Urtica dioica leaves-calcium alginate as a natural, low cost and very effective bioadsorbent beads in elimination of dyes from aqueous medium: Equilibrium isotherms and thermodynamic studies

Abstract

A very effective and low cost bioadsorbents derived from Urtica dioica leaf powder (UDL) and composite beads UDL encapsulated with calcium alginate (UDL/A) were used in removal of cationic dye crystal violet (CV) from aqueous medium. The new adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR) and isoelectric points (pHpzc). Adsorption was studied in batch system according to initial CV concentration (30–150 mg/L), contact time, pH (2–11), temperature (10 to 40 °C) and adsorbent mass (10 to 200 mg). UDL and UDL/A beads showed maximum CV adsorption of 137.8 and 121.8 mg/g for 150 mg/L initial CV dye concentration, pH 6.5, 1 g/L adsorbent dose, temperature of 23 ± 1 °C and contact time of 6 h. Analysis of kinetics data shows that adsorption of CV onto adsorbents was well described by pseudo-second order model. The equilibrium adsorption data fitted the Langmuir isotherm well with a maximum adsorption capacity of 1790 and 1107 mg/g respectively for UDL and UDL/A beads. Results of thermodynamic studies showed negative values of ΔG°; positive values of ΔH° 10.30 and 6.54 kJ/mol for CV onto UDL and UDL/A beads respectively. Adsorption processes are spontaneous, physical and endothermic in nature.