antara bahan dijerap dan bahan jerap yang berada dalam keseimbangan. Data keseimbangan yang diperolehi dianalisis menggunakan model Langmuir dan Freundlich. Kajian termodinamik digunakan untuk menilai parameter-parameter termodinamik; perubahan haba entalpi (ΔH °), perubahan tenaga Gibbs bebas (ΔG°) dan perubahan haba entropi (ΔS°). Ia bertujuan untuk mendapatkan maklumat mengenai jenis penjerapan (eksoterma atau endoterma). Empat pewarna reaktif jenis anion iaitu, Asid Biru 29 (AB29), Reaktif Hitam 5 (RB5), Reaktif Jingga 16 (RO16) dan Reaktif Merah 120 (RR120) digunakan untuk mendapatkan isoterma keseimbangan pada suhu 25 °C, 35 °C, 45 °C dan 55 °C. Berdasarkan klasifikasi Giles, isoterma yang dihasilkan adalah jenis L2, yakni menandakan bahawa pewarna-pewarna ini mempunyai afiniti tinggi kepada bahan penjerap, dan mempunyai persaingan lemah dengan molekul-molekul pelarut untuk menambat kepada tapak atau permukaan aktif bahan penjerap. Data keseimbangan yang diperolehi didapati sesuai dipadankan dengan model isoterma Langmuir dan Freundlich dengan pekali korelasi yang tinggi (R2 > 0.91), menunjukkan kemungkinan wujud kedua-dua ciri kehomogenan dan heterogen untuk proses penjerapan. Nilai negatif ΔG° menunjukkan proses penjerapan adalah spontan dan boleh dilaksanakan. Nilai negatif ΔH° adalah antara -20 dan -75 kJ/mol, dan ini mencadangkan proses penjerapan adalah eksoterma dan fizikal. Nilai negatif ΔS° adalah petanda penurunan gangguan dan kerawakkan penjerapan spontan pewarna reaktif pada bahan penjerap dwi hidroksida berlapis.

 

Kata kunci: pewarna anion, dwi hidroksida berlapis, isoterma keseimbangan, parameter termodinamik

 

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