Entrapment of Lentinus sajor-caju into Ca-alginate gel beads for removal of Cd(II) ions from aqueous solution: preparation and biosorption kinetics analysis

A white rot fungus species Lentinus sajor-caju biomass was entrapped into alginate gel via a liquid curing method in the presence of Ca(II) ions. The biosorption of cadmium(II) by the entrapped live and dead fungal biomass has been studied in a batch system. The heat-treatment process enhanced the biosorption capacity of the immobilized fungal biomass. The effect of initial cadmium concentration, pH and temperature on cadmium removal has been investigated. The maximum experimental biosorption capacities for entrapped live and dead fungal mycelia of L. sajur-caju were found to be 104.8±2.7 mg Cd(II) g⁻¹ and 123.5±4.3 mg Cd(II) g⁻¹, respectively. The kinetics of cadmium biosorption was fast, approximately 85% of biosorption taking place within 30 min. The biosorption equilibrium was well described by Langmuir and Freundlich adsorption isotherms. The change in the biosorption capacity with time is found to fit pseudo-second-order equations. Cadmium binding properties of entrapped fungal preparations have been determined applying the Ruzic equations. Since the biosorption capacities are relatively high for both entrapped live and dead forms, they could be considered as suitable biosorbents for the removal of cadmium in wastewater treatment systems. The biosorbents were reused in three consecutive adsorption/desorption cycles without significant loss in the biosorption capacity.     

Monomer,dimer, tetramer and salt: Structural variations in Zn(II) complexes of 4,4′-bipyridine-N,N′-dioxide

Complexes of Zn^II salts with 4,4′-bipyridine-N,N′-dioxide (bpdo) have been prepared by solvathermal and solvent layering methods. Three complexes were obtained from ZnBr₂: 1 is a 2D coordination polymer [Zn₂Br₄(bpdo)₂]_n, (2) a discrete trimetallic molecule [Zn₃Br₆(H₂O)₂(bpdo)₄] and 3 a salt [ZnBr₄][Zn(H₂O)₅(bpdo)]. Complexes 2 and 3 contain Zn^II ions in both octahedral and tetrahedral coordination geometry. While in 2, these are covalently linked by bridging bpdo ligands forming zwitterionic trimetallic molecules, in 3 there is complete charge separation into [ZnBr₄]²⁻ anions and [Zn(H₂O)₅(bpdo)]²⁺ cations. When Zn(NCS)₂ is used as starting material, a 1D coordination polymer [Zn(H₂O)₂ (bpdo)(NCS)₂]_n is obtained.