A comparative study on selective adsorption of metal ions using aminated adsorbents

It is well-known that chitosan consists of amino groups for the chelation of metal ions while NH2-MCM-41 has excellent adsorption selectivities for metals. This work compares both adsorption capacities and selectivities of chitosan and NH2-MCM-41. It has been found that chitosan has adsorption capacities of 1.76 mmol/g, 1.03 mmol/g and 1.30 mmol/g for Cu2+, Ni2+ and Zn2+ respectively whereas NH2-MCM-41 has adsorption capacity of 1.52 mmol/g, 0.8 mmol/g and 0.83 mmol/g for Cu2+, Ni2+ and Zn2+. The higher adsorption capacity in chitosan is attributed to its higher loading of amine groups. The single component adsorption isotherms were well-fitted using Freundlich model. The binary adsorptions of Cu2+-Zn2+ and Ni2+-Zn2+ systems showed similar adsorption selectivities for both adsorbents. However, chitosan has no preferential adsorption for Ni2+-Zn2+ system while NH2-MCM-41 has a good selectivity towards Zn2+. It is believed that the difference can be attributed to the heterogeneous surface of chitosan due to its organic nature. The multi-component adsorptions were best described by a multicomponent extended Freundlich model. Despite the surface functional group, this work indicates the importance of the adsorbent support on selective adsorption. (C) 2013 Elsevier Inc. All rights reserved

Mechanism of arsenic removal using chitosan and nanochitosan

Chitosan, a natural polysaccharide copolymer of glucosamine and N-acetyl-glucosamine, possesses one free primary amine and two free hydroxyl groups on each glucosamine unit. It has a polycationic nature and an abundance of amine functional groups. The sorption equilibrium and kinetics of arsenate onto chitosan flakes have been studied. The effect of pH on the adsorption capacity and the uptake kinetics is an important parameter to investigate the adsorption mechanism of anionic species such as arsenate ions on the protonated amine groups of chitosan. The equilibrium sorption and batch kinetic studies of arsenate ions on chitosan were performed at initial As concentration of 250-11,000 mu g L-1 and initial pH ranging from pH = 3.50-5.50. The experimental results showed that initially for approximately the first 30 min there is a rapid and high adsorption of arsenate ions onto the chitosan leading to a maximum uptake capacity after this short time. However, this stage is followed by a slow desorption of arsenate from the chitosan with a steady increase in solution pH. A novel reversible pseudo-first order kinetic model was developed and applied to correlate this newly reported adsorption-desorption phenomenon. The physical and chemical properties of chitosan were studied and presented in terms of its surface and structural Properties such as the degree of deacetylation, crystallinity, surface charge and its swelling properties. (C) 2013 Elsevier Inc. All rights reserved