2-Hydroxy-1, 4-napthoquinone solubilization,thermodynamics and adsorption kinetics with surfactant

2-Hydroxy-1, 4-napthoquinone (lawsone) natural red–orange dye was extracted from fresh henna (Lawsonia inermis) leaves in an alkaline media. The lawsone-surfactant solubilization constants (KLS) were calculated for the first time by using cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS). The standard free energy, concentration of solubilized lawsone and num-ber of lawsone molecules solubilized into micelles were calculated and discussed. Surface excess, mini-mum surface area per molecule, surface pressure, free energy (adsorption and aggregation) and equilibrium constants of different states were determined from tensiometry. Different metal ions (Ag+, Co2+, Cu2+, Ni2+, Fe3+, Zn2+and Al3+) were used to determine the complex forming ability with lawsone. Out of these, Ag+ions have strong binding capacity with lawsone. The adsorption of lawsone on the sur-face of glass with silver ions in presence of CTAB was also observed at pH≥9.0. The pseudo-first, second-order kinetic equation, intraparticles diffusion and Elovich models were used to determine the kinetics of lawsone adsorption onto the surface of glass and a probable mechanism has been discussed. Lawsone adsorption followed second-order kinetic equation (k2=0.019 g·mg-1·min-1).