Effects of temperature and pH on adsorption of basic brown 1 by the bacterial biopolymer poly( γ-glutamic acid)

• Published in: Bioresource technology Vol. 99; no. 5; pp. 1026 - 1035
• Main Authors: Inbaraj, B. Stephen, Chiu, C.P., Ho, G.H., Yang, J., Chen, B.H.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-03-2008; [New York, NY]: Elsevier Ltd; Elsevier
• Subjects: Adsorption; Azo Compounds - chemistry; Bacillus; Bacillus subtilis - metabolism; Basic brown 1; Biological and medical sciences; Biopolymers - chemistry; Biopolymers - metabolism; Coloring Agents - chemistry; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Kinetics; Poly( γ-glutamic acid); Polyglutamic Acid - analogs & derivatives; Polyglutamic Acid - chemistry; Polyglutamic Acid - metabolism; Temperature; Thermodynamics; Poly( γ-glutamic acid); pH; Temperature; Basic brown 1; Adsorption; Biopolymer; Temperature effect; Bacteria; Glutamic acid polymer; Poly(γ-glutamic acid)
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2007.03.008

Poly(
γ-glutamic acid) (
γ-PGA), an extracellular polymeric substance (EPS) synthesized by
Bacillus species, was explored to study its interaction with the basic brown 1 dye by conducting a systematic batch adsorption study as affected by two critical parameters, temperature and pH. Adsorption isotherms were closely predicted by Temkin equation among the eight isotherm models tested. The rate of adsorption was very rapid attaining equilibrium within 60
min and the kinetics were well described by both modified second-order and pseudo second-order models. Boyd’s ion exchange model, which assumes exchanges of ions to be a chemical phenomenon, also fitted the kinetic data precisely. The adsorption rate increased with increasing solution temperature, however, a reversed trend was observed for the adsorption capacity. Changes in enthalpy, entropy and free energy values revealed dye adsorption by
γ-PGA to be an exothermic and spontaneous process involving no structural modification in
γ-PGA, whereas the activation energy of 37.21
kJ/mol indicated dye adsorption to be reaction-controlled. Following a rise in solution pH, the dye adsorption increased and reached a plateau at pH 5, while the maximum release of dye from spent
γ-PGA occurred at pH 1.5, suggesting a possible ion exchange mechanism. Ion exchange adsorption of basic dyes by
γ-PGA was further proved by the presence of two new IR bands at ∼1600 and 1405.72
cm
−1, representing asymmetric and symmetric stretching vibration of carboxylate anion, for dye-treated
γ-PGA.