Immobilization of Phycocyanin in a Rice Hull Nanosilica/Calcium-Alginate Bead System for Cadmium Ion Remediation

Abstract

Phycocyanin (PC), the major phycobiliprotein found in the cyanobacterium Spirulina platensis, was explored as a biosorbent for cadmium removal in contaminated water. It was isolated from commercially available Spirulina tablets using 0.1 M phosphate buffer with 0.15 M NaCl (pH 7) and was purified using two-stage ammonium sulfate precipitation followed by gel filtration chromatography using Sephadex G-75. The water-soluble pigment protein thus obtained could not be directly used as a biosorbent and was subsequently immobilized on rice hull nanosilica using 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde as linkers resulting in a blue-green powder composite material (SAGPC). Optimum immobilization of PC on rice hull nanosilica was achieved by using 5% v/v APTES, 1.5% v/v glutaraldehyde, and 6 mg/mL PC solution. The immobilized PC was then prepared in the form of calcium-alginate beads (SAGPCAlg beads) to allow easy separation from effluents. The Cd adsorption efficiency (99.80 ± 0.20 %) and adsorption capacity (19.72 ± 0.38 mg/g) of SAGPC-Alg beads were determined through batch sorption experiments at room temperature using the optimum working conditions at pH 7, 0.1 g wet beads, 0.5 ppm initial Cd concentration, and 60-min shaking time.