We report here the rational design and the preparation of chitosan-derived adsorbent, trioctylmethyl ammonium carboxymethylated chitosan ([A336][CMCTS]) for the removal of Pb(H) from aqueous solutions. The adsorbent fabricates as such represents a rational approach to enhance the adsorption capabilities, as well as avoid the agglomerate of chitosan effectively. Through a series of carefully executed experiments, we discover that both the cations and anions parts contribute to the adsorption of Pb(II), thus propose an interesting ion-associated complex adsorption mechanism. The as-prepared [A336][CMCTS] displays excellent adsorption capabilities, has a adsorption capacity of 143.3 mg g(-1). 97.71% of Pb(II) in real waste water can be removed. This new design strategy and adsorption mechanism broadens the studies in this field and gives deep insight into Pb(II) adsorption behaviors. The as-prepared adsorbents are expected to be used for the removal of other heavy metal ions. (C) 2013 Elsevier B.V. All rights reserved.