Immobilization of thermotolerant intracellular enzymes on functionalized nanoporous activated carbon and application to degradation of an endocrine disruptor: kinetics, isotherm and thermodynamics studies

Abstract

A bacterium, Serratia marcescens capable of degrading the endocrine disruptor, 2-nitrophloroglucinol (NPG) was isolated from tannery wastewater contaminated soil. The mixed intracellular enzymes (MICE) produced from S. marcescens were extracted and characterized. The functionalized nanoporous activated carbon matrix (FNAC) was prepared to immobilize MICE. The optimum conditions for the immobilization of MICE on FNAC were found to be time, 2.5 h; pH, 7.0; temperature, 40 °C; concentration of MICE, 4 mg; particle size of FNAC, 300 μm and mass of FNAC, 1 g. The FNAC materials before and after immobilization of MICE were characterized using scanning electron microscopy, Fourier transform-infrared spectrophotometry and an X-ray diffractometer. The thermal behaviour of the free and the immobilized MICE was studied using thermogravimetric analysis. The immobilization of MICE on FNAC obeyed the Freundlich model and the immobilization process followed a pseudo second order kinetic model. MICE-FNAC matrix was used to degrade NPG in aqueous solution. The degradation of NPG by MICE-FNAC was optimum at contact time, 3 h; pH, 7.0; temperature, 40 °C; concentration of NPG, 20 μM and agitation speed, 70 rpm. The degradation of NPG was found to be enhanced in the presence of Zn²⁺, Cu²⁺, Ca²⁺ and V³⁺ ions. The degradation of NPG by MICE-FNAC was studied using UV-visible, fluorescence and FTIR spectroscopy. The degradation of NPG by MICE-FNAC was confirmed using HPLC, NMR and GC-MS spectroscopy.